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Eton 5: Simultaneous rocket measurements of the OH meinel Δυ = 2 sequence and (8,3) band emission profiles in the nightglow
Planer. Space Sci., Vol. 35, No. 9, pp. 1137-l 147, 1987 Printed m Great Britain.
ETON
W32-0633/87 $3.00+0.00 Pergamon Journals Ltd.
5 : SIMULTANEOUS ROCKET MEASUREMENTS OF THE OH MEINEL Au = 2 SEQUENCE AND (8,3) BAND EMISSION PROFILES IN THE NIGHTGLOW 1. C. McDADE and E. .I. LLEWELLYN Institute of Space and Atmospheric Studies, University of Saskatchewan, Saskatoon, Saskatchewan, Canada S7N OWO D. P. MURTAGH Meteorological Institute, Arrhenius Laboratory, Stockholm University, S-106 91 Stockholm, Sweden
R. G. H. GREER Department of Pure and Applied Physics, The Queen’s University of Belfast, Belfast BT7 lNN, U.K. (Received in$nalform
1 April 1987)
Abstract-Simultaneous rocket measurements of the emission profiles of the OH Meinel (8,3) band and the Au = 2 sequence at 1.61 pm are presented and analysed. It is shown that the u = 8 level of the hydroxyl radical must suffer significant loss in the mesosphere due to collisions with 0, and/or N,. The rate coefficients for this removal process are obtained, for certain limiting assumptions about the excitation mechanism, and the coefficients are found to be in good agreement with those deduced from an independent analysis of ground-based observations. A variety of kinetic models, which reproduce the observed (8,3) band profile in some detail, predict AU = 2 sequence emission profiles which compare favourably with the measured profile in their total zenith intensities but not in their altitude distributions. The differences between the measured and modelled AU = 2 altitude profiles suggest that the 1.61 ILrn observations may have been contaminated by some unidentified vehicle-induced emission.
I. INTRODUCTION
vibrational levels of OH must be populated of radiative cascade
Vibration-rotation transitions within the ground electronic state of the hydroxyl radical dominate the spectrum of the terrestrial nightglow, and although more than three decades have passed since the system was first identified by Meinel (1950), a complete understanding of the excitation mechanism has still not been achieved. It was originally suggested by Bates and Nicolet (1950) and is now generally accepted, that the reaction H+O$+OH(v
< 9)+02
OH(v’)~OH(v”)+hv and single-quantum, deactivation OH(v’) + Q
(1)
is the major source of the radiant energy. However, the nascent OH products of reaction (1) are found primarily in the vibrational levels v = 7, 8 and 9 (Charters et al., 1971; Murphy, 1971; Ohoyama et al., 1985) and it remains uncertain how the lower vibrational levels, responsible for most of the Meinel Band emission, become populated. If reaction (1) is the only chemical source of vibrationally excited hydroxyl, then the lower 1137
or multi-quantum,
&o.. 0”) -OH(v”)+Q.
as a result
(2) collisional
(3)
Over many years of study, conflicting assessments of the extent to which the Meinel Band emission can be explained by processes (l), (2) and (3) have been presented (Llewellyn et al., 1978; Takahashi and Batista, 1981 ; Turnbull and Lowe, 1983) and it has not yet been established whether an additional chemical source of vibrationally excited OH is involved. Most of the difficulties encountered in attempts to resolve this issue (most recently reviewed by Bates, 1982) stem from controversy over the absolute Meinel Band transition probabilities and the inconsistent use of quite diverse sets of vibrational deactivation rate coefficients. Some recent laboratory experiments by
1. C. MCDADE et al.
1138
Finalyson-Pitts and Kleindienst (198 1) and Greenblatt and Wiesenfeld (1982) have suggested that many of the vibrational deactivation rate coefficients, which have been widely used in Meinel Band studies, may be in serious error. As a consequence, doubt has been cast on many of the conclusions reached from previous work. In view of this, McDade and Llewellyn (1987) have used ground-based observations of the mean nightglow OH vibrational distribution in an attempt to re-evaluate some of these important coefficients. While the kinetic parameters deduced by McDade and Llewellyn (1987) do reproduce the altitude-integrated OH vibrational distribution, their approach suffers from the limitation that these parameters may not necessarily be consistent with the altitude profiles of the individual vibrational levels. In the present paper some of these kinetic parameters are independently derived from simultaneous rocket photometer measurements of the OH Meinel Au = 2 sequence and (8,3) band emission profiles which were cooordinated with a determination of the atomic oxygen concentrations. 2. THE
ROCKET OBSERVATIONS
The present observations were made as part of a multiple rocket investigation of nightglow excitation mechanisms, known by the acronym ETON, and described in more detail by Greer et al. (1986) in Part I of this series of papers. The OH(8,3) band emission profile was measured with a conventional forwardlooking filter photometer on a Petrel rocket, P228H, launched from South Uist, Scotland (57.36”N, 352.62”E) at 23 : 28 : 23 U.T. on 23 March 1982. The Au = 2 OH Meinel Band sequence in the 1.61 pm region was measured from the same rocket with a forward-looking radiometer which incorporated an interference filter, a lead sulphide detector and phasesensitive detection. This radiometer has been described in more detail by Solheim (1979). The filter
transmission characteristics for both instruments are listed in Table 1. The zenith intensity data, recorded on the upleg of the rocket flight, have been reduced to volume emission profiles using the procedures described by Greer et al. (1986) and Murtagh et al. (1984). In the case of the OH(8,3) band this included removal of a contribution to the signal from the nightglow continuum-a procedure expedited by a simultaneous measurement of the red continuum at 714Ow (Murtagh and Greer, 1984; McDade et al., 1986). Unfortunately little is known about any nightglow continuum that may contribute to the Au = 2 channel and, therefore, no attempt to correct for this has been made. The derived (8,3) band volume emission profile, corrected for the instrument capture function listed in Table 1, is shown in Fig. 1. The Au = 2 volume emission profile is also shown in Fig. 1 and corresponds to the sum of the individual (6-4) (5-3) (4-2) (3-l) and (220) band volume emission rates with each band weighted by its respective capture function. The atomic oxygen concentrations employed in the analysis, shown in Fig. 2, were measured, using the 01 resonance absorption and fluorescence technique, on another rocket, P234H, launched 26 min later (Greer et ul., 1986). 3. ANALYSIS
The measured total zenith intensities of the (8,3) band and Au = 2 sequence were 285 R and 149 kR, respectively, and are typical of those expected from ground-based observations (Krassovsky et al., 1962; Harrison and Kendall, 1973 ; Takahashi and Batista, 1982). It is clear from Fig. 1 that the derived Au = 2 emission rate not only peaks at a lower altitude than the (8,3) band but also exhibits a secondary maximum just below an altitude of 100 km. The peak heights of both profiles lie well within the ranges reported from previous rocket measurements of these two features (Packer, 1961; Baker and Waddoups, 1967; Evans et
TABLE 1. FILTER AND DETECTORCHARACTERISTICS
Instrument # 2
Instrument # 1 Filter peak Filter width Detector
7240 A 49A EMR 541 E-01
Capture
OH Meinel (8,3) : 0.24
functions*
* Capture
functions
are based on an OH rotational
1.61 pm 194ow PbS OH OH OH OH OH
Meinel Meinel Meinel Meinel Meinel
temperature
(64) (S-3) (4-2) (3-l) (2-O)
of 200 K.
: 0.22 : 0.73 : 0.87 : 0.42 : 0.18
OH Meinel band emission
1139
0
FIG.I.MEASUREDVOLUMEEMISSIONPROFILESOFTHE
al., 1973 ; Rogers el al., 1973 ; Good, 1976 ; Witt et al., 1979; Thomas and Young, 1981 ; Makino et ai., 1983; Lopez-Moreno et al., 1985) and it should be noted that the presence of a secondary maximum in the At> = 2 emission appears to be a common feature of the other reported measurements. There is, however, some evidence to suggest that this secondary maximum may not be real but is perhaps an artifact resulting from optical emission induced by the rocket vehicle as it penetrates the airglow layer (LopezMoreno et al., 1985). It must, therefore, be recognized that the present Au = 2 measurements may also have been affected by such a phenomenon. As the processes which contribute to the excitation
OH(8,3)
AZ’= 2
BANDAND
SEQUENCEAT
1.61pm.
of the lower v’ levels are so numerous and much less direct than those contributing to the excitation of the u = 8 level, it is really only possible to extract reliable and definitive kinetic information from the (8,3) band profile. 3. I. Tfie OH(8.3) band emission proJife If reaction (I) is the only chemical source of vibrationally excited OH then, under steady-state conditions, the (8,3) band volume emission rate is given by V(8 3) = ‘4(8,3)k,[Hl[O,l L(8)
.fVN4%8)+ ;x-%WQll x
+
_I_ .-._______ L(9)
(4)
where~(~) represents the fractional yield of level ‘b” .in reacion (I) and I;(a) represents the total atmospheric loss of level “u”. This total loss may be expressed as L(u) = A(r)+
~k?W[Ql
(5)
Q
where A(v) is the inverse radiative lifetime of level “v” and k:(v) is the total coefficient for removal of this level by all collisional processes involving the species
dLQ”. 0-A fOH
Frc.2.
omsi TY ccm-3,
~TOWlCOXYGENCONCENTRATlONSEMPLOYGDINTHE PRESENT ANALYSIS.
As already mentioned, most of the laboratory measured rate coefficients for collisional quenching of vibrationaily excited OH are now thought to be suspect (Finlayson-Pitts and Kleindienst, 1981 ; Greenblatt and Wiesenfeld, 1982) with the exception of that
I. C.
1140
MCDADE et al.
measured by Finlayson-Pitts and Kleindienst (198 1) for the total rate of removal of OH(v = 9) by 0,. However, it remains unclear whether this coefficient relates to single-quantum vibrational deactivation, multi-quantum deactivation or chemical removal of the v = 9 level. Because of this ambiguity the present results are analysed in terms of two limiting cases. In the first case it has been assumed that collisional removal of OH(v = 9) does not constitute a source of any other vibrationally excited level of OH-this will be referred to as the “sudden death” assumption. In the second case it has been assumed that collisional removal of OH(v = 9) by 0, results in the production of OH(v = 8)-this will be referred to as the “collisional cascade” assumption. In both cases it has been assumed that removal of OH(9) in the atmosphere by N, is negligible since Finlayson-Pitts and Kleindienst (1981) find this process to be at least 20 times slower than the corresponding 0, reaction. Under the “sudden death” assumption, all of the @(9,8) coefficients are zero and equation (4) reduces to
For all altitudes in the mesosphere and all published Meinel Band transitions probabilities, the bracketed term in equation (6) is dominated by the quantityf(8) i.e. radiative cascade from OH(u = 9) constitutes a negligible source of OH(v = 8). In addition, between altitudes of 80 and 100 km, reaction (I) is the major ozone removal process at night (Moreels er al., 1977 ; Allen et al., 1984) and equation (6) can be approximated by
V(8,3) =
A(*)+
~k8@Wl Q
*R)/A(8,3),
equal to 2.0 f0.3 x lo-” cm3 molec-‘, and suggests that ky(8)/A(8,3) must be less than -2 x 10-‘0cm3 molec’. The quality with which these kinetic parameters reproduce the observations is illustrated in Fig. 4, where the OH(8,3) band volume emission profile generated with the derived fitting coefficients and equation (7) is compared with the original data. Under the alternate “collisional cascade” assumption, where collisional loss of OH(u = 9) by 0, is assumed to populate OH(v = 8), the equivalent of equation (7) is
f@Y+P~*)P,1 I
(9)
(7)
where kz2 and k:l represent the termolecular rate coefficients for ozone formation with NZ and 0, as third bodies. A re-arrangement of equation (7) yields 1 ~ A(8,3)
P’?(8) +@(8)
A(9)+k:‘(9)[02]+k:(9)[0]
~(~,3)~Ol~0,1~~~~~~,l+~~2~021~f(8) L(8)
model atmosphere (Hedin, 1983) and the kinetic parameters of Table 2, is shown in Fig. 3. It is evident from this figure that the atmospheric loss of OH(v = 8) must be dominated by spontaneous emission and collisional removal by O,, or N,, and that any O-atom removal process must be relatively unimportant for this level. Because of the similar atmospheric scale heights of [O,] and [NJ (i.e. [NJ[OJ is approximately equal to a constant “R’) it is not possible to distinguish between the losses due to these species which may, for the present purposes, be treated as being entirely due to 0,. A statistically weighted least-squares fit of the data of Fig. 3 to the MSIS-83 [O,] profile yields an intercept term, A(8)/A(8,3), equal to 260 + 50, an [0,] fitting coefficient,
1
Equation (8) which defines the OH (u = 8) quenching profile, allows the atmospheric loss of this level to be evaluated, from the observations, as a function of altitude. The altitude dependence of the right-hand side of equation (8), calculated using the measured atomic oxygen and volume emission profiles, the [O,], [NJ and temperature profiles from the MSIS-83
where ky2(9,8) is identical to k:>(9)-the total rate coefficient for removal of OH(u = 9) by 0,. The value for k:>(9) measured by Finlayson-Pitts and Kleindienst (1981) is critically dependent upon the uncertain absolute (9,3) band transition probability. However, the quantity relevant here is A(9)/ky2(9) which is much less sensitive to the choice of absolute probabilities. The value inferred for this quantity from the Finlayson-Pitts and Kleindienst experiments using the transition probabilities of Mies (1974) is 3 x 10’3molec cm-3, and with the transition probabilities of Potter et al. (1971) the inferred value is 4 x 10’3 molec a mean value of cmm3. For A(9)/kyz(9,8) equal to 3.5 x 10’3molec cme3, and assuming the atmospheric loss of OH(v = 9) to be dominated by 02, a re-arrangement of equation (9) yields
OH Meinel band emission AND
TABLET. REACTIONS
Reaction
H + 0, -OH(a)
1141
ADOPTED COEFFICIENTS
Reference
Coefficient f(9) f(S) f(7) f(6) f(5) 1’(4)
+ 0,
= = = = = =
Ohoyama Ohoyama Ohoyama Ohoyama Ohoyama Ohoyama
0.32 0.29 0.19 0.06 0.06 0.06
et al. (1985)* et al. (1985)* et al. (1985)* et ~1. (1985)*
et al. (1985)* et al. (1985)*
OH(v’) + Q kp(O’~U”) >OH@“) + Q OH(u) + Q -
see Table 4
P
all products
I
k,M O+O,+M+O,+M *Adjusted in molecule.
kN 62 = 5.70 x 10-34(T/300)-~~~~ k’$ = 5.96 x 10-34(T/300))2.37
using the relative transition cm. set units.
probabilities
of Murphy
0
3
Lin and Leu (1982) Lin and Leu (1982) (1971). All coefficients
50
100
VOLUME EMISSIUN
FIG. 3. ALTITUDEDEPENDENCEOF THE RHS OFEQUAT~ON (8) (***W)AND THELEAST-SQUARES FIT (SOLIDCURVE)OBTAINED ASDESCRIBED INTHETEXT.
Error
-~ A&3) 1
bars correspond to the uncertainties emission rates of Fig. I.
A(S)+
in the volume
1 f (9)P*l 3.5x 1oJ3+[02]
000
1 i0
cm-’ se-3
FIG. 4. MEASURED
OH(8,3) BAND VOLUME EMISSION PROFILE (*****) AND THE PROFlLES GENERATED FROM THE “SUDDEN DEATH"(SOLIDCURVE)AND“COLLISIONALCASCADE"(BROKEN CURVE) FITTING COEFFICIENTSAS DESCRIBED 1N THE TEXT.
~Ol~~,l{~~~~~,1+~k)2~~~1~ V&3)
150 +hotons
data of Fig. 5 to the MSIS-83 [0,] profile yields an intercept term, A@)/A(8,3), equal to 24Ok 50 and an [O,] fitting coefficient,
~@@)[Ql 0
=
are
{k?W+k%8).
1 (10)
Equation (10) allows the OH(r = 8) quenching profile to be evaluated for the “collisional cascade” assumption. The altitude dependence of the righthand side of equation (10) is shown in Fig. 5 which indicates that the loss of OH(r = 8) must again be dominated by spontaneous emission and collisional removal by 02, and/or NZ. A least-squares fit of the
R}lA(8,3),
equal to 3.3kO.5 x IO-“cm’ molec’. The OH(8,3) band volume emission profile generated from equation (9) and the latter fitting coefficients, is shown in Fig. 4 and is very similar to both the measured profile and that generated for the “sudden death” assumption. One of the most significant aspects of the parameters deduced above is the value obtained for A@)/A(8,3). Several sets of Meinel Band transition probabilities exist in the literature and, as Table 3 shows, the A(8) : A&3) branching ratios obtained
1142
I. C. MCDADE ef al.
{kX8)+kX8) *R}lA(W, correspond
to values of {@(8)+#(8)
500
0
RHS fq.
1000
I500
2000
Cdimerrsionless>
FIG. 5. ALTITUDE DEPENDENCEOF THE RHS OF EQUATION (lo) (*****) AND THE LEAST-SQUARES FIT (SOLID CURVE) OBTAINED
Error
AS DESCRIBED
IN THE TEXT.
bars correspond to the uncertainties emission rates of Fig. 1.
TABLE 3. A(8)
in the volume
: .4(8,3) BRANCHING RATIOS FROM THIS
* R}/A(9),
equal to 5 x 10 -I4 and 8.5 x 10~“‘cm3molecc for the “sudden death” and “collisional cascade” assumptions, respectively. As shown in Figure 6, these quantities are very similar to those deduced by McDade and Llewellyn (1987) and, therefore, the latter parameters not only reproduce the mean OH vibrational distribution but are also consistent with the altitude profile of the OH(8,3) band. Although this consistency is most encouraging, the OH(8,3) band analysis does not allow the relative merits of the “sudden death” and “collisional cascade” models to be assessed as both models predict essentially the same (8,3) band volume emission profile. In order to identify the most appropriate mechanism a comparison of the measured and modeled 1.61 I.trn emission profiles may be more conclusive.
AND
OTHER STUDIES A(8) : A&3)
Reference
260 f 50
This work with the “sudden death” assumption This work with the “collisional cascade” assumption Murphy (1971) Mies (1974) Potter et ul. (1971)
240 2 50 320 445 1056
here are in better agreement with the relative transition probabilities of Murphy (1971) than with the other sets of probabilities widely used in Meinel Band studies. This adds to the body of evidence which suggests that the relative transition probabilities of Murphy are the most reliable (Takahashi and Batista, 198 1) and allows the values obtained here for j@(8)
+k$(8)
*R}/A(8,3)
to be compared with the parameters deduced by McDade and Llewellyn (1987). In the work of McDade and Llewellyn (1987), the relative transition probabilities of Murphy (1971) were adopted and values for {k:Q)+kl;+)*
R}/A(9)
were obtained for Meinel Band excitation models corresponding to both the “sudden death” and “collisional cascade” assumptions. With the relative transition probabilities of Murphy (1971) the values obtained in the present work for
3.2. The 1.61 pm emission pro$le As a number of OH bands and, therefore, excitation pathways contribute to the 1.61 pm emission it is not possible to extract specific kinetic parameters from the 1.61 pm profile, and the measured profile is used here simply to determine which of the models and parameters derived by McDade and Llewellyn (1987) best explain the observations. In all, two pairs of models are considered. The first pair of models are based on an extension of the “sudden death” models. The second pair of models-the “collisional cascade” models-are based on an extension of the “collisional cascade” assumption. The two models within each pair differ in the limiting assumptions that are made about the rate of removal of vibrationally excited OH by atomic oxygen. For the “with O-atom quenching” component of each pair it is assumed that O-atom removal of vibrationally excited OH does occur and that this loss process corresponds to either multiquantum deactivation to the v = 0 level or chemical removal of OH(z)). The rate coefficients for this process, k?(v), are assumed to be independent of the vibrational level and have values that correspond to the upper limits derived by McDade and Llewellyn (1987) as listed in Table 4. For the “no O-atom quenching” component of each pair it is assumed that collisional removal of all levels is effectively dominated by O,, or N2, and all of the k:(v) coefficients are taken to be zero. The 1.61 pm emission profiles expected for these models, under the conditions of the ETON experiment, have been calculated using the measured atomic
OH Meinel band emission
B
1143
3
8
T: s 7
6
wi
4
‘4 * r;
2
i“*” h.
2
I
e
0
123456789
123456785 VIBRA TIONAL
QUANTUM NUMBER
VIERA TIDNAL
QUANTUM NUMEER
FIG. 6. (a) UPPER AND LOWERLIMITSFOR{k~z(v)+k~z(~).R}/A(9) DEDUCED BY MCDADE AND LLEWELLYN (1987) FORTHELic~~~~~~~~A~ CASCADE”~ssu~m-ION (rRt.4i~o~Es)AND THEVALUEOBT.~INRD IN em PRESENT WORK (SOLID CIRCLE)FOR {k:2(8)+k:2(8)*R}/A(9). ( TRIANGLES)DEDUCED BY MCDADE AND LLEWELLYN (1987) (b) THE VALUES FOR C{@(u)/.4(9)}[Q]/(O,] FOR THE “SUDDEN
DEATH"
ASSUMPTION AND THE VALUE FOR {k:z(8)+k3(8)*R}/A(9) PRESENT WORK (SOLIDCIRCLE).
OBTAINED IN THE
TABLET. ADOPTED MODEL PARAMETERS*
Sudden death with O-atom quenching-@> kp(o)/A(9) = 1.5 x IO-r3
Sudden death with no O-atom quenching
{k(g~2(u)+k~2(1)).R}/A(9)
u
5.3 4.5 5.1 1.1 0.1 0.15 0.15 0.25 0.10
x x x x x x x x x
{/+(~,a-I)+!+(z.,u5.3 8.9 13.4 9.8 5.9 4.1 3.3 2.5 1.4
9 8 7 6 5 4 3 2 1 *All coefficients
oxygen
concentrations
together
5.3 8.8 12.9 9.0 4.8 2.9 1.8 0.9
1o-‘4 IO-l-’ lo-l4 lo-‘4 1o-14 lo-l4 lo-‘4 lo-l4 1omi4
are from McDade
with [O,], [NJ
and Llewellyn
and
temperature profiles from the MSIS-83 model (Hedin, 1983), the relative transition probabilities (1971) and the parameters
with O-atom = 6 x lo-‘r
{k~2(~,~)-l)+k~~(tl,~-l).R}/A(9)
l)*R}/A(9) x x x x x x x x x
1omt4 lo-l4 lo-l4 lo-l4 0 0 0 0 0
Collisional cascade quenching-kT(v)/A(9)
Collisional cascade with no O-atom quenching
u
jk~?(v)+k~?(u).R}/A(9) 5.3 x 4.3 x 4.9 x 1.0x
1om’4 lo-l4 lo-‘4 lo-l4 lo-l4 lom’4 lo-r4 lo-l4 lo-r4
x 1om’4 x IO-l4 x IO-l4 x lo-l4 x lo-r4 x lo-l4 x lo-l4 x lo-l4 0
(1987) and are in units of cm3 molec’
The absolute volume emission rate of each band contributing to the
1.61pm channel is given by
of Murphy
listed in Tables 2 and 4.
V(v',u") = A(c',v”)[OH(v’)]
(11)
I. C. MCDADE et al.
1144
50
0
100
VOLUME EMISSION
200x10”
I50
Cphotons
cm -3 eeo -!,
FIG. 7. MEASURED 1.61 pm VOLUMEEMISSIONPROFILE (****a) AND THE PROFILESCALCULATED UNDER THE “SUDDEN DEATH WITH NO O-ATOM QUENCHING” (. .) ; “SUDDEN DEATH WITH O-ATOM QUENCHING” (--) ; “COLLISIONAL CASCADE WITH NO O-ATOM QUENCHING” (---) AND “COLLISIONAL CASCADE WITH O-ATOM QUENCHING” (---) MODELSAS DESCRIBEDIN THE TEXT. The dotted and short dashed curves coincide.
which
may
be evaluated
the following expression down to v = v’
by recursive
application of (see Appendix) from v = 9
Ato’,v”)tOW~)l= +k:2[NJ}A(v’, +
9
v//)/A(9)
A(v’, v”)[OH(v*)][A(v*,
. o*=t.+,
+[0J{k:2(v*,v)+k~~(v*,
v)/A(9)
v). R&4(9)]
1 (12)
The 1.61 pm emission rates predicted by each model are shown in Fig. 7, where they are compared with the measured profile. Clearly, the total integrated intensities and peak emission rates of the modelled and measured profiles are in reasonably good agreement, but none of the four models successfully reproduces the shape of the measured 1.61 pm profile.
4. DISCUSSION
In the previous section it has been shown that the I) = 8 level of OH must suKer considerable loss in the mesosphere due to collisions with 02, and/or N2, and exhibit a half-quenching altitude of -91 km, if the
“sudden death” assumption is valid (Fig. 3), or - 95 km if the “collisional cascade” assumption is valid (Fig. 5). It is not possible to quantify the absolute rate coefficients for the collisional removal processes without assuming a vibrationally excited OH radiative lifetime. However, it has been demonstrated that the values obtained for the product of these coefficients and the v = 9 radiative lifetime are very similar to those inferred by McDade and Llewellyn (1987) from ground-based observations. Throughout the analysis it has been assumed that the rate of vibrationally excited hydroxyl production can be equated to that of ozone formation in the three-body recombination of atomic and molecular oxygen. This approach greatly simplifies the analysis as information about the hydrogen atom and ozone number densities is not required. This assumption may not be strictly valid for altitudes above - 95 km where the reaction between ozone and atomic oxygen may contribute to the total ozone loss rate (Moreels et al., 1977; Good, 1976). Any breakdown in this assumption would, therefore, result in an over-estimate of the total OH production rate at these higher altitudes. However, Fig. 4 would suggest that the OH production rates have, in fact, been under-estimated above 100km. This apparent anomaly could be explained if some additional source of ozone exists at the higher altitudes. This possibility has recently been discussed by Allen (1986) and it is interesting to note that the ozone production rates which would be required, above 100 km, to bring the measured and modelled OH(8,3) band emission profiles into better agreement are very similar to those suggested by the observations of Allen. In the analysis of the 1.61 pm emission it has been shown that the total measured zenith intensity is quite similar to that predicted by four different Meinel Band excitation models, all of which assume reaction (1) to be the only chemical source of vibrationally excited OH. However, none of these models predicts a 1.61 pm volume emission profile which is similar in shape to the measured profile. This difficulty in modelling the 1.61 pm emission be due to inadequacies
profile
may not necessarily
in the model parameters but could arise from erroneous structure in the derived 1.61 pm volume emission rates. As already mentioned, it is possible that the 1.61 pm measurements may have been contaminated by a vehicle-induced emission. If this is the case then it is perhaps more appropriate to compare the modelled and measured zenith intensity profiles rather than volume emission profiles. The measured and modelled zenith profiles arc shown in Fig. 8(a) where each modelled profile has been normalized to the zenith bright-
OH Meinel band emission
50
180
ZENITH BRIGHTNESS FIG. 8. (a)Tm
1145
Ckff>
ZENITH BRIGHTNESS PROFILES CORRESPONDING FIG. 7.
TO THE VOLUME EMISSION PROFILES SHOWN
IN
The modelled zenith profiles have been normalized using the factors : 0.79 for the “sudden death with no O-atom quenching” model (. .) ; 0.84 for the “sudden death with O-atom quenching” model (--) ; 0.79 for the “collisional cascade with no O-atom quenching” model (---) and 0.98 for the “collisional cascade with O-atom quenching” model (--). The dotted and short dashed curves coincide. (b)Tm RESIDUAL PROFILES CORRESPONDING TO THEDIFFERENCES BETWEEN THE MEASURED AND MODELLED ZENITH PROFILES SHOWN
ness measured before the rocket penetrated the OH layer. The required normalization factors are listed in the caption for Fig. 8(a) and all lie within the uncertainty of +_20% in the absolute calibration of the 1.61 pm radiometer (Greer et al., 1986). Clearly the “collisional cascade with O-atom quenching” and “sudden death with O-atom quenching” zenith profiles are in reasonably good agreement with the observations up to - 90 km ; however, above this altitude the modelled zenith brightnesses are too weak and do not exhibit the upper “shoulder” present in the measured profile. This shoulder is, of course, the source of the secondary maximum in the derived 1.6 1 pm volume emission profile and is evident in most other reported rocket measurements of the OH emission in this specral region (Evans et al., 1973 ; Good, 1976; Thomas and Young, 1981; Lopez-Moreno et al., 1985). Usually, as in the present case, the shoulder appears only as an inflexion in the zenith intensity profile and cannot be unambiguously attributed to anything other than a secondary maximum in the volume emission rate. However, in the work of LopezMoreno et al. (1985) an actual transient increase in zenith brightness was observed as the rocket penetrated the 92-97 km region. This could not have been simply due to a secondary maximum in the emission profile and is most easily explained in terms of a vehicle-induced glow. If a vehicle-induced glow is responsible for some of the differences between the measured and modelled profiles of Figs 7 and 8(a),
IN (a).
then, for a particular model to be viable, the modelled zenith brightness must be less than or equal to, the measured brightness at all altitudes. Clearly, only the models which include O-atom quenching come close to satisfying this criterion. The difference, or residual, profiles obtained from the data of Fig. 8(a) are shown in Fig. 8(b). Obviously, the residual “collisional cascade with O-atom quenching” zenith crofile is more consistently positive than the residual“‘sudden death with O-atom quenching” profile, but in view of the uncertainties inherent to the observations it would, perhaps, be premature to make any choice between these alternate models on the grounds of this observation alone. It should also be noted that the latter two residual profiles are remarkably similar, both in their shapes and magnitudes, to the vehicle-induced emission profiles obtained by Lopez-Moreno et al. (1985) from a comparison of their rocket ascent and descent data. This suggests that the “sudden death with O-atom quenching” and “collisional cascade with O-atom quenching” models, and parameters, of McDade and Llewellyn (1987) are not only consistent with the altitude profile of the u = 8 level but may, also, successfully predict the altitude profiles of the lower vibrational levels. However, the precision with which the latter two models do predict the low v’ profiles must remain unquantified in the absence of independent information about the altitude distribution of any vehicle-induced contamination in the 1.6 pm channel.
I. C. MCDADE et al. 5. CONCLUSIONS It has been shown that the z) = 8 level of vibrationally excited hydroxyl suffers significant deactivation in the mesosphere due to collisions with 0, and/or N2. Kinetic parameters related to these processes have been derived and are found to agree with those obtained from an independent analysis of groundbased observations. A variety of kinetic models fail to reproduce the detailed structure of the measured 1.61 pm emission profile and it has been suggested that the 1.61jtrn observations may have been contaminated by an unidentified vehicle-indu~d emission. If this is indeed the case, it would appear that a Meinet Band excitation model based on stepwise vibrational deactivation, with significant O-atom quenching, best explains the low v’ Meinel Band emission profiles, although the quality of the fit must be considered uncertain.
Acknowleu’qements-This work has been supported United Kingdom Sciences and Engineering &search cil and the Natural Sciences and Engineering Research cil of Canada.
by the dounCoun-
REFERENCI%S Allen, M. (1986) A new source of ozone in the terrestrial upper atmosphere? J. geophys. Res. 91,2844. Allen, M., Lunine, J. L. and Yung, Y. L. (1984) The vertical distribution of ozone in the mesosphere and lower thermosphere. J. geophys. Res. 89,484l. Baker, D. J. and Waddoups, R. 0. (1967) Rocket measurement of midlatitude night airglow emissions. J. geophys. Res. 72,4881. Bates, D. R. (1982) Airglow and aurora, in Applied Atomic Coilision Physics (Edited by Massey, I-i. S. W., Baderson, B. and McDaniel, E. W.), Vol. I, pp. 149-224. Academic Press, New York. Bates, D. R. and Nicolet, M. (1950) The photochemistry of atmospheric water vapour. J. geoph,vs. Res. 55, 301. Charters, P. E., MacDonald, R. G. and Polanyi, J. C. (1971) Formation of vibrationallv excited OH by the reaction H +O,. Appl. Optics 10, lf47. Evans, W. F. J., Llewellyn, E. J. and Valiance Jones, A. (1973) Altitude distribution of hydroxyl bands of the Au = 2 sequence in the nightglow. Can. .I. Phys. 51, 1288. Finlavson-Pitts, B. J. and Kleindienst, T. E. (1981) The reaction of hydrogen atoms with ozone as a source of vibrationallv excited OH(X”Il,),._, for kinetic studies. J. them. Phys.%, 5643. “’ _ Good, R. E. (1976) Determination of atomic oxygen density from rocket borne measurement of hydroxyl airglow. Planet. Space Sci. 24, 389. Greenblatt, G. D. and Wiesenfeld, J. R. (1982) Time-resolved emission studies of vibra~ionally excited hydroxyl radicals : OH{X’II, 0” = 9). J. geophys. Res. 87, 11145. Greer, R. G. H.. Murtagh, D. P., McDade, I. C., Dickinson, P. H. G., Thomas, L., Jenkins, D. B., Stegman, J., Llew-
ellyn, E. J., Witt, G., Mackinnon, D. J. and Williams, E. R. (1986) ETON I: a data base pertinent to the study of energy transfer in the oxygen nightglow. Platlet. Space Sci. 34,771. Harrison, A. W. and Kendall, D. J. W. (1973) Airgiow hydroxyl intensity measurements 0.6-2.3 p. Planet. Space Sci. 21, 1731. Hedin, A. E. (1983) A revised thermospheric model based on mass spectrometer and incoherent Scatter data : MSIS83. J. aeoohvs. Res. 88, 10170. Krassovsky; t. I., Shefov, N. N. and Yarin, V. I. (1962) Atlas ofthe airglow spectrum 300&124000.& Planet. Space Sci. 9,883. Lin, C. L. and Leu, M. T. (1982) Temperature and thirdbody dependence of the rate constant for the reaction O+OztM-+Oz+M. Int. J. Chem. Kinetics 14,417. Llewellyn, E. J., Long, B. H. and Solheim, B. H. (1978) The quenching of OH* in the atmosphere. Pkmet. Space Sci. 26, 525. Lopez-Moreno, J. J., Rodrigo, R. and Vidal, S. (1985) Radiative contamination in rocket-borne infrared photometric measurements. J. geophys. Res. 90, 6617. Makino, T., Yamamoto, H. and Sekiguchi, H,. (1983) AMtude profiles of OH and 0, near infrared airglows in the evening twilight. J. Geomugn. Geoelect. 35, 57. McDade, I. C. and Llewellyn, E. J. (1987) Kinetic parameters related to sources and sinks of vibrationally excited OH in the nightglow. J. geophys. Rex in press. Meinel, A. B. (1950) OH emission bands in the spectrum of the night sky 1. Astrophys. J. 111, 555. Mies, F. I-I. (1974) Calculated vibrational transition probabilities of OH(X%). J. molec. Specfrosc. 53, 150. Moreels, G., Megie, G., Valiance Jones, A. and Gattinger, R. L. (1977) An oxygen-hydrogen atmospheric model and its application on the OH emission problem. J. atoms. terr. Phys. 39, 551. Murphy, R. E. (1971) Infrared emission of OH in the fundamental and first overtone bands. .f. them. Phys. 54, 4852. Murtagh, D. P. and Greer, R. G. H. (1984) The nightglow hydroxyl (8-3) band emission-a comparison of experiment and theory, in Proc. 12th Annual Meeting on Atmospheric Studies by Optical Methods (Stockholm) (Edited by Witt, G.), p< 51. Murtagh, D. P., Greer, R. G. H., McDade, 1. C., Llewellyn, E. 3. and Bantle, M. (1984) Representative volume emission profiles from rocket photometer data. Ann. GeophJs. 2,467. Ohoyama, II., Kasai, T., Yoshimura, Y., Kimura, H. and Kuwata, K. (1985) Initiai distribution of vibration of the OH radicals produced in the H to? + OH(.X?‘I) + O7 reac_ tion. Chem. %ys. Left. 118,263. Packer. D. M. (1961) Altitudes of the night radi_ airglow _ ations. Ann. deoph&. 17, 61. Potter, A. E., Jr., Coltharp, R. N. and Worley, S. D. (1971) Mean radiative lifetime of vibrationally excited (v = 9) hydroxyl. Rate of the reaction of vibrationally excited hydroxyl (v = 9) with ozone. J. them. Phys. 54,992. Rogers, J. W., Murphys, R. E., Stair, A. T., Jr., Ulwick, J. C., Baker, K. D. and Jensen, L. L. (1973) Rocket-borne radiometer measurements of OH in the aurora1 zone. I. geophys. Res. 78, 7023. Solheim, B. II. (1979) MSc Thesis, The infrared atmosp~c~c system of oxygen in the nightglow. The University of Saskatchewan, Saskatoon, Canada. Takahashi, H. and Bat&, P. P. (1981) Simultaneous
1147
OH Meinel band emission measurements of OH(9,4), (83) (7,2), (6,2) and (5.1) bands in the airglow. J. geophys. Res. X6, 5632. Thomas, R. J. and Young, R. A. (1981) Measurement of atomic oxygen and related airglows in the lower thermosphere. J. geophys. Res. S&,7389. Turnbull, D. N. and Lowe, R. P. (1983) Vibrational popuIation distribution in the hydroxyl night airglow. Can. J. Phys. 61, 244. Witt, G., Stegman, J., Solheim, B. H. and Llewellyn, E. J. (I 979) A measurement of the O2 (b ‘C - X’X) atmospheric band and the 01(‘S) green line in the nightglow. Planer. space ‘sci. 27, 34 I.
1
+kF;‘+*, U)’ Rf[O,]] [A(u)+ p@(u) +~~~(uf~R)[O,l+k*~(u)[Ol~-‘.
(Al)
Multiplying both sides of equation (AI) by A(u’,u”) and dividing both the numerator and denominator of the RHS by A(9) yields .~(~)[O][O~]~~~~[O~]
A&‘, z:“)[OH(~)] = I +k:>[N,]}A(u’,
APPENDIX
Under steady-state conditions the concentration vibrational level of OH is given by
of each
[A(o*,a)/A(9)+
0”)/.4(9)+
2 A@‘, u”)[OH(v*)] ,**=p+I [O,l{k~qv*, u)
+ kE”+*. 2,)* R)/A(9)]
1
[{A(u)/A(9)j
+[o,Jfkq?(l;)+k~lfu).R)iA(9) +
[Olkm:.4(9)]-‘.
642)
ETON
W32-0633/87 $3.00+0.00 Pergamon Journals Ltd.
5 : SIMULTANEOUS ROCKET MEASUREMENTS OF THE OH MEINEL Au = 2 SEQUENCE AND (8,3) BAND EMISSION PROFILES IN THE NIGHTGLOW 1. C. McDADE and E. .I. LLEWELLYN Institute of Space and Atmospheric Studies, University of Saskatchewan, Saskatoon, Saskatchewan, Canada S7N OWO D. P. MURTAGH Meteorological Institute, Arrhenius Laboratory, Stockholm University, S-106 91 Stockholm, Sweden
R. G. H. GREER Department of Pure and Applied Physics, The Queen’s University of Belfast, Belfast BT7 lNN, U.K. (Received in$nalform
1 April 1987)
Abstract-Simultaneous rocket measurements of the emission profiles of the OH Meinel (8,3) band and the Au = 2 sequence at 1.61 pm are presented and analysed. It is shown that the u = 8 level of the hydroxyl radical must suffer significant loss in the mesosphere due to collisions with 0, and/or N,. The rate coefficients for this removal process are obtained, for certain limiting assumptions about the excitation mechanism, and the coefficients are found to be in good agreement with those deduced from an independent analysis of ground-based observations. A variety of kinetic models, which reproduce the observed (8,3) band profile in some detail, predict AU = 2 sequence emission profiles which compare favourably with the measured profile in their total zenith intensities but not in their altitude distributions. The differences between the measured and modelled AU = 2 altitude profiles suggest that the 1.61 ILrn observations may have been contaminated by some unidentified vehicle-induced emission.
I. INTRODUCTION
vibrational levels of OH must be populated of radiative cascade
Vibration-rotation transitions within the ground electronic state of the hydroxyl radical dominate the spectrum of the terrestrial nightglow, and although more than three decades have passed since the system was first identified by Meinel (1950), a complete understanding of the excitation mechanism has still not been achieved. It was originally suggested by Bates and Nicolet (1950) and is now generally accepted, that the reaction H+O$+OH(v
< 9)+02
OH(v’)~OH(v”)+hv and single-quantum, deactivation OH(v’) + Q
(1)
is the major source of the radiant energy. However, the nascent OH products of reaction (1) are found primarily in the vibrational levels v = 7, 8 and 9 (Charters et al., 1971; Murphy, 1971; Ohoyama et al., 1985) and it remains uncertain how the lower vibrational levels, responsible for most of the Meinel Band emission, become populated. If reaction (1) is the only chemical source of vibrationally excited hydroxyl, then the lower 1137
or multi-quantum,
&o.. 0”) -OH(v”)+Q.
as a result
(2) collisional
(3)
Over many years of study, conflicting assessments of the extent to which the Meinel Band emission can be explained by processes (l), (2) and (3) have been presented (Llewellyn et al., 1978; Takahashi and Batista, 1981 ; Turnbull and Lowe, 1983) and it has not yet been established whether an additional chemical source of vibrationally excited OH is involved. Most of the difficulties encountered in attempts to resolve this issue (most recently reviewed by Bates, 1982) stem from controversy over the absolute Meinel Band transition probabilities and the inconsistent use of quite diverse sets of vibrational deactivation rate coefficients. Some recent laboratory experiments by
1. C. MCDADE et al.
1138
Finalyson-Pitts and Kleindienst (198 1) and Greenblatt and Wiesenfeld (1982) have suggested that many of the vibrational deactivation rate coefficients, which have been widely used in Meinel Band studies, may be in serious error. As a consequence, doubt has been cast on many of the conclusions reached from previous work. In view of this, McDade and Llewellyn (1987) have used ground-based observations of the mean nightglow OH vibrational distribution in an attempt to re-evaluate some of these important coefficients. While the kinetic parameters deduced by McDade and Llewellyn (1987) do reproduce the altitude-integrated OH vibrational distribution, their approach suffers from the limitation that these parameters may not necessarily be consistent with the altitude profiles of the individual vibrational levels. In the present paper some of these kinetic parameters are independently derived from simultaneous rocket photometer measurements of the OH Meinel Au = 2 sequence and (8,3) band emission profiles which were cooordinated with a determination of the atomic oxygen concentrations. 2. THE
ROCKET OBSERVATIONS
The present observations were made as part of a multiple rocket investigation of nightglow excitation mechanisms, known by the acronym ETON, and described in more detail by Greer et al. (1986) in Part I of this series of papers. The OH(8,3) band emission profile was measured with a conventional forwardlooking filter photometer on a Petrel rocket, P228H, launched from South Uist, Scotland (57.36”N, 352.62”E) at 23 : 28 : 23 U.T. on 23 March 1982. The Au = 2 OH Meinel Band sequence in the 1.61 pm region was measured from the same rocket with a forward-looking radiometer which incorporated an interference filter, a lead sulphide detector and phasesensitive detection. This radiometer has been described in more detail by Solheim (1979). The filter
transmission characteristics for both instruments are listed in Table 1. The zenith intensity data, recorded on the upleg of the rocket flight, have been reduced to volume emission profiles using the procedures described by Greer et al. (1986) and Murtagh et al. (1984). In the case of the OH(8,3) band this included removal of a contribution to the signal from the nightglow continuum-a procedure expedited by a simultaneous measurement of the red continuum at 714Ow (Murtagh and Greer, 1984; McDade et al., 1986). Unfortunately little is known about any nightglow continuum that may contribute to the Au = 2 channel and, therefore, no attempt to correct for this has been made. The derived (8,3) band volume emission profile, corrected for the instrument capture function listed in Table 1, is shown in Fig. 1. The Au = 2 volume emission profile is also shown in Fig. 1 and corresponds to the sum of the individual (6-4) (5-3) (4-2) (3-l) and (220) band volume emission rates with each band weighted by its respective capture function. The atomic oxygen concentrations employed in the analysis, shown in Fig. 2, were measured, using the 01 resonance absorption and fluorescence technique, on another rocket, P234H, launched 26 min later (Greer et ul., 1986). 3. ANALYSIS
The measured total zenith intensities of the (8,3) band and Au = 2 sequence were 285 R and 149 kR, respectively, and are typical of those expected from ground-based observations (Krassovsky et al., 1962; Harrison and Kendall, 1973 ; Takahashi and Batista, 1982). It is clear from Fig. 1 that the derived Au = 2 emission rate not only peaks at a lower altitude than the (8,3) band but also exhibits a secondary maximum just below an altitude of 100 km. The peak heights of both profiles lie well within the ranges reported from previous rocket measurements of these two features (Packer, 1961; Baker and Waddoups, 1967; Evans et
TABLE 1. FILTER AND DETECTORCHARACTERISTICS
Instrument # 2
Instrument # 1 Filter peak Filter width Detector
7240 A 49A EMR 541 E-01
Capture
OH Meinel (8,3) : 0.24
functions*
* Capture
functions
are based on an OH rotational
1.61 pm 194ow PbS OH OH OH OH OH
Meinel Meinel Meinel Meinel Meinel
temperature
(64) (S-3) (4-2) (3-l) (2-O)
of 200 K.
: 0.22 : 0.73 : 0.87 : 0.42 : 0.18
OH Meinel band emission
1139
0
FIG.I.MEASUREDVOLUMEEMISSIONPROFILESOFTHE
al., 1973 ; Rogers el al., 1973 ; Good, 1976 ; Witt et al., 1979; Thomas and Young, 1981 ; Makino et ai., 1983; Lopez-Moreno et al., 1985) and it should be noted that the presence of a secondary maximum in the At> = 2 emission appears to be a common feature of the other reported measurements. There is, however, some evidence to suggest that this secondary maximum may not be real but is perhaps an artifact resulting from optical emission induced by the rocket vehicle as it penetrates the airglow layer (LopezMoreno et al., 1985). It must, therefore, be recognized that the present Au = 2 measurements may also have been affected by such a phenomenon. As the processes which contribute to the excitation
OH(8,3)
AZ’= 2
BANDAND
SEQUENCEAT
1.61pm.
of the lower v’ levels are so numerous and much less direct than those contributing to the excitation of the u = 8 level, it is really only possible to extract reliable and definitive kinetic information from the (8,3) band profile. 3. I. Tfie OH(8.3) band emission proJife If reaction (I) is the only chemical source of vibrationally excited OH then, under steady-state conditions, the (8,3) band volume emission rate is given by V(8 3) = ‘4(8,3)k,[Hl[O,l L(8)
.fVN4%8)+ ;x-%WQll x
+
_I_ .-._______ L(9)
(4)
where~(~) represents the fractional yield of level ‘b” .in reacion (I) and I;(a) represents the total atmospheric loss of level “u”. This total loss may be expressed as L(u) = A(r)+
~k?W[Ql
(5)
Q
where A(v) is the inverse radiative lifetime of level “v” and k:(v) is the total coefficient for removal of this level by all collisional processes involving the species
dLQ”. 0-A fOH
Frc.2.
omsi TY ccm-3,
~TOWlCOXYGENCONCENTRATlONSEMPLOYGDINTHE PRESENT ANALYSIS.
As already mentioned, most of the laboratory measured rate coefficients for collisional quenching of vibrationaily excited OH are now thought to be suspect (Finlayson-Pitts and Kleindienst, 1981 ; Greenblatt and Wiesenfeld, 1982) with the exception of that
I. C.
1140
MCDADE et al.
measured by Finlayson-Pitts and Kleindienst (198 1) for the total rate of removal of OH(v = 9) by 0,. However, it remains unclear whether this coefficient relates to single-quantum vibrational deactivation, multi-quantum deactivation or chemical removal of the v = 9 level. Because of this ambiguity the present results are analysed in terms of two limiting cases. In the first case it has been assumed that collisional removal of OH(v = 9) does not constitute a source of any other vibrationally excited level of OH-this will be referred to as the “sudden death” assumption. In the second case it has been assumed that collisional removal of OH(v = 9) by 0, results in the production of OH(v = 8)-this will be referred to as the “collisional cascade” assumption. In both cases it has been assumed that removal of OH(9) in the atmosphere by N, is negligible since Finlayson-Pitts and Kleindienst (1981) find this process to be at least 20 times slower than the corresponding 0, reaction. Under the “sudden death” assumption, all of the @(9,8) coefficients are zero and equation (4) reduces to
For all altitudes in the mesosphere and all published Meinel Band transitions probabilities, the bracketed term in equation (6) is dominated by the quantityf(8) i.e. radiative cascade from OH(u = 9) constitutes a negligible source of OH(v = 8). In addition, between altitudes of 80 and 100 km, reaction (I) is the major ozone removal process at night (Moreels er al., 1977 ; Allen et al., 1984) and equation (6) can be approximated by
V(8,3) =
A(*)+
~k8@Wl Q
*R)/A(8,3),
equal to 2.0 f0.3 x lo-” cm3 molec-‘, and suggests that ky(8)/A(8,3) must be less than -2 x 10-‘0cm3 molec’. The quality with which these kinetic parameters reproduce the observations is illustrated in Fig. 4, where the OH(8,3) band volume emission profile generated with the derived fitting coefficients and equation (7) is compared with the original data. Under the alternate “collisional cascade” assumption, where collisional loss of OH(u = 9) by 0, is assumed to populate OH(v = 8), the equivalent of equation (7) is
f@Y+P~*)P,1 I
(9)
(7)
where kz2 and k:l represent the termolecular rate coefficients for ozone formation with NZ and 0, as third bodies. A re-arrangement of equation (7) yields 1 ~ A(8,3)
P’?(8) +@(8)
A(9)+k:‘(9)[02]+k:(9)[0]
~(~,3)~Ol~0,1~~~~~~,l+~~2~021~f(8) L(8)
model atmosphere (Hedin, 1983) and the kinetic parameters of Table 2, is shown in Fig. 3. It is evident from this figure that the atmospheric loss of OH(v = 8) must be dominated by spontaneous emission and collisional removal by O,, or N,, and that any O-atom removal process must be relatively unimportant for this level. Because of the similar atmospheric scale heights of [O,] and [NJ (i.e. [NJ[OJ is approximately equal to a constant “R’) it is not possible to distinguish between the losses due to these species which may, for the present purposes, be treated as being entirely due to 0,. A statistically weighted least-squares fit of the data of Fig. 3 to the MSIS-83 [O,] profile yields an intercept term, A(8)/A(8,3), equal to 260 + 50, an [0,] fitting coefficient,
1
Equation (8) which defines the OH (u = 8) quenching profile, allows the atmospheric loss of this level to be evaluated, from the observations, as a function of altitude. The altitude dependence of the right-hand side of equation (8), calculated using the measured atomic oxygen and volume emission profiles, the [O,], [NJ and temperature profiles from the MSIS-83
where ky2(9,8) is identical to k:>(9)-the total rate coefficient for removal of OH(u = 9) by 0,. The value for k:>(9) measured by Finlayson-Pitts and Kleindienst (1981) is critically dependent upon the uncertain absolute (9,3) band transition probability. However, the quantity relevant here is A(9)/ky2(9) which is much less sensitive to the choice of absolute probabilities. The value inferred for this quantity from the Finlayson-Pitts and Kleindienst experiments using the transition probabilities of Mies (1974) is 3 x 10’3molec cm-3, and with the transition probabilities of Potter et al. (1971) the inferred value is 4 x 10’3 molec a mean value of cmm3. For A(9)/kyz(9,8) equal to 3.5 x 10’3molec cme3, and assuming the atmospheric loss of OH(v = 9) to be dominated by 02, a re-arrangement of equation (9) yields
OH Meinel band emission AND
TABLET. REACTIONS
Reaction
H + 0, -OH(a)
1141
ADOPTED COEFFICIENTS
Reference
Coefficient f(9) f(S) f(7) f(6) f(5) 1’(4)
+ 0,
= = = = = =
Ohoyama Ohoyama Ohoyama Ohoyama Ohoyama Ohoyama
0.32 0.29 0.19 0.06 0.06 0.06
et al. (1985)* et al. (1985)* et al. (1985)* et ~1. (1985)*
et al. (1985)* et al. (1985)*
OH(v’) + Q kp(O’~U”) >OH@“) + Q OH(u) + Q -
see Table 4
P
all products
I
k,M O+O,+M+O,+M *Adjusted in molecule.
kN 62 = 5.70 x 10-34(T/300)-~~~~ k’$ = 5.96 x 10-34(T/300))2.37
using the relative transition cm. set units.
probabilities
of Murphy
0
3
Lin and Leu (1982) Lin and Leu (1982) (1971). All coefficients
50
100
VOLUME EMISSIUN
FIG. 3. ALTITUDEDEPENDENCEOF THE RHS OFEQUAT~ON (8) (***W)AND THELEAST-SQUARES FIT (SOLIDCURVE)OBTAINED ASDESCRIBED INTHETEXT.
Error
-~ A&3) 1
bars correspond to the uncertainties emission rates of Fig. I.
A(S)+
in the volume
1 f (9)P*l 3.5x 1oJ3+[02]
000
1 i0
cm-’ se-3
FIG. 4. MEASURED
OH(8,3) BAND VOLUME EMISSION PROFILE (*****) AND THE PROFlLES GENERATED FROM THE “SUDDEN DEATH"(SOLIDCURVE)AND“COLLISIONALCASCADE"(BROKEN CURVE) FITTING COEFFICIENTSAS DESCRIBED 1N THE TEXT.
~Ol~~,l{~~~~~,1+~k)2~~~1~ V&3)
150 +hotons
data of Fig. 5 to the MSIS-83 [0,] profile yields an intercept term, A@)/A(8,3), equal to 24Ok 50 and an [O,] fitting coefficient,
~@@)[Ql 0
=
are
{k?W+k%8).
1 (10)
Equation (10) allows the OH(r = 8) quenching profile to be evaluated for the “collisional cascade” assumption. The altitude dependence of the righthand side of equation (10) is shown in Fig. 5 which indicates that the loss of OH(r = 8) must again be dominated by spontaneous emission and collisional removal by 02, and/or NZ. A least-squares fit of the
R}lA(8,3),
equal to 3.3kO.5 x IO-“cm’ molec’. The OH(8,3) band volume emission profile generated from equation (9) and the latter fitting coefficients, is shown in Fig. 4 and is very similar to both the measured profile and that generated for the “sudden death” assumption. One of the most significant aspects of the parameters deduced above is the value obtained for A@)/A(8,3). Several sets of Meinel Band transition probabilities exist in the literature and, as Table 3 shows, the A(8) : A&3) branching ratios obtained
1142
I. C. MCDADE ef al.
{kX8)+kX8) *R}lA(W, correspond
to values of {@(8)+#(8)
500
0
RHS fq.
1000
I500
2000
Cdimerrsionless>
FIG. 5. ALTITUDE DEPENDENCEOF THE RHS OF EQUATION (lo) (*****) AND THE LEAST-SQUARES FIT (SOLID CURVE) OBTAINED
Error
AS DESCRIBED
IN THE TEXT.
bars correspond to the uncertainties emission rates of Fig. 1.
TABLE 3. A(8)
in the volume
: .4(8,3) BRANCHING RATIOS FROM THIS
* R}/A(9),
equal to 5 x 10 -I4 and 8.5 x 10~“‘cm3molecc for the “sudden death” and “collisional cascade” assumptions, respectively. As shown in Figure 6, these quantities are very similar to those deduced by McDade and Llewellyn (1987) and, therefore, the latter parameters not only reproduce the mean OH vibrational distribution but are also consistent with the altitude profile of the OH(8,3) band. Although this consistency is most encouraging, the OH(8,3) band analysis does not allow the relative merits of the “sudden death” and “collisional cascade” models to be assessed as both models predict essentially the same (8,3) band volume emission profile. In order to identify the most appropriate mechanism a comparison of the measured and modeled 1.61 I.trn emission profiles may be more conclusive.
AND
OTHER STUDIES A(8) : A&3)
Reference
260 f 50
This work with the “sudden death” assumption This work with the “collisional cascade” assumption Murphy (1971) Mies (1974) Potter et ul. (1971)
240 2 50 320 445 1056
here are in better agreement with the relative transition probabilities of Murphy (1971) than with the other sets of probabilities widely used in Meinel Band studies. This adds to the body of evidence which suggests that the relative transition probabilities of Murphy are the most reliable (Takahashi and Batista, 198 1) and allows the values obtained here for j@(8)
+k$(8)
*R}/A(8,3)
to be compared with the parameters deduced by McDade and Llewellyn (1987). In the work of McDade and Llewellyn (1987), the relative transition probabilities of Murphy (1971) were adopted and values for {k:Q)+kl;+)*
R}/A(9)
were obtained for Meinel Band excitation models corresponding to both the “sudden death” and “collisional cascade” assumptions. With the relative transition probabilities of Murphy (1971) the values obtained in the present work for
3.2. The 1.61 pm emission pro$le As a number of OH bands and, therefore, excitation pathways contribute to the 1.61 pm emission it is not possible to extract specific kinetic parameters from the 1.61 pm profile, and the measured profile is used here simply to determine which of the models and parameters derived by McDade and Llewellyn (1987) best explain the observations. In all, two pairs of models are considered. The first pair of models are based on an extension of the “sudden death” models. The second pair of models-the “collisional cascade” models-are based on an extension of the “collisional cascade” assumption. The two models within each pair differ in the limiting assumptions that are made about the rate of removal of vibrationally excited OH by atomic oxygen. For the “with O-atom quenching” component of each pair it is assumed that O-atom removal of vibrationally excited OH does occur and that this loss process corresponds to either multiquantum deactivation to the v = 0 level or chemical removal of OH(z)). The rate coefficients for this process, k?(v), are assumed to be independent of the vibrational level and have values that correspond to the upper limits derived by McDade and Llewellyn (1987) as listed in Table 4. For the “no O-atom quenching” component of each pair it is assumed that collisional removal of all levels is effectively dominated by O,, or N2, and all of the k:(v) coefficients are taken to be zero. The 1.61 pm emission profiles expected for these models, under the conditions of the ETON experiment, have been calculated using the measured atomic
OH Meinel band emission
B
1143
3
8
T: s 7
6
wi
4
‘4 * r;
2
i“*” h.
2
I
e
0
123456789
123456785 VIBRA TIONAL
QUANTUM NUMBER
VIERA TIDNAL
QUANTUM NUMEER
FIG. 6. (a) UPPER AND LOWERLIMITSFOR{k~z(v)+k~z(~).R}/A(9) DEDUCED BY MCDADE AND LLEWELLYN (1987) FORTHELic~~~~~~~~A~ CASCADE”~ssu~m-ION (rRt.4i~o~Es)AND THEVALUEOBT.~INRD IN em PRESENT WORK (SOLID CIRCLE)FOR {k:2(8)+k:2(8)*R}/A(9). ( TRIANGLES)DEDUCED BY MCDADE AND LLEWELLYN (1987) (b) THE VALUES FOR C{@(u)/.4(9)}[Q]/(O,] FOR THE “SUDDEN
DEATH"
ASSUMPTION AND THE VALUE FOR {k:z(8)+k3(8)*R}/A(9) PRESENT WORK (SOLIDCIRCLE).
OBTAINED IN THE
TABLET. ADOPTED MODEL PARAMETERS*
Sudden death with O-atom quenching-@> kp(o)/A(9) = 1.5 x IO-r3
Sudden death with no O-atom quenching
{k(g~2(u)+k~2(1)).R}/A(9)
u
5.3 4.5 5.1 1.1 0.1 0.15 0.15 0.25 0.10
x x x x x x x x x
{/+(~,a-I)+!+(z.,u5.3 8.9 13.4 9.8 5.9 4.1 3.3 2.5 1.4
9 8 7 6 5 4 3 2 1 *All coefficients
oxygen
concentrations
together
5.3 8.8 12.9 9.0 4.8 2.9 1.8 0.9
1o-‘4 IO-l-’ lo-l4 lo-‘4 1o-14 lo-l4 lo-‘4 lo-l4 1omi4
are from McDade
with [O,], [NJ
and Llewellyn
and
temperature profiles from the MSIS-83 model (Hedin, 1983), the relative transition probabilities (1971) and the parameters
with O-atom = 6 x lo-‘r
{k~2(~,~)-l)+k~~(tl,~-l).R}/A(9)
l)*R}/A(9) x x x x x x x x x
1omt4 lo-l4 lo-l4 lo-l4 0 0 0 0 0
Collisional cascade quenching-kT(v)/A(9)
Collisional cascade with no O-atom quenching
u
jk~?(v)+k~?(u).R}/A(9) 5.3 x 4.3 x 4.9 x 1.0x
1om’4 lo-l4 lo-‘4 lo-l4 lo-l4 lom’4 lo-r4 lo-l4 lo-r4
x 1om’4 x IO-l4 x IO-l4 x lo-l4 x lo-r4 x lo-l4 x lo-l4 x lo-l4 0
(1987) and are in units of cm3 molec’
The absolute volume emission rate of each band contributing to the
1.61pm channel is given by
of Murphy
listed in Tables 2 and 4.
V(v',u") = A(c',v”)[OH(v’)]
(11)
I. C. MCDADE et al.
1144
50
0
100
VOLUME EMISSION
200x10”
I50
Cphotons
cm -3 eeo -!,
FIG. 7. MEASURED 1.61 pm VOLUMEEMISSIONPROFILE (****a) AND THE PROFILESCALCULATED UNDER THE “SUDDEN DEATH WITH NO O-ATOM QUENCHING” (. .) ; “SUDDEN DEATH WITH O-ATOM QUENCHING” (--) ; “COLLISIONAL CASCADE WITH NO O-ATOM QUENCHING” (---) AND “COLLISIONAL CASCADE WITH O-ATOM QUENCHING” (---) MODELSAS DESCRIBEDIN THE TEXT. The dotted and short dashed curves coincide.
which
may
be evaluated
the following expression down to v = v’
by recursive
application of (see Appendix) from v = 9
Ato’,v”)tOW~)l= +k:2[NJ}A(v’, +
9
v//)/A(9)
A(v’, v”)[OH(v*)][A(v*,
. o*=t.+,
+[0J{k:2(v*,v)+k~~(v*,
v)/A(9)
v). R&4(9)]
1 (12)
The 1.61 pm emission rates predicted by each model are shown in Fig. 7, where they are compared with the measured profile. Clearly, the total integrated intensities and peak emission rates of the modelled and measured profiles are in reasonably good agreement, but none of the four models successfully reproduces the shape of the measured 1.61 pm profile.
4. DISCUSSION
In the previous section it has been shown that the I) = 8 level of OH must suKer considerable loss in the mesosphere due to collisions with 02, and/or N2, and exhibit a half-quenching altitude of -91 km, if the
“sudden death” assumption is valid (Fig. 3), or - 95 km if the “collisional cascade” assumption is valid (Fig. 5). It is not possible to quantify the absolute rate coefficients for the collisional removal processes without assuming a vibrationally excited OH radiative lifetime. However, it has been demonstrated that the values obtained for the product of these coefficients and the v = 9 radiative lifetime are very similar to those inferred by McDade and Llewellyn (1987) from ground-based observations. Throughout the analysis it has been assumed that the rate of vibrationally excited hydroxyl production can be equated to that of ozone formation in the three-body recombination of atomic and molecular oxygen. This approach greatly simplifies the analysis as information about the hydrogen atom and ozone number densities is not required. This assumption may not be strictly valid for altitudes above - 95 km where the reaction between ozone and atomic oxygen may contribute to the total ozone loss rate (Moreels et al., 1977; Good, 1976). Any breakdown in this assumption would, therefore, result in an over-estimate of the total OH production rate at these higher altitudes. However, Fig. 4 would suggest that the OH production rates have, in fact, been under-estimated above 100km. This apparent anomaly could be explained if some additional source of ozone exists at the higher altitudes. This possibility has recently been discussed by Allen (1986) and it is interesting to note that the ozone production rates which would be required, above 100 km, to bring the measured and modelled OH(8,3) band emission profiles into better agreement are very similar to those suggested by the observations of Allen. In the analysis of the 1.61 pm emission it has been shown that the total measured zenith intensity is quite similar to that predicted by four different Meinel Band excitation models, all of which assume reaction (1) to be the only chemical source of vibrationally excited OH. However, none of these models predicts a 1.61 pm volume emission profile which is similar in shape to the measured profile. This difficulty in modelling the 1.61 pm emission be due to inadequacies
profile
may not necessarily
in the model parameters but could arise from erroneous structure in the derived 1.61 pm volume emission rates. As already mentioned, it is possible that the 1.61 pm measurements may have been contaminated by a vehicle-induced emission. If this is the case then it is perhaps more appropriate to compare the modelled and measured zenith intensity profiles rather than volume emission profiles. The measured and modelled zenith profiles arc shown in Fig. 8(a) where each modelled profile has been normalized to the zenith bright-
OH Meinel band emission
50
180
ZENITH BRIGHTNESS FIG. 8. (a)Tm
1145
Ckff>
ZENITH BRIGHTNESS PROFILES CORRESPONDING FIG. 7.
TO THE VOLUME EMISSION PROFILES SHOWN
IN
The modelled zenith profiles have been normalized using the factors : 0.79 for the “sudden death with no O-atom quenching” model (. .) ; 0.84 for the “sudden death with O-atom quenching” model (--) ; 0.79 for the “collisional cascade with no O-atom quenching” model (---) and 0.98 for the “collisional cascade with O-atom quenching” model (--). The dotted and short dashed curves coincide. (b)Tm RESIDUAL PROFILES CORRESPONDING TO THEDIFFERENCES BETWEEN THE MEASURED AND MODELLED ZENITH PROFILES SHOWN
ness measured before the rocket penetrated the OH layer. The required normalization factors are listed in the caption for Fig. 8(a) and all lie within the uncertainty of +_20% in the absolute calibration of the 1.61 pm radiometer (Greer et al., 1986). Clearly the “collisional cascade with O-atom quenching” and “sudden death with O-atom quenching” zenith profiles are in reasonably good agreement with the observations up to - 90 km ; however, above this altitude the modelled zenith brightnesses are too weak and do not exhibit the upper “shoulder” present in the measured profile. This shoulder is, of course, the source of the secondary maximum in the derived 1.6 1 pm volume emission profile and is evident in most other reported rocket measurements of the OH emission in this specral region (Evans et al., 1973 ; Good, 1976; Thomas and Young, 1981; Lopez-Moreno et al., 1985). Usually, as in the present case, the shoulder appears only as an inflexion in the zenith intensity profile and cannot be unambiguously attributed to anything other than a secondary maximum in the volume emission rate. However, in the work of LopezMoreno et al. (1985) an actual transient increase in zenith brightness was observed as the rocket penetrated the 92-97 km region. This could not have been simply due to a secondary maximum in the emission profile and is most easily explained in terms of a vehicle-induced glow. If a vehicle-induced glow is responsible for some of the differences between the measured and modelled profiles of Figs 7 and 8(a),
IN (a).
then, for a particular model to be viable, the modelled zenith brightness must be less than or equal to, the measured brightness at all altitudes. Clearly, only the models which include O-atom quenching come close to satisfying this criterion. The difference, or residual, profiles obtained from the data of Fig. 8(a) are shown in Fig. 8(b). Obviously, the residual “collisional cascade with O-atom quenching” zenith crofile is more consistently positive than the residual“‘sudden death with O-atom quenching” profile, but in view of the uncertainties inherent to the observations it would, perhaps, be premature to make any choice between these alternate models on the grounds of this observation alone. It should also be noted that the latter two residual profiles are remarkably similar, both in their shapes and magnitudes, to the vehicle-induced emission profiles obtained by Lopez-Moreno et al. (1985) from a comparison of their rocket ascent and descent data. This suggests that the “sudden death with O-atom quenching” and “collisional cascade with O-atom quenching” models, and parameters, of McDade and Llewellyn (1987) are not only consistent with the altitude profile of the u = 8 level but may, also, successfully predict the altitude profiles of the lower vibrational levels. However, the precision with which the latter two models do predict the low v’ profiles must remain unquantified in the absence of independent information about the altitude distribution of any vehicle-induced contamination in the 1.6 pm channel.
I. C. MCDADE et al. 5. CONCLUSIONS It has been shown that the z) = 8 level of vibrationally excited hydroxyl suffers significant deactivation in the mesosphere due to collisions with 0, and/or N2. Kinetic parameters related to these processes have been derived and are found to agree with those obtained from an independent analysis of groundbased observations. A variety of kinetic models fail to reproduce the detailed structure of the measured 1.61 pm emission profile and it has been suggested that the 1.61jtrn observations may have been contaminated by an unidentified vehicle-indu~d emission. If this is indeed the case, it would appear that a Meinet Band excitation model based on stepwise vibrational deactivation, with significant O-atom quenching, best explains the low v’ Meinel Band emission profiles, although the quality of the fit must be considered uncertain.
Acknowleu’qements-This work has been supported United Kingdom Sciences and Engineering &search cil and the Natural Sciences and Engineering Research cil of Canada.
by the dounCoun-
REFERENCI%S Allen, M. (1986) A new source of ozone in the terrestrial upper atmosphere? J. geophys. Res. 91,2844. Allen, M., Lunine, J. L. and Yung, Y. L. (1984) The vertical distribution of ozone in the mesosphere and lower thermosphere. J. geophys. Res. 89,484l. Baker, D. J. and Waddoups, R. 0. (1967) Rocket measurement of midlatitude night airglow emissions. J. geophys. Res. 72,4881. Bates, D. R. (1982) Airglow and aurora, in Applied Atomic Coilision Physics (Edited by Massey, I-i. S. W., Baderson, B. and McDaniel, E. W.), Vol. I, pp. 149-224. Academic Press, New York. Bates, D. R. and Nicolet, M. (1950) The photochemistry of atmospheric water vapour. J. geoph,vs. Res. 55, 301. Charters, P. E., MacDonald, R. G. and Polanyi, J. C. (1971) Formation of vibrationallv excited OH by the reaction H +O,. Appl. Optics 10, lf47. Evans, W. F. J., Llewellyn, E. J. and Valiance Jones, A. (1973) Altitude distribution of hydroxyl bands of the Au = 2 sequence in the nightglow. Can. .I. Phys. 51, 1288. Finlavson-Pitts, B. J. and Kleindienst, T. E. (1981) The reaction of hydrogen atoms with ozone as a source of vibrationallv excited OH(X”Il,),._, for kinetic studies. J. them. Phys.%, 5643. “’ _ Good, R. E. (1976) Determination of atomic oxygen density from rocket borne measurement of hydroxyl airglow. Planet. Space Sci. 24, 389. Greenblatt, G. D. and Wiesenfeld, J. R. (1982) Time-resolved emission studies of vibra~ionally excited hydroxyl radicals : OH{X’II, 0” = 9). J. geophys. Res. 87, 11145. Greer, R. G. H.. Murtagh, D. P., McDade, I. C., Dickinson, P. H. G., Thomas, L., Jenkins, D. B., Stegman, J., Llew-
ellyn, E. J., Witt, G., Mackinnon, D. J. and Williams, E. R. (1986) ETON I: a data base pertinent to the study of energy transfer in the oxygen nightglow. Platlet. Space Sci. 34,771. Harrison, A. W. and Kendall, D. J. W. (1973) Airgiow hydroxyl intensity measurements 0.6-2.3 p. Planet. Space Sci. 21, 1731. Hedin, A. E. (1983) A revised thermospheric model based on mass spectrometer and incoherent Scatter data : MSIS83. J. aeoohvs. Res. 88, 10170. Krassovsky; t. I., Shefov, N. N. and Yarin, V. I. (1962) Atlas ofthe airglow spectrum 300&124000.& Planet. Space Sci. 9,883. Lin, C. L. and Leu, M. T. (1982) Temperature and thirdbody dependence of the rate constant for the reaction O+OztM-+Oz+M. Int. J. Chem. Kinetics 14,417. Llewellyn, E. J., Long, B. H. and Solheim, B. H. (1978) The quenching of OH* in the atmosphere. Pkmet. Space Sci. 26, 525. Lopez-Moreno, J. J., Rodrigo, R. and Vidal, S. (1985) Radiative contamination in rocket-borne infrared photometric measurements. J. geophys. Res. 90, 6617. Makino, T., Yamamoto, H. and Sekiguchi, H,. (1983) AMtude profiles of OH and 0, near infrared airglows in the evening twilight. J. Geomugn. Geoelect. 35, 57. McDade, I. C. and Llewellyn, E. J. (1987) Kinetic parameters related to sources and sinks of vibrationally excited OH in the nightglow. J. geophys. Rex in press. Meinel, A. B. (1950) OH emission bands in the spectrum of the night sky 1. Astrophys. J. 111, 555. Mies, F. I-I. (1974) Calculated vibrational transition probabilities of OH(X%). J. molec. Specfrosc. 53, 150. Moreels, G., Megie, G., Valiance Jones, A. and Gattinger, R. L. (1977) An oxygen-hydrogen atmospheric model and its application on the OH emission problem. J. atoms. terr. Phys. 39, 551. Murphy, R. E. (1971) Infrared emission of OH in the fundamental and first overtone bands. .f. them. Phys. 54, 4852. Murtagh, D. P. and Greer, R. G. H. (1984) The nightglow hydroxyl (8-3) band emission-a comparison of experiment and theory, in Proc. 12th Annual Meeting on Atmospheric Studies by Optical Methods (Stockholm) (Edited by Witt, G.), p< 51. Murtagh, D. P., Greer, R. G. H., McDade, 1. C., Llewellyn, E. 3. and Bantle, M. (1984) Representative volume emission profiles from rocket photometer data. Ann. GeophJs. 2,467. Ohoyama, II., Kasai, T., Yoshimura, Y., Kimura, H. and Kuwata, K. (1985) Initiai distribution of vibration of the OH radicals produced in the H to? + OH(.X?‘I) + O7 reac_ tion. Chem. %ys. Left. 118,263. Packer. D. M. (1961) Altitudes of the night radi_ airglow _ ations. Ann. deoph&. 17, 61. Potter, A. E., Jr., Coltharp, R. N. and Worley, S. D. (1971) Mean radiative lifetime of vibrationally excited (v = 9) hydroxyl. Rate of the reaction of vibrationally excited hydroxyl (v = 9) with ozone. J. them. Phys. 54,992. Rogers, J. W., Murphys, R. E., Stair, A. T., Jr., Ulwick, J. C., Baker, K. D. and Jensen, L. L. (1973) Rocket-borne radiometer measurements of OH in the aurora1 zone. I. geophys. Res. 78, 7023. Solheim, B. II. (1979) MSc Thesis, The infrared atmosp~c~c system of oxygen in the nightglow. The University of Saskatchewan, Saskatoon, Canada. Takahashi, H. and Bat&, P. P. (1981) Simultaneous
1147
OH Meinel band emission measurements of OH(9,4), (83) (7,2), (6,2) and (5.1) bands in the airglow. J. geophys. Res. X6, 5632. Thomas, R. J. and Young, R. A. (1981) Measurement of atomic oxygen and related airglows in the lower thermosphere. J. geophys. Res. S&,7389. Turnbull, D. N. and Lowe, R. P. (1983) Vibrational popuIation distribution in the hydroxyl night airglow. Can. J. Phys. 61, 244. Witt, G., Stegman, J., Solheim, B. H. and Llewellyn, E. J. (I 979) A measurement of the O2 (b ‘C - X’X) atmospheric band and the 01(‘S) green line in the nightglow. Planer. space ‘sci. 27, 34 I.
1
+kF;‘+*, U)’ Rf[O,]] [A(u)+ p@(u) +~~~(uf~R)[O,l+k*~(u)[Ol~-‘.
(Al)
Multiplying both sides of equation (AI) by A(u’,u”) and dividing both the numerator and denominator of the RHS by A(9) yields .~(~)[O][O~]~~~~[O~]
A&‘, z:“)[OH(~)] = I +k:>[N,]}A(u’,
APPENDIX
Under steady-state conditions the concentration vibrational level of OH is given by
of each
[A(o*,a)/A(9)+
0”)/.4(9)+
2 A@‘, u”)[OH(v*)] ,**=p+I [O,l{k~qv*, u)
+ kE”+*. 2,)* R)/A(9)]
1
[{A(u)/A(9)j
+[o,Jfkq?(l;)+k~lfu).R)iA(9) +
[Olkm:.4(9)]-‘.
642)