- Email: [email protected]
Lifetime measurements of electronically excited C3(1Πu) radicals in different vibrational states
Volume
60. nmber
3
IS January
OF ELECTRONICAILY
JiIFETmElbIEAsIN DIFFERENT
VIBRATIONAL
1979
EXCITED C3(’ “u) RADICALS
STATES
KH. BECKER, T. TATARCZYK Gesamtho&sckz&Wuppertcl.Fachbereich9, PhysikaliwheUtemie. 56 Wuppenai, Germany
and J. RADIe-PERIC iktitut j%Pfiyskl&che 53 Bonn. Germmy
chernr2der Uidversitiit Bonn,
Received 1 June 1978 Revised manuscript received 17 October 1978
33e radiativelifetimesof nine vibrational kve!s of the Ca
- ‘C&l fIuorescence induced by a tunabledye laser.The lifetimesof the different tironic levelswere found to be Eonstantwrthinthe e~rimental exrorlimits, -ely, i. = <2oc,f 10) PT The colliiorul deactivation of the C3(%q statesby heIium gives rate constants between 25 and4 in lo-t1 cm3 moiea&‘l smi tits_
c3m,
I_Ixlrroduction
Becapuseof the astrophysical interest in the C3 radicalend its spectroscopic properties, knowledge
C, radicals play an important role in chemical systems of stars 1121 and comets [3-71, as well as in hydrocarbon flames [8-133 and carbon vapor [13,14] _ Emission spectra of C3 were frst observed from comets [31_ In laborato-ry studies C3 radicals can be produced either by flash photolysis [15--171 or in electrical dis&arges [ 18-20]_ The C, absorption spectra have been extensively studied in gaseous systems [15-171, in particular, in inert gas m3trices at low temperatures [2 l-273 _ A detailed spectroscopic identification of the eIectronictransition Cg(%I, IQ has been carried out by Gausset et al. [16]_ From the absorption spectra in the gas phase 1211 as well as in matrices [24;25 J values of the oscillator strength fhave been estimated; however, the error limits in these experiments were rather large. Theoretical calculations of the fvalues havebeen carried out by Williams {28], and, very recently, iu connection with the present work by Radi&Peri~ et al. 1293.
off values and Franck-Condon factors is of importance_ I;1 addition, there is general interest in the dependence of radiative and collisional lifetimes of electronic states in molecules on the vibrational quantum number. The present paper reports on direct lifetime measurements of the C3(llIu) radicals in different vlbratioti states. The isolated viironic states were populated from the electronic ground state by excitation with a tunable laser. Supplementary to the present experimental work one of the authors has used quanturn&en&al ab-initio methods for the calculation of the f values; the latter results have already been publlished [29].
502
2. Experimental The experiment3l set-up is shown in fig_ 1. The C, ra&cals were generated in a flow tube by a micro-
Volume
CHEPAICAL
60, number 3
PHYSICS LETTERS
DiSCRI kUNA+OR ,
Fig. 1. Experimentalset-up.
wave discharge through 1.5 mtorr ethylene in 1 to 5 torr heham. In the reaction zone the radicals were excited by a tunable nitrogen-laser-pumped dye la-
fb)
ser. Using the dyes ar-NPO and butyl-FBD the wave-
iength of the iaser could be tuned in the region of the C, absorption by a grating from 360 to 415 nm with a bandwidth of 0.15 nm_ The C3 rluorescence was observed at right angles to the laser beam by a monochromator combined with a photomultiplier (PMT 1). The time decay of the fluorescence was measured by the “time correiated single photon” technique (TCSP) described in previous work [30]. The fhrorescence intensity was monitored with a digital boxcar integrator triggered by the laser pulse from photomultiplier PMT 2_
3. Results
The observed C3 emission bands with an origin at 405 nm are shown together as excitation as well as fluorescence spectra in fig_ 2. The excitation spectrum is a plot of the fluorescence intensity as a function of the excitation wavelength which was tuned through the C, absorption_ Under these conditions, the fluorescence was observed at 407 run with a band pass of 5 nrn, where the fluorescence especially originates from the (000--020) band, It can be
Fig. 2. (a) Fluorescenceintensity,observedat 407 nm, as a function of the excitationwaveler@h. (b) Fluorescencespeztnun of the C& Iiu, 000) radical,excited from the ground state by laserlight at 388 sun_ seen from the spectrum that by observing the fluorescence at (4% + 2.5) nm, several vibronic states of C, can be selectively analyzed. For the fluorescence spectrum in fig. 2, the emitting state C,(llI,, 100) was populated from the ground state by the laser tuned to 388 nm_ The spectrum shows the bands (lOO-OOO), (loo-loo), and (100-200) with-a resolution of M = 5 mn_ Other u; and vi Ievels of Cg(%,) were populated in the same way. For +he ZJ~level, two components of different symmetry can be distinguished spectroscopically. The vibrational structure of the C3 spectrum is fairIy complex with many overlapping bands. Lifetime measurements of single vibronic states were therefore made by choosing the waveIengtb for exci503
Vohune 60, nmbfx
3
CHIMICAL
PHYSiCS
‘5 32llu2ly 1979
LEXTERS
Tab&? 1 NatwaS fifetimes ro and rate constants k~e for different vibrational levels of the C&IQ state
tation and observatim such that there was no interference of fhrorescenee from different vibrational Ievels- From the exponential decay of the fluorescence the decay constant R = S/r was derived where T is the lifetime. Due to cohisional deactivation of the viironic states, the K values have to be determined at different total pressures. Fig. 3 shows such i; Stem-Volmer plot K = K(&+) for the lowest vibrational level of C3CiEi,). Substituted in the formuIaK = I/?-+ f;k@f& the extrapolation to zero total pressure leads to _Ko or the inverse naturai hfetime r&l_ From the slope of the curve the quenching rate constant k,, can be derived. In tabie I, the naturai lii%e*&esr. and rhe rate constants kHe are &ted for 9 merent vibmtionaf levels of the C,flTi,) state; the data were calculated by the least-squares method. The experimental er&rs are given in terms of the standard deviation u as +20. Deactivation of the emitting states by other gases except helium can be excbrded. In particular, the ethylene pressure was varied from 05 to 5 mtorr at 2 torr total pressure without any observable change in the IiMimes.
4. Discussion According to the results listed in table 1, all decay curves of C,(liI,) for difierent vibrational quantum numbers lead at zero total pressure to the same natural lifetime r. = 200 ns, within the experimental error Emit, There is no indication of perturbations of 504
1011 moIecu?e-” s-l)
VibIiltiOId
Q
kHeX
state
(cm3
OQO cm,>
ZOO*7
3.14 f 020
Of0
202%8
2.14 + 022
0x0 (A,.$
202 * 10
254 t 0.22
010 cc;)
197 = 16
253 5 0.45
020 (rra
197 f 14
2.71 + 0.38
030 ‘qjJ
2035-11
3.50 = 0.24
040 0-q
204*19
3.49 t 056
100
198 i 12
3.13 i- 0.32
200
197 * 26
4.08 t 0.74
(Xg3
the exponential decay curves over a time period of at least 5 lifetimes. No change in lifetime was observed on varying the C, concentration. This indicates negligible radiation imprisonment. Calculations using the formula given by Holt [32] show that the effect of radiation trapping under the experimental conditions empioyed would be no greater than 0.5% The fact that the radiative lifetime does not depend on the vibrational quantum numbers suggests that the emitters are isolated vibronic states not influenced by vibronic interactions. Using the formula
f ul = 1.5/E%o, where u indicates the upper and 1 the iower state, and gllfu1
=glf&’
with the sta#i.stid weigh&g, for the upper and gt for the lower state, the electronic oseihator strength
fIu for absorption can be calculated from r. _Within the band system a mean wavenumber v’ = 24685 cm-l can be used as an adequate approximation in the calculation, From the present work, a value of flu = 0.02~ is obtained as oscillator strength for tire efectronic transition C3(1n, f lI;i). Table 2 contains the previorusly pub&bed fl,, values obtained from experimental as well as from theoretid work. No agreement with former experimental results
1.5 klualy
CHFMICAL PHYsIcS LETTERS
Volume 60, number3
Table 2 Experimentally and theoretically determined eIectronic oscilhtor strengthsf,,
for&e C&Q
+ ‘2;)
transition
Investigator
Year
Method
flu
Ref.
Brewerand Engelks
(1962)
gasPhase, absorption
O.i3
1211
Bargerand Broida
(1965)
matrix, absorption
0.06
/Xl
WlJJiZX
(1975)
theory
0.129
1281
Radi@e& et al.
(1977)
theory
0.061
1291
Riimelt et al.
(1978)
theory
0.0492
[311 a)
thk work
(1978)
g2s ph=se,
0.0246
fluorescence
a) Recently new calculationswith a more extendedtheoretical treatment gave a value off,, can be seen. All previous values are much greater_ The former absorption studies can only be raken as rough estimates, mainly due to the lack of an accurate vahre of the C3 concentration. In one paper [ZS] , afrfvahre of 0.06 is even explained as a lower limit offl,,. 1Veltner and McLeod [24] pubhshed the foE ]0wing_& values for the (000-000) transition: &, = 0.0007 foe = 0.0037
from C3 absorption in a neon matrix; from absorption in an argon mat-.
By using the Franck-Condon factors from recent theoretical calculations [29], a value of& = 0.016 is derived from the present experimental results. In this case, the present work gives higher values than the former experiments of Weltner and McLeod 1241. The recent theoreticalflu number 0.061 as a mean value for both ‘iI, components is in poor agreement with the present results. The better agreement of the the0retica.I value with the former experimental resuhs seems to be purely fortuitous. The slight dependence of the lifetime on the vibrational quantum number indicated in the theoretical work 1291 could not be confiied by the experimental results_ The collisional deactivation of C,(lII,) by helium gives rate constants between 2.5 and 4 in 10-11 cm3 ri~olecule-1 s-l units as shown in table I. This high quenching efficiency by helium is surprising and cannot be explained by a transfer of a relatively large amount of electronic energy from the C3( ‘IX,) state (= 3 ev) to translation of helium within 10 collisions. Such an efficiency is normally observed for transfer of a few wavenumbers of energy to helium. This
1979
= 0.0492.
therefore leads one to assume that cohisionally induced transitions to nearby states of C3 are occurring. &h our present knowledge of the C3 potentials, the only possible transitions are to vibrational levels of the C3(311u) state. Before further detailed expkmations of the quenching mechanism can be given, other collision partners for the C3(rlIu ,ul , ~2, us) should be studied. Such investigations planned for the firture should also give more information concerning the dependence of the rate constants on the vibrational levels.
Acknowledgement The authors thank Professor Buenker and Professor Peyerimhoff for many helpful discussions. The financial support by the “Deutsche Forschungsgemeiuschaft” and the “Fends der Chemischen Industrie” is gratefuiiy acknowledged.
References [l J D_P.Gika, Symp. Intern.As&on. Urion 52 (1973) 517. [2] J.D. Fix, Astrophys J. 203 (1976) 463. [3] W. Hugglns.Proc. Roy. Sot. 33 (1882) 1. [4] P. Swings,Mo~t.hIy Not&s Roy. Astron. Sot, 103 (1943) 92. [5] C_ Fehrenbach,Compt Rend_Acad_Sci_earls) 256
(1963) 3788. [6] J. Rake,C.W. McCracken,K.L. Hallamznd B.D. Dorm, Astron. Astrophys.SuppLSer. 23 (1976) l_ 505
Volume 60, nm&er
3
CHEMICAL
PHYSICS
f7] WAf_ Jackson, J. Photochem- 5 (1976) 107. [8] A-G. Gaydon, Spectroscopy of flames (Chapman and Ha& London. i957)_ [9] A-G. Gaydon and H-G_ Wolfhard, Flames, their structure, radiation and tempexature (Chapman and Hall, London, 1970)_ [IO] NIi. Kiess and A.M. Bass, J. Chem. Phys. 22 (1954) 569. [ll] G.V.Marrand R-W. NichoUs,Can.J. Fhys. 33 (1955) 394. 1121 NJI. Kiess and HP. Broida. Can_ J_ Phys 34 (1956) 1471. (131 ML Savadatti and H.P_ Broida, J. Chem. Phys. 45 (1966) 2390_ (141 J. Drowart, R-F. Burn, G. De_&%riaand M-G. Inghram, J. Chem Phys. 37 (1959) 1131. [15] JJi- CalIomon and D.A_ Ramsay, Can. J. Fhys. 35 (2957) 129. [16] L. Gausset, G_ Hz&wrg, A.. Lagerqvist and B. Rosen, Astrophys J_ 142 (1965) 45_ [17] A-l. Merer, Can. J. Phys. 45 (1967) 4103. [IS] A-E. Doughs, Astrophys. J. 124 (1951) 466. [19] K- CIusius and A-E- Do@as, Can_ J. Phys. 32 (1954) 319.
LETTERS
15 January 1979
[20] K_HH.Homann. W. Lange and H&g_ Wagner, Ber. Bunsenges. Physik. Chem. 75 (1971) 121, 1213 L. Brewer and JL_ -Ike, J. Ches, Phys- 36 (1962) 992_ [22] R.L- Barrr and HI’. Broida, J. Chem. Fhys- 37 (1962) 1152. 1231 W_ Weltner Jr., P3U_ Walsh and CL_ AngelI, 3_ Chem_ Phys 40 (1964) 1299. [24] W_ Weltner Jr_ and D. McLmd Jr., 1. Chem- Phys. 40 (1964) 1305_ 1251 R.L. Barger and H.P. Broida, J. Chem. Whys. 43 (1965) 2364. 1261 W. Weltner Jr. and D. McLeod Jr., J.Chem. Phys. 45 (1966) 3096_ 1271 ME_ Jacox and D-E_ Mil!igau, Chem. Phys_ 4 (1974) 45. [28] G.RJ. Williams, Chem. Phys. Letters 33 (1975) 582. [29] J. Radi&PeriE, J_ REmelt. S_D_ Peyerimhoffand RJ. Buenker. Chem_ Phys Letters 50 (i977) 344 [30] KX-L Becker, H. Engels and T. Tatarczyk, Chem. Phys. Letters 51 (1977) 111. [31] J. Riimelt, SD. Peyerimhoff and RJ. Buenker, Chem. Phys. Letters 58 (1978) 1. 1321 HX. Holt, Phys Rev. A 13 (1976) 1442.
60. nmber
3
IS January
OF ELECTRONICAILY
JiIFETmElbIEAsIN DIFFERENT
VIBRATIONAL
1979
EXCITED C3(’ “u) RADICALS
STATES
KH. BECKER, T. TATARCZYK Gesamtho&sckz&Wuppertcl.Fachbereich9, PhysikaliwheUtemie. 56 Wuppenai, Germany
and J. RADIe-PERIC iktitut j%Pfiyskl&che 53 Bonn. Germmy
chernr2der Uidversitiit Bonn,
Received 1 June 1978 Revised manuscript received 17 October 1978
33e radiativelifetimesof nine vibrational kve!s of the Ca
- ‘C&l fIuorescence induced by a tunabledye laser.The lifetimesof the different tironic levelswere found to be Eonstantwrthinthe e~rimental exrorlimits, -ely, i. = <2oc,f 10) PT The colliiorul deactivation of the C3(%q statesby heIium gives rate constants between 25 and4 in lo-t1 cm3 moiea&‘l smi tits_
c3m,
I_Ixlrroduction
Becapuseof the astrophysical interest in the C3 radicalend its spectroscopic properties, knowledge
C, radicals play an important role in chemical systems of stars 1121 and comets [3-71, as well as in hydrocarbon flames [8-133 and carbon vapor [13,14] _ Emission spectra of C3 were frst observed from comets [31_ In laborato-ry studies C3 radicals can be produced either by flash photolysis [15--171 or in electrical dis&arges [ 18-20]_ The C, absorption spectra have been extensively studied in gaseous systems [15-171, in particular, in inert gas m3trices at low temperatures [2 l-273 _ A detailed spectroscopic identification of the eIectronictransition Cg(%I, IQ has been carried out by Gausset et al. [16]_ From the absorption spectra in the gas phase 1211 as well as in matrices [24;25 J values of the oscillator strength fhave been estimated; however, the error limits in these experiments were rather large. Theoretical calculations of the fvalues havebeen carried out by Williams {28], and, very recently, iu connection with the present work by Radi&Peri~ et al. 1293.
off values and Franck-Condon factors is of importance_ I;1 addition, there is general interest in the dependence of radiative and collisional lifetimes of electronic states in molecules on the vibrational quantum number. The present paper reports on direct lifetime measurements of the C3(llIu) radicals in different vlbratioti states. The isolated viironic states were populated from the electronic ground state by excitation with a tunable laser. Supplementary to the present experimental work one of the authors has used quanturn&en&al ab-initio methods for the calculation of the f values; the latter results have already been publlished [29].
502
2. Experimental The experiment3l set-up is shown in fig_ 1. The C, ra&cals were generated in a flow tube by a micro-
Volume
CHEPAICAL
60, number 3
PHYSICS LETTERS
DiSCRI kUNA+OR ,
Fig. 1. Experimentalset-up.
wave discharge through 1.5 mtorr ethylene in 1 to 5 torr heham. In the reaction zone the radicals were excited by a tunable nitrogen-laser-pumped dye la-
fb)
ser. Using the dyes ar-NPO and butyl-FBD the wave-
iength of the iaser could be tuned in the region of the C, absorption by a grating from 360 to 415 nm with a bandwidth of 0.15 nm_ The C3 rluorescence was observed at right angles to the laser beam by a monochromator combined with a photomultiplier (PMT 1). The time decay of the fluorescence was measured by the “time correiated single photon” technique (TCSP) described in previous work [30]. The fhrorescence intensity was monitored with a digital boxcar integrator triggered by the laser pulse from photomultiplier PMT 2_
3. Results
The observed C3 emission bands with an origin at 405 nm are shown together as excitation as well as fluorescence spectra in fig_ 2. The excitation spectrum is a plot of the fluorescence intensity as a function of the excitation wavelength which was tuned through the C, absorption_ Under these conditions, the fluorescence was observed at 407 run with a band pass of 5 nrn, where the fluorescence especially originates from the (000--020) band, It can be
Fig. 2. (a) Fluorescenceintensity,observedat 407 nm, as a function of the excitationwaveler@h. (b) Fluorescencespeztnun of the C& Iiu, 000) radical,excited from the ground state by laserlight at 388 sun_ seen from the spectrum that by observing the fluorescence at (4% + 2.5) nm, several vibronic states of C, can be selectively analyzed. For the fluorescence spectrum in fig. 2, the emitting state C,(llI,, 100) was populated from the ground state by the laser tuned to 388 nm_ The spectrum shows the bands (lOO-OOO), (loo-loo), and (100-200) with-a resolution of M = 5 mn_ Other u; and vi Ievels of Cg(%,) were populated in the same way. For +he ZJ~level, two components of different symmetry can be distinguished spectroscopically. The vibrational structure of the C3 spectrum is fairIy complex with many overlapping bands. Lifetime measurements of single vibronic states were therefore made by choosing the waveIengtb for exci503
Vohune 60, nmbfx
3
CHIMICAL
PHYSiCS
‘5 32llu2ly 1979
LEXTERS
Tab&? 1 NatwaS fifetimes ro and rate constants k~e for different vibrational levels of the C&IQ state
tation and observatim such that there was no interference of fhrorescenee from different vibrational Ievels- From the exponential decay of the fluorescence the decay constant R = S/r was derived where T is the lifetime. Due to cohisional deactivation of the viironic states, the K values have to be determined at different total pressures. Fig. 3 shows such i; Stem-Volmer plot K = K(&+) for the lowest vibrational level of C3CiEi,). Substituted in the formuIaK = I/?-+ f;k@f& the extrapolation to zero total pressure leads to _Ko or the inverse naturai hfetime r&l_ From the slope of the curve the quenching rate constant k,, can be derived. In tabie I, the naturai lii%e*&esr. and rhe rate constants kHe are &ted for 9 merent vibmtionaf levels of the C,flTi,) state; the data were calculated by the least-squares method. The experimental er&rs are given in terms of the standard deviation u as +20. Deactivation of the emitting states by other gases except helium can be excbrded. In particular, the ethylene pressure was varied from 05 to 5 mtorr at 2 torr total pressure without any observable change in the IiMimes.
4. Discussion According to the results listed in table 1, all decay curves of C,(liI,) for difierent vibrational quantum numbers lead at zero total pressure to the same natural lifetime r. = 200 ns, within the experimental error Emit, There is no indication of perturbations of 504
1011 moIecu?e-” s-l)
VibIiltiOId
Q
kHeX
state
(cm3
OQO cm,>
ZOO*7
3.14 f 020
Of0
202%8
2.14 + 022
0x0 (A,.$
202 * 10
254 t 0.22
010 cc;)
197 = 16
253 5 0.45
020 (rra
197 f 14
2.71 + 0.38
030 ‘qjJ
2035-11
3.50 = 0.24
040 0-q
204*19
3.49 t 056
100
198 i 12
3.13 i- 0.32
200
197 * 26
4.08 t 0.74
(Xg3
the exponential decay curves over a time period of at least 5 lifetimes. No change in lifetime was observed on varying the C, concentration. This indicates negligible radiation imprisonment. Calculations using the formula given by Holt [32] show that the effect of radiation trapping under the experimental conditions empioyed would be no greater than 0.5% The fact that the radiative lifetime does not depend on the vibrational quantum numbers suggests that the emitters are isolated vibronic states not influenced by vibronic interactions. Using the formula
f ul = 1.5/E%o, where u indicates the upper and 1 the iower state, and gllfu1
=glf&’
with the sta#i.stid weigh&g, for the upper and gt for the lower state, the electronic oseihator strength
fIu for absorption can be calculated from r. _Within the band system a mean wavenumber v’ = 24685 cm-l can be used as an adequate approximation in the calculation, From the present work, a value of flu = 0.02~ is obtained as oscillator strength for tire efectronic transition C3(1n, f lI;i). Table 2 contains the previorusly pub&bed fl,, values obtained from experimental as well as from theoretid work. No agreement with former experimental results
1.5 klualy
CHFMICAL PHYsIcS LETTERS
Volume 60, number3
Table 2 Experimentally and theoretically determined eIectronic oscilhtor strengthsf,,
for&e C&Q
+ ‘2;)
transition
Investigator
Year
Method
flu
Ref.
Brewerand Engelks
(1962)
gasPhase, absorption
O.i3
1211
Bargerand Broida
(1965)
matrix, absorption
0.06
/Xl
WlJJiZX
(1975)
theory
0.129
1281
Radi@e& et al.
(1977)
theory
0.061
1291
Riimelt et al.
(1978)
theory
0.0492
[311 a)
thk work
(1978)
g2s ph=se,
0.0246
fluorescence
a) Recently new calculationswith a more extendedtheoretical treatment gave a value off,, can be seen. All previous values are much greater_ The former absorption studies can only be raken as rough estimates, mainly due to the lack of an accurate vahre of the C3 concentration. In one paper [ZS] , afrfvahre of 0.06 is even explained as a lower limit offl,,. 1Veltner and McLeod [24] pubhshed the foE ]0wing_& values for the (000-000) transition: &, = 0.0007 foe = 0.0037
from C3 absorption in a neon matrix; from absorption in an argon mat-.
By using the Franck-Condon factors from recent theoretical calculations [29], a value of& = 0.016 is derived from the present experimental results. In this case, the present work gives higher values than the former experiments of Weltner and McLeod 1241. The recent theoreticalflu number 0.061 as a mean value for both ‘iI, components is in poor agreement with the present results. The better agreement of the the0retica.I value with the former experimental resuhs seems to be purely fortuitous. The slight dependence of the lifetime on the vibrational quantum number indicated in the theoretical work 1291 could not be confiied by the experimental results_ The collisional deactivation of C,(lII,) by helium gives rate constants between 2.5 and 4 in 10-11 cm3 ri~olecule-1 s-l units as shown in table I. This high quenching efficiency by helium is surprising and cannot be explained by a transfer of a relatively large amount of electronic energy from the C3( ‘IX,) state (= 3 ev) to translation of helium within 10 collisions. Such an efficiency is normally observed for transfer of a few wavenumbers of energy to helium. This
1979
= 0.0492.
therefore leads one to assume that cohisionally induced transitions to nearby states of C3 are occurring. &h our present knowledge of the C3 potentials, the only possible transitions are to vibrational levels of the C3(311u) state. Before further detailed expkmations of the quenching mechanism can be given, other collision partners for the C3(rlIu ,ul , ~2, us) should be studied. Such investigations planned for the firture should also give more information concerning the dependence of the rate constants on the vibrational levels.
Acknowledgement The authors thank Professor Buenker and Professor Peyerimhoff for many helpful discussions. The financial support by the “Deutsche Forschungsgemeiuschaft” and the “Fends der Chemischen Industrie” is gratefuiiy acknowledged.
References [l J D_P.Gika, Symp. Intern.As&on. Urion 52 (1973) 517. [2] J.D. Fix, Astrophys J. 203 (1976) 463. [3] W. Hugglns.Proc. Roy. Sot. 33 (1882) 1. [4] P. Swings,Mo~t.hIy Not&s Roy. Astron. Sot, 103 (1943) 92. [5] C_ Fehrenbach,Compt Rend_Acad_Sci_earls) 256
(1963) 3788. [6] J. Rake,C.W. McCracken,K.L. Hallamznd B.D. Dorm, Astron. Astrophys.SuppLSer. 23 (1976) l_ 505
Volume 60, nm&er
3
CHEMICAL
PHYSICS
f7] WAf_ Jackson, J. Photochem- 5 (1976) 107. [8] A-G. Gaydon, Spectroscopy of flames (Chapman and Ha& London. i957)_ [9] A-G. Gaydon and H-G_ Wolfhard, Flames, their structure, radiation and tempexature (Chapman and Hall, London, 1970)_ [IO] NIi. Kiess and A.M. Bass, J. Chem. Phys. 22 (1954) 569. [ll] G.V.Marrand R-W. NichoUs,Can.J. Fhys. 33 (1955) 394. 1121 NJI. Kiess and HP. Broida. Can_ J_ Phys 34 (1956) 1471. (131 ML Savadatti and H.P_ Broida, J. Chem. Phys. 45 (1966) 2390_ (141 J. Drowart, R-F. Burn, G. De_&%riaand M-G. Inghram, J. Chem Phys. 37 (1959) 1131. [15] JJi- CalIomon and D.A_ Ramsay, Can. J. Fhys. 35 (2957) 129. [16] L. Gausset, G_ Hz&wrg, A.. Lagerqvist and B. Rosen, Astrophys J_ 142 (1965) 45_ [17] A-l. Merer, Can. J. Phys. 45 (1967) 4103. [IS] A-E. Doughs, Astrophys. J. 124 (1951) 466. [19] K- CIusius and A-E- Do@as, Can_ J. Phys. 32 (1954) 319.
LETTERS
15 January 1979
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