- Email: [email protected]
Possible production of O2(1Δg) and O2(1Σ+g) in the reaction of NO with O3
15 May I973
with rate constants kIa = I .J X IO- ““exp(-4 I so/k?q 7.1 x 20-13e.up(-2330/!W). (AI1 rate constants are given in mofecular units (cm3 moiecule and SEC),a$ the ‘hg md ‘22; states of 0, are abbreviated to o&z; and O,#>$ respectively.) Reaction {I a) pro-duces e~~~~r~~~~~~~~excited hro2 which emits a psendo-continuum [2] with a low-wavelength threshold of 590 nnl and a distribution which peaks at 1200 nm and extends to 2900 nm. Reaction (1) is 48 kca.I mole-! exothermic. Thus fo~a~~~n of either O&A) and k,,=
or O.&Z> is energetically
possibfe irr reaction
ftb).
At
moderate spectral resolution no emission from 02(A) (1270 nm) or Q&Z) (762 nm) was observed [2]. However, because of the low A factors for these traqsitions and the short reactive lifetimes of the O&A) and Q2fS) in the presence ofC$ only a tiali. fi%ction of.& molecules radiate and the emission &ll~be’very weak. A much larger fraction of the ex‘0cited NO:, fomrerl in reaction (la) radiates. Thus it is ;diffr< t% observe the G,(A) and O#) emission, .-
j78‘. _ I’
,,,
_’
”
;:.
:.
: 1
__._
‘.
__
‘_
_‘,
I_
:
,,
:.
:
,,
“,
..
;. “.
It is important to know if O,(A) is produced in reaction ( I b) since O?(h) is a possible o?ridant in polIu ted urban armospheres f3f, artd this reaction may also account 141 for the enhanced 02(b) air@ots emission associated with auroraf activity [5]. We have investigated the NO2 emission from the NO + 03 reaction at high resolution in the spectral region around 762 nm and 1270 nm. Upper Iimiis for O,(A) and 02(Z) production have been obtained using the photoIysis of 07JO~ mixtures at 253.7 nm as an internrrf standard,
The apparatus and detection q&em have been described in detail ~re~io~s~~ [Sj. il schematic diagram of the reaction vessel is’dlown in gig. 1I The 0, concentration was monitored by measuring the absorption of 253.7 nm radiation from a small Iow-pressure Hg lamp. The reaction vessel was surrounded by nine LLshaped low-pressure Hg iamps to provide for photolysis of O,lct, mixtures. The experimental procedure consisted in establishing a flow of O&J2 in the reaction vessel, photolysing a small fraction of the 03, and recording the emis-
Vofume 20, number 2
CkEhlKAL BaS04
PHYSICS
COATED Al
LETTERS REFkCTORS
ARTZ TUBES I PUMPLNG OUTLET
NiSC& SOLUTiON
HO~~ZO~T~L CONE OF SIGHT OF DETECTION SYSTEM--I Fig. 1. Schematic didgram of rencrion vessel.
sion of O,(A) or O&Z:). The 0, concentration was measured with the photoiysis lamps on and off to obtain the amount of 03 decomposed. The photolysis lamps were then turned off, and a small c&bra&d flow of NO was premixed with the 0,/O, just prior to entry into the reaction vessel; a spectral scan of the NO, contjnuum was then recorded,
3, Results and discussioI1 Typical spectra obtained in these experiments are sl~~wn in fig. 2. For all experiments the 0, pressure was 1.0 torr and the linear flow velocity 128 cm set-I. Other experimental conditions were as follows (where all pressures aze in mtorr): O,(A) emission, OS pressure 38.7,0, decomposed 5.8; NO, continuum 1270 nm, NO added 15.5, initial 03 38.5, US decomposed 16.2; O,(Z) emission, U3 pressure 39.40, decomposed 4.8; NO, c~ntin~~rn 762 nm, NO added 16.5, initial 0, pressure 38.&, 0, decomposed 17.0, The continuum emission ;::x!;;;ying the Ox(C) band resulted from fluorescence of the quartz cell :6]. Previous studies in our laboratories f6,7] using the same apparatus h3ve shown that the predominant f3te oi O,(A) and O#) is reaction with 0,. O,(h)+O,+2O.&I, *
(2)
‘Oz(C) f 0, + 20, + 0 -
13)
Wali deactivation of O,(A)
Oz(‘Aq)
,
.
e
760 WAVELENGTH
t
I
I
7722
nm
Fig. 2. Spectm showing uncorrected rehtivc intensity Of singlet 02 and NO1 c0nt~uum emissions. For expcrimcnra1 cie-
tails see text.
(41 is a significant but iess import& removai process for O,(A). The measured rate of wall deactivation in our apparatus is 131 0.5 set-l_ Collisional deactivation of CI,(L~) and O,(C) by O2 is unimportant [8I. The rates of reactions (2) and (31, taken from a recent review 179
CHEhllCAL PHYSICS LETTERS
VoIcme 20, number 2 article [9], are k2= 3.2 X lo-l5
and k,= 2.5 X lWxi. Deactivation of O,(A) and Oz(.xi by NO and NO, is totally negligible for our experimental conditions [8]. Thus, for a constant 0, pressure, the O,(A) and 02(Z) lifetimes remain unchanged with addition -of NO, and a direct comparison of O,(A) and O@) intensities for the experiments with and without NO is possibie. fn order to calculate the production of the two singlet states, the amount of 03 photolysis and the efficiency of the singiet 0, production mechanism must be known. Previous studies in our laboratories f6], using the same apparatus, have shown that photolysis of Og/c1? mixtures at 253.7 nm produces 02(A) directiY, 0, + IV -+ O,(A) + 0( ID) ,
(3
whereas O;(S) is produced by energy transfer from O(‘Dj, q’tij
+ 0, -+ Oz(-rj + O(3P) .
(6)
The available information on the efficiency of these reactions has been reviewed recentiy [9J, and it has
been concluded that the efficiency of both processes is c!cse to unity and certainly greater than 0.8. We have assumed an efticiency of unity for both processes in the following discussions. (For reaction (6) the efticiency is the fraction of O(D) + 0, deactivating collisions which result in the formation of 02(x).j in addition to the reactions already listed, the 0, decomposition is also controlled by the following reactions: O(lD> -+.03
420,
,
-+02f20,
o+02+o*-,03+03.
(7a) Vbl
(9)
In order to calculate the amount of 0, photoiysis from the observed amount of Oj decomposition, downstream from the photolysis region (see fig. I), we have numeric&y integrated the rate equations for reacrions (2)~(9) using a Runge-Kutta integration routine. This calculation has been described in detail previously [IO] and till only be outlined here. Secause 0( ID} reaction rates are almost collision limited ..
180 j,
‘.
15 May 1973
[9], Of ‘D) is always in ~hotochemi~~ equilibrium and only re!ative reaction rates are required to compute the fate of O( lD) [lO]. In our calculations we have assumed that k7/k6 = 9.7 [6] and k,, = k,, = 0.5 k,. The products of reaction (7) are uncertain [9] and we have arbitrarily made the assumption that k-y, = ?iTb. The effects of this assumption are not serious since more than 70% of the O(lD) reacts with 0, for our experimental conditions. The following rate constants [9] were used in the calculations of 03 decomposition: k, = 1.0 X lo-‘*, kg = 7.0 X lO-34 k, = 3.2 X i0--15, k, = 2.5X fO-IIand~~=O.5 ’ SCC-~.Tine rate expressions were integrated and the rate of photolysis was adjusted to obtain the observed amount of 0, decomposition. Note that, from fig. I, for a flow velocity of I28 cm see-l, the 0, spends 176 msec in the illuminated region and a further 164 msec between the end of the illuminated region and the 0, monitoring station. The photolysis intensity was assumed to be constant in the ~luminated region. The calculated amount of 0, photolysis for the O,(A) and 02(C) experiments in fig. 2 is 1.3 mtorr and I. I mtorr, respectively, i.e., a quantum yield of ==4for 03 destruction. At room temperature (29G”K), ~93% of the NO + 03 reaction occurs by process(lbj. Furthermore, this reaction is complete p99.7 of NO reacting) during the flow time from the input region to the Oj monitor@ station. The observed O3 decomposition corresponds, within experimental error, to the amount of KO added. This observation immediately rules out any substantial production of02(Aj or O,{X) in reaction (lb) since production of either species would lead to additional 0, destruction by reactions (2) and/or (3). From a comparison of the spectra in fig. 2 we conclude that any 02(A) emission present in the NO2 continuum is Iess than If30 of that observed from photolysis of 0,. Since the latter has been shown to result from production of I.3 mtorr of 02(A), and since 15 m torr of NO reacted with 0, by process (1 b), we conclude that less than 1.3/30 X 15 = l/300 of 0, produced in (1 b) is in the Oz(Aj state. Similar calculations for the spectra at 760 run, with the 29 sumption that any O&Z) emission present in the NO, continuum is less than l/l.5 of that observed from 0, photolysis, lead to an upper Emit of l/200 for O,(6) production.
CHEMICAL PHYSICS LETTERS
Volume 20, number 2
In the above calculations it has been implicitly assumed that equal production of singlet 0, from reaction (1 b) or from photolysis of 0, will priduce equal signals. It will be shown below that, if anything, singiet 0, from reaction (1 b) will be detected more efficiently thus not affecting the upper limits given above. Firstly, the average OS pressure is somewhat lower in the NO experiments resulting in a longer singlet 0, lifetime. Secondly, the distribution of singlet O2 in the reaction vessel will be different for the two sources since the NO + 0, mixing region occurs closer to the detection system than the illuminated region of the cell (see fig. 1). For a small segment of the source with uniform cross-sectional excitation the useful illumination entering the spectrometer slit is independent of the source to spectrometer separation provided that the cones of sight of the spectrometer are contained within the source; i.e., provided no vignetting occurs. If this latter condition is not met the illumination decreases with increasing source to spectrometer separation. Particularly for O,(A), which has a longer reactive lifetime, a larger fraction of the singlet 02 emission from 03 photoiysis occurs in a region of the cell where the field of view of the spectrometer is vignetted. (Because of the finite slit height (“2 cm) the outer vertical cone intersects the reaction vessel somewhat closer to the spectrometer than the horizontal cone shown in fig. 1.) Thus O,(A) and 01(E) will be sampled less efficiently if produced by 0, photolysis rather than reaction ( 1b) so that the above limits in 02(Z) and Oz(Aj production still hold. In two recent publications [ 11,121 it was shown that electronically excited NO,, produced by irradiation of NO, with visible light,kansferred energy coilisionally to 02 to produce O,(A). Since O*(A) emission was not observed in our NO/O3 experiments we can set upper iimits on the production of O,(A) by the reaction sequence: NO+03+NO;+02,
(la)
NO; + 0, --f NO, t O,(A), -+NO,+O,.
(1W (lob)
L
In the above discussion
it was shown that the
15 1May1973
O?(A) emission resulted from photolysis of I.3 mtorr of 0, [i.e., production of 1.3 mtorr of O,(4)] in OS/O, mixtures and that the intensity of t,his emission was at least 30 times greater than any 02(A) emission present in the NO/O, experiments. Therefore we may set an upper limit of 1.3/30 rntorr (= 4 X 10m5 torr) in the production of 02(A) from reactions (la) and 10) in the NO/O, experiments. For these experiments 15.5 mtorr of NO reacted with 03 of which approximately 8%, or 1.2 X low3 torr, reacts via process (la) at room temperature. The data of Thrush et al. [ 1(2] show that -0% of the NO; formed in reaction (la) is quenched by 0, for our esperimental conditions_ Therefore we may conclude that the efficiency of O,(A) production in reaction (10) is less than 4 X 10W5/0.9 X 1.2 X 10m3 or 4%. This conclusion is not surprising since Jones and Bayes [ 1 1; have determined efficiencies decreasing from 3.5% to 0.5% as the NO, excitation wavelength increased from 4200 A to 6200 PI and reaction (la) is only energetic enough to produce NO, with escitation equivalent to 6000 A radiation.
References [ 1) M.A.A. Ciyne, B.A. Thrush and R.P. Wsyne, fmnr Faraday See. 60 (1964) 359. [ 21 P.N. Clough and B.A. Thrush. Chcm. Commun. 71 (I 966) 783. [ 31 J.N. Pirts, Advan. Environmen. Sci. 1 (1969) 259. [4] J.F. Noson, private communication. [5] J.F. Noson, J. Geaphys. Res. 75 (1970) 1876. [61 hl. Gzuthier and D.R. SneIIi.nS, J. Chcm. Phys. 54 (1971) 4317. [71 F.D. Findlay and D.R. SneUing, J. Chem. Phys. 54 (1971) 2750. I81 K.H. Becker, W. Groth and U. Schurath, Chem. Phys. Letters 8 (1971) 259. f91 H.I. Schiff, Ann. Geophys. 28 (1972) 67. fro1 C.J. Fortin, D.R. Snelling and A. Tnrdif, Cert. J. Chem. 50 (1972) 2?47. [Ill I.T.N. Jones and K.D. Baycs, Chem. Phys. Letters I I (1971) 163. [I21 T. Frankiewicz and R.S. Berry, Environmcn. Sci. Tcchnol. 6 (1972) 365.
181
with rate constants kIa = I .J X IO- ““exp(-4 I so/k?q 7.1 x 20-13e.up(-2330/!W). (AI1 rate constants are given in mofecular units (cm3 moiecule and SEC),a$ the ‘hg md ‘22; states of 0, are abbreviated to o&z; and O,#>$ respectively.) Reaction {I a) pro-duces e~~~~r~~~~~~~~excited hro2 which emits a psendo-continuum [2] with a low-wavelength threshold of 590 nnl and a distribution which peaks at 1200 nm and extends to 2900 nm. Reaction (1) is 48 kca.I mole-! exothermic. Thus fo~a~~~n of either O&A) and k,,=
or O.&Z> is energetically
possibfe irr reaction
ftb).
At
moderate spectral resolution no emission from 02(A) (1270 nm) or Q&Z) (762 nm) was observed [2]. However, because of the low A factors for these traqsitions and the short reactive lifetimes of the O&A) and Q2fS) in the presence ofC$ only a tiali. fi%ction of.& molecules radiate and the emission &ll~be’very weak. A much larger fraction of the ex‘0cited NO:, fomrerl in reaction (la) radiates. Thus it is ;diffr< t% observe the G,(A) and O#) emission, .-
j78‘. _ I’
,,,
_’
”
;:.
:.
: 1
__._
‘.
__
‘_
_‘,
I_
:
,,
:.
:
,,
“,
..
;. “.
It is important to know if O,(A) is produced in reaction ( I b) since O?(h) is a possible o?ridant in polIu ted urban armospheres f3f, artd this reaction may also account 141 for the enhanced 02(b) air@ots emission associated with auroraf activity [5]. We have investigated the NO2 emission from the NO + 03 reaction at high resolution in the spectral region around 762 nm and 1270 nm. Upper Iimiis for O,(A) and 02(Z) production have been obtained using the photoIysis of 07JO~ mixtures at 253.7 nm as an internrrf standard,
The apparatus and detection q&em have been described in detail ~re~io~s~~ [Sj. il schematic diagram of the reaction vessel is’dlown in gig. 1I The 0, concentration was monitored by measuring the absorption of 253.7 nm radiation from a small Iow-pressure Hg lamp. The reaction vessel was surrounded by nine LLshaped low-pressure Hg iamps to provide for photolysis of O,lct, mixtures. The experimental procedure consisted in establishing a flow of O&J2 in the reaction vessel, photolysing a small fraction of the 03, and recording the emis-
Vofume 20, number 2
CkEhlKAL BaS04
PHYSICS
COATED Al
LETTERS REFkCTORS
ARTZ TUBES I PUMPLNG OUTLET
NiSC& SOLUTiON
HO~~ZO~T~L CONE OF SIGHT OF DETECTION SYSTEM--I Fig. 1. Schematic didgram of rencrion vessel.
sion of O,(A) or O&Z:). The 0, concentration was measured with the photoiysis lamps on and off to obtain the amount of 03 decomposed. The photolysis lamps were then turned off, and a small c&bra&d flow of NO was premixed with the 0,/O, just prior to entry into the reaction vessel; a spectral scan of the NO, contjnuum was then recorded,
3, Results and discussioI1 Typical spectra obtained in these experiments are sl~~wn in fig. 2. For all experiments the 0, pressure was 1.0 torr and the linear flow velocity 128 cm set-I. Other experimental conditions were as follows (where all pressures aze in mtorr): O,(A) emission, OS pressure 38.7,0, decomposed 5.8; NO, continuum 1270 nm, NO added 15.5, initial 03 38.5, US decomposed 16.2; O,(Z) emission, U3 pressure 39.40, decomposed 4.8; NO, c~ntin~~rn 762 nm, NO added 16.5, initial 0, pressure 38.&, 0, decomposed 17.0, The continuum emission ;::x!;;;ying the Ox(C) band resulted from fluorescence of the quartz cell :6]. Previous studies in our laboratories f6,7] using the same apparatus h3ve shown that the predominant f3te oi O,(A) and O#) is reaction with 0,. O,(h)+O,+2O.&I, *
(2)
‘Oz(C) f 0, + 20, + 0 -
13)
Wali deactivation of O,(A)
Oz(‘Aq)
,
.
e
760 WAVELENGTH
t
I
I
7722
nm
Fig. 2. Spectm showing uncorrected rehtivc intensity Of singlet 02 and NO1 c0nt~uum emissions. For expcrimcnra1 cie-
tails see text.
(41 is a significant but iess import& removai process for O,(A). The measured rate of wall deactivation in our apparatus is 131 0.5 set-l_ Collisional deactivation of CI,(L~) and O,(C) by O2 is unimportant [8I. The rates of reactions (2) and (31, taken from a recent review 179
CHEhllCAL PHYSICS LETTERS
VoIcme 20, number 2 article [9], are k2= 3.2 X lo-l5
and k,= 2.5 X lWxi. Deactivation of O,(A) and Oz(.xi by NO and NO, is totally negligible for our experimental conditions [8]. Thus, for a constant 0, pressure, the O,(A) and 02(Z) lifetimes remain unchanged with addition -of NO, and a direct comparison of O,(A) and O@) intensities for the experiments with and without NO is possibie. fn order to calculate the production of the two singlet states, the amount of 03 photolysis and the efficiency of the singiet 0, production mechanism must be known. Previous studies in our laboratories f6], using the same apparatus, have shown that photolysis of Og/c1? mixtures at 253.7 nm produces 02(A) directiY, 0, + IV -+ O,(A) + 0( ID) ,
(3
whereas O;(S) is produced by energy transfer from O(‘Dj, q’tij
+ 0, -+ Oz(-rj + O(3P) .
(6)
The available information on the efficiency of these reactions has been reviewed recentiy [9J, and it has
been concluded that the efficiency of both processes is c!cse to unity and certainly greater than 0.8. We have assumed an efticiency of unity for both processes in the following discussions. (For reaction (6) the efticiency is the fraction of O(D) + 0, deactivating collisions which result in the formation of 02(x).j in addition to the reactions already listed, the 0, decomposition is also controlled by the following reactions: O(lD> -+.03
420,
,
-+02f20,
o+02+o*-,03+03.
(7a) Vbl
(9)
In order to calculate the amount of 0, photoiysis from the observed amount of Oj decomposition, downstream from the photolysis region (see fig. I), we have numeric&y integrated the rate equations for reacrions (2)~(9) using a Runge-Kutta integration routine. This calculation has been described in detail previously [IO] and till only be outlined here. Secause 0( ID} reaction rates are almost collision limited ..
180 j,
‘.
15 May 1973
[9], Of ‘D) is always in ~hotochemi~~ equilibrium and only re!ative reaction rates are required to compute the fate of O( lD) [lO]. In our calculations we have assumed that k7/k6 = 9.7 [6] and k,, = k,, = 0.5 k,. The products of reaction (7) are uncertain [9] and we have arbitrarily made the assumption that k-y, = ?iTb. The effects of this assumption are not serious since more than 70% of the O(lD) reacts with 0, for our experimental conditions. The following rate constants [9] were used in the calculations of 03 decomposition: k, = 1.0 X lo-‘*, kg = 7.0 X lO-34 k, = 3.2 X i0--15, k, = 2.5X fO-IIand~~=O.5 ’ SCC-~.Tine rate expressions were integrated and the rate of photolysis was adjusted to obtain the observed amount of 0, decomposition. Note that, from fig. I, for a flow velocity of I28 cm see-l, the 0, spends 176 msec in the illuminated region and a further 164 msec between the end of the illuminated region and the 0, monitoring station. The photolysis intensity was assumed to be constant in the ~luminated region. The calculated amount of 0, photolysis for the O,(A) and 02(C) experiments in fig. 2 is 1.3 mtorr and I. I mtorr, respectively, i.e., a quantum yield of ==4for 03 destruction. At room temperature (29G”K), ~93% of the NO + 03 reaction occurs by process(lbj. Furthermore, this reaction is complete p99.7 of NO reacting) during the flow time from the input region to the Oj monitor@ station. The observed O3 decomposition corresponds, within experimental error, to the amount of KO added. This observation immediately rules out any substantial production of02(Aj or O,{X) in reaction (lb) since production of either species would lead to additional 0, destruction by reactions (2) and/or (3). From a comparison of the spectra in fig. 2 we conclude that any 02(A) emission present in the NO2 continuum is Iess than If30 of that observed from photolysis of 0,. Since the latter has been shown to result from production of I.3 mtorr of 02(A), and since 15 m torr of NO reacted with 0, by process (1 b), we conclude that less than 1.3/30 X 15 = l/300 of 0, produced in (1 b) is in the Oz(Aj state. Similar calculations for the spectra at 760 run, with the 29 sumption that any O&Z) emission present in the NO, continuum is less than l/l.5 of that observed from 0, photolysis, lead to an upper Emit of l/200 for O,(6) production.
CHEMICAL PHYSICS LETTERS
Volume 20, number 2
In the above calculations it has been implicitly assumed that equal production of singlet 0, from reaction (1 b) or from photolysis of 0, will priduce equal signals. It will be shown below that, if anything, singiet 0, from reaction (1 b) will be detected more efficiently thus not affecting the upper limits given above. Firstly, the average OS pressure is somewhat lower in the NO experiments resulting in a longer singlet 0, lifetime. Secondly, the distribution of singlet O2 in the reaction vessel will be different for the two sources since the NO + 0, mixing region occurs closer to the detection system than the illuminated region of the cell (see fig. 1). For a small segment of the source with uniform cross-sectional excitation the useful illumination entering the spectrometer slit is independent of the source to spectrometer separation provided that the cones of sight of the spectrometer are contained within the source; i.e., provided no vignetting occurs. If this latter condition is not met the illumination decreases with increasing source to spectrometer separation. Particularly for O,(A), which has a longer reactive lifetime, a larger fraction of the singlet 02 emission from 03 photoiysis occurs in a region of the cell where the field of view of the spectrometer is vignetted. (Because of the finite slit height (“2 cm) the outer vertical cone intersects the reaction vessel somewhat closer to the spectrometer than the horizontal cone shown in fig. 1.) Thus O,(A) and 01(E) will be sampled less efficiently if produced by 0, photolysis rather than reaction ( 1b) so that the above limits in 02(Z) and Oz(Aj production still hold. In two recent publications [ 11,121 it was shown that electronically excited NO,, produced by irradiation of NO, with visible light,kansferred energy coilisionally to 02 to produce O,(A). Since O*(A) emission was not observed in our NO/O3 experiments we can set upper iimits on the production of O,(A) by the reaction sequence: NO+03+NO;+02,
(la)
NO; + 0, --f NO, t O,(A), -+NO,+O,.
(1W (lob)
L
In the above discussion
it was shown that the
15 1May1973
O?(A) emission resulted from photolysis of I.3 mtorr of 0, [i.e., production of 1.3 mtorr of O,(4)] in OS/O, mixtures and that the intensity of t,his emission was at least 30 times greater than any 02(A) emission present in the NO/O, experiments. Therefore we may set an upper limit of 1.3/30 rntorr (= 4 X 10m5 torr) in the production of 02(A) from reactions (la) and 10) in the NO/O, experiments. For these experiments 15.5 mtorr of NO reacted with 03 of which approximately 8%, or 1.2 X low3 torr, reacts via process (la) at room temperature. The data of Thrush et al. [ 1(2] show that -0% of the NO; formed in reaction (la) is quenched by 0, for our esperimental conditions_ Therefore we may conclude that the efficiency of O,(A) production in reaction (10) is less than 4 X 10W5/0.9 X 1.2 X 10m3 or 4%. This conclusion is not surprising since Jones and Bayes [ 1 1; have determined efficiencies decreasing from 3.5% to 0.5% as the NO, excitation wavelength increased from 4200 A to 6200 PI and reaction (la) is only energetic enough to produce NO, with escitation equivalent to 6000 A radiation.
References [ 1) M.A.A. Ciyne, B.A. Thrush and R.P. Wsyne, fmnr Faraday See. 60 (1964) 359. [ 21 P.N. Clough and B.A. Thrush. Chcm. Commun. 71 (I 966) 783. [ 31 J.N. Pirts, Advan. Environmen. Sci. 1 (1969) 259. [4] J.F. Noson, private communication. [5] J.F. Noson, J. Geaphys. Res. 75 (1970) 1876. [61 hl. Gzuthier and D.R. SneIIi.nS, J. Chcm. Phys. 54 (1971) 4317. [71 F.D. Findlay and D.R. SneUing, J. Chem. Phys. 54 (1971) 2750. I81 K.H. Becker, W. Groth and U. Schurath, Chem. Phys. Letters 8 (1971) 259. f91 H.I. Schiff, Ann. Geophys. 28 (1972) 67. fro1 C.J. Fortin, D.R. Snelling and A. Tnrdif, Cert. J. Chem. 50 (1972) 2?47. [Ill I.T.N. Jones and K.D. Baycs, Chem. Phys. Letters I I (1971) 163. [I21 T. Frankiewicz and R.S. Berry, Environmcn. Sci. Tcchnol. 6 (1972) 365.
181