- Email: [email protected]
Relative quantum yields of O(1D) in Ozone Photolysis in the region between 250 and 300 nm
Volume 60, number I
CHFMICAL
PHYSICS LETTERS
IS December 1978
RELATIVE QUANTUM YIELDS OF O(‘D) IN OZONE PHOTOLYSIS IN THE REGION BETWEEN 250 AND 300 run * Paul IV- FAIRCHILD and Edward K.C. LEE Department of C3zemiUg , D’nivers@y of Gdifomia. Irvine, Gz!ifomia 92717, USA Received 7 A%1978; Revised manuscript received I September 19?8 Relative quantum yieldsof O(lDz) formation, @rel, for ozone photolysis in tie re@on of 250-300 nm have been determined in the_@sphaseat 23OC The NOa cheduminescen~ result& from the photoexcitation of an OS/N20 mWure was used in monitoring the O(“Dz) formation. The results show that the value of are1 remains constant throw&out the photoiysis waveIen& rq studied at 2-S mn inte_aLs.
I- Introduction ‘Ihe photolysis of ozone produces an elestronicaliy excited O(‘D) atom and 02(14s) molecule with a photochemicai threshoId near 3 IO run,
0, + Izv (x < 310 run) -+ O(lD) + O&A&
(1)
Although it is energetic&y possiiie to produce O(lD) and 02(lq) at waveIen,@s shorter than 266 nm, O3 f hv (A < 266 nm) + O(lD) •i-O&Z,‘),
(2)
only 02(l&) is produced at 253-7 run. The wav~engtb and temperature dependences of these processes are of considerable importance to the study of atmospheric chemistry. The reaction of O(ID) atoms with Hz0 vapor is the principal source of OH radicals,and the reaction of O(‘D) atom with N,O generates NO in the stratosphere. For these reasons, primery end secondary photochemical processes in the threshoId region around 313 run have ken investigated extensively using various experimental techniques [l-7]. Recent reviews on the state of knowfedge or the ozone photolysis are availabie in the literature [7-9j ) and therefo_m there is no need here to review it_ The data on the wavelength dependence of the
* l%is research has been supported by the Off&e of Naval Research Contract _X-O0014-75C-8 13.
36
O(lD) atom quantum yield, @[O(lD)] , in the 250290 nm region are only sparce [ 1.61, and it is frequently assumed to be unity. In order to provide some additional data in this region, we have carried out a measurement on the relative quantum yield, @n,l [C(‘D)] , as a function of wavelength between 250 and 300 run at room temperature (296 K)_ We have empIoyed the NO; chemihnninescencemethod (utilizing the O3/bIzO mixture) previously used by Moortgat et al. [4,5] and Philen et al. [7 1, since it is a very convenient method if a continuously tunable light source for photolysis of 0, is available_A tunable dye Iaser flash phatolysis was used for the previous studies in the region of 295-319 nm [5,7]. However, it is a ratherawkward method to use, if tutig over a wide wavelen,& range using severaldyes becomes necessary. This disadvantagecan be overcome, if a combination of a Xe arc Iamp and a scanning monochromator is used for recording a chemiluminescence excitation spectrum [lo] _ Although this latter experimentaI technique has a distinct disadvantage in terms of the light intensity, we feel that the convenience of having the capability for a wide tuning range in a short period of time during a series of experimental runs outweighs the disadvantage of the former experimental technique using a dye laser. The absorption coefficient of 0, increases whiie the intensity of the Xe arc Iarnp decreases toward shorter wavelength iu the 250-320 run range. Hence, chenriluminescence excitation intensity shows a relatively small, dynamic
Volume 60, number 1
CHJZMICALPHYSICS LETTERS
range of variation except near the 300 cm region where the absorption coefficient has a very steep wavelength dependence. This is further complicated by the fact that the quantum yield of O(lD) becomes zero at wavelengths longer than 313 run.
2. Experimental 2 L Luminesceizce setup The detail of the chemical reaction scheme involved in the NO; chemiluminescence detection method using an OS/N20 mixture for detecting the photolytic O(‘D) atoms has been fully described [4,5,7]__ The intensity of the chemiluminescence emission, 1,,0), has been shown to be rem@j = EI@QN,b,OjT,
(3)
where X is the photolysis wavelength, a@) is the , quantum yield for O(lDj production, Nabs@) is proportional to the number of absorbed photolysis quanta in the region of the reaction cell as viewed by the chemiluminescence detector, p is the geometric and spectral factor applied to the efficiency of chemiluminescence detector, and y is the “chemical” factor dictated by the chemiluminescence kinetics [7]. In order to keep 7 constant, we have fured the 03&O ratio to 1 : 10 as used previously_ In order to avoid the problem associated with “round-the-comer” effect* caused by the geometrical contribution to the variation in @, we have used a lower total pressure (0.6-2.0 torr) than in the earlier experiment [4,5,7]. This is particularly important at shorter wavelengths where the absorption coefficients are much greater and hence the light attenuation in the sample is substantial- Also the constant /3 is not truly independent of 7, since the NO; emission proMe is pressure dependent to some extent. However, the spectral contniution to the variation in /3 is constant, if the chemical composition is fured throughout the experiment. N.&X) was calculated with the values of I, and It * in a typicalluminescencemeasurementusiriga croS- or T-shapedcell, the effectiveviewinggeometry is decreased, if the optical density of the samplebecomes high. This is due to a shorterpenetrationdepthof the excitixxx light into the sample,which causesthe fast decaying,luminescent imageto disappeararound the corner(see ref_ [ 111%
15 December 1978
which was obtained from the Beer-Iambert expression hi (J&r>
=
law
-Wx,
(4)
using the incident photon-intensity (IO), the absorption cross section, o@), the concentration of O,, N, and the pathlength, x. The luminescence excitation spectrometer setup used in this experiment is &zly identical to that used earlier in our laboratory [; 11. The incident intensity of the exciting light was monitored by an RCA lIT?l photomultiplier viewing the rhodamine B solution quantum counter through% neutral density filter which attenuated the inteP,$ty of the rhodamine B fluorescence when it is too strong. The emission intensity of -Jle NO’, chemil~mines_cence was monitored by a dry-ice cooled EMI 9&S, B (extended S-2@ photomultiplier viewing the sample through a combination of two cut-off fiters, Schott KY-550 (550 nm cut-offj and Corning CS 2-73 (590 nm cut-off), which was designated to reduce the scattered exciting light. The incident light intensity with a 0.8 nm spectral bandwidth dropped by a factor of 3 going from 300 nm to 250 rum at =10F7 W level- The chemilumincscence intensity was measured with a standard photon counting setup. 2.2. Sample preparation Ozone was prepared by a commercial ozonator (Welsbach model T-408) and collected over silica and stored at dry-ice acetone temperature (-76°C). Ozone was purified before each run by several successive trap-to-trap distillations. N20 (Matheson, 99.0% minimum purity) was purified by freezing out NO as an impurity in an KFC~H~~slush (-13 1 .S°C) and by freezing out NO, as an impurity in a dry-ice acrone bath (-76°C). The pressure of the sample was monitored by a capacitance manometer (MKS Baratrcm, type 145 AHS-10) 10 torr head. A cross-shaped fluorescence cell with 38 mm diameter suprasil windows and a 100 mm absorption path length was used. Al! of the quantum yield measurements were carried out at room temperature (23°C). 2.3. Relative quantum
yields
Chemiluminescence si&
was counted for 40 s
37
Volume 60. number 1
CIiIS¶IcAL
PHYSICS
at each wavelength interval. The relative quantum was calculated with two simulyield, *=I taneously measured experimental values of the in-
lo(‘D)],
cident ii&t intensity and the chernikminescence intensity obtained at each successive wavelen,& interval, ta!!g into account of two correction factors. The fust correction involves the attenuation of the incident light intensity through the sample up to the viewing reggon at the center of the cell. The light attenuation wzs calculated assuming Beer’s law with the extinction coefficients given by Sanders and DeMore [12]+, and a maximum correction of =Qoc/o was made at 2.55 nm. If we used lower total pressure, this correction should not be necessary_ However, we found that the chemihuninescence intensity iu our system was maximized at a total pressure of 2.0 torr. We chose this pressure setting to optimize the signalto-noise ratio and to minimize the variation caused by the composition change due to the photolytic removal of ozone during ffic measurement. ‘ihe second correction involves the photolytic depletion of ozone during a series of measurements, and a maximum correction of ---2’S between the adjacent waveleng!! intervak was applied at 266 nm. If 2 fast flow system-was used, or if a fresh sample mixture was used in a static system for each chemiluminescence measurement at various wavelengths, this complication could have been avoided. However, we feel ‘&at the experimental uncertainty involved in the ozone pressure measurements for each wavelength interval may outweigh the probable error in the correction factor used for the pho%lytic ozone depletionme correction factor calculated from the observed value of the cumulative, ozone destruction incurred over 2 complete cycle of wavelength scan (30 intervais) assuming that the ozone destruction at each wavelength interval was proportional to the product of the absc@on coefficient and the photolysis light intensity-
3. Results and discussion Ihe chemihuninescence
intensity increased mono-
tonically by about 25-fold going from 300 nm to
+ mei_ data were used, because the literature data of Griggs [ 131 and Inn and Tanaka [ 141 could net be read off accurately from the published absorption curves
38
LJXTERS
15 December 1978
250 nm, mainly due to an increase in the 0,
absorp-
tion cross section. The observed intensity data were appropriately corrected as described earlier, for calculating the relative quantum yields of O(‘D) production in the ozone photolysk The results obtained in 4 determinationswere averaged for each photolysis wavelength, and they were normalized over the wavelen,& range studied to give an average of 1.00. The vdue at 300 nm was abnormally low, and therefore it was excluded in the foal normalization procedure on the assumption that the extremely low absorption coefficient at 300 nm was responsible for the very poor accuracy in measuring the ihemiluminescence signal. The values of aA [O(‘D)] as a function of photoIysis wavelength are shown in table 1 together with the 0, absorption cross sections used [ 12]_ Our data and the values reported in the literature [1,5,7, IS] are compared in fig. I _ Our present data on GX1 obtained in the wavelength range of 250-295 nm extends the earlier data obtained by Lin and DeMore [I] in the wavelength range of 275-310 nm. Our value at 300 nm is certainTabR 1 Rehtie quantum yields of O(l D) production in ozone photolysis at various wavelengths (23°C) Wavelength
Absorption
X (nm)
aoss section Q (IO-= cm2)a)
250
11.1 11.6 10-S 10.5
255 260 262
264
9-9
266 268 270
9.4 8.4 S-0
272 275 280 285
7.99 5.9, 4.01 2.47
290 295 300
1.4, O-8, O-42
1.06 0.95 1.35 1.04 1.00 1.06 1.06 1.08
+ * 5 f + f f -
0.15 O-06 0.10 0.13 0.05 0 05 0.07 0.12
1.032 0.08 0.97f 0.02 1.00f 0.07 1.02 0.88 0.87 0.58
c i: f *
0.09 0.03 0.07 0.16
a) Absorption aoss sections of ozone at room temperature given by Sanders and DeMore [ 121 were used b, An average of four det erminations for each wavelen&Z The relative valLw were normalized so that the wavelength average excluding the value at 300 nn gives 1.00 f 0.07.
Volume
60,nnmber 1
CAEZIICAL
PHYSICS LETTERS
15 December 1978
of the Jet Propulsion Laboratory, Pasadena, California, for snaking available to us their O3 absorption spectra in the 250-300 run region.
References [II CL
* (nd @rel[O(lD>] versus photolysis wavelen&. Ours (0); J&I and DeMore [ 11 (a); Jones and Wayne [ 151 (A); Arnold et al. 151 (-); Philen et al. 171 (- - -). Fig_ 1.
Iy too low, and our values at 290 and 295 nm could also be unreliable_ If we assume that our values in the US-290 nm range are correct because they are properly normalized to the values of Lin and DeMore [l] in the same wavelength range, the relative quantum yield of O(‘D) production is constant between 250 and 300 nm within one standard deviation of 7% (see footnote b of table 1). If these values are compared to the &solute quantum yield values of Jones and Wayne between 289 and 302 mn [15], our data supports the frequently assumed argument [1,6] based on the measurement made in liquid Ar at 253.7 run [16] that the absolute quantum yield of O(‘D) production is 1 .O between 250-300 urn. Achowiedgement We wish to thank Drs. W-B.. D&ore
Lin and W-B. De&fore,J. Photochem. 2 (1973/74) 161. [21 R. Simonaitis, S. Braslavsky, J. HeichJen and M. Nicobt, Chem. Phys. Letters 19 (1973) 601; S. Kuis, R. Shnonaitis and J. Heidclen, J. Geophys Res SO (1975) 1328. D. Martin, J. G&man and H.S. Sobnston, 167th American Qzemical Society Natirmal Meeting, Los AnseIes, Spring, 1974. G-K. Moortgat and P_ Wax-neck, 2. Naturforsch. 3Oa (1975) 835. I. Arnold, F-J. Comes and G.K. bfoortgat, Chem. Phys. _%..^. 24 (1977) 211. 0. Kajimoto and RJ. Cvetanovi&, Chem. Phyr Letters 37 (1976;) 533. D-L Philen, R-T. Watson and D-D. Davis, J. Chem. Phys 67 (1977) 3316 MJ. Molina, in: ~oroffuorome~es and ‘Je Stratosphere, NASA Reference Pnbhcation 1010, cd. RD. Hudson, August, 1977. R-F. Hampson Jr- and D. Garvin, Reaction Rate and Photocbemical Data for Atmospheric Chemistry, NBS Special Publications No. 513, May, 1978. p. 31. R.S. Lewis, K-Y. Targ and E-K-C_ Lee, 3. Chem_ Phys 65 (1976) 2910. L-J. VoJk and EK.C. Lee, J. Chem. Phys 67 (1977j236. S Sanders and W-B. De&fore, private ~mmuni~tionM. Griggs, J- Chem- Phys 49 (1968) 857_ EC-Y. Inn and Y. Tanaka, J- Opt. Sot. Am. 43 (1953) 870. 1-T-N. Jones and R-P. Wayne, Proc. Roy. Sot_ A319 (1970) 273. [is] W.B. De&Sore and 0-F. Raper, J. Chem. Phys. 44 (1966) 1780s
and S. Sanders
39
CHFMICAL
PHYSICS LETTERS
IS December 1978
RELATIVE QUANTUM YIELDS OF O(‘D) IN OZONE PHOTOLYSIS IN THE REGION BETWEEN 250 AND 300 run * Paul IV- FAIRCHILD and Edward K.C. LEE Department of C3zemiUg , D’nivers@y of Gdifomia. Irvine, Gz!ifomia 92717, USA Received 7 A%1978; Revised manuscript received I September 19?8 Relative quantum yieldsof O(lDz) formation, @rel, for ozone photolysis in tie re@on of 250-300 nm have been determined in the_@sphaseat 23OC The NOa cheduminescen~ result& from the photoexcitation of an OS/N20 mWure was used in monitoring the O(“Dz) formation. The results show that the value of are1 remains constant throw&out the photoiysis waveIen& rq studied at 2-S mn inte_aLs.
I- Introduction ‘Ihe photolysis of ozone produces an elestronicaliy excited O(‘D) atom and 02(14s) molecule with a photochemicai threshoId near 3 IO run,
0, + Izv (x < 310 run) -+ O(lD) + O&A&
(1)
Although it is energetic&y possiiie to produce O(lD) and 02(lq) at waveIen,@s shorter than 266 nm, O3 f hv (A < 266 nm) + O(lD) •i-O&Z,‘),
(2)
only 02(l&) is produced at 253-7 run. The wav~engtb and temperature dependences of these processes are of considerable importance to the study of atmospheric chemistry. The reaction of O(ID) atoms with Hz0 vapor is the principal source of OH radicals,and the reaction of O(‘D) atom with N,O generates NO in the stratosphere. For these reasons, primery end secondary photochemical processes in the threshoId region around 313 run have ken investigated extensively using various experimental techniques [l-7]. Recent reviews on the state of knowfedge or the ozone photolysis are availabie in the literature [7-9j ) and therefo_m there is no need here to review it_ The data on the wavelength dependence of the
* l%is research has been supported by the Off&e of Naval Research Contract _X-O0014-75C-8 13.
36
O(lD) atom quantum yield, @[O(lD)] , in the 250290 nm region are only sparce [ 1.61, and it is frequently assumed to be unity. In order to provide some additional data in this region, we have carried out a measurement on the relative quantum yield, @n,l [C(‘D)] , as a function of wavelength between 250 and 300 run at room temperature (296 K)_ We have empIoyed the NO; chemihnninescencemethod (utilizing the O3/bIzO mixture) previously used by Moortgat et al. [4,5] and Philen et al. [7 1, since it is a very convenient method if a continuously tunable light source for photolysis of 0, is available_A tunable dye Iaser flash phatolysis was used for the previous studies in the region of 295-319 nm [5,7]. However, it is a ratherawkward method to use, if tutig over a wide wavelen,& range using severaldyes becomes necessary. This disadvantagecan be overcome, if a combination of a Xe arc Iamp and a scanning monochromator is used for recording a chemiluminescence excitation spectrum [lo] _ Although this latter experimentaI technique has a distinct disadvantage in terms of the light intensity, we feel that the convenience of having the capability for a wide tuning range in a short period of time during a series of experimental runs outweighs the disadvantage of the former experimental technique using a dye laser. The absorption coefficient of 0, increases whiie the intensity of the Xe arc Iarnp decreases toward shorter wavelength iu the 250-320 run range. Hence, chenriluminescence excitation intensity shows a relatively small, dynamic
Volume 60, number 1
CHJZMICALPHYSICS LETTERS
range of variation except near the 300 cm region where the absorption coefficient has a very steep wavelength dependence. This is further complicated by the fact that the quantum yield of O(lD) becomes zero at wavelengths longer than 313 run.
2. Experimental 2 L Luminesceizce setup The detail of the chemical reaction scheme involved in the NO; chemiluminescence detection method using an OS/N20 mixture for detecting the photolytic O(‘D) atoms has been fully described [4,5,7]__ The intensity of the chemiluminescence emission, 1,,0), has been shown to be rem@j = EI@QN,b,OjT,
(3)
where X is the photolysis wavelength, a@) is the , quantum yield for O(lDj production, Nabs@) is proportional to the number of absorbed photolysis quanta in the region of the reaction cell as viewed by the chemiluminescence detector, p is the geometric and spectral factor applied to the efficiency of chemiluminescence detector, and y is the “chemical” factor dictated by the chemiluminescence kinetics [7]. In order to keep 7 constant, we have fured the 03&O ratio to 1 : 10 as used previously_ In order to avoid the problem associated with “round-the-comer” effect* caused by the geometrical contribution to the variation in @, we have used a lower total pressure (0.6-2.0 torr) than in the earlier experiment [4,5,7]. This is particularly important at shorter wavelengths where the absorption coefficients are much greater and hence the light attenuation in the sample is substantial- Also the constant /3 is not truly independent of 7, since the NO; emission proMe is pressure dependent to some extent. However, the spectral contniution to the variation in /3 is constant, if the chemical composition is fured throughout the experiment. N.&X) was calculated with the values of I, and It * in a typicalluminescencemeasurementusiriga croS- or T-shapedcell, the effectiveviewinggeometry is decreased, if the optical density of the samplebecomes high. This is due to a shorterpenetrationdepthof the excitixxx light into the sample,which causesthe fast decaying,luminescent imageto disappeararound the corner(see ref_ [ 111%
15 December 1978
which was obtained from the Beer-Iambert expression hi (J&r>
=
law
-Wx,
(4)
using the incident photon-intensity (IO), the absorption cross section, o@), the concentration of O,, N, and the pathlength, x. The luminescence excitation spectrometer setup used in this experiment is &zly identical to that used earlier in our laboratory [; 11. The incident intensity of the exciting light was monitored by an RCA lIT?l photomultiplier viewing the rhodamine B solution quantum counter through% neutral density filter which attenuated the inteP,$ty of the rhodamine B fluorescence when it is too strong. The emission intensity of -Jle NO’, chemil~mines_cence was monitored by a dry-ice cooled EMI 9&S, B (extended S-2@ photomultiplier viewing the sample through a combination of two cut-off fiters, Schott KY-550 (550 nm cut-offj and Corning CS 2-73 (590 nm cut-off), which was designated to reduce the scattered exciting light. The incident light intensity with a 0.8 nm spectral bandwidth dropped by a factor of 3 going from 300 nm to 250 rum at =10F7 W level- The chemilumincscence intensity was measured with a standard photon counting setup. 2.2. Sample preparation Ozone was prepared by a commercial ozonator (Welsbach model T-408) and collected over silica and stored at dry-ice acetone temperature (-76°C). Ozone was purified before each run by several successive trap-to-trap distillations. N20 (Matheson, 99.0% minimum purity) was purified by freezing out NO as an impurity in an KFC~H~~slush (-13 1 .S°C) and by freezing out NO, as an impurity in a dry-ice acrone bath (-76°C). The pressure of the sample was monitored by a capacitance manometer (MKS Baratrcm, type 145 AHS-10) 10 torr head. A cross-shaped fluorescence cell with 38 mm diameter suprasil windows and a 100 mm absorption path length was used. Al! of the quantum yield measurements were carried out at room temperature (23°C). 2.3. Relative quantum
yields
Chemiluminescence si&
was counted for 40 s
37
Volume 60. number 1
CIiIS¶IcAL
PHYSICS
at each wavelength interval. The relative quantum was calculated with two simulyield, *=I taneously measured experimental values of the in-
lo(‘D)],
cident ii&t intensity and the chernikminescence intensity obtained at each successive wavelen,& interval, ta!!g into account of two correction factors. The fust correction involves the attenuation of the incident light intensity through the sample up to the viewing reggon at the center of the cell. The light attenuation wzs calculated assuming Beer’s law with the extinction coefficients given by Sanders and DeMore [12]+, and a maximum correction of =Qoc/o was made at 2.55 nm. If we used lower total pressure, this correction should not be necessary_ However, we found that the chemihuninescence intensity iu our system was maximized at a total pressure of 2.0 torr. We chose this pressure setting to optimize the signalto-noise ratio and to minimize the variation caused by the composition change due to the photolytic removal of ozone during ffic measurement. ‘ihe second correction involves the photolytic depletion of ozone during a series of measurements, and a maximum correction of ---2’S between the adjacent waveleng!! intervak was applied at 266 nm. If 2 fast flow system-was used, or if a fresh sample mixture was used in a static system for each chemiluminescence measurement at various wavelengths, this complication could have been avoided. However, we feel ‘&at the experimental uncertainty involved in the ozone pressure measurements for each wavelength interval may outweigh the probable error in the correction factor used for the pho%lytic ozone depletionme correction factor calculated from the observed value of the cumulative, ozone destruction incurred over 2 complete cycle of wavelength scan (30 intervais) assuming that the ozone destruction at each wavelength interval was proportional to the product of the absc@on coefficient and the photolysis light intensity-
3. Results and discussion Ihe chemihuninescence
intensity increased mono-
tonically by about 25-fold going from 300 nm to
+ mei_ data were used, because the literature data of Griggs [ 131 and Inn and Tanaka [ 141 could net be read off accurately from the published absorption curves
38
LJXTERS
15 December 1978
250 nm, mainly due to an increase in the 0,
absorp-
tion cross section. The observed intensity data were appropriately corrected as described earlier, for calculating the relative quantum yields of O(‘D) production in the ozone photolysk The results obtained in 4 determinationswere averaged for each photolysis wavelength, and they were normalized over the wavelen,& range studied to give an average of 1.00. The vdue at 300 nm was abnormally low, and therefore it was excluded in the foal normalization procedure on the assumption that the extremely low absorption coefficient at 300 nm was responsible for the very poor accuracy in measuring the ihemiluminescence signal. The values of aA [O(‘D)] as a function of photoIysis wavelength are shown in table 1 together with the 0, absorption cross sections used [ 12]_ Our data and the values reported in the literature [1,5,7, IS] are compared in fig. I _ Our present data on GX1 obtained in the wavelength range of 250-295 nm extends the earlier data obtained by Lin and DeMore [I] in the wavelength range of 275-310 nm. Our value at 300 nm is certainTabR 1 Rehtie quantum yields of O(l D) production in ozone photolysis at various wavelengths (23°C) Wavelength
Absorption
X (nm)
aoss section Q (IO-= cm2)a)
250
11.1 11.6 10-S 10.5
255 260 262
264
9-9
266 268 270
9.4 8.4 S-0
272 275 280 285
7.99 5.9, 4.01 2.47
290 295 300
1.4, O-8, O-42
1.06 0.95 1.35 1.04 1.00 1.06 1.06 1.08
+ * 5 f + f f -
0.15 O-06 0.10 0.13 0.05 0 05 0.07 0.12
1.032 0.08 0.97f 0.02 1.00f 0.07 1.02 0.88 0.87 0.58
c i: f *
0.09 0.03 0.07 0.16
a) Absorption aoss sections of ozone at room temperature given by Sanders and DeMore [ 121 were used b, An average of four det erminations for each wavelen&Z The relative valLw were normalized so that the wavelength average excluding the value at 300 nn gives 1.00 f 0.07.
Volume
60,nnmber 1
CAEZIICAL
PHYSICS LETTERS
15 December 1978
of the Jet Propulsion Laboratory, Pasadena, California, for snaking available to us their O3 absorption spectra in the 250-300 run region.
References [II CL
* (nd @rel[O(lD>] versus photolysis wavelen&. Ours (0); J&I and DeMore [ 11 (a); Jones and Wayne [ 151 (A); Arnold et al. 151 (-); Philen et al. 171 (- - -). Fig_ 1.
Iy too low, and our values at 290 and 295 nm could also be unreliable_ If we assume that our values in the US-290 nm range are correct because they are properly normalized to the values of Lin and DeMore [l] in the same wavelength range, the relative quantum yield of O(‘D) production is constant between 250 and 300 nm within one standard deviation of 7% (see footnote b of table 1). If these values are compared to the &solute quantum yield values of Jones and Wayne between 289 and 302 mn [15], our data supports the frequently assumed argument [1,6] based on the measurement made in liquid Ar at 253.7 run [16] that the absolute quantum yield of O(‘D) production is 1 .O between 250-300 urn. Achowiedgement We wish to thank Drs. W-B.. D&ore
Lin and W-B. De&fore,J. Photochem. 2 (1973/74) 161. [21 R. Simonaitis, S. Braslavsky, J. HeichJen and M. Nicobt, Chem. Phys. Letters 19 (1973) 601; S. Kuis, R. Shnonaitis and J. Heidclen, J. Geophys Res SO (1975) 1328. D. Martin, J. G&man and H.S. Sobnston, 167th American Qzemical Society Natirmal Meeting, Los AnseIes, Spring, 1974. G-K. Moortgat and P_ Wax-neck, 2. Naturforsch. 3Oa (1975) 835. I. Arnold, F-J. Comes and G.K. bfoortgat, Chem. Phys. _%..^. 24 (1977) 211. 0. Kajimoto and RJ. Cvetanovi&, Chem. Phyr Letters 37 (1976;) 533. D-L Philen, R-T. Watson and D-D. Davis, J. Chem. Phys 67 (1977) 3316 MJ. Molina, in: ~oroffuorome~es and ‘Je Stratosphere, NASA Reference Pnbhcation 1010, cd. RD. Hudson, August, 1977. R-F. Hampson Jr- and D. Garvin, Reaction Rate and Photocbemical Data for Atmospheric Chemistry, NBS Special Publications No. 513, May, 1978. p. 31. R.S. Lewis, K-Y. Targ and E-K-C_ Lee, 3. Chem_ Phys 65 (1976) 2910. L-J. VoJk and EK.C. Lee, J. Chem. Phys 67 (1977j236. S Sanders and W-B. De&fore, private ~mmuni~tionM. Griggs, J- Chem- Phys 49 (1968) 857_ EC-Y. Inn and Y. Tanaka, J- Opt. Sot. Am. 43 (1953) 870. 1-T-N. Jones and R-P. Wayne, Proc. Roy. Sot_ A319 (1970) 273. [is] W.B. De&Sore and 0-F. Raper, J. Chem. Phys. 44 (1966) 1780s
and S. Sanders
39