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High resolution absorption cross-section measurements of N2O at 295–299 K in the wavelength region 170–222 nm
003? Oh33.X4S3n0+000 C' 1984 Pergmon PressLid
HIGH
RESOLUTION ABSORPTION CROSS-SECTION MEASUREMENTS OF N,O AT 295-299 K IN THE WAVELENGTH REGION 170-222 nm K. YOSHINO,
Harvard-
Smithsonian
0.
E. FREEMAN
and W. H. PARKIRSON
Center for Astrophysics,
Cambridge,
MA 02138, U.S.A.
AbstractHigh resolution absorption cross-section measurements of N,O at 295-299 K have been performed in the wavelength region 17&222 nm with a 6.65 m scanning spectrometerkpectrograph of sufficient resolution to yield cross-sections that are independent of the instrumental function. The measured cross-sections are presented graphically and are available throughout the region 44925558955 cm-r at intervals ofO.lL0.2 cm- ’ as a numerical tabulation stored on magnetic tape from the National Space Science Data Center, NASA/Goddard Space Flight Center, Greenbelt, MD 20771. U.S.A. Previously unresolved detailsofthe bandedstructurewhichissuperposedon thecontinuousabsorptionin theregion 174190nmare observed.
1. The cross-section
INTRODUCTION
measurements
of NzO
by Johnston
and Selwyn (1975) have established that the absorption at wavelengths greater than 260 nm is negligible, although such absorption had previously been thought responsible for significant atmospheric photolysis of N,O. That discovery exacerbated the problem of finding adequate atmospheric sinks for N,O, but this difficulty has lately been alleviated somewhat (Jackman and Guthrie, 1983; Froidevaux and Yung, 1982) by indications from stratospheric experiments (Frederick and Mentall. 1982: Herman and Mentall, 1982: Anderson and Hall. 1983) and laboratory results (Cheung et al., 1984) that previously accepted laboratory values of the absorption cross-section of O2 in the region 190-240 nm are too high. At shorter wavelengths, the cross-section of N,O and its temperature dependence have been measured recently by Hubrich and Stuhl (1980). Selwyn el ~1. (1977) and Selwyn and Johnston (1981). The latter two groups have found that in the region 173-190 nm the banded contributions superposed on the continuous absorption are more marked and structured than in previous studies (Zelikoff et al., 1953; Monahan and Walker, 1975). The observed structure and its temperature dependence are explained by Selwyn and Johnston (1981) in terms of absorption by N,O in which the ground state bending vibration is thermally excited. The cross-section measurements of NzO made by Selwyn rt al. (1977) and Selwyn and Johnston (1981) were performed photoelectrically at moderate resolution (0.075 mn) in the region 17222 10 nm. In addition, Selwyn and Johnston (1981) photographed the
absorption spectrum of N,O at room temperature at higher resolution (0.003 nm) with a 3 m vacuum spectrograph and found that, for the banded structure. the heights of the absorption peaks relative to adjacent valleys were two to four times greater than when their photoelectric instrument of lower resolution was used. In the present investigation we use a 6.65 m photoelectric scanning spectrometer/spectrograph of small enough instrumental band width, 0.0013 nm full width at half maximum (FWHM), to ensure that the absorption cross-section measured for N,O at room temperature in the region 170-222 nm is independent of the instrumental band width. Earlier cross-section measurements ofNzO, made with low resolutionin this wavelength region, have been reviewed by Hudson ( 1974).
2. EXPERIMENTAL
PROCEDURE
The experimental procedure with the 6.65 m photoelectric scanning spectrometer,/spectrograph (Yoshino et al., 1980) for measuring the absorption cross-section of N,O in the wavelength region 170P 222 nm is similar to that we have used for 0, in the region 179-202 nm (Yoshino et al., 1983). In brief, the interior of the 6.65 m instrument. at room temperature 295-299 K, is used as an absorption cell of optical path length 1300 cm for the N,O. The pressure, which ranges from 0.1 to 32 torr, is measured with an MKS Baratron capacitance manometer. The continuous background is provided by a d.c. discharge in H,. The N,O is purified by repeated fractional distillation. In preliminary experiments with N,O in an external
1219
1220
K. YCBHIN~
cell located between the H, discharge source and the entrance slit of the 6.65 m spectrometer/spectrograph, the sharp absorption lines of NO produced by photolysis of N,O were observed. In contrast, with N,O inside the spectrometer/spectrograph, the much reduced amount of continuous radiation admitted through the narrow entrance slit does not give rise to detectable absorption by NO. However, in one scan when a discharge pressure gauge was left on accidentally inside the spectrometer/spectrograph in the presence of N,O, the sharp rotational lines of the absorption bands of the NO thereby produced were seen superposed on the N,O absorption; at high resolution the sharpness of the NO lines permits detection of very low concentrations of NO. Photoabsorption measurements throughout the region 17&222 nm have been made in a series of overlapping scans, each covering a range of - 2.5 nm. Each such scan is performed with three different column densities of N,O. Entrance and exit slit widths of lOpmprovideaninstrumentalbandwidth(FWHM) of 0.0013 nm. The exit slit scans continuously along the focal surface of the spectrometer at a speed of 53.4 pm s-r, corresponding to a wavelength scan rate of 0.0032 nm s-’ ; the accumulated counts are recorded on magnetic tape at intervals of 0.187 s, corresponding to wavelength intervals of 0.0006 nm ( 5 0.2 cm- ‘). Wavelength calibration is accomplished by scanning the sharp emission lines of the Fourth Positive bands of CO before and after collection of photoabsorption data for N,O in each 2.5 nm region. The cross-section of N,O at a given wavelength is determined by averaging the values derived from the measured optical depths, In 1,/I, obtained with N,O pressures selected to give 0.5 < In I,/1 < 2.0. Noise reduction without loss of spectroscopic structure is achieved by taking unweighted averages over 100 adjacent channels ( - 0.06 nm).
3. RESULTS
et ul 15,
i
I
1 I
/
_I’
n_ 41”O”
B”““0
Wdvenumher
FIG. I. HIGH
RESOLUTION ABSORPTION CROSS-SECTION
(FWHM = 0.0013 nm) OFN,OATKOOMTEMPERATUKE(~~~299 K)INTTHEKEGIoN~~~~~S~~~~~ cm-‘(222-170nm). sections. The overall pattern of the cross-section throughout the entire region 44925558955 cm-’ is displayed in Figs. 1 and 2 where the cross-section is plotted on linear and logarithmic scales, respectively. In Fig. 3 we show the cross-section in the region 4550&49500 cm-’ (220-202 nm) for comparison with Fig. 1 of Selwyn et ul. (1977). In this “stratospheric window region” our cross-section for N,O at 295299 K, represented by the apparently continuous curve in Fig. 3, is essentially structureless. The discrete points are data from Table 1 of Selwyn ef al. (1977)
-IB:
I
AND DISCUSSION
The absorption cross-sections we have measured for N,O at room temperature (295-299 K) with an instrumental width (FWHM) of 0.0013 nm throughout the region 44925558955 cm-’ (222-170 nm) are available at intervals of 0.1-0.2 cm-’ (0.0006 nm) as a numerical tabulation stored on magnetic tape from the National Space Science Data Center, NASA/Goddard Space Flight Center, Greenbelt, MD 20771, U.S.A. The uncertainties of the measured cross-sections and wavelengths are estimated to be 2% and 0.001 nm, respectively. From those results we have prepared Figs. 14 to illustrate various aspects of the measured cross-
-21; :
/’
HIGH RESOLUTION ABSORPTION C‘KOSS-SECTION =0.0013 nm) OF N,O AT ROOM TEMP'&ATLIRE(29s 299 K) PLOTTED LOGARITHMICALLY 1N THE REGION 44925FIG.
2.
(FWHM
58955
cm-’
(222-170
nm).
Cross-section
measurements
of N,O at 295-299
FIG. 3. HIGH KESOLUTION ABSOKPTIOK CROSS-SECTION (FWHM = 0.0013 nm) OF N20 AT KOOM TEMPEKATUKE (295299 K) IN THE KEGION 45500&49500 cm-’ (220-202 nm) OF THE“STRATOSPHERICWINIX~W."
The discrete points represented by octagons and triangles are data of Selwyn rt trl. (1977) at temperatures 296 and 302 K, respectively. obtained with a resolution of 0.7 nm.
showing their cross-sections, obtained with a resolution of 0.7 nm, for N,O at 296 K for wavenumbers less than 47750 cm ’ and for N,O at 302 K for wavenumbers greater than 47750 cm ’ ; the former are in excellent agreement with our results, whereas the latter are 5-6”; higher, presumably as a result of the temperature difference. In Fig. 4 the cross-section is shown in detail for the
lii
FIG. 4. HIGH KESOLUTION AIISOKPTION CKOSS-SKTION (FWHM = 0.0013 nm) or NZO AT ROOM TEMPEKATUKE (295299 K) IN THE K~GION 52.500-57500 cm ’ (19&l 74 nm) OF THE RANDEDSTR1J(‘TURE.
K in the wavelength
region
17&222 nm
1221
region 52500&57500 (190-174 nm) where banded structure is superposed on the continuous absorption. Practically all of the structure seen is real and independent of the instrumental function. Comparison of Fig. 4 obtained with our instrumental width of00013 nm with Fig. 2 of Selwyn rf ul. (1977) obtained with a resolution of 0.075 nm reveals the extent to which additional structure is present in our cross-section and corroborates the existence of the gross features found by Selwyn ef ul. (1977). In this region it is difficult to make a definitive comparison of the magnitude of our cross-section. which contains detailed structure, with the less detailed results of Selwyn et ul. (1977). Moreover, the cross-sections in Table I of Selwyn et ul. (I 977) for N,O at 302 K are, for unknown reasons, often higher than those shown in their Fig. 2. The crosssections, for N,O at 302 K, estimated from the main peaks and valleys in their Fig. 2 are generally higher, by 1&4”i,, than our values for N,O at 295-299 K; differences of this size and scatter are within the mutual experimental error of the determinations and need not be attributed entirely to temperature dependence effects in this wavelength region. A&~~[erlyrment - We thank J. R. Esmond and N. Galluccio for technical assistance. The work reported was supported by the Atmospheric Sciences Division of the National Science Foundation under Grant ATM-8023200 to Harvard College. REFERENCES
.i\nderson, G. P. and Hall, L. A. (1983) Attenuation of solar irradiance in the stratosphere: spectrometer results between 191 and 207 nm. J. geophps. Rex 88, 6801. Cheung,A. S-C., Yoshino, K., Parkinson, W. H. and Freeman, D. E. (1984) Herzberg continuum cross-section ofoxygen in the wavelength region 193.5-204.0 nm; new laboratory measurements and stratospheric implications. Grophys. Rex Lrtt. (in press). Frederick, J. E. and Mental], J. E. (1982) Solar irradiance in the stratosphere: Implications for the Herzberg continuum absorption of 0,. Grophys. Rcrs. L&t. 9, 461. Froidevaux, L. and Yung, Y. L. (1982) Radiation and chemistry in the stratosphere: sensitivity to 0, absorption cross sections in the Herzberg continuum. Geophys. Rrs. Lcrt. 9, 854. Herman, J. R. and Mental], J. E. (1982) OZ absorption cross sections (187-225 nm) from stratospheric solar llux measurements. J. geophys. Res. 87, 8967. Hubrich, C. and Stuhl, F. (1980) The ultraviolet absorption of some halogenated methanes and ethanes of atmospheric interest. J. Photo&m. 12, 93. Hudson, R. D. (1974) Absorption cross sections of stratospheric molecules. Cnn. J. Chem. 52, 1465. Jackman, C. H. and Guthrie, P. D. (1983) Two-dimensional chemistry of the trace gases N,O, CFCI,. and CFzClz: Effectsofareducedabsorptioncrosssectionin theHerzberg continuum of molecular oxygen. E‘OS Trans. Am. Groph)s. Union64, 199. Johnston,H.S.and Selwyn,G. S.(1975)Newcrosssectionsfor
1222
K.
YOSHINO
the absorption of near ultraviolet radiation by nitrous oxide. Geophys. Res. Letr. 2, 549. Monahan,K. M. and Walker, W. C.(1975)Vacuum ultraviolet absorption spectra of solid N,O and CO, at 53 K. J. cke~n. Phys. 63, 1676. Selwyn, G. S. and Johnston, H. S. (1981) Ultraviolet absorption spectrum of nitrous oxide as a function of temperature and isotopic substitution. J. them. Phys. 74, 3791. Selwyn, G., Podolske, J. and Johnston. H. S. (1977) Nitrous oxide absorption spectrum at stratospheric temperatures. Geophys. Rrs. Lett. 4, 427.
rt
u/
Yoshino, K., Freeman, D. E., Esmond. J. R. and Parkinson, W. H. (1983) High resolution absorption cross section measurements and band oscillator strengths of the (1 ,O)-( 12,O) Schumann-Runge bands of 0,. Plunut.Space sci. 31, 339. Yoshino. K.. Freeman, D. E. and Parkinson, W. H. (1980) Photoelectricscanning(6.65 m) spectrometer for VUV cross section measurements. Appl. Opt. 19, 66. Zelikoff, M. K., Watanabe. K. and Inn. E. C(1953) Absorption coefficients of gases in the vacuum ultraviolet. Part II. Nitrous oxide. J. rhem Phys. 21. 1643.
HIGH
RESOLUTION ABSORPTION CROSS-SECTION MEASUREMENTS OF N,O AT 295-299 K IN THE WAVELENGTH REGION 170-222 nm K. YOSHINO,
Harvard-
Smithsonian
0.
E. FREEMAN
and W. H. PARKIRSON
Center for Astrophysics,
Cambridge,
MA 02138, U.S.A.
AbstractHigh resolution absorption cross-section measurements of N,O at 295-299 K have been performed in the wavelength region 17&222 nm with a 6.65 m scanning spectrometerkpectrograph of sufficient resolution to yield cross-sections that are independent of the instrumental function. The measured cross-sections are presented graphically and are available throughout the region 44925558955 cm-r at intervals ofO.lL0.2 cm- ’ as a numerical tabulation stored on magnetic tape from the National Space Science Data Center, NASA/Goddard Space Flight Center, Greenbelt, MD 20771. U.S.A. Previously unresolved detailsofthe bandedstructurewhichissuperposedon thecontinuousabsorptionin theregion 174190nmare observed.
1. The cross-section
INTRODUCTION
measurements
of NzO
by Johnston
and Selwyn (1975) have established that the absorption at wavelengths greater than 260 nm is negligible, although such absorption had previously been thought responsible for significant atmospheric photolysis of N,O. That discovery exacerbated the problem of finding adequate atmospheric sinks for N,O, but this difficulty has lately been alleviated somewhat (Jackman and Guthrie, 1983; Froidevaux and Yung, 1982) by indications from stratospheric experiments (Frederick and Mentall. 1982: Herman and Mentall, 1982: Anderson and Hall. 1983) and laboratory results (Cheung et al., 1984) that previously accepted laboratory values of the absorption cross-section of O2 in the region 190-240 nm are too high. At shorter wavelengths, the cross-section of N,O and its temperature dependence have been measured recently by Hubrich and Stuhl (1980). Selwyn el ~1. (1977) and Selwyn and Johnston (1981). The latter two groups have found that in the region 173-190 nm the banded contributions superposed on the continuous absorption are more marked and structured than in previous studies (Zelikoff et al., 1953; Monahan and Walker, 1975). The observed structure and its temperature dependence are explained by Selwyn and Johnston (1981) in terms of absorption by N,O in which the ground state bending vibration is thermally excited. The cross-section measurements of NzO made by Selwyn rt al. (1977) and Selwyn and Johnston (1981) were performed photoelectrically at moderate resolution (0.075 mn) in the region 17222 10 nm. In addition, Selwyn and Johnston (1981) photographed the
absorption spectrum of N,O at room temperature at higher resolution (0.003 nm) with a 3 m vacuum spectrograph and found that, for the banded structure. the heights of the absorption peaks relative to adjacent valleys were two to four times greater than when their photoelectric instrument of lower resolution was used. In the present investigation we use a 6.65 m photoelectric scanning spectrometer/spectrograph of small enough instrumental band width, 0.0013 nm full width at half maximum (FWHM), to ensure that the absorption cross-section measured for N,O at room temperature in the region 170-222 nm is independent of the instrumental band width. Earlier cross-section measurements ofNzO, made with low resolutionin this wavelength region, have been reviewed by Hudson ( 1974).
2. EXPERIMENTAL
PROCEDURE
The experimental procedure with the 6.65 m photoelectric scanning spectrometer,/spectrograph (Yoshino et al., 1980) for measuring the absorption cross-section of N,O in the wavelength region 170P 222 nm is similar to that we have used for 0, in the region 179-202 nm (Yoshino et al., 1983). In brief, the interior of the 6.65 m instrument. at room temperature 295-299 K, is used as an absorption cell of optical path length 1300 cm for the N,O. The pressure, which ranges from 0.1 to 32 torr, is measured with an MKS Baratron capacitance manometer. The continuous background is provided by a d.c. discharge in H,. The N,O is purified by repeated fractional distillation. In preliminary experiments with N,O in an external
1219
1220
K. YCBHIN~
cell located between the H, discharge source and the entrance slit of the 6.65 m spectrometer/spectrograph, the sharp absorption lines of NO produced by photolysis of N,O were observed. In contrast, with N,O inside the spectrometer/spectrograph, the much reduced amount of continuous radiation admitted through the narrow entrance slit does not give rise to detectable absorption by NO. However, in one scan when a discharge pressure gauge was left on accidentally inside the spectrometer/spectrograph in the presence of N,O, the sharp rotational lines of the absorption bands of the NO thereby produced were seen superposed on the N,O absorption; at high resolution the sharpness of the NO lines permits detection of very low concentrations of NO. Photoabsorption measurements throughout the region 17&222 nm have been made in a series of overlapping scans, each covering a range of - 2.5 nm. Each such scan is performed with three different column densities of N,O. Entrance and exit slit widths of lOpmprovideaninstrumentalbandwidth(FWHM) of 0.0013 nm. The exit slit scans continuously along the focal surface of the spectrometer at a speed of 53.4 pm s-r, corresponding to a wavelength scan rate of 0.0032 nm s-’ ; the accumulated counts are recorded on magnetic tape at intervals of 0.187 s, corresponding to wavelength intervals of 0.0006 nm ( 5 0.2 cm- ‘). Wavelength calibration is accomplished by scanning the sharp emission lines of the Fourth Positive bands of CO before and after collection of photoabsorption data for N,O in each 2.5 nm region. The cross-section of N,O at a given wavelength is determined by averaging the values derived from the measured optical depths, In 1,/I, obtained with N,O pressures selected to give 0.5 < In I,/1 < 2.0. Noise reduction without loss of spectroscopic structure is achieved by taking unweighted averages over 100 adjacent channels ( - 0.06 nm).
3. RESULTS
et ul 15,
i
I
1 I
/
_I’
n_ 41”O”
B”““0
Wdvenumher
FIG. I. HIGH
RESOLUTION ABSORPTION CROSS-SECTION
(FWHM = 0.0013 nm) OFN,OATKOOMTEMPERATUKE(~~~299 K)INTTHEKEGIoN~~~~~S~~~~~ cm-‘(222-170nm). sections. The overall pattern of the cross-section throughout the entire region 44925558955 cm-’ is displayed in Figs. 1 and 2 where the cross-section is plotted on linear and logarithmic scales, respectively. In Fig. 3 we show the cross-section in the region 4550&49500 cm-’ (220-202 nm) for comparison with Fig. 1 of Selwyn et ul. (1977). In this “stratospheric window region” our cross-section for N,O at 295299 K, represented by the apparently continuous curve in Fig. 3, is essentially structureless. The discrete points are data from Table 1 of Selwyn ef al. (1977)
-IB:
I
AND DISCUSSION
The absorption cross-sections we have measured for N,O at room temperature (295-299 K) with an instrumental width (FWHM) of 0.0013 nm throughout the region 44925558955 cm-’ (222-170 nm) are available at intervals of 0.1-0.2 cm-’ (0.0006 nm) as a numerical tabulation stored on magnetic tape from the National Space Science Data Center, NASA/Goddard Space Flight Center, Greenbelt, MD 20771, U.S.A. The uncertainties of the measured cross-sections and wavelengths are estimated to be 2% and 0.001 nm, respectively. From those results we have prepared Figs. 14 to illustrate various aspects of the measured cross-
-21; :
/’
HIGH RESOLUTION ABSORPTION C‘KOSS-SECTION =0.0013 nm) OF N,O AT ROOM TEMP'&ATLIRE(29s 299 K) PLOTTED LOGARITHMICALLY 1N THE REGION 44925FIG.
2.
(FWHM
58955
cm-’
(222-170
nm).
Cross-section
measurements
of N,O at 295-299
FIG. 3. HIGH KESOLUTION ABSOKPTIOK CROSS-SECTION (FWHM = 0.0013 nm) OF N20 AT KOOM TEMPEKATUKE (295299 K) IN THE KEGION 45500&49500 cm-’ (220-202 nm) OF THE“STRATOSPHERICWINIX~W."
The discrete points represented by octagons and triangles are data of Selwyn rt trl. (1977) at temperatures 296 and 302 K, respectively. obtained with a resolution of 0.7 nm.
showing their cross-sections, obtained with a resolution of 0.7 nm, for N,O at 296 K for wavenumbers less than 47750 cm ’ and for N,O at 302 K for wavenumbers greater than 47750 cm ’ ; the former are in excellent agreement with our results, whereas the latter are 5-6”; higher, presumably as a result of the temperature difference. In Fig. 4 the cross-section is shown in detail for the
lii
FIG. 4. HIGH KESOLUTION AIISOKPTION CKOSS-SKTION (FWHM = 0.0013 nm) or NZO AT ROOM TEMPEKATUKE (295299 K) IN THE K~GION 52.500-57500 cm ’ (19&l 74 nm) OF THE RANDEDSTR1J(‘TURE.
K in the wavelength
region
17&222 nm
1221
region 52500&57500 (190-174 nm) where banded structure is superposed on the continuous absorption. Practically all of the structure seen is real and independent of the instrumental function. Comparison of Fig. 4 obtained with our instrumental width of00013 nm with Fig. 2 of Selwyn rf ul. (1977) obtained with a resolution of 0.075 nm reveals the extent to which additional structure is present in our cross-section and corroborates the existence of the gross features found by Selwyn ef ul. (1977). In this region it is difficult to make a definitive comparison of the magnitude of our cross-section. which contains detailed structure, with the less detailed results of Selwyn et ul. (1977). Moreover, the cross-sections in Table I of Selwyn et ul. (I 977) for N,O at 302 K are, for unknown reasons, often higher than those shown in their Fig. 2. The crosssections, for N,O at 302 K, estimated from the main peaks and valleys in their Fig. 2 are generally higher, by 1&4”i,, than our values for N,O at 295-299 K; differences of this size and scatter are within the mutual experimental error of the determinations and need not be attributed entirely to temperature dependence effects in this wavelength region. A&~~[erlyrment - We thank J. R. Esmond and N. Galluccio for technical assistance. The work reported was supported by the Atmospheric Sciences Division of the National Science Foundation under Grant ATM-8023200 to Harvard College. REFERENCES
.i\nderson, G. P. and Hall, L. A. (1983) Attenuation of solar irradiance in the stratosphere: spectrometer results between 191 and 207 nm. J. geophps. Rex 88, 6801. Cheung,A. S-C., Yoshino, K., Parkinson, W. H. and Freeman, D. E. (1984) Herzberg continuum cross-section ofoxygen in the wavelength region 193.5-204.0 nm; new laboratory measurements and stratospheric implications. Grophys. Rex Lrtt. (in press). Frederick, J. E. and Mental], J. E. (1982) Solar irradiance in the stratosphere: Implications for the Herzberg continuum absorption of 0,. Grophys. Rcrs. L&t. 9, 461. Froidevaux, L. and Yung, Y. L. (1982) Radiation and chemistry in the stratosphere: sensitivity to 0, absorption cross sections in the Herzberg continuum. Geophys. Rrs. Lcrt. 9, 854. Herman, J. R. and Mental], J. E. (1982) OZ absorption cross sections (187-225 nm) from stratospheric solar llux measurements. J. geophys. Res. 87, 8967. Hubrich, C. and Stuhl, F. (1980) The ultraviolet absorption of some halogenated methanes and ethanes of atmospheric interest. J. Photo&m. 12, 93. Hudson, R. D. (1974) Absorption cross sections of stratospheric molecules. Cnn. J. Chem. 52, 1465. Jackman, C. H. and Guthrie, P. D. (1983) Two-dimensional chemistry of the trace gases N,O, CFCI,. and CFzClz: Effectsofareducedabsorptioncrosssectionin theHerzberg continuum of molecular oxygen. E‘OS Trans. Am. Groph)s. Union64, 199. Johnston,H.S.and Selwyn,G. S.(1975)Newcrosssectionsfor
1222
K.
YOSHINO
the absorption of near ultraviolet radiation by nitrous oxide. Geophys. Res. Letr. 2, 549. Monahan,K. M. and Walker, W. C.(1975)Vacuum ultraviolet absorption spectra of solid N,O and CO, at 53 K. J. cke~n. Phys. 63, 1676. Selwyn, G. S. and Johnston, H. S. (1981) Ultraviolet absorption spectrum of nitrous oxide as a function of temperature and isotopic substitution. J. them. Phys. 74, 3791. Selwyn, G., Podolske, J. and Johnston. H. S. (1977) Nitrous oxide absorption spectrum at stratospheric temperatures. Geophys. Rrs. Lett. 4, 427.
rt
u/
Yoshino, K., Freeman, D. E., Esmond. J. R. and Parkinson, W. H. (1983) High resolution absorption cross section measurements and band oscillator strengths of the (1 ,O)-( 12,O) Schumann-Runge bands of 0,. Plunut.Space sci. 31, 339. Yoshino. K.. Freeman, D. E. and Parkinson, W. H. (1980) Photoelectricscanning(6.65 m) spectrometer for VUV cross section measurements. Appl. Opt. 19, 66. Zelikoff, M. K., Watanabe. K. and Inn. E. C(1953) Absorption coefficients of gases in the vacuum ultraviolet. Part II. Nitrous oxide. J. rhem Phys. 21. 1643.