Schumann-Runge Bands Of Molecular Oxygen Research Articles

Quantum interference in the Schumann‐Runge bands of molecular oxygen

The photoabsorption cross section of O2 in the Schumann‐Runge bands is investigated theoretically using the coupled‐channel Schrödinger‐equations method. It is found that quantum interference between vibrational bands leads to significant asymmetry in the far line wings, a result supported by experimental evidence. Thus, Schumann‐Runge cross sections calculated with the usual band models based on Voigt line shapes may be in error in regions of weak absorption between vibrational band heads, suggesting the need to re‐evaluate aspects of atmospheric photochemistry sensitive to those regions.

Penetration of solar radiation in the Schumann-Runge bands of molecular oxygen: a robust approximation

The Schumann-Runge bands of molecular oxygen between 175 nm and 205 nm cover a spectral region of great importance for the effect of solar radiation in the middle atmosphere. The highly structured absorption cross sections that can be computed with good accuracy lead to prohibitive computer resources, however, when they have to be used in complex atmospheric models. Although various approximations have been developed, another approach is proposed to avoid spurious effects, even when the new approximations are used outside of their validity range, corresponding to a solar attenuation of the order of 10−10. Comparisons between exact computations and present approximations lead to satisfactory agreement.

Pressure-broadening in the Schumann-Runge bands of molecular oxygen

The pressure-broadened widths for selected rotational lines from the (2-0) to (15-0) Schumann-Runge bands of O 2 have been measured at pressures up to 60 atm. The self-broadening coefficient exhibits no dependence on rotation and a small dependence on vibration, in agreement with theoretical expectations, and may be taken as 0.20 cm -1/atm FWHM, implying an optical collision diameter of 6.2 Å. The broadened absorption lines are shifted towards longer wavelengths and are asymmetric with a steeper blue wing, both of these effects increasing with pressure.

Experimentally determined oscillator strengths and linewidths for the Schumann-Runge band system of molecular oxygen—III. The (7-0) to (19-0) bands

Experimental oscillator strengths and predissociation linewidths have been derived from equivalent width measurements at room temperature for the (11-0) to (15-0) Schumann-Runge bands of molecular oxygen, and at low temperature for the (15-0) to (19-0) bands, using the Adelaide 6 m vacuum ultraviolet monochromator operated at a resolution of 0.006 nm. Photometric methods were used to measure the ultraviolet absorption for 40 groups of ratational lines, and the resulting data were interpreted using a curve of growth type of analysis to give oscillator strengths and pre-dissociation linewidths. The variation of the oscillator strengths with N‴ within each band was found to agree well with the theoretical predictions of Allison, while the mean band oscillator strengths derived from the results are in good agreement with previous measurements. The results demonstrate the need for accurate data about multiplet line splittings. A revised analysis of previous data for the (7-0) to (14-0) bands is also presented.

Rotational variation of predissociation linewidths for the Schumann-Runge bands of molecular oxygen

Predissociation linewidths are presented as a function of rotation for the (3-0)-(14-0) Schumann- Runge bands of molecular oxygen. While there may be a slight tendency overall for the linewidths to increase with rotation, it is shown that previous assumptions of linewidths constant with rotation are generally valid within the experimental error for the range of rotation studied, N n ⩽ 21. There is no evidence for the sudden increase in linewidth with rotation reported elsewhere.

Atmospheric absorption in the O 2 Schumann-Runge band spectral range and photodissociation rates in the stratosphere and mesophere

A general analysis of the absorption of the Schumann-Runge bands of molecular oxygen has been made in order to compare the various experimental and theoretical results which have been obtained for an application to the O 2 atmospheric absorption and its photodissociation in the mesosphere and stratosphere. The different values of the oscillator strengths deduced from the laboratory absorption spectra and of the predissociation linewidths used for the calculation of the absorption have been compared. Calculations based on a Voight profile of the O 2 rotational lines have led to simple formulas for atmospheric applications taking into account that the total photodissociation rate in the stratosphere depends strongly on the absorption of solar radiation in the spectral range of the O 2 Herzberg continuum. Specific examples are given.

Experimentally determined oscillator strengths and linewidths for the Schumann-Runge band system of molecular oxygen—II. The (2-0) to (5-0) bands

Experimental oscillator strengths and predissociation linewidths have been measured at room temperature for the (2-0) to (5-0) Schumann-Runge bands of molecular oxygen using the Adelaide 6 m vacuum ultraviolet monochromator operated at a resolution of about 0.06 Å. Photoelectric detectors were used to measure the ultraviolet absorption at normally two different gas pressures for 37 groups of rotational lines, and the resulting data were interpreted using an equivalent width type of analysis. The variation with N″ of the oscillator strengths within each band was found to be smaller than that measured earlier for the higher vibrational bands. Measured oscillator strengths agree well with previously accepted values except for the (3-0) band, while the linewidths of the present work agree well with recent theoretical values for the (3-0) and (4-0) bands but are larger for the (2-0) and (5-0) bands. A modification was performed on the parameters of a recent theoretical predissociation model to produce excellent overall agreement between experimental and theoretical linewidths from ν' = 2 to 14. The present work provides results which can be used to construct accurate synthetic absorption profiles for studies of the atmospheric absorption of ultraviolet radiation by the Schumann-Runge bands.

ChemInform Abstract: PREDISSOCIATION LINEWIDTHS AND OSCILLATOR STRENGTHS FOR THE (2‐0) TO (13‐0) SCHUMANN‐RUNGE BANDS OF MOLECULAR OXYGEN

Chemischer InformationsdienstVolume 10, Issue 25 Physical Inorganic Chemistry ChemInform Abstract: PREDISSOCIATION LINEWIDTHS AND OSCILLATOR STRENGTHS FOR THE (2-0) TO (13-0) SCHUMANN-RUNGE BANDS OF MOLECULAR OXYGEN J. E. FREDRICK, J. E. FREDRICKSearch for more papers by this authorR. D. HUDSON, R. D. HUDSONSearch for more papers by this author J. E. FREDRICK, J. E. FREDRICKSearch for more papers by this authorR. D. HUDSON, R. D. HUDSONSearch for more papers by this author First published: June 19, 1979 https://doi.org/10.1002/chin.197925002AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat No abstract is available for this article. Volume10, Issue25June 19, 1979 RelatedInformation

Experimentally determined oscillator strengths and linewidths for the Schumann-Runge band system of molecular oxygen—I. The (6-0)–(14-0) bands

Experimental oscillator strengths and predissociated linewidths have been measured at room temperature for the (6-0)–(14-0) Schumann-Runge bands of molecular oxygen using the Adelaide 6 m vacuum u.v. monochromator operated at a resolution of about 0.06 Å. Photoelectric detectors were used to measure the u.v. absorption at two different gas pressures for 138 groups of rotational lines distributed throughout the (6-0)–(14-0) bands and the resulting data were interpreted using an equivalent width type of analysis. Experimental measurements of the variation with N″ of the oscillator strengths within each band have been obtained for the first time. Measured oscillator strengths are found to be somwhat higher in general than previously reported values with a slightly faster decrease as N″ increases than is predicted theoretically. The mean predissociated linewidths obtained for each band show a smooth variation with v′, agreeing well with other results for v′=12−14 and lying between previously reported experimental and theoretical values for v′=6−9. The present work provides results which can be used to construct highly accurate synthetic absorption profiles for studies of the atmospheric absorption of u.v. radiation by the Schumann-Runge bands.

Absorption and photodissociation in the Schumann-Runge bands of molecular oxygen in the terrestrial atmosphere

The penetration in the terrestrial atmosphere of solar radiation corresponding to the spectral range of the Schumann-Runge bands of molecular oxygen is analyzed between 1750 and 2050 Å. The variation of the absorption cross section with temperature is taken into account and it is shown that average O 2 absorption cross sections cannot lead to correct photodissociation coefficients. Reduction factors are defined in order to simplify the computation of the molecular oxygen photodissociation and to permit a simple determination of the photodissociation coefficients of any minor constituent with smoothly varying absorption cross section. Examples are given for O 2, H 2O, CO 2, N 2O, HNO 3 and H 2O 2. Numerical approximations are developed for three types of spectral subdivisions: Schumann-Runge band intervals, 500 cm −1 and 10 Å intervals. The approximations are valid from the lower thermosphere down to the stratosphere and they can be applied for a wide range of atmospheric models and solar zenith distances.

Opacity distribution functions and absorption in Schumann-Runge bands of molecular oxygen

Absorption cross sections have been calculated for molecular oxygen as a function of wavelength over the domain λ = 1750–2050 A ̊ for temperatures between 190 and 400°K. The spectrum has been divided into 19 wavelength intervals and opacity distribution functions have been constructed for each interval. Atmospheric photodissociation rates of O 2, O 3, CO 2, H 2O, H 2O 2, NO 2 and HNO 3 are presented.

On the behavior of nitrogen oxides in the stratosphere

A summary is presented of the relative importance of the principal aeronomic processes determining the vertical distribution of NO−NO2 in the stratosphere. Formation and destruction of nitric oxide are considered with transport processes for steady-state conditions. Estimates of the vertical distribution of NO x are made for extreme conditions of the eddy diffusion coefficient. It is pointed out that NO is determined by the values which are adopted for its photodissociation coefficient which is related to the absorption of solar radiation in the Schumann-Runge bands of molecular oxygen.

Absorption cross sections of the Schumann-Runge bands of molecular oxygen

A new study of the absorption bands of the Schumann-Runge system of molecular oxygen, which overlap the Herzberg continuum is made in order to improve the aeronomic calculations in the mesosphere and stratosphere. After a complete analysis performed at high resolution of the rotational structure from the (0-0) band at 2050 Å to the dissociation limit at 1750 Å, absorption cross section values for various rotational lines are measured from 2011·63 to 1763·66 Å using emission silicon lines of which wavelengths are known with high precision. The absorption cross sections are obtained with a 0.5 cm −1 resolution taking into account the rotational line shape due to predissociation, Franck-Condon factors and electronic absorption oscillator strengths.