Determination of Band Oscillator Strengths of Atmospheric Molecules from High Resolution Vacuum Ultraviolet Cross Section Measurements. Semiannual Status Report November 1, 1985-April 30, 1986

摘要

An account is given of progress in work on (1) the determination of band oscillator strengths of the Schumann-Runge absorption bands of (16)O2 and (18)O2 from cross section measurements conducted at 79 K; (2) the determination of the absolute absorption cross section of the Schumann-Runge bands of (16)O(18)O from optical depth measurements performed on mixtures of (16)O2, (18)O2 and (16)O(18)O at 79K; and (3) the influence of Schumann-Runge linewing contributions on the determination of the Herzberg continuum absorption cross section of (16)O2 in the wavelength region 194 to 204 nm. The experimental investigations are effected at high resolution with a 6.65 m scanning spectrometer which is, by virtue of its small instrumental width (EWHM = 0.0013 nm), uniquely suitable for cross section measurements of molecular bands with discrete rotational structure. Absolute cross sections, which are independent of the instrumental function and from which band oscillator strengths are directly determined, are measured for the absorption bands that are most predissociated. Such measurements are needed for (1) accurate calculations of the stratospheric production of atomic oxygen and heavy ozone formed following the photopredissociation of (18)O(16)O by solar radiation penetrating between the absorption lines of (16)O2; (2) elucidation of the mechanism of predissociation of the upper state of the Schumann-Runge bands; and (3) determination of the true shape of the Herzberg continuum cross section.