Decomposition of the photoabsorption continuum underlying the Schumann-Runge bands of 16O2-II. Role of the 1 3Πg state and collision-induced absorption

Abstract

Measurements are presented of molecular oxygen photoabsorption cross-sections and pressure coefficients taken at selected minima between rotational lines of the Schumann-Runge band system. Both room-temperature and liquid-nitrogen-temperature results are presented from 1760-1980 Å, and corrections are applied for the effect of the wings of the rotational lines. Absorption into the B3∑-u and A3∑+u+ and is found to be insufficient to account for the total observed cross-section, and it is proposed that transitions to the 13Πg valence state account for the remainder. The pressure dependence of the cross-sections is consistent with collision-induced enhancement of the intensities of the forbidden transitions X3∑-g → A3∑+g and X3∑-g → 1 3Πg, while the temperature dependence of the pressure coefficients is not consistent with absorption due to stable (O2)2 dimers.