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

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 1³Π_g 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 $\text{X}{}^3\text{∑}{}^{\mathrm{?}}{}_{\mathrm{g}}\text{→ 1}{}^3\text{Π}{}_{\mathrm{g}}$, while the temperature dependence of the pressure coefficients is not consistent with absorption due to stable (O₂)₂ dimers.