Collision-Induced Absorption Spectrum of Gaseous Oxygen at Low Temperatures and Pressures. I. The Δg1 ← 3Σg− System

The collision-induced absorption of the (0–0) and (1–0) bands of the Δg1 ← 3Σg− transition of oxygen has been studied in the gas phase from 87°–300°K. Low pressures were used and only binary collisions are important in inducing transitions. At low temperatures the absorption is enhanced because the attractive intermolecular potential causes clustering in the gas. However, no direct evidence for bound-state (O2)2 molecules was found. The frequency maxima of the absorption of collision pairs were only slightly shifted from those calculated from monomer oxygen. This suggests that the shapes of the internuclear potentials and separation of the Δg1 and Σg3 electronic states are little affected by these binary collisions. A near-Boltzmann relation of the broad band shapes, moreover, suggests that the intermolecular potentials for Δg1···3Σg−and3Σg−···3Σg+ interactions are nearly the same. The mechanisms of the induced absorption collisions are discussed.