Relaxation processes in excited CO states. I. Spin multiplet relaxation and radiative lifetimes of CO(d3Δ)ν=5

Abstract

Observations made of the d 3 Δ → a 3 Π 5,0 band of CO demonstrate that the d 3 Δ ν=5 level has a radiative lifetime strongly dependent on rotational level. This is a consequence of the interaction between d 3 Δ ν=5 and the nearby A 1 Π ν=1 level, which mixes the two states and causes strong d 3 Δ ν=5→ X 1 Σ + radiation to compete with d → a radiation as a depopulating mechanism from d 3 Δ ν=5 . Because of the selection rules governing optical transitions and perturbations, it is only the Ω 1 level of d 3 Δ ν=5 that is strongly perturbed, and relaxation of 3 Δ 1 to 3 Δ 2 and 3 Δ 3 as a function of rare gas collisions has been observed. Relaxation by Ar takes place at close to hard sphere collision frequency, with He being 5.5 times less efficient.