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

Observations made of the d3Δ→a3 Π 5,0 band of CO demonstrate that the d3Δν=5 level has a radiative lifetime strongly dependent on rotational level. This is a consequence of the interaction between d3Δν=5 and the nearby A 1Πν=1 level, which mixes the two states and causes strong d3Δν=5→ X1Σ+ radiation to compete with d→a radiation as a depopulating mechanism from d3Δν=5. Because of the selection rules governing optical transitions and perturbations, it is only the Ω 1 level of d3Δν=5 that is strongly perturbed, and relaxation of Δ13 to Δ23 and Δ33 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.