A study of the role of vibration–vibration exchange on the collisional deactivation of vibrationally excited singlet molecular oxygen

Abstract

A study of the role of vibration−vibration (V−V) exchange on the collisional deactivation of laser excited O₂(¹Δ_g) (v′ = 1) has been carried out. It is apparent that such exchange can be important only if deactivation of O₂(²Δ_g) (v′ = 0) occurs via intersystem crossing (E−V) to the O₂(³Σ⁻_g) (v = 5) state. A theoretical study of such a deactivation mechanism has been carried out (II), yielding results similar in form to those obtained previously (I), in which only vibration−translation (V−T) and electronic−translation deactivation (E−T) were considered. In either case two time constants appear, one characterizing the electronic E−T or E−V process and the other the V−T process. In Case I, the V−T deactivation occurs in the ¹Δ_g state, while in Case II it occurs in the ³Σ⁻_g ground electronic state. Theory suggests that since the vibrational spacing in the ¹Δ_g state is slightly less than in the ³Σ⁻_g state, V−T deactivation should occur at a more rapid rate in the former. Analysis of experimental data on the effect of He on the vibrational phase shift of laser excited O₂(¹Δ_g) (v′ = 1) yields a vibrational time constant significantly smaller than that obtained from earlier measurements under the same experimental conditions for O₂(³Σ⁻_g). From this it is concluded that O₂(¹Δ_g) does not readily communicate vibration to the ground electronic state and that vibrational deactivation in this state must occur by a V−T process.