Energy-dependence of vibrational relaxation between highly vibrationally excited KH (X1Σ+, ν″ = 14–23) and H2, and N2

Abstract

Vibrational state total relaxation rate coefficients, kν″ (M), for KH (ν″=14–23) by M=H2 and N2 have been investigated in an overtone pump–probe configuration. At ν″=14, 15, 16 and 17, the rate coefficients kν″ (M) increase linearly with vibrational quantum number. The region (ν″=18, 19, 20 and 21) where the dependence is much stronger than linear has significant contribution from multiquantum (Δν⩾2) relaxation. For ν″=18, 19, 20 and 21, 0.25, 0.31, 0.38 and 0.31 of the initially prepared population undergo two-quantum (Δν=2) vibrational relaxation in KH (ν″)+H2 collisions. In KH (ν″)+N2, the time profile of ν″=14(15) after preparation of ν″=19(20) was measured. A clear bimodal distribution is observed. The time scale of the first peak is much shorter than the known collisional lifetimes of the intervening vibrational levels and thus a sequential single-quantum relaxation mechanism can be explicitly ruled out. Relaxation of KD with D2 has been also investigated. The relaxation rate coefficients exhibit distinct maxima for both isotopes (KH and KD). We discuss possible explanation of the experimental results including mass effect, V–R energy transfer and V–V energy transfer.