Vibrational state-to-state resolution in the collisional relaxation of a highly vibrationally excited polyatomic: HCN

Abstract

The measurement of vibrational state-to-state population transfer for a highly vibrationally excited polyatomic molecule (ϵ vib≈9600 cm −1) is reported. This work combines direct overtone vibration excitation with LIF via and theà 1A″ state of HCN to obtain the rate k=(2.4±0.3)×10 −12 cm 3 molecule −1 s −1 for population transfer from (0, 0 0, 3) to (3, 0 0, 1). This channel accounts for 17% of the total depopulation of (0, 0 0, 3) indicating that intramolecular V—V transfer is important in the self-relaxation of HCN. We show that resonance-enhanced relaxation can account for the high efficiency of this channel and demonstrate that long-range dipole—dipole interactions can lead to enhanced relaxation between mixed states when coupled by Fermi resonance.