Rates and pathways of vibrational self-relaxation of HF(v=2) between 300 and 700 K

Abstract

The temperature dependencies of the total self‐relaxation rate constants for the vibrational deactivation of HF(v=2) and HF(v=1) and the state‐to‐state vibration‐to‐vibration (V–V) and vibration‐to‐translation‐and‐rotation (V‐T,R) energy transfer components of the HF(v=2) self‐relaxation process are measured using the overtone vibration excitation‐laser double resonance technique. The total self‐relaxation rate constants vary inversely with temperature. The much weaker temperature dependence of HF(v=2) self‐relaxation compared to that of HF(v=1) arises from the significant role of the V–V energy transfer route. Competition between energetics and collision duration results in a weaker inverse variation with temperature for the slightly endothermic V–V route than for the exothermic V‐T,R route for HF(v=2). The branching ratio for V–V energy transfer increases slightly with temperature and the data suggest that two quantum relaxation processes constitute no more than 10% of the total self‐relaxation of HF(v=2). The available temperature dependence data on self‐relaxation of HF(v=1–5) form a consistent picture in which the energetics of the V–V and V‐T,R relaxation pathways control their relative contributions to the total energy transfer.