Knowledge Bank

The rate constants for collisional deactivation of the $\nu =1$ level of CO by $H2,D2$ and He dilute in liquid Ar were measured using chopped blackbody excitation and signal-averaged detection of IR fluorescence decay. The ratios of the rate constants in the liquid phase to those for the same processes in the gas $phase1$ $(Kl/Kg)$ were found to be $\sim 1.1,0.8$ and 1.6 for $CO-H2,CO-D2$ and $CO-He$, respectively. These results do not agree well with most of the available models for vibrational relaxation in liquids, which predict that $kl$ should be several times $kg$.It is proposed that changes in the effective intermolecular potential introduced When the collision partners are put into solution lower the probability of energy transfer, and consequently the rate constant, when the mean kinetic energy is comparable to or smaller than the attractive energy between the interacting species. 1. M. Matti Maricq and C.J.S.M. Simpson, Chem. Phys. Lett., (to be published).