Vibrational energy transfer between CO and CH4, CD4, and CF4 in liquid Ar

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Abstract
Vibrational relaxation of CO (υ=1) by CH4, CD4, and CF4 in liquid Ar at 87 K has been studied. The IR fluorescence decay from CO (υ=1) excited by a blackbody source was used to monitor the rate of vibrational energy transfer. Order of magnitude calculations for the variety of V–V and V-T processes possible in these systems were used to select reasonable relaxation channels. These feasibility calculations together with decay measurements on several concentrations of CO and its collision partners enabled liquid state relaxation rate constants to be assigned. For the CO–CD4 and CO–CF4 systems, near-resonance energy transfer and conditions of concentration enabled us to measure the V-T rate constants for the first time for the relaxation of CD4 and CF4 by liquid Ar. These V–V and V-T rate constants were compared with the gas phase values obtained at the same temperature. We find that the liquid phase and gas phase rate constants are essentially the same. These results are found to be in reasonable accord with the predictions of simple models of vibrational relaxation in the liquid state.