Mechanisms of energy transfer in the deuterium fluoride systema)

Abstract

A three-dimensional trajectory study has been employed to determine rate coefficients as a function of temperature for the important energy-transfer processes that occur in DF(v1)+DF(v2) collisions. From this study, it was predicted that the v→v energy-transfer processes occur by means of Δv=±1 transitions and that the rate coefficients for the v→v processes DF(v1=1)+DF(v2) →DF(v′1=0)+DF(v′2=v2+1) with v2±1 through 5, respectively, decrease with increasing vibrational quantum number v. The computed rate coefficients for the v→v processes are k (v1=1, v2=1; v′1=0, v′2=2) =1.3×1013 cm3/mole sec and k (v1=1, v2; v′1=0, v′2=v2+1) =1.611−Hv2k (1,1;0,2) at 300° K. These v→v processes correspond to near-resonant vibration-to-vibration (v→v) intermolecular energy transfer. The v→R energy-transfer processes occur by converting multiple quanta of vibrational energy of a vibrationally excited DF molecule into rotational energy of the same molecule. This process is nonresonant v→R intramolecular energy transfer. These multiquantum v→R transitions provide more ways to distribute the vibrational energy of the vibrationally excited DF molecule into rotational energy and thereby populate its high rotational states. The high rotational quantum states are relaxed slowly by R→ (R′,T) processes. A rotational nonequilibrium model is used to calculate quenching rate coefficients for vibrational relaxation of DF(v1=1) by DF(v2=0). The results are in good agreement with available experimental data.