Coriolis-induced vibrational energy transfer in D2CO–D2CO collisions: A classical perspective

Abstract

Recent experimental studies of vibrational energy transfer in D2CO–D2CO collisions have demonstrated extraordinarily high cross sections for an intramolecular V–V process in which a vibrational quantum is transferred between the two low-frequency modes ν4 and ν6 . The key to understanding this process appears to be the strong Coriolis interaction between these modes; an approximate quantum treatment has demonstrated, however, that rotor asymmetry is also critical. In this paper a purely classical description of the energy-transfer mechanism is put forward. This description draws heavily upon two recent classical studies of the intramolecular dynamics of formaldehyde. It is argued that the energy transfer arises from a resonant interaction between the Coriolis-coupled vibrations and the nutation of an asymmetric top; this induces a slow flopping motion of the molecule’s dipole moment (superimposed upon end-over-end rotation) which is coupled to the vibrational dynamics. The torque on this dipole produced by a passing molecule can thus pump energy into the vibrations. Classical perturbation theory is used to obtain rough estimates of the energy-transfer cross sections, which agree reasonably well with the experimental values.