Vibrational energy transfer in organic molecules

Calculations are presented of rate constants for the relaxation and excitation of five different vibrational modes of C2H4 in three dimensional collisions with 3He and 4He. A form of the vibrational close-coupling, rotational infinite order sudden method has been used, especially modified for the collisions of organic molecules with atoms. The atom-molecule potential energy surface is obtained from self-consistent field data. Calculations of rate constants for the average vibration-translation energy transfer are in good agreement with those obtained in a laser double resonance experiment at a temperature of 462 K, but the agreement is not so good at lower temperatures.