Energy transfer in polyatomic molecules I. Catalysis of energy transfer with isotopic molecules

Dispersion of sound has been com pared for ethylene and tetradeutero-ethylene. Relaxation times of 0.26 and 0.14 us for these molecules follow the general trend with molecular frequencies predicted by theory. A quantitative account of th e observed ratio 1:2 of relaxation times can best be given by introducing the notion of ‘complex collisions’ and by abandoning the concept that the rate of activation of the lowest vibrational mode fully controls the rate of activation of higher modes. Small amounts of C2D4 or C2D2H2 act as energy transfer catalysts for ethylene. Both H2O and D2O likewise act as catalysts, approximately to the same extent. Theoretical interpretations of these findings are discussed.