Vibrational relaxation of C2H2 and C2D2 by vibration–rotation, translation (V–R, T) energy transfer

The collisional probabilities of relaxation and self-relaxation of the ν2, ν4 and ν5 modes in C2H2 and of the ν4 and ν5 modes in C2D2 have been calculated using the ‘effective mass theory’, which includes the effects of molecular rotation in facilitating vibrational energy transfer. The experimental data for C2D2 can be reproduced quite satisfactorily. However, the calculations do not support the previously proposed interpretation of experimental measurements on C2H2, and an alternative interpretation is suggested.