Relaxation of C₂D₂(ν₄, ν₅) by vibration–rotation, translation energy transfer

Abstract

A pulsed laser–photoacoustic technique has been used to measure effective collisional probabilities for relaxation of the two lowest coupled vibrational modes of C2D2 by several collision partners. At 300 K these probabilities are: C2D2, (8.2 ± 1)× 10–4; He, (10.5 ± 1)× 10–4; Ne, (5.2 ± 1)× 10–4; Ar, (5.9 ± 1)× 10–4; Kr, (8.1 ± 1)× 10–4; Xe, (8.6 ± 1.5)× 10–4; H2, (20 ± 4)× 10–4; D2, (23 ± 3)× 10–4; N2, (7.8 ± 1.7)× 10–4; CO, (6.9 ± 0.6)× 10–4. The experimental results for C2D2+ noble-gas mixtures are compared with: (a) laser-induced vibrational fluorescence measurements on the relaxation of C2H2 and (b) estimates of probabilities based on a simple first-order perturbation treatment which includes the effect of molecular rotation. The latter comparison suggests that rotation facilitates relaxation of the bending vibrations in C2D2(and C2H2).