VIBRATIONAL-RELAXATION OF C2H2(NU-3,NU-2+NU-4+NU-5) IN SELF-COLLISIONS AND IN COLLISIONS WITH THE NOBLE-GASES

Tuned output from an optical parametric oscillator has been used to excite C2H2 to levels within the v3,v2+v5) Fermi diad for measurements of vibrational energy transfer. By observing time-resolved infrared fluorescence in mixtures of C2H2 with noble gases in which the concentration of one or other component was systematically varied, the following rate constants (k/cm3 molecule-1 s-1 were obtained at 295 K: kC = (7.4±0.5)×10-11; k3 = (13.5±0.7)×10-13; k4He = (6.7±0.6)×10-13; kNe = (2.1±0.1)×10-13; kAr = (1.57±0.09)×10-13; kKr = (1.37±0.13)×10-13; kXe = (1.25±0.05)×10-13. Near-resonant vibration-vibration energy exchange processes are almost certainly responsible for the rapid self-relaxation. The results are compared with data reported previously for relaxation of C2H2 and C2D2 via their lowest v4,v5 levels and with the results of earlier theoretical calculations which demonstrate that rotation facilitates vibration-rotation, translation energy transfer especially in collisions with the heavier noble gases. © 1990.