Resonance enhancement of vibrational relaxation of glyoxal in collisions with helium at low temperatures

We have calculated rate constants for vibrational relaxation of the ν 7 torsional mode of trans-(S 1 ) glyoxal in collisions with helium at low temperatures (0.6–10.0 K). At T =3 K, orbiting resonances contribute as much as 34% to the rate constant for vibrational relaxation. The calculated probability per hard sphere collision of the transition (ν 7 =1, k =0→ν 7 =0) has been fitted to a power law ( P if = aT −b ) as a function of temperature. The values obtained for a and b agree quite well with experimental results for the transition (ν 7 =2, k =1→ν 7 =1).