VIBRATIONAL-RELAXATION OF GLYOXAL IN COLLISIONS WITH HE AND AR

Using the AVCC-IOS (azimuthal and vibrational close-coupled, infinite-order sudden) method, we have calculated efficiencies for vibrational relaxation of glyoxal in collisions with He and Ar at room temperature. For glyoxal-d2 (deuterated glyoxal) + He the calculated efficiency P(0(0), k = 0 --> 7(1)) is in reasonable agreement with experiment, but for glyoxal-d2 + Ar the calculated value of P(0(0), k = 0 --> 7(1)) is much lower than the experimental value. While part of the discrepancy may be due to the sudden approximation (to the slow rotations of the molecule) not being valid for behavier collision partners at thermal energies, our calculations nevertheless suggest that, especially for heavier collision partners, the experimental values of P(0(0) --> 7(1)) should be much too high because the question of how rotational relaxation should affect the measurement of vibrationally relaxed and unrelaxed emission was not considered in the experiment. For glyoxal-d2 + He, the calculated efficiencies P(8(1) --> 6(1)) and P(8(1) --> 8(1)7(1)) are in good agreement with experiment. Because the frequency difference between the nu-6 and the nu-8 modes is much smaller in glyoxal-h2 ("normal" or protonated glyoxal), for glyoxal-h2 + He the calculated efficiency P(8(1) --> 6(1)) is much higher than for glyoxal-d2 + He.