Stimulated Raman scattering measurements of V-V transfer in oxygen

We present new sets of V-V energy transfer rates for vibrational levels 0-5 in 0, at 300 K, using a stimulated Raman - spontaneous Raman pump/probe apparatus. Inferred rate coefficients, k(0,1)(upsilon,upsilon-1), equal to 2.6 +/- .5, 4.3 +/- 1.1 X 10(-13) cm(3) s(-1) for levels upsilon = 2 and 3 are found to agree, within the combined quoted uncertainty, with the recent data of Kalogerakis. For upsilon = 4 and 5, k(0.1)(upsilon,upsilon-1) is found to equal 7.1 x 10(-13) cm(3) s(-1) and 2.0 x 10(-13) cm(3) s(-1) +/-, respectively. In agreement with earlier observations by Diskin, it is found that previous semi-classical trajectory calculations underestimate O-2 V-V kinetics by approximately one order of magnitude. New calculations, invoking the same semi-classical formalism, require an increase in the attractive part of the intermolecular potential by a factor of approximately 1.75, in order to replicate the experimental data, a result which is considered non-physical. The purely repulsive Forced Harmonic Oscillator - Free Rotator model of Adamovich is found to under predict the absolute rates by a factor of approximately eight, but to predict the relative rates with reasonable accuracy. (c) 2005 Elsevier B.V. All rights reserved.