Stimulated Raman scattering measurements of V–V transfer in oxygen

Abstract

We present new sets of V–V energy transfer rates for vibrational levels 0–5 in O 2 at 300 K, using a stimulated Raman – spontaneous Raman pump/probe apparatus. Inferred rate coefficients, k 0 , 1 v , v - 1 , equal to 2.6 ± .5, 4.3 ± 1.1 × 10 −13 cm 3 s −1 for levels v = 2 and 3 are found to agree, within the combined quoted uncertainty, with the recent data of Kalogerakis. For v = 4 and 5, k 0 , 1 v , v - 1 is found to equal 7.1 × 10 −13 cm 3 s −1 and 2.0 × 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.