A fitting law for rotational transfer rates: An angular momentum model with predictive power

Osborne, Mark A.; McCaffery, Anthony J.
October 1994
Journal of Chemical Physics;10/1/1994, Vol. 101 Issue 7, p5604
Academic Journal
We have formulated a law for state-to-state rotational transfer (RT) in diatomic molecules based on the angular momentum (AM) theory proposed by McCaffery et al. [J. Chem. Phys. 98, 4586 (1993)]. In this, the probability of angular momentum change in the rotor is calculated by assuming the dominant process to be the conversion of linear to angular momentum at the repulsive wall of the intermolecular potential. The result is a very simple expression containing three variable parameters, each of which has physical significance in the context of the model. Fits to known RT data are very good and suggest strongly that linear to angular momentum change is indeed the controlling process in RT. The parameters of the fit are sufficiently available to give the model predictive power. Using this formulation, RT probabilities may be calculated for an unknown system with little more than the atomic masses, bond length, and velocity distribution. We feel that this represents an important step in the development of a simple physical picture of the RT process.


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