Quantum scattering of OH(X^2¿) with He(^1S): Propensity features in rotational relaxation at ultralow energies (8 pages)

The collisional relaxation of rotationally ``hot'' OH molecules in He as a buffer gas has been studied as a fully quantum event using an ab initio potential energy surface and the exact dynamical coupling of the relevant angular momenta during the process. The range of energies considered corresponds to the ultralow temperatures of cold traps and the calculations were carried out down to the Wigner regime of cross section behavior. It is shown that the general dependence of the inelastic processes on rotational angular momentum and parity clearly indicates a fairly marked size dependence of the final cross sections on the specific fine structure levels in which the target radical is being prepared to undergo relaxation.

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