Kinematic Model for Reaction. IV. Orientation and Isotope Effect in the Ar++HD Reaction

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Abstract
The kinematicmodel for reaction is used to evaluate the influence of molecular reorientation on the isotope effect in the reaction of Ar+ with HD. Since the centers of mass and charge do not coincide in HD, there is a torque on the molecule during the approach of the ion which enhances the possibility of collision with the hydrogen end of the molecule. Calculations were performed both with and without this effect for Ar+ lab energies in the range 10–70 eV. The results below 30 eV have no quantitative significance, but indicate that orientation could have a considerable effect. At higher energies, both calculations give quite reasonable predictions of the isotope effect; the orientation effect provides a noticable but small difference in the results. The range of relative kinetic energies for which the predicted isotope effects are within experimental error is the same range in which the kinematicmodel provides relatively accurate predictions of product angular and velocity distributions.