The effect of reagent rotation in the reaction OH( j)+H2( j′)→H2O+H

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Abstract
Classical trajectory calculations on the reaction OH( j)+H2( j’)→H2O+H have been carried out with j≤40 and j’≤15 on both the Schatz–Elgersma [Chem. Phys. Lett. 7 3, 21 (1980)] and the Rashed–Brown [J. Chem. Phys. 8 2, 5506 (1985)] potential energy surfaces. When there is no rotation in the OH, then a plot of reaction cross section, SR( j’) resembles that for an atom–diatom system: Just above threshold, rotation decreases reactivity for small j’, but increases it for high j’; at higher translational energies this trend is less obvious, but still present. When j’=0, then SR( j) is a complicated function, decreasing for low j, then climbing to a maximum, finally decreasing once more at very large values of j. We have also carried out calculations with isotopically substituted H in OH, and show that these effects scale as the mass of the hydrogen isotope. We show that this behavior is due to artifacts in both the potential surfaces. Using a simple model we are able to rationalize this behavior. Using this same model, together with a potential in which the artifacts are absent, we predict that rotation in OH will decrease reactivity rather less than was reported in previous trajectory studies [Schatz, J. Chem. Phys. 7 4, 1133 (1981); Rashed and Brown, J. Chem. Phys. 8 2, 5506 (1985)].