Kinetic isotope effects: Theoretical prediction of the thermal rate coefficient for the reaction D+O2→OD+O

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Abstract
Quasiclassical trajectory (QCT) and quasiclassical trajectory quantum mechanical threshold (QCT–QMT) calculations are reported for the reaction D+O2→OD+O. The thermal rate coefficient from the QCT–QMT analysis was determined to be k2 = 8.12×1015T−0.659 exp(−15 041/RT) cm3/mol s, for 250<TR1) H+O2→OH+O, the ratio k2/k1 is found to vary from 7.5 at 250 K to 0.8 at 2500 K. The primary isotope effects controlling this difference are the difference in zero‐point vibrational energies of the product diatoms at low temperature and the difference in reactant collision frequencies at high temperature. In addition the calculations show slightly less negative Arrhenius curvature (n2 = −0.659, n1 = −0.816) for R2 than for R1, an effect anticipated from the previous analysis. However, the magnitude of the difference between n1 and n2 is approximately the same as estimates of the maximum uncertainty in the calculations themselves. It is concluded that a factor of 2 in the mass of the attacking atom is not sufficient to distinguish accurately differences in Arrhenius curvature arising from the L+HH mass combination of the reactants, either theoretically or experimentally.