Atom—Molecule Kinetics Using ESR Detection. III. Results for O+D2→OD+D and Theoretical Comparison with O+H2→OH+H

Abstract

The technique described previously has been used to measure the rate constant k₂ for the reaction O+D₂→OD+D over the temperature range 416°—968°K. The data are strictly Arrhenius linear over this range and obey (cm³mole⁻¹•sec⁻¹) k₂=2.0×10¹³ exp(−11 000/RT). A new value of k₁ for O+H₂→OH+H at 357°K is also reported, which gives a distinct curvature to the low‐temperature end of the Arrhenius plot of the k₁ data reported earlier. In the range 416°—928°K, where both k₁ and k₂ are linear, interpretation is made in terms of absolute rate theory without tunneling. A potential‐energy surface for a linear transition complex was constructed by the semiempirical Sato method. The average value of the classical potential energy of activation calculated by independently fitting both sets of data is E_c=11 680±120 cal/mole. The theoretical ratio k₁/k₂ closely follows the experimental ratio in temperature dependence but is about 30% low in magnitude. The theoretical absolute values of the individual pre‐exponential factors are in fair agreement with experiment, although also low and not as satisfactory as was found in the D+H₂ and H+D₂ cases treated previously. Some measurements comparing the decay rates of O(³P₂) and O(³P₁) in reaction with H₂ are also given, which show that the equilibration rate between J=2 and J=1 states is probably much faster than any difference in chemical reaction rates.