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Free keywords:
H-2 activation; Metal catalysis; Statistical modelling; Temperature dependent kinetics
Abstract:
The temperature dependencies of the reactions MnO+ + H-2/D-2 from 150 to 600 K are measured in a selected- ion flow tube apparatus. The reactions are approximately 15% efficient at room temperature with rate constants (k = 2.7 +/- 0.7 x 10(-10) cm(3) s(-1) for H-2 and 1.5 +/- 0.4 x 10(-10) cm(3) s(-1) for D-2 at 300 K) that vary as T-1.1 +/- 0.2 and T-1.3 +/- 0.2, respectively. Both Mn+ and MnOH+/D+ products are observed, with Mn+ being the minority product in the H-2 reaction, but the majority product in the D-2 reaction. Reaction coordinates are explored using a variety of density functional methods, with quantitative but not qualitative differences in the results. Unlike the analogous FeO+ + H-2 reaction, no evidence for spin inversion prior to the rate-limiting transition state is found. A crossing between septet and quintet potential energy surfaces in the product well exists, and the possibility of spin inversion on the way to products is discussed. The reaction coordinates inform a statistical treatment of the reaction, which well reproduces all kinetic results, including the product branching inversion observed due to isotope substitution.
