Search

Quantum mechanical calculations for the thermal rate constant of the combustion related reaction, CH4 + H → CH3 + H2, are reported. Benchmark full-dimensional results are given and compared to those derived from classical transition state theory as well as to some published reduced dimensionality results. The role played by some of the different degrees of freedom in the reactive process is investigated by comparing additional reduced dimensionality results to the exact ones. This proves valuable for the development of possible strategies to study involved reactive processes.

Detailed energy dependences of state-to-state and state-to-all integral cross sections have been studied by means of exact three-dimensional hyperspherical calculations, for the complex-forming Ne + H2⁺ → NeH⁺ + H reaction. Integral cross sections show an outstandingly marked structure as a function of energy. This structure has been characterized analyzing the state-to-state contributions, on one hand, and the partial cross section cumulative sums as a function of the total angular momentum quantum number J, on the other. As expected, the key fact is that strongly bound metastable states lead to peaks in the above quantities narrow enough to avoid an effective quenching of the resulting structure, when summing either over J or over final product states. This feature, which has already been found for other complex-forming reactions, indicates that quantum effects can be more relevant than expected, so as to require their explicit consideration when accurately characterizing a reactive event. Additionally, the implications of the observed behavior for the J-shifting approximation have been analyzed. In particular, it is shown how a clear J-shifting behavior is found for low J, Ω = 0. However, it is lost as higher J values are considered (for Ω = 0) or, as it is well-known, higher Ω projections are included in the calculation. A rationale for this behavior is presented.