A seven-dimensional quantum study of the H+CH4 reaction

The initial state selected time-dependent wave packet method has been developed to study the $\mathrm{H}+{\mathrm{CH}}_4$ reaction in seven dimensions by employing the model developed by Palma and Clary [J. Chem. Phys. 112, 1859 (2000)]. The latter eight-dimensional model only assumes that the nonreacting ${\mathrm{CH}}_3$ group keeps a $C_{\text{3V}}$ symmetry in reaction. The CH bond lengths in the nonreacting ${\mathrm{CH}}_3$ group were fixed in the study to reduce the number of degrees of freedom to seven. Our calculations reveal that it is very important to accurately deal with the umbrella motion of the ${\mathrm{CH}}_3$ group while studying this reaction. We investigated the effects of the fundamental vibrational excitations of ${\mathrm{CH}}_4$ on the reaction. Finally, we compare our rate constant for the ground rovibrational initial state with available experimental and other theoretical results.