Seven-degree-of-freedom, quantum scattering dynamics study of the H2D++H2 reaction.

A quantum scattering dynamics, time-dependent wavepacket propagation method is applied to study the reaction of H₂D⁺+H₂→H₃⁺+HD on the Xie–Braams–Bowman potential energy surface. The reduced-dimensional, seven-degree-of-freedom approach is employed in this calculation by fixing one Jacobi and one torsion angle related to H₂D⁺ at the lowest saddle point geometry of D_2d on the potential energy surface. Initial state selected reaction probabilities are presented for various initial rovibrational states. The ground state reaction probability shows no threshold for this reaction, in other words, this reaction can occur without an activation barrier. The vibrational excitation shows that the stretching motion of H⁺–HD only has a small effect on the reaction probability; the vibrational excitation of HD in H₂D⁺ hinders the reactivity. By contrast, rotational excitation of H⁺–HD greatly enhances the reactivity with the reaction probability increased double or triple at high rotational states compared to the ground state. Reactive resonances, seen in all the initial state selected reaction probabilities, are also found in the integral cross section for the ground state of H₂D⁺ and H₂. The thermal rate coefficient is also calculated and is found to be in semiquantitative agreement with experiment; however, quantum scattering approaches including more degrees of freedom, especially including all the angles, are necessary to study this reaction in the future. [ABSTRACT FROM AUTHOR]