Approximate quantum scattering studies of the CN+H₂ reaction

Reduced dimensionality quantum scattering calculations have been carried out for the H₂+CN→HCN+H reaction. A new potential energy surface, which has recently been developed on the basis of extensive ab initio molecular orbital calculations, has been employed. In order to study the effect of H₂CN complex-formation on the hydrogen abstraction, three active degrees of freedom have been considered in the scattering calculations: the H-H internuclear distance, the H-G_CN distance (where G_CN is the center of mass of CN) and the angle between H-H and H-G_CN. This reduces the problem to the usual atom-diatom scattering calculation for H₂+A, where A represents a pseudoatom. A hyperspherical coordinate coupled-channel method has been used to solve the Schrodinger equation. The reaction probabilities calculated show that H₂CN complex-formation mechanism is not important for the hydrogen abstraction channel in the energy range considered in the present calculations. On the other hand, complex-formation is important for inelastic processes such as H+HCN(v,j)→H+HCN(v′,j′), where v and j are the C-H local vibrational and rotational quantum numbers of HCN. This is consistent with previous full-dimensional quasiclassical trajectory calculations. The reaction probabilities, final vibrational distributions, and thermal rate constants calculated with the present reduced dimensionality theory have been critically compared with those calculated using quasiclassical trajectories and with other approximate quantum scattering methods including the adiabatic-bend approximation and the rotating-bond approximation.