Quantum theory of four-atom reactions using arrangement channel hyperspherical coordinates: Formulation and application to OH+H2↔H2O+H

An arrangement channel hyperspherical coordinate method for performing quantum scattering calculations on four-atom reactions is formulated. This method treats the vibrational and rotational states in different arrangement channels by a close-coupling expansion in nonorthogonal functions. The method is applied to the calculation of state-to-state probabilities for the ${\mathrm{OH+H}}_{\mathrm{2}}{\mathrm{\to H}}_{\mathrm{2}}\mathrm{O+H}$ reaction. Good agreement is found with cumulative and state-selected reaction probabilities previously calculated by other methods. The major advantage of this general approach is that the whole $S$ matrix can be obtained in a single calculation.