Adiabatic T matrix theory for three dimensional reactive scattering: Application to the (H, H2) system

We present an adiabatic transition matrix (T matrix) method of atom--molecule reactive scattering. In this method, the coupling between vibrational and rotational motions is taken into account for obtaining the adiabatic molecular wave functions. These wave functions are expanded in terms of the basis functions taken from the eigenfunctions of a double well potential. From the full potential surface in the linear configuration of three atoms, the double well potential is obtained. Convergence of the expansion is achieved for evaluating the adiabatic wave functions and two body atom--molecule interaction potential. Cross sections are computed with the T matrix method employing the converged adiabatic wave functions. Numerical results for the H+H2 reactive cross section on an ab initio potential surface are presented. Results on D+H2 reaction will be reported in a subsequent paper. The differential cross sections and final state distributions computed from the present adiabatic T matrix method are similar to ones obtained from the adiabatic distorted wave approximation which we published earlier. However, the absolute cross section from the present approach is considerably larger than the previous one. The present results on the reactive cross section are in very good agreement with those obtained from a close coupling calculation. The present cross sections are much bigger than the classical ones in the threshold region. Among the cross sections from various T matrix approaches, the present one is the largest and seems to be most accurate