Quantum mechanical calculations of rotational transitions in H-H₂ collisions

We report quantum mechanical cross sections and rate coefficients for rotational transitions due to collisions of hydrogen atoms with hydrogen molecules. The sensitivity of the results to the nature of the potential energy surface and to the scattering formulation is investigated. We find that the rigid rotor and harmonic oscillator approximations are inadequate to describe the dynamics. We make use of the most reliable of the potential energy surfaces in a close-coupled description of the nonreactive scattering that takes the vibrational motion into account, and we calculate rate coefficients for rotational transitions at temperatures below 1000 K, where the reactive channels may be neglected.