Vibrational-rotational energy transfer in H2-H2 collisions:: III.: Ortho-ortho collisions

A recently proposed [1999, J. chem. Phys., 111, 2401 and 1999, Chem. Phys. Lett., 312, 530] new semi-classical decoupling procedure for rotational projection states in ro-vibrationally inelastic atom-diatom and diatom-diatom collisions is applied to inelastic collisions in molecular hydrogen. The role of initial rotational excitation of both collision partners in the ro-vibrational transitions, attached to the vibrational (10 --> 00) transition in ortho-H-2, is analysed in detail. The computed vibrational self-relaxation rate constant for ortho-H-2 (as earlier for para-H-2, too) is in good quantitative agreement (within a factor of 2) with experimental data over the whole experimentally investigated temperature range, 50-3000 K. This also indicates that the more detailed (non-measured) rate constants for ro-vibrational state-to-state transitions in molecular hydrogen, calculated by our new model, are sufficiently accurate for astrophysical applications.