Vibrational–rotational energy transfer in H2–H2 collisions: II. The relative roles of the initial rotational excitation of both diatoms

A recently proposed [J. Chem. Phys. 111 (1999) 2401] new semi-classical decoupling procedure for rotational projection states in ro-vibrationally inelastic atom–diatom and diatom–diatom collisions is extended and 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 para-H2, is analyzed in detail. The computed vibrational self-relaxation rate constant for para-H2 is in a good quantitative agreement (within a factor of 2) with experimental data over the whole experimentally investigated temperature range, 50–3000 K.