Rotational Quenching Rate Coefficients for H2in Collisions with H2from 2 to 10,000 K

Abstract

Rate coefficients for rotational transitions in H2 induced by H2 impact are presented. Extensive quantum mechanical coupled-channel calculations based on a recently published (H2)2 potential energy surface were performed. The potential energy surface used here has been demonstrated to be more reliable than surfaces used in previous work. Rotational transition cross sections with initial levels of -->J ≤ 8 were computed for collision energies ranging between 10−4 and 2.5 eV, and the corresponding rate coefficients were calculated for the temperature range -->2 ≤ T≤ 10,000 K. In general, agreement with earlier calculations, which were limited to 100-6000 K, is good, although discrepancies are found at the lowest and highest temperatures. Low-density-limit cooling functions due to para- and ortho-H2 collisions are obtained from the collisional rate coefficients. Implications of the new results for nonthermal H2 rotational distributions in molecular regions are also investigated.