Rotational excitation of interstellar OH by para- and ortho-H2

Abstract

In warm and dense interstellar clouds, the amount of ortho-H 2 is comparable to that of para-H 2 . Yet most models of the excitation of interstellar molecules have considered only para-H 2 . Calculations of the rate coefficients for rotational excitation of OH by both para- and ortho-H 2 in their ground states within the coupled-states formulation are presented. The coupled states results are shown to reproduce satisfactorily the more accurate close-coupling calculations. The importance of inclusion of ortho-H 2 (j=1) in the OH excitation is explored using statistical equilibrium models