Rate coefficients for state-to-state rotational transitions in CO induced by both para-and ortho-H 2 collisions are presented. The results were obtained using the close-coupling method and the coupled-states approximation, with the CO-H 2 interaction potential of Jankowski & Szalewicz (2005). Rate coefficients are presented for temperatures between 1 and 3000 K, and for CO(v = 0, j) quenching from j = 1 − 40 to all lower j ′ levels. Comparisons with previous calculations using an earlier potential show some discrepancies, especially at low temperatures and for rotational transitions involving large |∆j|. The differences in the well depths of the van der Waals interactions and the anisotropy of the two potential surfaces lead to different resonance structures in the energy dependence of the cross sections which influence the low temperature rate coefficients. Applications to far infrared observations of astrophysical environments are briefly discussed.

Most of the information about the environment of the early Universe comes to us from radiation emitted from atoms and molecules. An understanding of the relevant atomic and molecular processes is needed to correctly interpret this radiation. Atomic and molecular process also control the evolution of the early Universe. In this paper, we review the atomic and molecular processes that are important in the early Universe.

The chemistry of deuterium, as well as that of hydrogen and helium, in the postrecombination era of the expanding early universe is presented. A thorough survey of all potentially important gas-phase reactions involving the primordial elements produced in the Big Bang, with a particular emphasis on deuterium, is given. The reaction set, consisting of 144 processes, is used in a nonequilibrium chemistry model to follow the production of primordial molecules in the postrecombination era. It is found that signiÐcant deuterium fractionation occurs for HD`, HD, and while the abundance of D`is reduced H 2 D`, compared to the proton abundance. Even with the enhanced fractionation of its abundance is H 2 D`, predicted to be too small to cause any interesting cosmological consequences, such as possible attenuation of spatial anisotropies in the cosmic background radiation Ðeld, detections of the epochs of reionization and reheating, or constraints on the primordial deuterium abundance. HD, being the second most abundant primordial molecule after may play a role in subsequent structure formation because of its H 2 , cooling radiation. Subject headings : cosmic microwave background È early universe È molecular processes È nuclear reactions, nucleosynthesis, abundances

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Much of the baryonic matter in the Universe is in the form of H 2 which includes most of the gas in galactic and extragalactic interstellar clouds. Molecular hydrogen plays a significant role in establishing the thermal balance in many astrophysical environments and can be important as a spectral diagnostic of the gas. Modeling and interpretation of observations of such environments requires a quantitatively complete and accurate treatment of H 2 . Using this micro-physical model of H 2 , illustrative calculations of prototypical astrophysical environments are presented. This work forms the foundation for future investigations of these and other environments where H 2 is an important constituent. 1 0, 2 J ∆ = ± 0, 1 J ∆ = ± 1 J ∆ = ± . For C + , the