We report quantum-mechanical close-coupling calculations for rotational state resolved cross sections for p-H 2 +HD collisions. The low temperature limit of p-H 2 +HD is investigated, which is of significant astrophysical interest in regard to the cooling of primordial gas and the interstellar media. Sharp resonances have been reproduced in the cross sections of some transition states at very low kinetic energies, E

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In this work we report the results of calculation for quantum-mechanical rotational transitions in molecular hydrogen, H 2 , induced by an ultracold ground-state antihydrogen atom H 1s . The calculations are accomplished using a nonreactive close-coupling quantum-mechanical approach. The H 2 molecule is treated as a rigid rotor. The total elastic-scattering cross section σ el ( ) at energy , state-resolved rotational transition cross sections σ jj ( ) between states j and j , and corresponding thermal rate coefficients k jj (T ) are computed in the temperature range 0.004 K T 4 K. Satisfactory agreement with other calculations (variational) has been obtained for σ el ( ).

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Quantum-mechanical close-coupling calculations for state-to-state cross sections and thermal rates are reported for H2+H2 collisions. Two recently developed potential energy surfaces (PES) for the H2−H2 system are applied, namely, the global potential surface from the work of A.I. Boothroyd, P.G. Martin, W.J. Keogh, M.J. Peterson, J. Chem. Phys., 116 (2002) 666, and a restricted, model surface from the works of P. Diep, J.K. Johnson, J. Chem. Phys., 113 (2000) 3480; ibid. 112, 4465. The low temperature limit is investigated. We found significant differences in cross sections and corresponding thermal rates calculated with these two PESs.