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Published on: August 13, 2020
Rotational excitation of thioformaldehyde (H2CS) in collisions with molecular hydrogen
1Department of Chemistry, The Johns Hopkins University, Baltimore, Maryland 21218-2685, USA.
Abstract:
Thioformaldehyde (H2CS) has been observed in the interstellar medium (ISM). Accurate determination of column densities of the two nuclear spin modifications of H2CS in the low-density environment of the ISM ideally necessitates the use of a radiative transfer model. Such a model requires the availability of rate coefficients for inelastic rotational transitions in H2CS induced by collisions with the dominant hydrogen molecule in the ISM. To compute these rate coefficients, a potential energy surface (PES) for the interaction of H2CS with H2 is computed in this study by the explicitly correlated coupled cluster method including single, double, and (perturbatively) triple excitations [CCSD(T)-f12a] and a correlation-consistent aug-cc-pVTZ basis. The geometries of the molecules were fixed. The calculated points on the PES were fit to a functional form suitable for quantum scattering calculations. The well depth De of the H2CS-H2 PES was determined to equal 318.1 cm-1, and the equilibrium intermolecular separation was found to be 6.18a0. Time-independent quantum scattering close coupling calculations were performed to compute state-to-state cross sections and rate coefficients for transitions between the H2CS rotational levels induced by collisions with the hydrogen molecule.
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