Benhui Yang

BASECOL2012: A collisional database repository and web service within the Virtual Atomic and Molecular Data Centre (VAMDC)

The BASECOL2012 database is a repository of collisional data and a web service within the Virtual Atomic and Molecular Data Centre (VAMDC, http://www.vamdc.eu). It contains rate coefficients for the collisional excitation of rotational, ro-vibrational, vibrational, fine, and hyperfine levels of molecules by atoms, molecules, and electrons, as well as fine-structure excitation of some atoms that are relevant to interstellar and circumstellar astrophysical applications. Submissions of new published collisional rate coefficients sets are welcome, and they will be critically evaluated before inclusion in the database. In addition, BASECOL2012 provides spectroscopic data queried dynamically from various spectroscopic databases using the VAMDC technology. These spectroscopic data are conveniently matched to the in-house collisional excitation rate coefficients using the SPECTCOL sofware package (http:// vamdc.eu/software), and the combined sets of data can be downloaded from the BASECOL2012 website. As a partner of the VAMDC, BASECOL2012 is accessible from the general VAMDC portal (http://portal.vamdc.eu) and from user tools such as SPECTCOL.

Quantum dynamics of CO-H2 in full dimensionality

Accurate rate coefficients for molecular vibrational transitions due to collisions with H₂, critical for interpreting infrared astronomical observations, are lacking for most molecules. Quantum calculations are the primary source of such data, but reliable values that consider all internal degrees of freedom of the collision complex have only been reported for H₂-H₂ due to the difficulty of the computations. Here we present essentially exact, full-dimensional dynamics computations for rovibrational quenching of CO due to H₂ impact. Using a high-level six-dimensional potential surface, time-independent scattering calculations, within a full angular momentum coupling formulation, were performed for the de-excitation of vibrationally excited CO. Agreement with experimentally determined results confirms the accuracy of the potential and scattering computations, representing the largest of such calculations performed to date. This investigation advances computational quantum dynamical studies representing initial steps towards obtaining CO-H₂ rovibrational quenching data needed for astrophysical modelling.

Low energy H+CO scattering revisited - CO rotational excitation with new potential surfaces

Context. A recent modeling study of brightness ratios for CO rotational transitions in gas typical of the diffuse ISM by Liszt found the role of H collisions to be more important than previously assumed. This conclusion was based on recent quantum scattering calculations using the so-called WKS potential energy surface (PES) which reported a large cross section for the important 0 → 1 rotational transition. This result is in contradiction to one obtained using the earlier BBH PES for which the cross section is quite small and which is consistent with an expected homonuclear-like propensity for even ∆J transitions. Aims. We revisit this contradiction with new scattering calculations using two new ab initio PESs that focus on the important longrange behavior and explore the validity of the apparent departure from the expected even ∆J propensity in H-CO rotational excitation obtained with the WKS PES. Methods. Close-coupling (CC) rigid-rotor calculations for CO(v = 0, J = 0) excitation by H are performed on four different PESs. Two of the PESs are obtained in this work using state-of-the-art quantum chemistry techniques at the CCSD(T) and MRCI levels of theory. Results. Cross sections for the J = 0 → 1, as well as other odd ∆J, transitions are significantly suppressed compared to even ∆J transitions in thermal energy CC calculations using the CCSD(T) and MRCI surfaces. This is consistent with the expected even ∆J propensity and in contrast to CC calculations using the WKS PES which predict a dominating 0 → 1 transition. Conclusions. Inelastic collision cross section calculations are sensitive to fine details in the anisotropic components of the PES and its long-range behavior. The current results obtained with new surfaces for H-CO scattering suggest that the original astrophysical assumption that excitation of CO by H2 dominates the kinetics of CO in diffuse ISM gas is likely to remain valid.

ON THE VALIDITY OF COLLIDER-MASS SCALING FOR MOLECULAR ROTATIONAL EXCITATION

Rate coefficients for collisional processes such as rotational and vibrational excitation are essential inputs in many astrophysical models. When rate coefficients are unknown, they are often estimated using known values from other systems. The most common example is to use He-collider rate coefficients to estimate values for other colliders, typically H

Close-coupling study of rotational energy transfer and differential scattering in H2O collisions with He atoms

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Quenching of rotationally excited CO by collisions with H2

, using scaling arguments based on the reduced mass of the collision system. This procedure is often justified by the assumption that the inelastic cross section is independent of the collider. Here we explore the validity of this approach focusing on rotational inelastic transitions for collisions of H, para-H

ROTATIONAL QUENCHING OF ROTATIONALLY EXCITED H2O IN COLLISIONS WITH He

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Full-dimensional quantum dynamics of CO in collision with H2

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A close-coupling study of vibrational-rotational quenching of CO by collision with hydrogen atoms

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QUANTUM CALCULATION OF INELASTIC CO COLLISIONS WITH H. II. PURE ROTATIONAL QUENCHING OF HIGH ROTATIONAL LEVELS

He, and