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Collisional energy transfer under cold conditions is of great importance from the fundamental and applicative point of view. Here, we investigate low temperature collisions of the SH- anion with He. We have generated a three-dimensional potential energy surface (PES) for the SH-(X¹Σ+)-He(¹S) van der Waals complex. The ab initio multi-dimensional interaction PES was computed using the explicitly correlated coupled cluster approach with simple, double, and perturbative triple excitation in conjunction with the augmented-correlation consistent-polarized valence triple zeta Gaussian basis set. The PES presents two minima located at linear geometries. Then, the PES was averaged over the ground vibrational wave function of the SH- molecule and the resulting two-dimensional PES was incorporated into exact quantum mechanical close coupling calculations to study the collisional excitation of SH- by He. We have computed inelastic cross sections among the 11 first rotational levels of SH- for energies up to 2500 cm-1. (De-)excitation rate coefficients were deduced for temperatures ranging from 1 to 300 K by thermally averaging the cross sections. We also performed calculations using the new PES for a fixed internuclear SH- distance. Both sets of results were found to be in reasonable agreement despite differences existing at low temperatures confirming that accurate predictions require the consideration of all internal degrees of freedom in the case of molecular hydrides. The rate coefficients presented here may be useful in interpreting future experimental work on the SH- negative ion colliding with He as those recently done for the OH- -He collisional system as well as for possible astrophysical applications in case SH- would be detected in the interstellar medium. [ABSTRACT FROM AUTHOR]

The interaction potential energy surface of the methinoposphide (HCP)-H2 complex is calculated at the ab initio coupled-cluster level of theory with an aug-cc-pVTZ Gaussian basis set. The [H-C] and [C-P] bond lengths of HCP are set to their values at the linear equilibrium ground vibrational level of the molecule. The calculated interaction energy presents two minima located 106.3 and 67.6 cm-1 below the HCP+H2 dissociation limit. Using the interaction potential obtained, we have computed collision excitation cross sections in the close-coupling approach and downward rate coefficients at low temperature, i.e., T≤70 K. These quantities are significantly magnified in comparison with their counterparts for the HCP-He collisions. It is shown that there is a propensity toward ΔJ=1 transitions. [ABSTRACT FROM AUTHOR]

In this paper, we focus on the determination of the rotational excitation rate coefficients of the first observed molecule containing noble gas 36ArH+ isotope by He. Hence, we present the first potential energy surface (PES) of ArH+ --He van der Waals system. The interaction PES of the ArH+ (X¹ Σ)+-He(¹S) complex is calculated by the ab initio explicitly correlated coupled cluster with single, double, and perturbative triple excitation (CCSD(T)-F12) method in connection with the augmented correlation consistent triple zeta Gaussian basis (aug-cc-pVTZ). The interaction potential presents two global minima of 708.00 and 172.98 cm-1 below the ArH+ (X¹ Σ +)-He(¹S) dissociation limit. Using the PES obtained, we have computed integral inelastic cross-sections in the close-coupling approach among the first 11 rotational levels of ArH+ for energies up to 2500 cm-1. Downward rate coefficients were determined at low temperature (T ≤ 300 K). It is expected that the data worked out in this study may be beneficial for further astrophysical investigations as well as laboratory experiments. [ABSTRACT FROM AUTHOR]

Abstract: Using the Coupled Cluster with Single and Double and Perturbative Triple excitations method and the aug-cc-pVQZ basis set, we have computed a two-dimensional potential energy surface for the van der Waals complex SiH+(X 1Σ+)+He(1S). Bond functions were placed at mid-distance between the center of mass of SiH+ and He atom for a better description of the intersystem correlation interaction energy. The potential energy surface presents a global minimum of ∼308cm−1 below the SiH+–He dissociation limit. By fitting the potential energy surface on a basis of Legendre polynomials functions, we have derived collisional excitation cross sections for the SiH+ collisions with He in the Close Coupling approach. Downward rate coefficients are inferred at low temperature by averaging the cross sections over a Maxwell-Boltzmann velocity distribution. A propensity towards ΔJ even parity transitions is observed in almost the entire range of energy spanned. It is expected that the data worked out in this study may enhanced further astrophysical investigations as well as laboratory experiments. [Copyright &y& Elsevier]

Abstract: We report coupled-cluster [CCSD(T)] ab initio calculations of the two-dimensional interaction potential energy surface of the HCP–He complex. The aug-cc-pVTZ and aug-cc-pVQZ gaussian basis sets are used. HCP is held fixed at its linear equilibrium ground vibrational level with the corresponding [H–C] and [C–P] bond lengths set to the values 2.016bohrs and 2.914bohrs, respectively. Our calculations are corrected for basis set superposition errors (BSSE). The PES obtained with the above triple zeta basis set has two minima located 22.018cm−1 and 14.808cm−1 below the HCP+He dissociation limit. These well depths are shifted to 23.505cm−1 and 15.949cm−1, respectively, when the quadruple zeta basis set is used. Our PESs are fitted on a basis of Legendre polynomial functions and state to state rotational integral cross sections of the HCP collision with He are calculated in the close-coupling (CC) approximation. Downward rate coefficients are inferred at low temperature () by averaging the cross sections over a Maxwell–Boltzmann velocity distribution. An analysis of our results shows that for kinetic energies greater than ∼60cm−1, the transition dominates. The numbers derived here may be very useful for astrophysical observations. [Copyright &y& Elsevier]

Rotational excitation cross sections and rate coefficients for the inelastic collision of HCNO by He atom are computed at low temperature. To perform this, an interaction potential energy surface of the HCNO( X 1 Σ + )–He( 1 S ) van der Waals complex is obtained at the CCSD(T)/aug-cc-pVQZ level of theory. This potential presents a well depth of about 64.14 cm −1 below the HCNO–He dissociation limit. The cross sections are obtained in the close coupling scheme and rate coefficients inferred by averaging the cross sections over a Maxwell–Boltzmann velocity distribution. A propensity towards Δ J = 1 transitions is observed. [ABSTRACT FROM AUTHOR]