The interaction potential energy surface of the methinoposphide (HCP)-H(2) 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+H(2) 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

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We report on the calculation of collision induced rotational excitation cross sections and rate coefficients of AlF by He atom at low temperature. These quantities were obtained by first computing the interaction potential energy surface (PES) of the AlF(X 1 + )-He( 1 S) van der Waals complex at the ab initio Coupled Cluster with Single and Double and perturbative Triple excitations [CCSD(T)] level of theory. The aug-cc-pVQZ Gaussian basis, to which was added a set of bond functions, was used for that purpose. The calculations account for basis set superposition errors (BSSE). The interaction potential presents a minimum of ∼24 cm −1 below the AlF-He dissociation limit. The PES was fitted on a basis of Legendre polynomial functions to allow for the calculation of cross sections in the closecoupling (CC) approach. By averaging these cross sections over a Maxwell-Boltzmann velocity distribution, rate coefficients were inferred at low temperatures (T ≤ 300 K). From our computations, a propensity towards J = 1 transitions is observed.

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