Low‐Temperature Rate Constants for Rotational Excitation and De‐excitation of C₃(X ¹Σ$^{+}_{g}$ ) by Collisions with He (¹S)

Abstract

The low-temperature rotational (de-) excitation of C 3 (X 1 AE þ g ) by collisions with He ( 1 S ) is studied using an ab initio potential energy surface (PES). This PES has been calculated using the single-and double-excitation coupledcluster approach with noniterative perturbational treatment of triple excitations [CCSD( T)] and the augmented correlation-consistent triple-basis set (aug-cc-pVTZ ) with bond functions. This PES is then incorporated in full close-coupling quantum scattering calculations for collision energies between 0.1 and 50 cm À1 in order to deduce the rate constants for rotational levels of C 3 up to j = 10, covering the temperature range 5Y15 K.

Hyperfine excitation of HCN by H2 at low temperature

“…It has been shown recently (Lique et al 2005; Ben Abdallah et al 2008; Lique & Kłos 2008) that the use of aug‐cc‐pVTZ + 3s 3p 2d 1f basis set leads to results comparable in accuracy to the computed potential energies obtained with the larger aug‐cc‐pVQZ sets, but with a considerable benefit on CPU time. The counterpoise procedure (Boys & Bernardi 1970) was used at all geometries for correction of the basis set superposition error (BSSE): where the energies of the HCN and H 2 subsystems are computed with the full (five atoms plus bond functions) basis.…”

“…This procedure was motivated by the fact that the midbond functions are mostly responsible for saturating the dispersion energy (Williams et al 1995) which decays as R −6 . It has been shown recently (Lique et al 2005;Ben Abdallah et al 2008;) that the use of aug-cc-pVTZ + 3s 3p 2d 1f basis set leads to results comparable in accuracy to the computed potential energies obtained with the larger aug-cc-pVQZ sets, but with a considerable benefit on CPU time. The counterpoise procedure (Boys & Bernardi 1970) was used at all geometries for correction of the basis set superposition error (BSSE):…”

Molecular Excitation in the Interstellar Medium: Recent Advances in Collisional, Radiative, and Chemical Processes

“…Rotational (de-)excitation of C 3 ( 1 Σ + ) by collisions with He was studied in 2008 by Ben Abdallah et al 71 for low kinetic energies, in order to restrict the study within the ground vibrational…”

On the use of explicitly correlated treatment methods for the generation of accurate polyatomic –He/H2 interaction potential energy surfaces: The case of C3–He complex and generalization

“…19, 20. Rate constants for rotational (de-)excitation of C 3 )(X 1 g + ) by He ( 1 S) were computed for the first time, in 2008, by Ben Abdallah et al, 21 after incorporation of a 2D interaction PES into full close-coupling quantum scattering calculations within the rigid monomer approximation (RMA). The 2D-PES was generated at the CCSD(T)/aug-cc-pVTZ + 3s3p2d1f bond functions (denoted hereafter as 2D-BA) and it was developed over R (distance between this center of mass and the He atom, Figure 1) and θ (defining the rotation of He around C 3 , Figure 1) Jacobi coordinates, where the C 3 molecule was kept fixed to its structure at the ground vibrational state (r 0 = 1.2772 Å, 22,23 i.e., linear C 3 bond distances).…”

“…Both PESs correlate to the C 3 (X 1 g + ) + He( 1 S) in the asymptote region. For the 2D-PES (4D-PES), we use a similar coordinate system and an analytical fitting procedure than Ben Abdallah et al 21 and Denis-Alpizar et al, 25 which allows direct comparison of our explicitly correlated PESs with those deduced using the standard coupled cluster techniques. After dynamical computations, we also compare the pattern of bound rovibrational levels of this complex derived using both sets of PESs and the cross sections for the (de-)excitation of C 3 by He.…”