Hyperfine excitation of NS+ due to para-H2(j = 0) impact

Abstract

Sulphur bearing nitrogenous compounds have been observed in space over this last decade. Modelling their abundances has been done using rate coefficients of isoelectronic molecules. In order to satisfy the astrophysical precision required, we report the actual rate coefficients of NS+ induced by collision with the most abundant interstellar species (para-H2). Considering the 23 low-lying rotational levels of NS+, we were able to compute the (hyperfine) rate coefficients up to 100 K. These latter were carried out by averaging cross-sections over the Maxwell–Boltzmann velocity distribution. The state-to-state inelastic cross-sections were determined in the quantum mechanical close coupling approach for total energies ranging up to 1400 cm−1. These dynamic data result from a four dimensional potential energy surface (4D-PES) which was spherically averaged over the H2 orientations. The 4D-PES was calculated using the explicitly correlated coupled cluster method with simple, double, and non-iterative triple excitation (CCSD(T)–F12) connected to the augmented–correlation consistent–polarized valence triple zeta Gaussian basis set (aug–cc–pVTZ). The so-averaged PES presents a very deep well of 596.72 cm−1 at R = 5.94 a0 and θ1 = 123.20°. Discussions on the propensity rules for the (hyperfine) rate coefficients were made and they are in favour of (Δj = ΔF) Δj = 1 transitions. The results presented here may be crucially needed in order to accurately model the NS+ abundance in space. In addition, we expect that this paper will encourage investigations on the sulphur bearing nitrogenous compounds.

The excitation of CNCN in the interstellar medium: hyperfine resolved rate coefficients and non-LTE modelling

“…Concerning the hyperfine transitions shown in panels (b) and (c), rate coefficients for which Δ = Δ 1 and Δ = Δ 1 = Δ absolutely outweigh for all temperatures, respectively. Such behaviours were seen and discussed in previous works (Ben Abdallah et al 2012;Bop 2019;Balança et al 2020). At low temperature, the favored hyperfine transitions are at least one order of magnitude greater than the less pronounced ones.…”

Rotational excitation of NS+ by H2 revisited: A new global potential energy surface and rate coefficients

“…The potential well depth is thus similar to that of Bop 6 which is located at -848.24 cm −1 below the dissociation limit ACCEPTED MANUSCRIPT / CLEAN COPY of the complex. With respect to the interaction potentials where helium was used as projectile, 4,5 the new global minimum is about 5 times deeper.…”

“…(θ H 2 , φ ) = (0, 0), (90, 0) and (90, 90) as previously done by Bop. 6 The bottom panel of Fig. 5 shows a perfect agreement clearing out any suspicion on the different coordinate systems used in the construction of the PESs.…”

“…In this work, we used as Bop 6 the state-of-the art CCSD(T)-F12/aug-cc-pVTZ level of theory 9,10 implemented in the MOLPRO molecular package version 2010 11 for all ab initio calculations. We improved the PES Bop 6 by (i) fully describing the H 2 rotations and (ii) explicitly treating the long-range interaction potential using a multipolar expansion.…”

“…Due to the fact that He is seen as a bad template for para-H 2 (p-H 2 ) in the case of charged species, Bop 6 reassessed the hyperfine rate coefficients corresponding to the 23 low-lying rotational levels of NS + for temperatures up to 100 K, but using p-H 2 ( j 2 = 0) as projectile. These calculations were based on a 4D PES, computed at the CCSD(T)-F12/aug-cc-pVTZ level of theory, which was thereafter averaged over the orientations of H 2 (denoted hereafter as model treatment).…”