Rotational excitation of the interstellar NH2 radical by H2

Abstract

We present quantum close-coupling calculations for the rotational excitation of the interstellar amidogen radical NH due to collisions with H molecules. The calculations are based on a recent, high-accuracy full-dimensional NH potential energy surface adapted for rigid-rotor scattering calculations. The collisional cross section calculations are performed for all transitions among the first 15 energy levels of both ortho- and para-NH and for total energies up to 1500 cm. Both para- and ortho-H colliding partners are considered. The cross sections for collision with para- and ortho-H are found to differ significantly, the magnitude of the ortho-H ones being dominant. No strong propensity rules are observed but transitions with Δk=0 are slightly favored.

Collisional excitation of NH3 by atomic and molecular hydrogen

“…The NH3-H PES is thus described as a function of three coordinates: the distance R between the center of mass of NH3 and the H atom, and two spherical angles. As the original routine of Li & Guo (2014) employs internuclear coordinates, the spherical to cartesian transformation was employed to determine the cartesian positions of the H atom in the ammonia body-fixed frame (see Bouhafs et al (2017) for the general transformation in NH2-H2). The original fit of Li & Guo (2014) was employed to generate interaction energies on a dense grid of 90,000 geometries, chosen for 30 distances R (in the range 3-20 a0) via random sampling for the angular coordinates.…”

“…In addition, we provide the first set of rate coefficients for the NH3-H collisional system. For these calculations, we use the accurate full-dimensional NH4 PES of Li & Guo (2014) which was recently employed in a NH2-H2 scattering study (Bouhafs et al 2017).…”

Collisional rates based on the first potential energy surface of the NeH+ −He system

“…The level of theory used in this work (CCSD(T)-F12/aug-cc-pVTZ) is well studied in the literature (Ajili et al 2016;Bouhafs et al 2017). However, we present in Table 1 some ab initio Table 1.…”

Sodium hydride NaH(X1Σ+) in collision with helium He(Bop1, Faye2, Hammami3 2019Chemical Physics1000View full textAdd to dashboardCite

“…19 Bouhafs et al mentioned that state-averaged geometries are reliable approximations in order to take into account the vibrational effects with rigid-rotor PESs. 20 All these findings support that rigidrotor interaction potentials constructed using experimental equilibrium geometries are not suitable to generate reliable collisional data. Therefore, to give a better insight of rigid-rotor potentials accuracy, we computed new PESs of the NaH-He system using state of the art approach.…”