Collisional excitation of NH(3Σ−) by Ar: A new ab initio 3D potential energy surface and scattering calculations

Abstract

Collisional excitation of light hydrides is important to fully understand the complex chemical and physical processes of atmospheric and astrophysical environments. Here, we focus on the NH(X 3 Σ − )-Ar van der Waals system. First we have calculated a new three-dimensional Potential Energy Surface (PES), which explicitly includes the NH bond vibration. We have carried out the ab initio calculations of the PES employing the open-shell single-and double-excitation couple cluster method with non-iterative perturbational treatment of the triple excitations [RCCSD(T)]. To achieve a better accuracy, we have first obtained the energies using the augmented correlationconsistent aug-cc-pVXZ (X = T, Q, 5) basis sets and then, we have extrapolated the final values to the complete basis set limit. We have also studied the collisional excitation of NH(X 3 Σ − )-Ar at the close-coupling level, employing our new PES. We calculated collisional excitation cross sections of the fine-structure levels of NH by Ar for energies up to 3000 cm −1 . After thermal average of the cross sections we have then obtained the rate coefficients for temperatures up to 350 K. The propensity rules between the fine-structure levels are in good agreement with those of similar collisional systems, even though they are not as strong and pronounced as for lighter systems, such as NH-He. The final theoretical values are also compared with the few available experimental data.I.

Low-temperature reaction dynamics of paramagnetic species in the gas phase

“…The calculations identified a preference for maintaining the orientation of the electron spin-with transitions that conserved electron spin exhibiting larger cross sections. These findings are consistent with other studies on the NH molecule; 116,117 calculations at higher collision energies, in addition to further experimental work, are anticipated in the coming years.…”

Low-Energy Collisions of Zeeman-Decelerated NH Radicals with He Atoms

“…Trapping in the X 3 Σ – state has already been achieved via the buffer gas cooling technique − and after Stark deceleration in the metastable a 1 Δ state prior to optical transfer into the X 3 Σ – electronic ground state . Furthermore, NH is an important species in astrochemistry, and pronounced scattering resonances at temperatures below 150 K are theoretically predicted for collisions between NH and He atoms or H 2 molecules. ,− Finally, the NH molecule provides interesting prospects to control collisions or chemical reactions using externally applied electric or magnetic fields. , …”

Collision-Induced Rotational Excitation of CO2 by N(4S) Atoms: A New Ab Initio Potential Energy Surface and Scattering Calculations

“…1 They also contribute to understanding the important mechanisms in the fields of astrophysics, physics, and chemistry. 2 The research on rotational transitions (RTs) during collisions, especially the calculation of the state-to-state collisional cross sections and rate coefficients, strengthens the understanding of molecular phenomena and bridges the macroscopic−microcosmic interphase. 1 Carbon dioxide is an indispensable component in the atmospheres of terrestrial planets (TPs), Earth, Mars, and Venus, leading to the well-known strong mid-infrared (mid-IR) spectral lines.…”

“…Inelastic collisions of molecules and atoms affect a wide range of physical and chemical phenomena in the atmosphere; for example, diffusion, planetary atmospheric evolution, broadening of spectral lines, rotational and vibrational excitation, shock wave properties, etc . They also contribute to understanding the important mechanisms in the fields of astrophysics, physics, and chemistry . The research on rotational transitions (RTs) during collisions, especially the calculation of the state-to-state collisional cross sections and rate coefficients, strengthens the understanding of molecular phenomena and bridges the macroscopic–microcosmic interphase .…”