Rotational excitation of sodium hydroxide molecule (NaOH) by helium (He) at low temperature

Abstract

This paper reports the rotational excitation of the alkali sodium hydroxide molecule (X 1 S + ) by collision with helium atom. We present a new 2D potential energy surface (PES) for NaOH-He van der Waals complex. The PES was computed at the coupled cluster level of theory with single, double and perturbative triple excitation (CCSD(T)) using the aug-cc-pVQZ basis sets for the four atoms with bound functions. A global minimum of −100.15 cm −1 is found at linear geometry He-NaOH and a local minimum of −21.94 cm −1 is located at linear geometry He-HONa. The scattering calculations were performed, via close coupling approach, for a grid of total energies up to 1500 cm −1 to ensure converged state-to-state rate coefficients for kinetic temperatures ranging from 5K up to 300K among the first 13 rotational levels. Propensity rules that favor Δj=±1 transitions are found. These new rates have great potential for NaOH detection in the interstellar medium.

Cross-section investigation of MgOH (X 2 Σ + ) fine-structure excitation by helium

“…This observation is expected from radial terms, V λ (R), of the potential energy seeing as V 1 and V 3 are the most important coefficients in terms of magnitude (see section 2, figure 3). In fact, this propensity rule aspect is characteristic of metal hydroxide crosssections seeing that similar results are observed for AlOH and NaOH cross-sections, where odd Δ j processes are predominant [21,22]. Furthermore, when we compare transitions by pairs, for ΔN = 1 we have two transitions that correspond to Δ j = 0 and Δ j = 1; as clearly seen, the excitation associated with ΔN = Δ j = 1 (0 0.5 → 1 1.5 ) is favored compared to ΔN = 1 = Δ j = 0.…”

“…Similar findings are observed for the AlOH-He interacting system, where a single minimum with a well depth of 32.68 cm −1 located at (θ = 0 • ; R = 8.2 bohr) on the side of the H atom was found [21]. However, in the case of the NaOH-He system two minima are found; a global minimum with a well depth of 100.15 cm −1 located at (θ = 180 • ; R = 7.8 bohr) on the side of the Na atom and a local minimum with a well depth of 21.94 cm −1 corresponding to the configuration (θ = 0 • ; R = 7.5 bohr) on the side of the H atom [22]. In order to explain the observed feature for the present interacting system (MgOH-He), we calculate the charge distribution over Mg, O, and H atoms using the RCCSD(T)/aV5Z level of theory as listed in table 3.…”