ArH2+ and NeH2+ as Global Minima in the Ar+/Ne+ + H2 Reactions: Energetic, Spectroscopic, and Structural Data

TL;DR

This study uses high-level quantum chemical calculations to identify ArH2+ and NeH2+ as global minima in their respective reactions, providing spectroscopic data to aid in their detection in the interstellar medium.

Contribution

It reveals that ArH2+ and NeH2+ are key intermediates in noble gas ion reactions and supplies detailed spectroscopic parameters for their identification.

Findings

ArH2+ and NeH2+ are global minima on their potential energy surfaces.

Spectroscopic data for NeH2+ and ArH2+ are provided, including isotopologues.

Large dipole moments suggest these ions are detectable in space.

Abstract

In light of the recent discovery of ArH+ in the Crab nebula, it is shown through high-level quantum chemical comptuations that the global minima on the Ar+/Ne+ + H2 potential energy surfaces are ArH2+ and NeH2+. Hence, ArH2+ may be a necessary intermediate in the Ar+ + H2 -> ArH+ + H formation reaction proposed in the same work where ArH+ is first reported in the Crab nebula. ArH2+ is also probably an intermediate in the alternative Ar + H+2 -> ArH+ + H reaction. Additionally, it is shown that Ne+ + H2 -> NeH+2 will subsequently most likely yield Ne + H+2 and not NeH+ + H offering a possible rationale as to the absence of NeH+ in spectra obtained from the interstellar medium (ISM). Following from this, spectroscopic data (both rotational and vibrational) are provided for NeH2+ and ArH2+ through the use of highly-accurate quantum chemical quartic and cubic force fields. All possible isotopologues are also included for 20Ne, 22Ne, 36Ar, 38Ar, 40Ar, 1H, and D. The dipole moments for these systems are quite large at 5.61 D for NeH2+ and 4.37 D for ArH2+. The spectroscopic constants provided will aid in the potential detection of these open-shell noble gas dihydride cations in the ISM.