Theoretical study of ArH+ dissociative recombination and electron-impact vibrational excitation

Abstract

Cross sections are presented for dissociative recombination and electron-impact vibrational excitation of the ArH + molecular ion at electron energies appropriate for the interstellar environment. The R-matrix method is employed to determine the molecular structure data, i.e. the position and width of the resonance states. The cross sections and the corresponding Maxwellian rate coefficients are computed using a method based on the Multichannel Quantum Defect Theory. The main result of the paper is the very low dissociative recombination rate found at temperatures below 1000K. This is in agreement with the previous upper limit measurement in merged beams and offers a realistic explanation to the presence of ArH + in exotic interstellar conditions.

Computational Characterization of Astrophysical Species: The Case of Noble Gas Hydride Cations

“…In Table 3, the equilibrium distances and corresponding well depths are collected for all NgH + under study, and compared with those reported previously. In particular, when the results obtained in the present work are compared with the available in the literature, the trends observed are depended on the 2016), (c) Gerivani et al (2015), (d) Stolyarov and Child (2005), (e) Alekseyev et al (2007), and (f) Abdoulanziz et al (2018).…”

“…Previous theoretical studies on the ground state ArH + have also determined equilibrium energies and bondlengths from MP2, CCSD(T), and MRCI calculations (Hirst et al, 1992;Stolyarov and Child, 2005;Alekseyev et al, 2007;Coxon and Hajigeorgiou, 2016;Abdoulanziz et al, 2018), and in Table 3 some of them are listed. One can see that both CCSD(T)/CBS [56] and MRCI+Q values predict stronger Ar-H + interaction by 119 cm −1 and shorter bondlength by 0.0009 Å than the most recent results published so far (Abdoulanziz et al, 2018). (blue lines) and ArH + (green lines) as a function of R. Electric dipole moments µ are with respect to Ng atom as origin, while µ ′ with respect to the HeH + center of mass are also given for comparison reasons from (a) Hirst et al (1992), (b) Gerivani et al (2015), and (c) Juřek et al (1995).…”

“…FIGURE 3 | Total (left) and potential (right) energies of NeH + (upper) and ArH + (lower) molecules as a function of R bondlength obtained from the present CCSD(T)/CBS[56] calculations, and comparison with data available in previous studies from (a) Hirst et al (1992), (b) Coxon and Hajigeorgiou (2016),(c) Gerivani et al (2015),(d) Stolyarov and Child (2005), (e)Alekseyev et al (2007), and(f) Abdoulanziz et al (2018).…”

“…Later on, the rovibrational bands of the fundamental state of ArH + in the infrared (IR) spectrum have been assigned using experimentally synthesized molecules (Brault and Davis, 1982 ), providing its spectroscopic constants. More recently, several theoretical studies have been reported including ab initio or spectroscopic-derived potential curves of its ground state up to dissociation (Hirst et al, 1992 ; Coxon and Hajigeorgiou, 2016 ), as well as electronically excited states for investigating its photodissociation processes (Stolyarov and Child, 2005 ; Alekseyev et al, 2007 ; Abdoulanziz et al, 2018 ).…”

Relaxation of ArH+by collision with He: Isotopic effects

“…(1) and (2) the produced diatom can be formed in an excited vibrational state (Denis-Alpizar et al 2017). The vibrational excitation of ArH + by electron-impact was investigated (Abdoulanziz et al 2018); however, the only theoretical study that reports the rate coefficients for the collision of ArH + with He (Bop et al 2017) was done using a two-dimensional potential energy surface (PES) at the explicitly correlated coupled cluster with single, double, and perturbative triple excitations (CCSD(T)-F12) level of theory where the diatomic molecule was considered as a rigid rotor. To our knowledge, a full three-dimensional PES for the ArH + +He complex does not exist; therefore, the vibrational relaxation for this collision has not been considered so far.…”