Formation of NaCl through radiative association: Computations accounting for non-adiabatic dynamics

Abstract

The radiative association (RA) rate constant is computed for the formation of the diatomic sodium chloride (NaCl) molecule in the temperature interval 1 K–30 K. At these temperatures, RA of NaCl through non-adiabatic dynamics is important. A scattering program has been implemented to carry out calculations of RA cross sections, accounting for coupled dynamics on the lowest ionic and the lowest neutral diabatic 1Σ+ states. The study shows that the non-adiabatic treatment gives a cross section that exceeds that of conventional adiabatic dynamics by one to four orders of magnitude. The contribution to the RA rate constant from Na and Cl approaching each other in the A1Π state has also been computed using an established quantum mechanical method. Ab initio data from the literature have been used for the potential energy curves, the diabatic coupling, and the electric dipole moments of NaCl.

Formation of NaCl by radiative association in interstellar environments

“…comm.). The subroutines for radiative-association and bound-state computations were implemented by Gustafsson (2020).…”

“…The continuum radial wave functions were calculated by the renormalized Numerov method (Numerov 1923). The discrete variable representation was used for the bound-state radial wave function calculation (Colbert & Miller 1992) with the same input parameters as Gustafsson (2020). The trapezoidal method was used for the integration over collision energy in Eq.…”

“…Temperature-dependent RA rate coefficients belong to the input data for various interstellar-environment models and, because they are very difficult to measure experimentally, their accurate calculations are of increased importance. In the recent study Gustafsson (2020), the rate coefficients for radiative association of sodium with chloride in the temperature range 1-30 K were calculated. In that fully quantum mechanical approach, the nonadiabatic coupling between the ionic and atomic electronic states was accounted for, thus resulting in two-channel coupled calculations.…”

“…Our fully quantum mechanical study follows that of Gustafsson (2020) and concentrates on the conditions present in some environments, where the NaCl molecules have been observed. For this purpose, it significantly extends the temperature range to 30-750 K, which should cover local temperatures in the CRL 2688 shocks (Highberger et al 2003), the IRC+10216 expanding shell (Agúndez et al 2012), and the accretion disk of Orion SrcI (Ginsburg et al 2019).…”

Formation of CO through C (2s 22p 2 3P) and O (2s 22p 4 3P) Radiative Association

“…These theories and methods of radiative association for diatomic molecules and ions are well established and summarized in the work of Nyman et al (2015), and have been used for dealing with many diatomic molecules and ions, such as CO , PO (Andreazza et al 2016), SiO (Cairnie et al 2017), CS (Forrey et al 2018), CO + (Zámečníková et al 2020), MgO (Bai et al 2021), + N 2 (Qin et al 2021), AlO (Bai et al 2022), etc. In addition, recent developments in the theories and methods for radiative association include the Sturmian quantum kinetic theory (Forrey 2015), the surface-hopping model of spontaneous electronic transitions (Szabó & Gustafsson 2017), the extension of radiative association for local thermal equilibrium (Gustafsson & Forrey 2019), and the treatment of non-adiabatic couplings (Gustafsson 2020).…”