Theoretical study of the ArH+ photodissociation

Abstract

The multireference Spin–Orbit (SO) Configuration Interaction (CI) method in its Lambda–S Contracted SO–CI (LSC–SO–CI) version is employed to calculate potential energy curves for the ground and low-lying excited states of the ArH⁺ cation. For the first time, electric dipole moments are also computed in the approach, including SO coupling for transitions to the states responsible for the first absorption continuum (A-band) of ArH⁺. On this basis, the partial and total absorption spectra in this energy range are obtained. It is shown that absorption in the A-band is dominated by the parallel A¹Σ⁺ ← X¹Σ⁺ transition. In the low-energy part of the band (<95 × 10³ cm⁻¹) the absorption is caused by the perpendicular B¹Π ← X¹Σ⁺ excitation, but transitions to the b³Π_0⁺,1 states are also not negligible. The branching ratio Γ for the final photodissociation products is calculated and it is shown to increase smoothly from 0 in the red tail of the band to 1 at E ≥ 10⁵ cm⁻¹. The latter value corresponds to the exclusive formation of the spin-excited Ar⁺(²P_1/2) ions, and thus leads to the inverse population of the Ar⁺(²P_1/2 − ²P_3/2) ion states.