Potential energy curves (PECs), dipole moments (DMs) and transition dipole moments (TDMs) of the X²Π, a⁴Σ^-, A²Σ^-, b⁴Π, B²ΣΔ, C²Σ⁺, D²Π, 2²Σ⁺ states correlating with the three lowest dissociation channels of AsH⁺cation are calculated by using the multireference configuration interaction (MRCI) method. The Davidson corrections, core-valence (CV) correlation and spin-orbit coupling (SOC) effects are considered. The aug-cc-pV5Z all-electron basis set of H atom and the aug-cc-pwCV5Z-PP pseudopotential basis set of As atom is selected in the calculation.
In the complete active space self-consistent field (CASSCF) calculation, H (1s) and As (4s4p) shell are selected as active orbital, As (3p3d) shells are selected as closed orbital, which keeps doubly occupation, the rest electrons are in the frozen orbital. In the MRCI calculation, As (3p3d) shells are used for CV correlation, the calculation accuracy can be improved. SOC effects are considered with Breit-Pauli operators.
All calculated states are bound states. The X²Π is the ground state, which is a depth potential well, the dissociation energy is 3.100 eV. The b⁴Π, C²Σ⁺ and D²Π are weakly bound states. The spectroscopic parameters are obtained by solving radial Schrodinger equation. To the best of our knowledge, there have not any study on the spectroscopy of AsH⁺ cation. Compared with Ⅴ-hydride cations MH⁺ (M = N, P, As), the order of the energy levels of the low-lying states for three ions are same. The dissociation energy and harmonic frequency both decreases with increase the atomic weight of M.
At spin-free level, the PECs of b⁴Π and B²Δ states cross at about 1.70 Å. When SOC effects are taken into account, according to the rule of avoid-crossing, the B²Δ_3/2 and B²Δ_5/2 states change to the double potential wells, and the avoided crossing between the B²Δ_3/2 (B²Δ_3/2) and b⁴Π_3/2 (b⁴Π_5/2) states is observed, respectively. The transition dipole moments (TDMs) of the A²Σ^-→X²Π,a⁴Σ_1/2^-,X²Π_1/2 and A²Σ_1/2^-→X²Π_1/2 transitions are also calculated. The TDM at equilibrium distance of the a⁴Σ_1/2^-→X²Π_1/2 spin-forbidden reaches 0.036 Debye, therefore, the SOC effect plays an important role. Based on the accurately PECs and PDMs, the Franck-Condon factors, spontaneous radiative coefficients and spontaneous radiative lifetimes of the A²Σ^-→X²Π,a⁴Σ_1/2^-→和X²Π_1/2 and A²Σ_1/2^-→X²Π_1/2 transitions are also calculated.