A theoretical study of the A 1Π←X 1Σ+ system of SiH+

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Abstract
Theoretical studies have been performed on the X 1Σ+ and A 1Π states of SiH+. The complete active space, self‐consistent field (CASSCF) and many‐body perturbation theory (MBPT) methods were employed for the X 1Σ+ and state while the A 1Π excited state potential energy curve was studied by using CASSCF, multireference contracted configuration interaction (MR CCI, (MR CEPA), and coupled pair functional (CPF) approaches. Excellent agreement was obtained with experiment for the X state spectroscopic parameters (CASSCF): re=1.505 (1.50 Å; D0=3.30 (3.22±0.03) eV; ωe=2161 (2155) cm−1; ΔG1/2=2093 (2089) cm−1, with experimental values within parentheses. The shape of the potential curve for the A state was very sensitive to the basis set and higher order electron correlation. The best results, obtained with the CPF method, were re=1.888 (1.871) Å; D0=0.15 (0.15±0.03) eV; ωe=438 (448) cm−1; ΔG1/2=318 (389) cm−1. The computed f0,0 oscillator strength for the A←X transition was 1.2×10−3 which falls between the laboratory value, (2.4±1)×10−3, and a value obtained from the solar spectrum, 0.5×10−3. The computed life time for the v’=0 state is 956 ns to be compared to the experimental value 1025±80 ns.