Spectroscopic parameters and molecular constants of 75As32S+ and 75As34S+

Abstract

The ground state X3Σ- and low-lying excited electronic state A1Π of AsS+ ion are investigated employing the full valence complete active space self-consistent field method combined with the highly accurate valence internally contracted multireference configuration interaction (MRCI) approach. The basis set used in the calculations is Dunning correlation-consistent basis set, aug-cc-pV5Z. To improve the quality of the potential energy curves (PECs), three kinds of corrections are considered in the present work. First, the Davidson modification is adopted to deal with the size-extensity errors from the MRCI calculations. Then, relativistic correction is calculated by the second-order Douglas-Kroll Hamiltonian approximation at the level of cc-pVQZ basis set. Finally, to eliminate the truncation errors of the basis set, the PECs of the two electronic states for each species are extrapolated to the complete basis set limit by the two-point energy extrapolation scheme. Two large basis sets, i.e., aug-cc-pVQZ and aug-cc-pV5Z, are used to perform the extrapolation calculations. With the aid of VIBROT program, all the PECs of X3Σ- and A1Π obtained here are fitted to the analytical forms, which are used to derive the spectroscopic parameters (De, D0, ωeχe, αe and Be) of 75As32S+ and 75As34S+. The effects of the Davidson modification, relativistic correction and basis set extrapolation are discussed respectively. The results indicate that the quality of almost all the spectroscopic parameters is improved by considering these corrections, which exhibit excellent agreement with the experimental data. Besides, the first 10 vibrational states for the two electronic states of 75As32S+ and 75As34S+ are determined when the rotational quantum number J equals zero. For the first 10 vibrational states, the vibrational level G(ϒ), inertial rotation constant Bv, and centrifugal distortion constant Dv are evaluated when J=0.