An accurate description of the ground and excited states of SiH

Abstract

The astrophysical importance of the SiH radical has motivated significant experimental and theoretical work. However, only the X 2 ⌸ and A 2 ⌬ states of SiH have been extensively investigated experimentally, while the study of higher excited states is rather limited. From a theoretical point of view, most of the studies have been focused on spectroscopic and thermochemical quantities of the ground state. The lack of accurate spectroscopic parameters (r e ,D e , e , e x e ,␣ e ,D e ,T e ) pertaining to higher excited states was the driving force of the present work, in line with our previous study of the isovalent CH molecule ͓A. Kalemos, A. Mavridis, and A. Metropoulos, J. Chem. Phys. 111, 9536 ͑1999͔͒. Using the multireference configuration interaction approach coupled with very large correlation-consistent basis sets, we have constructed potential energy curves for 18 molecular states correlating to Si( 3 P,At the same level, the potential energy curve of the ground SiH ϩ state (X 1 ⌺ ϩ ) has also been constructed. We report total energies, dissociation energies, and the usual spectroscopic constants for 28 2 H and for all states studied. Most of our results are in excellent agreement with existing experimental values. In particular, we believe that our dissociation energy for the X state, D e ϭ73.28 kcal/mol, is the most reliable reported so far in the literature.

Inelastic silicon-hydrogen collision data for non-LTE applications in stellar atmospheres

“…SiH ab initio potential energies have been calculated for only a few of the lowest lying states in different molecular symmetries (Kalemos et al 2002). Nonadiabatic coupling matrix elements have not been calculated, and this prevents performing a detailed, full quantum study of these collisions.…”

“…3 and 4, respectively. The ab initio adiabatic potentials for the four lowest 2 Σ + states and for the three lowest 2 Π states are calculated by Kalemos et al (2002), while the higher-lying state potentials are obtained by means of the model approach described by Belyaev (2013a).…”

“…Adiabatic potential energies for SiH( 2 Σ + ) states. The four loweststate potentials are the accurate ab initio data (Kalemos et al 2002), other potentials are estimated by the asymptotic approach. The labels j at correspond to the atomic channels in Table 1.…”

“…The four loweststate potentials are the accurate ab initio data (Kalemos et al 2002), other potentials are estimated by the asymptotic approach. The labels j at correspond to the atomic channels in Table 1. to treat the nonadiabatic nuclear dynamics, while for the former there is no particular order of nonadiabatic regions passed by the system, so one has to use the branching-probability-current method or something similar.…”

“…Longrange adiabatic potential energies can be estimated by means of the semi-empirical asymptotic method (Olson et al 1971) within the model approach proposed in Belyaev (2013a). Since the ionic Si + + H − state (Si + in the ground state) exists in the 2 Σ + and 2 Π molecular symmetries and spin-orbit couplings can be neglected (see Kalemos et al 2002, and references therein), only the 2 Σ + and 2 Π molecular states are included in the present consideration, and nonadiabatic transitions within each of these symmetries are treated separately.…”