Valence states of the SiS molecule: Analysis of perturbations in the A1Π- X1Σ + system

Abstract

The results of a detailed rotational analysis of bands of the A 1Π- X 1Σ + systems both of 28SiS and of 30SiS are given. Perturbations caused by interactions with two singlet states, D 1Δ and C 1Σ −, and with two triplet states, e 3Σ − and d 3Δ, are analyzed. The use of three different methods, based (i) on Franck-Condon factors, (ii) on isotope shifts, and (iii) on the identification of perturbing levels which cross more than one vibrational level of A 1Π, to determine the vibrational numbering in the perturbing states is examined and for three of the above electronic states an unambiguous numbering is derived. Two alternative consecutive vibrational numberings for D 1Δ are suggested. Method (i) is unreliable here, because of the very high vibrational quantum numbers of the levels that perturb A 1Π. RKR potentials are constructed and thence, with calculated Franck-Condon factors, values of the electronic interaction constants are derived for the interactions between the perturbing states and A 1Π. The values so obtained are compared with those for CO, CS, and SiO, and with estimates from ab initio calculations.