ASSIGNMENT OF PERTURBATIONS IN THE $D^{1}\Pi - X^{1}\Sigma^{+}$ SYSTEM OF SiS

Abstract

Spectroscopice perturbations are characterized in terms of interaction matrix elements which, within the framework of the Born-Oppenheimer approximation may in turn be represented as a product of electronic, vibrational, and rotational factors. The vibrational and rotational dependence of interaction matrix elements can provide a wealth of information about poorly characterized perturbing states: perturbing state symmetries can be determined from the J dependence of interaction matrix elements; absolute energies of perturbing states with respect to the ground state of a molecule can be determined from the vibrational dependence of matrix $element.^{1}$ Spectra of the $D^{1}\Pi - X^{1}\Sigma^{+}$ system of SiS reported by Lagerqvist et al.,$^{2}$ in 1952, have been reanalyzed using a least squares procedure. It was necessary to reassign the J numbering in some Q branches. Low lying states of SiS arise from the following configurations: [FIGURE] A determination of the absolute vibrational numbering of the $e^{3}\Sigma^{-}$ state and a distinction between $^{1}\Delta$ and $^{3}\Delta$ perturbations are possible from least squares fitted matrix elements.