A theoretical investigation of the adiabatic and diabatic behavior of the core-excited states of CH 3SH

Abstract

The adiabatic and diabatic behavior of the first pair of core-excited states of CH 3SH have been studied. The potential energy curves (PECs) obtained for small geometry changes simulating various vibrational modes have been calculated by an SCF-CI procedure. Though adiabatic PECs display a complex behavior, the diabatic ones exhibit simple trends. For all types of elementary motion, one diabatic PEC always has a dominant σ* (SC) character associated with p (valence and Rydberg) character on S, while the second one bears σ* (SH) and s (valence and Rydberg) characters on S. The relative variations of these components may be explained using a simple qualitative model based on diabatic MO correlations. It is shown that the diabatic state that is likely to yield a sizeable centrifugal barrier bears at the same time σ* (SC) character. The actual nature of the matrix elements used for obtaining diabatic states allows for establishing a parallel with the behavior of CH 3SH −.