Structure and electronic spectra of small free radicals by quantummechanical methods

Abstract

AbstractLarge‐scale multi‐reference configuration interaction calculations are carried out for the prediction of potential energy curves of several small radicals in their ground and excited valence‐shell and Rydberg states. The Gaussian AO basis employed therein is of double‐zeta plus polarization quality and includes up to f functions and semi‐diffuse p and d functions for proper description of charge‐transfer and correlation effects. Special emphasis is placed on AH and AH2 systems and their positive and negative ions with A=Si, P and S from the second‐row and on the distinctions relative to their first‐row analogues. Various properties such as spin‐orbit splittings and radiative lifetimes are also calculated. The importance of configuration interaction treatments for the correct prediction of the ordering of states in the transition metal hydrides ScH, ScH+, TiH and TiH+ is also pointed out. The relative stability of states in a large number of AB systems with A and B from the first and/or second‐row is discussed in light of their importance for larger systems with an AB center and with respect to their photoelectron spectrum which oftentimes does not allow the direct intercombination between ground states of neutral systems and their corresponding ions. The work should demonstrate the capability of today's theoretical ab initio methods for obtaining reliable information for small systems parallel or complementary to experimental studies.