Abstract
We present a diabatic representation of the potential energy curves (PECs) for the 4Π states of SH. Multireference, configuration interaction (MRCI) calculations were used to determine high-accuracy adiabatic PECs of both SH and SH+ from which the diabatic representation is constructed for SH. The adiabatic PECs exhibit many avoided crossings due to strong Rydberg-valence mixing. We employ the block diagonalization method, an orthonormal rotation of the adiabatic Hamiltonian, to disentangle the valence autoionizing and Rydberg 4Π states of SH by constructing a diabatic Hamiltonian. The diagonal elements of the diabatic Hamiltonian matrix at each nuclear geometry render the diabatic PECs and the off-diagonal elements are related to the state-to-state coupling. Care is taken to assure smooth variation and consistency of chemically significant molecular orbitals across the entire geometry domain.