A theoretical study of the solvent shift to the transition in formaldehyde with an effective discrete quantum chemical solvent model including non-electrostatic perturbation

Abstract

An effective solvent model with an explicit solvent representation is described. The modelled perturbation of the solute due to the discrete solvent molecules includes polarization and a non-electrostatic interaction. The latter depends on the overlap between the solute wave function and the solvent orbitals and approximately accounts for the restraint the Pauli principle puts on the space which the solute wave function is allowed to occupy, and consequently also models the exchange repulsion between solute and solvent. The wave function of the solute is a linear combination with variational coefficients of orthogonal states obtained with the complete active space state interaction (CASSI) method. With this model, the solvent shift to the n→ π* transition in hydrated formaldehyde is studied and the analysis of the results investigates the different contributions to the total shift; the non-electrostatic interaction is found to be of significance and capable of coupling with the electrostatic interaction in qualitatively different ways for the ground and first excited state. Solvent density distributions for hydrated formaldehyde are also reported.