First electronically excited state of the water–argon complex: an analytical fit to the CASPT2 potential

An analytical force field for the study of water photolysis and the cage effect in argon environment is constructed. A set of more than 200 ab initio CASPT2 points mapping important regions on the first exited potential energy surface of the H2O–Ar cluster is fitted to a physically justified empirical model and the quality of the fit is discussed.