PERTURBATION-THEORY MODEL OF MOLECULAR RYDBERG ORBITALS - APPLICATIONTO POLYATOMIC-MOLECULES - WATER, FORMALDEHYDE, ACETONE AND ACETALDEHYDE

A perturbation theory method for the calculation of the Rydberg orbita ls of polyatomic molecules, their energies and physical distribution, is developed. A set of atomic orbitals of a model atom is perturbed by a potential representing the difference between the one-electron Coul ombic potential affecting the Rydberg electron in the atom and in the molecule. The potential recently developed for diatomic molecules is g eneralised for polyatomic molecules and a computational scheme is pres ented. The method is applied to the four molecules in the title and th e results are compared with experimental data and previous theoretical results on the molecules. The method is found to give good agreement for the energies of the Rydberg states and consistently predict the co rrect order of molecular held splitting of Rydberg orbitals of the sam e atomic I quantum number. It is found that for the molecules with at least a rotational axis of symmetry the spatial distribution of the or bitals is not much different from the atomic precursors. For the case of the lowest symmetry molecule acetaldehyde it is found that orbitals obeying the Rydberg formula have shapes very different from atomic di stributions. There is a shift from atomic to molecular distribution, c aused by strong mixing of basis orbitals of different l quantum number s, when the molecule has less than rotational symmetry. The results ar e compared with a number of empirical observations made concerning mol ecular Rydberg orbitals.