Perturbation theory model of molecular Rydberg orbitals Application to polyatomic molecules; water, formaldehyde, acetone and acetaldehyde

Abstract

A perturbation theory method for the calculation of the Rydberg orbitals 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 Coulombic potential affecting the Rydberg electron in the atom and in the molecule. The potential recently developed for diatomic molecules is generalised for polyatomic molecules and a computational scheme is presented. The method is applied to the four molecules in the title and the 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 correct order of molecular field splitting of Rydberg orbitals of the same atomic l quantum number. It is found that for the molecules with at least a rotational axis of symmetry the spatial distribution of the orbitals 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 distributions. There is a shift from atomic to molecular distribution, caused by strong mixing of basis orbitals of different l quantum numbers, when the molecule has less than rotational symmetry. The results are compared with a number of empirical observations made concerning molecular Rydberg orbitals.