Calculation of the Rydberg-state energies ofHCl

A recently developed perturbation theory method for the calculation of the energies of molecular Rydberg orbitals of diatomic molecules is extended to allow the calculation of the energies of Rydberg states above the ground state of the HCl molecule. With the exception of the lowest energy states, the calculated energies agree to within 1% with the experimental absorption spectroscopy values. This is achieved using only one selectable parameter which is determined by a simple algorithm. All other parameters are determined by the initial choice of a model system or by experiment for the spin–orbit coupling constant and the ionisation potential.