Electron-gas model for open shell–closed shell interactions. I. Application to the emission spectra of the diatomic noble-gas halides

Abstract

We extend the electron-gas method of calculation of interatomic forces to the case of one open shell atom interacting with one closed shell atom. The simple case chosen for investigation is the class of noble-gas monohalide excimers. We concentrate on their spectra as numerous data have recently become available. We describe how to extend the electron-gas model to deal with one open shell atom, emphasizing how to set up the two molecular symmetry states. The two main sets of transitions in the noble-gas monohalide spectra are interpreted. For the short-wavelength set, we show that the near degeneracy of the Σ and Π excited ionic states found in a recent configuration interaction study of KrF also takes place in the other members of the molecular class. For the long-wavelength set, we give a simple explanation for the relative pressure sensitivity. Our conclusion is that the electron-gas model can be extended to the calculation of the Π state, but not the Σ state, resulting from the interaction between an atom with one open p shell and a closed shell atom.