Absorption spectra of alkali halide molecules in the vacuum ultraviolet

Abstract

The ultraviolet (UV) and vacuum ultraviolet (VUV) absorption spectra of three alkali halide molecules CsF, CsCl, and RbF have been determined experimentally. The longest wavelength absorption features are attributed to bound–free or bound–weakly bound transitions where the upper state correlates to ground state alkali and halogen atoms. The absorption at shorter wavelengths is due to transitions from the bound ground state to excited states that correlate to excited alkali and neutral halogen atoms. The covalent repulsive curves of CsF were found to have a close resemblance to the curve corresponding to the first ionization potential of CsF. The peak absorption cross sections are similar for the CsF and RbF molecules. CsCl molecules have a three to four times larger absorption cross section for the analogous upper states. The absorption oscillator strengths have been determined from the measured absorption cross sections, and are compared to those of other alkali halide molecules that have UV absorptions.