PRESSURE EFFECTS ON VACUUM ULTRAVIOLET SPECTRA.

Author Institution: Bell Telephone Laboratories Incorporated, Murray HillIt has been found that certain features in the vacuum ultraviolet spectra $(2000-1300{\AA})$ of many molecules are considerably modified in the presence of modest pressures (100-150 atm) of either nitrogen or helium perturber gas. Specifically, if a transition is a valence shell one, then the pressures employed here are far too low to cause any shift or broadening of the spectral features, whereas at the same pressures, Rydberg transitions respond by broadening completely asymmetrically to the high frequency side. The asymmetric broadening is thought to be due to the exchange repulsion experienced by an adsorber-perturber pair when the absorber increases its effective diameter by several ${\AA}$, as occurs in Rydberg excitations. Using this simple technique, various bands in the spectra of oxygen, benzene, ethylene, acetone, nitric oxide, and norbornadiene have been classified as either valence shell or Rydberg. Pressurizing the Rydberg excitation of methyl iodide leads to the appearance of satellite bands displaced to the blue of the unperturbed transition