High-resolution molecular inner-shell electron spectroscopies

Abstract

High-resolution inner-shell photoelectron and resonant Auger electron spectroscopies are examined as probes of the local chemical environment of specific atoms within a molecule. The C 1s spectra of CH4 are reported at an experimental resolution better than the natural line width. The spectra were analyzed to extract the basic physical information contained in the line width, vibrational spacings, and vibrational intensities. Spectra of C2H2 were measured at a range of photon energies above the C 1s ionization threshold. The spectra were measured at the highest possible resolution to obtain intensity ratios for the symmetry split C 1s photoelectron lines. A definitive assignment of a shape resonance in the kσu photoionization channel was obtained from these results. Photoelectron spectra of ropyne, HC≡CCH3, were measured at high resolution and a definitive assignment of the three peaks was obtained from spectra of the model compounds ethane and ethyne (CH3CH3 and HC≡CH,) and theoretical calculations of the vibrational structure. Angle-resolved molecular-field split S 2p photoelectron spectra of COS are reported and the methods used to extract body-frame information from these spectra described. Resonant Auger electron spectra of CO measured at the three vibrational levels of the C 1s−12π* inner-shell excited state were obtained at about half the intrinsic line width of the inner-shell hole state. The spectra are shown to be a sensitive probe of the geometry of the intermediate excited state and allow access to portions of the final state (one valence hole) potential energy surfaces not open to Franck-Condon transitions from the ground-state neutral molecule.