Vibrational Structure and Vibronic Coupling in the Carbon 1s Photoelectron Spectra of Ethane and Deuteroethane

The carbon 1s photoelectron spectrum of ethane, C 2 H 6, has been measured at a photon energy of 329 eV and an instrumental resolution of 70 meV. The spectrum shows a rich vibrational structure which is resolved using least-squares fits to the data. Only C−H stretching and CCH bending modes contribute significantly to the spectrum. The lack of excitation of the C−C stretching mode is explained in terms of changes in hybridization at the spectator carbon. To investigate the possibility of incomplete localization of the core hole, the spectra of C 2 H 6 and C 2 D 6 were measured at higher experimental resolution (35 meV). The spectra are accurately fit by a model based on ab initio calculations of the vibrational energies and the geometry changes following ionization, and including vibronic coupling of the two degenerate, localized hole states. A small splitting on the order of 10−20 meV is found for the 2 A 2u and 2 A 1g core-ionized states.