Vibronic structure in the carbon 1s photoelectron spectra of HCCH and DCCD- art. no. 012506

The carbon is photoelectron spectra of HCCH and DCCD have been measured at a photon energy of 330 eV and an instrumental resolution about half the nat ural linewidth. The vibrational structure in the spectra has been analyzed in terms of a model in which the parameters are the force constants for car bon-carbon and carbon-hydrogen stretching in the core-ionized molecules and the changes in bond lengths between the core-ionized and neutral molecules . Within this model. three different approaches to core-hole localization h ave been considered. Treating the core hole as completely localized, with t he molecular motion following the diabatic energy surfaces, does not descri be the data correctly. Treating the con hole as completely delocalized, wit h the molecular motion following the adiabatic surfaces. gives a good fit t o the spectra but leads to zero-point energies that are completely unreason able. A fit that takes into account vibronic coupling between the Vibration al manifolds of the (2)Sigma (+)(u) and (2)Sigma (+)(g) electronic states o f the ion gives good agreement with the data and leads to reasonable molecu lar parameters. Ab initio calculations of the molecular properties of the c ore-ionized molecule give results that are in excellent agreement with thos e obtained from this fit. The lifetime width for the carbon 1s hole state i s 106 +/- 2 meV, significantly higher than for CH4 (95 +/- 2 meV). This res ult is not in accord with predictions based on a one-center model of Auger decay.