Core Excitation and Ionization of Molecules

A progress report is given on recent experimental studies of core excitation and inoization of free-molecules in the VUV and soft x-ray (50 to 2600 eV) by electron impact and x-ray photoabsorption (XAS) techniques. The current capabilities of inner shell electron energy loss spectroscopy (ISEELS) and XAS for gas phase studies are compared, with focus on: Dipole versus non-dipole excitations, electric dipole oscillator strength determination, and bond length correlations. Recent studies of ionic fragmentation of molecules induced by tuned x-rays are discussed with regard to the possibility of site-selective fragmentation via core excited state. Using organometallic compounds as an intermediate, connections are made between the core excitation spectra of free molecules and those of surface absorbed molecules, as measured by near-edge x-ray absorption fine structure (NEXAFS) or reflection near-edge energy-loss fine structure (NEELFS) spectroscopies.