VIBRATIONAL STRUCTURE IN THE CARBON 1S IONIZATION OF HYDROCARBONS - CALCULATION USING ELECTRONIC-STRUCTURE THEORY AND THE EQUIVALENT-CORES APPROXIMATION

A simple ab initio procedure is used to calculate the vibrational stru cture observed in the carbon 1 s ionization of seven hydrocarbons (met hane, deuteromethane, ethane, ethene, deuteroethene, ethyne, and deute roethyne), with good agreement between experiment and theory. The meth od involves use of the equivalent-cores approximation, localized holes in molecules with equivalent carbons, and the harmonic oscillator app roximation. The approach provides insight into the vibrational modes o f the core-ionized molecules. It is potentially useful in extracting c arbon 1 s ionization energies from spectra from molecules having inequ ivalent carbons or in finding information on inner-hole lifetimes from inner-shell spectra. (C) 1998 American Institute of Physics.