Vibrational structure in the carbon 1s ionization of hydrocarbons: Calculation using electronic structure theory and the equivalent-cores approximation

Abstract

A simple ab initio procedure is used to calculate the vibrational structure observed in the carbon 1s ionization of seven hydrocarbons (methane, deuteromethane, ethane, ethene, deuteroethene, ethyne, and deuteroethyne), with good agreement between experiment and theory. The method involves use of the equivalent-cores approximation, localized holes in molecules with equivalent carbons, and the harmonic oscillator approximation. The approach provides insight into the vibrational modes of the core-ionized molecules. It is potentially useful in extracting carbon 1s ionization energies from spectra from molecules having inequivalent carbons or in finding information on inner-hole lifetimes from inner-shell spectra.