Core-Hole Molecular Frame X-Ray Photoelectron Angular Distributions as Molecular Geometry Probes

We present experimental and theoretical results for the angular dependence of electrons ejected from the core orbitals of ethane (C$_{2}$H$_{6}$) and tetrafluoromethane (CF$_{4}$) in an effort to understand the origin of the imaging effect by which the molecular frame photoelectron angular distributions (MFPADs) for removing an electron from a 1s orbital effectively image the geometry of a class of molecules. At low energies, our calculations predict the same imaging effect in C$_{2}$H$_{6}$ previously found in CH$_{4}$, H$_{2}$O and NH$_{3}$. By contrast, in experiment and calculations CF$_{4}$ displays an anti-imaging effect, whereby the electron ejected by core photoionization has the tendency to avoid molecular bonds, if averaged over directions of polarization of the incident X-ray beam. Our measurements employ the COLTRIMS method and the calculations were performed with the Complex Kohn Variational method.