Relationship between polarization-averaged molecular-frame photoelectron angular distributions and geometry

We present a theoretical study of vibrationally resolved and unresolved molecular-frame photoelectron angular distributions (MFPADs) resulting from K-shell photoionization of N2, CO, C2H2, NH3, CH4, CF4, BF3, and SF6 in the range of photoelectron energies 0–500 eV. We show that the MFPADs of NH3 and CH4, averaged over the polarization direction, image the molecular geometry at very low energies but also at selected higher energies. For all other molecules, the MFPADs do not image the system’s geometry. However, for molecules containing heavy atoms in the periphery, CF4, BF3, and SF6, and for N2 and CO, the polarization-averaged MFPADs reflect the partial accumulation of the photoelectron density in the region surrounded by the peripheral atoms. For energies at which this accumulation occurs, the MFPADs encode information about the three dimensional arrangement of the system. In general, the polarization averaged MFPADs remain quite anisotropic even at photoelectron energies as high as 500 eV