Lineshape Models in Inner-shell Photoelectron Spectra of Free Molecules and Clusters

Abstract

Investigating the nature of molecules and clusters is of paramount importance for our understanding of the composition and the properties of matter. X-ray photoelectron spectroscopy is one of the most powerful techniques for obtaining information at the fundamental level about molecules and clusters. Our interest in this particular kind of spectroscopy derives from its ability to probe individual atoms in a molecule and their chemical surrounding. Experimental core-level photoelectron spectra show great complexity, even for simple molecules. Hence, developing theoretical lineshapes to model and interpret experimental spectra is necessary. This thesis is devoted to the development of novel theoretical methods for modeling x-ray photoelectron spectra of molecules and clusters. It also demonstrates how these models can be used as means of extracting chemical information from experimental spectra. In this thesis, the carbon 1s photoelectron spectrum of gas-phase ethanol has been investigated by calculations, and found to be significantly influenced by the presence of a conformational equilibrium. Furthermore, theoretical models have been used to analyze inner-shell photoelectron spectra of clusters made up of either argon, methane, or methanol molecules. With the help of these models we have been able to interpret the experimental spectra in terms of chemical shifts, vibrations, and the chemical surrounding of atoms (molecules) in the cluster. The results are very interesting and will, hopefully, contribute to the development of the current understanding of the structures and properties of clusters.