Speaker: Mahmoud Abu-Samha (IFA) Title: Insight to intermolecular bonding from core-level photoelectron spectroscopy Time: Today, 15.15 Place: Fysisk Auditorium Abstract: Molecular clusters are conglomerates of molecules such that the diameter of the cluster typically lies in the range of 1-100 nm. The clusters are held together by three main mechanisms of intermolecular bonding: dispersion interactions, electrostatic interactions, and hydrogen bonding. Molecular clusters are of interest because they form a sensitive testing ground for our understanding of molecular interactions at interfaces, in the bulk, and in the transition zone between these. Moreover, the study of the geometric structure and stability of molecular clusters, as a function of size, may give important information on nucleation and crystal-growth phenomena. Synchrotron-based core-level spectroscopy appears as a promising tool for the exploration of structure and properties of atomic and molecular clusters. This class of techniques include X-ray Absorption Spectroscopy (XAS), Auger Electron Spectroscopy (AES), and X-ray Photoelectron Spectroscopy (XPS). Core-level XPS is particularly promising for studying molecular clusters because the spectra are less complicated than the XAS and AES, and yet carry information about the local surroundings of the ionization site. In this talk, I will discuss the potential of core-level photoelectron spectroscopy as a technique for studying neutral, gas-phase molecular clusters, with particular focus on intermolecular bonding mechanism. Peter Staanum and Nicolai Nygaard