Gas phase molecular relaxation probed by synchrotron radiation experiments

Abstract: This thesis presents experimental studies of gas phase molecular relaxation after excitation with synchrotron photons in the 15-35 eV and in the 70-350 eV regions. In the 15-35 eV region, molecular relaxation by neutral dissociation processes and non Franck-Condon effects in N2 and O2 molecules have been studied by means of dispersed fluorescence and photoelectron spectroscopy experimental techniques, respectively. From the dispersed fluorescence data, excitation functions for the measured atomic fluorescence spectra have been obtained. From the recorded photoelectron spectra vibrational branching ratios have been produced. The results obtained reveal that Rydberg series and singly and doubly excited valence states of the appropriate symmetry energetically accessible in the studied region and interactions between them account for most of the observed effects in these two type of experiments. In the 70-350 eV range, molecular relaxation processes resulting in fragmentation of CD4 and SF6 after absorption of synchrotron light have been studied by energy resolved electron ion coincidence technique using a multicoincidence experimental station developed by our group during the last five years for such type of experiments. The coincidence measurements yielded mass spectra from which information about the kinematics of the detected fragments has been deduced by means of Monte Carlo simulations of the experimental peak shapes. The obtained results show completely different dissociation patterns depending on the molecular electronic states studied. These patterns reflect the bonding properties of the excited orbitals and they permit the description and in some cases the identification of the different molecular relaxation pathways observed. The achievements presented in this thesis exemplify the potential of the multicoincidence station used in the reported experiments.