Laser surface interaction for the generation of heavy cations and nanoparticles and their gas-phase studies

Abstract

In this thesis, we studied the recombination of the Azulene (C H ), Acenaphthene (C H ), Anthracene (C H ), and Pyrene (C H ) ions with electrons, with the FlaPI (Flowing Afterglow with Photo Ions) method. The ionic species in the flowing afterglow are spatially characterized by a quadrupole mass spectrometer and the electron concentration is measured by means of a movable Langmuir probe. We developed a new method L2DI (laser desorption / laser ionization) based on the FlaPI method for studying the recombination kinetics of much larger PAHs. We measured the PAH ions concentration decay in time in function of the presence of electrons. We assessed different methods for recovering the recombination rate coefficient. Preliminary results obtained with L2DI method is reported in this thesis. We used a CRESU (Cinétique de Réaction en Ecoulement Supersonique Uniforme) reactor to produce the nanoparticles of PAH molecules at low temperature, which are deposited onto surfaces. The samples were then analyzed ex-situ by AFM (Atomic Force Microscopy) in tapping mode. This method of characterization was tested previously by analyzing small soot particles generated by a diffusion flame and deposited onto mica surfaces.