Giovanni Meloni
University of San Francisco, USA
Title: Synchrotron Multiplexed Photoionization Mass Spectrometric Investigations in Combustion and Atmospheric Chemistry
Biography
Biography: Giovanni Meloni
Abstract
Synchrotron Multiplexed Photoionization Mass Spectrometry has proven to be a powerful and reliable experimental technique to probe reactions relevant to both combustion and atmospheric chemistry by characterizing products and intermediates, energetically via photoionization spectra and kinetically via time traces. The versatility of a side-sample flow tube reactor employing flash photolysis initiation of the reactions has been satisfactorily proven in recent years. The synchrotron multiplexed photoionization mass spectrometer at the Advanced Light Source (ALS) of Lawrence Berkeley National Laboratory will be described and specific examples will be presented. As a result of the multiplexing capabilities of this apparatus, each set of data comprises a three-dimensional data block of time, mass-to-charge ratio, and photon energy as function of ion intensity. The reaction is initiated when the photolysis laser is fired, i.e., this corresponds to the reaction starting time t0. The species generated in the reactions can be followed in time and energy to provide kinetic traces and photoionization (PI) spectra, which is a plot of the ion signal of a chosen mass-to-charge ratio versus the photon energy. The PI plots are of great importance in product identification because each species has specific Franck-Condon factors that translate into different shapes of the photoionization spectra. In addition, photoionization spectra not only assist in product identification, but also provide information relating to the relative concentrations of products of interest through the measurement of their photoionization cross-sections.