University of San Francisco, USA
Title: Multiplexed synchrotron photoionization mass spectrometry: Characterization of combustion and atmospheric reactions
Biography: Giovanni Meloni
Synchrotron multiplexed photoionization mass spectrometry has proven to be a powerful and reliable experimentaltechnique to probe precise reactions relevant to both combustion and atmospheric chemistry by characterizing productsand intermediates, energetically via photoionization spectra and kinetically via time traces. The versatility of a side-sample flowtube reactor employing flash photolysis initiation of the reactions has been satisfactorily proven in recent years. The continuouslytunable synchrotron radiation is employed as the photoionization source. The synchrotron multiplexed photoionization massspectrometer at the advanced light source (ALS) of Lawrence Berkeley National Laboratory will be described and specificexamples will be presented. As a result of the multiplexing capabilities of this apparatus, each set of data comprises a threedimensionaldata block of time, mass-to-charge ratio, and photon energy as function of ion intensity. The reaction is initiatedwhen the photolysis laser is fired, i.e., this corresponds to the reaction starting time t0. The species generated in the reactionscan be followed in time and energy to provide kinetic traces and photoionization (PI) spectra, which is a plot of the ion signalof a chosen mass-to-charge ratio versus the photon energy. The PI plots are of great importance in product identificationbecause each species has specific Franck-Condon factors that translate into different shapes of the photoionization spectra. Inaddition, 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.