The influence of the ambient atmosphere on the dynamics of plasma expansion, besides the interaction between excited plasma and gas molecules, has been studied for specific organic aromatic compounds. To analyze the influence of air on the formation pathways of atomic and molecular species inside the plasma plume, the spectral emissions in laser-induced breakdown spectroscopy (LIBS) of 2,4,6-trinitrotoluene (TNT) and pyrene were compared at different pressure environments, from high vacuum to atmospheric pressure. Pelletized samples of the compounds were introduced in a vacuum chamber for excitation with the fourth harmonic output of an Nd : YAG laser (266 nm). The optical emission signal was collected with an optical fiber connected to a spectrograph fitted with a intensified charge-coupled device detector. Results from LIBS spectra indicate that changes in pressure level affect the kinetics of the characteristic excited species and their spatial distribution inside the plasma plume.

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