Laser-induced plasma spectroscopy of organic compounds. Understanding fragmentation processes using ion–photon coincidence measurements

Abstract

Coincidence detection is of interest to get as much information as possible about transient events occurring in laser induced plasmas. The present work is focused on coincidence ion–photon detection of laser plasmas of high-energy organic compounds (TNT and DNT) in a condensed phase irradiated with UV laser pulses using an advanced instrument for simultaneous monitoring of both types of chemical species generated. The optical emission spectrum is acquired from atoms, atomic ions and diatomic molecules, whereas the mass spectrum derives from fragment ions of the molecule. These fragments result from direct ionization or may be formed through indirect pathways. Fluence-resolved experiments showed the evolution of the main optical-mass signals in the acquired spectra for a limited energetic range, showing the different stages of lifetime of plasma: the rising thresholds and extinction of the different atomic and molecular studied species, besides the breakage of the aromatic ring and the later excitation of ionic species at a higher fluence level.