Observation of atomic carbon during photodissociation of nitrotoluenes in the vapor phase

Hergen Eilers; Helena Diez-y-Riega

doi:10.1117/12.2050016

29 May 2014 Observation of atomic carbon during photodissociation of nitrotoluenes in the vapor phase

Hergen Eilers, Helena Diez-y-Riega

Proceedings Volume 9073, Chemical, Biological, Radiological, Nuclear, and Explosives (CBRNE) Sensing XV; 90730T (2014) https://doi.org/10.1117/12.2050016
Event: SPIE Defense + Security, 2014, Baltimore, MD, United States

Abstract

We perform laser-induced photodissociation fluorescence spectroscopy on mononitrotoluenes (MNTs) and dinitrotoluenes (DNTs) in the vapor phase and observe the spectrally overlapping fluorescence from nitric oxide (NO) and carbon (C). Energy-dispersive x-ray spectroscopy (EDS) and Raman spectroscopy of deposits found in the sample chamber confirm the presence of carbon. By comparing the observed fluorescence intensities with the Franck-Condon factors for NO, we are able to identify the presence or absence of fluorescence from carbon. 2-nitrotoluene and 4- nitrotoluene show carbon fluorescence for gate delays of up to 500 ns, while 2,4-dinitrotolune, 3,4-dinitrotolune, and 2,6-dinitrotolune show carbon fluorescence for gate delays of at least up to 1500 ns. The spectroscopic signal from atomic carbon in the vapor phase is observed at concentrations as low as 10 ppt. Based upon the observed S/N, detection at even lower concentrations appears feasible. Several non-nitrotoluene molecules including nitrobenzene, benzene, toluene, and CO₂, are tested under identical conditions, but do not show any carbon emission. The presence of extra NO (simulation of NO pollutants) in the samples improves the S/N ratio for the detection of carbon. Energy transfer from laser-excited molecular nitrogen to NO, multiple decomposition channels in the electronic excited state of the nitrotoluene molecules, and interaction of NO with the excited-state decomposition process of the nitrotoluene molecules may all play a role.

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Hergen Eilers and Helena Diez-y-Riega "Observation of atomic carbon during photodissociation of nitrotoluenes in the vapor phase", Proc. SPIE 9073, Chemical, Biological, Radiological, Nuclear, and Explosives (CBRNE) Sensing XV, 90730T (29 May 2014); https://doi.org/10.1117/12.2050016

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KEYWORDS

Luminescence

Carbon

Molecules

Nitrogen

Molecular lasers

Fluorescence spectroscopy

Spectroscopy

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