A novel contrast of the reactions of 2,4,6-trinitrotoluene (TNT) in atmospheric-pressure O2 and N2 plasma: Experimental and theoretical study

Negative-mode ion/molecule reactions of 2,4,6-trinitrotoluene (TNT) generated in atmospheric-pressure O-2 and N-2 corona discharge plasmas were studied. In the O-2 plasma, charge transfer reaction, O-2(-center dot) + TNT -> O-2 + TNT-center dot, was found as the major reaction channel. The proton abstraction reaction, O-2(-center dot) + TNT -> O2H center dot + [TNT - H+](-), was negligible, which is in sharp contrast to the formation of [DNT - H+] and [NT - H+] (DNT: 2,4-dinitrotoluene and NT: 2-nitrotoluene). TNT-center dot further reacts with O-3 to form [TNT-NO center dot](-) and [TNT-OH center dot](-). In atmospheric-pressure N-2 plasma, TNT-center dot was detected as the dominant ion with no fragment ions. Adiabatic electron affinity (EA) of TNT was estimated by density functional theory (DFT) calculations as 2.08 eV. The precise mechanisms of the charge transfer, O-2(-center dot) + TNT -> TNT-center dot + O-2 , and TNT-center dot + O-3 were examined by the frontier-orbital theory. The charge transfer may be attained by the specific O-2(-center dot) coordination on the benzene ring of TNT. Reaction paths of [TNT + O-3](-center dot) leading to [TNT - OH center dot](-) and [TNT - NO center dot](-) were investigated by bimolecular reaction of TNT center dot- with O-3. The formation of [TNT-NO center dot](-) was found to be energetically more favorable than that of [TNT-OH center dot](-). (C) 2020 Published by Elsevier B.V.