The use of rovibrationally excited NO photofragments as trace nitrocompounds indicators

Abstract.

A one-color laser performs photolysis of nitrocompounds and laser-induced fluorescence to monitor the generated NO photofragments and to sensitively detect vapor trace amounts of nitrocompounds. The NO is monitored via excitation and emission through A²Σ⁺(v^′=0)?X²Π(v^′′=2-0) and A²Σ⁺(v^′=0)?X²Π(v^′′=0,1) transitions, respectively. It is found that NO photofragments populate the vibrationless ground state and also the first two vibrationally excited states. The analytical performance of the method is demonstrated on 2,4 dinitrotoluene (DNT) via excitation through A²Σ⁺(v^′=0)?X²Π(v^′′=2). The achieved limits of detection are 3.7 and 2.7 parts per billion (ppb) by weight of gaseous DNT in 100 and 500 Torr of air, for 30 s integration time. The application of this scheme for trace nitrocompound detection has the advantage that no background of ambient ground-state NO interferes and that the fluorescence is collected at shorter wavelengths than the exciting radiation, precluding background fluorescence.