Dinitrobenzene detection by use of one-color laser photolysis and laser-induced fluorescence of vibrationally excited NO

Trace concentrations of 1,4-dinitrobenzene (DNB) are detected by a combination of laser photolysis and laser-induced fluorescence. A one-color laser is applied to induce DNB photodissociation and for subsequent detection of NO photofragments by excitation and emission through A(v′ = 0) 4 ←X(v″ = 0 − 2) and A(v′ = 0) 4 ←X(v″ = 0,1) transitions, respectively. The resulting NO rovibrational excitation spectra serve as markers for the presence of DNB. The NO is produced in vibrational ground and excited states with peak height ratios of (v″ = 0):(v″ = 1):(v″ = 2) 5 1:0.5:0.13. The limits of detection of DNB mixed with 100 or 500 Torr of air with v″ = 2 excitation at 248 nm are 13 and 11 parts in 109 by weight, respectively, for a 30-s integration time. The application of this scheme for DNB detection has the advantage that no ambient ground state NO interferes and that the fluorescence is collected at shorter wavelengths than the exciting radiation, precluding background fluorescence.