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 combinat ion of laser photolysis and laser-induced fluorescence. A one-color laser i s applied to induce DNB photodissociation and for subsequent detection of N O photofragments by excitation and emission through A(nu' = 0) <-- X(nu " = 0 - 2) and A(nu' = 0) --> X(nu " = 0, 1) transitions, respectively. The re sulting NO rovibrational excitation spectra serve as markers for the presen ce of DNB, The NO is produced in vibrational ground and excited states with peak height ratios of(nu " = 0):(nu " = 1):(nu " = 2) = 1:0.5:0.13. The li mits of detection of DNB mixed with 100 or 500 Torr of air with nu " = 2 ex citation at 248 nm are 13 and 11 parts in 10(9) by weight, respectively, fo r 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 radiatio n, precluding background fluorescence. (C) 1999 Optical Society of America.