Rotational energy transfer in NO (A 2Σ+,v′=0) by N2 and O2 at room temperature

State-to-state rotational energy transfer (RET) rate coefficients for NO (A 2Sigma+, v'=0, J=5.5, 11.5, 17.5) were measured for N2 and O2 at room temperature using a pump-probe method. The NO A 2Sigma+ state is prepared by 226 nm light and the RET is monitored by fluorescence from the D 2Sigma+ v'=0 state, following excitation by a time-delayed laser at approximately 1.1 microm. Additionally, total collisional removal and final state distributions were measured exciting in the Q1+P21 band head, to simulate an NO laser-induced fluorescence atmospheric monitoring scheme. Time-resolved modeling is used to understand relaxation mechanisms and predict relaxation times in ambient air. H2O at atmospherically relevant concentrations does not affect the degree of RET in ambient air.

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) <-- X(v" = 0 - 2) and A(v' =0) --> 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) = 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 10(9) 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.

Atmospheric ammonia measurement using a VUV/photo-fragmentation laser-induced fluorescence technique

Vacuum ultraviolet/photofragmentation laser-induced fluorescence has been demonstrated to be a highly specific and sensitive method for the quantitative measurement of atmospheric ammonia (NH(3)). The fluorescence detected in this approach results from the two 193-nm photon photofragmentation step NH(3)?NH(2)? NH(b(1)Sigma(+)) followed by the excitation of the NH(b(1)Sigma(+)) NH(c(1)Pi) transition via a 450-nm photon with final emission being observed from the NH(c(1) Pi) NH(a(1)Delta) transition at 325 nm. Limits of detection for the instrumentpresented here are < 10 pptv and < 4 pptv for 1- and 5-min integration periods, respectively, in ambient sampling conditions. The technique is free from interferences and system performance does not significantly degrade in adverse sampling conditions (i.e., rain, fog, clouds, haze, etc.). Spectroscopic selectivity in the NH(b(1)Sigma(+))?NH(c(1)Pi) transition is sufficient to resolve (15)NH(3) and (14)NH(3) contributions for use in atmospheric tracer studies. Average ammonia measurements at Stone Mountain, GA, ranged from approximately 110 pptv for air temperatures <5 degrees C to approximately 240 pptv for air temperatures >/=<5 degrees C over the period from Dec. 1987 to the end of Apr. 1988.