(2+2) Resonance-Enhanced Multiphoton Ionization (REMPI) and Photoacoustic (PA) Spectroscopic Detection of Nitric Oxide (NO) and Nitrogen Dioxide (NO2) Near 454nm.

Trace concentrations of NO and NO2 are detected with a dye laser operating near 454 nm. NO is detected by a 2 2 resonance-enhanced multiphoton ionization process by means of NO A 2sigma-X 2Pi0, 0 transitions with miniature electrodes, and NO2 is detected by a one-photon absorption photo acoustic process by means of NO2 Atilde 2B10, 8, 0 - Xtilde 2A10, 0, 0 transitions with a miniature microphone. Rotationally resolved excitation spectra show that the spectral resolution is sufficiently high to identify these species at 1 atm. The techniques analytical merits are evaluated as functions of concentration, pressure, and laser intensities. Low laser intensities favor NO2 photoacoustic detection whereas high laser intensities favor NO ionization. Limits of detection signal-to-noise ratio 3 of 160 parts in 10exp 9 for NO and 400 parts in 10exp 9 for NO2 are determined at 1 atm for a 10-s integration time. Signal response and noise analyses show that three decades of NONO2 mixtures can be measured with a computational relative error in concentration that is three times the relative error in measuring the NO and NO2 signals.