Accession Number : ADA300053

Title :   Detection of NOx Compounds by Laser-Induced Photofragmentation/Photoionization Spectrometry.

Descriptive Note : Final rept. Apr-Jan 95,

Corporate Author : ARMY RESEARCH LAB ABERDEEN PROVING GROUND MD

Personal Author(s) : Sausa, R. C. ; Simeonsson, J. B. ; Lemire, G. W.

PDF Url : ADA300053

Report Date : SEP 1995

Pagination or Media Count : 38

Abstract : Laser-induced photofragmentation/photoionization (PF/PI) spectrometry has been used to detect trace ambient concentrations of NO, NO2, HNO3 and CH3NO2. The method uses a single laser operating near 226 nm to both fragment the parent molecule and photoionize the resultant NO fragment by a 1+1 resonance-enhanced multiphoton ionization (REMPI) process via its A(2)sigma (+) <-- X(2)Pi (0,0) band. Ion detection is accomplished by using a pair of miniature electrodes. Use of a single laser and optogalvanic ion detection greatly simplifies the instrumental requirements of the method and allows for real-time, in situ monitoring of the above-mentioned compound under ambient conditions. Analytical merits of the technique have been evaluated as a function of the sampling pressure and detection electrode voltage. Limits of detection (LODS) determined for NO, NO2, HNO3, and CH3NO2 are 1 ppbv, 22 ppbv, 5 ppbv, and 220 ppbv, respectively, using 10 micro J of pulse energy and an integration time of 10 s. Results of the study indicate that PF/PI spectrometry enables a simple instrument design to be used for sensitive measurements of these compounds. The high sensitivity is a reflection of the high efficiency of each of the PF and PI processes employed. The ability to use low fluences has the added benefit of suppressing nonresonant multiphoton ionization background signals.

Descriptors :   *DETECTION, *FRAGMENTATION, *PHOTOCHEMICAL REACTIONS, *SPECTROMETRY, *LASERS, *PHOTOIONIZATION, *NITROGEN OXIDES, REQUIREMENTS, IONS, MEASUREMENT, HIGH RATE, MOLECULES, ENERGY, EFFICIENCY, VOLTAGE, LASER APPLICATIONS, PULSES, ELECTRODES, SAMPLING, PRESSURE, INSTRUMENTATION, MINIATURIZATION, HIGH SENSITIVITY.

Subject Categories : Inorganic Chemistry
      Radiation and Nuclear Chemistry
      Lasers and Masers
      Atomic and Molecular Physics and Spectroscopy

Distribution Statement : APPROVED FOR PUBLIC RELEASE