II. Quantitative Analysis of NO-NO2 Mixtures by Laser Photofragmentation/Fragment Ionization at 226 and 452 nm
Abstract
Laser-induced photofragmentation with fragment ionization is used to detect and spectrally differentiate trace concentrations of NO2 from NO in NO-NO2 mixtures. A laser operating near 226 or 452 run ionizes the target molecules, and the resulting electrons are collected with miniature electrodes. NO is detected by (1+1) resonance-enhanced multiphoton ionization by means of its A(sup 2)Sigma(+) left arrow X(sup 2)II (0,0) transitions near 226 run, whereas NO2 is detected near 226 run by laser photofragmentation with subsequent NO fragment ionization by means of both its A(sup 2)Sigma(+) X(sup 2)II (0,0) and (1,1) transitions. The NO fragment generated from the photolysis of NO2 is produced rovibrationally excited with a significant population in the first vibrational level of the ground electronic state (X(sup 2)II, v" = 1). In contrast, 'ambient' NO has a room-temperature, Boltzmann population distribution favoring the lowest ground vibrational level (X(sup 2)II, v" = 0). Thus, discrimination is possible when the internal energy distributions of both fragment NO and ambient NO are probed. This approach is also demonstrated using visible radiation, further simplifying the experimental apparatus because frequency doubling of the laser radiation is not required. Up to three decades of NO-NO2 mixtures are measured with limits of detection (S/N = 3) in the low ppb for both NO and NO2 for a 10-s integration time using both ultraviolet or visible radiation.
Document Details
- Document Type
- Technical Report
- Publication Date
- May 01, 2001
- Accession Number
- ADA392012
Entities
People
- Robert L. Pastel
- Rosario C. Sausa
Organizations
- United States Army Research Laboratory