Sensitive detection of NH2 in shock tube experiments using frequency modulation spectroscopy
✍ Scribed by M. Votsmeier; S. Song; D. F. Davidson; R. K. Hanson
- Publisher
- John Wiley and Sons
- Year
- 1999
- Tongue
- English
- Weight
- 165 KB
- Volume
- 31
- Category
- Article
- ISSN
- 0538-8066
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✦ Synopsis
Frequency modulation detection of NH 2 in shock tube kinetic experiments is demonstrated with sensitivities of 0.5 ppm in a single pass and 0.25 ppm in a double pass configuration 1.3 atm, detection bandwidth 1 MHz, shock tube diameter). This (1500 K, 15 cm corresponds to a minimum detectable absorption of 0.01% and 0.005%, respectively, which represents an improvement of more than a factor of 20 when compared to conventional laser absorption detection.
The feasibility of quantitative absolute concentration measurements is demonstrated using CH 3 NH 2 as a precursor for the preparation of known NH 2 concentrations. The uncertainty for absolute concentration measurements is estimated to be Ϯ10% if a suitable precursor for direct shock tube calibration measurements can be used, and Ϯ15% if an alternative calibration scheme based on the detection of the signal generated by a scanning etalon in reflective mode is used.
FM detection has been applied to determine the rate coefficient of the thermal decomposition of CH 3 NH 2 :
over the temperature range and at pressures near 1.3 atm. The rate coefficient 1530-1975 K was found to be:
This is in good agreement with a recent determination using conventional laser absorption detection of the NH 2 radical.