Investigation of effective line strengths of N(2)O(4) at 7.8 μm using a continuous-wave quantum cascade laser spectrometer.

The spectral line positions and effective line strengths of dinitrogen tetroxide (NO) in the range of 1279.8-1282.5 cm were measured using a continuous-wave quantum cascade laser spectrometer. A data processing program developed in MATLAB was used to fit the spectral data with Voigt, Rautian, and Galatry line profiles. The performance of different spectral line profiles was evaluated, and the Rautian profile achieved the best fit with faster calculations, making it ideal for real-time and long-term monitoring. The maximum uncertainties in the measured line positions and intensities are 1.95*10 cm and 6.47 %, respectively. The line position uncertainty is mainly from reference spectral lines, while intensity uncertainty is due to NO concentration calculations and fitting errors. These results aid in gas leak monitoring and spectral analysis of NO, as well as in studying nitrogen oxide reaction processes.