Measurements of NH3 linestrengths and collisional broadening coefficients in N2, O2, CO2, and H2O near 1103.46 cm−1

Abstract

Laser-based ammonia gas sensors have useful applications in many fields including combustion, atmospheric monitoring, and medical diagnostics. Calibration-free trace gas sensors require the spectroscopic parameters including linestrengths and collisional broadening coefficients to be known. Ammonia's strong ν2 vibrational band between 9−12μm has the high absorption strength needed for sensing small concentrations. Within this band, the 1103.46cm−1 feature is one of the strongest and has minimal interference from CO2 and H2O. However, the six rotational transitions that make up this feature have not been studied previously with absorption spectroscopy due to their small line spacing ranging from 0.004 to 0.029cm−1. A tunable quantum cascade laser was used to accurately study these six transitions. A retrieval program was used to determine the linestrengths and collisional broadening coefficients based on Voigt and Galatry profiles. The experiments were performed with ammonia mixtures in nitrogen, oxygen, water vapor, and carbon dioxide at room temperature in an optical cell. These data are going to aid in the development of quantitative ammonia sensors utilizing this strong absorption feature.