TITLE:
High-Resolution Spectroscopic Characterization of the ν2 saQ(6, 3) Rovibrational Transition of Ammonia, an Important Air-Quality Pollutant, Using an Ultra-Stable Laser Spectrometer
AUTHORS:
Papa Lat Tabara Sow, Fama Diop, Youssou Gning, Mamadou Lamine Samb, Senghane Mbodji
KEYWORDS:
Ammonia (NH3), Ultra-Stable Laser, Voigt Profile, Line-Shape Analysis, Frequency Metrology, Phase Locking
JOURNAL NAME:
American Journal of Analytical Chemistry,
Vol.17 No.10,
October
21,
2026
ABSTRACT: This paper reports a high-resolution spectroscopic study of the ν2 saQ(6, 3) rovibrational transition of ammonia (NH3) near 10 µm, performed with an ultra-stable laser. Forty-six absorption spectra were recorded at 300 K and 10 Pa and processed with an automated non-linear fitting procedure implemented in Python. Two line-shape models were compared: a Gaussian profile, accounting for Doppler broadening only, and a Voigt profile, obtained from the convolution of the Doppler and collisional (Lorentzian) contributions. The Gaussian model converged for all 46 spectra and provided a numerically robust estimate of the transition frequency, whereas the Voigt model, although physically more complete, converged for only 22 of the 46 spectra, reflecting its greater sensitivity to the signal-to-noise ratio and to baseline quality in the wings of the line. Residual analysis shows that a purely Doppler profile does not fully reproduce the observed line shape, while Voigt residuals remain structured for several spectra with lower spectral quality. The central frequency obtained in this work, 28,953,694.0613 MHz, is consistent with the range of previous experimental determinations of this transition and falls within about 1 MHz of the ab initio prediction, with the smallest deviation among the values compared, an observation that should be read as indicative rather than as a demonstration of superior accuracy, since no formal uncertainty budget is available for the present measurement. These results provide a methodological basis for further studies of pressure-broadening parameters and of the atmospheric applications of this transition.