Spectroscopic line parameters in the 4ν2 band of NH3 and line intensities in the ν1, ν3 and 2ν4 bands

Abstract

In this work, self-broadening coefficients as well as self-shift coefficients have been measured for the first time in 4ν2 overtone of NH3 at T = 295 K using a high-resolution Fourier transform spectrometer. The spectra were analyzed with nonlinear least-squares multi-pressure fitting procedure to eight spectra of pure NH3. The results are discussed as a function of the J and K rotational quantum numbers and the branches.The line intensities of this band as well as those of the ν1 and ν3 bands lying in the same region as the 4ν2 overtone were retrieved using the same spectra. These data together with those of 2ν4 band, subject of our previous work [1], allow us to derive the transition dipole moments squared for a total of about 760 lines which were found to exhibit strong J and K dependences. These moments were also derived for 63 lines of the ΔK = ±2, ±3 forbidden transitions of the 2ν4±2 sub-band. These dependences are mainly caused by Fermi and Coriolis interactions transferring intensities between the modes forming the 3 µm region system.The analysis of these moments allows us to derive a consistent set of line intensity parameters such as vibrational transition moments, band intensities as well as Herman-Wallis coefficients. The derived parameters are found to be in agreement with previous data.