Absolute line intensities and first measurements of self-collisional broadening and shift coefficients in the 2ν4 band of NH3

Abstract

Absolute line intensities and a first determination of self-broadening and shift coefficients are presented here, deduced from room temperature measurements for 302 rovibrational lines of NH3 in the 2ν4 band, using Fourier transform infrared spectroscopy. These lines, ranging from 1 ≤ J ≤ 11 to 0 ≤ K ≤ 11, are located in the 3060–3580 cm−1 spectral range. The lines were fitted with a single spectrum non-linear least squares fitting procedure. The absence of signature in the residuals suggests that the Voigt profile is well suited to fit the experimental line shapes without the need of taking into account line mixing effects, in the pressure range used. Average absolute accuracies of the measurements are estimated to ±4% for line intensities and self-broadening coefficients and to ±13% for self-shift coefficients. The J and K dependences of the self-broadening coefficients have been observed and modeled using an empirical polynomial expression. The results are compared with previous experimental and calculated data. Our absolute line intensities, S0, are in good agreement with previous work and HITRAN2016 database, but with a reduced uncertainty. The self-broadening coefficients, γ0, as well as the pressure shift coefficients, δ0, are in reasonable agreement with those reported for various vibrational bands in the 3 µm spectral region, which indicates that no obvious vibrational dependence was observed. For shift coefficients, it should be noted that this is not the case in many studies which put in evidence a large dependence with vibrational excitation. This study complements the existing line parameters in the 3 µm spectral region, essential for the analysis of atmospheric spectra. For this purpose, the complete list of measurements is provided as supplementary material.