Oxygen, nitrogen and air-broadening and shift coefficients in the ν2 band of CH3I at room temperature

Abstract

In this study, foreign-gas broadening and shift coefficients of CH₃I spectral lines in collision with N₂, O₂, and air were measured for ro-vibrational transitions in the ν₂ band using high-resolution Fourier Transform spectrometer at SOLEIL Synchrotron facility. The results were obtained by analyzing room temperature (T = 296 K) absorption spectra with a mono-spectrum non-linear least squares fitting of Voigt profile. The measured O₂-broadening coefficients range from 0.0554 to 0.1269 cm^–1atm^–1 with an average value of 0.0849 cm^-1atm^-1. Those with N₂ collider vary from 0.0556 to 0.1466 cm^-1atm^-1 with an average value of 0.0926 cm^-1atm^-1. Then, we deduced those with air. The CH₃I–air broadening coefficients are found to range from $0.0599$ to $0.1370$cm^–1atm^–1. The measured shift coefficients are bipolar. They range from -0.0282 to 0.0309 cm^-1atm^-1, from -0.0299 to 0.0269 cm^-1atm^-1 and from -0.0268 to 0.0219 cm^-1atm^-1 for O₂, N₂ and air collisions, respectively. The average accuracies of the measured O₂-broadening and shift coefficients were estimated to be about 6.9% and 15.9 %, respectively; those of N₂ are estimated to be about 8.6 % and 19.9 %. The J- and K-rotational dependences of broadening coefficients have been observed and modeled using an empirical law reproducing the measured coefficients to within ∼7.4 %. The comparison of the measured data with values reported in the literature illustrates no vibrational effect in the broadening and shifts. The present results should be valuable for estimating the CH₃I abundance in the atmosphere, and for testing theoretical models predicting pressure broadening coefficients and collision induced shifts.