Diode-laser spectroscopy: Temperature dependence of R (0) line in the ν4 band of CH 4 perturbed by N 2 and O 2

Abstract

In this paper, we present a line profile study of the R (0) line in the ν 4 band of methane diluted in nitrogen and oxygen, from room temperature to 153 K. The measurements were performed over a total pressure range from 14 to 128 mbar. The collisional broadening and narrowing (Dicke effect) coefficients are derived from a fit of the experimental spectra by using the soft and hard collision models, taking into account the Dicke effect. For higher pressures, we have fitted the data with a model taking into account simultaneously the Dicke narrowing and the speed dependence effect. Finally, we have deduced the parameter n of the temperature dependence (inverse power law) of the broadening coefficients for the CH 4–N 2 and CH 4–O 2 gas mixtures.