Line-strengths, collisional coefficients and narrowing parameters in the ν3 band of methane: H2, He, N2, O2, Ar and CO2 collider effects

Abstract

The ν3 fundamental absorption band of methane (12CH4) dominates the 3.3–3.4 μm infrared spectral window and has been extensively used for atmospheric, planetary and astrophysical investigations. Spectroscopic data, such as line positions, line-strengths and foreign-collisional coefficients, are needed to analyze the infrared spectra of planetary atmospheres for the understanding of relevant physical chemistry. In this study, high-resolution infrared spectra of 12CH4 belonging to the ν3 fundamental vibrational band are recorded over 2884–2969 cm−1 with a difference–frequency–generation (DFG) laser having a linewidth of Δν ≈ 0.0002 cm−1. Line-strengths as well as H2-, He-, N2-, O2-, Ar- and CO2- broadening coefficients are determined for 49 methane transitions at room temperature. Data are retrieved using Voigt and Galatry profiles to compute the measured line shape of each individual transition at various pressures. Narrowing coefficients due to Dicke effect are also determined. The new data extend and supplement previous measurements over the target spectral region (2884–2969 cm−1) where very fewer studies are reported. In particular, the present work is the first known complete determination of broadening data and narrowing parameters at high rotational quantum numbers of the P-branch of the ν3-CH4 band.