Self-, N2, O2, H2, Ar, and He broadening in the ν3 band Q branch of CH4

Abstract

Self-, N2-, O2-, H2-, Ar-, and He-broadening coefficients, pressure shifts, and integrated intensities have been measured for most transitions in the Q branch of the ν3 fundamental band of methane using a difference-frequency laser spectrometer. A systematic dependence of the broadening coefficients on the tetrahedral symmetry species and order index is observed with striking similarities for N2, O2, and Ar and for H2 and He buffer gases. Comparison with earlier measurements on other bands and branches of methane indicates very little vibrational, branch, or carbon isotope dependence. Dicke narrowing is evident at intermediate pressures, yielding an average narrowing coefficient and an optical diffusion constant for each gas mixture. A small amount of line mixing is evident for strongly overlapped lines near atmospheric pressure from nonlinear deviations of the observed spectra from the contours extrapolated from lower pressure measurements.