Measurements of argon broadened Lorentz width and pressure-induced line shift coefficients in the ν_4 band of ^12CH_4

Abstract

Room temperature argon broadened halfwidth and pressure-induced line shift coefficients have been determined for 118 transitions in the nu(4) band of (12)CH(4) from analysis of high resolution laboratory absorption spectra recorded with the McMath Fourier transform spectrometer operated on Kitt Peak by the National Solar Observatory. Transitions up to J''= 12 have been measured using a nonlinear least-squares spectral fitting procedure. The variation of the measured halfwidth coefficients with symmetry type and rotational quantum number is very similar to that measured previously for N(2) and air broadening, but the absolute values of the argon broadening coefficients are all smaller. On average, the ratio of the argon broadened halfwidth coefficient to the corresponding N(2) broadened halfwidth coefficient is 0.877 +/- 0.017 (2sigma). More than 95% of the pressure-induced shifts are negative with values ranging from -0.0081 to +0.0055 cm(-1) atm(-1). The pressure shifts in argon are nearly equal to corresponding values measured previously in N(2) and air.