A multispectrum analysis of the v4 band of 13CH4: Widths, shifts, and line mixing coefficients

Line positions, Lorentz air-broadened half width and air pressure-induced shift coefficients have been measured for nearly 200 transitions in the v(4) band of (CH4)-C-13 from high-resolution spectra recorded with the McMath-Pierce Fourier transform spectrometer. Three room temperature spectra of (CH4)-C-13 used in the previous study of Malathy Devi et al. (Air-broadened Lorentz halfwidths and pressure-induced line shifts in the v(4) band of (CH4)-C-13. Appl. Opt. 1988; 27: 2296-2308) were analyzed together with a large number of additional spectra of self- and air-broadened CH4 recorded at 210-314 K and one room-temperature spectrum of self-broadened (CH4)-C-13. Analyses applying the multispectrum nonlinear least squares fitting technique were performed to retrieve the spectral line parameters. In addition to air-broadened half width and shift coefficients, self-broadened half width and shift coefficients were determined for at least 56 (CH4)-C-13 v(4) transitions. Off-diagonal relaxation matrix element coefficients for air-broadened line mixing were also determined for 28 pairs of P and R transitions in a number off manifolds, and mixing parameters for self-broadening were also determined for some of these pairs. Temperature-dependences of the pressure-induced shift and mixing parameters for the (CH4)-C-13 lines could not be determined from the spectra used in the present analysis, but temperature dependences of the half width coefficients were determined for the strongest transitions. The results of this study are compared with other studies of air- and self-broadened (CH4)-C-13 and 120-14. Published by Elsevier Ltd.