A multispectrum analysis of the ν4 band of 13CH4: Widths, shifts, and line mixing coefficients

Abstract:

Line positions, Lorentz air-broadened half width and air pressure-induced shift coeffi-cients have beenmeasured for nearly 200 transitions in the n4 band of 13CH4 from high-resolution spectra recorded with the McMath-Pierce Fourier transform spectrometer.Threeroom temperature spectra of 13CH4 used in the previous study of Malathy Devi et al.(Air-broadened Lorentz halfwidths and pressure-induced line shifts in the n4 band of13CH4. Appl. Opt. 1988; 27: 2296–2308) were analyzed together with a large number ofadditional spectra of self- and air-broadened CH4 recorded at 210–314 K and one room-temperature spectrum of self-broadened 13CH4. Analyses applying the multispectrumnonlinear least squares fitting technique were performed to retrieve the spectral lineparameters. In addition to air-broadened half width and shift coefficients, self-broadenedhalf width and shift coefficients were determined for at least 56 13CH4n4 transitions. Off-diagonal relaxation matrix element coefficients for air-broadened line mixing were alsodetermined for 28 pairs of P and R transitions in a number of J manifolds, and mixingparameters for self-broadening were also determined for some of these pairs. Tempera-ture-dependences of the pressure-induced shift and mixing parameters for the 13CH4lines could not be determined from the spectra used in the present analysis, buttemperature dependences of the half width coefficients were determined for thestrongest transitions. The results of this study are compared with other studies of air-and self-broadened 13CH4 and 12CH4.