Multispectrum analysis of self- and N 2-broadening, shifting and line mixing coefficients in the ν6 band of 12CH 3D

Abstract

A multispectrum nonlinear least-squares fitting technique has been applied to determine accurate zero-pressure line center positions, Lorentz self- and N 2-broadening coefficients and self- and N 2-induced pressure shift coefficients of transitions in the ν 6 (E) perpendicular band of 12CH 3D between 1035 and 1270 cm −1 . Seventeen high-resolution (0.002– 0.006 cm −1 ) room temperature absorption spectra recorded with two Fourier transform spectrometers (FTS) were analyzed together. Self-broadening coefficients for over 700 transitions and self-shift coefficients for more than 600 transitions were determined. Measurements of nitrogen-broadening coefficients for more than 480 transitions and nitrogen pressure induced shift coefficients for nearly 430 transitions were also made. The measurements include transitions with rotational quantum numbers as high as J″=18 and K″=15 and several forbidden transitions. The measurements were made in all six sub-bands ( P P, P Q, P R, R P, R Q and RR). The measured self-broadening coefficients vary from 0.025– 0.096 cm −1 atm −1 at 296 K and the N 2-broadening coefficients from 0.02 to 0.08 cm −1 atm −1 at 296 K . Self-induced-shift coefficients range from −0.014 to +0.004 cm −1 atm −1 while the nitrogen-induced-shift coefficients vary from −0.013 to +0.008 cm −1 atm −1 . Very few of the measured pressure-shift coefficients were positive, and the positive shift coefficients were mostly associated with the J″= K″ transitions in the PQ sub-bands. The off-diagonal relaxation matrix element coefficients of a number of transitions with K″=3 doublets for both self- and N 2-broadening were also obtained. The results obtained with the two different broadening gases are compared and discussed. Comparisons with previous values from the literature are also made.