Self- and N 2-broadening, pressure induced shift and line mixing in the ν5 band of 12CH 3D using a multispectrum fitting technique

Abstract

We report the first measured Lorentz self- and nitrogen-broadening and the corresponding pressure-shift coefficients in the ν 5(E) perpendicular band of 12CH 3D between 1275 and 1600 cm −1 . The multispectrum fitting technique allowed us to analyze simultaneously both self-broadened and N 2-broadened spectra recorded at 0.005 to 0.006-cm −1 resolution with a Fourier transform spectrometer located at Kitt Peak. Self-broadening coefficients for over 550 transitions and self-shift coefficients for more than 480 transitions with rotational quantum numbers up to J″=17 and K″=14 were determined. Nitrogen-broadening and nitrogen pressure-induced shift coefficients were determined for more than 300 of those transitions. The measured broadening coefficients vary from 0.020 to about 0.091 cm −1 atm −1 at 296 K . The measured pressure-shift coefficients had values extending from about −0.014 to +0.005 cm −1 atm −1 . Very few of the pressure-shift coefficients were positive, and the positive pressure-shift coefficients were mostly associated with the J″= K″ transitions in the PQ sub-bands. The J″= K″ transitions in the PP and RR sub-bands were associated with the smallest broadening coefficients. Our measurements also included 46 forbidden lines with ΔK=±2 (10 O P, 9 O Q,3 Q P, 7 Q Q, 1 Q R, 13 S Q and 3 SR). The off-diagonal relaxation matrix element coefficients, W ij , in cm −1 atm −1 at 296 K which are associated with line mixing were determined for a few transitions with K″=3 (A +A −splitting) in the P P, P Q and RP sub-bands. We have examined the dependence of the measured parameters on J, K quantum numbers and also developed empirical expressions to describe the broadening coefficients in terms of J and K.