Knowledge Bank

A multispectrum nonlinear least-squares sitting $techniquea$ has been used to determine Lorentz $N2$-broadening and pressure-induced shift coefficients for a large number of transitions in the $\nu 3$ and $\nu 6$ fundamental bands of $\mathrm{<mrow\; data-mjx-texclass="ORD">12</mrow>}CH3D$ in the region from 1060 to $1640cm-1$. We analyzed a total of 17 high-resolution (0.002 to $0.006cm-1)$ room temperature absorption spectra recorded with the Bruker IFS 120 HR at PNNL and the 1-m Fourier transform spectrometer (FTS) at the McMath-Pierce facility of the National Solar Observatory at Kitt Peak. Our multispectrum analysis technique allowed us to simultaneously analyze both self-broadened and $N2$-broadened spectra. The data set included 13 spectra of 98% pure $CH3D$ at pressures of 0.1 to 303 torr in cells with path lengths of 10 to 2486 cm and 4 spectra of lean mixtures $(\approx 1$ of $CH3D$ in research grade nitrogen at total pressures between 100 and 400 torr in a 25 cm cell. $N2$-broadening coefficients for over 800 transitions and shift coefficients for more than 600 transitions in the $\nu 3$ and $\nu 6$ bands were determined. Transitions with rotational quantum numbers up to $J\prime \prime =15$ and $K\prime \prime =14$ were analyzed, $N2$- broadening coefficients were measured in all six $\nu 6$ sub-bands $(PP,PQ,PR,RP,RQ$ and ). The measured broadening coefficients vary from about 0.02 to $0.09cm-1$ $atm-1$ at 296K. Most of the measured pressure-shift coefficients are negative with values extending from about $-0.014to+0.005cm-1atm-1$. Very few of the measured shift coefficients are positive, and the positive shifts are mostly associated with the $J\prime \prime =K\prime \prime$ transitions in the sub-bands. $J\prime \prime =K\prime \prime$ transitions are also associated with the smallest broadening coefficients in both the $\nu 5$ and $\nu_{6} $ bands.