TUNABLE DIODE LASER STARK SPECTRA OF $CD_{3}OH$

$^{1}$R. M. Lees and J. G. Baker, J. Chem. Phys. 48, 5299 (1968).Author Institution:We obtain Doppler resolution limited $(\Delta\nu \simeq 0.0020 \mbox{cm}^{-1})$ spectra of the P and R multiplets for J $\leq 10$ of the $10 \mu m C-O$ stretch band $(\nu_{4})$ of $^{12}CD_{3} ^{16}OH$ using a tunable diode laser. These multiplets are composed of 3J and 3J+3 lines for the P and R multiplets, respectively, the individual lines being associated with the hindered rotation and K substructure. The inta-multiplet spreading is $\simeq 0.1 \mbox{cm}^{-1}$, in contrast to $CH_{3}OH$, where the spreading is $\sim 1.0 \mbox{cm}^{-1}$. We are able to resolve most of the substructure and assign the transitions in the low-J multiplets. The assignments are based primarily on the results of Stark-difference spectra, combined with the microwave ground state $data^{1}$ and the intensities expected theoretically. The A, K=0 and $A^\pm$, K=1 lines, due to their negligible Stark effects, can be readily assigned from ``high’’ field spectra $(\sim 2\times 10^{3} \mbox{v/cm})$. The Stark components of the remaining lines are so severely overlapped at high fields, however, that the systematics in the ``low’’ field $(\sim 400 \mbox{v/cm})$ Stark difference spectra are most useful in making their assignments. From combination relations we find the ground and excited state $A^\pm$, K=1 asymmetry splitting parameters to be $\delta_{1}^{\prime} = (8.5450 \pm 0.0080) \times 10^{-3} \mbox{cm}^{-1}$ and $\delta_{1}^{\prime} = (9.7706 \pm 0.0080)\times 10^{-3} \mbox{cm}^{-1}$, respectively, where the energy separation of the asymmetry split levels varies as $\delta J(J+1)$. The data are recorded digitally using a rapid-scan, double-beam system and the spectra are plotted on a linearized wave-number axis with the aid of a computer. Relative frequency is determined from the co-recorded channel spectrum of a germanium etalon to a precision of $\pm 3\times10^{-4} \mbox{cm}^{-1}$, while absolute frequency accurate to $\pm 1\times10^{-3} \mbox{cm}^{-1}$ is obtained from FTIR spectra calibrated against the 10 $\mu m CO_{2}$ laser lines measured in absorption