Knowledge Bank

The $\nu 6$ (E) fundamental vibration-rotation band of monodeuteromethane() has been recorded in the spectral range 1033-1275 $cm-l$ with resolution of approximately $0.04cm-1$. Of the 669 transitions with $J\prime \le 17$ identified, 633 have been retained for the determination of the rotational levels in the upper state $\nu 6=1$. The Coriolis interaction between the $v6=1(E)$ and $v3=1(A1)$ vibrational states of $\mathrm{<mrow\; data-mjx-texclass="ORD">12</mrow>}CH3D$ results in large $A1A2$ splittings of Levels with $v6=1$ and $\mid K-\ell 6\mid =0$ or 3; the mixing in K and $\ell 6$ also gives rise to some ten forbidden transitions observed in the spectra. These effects have been explained very well within the formulation based on the contact transformation method. Values of 15 molecular structure constants of the $v6=1$ state have been determined from a least-squares analysis of the 633 retained transitions. These constants can be used to estimate values of the upper state energies up to fourth order, and through them the spectral positions of the 633 retained transitions are reproduced with an overall standard deviation of $0.013cm-1$, which is within experimental uncertainties.