Knowledge Bank

The methyl-deformation bands of $\mathrm{<mrow\; data-mjx-texclass="ORD">13</mrow>}CD3$OH have been studied by high-resolution Fourier transform spectroscopy in the region $1030-1180cm-1$, lying above the strong $C-O$ stretching band. The symmetric-deformation band is the umbrella mode and shows a reasonably well-developed P, Q and R branch structure. The R-branch spacing is clearly larger than that of the P branch, showing that the B-value increases in going to the excited umbrella-bending state. Numerous individual P, Q and R branch series have been identified and analyzed, along with interesting Fermi and Coriolis resonances observed in the spectrum. The torsional energy levels of the excited methyl-deformation state follow the oscillatory pattern with K found for the ground state, but with a slightly increased amplitude. This implies that the barrier to internal rotation is somewhat lower in the excited state, contrary to results found for other vibrational modes. A least squares fit to the IR series origins, with the ground state molecular constants held fixed, gives an excited deformation state barrier of $V3=325(16)cm-1$, a 12% decrease from the ground state value of $370cm-1$. However, $V3$ is strongly correlated in the fit with the framework moment of inertia $Ia1$, which shows a suspiciously large 11% increase, hence the actual value of $V3$ is still preliminary and should be viewed with caution.""