The Interaction Between Rotation and Oscillation in Deutero-Formaldehyde

The unsymmetrical broadening of the $Q$ branch toward higher frequencies in the parallel type bands near 1100 ${\mathrm{cm}}^{-1\mathrm{}}$ in the absorption spectrum of deutero-formaldehyde is taken as a manifestation of convergence toward lower frequencies rather than, as is usual, in the case of infra-red bands, toward higher frequencies. This phenomenon is accounted for by taking into account an interaction between rotation and oscillation of the Coriolis type arising from the accidental degeneracy of the three vibration frequencies, belonging to three different symmetry classes, falling near 900 ${\mathrm{cm}}^{-1\mathrm{}}$, 1000 ${\mathrm{cm}}^{-1\mathrm{}}$ and 1100 ${\mathrm{cm}}^{-1\mathrm{}}$.