VIBRATIONAL MODE-SPECIFIC TUNNELING SPLITTINGS IN THE APPROXIMATELY-A STATES OF DEUTERATED TROPOLONES

The electronic spectra have been measured for jet-cooled tropolone-3-d (3DTRN), tropolone-4-d (4DTRN), and tropolone-5-d (5DTRN) to investigate the effect of a very weak perturbation due to the substitution of a deuterium atom in the skeletal seven-membered ring on the average geometries and the tunneling splittings for the vibrationally excited levels in the A states. The vibrational fundamental for nu'13 has changed significantly in the order 3DTRN > 4 DTRN > 5DTRN, whereas that of nu'14 has been found to be almost constant. This suggests that nu'13 involves the motions of the hydrogen atoms in positions 3, 4, and 5, while those of the hydrogen atoms at the same positions are insignificant in nu'14. The tunneling splittings for nu'13 have decreased remarkably in 4DTRN and 3DTRN, indicating that the motions of the hydrogen atoms in positions 3 and 4 are strongly coupled with the motion of the hydroxylic proton in nu'13. On the other hand, very slight changes have been found in the tunneling splitting of nu'14. Similarly, changes in the tunneling splittings for several modes due to the substitution of a deuterium atom had been examined. It has been suggested that the motions of the light atoms as well as the heavy atoms are coupled with the proton-transfer coordinates.