John
C. Keske and David F. Plusquellic
Optical
Technology Division, National Institute of Standards and Technology, Gaithersburg,
Maryland 20899-8441
Hydrogen
bonding and intramolecular proton transfer are being investigated in jet
cooled tropolone and tropolone-water complexes by high-resolution MW and
UV spectroscopies. Tropolone is a seven-member ring compound with an OH..O
moiety that undergoes tautomerization across a symmetric double minimum
potential surface. The two isoenergetic configurations of the molecule
are separated by a small barrier that results in facile tunneling of the
hydrogen atom. Analysis of the spectra reveals nearly a 20 fold increase
in the tunneling splitting from the S0 to S1 levels.
Most remarkably, with the addition of one water molecule to tropolone the
observed tunneling splitting vanishes. This is likely due to the
destruction of the symmetric potential by the addition the water molecule.
Only two possible ab initio structures of the tropolone-water complex
are consistent with the experimental results. Further studies, on 5-methyltropolone,
are being pursued to examine the interactions of a methyl torsion with
the proton transfer coordinate.