INTRAMOLECULAR PROTON TUNNELLING DYNAMICS AND AN ISOTOPICALLY DEPENDENT EQUILIBRIUM GEOMETRY IN THE $^{1}\pi - \pi^{*}$ EXCITED STATE OF TROPOLONE

Abstract

Tropolone fluoresces when excited near 370 nm in neon matrices. The phenolic proton tunnels between two equivalent molecular $C_{S}$ structures in the vibrationally relaxed, ""v=0"" levels of both ground and excited electronic states. The ground electronic state, upper tunnleling component $0^{-}$ is substantially thermally populated at $3.5^{\circ} K$ in neon. Small upper limits on the ground state tunnelling splittings enable the gas phase data of Alves and Hollas [Mol. Phys. 23, 927 (1973)] to be analyzed characterizing the double minimum potential in the excited electronic state. The tunneling reduced mass is very close to that of free proton (deuteron). Vibronic analysis of the tropolone fluorescence shows that there are C-C-C bends and C-0 stretches present due to penetration of the ""v-0"" wavefunction tail into the forbidden barrier region in the hydride. These bands are much weaker in the deuteride.