Cooperative proton transfer and tunneling in dye doped benzoic acid crystals

In seleno-indigo doped benzoic acid crystals, the energy level structure of a pair of benzoic acid dimers coupled to the impurity center is characteri zed by optical spectroscopy and transient hole burning in electric fields. The lowest energy states involve degenerate, polar proton configurations. P roton tunneling lifts this degeneracy. The tunneling matrix element for pro ton transfer in a benzoic acid dimer equals 6.5 +/- 1.5 GHz, a value compar able to those found with other guest molecules. Relaxation between the two ground state levels involves the concerted motion of four protons and deter mines the intensity distribution of the fine structure observed in hole bur ning. (C) 1999 Elsevier Science B.V. All rights reserved.