PROTON-TRANSFER DYNAMICS IN THE HYDROGEN-BOND - A DIRECT MEASUREMENT OF THE INCOHERENT TUNNELING RATE BY NMR AND THE QUANTUM-TO-CLASSICAL TRANSITION

The incoherent tunnelling rate for proton transfer in the hydrogen bon ds of benzoic acid dimers has been measured by field cycling NMR from the dispersion of the proton spin-lattice relaxation time which maps o ut the spectral density function directly. The intermediate region bet ween quantum and classical dynamics has been studied by measuring the inverse correlation time for proton transfer as a function of temperat ure and the contribution made by tunnelling in the excited states of t he double minimum potential has been determined. (C) 1997 Elsevier Sci ence B.V.