INDICATIONS OF PROTON TUNNELING IN THE PROTON GLASS (BETAINE PHOSPHATE)(0.15)(BETAINE PHOSPHITE)(0.85) FROM ENDOR AND PULSED ESR STUDIES

The local proton order in the proton glass (betaine phosphate)(0.15) ( betaine phosphite)(0.85) is studied by means of electron nuclear doubl e-resonance and two-dimensional electron spin-echo envelope modulation (ESEEM) techniques. The experimental results allow very detailed comp arisons with theoretical models such as the one-, and three-dimensiona l random-bond random-field (RBRF) Ising glass model. The attempt to de scribe the experimental behavior within the framework of the random-bo nd random-field (RBRF) Ising glass, which was worked out for deuteron glasses, suffers in conspicuous insufficiency at least at lower temper atures. Taking the influence of proton tunneling into account by using the stochastic model of a quantum RBRF Ising glass, the experimental results can fully be described. Furthermore, ESEEM experiments on a pa rtially deuterated BP0.15BPI0.85 crystal confirm the different local p olarization behavior in the protonated and deuterated hydrogen bonds i n agreement with the model expectation.