A NEW VIEW OF THE QUANTUM DYNAMICS FOR PROTON-TRANSFER ALONG HYDROGEN-BONDS - VIBRATIONAL SPECTROSCOPY WITH NEUTRONS

Inelastic neutron scattering is an ideal tool to observe proton transf er dynamics along hydrogen bonds in the quantum regime. ''Tunnelling'' transitions associated with the quantum transfer of a single proton h ave been observed for potassium hydrogen carbonate, KHCO3, and similar hydrogen bonded complexes in the solid state. More recently, the tunn elling transition was observed for a polypeptide: polyglycine II. The ''tunnelling'' bands are rather sharp. Therefore, the proton transfer is largely decoupled from the heavy atom dynamics. Force-field calcula tions including INS intensities confirm that the proton dynamics are a lmost totally decoupled from those of the surrounding heavy atoms. Thi s is in contrast to the ''vibration assisted tunnelling'' model that s upposes a large modulation of the double minimum potential by the low frequency modes of the hydrogen bond. The double minimum potential fun ctions governing the proton transfer are discussed.