OPTICAL PROBES OF PROTON TUNNELING IN MOLECULAR-SOLIDS

Low-temperature optical spectroscopy of guest-host molecular crystal s ystems provides a very sensitive tool to study proton tunneling proces ses. Examples include the light-induced creation and evolution of ''pr oton defects', translational tunneling along hydrogen bonds as well as rotational tunneling of methyl groups. Absorption spectra at 2 K of g amma-picoline single crystals evolve over time scales of days due to t he slow spin conversion of the methyl groups which leads to an orderin g of the crystal.