Optical Studies of Proton Transfer Processes at Low Temperatures in Hydrogen Bonded Molecular Crystals

Abstract

The tautomerization of carboxylic acid dimers at low temperatures is an example of a translational tunneling system. It provides a model for the study of the interplay of tunneling and relaxation in a condensed phase environment. A new experimental approach for the study of such systems was made possible by the discovery of dilute mixed crystal systems of indigo dyes in benzoic acid. The spectral changes of the dye can be used as very sensitive probes of the structure and the dynamics of neighboring benzoic acid dimers. The, measured rates of tautomerization and the deuteration effect are discussed in relation to previous measurements by NMR at higher temperatures and with regard to the reaction coordinate.