The ground state tunneling splitting of the 2-pyridone · 2-hydroxypyridine dimer

The symmetric tautomerization of the 2-pyridone · 2-hydroxypyridine complex has been investigated by quantum chemical methods. This reaction is accomplished by an intermolecular double proton transfer between the monomer units. The barrier of the proton transfer is found to be 9.45-9.85 kcal/mol depending on the level of theory. The ground state tunneling splitting that can be expected for proton exchange in a symmetric double well potential is computed by a recently developed accurate method and was shown to be 1x108 s-1. This finding is in contradiction to the analysis of recent experimental results of Borst et al. [Chem. Phys. 283 (2002) 341], as they propose that their measured splitting of 5x108 s-1 exclusively arises from the splitting in the first excited state. Our results suggest that the measured splitting may be interpreted as either the difference between the tunneling splittings of the ground state and the first excited state or the ground state tunneling splitting itself