PROTON TUNNELING IN PORPHYCENE SEEDED IN A SUPERSONIC JET

Porphycene, a constitutional isomer of porphyrin, was investigated in a supersonic jet expansion using laser-induced fluorescence and hole b urning techniques. The Lines recorded in the fluorescence excitation s pectrum were split into doublers. No splitting was detected if one or both inner hydrogen atoms were replaced by deuterium. The doublet stru cture also disappeared upon formation of a complex between porphycene and water or alcohol. These findings indicate that the origin of the d oublet structure in bare porphycene is the tunneling splitting due to the exchange of two inner protons between the nitrogen atoms. From the spectral response to deuteration, and to a change in cooling conditio ns, it is deduced that the tunneling splitting is higher in the ground state than in the first excited singlet state. (C) 1998 Elsevier Scie nce B.V. All rights reserved.