Knowledge Bank

``Channel Three” refers to the intramolecular mechanism responsible for the sudden and anomalous fluorescence quenching at about $3,000 cm^{-1} $ above the origin of the benzene $S_{1} $ state. Previous $studies1$ found high rotational selectivity in Channel Three, suggesting that Channel Three is promoted by rotation induced vibrational mixing. This hypothesis is born out in the study of the fluorescence decay in benzene/acetylene complexes. Dramatic increase in fluorescence lifetimes and yields, in comparison with the benzene molecule, in the Channel Three region was observed in certain structural isomers of the benzene/acetylene complexes in which the molecular rotation of benzene along its top axis is hindered by intermolecular interactions.