where η is the dynamic viscosity of the solvent, R is the radius of a single solvent molecule, and M is the molecular mass. It should be noted that Kramers' model is one dimensional; a mode at both the Franck-Condon point and the transition state of highest similarity should be used. Using this formalism, Hoche and co-workers found rates were strongly dependant on the solvent used. The fastest rate was observed for methylcyclohexane, with a rate of 3 × 10 12 s -1 , and slows down to 2.2 × 10 7 s -1 when using dimethyl sulfoxide. In this paradigm, it is observed that in the lower polarity solvents, the conical intersection transition dominate loss, harmonic transitions are dominant in higher polarity solvents (Figure ). The compared harmonic rates are calculated using a Fermi's Golden Rule methodology. Blacker and co-workers similarly examined internal conversion at a conical intersection in nicotinamide adenine dinucleotide and nicotinamide adenine dinucleotide phosphate, and noted an exponential relationship between viscosity and the rate constant for both the short and long components of the well known bi-exponential fluorescent spectra (Figure ).