In search of the molecular triplet of C₆₀ using low temperature Raman spectroscopy

The excited state properties of C₆₀ thin films have been probed in the temperature range 77-273K using Raman spectroscopy. The change in the Raman, 2A_g mode of C₆₀ (whose position is largely independent of temperature) was monitored as a function of the excitation intensity at 514.5nm. This mode normally positioned at 1469cm^-1, was seen to shift reversibly to a lower Raman frequency with increasing laser intensity. Two excited state species have been identified. The first, at 1466cm^-1 has been associated with the molecular triplet of C₆₀. The second species at 1463cm^-1, has been speculated to be an excited state co-operative involving two or more excited states in the solid and is seen to be intrinsic to solid state C₆₀ below the phase transition.