Fluorescence and Internal Conversion in Naphthalene Vapor

The fluorescence spectrum of naphthalene vapor has been investigated upon excitation in the second excited singlet state. Although no collisions occur during the lifetime of the second excited state, fluorescence is observed to originate in the first excited state, indicating that internal conversion is an intramolecular process in this case. The intensity of fluorescence from the second excited state is established to be not more than 0.002 of that from the first state. Some comments are made on the theory of radiationless transitions.