Fluorescence of benzene vapor has been measured at room temperature in the presence of a number of hydrocarbons in order to determine the rates of collisional deactivation of the excited benzene singletlpar;1B2urpar;. A distinct although small efficiency is shown by monohyphen;olefins with larger number of alkyl substituents on the double bond, such as trimethylethylene and tetramethylethylene. The rates of fluorescence quenching parallel approximately the corresponding rates of energy transfer from the benzene tripletlpar;2B1urpar;. Conjugated dienes are much more efficient quenchers both of the singletlpar;1B2urpar;and of the tripletlpar;3B1urpar;benzene. Nonconjugated dienes, on the other hand, show in both cases an efficiency which is approximately comparable to that of the monohyphen;olefins.
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