Electron energy loss measurements on pyrene (C16H10) vapor

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Abstract
Electron energy loss spectra from 0 to 25 eV were measured with 50 keV electrons on pyrene vapor. The results indicate the existence of five strong excitations between 3.9 and 7.0 eV, identified as π–π* excitations. Four of them exhibit vibrational sublevels with 0.17 eV energy separation. Less pronounced maxima of the energy loss function are observed between 8 and 11 eV, which cannot be interpreted conclusively. Broader structures between 11 and 18 eV are attributed to excitations involving σ states. The present results are related to absorption measurements on pyrene in solution and to investigations of pyrene single crystals. Values for the solution and crystal shift of the different π–π* excitations are obtained (∼−0.2 eV).