Electron energy loss measurements on pyrene (C16H10) vapor

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 sigma 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 (approx.-0.2 eV)