Electronic Excitation to Singlet States of 1,3-C4F6, c-C4F6 and 2-C4F6 by Electron Impact - Electron Energy-Loss Spectroscopy and ab lnitio Calculations

We report on the first measurements of the electron impact electronic excitation cross sections for C 4F 6 isomers, hexafluoro-1,3-butadiene (1,3-C 4F 6), hexafluorocyclobutene (c-C 4F 6), and hexafluoro-2-butyne (2-C 4F 6), measured at 100 eV, 3° scattering angle, while sweeping the energy loss over the range 2.0-15.0 eV. Under these experimental conditions, optically allowed transitions are favored. The electronic state spectroscopy has been investigated and the assignments supported by quantum chemical calculations. The n = 3 members of the Rydberg series have been assigned converging to the lowest ionization energy limits of the C 4F 6 isomers and classified according to the magnitude of the quantum defects (δ).