Perfluorocyclobutane electronic state spectroscopy by high-resolution vacuum ultraviolet photoabsorption, electron impact,HeIphotoelectron spectroscopy, andab initiocalculations

Abstract

The electronic state spectroscopy of perfluorocyclobutane $(c\text{\ensuremath{-}}{\mathrm{C}}_{4}{\mathrm{F}}_{8})$ has been investigated using high resolution vacuum ultraviolet (vuv) photoabsorption spectroscopy in the energy range $6.0--11\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$. The electron energy loss spectrum (EELS) was also recorded in the nonelectric dipolar interaction mode ($100\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$ incident energy, 10\ifmmode^\circ\else\textdegree\fi{} scattering angle) over the $8--14\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$ energy-loss range and the excited states in the $11--14\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$ spectral region have been observed. An $\mathrm{He}\phantom{\rule{0.2em}{0ex}}I$ photoelectron spectrum recorded between 11.0 and $19.8\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$ is compared with earlier lower resolution results. This has allowed us to derive a more precise value of $12.291\ifmmode\pm\else\textpm\fi{}0.002\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$ for the ground neutral state vertical ionization energy. All spectra presented in this paper represent the highest resolution data yet reported for perfluorocyclobutane, to the best of our knowledge. Ab initio calculations have been performed for helping in the assignment of the spectral bands for both neutral excited states and ionic states.