High resolution carbon 1 s and valence shell electronic excitation spectra of trans-1,3-butadiene and allene studied by electron energy loss spectroscopy

Abstract

The high resolution inner shell electron energy loss spectra of trans-1,3-butadiene and alllene are presented. Also reported are the wide range (5–25 eV) valence shell electron energy loss spectra of these molecules. The inner shell spectra show intense C 1 s→ * transitions well below the Rydberg structure. Transitions to both π * levels in trans-1,3 butadiene are clearly identified. Both molecules show significant structures above the C Is edges which are attributed to σ * shape-resonances as well as double excitations and “shake-up”. Comparisons are made between the inner shell and valence shell spectra. The transitions identified in the inner shell spectra of butadiene and allene help clarify the assignments of the valence shell spectra because of the essential transferability of Rydberg term values. The assignments of the valence shell spectrum of allene are, in turn, helpful in assessing the great variety of published theoretical investigations of this spectrum. In particular, earlier predictions of the π→π * transition in allene at 7.2eV are supported, in disagreement with a more recent calculation.