Inner shell electron-energy loss spectroscopy of some heterocyclic molecules

The carbon K-shell spectra of gaseous furan, pyrrole, tetrahydrofuran, pyrrolidine, tetrahydropyran, and piperidine have been recorded by electron energy loss spectroscopy (ISEELS) under electric dipole scattering conditions (2.5 keV impact, small angle.) The spectra are dominated by transitions to unoccupied valence states of π and σ symmetry. Features attributed to transitions to π*(CH 2 ) levels are consistently observed below the ionization threshold in the spectra of the saturated species. the positions of continuum features are generally in agreement with a previously documented correlation with bond lengths. Additional weak continuum features are observed in the smaller saturated heterocyclic species which are ascribed to delocalized σ* states.