| Abstract
| - The energies of vertical electron attachment to cyclobutanone, its 2- and 3-oxa derivatives, 1,2-cyclobutanedione,and 2,2‘,4,4‘-tetramethyl-1,3-cyclobutanedione have been measured in the 0−6 eV energy range by means ofelectron transmission spectroscopy. The energies of temporary anion formation are nicely reproduced byshifting and scaling the virtual π* orbital energies calculated for the MP2/6-31G*-optimized geometries ofthe neutral molecules. The linear correlation between experimental and calculated energy values reported inthe literature for the empty π*CC orbitals fits the present data on the π*CO orbitals with the same accuracy.The two π* anion states observed in the ET spectrum of the 1,3-dione (split by 1.25 eV) are assigned to thein-phase and out-of-phase combinations in order of increasing energy, i.e., the sequence dictated by through-space interaction. The calculations indicate a large through-space splitting (>2 eV) of the empty carbonyl π*orbitals, reduced by through-bond destabilization of the in-phase combination.
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