Reference Label	Details
Heilbronner 1971	E. Heilbronner, R. Gleiter, H. Hopf, V. Hornung, and A. De Meijere, Helv. Chim. Acta 54, 783-794 (1971) Photoelectron-Spectroscopic Evidence for the Orbital Sequence in Fulvene and 3,4-Dimethylenecyclobutene