Figure 1.

He(I) UV photoelectron spectra of the model compounds, 1-MeC and 1-MeT, showing assignments and vertical IPs associated with the five highest occupied molecular orbitals. Theoretical ionization potentials obtained from 3–21G SCF calculations are given above the spectra. The lowest energy experimental adiabatic IPs are also given. For each model compound, orbital diagrams illustrate major atomic orbital contributions to the five highest occupied molecular orbitals (B₁–B₅). Positive regions of the orbital wave functions are shaded. For π orbitals (B₁, B₂, and B₅ of 1-MeC and B₁, B₃, and B₅ of 1-MeT) the viewing angle is different than for loan-pair orbitals (B₃ and B₄ of 1-MeC and B₂ and B₄ of 1-MeT).