Inner-Shell Excitations in Weak-Bond Molecules

It is proposed that Rydberg and valence sigma* conjugate orbitals have separate existences and can be seen in the same spectrum if the sigma* MO can be disentangled from the Rydberg manifold. Because the energy of the sigma* MO is a consequence of the sigma-sigma* split resulting from bond formation, the spectra of molecules having weak bonds should show low-lying transitions to sigma* in addition to the conjugate Rydberg bands. Inelastic electron scattering spectra in the x-ray region (270-730 eV) of molecules having bond strengths in the 20-50 kcal/mol regime clearly show well-isolated transitions to low-lying sigma* MOs, and in some cases the simultaneous presence of virtual sigma* and Rydberg conjugate orbitals.