A Typical binding energies of sigma-orbitals

[Nabla94]

I'm interested in typical electron binding energies of conjugated materials such as pentacene. The carbon 1s energy is easy to find in literature (-285 eV), typical 2π and 2π* binding energies are in the range of few eV (-10 eV ... -2 eV) depending on the size of the conjugated system. But typical 2σ and 2σ* binding energies, which should be rather independent of the conjugated system (just like C 1s) are difficult to find. They should be located below and above those of 2π and 2π*, respectively. Does this mean that 2σ* energies are positive?

 

[DrDu]

I would look up parameters from Extended Hückel Theory (EHT).