Are HOMO and -IP values equal in experimental measurements? Does exist an experimental method giving different values for HOMO and -IP of a molecule? Is it meaningful? Cyclic voltammetry, photoemission spectroscopy,..?
The ionization potential IP(the whole molecule) of a molecule can be approximated as the HOMO absolute E(the energy). The electron affinity can be related to the energy of the LUMO level(the energy).
Dear Chen
Thank you for ur response. But I want to know whether always -IP is equal to HOMO or one can obtain different values as well
The ionization potential IP(the whole molecule) is equal to the energy difference between HOMO and vacuum level. The absolute zero energy is the vacuum level.
IP can be measured experimentally, while a HOMO energy is a theoretical concept which has sense only within the one-electron approximation (like in Hartree-Fock theory). The ionization potential can be approximated by the HOMO energy within the Koopmans theorem, this is why these two quantities are mistakedly treated as identical by some people. So the answer is: no.
Standard hydrogen electrode(SHE) is typically used for reference potential. The absolute potential of the SHE is 4.44 ± 0.02 V at 25 °C. Therefore, for any electrode at 25 °C:
E(abs) = E(SHE) + 4,44 V
(abs) denotes the absolute potential
(SHE) denotes the electrode potential relative to the standard hydrogen electrode.
Dear Prof Korona and Prof. Chen thank you for your time you have spent answering this question.
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