CHEMICAL AND THEORETICAL BACKGROUND
Box 4.1 Photoelectron spectroscopy (PES)
The energies of occupied atomic orbitals and molecular orbitals
can be studied by photoelectron spectroscopy (PES). In a
PES experiment, an atom or molecule is irradiated with electromagnetic
radiation of energy E, causing electrons to be
ejected from the system. Each electron possesses a characteristic
binding energy and must absorb an amount of energy
equal to, or in excess of, this binding energy if it is to be
ejected. The energy of an ejected electron is that in excess
of the binding energy assuming that E is greater than the
binding energy.
Excess energy of electron ¼ E (binding energy of electron)
Since the excess energy can be measured and E is known, the
binding energy can be determined. Koopmans’ theorem