Ionization Energy

Ionization Energy:

 Ei (SI unit: kJ mol–1 or J per molecule) The minimum energy required to remove an electron from an isolated MOLECULAR ENTITY (in its vibrational GROUND STATE) in the gaseous phase. If the resulting molecular entity is considered to be in its
vibrational ground state, one refers to the energy as the
“adiabatic ionization energy.” If the molecular entity produced possesses the vibrational energy determined by the Franck-Condon principle (according to which the electron ejection takes place without an accompanying change in molecular geometry), the energy is called the “vertical ionization energy.” The name “ionization energy” is preferred to the somewhat misleading
earlier name “ionization potential.”