https://doi.org/10.1351/goldbook.I03199
Minimum energy required to eject an electron out of a neutral atom or molecule in its @[email protected] The @[email protected] @[email protected] energy refers to the formation of the molecular ion in its ground vibrational state and the @[email protected] energy applies to the transition to the molecular ion without change in geometry. This quantity was formerly called @[email protected] The second @[email protected] energy of an atom is the energy required to eject the second electron from the atom (energy for the process I03199.png).
Sources:
Green Book, 2nd ed., p. 20 [Terms] [Book]
PAC, 1994, 66, 1077. (Glossary of terms used in physical organic chemistry (IUPAC Recommendations 1994)) on page 1128 [Terms] [Paper]