energy level 

of a free atom, ion or molecule
Synonym: energy state
https://doi.org/10.1351/goldbook.08246
Set of one or more stationary quantum states of a free atom, ion, or molecule having a particular internal energy.
Note:
SI unit: J. Common unit: electron volt, symbol eV, where 1 eV=1.602176634E−19J. Energy levels are also expressed as kJmol−1.
Source:
PAC, 2021, 93, 647. (Glossary of methods and terms used in analytical spectroscopy (IUPAC Recommendations 2019)) on page 658 [Terms] [Paper]
Citation: 'energy level' in IUPAC Compendium of Chemical Terminology, 5th ed. International Union of Pure and Applied Chemistry; 2025. Online version 5.0.0, 2025. https://doi.org/10.1351/goldbook.08246 RIS BibTex EndNote
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