optical spectroscopy 

https://doi.org/10.1351/goldbook.O04314
The study of systems by the electromagnetic radiation with which they interact or that they produce. By convention, spectroscopic properties are expressed in terms of wavelength in vacuo, not the wavelength within the medium being studied.
Source:
PAC, 1985, 57, 105. (Names, symbols, definitions and units of quantities in optical spectroscopy (Recommendations 1984)) on page 107 [Terms] [Paper]
Citation: 'optical spectroscopy' 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.O04314 RIS BibTex EndNote
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Last revised: February 24, 2014