This technique can be defined as a type of spectroscopy that is used to examine the ability of an analyte to interact with ultraviolet or visible light through absorption.
Light in the ultraviolet or visible range has the same amount of energy as occurs between the energy levels for some of the electrons in molecules.
If the energy of this light exactly matches a difference in one of the energy levels, the electron will move from an orbital in a lower energy state to an empty orbital in a higher energy state if the molecule absorbs this light.
The absorption of both ultraviolet and visible light, especially in the range of 200–780 nm, often involves electronic transitions in molecules by electrons or nonbonded electrons (n) as they go to an excited electron state.
For this reason, organic molecules with only single bonds and σ electrons, but no electrons or nonbonded electrons, tend to not absorb in this region of the UV‐vis spectrum.