Wavelength, wavenumber or frequency at which the total energy emitted by a sample as heat does not change upon a chemical
reaction in or a physical change of the sample. Its position depends on the experimental
conditions.
Note:
The spectral differences between the isosbestic points and the iso-optoacoustic points are the result of the non-linear relationship
between the molar absorption coefficient and the photoacoustic signal.
Source:
PAC, 2007, 79, 293
(Glossary of terms used in photochemistry, 3rd edition (IUPAC Recommendations 2006))
on page 358