https://doi.org/10.1351/goldbook.08590
Spectrum of a material under the influence of an applied external perturbation represented by a variable \(\tau\), relative to a reference spectrum.
Note:
The reference spectrum may be chosen in many ways; e.g., it may be the average over \(\tau\), of the observed spectrum, or it may be zero.
The reference spectrum may be chosen in many ways; e.g., it may be the average over \(\tau\), of the observed spectrum, or it may be zero.