| Abstract
| - Generalized two-dimensional correlation spectroscopy (2D-COS) establishes correlations between intensityvariations within a series of ordered spectra generated by an external perturbation. The influence of the referencespectrum on the synchronicity has been investigated by using spectral simulations and mathematical analysis.With a two-state model, it is found that for two synchronous bands, 2D asynchronous peaks appear when noreference is used, whereas when the mean or the first spectrum of the series is chosen, no asynchronous peakoccurs, as expected. In the latter cases, the intensity ratio of the dynamic spectra is constant throughout theexperiment, which is not the case if a reference is not subtracted. The proportionality constant is equal to theratio of the amplitudes of the intensity variations. This result is mathematically demonstrated and generalizedto any form of intensity variation: if the intensity ratio of two bands is constant throughout the experiment,the elements of the 2D asynchronous matrix are zero at any wavenumber. In addition, it is established thatany spectrum of the series can be used as a reference to evidence the occurrence of synchronisms. In the caseof linear intensity variations, the correlations between two bands are always synchronous as long as a spectrumof the series or the mean spectrum is chosen as the reference. Thus, it is very difficult to determine whetherthe intensity variations have different variation rates. All the conclusions drawn from the mathematical analysisare confirmed with spectral simulations. These mathematical considerations are applied to absorbance spectra.
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