Two-dimensional codistribution spectroscopy to determine the sequential order of distributed presence of species

Two-dimensional codistribution spectroscopy (2DCDS), a technique designed specifically for the analysis of population dynamics, such as temporal distributions of species during a chemical reaction, is described. 2D codistribution analysis focus on the signal features reflecting the distributed presence of species, instead of the variation patterns of perturbation-induced deviations from the reference state, which has been traditionally analyzed by two-dimensional correlation spectroscopy (2DCOS). This technique is derived from the moment analysis of spectral intensity distributions along the perturbation variable axis within a well-defined observation interval. Derivation and properties of 2D codistribution spectra are provided, and comparison is made to 2D correlation spectroscopy with the help of simulated IR spectra generated from model chemical reactions.