ABSTRACT
Two-dimensional (2D) correlation spectroscopy is a new spectral analysis method where the spectral intensity is plotted as a function of two independent spectral variables; e.g., wavenumber, wavelength, or frequency [1-4]. Peaks appearing on a 2D spectral plane provide useful information not readily accessible from a conventional one-dimensional spectrum. Figure 4.1a and Figure 4.1b show examples of three-and two-dimensional representations of a 2D vibrational correlation spectrum, respectively [5]. The threedimensional representation provides the best overall view of the intensity profile of a correlation spectrum while the contour map representation is better for observing the detailed peak shapes and positions. Correlations among bands that belong to the same chemical group, or groups interacting strongly, can be investigated by means of 2D correlation spectroscopy. Figure 4.2 illustrates the general conceptual scheme for obtaining a 2D correlation spectrum. The primary component of the experimental procedure used in 2D correlation spectroscopy is an external perturbation applied to stimulate a system. When an external perturbation is applied to a system, some selective changes in the state, order, or surroundings of constituents occur. The excitation and subsequent relaxation process toward the equilibrium is monitored with an electromagnetic probe. The overall response of the stimulated system to the applied external perturbation leads to distinctive variations in the measured spectrum. The spectral changes are then transformed into 2D spectra by means of a correlation method.
