Closer examination of two-trace two-dimensional (2T2D) correlation spectroscopy

Abstract

Two-trace two-dimensional (2T2D) correlation spectroscopy compares a pair of spectra by applying a form of cross correlation analysis. Planar maps of correlation intensities with two independent axes of spectral variables, like IR wavenumbers, are obtained. 2T2D correlation takes advantage of the fact that spectral intensities of bands arising from the same origin cannot change independently of each other and must be synchronized. In contrast, intensities arising from different sources often change asynchronously. Using cross peaks observed in the correlation spectra, one can distinguish and classify different contributing species represented in the original pair of spectra in a systematic manner. Highly overlapped neighboring bands originating from different sources can also be identified by the presence of asynchronous cross peaks, thus enhancing the apparent spectral resolution. It can be mathematically shown that 2T2D correlation is a special case of the well-established generalized 2D correlation scheme, where the two traces of the measured spectra are combined with an additional null spectrum with all the elements set to be zero for the analysis. This realization makes it possible to utilize existing software for generalized 2D correlation for routine 2T2D analysis.