Pattern Recognitions of Band Shifting, Overlapping, and Broadening Using Global Phase Description Derived from Generalized Two-Dimensional Correlation Spectroscopy

Abstract

In this paper we propose a new method for pattern recognitions of band shifting, overlapping, and broadening using a global phase map derived from generalized two-dimensional correlation spectroscopy (global 2D phase map). To obtain the distinct patterns for band shifting, overlapping, and broadening, original spectra are subjected to scaling so that the spectra after the scaling do not cross one another. After such pretreatment the band shifting creates the tilting of a correlation plane, the band overlapping yields four flat terraces, and the band broadening generates an asymmetric curved plane with respect to the diagonal line in the global 2D phase map. An example of the application of this method has been investigated using two bands due to the CH2 symmetric stretching and CN stretching vibrations in temperature-dependent infrared (IR) transmission spectra of an eleven-layer Langmuir–Blodgett (LB) film of 2-dodecyl-7,7,8,8-tetracyanoquinodimethane (dodecyl-TCNQ). The global 2D phase maps develop the clearly distinct patterns due to the shifting, overlapping, and broadening even if the shifting and broadening bands are overlapped with other bands.

Advances in two-dimensional correlation spectroscopy

“…A large number of model spectral maps were compiled by these authors for the identification of peak patterns. Pattern recognition on features of 2D global phase maps was also attempted by Morita and Ozaki [77] based on band shift, overlapping, and broadening of peaks.…”

“…2D global phase angle maps were used to study a Langmuir-Brogett film of dodecyl TCNQ under varying temperature [91]. Pattern recognition method was proposed for analyzing features of 2D global phase map based on band shift, overlapping, and broadening of peaks [77]. Chin and Lin [92] employed generalized 2D correlation as a useful tool to study reaction kinetics involving parallel reaction paths, as clear asynchronous peaks develop for reactant and product pairs.…”

Concerning the spectral resolution enhancement of dynamic 2D-IR

“…It is worth noting that, during the transition from dynamic 2D-IR to generalized 2D-IR, the major advantages of the former were adopted. Despite of the generally accepted spectral resolution enhancement, a number of studies [19][20][21][22][23][24][25][26], including our systematic studies in polymers [27][28][29][30][31], have been carried out to investigate the effect of variables, such as overlapping bands, bandwidth change, peak shift and data set on the final results in generalized 2D-IR. It has been found that the new features revealed in the 2D plots do not necessarily correspond to real infrared absorption bands.…”

Application of 2D correlation spectroscopy with MCR in the preparation of glycerol polyesters

“…This approach has been applied, for example, to elucidate the photopolymerization of acrylic and epoxy monomers and to the transetherification and selfcondensation reactions in a melamine/formaldehyde resin [8,9]. In addition to the ability of correlation spectroscopy to characterize such temporal spectral changes it can be used to resolve complicated regions of a spectrum, identify band patterns, and interpret synchronous versus asynchronous correlation spectra [10][11][12].…”