Pattern recognitions of band shifting, overlapping, and broadening using global phase description derived from generalized two-dimensional correlation spectroscopy

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.