Two-Dimensional Infrared (2D IR) Spectroscopy: Theory and Applications

TLDR

Two-dimensional infrared (2D IR) spectroscopy is a novel vibrational technique that maps interactions among functional groups by correlating IR signals across two wavenumbers. In 2D IR, cross‑correlation of IR signal fluctuations induced by an external perturbation produces a two‑dimensional spectrum that simplifies overlapping peaks, enhances resolution, and enables unambiguous band assignments. Illustrative spectra of atactic polystyrene and the proteinaceous component of human stratum corneum show the method’s ability to resolve complex chemical interactions.

Abstract

A novel concept in vibrational spectroscopy called two-dimensional infrared (2D IR) spectroscopy is described. In 2D IR, a spectrum defined by two independent wavenumbers is generated by a cross-correlation analysis of dynamic fluctuations of IR signals induced by an external perturbation. 2D IR spectra are especially suited for elucidating various chemical interactions among functional groups. Notable features of the 2D IR approach are: simplification of complex spectra consisting of many overlapped peaks; enhancement of spectral resolution by spreading peaks over the second dimension; and establishment of unambiguous assignments through correlation analysis of bands selectively coupled by various interaction mechanisms. The procedure for generating 2D IR correlation spectra and the properties of the 2D spectra are discussed in detail. Examples of 2D IR spectra are presented for atactic polystyrene and the proteinacious component of human stratum corneum to demonstrate the utility of this technique.