Abstract:

Excess spectroscopy was proposed following the idea of excess thermodynamic functions. It is complementary to classical excess functions because it provides rich information on molecular interactions. In this review, we introduce in detail the concept of excess spectroscopy and the measurement of excess spectra for the case of infrared spectroscopy. We then describe the merits of using excess spectroscopy to enhance apparent spectral resolution, judge the non-ideality of mixtures, determine the selectivity of molecular interactions, identify distinct species or clusters in solutions, and provide information related to charge distributions in molecules. Following this, we review the progress in methodology where excess spectroscopy is extended to partial molar excess spectroscopy and Raman spectroscopy. The extension of binary mixtures to pseudo binary mixtures and/or liquid samples to solid samples is also described. Finally, we discuss several recent applications of excess spectroscopy in the study of hydrogen-bonding interactions in ionic liquid-molecular solvent systems, halogen-bonding interactions in benzene derivative-dimethylsulfoxide (DMSO) mixtures, and interactions between inorganic cations/anions and water molecules. Clearly, excess spectroscopy has opened a new window through which we can view rich information about molecular interactions.

Key words: Excess spectra, ATR-IR, Hydrogen bond, Halogen bond, Molecular interaction, Cluster, Species identification