3 - Methods to Observe and Describe H-Bonds

Abstract

This chapter describes various methods to observe or describe H-bonds. Among them are experimental methods that allow the measuring of various quantities that are related to these H-bonds. Experimental methods, including most of the methods, have been divided into calorimetry—an old but still interesting method—and “other” methods that encompass most of more recent experimental methods. These other methods have been divided into “absorption” or first-order methods and “scattering” or second-order methods. Infrared spectroscopy, not described here, is included in the category of absorption, first-order methods. Three types of properties are particularly important for H-bonds: thermodynamics, geometry, and dynamics. Thermodynamics quantities, such as enthalpies H, may be directly measured by calorimetry on simple H-bonds found in systems that exhibit ideally a single type of H-bonds. Geometrical quantities rely on three basic methods: rotational spectroscopy, X-ray or neutron diffraction, and infrared (IR) spectroscopy. Dynamic quantities such as spectroscopic constants are obtained from IR or Raman spectra. IR spectra are by far the most precise method to measure such quantities related to intramonomer vibrations.