ABSTRACT
The molecular spectroscopy of adsorbed chemical species has two principal subdivisions: invasive methods, such as X-ray photoelectron or secondary ion mass spectrometry, that require sample desiccation and high vacuum, and noninvasive methods that require little or no alteration of a sample from its natural state. The use of nuclear magnetic resonance (NMR) spectroscopy to study surfaces has a shorter history and fewer applications than vibrational spectroscopies, the primary reason being that the sensitivity of NMR is intrinsically much lower than IR. Vibrational spectroscopy is recognized as a sensitive method, but interferences from water, trace impurities, and surface hydroxyls have limited its use on environmental particles. A straightforward method of studying cation adsorption is to use a spectroscopic technique that can give information about the cation itself, e.g., ultraviolet, extended X-ray absorption fine structure, or NMR spectroscopy. Vibrational and NMR spectroscopy provide powerful tools to examine the surface chemistry of naturally occurring inorganic particles.
