Raman and Nuclear Resonant Spectroscopy in Geosciences

Herein is presented a review of recent technical advances in Raman and nuclear resonance spectroscopy (both Mössbauer spectroscopy and nuclear resonant inelastic Xray scattering spectroscopy (NRIXS)), as they have great implications for geoscience. Optical and X-ray spectroscopies probe different momentum and energy transfers caused by interactions between the incident light and the lattice, making them complementary and applicable to numerous scientific applications. Raman spectroscopy measures the optical vibrational modes at infinitely small momentum transfer whereas Mössbauer spectroscopy imparts negligible momentum transfer but can distinguish hyperfine interactions (quadrupole splitting, chemical shift, and magnetism) with neV energies. NRIXS measures the phonon density of states, which can be used to derive vibrational, thermodynamic, elastic, and electronic properties of the materials. Raman spectroscopy provides valuable and easily interpretable information about material properties using a Chapter 14 Treatise on Geochemistry 2 number of experimental platforms such as noninvasive tomographic imaging of minerals with sub-micrometer spatial resolution, in situ studies under extreme conditions of high pressure and temperature (P-T), and as a remote mineralogical and organic/biological probe for planetary exploration missions. The advent of synchrotron Mössbauer and NRIXS experiments provides a unique capability to probe the properties of ironcontaining minerals that exist in the Earth’s interior at high P-T conditions, as well as materials from the surface of Mars and the Moon. These recent and exciting developments have become possible because of the availability of dedicated synchrotron radiation beamlines, and the successful operation of two miniaturized Mössbauer spectrometers on the surface of Mars. The techniques addressed here permit the study of vibrational, electronic, elastic, and thermodynamic properties of planetary materials under variable thermodynamic conditions, making them highly valuable in geoscience implications. Chapter 14 Treatise on Geochemistry 3