Spectroscopy — IR, Raman, NMR, NQR, EPR, NGR (Mössbauer), XAS, EXAFS, ESCA, XPS

Abstract

All spectroscopic techniques described here provide information on the local environment of specific types of atoms, and all depend on some process associated with a characteristic energy change. Infrared (IR) and Raman Spectroscopy (RS) depend on vibration or rotation of bonded atoms. Nuclear Magnetic and Electric Quadrupole Resonance (NMR, NQR) depend on transitions between quantized energy levels for interactions of the magnetic dipole and electric quadrupole of an atomic nucleus with the crystal field. Electron Paramagnetic Resonance (EPR) arises similarly for an uncoupled electron spin. Nuclear Gamma-Ray (Mössbauer) Resonance (NGR) measures the effect of the crystal field on the energy difference between an excited and an un- excited state of an atomic nucleus. Various X-ray spectroscopic techniques exploit the energy levels for the orbital electrons, which again depend on the crystal field and the chemical bonding. Ejection of an orbital electron by an incoming X-ray photon is followed by filling of the hole by another electron together with emission of a new X-ray photon or an Auger electron. X-Ray Absorption (XAS) measures the energy required to eject an orbital electron. Phase interference between the waves for the ejected electron and the bound electrons leads to Extended X-Ray Absorption Fine Structure (EXAFS). Auger electrons and emitted X-ray photons are used in Electron Spectroscopy for Chemical Analysis (ESCA) and X-Ray Photon Spectroscopy (XPS).