page_title: Mössbauer spectroscopy
section_title: Quadrupole splitting
hierarchical_section_title: Mössbauer spectroscopy / Analysis of Mössbauer spectra / Quadrupole splitting
context_page_description: Mössbauer spectroscopy is a spectroscopic technique based on the Mössbauer effect. This effect, discovered by Rudolf Mössbauer in 1958, consists of the nearly recoil-free emission and absorption of nuclear gamma rays in solids. The consequent nuclear spectroscopy method is exquisitely sensitive to small changes in the chemical environment of certain nuclei.
  Typically, three types of nuclear interactions may be observed: the isomer shift due to differences in nearby electron densities, quadrupole splitting due to atomic-scale electric field gradients; and magnetic Zeeman splitting due to non-nuclear magnetic fields. Due to the high energy and extremely narrow line widths of nuclear gamma rays, Mössbauer spectroscopy is a highly sensitive technique in terms of energy resolution, capable of detecting changes of just a few parts in 10¹¹. It is a method completely unrelated to nuclear magnetic resonance spectroscopy.
context_section_description: Quadrupole splitting reflects the interaction between the nuclear energy levels and surrounding electric field gradient (EFG). Nuclei in states with non-spherical charge distributions, i.e. all those with spin quantum number (I) greater than 1/2, may have a nuclear quadrupole moment. In this case an asymmetrical electric field (produced by an asymmetric electronic charge distribution or ligand arrangement) splits the nuclear energy levels.
  In the case of an isotope with a I = 3/2 excited state, such as ⁵⁷Fe or ¹¹⁹Sn, the excited state is split into two substates mI = ±1/2 and mI = ±3/2. The ground to excited state transitions appear as two specific peaks in a spectrum, sometimes referred to as a "doublet". Quadrupole splitting is measured as the separation between these two peaks and reflects the character of the electric field at the nucleus.
  The quadrupole splitting can be used for determining oxidation state, spin state, site symmetry and the arrangement of ligands.
caption: Fig. 3: Sodium nitroprusside is a common reference material exhibiting quadrupole splitting.