Experimental Methods of Investigation of Electron Spin Interactions Based on ESR Phenomena: Continuous Wave EPR Measurements

Abstract

The method of electron spin resonance (ESR, Sect. 3.1) has proven to be the leading approach in the investigation of electron spin interactions in chemistry, biology and physics. Structural and dynamic properties of molecular objects of interest can be measured and characterized by suitable parameters through an arsenal of experimental ESR methods including conventional Continuous wave (CW ESR), electrically (ED ESR) and optically (OD ESR) detected ESR and advanced pulse techniques. The CW technique is used for collecting information of interest through the analysis of ESR spectra or saturation curves, obtained from electron-electron double resonance (ELDOR) or double electron-electron resonance (DEER), electron-nuclear double resonance (ENDOR) or multifrequency ESR (MF ESR) techniques. OD ESR makes it possible to acquire good ESR, ELDOR and ENDOR spectra using the simple and very sensitive luminescence technique. Application of such methods as two-dimensional ESR (2D ESR), (fried) two-dimensional electron-electron double resonance (2D-ELDOR), ENDOR with circularly polarized radiofrequency fields (CP-ENDOR), electron-nuclear-nuclear resonance (double ENDOR), proton-electron double resonance imaging (PEDRI), and electron-nuclear-nuclear triple resonance (TRIPLE) can be more informative than simple CW ESR experiments for appropriate systems. Methods of reaction yield detection magnetic resonance (RYDMR) and magnetically affected reaction yield (MARY) can also be used in the context of CW and pulse techniques. This chapter briefly describes theoretical grounds and typical application of the various methods of modern CW ESR spectroscopy, which continue to evolve synergetic and at a rather rapid pace.