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. Author manuscript; available in PMC: 2009 Oct 26.
Published in final edited form as: Prog Nucleic Acid Res Mol Biol. 2008;82:147–197. doi: 10.1016/S0079-6603(08)00005-6

Fig. 2.

Fig. 2

Electron spin energy level diagram and the continuous-wave EPR spectrum. (A) A schematic of the energy levels of an electron spin. In the absence of an applied magnetic field, the energy levels corresponding to the two electron spin states (Sz = ±1/2) are degenerate (purple line). In the presence of an applied magnetic field, the electron energy levels separate according to the spin quantum number Sz (the Zeeman effect) and the nuclear spin quantum number MI (the hyperfine interaction). (B) A representative EPR spectrum. The spectrum is obtained by varying the applied magnetic field strength at a fixed microwave frequency, and is shown as the first derivative of the absorption spectrum. The three peaks correspond to the three transitions indicated by the dotted arrows in the energy diagram shown in (A).