Electronic g value

From this final equation it may be observed that large deviations from the free electron g value occur when (a) the integral (0O Lz2 0O) is nonzero and (b) excited electronic states are rather close in energy to the ground state. The other principal values of the g tensor have the same form as shown in Eq. (18C). 

The symmetry of Oj on the adsorption site can also be mono- or triclinic. In a field of triclinic symmetry, the g value expressions differ from those of orthorhombic symmetry and calculations show that both gxx and gn can exceed the free electron g value. This case has been considered by Miller and Haneman (47) for OJ adsorbed on elemental semiconductors. 

The electron spin resonance (ESR) spectra of the radical ions of 230 indicate there are no large deviations from the free-electron g value that would have been expected had the 3d orbitals of the sulfur atom played an important part in influencing the spin density of the molecule. Consequently, structure 230 may not be the main contributor to the electronic structure of the compound. Such stability in this compound could be attributed to the inertness of the NSN group and the presence of the aromatic naphthalene ring. However, the H-NMR chemical shifts (8 = 4.45 ppm) suggest the compound is antiaromatic. The compound is therefore referred to as an ambiguous aromatic compound (78JA1235). 

The g value for a free electron is 2.0023. The principal source of the local magnetic fields, which causes the g factor to deviate from the free electron g value, is an orbital magnetic moment introduced by a mixing of excited states into the ground state. 

Breit was the first to suggest [3] that the unanticipated results of hyperfine measurements [4,5] may be explained if the electron g value deviates slightly from 2, the Dirac value. This observation was soon confirmed by the experiment of Kusch and Foley [6]. Together with the discovery of the Lamb shift in the spectrum of hydrogen atom, this provided a timely stimulus for the renormalization... 

The effect of suUur participation on the orbital g -shifts in the EPR spectra, illustrated in Pig. 20, accounts for the qualitatively different spectra observed for tyrosyl phenoxyl and Tyr-Cys phenoxyl radicals (Gerfen et al., 1996). The rhombicity of the simple tyrosyl radical EPR spectrum is a consequence of the splitting between gx and gy principal g -values. These g -shifts deviate from the free electron g--value ge = 2.00023) as a result of orbital angular momentum contributions. While a nondegenerate electronic state (such as the A" ground state for ere) contains no hrst-order unquenched orbital momentum, second-order spin-orbit mixing between close-lying a and a" functions results... 

The Zeeman term is considered first and the hyperfine interaction is discussed in Section 4.2.2. The free electron g-value of = 2.0023 is shifted when the electron is surrounded by material, because of the spin-orbit coupling to the other electron states. The shift is... 

Group 3 (Sc, Y, La) metallofullerenes exhibit ESR hfs, which provides us with important information on the electronic structures of the metallofullerenes. Typical ESR-active monometallofullerenes are La Cs2, Y Cs2, and Sc C82- The ESR hfs of a metallofullerene was first observed in La Cs2 by the IBM Almaden group (Johnson et al., 1992) (Eigure 15) and was discussed within the framework of an intrafullerene electron transfer. The observation of eight equally spaced lines provides evidence of isotropic electron-nuclear hyperfine coupling (hfc) to La with a nuclear spin quantum number I = 7/2. The observed electron g-value of 2.0010, close to that measured for the Ceo radical anion (Allemand et al., 1991 Krusic et al., 1991), indicates that a single unpaired electron resides in the LUMO of the carbon cage. They also observed hyperfine... 

Figure 4. Nomogram for interpretation of the 2p i magnetic field components of the Si and S donors. The free-electron g value is assumed, a hole k value of k = 0.65 is then measured. (Reproduced with permission from Ref. 24. Copyright 1983 American Physical Society.)...

There are many sources that contribute to an ESR spectrum. Apart from the applied external field, local magnetic fields are also created within the sample by other unpaired electrons in the molecule or the surroundings, or from magnetic nuclei in the molecule/ion. There may also be contributions to the hf structure arising from the orbital angular momentum of the electron, which will influence the electronic g-value. In the present calculations, the g-value of the free electron, g = 2.0023, is assumed throughout. 

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