Spin state energy gap

Figure 3.8. (a) Spin state energy gaps (AE) for two different nuclei at field strength Bq. (b) Resulting frequency-sweep NMR spectrum. 

Figure 3.9. (a) The B0 field strength required for two different nuclei to attain the same spin state energy gap AE. (b) Resulting field-sweep NMR spectrum. 

The correlations illustrated in Figure 5 recall a long-ago-established inverse correlation between Co chemical shifts and ligand field strength in low-spin Co complexes. More specifically, the reciprocal of the i (ground state)-ri (excited state) energy gap is proportional to the downfield Co chemical shift in low-spin Co complexes. Interestingly, the extreme relative... 

Ah initio programs attempt to compute the lowest-energy state of a specified multiplicity. Thus, calculations for different spin states will give the lowest-energy state and a few of the excited states. This is most often done to determine singlet-triplet gaps in organic molecules. 

All but two of the known synthetic iron(IV)-oxo compounds are low-spin, 5=1 [202, 240]. The first example of an iron(IV)-oxo model compound with spin 5 = 2 was the quasioctahedral complex [(H20)5Fe =0] (5 = 0.38 mm s, A q = 0.33 mm s ) which was obtained by treating [Fe°(H20)6] with ozone in acidic aqueous solution [204]. The spin state of iron in this type of structure is determined by the energy gap between the d,2 y2 and the d y orbitals [241]. The weak water ligands induce a sufficiently small gap being less than the spin paring energy and stabilizing the HS state (Fig. 8.25, case a). 

Lanthanide ions offer several salient properties that make them especially attractive as qubit candidates (i) their magnetic states provide proper definitions of the qubit basis (ii) they show reasonably long coherence times (iii) important qubit parameters, such as the energy gap AE and the Rabi frequency 2R, can be chemically tuned by the design of the lanthanide co-ordination shell and (iv) the same molecular structure can be realized with many different lanthanide ions (e.g. with or without nuclear spin), thus providing further versatility for the design of spin qubits or hybrid spin registers. 

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