A spin state

In the second case, the 180° pulse is applied only to nucleus A, causing an exchange of spin labels of the A spin states to occur, so the direction of rotation of the X magnetization vectors is reversed during the second... 

Fig. 1. Schematic one-dimensional cross section through the Gibbs free energy surface G(R) of a spin-state transition system along the totally symmetric stretching coordinate. The situation for three characteristic temperatures is shown (B = barrier height, ZPE = zero-point energy, 28 = asymmetry parameter, J = electronic coupling parameter, AG° = Gh — GJ...

Of considerable interest is the pressure dependence of a spin-state transition which will be considered in Sect. 8 in some detail. It is assumed that the pressure... 

Perturbation of a spin-state equilibrium by ultrasound results in the absorption of sound, the absorption coefficient a (neper cm ) being determined as a function of frequency /(Hz) according to ... 

The description of states participating in a spin-state transition as electronic isomers with discrete nuclear configurations, in particular different metal-ligand distances, requires that separate electronic and vibrational spectra of the two spin states exist. Indeed, a superposition of the individual vibrational spectra of the two states is in general observed, the relative contribution of the states being a function of temperature [41, 139, 140, 141, 142]. This observation sets a lower limit for the spin-state lifetime longer than the nuclear vibrational period, i.e.,... 

The simultaneous observation of the two EPR spectra has been reported in particular for several tris(dithiocarbamato)iron(III) complexes [Fe(R2NC(S)S)3] where R = cyclohexyl [143], hydroxyethyl [144], and n-butyl [145, 146]. In addition, a considerable number of iron(III) complexes of the type [Fe" -N402] has been found which show EPR spectra of both the HS and LS isomers. These comprise [Fe(X-SalEen)2] Y2 where X-SalEen is the Schiff-base ligand obtained by condensation of X-substituted salicylaldehyde and IV-ethylethylenediamine [147] and similar compounds [100, 148, 149, 150, 151]. For the cobalt(II) complex [Co(terpy)2] (004)2, it is not completely clear whether the two observed EPR spectra are due to HS and LS states related by a spin-state transformation [152]. 

The nitrosyl iron complex Fe( J-mph) NO shows a spin-state transition between the S = f and S = ground states. The structure of the complex is characterized by ... 

Upper limit to Value of R(LT) corresponds to incomplete HS - LS transformation Donor atom set of central Fe atom, the only one showing a spin-state transition Two crystallographically independent iron(III) atoms involved, only one showing a spin-state transition... 

It should be noted that the structural changes which occur in the course of a spin-state transition are concentrated in the central region of the molecule and these changes are considerably larger than any modification encountered in... 

One of the first uses of ESR spectra to measure the rate of a chemical reaction was by Ward and Weissman in the early 1950s.1 They made use of a form of the Heisenberg uncertainty principle (eqn 5.1) to relate the lifetime of a spin state to the uncertainty in the energy of the state. 

Thus, if the lifetime of a spin state is 81, the energy level is broadened by an amount H/81, with consequences for ESR line widths. Ward and Weissman1 added some unreduced naphthalene to a solution of the radical anion, and, from the observed broadening, computed 81, and from 8/ the rate constant for the electron transfer reaction ... 

Figure 8.18 TbPc2-based molecular spin-tronic devices, (a) Graphene nanotransistor with sensitivity at the single-molecule level [39, 256], (b) Scheme of the supramolecular spin valve architecture [217]. (c) Scheme of the carbon nanotube NEMS. The magnetization reversal of a TbPc 2 SIMM from a spin state Jz = +6 to Jz = -6 results in a rotation...

As with polarization, the orientation of spin is represented by state vectors. Just like ix and jy which serve as base vectors to decompose polarization vectors such as the diagonal vector considered above, a spin state like Sy can be represented by a vector s+, which is a linear combination of two base vectors s+ and s. This decomposition could be formulated, by analogy as... 

Compound T(K) Fe—O Fe Ncentral Fe-Nouter (A) Spin state References... 

This expression is of the order of what one would calculate by squaring Equation (15) and summing to get the mean square field. The difference is due to the fact that two nuclear spins can simultaneously flip so as to conserve magnetic energy since they are coupled by the dipolar interaction. This process limits the lifetime of a spin state and gives rise to an additional line breadth. For two nonidentical nuclei such processes do not con-... 

Reduction of p-oxo-bis[tetraphenylporphin iron(iii)] with sodium amalgam gives several products sequentially. The first reduction product is the radical-anion [(tpp)Fe ] , which has a spin state of - at 77 K and at 300 K. This is the first reported study of an Fe -porphyrin.Mossbauer data on a range of tetra-aryl-substituted iron-porphines and their p-oxo-bridged derivatives have been reported. A crystallographic study on bis(imidazole) otPy -tetraphenylporphinatoiron(iii) chloride-methanol solvate shows the [FeN ] core to be quasitetragonal. An n.m.r. study has been made of the related... 

Consider a system of n electrons in a spin state S. We know that there are for n linearly independent orbitals... 

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