Spin hamiltonian parameters

The ESR measurements were made at RT or 77 K on a Varian E-9 spectrometer (X-band), equipped with an on-line computer for data analysis. Spin-Hamiltonian parameters (g and A values) were obtained from calculated spectra using the program SIM14 A [26]. The absolute concentration of the paramagnetic species was determined from the integrated area of the spectra. Values of g were determined using as reference the sharp peak at g = 2.0008 of the E i center (marked with an asterisk in Fig. 3) the center was formed by UV irradiation of the silica dewar used as sample holder. 

Neese, F., Solomon, E.I. Calculation and interpretation of spin-Hamiltonian parameters in transition metal complexes. In Miller, J.S., Drillon, M. (eds.) Magnetoscience - From Molecules to Materials, vol. 4, p. 345. Wiley, Weinheim (2003)... 

Once a hyperfine pattern has been recognized, the line position information can be summarized by the spin Hamiltonian parameters, g and at. These parameters can be extracted from spectra by a linear least-squares fit of experimental line positions to eqn (2.3). However, for high-spin nuclei and/or large couplings, one soon finds that the lines are not evenly spaced as predicted by eqn (2.3) and second-order corrections must be made. Solving the spin Hamiltonian, eqn (2.1), to second order in perturbation theory, eqn (2.3) becomes 4... 

The spectrum of the low-spin manganese(n) complex, [Mn(dppe)2(CO)(CN-Bu)]2+, (dppe = Ph2PCH2CH2PPh2), in a CH2C12/THF glass is shown in Figure 4.4(a).24 The spin Hamiltonian parameters, obtained from least-squares... 

Table 5.1 shows the spin Hamiltonian parameters for some of the complexes. The equilibrium constants and rate constants are given in Table 5.2. 

The EPR spectrum is a reflection of the electronic structure of the paramagnet. The latter may be complicated (especially in low-symmetry biological systems), and the precise relation between the two may be very difficult to establish. As an intermediate level of interpretation, the concept of the spin Hamiltonian was developed, which will be dealt with later in Part 2 on theory. For the time being it suffices to know that in this approach the EPR spectrum is described by means of a small number of parameters, the spin-Hamiltonian parameters, such as g-values, A-values, and )-values. This approach has the advantage that spectral data can be easily tabulated, while a demanding interpretation of the parameters in terms of the electronic structure can be deferred to a later date, for example, by the time we have developed a sufficiently adequate theory to describe electronic structure. In the meantime we can use the spin-Hamiltonian parameters for less demanding, but not necessarily less relevant applications, for example, spin counting. We can also try to establish... 

For matrices of modest dimensions 1024 matrix diagonalizations may not be a serious CPU problem for a PC, but if we include (as we will in the next chapter) distributions in the spin Hamiltonian parameters the required CPU time goes up by, say, two orders of magnitude, and if we want to implement automatic minimization, we must pay with another two or three orders of magnitude in CPU-time. 

This chapter considers the distribution of spin Hamiltonian parameters and their relation to conformational distribution of biomolecular structure. Distribution of a g-value or g-strain leads to an inhomogeneous broadening of the resonance line. Just like the g-value, also the linewidth, W, in general, turns out to be anisotropic, and this has important consequences for powder patterns, that is, for the shape of EPR spectra from randomly oriented molecules. A statistical theory of g-strain is developed, and it is subsequently found that a special case of this theory (the case of full correlation between strain parameters) turns out to properly describe broadening in bioEPR. The possible cause and nature of strain in paramagnetic proteins is discussed. 

When the anisotropic spin Hamiltonian parameters g, and are obtained from the powder spectrum in the rigid limit, one can dehne the quantities... 

For relatively simple systems of high symmetry (or for systems assumed to be simple) the system spin Hamiltonian parameters are readily relatable to those of the individual centers, for example,... 

The zero-field spin Hamiltonian parameters, D and E, are assumed to be distributed according to a normal distribution with standard deviations oD and aE, which we will express as a percentage of the average values (D) and (E). -Strain itself is not expected to be of significance, because the shape of high-spin spectra in the weak-field limit is dominated by the zero-field interaction. 

Section 3, the main section of this paper, deals with the NMR of bulk semiconductors. Section 3.1 lists the various relevant terms in the NMR spin Hamiltonian. The NMR techniques and strategies that can be employed to obtain the individual NMR parameters of the spin Hamiltonian and theoretical calculations of NMR parameters will be discussed in Sect. 3.2. The remaining subsections will provide examples from the important classes of semiconductors that illustrate the measurement and interpretation of each of the spin Hamiltonian parameters, with an emphasis on what information about semiconductors the parameters convey. 

EPR spin Hamiltonian parameters (at 77 K) ofTi3+ in titanosilicate molecular sieves generated by... 

Cu0(l)-Zr02(99), on the other hand, contained only two types of Cu + species viz., isolated Cu + ions (II) and interacting Cu ions (III) (Fig. 11.12, curve c). The spin Hamiltonian parameters of these species are different from Cu0(l)-Ce02(99). Unlike in Cu0(l)-Ce02(99) (Fig. 11.12, curve a), the perpendicular Cu-hyperfine features could not be resolved in Cu0(l)-Zr02(99) (Fig. 11.12, curve c). Type m species of CuO-Zr02 showed a signal at gav = 2.12. 

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