Isotropic hyperfine

Determination of relative signs of isotropic hyperfine coupling constants J. Chem. Rhys. 63 3515-22... 

In this exercise, we will predict the isotropic hyperfine splitting in HNCN radical at a... 

Gaussian computes isotropic hyperfine coupling constants as part of the population analysis, given in the section labeled "Fermi contact analysis the values are in atomic-units. It is necessary to convert these values to other units in order to compare with experiment we will be converting from atomic units to MHz, using the following expressions ri6ltYg ... 

Compute the isotropic hyperfine coupling constant for each of the atoms in HNCN with the HF, MP2, MP4(SDQ) and QCISD methods, using the D95(d,p) basis set Make sure that the population analysis for each job uses the proper electron density by including the Density=Current keyword in the route section. Also, include the 5D keyword in each job s route sectionfas was done in the original study). 

The electron densities for a spin electrons and for spin electrons are always equal in a singlet spin state, but in non-singlet spin states the densities may be different, giving a resultant spin density. If we evaluate the spin density function at the position of certain nuclei, it gives a value proportional to the isotropic hyperfine coupling constant that can be measured from electron spin resonance experiments. 

In the following, all isotropic hyperfine coupling constants were calculated using the BLYP functional and the EPR-II basis set. A full geometry optimization was done in all cases. 

The and operators determine the isotropic and anisotropic parts of the hyperfine coupling constant (eq. (10.11)), respectively. The latter contribution averages out for rapidly tumbling molecules (solution or gas phase), and the (isotropic) hyperfine coupling constant is therefore determined by the Fermi-Contact contribution, i.e. the electron density at the nucleus. 

As can be seen from Table 2, the agreement between measured and calculated isotropic hyperfine coupling parameters is good, confirming previous interpretations [9] of ESR data. 

Isotropic Hyperfine coupling constants an are related to the spin densities p(rN) at the corresponding nuclei by... 

FIGURE 5.1 Isotropic hyperfine pattern for 51VIV in S-band. The spectrum is from V0S04 in aqueous solution. Use of the low frequency enhances the second-order effect of unequal splitting between the eight hyperfine lines. 

McConnell, H.M. and Chesnut, D.B. 1958. Theory of isotropic hyperfine interactions in ir-electron radicals. The Journal of Chemical Physics 28 107-117. 

Table 5 Isotropic hyperfine g-value and coupling constants in mT...

Fig. 2. The mSR frequency spectrum of GaAs at 10 K in an external field of 1.15 T applied along a <110) direction. The upper two frequencies result from Mu that has an isotropic hyperfine interaction. The starred frequencies are from Mu that have hyperfine interactions axially symmetric about (111) axes. The angles in brackets refer to the direction of the external field with respect to the Mu symmetry axes. The frequency labelled vis due to a diamagnetic center. From Kiefl et al. (1985).

Another unusual feature of CuCl and CuBr is the presence of two Mu centers with nearly identical isotropic hyperfine parameters. One of the centers, Mu7, occurs preferentially at low temperatures but is metastable as evidenced by a thermally activated transition to the second center, Mu77 (see Fig. 13). As the temperature increases, the effects of this transition first appear as an increse of the Mu7 depolarization rate (lifetime broadening). At higher temperatures the transition becomes fast enough so that... 

Using the approach described in the previous section, Van de Walle (1990) also calculated the isotropic hyperfine constant for muonium at T in Si. The calculated value for iK0)]x/ experimental result (0.45) for normal muonium in Si. Motional averaging slightly lowers the theoretical value, bringing it in even closer agreement with experiment. 

The observation that the isomer shift varies between 0.39 mm s 1 at 4 K and 0.54 mm s-1 at 80 or 298 K only, irrespective of the charge n of the complexes (n = 0, 1,2), immediately implies that all complexes contain an octahedral, high-spin ferric ion (d5, S = ). Furthermore, from the applied-field Mossbauer spectra of [Fem(LBuMet)] (.S t = f), [Fem(LBuMet )]+ (5t = 2), and [Fem(LBuMet )]2+ (5t = ) intrinsic isotropic hyperfine couphng constants, AFe/gNpN, of -21.4, -21.0, -20.8 T, respectively, have been established. These values are also typical of high-spin iron(III). 

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