Zero-field splitting parameters, calculations

In 1987 we reported26 that the three possible C3H2 isomers S-2, T-36, and S-37 can be transformed into each other under photochemical conditions. For several reasons propargylene (36) attracted our attention On the one hand the first C3H2 parent species, identified by direct spectroscopic methods, was triplet propargylene (T-36). Its ESR spectrum was published in 1965,63 and, based on the zero-field-splitting parameters, a linear or nearly linear structure was derived. On the other hand, the structural elucidation of 36 by comparison of the calculated and experimental IR spectra turned out to be rather difficult.64... 

Fig. 23 Experimental (a) and calculated (b) electronic Raman profiles, corresponding to the E(C3) transition depicted in Fig. 22. The theoretical profiles were calculated with AX = 107cm A = 2720 cm hco = 800 cm and T = 14.5 K. The value of used to calculate each profile is given in the figure, along with calculated (b) and experimental (a) values of the zero-field-splitting parameter, D. The electronic Raman transitions were folded with a Lorentzian bandshape, with constant width of 15 cm across the spectrum after [56]...

Time-resolved EPR spectroscopy is particularly useful for selective observation of triplet species. By the use of the zero-field splitting parameters D and j obtained from the spectral pattern of each triplet species, the actual conformation can be predicted reasonably well, when those parameters are simulated by theoretical calculation. The time-dependent changes in the spin polarization along the x, y, and z principal axes can provide information concerning the spin-orbit coupling in each direction. 

Except in the highest symmetry cases, ab initio calculation of zero-field splitting in organic molecules requires the use of H , an operator that has only a two-electron part. Then the heavy computation involving two-electron terms cannot be avoided regardless of what spin-orbit Hamiltonian is used. These calculations are difficult because the correlation of the electrons has to be described very well before the zero-field splitting parameters are calculated accurately. Of the... 

Vahtras et al. used the CASSCF(6,6)/DZP and atomic mean-field approximations to calculate the zero-field splitting parameters of benzene, including both spin-spin coupling to the first order and spin-orbit coupling to the second order of... 

The zero field splitting parameter D was found to be in the range 0.2 < D < 1 cm by a perturbation theory calculation which assumed trigonal (or tetragonal) distortion of the predominately octahedral crystal field symmetry. It was necessary to include in the calculation a lower symmetry zero field splitting E(S/ — 8 ) in addition to the axially symmetric term in order to explain the spectrum,... 

S =. As pointed out by Ohno et al. 45) the molecular orbital calculation for the ferric case lacks internal consistency. Hence we turn to the information based on ESR experiments. As has been discussed in Ch. VII, the zero field splitting parameter which appears in the spin Hamiltonian (Eq. 131) may be estimated from the orbital energies derived from ESR data on the low spin hemoglobin azide (Fig. 23). Using the values... 

Table 5 Zero-field splitting parameters E and D (K) for some transition metal complexes calculated with the PBE fimctional and performing a structural optimization except for the Fe4 complex where the experimental structure was employed...

V. G. Malkin, M. Kaupp. Calculation of zero-field splitting parameters Comparison of a two-component noncolinear spin-density-functional method and a one-component perturbational approach. 

D. Ganyushin, F. Neese. First-principles calculations of zero-field splitting parameters. /. Chem. Phys., 125 (2006) 024103. 

Vahtras, O., Loboda, O., Minaev, B., Agren, H., Ruud, K. (2002). Ab initio calculations of zero-field splitting parameters. Chemical Physics, 279, 133. 

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