Temperature spinning profile

Figure 6. Species profiles in a rotating disk CVD reactor. Inlet gas is 0.1 percent silane in a carrier of 99.9 percent helium. The disk temperature is 1000 K and the spin rate is 1000 rpm.

The Florence NMRD program (8) (available at www.postgenomicnmr.net) has been developed to calculate the paramagnetic enhancement to the NMRD profiles due to contact and dipolar nuclear relaxation rate in the slow rotation limit (see Section V.B of Chapter 2). It includes the hyperfine coupling of any rhombicity between electron-spin and metal nuclear-spin, for any metal-nucleus spin quantum number, any electron-spin quantum number and any g tensor anisotropy. In case measurements are available at several temperatures, it includes the possibility to consider an Arrhenius relationship for the electron relaxation time, if the latter is field independent. 

The temperature dependence of the MRD profile for the protein-water systems where the protein is magnetically a solid, is remarkably weak. The relaxation rate is proportional to IjT, which is consistent with Eq. (4) that was derived on the assumption that the relaxation process is a direct spin-phonon coupling rather than an indirect or Raman process. If it were a Raman process, there would be no magnetic field dependence of the relaxation rate therefore, the temperature dependence provides good evidence in support of the theoretical foundations of Eq. (6). 

Balcom et al. developed a novel diagnostic technique suitable for a thin-film by MRI.42 The authors obtained one-dimensional water content profiles with nominal resolution of 6 p,m using a prototype resonator and double half k-space spin echo single-point imaging (SPI) technique.15 Even at room temperature, partial dehydration of the membrane in the anode side was captured clearly with high spatial resolution. 

In a recent study of the peak profiles of X-ray powder diffraction on [Fe(phen)2(NCS)2] as a function of temperature, particularly near the transition temperature Tc, different patterns have been found for the two spin state phases70 . From these observations a structural change going along with the spin state change in I can no longer be ruled out. 

Distinct and different peak profiles of X-ray powder diffraction on [Fe(4,7-(CH3)2-phen)2(NCS)2] have been observed for the 5T2 and A, phases, respectively183). The intensities of the lines show the same temperature dependence and the same hysteresis behaviour as the area fractions of the HS and the LS quadrupole doublets, respectively, of the Mossbauer spectra. These studies183) provide clear evidence for a simultaneous change of the electronic spin state and of the crystallographic properties. 

A pronounced hysteresis of ATC = 9.5 K has been observed (Tc = 181.86 K for rising and Tc = 172.33 K for falling temperature). The authors attempted to describe the results with the thermodynamic model for spin transitions of Slichter and Drickamer 91 Different diffraction patterns were recorded above and below Tc, where only one spin isomer was present (see Fig. 39). This provides evidence that a crystallographic phase change accompanies the abrupt spin phase transition in this compound. The temperature dependence of the peak profiles was found to follow that of the HS fraction as derived from the Mossbauer spectra, which shows that the crystallographic phase change is directly associated with the interconversion of the two spin phases. The Debye-Waller factors were evaluated for the two spin phases they showed at Tc a discontinuity of Af 35% on going from the HS to the LS phase. The shape of the transition curve near Tc and Tc itself, were somewhat different in three independently prepared samples. 

Fig. 39. Peak profiles of X-ray powder diffraction on Fe(bt)2-(NCS)21 in the temperature region of the spin transition (from Ref. 124)...

Figure 8. Species profiles in a rotating-disk CVD reactor. Inlet gas is 0.1% silane in carrier of 99.9% helium. The disk temperature is 1000 K and the spin rate is 1000 rpm. Reprinted with permission from R. J. Kee, G. H. Evans, and M. E. Coltrin in Supercomputer Research in Chemistry and Chemical Engineering (K. F. Jensen and D. G. Truhlar, eds.), p. 334. ACS Symposium Series 353, American Chemical Society, Washington, D.C., 1987 [31]. Copyright 1987 American Chemical Society.

The rebound mechanism, though in a modified version, has been recently supported by theoretical calculations of KIF using the density functional theory (Yoshizawa et al., 2000). The calculations demonstrate that the transition state for the H-atom abstraction from ethane involves a linear [FeO.H...C] array a resultant radical species with a spin density of nearly one is bound to an iron-hydroxy complex, followed by recombination and release of product ethanol. According to the calculation of the reaction energy profile, the carbon radical species is not a stable reaction intermediate with a finite lifetime. The calculated KIF at 300 K is in the range of 7-13 in accord with experimental data and is predicted to be significantly dependent on temperature and substituents. It was also shown from femtosecond dynamic calculations in the FeOVCH4 system that the direct abstraction mechanism can occur in 100-200 fs. 

Figure 7 Properties of the mixed compounds (TMDTDSF)2PF6 (a) Faraday susceptibility and resistivity (insert) (b)77Se 7Y1 versus temperature profile showing the onset of a SDW ground state at 7 K (c)777 f1 versus T, revealing the 2kF SDW contribution below 7p which is plotted versus temperature in part (d). (e) 2kF one-dimensional scattering amplitude and linewidth, which is the signature of spin-Peierls fluctuations vanishing below 2 K when SDW fluctuations are taking over (after Ref. 49). (From Refs. 48 and 51.)...

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