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1.
The characteristics of spontaneous Raman scattering from solutions of diatomic molecules are reviewed, especially with regard to what they may tell one about the dynamics of molecular motion. In the limit of extreme motional narrowing the polarized component of the Q branch is a lrentzian with a width which depends upon the rate (τ-1) of dephasing of the molecular vibrations. An approximate, closed, quantum-mechanical expression for the contribution of ‘translational-translational’ quasielastic scattering to τ-1, called τph -1(T-T), is derived. The translational states of the liquid are determined by invoking the Lennard-Jones-Devonshire (LJD) cell model. The full LJD cell potential is replaced by an harmonic approximation thereto. The dependence of the τph(T-T) upon thermodynamic variables and microscopic properties is discussed. The derived expression for τph -1 (T-T) is then used to compute upper bounds on τ for liquid N2 and O2, for which experimental data are available. It is concluded that the T-T quasielastic scattering mechanism is essentially negligible and that other mechanisms must be dominant in determining τ. In particular, it is suggested that solvent-induced vibrational-reorientational coupling may be quite important.  相似文献   

2.
The electron spin-lattice and spin-spin phase relaxation measurements of Cu2+ ions in various crystals are reviewed and discussed. Examples of the Debye temperature determination from a wide temperature range measurements of the spin-lattice relaxation time T1 are shown. An influence of the Jahn-Teller dynamics on T1 is presented. The phase relaxation described by the phase memory time TM is affected by temperature due to the spin packet width modulation by molecular motions. The TM is anisotropic in crystals and can be different for different hyperfine lines of an EPR spectrum.  相似文献   

3.
The temperature dependence of spin-lattice relaxation rates was analyzed for four high-spin nonheme iron proteins between 5 and 20 K, for three high-spin iron porphyrins between 5 and 118 K, and for four high-spin heme proteins between 5 and 150 to 298 K. For the nonheme proteins the zero-field splittings, D, are less than 0.7 cm(-1), and the relaxation is dominated by the Orbach and Raman processes. For the iron porphyrins and heme proteins D is between 4 and 12 cm(-1) and the relaxation is dominated by the Orbach process between about 5 and 100 K and by a local mode at higher temperatures. The relaxation rates for the heme proteins in glassy matrices extrapolated to values at room temperature that are similar to values obtained by NMR relaxivity in fluid solution. This similarity suggests that for high-spin Fe(III) heme proteins with effective intramolecular spin-lattice relaxation processes, the additional motional freedom gained when a relatively large protein goes from glassy solid to liquid solution at room temperature has little impact on spin-lattice relaxation.  相似文献   

4.
Measurements of the neutron scattering static structure factor S(Q) are reported for orthobaric liquid fluorine at 77K for an incident wavelength of 1·2Å. The observed S(Q) and the atom-atom correlation function are discussed and compared with those of other halogens and oxygen. From the d(r) pair distribution function it is shown that liquid fluorine has a coordination number of first neighbours more similar to liquid oxygen than halogens. The number of atoms in the first and second coordination shell is in good agreement with a close-packed arrangement of atoms.  相似文献   

5.
The temperature dependence of X-band electron spin-lattice relaxation between about 10 and 300 K in magnetically dilute solids and up to the softening temperature in glassy solvents was analyzed for three organic radicals and 14 S = 12 transition metal complexes. Contributions from the direct, Raman, local vibrational mode, thermally activated, and Orbach processes were considered. For most samples it was necessary to include more than one process to fit the experimental data. Debye temperatures were between 50 and 135 K. For small molecules the Debye temperature required to fit the relaxation data was higher in 1:1 water:glycerol than in organic solvents. For larger molecules the Debye temperature was less dependent upon solvent and more dependent upon the characteristics of the molecule. The coefficients of the Raman process increased with increasing g anisotropy and decreasing rigidity of the molecule. For the transition metal complexes the data are consistent with major contributions from local modes with energies in the range of 185 to 350 K (130 to 240 cm-1). The coefficient for this contribution increases in the order 3d < 4d transition metal. For C-60 anions there is a major contribution from a thermally activated process with an activation energy of about 240 cm-1. For low-spin hemes the dominant contribution at higher temperatures is from a local mode or thermally activated process with a characteristic energy of about 175 cm-1.  相似文献   

6.
Electron spin relaxation times of a Nycomed triarylmethyl radical (sym-trityl) in water, 1:1 water:glycerol, and 1:9 water:glycerol were measured at L-band, S-band, and X-band by pulsed EPR methods. In H(2)O solution, T(1) is 17+/-1 micros at X-band at ambient temperature, is nearly independent of microwave frequency, and exhibits little dependence on viscosity. The temperature dependence of T(1) in 1:1 water:glycerol is characteristic of domination by a Raman process between 20 and 80 K. The increased spin-lattice relaxation rates at higher temperatures, including room temperature, are attributed to a local vibrational mode that modulates spin-orbit coupling. In H(2)O solution, T(2) is 11+/-1 micros at X-band, increasing to 13+/-1 micros at L-band. For more viscous solvent mixtures, T(2) is much shorter than T(1) and weakly frequency dependent, which indicates that incomplete motional averaging of hyperfine anisotropy makes a significant contribution to T(2). In water and 1:1 water:glycerol solutions continuous wave EPR linewidths are not relaxation determined, but become relaxation determined in the higher viscosity 1:9 water:glycerol solutions. The Lorentzian component of the 250-MHz linewidths as a function of viscosity is in good agreement with T(2)-determined contributions to the linewidths at higher frequencies.  相似文献   

7.
Low-temperature (4-55 K) pulsed EPR measurements were performed with the magnetic field directed along the z-axis of the g-factor of the low-symmetry octahedral complex [(63)Cu(L-aspartate)(2)(H2O)2] undergoing dynamic Jahn-Teller effect in diaqua(L-aspartate)Zn(II) hydrate single crystals. Spin-lattice relaxation time T(1) and phase memory time T(M) were determined by the electron spin echo (ESE) method. The relaxation rate 1/T(1) increases strongly over 5 decades in the temperature range 4-55 K. Various processes and mechanisms of T(1)-relaxation are discussed, and it is shown that the relaxation is governed mainly by Raman relaxation processes with the Debye temperature Theta(D)=204 K, with a detectable contribution from disorder in the doped Cu(2+) ions system below 12 K. An analytical approximation of the transport integral I(8) is given in temperature range T=0.025-10Theta(D) and applied for computer fitting procedures. Since the Jahn-Teller distorted configurations differ strongly in energy (delta(12)=240 cm(-1)), there is no influence of the classical vibronic dynamics mechanism on T(1). Dephasing of the ESE (phase relaxation) is governed by instantaneous diffusion and spectral diffusion below 20 K with resulting rigid lattice value 1/T(0)(M)=1.88 MHz. Above this temperature the relaxation rate 1/T(M) increases upon heating due to two mechanisms. The first is the phonon-controlled excitation to the first excited vibronic level of energy Delta=243 cm(-1), with subsequent tunneling to the neighbor potential well. This vibronic-type dynamics also produces a temperature-dependent broadening of lines in the ESEEM spectra. The second mechanism is produced by the spin-lattice relaxation. The increase in T(M) is described in terms of the spin packets forming inhomogeneously broadened EPR lines.  相似文献   

8.
T 1 andT m for nitridochromium(V) tetratolylporphyrin and nitridochromium(V) octaethylporphyrin were measured by saturation recovery and electron spin echo EPR, respectively, between 10 and 130 K. The temperature dependence of 1/T 1 was similar to that observed previously for chromium(V) complexes of hydroxycarboxylic acids. The spin lattice relaxation rate was faster in the perpendicular plane (the porphyrin plane) than normal to this plane. 1/T m was orientation dependent with the fastest rates observed for orientations intermediate between the principal axes. The orientation dependence of 1/T m increased with increasing temperature and decreasing rigidity of the matrix, and is attributed to molecular motion.  相似文献   

9.
Electron spin-lattice relaxation rates for the low-spin [Rh(CN)(6)](4-) complex in KCl were measured by the inversion recovery and saturation recovery techniques, in the range of 5 to 30 K. Angular variation experiments indicate that electron spin-lattice relaxation times present axial symmetry. The data fit very well to a relaxation process involving localized anharmonic vibration modes, also responsible for the g tensor temperature dependence.  相似文献   

10.
Electron spin resonance relaxation times were measured for the radiation induced radical ion SeO43? in selenium doped KDP single crystals. The spin-lattice relaxation time was found to obey the relation T1R?1 = AT + BT50θ2T x4csch2x dx from 7 K to 200 K except in the neighborhood of the transition temperature where the data fit the expression T1?1 = T1R?1b±T ? Tcm± where θ is the Debye temperature and the plus and minus signs refer to data at temperatures above and below Tc respectively.  相似文献   

11.
A theory for paramagnetic relaxation enhancement (PRE) in systems with S> 1 at low magnetic field is developed for the case when the fluctuations of zero-field splitting (ZFS) in the molecular frame are larger than the averaged ZFS. The validity limits of the new theory are discussed, and its performance is evaluated by comparisons with the general slow-motion approach. The relevance of the new approach for the proton PRE in aqueous solution of Ni(II) is discussed.  相似文献   

12.
Electron spin echo measurements on neutral poly (thiophene) show a clear modulation of the spin-echo decay. Analysis of the modulation and its Fourier transformed (ω) power spectrum indicates that the wave function of the spin defect is extended over ~ 25 proton nuclei. The functional behavior of the longitudinal relaxation, T1, versus temperature is very similar to that observed previously for (CH)x, although T1 values for poly (thiophene) are significantly longer.  相似文献   

13.
The processes of the electron paramagnetic relaxation, molecular motions and structural changes in aqueous solutions of manganese nitrate have been investigated by direct measurement of spin-lattice (T 1) and spin-spin (T 2) relaxation times for a wide range of concentrations, temperatures and viscosities. T 1 and T 2 were measured by a non-resonance absorption method.

It was discovered that some structural regions exist at the different concentrations of Mn(II) ions in solution. So, the structure of highly concentrated solutions may be considered as one of the corresponding crystallohydrate. The structural microinhomogeneities were observed also in the intermediate concentration range at definite temperatures. It is shown that the relaxation mechanism proposed by Bloembergen and Morgan is not effective in the concentration range studied by us.

The analysis of relaxation times and E.P.R. spectra has shown the formation of ‘liquid microphases’ at the freezing point of the solution. Such microphases can exist at temperatures a few tenths of a degree below the solvent freezing point, and its composition considerably differs from the initial solution.

The correlation times for intramolecular and intermolecular electron relaxation mechanisms are evaluated and their nature is discussed.  相似文献   

14.
Electron spin phase memory times,T m, as a function of temperature were measured for Cu(II) bis(diethyldithiocarbamate), Cu(Et2dtc)2; Cu(II) bis(diethyldithiophosphate), Cu(Et2dtp)2; Cu(II) bis(diphenyldithiophosphate), Cu(Ph2dtp)2; Cu(II) tetratolylporphyrin, CuTTP; vanadyl 5-(4-carboxyphenyl)-10,15,20-tritolylporphyrin, VOTTP-COOH; and Ag(II) tetratolylporphyrin, AgTTP, doped into powdered samples of closely-related diamagnetic hosts. For the three metalloporphyrins, the electron spin relaxation rate (1/T m) increased monotonically with increasing temperature. However the temperature dependence of the relaxation rate was not monotonic for the three other Cu(II) complexes. For Cu(Et2dtc)2 and Cu(Et2dtp)2 the temperature dependence of 1/T m between about 85 and 130 K is attributed to the effects of methyl rotation, with activation energies of 1.0 kcal/mole. Between 120 and 250 K the 1/T m data for Cu(Ph2dtp)2 exhibit effects that are attributed to motion of the phenyl rings.  相似文献   

15.
16.
The magnetic coupling between Fe(III) and Cu(II) and the relaxation behavior of the spin centered at the iron have been studied in di- and trinuclear clusters. The experimental spectra have been analyzed in terms of a simple cross-relaxation model. In the strongly coupled trimer the relaxation rates are determined by a Boltzmann factor and a single field- and temperature-independent scaling parameter1 w 0, while the weakly coupled dimer exhibits obviously a more complex behavior.  相似文献   

17.
Satellite structure in the X-ray photoelectron (Cu 2p) spectra of some squareplanar cupric complexes has been compared to electron paramagnetic resonance and electronic spectra results on the electronic structure of these complexes. It is shown that these satellites can be assigned to various ligand → metal 3d or ligand → ligand* transitions within the monopole selection rules of the sudden approximation.  相似文献   

18.
The copper K-absorption edge in the complexes Cu(ammonia)2 C2O4, Cu(methylamine)2 C2O4, Cu(ethylamine)2 C2O4 and Cu(aniline)2 C2O4 has been investigated using the Cauchois-type bent crystal X-ray spectrograph. Three peaks, A, B and C, observed in the edges have been explained on the basis of molecular orbital theory.  相似文献   

19.
20.
The charged states of atoms in unsubstituted copper(II) phthalocyanine (CuPcH16) and hexade-cafluorinated copper(II) phthalocyanine (CuPcF16) complexes and in thin films of them deposited on silicon substrates by vacuum thermal evaporation are investigated by X-ray photoelectron spectroscopy (XPS). The C(1s), N(1s), Cu(2p) core level energies and the charged states of atoms in the studied complexes are calculated using the DFT method. The performed experimental study and theoretical calculations show that the introduction of electron acceptor substituents into benzene rings mostly affects the atoms of benzene rings and insignificantly affects the charge state of nitrogen atoms in the pyrrole ring.  相似文献   

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