Resonance Spectra Of Single Crystals Research Articles

The orientations and dynamics of ethanol guest molecules in the clathrate of Dianin's compound

In the clathrates of Dianin's compound the guests are trapped in cages formed by six host molecules. Two ethanol molecules can be enclosed by each cage. Deuteron nuclear magnetic resonance spectra of single crystals of Dianin's compound with ethanol-OD, ethanol-1,1-D2 and ethanol-2,2,2-D3 as a guest were recorded in the temperature range 10 K < T < 310 K. Only at T < 25 K the guests are found to be immobile enough to allow the determination of the bond directions of the different deuterons from the unique eigenvectors of the quadrupole coupling (qc) tensors. The measured qc tensors of the hydroxyl and of the methylene deuterons are used to determine the orientations of the ethanol molecules as a whole. These can occupy six distinct sites. The two ethanol molecules in a given cage are linked by a weak hydrogen bond. The dynamics of the ethanol guests is elucidated by line shape analyses and by deuteron two-dimensional exchange spectroscopy. It is found to be rather complex, consisting of three different ty...

Electron spin resonance and optical spectral studies of heptaaquatris[maleato(1-)]-RE (RE = Nd(III), Gd(III))

The electron spin resonance spectra of single crystals of Gd 3+ doped neodymium(III) maleate heptahydrate (NdMHH) have been investigated at room temperature. The transitions arise from a single type of site with g | = 1.987±0.002 and g ⊥ = 2.000±0.002. The g-shifts from the free electron value and the theoretical value have been attributed to the mixing of 8 S 7 2 and 6 P 7 2 states. The angular variations in mutually orthogonal systems were studied and the spin-Hamiltonian analysis gave rise to crystal field parameters b 0 2 = 264.3 ± 1, b 0 4 = 0.99±0.01, b 0 6 = 0.27±0.01, b 2 2 = -92.7±1, b 4 4 - b 2 4 = -135.4±1 and b 6 6 - b 4 6 + b 2 6 = - 345.2±1 in units of 10 −4 cm −1. The experimentally measured intensities of the absorption spectra were analyzed on the basis of Judd—Ofelt theory which gave rise to the parameters τ 2 = 1.3 × 10 −9, τ 4 = 50.8 × 10 −9 and τ 6 = 35.1 × 10 −9. The crystal field parameters, the g-values and the intensity analysis of the visible spectra all provide evidence for distortions from cubic symmetry. The absence of any significant change in the presence of a large electrolyte concentration is attributed to absence of changes in the near neighbour environments. On the other hand, an increase in pH is found to shift the hypersensitive bands to longer wavelengths due to chelation effects.

Multiplet structure in the 35,37Cl ligand electron nuclear double resonance spectra of single crystals of Cu(II)-doped histidine hydrochloride monohydrate

Multiplet structure was observed at 4.2 K in the 35,37Cl ligand electron nuclear double resonance (ENDOR) spectra of single crystals of Cu(II)–doped histidine hydrochloride monohydrate. By using second-order perturbation theory we show clearly that the observed multiplet structure arises from the 63Cu and 35,37Cl indirect nuclear spin–spin interaction. Our theoretical analysis in general because it encompasses the anisotropies of both the g and hyperfine tensors, and also allows for the quantization of the nuclear spins along the effective field at each nucleus.

A single-crystal electron spin resonance study of manganese(II)-doped zinc maleate tetrahydrate

The electron spin resonance spectra of single crystals of manganese(II)-doped zinc maleate tetrahydrate have been investigated at room temperature. The transitions arise from a single type of site with gxx= 2.010, gyy= 1.992, and gzz= 2.035. The g shifts from the free spin value have been attributed to an electron-transfer process from the ligands to the S state ion. The observed angular variation of the allowed hyperfine transitions is in good agreement with theory. The spin-Hamiltonian parameters D= 360.5 × 10–4, E= 66.8 × 10–4, a=–8.9 × 10–4, and A=–87.0 × 10–4 cm–1 have been deduced. From the A value an ionicity of 96.5% is derived for the metal–ligand bonding. The analysis of forbidden hyperfine transitions leads to Q′= 1.58 × 10–4 and Q″= 0.28 × 10–4 cm–1 for the axial and rhombic components of the quadrupole coupling tensor respectively for the 55Mn nucleus.

Electron paramagnetic resonance of Fe 3+ in bismuth germanium oxide single crystals

The electron paramagnetic resonance spectrum of single crystals of Bi 12GeO 20 doped with iron ions has been measured at X band at temperatures between 4.2 and 200 K. The analysis of the experimenal data has shown that iron ions are in the 3d valence state and are located in a tetrahedral position. The spin Hamiltonian parameters have been determined. The temperature variation of the spin Hamiltonian parameters has been investigated and interpreted in terms of spin-lattice coupling.

Pairwise trapping of radicals in single crystals of n-decane irradiated at 1.5 and 4.2°K

The electron spin resonance spectra of single crystals of n-decane-d22, n-decane-h22, and their mixtures irradiated and measured at 1.5 and 4.2°K have been studied to shed light on the mechanisms of alkyl radical formation in saturated hydrocarbons. From the analyses of low temperature spectra and of the spectral changes caused by thermal annealing, it is suggested that almost all alkyl radicals are inherently formed in pairs and that the initial radical pair formation is fairly random especially for distant radical pairs, although there is some preference in the short range reactions for forming very close radical pairs with separation shorter than 6 Å. The predominant radical pairs in deuterated crystals irradiated at 1.5 and 4.2°K have separations ranging 6–25 Å. The spatial distribution of the generation of paired radicals depends upon irradiation temperature. Radical site migration takes place even at 35°K. There is a remarkable mass effect on the spatial distribution of the paired radicals. The deuterated crystals give much smaller spatial distribution. Random scission of the C–H bonds at any carbon atom seems to take place at 4.2°K.

Preliminary Report on the Electron Paramagnetic Resonance Spectra of Single Crystals of Bovine Erythrocyte Superoxide Dismutase

Abstract Electron paramagnetic resonance spectra were recorded from single monoclinic crystals of bovine erythrocyte superoxide dismutase. Spectra were taken at various angles of rotation about the c (or blue optic) axis (Richardson, D. C., Bier, C. J., and Richardson, J. S. (1972), J. Biol. Chem. 247, 6368–6369) and about the a or b (green optic) axis of the crystal. Rotation about the blue axis (H in ab plane) yields the information that the Z components of all Cu(II) g tensors lie substantially in the ab plane, and this is confirmed by rotation about one of the green axes which yielded only very small Z component resonances (H in ac or bc plane). A maximum of eight hyperfine components were observed regardless of the orientation of the crystal. There appear to be two distinct groups of eight symmetrically degenerate (at least along their Z axes) Cu(II) ions, and the common Z axes of these two groups are off parallel by only a few degrees.

A Simple Automatic Single Crystal Goniometer for Electron Spin Resonance Spectroscopy

A goniometer is described which permits automatic aquisition of electron spin resonance spectra of single crystals upon rotation about one axis in the magnetic field by means of an interface between the magnetic field sweep unit of the spectrometer and a stepper motor as rotating device.

ESR Study of the Chlorofluoroacetamide Radical in Irradiated Dichlorofluoroacetamide Single Crystals

The electron spin resonance spectra of single crystals of dichlorofluoroacetamide and N, N-dideutero-dichlorofluoroacetamide irradiated with x-rays at 77°K and later warmed to 170°K, have been assigned to · CClFCONH2 and · CClFCOND2, respectively. A tensor Hamiltonian fit to the spectra have yielded either complete or partial hyperfine splitting tensors for fluorine-19, chlorine-35, carbon-13, and nitrogen-14 in addition to the chlorine-35 quadrupole coupling and the g tensor. These results along with a CNDO/2 molecular orbital calculation indicates that the · CClFCONH2 radical is a planar π radical. An INDO molecular orbital calculation was carried out for the · CH2CONH2, · CFHCONH2, and · CF2CONH2 radicals in order to interpret the experimentally observed amide nitrogen and proton splitting variations.

Electron paramagnetic resonance of osmium-doped trichlorotris(diethylphenylphosphine)rhodium(III)

The paramagnetic resonance spectrum of single crystals of RhCl3(PEt2Ph)3 doped with osmium has been measured at 77 K. No hyperfine structure is resolved and the g-tensor has principal values 3.32, 1.44 and 0.32. These values are analyzed using an extended form of the standard theory for low-spin d5, including configuration interaction. The effective value of the spin-orbit coupling is 2650 ± 100 cm–1 and the orbital reduction factor is 0.80 ± 0.01. The anisotropy is compared with the molecular structure and interpreted in terms of the π-bonding properties of the ligands.

Single crystal studies of electric field gradients in dilute alloys I. Aluminium based crystals

A study of the nuclear magnetic resonance spectrum of single crystals of three alloys of aluminium containing 0.5 at% Mg, Ga and Ge impurities respectively has revealed the presence of weak satellite lines whose dependence upon the orientation of the crystal in the magnetic field establishes that they originate at host sites which are nearest neighbours to the impurity. The Ga and Ge results contradict the earlier interpretation of Minier based upon pure quadrupole resonance studies and the new assignment is in greatly improved agreement with the theoretical calculations of Fukai and Watanabe.

Electromagnetic Properties of Hemoproteins: IV. SINGLE CRYSTAL ELECTRON PARAMAGNETIC RESONANCE SPECTROSCOPY OF HEMOPROTEINS AT AMBIENT TEMPERATURE

Abstract Electron paramagnetic resonance spectra of single crystals of myoglobin fluoride and hemoglobin fluoride were recorded at both cryogenic and ambient temperatures. Analysis of angular variations of line widths at these temperatures indicates that the misorientation of the heme plane in myoglobin crystals, which is considered responsible for the unusually broad resonance lines in these crystals, is not an artifact of the freezing process, but a characteristic inherent to the protein crystals as they are grown. Single crystal electron paramagnetic resonance spectroscopy at ambient temperature opens the possibility of the determination of the intracrystalline orientation of the heme groups in other hemoprotein crystals, the structure of which is readily damaged upon freezing.

The spin Hamiltonian for completely anisotropicg-factor and hyperfine coupling tensors

The nature of the approximations underlying the standard methods of interpreting anisotropic electron spin resonance spectra of single crystals are explicated. Equations are derived for an unpaired electron interacting with a spin-1/2 nucleus when both the electronicg-factor and the hyperfine interactionT are anisotropic.

Electron paramagnetic resonance study of the stereochemistry of nitrosylhemoglobin.

Paramagnetic resonance spectra of single crystals of nitrosylhemoglobin (HbNO) have been obtained at − 195°C. There are four nonequivalent paramagnetic atoms which form two sets; the members of each set are related by the [010] dyad axis. The principal values of the g tensor are: gxx = 2.0820, gyy = 2.0254, and gzz = 1.9909; the isotropic g value is 2.039. The principal values of the hyperfine A tensors are: Tξξ = 77 MHz, Tηη = 54 MHz, and Tξξ = 18 MHz; the isotropic coupling constant has a value of 50 MHz. The calculated principal values for the dipolar T′ tensors are: tξξ′ = 27 MHz, tηη′ = 5 MHz, and tξξ′ = −32 MHz. The principal axes of the g tensor do not coincide with these of the T tensor; the results were interpreted to give a bent Fe–N–O angle of 110°. The N–O axes of the ligands of one set lie in the ab plane; those of the others are inclined at an angle of about 80° to the ab plane. The electrostatic interaction of the oxygen atom with the imidazolium group of the distal histidine and the nonpolar evnironment in the vicinity of the heme probably contribute to the stabilization of this particular Fe–N–O bond.

ESR Spectrum of the Radical Species Trapped in X-Irradiated Single Crystals of Dimethyl (9-fluorenyl) Sulfonium Bromide

The electron spin resonance spectrum of single crystals of dimethyl (9-fluorenyl) sulfonium bromide, irradiated with x-rays at room temperature, reveals the presence of three free-radical species. Two of these have been identified with reasonable certainty as (CH3)2SBr (A) and 9-fluorenyl (B). The third radical (C) is probably one in which the unpaired electron is mainly localized on a sulfur atom i.e., RS. The components of the hyperfine coupling and g tensors for these radicals have been determined and the results discussed in terms of the electronic structure of these radicals. For radical A the 79Br and 81Br nuclear quadrupole coupling constants were also determined.

Effect of charge compensation in calcium tungstate: Ytterbium

The paramagnetic resonance spectra of single crystals of CaWO 4:Yb have been examined to determine the extent to which crystals charge compensated with sodium have ytterbium ions in sites with lower than tetragonal symmetry. The spectra of crystals prepared with niobium and with no impurity ion added for charge compensation were also examined. To varying extents all crystals showed the presence of Yb 3+ ions in sites with several types of local symmetry. In a sample grown from a melt containing a ratio of sodium to ytterbium of eight to one, approximately 71 per cent of the Yb 3+ ions occupy sites with tetragonal symmetry. It is concluded that much of the unexplained structure observed in the optical spectra of this crystal may be due to Yb 3+ in sites with lower than tetragonal symmetry.

THE PROTON MAGNETIC RESONANCE OF HgSO4∙1H2O

The proton magnetic resonance spectrum of single crystals of HgSO∙1H2O has been investigated. This crystal is of interest since, according to the X-ray structure analysis, it appears likely that one of the protons of the water molecule is hydrogen-bonded in the structure, while the other is free. Two non-equivalent sets of parallel H–H vectors have been observed in agreement with the crystal symmetry. The angles of one of the intramolecular H–H vectors with the crystallographic axes are α = 58°, β = 95°, and γ = 36°. The results are consistent with the suggestion that one of the protons does not form a hydrogen bond in the crystal.

Electron spin resonance of colour centres in γ-irradiated planar lead halides

The electron spin resonance spectra of single crystals of two of the planar lead halides, chloride and iodide, irradiated at liquid nitrogen temperatures with γ-rays from a cobalt source, have been investigated at 9.5 Gcsec. In both halides the spectrum as observed at low temperatures consists of two asymmetric lines with g-factors close to 1.999 and 2.006 which are presumably associated with trapped electrons and holes respectively. The halfwidths are 3 and 10 G respectively even at concentrations exceeding 1018 cm−3 which suggests exchange narrowing, and the relaxation behaviour follows the simple Bloch theory. The characteristic line shape and the absence of orientation dependence are explained by assuming that the resonances arise from a random distribution of anisotropic spin systems. The observed line shapes are compared with the theoretical resonance profiles for a powder-like assembly of spins having three unequal g-components. This indicates that the surroundings of the resonance centres have a glass-like structure and suggests that the trapping sites are jogs in dislocation lines. The remarkably high efficiency of generation of radiation centres (only 3 eV absorbed γ-energy are required per centre) and the high equilibrium concentration of 1019 cm−3 at a γ-dose rate of 2.2 Mrhr suggest further that this large scale deformation is produced by a radiation-induced mechanism of multiplication and motion of dislocations.

The proton magnetic resonance study of the structure of Na 2Zn(SO 4) 2·4H 2O

The proton magnetic resonance spectra of single crystals of Na 2Zn(SO 4) 2·4H 2O have been investigated and the orientations of the water molecules have been determined. Using the heavy atom structure determined by X-rays a system of hydrogen bonds between water and sulphate oxygens has been proposed.

Proton Magnetic Resonance Study of the Structure of Two Tutton's Salts

Proton magnetic resonance spectra of single crystals of two Tutton's salts, K2Zn(SO4)2·6H2O and K2Mg(SO4)2·6H2O, have been studied and the orientations of the water molecules in the structure have been determined. Using the heavy-atom structure of (NH4)2Mg(SO4)2·6H2O as determined by x-ray diffraction, a system of hydrogen bonds between the water and sulfate oxygens in Tutton's salts has been proposed. It appears that the x-ray structure needs considerable refinement.