Single Resonance Line Research Articles

Electron capture and target excitation in slow ion-alkali atom collisions

Experimental cross sections for single electron capture and target atom resonance line emission in impact of singly charged ions (He+, Ne+, Ar+, C+, N+, O+) on respectively Li(2s) and Na(3s) are presented and compared with semiempirical calculations of the Demkov-Olson type. It is shown that such calculations can still be useful despite involvement of metastable primary ion admixtures and several final states. In addition, observed undulations in the impact energy dependence of electron capture — and target excitation cross sections are discussed.

Observation of optically detected magnetic resonance signals in AlxGa1−xAs

Optically detected magnetic resonance (ODMR) techniques which utilize weak spin effects on deep photoluminescence have been applied to MBE AlxGa1−xAs. ODMR [unlike conventional electron paramagnetic resonance (EPR)] experiments is ideally suited for thin epitaxial samples. Using this technique we have obtained results on molecular-beam epitaxy (MBE) AlxGa1−xAs grown at substrate temperatures of 570 and 620 °C. The four-line ODMR spectrum observed from AlxGa1−xAs at low x values is attributed to Ga atoms not on their normal sites. The physical defect we have ascribed to this signal is a Ga interstitial. To our knowledge this is the first observation of a self-interstitial in the GaAs–AlxGa1−xAs system. We suggest that the level ME6 observed in deep-level transient spectroscopy (DLTS) experiments on MBE grown under similar conditions is the Ga interstitial observed in the ODMR experiment. For x>0.3 the Ga spectrum is still observed but an additional single unsplit magnetic resonance line appears which might be due to oxygen.

Soliton spin density in polyacetylene studied by endor in pristine and 13C-enriched cis-rich sample

ENDOR measurements were performed on pristine and 13C-enriched undoped cis -rich (CH) X down to 4K. Temperature dependence of the spectra in 13C-enriched system revealed that the structures observed at higher temperatures, which were formerly assigned to proton or 13C hyperfine tensor components by Thomann et al. , grow into sharp single resonance lines as the temperature is lowered. The frequencies of those lines have been found to be related to proton and 13C nuclear frequencies. For example, the structure around 7.3 MHz, which was assigned to a 13C tensor component, is the second harmonic of 13C nuclear frequency. Comparison of the spectra between pristine and 13C-enriched system clearly showed that the intrinsic spin density of the soliton, confirmed by our previous ENDOR analysis in pristine system, is not observable in the latter system because of the line shape distortion due to the overlapping of those structurs due to nuclear frequencies.

Mössbauer effect and electron spin resonance study of CdxMg1−xFe2O4 system

This work deals with the application of Mossbauer Effect (ME) in studying the crystal electric field and the cation distribution among tetrahedral (A) and the octahedral (B) sites of the spinal structure in the ferrite system Cdx Mg1−x Fe2O4 (x=0, 0.2,...1). The electron spin resonance technique (ESR) was also applied for studying this ferrite system. It was possible to characterize the ESR spectra of ferrite through the combination with the ME spectra. The ESR spectra of magnesium ferrite showed two resonance positions of Fe3+ ions and indicated that a strong exchange interaction is dominant in the pure Mg-ferrite. For high Cd concentration ferrites only single resonance line was observed. These results could be interpretted on the basis of the ME results where it indicated that Cd2+ ions prefer tetrahedral positions, forcing the Fe3+ ions from these positions to join those in the octahedral sites. The complete site occupation with different types of cations was successfully achieved from the ME spectra. The values of the quadrupole splitting indicated that for each ferrite in the system there exists an electric field gradient surrounding the Fe3+ ions in each of the octahedral and tetrahedral sites. The increase in the Mg-concentration increases the symmetry of the electric field at these sites.

Theory and simulation of NMR spectroscopic imaging and field plotting by projection reconstruction involving an intrinsic frequency dimension

Intrinsic frequency differences in an NMR signal may be regarded as describing a projection of a pseudo-object on a nonspatial axis. The frequency differences produced by imposition of a linear field gradient on an object with a single sharp resonance line describe a projection of the object on axes in ordinary space. When differences of both kinds exist in a signal, it corresponds to a projection of a pseudoobject along some direction in a space defined by an intrinsic frequency axis as well as by the usual spatial axes. The projection directions relative to the intrinsic frequency axis in this space depend upon the gradient amplitudes. This general formulation permits such intrinsic frequency differences as those resulting from spectra and magnetic field inhomogeneities to be recovered by projection reconstruction methods, and clearly resolved images of spatial distributions of the nuclear spin magnetization to be obtained in the presence of such differences. In the full-volume case, because rapidly switched gradients are not required to do volume imaging with this technique, it may be used with any NMR spectrometer (even with cw spectra); this is not the case with techniques employing selective excitation and multidimensional Fourier transforms (I). We present here the general theoretical formulation of this new technique and computer simulations in two

109Ag NMR-Study of the Selective Solvation of the Ag+ Ion in Solvent Mixtures of Water and the Organic Solvents: Pyridine, Acetonitrile, and Dimethyl Sulfoxide

In mixtures of water (W) and one of the organic solvents pyridine, acetonitrile, and dimethyl sulfoxide (O), the silver ion forms the following solvate complexes: AgW2, AgWO, and Ag02. The chemical shift of 109Ag is strongly affected by the ligating solvent molecules, and replacing the ligand W by one of the three organic ligands yields a higher Larmor frequency. In solvent mixtures, only a single resonance line has been observed because of rapid chemical exchange. The measured chemical shifts in the range up to 400 ppm are mean values of the chemical shifts of the different solvate species in a given mixture, weighted with their relative concentrations. The 109Ag chemical shifts were determined for 0.05 to 0.15 molal solutions of AgNO3, as functions of the mole fractions of the solvent components. Using a Gaussian least squares fitting routine, the individual chemical shifts of the Ag+ solvate complexes and the corresponding equilibrium constants were determined. This fit was successful for the whole mole fraction range of DMSO, while in the solvent systems with acetonitrile and with pyridine at higher concentrations of the organic component the chemical shift is influenced by more than two solvent molecules. In these cases equilibrium constants were calculated from chemical shift data for solutions of low mole fraction of acetonitrile and pyridine.

Temperature dependence of 35Cl NQR in 2,6-dichloropyridine

Chlorine NQR in 2,6-dichloropyridine has been investigated in the temperature range 77 K to room temperature and a single resonance line has been observed throughout. Using this data, torsional frequencies of the molecule have been evaluated on the basis of both the Bayer theory and the modified Bayer theory incorporating Tatsuzaki correction.

Electron spin resonance in Langmuir films of merocyanine dyes

Electron spin resonance measurements were performed on Langmuir films of merocyanine dyes with three different donor nuclei at room temperature and 77 K. Each system showed a single anisotropic resonance line with a g factor close to 2.00. The spin concentration and its change due to illumination were markedly dependent on the donor nuclei, the dye concentration and the heat treatment, which affect the existence and type of chromophore aggregation. The system with benzothiazole as a donor nucleus, for example, showed an exceptionally high and stable spin concentration (1 spin per several hundred molecules) at higher dye concentrations except at a certain concentration. The spin concentration, however, drastically decreased to about one-twentieth and the lineshape changed after the chromophore aggregation was destroyed by heating the sample at 90°C for 30 min. This suggests that the generation of the stable spin species in high concentration is closely related to chromophore aggregation in this system.

Synthesis of triphenylphosphonopropionbetainetriorganotin(IV) salts [(C 6H 5) 3P(CH 2) 2CO 2SnR 3] +X −, by nucleophilic displacement of anions from triorganotins

Trimethyl- and triphenyl-tin(IV) hydroxide act on triphenyl(2-carboxyethyl)-phosphonium hydrochloride, which is made from 3-chloropropionic acid and triphenylphosphine, to release water in the presence of dimethylformamide (DMF) as a catalyst. The water is azeotropically distilled to drive the reaction forward and produce triphenylphosphonopropionbetainetrimethyl- and triphenyl-tin(IV) chlorides in high yield. The latter product also results from the displacement of chloride from triphenyltin(IV) chloride by the phosphobetaine, (C 6H 5) 3P(CH 2) 2CO 2, which is made by treating the phosphonium hydrochloride with bicarbonate, and the compounds [(C 6H 5) 3P(CH 2) 2CO 2Sn(C 6H 5) 3] +X − where X = Cl, Br, I, N 3, NCS, NO 3, B(C 6H 5) 4 and Co(CO) 4 are made in the same way. The acetate salt results from metathesis from the chloride and lead(II) acetate. A double salt, [(C 6H 5) 3P(CH 2) 2CO 2SnR 3] + [R 3SnX 2] −, is formed for X = Cl, Br and N 3 by adding additional (C 6H 5) 3SnX to the already-formed simple salts. Double salts are also obtained from the 1 1 reactions between the phosphobetaine and triphenyltin(IV) isocyanate and methyldiphenyltin(IV) chloride. The phosphonium chloride double salt could be converted to the thiophosphonium derivative by heating with elemental sulfur in ethanol. The products of these novel nucleophilic displacement reactions are high melting solids. Tin-119m Mössbauer data are consistent with five-coordinated, triorganotin(IV) formulations with the exception of the diphenyl(8-hydroxyquinolinato)tin(IV) chloride salt in which the tin atom is six-coordinated, and the diphenyltin system cis-oriented. The parameters otherwise do not change with the nature of the X group, which is the tetracarbonylcobaltate derivative is tetrahedral by infrared, establishing the ionicity of the products. The chloride exhibits a molar conductivity indicative of a 1 1 electrolyte in DMF. A bridging acetate structure in the solid is consistent with the lowered ν(CO 2) frequencies. The Mössbauer spectra of the double salts give simple doublets of lowered isomer shift (IS) and raised quadrupole splitting (QS) which may arise from a cross-linking ion pairing of the polymer chains in the solid, and the NMR spectra of the two methyltin derivatives shows only a single resonance line and tin satellites which is rationalized by a dynamic exchange process. The products are formulated as associated in carboxylate polymers with dangling triphenylphosphonium cations.

Incorporation of a ganglioside and spin-labeled ganglioside analogue into cell and liposomal membranes.

When an aqueous solution of a spin-labeled "two tail" gangliosidoid was incubated with liposomes or sheep erythrocytes, the broad single resonance line in the ESR spectrum disappeared and a signal showing an anisotropic motion appeared, indicating that the spin-labeled "two tail" gangliosidoid in the micellar state was transferred to the lipid phase of the acceptor membranes. The transfer was temperature- and time-dependent, irrespective of the acceptor membranes, indicating that the rate of transfer is determined by the escape of monomers from the micelles. The kinetics and temperature-dependence of the association of ganglioside II3NeuAc-GgOse4Cer with sheep erythrocytes was very similar to that of the "two tail" gangliosidoid, indicating that parts of ganglioside II3NeuAc-GgOse4Cer could be incorporated into the lipid phase of membranes via a similar mechanism.

Hyperfine splitting in the elpasolite Cs 2NaHoF 6, measured by enhanced 165Ho NMR

The cubic elpasolite Cs 2NaHoF 6 is a Van Vleck paramagnet with a nonmagnetic γ 3 ground state and an enhanced nuclear magnetic moment. Above 2 K a single resonance line of the Ho nuclei is seen. At 20 mK a resolved nuclear resonance line spectrum is observed, enabling the determination of the hyperfine and quadrupolar interaction parameters. It is argued that a phase transition occurs above 20 mK.

Quadrupole effects in high-resolution phosphorus-31 solid-state NMR spectra of triphenylphosphine copper(I) complexes

High-resolution 31P solid-state NMR spectra of triphenylphosphine copper(I) complexes, obtained by combining proton dipolar decoupling, proton-phosphorus cross polarization, and magic-angle sample spinning, often reveal asymmetric quartets rather than single resonance lines. These splittings arise from coupling with the nuclear spin 3 2 of the quadrupolar copper nucleus. Theoretical NMR spectra of spins I = 1 2 coupled to spins S > 1 2 are presented for powders spinning at the magic angle. Scalar as well as dipolar interactions are considered for the S = 1 and S = 3 2 cases. The magnetic field dependence of the observed asymmetric quartets in bis(triphenylphosphine)copper(I)nitrate can be accounted for by assuming a combination of scalar and dipolar coupling between phosphorus and copper. The spectra allow the determination of the scalar coupling constant, the dipolar coupling constant, and the copper quadrupole constant. Also, their signs can be established.

Spectroscopie résonance électrique des jets moléculaires : formes des raies de résonance en présence d'effet Doppler

We describe effects related to the overlapping of Doppler lines (50 MHz to 1.5 GHz frequency band) in molecular beam electron resonance spectroscopy. We study the line shape when the width of one single resonance line is greater or smaller than the Doppler shift. Several results in low irradiation fields can be explained as interference of transition probability amplitude. In strong fields, the oscillations of the transition probability can increase and we observe also multiphoton transitions (incident and reflected photons). We show how important the effect of the phase of the reflection coefficient is.

Electron paramagnetic resonance ofGd3+in platinum

We have observed the electron paramagnetic resonance (EPR) of ${\mathrm{Gd}}^{3+}$ in both polycrystalline and single-crystal samples of dilute Pt: Gd alloys. The polycrystalline samples display a single resonance line whose thermal broadening is concentration dependent. Fully resolved fine structure appropriate to ${\mathrm{Gd}}^{3+}$ in a cubic environment is obtained from the single-crystal samples. From these results a value for ${b}_{4}^{0}$ of +86 G is deduced, a value some three times larger than that found to date in any other cubic pure metals. It is shown conclusively that the experimental spectra from the single-crystal samples consist of the resolved single-ion fine-structure spectrum and an additional cluster line with the same $g$ value as the single-ion spectrum. For most directions in the {110} plane excellent agreement is obtained between the single-ion spectra and those simulated using the Barnes-Plefka motional-narrowing theory. The existence and behavior of the cluster line is qualitatively explained in terms of a cross-relaxation process. Finally it is shown that the excitation energy ${E}_{\ifmmode\pm\else\textpm\fi{}}$ for the process $4{f}^{7}\ensuremath{\rightarrow}4{f}^{8}$ as involved in EPR is not the same as measured by optical experiments such as x-ray photoemission spectroscopy. A theory which describes this is capable of explaining the experimental exchange and crystal-field parameters.

ESR studies of a nitrogen defect in irradiated potassium azide

An electron spin resonance study has been conducted on a new paramagnetic defect center in irradiated potassium azide. Irradiation of a single crystal of KN3 with x rays at 77 K resulted in the formation of the defect which was characterized by a single structureless resonance line having considerable anisotropy. Effective g values along the principal axes were measured at 77 K and were found to be 6.16, 1.719, and 0.579 along the crystal [001], [110] and [11̄0] directions, respectively. The rotational spectra could not be fit, however, with a spin one half Zeeman Hamiltonian, leading to the conclusion that only one transition of a spin greater than one half system was being observed. Measurements at temperatures other than 77 K showed a strong temperature dependence of the effective g values which would be consistent with a temperature dependent fine structure term in the spin Hamiltonian. The defect was found to be stable to about 130 K. Isothermal annealing measurements indicated a first order decay with an activation energy of 0.39 eV and a characteristic frequency of about 1012 Hz. Irradiation of a single crystal with ultraviolet light resulted in the formation of a defect with the same effective g values, but a narrower resonance line having hyperfine structure indicative of interaction with a single nitrogen nucleus.

F. M. R. characterization of exchange-coupling between a soft and a hard magnetic film

The exchange coupling mechanism of a composite film built up of a soft and a hard ferromagnet is investigated by F. M. R. measurements. The soft NiCoP layer exhibits a well defined spin wave spectra which obeys fairly well a quadratic dispersion law, with a relaxation frequency λ, which is fairly low. The hard CoP film presents a single resonance line with an extremely broad linewidth (ΔH= 2000–3000 Oe). The exchange coupling is investigated on composite film built up of the two layers by varying the thickness of the CoP layer in a systematic way, and it is shown that the linewidth ΔHn of various S. W. modes corresponding to the soft film increases as a function of CoP film thickness. The results are discussed using an exchange coupled model where the loss due to the hard film is included in the computation.

Structural phase transition in various methylammonium hexahalometallates(IV) as studied by the NQR of halogens

The temperature dependence of halogen NQR frequencies was determined for various methylammonium hexahalometallates(IV): (MA) 2MCI 6; M=Se, Pd, So, Pt, and Ph, (MA) 2MBrb 6; M= Se, Pd, Sn, and Pt, and (MA) 2PtI 6. A single resonance line for each isotope in the chlorine and the bromine complexes and only one v 1 line of iodine-127 for the iodine complex were observed at various temperatures studied, indicating that all halogen atoms are crystallographically equivalent in crystals. At liquid nitrogen temperature, both v 1 and v2 lines of the iodine complex were observed. X-ray powder patterns taken at room temperature revealed that all of these complexes form crystals isomorphous with each other belonging to the space group R 3 ¯ m . The crystal structure describable as a rhombohedrally distorted K 2PtCl 6 type is consistent with the results of the present NQR measurements. All the complexes studied show an anomaly in the temperature variation of NQR frequencies below dry-ice temperature. The anomaly was attributed to a structural phase transition from the results of DTA. The transition temperatures determined are concentrated in a rather narrow range of temperature, and no remarkable size effect due to complex anions can be observed. A possible structure of these compounds in the low-temperature phase is deduced, and the mechanism by which the phase transition takes place is discussed.

Mössbauer resonance inPu240

The Moessbauer resonance of the 42.9-keV ..cap alpha.. transition in /sup 240/Pu has been observed. As source activity, the ..cap alpha.. parent /sup 244/Cm, with half-life of 18.1 yr, was used. For a CmO/sub 2/ source and a PuO/sub 2/ absorbed at 4.2 and 77 K, a single resonance line with a width of about 20% larger than the natural width of 40 mm/sec was observed. In the hexavalent plutonyl compound PuO/sub 2/C/sub 2/O/sub 4/, a quadrupole interaction of vertical-bar e/sup 2/qQ vertical-bar = 95 mm/sec was found. No isomer shifts could be detected.

ESR Spectra of the Molten MnCl2–KCl System

Paramagnetic resonance data are presented for the molten MnCl2–KCl system containing 0.01–100 mol% of MnCl2. For The specimens containing MnCl2 less than 0.5 mol%, the hyperfine structure with A=75–77 gauss is observed. For the melts with higher MnCl2 concentration, a single Lorentz-type resonance line is observed. The linewidth increases due to magnetic dipolar interaction in the concentration range 10–30 mol% and it decreases due to exchange interaction in the range 30∼100 mol%. It is found that the electron exchange between Mn2+ ions in this molten system is possible through covalent bridge Mn2+–Cl-–Mn2+.

Hydrogen bond among the ionic groups of ampholytic phospholipid

The nature of interaction among the ionic groups of lipids was studied by proton NMR measurements for ampholytic analogues of phospholipids, each differing in structural separation between PO 4 − and NH 3 + groups. Single resonance lines observed for the ionic protons of lipids in deuterochloroform indicate the rapid exchange of protons between PO 4H and NH 3 +, and showed that the two groups interact intramolecularly and/or intermolecularly by forming a hydrogen bond. The hydrogen bond is found to be weak for dipalmitoylphosphatidyl-propanolamine and -butanolamine but strong for both the -ethanolamine and -pentanolamine. The hydrogen bond counteracts with calcium binding and is almost broken for calcium complexes of the lipids.