Single Narrow Line Research Articles

HSTSpectra of the Jovian Ultraviolet Aurora: Search for Heavy Ion Precipitation

Ultraviolet spectra using Hubble Space Telescope sampled between 1250 and 1680 A at spectral resolution ≤0.57 A are reported for characteristically bright regions of Jupiter's morning and afternoon northern aurora. Several observed spectra exhibit sharply enhanced resolution. We interpret this as bright auroral emission foreshortened on the morning limb with a maximum intensity at least as high as 2000 kR. We have searched for evidence that the primary precipitating particles exciting the aurora include the heavy ions known to exist in Jupiter's plasma torus and magnetosphere. We have also searched for such ambient heavy ions and neutrals at rest in the auroral ionosphere, the end products of previous precipitation, excited by the auroral cascade. We argue that primary emission would be characterized by a dramatically Doppler-broadened (~10-15 A) and redshifted line profile resulting from the cascade process and the angle between the line of sight and the magnetic field lines in the atmosphere. In contrast, ambient emission would be distinguished by narrow emission lines. We have modeled the theoretical sulfur and oxygen line shapes for ion precipitation and conclude that electron precipitation is responsible for most of the H2 emissions. O ions contributed <13% of the precipitating energy flux, and S ions contributed <50%. This dominance suggests that field-aligned magnetospheric currents are more important than energetization of energetic ions and subsequent scattering by plasma waves as a mechanism for generating the Jovian aurora. We set an upper limit over our spectra of 35-43 R to the emission from ambient oxygen and sulfur ions and their neutrals, except that for the S II 1256 triplet, the upper limit for the nominally brightest line, at 1260 A, is 74 R. Hence, we find no evidence for the accumulation of sulfur in the auroral ionosphere. A single narrow emission line from an unidentified ambient specie near 1254 A may be detected at the 4 σ level, introducing the possibility of complex auroral aeronomy. Differences were observed in the auroral spectral hydrocarbon absorption at different locations, which cannot be interpreted without ambiguity between auroral and atmospheric structural causes. We have found that the brighter emission in an auroral sector consistently shows more spectral hydrocarbon absorption than the dimmer emission. We suggest two alternative physical explanations for this phenomenon.

Optical power limiting and stabilization based on a novel polymer compound

Optical power limiting and stabilization based on the two-photon absorption (TPA) mechanism is performed in a polymer solution excited by /spl sim/810 nm and /spl sim/7-ns laser pulses. The solute is a novel polymer, a poly(2,5-dialkoxy-p-phenylene ethynylene) derivative (EBO-OPPE). Using 1-cm path-length EHO-OPPE solution in chloroform of d/sub 0/=0.03 mol of repeat unit/liter as the nonlinear absorptive medium, the dynamic transmission changes from T=0.92 to 0.28 when the input intensity of the /spl sim/810-nm laser beam is increased from I/sub 0/=15 to 600 MW/cm/sup 2/. The measured nonlinear absorption coefficient is 14.5 cm/GW. Optical power stabilization is demonstrated at an average input intensity level of I/sub 0//spl ap/400 MW/cm/sup 2/ with a /spl Delta//spl ap//spl plusmn/25% peak-power fluctuation of the laser pulse. After passing through the nonlinear medium, the output peak-power fluctuation is reduced to /spl Delta//spl ap//spl plusmn/8%. The spectral-width effect of the input laser beam on the nonlinear absorption of the EHO-OPPE solution is investigated. For three different spectral structures of the input laser beam (single narrow spectral line, multiple spectral lines, and broad spectral band), measured values of TPA cross section for EHO-OPPE are /spl sigma//sub 2/=66, 80, and 101/spl times/10/sup -20/ cm/sup 4//GW, respectively. This means that EHO-OPPE is one of the best known nonlinear absorptive materials for power limiting purposes.

2H NMR evidence for dynamic disorder in human skin induced by the penetration enhancer azone

Penetration enhancers mediate trans-dermal drug delivery. The penetration enhancer dodecyl-azacycloheptanone (Azone ®) was characterized in situ with 2H NMR on human stratum corneum treated with either uniformly deuterated Azone ® or penetration enhancer with only the entire chain deuterated, in both cases in propylene glycol. The 2H NMR spectrum at ambient temperature constitutes a single narrow line only 180 Hz wide. This contrasts with the complex lineshapes 1–25 kHz wide commonly observed for methylene deuterons of lipids in a bilayer gel phase. Hence there is no evidence for differences in orientational behaviour between different deuterons at ambient temperature. The narrow line translates into a low overall order parameter S CD < 0.0008, for all deuterons, revealing rapid motion of the entire enhancer with correlation times t c ⪡ 6 × 10 −6 s, in all possible directions. At temperatures of about 150 K a 2H NMR pattern characteristic for a random isotropic powder was observed on samples of stacked stratum corncum sheets at different orientations with respect to the magnetic field. This provides strong evidence for random isotropic freezing of the Azone ® molecules upon cooling. The The 2H NMR data suggest than incubation with Azone ® in propylene glycol provokes dynamic structural disorder of the intercellular lamellar lipid structure throughout the stratum corneum and possibly even the creation of fluid domains involving the intercellular lipids, which may be essential for the penetration enhancing effect.

Redeterminations of the solid-state structures of trimethylarsenic dibromide, Me 3AsBr 2, and trimethylantimony dibromide, Me 3SbBr 2, by X-ray crystallography and solid state 13C MAS NMR evidence for a highly symmetrical D3h, non-ionic structure for Me 3SbBr 2

The crystal structure of trimethylantimony dibromide, Me 3AsBr 3, has been redetermined 24 years after its first characterization and that of trimethylarsenic dibromide, Me 3SbBr 2, 57 years later. Unlike the earlier As structure, the new determination provides bond distances and angles similar to those found in related compounds, but it does confirm the ionic nature of the structure, i.e. [MeAsBr] +Br. The new Sb determination reveals a rigorously trigonal bipyramidal, D 3h structure. This is in contrast to the earlier determination which described the structure in terms of ionic (axial) distortions. It has been determined that refinement of the current data for Me 3SbBr 2 in the space groups previously reported for the “ionic” structures produces ionic distortions, whereas none is found in the correct centrosymmetric space group P6 3/ mmc. From a variety of perspectives, the results are crystallographically inferior in the space groups that produce the “ionic” distortions. In support of the crystallographic results, the solid-state MAS 13C NMR spectrum has also been obtained. The narrow single line observed is consistent only with a high symmetry electrical environment in the vicinity of the Sb and Br quadrupolar nuclei.

EPR study of radical anions of C60 and C70

Utilizing highly polar solvents for the stabilization of Fullerene anions, electrochemical and chemical reduction resulted in narrow single line EPR spectra for the monoanions of C60 and C70 being characterized byg=2.0001(1), ΔB=0.075 mT,g=2.0019(1), ΔB=0.016 mT, respectively. Apparently, the orbital degeneracy of the C60 monoanion is lifted under these conditions to such an extent, that the abnormal large spin lattice relaxation rate believed to be responsible for the approximately 5 mT line width of the monoanion is sufficiently reduced.13C enrichment resulted in noticeable line broadening, allowing an estimate of the average13C hyperfine coupling constantaave=0.1 mT.

11B NMR studies of the short range order in wide composition range xNa2S + (1 − x)B2S3 glasses

The 11 B NMR spectra of high purity (low oxygen contamination) x Na 2 S+ (1 − x )B 2 S 3 glasses with 0 ≤ x ≤ 0.80 are reported. Glasses were prepared in both the low alkali (0 ≤ x ≤ 0.30) and high alkali (0.60 ≤ x ≤ 0.80) glass-forming ranges. These two glass-forming ranges are similar in composition to the two glass-forming ranges in the analogous x Na 2 O + (1 − x )B 2 O 3 system. As in this latter system, the 11 B NMR spectrum of vitreous B 2 S 3 (v-B 2 S 3 ) consists of a quadrupolar broadened single line and confirms the short range order (SRO) of trigonally coordinated borons. As Na 2 S is added, again in similarity to the oxide system, a single narrow line grows at the resonance frequency and confirms the SRO of the highly symmetric tetrahedral boron group. By contrast with the oxides, however, the fractions of tetrahedral borons that are created by the addition of Na 2 S to B 2 S 3 are a factor of three to four times greater at any given composition. Here, rather than forming two tetrahedral borons for each added S = anion, the rate is likely to be six or eight tetrahedral borons per added S = anion. A structural model incorporating this feature of the sulfide glasses has been developed. After this initial large increase in the fraction of tetrahedral borons in the low alkali glass-forming region, the fraction begins to decrease, and by 75 mol% Na 2 S is approximately zero. This decrease in the tetrahedral boron fraction is associated with the formation of the trigonal, totally depolymerized orthothioborate group, Na 3 BS 3 .

Observation of a Pake doublet in the 1H nuclear-magnetic-resonance spectrum of CeNiInHx.

$^{1}\mathit{H}$ nuclear-magnetic-resonance (NMR) studies have been performed in ${\mathrm{CeNiInH}}_{\mathit{x}}$ (x=1.0 and 1.6) in the temperature range 140--300 K. Near 300 K, the $^{1}\mathrm{H}$ NMR spectra show a single narrow line. Below about 210 K, the spectra look very much like a Pake doublet on which a central narrow line is superimposed. The experimental $^{1}\mathrm{H}$ NMR spectrum of ${\mathrm{CeNiInH}}_{1.0}$ at 140 K has been fitted to a theoretical line shape consisting of a doublet and a central Lorentzian line. This fitting yields a proton-proton separation of about 1.48 \AA{}\ifmmode\pm\else\textpm\fi{}0.02. The ordered arrangement of the paired protons in CeNiIn has been discussed in terms of the proposed hydrogen sites in isostructural systems.

Quantum size effect in sodium: NMR and ESR in small Na particles in zeolite y

The Na exchanged zeolite Y has been reacted with sodium or cesium metal vapor. For low concentration of the metal vapor, hyperfine ESR signal was observed, characteristic of ionic cluster species Na 43+ in the sodalite cages of the zeolite. Exposure to higher concentration leads to a single ESR narrow line which is attributed to Na small metallic particles inside the zeolite cavities. The metallic signal linewidth shows no temperature dependence in the range 4 to 300 K, which indicates a quenching of the bulk metal relaxation mechanisms. The signal intensity obeys Curie law in the same temperature range, in agreement with theoretical models for small metal particles. 23 Na NMR spectrum of (Na-Y) highly loaded with Na shows a very broad unshifted line with respect to sodium diamagnetic compound. This line is attributed to Na even metallic particles with a large size distribution. In the case of (Na-Y) highly loaded with Cs, the room temperature 23Na NMR spectrum shows two highly shifted narrow lines and a broad unshifted line. The latter should have the same origin as in the concentrated (Na-Y) with Na. The shifted lines are assigned to the Knight shifts in (Na/Cs) alloy particles which are formed by an exchange between the cesium and the Na cations of the zeolite framework. Such observation is being reported for the first time in the alkali-metals loaded zeolites.

Diffusion and spatially resolved NMR in Berea and Venezuelan oil reservoir rocks

Conventional and spatially resolved proton NMR and relaxation measurements are used in order to study the molecular motions and the equilibrium and nonequilibrium diffusion of oils in Berea sandstone and Venezuelan reservoir rocks. In the water-saturated Berea a single line with T 2 ∗ ⋍ 150 μ sec is observed, while the relaxation recovery is multiexponential. In an oil reservoir rock (Ful 13) a single narrow line is present while a distribution of relaxation rates is evidenced from the recovery plots. On the contrary, in the Ful 7 sample (extracted at a deeper depth in a different zone) two NMR components are present, with 3.5 and 30 KHz linewidths, and the recovery plot exhibits biexponential law. No echo signal could be reconstructed in the oil reservoir rocks. These findings can be related to the effects in the micropores, where motions at very low frequency can occur in a thin layer. From a comparison of the diffusion constant in water-saturated Berea, D ⋍ 5 × 10 −6 cm 2/sec , with the ones in model systems, the average size of the pores is estimated around 40 Å. The density profiles at the equilibrium show uniform distribution of oils or of water, and the relaxation rates appear independent from the selected slice. The nonequilibrium diffusion was studied as a function of time in a Berea cylinder with z axis along H 0, starting from a thin layer of oil at the base, and detecting the spin density profiles d( z, t) with slice-selection techniques. Simultaneously, the values of T 1's were measured locally, and the distribution of the relaxation rates was observed to be present in any slice. It turns out that water is diffusing at a fast rate, while oil diffuses three orders of magnitude slower. The continue source diffusion does not follow a simple Fickian law, while the finite source diffusion shows a pluglike propagation.

Electron and nuclear structural characterization of natural, synthetic, homoepitaxial and polycrystalline low pressure chemically vapour-deposited diamond

Secondary-electron emission used to characterize the band structure of diamond is found to verify the electronic structure of <100> and <111> homoepitaxial and polycrystalline films grown by low pressure chemical vapour deposition (LPCVD) on various silicon substrates in agreement with that for natural diamond. 57Fe Mössbauer spectroscopy of natural and synthetic diamonds reveals the presence of carbides, and the unique occurence of superparamagnetism in these insulating matrices resulting from catalytic residues respectively. Rutherford backscattering, combined with ion channelling, determines the substrate interfacial and bulk integrity of the homoepitaxial films. All films exhibited a Raman signature of a single narrow line at 1332 cm−1 with no discernible graphitization or sp2 bonding.

Electron–nuclear double resonance of long-lived radicals in aged X- and Y-type zeolite catalysts

During the conversion of 2-methylfuran to 2-methylthiophen on MNaX and MNaY zeolite catalysts (M = Li, Na, K, Rb, Cs), stable radicals are formed. We investigated these by ENDOR spectroscopy. 1H and 23Na ENDOR were observed with any aged catalyst. 7Li and 133Cs ENDOR were also observed, respectively, in lithium- and caesium-substituted zeolites. The 1H ENDOR consists of the superposition of a broad doublet and a narrow single line. 7Li and 23Na ENDOR are single Lorentzian lines centred about the respective free nucleus frequency. In contrast, 133Cs ENDOR is a well resolved doublet. An accurate lineshape analysis was carried out based on models available in the literature. It was found that the observed proton splittings must be ascribed to an isotropic hyperfine interaction. A correlation was found between the experimental proton coupling constant and the calculated lattice oxygen charge. The paramagnetic centre can reasonably be pictured as an AlO˙4 site. The caesium cation showed markedly different behaviour with respect to the lighter alkali-metal cations.

Simulations of mode reduction with an intracavity etalon in an RF-Linac based FEL

Coherence between successive light pulses from an rf-linac based FEL can be induced by means of an intracavity interferometric element such as an etalon. This considerably reduces the number of active cavity modes and facilitates the selection of a single narrow line from the laser output. Computer simulations for the operation of an etalon in the FELIX design are shown. The model based on the wave equation driven by single particles has been applied in simulations using a small number (up to six) of initially independent pulses. The case with 40 separate pulses in the cavity is treated with a simpler model. The simulations show that a low-finesse etalon suffices to obtain a large degree of coherence between successive pulses. Saturated operation in a reduced number of modes, but with the same total power, is attained with a delay of a few microseconds.

Anomalous local hopping of Sn impurities in lead.

The Moessbauer spectral intensity of {sup 119}Sn impurities in Pb with concentration of 5%, 2%, 1%, and 1/2% is measured as a function of temperature. A single narrow line is observed which slightly narrows as the temperature increases. Above a temperature {ital T}{sub {ital c}}{much lt}T{sub m}, the bulk melting temperature, the Moessbauer integrated intensity drops precipitously from a Debye-Waller behavior. Analysis of the results shows that a small region around each Sn atom is in a state of relatively large entropy, suggesting a local behavior more similar to a liquid than a solid.

Dynamics and Fourier transform studies of the excitonic optical Stark effect

The authors study the optical Stark effect on the exciton of bulk gallium arsenide using high-repetition-rate femtosecond laser pulses. They distinguish three regimes: quasi-permanent, dynamic, and nonadiabatic. In the dynamic case they develop and demonstrate experimentally a technique of dynamics measurement based on the Fourier transform of the absorption spectra. This method has the advantages of being single-shot, of discriminating between a shift and an absorption strength change, and of separating the contribution of a single narrow line from the other spectral components. >

Novel charge-tranfer salts based on the isoindolo[1,2,3-de]quinolizinium: An aza-analog of fluoranthene

Cation radical salts of arenes have been the subject of much recent attention since the discovery of their very narrow ESR line (10–20 mG). The 2:1 fluornthenium salt, for example, exhibits 1-D stacks with a characteristic mode of overlap. In order to modify the electronic properties of the fluoranthene molecule, without disturbing its geometry and hence the possibility of a well defined stacking, we prepared an aromatic, closed-shell cation, “aza” analog of the fluoranthene. The efficient three-steps synthesis of isoindolo[1,2,3-de]quinolizinium bromide and its X-ray molecular structure are described. A TCNQ salt prepared by electrocrystallisation presents an activated conductivity ( σ RT = 5 ω −1cm −1), a single narrow ESR line ( ΔH RT = 310 mG) and a Pauli-like susceptibility down to 70 K.

Spectral characteristics of laser cavities employing multipass grating interferometers as output couplers

The spectral characteristics of laser cavities terminating in a multipass grating interferometer are investigated. It is shown that, in presence of internal apertures, the frequency profile of the intracavity electric field is characterized by a predominant, very narrow single line that can easily be tuned over spectral intervals that are much larger than the interferometer’s free-spectral range. This is a consequence of the combined action of the interferometer and of the intracavity apertures that select both the transverse mode and a restricted portion of the k space. Experimental evaluation of the spectral behavior of a TEA CO2 laser is reported, and possible application to single-longitudinal-mode operation of broadly tunable lasers is discussed.

Magic-angle spinning and the transition to the static limit

Magic-angle spinning is properly viewed as a method of coherent averaging whereby the mechanical rotation of a sample in an external magnetic field is used to impart a periodic time dependence to the anisotropic interactions of the nuclear spins (I, 2). The averaging effected in this way depends on the relationship between the rate of rotation and the width of the resonance line to be narrowed, generally falling into one of three classes. At one extreme is the isotropic limit, reached when the rotation rate w, greatly exceeds the breadth A of the anisotropic spectrum. Here averaging is complete and the spectrum reduces to a single narrow line positioned at the mean of the three principal values of the coupling tensor. The system behaves as if it were governed by an isotropic Hamiltonian. At intermediate rates of rotation, however, where w, A, the anisotropy of the coupling leads to the formation of sidebands around the isotropic resonance. The intensities of these sidebands are complicated functions of both the anisotropy and asymmetry of the coupling tensor and of the rotation rate, but as the ratio q/A becomes progressively smaller the sideband envelope usually begins to resemble the spectrum of a stationary sample (3, 4). Finally, in the limit q/A = 0, coherent averaging is ineffective and the sidebands coalesce to produce the expected powder pattern. Although these results may seem straightforward, we nevertheless can predict some interesting effects for single crystals during the transition to the static limit, i.e., as o, + 0. In particular, the crossover from a magic-angle spectrum to a static spectrum is not smooth, and, under certain conditions, sidebands persist even when the rate of rotation is very low. Furthermore, the intensities of these signals differ substantially from those originating from a stationary crystal. These phenomena, which are masked in polycrystalline systems, help clarify and put into prospective the often repeated assertion that a sideband pattern obtained under slow spinning is suggestive of the static powder pattern. The rotation of the sample is best viewed in a reference frame w fixed in the rotor, related to the laboratory frame via the Euler angles (0, 8, = -tan-’ fi, -WJ) and related to the principal axis system of a coupling tensor R via the Euler angles (a, @ , y). In this frame of reference the external field B,-, pmcesses about the z axis, maintaining a constant polar angle 8, while sweeping out a time-dependent azimuth w,t. The z axis of R remains tixed in the rotor frame, with polar angle /3 and aximuthal angle (Y, as shown in Fig. 1. Without loss of generality we can restrict the problem to an axially

IR, ESR and resistivity measurements on amorphous silicon oxi-nitride films prepared by PECVD at low temperature

We have measured IR and ESR absorption spectra and the resistivity of SiO x N y H z films grown by PECVD of SiH 4 and N 2 O. For x ≅ 2, we have Si-O, O-H and N-H bands in the IR spectrum and a single narrow line in the ESR spectrum attributed to non-bridging oxygen centers with g = 2.0007. The hopping conductivity is low (210 −17 Ω −1 cm −1 ). The results lead us to propose that for x between 0.7 and 1.2, our samples present SiO x H z and SiN y H z separated zones. The first where OSiO 2 Si, HSiO 3 and HSiO 2 Si configurations observed in the IR spectrum correspond to the centers found at g ≅ 2.001 in the ESR spectrum (· SiO 3 and ·SiO 2 Si). The second where NSiN 2 Si, NSiNSi 2 , HSiN 2 Si and HSiNSi 2 configurations of the IR spectrum give rise to ·SiN 2 Si and ·SiNSi 2 ESR centers (g between 2.0034 and 2.0043). In these silicon rich materials, the hopping conductivity remains low (8 10 −17 Ω −1 cm −1 )

ESR studies of polyacenic semiconductive material

ESR measurements have been performed on the polyacenic material prepared by the pyrolytic treatment of phenol-formaldehyde resin. Six kinds of samples (A)-(F) with various electrical conductivity (σ) were employed for the measurements. Each sample shows a single narrow line, the g-values of which suggest the existence of unpaired electrons of π-type. If the sample (F) ( σ = 1 × 10° S cm −1) the single narrow line becomes drastically diminished in the presence of a small amount of oxygen.

ESR study of carbonization of polyimide (Kapton H) film induced by 1 MeV N 2+-irradiation

ESR spectra of N 2 +-irradiated polyimide (Kapton) films have been investigated as a function of the irradiation dose. Two narrow single lines with slightly different g-values close to 2.003 have been detected in the highly irradiated Kapton films, and they have tentatively been assigned to giant aromatic radicals being in the areas of different carbonization stages. The Kr + -irratiation has given ESR spectra similar to those by the N 2 +-irradiation. Some different features of the ESR spectra between the carbonaceous substances produced by ion-irradiation and those by pyrolysis have been discussed.