Showing papers on "Resonance published in 1968"

Microwave Bandpass Filters Containing High-Q Dielectric Resonators

Abstract: This paper is concerned with dielectric disks used as resonators in microwave bandpass filters. For many years it has been known that modes of resonance occur in isolated dielectric bodies having air boundaries, and that very compact high-Q resonators can be achieved when /spl epsiv/ /sub r/, is high and tan /spl delta/ is low. High-purity TiO/sub 2/ ceramic material, for example, has an /spl epsiv/ /sub r/ about 100, tan /spl delta/ about 0.0001, and Q/sub u/ about 10 000. Practical applications of dielectric resonators have previously been limited by insufficient design information. Formulas are derived for the coupling coefficient between adjacent dielectric-disk resonators within a metal waveguide below cutoff. This metal enclosure is necessary for shielding and to prevent radiation loss. Comparisons between theoretical and experimental coupling coefficient values show very good agreement in each of the three bandpass configurations treated in this paper. Techniques of loop and probe coupling to the end resonators of a multiresonator bandpass filter are discussed and methods of supporting the resonators are suggested. The conclusion is made that microwave dielectric resonators offer important size reductions compared to conventional resonators of similar high Q, but that the center-frequency change of the dielectric resonators as a function of temperature is excessive for many applications. Temperature stabilization is one solution, but preferably a material should be developed having electrical characteristics similar to TiO/sub 2/ ceramic, but with at least an order of magnitude improvement in temperature sensitivity.

Resonant scattering of electrons by molecules

Abstract: In this article the effect of resonances (i.e. metastable states capable of decaying by electron emission) on electron-molecule and heavy particle collisions is considered. In part I resonances are classified into different types: shape resonances, and electron-excited and nuclear-excited Feshbach resonances. Many of the observed resonances and their properties are discussed in terms of this classification. In part II resonance scattering theory is summarized. A survey is given of experiments, and their theoretical analysis, on resonance phenomena in processes such as vibrational excitation and dissociative attachment of molecules by electron impact and electron detachment in atom-atom collisions.

A conformational analysis of gramicidin S-A by nuclear magnetic resonance

Abstract: Currently there is great interest in the precise conformation of complicated natural products in solution. Nuclear magnetic resonance (NiVIR) has great promise in this connection and has made possible a high degree of sophistication in the conformational analysis of the steroids. However, less progress has been made with peptides. In this paper, we wish to report our analysis of 100and 220-AMc N1\MIR spectra of the cyclic antibiotic decapeptide gramicidin S-A in solution. Methods.-Proton magnetic resonance spectra were obtained on Varian Associates high-resolution spectrometers operating at 100 and 220 Mc. The internal reference was tetramethylsilane (TMS), which appears at 0 ppm in all spectra. Sample colncentrations were 3-6%o (gm/100 ml). The normal operating temperature was 320. Gramicidin S-A was isolated from a crude preparation by countercurrent distributionib and lyophilized in glacial acetic acid. Deuterated dimethylsulfoxide (DMS0) and deuterated methanol (CD30D) were purchased from NMR specialties. DMSO-d6 was dried when necessary over calcium hydride. Results and Discussion. A twofold axis of molecular symmetry in the crystal has been demonstrated for gramicidin-S by X-ray crystallography.2 From the known amino acid sequence,3' 4 it seemed likely that this conformation would hold in solution; this is confirmed by the NMIR results reported here. Ten amino acid residues, two of each kind, are present. The strong single resonance band at 7.3 ppm in CD30D (and in DMSO if the partially interfering amide signal is subtracted, see later) must result from the ten aromatic protons of the two phernylalanines. With this as a basic inference, integration under the peak areas assigned to amide bands then corresponds to two protons for each of four regions, although these areas are not all clearly separated by a single solvent and temperature condition. Their assignment to a particular amino acid residue is made possible by decoupling and deuterium exchange experiments as outlined below. The assignments of the proton chemical shifts in the gramicidin S-A spectra are based on the following: (a) comparison with NMVIR spectra of constituent amino acids and known peptides; (b) spectra taken on instruments of varying field strengths (60, 100, and 220 Mc); (c) spectra taken in solvents that promote and solvents that prohibit proton exchange; (d) double resonance experiments; and (e) variable temperature spectra. Decoupling experiments were necessary in order (a) to show that the splitting of the amide proton peaks was due to spin-spin interaction and not to chemical shifts (a fact also proved by the invariability of the amide coupling constants in both the 100and 220-Mic spectra) and (b) to determine which Ca, C:, and NH protons are coupled together. The coupling constants between these types of protons will be designated Ja,3 and JNC. A knowledge of these should define the stereochemistry around the C -C and N-C" bonds.

Electron–Electron Double Resonance of Free Radicals in Solution

Abstract: The technique of electron–electron double resonance, in which one part of the EPR spectrum of a paramagnetic sample is irradiated with an intense microwave field and the effect of this intense field on other parts of the spectrum is determined utilizing a second weak microwave field, has been applied to free radicals in solution. EPR signals detected by the weak microwave source are reduced in intensity when the two frequencies are separated by an integral number of hyperfine intervals. In some cases this reduction is as much as 40%. A bimodal cavity of novel design capable of supporting the two resonant microwave modes is described. A nitroxide radical has been investigated in greatest detail. Two mechanisms have been identified: rapid nuclear relaxation induced by electron–nuclear dipolar (END) interaction, which is dominant at low concentrations and temperatures, and Heisenberg exchange (HE), dominant at high concentrations and temperatures. A theoretical analysis of the relaxation processes is present...

"Bolometric" Technique for the rf Spectroscopy of Stored Ions

Abstract: A simple technique is proposed in which rf transitions between suitable energy levels of an atomic or molecular ion, a member of a stored, radiatively thermalized ion gas, may be detected by monitoring the translational temperature of the ion gas. An experimental study of the cyclotron resonance of an electron gas confined in a Penning trap demonstrates its usefulness, and possible applicability to spin resonance.

Sensitive Detection of Nuclear Quadrupole Interactions in Solids

Abstract: The pure nuclear quadrupole resonance of a low-abundance spin species in zero field is observed for molar concentrations as low as one part in ${10}^{7}$ by the application of a nuclear-double-resonance method. The quadrupole resonance is measured in terms of a decrease in the magnetic order of abundant nuclei which are dipolar-coupled to the low-abundance nuclear species. The double-resonance process is analyzed from the point of view of two energy reservoirs coupled by a dipolar perturbation, and spin diffusion among abundant nuclei is included phenomenologically. Radio-frequency power, which causes the main quadrupole transitions of rare spins, is frequency-modulated to provide saturation in the rotating frame and to enable identification of unknown spin transitions. The pure nuclear quadrupole resonance of Na and Cl nuclei near impurities and imperfections in NaCl is measured. Particular attention is given to the resonances associated with ${\mathrm{K}}^{+}$ and ${\mathrm{Br}}^{\ensuremath{-}}$ ions injected as impurities into the NaCl lattice. An unsuccessful search in zero field has been made for the naturally abundant 0.0156% deuterium quadrupole resonance in CaS${\mathrm{O}}_{4}$\ifmmode\cdot\else\textperiodcentered\fi{}2${\mathrm{H}}_{2}$O and ${\mathrm{C}}_{10}$${\mathrm{H}}_{8}$, where the proton resonance is monitored as the abundant nuclear species. The proton dipolar absorption in zero magnetic field is anomalously broad and overlaps too much with the deuterium quadrupole resonance to permit independent observation of the latter. A narrowing of proton dipolar absorption in zero field is observed for strong radio-frequency fields larger than internal dipole fields.

Ion Cyclotron Resonance Spectroscopy Cyclotron double resonance provides a new technique for the study of ion-molecule reaction mechanisms

Abstract: Ion cyclotron resonance spectroscopy, discussing fundamentals, instrumentation and ion-molecule chemistry applications

Oscillatory energy dependence of resonant electron-molecule scattering

Abstract: The cross sections for the vibrational excitation of N2 molecules bombarded by electrons show a strong peak between 2 and 3 eV, split up into a regular sequence of minor peaks reminiscent of distinct resonances. However, the minor peaks appear in the different final channels at different energies and with slightly different spacings, a behaviour which could be understood on the resonance picture only as the result of some interference effect. An explanation of the phenomenon is offered, based on the assumption (for which reasons are given) that the nuclear wave function in the intermediate N2- ion is a standing wave whose amplitude varies slowly, and whose nodes move slowly as the energy changes. As the nodes drift over the nodes of the final states of the residual molecule, the overlap integrals of the intermediate and final states oscillate, and hence the cross sections oscillate too. The spacing of the minor peaks in energy and their relative displacement for the different final states can be understood in terms of the drifting nodes in an energy representation, and in the corresponding time representation in terms of the motion of the nuclear wave packet.

Exciton Luminescence of CuCl, CuBr and CuI Single Crystals

Abstract: Emission, absorption and reflection spectra have been studied on single crystals of cuprous halides. Three types of emission are observed: 1) resonance emission due to the annihilation of the lowest energy intrinsic exciton, 2) narrow lines due to bound excitons at defects or impurities, 3)broad bands and overlapping equidistant narrow bands. In the excitation spectrum for the resonance emission a structure of equal spacing, which corresponds to the longitudinal optical (LO) phonon energy, is found in the exciton absorption band region at low temperatures below 40°K. The resonance emission bands in CuBr and emission lines belonging to the type 2) in CuI are accompanied by the LO phonon assisted satellite bands. The LO phonon energies are obtained as 210±12, 166±7 and 151±8 cm -1 in CuCI, CuBr and CuI crystals, respectively.

Dynamic Jahn-Teller Effect in Octahedrally Coordinated d 1 Impurity Systems

Abstract: We have calculated the effect of first- and second-order spin-orbit, trigonal, and Zeeman interactions within the vibronic states of the ${d}^{12}{T}_{2}$ term, and also the smaller configurational interaction with the excited $^{2}E$ term. A model is used which includes only interactions with vibrational modes having ${E}_{g}$ symmetry about the impurity site. It is found that second-order vibronic effects can be very important even though the electron lattice coupling may be relatively weak. The uniform partial quenching of crystal-field splittings, characteristic of a first-order vibronic calculation, is modified in second order. The recently observed far-infrared spectra of ${\mathrm{Al}}_{2}$${\mathrm{O}}_{3}$:${\mathrm{Ti}}^{3+}$ and ${\mathrm{Al}}_{2}$${\mathrm{O}}_{3}$:${\mathrm{V}}^{4+}$ can be explained quantitatively by the inclusion of these second-order terms. Moreover, our calculations explain for the first time the hitherto anomalous ground-state $g$ values of ${\mathrm{Al}}_{2}$${\mathrm{O}}_{3}$:${\mathrm{Ti}}^{3+}$. For ${\mathrm{Al}}_{2}$${\mathrm{O}}_{3}$:${\mathrm{V}}^{4+}$, the ground-state spin resonance has not been positively identified, but we predict ${g}_{\ensuremath{\parallel}}\ensuremath{\approx}1.5$, ${g}_{\ensuremath{\perp}}\ensuremath{\approx}0$. We find Jahn-Teller energies of 200 and 320 ${\mathrm{cm}}^{\ensuremath{-}1}$ for ${\mathrm{Al}}_{2}$${\mathrm{O}}_{3}$:${\mathrm{Ti}}^{3+}$ and ${\mathrm{Al}}_{2}$${\mathrm{O}}_{3}$:${\mathrm{V}}^{4+}$, respectively, and an effective ${E}_{g}$ mode frequency of 200 ${\mathrm{cm}}^{\ensuremath{-}1}$.

Linewidth and Relaxation Processes for the Main Resonance in the Spin‐Wave Spectra of Ni–Fe Alloy Films

Abstract: Measurements of the position and linewidth of the main resonance in the spin‐wave spectra of 80% Ni‐20% Fe evaporated films 150 to 3200 A thick at frequencies from 0.8 to 4.0 GHz, at room temperature and with the static magnetic field perpendicular to the film plane have been performed. The center field for resonance was independent of thickness and consistent with the Kittel resonance condition for the uniform precession. The linewidth was about 30 Oe (measured as the field separation of inflection points on the absorption curve), independent of film thickness and frequency. The linewidth data have been compared to previous data for resonance with the static field parallel to the film plane and interpreted in terms of relaxation processes for the uniform precession. In general, frequency‐swept linewidths, not field‐swept linewidths, are proportional to the relaxation rate and are the quantities which should be compared. The frequency‐swept linewidth for perpendicular resonance is equal to that obtained for parallel resonance in films thinner than 500 A. This result indicates that two‐magnon scattering between the uniform precession mode and spin‐wave states for which the exchange energy term is large (wavenumber k appreciably different from zero) does not contribute to the perpendicular resonance linewidth and is the origin of the linewidth increase with thickness for parallel resonance. It appears that scattering to states with k≈0 and exchange conductivity broadening are the most reasonable sources for the residual 30 Oe linewidth.

Dipole Moments of Some Alkali Halide Molecules by the Molecular Beam Electric Resonance Method

Abstract: Author(s): Hebert, A.J.; Lovas, F.J.; Melendres, C.A.; Hollowell, C.D.; Story, T.L.; Street, K.

Study of the Josephson Plasma Resonance

Abstract: We report direct observation of the plasma resonance in Josephson tunnel junctions. The properties of the plasma mode are found to agree quantitatively with theoretical predictions.

Electron Spin Resonance Spectra of Gamma‐Ray‐Irradiated Phosphate Glasses and Compounds: Oxygen Vacancies

Abstract: The electron spin resonance spectra of γ‐ray‐irradiated glassy and polycrystalline phosphorus pentoxide and alkali phosphates with molar ratios of phosphorus pentoxide to alkali oxide ranging from 3.33 to 0.625 have been observed at 10 and 35 Gcps and at 300° and 78°K. Well‐resolved hyperfine doublets were observed in each glass or polycrystalline powder. Additional resonances were also present in all the specimens but these are not discussed. The widths and shapes of the doublets were independent of temperature and only small alterations in the shapes of each component of a doublet were found as a function of frequency. One set of doublets has been discussed elsewhere and is not considered. Those doublets which are discussed are attributed to an electron trapped at a nonbridging oxygen vacancy. Interaction of the electron with the nearest‐neighbor 31P nucleus (100% natural abundance, I = 12) produces the doublet structure. These doublets exhibited isotropic hyperfine interactions ranging from 1880 to 449...

Nuclear Magnetic Double-resonance Study of the Hindered Internal Rotation in Formamide

Abstract: The nitrogen-14 quadrupole relaxation broadening effect on the proton spectrum of formamide was eliminated by a 1H–{14N} double resonance technique. The completely-decoupled proton spectra of formamide in the neat liquid and in acetone, dioxane, and water solutions were observed at several temperatures. The spectra observed at room temperature were analyzed on the basis of an ABC system, while the spectra at higher temperatures (∼100°C) were analyzed on the basis of an AB2 system. From the changes in the resonance lines of the formyl proton with the temperature, the values of the activation energy for the hindered internal rotation about the C–N bond, Earot, and for the intermolecular proton exchange involving the amine protons, Eaex, were obtained. It has been found that the hydrogen-bond formation on the carbonyl oxygen of formamide increases the Earot value and the magnitude of the vicinal coupling constants, while it decreases the magnitude of the geminal coupling constant.

Computational Investigation of Internal Excitation in Nonreactive Molecular Collisions: Resonances in Rotational Excitation

Abstract: Resonances in subexcitation molecular collisions are demonstrated by exact numerical solution of the close‐coupled integral equations for rotational excitation including closed channels in the total‐angular‐momentum representation. These results serve as a reference for comparing various approximate theoretical predictions. In particular, the limitations of the adiabatic approximation are exhibited. The resonance energies can be essentially predicted by a “best local” potential approximation. The resonance line shapes are fitted by a simple Breit–Wigner form.

Computation of optical resonator modes by the method of resonance excitation

Abstract: A novel computational method is used to calculate the modes of an optical resonator. The method is a computer simulation of the physical experiment of exciting a resonator externally and adjusting its length to resonate the various modes; the output at each resonance is purified by means of mode filters consisting of suitably adjusted resonators in tandem. The method is powerful and useful, and is applicable to resonators of arbitrary configuration. Calculated results for a Fabry-Perot resonator with a Fresnel number of ten are presented.

Paramagnetic Resonance Spectra of O− Trapped in Alkali Iodide Crystals

Abstract: The impurity ion O− has been introduced into alkali iodide crystals and detected at 4°K by EPR spectroscopy. A quantitative understanding of the g factor and 17O hyperfine interaction was obtained with the aid of equations derived in a recent analysis of the analogous S− impurity.