Showing papers on "Resonance published in 1984"

Determination of intramolecular bond lengths in gas phase molecules from K shell shape resonances

Abstract: A systematic analysis of K shell excitation spectra of gas phase molecules containing B, C, N, O, and F reveals a correlation between the position of a characteristic K shell excitation feature, the σ shape resonance, and the intramolecular bond length. When referenced to the 1s ionization threshold the position of the σ shape resonance is found to vary linearly with the internuclear distance between the pair of atoms which gives rise to the scattering resonance. This linear relationship holds remarkably well within different classes of molecules characterized by the total number of electrons (sum of atomic numbers) for a given pair of atoms. The empirically derived rules are compared with the predictions of a full multiple scattering theory treatment. Comparison of empirical experimental and first‐principle theoretical results allows the prediction of the average intramolecular muffin tin potential in the presence of the core hole.

Improved quartz crystal microbalance technique

Abstract: The importance of using the most pertinent mathematical description of the mass load versus frequency relation for quartz crystal thin‐film thickness monitors is reviewed. The different usable crystal load ranges of the so‐called frequency‐ and period‐measurement techniques in comparison with the Z‐Match technique are calculated for most of the commonly used deposition materials. A new thin‐film thickness monitoring procedure is described, which takes the influence of the acoustic film properties on the mass load versus frequency slope into consideration without need for the explicit knowledge of the acoustic impedance ratio z of the deposited film and the quartz crystal. It is shown how the effective z value in the composite resonator built by the quartz crystal and the deposited foreign layer can be derived from a measurement of a quasiharmonic overtone resonance frequency in addition to the commonly practiced exclusive measurement of the fundamental resonance frequency. The presently established relati...

Nonlinear Faraday resonance

Abstract: A cylinder containing liquid with a free surface is subjected to a vertical oscillation of amplitude eg/ω2 and frequency 2ω, where ω is within O(eω) of the natural frequency of a particular (primary) mode in the surface-wave spectrum and 0 δ, where δ is the damping ratio (actual/critical) of the primary mode, is a necessary condition for subharmonic response of that mode. Explicit results are given for the dominant axisymmetric and antisymmetric modes in a circular cylinder. Internal resonance, in which a pair of modes have frequencies that approximate ω and 2ω, is discussed separately, and the fixed points and their stability for the special case ω2 = 2ω1 are determined. Internal resonance for ω2 = ω1 is discussed in an appendix.

Bubble size measurements using the nonlinear mixing of two frequencies

Abstract: A double frequency method of measuring bubble size which has better spatial resolution than previous techniques, is described. Bubbles are insonified simultaneously by a swept, relatively low, ‘‘pumping’’ frequency near their resonance and a high ‘‘imaging’’ frequency. Theoretical expressions are derived for the sound scattered by a bubble under the influence of these two frequencies. Existence of sharp resonance behavior in the scattered sound at the sum frequency is shown both theoretically and experimentally.

Frequency Shifts of an Electric-Dipole Resonance near a Conducting Surface

Abstract: The resonance frequency of an electric dipole placed near a conducting surface is shifted by the dipole-surface interaction. The observation and measurement of these shifts at optical frequencies is reported for an experimental system that consists of a metal-island film spaced a distance d from a continuous Ag film. The dependence of the shift in the frequency of the island resonance on d shows good agreement with that predicted by a classical theory of the dipole-surface interaction.

The resonance Raman spectrum of phenoxyl radical

Abstract: The Raman spectra of phenoxyl, phenoxyl‐d5, and phenoxyl‐2,4,6‐d3 radicals produced pulse radiolytically in aqueous solutions and observed by time resolved resonance Raman methods are reported. Excitation was mainly in the narrow and moderately intense (0,0) phenoxyl absorption band at 400 nm. These Raman spectra are superimposed on a broad fluorescence in the region of 410–440 nm which is also ascribed to the phenoxyl radical. A very intense Raman band, which is assigned to a mode principally involving the CO stretch (Wilson 7a), is observed at 1505 cm−1. In the fully and partially deuterated radicals this band is at 1489 and 1487 cm−1, respectively, indicating that in the latter instance the vibration is shifted toward a lower frequency, probably by Fermi resonance with an underlying weak vibration. In the protonated radical moderately intense bands are also observed at 990 and 528 cm−1. The higher of these, by virtue of its considerably lower frequency in the deuterated radicals, is assigned to a CH bending mode (Wilson 18a). The other is affected very little by the substitution and is assigned to a CCC bending mode (Wilson 6a). Weak bands at 1157, 1056, and 865 cm−1 in phenoxyl, phenoxyl‐2,4,6‐d3, and phenoxyl‐d5 radicals are assigned to a second CH bending mode (Wilson 9a). Two weak bands are also reported at 1398 and 1331 cm−1 and are attributed to the nontotally symmetric 19b and 14 modes. No Raman band is, however, observed in the 1550–1650 cm−1 region where the Wilson 8a ring stretching motion prominent in semiquinone radicals is expected. The excitation profile of the 1505 cm−1 emission largely follows the narrow absorption spectrum of the radical in the region of 400 nm. Below 390 nm, where the electronic excitation in resonance is to an upper vibrational level, resonance enhancement of the Raman signals is reduced by more than an order of magnitude. The decay of the radical at 10−4 M, as monitored by its Raman signal, corresponds to its loss mainly in second order processes having a rate constant of (2.6±0.3)×109 M−1 s−1, in agreement with measurements by absorption methods at a 50‐fold lower concentration.

Apparatus and method for nuclear magnetic resonance scanning and mapping

Abstract: An improved apparatus and method for analyzing the chemical and structural composition of a specimen including whole-body specimens which may include, for example, living mammals, utilizing nuclear magnetic resonance (NMR) techniques. A magnetic field space necessary to obtain an NMR signal characteristic of the chemical structure of the specimen is focused to provide a resonance domain of selectable size, which may then be moved in a pattern with respect to the specimen to scan the specimen.

Ultraviolet resonance Raman spectrometry for detection and speciation of trace polycyclic aromatic hydrocarbons

Abstract: A novel UV resonance Raman spectrometer has been utilized for the UV resonance Raman study of polycyclic aromatic hydrocarbons (PAH). This work represents the first application of Raman spectrometry to determination of trace polycyclic aromatic hydrocarbons such as napthalene, anthracene, phenanthrene, and pyrene and various substituted derivatives. The data illustrate that UV resonance Raman enhancement is sufficient to study trace levels of these species, down to the 20 ppb level. The factors which determine the detection limit for UV resonance Raman measurements are disucssed. The resonance Raman intensities strongly depend upon the excitation wavelength. Thus, by a judicious choice of excitation wavelength it should be possible to selectively excite individual PAH species in mixtures. Resonance Raman studies of anthracene and its 2-methyl, 9-methyl, 9-phenyl, and 9,10-diphenyl derivatives demonstrate that the Raman frequency and intensity differences permit easy differentiation between these structurally similar species. The potential utility of this new technique for the speciation and detection of PAH's in complex matrices is discussed.

Photoexcitations in poly (thiophene): Photoinduced infrared absorption and photoinduced electron-spin resonance

Abstract: Infrared absorption and electron-spin resonance are used to study the photoexcitations of poly (thiophene). The results indicate photoproduction of both charge- and spin-carrying species.

Observation of period doubling and chaos in spin-wave instabilities in yttrium iron garnet

Abstract: Ferromagnetic resonance in a polished 0.047-cm-radius sphere of gallium-doped yttrium iron garnet is studied at 1.3 GHz in a magnetic field of 460 G. A second-order Suhl instability is observed, owing to the nonlinear coupling of the precessing uniform magnetization with spin waves. This is detected by the onset of auto-oscillations of the magnetization. One of these modes with frequency \ensuremath{\approx}16 kHz corresponds to the lowest spherical dimensional resonance of a packet of spin waves of small wave vector and long lifetime (\ensuremath{\approx} ${10}^{3}$ cycles). From real-time signals, spectral analysis, and return maps this mode is found to display chaotic dynamics as the driving rf field is increased: thresholds for the onset of period-doubling bifurcations, chaos, and periodic windows. Some observed return maps bear resemblance to the two-dimensional area-preserving quadratic map of H\'enon. The system has several attractors and displays "solid-state turbulence," analogous to that in fluids.

Theoretical study of complex resonances near ionization thresholds: Application to the N 2 photoionization spectrum

Abstract: A "complex" resonance, due to the autoionization of a Rydberg series close to its ionization limit perturbed by an interloper, appears frequently in photoionization spectra. This resonance structure is studied by means of an analytical formula derived from a multichannel quantum-defect treatment involving one open and two closed channels. Model calculations demonstrate the effect of the interaction between the two closed channels. Examples taken from the Ba and ${\mathrm{H}}_{2}$ spectra are discussed. Finally, we reproduce the general feature of a complex resonance observed in the 785-\AA{} region of the ${\mathrm{N}}_{2}$ photoionization spectrum, using ab initio electronic parameters and taking account of the rotational structure.

Nuclear shape at high spin and excitation energy

Abstract: High-energy gamma rays from the deexcitation of giant dipole resonance modes have been measured for the decay of /sup 108/Sn and /sup 166/Er. The structure of the observed resonances can be correlated with the shapes of these nuclei at high excitation energy (E(approx. =60 MeV). For the deformed system /sup 166/Er a shape change with increasing temperature is suggested.

Transverse Resonance Analysis of Finline Discontinuities

Abstract: A transverse resonance technique is used to compute the resonant frequencies of a finline resonator containing the discontinuity to be analyzed. From this, the parameters of the equivalent circuit of the discontinuity are evaluated as functions of frequency and geometry of the structure.

The rotational spectrum and structure of NH3–HCN

Abstract: The microwave spectrum of H3N–HCN has been measured using the molecular beam electric resonance technique. A symmetric top spectrum is observed and the following spectroscopic constants were obtained::[RW2:B0(MHz):3016.756 1(24)]

Raman spectra of solid films 3—Mg, Cu and Zn phthalocyanine complexes†

Abstract: Thin solid films of Mg, Cu and Zn phthalocyanine complexes have been studied using Raman spectroscopy. Laser excitation lines near resonance and in resonance with the electronic absorption band of the substrate have been used. A description of vibrational modes is given and correlations in vibrational properties of the series are discussed.

Whistler mode turbulence generated by electron beams in earth's bow shock

Abstract: The Landau and cyclotron growth rates of whistler mode waves in the earth's bow shock are calculated by using electron distribution functions obtained with the fast plasma experiment on ISEE 2. Three electron distribution functions measured within the transition region of the shock are analyzed. These functions spontaneously generate whistler mode waves with plasma rest frame frequencies between about 0.1 and 100 Hz. The wave normal angles of the generated whistlers range from 0 deg to the resonance cone angle. Electromagnetic Landau resonance and/or cyclotron resonance contribute to wave growth over the range of observed velocity distributions. Waves generated by the normal cyclotron resonance have wave vectors directed toward the solar wind, while those generated by the Landau and the anomalous cyclotron resonances have vectors directed toward the magnetosheath. The preditions of the study are in qualitative agreement with observations of whistler mode waves near the earth's bow shock.

Resonant Alfvén waves excited by a sudden impulse

Abstract: On March 6, 1979, long-period hydromagnetic waves were excited in the forenoon magnetosphere by a sudden impulse (SI). The plasma drift velocity and magnetic field oscillations associated with these waves were observed by the electron gun experiment and the magnetometer, respectively, onboard the GEOS 2 satellite in the equatorial plane. The waves had both compressional and transverse components and had their probable source in a single, tailward traveling, large-scale magnetopause surface “wavelet” (i.e., a single rarefaction/compression pulse) caused by the passage of an interplanetary shock front. This surface wavelet apparently coupled into the inner magnetosphere via the field line resonance mechanism. The satellite observations and the Poynting vectors calculated from these are consistent with a location of the resonance region earthward of GEOS 2 during the first 5 min after the SI while the satellite was located just inside the resonance region at later times. This shift in the relative location of the resonance region was probably caused by an increase of the Alfven velocity as a result of the compression of the magnetosphere associated with the sudden impulse. The stronger-than-usual compressional magnetic field component most likely had its origin in the relatively larger wavelength of the SI-excited surface wavelet (compared with that of Kelvin-Helmholtz-excited surface waves).

Resonance Raman spectra of S2TPP, SSeTPP, Se2TPP, and H2TPP extended tetraphenylporphine vibrational assignments and bonding effects

Abstract: Spectre de resonance Raman de S 2 IPP, SSeTPP, Se 2 TPP et H 2 TPP par excitation laser dans les composantes de haute energie (520 nm) de la bande Q. On obtient ainsi un spectre de grande qualite. On a pu identifier les modes specifiques du thiophene et du selenophene parmi tous les modes attribues

CO2 and CO laser microwave double resonance spectroscopy of OCS: Precise measurement of dipole moment and polarizability anisotropy

Abstract: Laser–microwave double resonance (LMDR) with high electric field was applied to the OCS molecule. Stark Lamb‐dip spectra due to the infrared transitions of the 2ν2(0200–0000, 9.6 μm), 2ν1 (2000–0000, 5.8 μm), and ν1+2ν2 (1200–0000, 5.3 μm) bands were observed with the CO2 and CO lasers. The spectra due to the corresponding hot bands; 0310–0110, 0400–0200, 1200–1000, 1310–1110; 2110–0110, 3000–1000; 1400–0200, 1420–0220, 1510–0310, 2200–1000; and a few bands of OC34S and O13CS were also identified. Associated with these infrared transitions, more than 90 LMDR signals were detected and assigned to rotational transitions in the 11 vibrational states 0000, 1000, 2000, 0110, 0200, 0220, 0310, 0400, 1200, 1420, and 2200 of the normal species, and in the two vibrational states 0000 and 0200 of both OC34S and O13CS. Dipole moments were determined with accuracies (2.5σ) better than 2×10−5 D for all these vibrational states. Polarizability anisotropies were also obtained for some states. The data for the ground ν1 ...

High pressure Raman study of intermolecular interactions and Fermi resonance in liquid ethylene carbonate

Abstract: The Raman band of the ring vibration (ν5) and the Fermi resonance between the carbonyl stretching (ν2) and the first overtone of the ring breathing vibration (2ν7) have been studied in liquid ethylene carbonate in the pressure range between 1 and 3000 bar and at temperatures from 40 to 160 °C. The relative changes of the transition dipole moments of both bands in resonance are estimated from the measurements of their intensity ratios. The knowledge of these parameters enables a comparison of the experimental frequency noncoincidence effect between isotropic and anisotropic components of the bands and the theory based on strong dipole moment coupling. The noncoincidence effect for the ν5 vibration are also explained in terms of this theory. The pressure induced frequency shifts of the bands are interpreted qualitatively by the permanent dipole–dipole coupling model.

Interactions of nearshore bars with incoming wave groups

Abstract: Results from a theoretical model of long wave generation by a time varying break point over a linear shore parallel bars are presented. Standing wave solutions between the shoreline and the mean break point over the bar are obtained, and two possible resonance conditions are identified. First, a quarter wave resonance condition is defined, having a node in the sea surface elevation at the forcing region over the bar. Second, a half wave resonance occurs when the surface elevation has an antinode at the bar crest. The model results predict a resonant response corresponding to the half wave resonance but a quarter wave resonance is not seen, the response being limited by an outgoing energy flux in the form of a seaward propagating progressive wave. The occurrence of an elevation antinode at the bar crest leads to the possibility of convergence in suspended load at this point and hence to a possible mechanism for the maintenance of the bar. At resonance the constructive modes, those tending to maintain the bar, are amplified, while the destructive modes, those tending to create a trough at the bar position, are actually suppressed by the topography.

Wave amplification in line-driven winds.

Abstract: The dynamical effect of scattered line photons is investigated in relation to the amplification of radiative-acoustic waves propagating radially in the acceleration zones of line-driven winds. For wavelengths long compared to the Sobolev length, Abbott's analysis is confirmed. For short wavelengths, on the other hand, a damping effect (line drag) is found which, for lines formed by coherent scattering, exactly cancels the destabilizing effect found by earlier investigators assuming line formation by pure extinction. Moreover, for optically thin perturbations in the outer parts of winds, line drag results in a damping contribution from resonance lines that are strongly shadowed by neighboring resonance transitions. Because radiative driving is dominated by lines that are effective resonance transitions, these effects imply a substantial downward revision of previously estimated growth times. Line-driven winds would seem therefore not to be as highly unstable as hitherto claimed.