Showing papers on "Resonance published in 1977"

The Structure of Water Dimer from Molecular Beam Electric Resonance Spectroscopy.

Abstract: Molecular beams of hydrogen bonded water dimer, generated in a supersonic nozzle, have been studied using electric resonance spectroscopy. Radiofrequency and microwave transitions have been observed in (H2 16O)2, (D2 16O)2, and (H2 18O)2. Transitions arising from both pure rotation and rotation–tunneling occur. The pure rotational transitions have been fit to a rigid rotor model to obtain structural information. Information on the relative orientation of the two monomer units is also contained in the electric dipole moment component along the A inertial axis μa, which is obtained from Stark effect measurements. The resultant structure is that of a ’’trans‐linear’’ complex with an oxygen–oxygen distance ROO of 2.98(1) A, the proton accepting water axis is 58(6) ° with respect to ROO, and the proton donating water axis at −51(6) ° with respect to ROO. This structure is consistent with a linear hydrogen bond and the proton acceptor tetrahedrally oriented to the hydrogen bond. The limits of uncertainty are wh...

Atomic and laser spectroscopy

Abstract: 1. Introduction 2. Review of Classical Electrodynamics 3. Review of Quantum Mechanics 4. The Spontaneous Emission of Radiation 5. Selection Rules for Electric Dipole Transitions 6. Measurement of Radiative Lifetimes of Atoms and Molecules 7. Forbidden Transitions and Metastable Atoms 8. The Width and Shape of Spectral Lines 9. The Absorption and Stimulated Emission of Radiation 10. Radiative Transfer and the Formation of Spectral Lines 11. Population Inversion Mechanisms in Gas Lasers 12. Resonant Modes of Optical Cavities 13. Saturation Characteristics and the Single-Frequency Operation of Gas Lasers 14. Turnable Dye Lasers and Atomic Spectroscopy 15. The Hanle Effect and the Theory of Resonance Flourescence Experiments 16. Optical Double Resonance Experiments 17. Optical Pumping Experiments 18. The Hyperfine Structure of Atoms and its Investigation by Magnetic Resonance Methods Appendix

Heating tokamaks via the ion-cyclotron and ion-ion hybrid resonances

Abstract: The ion-ion hybrid resonance can occur at high plasma densities in tokamaks and thereby absorb energy from the fast magnetosonic mode which would otherwise propagate freely. Ion-cyclotron resonance regions, although they occur in the low-density peripheral plasma, can nonetheless cause sufficient absorption to compete with fundamental cyclotron resonance damping by ions. For the ion-ion hybrid resonance it is shown that: (1) the energy absorption occurs via a sequence of mode conversions. (2) A poloidal field component normal to the ion-ion hybrid mode conversion surface strongly influences the mode conversion process, so that roughly equal electron and ion heating occurs in the present proton-deuterium experiments, while solely electron heating is predicted to prevail in deuterium-tritium reactors. (3) The ion-ion hybrid resonance suppresses toroidal eigenmodes. (4) Wave absorption in minority fundamental ion-cyclotron heating experiments will be dominated by ion-ion hybrid mode conversion absorption for minority concentrations exceeding roughly 1%.

Mode Conversion of the Fast Magnetosonic Wave in a Deuterium-Hydrogen Tokamak Plasma

Abstract: Model conversion from the fast magnetosonic wave to a slow wave near the two-ion hybrid resonance is shown to explain recent experimental fast-wave damping results. A model for tunneling and mode conversion of the fast wave in the two-ion resonance zone incorporating k/sub parallel/ and plasma-density and magnetic-field profiles is used to explain the observations. The strong dependence of the absorption on k/sub parallel/ and the species concentration which is obtained has important consequences for major plasma-heating programs which are planned for tokamaks.

Molecular beam electric resonance study of formaldehyde, thioformaldehyde, and ketene

Abstract: Molecular beam electric resonance spectroscopy has been carried out on formaldehyde, H2CO; thioformaldehyde, H2CS; and ketene, H2CCO. Transitions from 1 to 2500 MHz were studied. The high frequency work utilized a new type resonance field of microstrip line configuration. The diagonal tensor elements for all the hyperfine interactions of protons in all three molecules are reported. 13C hyperfine elements for H2 13CO and D hyperfine elements for D2CCO are also given. The electric field gradient tensor at deuterium in ketene is not coincident with cylindrical C–D bonds. Precise dipole moments are obtained for H2CO, D2CO, H2 13CO, H2CO(ν4=1), H2CO(ν6=1), H2CS, H2CCO, and D2CCO.

Homogeneous linewidth of the S1←S0 transition of free‐base porphyrin in an n‐octane crystal as studied by photochemical hole‐burning

Abstract: The homogeneous linewidth of the 0–0 band of the S1←S0 transition of free‐base porphyrin (H2P) in an n‐octane matrix and its temperature dependence (T=1.5–4.2 K) have been measured by means of photochemical hole‐burning. The linewidth extrapolated to T=0 is ∼9 MHz for the two types of sites which have been investigated, and it appears to be determined entirely by the decay time of the emitting state S1 (17 ns). The temperature dependence of the linewidth is strongest for the thermodynamically less stable sites. The increase in linewidth with temperature may arise from a relaxation process involving a low frequency resonance mode (∼5 cm−1) localized at the H2P molecules. At 77 K the homogeneous linewidths are comparable to the inhomogeneous widths of 3–4 cm−1; hence, hole–burning is no longer observed.

Laser Excitation and Ionization in a Dense Li Vapor: Observation of the Even-Parity, Core-Excited Autoionizing States

Abstract: The first optical absorption from excited states to autoionizing core-excited levels has been observed in lithium. A 1-MW dye laser tuned to the $1{s}^{2}2s\ensuremath{\rightarrow}1{s}^{2}2p$ resonance produced \ensuremath{\sim}${10}^{16}$ excited atoms/${\mathrm{cm}}^{2}$ in a heat-pipe oven. Far-uv absorption spectra of ${\mathrm{Li}}^{*}(2p)$ and ${\mathrm{Li}}^{+}$ were obtained. A curve of the evolution from excited neutrals to \ensuremath{\sim}95% ions is presented, and the significance of the Li observations for understanding the ionization mechanism is discussed.

Resonance Raman spectra of metalloporphyrins. Effects of Jahn–Teller instability and nuclear distortion on excitation profiles of Stokes fundamentals

Abstract: Excitation profiles of depolarized modes (blg, b2g) in Ni etioporphyrin I exhibit marked 0–0 resonance Raman intensity upon Q‐band excitation. By contrast, inversely polarized Raman scattering (a2g) is stronger with 0–1 excitation. Within the crude Born–Oppenheimer approximation, a theoretical model is presented which explains the 0–0 enhancements of depolarized modes as arising from interference of intermanifold (Q –B) and intramanifold (Q –Q) vibronic coupling. Comparison of computed and observed excitation profiles shows that a weak Jahn–Teller distortion is present in the Q state. The vibronic model predicts behavior of Raman intensity in the B (Soret) electronic state. Evidence of increased vibronic coupling of both 400 and 1365 cm−1 polarized vibrations (a1g) is found in chromium tetraphenylporphyrin with the appearance of a supernumerary peak at 1400 cm−1 in the excitation profile of the 400 cm−1 vibration. Excitation profiles of a2g modes in the chromium complex exhibit an apparent decrease in exc...

On optical dispersion in transparent molecular systems

Abstract: In a “crossed photon beams” experiment the action of light in a transparent medium is studied by Mossbauer resonance. Using cooled, temperature stabilized targets such as sodium nitroprusside, olivine and glasses, containing iron, no change of the hyperfine spectrum was observed by illumination with normal incoherent light of low intensity within the region of normal dispersion in agreement with the theory of optical dispersion. There was, however, no agreement with theoretical expectation when sodium nitroprusside (whose structure is, therefore, reviewed in detail under the aspects of dispersion) was irradiated by laser light with otherwise unchanged experimental conditions, as intensity and range of wavelengths. A new kind of molecular state, producable only by polarized light, was observed. Its radiative lifetime is practically infinite, but it is thermally instable at elevated temperatures. The Mossbauer spectrum reveals a quadrupole splittingΔE Q= (+)(2.7357±0.0040)mm/s and an isomer shiftδ=}-(0.183±0.006)mm/s (relativ to Fe(Pd)) at 100 K, markedly different from the normal groundstate. In the new state the axial symmetry, the sign of thez-component, and the three principal tensor axes of the electric field gradient at the Fe central atom coincide within the experimental limits of error with those of the groundstate.

Optical excitation of surface plasma waves in layered media

Abstract: The method of frustrated total reflection is used to optically excite electromagnetic surface plasma waves (SPW) in two different layered structures. The first system studied has two films (Mg${\mathrm{F}}_{2}$-Ag) between glass and air, and the second has three films (Ag-Mg${\mathrm{F}}_{2}$-Ag) between glass and air. Surface roughness of the evaporated Mg${\mathrm{F}}_{2}$ films is found to increase with film thickness and this roughness has a pronounced effect on the SPW resonances. A cermet is imagined to form at the Mg${\mathrm{F}}_{2}$-Ag interface, and its effective optical constants can be evaluated using the Maxwell Garnett theory. If this cermet is treated as a separate layer in the structure, then good agreement is found with the experimentally observed resonances. A calculation of the Poynting vector field, current distributions, and surface charge densities, resulting from an incident monochromatic plane wave, shows the different modes of oscillation corresponding to each resonance.

Spin‐wave resonance spectra of inhomogeneous bubble garnet films

Abstract: Spin‐wave resonance at 10 GHz has been observed in thin (? 5 μm) garnet films of approximate composition Y2.85La0.15Fe3.75Ga1.25O12. The films were grown by LPE on [111]‐oriented gadolinium gallium garnet substrates, both from a nonstirred melt (vertical mode of dipping) and a stirred melt (horizontal dipping, applying axial substrate rotation). The spectra exhibit large numbers of strongly excited modes with large deviations from quadratic spacing, which are interpreted in terms of a volume inhomogeneity of the uniaxial anisotropy constant Ku. Two models are used to explain the experimental spectra. In one model the film is considered as being built up of exchange coupled layers having different uniaxial anisotropy constants Ku. In the second model it is assumed that Ku varies linearly with the distance from the substrate, but with different slopes in different regions. No pinning is assumed at the surfaces. A simple graphical method is presented for determining the normal modes of films with these types...

Bunch Lengthening and Microwave Instability

Abstract: A single-bunch instability that leads to blow-up of bunch area and microwave signals (100 MHz to 3 GHz) has been observed in the pS1) and the ISR2). A similar instability may cause bunch lengthening in electron storage rings. Attempts to explain this as a high-frequency coasting-beam instability require e-folding rates faster than a synchrotron period, and wavelengths shorter than a bunch length. In this case, the usual Keil-Schnell coasting-beam criterion3) is used, but with local values of bunch current and momentum spread, as suggested by Boussard1). This yields |Z/n| ? 13 ? for the ISR, and values about five to ten times larger for the PS. The restricitons mentioned above, however, are not fulfilled near threshold, or for frequencies as low as 100 MHz.

Theory of the vibrational structure of resonances in electron-molecule scattering

Abstract: We derive a simple Hamiltonian representing the coupling of an electronic level of positive energy to the continuum of scattering states as well as to the molecular vibrations. By summing the perturbation series for the $S$ matrix to infinite order in the bound-state-continuum interaction, an effective non-Hermitian boson Hamiltonian describing the dynamics of vibrational motion in the resonance state is obtained. It is shown that the effective Hamiltonian can be diagonalized, yielding explicit expressions for the vibrational excitation cross sections. The theory is applied to two representative examples, the 3.8-eV shape resonance in C${\mathrm{O}}_{2}$ and the 2.4-eV shape resonance in ${\mathrm{N}}_{2}$. The results exhibit a clear improvement over those obtained with existing theories, which express the cross sections in terms of conventional Franck-Condon factors. The influence of the anharmonicity of the potential functions on the structure of the vibrational excitation functions is discussed.

Modification of resonance Raman scattering in very intense laser fields

Abstract: The general method developed in a previous paper (see ibid., vol.10, p.345 (1977)) is applied to the problem of resonance Raman scattering in very intense laser fields. At very low intensities the spectrum consists of three monochromatic lines (Rayleigh, Raman Stokes and anti-Stokes) which split into a triplet and two doublets when the laser light, tuned on one of the two transitions connecting the upper state to the two lower sublevels, has a sufficiently high intensity to saturate this transition but not the second one. The Raman and Rayleigh lines are completely mixed when the intensity becomes so high that both transitions are saturated. The corresponding evolution of the spectrum is determined. Optical-pumping effects leading to asymmetries in the fluorescence spectrum are taken into account.

Modes in SAW grating resonators

Abstract: A Rayleigh wave of finite width, propagating along the surface of an isotropic medium, is shown to obey approximately a paraxial wave equation if the width is large compared with a wavelength. Results of laser wave propagation can be applied to the Rayleigh‐wave case. Furthermore, an equation is derived for the two‐dimensional Rayleigh‐wave propagation underneath a grating surface. A grating of finite width is shown to provide transverse confinement (guidance) of the wave. The mode patterns are obtained of the fundamental and higher‐order guided modes under uniform gratings of finite width. For a grating resonator formed of two uniform gratings separated by a quarter‐wave section, a variational expression is developed for the resonance frequencies. Using a simple mode pattern for the trial solution, the resonance frequencies of the higher‐order modes are evaluated. They all lie on the high side of the Bragg frequency, increasing with increasing mode number.

Resonance Charge Transfer and Population Inversion Following C 5 + and C 6 + Interactions with Carbon Atoms in a Laser-Generated Plasma

Abstract: Enhanced population of the $n=4$ excited state is measured in both ${\mathrm{C}}^{4+}$ and ${\mathrm{C}}^{5+}$ ions in agreement with a theory for formation by resonance charge transfer between carbon ions and atoms. A background gas modifies and mixes the interacting particles originating from a carbon surface vaporized by a focused laser beam. Population inversions capable of producing quasi-cw amplification in the extreme ultraviolet region are measured.

Narrow resonances of two-photon absorption of super-narrow pulses in a gas

Abstract: A scheme to generate oppositely travelling super-narrow pulses is proposed. These resonant peaks are produced when the sum of frequencies of two synchronized modes coincides with the transition frequency. Their widths are not determined by the pulse duration but rather by the homogeneous width of the two-photon transition. The resonance intensity turns out to be the same as that at the single-frequency condition with the same power.

Some O I oscillator strengths and the interstellar abundance of oxygen

Abstract: Calculated and experimental oscillator strengths for the O I intersystem line at 1356 A and for other O I lines of interest in interstellar absorption-line studies are discussed. Attention is given to experimental f-values for the lines at 1302, 1305, and 1306 A, previous work on the f-values for the lines at 1356 and 1359 A, wave-function expansion, and calculations for permitted as well as intercombination lines. Copernicus observations of several interstellar absorption lines due to O I, C II, P II, and Ni II toward Zeta Oph are reported, equivalent widths are determined, and a curve-of-growth analysis is performed for the O I absorption lines. Oscillator strengths are recommended for the far-UV resonance lines of O I, and it is concluded that the oxygen in the interstellar H I regions toward Zeta Oph is depleted by 45% to 69%.

Gyromagnetic resonance fourier transform zeugmatography

Abstract: An improved technique is disclosed for forming two- or three-dimensional images of a macroscopic sample by means of gyromagnetic resonance. A train of free induction decay transient resonance signals are induced and detected from a sample in a region to be imaged. A sequence of pulsed magnetic field gradients are applied during the series of free induction decay signals to derive sets of gyromagnetic resonance data as a function of the changing magnetic field gradients. Two- or three-dimensional images are reconstructed from the sets of resonance data by two- or three-dimensional Fourier transformation.