Showing papers on "Resonance published in 1981"
TL;DR: In this article, a hybrid rf/optical technique for studying sub-Doppler saturated absorption/dispersion resonances with excellent precision and symmetry is discussed, and a new level of accuracy for laser locking to an optical resonance is achieved.
Abstract: We discuss a refined, hybrid rf/optical technique for studying sub‐Doppler saturated absorption/dispersion resonances with excellent precision and symmetry. Sensitivity is limited mainly by fundamental noise in the signal. Resonance profiles obtained in I2 are in remarkable agreement with theory. The method promises a new level of accuracy for laser locking to an optical resonance.
319 citations
TL;DR: It is found that since the oscillating components are adjusted to the same frequency, the spin systems are in resonance and mutual spin flips can occur and heat can flow between the reservoirs, and they equilibrate to a common spin temperature.
Abstract: Publisher Summary This chapter discusses solid state nuclear magnetic resonance of lipid bilayers. The shortcomings of conventional high-resolution spectroscopy when applied to lipid bilayers are presented. The resolution in multiple-pulse experiments has been limited to 1–2 ppm and these techniques have been useful only for studies of small molecules. A method for obtaining high-resolution spectra of solids relies on the spatial factor to attenuate and is referred to as dilute spin spectroscopy. It is found that since the oscillating components are adjusted to the same frequency, the spin systems are in resonance and mutual spin flips can occur and heat can flow between the reservoirs, and they equilibrate to a common spin temperature. It is convenient to add an echo pulse to the experiment at the dilute spin frequency, as is shown in the chapter. The purpose of this pulse is to delay data acquisition until the receiver and filters of the spectrometer recover from the radiofrequency pulse. It is suggested that the sidebands can be used to obtain information on chemical shift and electric field gradient tensors.
254 citations
TL;DR: In this article, a simple estimate of the effect of the Δ resonance on isovector M1 and Gamow-Teller moments in nuclei is made based on the quark model.
212 citations
PARC1
TL;DR: In this article, an autocompensation mechanism was proposed for defect formation on doped and compensated hydrogenated amorphous silicon, and the first observation of metastable light-induced electron spin resonance (ESR) signal in $a$-Si: H.
Abstract: Luminescence, electron spin resonance (ESR), optical absorption, conductivity, and composition data are measured on doped and compensated hydrogenated amorphous silicon. In material singly doped with boron or phosphorus, a variety of experiments indicates the introduction of a large defect density (up to ${10}^{18}$ ${\mathrm{cm}}^{\ensuremath{-}3}$) of the dangling-bond type. Compensation increases the luminescence efficiency, but the luminescence peak shifts strongly to lower energy. Compensation reduces the ESR resonance at $g=2.0055$, but a broad resonance characteristic of a hole trap remains. We deduce that compensation reduces the dangling-bond density, but introduces a new band of localized states above the valence-band edge. We associate these new states with boron-phosphorus complexes whose origin is a chemical interaction occurring during deposition. Changes in the dangling-bond density with doping and compensation lead us to propose an autocompensation mechanism of defect formation. Also reported is the first observation of a metastable light-induced ESR signal in $a$-Si: H.
211 citations
TL;DR: In this paper, the effect of vibrational preionization on the total and partial oscillator strength distributions and photoelectron angular distribution in H2 for excitation between 790 and 760 A.
Abstract: Multichannel quantum defect theory has been used to calculate the effect of vibrational preionization on the total and partial oscillator strength distributions and photoelectron angular distribution in H2 for excitation between 790 and 760 A. The total oscillator‐strength distribution obtained agrees well with the high‐resolution photoionization data of Dehmer and Chupka. The partial oscillator strength resonance profiles are predicted to have different shapes in different vibrational ionization channels, while their widths change little with channel. The preionization resonances are also predicted to affect the angular distribution asymmetry parameters b over a broader range than they affect the oscillator strength distribution. The gross features of the preionization resonances are discussed in terms of approximate solutions of the MQD equations.
127 citations
TL;DR: In this paper, the upgoing thermal ionospheric electrons falling through a field-aligned potential drop on the order of their thermal energy were measured with amplitudes of 1-5 µ A/m².
Abstract: Downward currents in auroral regions are commonly measured with amplitudes of 1–5 µ A/m². Such currents are likely the result of upgoing thermal ionospheric electrons falling through a field-aligned potential drop on the order of their thermal energy. Similar distributions of upgoing ionospheric electrons may also occur in regions of diffuse auroral electron precipitation to preserve current continuity in the presence of the loss of the precipitating electrons to the ionosphere. The drift velocity of the upgoing electrons is sufficient to excite electrostatic ion-cyclotron waves. In addition to being in Landau resonance with the upgoing electrons, these waves cyclotron resonate with the upgoing thermal ions with a parallel energy of several eV. Calculated quasi-linear diffusion rates using measured wave spectra indicate the resonant ions can be heated to perpendicular energies on the order of 100 times the initial ion thermal energy. Comparison with auroral particle observations, both at low altitude (∼1500 km) and higher altitude (∼6000 km) shows that ion-conic distributions can readily be explained by such quasi-linear diffusion. The results imply that conic distributions should not occur simultaneously with the keV electron precipitation associated with discrete arcs in regions of upward current but should occur in regions of upgoing ionospheric electrons which may include regions near the edges of auroral arcs and regions of diffuse auroral electron precipitation.
126 citations
TL;DR: In this paper, the refractive indices of rare gases have been measured by Fabry-Perot interferometry down to 140 nm and a value of 0.268±0.008 was derived for the oscillator strength of the first resonance line at 146.9 nm.
Abstract: The refractive indices of rare gases have been measured by Fabry-Perot interferometry down to 140 nm. Dispersion relations of the Sellmeier form are given and the results are compared with data found in the literature. For xenon, a value of 0.268±0.008 is derived for the oscillator strength of the first resonance line at 146.9 nm.
122 citations
TL;DR: In this paper, the rotational, nuclear quadrupole coupling and spin-rotation constants of the ground electronic state treated as a singlet state were determined for (NO)2 using the technique of molecular beam electric resonance spectroscopy.
Abstract: Microwave and radiofrequency spectra have been observed for (NO)2 using the technique of molecular beam electric resonance spectroscopy. Precise values have been determined for rotational, nuclear quadrupole coupling and spin-rotation constants of the ground electronic state treated as a singlet state. The values obtained are A = 25829·4803(20) MHz, B = 5614·3093(4) MHz, C = 4605·4396(12) MHz xaa = -4·0652(2) MHz, xbb - xcc = -8·5498(6) MHz caa = 10·4(5) kHz, cbb = 13·8(4) kHz, ccc = 0·8(4) kHz. The electric dipole moment has also been determined: μ = 0·17120(2) D. From these data (NO)2 is interpreted to have a symmetric cis-planar structure with the structural parameters r NN = 2·33(12) A, r NO = 1·15(1) A, ∠NNO = 95(5), 1/2(r NN + r NO) = 2·444(8) A. The quadrupole coupling constants of the nitrogen nuclei and the dipole moment demonstrate that little electron rearrangement occurs on dimer formation. In addition xaa and xbb - xcc indicate that the unpaired π electrons lie in the plane of the dimer imply...
109 citations
TL;DR: In this article, a single 24Mg+ ion has been laser cooled in a Penning trap and its optical spectrum observed by a double resonance technique, which implies a cyclotron-magnetron temperature of 50 ± 30 mK.
108 citations
TL;DR: In this paper, high-resolution Stark-hyperfine transition measurements have been made on the J = 1, K = 0, J = 0 and K = 1 levels of ammonia using molecular beam electric resonance spectroscopy.
107 citations
TL;DR: In this article, the rate coefficients for the reactions N + OH → NO + H (1) and O + O → O2+ H (2) have been determined, in direct experiments, from 250 to 515 K.
Abstract: Rate coefficients for the reactions N + OH → NO + H (1) and O + OH → O2+ H (2) have been determined, in direct experiments, from 250 to 515 K. A discharge-flow system is used to generate measured concentrations of N or O; then OH radicals are formed by flash photolysis of H2O and monitored by resonance fluoresence as they are removed by reaction (1) or (2) under pseudo-first-order conditions. The results are fitted to the rate expressions: k1=(2.21 ± 0.18)×10–10T–0.25 ± 0.17 cm3 molecule–1 s–1, k2=(6.65 ± 0.23)×10–10T–0.50 ± 0.12 cm3 molecule–1 s–1 where the errors represent 95% confidence intervals within the range of temperature covered in the experiments. The rate coefficient k2 is compared with a calculation assuming that the reaction proceeds via a bound state HO2 collision complex.
TL;DR: In this paper, the first resonance Raman spectra of benzene and deuterobenzene were reported, which are dominated by the overtones and combinations of the vibronically active e2g modes in this dipole forbidden transition, as well as the fundamental, overtone and combination of ν1, the a1g ring breathing mode.
Abstract: The first resonance Raman spectra of benzene and deuterobenzene are reported. Resonance excitation with the second excited singlet transition (1B1u) is obtained with 212.8 nm radiation. These resonance Raman spectra are dominated by the overtones and combinations of the vibronically active e2g modes in this dipole forbidden transition, as well as the fundamental, overtone, and combination of ν1, the a1g ring breathing mode. All of the observed features, including relative intensities and depolarization ratios, are fully rationalized within the context of the vibronic theory once the 3N‐6 multidimensionality of the vibrational sublevels is exposed. The ν8 e2g mode is found to be the most vibronically active mode in the 1B1u transition, in agreement with all calculations. However, in contrast to these calculations, the Raman analysis finds that ν9, not ν6, is the next most vibronically active e2g mode in this transition. These results parallel the observed pattern of vibronic intensities in the 3B1u→1A1g phosphorescence spectra.
TL;DR: In this paper, the energy systematics of the giant Gamow-Teller resonance and a charge exchange resonance excited by a L = 1, S = 1 interaction are presented.
TL;DR: Results for size parameters that satisfy resonance conditions for various atural modes of oscillation of the cylinder clearly illustrate the physical significance of n and l and show that the internally reflected circumferential waves are localized near, but not confined to, the cylinder surface.
Abstract: Calculations of the electric field distribution within and around an infinite circular dielectric cylinder, having a relative index of refraction of 1.53 and illuminated with plane-wave radiation of wavelength λ, have been performed for size parameters ranging from 39 to 51. Results for size parameters that satisfy resonance conditions for various natural modes of oscillation of the cylinder (mode number n = 53; order numbers l = 1–5) clearly illustrate the physical significance of n and l and show that the internally reflected circumferential waves are localized near, but not confined to, the cylinder surface.
TL;DR: In this paper, a double Penning trap structure has been built which permits one to trap a positron in a well-compensated experiment trap where measurements have yielded the geonium positron g-factor anomaly, g(e/sup +/)/2-1equivalenta(e /sup +/) = (1 159 652 222 +- 50) x 10/sup -12).
Abstract: A new double Penning trap structure has been built which permits one to trap a positron in a well-compensated experiment trap where measurements have yielded the geonium positron g-factor anomaly, g(e/sup +/)/2-1equivalenta(e/sup +/) = (1 159 652 222 +- 50) x 10/sup -12/. The uncertainty is based on the resonance linewidths and an estimate of the remaining systematic error associated with extrapolating to zero spin-flip power. When compared to the electron-spin anomaly, a positron/electron g-factor ratio of 1+(22 +- 64) x 10/sup -12/ is obtained.
TL;DR: The rotational spectra of four isotopes of the weakly bound complex N2O-HF have been measured by molecular beam electric resonance spectroscopy as discussed by the authors, and the following spectroscopic constants and structural parameters were derived from the observations:
Abstract: The rotational spectra of four isotopes of the weakly bound complex N2O–HF have been measured by molecular beam electric resonance spectroscopy. The following spectroscopic constants and structural parameters were derived from the observations: In the average structure, the N2O axis makes an angle of ∼47° with a line rc.m. drawn between the centers of mass of the two submolecules. HF is hydrogen bonded toward the oxygen on N2O to form an angle of ∼31° with the center of mass line.
TL;DR: In this article, the effects of oxygen-dependent shortening of the electron spin relaxation times of nitroxide spin labels were studied in dispersions of dimyristoylphosphatidylcholine (DMPC) and dipalmitoyl-phosphate-morphosynthetic choline (DPPC).
TL;DR: In this article, the electron-impact intramolecular vibrational and vibronic excitation of disordered multilayer films with primary energies varying from 2 to 20 eV was studied.
Abstract: Electron-impact intramolecular vibrational and vibronic excitation of disordered multilayer ${\mathrm{O}}_{2}$ films is studied with primary energies varying from 2 to 20 eV The intensity of the $v=1$ to $v=4$ vibrational modes of ground state ${\mathrm{O}}_{2}$ exhibits a broad resonance as a function of electron energy At the resonance maximum the vibrational intensities are enhanced by one to two orders of magnitude The resonance appears to be derived from gas-phase ${\mathrm{O}}_{2}$ quasibound states
TL;DR: In this paper, the surfaces for the three strongest secular resonances have been located as a function of proper semimajor axis, eccentricity, and inclination for semi-major axes between 1.25 and 3.5 AU.
TL;DR: In this article, a vibrational analysis of Ru(bpy) 2+* 3 and comparison with the RR spectrum of free bpyXXX shows that Ru((bpy)-2+*3) is essentially [Ru III (bpy)/bpyXXX] 2+.
TL;DR: The normal mode patterns confirm previous inferences, based on selective effective of chemical substitutions, of localization to certain regions of the molecule and interpret the observed variability of the prominent RR bands among different flavoproteins on the basis of protein-isoalloxazine interactions.
Abstract: The normal modes of lumiflavin (10-methyliso-alloxazine) are analyzed with a valence force field constructed with bond length-stretching force constant correlations and bending and interaction force constants transferred from small ring molecules. Observed resonance Raman (RR) bands of flavin are assigned to calculate modes on the basis of frequency and isotope shift matching. The normal mode patterns confirm previous inferences, based on selective effective of chemical substitutions, of localization to certain regions of the molecule. These results are used to interpret the observed variability of the prominent RR bands among different flavoproteins on the basis of protein-isoalloxazine interactions.
TL;DR: In this article, a silica supported Ni catalyst has been investigated by electron magnetic resonance between 293 and 4.2 K. A relatively narrow absorption signal with linewidth ΔHpp?400 Oe is observed at temperatures?150 K as a result of motional averaging of the magnetocrystalline anistropy field Ha of the Ni particles resulting from superparamagnetism.
Abstract: A silica supported Ni catalyst has been investigated by electron magnetic resonance between 293 and 4.2 K. A relatively narrow absorption signal with linewidth ΔHpp?400 Oe is observed at temperatures ?150 K as a result of motional averaging of the magnetocrystalline anistropy field Ha of the Ni particles resulting from superparamagnetism. Broadening of the resonance occurs at lower temperatures because of a reduction of the influence of thermal fluctuations. A line shape analysis of the observed resonance signals is carried out employing the theory of ferromagnetic resonance in polycrystalline material. The calculated anisotropy field is reduced in the particles as compared to bulk Ni. The Landau–Lifshitz relaxation frequency obtained from the calculated ’’single crystal’’ linewidths are found to be larger than those of bulk Ni single crystals. Concurrently with line broadening, the resonance shifts to lower magnetic fields. The resonance shifts are approximately Ha/2. The appearance of magnetoelastic eff...
TL;DR: In this paper, the authors discuss the resonance Raman spectroscopy of hemoglobin and emphasize the Raman polarizability tensor, which is an ideal probe of heme geometry and bonding.
Abstract: Publisher Summary This chapter discusses resonance Raman spectroscopy of hemoglobin. Resonance Raman spectroscopy is almost an ideal probe of heme geometry and bonding in hemoglobin and myoglobin. The technique is ideally suited for aqueous protein solutions at concentrations variable from the physiological heme concentration in the red blood cell to the submicromolar level. The technique is also easily utilized for single-crystal protein studies or for studies of model heme complexes in organic solution or in the form of the single crystals used for X-ray diffraction structural determinations. The advances in the resonance Raman technique over the past few years have been phenomenal. The harvesting of these advances in terms of an understanding of hemoglobin cooperativity is beginning to present new reliable data on the heme conformational dependence upon protein structure. Raman results have presented data that have challenged the present models for hemoglobin cooperativity. In addition to this, the chapter also emphasizes the Raman polarizability tensor.
TL;DR: In this paper, the authors used a spherical acoustic resonator to measure the speed and attenuation of sound in C2H4 in the temperature range 0 −100 ˚ c and the pressure range 0.15 −1.0 MPa.
Abstract: The spherical acoustic resonator is a remarkably accurate and convenient tool for the measurement of thermophysical properties of gases at low and moderate densities. The speed of sound (c) in a gas of interest can be measured with an accuracy of 0.02% merely by measuring the frequencies of the radial resonances when the resonator is filled with the gas of interest and then repeating the frequency measurements with a reference gas such as argon. The resonance frequencies of the radial modes are easily measured because these modes have very high Q’s, typically 2000–10 000. In this work the precision and accuracy of speed of sound measurements have been substantially improved by including a detailed acoustic model of the resonator in the analysis. Many of the important parameters of the model can be determined from acoustic measurements: Painstaking mechanical measurements are not required. We have used a spherical resonator to measure the speed and attenuation of sound in C2H4 in the temperature range 0–100 °C and the pressure range 0.15–1.0 MPa. Our measured values of c in C2H4 have a precision of 0.003% and agree with those of Gammon within the scatter of Gammon’s data (±0.02%). This agreement is remarkable when one considers that our spherical resonator is operated in the frequency range 4–13 kHz while Gammon has used a more conventional, cylindrical, variable path, acoustic interferometer operating at 500–2500 kHz. To attain this agreement, we did not have to make any highly accurate measurements other than frequency. Our measured values of the bulk relaxation frequency of C2H4 are within the scatter of the more recent values of the literature. In the course of our ’’calibration’’ measurements with argon we have redetermined the leading acoustic virial coefficient of argon. Our values for the virial are in satisfactory agreement with those in the literature. We include several practical suggestions for increasing the accuracy and/or versatility of spherical resonators.
TL;DR: In this paper, static exchange and static exchange plus polarisation calculations are carried out for elastic electron and positron scattering with Be, Mg and Ca. All three atoms are found to have a low-lying 2P resonance in the electron scattering case.
Abstract: Static exchange and static exchange plus polarisation calculations are carried out for elastic electron and positron scattering with Be, Mg and Ca. All three atoms are found to have a low-lying 2P resonance in the electron scattering case. Magnesium and calcium are also predicted to have higher lying 2D shape resonances near 2.0 and 0.7 eV, respectively. The 2D resonance in Mg is very weak and broad ( Gamma >3.0 eV) while that in Ca is much more pronounced and is much narrower ( Gamma approximately 0.6 eV). These findings are in agreement with recent experiments. In addition a very broad feature appears in e--Be d-wave scattering near 5 eV. While maxima occur in the p-wave cross sections for positron scattering, these do not appear to be due to resonances. However, evidence is provided for exceptionally broad resonances in d-wave positron scattering and for a virtual (or antibound) state in s-wave scattering.
TL;DR: In this article, the authors present a theoretical model for the interaction of a beam of two-level atoms with a resonant laser beam and show that the radiation force, while averaging to zero at resonance, produces a transverse spread of the atomic velocities.
Abstract: We present a theoretical model for the interaction of a beam of two-level atoms with a resonant laser beam. It is shown that the radiation force, while averaging to zero at resonance, produces a transverse spread of the atomic velocities. If radiative damping is ignored, this spread increases linearly with time and finally saturates towards a steady value. Although the spread has a quantum-mechanical origin, we show that it is possible, in the limit $\ensuremath{\hbar}k\ensuremath{\rightarrow}0$, to describe the phenomenon in terms of differential equations of motion for the atomic translational variables, as in the classical case. In this model it is also possible to describe the effects of radiative damping, as well as other additional effects, which may occur in a real experiment. Finally a comparison of our results with experimental data, recently obtained on an Na atomic beam, has been made. Although an order-of-magnitude fit of the experimental data could be obtained, the weights of the different causes, reducing the spread, were found to be ambiguous and have been left partly open.
TL;DR: In this paper, a σ-type shape resonance 7-8 eV above threshold is presented for the 4σ derived ionic states of NO. The energy position of this resonance is compatible with a simple kinematic scattering model.
TL;DR: In this article, the excitation functions of angle-integrated cross sections for elastic scattering and reactions show narrow, highly correlated structures. But they are interpreted as having quasimolecular or fission-isomeric nature.
Abstract: Detailed excitation functions of angle-integrated cross sections for $^{28}\mathrm{Si}$+$^{28}\mathrm{Si}$ elastic scattering and reactions show narrow, highly correlated structures. These resonances have enhanced partial widths for decay into two $^{28}\mathrm{Si}$ fragments and are interpreted as having quasimolecular or fission-isomeric nature.
TL;DR: In this article, the magnetic properties of the implanted layer in thin garnet films can be obtained from ferromagnetic resonance experiments using parallel spectra alone, and an approximate profile of implantation induced anisotropy is obtained using perpendicular resonance alone.
Abstract: Magnetic properties of the implanted layer in thin garnet films can be obtained from ferromagnetic resonance experiments. Approximate profiles of implantation induced anisotropy can be obtained using perpendicular resonance alone. For maximum information and accuracy, both perpendicular and parallel resonance spectra are needed, and measurements should be made on a number of samples from which varying amounts of the implanted layer have been removed by ion milling. For narrow linewidth materials it is possible to deduce profiles of H k , 4πM, and A and to determine the value of g in the implanted layer. Methods are presented for the accurate calculation of parallel ferromagnetic resonance (FMR) spectra with depth varying magnetic parameters. This method of analysis has been successfully applied to a yttrium iron garnet (YIG) film substituted with Gd, Tm, Ga, and implanted with He ions at 140 keV with a density of 3 × 1015cm-2.
TL;DR: In this paper, a difference frequency resonance was observed for the 747 cm−1 vibration in the first excited singlet state of pentacene in benzoic acid, and the resonance is absent at low temperature (4.5 K) and its appearance was exponentially activated with an activation energy of 13.8 cm− 1.