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The beam-foil time-of-flight method has been used to investigate radiative lifetimes and transition rates involving allowed intrashell transitions within the L shell of highly ionized sulfur. The results for these transitions, which can be particularly correlation-sensitive, are compared with current calculations based upon multiconfigurational models.
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Recent work aimed at determining the absolute rovibrational transition intensities for the ground electronic state of the hydroxyl radical is reviewed. Two new sets of Fourier transform emission spectra of OH are described which were recorded at the University of Paris and at the Kitt Peak National Solar Observatory.
Reliable experimental diople moments are available for the ground states of SeH and BrH whereas no values have been reported for GaH and AsH a recently reported experimental dipole moment for GeH of 1.24 + or -0.01 D has been seriously questioned, and a much lower value of, 0.1 + or - 0.05 D, suggested. In this work, we report accurate theoretical dipole moments, dipole derivatives, dissociation energies, and spectroscopic constants (tau(sub e), omega(sub e)) for the ground states of GaH through BrH.
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Interatomic electric dipole moment coefficient derivation by approximation involving accessible atomic properties, noting application to H atoms
Methods for calculating cross sections for the breakup of high-energy heavy ions by the combined nuclear and coulomb fields of the interacting nuclei are presented. The nuclear breakup contributions are estimated with an abrasion-ablation model of heavy ion fragmentation that includes an energy-dependent, mean free path. The electromagnetic dissociation contributions arising from the interacting coulomb fields are estimated by using Weizsacker-Williams theory extended to include electric dipole and electric quadrupole contributions. The complete computer code that implements the model is included as an appendix. Extensive comparisons of cross section predictions with available experimental data are made.
Quantum mechanical optical potential methods for calculating inclusive isotope and element production cross sections from the fragmenting of heavy nuclei by intermediate- and high-energy protons and heavy ions are presented based upon a modified abrasion-ablation-FSI (frictional spectator interaction) collision model. The abrasion stage is treated as a quantum mechanical knockout process that leaves the residual prefragment in an excited state. Prefragment excitation energies are estimated using a combined liquid drop and FSI method. In ablation the prefragment deexcites by particle and photon emission to produce the final fragment. Contributions from electromagnetic dissociation to single nucleon removal cross sections are incorporated using a Weiszacker-Williams theory that includes electric dipole and electric quadrupole interactions. Estimates of elemental and isotopic production cross sections are in good agreement with published cross section measurements for a variety of projectile-target-beam energy combinations.
A new experimental technique is developed to simultaneously measure the wave propagation direction and the effective length of a small (L value much smaller than wavelength) electric dipole antenna on a spin-stabilized satellite in the magnetosphere. The technique relies on the near simultaneous measurement of single components of the electric and magnetic fields of a coherent VLF signal injected into the medium from a ground-based source. The spin fading characteristics of the signal received by the electric dipole and the magnetic loop antenna permit the measurement of the wave normal direction assuming whistler-mode propagation. In-situ and remote measurements of the local cold plasma density are used to determine the refractive index. The wave electric field is then inferred from the wave magnetic field as measured on the loop antenna, the refractive index and the direction of propagation. Comparing this electric field with the measured voltage across the dipole antenna leads to the determination of the effective length of the receiving electric dipole. The technique is applied to data from the Dynamics Explorer 1 satellite observations of whistler mode signals injected into the magnetosphere from the Siple, Antarctica, VLF transmitter. In one case, with the measured background cold plasma density being 15 el/cu cm, the effective length of the 200 m-long electric dipole antenna is found to be 222 + or - 56 m, i.e., about twice the conventional value.
The ISEE-1 and ISEE-2 plasma wave experiments are designed to provide basic information on wave-particle interactions in the earth's magnetosphere and in the solar wind. The ISEE-1 plasma wave instrument uses three electric dipole antennas with lengths of 215, 73.5 and 0.61 m for electric field measurements, and a triaxial search coil antenna for magnetic field measurements. The ISEE-2 instrument uses two electric dipole antennas with lengths of 30 and 0.61 m for electric field measurements and a single-axis search coil antenna for magnetic field measurements. The primary scientific objectives of the experiments are described, including the resolution of space-time relationships of plasma wave phenomena and VLBI studies. The instrumentation is described, with emphasis on the antennas and the electronics.
The excitation function of H Ly-alpha from the astrophysically important dissociation of electron-excited H2 over the range 10-700 eV has been measured. The analysis predicts the cross section to energies higher than the present experimental limit, and it is found that the predicted shape is in close agreement with measured results. At 6 eV the cross section is dominated by the electric dipole first Born component, while at 100 eV the electric dipole component constitutes 73 percent of the total H(2p) cross section. The cross sections of the H(2s) and H(1s) components are calculated.
The electromagnetic fields experiment on IMP-J used two electric dipole antennas and a triaxial search coil magnetic antenna to sense the electric and magnetic field of plasma waves in space. The electric dipole antennas consisted of a fine wire, 0.021 inches in diameter, with a nominal extended tip-to-tip length of 400 ft. The outermost 50 ft. of each element was conducting and the rest of the antenna was covered with an insulating coating. The search coil antennas each consisted of a high mu core with two separate windings of 40,000 turns each to sense ac magnetic fields. The search coils had a length of 18 inches tip-to-tip and are mounted on the end of a boom. The axes of the x prime and y prime search coil antennas were parallel to the x prime and y prime electric antenna axes.
Transition metal doped solids are of significant current interest for the development of tunable solid-state lasers for the near and mid-infrared (1-4 pm) spectral region. Applications of these lasers include basic research in atomic, molecular, and solid-state physics, optical communication, medicine, and environmental studies of the atmosphere. In transition metal based laser materials, absorption and emission of light arises from electronic transitions between crystal field split energy levels of 3d transition metal ions. The optical spectra generally exhibit broad bands due to the strong interaction between dopant and host (electron-phonon coupling). Broad emission bands offer the prospect of tunable laser activity over a wide wavelength range, e.g. the tuning range of Ti:Sapphire extends from 700-1100 run. The only current transition metal laser operating in the mid-infrared wavelength region (1.8-2.4 micro-m) is CO(2+):MgF2, but its performance is severely limited due to strong nonradiative decay at room temperature. Based on lifetime data, the quantum efficiency is estimated to be less than 3 deg/0 11,21. In general, the probability for non-radiative decay via multi-phonon relaxation increases with decreasing energy gap between ground and excited state. Therefore, efficient transition metal lasers beyond -1.6 micro-m are rare. Recently, tunable laser activity around 2.3 micro-m was observed from Cr doped ZnS and ZnSe. The new lasing center in these materials was identified as Cr(2+) occupying the tetrahedral Zn site. Tetrahedrally coordinated optical centers are rather unusual among transition metal lasers. Their potential usefulness, however, has been demonstrated by the recent development of near infrared laser materials such as Cr:forsterite and Cr:YAG, which are based on tetrahedrally coordinated Cr(4+) ions. According to the Laporte selection rule, electric-dipole transition within the optically active 3d-electron shells are parity forbidden. However, a static acentric electric crystal field or the coupling of asymmetric phonons can force electric-dipole transitions by the admixture of wave functions with opposite parity. Tetrahedral sites lack inversion symmetry which provides the odd-parity field necessary to relax the parity selection rule. Therefore, high absorption and emission cross sections are observed. An enhanced radiative emission rate is also expected to reduce the detrimental effect of non-radiative decay. Motivated by the initial results on Cr doped ZnS and ZnSe, we have started a comprehensive effort to study Cr(2+) doped II-VI semiconductors for solid-state laser applications. In this paper we present the optical properties and the demonstration of mid-infrared lasing from Cr doped Cd(0.85)Mn(0.15)Te.
In the coupled-dipole method, an arbitrary particle is modeled as an array of N polarizable subunits, each of which gives rise to only electric dipole radiation. The Clausius-Mosotti relation is widely used to calculate the polarizability of the subunits that correspond to the dielectric function of the particle that the array represents. The Clausius-Mosotti relation is replaced here with an exact expression for the electric dipole polarizability, and improvement is found in extinction calculations for spheres as compared with Mie theory. Near a Froehlich frequency the coupled-dipole method yields extinction cross sections for spheres and spheroids that compare favorably with the continuous distribution of ellipsoids method and measured values.
Fields generated by infinitesimal, arbitrarily oriented, electric-dipole source located in isotropic medium bounded by parallel plane- stratified, anisotropic media
Far-infrared bolometric detectors are used extensively in ground-based and space-borne astronomy, and thus it is important to understand their optical behaviour precisely. We have studied the intensity and polarisation response of free-space bolometers, and shown that when the size of the absorber is reduced below a wavelength, the response changes from being that of a classical optical detector to that of a few-mode antenna. We have calculated the modal content of the reception patterns, and found that for any volumetric detector having a side length of less than a wavelength, three magnetic and three electric dipoles characterize the behaviour. The size of the absorber merely determines the relative strengths of the contributions. The same formalism can be applied to thin-film absorbers, where the induced current is forced to flow in a plane. In this case, one magnetic and two electric dipoles characterize the behaviour. The ability to model easily the intensity, polarisation, and straylight characteristics of electrically-small detectors will be of great value when designing high-performance polarimetric imaging arrays.
This work was initiated to compare absolute line intensities retrieved with the Kitt Peak FTS (Fourier Transform Spectrometer) and Ames BOMEM FTS. Since thermal contaminations can be a problem using the BOMEM instrument if proper precautions are not taken it was thought that measurements done at 6300 per cm would more easily result in satisfactory intercomparisons. Very recent measurements of the CO 3 <-- 0 band fine intensities confirms results reported here that the intensities listed in HITRAN (High Resolution Molecular Absorption Database) for this band are on the order of six to seven percent too low. All of the infrared intensities in the current HITRAN tabulation are based on the electric dipole moment function reported fifteen years ago. The latter in turn was partly based on intensities for the 3 <-- 0 band reported thirty years ago. We have, therefore, redetermined the electric dipole moment function of ground electronic state CO.