Photolytic production of Fe3+ in CaS

Calcium sulfide powder containing iron as an impurity was irradiated with 580, 366 or 254 nm light at 77 K. Irradiation enhanced a broad (16 G peak-to-trough) electron paramagnetic resonance (EPR) signal at g = 2.017 and caused six sharp (～1 G) lines to appear in the X-band EPR spectrum at 347, 529, 956, 1963, 3547 and 5376 G. Enrichment of CaS with Fe²⁺ produced samples with similar photochemistry. It is proposed that irradiation causes the reaction Fe²⁺ + trap → Fe³⁺ + trap^?, whose products give rise to six sharp EPR lines assigned to Fe³⁺ and a broad line associated with trap^?. Both hyperfine splitting by ⁵⁷Fe (13 G) and superhyperfine splitting by ³³S (11.4 G) are observed in the six line spectrum. The environment of the photo-generated Fe³⁺ has less than octahedral symmetry. V²⁺ was observed at octahedral sites in unirradiated CaS for the first time, and is characterized by the EPR parameters g = 1.961 and A (hyperfine coupling) = 74.6 × 10^?4 cm^?1. EPR signals due to Mn²⁺ and Cr³⁺ at octahedral sites and Fe³⁺ at a low symmetry site were also observed in unirradiated CaS.     

Synthesis and characterization of poly(ethylene glycol) derivatives

Five general routes for the preparation of polyoxyethylene [generally referred to as poly(ethylene glycol) or PEG] derivatives are described. These routes are (1) nucleophilic displacements with the alkoxide of PEG, (2) nucleophilic displacement on PEG–tosylate, –mesylate, or –bromide, (3) reductive amination of PEG–aldehyde, (4) reductive amination of PEG–amine, and (5) nucleophilic displacements on the s-triazine derivatives prepared from s-triazine trichloride (cyanuric chloride) and PEG. Eighteen derivatives are prepared and potential applications to catalysis, cell purifications, and other areas are discussed briefly.     

Measured mixer noise temperature and conversion loss of a cryogenic Schottky diode mixer near 800 GHz

We accurately measured the noise temperature and conversion loss of a cryogenically cooled Schottky diode operating near 800 GHz, using the UCB/MPE Submillimeter Receiver at the James Clerk Maxwell Telescope. The receiver temperature was in the range of the best we now routinely measure, 3150 K (DSB). Without correcting for optical loss or IF mismatch, the raw measurements set upper limits ofT _M=2850 K andL _M=9.1 dB (DSB), constant over at least a 1 GHz IF band centered at 6.4 GHz with an LO frequency of 803 GHz. Correction for estimated optical coupling and mismatch effects yieldsT _M=1600 K andL _M=5.5 dB (DSB) for the mixer diode itself. These values indicate that our receiver noise temperature is dominated by the corner cube antenna's optical efficiency and by mixer noise, but not by conversion loss or IF mismatch. The small fractional IF bandwidth, measured mixer IF band flatness from 2 to 8 GHz, and similarly good receiver temperatures at other IF frequencies imply that these values are representative over a range of frequencies near 800 GHz.     

Spin-orbit coupling in nitrite ion and nitrite salts

The absorption intensity of the³B₁ ¹A₁ transition of nitrite salts of the non-transition metals is markedly dependent on the metal counterion and is causative of the yellow-orange colors of the heavier-metal salts. It is assumed that spin-orbit coupling is responsible for this phenomenon; this assumption is investigated here using semi-empirical one-electron calculations and is validated. The subjects of covalent bonding in metal salts, charge transfer transitions in such systems and the S _j S ₀ electronic spectroscopy of nitrite salts are also investigated.This work was supported by contracts between the United States Atomic Energy Commission — Biology Branch and the United States Air Force with the Louisiana State University.     

Mössbauer measurements of the bipyramidal lattice site in BaFe12O19

Mössbauer measurements have been made on polycrystalline barium ferrite samples. The subspectrum corresponding to the iron ion in the bipyramidal lattice site in the temperature range from T = 4.2K up to T = 870K was obtained. Based on the temperature dependence of the unusually large quadrupole splitting due to ferric iron in the bipyramidal position, a model of this lattice site is proposed in which the iron ion is located at one of two equivalent positions of Wyckhoff notation 4e, separated by a potential barrier. At sufficiently high temperature the ion jumps between the two 4e sites with a jump frequency which is greater than the inverse of the lifetime of the 14.4 keV state of ⁵⁷Fe. This is in agreement with Mössbauer measurements, molecular-orbital studies and previous X-ray data.     

Temperature and field dependent scattering in noble metal alloys

The scattering formalism of Blaker and Harris which is appropriate to potential scattering in dilute cubic alloys is modified to include the spin-dependent scattering. An expression for the total T-matrix which describes the ordinary and exchange scattering by magnetic impurities is obtained. The new formalism is compared with other work in the area and is used to discuss the dHvA data for Kondo alloys based on Cu and Au.     

Potentiometrische p-Bestimmung

Ohne Zusammenfassung     

Second-harmonic tomography of tissues

A novel noninvasive second-harmonic-generation tomographic method of mapping the structure of animal tissues by use of 100-fs laser pulses at 625nm is described. Subsurface structures were measured with this approach, which is potentially a symmetry-sensitive tool for optical histological reconstruction.     

Optical parametric oscillators pumped by population-trapped atoms

We describe an optical parametric oscillator that is pumped by population-trapped atoms that are prepared with maximum coherence. The oscillator is based on the use of an effective nonlinear susceptibility that is of the same order as the linear susceptibility. Because the parametric gain is obtained in a single coherence length, the gain bandwidth can exceed the degenerate frequency. In Pb vapor the calculated gain is maximized at 1.88 microm and has a bandwidth of ~7500 cm(-1).