Solvent effects on the nitrogen hyperfine splitting constant of the t-butyl-t-butoxy nitroxyl radical

A decrease in nitrogen hyperfine splitting constant (N-hfsc) with increasing solvent polarity is reported for $\text{t}$-butyl $\text{t}$-butoxy nitroxyl radical produced by trapping $\text{t}$-butoxyl radical with 2-methyl-2-nitrosopropane.     

Synthesis and characterization of volatile liquid cobalt amidinates

Three new volatile cobalt amidinate compounds were prepared: Co(tBuNC(R)NEt)2, R=Me, Et and n-Bu. They were characterized by elemental analysis, 1H NMR, X-ray structure analysis, melting point, vapor pressure, vaporization rate, thermal stability and chemical reactivity. They were found to evaporate cleanly without decomposition. Two of them are liquids at room temperature, allowing for more convenient preparation, handling and purification by distillation. They are highly reactive compounds that have been found to be suitable precursors for vapor deposition of cobalt metal, cobalt nitride and cobalt oxide. A new synthetic method allows for the facile and inexpensive preparation of large quantities of these compounds.     

Collisional deactivation of Ba 5d7p (3)D1 by noble gases

Collisional deactivation of the 5d7p (3)D1 state of Ba by noble gases is studied by time- and wavelength-resolved fluorescence techniques. A pulsed, frequency-doubled dye laser at 273.9 nm excites the 5d7p (3)D1 level from the ground state, and fluorescence at 364.1 and 366.6 nm from the 5d7p (3)D1 --> 6s5d (3)D1 and 5d7p (3)D1 --> 6s5d (3)D2 transitions, respectively, is monitored in real time to obtain the deactivation rate constants. At 835 K these rate constants are as follows: He, (1.69 +/- 0.08) x 10(-9) cm(3) s(-1); Ne, (3.93 +/- 0.14) x 10(-10) cm(3) s(-1); Ar, (4.53 +/- 0.15) x 10(-10) cm(3) s(-1); Kr, (4.64 +/- 0.13) x 10(-10) cm(3) s(-1); Xe, (5.59 +/- 0.22) x 10(-10) cm(3) s(-1). From time-resolved 5d7p (3)D1 emission in the absence of noble gas and from the intercepts of the quenching plots, the lifetime of this state is determined to be 100 +/- 1 ns. Using time- and wavelength-resolved Ba emission with a low background pressure of noble gas, radiative lifetimes of several near-resonant states are determined from the exponential rise of the fluorescence signals. These results are as follows: 5d6d (3)D3, 28 +/- 3 ns; 5d7p (3)P1, 46 +/- 2 ns; 5d6d (3)G3, 21.5 +/- 0.8 ns; 5d7p (3)F3, 48 +/- 1 ns. Integrated fluorescence signals are used to infer the relative rate constants for population transfer from the 5d7p (3)D1 state to eleven near-resonant fine structure states.     

Preparation and characterization of MgB2 superconductor

The MgB₂ superconductor, synthesized using solid-state and liquid-phase sintering methods, have been characterized for various properties. The upper critical field, irreversibility line and critical current density have been determined using magnetization data. The current-voltage characteristics recorded under an applied magnetic field revealed the existence of vortex glass transition. The surface analysis using X-ray photoelectron spectroscopy shows that MgB₂ is sensitive to atmospheric degradation.     

On the Permutation Behaviour of Dickson Polynomials of the Second Kind

The known permutation behaviour of the Dickson polynomials of the second kind in characteristic 3 is expanded and simplified.     

Transfer characteristics of radiocaesium from soils to permanent pasture.

Depth profile measurements of 137Cs and 134Cs were carried out in 11 permanent pastures that had been exposed to fallout from the Chernobyl accident. In addition to gamma-ray spectrometric analysis, the selected pastures were characterized by several soil parameters, the influence of which on transfer was investigated. Sampling of soil and pasture grass was undertaken during a period extending from the Spring of 1987 to the Autumn of 1988. The results show that there has been limited downward migration of Chernobyl-derived caesium. In October 1988 more than 88% of the 137Cs attributable to Chernobyl was mainly confined to the top 10 cm of undisturbed soil, with 79% on average in the top 5 cm. The distribution of pre-Chernobyl caesium at the 11 sites was also evaluated. In an investigation of the influence of soil parameters on transfer to grass, a negative correlation with pH was observed in 1987. In April 1987 concentration ratios for 137Cs in grass ranged from 0.03 to 0.49. In general, comparison of the concentration ratio values showed a decreasing trend over the 18 months.     

Laser photodissociation of s-tetrazine: Product vibrational excitation

The photosensitive and thermally unstable molecule s-tetrazine decomposes to yield one nitrogen molecule and two HCN molecules. Following pulsed irradiation of tetrazine vapor at 492.3 nm, we have observed time resolved infrared fluorescence from HCN(001). In a similar experiment, small quantities of CO₂ were added to the sample cell, and we observed infrared fluorescence from CO₂ (001) populated by VV energy transfer. From fluorescence intensity measurements, we have been able to estimate the amount of excitation in certain product vibrations. We conclude that ≈ 1% of the HCN is produced in the (001) state, and the “equivalent” of ≈ 0.1 quantum of N₂ vibrational excitation is excited. This latter figure may include some excitation of HCN (ν₁), but the measured energy transfer rate coefficients are consistent with N₂ excitation. The small amount of HCN(ν₃) and N₂ vibrational excitation is surprising, as the photodissociation is exothermic by more than 100kcal/mole.     

Variation of fragmentation with ring size in cyclic α-amino acids

High resolution mass measurements, defocused metastable ion detection and deuterium labeling experiments have been employed in an investigation of the electron-impact induced decomposition of a series of carbocyclic amino acids, which varied in ring size from three to eight carbon atoms. About 50 per cent of the total ion current is carried by [M ? COOH]⁺ ions in the spectra obtained from compounds with five to eight carbon atoms in the ring. This is analogous to the fragmentation of the open chain naturally occurring amino acids. The behavior of the compounds with the two smallest rings is anomalous, reflecting to a larger extent the influence of the ring itself. Special attention has been given the loss of H₂O and NH₄ from ionized species of 1-aminocyclopropanecarboxylic acid.