Microwave spectra, geometries, and hyperfine constants of OCAgX (X = F, Cl, Br)

A pulsed jet cavity Fourier transform microwave spectrometer has been used to measure the rotational spectra of OCAgX (X = F, Cl, Br) in the frequency range 5-22 GHz. Metal atoms were generated via laser ablation and were allowed to react with CO and a halide precursor, prior to stabilization of the products within a supersonic jet of argon. These are the first experimental observations of OCAgF and OCAgBr, and the first high resolution spectroscopic study of OCAgCl. All three molecules are linear. Accurately determined rotational constants have been used to evaluate the various internuclear distances, which are found to be consistent with trends established for OCAuX and OCCuX species. The C-O distances are short, and the M-C distances are significantly longer than those in other molecules containing a metal-carbonyl bond. Precise values of centrifugal distortion constants and halogen nuclear quadrupole coupling constants have also been determined. The coupling constants are compared with the results of previous studies of OCCuX and OCAuX and are used to infer trends in the electron distributions of the molecules. Ab initio calculations have been performed and employed to predict the geometries, vibrational frequencies, and Mulliken valence orbital populations of the various species.     

Solid supported fluoronitroaryl triazenes as immobilized and convertible Sanger reagents--synthesis and SNAr reactions towards a novel preparation of 1-alkyl-5-nitro-1H-benzotriazoles

Synthesis of novel fluoronitroaryl triazenes in liquid phase and on solid support have been described; mild displacement of the fluoride ion with various nucleophiles provides access to substituted arenes which in turn can be cleaved to provide a unique access to 1-alkyl-5-nitro-1H-benzotriazole.     

Noncovalent engineering of carbon nanotube surfaces by rigid,functional conjugated polymers

We report a new nonwrapping approach to noncovalent engineering of carbon nanotube surfaces by short, rigid functional conjugated polymers, poly(aryleneethynylene)s. Our technique not only enables the dissolution of various types of carbon nanotubes in organic solvents, which represents the first example of solubilization of carbon nanotubes via pi-stacking without polymer wrapping, but could also introduce numerous neutral and ionic functional groups onto the carbon nanotube surfaces.     

Laser-induced-fluorescence characteristics of a helium arcjet flow

Laser-induced fluorescence is used to characterize the axial velocity and temperature field at the exit plane of a low-power helium arcjet. Two cases were examined, one in which the mass-flow rate was changed at a constant current, and the other where the current was changed at a constant mass-flow rate. At constant mass-flow rate, the velocity scales with the increase in power. At constant current, a higher specific energy results in an unexpected lower mean exit velocity. The temperature profiles show that the nozzle-wall temperature is greater than the mean exit temperature. Along the axis of the arcjet, these measurements indicate the presence of a shock less than one nozzle diameter downstream of the exit. Received: 10 July 2002 / Published online: 22 November 2002 RID="*" ID="*"Corresponding author. Fax: +1-650-723-1748, E-mail: qwalker@stanford.edu     

A two-component pericyclic reaction for synthesis of substituted benzofurans and aryl-quaternary carbon bonds

The reaction shown is presumed to be a new [3,3]-sigmatropic rearrangement involving an O-arylsulfoxonium species or related sulfurane. It allows a sulfoxide and a phenol to be joined and rearranged in one operation at or below room temperature, coupling an aromatic to a quaternary carbon and creating benzofurans or articulated dihydrobenzofurans in a number of examples.     

Thermal analysis and the scientific conservation of cultural materials

Prior to treatment, letters dating from 1665–66 were characterised using SEM, FTIR, ESCA or XPS, TG, TMA and DLTMA. All three papers were similar in composition and were basically cellulosic materials. Two which had been sent from Lisbon contained trace amounts of Fe and Cu; these impurities were also present in a letter sent from Dublin. All three letters had been written with iron gall ink. The letter from Dublin had an additional feature in the ink in the form of small bright specks of mica. The papers were examined after conservation treatment using the above same techniques in an attempt both to determine and quantify any changes which had occurred during the treatment process. Scanning electron micrographs showed that propounced changes had occurred to the surfaces of the treated papers. With XPS it was possible to measure the change in the surface composition of the papers which occurred on treatment. It was also found that the treatment reduced the thermal stability of the papers in all three cases.     

MiniMax: What has been learned thus far

Summary A small experiment, ?MiniMax?, has been set up in the C0 intersection region of the Fermilab Tevatron to seek evidence for disoriented chiral condensates and to study other forward physics phenomena. The experiment consists of a proportional wire chamber telescope accompanied by scintillation (trigger) counters, a lead converter, and followed by an electromagnetic calorimeter. The solid angle accepted is a cone centered at pseudorapidity (η) of 4.1 and of radius (in η-ϕ space) of about 0.6. Over 2.5 million events thus far have demonstrated the successful operation of the apparatus, however to date the analysis has not progressed sufficiently to permit any conclusions concerning disoriented chiral condensates. presented byL. W. Jones Paper presented at the Special Session on very high-energy cosmic-ray interactions (superfamilies) of the XXIV International Cosmic-Ray Conference, Rome, August 28–September 8, 1995.     

Single axial mode pumping and external mirror operation of a pulsed spin-flip Raman laser at 10.6 μm

By the addition of an external cavity to a single axial mode, TEA CO₂ laser pumped, In Sb spin-flip Raman laser, a tenfold increase in first Stokes output and a twenty-five fold increase in second Stokes and anti-Stokes outputs has been observed.     

Band crossing in 162Dy: Characterisation of negative-parity yrast and yrare sequences

The crossing of an octupole band by a rotation-aligned two-quasiparticle band has been observed in detail in ¹⁶²Dy. Both the yrast and yrare states are identified from the band heads (I =2 and I = 5) to high spin (I ～ 14), with band crossing in both the even-spin and odd-spin sequences.