Pseudorapidity distributions of charged particles from Au + Au collisions at the maximum RHIC energy,square root[s(NN)] = 200 GeV

We present charged-particle multiplicities as a function of pseudorapidity and collision centrality for the 197Au+197Au reaction at square root[s(NN)] = 200 GeV. For the 5% most central events we obtain dN(ch)/deta/(eta = 0) = 625+/-55 and N(ch)/(-4.7< or =eta < or =4.7) = 4630 +/- 370, i.e., 14% and 21% increases, respectively, relative to square root[s(NN)] = 130 GeV collisions. Charged-particle production per pair of participant nucleons is found to increase from peripheral to central collisions around midrapidity. These results constrain current models of particle production at the highest RHIC energy.     

Secondary ion mass spectra of alkali halides

Mass spectra of positive and negative secondary ions from various alkali halides have been measured in the Manitoba time-of-flight mass spectrometer. The ions were produced by Cs⁺ and K⁺ bombardment at primary ion energies of 3 to 19 keV for the positive spectra, and 11 to 28 keV for the negative spectra. The ions measured were those emitted within a time interval ～ 20 ns after the primary ion impact. The secondary ion yields are strongly dependent on the sample composition and treatment; prior irradiation may change the yield by an order of magnitude or more. The secondary ion yields also depend strongly on the energy loss of the primary ion, but the ratio of yields of different cluster ions from a given target is almost independent of this parameter. The results appear to be consistent with models in which the clusters are ejected directly from the target, but do not determine whether or not they possess the original surface structure. The results may also be described by a recombination model if the recombination is essentially complete.     

Rapidity dependence of charged antihadron to hadron ratios in Au+Au collisions at sqrt[s(NN)]=200 GeV

We present ratios of the numbers of charged antihadrons to hadrons (pions, kaons, and protons) in Au+Au collisions at sqrt[s(NN)]=200 GeV as a function of rapidity in the range y=0-3. While the ratios at midrapidity are approaching unity, the K(-)/K(+) and p;/p ratios decrease significantly at forward rapidities. An interpretation of the results within the statistical model indicates a reduction of the baryon chemical potential from mu(B) approximately 130 MeV at y=3 to mu(B) approximately 25 MeV at y=0.     

Rh(II)-catalysed room temperature aziridination of homoallyl-carbamates

Rhodium(II) catalysts and PhIO in benzene convert homoallylic carbamates into the corresponding aziridines at room temperature.     

Near-ultraviolet-induced matrix-assisted laser desorption/ionization as a function of wavelength

The matrix-assisted laser desorption/ionization (MALDI) effect for the ablation of polypeptide ions was studied as a function of wavelength in the range 360–450 nm, using a tunable titanium:sapphire laser and the matrices (trans)α-cyano-4-hydroxycinnamic acid, (trans)3,5-dimethoxy-4-hydroxycinnamic acid, and (trans)β-indoleacrylic acid. The results demonstrated that the qualitative aspects of the MALDI effect remained largely unchanged as a function of wavelength until the matrix crystal’s absorption coefficient approached 6 × 10⁴ cm^?1. Wavelengths at which the absorption coefficient was lower than this value did not produce observable polypeptide ions. In the range of wavelengths where polypeptide ions could be observed, the effect was generated only when the average energy absorbed in the 10-nm layer immediately below the crystal surface was >8 kJ/cm³ regardless of the total amount of energy absorbed in the remainder of the crystal. It was demonstrated that on the basis of the other results in this paper and those in the literature that the mechanism that generates polypeptide ions cannot be either photochemically induced or the same mechanism that gives rise to matrix ions. A model for ionization is proposed that decouples matrix and protein ionization in a simple manner that has direct analogy to the behavior of ionic solutes in polar solvents. The model satisfies the currently available experimental evidence and unifies the results obtained by MALDI at all wavelengths.     

Phenomenological models for matrix-assisted laser desorption ion yields near the threshold fluence

Phenomenological models were proposed to explain the experimentally observed dependence of protein ion yields with laser fluence in matrix-assisted laser desorption. Assuming that the illuminating laser had a Gaussian intensity profile at the sample being examined, it was possible to fit the experimental points with a model that only assumes a fluence threshold for ion production. No additional dependence of protein ion yield on illuminating fluence above the threshold value was necessary to explain the data.