A study of some potassium hexachlorometallate complexes using electron spectroscopy

X-ray photoelectron (ESCA) spectra of the core (Cl 2p K 2p and metal 4f, if present) and valence orbitals are reported for K₂ReCl₆, K₂OsCl₆, K₂IrCl₆· 3 H₂O, K₂PtCl₆, K₃MoCl₆, and K₂SnCl₆. The K 2p_{$\text{3}\text{2}$} binding energy was found to be nearly constant (292.7 eV) and that of Cl to increase very slightly with increasing atomic number for the third row transition metals. The chemical shifts of Re(IV), Os(IV), Ir(IV), and Pt(IV) relative to the metals were in qualitative agreement with atomic calculations utilizing configurations obtained from extended Hückel calculations. The valence spectra of the transition metal complexes exhibit a three-band structure. On the basis of MO results and intensity considerations the high binding energy band is assigned as a composite of the a_1g, e_g, 1t_2g MO's. The middle band represents the t_2u, 2t_1g MO's; and the low binding energy band the 2t_2g MO. Calculated nd orbital photoionization cross sections correlate reasonably well with the relative intensifies of the valence manifolds. Comparison of band separations and charge-transfer transition energies suggests that interelectronic repulsion and MO energy separation contribute about equally to the overall charge-transfer energy.     

Local structure of isolated positively charged muonium as an analog for the hydrogen ion in p-type GaAs

We determine the local structure of isolated positively charged muonium (Mu+) in heavily doped p-type GaAs based on muon level crossing resonance and zero applied field muon spin depolarization data. These measurements provide the first direct experimental confirmation that Mu+, and by analogy H+, is located within a stretched Ga-As bond. The distances between Mu+ and the nearest neighbor Ga and As atoms are estimated to be 1.83 +/- 0.10 A; and 1.76 +/- 0.10 A, respectively. These results are compared to existing theoretical calculations on the structure of hydrogen in GaAs and additionally provide data on the induced electric field gradients.     

Measurement of the total active 8B solar neutrino flux at the Sudbury Neutrino Observatory with enhanced neutral current sensitivity

The Sudbury Neutrino Observatory has precisely determined the total active (nu(x)) 8B solar neutrino flux without assumptions about the energy dependence of the nu(e) survival probability. The measurements were made with dissolved NaCl in heavy water to enhance the sensitivity and signature for neutral-current interactions. The flux is found to be 5.21 +/- 0.27(stat)+/-0.38(syst) x 10(6) cm(-2) s(-1), in agreement with previous measurements and standard solar models. A global analysis of these and other solar and reactor neutrino results yields Deltam(2)=7.1(+1.2)(-0.6) x 10(-5) eV(2) and theta=32.5(+2.4)(-2.3) degrees. Maximal mixing is rejected at the equivalent of 5.4 standard deviations.     

Development and optimisation of a novel genetic algorithm for studying model protein folding

Determination of the native state of a protein from its amino acid sequence is the goal of protein folding simulations, with potential applications in gene therapy and drug design. Location of the global minimum structure for a given sequence, however, is a difficult optimisation problem. In this paper, we describe the development and application of a genetic algorithm (GA) to find the lowest-energy conformations for the 2D HP lattice bead protein model. Optimisation of the parameters of our standard GA program reveals that the GA is most successful (at finding the lowest-energy conformations) for high rates of mating and mutation and relatively high elitism. We have also introduced a number of new genetic operators: a duplicate predator—which maintains population diversity by eliminating duplicate structures; brood selection—where two parent structures undergo crossover and give rise to a brood of (not just two) offspring; and a Monte Carlo based local search algorithm—to explore the neighbourhood of all members of the population. It is shown that these operators lead to significant improvements in the success and efficiency of the GA, both compared with our standard GA and with previously published GA studies for benchmark HP sequences with up to 50 beads.     

A determination of the Cabibbo-Kobayashi-Maskawa parameter |V us| using KL decays

We present a determination of the Cabibbo-Kobayashi-Maskawa parameter |V(us)| based on new measurements of the six largest K(L) branching fractions and semileptonic form factors by the KTeV (E832) experiment at Fermilab. We find |V(us)|=0.2252+/-0.0008(KTeV)+/-0.0021(ext), where the errors are from KTeV measurements and from external sources. We also use the measured branching fractions to determine the CP violation parameter |eta(+-)|=(2.228+/-0.005(KTeV)+/-0.009(ext))x10(-3).     

Measurements of the Decay KL-->e+ e- mu+ mu-

The KTeV experiment at Fermilab has isolated a total of 132 events from the rare decay K(L)-->e+ e- mu+ mu-, with an estimated background of 0.8 events. The branching ratio of this mode is determined to be [2.69+/-0.24(stat)+/-0.12(syst)]x10(-9), with a radiative cutoff of M(2)(ee mu mu)/M(2)(K)>0.95. The first measurement using this mode of the parameter alpha from the D'Ambrosio-Isidori-Portolès (DIP) model of the K(L)gamma*gamma* vertex yields a result of -1.59+/-0.37, consistent with values obtained from other decay modes. Because of the limited statistics, no sensitivity is found to the DIP parameter beta. We use this decay mode to set limits on CP and lepton violation.     

Stereoselective synthesis of beta-(chloro)vinylsilanes using a regio- and (E)-stereoselective bis-stannylation of unsymmetrically substituted butadiynes: application to the synthesis of a masked triyne

[reaction: see text] A highly regio- and stereoselective bis-stannylation of unsymmetrically substituted butadiyne 3 provides bis-stannane 4. Selective lithiation of the internal tin residue effects a 1,4-retro-Brook rearrangement to afford vinylsilane 5. This was elaborated into the novel diethynylethene 1, which also functions as a masked triyne.