Forbidden rotational transitions in symmetric top molecules

The intensities of the forbidden Δk = ±6 and ±4 transitions in symmetric top molecules arising from rotational intensity borrowing are reported. A perturbation theoretical approach has been used to study the mixing of wavefunctions produced by the additional splitting term in the rotational Hamiltonian of C_3v or C_4v-type molecules. Numerical values are presented for PH₃, PD₃, and BrF₅ molecules. The importance of these results in structural analysis and astrophysical studies is discussed.     

Evolution of microcrystalline growth pattern by ultraviolet spectroscopic ellipsometry on Si:H films prepared by Hot-Wire CVD

Ultra-violet spectroscopic ellipsometry has been applied successfully to determine the evolution of μc-Si:H film structure, including incubation layer, bulk layer and the growth zone and surface over-layer, their individual thickness and composition. In view of the availability of a significantly high atomic H density in H₂-diluted SiH₄ ensemble in Hot-Wire CVD, microcrystallization seems to be achieved easily at a low substrate temperature. Atomic H induced etching at the growing network has been identified as instrumental in controlling the microcrystallization in Si:H. Sharp elimination of the incubation layer as well as surface roughness and significant improvement in the overall crystallinity was obtained on increase in H₂ dilution to SiH₄. A H₂ dilution limited sharp transition from an amorphous dominated (a+μc)-Si mixed phase to a virtually amorphous free μc-Si phase has been identified. However, enhanced atomic H reactivity at the growth zone beyond the attainment of the amorphous free bulk and the surface layer induces porosity in the network and a gradual deviation from crystallinity.     

A convenient synthesis of methylindium(III) dithiolate complexes—precursors for indium sulfides

Methylindium(III) dithiolate complexes of the general formulae [Me₂In(S^∩S)] ( 1 ) and [MeIn(S^∩S)₂] ( 2 ) [S^∩S = (EtO)₂PS₂^?, (PrⁱO)₂PS₂^?, Et₂NCS₂^?, , O(CH₂CH₂)₂NCS₂^?, EtOCS₂^? and PrⁱOCS₂^?] have been isolated conveniently by the reaction of Me₃In·OEt₂ with In(S^∩S)₃ ( 3 ) in an appropriate stoichiometry. Both 1 and 2 have been characterized by indium analysis, IR, NMR (¹H, ¹³C{¹H} and ³¹P{H}) and mass spectral data. NMR data of 3 are also included for comparison. The Me–In and S^∩S resonances are sensitive to the number of methyl groups attached to indium metal. The mass spectral data indicate that these complexes are monomeric in nature. The thermal behavior of a few complexes has been investigated. The xanthate and dithiocarbamate complexes on pyrolysis under dynamic vacuum or flowing nitrogen atmosphere gave either In₂S₃ or a mixture of InS, In₂S₃ and In₆S₇, which were characterized using EDAX and powder XRD. Copyright © 2005 John Wiley & Sons, Ltd.     

Influence of solvent and substituent on excited state characteristics of laser grade coumarin dyes

Absorption and fluorescence emission of 4 and 7 substituted coumarins viz. C 440, C 490, C 485 and C 311 have been studied in various polar and non-polar organic solvents. These coumarin dyes are substituted with alkyl, amine and fluorine groups at 4- and 7-positions. They give different absorption and emission spectra in different solvents. The study leads to a possible assignment of energy level scheme for such coumarins including the effect on ground state and excited state dipole moments due to substitutions. Excited state dipole moments of these dyes are calculated by solvetochromic data experimentally and theoretically these are calculated by PM 3 method. The dipole moments in excited state, for all molecules investigated here, are higher than the corresponding values in the ground state. The increase in dipole moment has been explained in terms of the nature of excited state and resonance structure.     

Gamma Radiation Induced Biodegradable Shellac Films Treated by Acrylic Monomer and Ethylene Glycol

In this study the mechanical properties of shellac films, prepared by solution casting, were evaluated with varying amounts of Ethylene Glycol (EG) and 2-Ethyl-2-(hydroxymethyl)-1,3-propandiol-trimethacrylate (EHMPTMA). Mechanical properties such as tensile strength (TS) and elongation at break (Eb) of the raw shellac film were found to be 1.86 MPa and 4%, respectively. A series of formulations was prepared using shellac and varying percentages of EG and EHMPTMA in methanol. The films were prepared and irradiated under gamma (Co-60) radiation at different doses (50–500 krad). Grafting of EHMPTMA showed better results compared to raw shellac and EG treated films. Thermal properties, degradation tests in water and soil of the films were also evaluated.     

Working group report: Neutrino physics

This is the report of the neutrino physics working group at WHEPP-X. We summarize the problems selected and discussed at the workshop and the papers which have resulted subsequently.      

Error propagation in normalization of stable isotope data: a Monte Carlo analysis

A higher analytical precision of a stable isotope ratio mass spectrometer does not automatically guarantee accurate determination of the true isotope composition (δ‐value) of samples, since estimates of true δ‐values are obtained from the normalization of raw isotope data. We performed both Monte Carlo simulations and laboratory experiments to investigate aspects of error propagation during the normalization of carbon stable isotope data. We found that increasing both the number of different reference standards and the number of repetitions of each of these standards reduces the normalization error. A 50% reduction in the normalization error can be achieved over the two‐point normalization by either analyzing two standards four times each, or four standards two times each. If the true δ‐value of a sample is approximately known a priori, the normalization error may then be reduced through a targeted choice of locally optimal standards. However, the difference in improvement is minimal and, therefore, a more practical strategy is to use two or more standards covering the whole stable isotope scale. The selection of different sets of standards by different laboratories or for different batches of samples in the same laboratory may lead to significant differences in the normalized δ‐values of the same samples, leading to inconsistent results. Hence, the same set of standards should always be used for a particular element and a particular stable isotope analytical technique. Copyright © 2010 John Wiley & Sons, Ltd.     

Self-assembled monolayers of Aβ peptides on Au electrodes: an artificial platform for probing the reactivity of redox active metals and cofactors relevant to Alzheimer's disease

The water-soluble hydrophilic part of human Aβ peptide has been extended to include a C-terminal cysteine residue. Utilizing the thiol functionality of this cysteine residue, self-assembled monolayers (SAM) of these peptides are formed on Au electrodes. Atomic force microscopy imaging confirms formation of small Aβ aggregates on the surface of the electrode. These aggregates bind redox active metals like Cu and cofactors like heme, both of which are proposed to generate toxic partially reduced oxygen species (PROS) and play a vital role in Alzheimer's disease. The spectroscopic and electrochemical properties of these Cu and heme bound Aβ SAM are similar to those reported for the soluble Cu and heme bound Aβ peptide. Experiments performed on these Aβ-SAM electrodes clearly demonstrate that (1) heme bound Aβ is kinetically more competent in reducing O(2) than Cu bound Aβ, (2) under physiological conditions the reduced Cu site produces twice as much PROS (measured in situ) than the reduced heme site, and (3) chelators like clioquinol remove Cu from these aggregates, while drugs like methylene blue inhibit O(2) reactivity of the heme cofactor. This artificial construct provides a very easy platform for investigating potential drugs affecting aggregation of human Aβ peptides and PROS generation by its complexes with redox active metals and cofactors.