Generation of high O2 (a1Δg) concentrations in O2/H2 mixtures

The effect of hydrogen on the concentration of singlet oxygen in the a¹Δ_g and b¹Σ states, generated from a microwave discharge in O₂ and in an O₂/Ar mixture, was studied in flow reactors. The addition of hydrogen, in a range of 0.01–1 of concentration of the O₂, increased the yields of singlet oxygen by factor of 5–20. In addition to the higher O₂ (a and b) concentrations, the addition of hydrogen removed the usual NO₂ fluorescence, making observation of the O₂(b → X) transition at 762 nm much easier in the flow reactor. © 2005 Wiley Periodicals, Inc. Int J Chem Kinet 38: 12–17, 2006     

An experimental and theoretical study of spin-spin coupling in chlorosilanes

An experimental and theoretical study of the absolute value of the one-bond spin-spin coupling constant |(1)J(Si,H)| in SiH(n)Cl(4-n) (n = 0-4) dissolved in THF-d(8) is presented. We found |(1)J(Si,H)| to increase with an increasing number of chlorine substituents, and the quantitative changes were found to differ from the values previously reported for the same compounds dissolved in cyclohexane-d(12). We also report on the variations in |(1)J(Si,H)| as a function of temperature, which we found to be linearly temperature dependent for the chlorine-substituted silanes and temperature independent for SiH(4). Furthermore, the temperature dependence of |(1)J(Si,H)| varied between the different chlorosilanes. Solvent-solute interactions were studied by quantum chemical DFT calculations. The variations in chloro-silane bond lengths upon adduct formation and the different adduct interaction energies may explain the temperature dependences of the coupling constants.     

The crystal structure and surface energy of NaAlH4: a comparison of DFT methodologies

This paper presents a comparison of the bulk structure, cleavage energies, and local densities of states of solid NaAlH4 calculated using several different density functional theory methodologies. Good agreement is obtained for the bulk crystal structure. Larger differences become apparent for the calculated surface energies and local densities of states. The (001) NaAlH4 surface is clearly identified as the most stable surface, followed by the (112) and (101) surfaces, with the (100) surface being the least stable. We present an analysis of the local density of states of atoms in the exposed NaAlH4 surface.     

Accurate measurements of 13C-13C J-couplings in the rhodopsin chromophore by double-quantum solid-state NMR spectroscopy

A new double-quantum solid-state NMR pulse sequence is presented and used to measure one-bond 13C-13C J-couplings in a set of 13C2-labeled rhodopsin isotopomers. The measured J-couplings reveal a perturbation of the electronic structure at the terminus of the conjugated chain but show no evidence for protein-induced electronic perturbation near the C11-C12 isomerization site. This work establishes NMR methodology for measuring accurate 1JCC values in noncrystalline macromolecules and shows that the measured J-couplings may reveal local electronic perturbations of mechanistic significance.     

Nonsymmetric interpolation macdonald polynomials and \mathfrak{g}\mathfrak{l}_n basic hypergeometric series

The Knop-Sahi interpolation Macdonald polynomials are inhomogeneous and nonsymmetric generalisations of the well-known Macdonald polynomials. In this paper we apply the interpolation Macdonald polynomials to study a new type of basic hypergeometric series of type . Our main results include a new q-binomial theorem, a new q-Gauss sum, and several transformation formulae for series. *Supported by the ANR project MARS (BLAN06-2 134516). **Supported by the NSF grant DMS-0401387. ***Supported by the Australian Research Council.     

Nonlinear fiber-optic strain sensor based on four-wave mixing in microstructured optical fiber

We demonstrate a nonlinear fiber-optic strain sensor, which uses the shifts of four-wave mixing Stokes and anti-Stokes peaks caused by the strain-induced changes in the structure and refractive index of a microstructured optical fiber. The sensor thus uses the inherent nonlinearity of the fiber and does not require any advanced postprocessing of the fiber. Strain sensitivity of -0.23 pm/με is achieved experimentally and numerical simulations reveal that for the present fiber the sensitivity can be increased to -4.46 pm/με by optimizing the pump wavelength and power.     

Atmospheric chemistry of CCl2FCH2CF3 (HCFC-234fb): Kinetics and mechanism of reactions with Cl atoms and OH radicals

The atmospheric chemistry of CCl₂FCH₂CF₃ (HFCF-234fb) was examined using FT-IR/relative-rate methods. Hydroxyl radical and chlorine atom rate coefficients of k(CCl₂FCH₂CF₃+OH)= (2.9 ± 0.8) × 10⁻¹⁵ cm³ molecule^–1 s^–1 and k(CCl₂FCH₂CF₃+Cl)= (2.3 ± 0.6) × 10⁻¹⁷ cm³ molecule^–1 s^–1 were determined at 297 ± 2 K. The OH rate coefficient determined here is two times higher than the previous literature value. The atmospheric lifetime for CCl₂FCH₂CF₃ with respect to reaction with OH radicals is approximately 21 years using the OH rate coefficient determined in this work, estimated Arrhenius parameters and scaling it to the atmospheric lifetime of CH₃CCl₃. The chlorine atom initiated oxidation of CCl₂FCH₂CF₃ gives C(O)F₂ and C(O)ClF as stable secondary products. The halogenated carbon balance is close to 80% in our system. The integrated IR absorption cross-section for CCl₂FCH₂CF₃ is 1.87 × 10⁻¹⁶ cm molecule⁻¹ (600–1600 cm⁻¹) and the radiative efficiency was calculated to 0.26 W m⁻² ppb¹. A 100-year Global Warming Potential (GWP) of 1460 was determined, accounting for an estimated stratospheric lifetime of 58 years and using a lifetime-corrected radiative efficiency estimation.