Mechanisms of one-electron capture by slow He2+, C4+ and O6+ ions in collisions with CH4

Translational energy spectroscopy (TES) has been used to study one-electron capture by He2+, C4+, and O6+ ions in collisions with CH4 within the range 200 - 2000 eV amu—1. In each case the main collisions mechanisms and product channels have been identified. The measurements reveal significant differences in the way the dissociative and non-dissociative mechanisms contribute to electron capture. However, in all cases, the highly selective nature of the charge transfer process is confirmed in spite of the wide range of energy defects associated with possible product channels.

Diagnostic studies of species concentrations in a capacitively coupled RF plasma containing CH4-H2-Ar

Three plasma diagnostic methods, tunable infrared diode laser absorption spectroscopy, optical emission spectroscopy and microwave interferometry have been used to monitor concentrations of transient and stable molecules, CH3, CH4, C2H2, C2H6, and of electrons in capacitively coupled CH4-H-2-Ar radiofrequency (RF) plasmas (f(RF) = 13.56 MHz, p = 100 Pa, phi (total)= 66 sccm) for various discharge power values (P = 10-100 W) and gas mixtures. The degree of dissociation of the methane precursor varied between 3% and 60%. The methyl radical concentration was found to be in the order of 10(12) molecules cm(-3) and the electron concentration in the order of loll cm(-3). The methyl radical concentration and the concentrations of the stable C-2 hydrocarbons, C2H2 and C2H6, produced in the plasma, increased with discharge power. The fragmentation rates of the methane precursor and conversion rates to the measured C-2 hydrocarbons were estimated in dependence on discharge power. Radial distributions of the electron and methyl radical concentrations, and of the gas temperature were measured for the first time simultaneously in the plasma region between the discharge electrodes. The measurements allow us to draw qualitative conclusions on the main chemical processes and the plasma chemical reaction paths.

The possibility of single C-H bond activation in CH4 on a MoO3-supported Pt catalyst: A density functional theory study

Methane activation is a crucial step in the conversion of methane to valuable oxygenated products. In heterogeneous catalysis, however, methane activation often leads to complete dissociation: If a catalyst can activate the first C-H bond in CH4, it can often break the remaining C-H bonds. In this study, using density functional theory, we illustrate that single C-H bond activation in CH4 is possible. We choose a model system which consists of isolated Pt atoms on a MoO3(010) surface. We find that the Pt atoms on this surface can readily activate the first C-H bond in methane. The reaction barrier of only 0.3 eV obtained in this study is significantly lower than that on a Pt(111) surface. We also find, in contrast to the processes on pure metal surfaces, that the further dehydrogenation of methyl (CH3) is very energetically unfavorable on the MoO3-supported Pt catalyst. (C) 2002 American Institute of Physics.

New families of enantiopure cyclohexenone cis-diol, o-quinol dimer and hydrate metabolites from dioxygenase-catalysed dihydroxylation of phenols

Toluene dioxygenase-catalysed cis-dihydroxylation of phenols has led to the discovery of new enantiopure cyclohexenone cis-diol, o-quinol dimer and phenol hydrate metabolites having synthetic potential.

Solid-bound, proton-driven, fluorescent ‘off–on–off’ switches based on PET (photoinduced electron transfer)

Anthracene-based, H+-driven, ‘off–on–off’ fluorescent PET (photoinduced electron transfer) switches are immobilized on organic and inorganic polymeric solids in the form of Tentagel® and silica, respectively. The environment of the organic bead displaces apparent switching thresholds towards lower pH values whereas the Si–O- groups of silica electrostatically cause the opposite effect. These switches are ternary logic gate tags, one of which can be particularly useful in strengthening molecular computational identification (MCID) of small solid objects.

On the Uncoded BER Performance Bound of the IEEE 802.16d Channel

In this letter, the performance bound of the IEEE 802.16d channel is examined analytically in order to gain an insight into its theoretical potential. Different design strategies, such as orthogonal frequency division multiplexing (OFDM) and single-carrier frequency-domain equalization (SC-FDE), time-domain decision feedback equalization (DFE), and sphere decoder (SD) techniques are discussed and compared to the theoretical bound.