Showing papers in "The Journal of Physical Chemistry in 2010"

Three Phase Interfaces at Electrified Metal−Solid Electrolyte Systems 1. Study of the Pt(hkl)−Nafion Interface

Abstract: A voltammetric fingerprinting approach has been used to probe the nature of Pt−Nafion three phase interfaces for Pt(hkl) and polycrystalline platinum surfaces. Nature of adsorbing species is identified as the sulfonate anions via CO charge displacement technique. The affinity for the sulfonate anions to adsorb on the electrode surface is investigated. Adsorption strength of the sulfonate anions with the electrode surface is compared with other strongly adsorbing anions such as (bi) sulfates and chlorides. Various factors that influence the adsorption properties of the sulfonate anions are studied. Nature and strength of the anion interaction with various surface geometries is also discussed. A physical model is presented to describe the observed phenomena.

CoNi Bimetallic Nanofibers by Electrospinning: Nickel-Based Soft Magnetic Material with Improved Magnetic Properties

Abstract: Recently, bimetallic nanostructures have received special interest due to their promising chemical and physical properties. In the literature, various complicated processes have been reported for the preparation of several bimetallic materials in a nanoparticulate shape. In this study, nanofibers, rather than nanoparticles, composed of cobalt and nickel are introduced; these nanofibers have been prepared by a facile technique, electrospinning. Typically, calcination of electrospun mats originating from nickel acetate, cobalt acetate, and poly(vinyl alcohol) in argon atmosphere led to complete elimination of the utilized polymer and abnormal decomposition of the metallic acetates to produce CoNi nanofibers. Physiochemical characterization indicated that both Ni and Co are uniformly distributed along the obtained nanofibers in the same profile which indicates that Ni and Co have been combined at the crystalline level. The prepared CoNi nanofibers revealed better magnetic properties compared with those of Co...

Theoretical Characterization of the Air-Stable, High-Mobility Dinaphtho[2,3-b:2′3′-f]thieno[3,2-b]-thiophene Organic Semiconductor

Abstract: Recently, an optimum mobility of 8.3 cm2/(Vs) has been measured for single-crystal organic field-effect transistors based on the dinaphtho[2,3-b:2′,3′-f]thieno[3,2-b]-thiophene (DNTT) molecule. Here, on the basis of quantum chemistry calculations and molecular dynamics simulations, we investigate the microscopic charge transport parameters of the DNTT molecule and crystal. Our findings confirm that the moderate anisotropy of the hole mobility in DNTT is highly dependent on the presence of in-plane herringbonelike intermolecular interactions with large electronic coupling (transfer integral) values (ca. 0.1 eV). Also, we demonstrate that the π-extended heteroaromatic structure leads to strong electronic coupling interactions among neighboring molecules and to a decrease of the intramolecular reorganization energy. In DNTT, thermal modulations of the electronic couplings at 300 K remain small when compared to those exhibited by the pentacene single crystal. This theoretical study suggests that heteroacenes ...

Determination of Successive Complexation Constants in an Ionic Liquid: Complexation of UO22+ with NO3- in C4-mimTf2N Studied by UV-Vis Spectroscopy

Abstract: The complexation of UO22+ with NO3− has been investigated in the ionic liquid 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide by UV−vis spectroscopy at T = 18.5 °C. The complexation i...

Two-Layer Mutiple Trapping Model for Universal Current Transients in Molecularly Doped Polymers

Abstract: The mechanism of charge transport in molecularly doped polymers has been the subject of much discussion over the years. In this paper, data obtained from a new experimental variant of the time-of-flight (TOF) technique, called TOF1a, are compared to the predictions of a two-layer multiple trapping model (MTM) with an exponential distribution of traps. In the recently introduced TOF1a experimental variant, the charge generation depth is varied continuously, from surface generation to bulk generation, by varying the energy of the electron-beam excitation source. This produces systematic changes in the shape of the current transient that can be compared to predictions of the two-layer MTM. In the model, one additional assumption is added to the homogeneous MTM, namely: that there exists a surface region, on the order of a micrometer thick, in which the trap distribution is identical to the bulk, but has a higher trap concentration. We find that the characteristic experimental features of an initial spike, a ...

Atmospheric Implications for Formation of Clusters of Ammonium and 1−10 Water Molecules

Abstract: A mixed molecular dynamics/quantum mechanics model has been applied to the ammonium/water clustering system. The use of the high level MP2 calculation method and correlated basis sets, such as aug-cc-pVDZ and aug-cc-pVTZ, lends confidence in the accuracy of the extrapolated energies. These calculations provide electronic and free energies for the formation of clusters of ammonium and 1-10 water molecules at two different temperatures. Structures and thermodynamic values are in good agreement with previous experimental and theoretical results. The estimated concentration of these clusters in the troposphere was calculated using atmospheric amounts of ammonium and water. Results show the favorability of forming these clusters and implications for ion-induced nucleation in the atmosphere.

IR Characterization of Tip-Functionalized Single-Wall Carbon Nanotubes

Abstract: Vibrational frequencies of functionalized groups (−COOH, −CONH2, and −COOCH3) of tip-modified single-wall carbon nanotubes are estimated using density functional theory Both metallic (5,5) and sem

Kinetics of the Thermal Reaction of H Atoms with Propyne | NIST

Abstract: The reaction of hydrogen atoms with propyne (CH[triple bond]CCH(3)) was investigated in a heated single pulse-shock tube at temperatures of 874-1196 K and pressures of 1.6-7.6 bar. Stable products from various reaction channels (terminal and nonterminal H addition, and by inference H abstraction) were identified and quantified by gas chromatography and mass spectrometry. The rate constant for the channel involving the displacement of methyl radical from propyne (nonterminal H addition) was determined relative to the methyl displacement from 1,3,5-trimethylbenzene (135-TMB), with k (H + 135-TMB --> m-xylene + CH(3)) = 6.70 x 10(13) exp(-3255/T[K]) cm(3)/mol x s, k(H+propyne-->CH[triple bond]CH+CH3))=6.26 x 10(13) exp(-2267/T[K]) cm3/mole x s. Our results show that the acetylene to allene yield is approximately 2 at 900 K, and decreases with increasing temperature. The rate expression is: k(H+propyne-->CH2=C=CH2+H))=2.07 x 10(14) exp(-3759/T[K]) cm3/mole x s. This is a lower limit for terminal addition. Kinetic information for abstraction of the propargylic hydrogen by H was determined via mass balance. The rate expression is approximately k(H+CH3C[triple bond]CH-->CH[triple bond]C-CH2+H2))=1.20 x 10(14) exp(-4940/T[K])cm3 /mole x s and is only 10% of the rate constant for acetylene formation. All channels from H atom attack on propyne at combustion temperatures have now been determined. Comparisons are made with results of recent ab initio calculations and conclusions are drawn on the quantitative accuracy of such estimates.