摘要:

AbstractThe rate constants for the reactions HCO+H → products (1) and HCO+D → products (2) were determined at room temperature in an isothermal discharge flow reactor. Atom and radical concentrations in the reactions were monitored using Electron Paramagnetic Resonance (EPR) for H and D atoms and Far Infrared Laser Magnetic Resonance (FIR‐LMR) and Laser Induced Fluorescence (LIF) for HCO. The overall rate constants describing the decay of the HCO concentrations with H and D, respectively, were found to bek1=(6.8±2.0)×1013cm3mol−1s−1andk2=(8.3±2.5)×1013cm3mol−1s−1. The results are discussed assuming a mechanism that allows for parallel reaction pathways via a direct H atom abstraction reaction or via an addition‐elimination reaction through a short‐lived highly vibrationally excited

ISSN:0005-9021    

DOI:10.1002/bbpc.19981020702

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1998

数据来源: WILEY

摘要:

AbstractThe deposition of diamond films in acetylene‐oxygen flames with different amounts of acetone in the source gas was investigated. Diamond films were deposited on molybdenum at temperatures between 1070 and 1420 K using a welding torch. The temperature as well as the stoichiometry dependence of the growth rate and quality of the diamond films were examined. The concept of supersaturation was adapted in order to have an transferable measure of the equivalence ratio. A sharp change of the diamond morphology from (111) to (100) planes between 1320 and 1370 K and between 6 and 7% supersaturation was found. The growth rate as a function of time was measured for deposition times between 2.5 and 180 min. Acetone influences the optimal conditions of the diamond deposition, the growth rate and the quality of the films. This influence was investigated in two different experiments. First, the acetone/acetylene ratio was varied with fixed supersaturation, whereas, in the second series, the supersaturation was increased by adding acetone, with keeping the acetylene flow fixed. It was found that small amounts of acetone have a positive effect on the film quality and increase the growth rate. This result may be qualitatively understood by an increase of hydrogen atom and methyl radical concentrations upon acetone additio

ISSN:0005-9021    

DOI:10.1002/bbpc.19981020703

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1998

数据来源: WILEY

摘要:

AbstractThe real time kinetics of adsorption and desorption of HCl on ice have been studied in a very low pressure reactor (Knudsen cell). We used two complementary techniques, namely pulsed valve or transient supersaturation and steady state experiments. The kinetics of adsorption, following a first order rate law, has been found to depend on the number of HCl molecules in a pulse for transient supersaturation and on the HCl partial pressure or flow rate in steady state experiments. The uptake coefficient γ ranges from 0.34 to 0.22 in the temperature range 190 to 210 K for dry adsorption leading to a quasi‐liquid state of HCl on ice and from 0.31 to 0.13 for adsorption leading to a liquid solution of HCl. In both cases a negative temperature dependence for uptake of HCl on ice of −1.8±0.5 and −3.1±0.5 kcal/mol has been observed. In addition, the fraction of HCl that could be retrieved by desorption after dosage with HCl depended strongly on the thermodynamic state of the HCl/ice substrate as well as on the temperature and varied in the range from 10 to 80%. We determined the rate of irreversible surface‐to‐bulk loss, with a limiting rate of 1.0·1013molecule s−1cm−2at 200 K. In addition, we studied the kinetics of adsorption of HBr and HI on ice resulting in γ values similar to HCl. However, ice in the range 190 to 210 K did not support any measurable vapor pressure of both HBr and HI after adsorption of up to several formal monolayers

ISSN:0005-9021    

DOI:10.1002/bbpc.19981020704

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1998

数据来源: WILEY

摘要:

AbstractAdsorbate‐adsorbent systems characterized by a stationary particle exchange with their surrounding are considered. Depending on the considered processes, like, e.g., tracer exchange or particle conversion, the behaviour of such a system may be described by a number of characteristic functions (tracer exchange curves, effectiveness factor, residence time distribution, transit time distribution, and others) whose particular shape is determined by the properties of the underlying transport mechanisms. It is shown that, under very general assumptions (mainly stationarity), there are one‐to‐one relations between these characteristic functions. Owing to these relations, the behaviour in a given process may be determined from that in a completely different one, without the need of any explicit information about the underlying transport mechanisms. The paper derives a great variety of relations (including equations for the analysis of a number of frequently used experimental setups) and discusses the information content as well as general properties of the characteristic func

ISSN:0005-9021    

DOI:10.1002/bbpc.19981020705

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1998

数据来源: WILEY

摘要:

AbstractComposites of a solid ionic conductor (copper(I) bromide) and an insulator (titanium dioxide) with carefully characterized purity and grain size are studied by impedance spectroscopy. The experimental dependence of electrical conductivity on temperature, volume fractions and grain sizes of the components is reported and interpreted in the framework of the space charge layer concept. An enhancement of conductivity by several decades compared with pure copper(I) bromide is observed and described by a percolation‐type model, which takes the effects of grain sizes and interfacial interactions into accoun

ISSN:0005-9021    

DOI:10.1002/bbpc.19981020706

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1998

数据来源: WILEY

摘要:

AbstractExperimental data of the molar excess enthalpy of 17 binary alkanol+amine mixtures are presented obtained at 298.15 K by using an isoperibolic titration calorimeter (LKB 8700). The data are used for testing the ERAS model which accounts for self association and cross association of mixtures containing hydrogen bonds in the liquid state as well as for free volume effects based on an equation of state which incorporates the chainlike association of the molecules. Self association and cross association enthalpies of the hydrogen bonds are obtained as well as association constants providing an insight into the intermolecular structure of this kind of liquid mixtures.

ISSN:0005-9021    

DOI:10.1002/bbpc.19981020707

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1998

数据来源: WILEY

摘要:

AbstractSolvatochromic shifts of the five probe indicators 2‐nitroaniline, 4‐nitroaniline, 4‐nitroanisole, 4‐nitrophenol, and N,N‐dimethyl‐4‐nitroaniline have been used to specify the solvatochromic solubility parameters π* and β of the five pure fluids CO2, N2O, CClF3, SF6, and NH3according to Kamlet, Abboud, and Taft by means of UV/VIS spectroscopy. Three isotherms, nearcritical and supercritical, were examined, for the first time from zero pressure up to 100 MPa. Except NH3with β≈︁0.70 (293 K), 0.65 (333 K), and 0.55 (413 K) at 100 MPa, respectively, all other fluids do not show significant basicity at any temperature and pressure conditions. Plotting π* vs reduced density of any fluid results in steeply increasing curves with maximum enhanced π* data at reduced densities of about 0.6 which continuously level out and finally rise again asymptotic

ISSN:0005-9021    

DOI:10.1002/bbpc.19981020708

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1998

数据来源: WILEY

摘要:

AbstractPicosecond UV pump/IR probe experiments were carried out on bis(1‐naphthoyl)peroxide (1) and ontert‐butyl‐peroxy‐2‐naphthylcarbonate (2) dissolved in CCl4. After excitation by a 308 nm pulse the formation of CO2is measured with a time resolution of 1.8 ps via the IR‐absorption of the v3‐mode at around 2340 cm−1for delay times up to 550 ps. A pronounced temporal and spectral evolution of the v3‐absorption band of CO2is found which is assigned to the initial formation of vibrationally excited CO2and subsequent vibrational cooling by energy transfer to the surrounding solvent. CO2concentration versus time profiles are obtained from the time dependence of the integrated v3‐band absorbance. The data suggest that2decomposes in a consecutive stepwise process whereas1undergoes concerted bond scission leading to CO2formation within the time resolutio

ISSN:0005-9021    

DOI:10.1002/bbpc.19981020709

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1998

数据来源: WILEY

摘要:

AbstractA slow relaxation (“memory effect”) was found to proceed in a poly(o‐toluidine) layer, placed at platinum electrode, whereas no slow relaxation was observed in poly(N‐methylaniline). The difference between these two ring‐ and N‐methylsubstituted polyaniline derivatives is discussed in terms of redox and doping processes, taking place during their redox inte

ISSN:0005-9021    

DOI:10.1002/bbpc.19981020710

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1998

数据来源: WILEY

摘要:

AbstractWe investigate the finite size dependences of the tracer surface diffusion coefficient in the vicinity of a second order phase transition. For this purpose, we use a lattice gas model of repulsively interacting particles on a square lattice. For all lattice sizesLstudied, the tracer diffusion coefficient,Dt, is a smooth function of temperature. There are no anomalies in the direct temperature dependence ofDtnear the critical temperatureTc. However, its derivative, dDt/d(1/kBT), exhibits cusp‐like anomalies which are largely pronounced for large lattice size

ISSN:0005-9021    

DOI:10.1002/bbpc.19981020711

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1998

数据来源: WILEY