摘要:

AbstractThe reaction3CH2+ NO was studied behind incident shock waves over the temperature range 1100–2600 K by following the H and O atom formation with Atomic Resonance Absorption Spectroscopy (ARAS) and the OH radical formation with Laser Absorption. In the temperature range from 1100 to 2500 K the rate constant of the H atom formation formally attributed to a reaction channel giving HCNO+H (1 h) obtained on the basis of the experiments reported here isk1h= 10(12.4 ± 0.2).exp (‐(25 ± 2) kJ mol−1/RT) cm3mol−1s−1.The rate constant of the channel leading to HCN + OH (1d) was determined to bek1d= 10(11.7 ± 0.3).exp (‐(12 ± 2) kJ mol−1/RT) cm3mol−1s−1.The evaluation of the experimental profiles by means of computer simulation leads to an overall rate constant of aboutk1= (1 ± 0.5)·1012cm3mol−1s−1without any noticeable temperature dependence within the error limits in the temperature range from 1200 to 2600 K. The contribution of a reaction channel leading directly or indirectly to O (or N) atoms was found to be less than 15% of the overall reaction a

ISSN:0005-9021    

DOI:10.1002/bbpc.19950990202

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

年代:1995

数据来源: WILEY

摘要:

AbstractThe reactions of NH in its electronic ground state with benzene (1), 1,3‐butadiene (2) and acetylene (3) were investigated behind incident shock waves using narrow line width absorption detection of NH(X3Σ). The experiments were performed with very low initial concentrations of HN3which was used as NH(X3Σ−) source to reduce the influence of secondary reactions. Thus it became possible to measure kinetic data for the reactions of NH (X3Σ−) with these hydrocarbons directly. The following rate constants were obtained in the temperature range 1100 to 1500 K, resp. 1400 to 1700 K (acetylene):k1= 10(14.2±0.3)exp (‐(76±8) kJ mol−1/RT) cm3/mol sk2= 10(13.9±0.3)exp (‐(45±7) kJ mol−1/RT) cm3/mol sk3= 10(14.7±0.3)exp (‐(59±

ISSN:0005-9021    

DOI:10.1002/bbpc.19950990203

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

年代:1995

数据来源: WILEY

摘要:

AbstractThe reactions of 2‐, 2,6‐ and 2,7‐anthraquinone (di) sulphonate radical ions with the paramagnetic ions Fe(CN)36, Cu2+, IrCl2‐6and Fe3+have been studied at different pH‐values at room temperature, in order to investigate the role of spin states on electron transfer. With 2‐anthraquinone sulphonate the rate constants are in the range 2.6 ‐ 7 × 108mol−1dm3s−1, and for the other two anthraquinone derivatives the rate constants span over two orders of magnitude from 107to 109mol−1dm3s−1. The experimental rate constants have been compared with the predictions of the Marcus Cross‐Relation, taking also into account the contribution of the diffusion pathway in our calculations.The predicted values are systematically larger than the experimental values. This systematic deviation is justified in the present work as due to the spin‐forbidden character of the reactions studied. The need for suited corrections in the current electron transfer

ISSN:0005-9021    

DOI:10.1002/bbpc.19950990204

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

年代:1995

数据来源: WILEY

摘要:

AbstractFluorescence quenching through intramolecular electron transfer (ET) was studied in N‐(ω‐sulfonatoalkyl)‐ and N‐(ω‐carboxyalkyl)‐quinolinium betaines by stationary and time‐resolved fluorescence spectroscopy in the solvents water and acetonitrile. These substances are zwitterionic in the ground and local excited state of the quinolinium chromophore. In the sulfonato compounds fluorescence quenching through ET does not occur in water, whereas quenching is efficient in acetonitrile. A surprising opposite behaviour is observed for the carboxylato compounds: quenching is efficient in water whereas it is inefficient in acetonitrile. Semiempirical calculations were used to derive the parameters needed for the description of the quenching process by non‐adiabatic Bixon‐Efrima‐Jortner‐theory. These parameters include the solvent (λs) and the intrinsic (λv) contributions to the total reorganisation energy λ and the approximate free energy of reaction ΔG°. The vibrational motion of an aromatic C‐H bond influenced by the interaction with the negatively charged donor was taken as the major intramolecular accepting mode. ET fluorescence quenching in the present compounds and solvents may be interpreted in terms of the “normal” and the

ISSN:0005-9021    

DOI:10.1002/bbpc.19950990205

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

年代:1995

数据来源: WILEY

摘要:

AbstractA kinetic study is presented of the electronic energy distribution in SrF following the reaction of the electronically excited strontium atom, Sr(5s5p(3Pj)), 1.807 eV above its 5s2(1S0) electronic ground state, with CH3F. This optically metastable atom was generated by pulsed dye‐laser excitation of ground state strontium vapour to the Sr(53P1) state at λ = 689.3 nm (Sr(53P1←51S0)) at elevated temperature (850 K) in the presence of excess helium buffer gas in a slow flow system, kinetically equivalent to a static system. The decay of Sr(53PJ) was then monitored by time‐resolved atomic fluorescence from Sr(53P1) at the resonance wavelength following rapid Boltzmann equilibration within the3PJspin‐orbit manifold. Electronically excited SrF resulting from reaction of the excited atom with CH3F was also recorded in the time‐domain via the systems SrF(A2→1/2ΣX2Σ+) (νv= 0, λ = 662 nm), SrF(A2×3/2ΔX2Σ+) (ν = 0, λ = 652 nm) and SrF(B2Σ+X2Σ+) (νv= 0, λ = 579 nm). The A2(181.9 kJ mol−1) and B2Σ+(206.6 kJ mol−1) states of SrF are both energetically accessible on collision between Sr(3P) and CH3F. Both the atomic and molecular (A,B‐X) chemiluminescence emissions are shown to be exponential in form and characterised by first‐order decay coefficients which are found to be equal under identical conditions within experimental error. SrF(A2) and SrF(B2Σ+) are thus both shown to arise from direct reaction with CH3F. Further, the combination of integrated atomic and molecular intensity measurements, coupled with optical sensitivity calibration, enables estimates of the branching ratios into the A1/2,3/2, B and X states arising from Sr(53PJ) + CH3F to be made yielding the following results: A1/2, 6.4 × 10−3; A3/2, 1.5×10−3; B, 1.1x10−4; X, 0.992. The results obtained here are compared with analogous chemiluminescence studies on Sr(3P) with other halides obtained from molecular beam measurements and with previous kinetic measurements on SrCl, Br(A2, B2+ ‐X2Σ+) that we have reported. The results are also compared with those from a series of investigations we have presented from time‐domain investigations of molecular emissions from CaF, Cl, Br, I (A,B‐X) arising from t

ISSN:0005-9021    

DOI:10.1002/bbpc.19950990206

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

年代:1995

数据来源: WILEY

摘要:

AbstractThe densityC(x, t) of adsorbates (water, cyclohexane) at moving liquid/gas boundaries in samples of compacted zeolite NaX has been observed by neutron transmission experiments with a resolution dx= 0.2 cm, dt= 30 s, over a distance of 20 cm and during a time of observation up to 400 hours. The front of humidity migrates, driven by capillary forces, from the wet to the dry side of the sample with an initial velocity of about 10−6ms−1. In terms of a capillary model the absorbate moves with a pseudo‐diffusion‐coefficient in the order of 10−7m2s−1. The velocity slows down to 10−7m s−1if the amount of adsorbate is limited. A slow process of redistribution of the fluid takes place which does not smoothen the profile of the density of mobile molecules at the liquid/gas boundary in the porous solid, as one would expect in the case of diffusive motions of molecules at gradients in a homogeneous phase of an adsorbate. The step of density observed at the moving liquid/gas boundary is formed according to a dispersion/diffusion coefficientD(C)of

ISSN:0005-9021    

DOI:10.1002/bbpc.19950990207

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

年代:1995

数据来源: WILEY

摘要:

AbstractThe 2,4,6‐trimethyl cyclohexadienyl radical adsorbed on a fully hydroxylated silica surface was investigated using the time‐differential and time‐integrated muon spin resonance techniques near avoided crossings of magnetic energy levels in high longitudinal magnetic fields. Information about surface diffusion is obtained from the relaxation resulting from the partial averaging of the hyperfine anisotropy when the adsorbed species diffuses over the surface of a sphere. A Redfield formalism is developed to analyse the stochastic motion in terms of diffusion coefficients. The results agree with those of a stochastic Liouville approach reported previously. Diffusion of the trimethyl‐substituted radical is described by the same Arrhenius frequency factor but a considerably higher activation energy than that of the unsubstituted a

ISSN:0005-9021    

DOI:10.1002/bbpc.19950990208

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

年代:1995

数据来源: WILEY

摘要:

AbstractProton spin‐lattice relaxation timesT1andT1as well as the proton second moment have been measured for polycrystalline methyl α‐D‐glucoside, methyl β‐D‐glucoside and methyl β‐D‐galactoside over a wide temperature range. Analyses of the experimental data have yielded information about intramolecular reorientations in the solid state. C3reorientations of methyl groups take place in all the samples. Potential energy calculations have shown that the CH2OH group can execute trans‐gauche jumps between two potential minima separated by 120. Analyses of theT1and second moment data have confirmed the presence of this conformational motion. A weak relaxation mechanism, related to the dynamics of an OH group, has been revealed in meth

ISSN:0005-9021    

DOI:10.1002/bbpc.19950990209

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

年代:1995

数据来源: WILEY

摘要:

AbstractThe electrochemically modulated infrared spectroscopy (EMIRS) is a highly sensitive in‐situ technique to obtain vibrational spectra of species adsorbed on metal electrodes. The contribution discusses the influence of several experimental parameters as the electrode potential, the frequency and amplitude of the superposed potential modulation and the pH value of the electrolyte on the spectra of water molecules within the Helmholtz Double Layer at a platinum surface. The spectra contain significant information about conformational changes of water molecules, which are coadsorbed by atomic hydrogen on the platinum surface. The comparison of experimental results to those of theoretical calculations with Lagrange formalism indicates that, modulating the potential of a positively charged electrode, a complex molecule structure is varied at the surfac

ISSN:0005-9021    

DOI:10.1002/bbpc.19950990210

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

年代:1995

数据来源: WILEY

摘要:

AbstractA system of two time‐dependent, first order differential equations of electrical membrane resistance and of hydrostatic pressure is derived. The equations are based on a set of flux equations for a 1,–1 valent electrolyte, combined with the equation of continuity, and the condition for conservation of mass. New insight into the functioning of the membrane oscillator is gained by the strict derivation of the relaxation equation of the averaged salt concentration with convection from the general partial differential equation. This relaxation equation is successfully transformed into the useful time‐dependent first order differential equation of the function of the electrical membrane resistance. Thereby the postulated relation for the concomitant changes of the electrical membrane resistance and the averaged salt concentration in the membrane phase is employed. The equations describe both the stationary and the non‐stationary states of Teorell's membrane oscillator. Particularly, the stationary pressure‐dependent, non‐monotonous current‐voltage curves and the current‐dependent, non‐monotonous pressure‐volume flux relations are calculated. These characteristics form the basis for mechano‐electrical transduction. Furthermore, the relaxation oscillations of membrane voltage, volume flux and hydrostatic pressure and the corresponding electroosmotic and hydrodynamic phase planes, representing stable limit cycles, are described. The stability criteria of the time‐depende

ISSN:0005-9021    

DOI:10.1002/bbpc.19950990211

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

年代:1995

数据来源: WILEY