The catalytic decomposition of formic acid by a polycrystalline platinum surface was studied by use of modulated molecular beam techniques with mass spectrometric phasesensitive detection. Kinetic information about elementary surface reaction steps was obtained. The formation of CO2 was found to be a monomolecular, whereas that of D2 was a bimolecular process. The resulting reaction mechanism may be described as follows: The rate constants in dependence from the surface temperature t0 are The sticking probability η is provided by the temperature dependence of the intensity of the nonreactive scattered formic acid molecules; the rate constants kd1 and kd2 are derived from the measured phase shift between reactive and nonreactive scattered particles. From the phase angle ?, the average surface residence time τ of the intermediates is computed: 3.7 ? τDCOO ? 0.41 msec (418 ? T0 ? 505 K), 31.8 ? τD ? 11.6 msec (418 ? T0 ? 460 K). The difference between τD and τDCOO is because of the different molecularity of desorption. 相似文献
The cyclotron resonance of inversion-layer electrons on (100)p-type Si is found to depend sensitively on an externally applied compressive stress. At low temperatures (T ? 10 K) we observe a considerable increase of the cyclotron mass m1c with stress S along the [001] direction. The effect is most strongly observed at low electron densities ns. For and ns~2 × 1011cm-2 we obtain instead of the expected 0.2m0. Along with this change of a strong narrowing of the resonance is noted. Raising the temperature gives an additional ns- dependent increase of . 相似文献
Using the re-equilibration kinetic method the chemical diffusion coefficient in nonstoichiometric chromium sesquisulfide, Cr2+yS3, has been determined as a function of temperature (1073–1373 K) and sulphur vapour pressure (10?104 Pa). It has been found that this coefficient is independent of sulphur pressure and can be described by the following empirical equation: . It has been shown that the mobility of the point defects inCr2+yS3 is independent of their concentration and that the self-diffusion coefficient of chromium in this sulfide has the following function of temperature and sulphur pressure: . (cm2s?1). 相似文献
Dependence of static dielectric susceptibility and correlation length of charge density waves (CDW) with weak defects on parameter of incommensurability with lattice is investigated. In almost commensurate phase (h?hchc), and Rc ~ (h ? hc). In. Far from commensurability , , where a is the dimensionless ratio of random potential intensities, corresponding to backward and forward scattering impurities. 相似文献
Medium resolution infrared grating spectra of gaseous ketene, H2CCO were recorded between 1000 and 400 cm?1, both at instrument temperature (40°C) and with cooling (?40°C). Interferometric Fourier spectra were also measured at ?70°C with resolution 0.22 cm?1 between 450 and 330 cm?1. The K structure of the fundamentals ν5, ν6, ν8, and ν9 was assigned. These fundamentals are coupled by a-axis Coriolis interactions. These couplings were analysed on the symmetric top basis for setting up the perturbation matrix and by utilizing the K-dependent Coriolis shifts of levels. A preliminary analysis of the Coriolis intensity anomalies was also undertaken.Band center values from combination differences are and . Synthetic spectra indicate the band origins of ν8 and ν9 to be close to 977.8 and 439.0 cm?1, respectively. Estimates of Coriolis coupling constants obtained from synthetic spectra are , , , and . Approximate ratios of unperturbed vibrational transition moments obtained from spectral simulations are . 相似文献
The electrical resistivity of amorphous carbon films getter-sputtered at 95°K is well fitted between 300 and 20°K by the relation with T0 ? 7 × 107K. This behavior suggests a hopping conductivity very similar to that found in other amorphous semiconductors. 相似文献
The binding energies of the ΛΛ hypernuclei 10ΛΛBe and 6ΛΛHe are calculated variationally with a 2α + 2Λ and with an α + 2Λ model, respectively. For 10ΛΛBe the integrations were made with Monte Carlo techniques while for 6ΛΛHe direct numerical methods were used. A wide range of phenomenological ΛΛ potentials based on meson-exchange models was considered. An approximately universal linear relation between the calculated values of and of is obtained. For the experimental value of this relation predicts a much too small value of , well below the lower limit of the quoted experimental value of 10.9 ± 0.6 MeV. For ΛΛ potentials with repulsive cores the relations, for a given , between the low-energy ΛΛ scattering parameters a, r0 and the intrinsic range b are both approximately universal and independent of the detailed potential shape. For the experimental value of the preferred values are 2.5 ? ?a ? 3.5 fm, 2.6 ? r0 ? 3.1 fm. The large and negative values of a correspond to conditions not too far from a bound 1S0 ΛΛ state and could indicate a 6-quark dibaryon state with the same quantum numbers and above the ΛΛ threshold. 相似文献
A continuous metal-nonmetal transition is observed in solid ArLa mixtures. The d.c. conductivity σ starts at a La atomic fraction cLa ? 0.15 with and increases exponentially with cLa until σ reaches the minimum metallic conductivity at cLa ? 0.4. The temperature dependence of σ shows variable range hopping between localized states for c>La ? 0.4 and metallic behaviour for 相似文献
Hyperfine structure of the (0, 0, 1) - (1, 0, 1) transition of methanol has been investigated by beam absorption and of the (J, 1, 3?) → (J, 1, 3+) transitions for J = 2, 3, and 6 by beam-maser spectroscopy. The best-fit results for the spin-rotation and spin-spin coupling constants and , respectively, are in kHz1: , , , , , and (. 相似文献
The temperature dependence of the field emission flicker noise spectral density functions has been investigated for potassium adsorbed on tungsten (112) planes by a probe hole technique. By integration of the spectral density functions the noise power for different frequency intervals Δ? is obtained. From the exponential temperature dependence of noise power “activation energies” qΔ? are determined. Plots of these energies versus coverage show a similar “oscillating” behaviour as recently found for or which indicates phase transitions of the adsorbed potassium submonolayers. The noise activation energies are discussed in terms of existing models and a comparison is made between the experimental q values and surface diffusion energies Ed as determined by conventional methods. 相似文献
The band-gap narrowing ΔEg, opt and ΔEg, elec (or ΔEg, eff) for optical and electrical energy gaps of the n-type impure silicon at 300 K, are investigated based on simplified models of heavily doped semiconductors. It is suggested that, for is significantly larger than ΔEg, opt, in good agreement with observed results. This difference is caused especially by the effect of the polaron. 相似文献
The observed phase transitions in Tetrathiafulvalene-Tetracyanoquinodimethane (TTF-TCNQ) are discussed using a simple model for the interchain coupling of charge density waves. Estimates based on Coulomb energies show that for 38 K < T < 49 K the components and qz of the wave vector associated with the charge density wave satisfy , with and T2 = 49 K. A possible mechanism for the first order transition at 38 K is proposed. The results are compared with neutron and X-ray scattering and with isotope shifts of the transition temperatures. 相似文献
Reflectance spectra were measured on ZnTe in magnetic fields up to 18 T for B ? [100] and B ? [110]. The experiments yield renormalized valence band parameters and , corresponding to bare parameters γ2 = 0.95 ± 0.09 and γ3 = 1.48 ± 0.14. From the free exciton Rydberg energy we derive a reduced exciton polaron mass m0 0.080 ± 0.005 and a bare reduced mass m0 0.074 ± 0.005, corresponding to and γ1 = 4.4 ± 0.7 for an electron effective polaron mass . We further calculate the exciton diamagnetic shift rate according to existing low-field theories modified by a variational calculation taking into account polaron effects and valid up to γ ? 1. The difference between experiment and theory is 10% and the agreement is considered satisfactory. 相似文献
In quark gluon theory with very small bare masses, -ψ, spontaneous breakdown of chiral symmetry generates sizable masses Mu, Md, Ms, … We find (. Scalar densities have well determined non-zero vaccum expectations at an SU(3) breaking of the vacuum c′ ≡ 〈0|u8|〉/〈0|uo|0〉 ≈ ? 16% 相似文献
We have evaluated the parity-violation contribution in atoms in the framework of SO(3) gauge theory. Various hadronic models have been used: first, for simplicity, the unrealistic five-quark one, next, others involving three ordinary SU(3) triplets for which all unwanted strangeness-changing processes are suppressed, up to order . In the free quark approximation, we obtain quite similar parity-violation effects which are proportional to (ΔM2 is the difference of squared masses of leptons (MX02 ? Mν2 = MX02), or of quarks (ΔMq2)). Namely, in large atoms (Z ? 1) the electronic contribution which is proportional to gives the largest effect (are the spin, momentum operators and mass of the lepton). Parity-violating effects in SO(3) gauge models are ?10?4 smaller than those evaluated in the Weinberg theory with a neutral parity-violating current and will remain undetectable in the near future. 相似文献
The charge density wave transition in 2H-TaS2near 75 K has been observed to be incommensurate, using electron diffraction, with along the 〈10.0〉 directions which, within the experimental uncertainty, remains temperature independent to about 14 K. Incommensurate charge density formation is also observed in AgxTaS2 samples for with an increase in q1 to when x?0.26. Within the experimental error q1 appears to be temperature independent to 25 K. 相似文献
Let ,m? 1.Consider the operatorT0 = ?Δ+q with domain consisting of all bounded measurable functions , having bounded support, for which the distribution ?Δu+qu belongs to . The main result of the paper is essential self-adjointness of . The proof is independent of a method due to Kato who recently established the self-adjointness of a maximal Schrödinger operator corresponding to such potential. 相似文献
Small-angle X-ray scattering of the liquid sodium-37 w/o lithium system in the range yields the critical exponents v = 0.655 ± 0.030 and λ = 1.296 ± 0.061 for the temperature dependence of the correlation length η and of the coefficient (?c/?μ)T, P respectively. 相似文献
Elastoresistances of TCNQ high conducting salts have been measured at room temperature by an original strain gauge technique. The effects, on the longitudinal and transverse resistivities ?, of an elementary uniaxial strain ? applied along one of the three axes, a, b or c1 respectively, have been estimated.For TTF-TCNQ, they are: ; ; (5% risk).So, in an hydrostatic pressure experiment, the fraction of piezoresistivity attributable to transverse effects is 43± 10% of the total value χb (Kba and Kbc effects accumulated).Low values have been found for the anisotropy (?a/?b) variations due to strains. So one may write: ; ; .The TTF-, HMTTF-, TSF-, HMTSF-TCNQ elastoresistance values are coherent with the previously measured hydrostatic pressure piezoresistivity values.All these experimental results are in good agreement with a model where the longitudinal but also the transverse elastoresistivities are essentially due to variations with strains of the longitudinal scattering time τν defined by σb = ne2τν/m1. 相似文献
Using a recent theoretical method, the ratio of nuclear matrix elements was determined to be either 20.50+0.35?0.55 or 25.22+0.28?0.17 in the second-forbidden nonunique decay of 8 × 104 y 59Ni. These values of R were obtained from a value of L3/K = 0.008 ± 0.002 found by subtracting the theoretical ratio = 0.113 (based on QPEC = 1070 ± 8 keV) from the total ratio L/K = 0.121 ± 0.002, which was measured with a reactor-produced, doubly-mass-separated 59Ni source introduced as gaseous nickel-ocene, (C5H5)2, into a wall-less, anticoincidence, multiwire proportional counter. The 854–1008 eV L and the 8.33 keV K peaks were measured simultaneously. 相似文献