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1.
Atsushi Shinohara Toshiharu Muroyama Junichirou Shintai Eugene Taniguchi Tadashi Saito Taichi Miura Nobutsugu Imanishi Yoshio Yoshimura Michiaki Furukawa 《Hyperfine Interactions》1994,84(1):569-574
The transfer of negative pions captured by hydrogen to heavier atoms has been investigated in a series of alcohols by measuring both 2 rays from 0 decay and pionic X rays. Capture rates for the pionic hydrogen of different chemical states in the molecule were determined from a comparison between the data for the ordinary compound and the deuterated one. The external transfer in the condensed phase was revealed by the dependence of the capture rate of hydrogen on the number of carbon atoms in the alkyl group. The influence of the chemical structure on the transfer process is discussed with respect to the large difference between the relative transfer rates,
C=1.5±0.2 and
O = 4.5±0.4, corresponding to carbon and oxygen, respectively. 相似文献
2.
D. Horváth 《Hyperfine Interactions》1993,82(1-4):483-494
Measurements of the probability of pion capture by hydrogen provide information on the properties of the chemical bond of hydrogen in molecules. This is demonstrated in the examples of the temperature dependence of pion capture in hydrogen-bonded liquids and of the influence of the position of the hydrogen atom in molecules. For the proper analysis and interpretation of the pion capture data we studied the effects of pion transfer from p– to heavier atoms. Measurements were made in H2 + D2 mixtures and in alcohols. Together with the information available on the muon capture and cascade processes, the pion transfer results could be used for understanding muon transfer and, in particular, to estimate the parameterq
1s in muon catalysed fusion. 相似文献
3.
4.
The mechanisms of inelastic scattering of low-energy protons with a kinetic energy of 2–7 eV by C6H6, C6F12, C60, and C60F48 molecules are studied using the methods of quantum chemistry and nonempirical molecular dynamics. It is shown that, for the C6H6 + proton and C60 + proton systems, starting from a distance of 6 Å from the carbon skeleton, the electronic charge transfer from the aromatic molecule to H+ occurs with a probability close to unity and transforms the H+ ion into a hydrogen atom and the neutral C6H6 and C60 molecules into cation radicals. The mechanism of interaction of low-energy protons with C6F12 and C60F48 molecules has a substantially different character and can be considered qualitatively as the interaction between a neutral molecule and a point charge. The Coulomb perturbation of the system arising from the interaction of the noncompensated proton charge with the Mulliken charges of fluorine atoms results in an inversion of the energies of the electronic states localized, on the one hand, on the positively charged hydrogen ion and, on the other hand, on the C6F12 and C60F48 molecules. As a result, the neutral molecule + proton state becomes the ground state. In turn, this inversion makes the electronic charge transfer energetically unfavorable. Quantum-chemical and molecular-dynamics calculations on different levels of theory showed that, for fluorine derivatives of some aromatic structures (C6F12, C60F48), the barriers to proton penetration through carbon hexagons are two to four times lower than for the corresponding parent systems (C6H6, C60). This effect is explained by the absence of active π-electrons in the case of fluorinated molecules. 相似文献
5.
Dilara Özbakır Işın 《Molecular physics》2013,111(24):3578-3588
Anthraquinones are located in an important class of natural compounds having antioxidant properties. Quantum chemical calculations based on the density functional theory were employed to study the relationship between the structure and the antioxidant activity of four hydroxyanthraquinones. The solvation effects on the antioxidant activity were taken into account by using the conductor-like polarisable continuum model with different dielectric constants (ε = 2.25, C6H6; ε = 78.39, H2O). The three antioxidant action mechanisms, hydrogen atom transfer (HAT), single electron transfer-proton transfer and sequential proton loss electron transfer (SPLET) were elucidated. The reaction enthalpies related to the steps in these mechanisms were computed in gas phase and solvents. The calculated results are in line with experimental values. The results showed that HAT was the most favourable mechanism for describing the antioxidant activity of hydroxyanthraquinones in the gas phase and in benzene, whereas in aqueous solution, SPLET represented the most thermodynamically plausible reaction pathway. 相似文献
6.
V. A. Pushkarchuk S. Ya. Kilin A. P. Nizovtsev A. L. Pushkarchuk V. E. Borisenko C. von Borczyskowski A. B. Filonov 《Optics and Spectroscopy》2005,99(2):245-256
The electronic and spin properties of different nanocrystals of carbon are studied. The properties of these cluster systems are modeled in terms of the ab initio (Hartree-Fock) and semiempirical (PM3, AM1) quantum-chemical methods. The calculations are performed for different carbon nanocluster systems: defect-free and with [NV]? centers, hydrogen passivated (C38H42, C71H84, C86H78), and with a free (unpassivated) surface (C38, C71, C86). The spin properties of unhydrated nanoclusters were studied for the first time. The structure of all the clusters under study was optimized using the total energy minimization principle. It is shown that, in the case of hydrated carbon nanocrystals passivated by hydrogen atoms, diamond-like clusters are formed. The atomic structure of an unpassivated nanocrystal depends on the number of atoms in the cluster, as well as on its initial geometrical parameters. In some cases, clusters with a fullerene-like surface are formed. In hydrogenpassivated diamond nanocrystals with [NV]? centers, the spin density is localized at the nuclei of C atoms nearest to the center vacancies. For the unpassivated counterparts, the spin density is localized at the nuclei of C atoms forming the surface of the corresponding nanocrystal. 相似文献
7.
The binding energy of a hydrogen molecule on metal atoms (Li, Be, Na, and Mg) attached to aromatic hydrocarbon molecules (benzene
and anthracene) was calculated using an ab initio molecular orbital method at the MP2(FC)/cc-pVTZ level with basis set superposition
error (BSSE) correction. The energy tended to become more negative as the metal atom had a more positive charge and a smaller
radius. The energies of Li2C6H6-H2, Li2C14H10-H2, Na2C14H10-H2, and MgC14H10-H2 were −2.7 to −2.2, −4.0 to −3.1, −2.8 to −0.3, and −1.3 kcal/mol, respectively. Most of these energies were more negative
than those on the hydrocarbons without metal atoms (ca. −1 kcal/mol). Analyzing the Lennard–Jones type potential with the
parameters determined by the MP2 calculations, it was found that these energies mainly consisted of the induction force caused
by the positive charge of the metal atom and the dispersion force from the nearest C6-ring. The energy of BeC14H10-H2 was more negative (−8.6 kcal/mol) than of the other complexes. The hydrogen molecule in this complex had a comparatively
longer H–H distance and a more positive H2 charge than the others. These data suggest that the hydrogen adsorption on this complex involves a charge transfer process
in addition to physisorption interactions. The hydrogen binding energies in some Li2C14H10-H2 systems (∼−4.0 kcal/mol) and BeC14H10-H2 are promising to operate hydrogen storage/release at ambient temperature with moderate pressure. 相似文献
8.
采用密度泛函理论中的广义梯度近似(generalized gradient approximation,简称GGA),对内掺氢分子富勒烯H2@C60及其二聚体的几何结构和电子结构进行了计算研究.发现无论是在H2@C60单体,还是在其二聚体中,氢倾向以分子形式存在于碳笼中心处,且在室温下氢分子可以做自由旋转.电子结构分析表明,氢分子掺入到C60和C120中,仅对距离费米能级以下-8eV至-5eV能级处有一定的贡献,其他能级的分布和能隙几乎没有变化.
关键词:
几何结构
电子结构
密度泛函 相似文献
9.
The radiative pion capture rate in 12C and 6Li leading to bound final states is calculated using the impulse approximation. The T-matrix is obtained from the time-reversed pion photo-production amplitude and initial-state distortion of the bound pion is taken into account. Using recently published capture schedules for pionic atoms the branching ratio R is calculated and compared to experimental values. The agreement is excellent if those experimental values are used that have been obtained by direct observation of the emitted γ-ray and if an optical-model value for the total 2P absorption width in 12C is used. 相似文献
10.
Taketoshi Matsumoto Patricia Nickut Kazuya Watanabe Tatsuya Tsukuda Katharina Al-Shamery 《Surface science》2007,601(22):5226-5231
Reduction of oxidized gold nanoclusters by exposures to foreign gases and irradiation of UV photons has been investigated using X-ray photoelectron spectroscopy. Gold nanoclusters with narrow size distributions protected by alkanethiolate ligands were deposited on a TiO2(1 1 0) surface with dip coating. Oxygen plasma etching was used for removal of alkanethiolate ligands and oxidization of gold clusters. The oxidized gold clusters were exposed to CO, C2H2, C2H4, H2, and hydrogen atoms. Although, C2H4 and H2 did not show any indications of reduction of oxidized gold clusters, CO, C2H2, and hydrogen atoms reduced the oxides on gold cluster surfaces. Among them, hydrogen atoms were most effective for reduction. Irradiation of UV photons around 400 nm could also reduce the oxidized gold clusters. The photochemical reduction mechanism was proposed as follows. The photo-reduction was initiated by electronic excitation of gold clusters and oxygen atoms activated reacted with carbon atoms at the surfaces of gold clusters. Carbon species were likely absorbed in gold clusters or remained at the boundaries between gold clusters when gold clusters agglomerated during oxygen plasma exposures. As the photochemical reduction progressed, carbon atoms segregated to the surfaces of gold clusters. 相似文献
11.
The influence of the chemical functionalization of graphene on the interfacial bonding characteristics between graphene and polymer was investigated using molecular mechanics and molecular dynamics simulations. In this study, three chemical functionalization, (a) phenyl groups, (b) -C6H13 and(c) -C2H4(C2H5)2, which have the same number of carbon atoms, were chosen to investigate the influence of the structure of functionalized groups on the bonding energy and shear stress in the graphene-polyethylene (PE) composites. Our simulations indicated that, the interfacial bonding energy between the graphene modified by -C6H13 groups and PE matrix has the strongest enhancement, but the shear force between the graphene modified by -C2H4(C2H5)2 groups and PE matrix is the strongest in the graphene-polymer composites. Therefore, the suitable structure of chemical groups to the graphene surface may be an effective way to significantly improve the load transfer between the graphene and polymer when graphene is used to produce nanocomposites. 相似文献
12.
Density functional theory has been employed to optimize the structure of endohedral doped C20 fullerene. We have also investigated electronic properties. We have found that C20 cage can accommodate up to 8 hydrogen atoms. Some hydrogen atoms get chemisorbed on the inner surface of C20 cage and form C-H bond. Structural deformation is found to increase with increase in H-atoms. From the analysis of electronic properties, we observe that due to endohedral doping of hydrogen atoms inside C20, H-atoms acquire net negative charge by accepting electrons and fullerene molecules acquire positive charge by donating electrons to H-atoms. For endohedral complexes where H3 triangular molecule formation takes place, the nature of net charge transfer changes, i.e. fractional electronic charge is transferred from H-atoms to fullerene. C20 doped with odd number of H-atoms should be more reactive compared to the even number case. Most of the present results are similar to those of endohedral C60. 相似文献
13.
A framework for analyzing the Doppler broadening of the X-ray lines in pionic hydrogen is proposed. It is shown that the kinetic energy distributions at the instant of the
(n = 2-4) radiative transitions are related to each other. In order to establish the connection, the collisional processes for pionic hydrogen scattering from hydrogen atoms and molecules have been calculated in different models. The proposed method can be used to determine reliably the strong interaction width of the ground state of pionic hydrogen from the X-ray line profiles measured recently at the Paul-Scherrer-Institut.Received: 6 August 2004, Published online: 28 September 2004PACS:
34.50.-s Scattering of atoms and molecules - 36.10.Gv Mesonic atoms and molecules, hyperonic atoms and molecules 相似文献
14.
The oxidation of H2C16O by adsorbed 18O was studied on an Cu(110) sample by temperature programmed reaction spectroscopy. Formaldehyde exchanged its oxygen with surface 18O upon adsorption to yield H2C18O(a) and 16O(a). Formaldehyde was also oxidized by surface 16O and 18O atoms to H2COO which subsequently released one of the hydrogen atoms to form HCOO. The evolution of H2 from the Cu(110) surface was desorption limited, and the low pre-exponential factor for the recombination of the surface hydrogen atoms suggested stringent requirement on the trajectories of the colliding partners. The formate was very stable and dissociated at elevated temperatures to simultaneously yield H2 and CO2. The surface concentration of 18O exerted a pronounced affect on the activity of the oxidation of formaldehyde on Cu(110). 相似文献
15.
The effect of the hydrogen fluoride chain on the aromaticity of C6H6 in the C6H6···(HF)1–4 complexes
The effect of the hydrogen fluoride chain ((HF)n) on the aromaticity and π character of C–C bonds of C6H6 in the C6H6···(HF)n (n = 1–4) complexes were investigated using density functional theory employing RM05 functional. It was found that the binding energy between C6H6 and different (HF)n chains showed a maximum at n = 3 (C6H6···(HF)3). Also, the π–hydrogen interaction (πHI) and the bifurcated fluorine interaction (BFI) increased and decreased the π character of the C–C bond of C6H6, respectively. In addition, the change of aromaticity of the C6H6 due to the interaction with the HF chains was also studied using three different aspects such as aromatic fluctuation index (FLU), average two centre index (ATI) and proton nuclear magnetic resonance (HNMR) spectrum. The most change in the aromaticity happens when the C6H6 interacts with (HF)3 chain. The variation of aromaticity with the binding energy and the summation of two-body terms were investigated and very good linear correlations were observed. 相似文献
16.
《Nuclear Physics A》1998,628(3):403-416
We study (n, d) and (d, 3He) reactions on 208Pb leading to deeply bound pionic atoms with one neutron hole being left. We develop a theoretical model to calculate cross sections of deeply bound pionic atoms and quasi-elastic pion production. The results are compared with data which have been obtained so far. We show that the theoretical model describes the data of both reactions well. 相似文献
17.
Muonic and pionic X-rays of the L- and M-series in C and O have been measured with a Si(Li) detector in the energy range between 7 keV and 60 keV. The target consisted of mylar (C5H4O2). Energies and intensities of 21 transitions have been determined. The strong interaction shift of the pionic 2p level in O was measured and found to be +4.1 ±2.3 eV. The measured width of this level is 11±6 eV. The measured yields have been compared with cascade calculations. 相似文献
18.
E. Kucharska J. Lorenc W. Sasiadek H. Ban‐Oganowska Z. Talik J. Hanuza M. Maczka 《Journal of Raman spectroscopy : JRS》2009,40(12):2123-2134
This paper reports on room‐temperature infrared (IR) and Raman studies and vibrational characteristics of amide and thiocyano groups of R‐NH‐CO‐CH2‐SCN n‐alkylamides of thiocyanoacetic acid (R = C8H17, C9H19, C12H25 and C14H29). Their molecular structure has been proposed on the basis of optimization process. The experimental wavenumbers have been compared to those obtained from discrete Fourier transform (DFT) quantum chemical calculations performed with the use of B3LYP/6–31G(d,p) approximation. The role of the hydrogen bonds in the stabilization of the structure has been analyzed. It was found that the hydrogen bonding and strong dynamic interactions between the unit cell components are responsible for the deviation of several theoretical wavenumbers from the experimental ones. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
19.
Tanh Le Cong 《Proceedings of the Combustion Institute》2009,32(1):427-435
An experimental investigation of the oxidation of hydrogen diluted by nitrogen in presence of CO2 was performed in a fused silica jet-stirred reactor (JSR) over the temperature range 800-1050 K, from fuel-lean to fuel-rich conditions and at atmospheric pressure. The mean residence time was kept constant in the experiments: 120 ms at 1 atm and 250 ms at 10 atm. The effect of variable initial concentrations of hydrogen on the combustion of methane and methane/carbon dioxide mixtures diluted by nitrogen was also experimentally studied. Concentration profiles for O2, H2, H2O, CO, CO2, CH2O, CH4, C2H6, C2H4, and C2H2 were measured by sonic probe sampling followed by chemical analyses (FT-IR, gas chromatography). A detailed chemical kinetic modeling of the present experiments and of the literature data (flame speed and ignition delays) was performed using a recently proposed kinetic scheme showing good agreement between the data and this modeling, and providing further validation of the kinetic model (128 species and 924 reversible reactions). Sensitivity and reaction paths analyses were used to delineate the important reactions influencing the kinetic of oxidation of the fuels in absence and in presence of additives (CO2 and H2). The kinetic reaction scheme proposed helps understanding the inhibiting effect of CO2 on the oxidation of hydrogen and methane and should be useful for gas turbine modeling. 相似文献
20.
The ) self-energy in a nuclear medium is shown to be highly non-linear in density, when proper care is taken of the virtual meson propagation in the medium and retardation effects. As a consequence the p-wave absorptive potential for pionic atoms diverges appreciably from the standard ρ2 form. A fit to the existing data on pionic atoms is carried out with the new functional of the density and turns out to be as good as those with the ρ2 functional. The successful fits with such different density functionals are due to a very narrow range of nuclear effective densities felt by the pion in the observed pionic atoms. The influence of these effects in related problems is discussed along with the suggestion to widen the range of nuclear densities felt by the pions by looking at other nuclear phenomena. 相似文献