共查询到20条相似文献,搜索用时 15 毫秒
1.
F.F. Roelandt D.F. van de Vondel G.P. van der Kelen 《Journal of Molecular Structure》1978,50(1):147-153
Changes in molecular properties and in the electronic charge distribution of the molecules SiH4, SiH3F and SiH2F2 are studied within the framework of the ab initio Hartree—Fock SCF—LCAO—MO method. The ionisation potentials, calculated with the use of Koopmans' theorem, correlate well with the experimental vertical ionisation potentials. The combined s and p electronic populations of the Si atom are not substantially altered when adding Si 3d functions to the basis set. 相似文献
2.
The laser-induced fluorescence of the SiH2 radical was observed in the photolysis of phenylsilane by an ArF excimer laser in the 550–650 nm range. The apparent fluorescence lifetime is 60 ± 5 ns at 580.1 nm. The bending vibrational spacing in the ground state was found to be 990 ± 20 cm?1 from the dispersed fluorescence spectrum. 相似文献
3.
The molecular structures of SiH3N3 and (SiH3)2 NCN have been determined by electron diffraction : SiH3N3 has a non-linear SiN3 skeleton, and (SiH3)2 NCN is a carbodiimide with SiNCN Si probably linear. A new model is proposed which rationalises the observed geometry of a number of molecular pseudohalides. 相似文献
4.
Mean amplitudes and shrinkages are calculated from spectroscopic data for SiH3NCO, SiD3NCO, SiH3NCS and SiD3NCS. The lowest frequency (ν10) in each of the molecules is uncertain, and its influence on the calculated amplitude parameters is investigated. The results are compared with electron diffraction studies. 相似文献
5.
Minh Tho Nguyen Debasis Sengupta L. G. Vanquickenborne 《Chemical physics letters》1995,240(5-6):513-520
Potential energy surfaces of the reaction of SiH2 and C2H2 (and C2D2) have been calculated by means of ab initio molecular orbital theory at the QCISD/6-311G++(2df, 2p)//MP2/6-31G(d, p) level with corrections for the triple excitations to the QCISD energies. The barrier heights for the two reaction channels of the adduct, thus calculated, were further utilized for the dynamical calculation of the rate constants in the framework of quantum statistical Rice-Ramsperger-Kassel theory. Contributions of the rate constants of the various pathways to the total rate constant (KT) for the disappearance of the reactants are critically examined and compared with experiment. The pressure dependence of KT(C2H2) is primarily due to the formation of silirene. KT(C2D2) is consistently higher than KT(C2H2). The standard heat of formation of silirene is predicted to be 72.1 ± 3 kcal/mol. Rearrangement of silirene to vinylsilylene requires an activation energy smaller than that to silylacetylene. 相似文献
6.
The time-resolved laser magnetic resonance (LMR) method has been applied to kinetic measurements for the first time. An intracavity spectrometer based on a CO2 laser with resonant modulation of the magnetic field and with phase-sensitive detection of the signal has been used. Kinetic curves of generation and disappearance of CI atoms and SiH3 radicals were obtained in the pulse photolysis of a mixture of S2Cl2 + SiH4 under the fourth harmonic of a Nd laser (265 nm, 0.5 mJ, 12.5 Hz) at a total pressure of 520–980 Pa (he as diluent) and a temperature of 326 K. The reagent concentrations were: [S2Cl2 = (2.0?10.2)×1014 cm?3, [SiH4 = (2.4?17.4)×1013 cm?3. To remove the transition saturation, 5.3×1015 cm?3 CCl4 was introduced into the reactor. The fraction of dissociated S2Cl2 was 1‰ Rate constants of the reactions (I) Cl+S2Cl2 → products, (II) Cl+SiH4 → HCl+SiH3 and a preliminary rate constant of the reaction (III) SiH3 + S2Cl2 → products were obtained: k1 ≤ (4.3±1.2)×10?12 cm3/s, k2 = (2.3±0.5)×10?10 cm3/s, k3 = (2.4±0.5)×10?11 cm3/s. At a signal-to-noise ratio of 1:1, 1000 pulses and a 12 cm long detection zone the sensitivity to Cl atoms and to SiH3 radicals was 4×1010 cm?3 and = 1011 cm?3, respectively. The time resolution of the method was 4 μs. The method is shown to be promising for kinetic investigations and experiments on fast processes. 相似文献
8.
有机电致发光材料是国际上的研究热点之一。本文采用量子化学方法,研究了环戊二噻吩CH2和SiH2取代对其与2,1,3-苯并噻二唑和三苯胺的化合物光电性质的影响。研究结果表明,CH2取代对母体分子的电子和光谱性质的影响比SiH2取代明显。SiH2取代使吸收和发射光谱的振子强度增大的程度大于CH2取代,更有利于发光强度的提高。CH2和SiH2取代衍生物的空穴和电子重组能的差值极小,可以作为有机电致发光二极管中双极性电荷传输材料。静电势能结果表明,SiH2取代衍生物的稳定性高于母体分子的稳定性。通过探索分子结构与性质间关系,为实验设计合成新的有机电致发光材料提供了理论支持。 相似文献
9.
Shen-Min Li Xin Yu Zhen-Feng Xu Ze-Sheng Li Chia-Chung Sun 《Journal of Molecular Structure》2001,540(1-3):221-229
Ab initio direct dynamics method has been used to study the title reaction. Electronic structure information including geometries, gradients and force constants (Hessians) are calculated at the UQCISD/6-311+G** level. Energies along the minimum energy path are improved by a series of single-point G2//QCISD calculations. The changes of the geometries, vibratioanal frequencies, potential energies and total curvature along the reaction path are discussed. The rate constants in the temperature range 200–3000 K are calculated by canonical variational transition state theory with small-curvature tunneling correction (CVT/SCT) method. The results show that the variational effect is small and in the lower temperature range, the small curvature tunneling effect is important for the reaction. 相似文献
10.
N. K. Serdyuk V. V. Gutorov V. N. Panfilov 《Reaction Kinetics and Catalysis Letters》1981,16(4):393-397
Photobromination of SiH4 under uv-irradiation at various wavelengths has been studied. Rate constants for the elementary reactions Br(2P3/2)+SiH4HBr+SiH3 (k=3.2×10–11 exp(–21.8±2.5)/RT, cm3/s) and Br* (2P1/2)+SiH4HBr+SiH3 (k*=(3±1)×10–13 cm3/s) have been determined in the temperature range from 300 to 415 K.
- . Br(2P3/2)+SiH4HBr+SiH3, k=3,2×10–11 exp (–21,8±2,5)/RT 3/ Br*(2P1/2)+SiH4HBr+SiH3, k*=(3±1)×10–13 3/ 300–415 K.相似文献
11.
采用密度泛函理论B3LYP方法研究了SiH2自由基与HNCO的反应机理, 并在B3LYP/6-311++G**水平上对反应物、中间体、过渡态进行了全几何参数优化, 通过频率分析和内禀反应坐标(IRC)确定了中间体和过渡态. 为了得到更精确的能量值, 又用QCISD(T)/6-311++G**方法计算了在B3LYP/6-311++G**水平优化后的各个驻点的相对能量. 计算结果表明SiH2自由基与HNCO的反应有五条反应通道, 其中顺式反应通道SiH2+HNCO→IM3→ TS4→IM5→TS5→IM6→SiH2NH+CO反应能垒最低, 为主反应通道. 相似文献
12.
The first band in the vacuum ultraviolet photoelectron spectrum of the silyl radical, corresponding to the process SiH3 (X 1A′1) ← SiH3(X 2A1), has been observed with HeI radiation. Extensive vibrational fine structure associated with the SiH3+ deformation vibration was observed in this band and analysis of the structure gave a value of ω = 820 = 40 cm-1 for the out-of-plane deformation mode in the ion. The vertical and adiabatic ionization energies were measured as 8.74 = 0.01 eV and 8.14 ± 0.01 eV respectively and use of the latter value together with the established heat of formation of the silyl radical allows an improved heat of formation of SiH3-. ΔH2980 (SiH3-) to be derived as 980 ± 7 kJ mol?1. 相似文献
13.
Time-of-flight powder neutron diffraction data have been used to refine the crystal structure of the ordered, distorted perovskite Sr2YRuO6. Yttrium and ruthenium are octahedrally coordinated in this material with average MO bond lengths of 2.202 and 1.955 Å, respectively. Constant wavelength neutron diffraction data show that Sr2YRuO6 is a Type I antiferromagnet at 4.2 K with an ordered magnetic moment of 1.85 μB per Ru5+ ion. The Néel temperature of Sr2YRuO6 was determined to be 26 K. The data suggest that the 4d3 electrons in this material are localized rather than itinerant. 相似文献
14.
Profile analysis of high-resolution, powder neutron-diffraction data was used to refine the previously reported structures of the ordered, distorted perovskites Ba2LaRuO6 and Ca2LaRuO6. Low-temperature neutron diffraction experiments showed that, at 2K, the former is a Type IIIa antiferromagnet while the latter is Type I. Both compounds have an ordered magnetic moment of per Ru5+ ion. The Néel temperature of Ba2LaRuO6 was determined to be 29.5K, and the covalent mixing between the ruthenium and nearest-neighbor anions is described by A2π = 8.2 ± 1% for Ba2LaRuO6 and 8.6 ± 1% for Ca2LaRuO6. The ionic radius of a Ru5+ ion is 0.56 Å. These data are consistently interpreted within the framework of a strongly correlated, half-filled π1 band. Extension of this interpretation to the magnetic data for the perovskites CaRuO3 and SrRuO3 leads to a fundamental theoretical prediction. 相似文献
15.
Single crystals of a new form of L-Ta2O5 with a 19×b superstructure have been synthesised by flux growth. The phase is most likely stabilised by the incorporation of a small amount of lithium (0.14 wt% Li) from the flux. The phase has C-centred monoclinic symmetry with , (), , γ=90.00(1)°. The structure was refined in space group C112/m to R1=0.044 for 814 unique reflections with F>4σ(F). The structure can be described as comprising chains of edge-shared TaO7 pentagonal bipyramids that are regularly folded at (010) planes to give sinusoidal chains along [010]. These chains are interconnected along [100] and [001] by corner sharing, creating inter-chain regions that are occupied by isolated TaO6 octahedra and pairs of corner-shared octahedra. A comparison with published data for high-quality refinements of related structures has led to the development of a general model that can explain the structural chemistry variations in the known L-Ta2O5-related structures. A shorthand notation is presented for representing the structures, based on the sequence along [010] of the interchain octahedra. 相似文献
16.
In urea and its structural analogues differences in excess of 100 ppm are found in the nitrogen screening constants for the amide- and isoamide-type structures. The nitrogen chemical shifts are interpreted within the framework of Pople's gauge dependent atomic orbital approximation using INDO molecular orbitals. It is demonstrated that this method provides reasonable values for nitrogen absolute screening constants. The experimental data reported should be useful in examinations of tautomeric equilibria in amides and related structures. 相似文献
17.
M. Snels 《Chemical physics letters》1987,140(6):543-547
The observed difference in transition strength for (SF6)2, (SiF4)2 and (SiH4)2 IR-predissociation spectra is explained by induction effects (μ012/R126) which have to be included in the interaction Hamiltonian in addition to the dominant dipole-dipole term (μ012/R123). 相似文献
18.
The crystal structure of Sr2ErRuO6 has been refined from neutron powder diffraction data collected at room temperature; space group P21/n, A = 5.7626(2), B = 5.7681(2), C = 8.1489(2) Å, β = 90.19(1)°. The structure is that of a distorted perovskite with a 1:1 ordered arrangement of Ru5+ and Er3+ over the 6-coordinate sites. Data collected at 4.2 K show the presence of long range antiferromagnetic order involving both Ru5+ and Er3+. The temperature dependence of the sublattice magnetizations is described. The crystal structure of Ca2NdRuO6 is also that of a distored perovskite (P21/n, A = 5.5564(1), B = 5.8296(1), C = 8.0085(1) β = 90.19(1)°. The β = 90.07(1)°) with a random distribution of Ca2+ and Nd3+ on the A site and a 1:1 ordered arrangement of Ca2+ and Ru5+ on the 6-coordinate B sites. The Ru5+ sublattice is antiferromagnetic at 4.2 K but there is no evidence for magnetic ordering of the Nd3+ ions. Ca2HoRuO6 is also a distorted perovskite (P21/n, A = 5.4991(1), B = 5.7725(1), C = 7.9381(2), β = 90.18(1)° at 4.2 K) with a cation distribution best represented as Ca1.46Ho0.54[Ca0.54Ho0.46Ru]O6. There is no ordering among the Ca3+ or Ho3+ ions on either the A or the B sites, but the Ca/Ho ions form a 1:1 ordered arrangement with Ru5+ on the B sites. At 4.2 K the Ru5+ ions adopt a Type I antiferromagnetic arrangement but there is no evidence of long range magnetic ordering among the Ho3+ ions. 相似文献
19.
Athena S. Sefat Andriy M. Palasyuk Sergey L. Bud’ko John D. Corbett Paul C. Canfield 《Journal of solid state chemistry》2008,181(2):282-293
Single crystals of CeAu4Si2 and CeAu2Si2 have been grown out of ternary fluxes rich in Au, and the former, also by sintering the stoichiometric composition at 750 °C. The single-crystal X-ray refinement result for CeAu4Si2 is orthorhombic, Cmmm (No. 65, Z=2), different from a tetragonal result found from an X-ray powder diffraction refinement [H. Nakashima, et al., J. Alloys Compds. 424 (2006) 7]. For CeAu2Si2, this is the first report of the stoichiometric crystalline phase, in the known tetragonal I4/mmm structure. The anisotropic field- and temperature-dependent magnetizations, as well as specific heat and resistivity data are compared. Although both compounds have related structural packing, they present unique magnetic features. CeAu2Si2 is a typical antiferromagnet with TN=8.8(1) K and CeAu4Si2 features a ferromagnetic component below Tc=3.3(1) K. Both phases have effective moments close in value to that of free Ce3+. 相似文献
20.
The crystal structures of two new oxides, BiReO4 and BiRe2O6, have been determined by single-crystal X-ray methods using an Enraf-Nonius CAD-4F diffractometer. BiReO4 crystallizes as red metallic needles in the space group Cmcm, cell dimensions a = 3.839(1) Å, b = 14.914(2) Å, c = 5.534(1) Å, Z = 4. The structure consists of sheets of corner-shared octahedra (composition ReO4) linked by Bi atoms (R = 2.55%). BiRe2O6 crystallizes as black metallic plates in the space group C2/m, cell dimensions a = 5.516(1) Å, b = 4.906(1) Å, c = 8.384(1) Å, β = 106.71(1)°, Z =2. The structure consists of layers containing Re2O10 units linked together by corner sharing of the octahedra, alternating with layers of Bi atoms (R = 2.61%). The structure is disordered due to the random stacking of the Re layers. The Re---Re distance of 2.5 Å in the Re2O10 unit is comparable to that found in similar compounds. Both compounds exhibit stereochemically active lone pairs. 相似文献