共查询到20条相似文献,搜索用时 546 毫秒
1.
Ab initio molecular orbital theory was used to determine the equilibrium structure and vibrational frequencies of Fe 2Cl 6 and FeAlCl 6. The equilibrium structure the Fe 2Cl 6 dimer has D2h symmetry with a planar arrangement of the four membered {FeCl brFeCl br} ring, similar to the Al 2Cl 6 dimer. The calculated bond distances and vibrational frequencies are in good agreement with experiment. The potential energy surface for the puckering of the {FeCl brFeCl br} ring is extremely flat. This prevents an unambiguous assignment of either D2h or C2v symmetry to the Fe 2Cl 6 structure in electron diffraction measurements. The FeAlCl 6 molecule is found to have a C2v structure similar to Fe 2Cl 6 with vibrational frequencies in good agreement with experiment. 相似文献
2.
Excess molar enthalpies HE and excess molar volumes VE have been measured, as a function of mole fraction x1, at 298.15 K and atmospheric pressure for the five liquid mixtures ( x11,4-C 6H 4F 2 + x2n-C lH 2l+2), l = 7, 8, 10, 12 and 16. In addition, HE and excess molar heat capacities CPE at constant pressure have been determined for the two liquid mixtures ( x1C 6F 6 + x2n-C lH 2l+2), l = 7 and 14, at the same temperature and pressure. The instruments used were flow microcalorimeters of the Picker design (the HE version was equipped with separators) and a vibrating-tube densimeter, respectively. The excess enthalpies of the five difluorobenzene mixtures are all positive and quite large; they increase with increasing chain length l of the n-alkane from HE(x1 = 0.5)/(J mol−1) = 1050 for l = 7 to 1359 for l = 16. The corresponding excess volumes VE are all positive and also increase with increasing l: VE(x1 = 0.5)/(cm3 mol−1) = 0.650 for l = 7 and 1.080 for l = 16. Interestingly, the excess enthalphies of the corresponding mixtures with hexafluorobenzene are only about 5% larger, whereas the excess volumes of (x1C6F6 + x2n-ClH2l+2) are roughly twice as large as those of their counterparts in the series containing 1,4-C6H4F2. Specifically, at 298.15 K HE(x1 = 0.5)/(J mol−1) = 1119 for (x1C6F6 + x2n-C7H16) and 1324 for (x1C6F6 + x2n-C14H30), and for the same mixtures VE(x1 = 0.5)/(cm3 mol−1) = 1.882 and 2.093, respectively. The excess heat capacities for both systems are negative and of about the same magnitude as the excess heat capacities of mixtures of fluorobenzene with the same n-alkanes (Roux et al., 1984): CPE(x1 = 0.5)/(J K−1 mol−1) = −1.18 for (x1C6F6 + x2n-C7H16), and −2.25 for (x1C6F6 + x2n-C14H30). The curve CPE vs. (x1 for x1C6F6 + x2n-C14H30) shows a sort of “hump” for x1 0.5, which is presumed to indicate emerging W-shape composition dependence at lower temperatures. 相似文献
3.
This work uses ab initio calculations to obtain harmonic frequencies and anharmonic constants for the O–H symmetric and asymmetric stretches of H 2SO 4 in its C2, Cs, C1a, and C1b configurations. In addition, a high-resolution potential energy surface is calculated as a function of both O=S–O–H dihedral angles in order to accurately obtain minimum and saddle point energies. The resulting peak positions and Boltzmann populations are compared to experimental frequencies and intensities and provide evidence for the assignment of rotamers in H 2SO 4 as suggested in recent work. 相似文献
4.
The symmetry unrestricted C 36F 2 isomers formed from fullerene C 36, the initial symmetry of which is C6v, C6h, or D2d, have been extensively studied with semi-empirical (AM1 and PM3) calculations. Based on the relationship between the isomer's stability and the adding positions, three patterns of the adding sites of F 2 moiety in the additive reactions have been deducted. The results of the π-orbital axis vector (POAV) analysis indicate that the chemical reactivity of C 36 is the result of the high strain in the C 36 cage. But, in order to form stable compounds, the effects, which guide the F 2 moiety to select carbon atoms in the C 36 cage, are dominated by the conjugate effect in C 36F 2 system rather than the strain release in the C 36 cage. 相似文献
5.
Four neutral bimetallic clusters X 2M 2 (X=Si, Ge, M=Al, Ga) are investigated using density functional theory (DFT) and post-HF methods. The calculated results show that each of four X 2M 2 species has two energetically close stable isomers with rhombic structure ( D2h symmetry) and trapezoidal structure ( C2v symmetry) respectively. For the Ge 2Al 2 species the rhombic ( D2h) isomer is the ground state, whereas for other three species Ge 2Ga 2, Si 2Al 2, and Si 2Ga 2, the trapezoidal ( C2v) isomers are the ground states. The calculated magnetic susceptibility anisotropy ( χanis) and nucleus-independent chemical shift (NICS) indicate that a strong diatropic ring current exists in the two heterocyclic planar isomers, suggesting they are highly aromatic. A detailed molecular orbital analysis further reveals that both heterocyclic isomers possess multiple aromaticity derived from one delocalized π MOs and two delocalized σ MOs. 相似文献
6.
At present C 94 is one of the highest sets of isomeric fullerenes that has been characterized by 13C NMR spectra. This contribution reports quantum-chemical computations on the C 94 system. The complete set of 134 isolated-pentagon-rule isomers of C 94 is described by four semiempirical quantum-chemical methods (MNDO, AM1, PM3, and SAM1). The C 94 energetics is also checked with Hartree–Fock SCF calculations in the standard 4-31G basis set (HF/4-31G). The calculations point out a C2 structure as the system ground state. As energetics itself cannot produce reliable relative stabilities at high temperatures, entropy terms are also computed and the relative-stability problem is entirely treated in terms of the Gibbs function. The lowest-energy structure remains the most populated isomer at higher temperatures. However, several other structures show significant populations at higher temperatures. The six most populated species at the AM1 computational level read: C2, C2, C1, C1, Cs, and C2. This selected six-membered isomeric set indeed contains the four symmetries observed in the available experiment ( C2, Cs, C2, and C2). This incidence represents a good agreement with the experiment and can be viewed as another evidence that the supposed inter-isomeric thermodynamic equilibrium does exist in experiments. 相似文献
7.
Employing the electrochemical cells with the solid oxide electrolyte Kanthal + Re, Te(l), TeO2(s)O−2 air, Pt Pt + Re, Sb2O3(s), Sb2O4(s)O−2 air, Pt Pt + Re, Sb2O3(s), Sb2O4(s), Te(l)O−2 air, Pt the equilibrium oxygen potential in the pseudobinary Te-TeO 2, Sb 2O 3-Sb 2O 4 and in the Sb 2O 3-Sb 2O 4-Te pseudoternary systems was determined in the temperature range 700-1173 K. In addition, the pseudobinary sections Sb 2O 3-Te, Sb 2O 3-Sb 2O 4 (1:1)-Te and Sb 2O 4-Te were examined by DTA in the temperature range 500-1300 K. Using these results the evolution of the pseudoternary system with temperature can be suggested. It was found that, at 718 K, a ternary eutectic with a composition close to pure Te appears in the system. At a higher temperature, 920 K, another liquid phase is formed, which is characteristic of the ternary four-phase equilibrium L 2 + Sb 2O 4(s) + Sb 2O 3(s) = L 1. 相似文献
8.
The geometric structures and conformational properties of trifluoromethanesulfonic anhydride, (CF 3SO 2) 2O, and bis(trifluoromethylsulfonyl)difluoromethane, (CF 3SO 2) 2CF 2 have been studied by gas electron diffraction (GED) and ab initio calculations (HF/3–21G*). The calculations predict for both systems two stable conformers with C2 symmetry and one with C1 symmetry. In both compounds structures with C2 symmetry and dihedral angles SOSC ≈ 100° ((CF 3SO 2) 2O) and SCSC≈ 150° ((CF 3SO 2) 2CF 2 are lowest in energy. According to the GED analyses the dominant conformer of (CF 3SO 2) 2O 2 possesses C2 symmetry with SOSC dihedral angles of 99.1(14)°. The presence of up to 30% of the two other conformers cannot be excluded; for (CF 3SO 2) 2CF 2 only one conformer with C2 symmetry and SCSC dihedral angles of 143(2)° is observed. A complete set of geometric parameters is given. 相似文献
9.
The geometric structures and conformational properties of trifluoromethanesulfonic anhydride, (CF 3SO 2) 2O, and bis(trifluoromethylsulfonyl)difluoromethane, (CF 3SO 2) 2CF 2 have been studied by gas electron diffraction (GED) and ab initio calculations (HF/3–21G*). The calculations predict for both systems two stable conformers with C2 symmetry and one with C1 symmetry. In both compounds structures with C2 symmetry and dihedral angles SOSC ≈ 100° ((CF 3SO 2) 2O) and SCSC ≈ 150° ((CF 3SO 2) 2CF 2) are lowest in energy. According to the GED analyses the dominant conformer of (CF 3SO 2) 2O possesses C2 symmetry with SOSC dihedral angles of 99.1(14)°. The presence of up to 30% of the two other conformers cannot be excluded; for (CF 3SO 2) 2CF 2 only one conformer with C2 symmetry and SCSC dihedral angles of 143(2)° is observed. A complete set of geometric parameters is given. 相似文献
10.
The electron scattering pattern of gaseous dicyclopentadienylberyllium, Cp 2Be, has been recorded from s = 2.00 to 39.00 Å −1 with a nozzle temperature of about 120°C. Molecular models of D5d symmetry or models containing one π-bonded and one σ-bonded Cp ring are not compatible with the data. The possibility the gaseous Cp 2Be consists fo a mixture D5d and π-Cp, σ-Cp conformers is considered and rejected. A model of C5v symmetry can be brought into satisfactory agreement with the data. It is also found that a slip sandwich model obtained from the C5v model by moving sideways the ring which is at the greatest distance from Be, while keeping the two rings essentially parallel is compatible with the electron diffraction data. The best fit between experimental and calculated intensity curves is obtained with a model with a sideways slip of 0.8(1) Å. This model is similar to that indicated by the X-ray diffraction investigations by Wong and coworkers [4,5]. It is suggested that the potential energy of the molecule does not change much as the magnitude of the slip changes and that the molecule thus undergoes large amplitude vibration. 相似文献
11.
The infrared spectra of cis-3-hexene and trans-3-hexene dissolved in liquid argon have been obtained at temperatures from 93 to 120 K. The absorptions were observed with a low-temperature cell and a Fourier transform infrared spectrophotometer. Ab initio molecular orbital calculations were performed to obtain the equilibrium geometry, vibrational frequencies, force fields, and infrared intensities. The calculations were done at the Hartree-Fock level using 6-31G basis set. The Cartesian force fields from ab initio calculations have been converted to the force field in symmetry coordinates. The scale factors of ab initio calculated force fields were determined. Normal coordinate calculations were performed using a scaled quantum mechanical (SQM) force field. Vibrational normal modes calculated for the lowest energy rotamers of cis- and trans-3-hexene have been assigned to infrared absorption bands observed in liquid argon solution. The assignments were based on calculated frequencies and potential energy distributions. The equilibrium geometries of the two lowest energy rotamers (symmetry C2 and Cs) of cis-3-hexene and of the three lowest energy rotamers (symmetry Ci, C2, and C1) of trans-3-hexene were calculated. Variable temperature studies of the infrared spectrum of cis- and trans-3-hexenes dissolved in liquid argon were done to obtain the Δ H of conversion between the rotamers C2 and Cs of cis-3-hexene and between the rotamers Ci, C2, and C1 of trans-3-hexene. 相似文献
12.
The mechanism of the H 2NO( 2B 1)→NO( 2Π)+H 2 reaction has been examined using ab initio molecular orbital methods. Ground-state and first-excited-state potential surfaces were plotted at the FOCI/cc-pVTZ level of theory as functions of two appropriate internal degrees of freedom. A conical intersection was found on the Cs pathway that is symmetric with respect to the plane perpendicular to the molecular plane of C2v H 2NO( 2B 1). It is therefore considered that trajectories that start from H 2NO( 2B 1) towards the product region detour around the conical intersection, pass through the neighborhood of the transition state that is located at the saddle point on the Cs pathway, and finally reach the products, NO( 2Π)+H 2. Thus we can explain the mechanism of the H 2NO( 2B 1)→NO( 2Π)+H 2 reaction, which has remained unclear to date. 相似文献
13.
Pseudostate decomposition of static dipole polarizabilities for ground state H 2+ from a Givens-Householder diagonalization of the excitation operator ( H" height="17" width="20"> 0− E0) over an N-term basis of appropriate symmetry allows for a rapidly convergent evaluation of C6 dispersion coefficients for H 2+–H 2+. 27-term pseudospectra of hypergeneralized James functions with a 30-term GGJ + unperturbed wavefunction with an optimized scale factor δ=0.918 at R=2 0 give C6 and γ 6 values that are accurate to no less than nine significant figures. 相似文献
14.
A metal-organic complex, which has the potential property of absorbing gases, [LaCu 6(μ-OH) 3(Gly) 6im 6](ClO 4) 6 was synthesized through the self-assembly of La 3+, Cu 2+, glycine (Gly) and imidazole (Im) in aqueous solution and characterized by IR, element analysis and powder XRD. The molar heat capacity, Cp,m, was measured from T = 80 to 390 K with an automated adiabatic calorimeter. The thermodynamic functions [ HT − H298.15] and [ ST − S298.15] were derived from the heat capacity data with temperature interval of 5 K. The thermal stability of the complex was investigated by differential scanning calorimetry (DSC). 相似文献
15.
A new 1.75 μm infrared emission transition of Y 2O 3:Er 3+ is assigned to the 4S 3/2 → 4I 9/2 transition of Er 3+ ions situated at the C2 sites of cubic RE 2O 3 (RE = Y, Gd, Lu). The intensities of features in the 1.54 μm 4I 15/2– 4I 13/2 absorption transition due to Er 3+ at S6 and C2 sites are consistent with the site occupation ratio and the relative magnetic dipole–electric dipole intensity contributions of Er 3+ at the different sites. The 1.54 μm emission lines are predominantly from Er 3+ ions at C2 sites. The different behaviours of the emission intensities 1.75 and 1.54 μm groups with change in Er 3+ dopant ion concentration, preparation technique, Yb 3+ co-doping, temperature change and different excitation line are rationalized. 相似文献
16.
The complex [H 3NCH 2CH 2NH 3][PdBr 6] has been isolated as well-formed brown crystals. The Raman (single crystal) and FTIR (wax disc) spectra of the complex have been recorded but the band assignments are complicated by extensive factor group splitting and resonance effects. The crystal belongs to space group Pnnm, with Z = 2, each ion occupying sites of 2/ m ( C2h) symmetry. The [PdBr 6] 2− ion is very close to octahedral, the two unique PdBr distances, 2.466(3) and 2.470(3) Å, being equal within experimental error and the BrPdBr angles being 90 ± 0.8°. The diammonium cation has an extended, planar, trans structure. 相似文献
17.
The macrocyclic compound, [1,2-C 2B 10H 10-1,4-C 6H 4-1,7-C 2B 10H 10-1,4-C 6H 4] 2 (5)—a novel cyclooctaphane, was prepared by condensation of the C,C′-dicopper(I) derivative of meta-carborane with 1,2-bis(4-iodophenyl)- ortho-carborane. The X-ray crystal structure of 5·C 6H 6·6C 6H 12 was determined at 150 K, revealing an extremely loose packing mode. Molecule 5 has a crystallographic Cs and local C2v symmetry; the macrocycle adopts a butterfly (dihedral angle 143°) conformation with the ortho-carborane units at the wingtips and the phenylene ring planes roughly perpendicular to the wing planes. Multinuclear NMR spectra suggest that molecule 5 in solution inverts rapidly via the planar D2h geometry, which (from ab initio HF/6-31G* calculations) is only 1 kcal mol −1 higher in energy than the C2v one. An attempt to prepare an even larger macrocycle, comprising three para-carborane and three ortho-carborane units linked by six para-phenylene units, was unsuccessful. 相似文献
18.
The polarized absorption infrared (IR) and polarized Raman spectra of a CsHSO 4 single crystal at room temperature are presented and discussed in relation to the X-ray crystal structure. Breakdown of the selection rules for the X-ray determined C2h factor group is observed. The vibrational factor group appears to be C2. This implies C1 site symmetry for the SO 2−4 ions. The polarization features of the HSO −4 ion vibrations are predicted assuming that the longest S---OH bond vibrates independently of the SO 3 group vibrations. The ABC structure of the IR and Raman band arising from the νOH stretching vibration is explained on the basis of Fermi resonance. 相似文献
19.
The molecular structure of TeCl 2Br 2 in the vapour phase is reconsidered in the light of the recently published X-ray crystal structure for TeCl 4. Normal coordinate calculations are performed on molecular TeCl 2Br 2 in its three possible symmetries using force fields derived from the parent molecules TeCl 4 and TeBr 4. The calculations indicate that the data for molecular TeCl 2Br 2 can best be interpreted as arising from a mixture of at least the two high symmetry conformers rather than just the low symmetry C1 molecule as previously reported. 相似文献
20.
Assignments of a certain number of vibrational bands of (CO)Fe(PF 3) 4 are made with reference to the C3v and C2v isomers. A study of the Raman and
spectra at low temperature revealed that in the solid state only one isomer exists. Furthermore, a comparative study of liquid (CO)Fe(PF 3) 4 and HCo(PF 3) 4 of molecular symmetry C3v was made. These two approaches made it possible to determine the difference in enthalpy between the two isomers of the iron complex (+0-52±0.05 kcal.mole −1) in the liquid state, as well as to verify the assignments proposed previously. The greater stability of the C2v isomer is discussed. 相似文献
|