Calculation of harmonic force constants,vibrational frequencies and integrated intensities of some organic molecules using the MINDO—Forces method

The harmonic force constants, vibrational frequencies and integrated intensity ratios of CH₂, H₂O, CH₂O, C₂H₂, CO₂, HCN, CH₃, CH₄, and C₂H₄ have been calculated using the MINDO—FORCES program and the Pulay method for the calculation of the molecular force constants. The results obtained are in general quite satisfactory when compared with available literature values. The results are, however, not as satisfactory in case of molecules containing heteroatoms, due to the neglect of some dipolar repulsion integrals for the heteroatoms by the MINDO/3 method. Calculated integrated intensities for CH₃ and C₂H₄ agree well with experimental results. The calculated integrated intensities for other molecules are obtained for the first time and no comparison with published data is therefore possible.Part of the M.Sc. Thesis of K. H. A. 1978.     

Energy disposal in gas-phase nucleophilic displacement reactions

The partitioning of reaction exothermicity into relative translational energy of the products of gas-phase S_N2 (F^? + CH₃Cl) and nucleophilic aromatic substitution (F^? + C₆H₅Cl) reactions has been investigated using kinetic energy release Fourier transform ion cyclotron resonance spectroscopy. The chloride product ion is observed to be highly translationally excited for the S_N2 reaction, indicating a cold internal energy distribution for the products. For the chlorobenzene reaction the products are not generated with large translational energies. The results are compared with a statistical model. Ion-intensity profiles for the CH₃Cl reaction deviate significantly from the statistical model whereas the chlorobenzene results are consistent with this model. The kinetic energy release for the CH₃C1 reaction is compared with energy-disposal results for the photodissociation and dissociative electron-attachment processes of halomethanes. In all three cases a node in the molecular orbital between the carbon atom and the departing halogen results in a repulsive energy release. Ion-retention curves for the nucleophilic aromatic substitution reaction are consistent with the existence of a long-lived ion-dipole complex on the exit channel for this reaction.     

Applications of ESCA to polymer chemistry: Studies of some nitroso rubbers

Molecular core binding energies of the polymers formed by copolymerization of CF₃NO with CF₂?CF₂, CF₂?CFCl, and CF₂?CFH, respectively, have been studied by means of ESCA. The results are interpreted in terms of CNDO/2 SCF MO calculations on some model systems. Some evidence for structural irregularity is found for the copolymers with CF₂?CFCl and with CF₂?CFH. The reaction mechanism for the polymerization is also discussed in terms of the experimental results and INDO SCF MO calculations.     

Theoretical investigation for spectroscopic constants of ground-state alkaline-earth dimers with high accuracy

In this work, we provide highly accurate theoretical estimates for spectroscopic constants of the ground-state alkaline-earth dimers (Ca₂, Sr₂, and Ba₂). Electron correlation energies are calculated with coupled-cluster method at the single, double, and noniterative triple excitations [CCSD(T)] level, and the effects of full triples as well as quadruple excitations are also taken into account at the CCSDT and the CCSDT(Q) level. Our results demonstrate that high-order electron correlation is important to achieve results with high accuracy. We also find that results for Ca₂ with counterpoise corrections, which are designed to eliminate the basis set superposition error, deviate further away from those at the complete basis set limit than the uncorrected ones. The calculated binding energies and equilibrium bond lengths for Ca₂ and Sr₂ are in excellent agreement with recent experimental data. On the other hand, our results for Ba₂ are quite different from previous theoretical data, and there is no available experimental equilibrium bond length and binding energy for calibration. Based on the performance of the adopted approach for Ca₂ and Sr₂, our results should be more reliable and could be helpful for future investigations.     

Relativistic electronic structures of the Ag2 and Au2 molecules

The relativistic electronic structures of the Ag₂ and Au₂ molecules have been calculated using the recently developed self-consistent-field Xα Dirac-scattered-wave programs. Calculations have been carried out for transition energies and ionization potentials for selected molecular orbitals. The results indicate a large degree of s-d hybridization in the ground state of the Au₂ molecule. The calculations are in good agreement with other theoretical work and with existing experimental results.     

Calculation of partition functions of tetra-atomic molecules

A calculation of partition functions of tetra-atomic molecules performed on the basis of the date obtained by means of the ab initio quantum mechanical method is proposed. The symmetry coordinates are used for partitioning the vibrational secular problem. The results for N₂H₂ and C₂H₂ molecules are presented. The accuracy is found to be comparable with those of results obtained using the experimentally derived structural parameters.     

The Lewis acidity of bismuth(III) halides: a DFT analysis

The Lewis acidity of BiX₃ (X=Cl, Br, I) is explored using density-functional theory (DFT) studies of simple complexes with various alcohol and carbonyl substrates. The calculated relative energies of the complexes follow the trend of hardness for BiX₃ (Cl>Br>I). The observed halogen exchange reaction of BiCl₃ with alcohols and alkyl halides is discussed in terms of the computational results as well as theories of hardness and carbocation stability. The DFT results predict similar activation of substrates by molecular BiI₃ relative to BiBr₃, which is inconsistent with experimental results, which show no reactivity for the iodide in nonpolar solvents. However, the molecular form is unlikely in these solvents as BiI₃ is an ionic salt in contrast to the chloride and bromide, which are covalent solids.     

Investigation of Poly(ether-b-amide)/Nanosilica Membranes for CO2/CH4Separation

The results of molecular dynamics （MD） simulations on transport process of CO2 and CH4 gases in poly（ether-b- amide） （PEBAX）/nanosilica membranes are discussed. The diffusion coefficients for CH4 and CO2 gases at 6 cases with different amounts of nanosilica loading in the simulation boxes are presented. The results show that diffusion coefficients for CO2 gas in all cases are larger than those for the CH4 one. Moreover 10% nanosilica loading case shows maximum effects on diffusion coefficients and improves them by more than 68% and 157% for CO2 and CH4 gases, respectively. Additionally, the results of 3-D Cartesian trajectories and displacements curves are presented and the jumping attempt of CO2 is significantly more than that of CH4. Due to the rubbery state of PEBAX membranes in ambient temperature, the results confirm that channel lifetimes are very short and then back diffusion is not observed for this polymer.     

Investigations of CsCl,K2SO4, and K2CrO4 as high temperature calibrants for differential scanning calorimetry

The selection of reference materials having calibration quality data sets is essential to meaningful measurements with DSC. In the present work the results of critical evaluations of the data sets for such materials are reported. New studies for three salt systems, CsCl, K₂SO₄, and K₂CrO₄ as calibrants for high temperature DSC, were undertaken, and are reported. The studies were extended to include Bi and KNO₃, two prospective candidate materials for measurements at lower temperatures, and these results are also reported herewith.     

Thermal behaviour of the homopolynuclear glyoxylate complex combinations with Cu(II) and Cr(III)

Homopolynuclear complexes of Cu(II) respectively Cr(III) with the glyoxylate dianion, C₂H₂O₄ ^2-, have been studied in non-isothermal regime in air and nitrogen. The results of the non-isothermal analysis performed for the synthesised complexes, Cu(C₂H₂O₄)·0.5H₂O, respectively [Cr₂(OH)₂(C₂H₂O₄)₂(OH₂)₄]·2H₂O, correlated with the results of the IR and TG analysis of the compounds obtained by thermal treatment from the initial complexes and the results of the GLC and XR analysis have led to the establishment of the thermal decomposition mechanisms for the two studied complexes. The decomposition mechanisms confirm the stoichiometric and structural formulae proposed for the two synthesised homopolynuclear complexes. This revised version was published online in July 2006 with corrections to the Cover Date.     

The vibrational relaxation of H2. I. Experimental measurements of the rate of relaxation by H2, He,Ne, Ar,and Kr

The vibrational relaxation of gaseous H₂ in mixtures with He, Ne, Ar, and Kr was studied by the laser Schlieren technique in incidents shock waves at 1350–3000 K. From the results of 155 experiments the following standard relaxation times for self-relaxation of H₂ and relaxation of H₂ by He, Ne, Ar and Kr were obtained:

pτ is in atm s, and the qouted uncertainties are standard deviations. The results for H₂/H₂ and H₂/Ar are in very good agreement with previous results of Kiefer and Lutz, and the extrapolated for H₂/H₂, H₂/He and H₂/Ar agree very well with low temperature data Ducuing.The linear mixture rule for a additivity of relaxation rates was found to hold, to within experimental accuracy, for the mixtures studied in the present work.     

Softening of C-H Symmetric Stretching Vibrational Modes for CH2 and CH3 Radicals Adsorbed on Cun (n=1-6) Clusters

The properties of C-H vibration softening for CH₂ and CH₃ radicals absorbed on Cu_n(n=1-6) clusters have been investigated, using the density functional theory with hybrid functional. The results indicate that the absorption of CH₂ on Cu clusters is stronger than the case of CH₃. The vibrational frequencies of C-H bonding agree with the experimental results obtained for CH₂ and CH₃ absorbed on Cu(111). With the increase of cluster size, the softening (Einstein shift) of C-H vibrational modes become stronger.     

Spectroscopic calculations for the (CH3)3N · BF3 and (CH3)3N · BCL3 complexes

Mean amplitudes of vibration and perpendicular amplitude correction coefficients are calculated for (CH₃)₃N · BF₃ and (CH₃)₃N · BCl₃ complexes using different versions of force fields originating from spectroscopic studies with somewhat different assignments. The results are discussed in conjunction with the electron diffraction results and bonding features.     

Dynamics simulation and reaction pathway analysis of characteristics of soot particles in ethylene oxidation at high temperature

Soot particles characteristics were investigated numerically for high temperature oxidation of C₂H₄/O₂/N₂ (C/O ratio of 2.2) in a closed jet-stirred/plug-flow reactor (JSR/PFR) system. Based on the growth mechanism of polycyclic aromatic hydrocarbons (PAHs), two mechanisms were used to explore the formation pathways of soot precursors and soot. Numerical results were compared with the experimental and reference data. The simulation results show that the value predicted for small molecule intermediates within A1 gives a strong regularity, consistent trend with reference data. However, with the hydrogen-abstraction-carbon-addition (HACA) growth mechanism, the predicted value for beyond-A1 PAH macromolecules and soot volume fraction are smaller than the experimental data. The results also show that the predicted soot volume fraction is in good agreement with experimental data when a combination of the HACA and PAHs condensation (HACA + PAH-PAH) growth mechanisms is used. Analyses of the A1 sensitivity and reaction pathway elucidated that A1 are mainly formed from C₂H₃, C₂H₂, C₃H₃, C₆H₅OH, A1C₂H and A1-. The reaction 2C₃H₃ → A1 is the dominant route of benzene formation. The prediction results and an analysis of the A3 reaction pathway indicate that the growth process from benzene to larger aromatic hydrocarbons (beyond two-ring polycyclic aromatic hydrocarbons [PAHs]) goes by two pathways, i.e., HACA combined with the PAH-PAH radical recombination and addition reaction growth mechanisms.     

Quantum mechanical determination of rates of reactions involving hydrogen isotopes

A three-dimensional, quantum mechanical, coupled channel distorted wave approximation is used for calculating thermal rate constants for the isotopic D + H₂, H + D₂, Mu + H₂, and para to ortho H + H₂ exchange reactions using the most accurate available potential surface. The calculated cross sections for the H+H₂ reaction are found to be in excellent agreement with converged close coupling results. Rate constants obtained from the cross sections are compared with the available experimental results.     

Mo_2C/γ-Al_2O_3催化剂上苯加氢反应的原位红外光谱研究

采用程序升温反应法制备了钝化态、还原钝化态和新鲜态Mo2C/γ-Al2O3催化剂,结合原位红外光谱表征技术和反应性能评价,考察、比较了三种催化剂苯加氢反应活性.原位红外光谱结果表明,新鲜态Mo2C/γ-Al2O3催化剂在室温就显示了较好的苯加氢反应活性,表现了类贵金属的催化活性.CO吸附在反应前后新鲜态Mo2C/γ-Al2O3催化剂上的对比结果表明,低价态的Mo位(Moδ+(0δ2))是苯加氢反应活性中心.三种催化剂的反应活性结果表明,新鲜态Mo2C/γ-Al2O3催化剂反应活性最好,催化剂寿命最长,失活之后在500°C下H2处理即可恢复原有活性.     

Dipole oscillator strength distributions,sums, and dispersion energy coefficients for CO and CO2

Globally reliable dipole oscillator strength distributions (DOSDs) have been constructed for ground state CO and CO₂ molecules; the DOSD for CO corresponds to photon energies greater than the electronic absorption threshold while that for CO₂ includes the infrared part of the spectra as well. The recommended DOSDs are used to evaluate the isotropic dipole—dipole dispersion energies for the COCO, COCO2 and CO2CO2 interactions as well as the molar refractivities, as a function of wavelength, and the dipole sums, S_k, k = 2(?1) -4, -6, -8, -10, for the two molecules. Pseudo-DOSD representations of the recommended DOSDs are provided which allow the efficient accurate evaluation of the dispersion energy coefficients C₆ for the interaction of CO or CO₂ with a variety of other atoms and molecules. Previous results for C₆ are found to be in disagreement with our recommended results for interactions involving CO₂. The results of this paper are used to give a reasonably general discussion of the difficulties associated with obtaining reliable results for C₆ by using Padé approximant bounding methods.     

Flow-calorimetric massic heat capacity cpof ( 0.5CFCl3 + 0.5 CF2ClCFCl2) at pressures up to 30 MPa and temperatures between 288 K and 503 K

The massic heat capacity values c_pof CFCl₃and CF₂ClCFCl₂and of (0.5CFCl₃ +  0.5CF₂ClCFCl₂) were measured with high accuracy with a flow apparatus. The results for the pure substances were published in an earlier paper. The present paper contains the results for the mixture. The density of the data on the ( p, T)-surface is enlarged in the critical regions of the pure substances. This should enlarge the sensitivity with which mathematical models for the mixing effect can be adapted to the data.     

Enhancing of asphaltene adsorption onto Fe3O4 nanoparticles coated with metal-organic framework Mil-101 (Cr) for the inhibition of asphaltene precipitation

In this study, the potential of MOF (Mil-101-Cr)-coated Fe₃O₄ magnetic nanoparticles (Fe₃O₄-MOF MNPs) for asphaltene adsorption was investigated for the first time and the results were compared with magnetic Fe₃O₄ nanoparticles (Fe₃O₄ MNPs). The coprecipitation method was used for the synthesis of both nanoparticles and were verified using x-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and field emission scanning electron microscopy (FE-SEM). The initial asphaltene concentration, nanoparticles concentration, and temperature were the investigated parameters that influenced the adsorption capacity. Increasing the asphaltene concentration, decreasing the mass of nanoparticles, and reducing the temperature could enhance the maximum asphaltene adsorption capacities of 0.79 for Fe₃O₄ MNPs and 0.98?mg?m^?2 for Fe₃O₄-MOF MNPs. Adsorption isotherms tests showed that the Langmuir model was in agreement with the experimental data. In addition, the evaluation of adsorption kinetics demonstrated that the pseudo-second-order Lagergren model predicted the results more precisely. The amount of asphaltene adsorption for Fe₃O₄-MOF MNPs was higher than that for Fe₃O₄ MNPs. These results recommend the application of MOF as an appropriate and effective coating for enhancing asphaltene adsorption.     

Rhenium/rhenium oxide nanoparticles production using femtosecond pulsed laser ablation in liquid

In this study, rhenium/rhenium oxide nanoparticles (Re / ReO₃ NPs) have been produced for the first time in ultrapure water by using Femtosecond Pulsed Laser Ablation in Liquid (fsPLAL) method. X-Ray Diffraction (XRD) measurements and results obtained for NPs show the existence of well-crystallized peaks and preferred phases. Re NPs have hexagonal structure while ReO₃ NPs have the perovskite-like cubic crystal structures. The Re / ReO₃ ratio is also determined to be 53 / 47 with ~ 20 nm crystallite size, while pure ReO₃ crystallite sizes were measured to be ~ 25 nm. The TEM results have shown that the produced particles have a spherical shape, and particle sizes changes between ~ 20 nm and ~ 60 nm. The crystallite size is similar due to XRD results. Obtained nanoparticles exhibit promising applications for photonic devices with broad bandgap values which have measured to be 4.71 eV for Re / ReO₃ NPs mixture and 4.36 eV for pure ReO₃ NPs.