Infrared crystal spectra of C2H4, C2D4, and as-C2H2D2 and the general harmonic force field of ethylene

Carbon-13 frequency shifts for C₂H₄, C₂D₄, and as-C₂H₂D₂ have been measured in isotopic solid solutions in crystalline films at 60 K. All but two of the shifts (for as-C₂H₂D₂) are compatible with recently determined ζ data for C₂H₄, with ¹³C frequency shifts for C₂H₄ and C₂D₄ in the gas phase and with conventional frequency data. Together, these data completely determine with precision all 18 parameters of the GHFF for ethylene, the previous ambiguity in choice between two sets of A_g species force constants being removed. The force field reproduces closely the observed centrifugal distortion constants for C₂H₄, a ζ constant observed for trans-C₂H₂D₂, and the inertia defects for C₂H₄, C₂D₄, and as-C₂H₂D₂. Vibration and rotation constants for all isotopically deuterated ethylenes are calculated.Possible explanations for the two anomalous crystal shifts in as-C₂H₂D₂ involve the effects of the crystal field, and failure of the use of Dennison's rule for making anharmonic corrections to the shifts. The former explanation is preferred as a result of thorough analysis of the anharmonicity constants for as-C₂H₂D₂ determined from many overtone and combination bands in the gas and crystal spectra.     

Room-temperature chemisorption of chloroethylenes on Si(1 1 1)7 × 7: formation of surface vinyl,vinylidene and their chlorinated derivatives

Chemisorption of a family of six chloroethylenes (C₂H₃Cl, 1,1-C₂H₂Cl₂, cis-1,2-C₂H₂Cl₂, trans-1,2-C₂H₂Cl₂, C₂HCl₃, and C₂Cl₄) on Si(1 1 1)7 × 7 at room temperature (RT) has been investigated by vibrational electron energy loss spectroscopy (EELS). The characteristic vibrational EELS features have been used to identify the prominent surface species upon RT adsorption. Like ethylene, C₂H₃Cl has been found to predominantly adsorb in a di-σ bonding geometry to the Si surface, while 1,1-C₂H₂Cl₂, cis- and trans-1,2-C₂H₂Cl₂, C₂HCl₃ and, to a lesser extent, C₂Cl₄ appear to undergo dechlorination upon adsorption to form chlorinated vinyl adspecies involving single-σ bonding structures. Evidence of vinylidene (>CCH₂) has been obtained for the first time on a semiconductor surface for the adsorption of 1,1-C₂H₂Cl₂. The present work illustrates that the molecular structure and the Cl content of chloroethylenes play a crucial role in controlling not only the adsorption geometry but also the extent of dechlorination and the resulting adspecies upon RT adsorption on Si(1 1 1).     

Computational design of multi-states monomolecular device using molecular hydrogen and C<Subscript>20</Subscript> isomers

We perform detailed calculations for the interaction of molecular hydrogen with C₂₀isomers in the framework of density functional theory method. The adsorption of H₂ outside the C₂₀-e isomer with parallel orientation with respect to the plane of the hexagon is found to be the most stable adsorption configuration. Thus this might have potential for the hydrogen storing. We have also investigated the number and the position of adsorption sites in the pentagon for the parallel configurations of the H₂/C₂₀ systems. We find two stable configurations of the molecule for the C₂₀-bowl isomer that have a small difference in energy. Thus, surprisingly, despite their apparent simplicity these H₂/C₂₀-bowl systems are shown to exhibit the flip-flop motion by a small current pulse. Hence, it might be a candidate for multi-states monomolecular device. Convenient experimental techniques such as field emission microscopy are proposed to test these predictions.     

Isomerization of C3H3NO isomers: ab initio study

The structures and isomerization process of C₃H₃NO species have been explored at the MP2/6–311++G(d,p) level of theory of the ab initio method. Eleven minima and four interconversion transition states have been identified. The zero-point vibrational energy corrections were made to predict reliable energies. We predict a five-membered ring-like structure to be the lowest energy isomer, which is 177.73?kcal?mol^?1 more stable than the least stable isomer X found on the potential energy surface. The transition states and minima isomers were verified by frequency calculation. Intrinsic reaction coordinate (IRC) calculations have been performed to confirm that each transition state is linked by the desired reactants and products. The isomer stabilities have been studied using the relative energies, chemical hardness and chemical potential. The MHP principle could not predict the order of stability for C₃H₃NO isomers as arrived at with the relative energies. The role of intramolecular hydrogen bonds on the equilibrium structure has been discussed. The energy barrier and reaction enthalpy have been calculated during isomerization.     

密度泛函理论计算内掺氢分子富勒烯H2＠C60及其二聚体的几何结构和电子结构

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     

J-aggregates of pseudoisocyanine with long alkyl substituents in thin films: Synthesis, spectral properties, and thermal stability

The formation and properties of J-aggregates in thin solid films of pseudoisocyanines with long N-alkyl groups, obtained by centrifuging from solutions in organic solvents, were studied. It is shown for the first time that nonsymmetric cyanine dyes, containing a C₂H₅ group at one nitrogen atom and a C₁₀H₂₁, C₁₅H₃₁, or C₁₈H₃₇ group at another nitrogen atom, spontaneously form J-aggregates stable at room temperature and pressing a narrow absorption band with a half-width at half maximum of 200 cm^?1. The thermal stability of J-aggregates in thin films of pseudoisocyanines with alkyl substituents decreases in the following order: C₂H₅-C₂H₅> C₂H₅-C₆H₁₃>C₂H₅-C₁₈H₃₇>C₂H₅-C₁₀H₂₁>C₂H₅-C₁₅H₃₁. By introducing 1-octadecyl-2-methylquinolinium iodide in the film, it was found that the J-aggregates studied consist of a small number (2–4) of dye molecules.     

Ethylene adsorption on the Pt-Cu bimetallic catalysts. Density functional theory cluster study

The adsorption of ethylene on Cu₁₂Pt₂ clusters has been studied within the density functional theory (DFT) approach to understand the high ethylene selectivity of Cu-rich Pt-Cu catalyst particles in the reaction of hydrogen-assisted 1,2-dichloroethane dechlorination. The structural parameters for Cu₁₂Pt₂ clusters with D_4h, D_2d, and C_3v symmetry have been calculated. The relative stability of the isomeric Cu₁₂Pt₂ clusters follows the order: C_3v > D_2d > D_4h. Each isomer has an active site for ethylene adsorption that consists of a single Pt atom surrounded by Cu atoms. The interaction of ethylene with the active site yields a π-C₂H₄ adsorption complex. The strongest π-C₂H₄ complex forms with the cluster of C_3v symmetry; the bonding energy, ΔE_π(C₂H₄), is −15.6 kcal mol⁻¹. The bonding energies for the π-C₂H₄ complex with Cu₁₄ and Pt₁₄ clusters are −6.5 and −18.8 kcal mol⁻¹, respectively.The addition of Pt to Cu modifies the valence spd-band of the cluster as compared to a Cu₁₄ cluster. The DOS near the Fermi level increases when C₂H₄ adsorbs on the Cu₁₂Pt₂ cluster. As well, the center of the d-band shifts toward lower binding energies. Ethylene adsorption also induces a number of states below the d-band. These states correspond to those of gas-phase C₂H₄.The vibrational frequencies of C₂H₄ adsorbed on the clusters of D_4h and C_3v symmetry have been calculated. The phonon vibrations occur below 250 cm⁻¹. The intense bands around 200 cm⁻¹ are attributed to stretching vibrations of the Pt-Cu bonds normal to the cluster surface. The stretching vibrations of the Pt-C bonds depend on the local structure of the active site: ν_s(Pt-C) = 268 cm⁻¹ and ν_as(Pt-C) = 357 cm⁻¹ for the cluster of the D_4h symmetry; ν_s(Pt-C) = 335 cm⁻¹ and ν_as(Pt-C) = 397 cm⁻¹ for the cluster of the C_3v symmetry. Bands in the range of 800-3100 cm⁻¹ are attributed to vibrations of the adsorbed C₂H₄ molecule. The signature frequencies of the π-C₂H₄ adsorption complex are the δ_s(CH₂) deformation vibration at ∼1200 cm⁻¹ and the ν(C-C) stretching vibration at ∼1500 cm⁻¹. These vibration are absent for di-σ-C₂H₄ adsorption complexes.     

Effect of chemisorption structure on the interfacial bonding characteristics of graphene-polymer composites

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.     

Optical properties of natural quantum-well compounds (C6H5-CnH2n-NH3)2PbBr4 (n=1-4)

This paper describes the synthesis and characterization of self-assembled organic-inorganic layered perovskite compounds, (C₆H₅-C_nH_2n-NH₃)₂PbBr₄ (n=1-4). the effect of the number of carbon atoms of the alkyl chain length (n) on optical properties has been studied. (C₆H₅-C_nH_2n-NH₃)₂PbBr₄ films fabricated by spin-coating are microcrystalline form, single phase and oriented with the c-axis. Crystallinity, the maximum PL intensity and the lifetime of exciton emissions varied with the number of carbon atoms. the lowest-energy exciton splits into a few fine-structure levels at low temperatures. Time-resolved photoluminescence spectra reveal that (C₆H₅-C_nH_2n-NH₃)₂PbBr₄ shows both singlet and triplet excitons. with decreasing temperature, triplet exciton emissions become dominant for (C₆H₅-C_nH_2n-NH₃)₂PbBr₄ (n=1-3), while (C₆H₅-C₄H₈-NH₃)₂PbBr₄ shows mainly singlet exciton emissions. The intersystem crossing from excited singlet state to triplet state plays an important role in the relaxation process of excitons.     

Theoretical kinetics of HO2 + C5H5: A missing piece in cyclopentadienyl radical oxidation reactions

The resonantly-stabilized cyclopentadienyl radical (C₅H₅) is a key species in the combustion and molecular growth kinetics of mono and poly-aromatic hydrocarbons (M/PAHs). At intermediate-to-low temperatures, the C₅H₅ reaction with the hydroperoxyl radical (HO₂) strongly impacts the competition between oxidation to smaller products and growth to PAHs, precursors of soot. However, literature estimates for the HO₂ + C₅H₅ reaction rate are inaccurate and inconsistent with recent theoretical calculations, thus generating discrepancies in global combustion kinetic models. In this work, we perform state-of-the-art theoretical calculations for the HO₂ + C₅H₅ reaction including variable reaction coordinate transition state theory for barrierless channels, accurate thermochemistry, and multi-well master equation (ME) simulations. Contrary to previous studies, we predict that OH + 1,3-C₅H₅O is the main reaction channel. The new rate constants are introduced in two literature kinetic models exploiting our recently developed ME based lumping methodology and used to perform kinetic simulations of experimental data of MAHs oxidation. It is found that the resonantly-stabilized 1,3-C₅H₅O radical is the main C₅H₅O isomer, accumulating in relevant concentration in the system, and that the adopted lumping procedure is fully consistent with results obtained with detailed kinetics. The reactivity of C₅H₅O with OH and O₂ radicals is included in the kinetic mechanisms based on analogy rules. As a result, C₅H₅O mostly reacts with O₂ producing smaller C₃/C₄ species and large amounts of C₅H₄O, suggesting that further investigations of the reactivity of both C₅H₅O and C₅H₄O with oxygenated radicals is necessary. Overall, this work presents new reliable rate constants for the HO₂ + C₅H₅ reaction and provides indications for future investigations of relevant reactions in the sub-mechanisms of cyclopentadiene and MAH oxidation.     

Photoelectron spectra of ethylene and of the six deuterated derivatives

The photoelectron spectra of C₂H₄ and of six deuterated molecules of ethylene — C₂D₄, C₂D₃H, C₂H₃D, cis-C₂H₂D₂, trans-C₂H₂D₂ and gem-C₂H₂D₂ — have been recorded with the 584-Å resonance line of He. The adiabatic ionization potentials of the X²B_3u and the ²B_3g states of the seven isotopic components have been determined with an accuracy of about 7 meV. The ionization potentials of the other excited electronic states have been measured with a lower accuracy owing to a less well defined onset. The measured ionization potentials of C₂H₄ are 10.514 eV, 12.431 eV, 14.4₃ eV, 15.7₄ eV and 18.7 eV. The vibrational structure of the first electronic band shows that the two normal modes ν₂ (symmetric CC stretching) and ν₃ (symmetric HCH bending) are excited simultaneously. The measured vibrational frequencies show no abnormal isotopic effect if the assignment given in the literature for the ν₂ and ν₃ modes in C₂H₄⁺ are reversed and if a stronger excitation of the ν₃ symmetric bending mode in the least deuterated compounds is assumed. The vibrational modes most strongly excited in the second and third electronic bands are ν₁ (symmetric CH stretching) and ν₃, and in the fourth band ν₃.     

Oxygen as promoter or poison in the catalytic dissociation of H2, C2H4, C2H2, and NH3 on Palladium

The dissociation rates of H₂, C₂H₄, C₂H₄, and NH₃ have been studied on oxygen covered Pd surfaces by measuring the water desorption rates during exposure to each of the molecules. These results are correlated with the hydrogen response of a Pd-MOS structure. The measurements show a trend (at 473 K) where oxygen blocks H₂ dissociation, blocks C₂H₄ dissociation only above a certain oxygen coverage, has no influence on C₂H₂ dissociation, and promotes NH₃ dissociation.     

Einstein<Emphasis Type="Italic">A</Emphasis>-coefficients for rotational transitions in the ring-chain isomer of C<Subscript>5</Subscript>H<Subscript>2</Subscript>

Laboratory formation of four isomers of C⁵H² molecule is reported and detection of the ring-chain isomer (isomer 1) of C₅H₂ in cosmic objects has been suggested. For identification of a molecule in cosmic objects, one of the required input data is EinsteinA-coefficients (radiative transition probabilities) for the molecule. Here, we report EinsteinA-coefficients for electric dipole transitions in the ring-chain isomer of C₅H₂ among the rotational levels of the ground electronic and ground vibrational states up to 21 cm⁻¹.     

DFT study of hydrogen storage in Pd-decorated C60 fullerene

Hydrogen storage reactions on Pd-doped C₆₀ fullerene are investigated by using the state-of-the-art density functional theory calculations. The Pd atom prefers to bind at the bridge site between two hexagonal rings, and can bind up to four hydrogen molecules with average adsorption energies of 0.61, 0.45, 0.32, and 0.21 eV per hydrogen molecule. With no metal clustering, the system gravimetric capacities are expected to be as large as 5.8 wt%. While the desorption activation barriers of the complexes nH₂ + Pd–C₆₀ with n = 1 are outside the department of energy (DOE) domain (?0.2 to ?0.6 eV), the desorption activation barriers of the complexes nH₂ + Pd–C₆₀ with n = 2–4 are inside this domain. While the interaction of 1H₂ with Pd + C₆₀ is irreversible at 459 K, the interaction of 2H₂ with Pd + C₆₀ is reversible at 529 K. The hydrogen storage of the irreversible 1H₂ + Pd–C₆₀ and reversible 2H₂ + Pd–C₆₀ interactions are characterised in terms of densities of states, infrared, Raman, and proton magnetic resonance spectra, electrophilicity, and statistical thermodynamic stability.     

Comparative Raman study of the Ti complex Cp2Ti(η2-C60) · C6H5CH3 and TixC60 films

Raman spectra from the first Ti fullerene complex Cp ₂Ti(η²-C₆₀) · C₆H₅CH₃ are presented. Compared to spectra of pure C₆₀, the spectra of the Ti complex exhibit a number of new peaks due to the symmetry lowering for C₆₀. The A _g(2) mode is downshifted by 12 cm⁻¹ compared to C₆₀, which corresponds to a charge transfer of one electron per Ti-C₆₀ bond. This value (6 cm⁻¹ for one transferred electron) is identical to the downshift of the A _g(2) mode in alkali metal fullerides with ionic bonding. The spectra of Cp ₂Ti(η²-C₆₀) · C₆H₅CH₃ were compared to the spectra of evaporated Ti_xC₆₀ films. The A _g(2) mode in Ti₄C₆₀ showed a downshift of about 25 cm⁻¹ compared to pure C₆₀, which corresponds to a charge transfer of one electron per Ti atom; this is similar to the ionic alkali metal fullerides and different from η²-C₆₀-type bonding. From Fizika Tverdogo Tela, Vol. 44, No. 3, 2002, pp. 483–485. Original English Text Copyright ? 2002 by Talyzin, Jansson, Usatov, Burlakov, Shur, Novikov. This article was submitted by the authors in English.     

Theoretical characterisation of irreversible and reversible hydrogen storage reactions on Ni-doped C60 fullerene

An attempt has been made to characterise the irreversible and reversible hydrogen storage reactions on Ni-doped C₆₀ fullerene by using the state of the art density functional theory calculations. The single Ni atom prefers to bind at the bridge site between two hexagonal rings of C₆₀ fullerene, and can bind up to four hydrogen molecules with average adsorption energies of ?0.85, ?0.83, ?0.58, and ?0.31 eV per hydrogen molecule. No evidence for metal clustering in the ideal circumstances and the hydrogen storage capacity is expected to be as large as 8.9 wt%. While the desorption activation barriers of the complexes nH₂NiC₆₀ (n = 1, 2) are outside the desirable energy window recommended by the department of energy for practical applications (–0.2 to –0.6 eV), the desorption activation barriers of the complexes nH₂NiC₆₀ (n = 3, 4) are inside this window. The irreversible 2H₂ + NiC₆₀ and reversible 3H₂ + NiC₆₀ interactions are characterised in terms of several theoretical parameters such as: (1) densities of states and projected densities of states, (2) pairwise and non-pairwise additivity, (3) infrared, Raman, and proton magnetic resonance spectra, (4) electrophilicity, and (5) statistical thermodynamic stability.     

EFFECT OF ATOMIC HYDROGEN ON THE ACETYLENE-ADSORBED Si(100)(2×1) SURFACE AT ROOM TEMPERATURE

High resolution electron energy loss spectroscopy, low energy electron diffraction and quadrupole maas spectrometer (QMS) have been employed to study the effect of atomic hydrogen on the acetylene-saturated pre-adsorbed Si(100)(2×1) surface and the surface phase transition at room temperature. It is evident that the atomic hydrogen has a strong effect on the adsorbed C₂H₂ and the underlying surface structure of Si. The experimental results show that CH and CH₂ radicals co-exist on the Si surface after the dosing of atomic hydrogen; meanwhile, the surface structure changes from Si(100)(2×1) to a dominant of (1×1). These results indicate that the atomic hydrogen can open C=C double bonds and change them into C-C single bonds, transfer the adsorbed C₂H₂ to C₂H_x(x = 3,4) and break the underlying Si-Si dimer, but it cannot break the C-C bond intensively. The QMS results show that some C₄ species axe formed during the dosing of atomic hydrogen. It may be the result of atomic hydrogen abstraction from C₂H_x which leads to carbon catenation between two adjacent C-C directs. The C₄ species formed are stable on Si(100) surfaces up to 1100 K, and can be regarded as the potential host of diamond nucleation.     

A statistical model for the product energy distribution in reactions leading to prompt dissociation

Direct dynamics calculations have been performed for three reactions: C₃H₈ + H → i-C₃H₇ + H₂, C₃H₈ + H → n-C₃H₇ + H₂, and C₂H₃ + O₂ → HCO + CH₂O. The fraction of the population for the radical products that promptly dissociates is computed. The results for C₃H₈ + H are qualitatively similar to previous results for C₃H₈ + OH, but the new results exhibit a slightly higher branching fraction for prompt dissociation products, owing to the fact that a greater fraction of the internal energy in the transition state ends up in the radical. For C₂H₃ + O₂ → HCO + CH₂O, the fraction of HCO that promptly dissociates is in excess of 99%. Consequently, the main product for C₂H₃ + O₂ at lower temperatures should be written as H + CO + CH₂O and not HCO + CH₂O. These results are then compared with four previous systems: CH₂O + H → HCO + H₂, CH₂O + OH → HCO + H₂O, C₃H₈ + OH → i-C₃H₇ + H₂O, and C₃H₈ + OH → n-C₃H₇ + H₂O. Based upon these seven system, several statistical models are presented. The goal of these statistical models is to predict the fraction of the transition state energy that ends up in the rovibrationally excited radical. On average, these statistical models provide an excellent prediction of product energy distribution. Consequently, these models can be used instead of costly trajectory simulations for predicting prompt radical dissociation for larger species.     

Dehydrogenation of acetylene and ethylene studied on clean and oxygen covered palladium surfaces

The interaction of acetylene and ethylene with a clean and oxygen covered Pd surface has been studied at a temperature of 473 K. The measurements were performed on a hydrogen sensitive Pd-MOS structure making it possible to obtain direct information on the dissociation of both hydrogen and oxygen containing species on a palladium surface. Desorption studies were also performed as well as ultraviolet photoelectron spectroscopy and work function measurements. The studies show that both acetylene and ethylene adsorb dissociatively at this temperature leaving mainly carbon on the surface. When an oxygen covered Pd surface is exposed to C₂H₂ or C₂H₄ carbon dioxide and water will be formed and desorb until the surface is oxygen free. In the case of acetylene the presence of preadsorbed oxygen does not block or prevent the C₂H₂ dissociation on the surface. For C₂H₄, a large preadsorbed oxygen coverage (⪆ 0.45) will have an impeding effect on the dissociation. The CO₂ desorption is oxygen coverage dependent contrary to the H₂O desorption. This is due to the fact that hydrogen has a large lateral mobility on the surface while carbon has not. Both the CO₂ and H₂O reactions are, however, due to the same type of mechanisms.     

Mössbauer effect studies on alkali tris (malonato) ferrates(III)

Mössbauer spectra of alkali tris(malonato) ferrates(III) i.e. M₃[Fe(C₃H₂O₄)₃].4H₂O(M=Li, Na, K, NH₄) at 298±2K display a single broad absorption band due to spin lattice relaxation effect. The isomer shift values indicate these complexes to be high spin with octahedral symmetry. The isomer shift shows a decreasing trend with the increase in electronegativity/polarizing power of the substituent cation (Li⁺, Na⁺, K⁺, NH₄ ⁺). A linear correlation between isomer shift values and the (Fe-O) stretching freguencies has also been observed.