Infrared spectra of molecular chlorine complexes with acetylene,ethylene and propylene at low temperatures

Infrared spectra of molecular complexes of C₂H₂Cl₂, C₂D₂Cl₂, C₂H₄Cl₂, C₂D₄Cl₂, and C₃H₆Cl₂ were obtained after simultaneous slow deposition of both components on the cooled window of an optical cryostat at 75°K. Chlorine addition reactions to the multiple bond start in these systems at 90–100°K.     

The calculation of molecular and cluster auger spectra

The work of Asaad and Burhop and of Shirley on atoms is Shown to form the basis of a useful theory for the analysis of molecular core-valence-valence Auger spectra. If the static relaxation term of Shirley is neglected, the theory requires only a single SCF calculation on the neutral molecule. Since this approximation seems justified for the class of itinerant holes, the theory not only pemits the interpretation of the spectra of molecules considerably larger than previously analyzed, but potentially the spectra of chemisorbed molecules from cluster calculations. Theory and experiment are compared for the carbon KW spectra ofCH₄, C₂H₂, C₂H₄ and CH₃OH.     

Localized states in molecular auger spectra

The influence of the degree of localization of the two final holes on the Auger spectra of a simple diatomic molecule is analysed in detail and cases where such effects may be observed experimentally are discussed. The results are compared with studies of the valence band Auger spectra of solids.     

Effects of electron polarization on the auger spectra of lanthanum oxide

The SCF-X scattered-wave method has been used in the quasirelativistic approximation to calculate the energies and relative intensities of the transitions in the M₄, ₅N₄,₅V and N₄,₅VV Auger electron spectra AES of lanthanum in the LaO ₆ ^9– cluster, which is taken as a model for crystalline La₂O₃. A study has been made of the influence of relaxation effects on the AES. The AES intensity distribution is largely determined by the population of the 4f states of La in the initial state of the Auger process. The AES for lanthanum in La₂O₃ are interpreted from the calculations.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 22, No. 2, pp. 207–210, March–April, 1986.     

Radio-frequency gas-discharge polymerization of ethylene and acetylene

The results of an experimental study of ethylene and acetylene polymerizations under conditions of high-frequency gas-discharge plasma are described. As established by mass spectroscopy, polymerization of ethylene in a plasma is accompanied by partial dissociation to hydrogen and acetylene which in turn polymerizes. When acetylene is used as monomer, its polymerization is rapid and is not accompanied by dissociation or other side reactions. Acetylene polymerization proceeds entirely in the gas phase to give a dispersed amorphous product with a stoichiometric C:H = 1:1.     

Quantum-chemical modeling of ethylene and acetylene adsorption on gold clusters

The interaction of ethylene and acetylene molecules with planar (2D) and nonplanar (3D) gold clusters Au _n (n = 10, 12, 20) was studied by the density functional theory (DFT) method. The coordination of hydrocarbons at the vertices, edges, and fragments of the Au₃ cluster was shown to form π, di-σ, and μ type complexes, respectively. The standard Gibbs energy and the C-C bond length of the hydrocarbon change during its adsorption in the series μ > di-σ > π complexes. The highest selectivity in adsorption of acetylene relative to that of ethylene was achieved on Au₁₂ (3D) and Au₂₀ (2D) clusters.     

Low-energy electron-impact excitation spectra of acetylene

Low-energy (0–5 V above threshold) electron-impact excitation spectra and a transmission spectrum are presented for acetylene. It is found that excitation via temporary negative ions plays a dominant role. Assignments are suggested for the observed electronic excitation processes.     

Arrhenius constants for the reactions of ozone with ethylene and acetylene

The kinetics of ozonation of C₂H₄ and C₂H₂ have been studied in the gas phase from ?40 to ?95°C (C₂H₄) and +10 to ?30°C (C₂H₂). The O₃ concentrations were near 10^?4 M, and the hydrocarbons were present in 2- to 25-fold excess. A few experiments with propylene were also carried out. The reactions were followed by observing the rate of decay of O₃ absorption at 2537 Å. Reaction stoichiometries and effects of added O₂ were investigated. The second-order rate constant for C₂H₄ was log k(M^?1 sec^?1) = (6.3 ± 0.2) – (4.7 ± 0.2)/θ (θ = 2.3RT). The rate was independent of the presence of excess O₂. Rate measurements for C₃H₆ were less accurate because of aerosol interference. Combined with room temperature measurements of other workers, the C₃H₆ rate constant was log k(M^?1 sec^?1) = (6.0 ± 0.4) – (3.2 ± 0.6)/θ. The C₂H₂ rate constant was log k(M^?1 sec^?1) = (9.5 ± 0.4) – (10.8 ± 0.4)/θ. In the case of C₃H₆ the major product was propylene ozonide. Ethylene did not yield the ozonide, and the products of the O₃–C₂H₄ and O₃–C₂H₂ reactions were not identified. Pre-exponential factors for the olefin reactions are consistent with a five-membered ring transition state formed by 1,3 dipolar cycloaddition of O₃. For C₂H₂, however, the much higher observed A factor suggests a different mechanism. Possible transition states for the O₃–C₂H₂ reaction are discussed.     

Calculations on the electronic spectra of anilino,phenoxyl and benzyl radicals

The electronic spectra of benzyl, anilino and phenoxyl have been calculated, using two well known SCF-MO methods. Good agreement is found with experiment in all instances. However, the calculations still cannot explain the red shift produced by the addition of an extra electron to benzyl.

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Zesummenfassung Die Elektronenspektren des Benzyl-, Anilino- und Phenoxylradikals sind mit Hilfe zweier wohlbekannter SCF-MO-Methoden berechnet worden. Die Übereinstimmung mit den Experimenten ist überall gut. Die Rechnungen können jedoch nicht die Rotverschiebung erklären, die beim Hinzufügen eines Elektrons zum Benzylradikal erzeugt wird.

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Resume On calcule les spectres électroniques des radicaux benzyle, anilino et phénoxyle par deux méthodes SCF-MO bien connues. L'accord avec l'expérience est bon partout. Cependant, ces calculs n'expliquent pas l'effet bathocrome de l'addition d'un électron au benzyle.

     

Calculations on the spectra and nonlinear third-order optical susceptibility of c70

The equilibrium geometry and UV-visible spectra of C₇₀ were examined using semiempirical INDO /2 and INDO /CI methods. The results obtained are in good accord with experimental results. On the basis of correct electronic spectra, calculations of the nonlinear third-order optical susceptibility (γijkl) of C₇₀ were performed using the INDO /SDCI method combined with a sum-over-states expression. The calculated value for <γ> (-2 ω, ω, ω, O) is 0.882 × 10^?33 esu (ω = 1.91 μm), which is in good agreement with observation. © 1994 John Wiley & Sons, Inc.     

Dynamic screening and interference effects in X-ray and auger emission spectra

We study X-ray and Auger emission spectra from initial core holes which are strongly influenced by many-electron effects of giant Coster-Kronig type. In particular we include the dynamics of relaxation and decay processes in a systematic manner both in the spectral function of the initial-state core-hole (self-energies) and in the emission matrix elements (vertex corrections). We explicitly demonstrate that proper dressing of the emission matrix element guarantees that the sum of all branching ratios become unity (conservation of probability). Finally, we present numerical calculations of the 4p ^?1?4d ^?1 X-ray emission spectrum in Xe, illustrating the importance of a systematic treatment of self-energy and vertex corrections.     

EOM/Propagator ionization potentials: Effect of an extended operator manifold on the predicted valence-shell ionization spectra of ethane,ethylene, and acetylene

The orthogonalized direct diagonalization (ODD ) method is used to predict the valence-shell ionization spectra for the series of hydrocarbons ethane (C₂H₆), ethylene (C₂H₄), and acetylene (C₂H₂) within an EOM /propagator formalism. Both (a) third-order and (b) higher-order (with h₅ terms in the excitation operator manifold) calculations are presented in order to illustrate the effect of the extended operator manifold on the predicted valence-shell spectra. It is shown that the major effect of the h₅ manifold is concentrated in its “occupied” part. Along with a general shifting of the main lines for outer valence ionizations to lower values (together with a slight reduction in pole strength), it is found that the effect of the h₅ manifold in the inner valence region is dependent on the system being studied.     

Equivalent cores and transition potentials for ESCA shifts and auger electron spectra

A simple derivation of transition potentials, based on equivalent cores and the Hellman-Feynman theorem, is given. It relates to previously given transition potential models with the potential at the ionisation site, which has a modified nuclear charge, thus including relaxation.     

Heats of formation of triplet ethylene, ethylidene, and acetylene

Heats of formation of the lowest triplet state of ethylene and the ground triplet state of ethylidene have been predicted by high level electronic structure calculations. Total atomization energies obtained from coupled-cluster CCSD(T) energies extrapolated to the complete basis set limit using correlation consistent basis sets (CBS), plus additional corrections predict the following heats of formation in kcal/mol: DeltaH0r(C2H4,3A1) = 80.1 at 0 K and 78.5 at 298 K, and DeltaH0t(CH3CH,3A' ') = 86.8 at 0 K and 85.1 at 298 K, with an error of less than +/-1.0 kcal/mol. The vertical and adiabatic singlet-triplet separation energies of ethylene were calculated as DeltaES-T,vert = 104.1 and DeltaES-T,adia = 65.8 kcal/mol. These results are in excellent agreement with recent quantum Monte Carlo (DMC) values of 103.5 +/- 0.3 and 66.4 +/- 0.3 kcal/mol. Both sets of computational values differ from the experimental estimate of 58 +/- 3 kcal/mol for the adiabatic splitting. The computed singlet-triplet gap at 0 K for acetylene is DeltaES-T,adia(C2H2) = 90.5 kcal/mol, which is in notable disagreement with the experimental value of 82.6 kcal/mol. The heat of formation of the triplet is DeltaH0tC2H2,3B2) = 145.3 kcal/mol. There is a systematic underestimation of the singlet-triplet gaps in recent photodecomposition experiments by approximately 7 to 8 kcal/mol. For vinylidene, we predict DeltaH0t(H2CC,1A1) = 98.8 kcal/mol at 298 K (exptl. 100.3 +/- 4.0), DeltaH0t(H2CC,3B2) = 146.2 at 298 K, and an energy gap DeltaES-T-adia(H2CC) = 47.7 kcal/mol.     

Effect of acetylene on the γ-radiation-induced polymerization of ethylene

The effects of acetylene on the γ-radiation-induced polymerization of ethylene were studied from the viewpoint of the gaseous products and polymer structure. The experiments were carried out under a pressure of 400 kg/cm²; the temperature was 30°C; the does rate was 1.1 × 10⁵ rad/hr; and the acetylene content was 0–20%. The solid polymer was obtained in the polymerization of ethylene containing 2.2% acetylene, while the monomer containing 19.7% acetylene gave a yellowish viscous oil. The polymer yield and molecular weight decreased remarkably with acetylene content. The main gaseous product was hydrogen, and trace amounts of butane, butene-1, butadiene-1,3, and benzene and its derivatives were also observed. The rate of formation of hydrogen was almost independent of acetylene content and there was no difference in acetylene contents before and after the irradiation was found. The infrared spectra of the polymers showed the presence of vinylidene, trans-vinylene, and terminal vinyl unsaturations, 1,4-disubstituted benzene, and carbonyl groups. The contents of trans-vinylene, terminal vinyl, and methyl groups increased with acetylene content, and that of vinylidene was independent of acetylene content. The monomer reactivity ratios of ethylene and acetylene were evaluated as 45.5 and 66.0, respectively. On the basis of the results, the effects of acetylene on the γ-radiation-induced polymerization of ethylene were discussed.     

Raman spectra from ethylene and deuterated ethylene chemisorbed on a silica-supported nickel catalyst

The Raman spectra of ethylene and deuterated ethylene chemisorbed on silica-supported nickel have been measured in the frequency range 50–3400 cm^?1. At room temperature, a Raman spectrum is observed which corresponds to ethylene chemisorbed under dehydrogenation and it is rather similar to the spectrum of chemisorbed acetylene. For a comparison therefore, the Raman spectra of acetylene and deuterated acetylene were also measured. In addition, the vibrational spectrum of chemisorbed benzene was recorded. At temperatures T ? 200 K, ethylene is found to be associatively chemisorbed without dehydrogenation.The vibrations observed are described in the approximation of a surface molecule with covalent bonding to two or three surface nickel atoms. The symmetry seems to be slightly distorted C_2v or C_s. The vibrational spectrum is discussed with respect to a metal- surface selection rule. In order to improve the reliability of the assignments for localized vibrational modes, a normal coordinate analysis and a force constant calculation have been done for chemisorbed acetylene.     

A comparative ab initio study of ethylene,acetylene and benzene

Ground state properties have been calculated by use of a medium-sized Gaussian basis set and comparison with other bases has been made. Contraction to double-zeta of a comparatively small basis is found to be superior to a large set of primitive Gaussians contracted to minimal basis. Molecular optimization is not important for double-zeta bases. Inclusion of a balanced set of polarization functions is essential in all cases studied. Population analysis gives a certain insight in molecular properties but contour maps are found to be significantly superior. This is demonstrated on bonding properties of corresponding orbitals within the series. In case of benzene Slater's energyband plot is shown to be useful for classifying bonding properties.