Optical and conductive properties of AlSi-alloy/SiCp composites: application in modelling CO2 laser processing of composites

The optical properties—reflectivity, real part of the refractive index, absorption coefficient as well as the thermal and electrical conductivity of AlSi-alloy/SiC_p composite were measured. The optical parameters and both conductivities decreased with the increase of SiC_p particles volume in AlSi-alloy matrix. This decrease was almost linear for the volume fraction of SiC_p particle up to 10 vol% of the total mass of the composite. For the 15 vol% of SiC_p particles, the departure from linearity is connected with the presence of additional phases in AlSi-alloy/SiC_p composite materials. The measured temperature dependencies of optical reflectivity and electrical conductivity for AlSi-alloy/SiC_p 15 vol% are of metallic character. Modelling of the interaction of the CO₂ laser radiation with AlSi-alloy/SiC_p 15 vol% composite should allow to estimate the initiation time at which the surface composite reaches melting temperature.     

Do intramolecular halogen bonds exist? Ab initio calculations and crystal structures’ evidences

Cl···O intramolecular contacts are analysed here. Hence the Cambridge Structural Database (CSD) search was performed to find five-membered Cl–C=C–C=O pseudo-rings closed through Cl···O intramolecular contacts. Such rings were analysed and it was found that some of Cl···O distances are smaller than the corresponding sum of van der Waals radii. Additionally ab initio MP2/6-311++G(d,p) calculations and AIM analyses were carried out here on 3-chloropropenal and its fluoro derivatives to deepen the nature of intramolecular Cl···O interactions, some of findings may indicate that they are attractive and stabilizing ones. This paper is dedicated to Prof. T. M. Krygowski on the occasion of his 70th birthday     

IR-spectroscopic studies of the interaction of propylene and acrolein with a CoMoO4 catalyst

IR spectra of propylene and acrolein adsorbed at different temperatures on CoMoO₄ supported on MgO were recorded. Four different surface species were found: a -complex, an oxygen bonded carbonyl complex, acrylic acid and a carboxylate type complex. The mechanism of their transoformation is discussed.

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- CoMoO₄ MgO. , 4 : -, , , . .

     

C-H...N and C-H...S hydrogen bonds--influence of hybridization on their strength

Simple complexes connected through C-H...S and C-H...N interactions are investigated: CH4...NH3, C2H4...NH3, C2H2...NH3, CH4...SH2, C2H4...SH2, and C2H2...SH2. Ab initio and DFT calculations are performed (SCF, MP2, B3LYP) using different basis sets up to the MP2/aug-cc-pVQZ//MP2/aug-cc-pVDZ level of approximation. The Bader theory is applied since MP2/6-311++G(d,p) wave functions are used to find and to characterize bond critical points in terms of electron densities and their Laplacians. The influence of hybridization on the properties of C-H...S and C-H...N systems is also studied showing that the strength of such interactions increases in the following order: C(sp3)-H...Y, C(sp2)-H...Y, C(sp)-H...Y, where Y = S, N--it is in line with the previous findings on C-H...O hydrogen bonds. The results also show that CH4...SH2 and C2H4...SH2 complexes should be rather classified as van der Waals interactions and not as hydrogen bonds. The frequency associated with the C-H stretch of C(sp3)-H...S is blue-shifted.     

Derivative of the exponential mapping for infinite dimensional lie groups

It is proved that for infinite dimensional Lie groups in the sense of the differential calculus of Frölicher and Kriegl the derivative of the exponential mappings is given by the formula d(exp)(X)Y=d_exp(X)(e) ₀ ¹ Ad_exp(–tX) Y dt, where stands for the left translation ande is the neutral element.This work was supported by the Alexander von Humboldt-Stiftung.     

Attractive halogen–halogen interactions: F3CCl⋯FH and F3CCl⋯FCH3 dimers

The F₃CCl?FH and F₃CCl?FCH₃ dimers, which feature the halogen–halogen contacts, are investigated at MP2/6–311++G(d,p) and MP2/aug–cc–pVDZ levels of approximation. The binding energies of these complexes are found to be comparable to those of the weak hydrogen bonds. In both complexes the Cl?F are found to be significantly shorter than the sum of the corresponding van der Waals radii. The C–Cl?F contacts are also found to exhibit certain deviation from linearity. However, the energy differences between linear and bent structures are very small and primarily accounted for by electrostatic interactions between remote parts of the dimer. This indicates a high conformational flexibility of the halogen–halogen contacts and may help to explain the diversity of structural features in crystals formed by halogen-containing molecules. In both dimers the halogen–halogen interaction leads to certain shortening of the C–Cl electron accepting bond. This is accompanied by a small increase of the C–Cl stretching frequency. Hence, the two investigated dimers can possibly be classified as the blue-shifting halogen–halogen contacts.     

Hydration of GABA and of the GABA·ZN2+ complex: A Monte Carlo simulation study

With empirical and theoretical atom–atom potentials the GABA·nH₂O, n = 25, 192 and GABA·Zn²⁺ · nH₂O, n = 25, 50, 100 complexes are simulated at 298.15 K by the Monte Carlo technique. The results show that the carboxyl group of GABA coordinates six water molecules. Two geometries of the GABA·Zn²⁺ complex, corresponding to the “direct” and “through-water” interaction of Zn²⁺ with the carboxyl group of GABA were found. For the latter interaction a GABA·Zn²⁺ · 6H₂O complex was found whereas the hydration of the former interaction leads to a GABA·Zn²⁺ · 5H₂O complex. Here the carboxyl group of GABA displaces only one water molecule in the first hydration shell of Zn²⁺. Energetically the “direct” and “through-water” geometries seem to be competitive, the former being slightly favored.