Ab initio CCSD(T) and MRD-CI study of excited states and the electronic spectrum of linear C5

Large-scale ab initio coupled cluster and multi-reference configuration interaction calculations (MRD-CI) are carried out to determine the equilibrium geometry and the vertical electronic spectrum of linear C₅⁺. Contrary to prior theoretical estimates we find three low-lying states within an energy range of 0.3 eV: ²Σ_u⁺, ²Σ_g⁺ and ²Π_g and a symmetric arrangement of nuclei. Transitions from ²Σ_u⁺ to these low-lying states are dipole-allowed; sizeable oscillator strengths are computed for the ²Π⁺_g←X²Σ_u⁺ transition at 2.62 eV and the ²Σ_g←X²Σ_u⁺ transition at 3.36 eV and should give a guide to spectroscopic identification of linear C₅⁺.     

[(α‐Imino)enamino]phosphonium salts from propyne iminium salts and a phosphorane imine

Propyne iminium triflates R¹C(N⁺R³R⁴)CCR² CF₃SO readily react with Ph₃PNPh to form 1:1 adducts which formally result from a metathetical addition of the phosphorane imine across the triple bond of the alkyne. These adducts are best described as enamino‐phosphonium salts or iminio‐substituted phosphorus ylides. The configuration of these salts has been determined from NMR data and an X‐ray crystal structure analysis of salt 3h . The base‐induced elimination of the PPh₃ substituent from enamino‐phosphonium salt 3a was studied. © 2005 Wiley Periodicals, Inc. Heteroatom Chem 16:437–446, 2005; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/hc.20131     

Heat transfer considerations in design of a batch tube reactor for biomass hydrolysis

Biologic conversion of inexpensive and abundant sources of cellulosic biomass offers a low-cost route to production of fuels and commodity chemicals that can provide unparalleled environmental, economic, and strategic benefits. However, low-cost, high-yiel technologies are needed to recover sugars from the hemicellulose fraction of biomass and to prepare the remaining cellulose fraction for subsequent hydrolysis. Uncatalyzed hemicellulose hydrolysis in flow-through systems offers a number of important advantages for removal of hemicellulose sugars, and it is believed that oligomers could play an important role in explaining why the performance of flow-through systems differs from uncatalyzed steam explosion approaches. Thus, an effort is under way to study oligomer formation kinetics, and a small batch reactor is being applied to capture these important intermediates in a closed system that facilitates material balance closure for varying reaction conditions. In this article, heat transfer for batch tubes is analyzed to derive temperature profiles for different tube diameters and assess the impact on xylan conversion. It was found that the tube diameter must be <0.5 in, for xylan hydrolysis to follow the kinetics expected for a uniform temperature system at typical operating conditions.     

Limitations of computing time savings in variational multirate integrations

For systems that contain slow and fast dynamics, variational multirate integration schemes are used. These schemes split the system into parts which are simulated using a time grid consisting of micro and macro nodes. This leads to computing time savings, however not unlimited, for a certain number of micro steps per macro step the computing time is minimal. To find a relation between this minimum computing time and the number of variables in the system, the computing time for the Fermi-Pasta-Ulam problem (FPU) is measured for different numbers of masses and different numbers of micro steps. In addition, the numerical convergence of the variational multirate integration is shown for the FPU. (© 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

A structure preserving approach to the simulation of non-smooth dynamics

The investigated multibody dynamics involve perfectly elastic, partially elastic and perfectly plastic contacts and a structure preserving approach is used in forward dynamics and optimal control simulations. The applied mechanical integrator is based on a constrained version of the Lagrange-d’Alembert principle and it represents exactly the behaviour of the analytical solution concerning the consistency of momentum maps and symplecticity: it is called symplectic momentum scheme. To guarantee the geometric exactness during the establishing or releasing of contacts, the non-smooth problem is solved including the computation of the contact configuration, time and force, instead of relying on a smooth approximation of the contact problem via a penalty potential. (© 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Photoinitiators with Functional Groups 9: New Derivatives of Covalently Linked Benzophenone-amine Based Photoinitiators

As it had been shown that some covalently bound benzophenone (BP)—phenylglycine derivatives act as remarkable monomolecular Type II photoinitiators for radical polymerization, structural variations were investigated. The influence of the linking position between BP and the coinitiator and the coinitiator structure itself were considered. Furthermore, water soluble monomolecular BP-glycine based PIs were developed. While in UV-spectroscopy similar absorption behavior were found for all compounds, photo-DSC experiments revealed that derivative 2 has the most effective constitution.     

Ultrathin-Layer Chromatography (UTLC)

Ultrathin-layer chromatography (UTLC) differs from high-performance thin-layer chromatography (HPTLC) and from thin-layer chromatography (TLC) in two basis things: the layer thickness, and the migration distances of the analytes. UTLC has a monolithic or a nanostructured stationary silica gel phase bound directly to the glass plates. Layer thickness in UTLC is 10 μm, instead of 100–250 μm in HPTLC. Migration distances are in the range of 1–3 cm for UTLC, instead of 8–10 cm for HPTLC. Therefore, the major advantages of UTLC over HPTLC and TLC are the shorter development times and higher separation efficiency and sensitivity. Moreover, separations on UTLC plates require smaller reagent and sample volumes. However, the UTLC plates are very difficult to manage with the TLC and HPTLC equipment currently available. Therefore, the next challenge in this area is the development of an inexpensive solution with appropriate instrumentation (sensitive optical scanners and sample application systems). UTLC had been used for separations of many compounds, e.g., pharmaceutically active ingredients, pesticides, plasticisers, natural products, and other chemical substances.     

Theoretical study of cyclopropene and its C3H4 isomers

Ab initio SCF MO and CI calculations are reported for the three C₃H₄ isomers cyclopropene, methylacetylene and allene. The closed shell nature of each of these molecules allows for a good theoretical comparison of their stabilities and ionization potentials by the SCF method. It is pointed out that cyclopropene differs from most 22 electron systems with a triatomic skeleton in that it possesses a non-linear equilibrium structure; this fact is related to its unusual ground state electronic configuration, which corresponds to a highly excited state in simple triatomics such as CO₂ and N ₃ ^– . The electronic spectrum and the methylene rotational barrier of cyclopropene are also investigated.

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Zusammenfassung Es wird über Ergebnisse von ab initio SCF-MO- and CI-Berechnungen der drei C₃H₄-Isomere Cyclopropen, Methylacetylen und Allen berichtet. Da alle drei Moleküle closed shell Charakter besitzen, ist ein guter theoretischer Vergleich ihrer relativen Stabilität sowie ihrer Ionisierungspotentiale mit Hilfe von SCF-Rechnungen möglich. Weiterhin wird darauf hingewiesen, daß sich Cyclopropen von den meisten dreiatomigen Systemen (Wasserstoffe werden nicht gezählt) mit 22 Elektronen dadurch unterscheidet, daß seine schweren Atome nicht in einer linearen Kette angeordnet sind. Diese Tatsache steht im Zusammenhang mit seiner ungewöhnlichen Elektronenkonfiguration im Grundzustand, welche bei einfachen dreiatomigen Molekülen wie CO₂ und N ₃ ^– einem hoch angeregten Zustand entspricht. Das Elektronenspektrum sowie die Methylen-Rotationsbarriere von Cyclopropen werden ebenfalls untersucht.

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Résumé Calculs ab initio SCF MO et CI pour les trois isomères C₃H₄; cyclopropène, methylacetylène et allène. Ces molécules étant à couches complètes, la méthode SCF permet une bonne comparaison de leurs stabilités et de leurs potentiels d'ionisation. On fait remarquer que le cyclopropène diffère de la plupart des systèmes à 22 électrons à squelette triatomique en ce qu'il présente une structure d'équilibre non linéaire; ce fait est relié à la configuration électronique particulière de l'état fondamental qui correspondrait à un état hautement excité dans des molécules triatomiques simples comme CO₂ et N ₃ ^– . Le spectre électronique et la barrière rotationnelle du méthylène dans le cyclopropène ont aussi été étudiés.

     

On the structure of (Ti, Al)N-PVD coatings

Thin films of the ternary system Ti---Al---N, produced by PVD magnetron sputtering, show excellent wear-resistance and microhardness. It could be proved that a composition of the form (Ti, Al)N grows up a TiN lattice. Up in a 30 at.% aluminium can be solved in this lattice with decreasing lattice parameters. The ternary H-phase Ti₂AlN has not been deposited as the deposition temperatures are too low.