The electronic structure of small sodium clusters

Ab initio molecular orbital calculations using the STO3-21G basis set has been carried out for the cluster series Na _n ⁺ , Na _n , and Na _n ^– (wheren=2–7). The basis set is shown to be reliable compared with more extensive basis sets at the Hartree-Fock level. Thirty-one optimized structures are reported and discussed, many of which (especially for the anions) have not been considered. The STO3-21G//STO3-21G calculations suggest that for most of the species the optimum geometries are planar. In particular, the optimized structures for the anionic species should provide a starting point for more sophisticated configuration interaction calculations.     

In-situ HEED structure analysis of AlNx films grown by the simultaneous use of a radical beam source and ICB technique

A reactive ionized cluster beam technique (RICB) which was composed of a conventional ICB source and a radical beam source has been used to deposit stable and metastable polycrystalline AlN_x (0x1) films. Using in-situ high energy electron diffraction (HEED) at grazing incidence geometry, crystallographic properties such as structure, preferred orientation and interplanar dspacing values were determined and the relation to deposition parameters investigated. It could be shown that the simultaneous use of the ICB technique and a radical beam source to separately control the kinetic energy of the Al ions and the dissociation rate of molecular nitrogen, allows AlN films to be deposited with variable composition and crystal structures. In-situ HEED used in the transmission mode is an effective tool to investigate the crystallography of growing compound films such as AlN_x.     

Die Struktur des Pentaphenyldisilans

Structure of Pentaphenyldisilane For the first time Pentaphenyldisilane was prepared by Gilman and Goodman. It is produced by the reaction of Ph₃SiLi with Ph₂ClSiH. The crystal structure presents an ideally staggered conformation. The distance d(Si? Si) = 235.7 pm corresponds to a normal single bond length. This emphasizes the complete relief of the central Si? Si bond by the insertion of only one hydrogen atom.     

The collisional quenching of O2*(1Δg) by NO and CO2

Rate coefficients for the collisional quenching of O₂^*(¹Δ_g) by NO and CO₂ at 2–8 torr and 300 K have been determined. k_NO = (2.48 ± 0.23) × 10^?17 cm³ molecule^?1 s^?1 and

= (2.56 ± 0.12) × 10^?18 cm³ molecule^?1 s^?1.     

The electronic structure of molecules by a many-body approach : II. Ionization potentials one-electron properties of pyridine and phosphoridine

The valence ionization potential (IPs) of pyridine and phosphoridine are studied by an ab initio many-body approach which includes the effects of electron correlation and reorganization beyond the Hartree-Fock approximation. For pyridine the order of the first three IPs is a₂(π), a₁(n), b₁(π), but the IPs of the a₂ and a₁ orbitals are so close together that they have to be regarded as identical in binding energy, which is also concluded from experiment. Whereas for pyridine the ordering of the IPs calculated in the HF approximation is incorrect, it is correct for phosphoridine. For this latter molecule the first three ionization potentials are due to ionization from the b₁(π), a₂(π), and a₁(n) orbitals. Several one-electron properties are calculated and compared with experimental and other theoretical data. The localized molecular orbitals are discussed as well.     

FRIEDEL-CRAFTS-Reaktionen der C7-, C8- und C12-Cycloalkane mit Kohlenmonoxid

The reaction of cycloheptane, cyclooctane, and cyclododecane with carbon monoxide under pressure in the presence of anhydrous aluminium chloride has been investigated. Cycloheptane leads to acetylcyclohexane and trans-2-methyl-cyclohexane carboxylic acid as main products. Cyclooctane yields 3- and trans-4-acetyl-methylcyclohexane and various dimethylcyclohexane carboxylic acids. From cyclododecane a mixture of numerous ketones has been obtained besides a mixture of acids.     

Current-induced coupling between conductance channels in membranes

The driven system of conducting channels in a nerve membrane is investigated. A current flow generates a coupling between the channels: the current through a channel is influenced by the presence of other conducting channels via the deformation of the equipotential surfaces within the media adjacent to the membrane. We derive an integral equation for the membrane voltageV(s) (s in the membrane plane) and solve it for different membrane conductance distributions(s) including models for stochastic distributions of conducting channels.V(s) is a nonlinear functional of(s). The system of coupled channels is compared with an Ising model. The system exhibits a multi-channel interaction which can be characterized by two different rangesd _int andD ₁. For a mean channel distanced ₀d _int interaction effects are negligible, and ford ₀D ₁ all channel-voltages are equal and thus represent a mean-field for the channels. Increasing conductivity of the medium decreasesd _int and increasesD ₁. With experimental data on sodium channels in nerve membranes we find:d _intd ₀, i.e. a 50% decrease of the channel-voltages by the interaction, andD ₁10³10⁴ d ₀, which indicates mean-field behaviour of the channels. In a subsequent paper we shall treat the statistics of channels which open and close stochastically under the influence of the local membrane voltage.     

Konstruktion von Fundamentallösungen für Convolutoren in roumieuschen Ultradistributionsräumen

Fundamental solutions in a space D(M_p) of Roumieu ultradistributions are constructed for convolutors f whose Fourier transform is slowly decreasing. The solutions are of exponential growth if satisfies a stronger condition. These results include a constructive proof of the known existence theorem of Chou. For families of convolutors our method yields solutions which depend continuously on parameters.     

Laser-supported detonation waves and material processing with pulsed CO2 lasers

Summary The processing of metals with short CO₂ laser pulses is strongly influenced by an air-breakdown plasma (LSD-wave). Material removal is possible only if the duration of this LSD-wave can be kept short compared with the length of the laser pulse. A simple model for the calculation of is developed allowing the derivation of an analytic formula and leading to good agreement with experimental data.

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Zusammenfassung Die Bearbeitung von Metallen mit kurzen CO₂-Laserpulsen wird von einem Air-Breakdown-Plasma (LSD-Welle) stark beeinflusst. Materialabtragung ist nur dann möglich, wenn die Dauer dieser LSD-Welle wesentlich kürzer ist als die gesamte Pulslänge. Es wird ein einfaches Modell für die Berechnung von entwickelt. Daraus lässt sich ein analytischer Ausdruck herleiten. Die Resultate stehen in guter Uebereinstimmung mit experimentellen Daten.