Structures of tin cluster cations Sn3(+) to Sn15(+)

We employ a combination of ion mobility measurements and an unbiased systematic structure search with density functional theory methods to study structure and energetics of gas phase tin cluster cations, Sn(n)(+), in the range of n = 3-15. For Sn(13)(+) we also carry out trapped ion electron diffraction measurements to ascertain the results obtained by the other procedures. The structures for the smaller systems are most easily described by idealized point group symmetries, although they are all Jahn-Teller distorted: D(3h) (trigonal bipyramid), D(4h) (octahedron), D(5h) (pentagonal bipyramid) for n = 5, 6, and 7. For the larger systems we find capped D(5h) for Sn(8)(+) and Sn(9)(+), D(3h) (tricapped trigonal prism) and D(4d) (bicapped squared antiprism) plus adatoms for n = 10, 11, 14, and 15. A centered icosahedron with a peripheral atom removed is the dominant motif in Sn(12)(+). For Sn(13)(+) the calculations predict a family of virtually isoenergetic isomers, an icosahedron and slightly distorted icosahedra, which are about 0.25 eV below two C(1) structures. The experiments indicate the presence of two structures, one from the I(h) family and a prolate C(1) isomer based on fused deltahedral moieties.     

Compact diode-pumped 1.1 kW Yb:YAG Innoslab femtosecond amplifier

We demonstrate a compact diode-pumped Yb:KGW femtosecond oscillator-Yb:YAG Innoslab amplifier master oscillator power amplifier (MOPA) with nearly transform-limited 636 fs pulses at 620 W average output power, 20 MHz repetition rate, and beam quality of M(x)(2) = 1.43 and M(y)(2) = 1.35. By cascading two amplifiers, we attain an average output power of 1.1 kW, a peak power of 80 MW, and a 615 fs pulse width in a single linearly polarized beam. The power-scalable MOPA is operated at room temperature, and no chirped-pulse amplification technique is used.     

Improvements on the direct SCF method

Three improvements on the direct self-consistent field method are proposed and tested which together increase CPU-efficiency by about 50%: (i) selective storage of costly integral batches; (ii) improved integral bond for prescreening; (iii) decomposition of the current density matrix into a linear combination of previous density matrices—for which the two-electron contributions to the Fock matrix are available—and a remainder ΔD, which is minimized; construction of the current Fock matrix only requires processing of the small ΔD which enhances prescreening.     

Theoretical investigation of structure and stability of oligomers of LiH,NaH, LiF,and NaF

The molecules Li_nH_n, Na_nH_n, Li_nF_n, n=1,..., 4, and NaF and Na₂F₂ are investigated by means of extended basis set SCF and CEPA-PNO computations. In analogy to the D _2h structure of dimers, it is found that trimers have a planar cyclic D _3h equilibrium geometry. For the tetramer of LiH and NaH, the D _4h structure has about the same energy as the 3-dimensional T _d structure, whereas the latter is definitely favoured for Li₄F₄. Correlation effects are investigated for the oligomerization of LiH and the dimerization of LiF. The effect of electron correlation on corresponding E turns out to be small (<4 kJ/mol), except for the case that the T _d tetramer is involved which has a rather large correlation energy.     

Angular Distortions at Tetracoordinate Carbon Planoid Configurations in Substituted Spiro[4.4]nonanes

The configuration of the spiro centre in polycyclic compounds containing a spiro[4.4]nonane substructure is analyzed in terms of symmetry coordinates. As revealed by X-ray structures of such compounds, the local distortions around the quaternary C-atom are dominated by a decrease of the ring-bond angles at the spiro centre and a twist of one ring relative to the other. The planoid deformations given by the planarization index P_C are comparatively small for spiro[4.4]nonanes, which contain either no additional bridges between the rings or only α,β′–or β,β′-polymethylene bridges. This indicates that the local strain in the spiro C(C)₄ fragments is rather small.     

Planarization of Tetracoordinate Carbon Atom. Synthesis of 13-oxa-14-oxo-pentacyclo [5.5.2.1.04,15010,15]pentadecane,a bridged ‘tetraquinacane’ preliminary communication

Structural aspects of planoid deformation of tetracoordinate carbon atom, particularly those in annulenes with central carbon atom are discussed. [12] Annulene 11 with central carbon atom is proposed as compound with strong planoid deformation around the internal carbon centre. The synthesis of a saturated precursor 15 is described.     

Isomerisierung der Bis(triphenylphosphin)platin(0)-Komplexe von Bicyclo[4.2.1]non-1-en und Bicyclo[4.2.1]non-1(8)-en

Isomerization of the Bis(triphenylphosphine)platin(0) Complexes of Bicyclo[4.2.1]non-1-ene and Bicyclo[4.2.1]non-1(8)-ene Isomrisation of the Bredt-Olefins 3 and 7 as the bis (triphenylphosphine)-Pt(0) complexes 1 and 8 , respectively, has been observed. The bridgehead-olefin 3 as well as the bicyclic olefins 4 , 5 and 6 have also been isomerized with catalytical amounts of (ethylene)bis(triphenylphosphine)platinum(0) ( 2 ).