Reduced Doppler absorption profile in atomic and molecular beams

The formation of the Doppler absorption profile P(ν) upon optical excitation of particles in the volume of effusion or gas-dynamic atomic and molecular beams by laser light propagating in a direction orthogonal (reduced) to the beam axis is considered. The analytical expressions for P(ν) are obtained for different types of beams and the specific features of the reduced absorption profile are studied as functions of the beam parameters. The function P(ν) is shown to be considerably different from the standard Gaussian shape. It is demonstrated that the calculated absorption spectrum at the frequencies of the sodium resonance lines D _1,2 agrees well with experiment.     

Key intermediates in metallocene-and post-metallocene-catalyzed polymerization

The structures of intermediates formed upon the activation by methylaluminoxane (MAO) of a wide range of metallocene and post-metallocene catalysts of olefin polymerization were studied by ¹³C, ¹H, and ¹⁹F NMR. For all metallocenes considered (L₂ZrCl₂ and L₂TiCl₂), under conditions similar to real polymerization conditions (Al/Zr > 200), two types of intermediates were identified in the reaction solution, namely, heterodinuclear ion pairs [L₂ M(μ-Me)₂AlMe₂]⁺[Me-MAO]^? (III) and zwitterionic intermediates L₂ MMe⁺←Me-Al^?≡MAO (IV (M = Zr, Ti). The relative concentration of III increases with an increase in the Al/Zr ratio. In the post-metallocene/MAO catalytic systems, the reaction solution can be dominated either by heterodinuclear pairs of type III (bis(imino)pyridyl iron complexes) or by zwitterionic intermediates of type IV (half-titanocenes, complexes with restricted geometry). Both species III and species IV catalyze olefin polymerization. Both the species initiating polymerization, [L ₂ ^′ TiMe(S)]⁺[Me-MAO]^?, and the species responsible for chain growth, [L [L ₂ ^′ TiP]⁺[Me-MAO]^? (P is the polymer chain, and S is a solvent molecule), were characterized in the bis(phenoxyimine) titanium complex/MAO system.     

Synthesis, structures, and electrophysical properties of single crystals of solid solutions CdGeAs2:Mn(x) and Cd0.964Zn0.036GeAs2:Mn(x)

Single crystals of the solid solutions CdGeAs₂:Mn(x) and Cd_0.964Zn_0.036GeAs₂:Mn(x) have been grown by the vertical Bridgman method. An X-ray diffraction study has demonstrated that Cd_0.964Zn_0.036GeAs₂ (I), Cd_0.964Zn_0.036GeAs₂:Mn (1.5 wt%) (II), and Cd_0.964Zn_0.036GeAs₂:Mn (2.18 wt %) (III) retain the CdGeAs₂ structure (tetragonal system, space group I 2d). The unit cell parameters of the solid solutions are as follows: a = b = 5.934(1) ?, c = 11.219(2) ? for I; a = b = 5.919(1) ?, c = 11.204(2) ? for II; and a = b = 5.918(1) ?, c = 11.208(2) ? for III. Many of Mn atoms in II and III occupy interstitial sites in the crystal lattice. Selected electrical and magnetic properties of single crystals of CdGeAs₂:Mn(x) are discussed. Original Russian Text ? S.G. Mikhailov, K.K. Palkina, A.V. Molchanov, S.F. Marenkin, T.V. Filippova, L.I. Ochertyanova, I.S. Zakharov, A.V. Kochura, R. Laiho, E. Lahderanta, A. Lashkul, M.A. Shakhov, 2007, published in Zhurnal Neorganicheskoi Khimii, 2007, Vol. 52, No. 11, pp. 1879–1885.     

Palladium-catalyzed asymmetric phosphination. Scope, mechanism, and origin of enantioselectivity

Asymmetric cross-coupling of aryl iodides (ArI) with secondary arylphosphines (PHMe(Ar'), Ar' = (2,4,6)-R3C6H2; R = i-Pr (Is), Me (Mes), Ph (Phes)) in the presence of the base NaOSiMe3 and a chiral Pd catalyst precursor, such as Pd((R,R)-Me-Duphos)(trans-stilbene), gave the tertiary phosphines PMe(Ar')(Ar) in enantioenriched form. Sterically demanding secondary phosphine substituents (Ar') and aryl iodides with electron-donating para substituents resulted in the highest enantiomeric excess, up to 88%. Phosphination of ortho-substituted aryl iodides required a Pd(Et-FerroTANE) catalyst but gave low enantioselectivity. Observations during catalysis and stoichiometric studies of the individual steps suggested a mechanism for the cross-coupling of PhI and PHMe(Is) (1) initiated by oxidative addition to Pd(0) yielding Pd((R,R)-Me-Duphos)(Ph)(I) (3). Reversible displacement of iodide by PHMe(Is) gave the cation [Pd((R,R)-Me-Duphos)(Ph)(PHMe(Is))][I] (4), which was isolated as the triflate salt and crystallographically characterized. Deprotonation of 4-OTf with NaOSiMe3 gave the phosphido complex Pd((R,R)-Me-Duphos)(Ph)(PMeIs) (5); an equilibrium between its diastereomers was observed by low-temperature NMR spectroscopy. Reductive elimination of 5 yielded different products depending on the conditions. In the absence of a trap, the unstable three-coordinate phosphine complex Pd((R,R)-Me-Duphos)(PMeIs(Ph)) (6) was formed. Decomposition of 5 in the presence of PhI gave PMeIs(Ph) (2) and regenerated 3, while trapping with phosphine 1 during catalysis gave Pd((R,R)-Me-Duphos)(PHMe(Is))2 (7), which reacted with PhI to give 3. Deprotonation of 1:1 or 1.4:1 mixtures of cations 4-OTf gave the same 6:1 ratio of enantiomers of PMeIs(Ph) (2), suggesting that the rate of P inversion in 5 was greater than or equal to the rate of reductive elimination. Kinetic studies of the first-order reductive elimination of 5 were consistent with a Curtin-Hammett-Winstein-Holness (CHWH) scheme, in which pyramidal inversion at the phosphido ligand was much faster than P-C bond formation. The absolute configuration of the phosphine (SP)-PMeIs(p-MeOC6H4) was determined crystallographically; NMR studies and comparison to the stable complex 5-Pt were consistent with an RP-phosphido ligand in the major diastereomer of the intermediate Pd((R,R)-Me-Duphos)(Ph)(PMeIs) (5). Therefore, the favored enantiomer of phosphine 2 appeared to be formed from the major diastereomer of phosphido intermediate 5, although the minor intermediate diastereomer underwent P-C bond formation about three times more rapidly. The effects of the diphosphine ligand, the phosphido substituents, and the aryl group on the ratio of diastereomers of the phosphido intermediates Pd(diphos*)(Ar)(PMeAr'), their rates of reductive elimination, and the formation of three-coordinate complexes were probed by low-temperature 31P NMR spectroscopy; the results were also consistent with the CHWH scheme.     

Lower dimension vacuum defects in lattice Yang-Mills theory

We overview lattice data on d = 0, 1, 2, 3 dimensional vacuum defects in lattice four-dimensional SU(2) (SU(3)) gluodynamics. In all the cases, defects have a total volume which scales in physical units (with zero fractal dimension). In the case of d = 1, 2, the defects are distinguished by ultraviolet divergent non-Abelian action as well. This sensitivity to the ultraviolet scale allows us to derive strong constraints from the continuum theory on the properties of the defects, which turn out to be satisfied by the lattice data. We discuss a classification scheme of the defects which allows us to (at least) visualize the defect properties in a simple and unified way. A not-yet-checked relation of the defects to the spontaneous chiral symmetry breaking is suggested by the scheme. Finally, we present some arguments that the defects considered could become fundamental variables of a dual formulation of the theory.     

Catalytic phosphorylation of silicon-containing alcohols

Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 10, p. 2397, October, 1989.     

Catalytic phosphorylation of polyfluoroalkanols Communication 10. Catalytic phosphorylation of α-polyfluoroalkylbenzyl alcohols by diaryl chlorophosphates

Conclusions Irrespective of the structure of the alcohol and the reaction conditions, catalytic phosphorylation of -polyfluoroalkylbenzyl alcohols by diaryl chlorophosphates leads exclusively to -polyfluoroalkylbenzyl diaryl phosphates.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 4, pp. 878–882, April, 1985.