Synthesis and Characterization of [Br3][MF6] (M=Sb,Ir), as well as Quantum Chemical Study of [Br3]+ Structure,Chemical Bonding,and Relativistic Effects Compared with [XBr2]+ (X=Br,I, At,Ts) and [TsZ2]+ (Z=F,Cl, Br,I, At,Ts)

[Br₃][SbF₆] and [Br₃][IrF₆] were synthesized by interaction of BrF₃ with Sb₂O₃ or iridium metal, respectively. The former compound crystallizes in the orthorhombic space group Pbcn (No. 60) with a=11.9269(7), b=11.5370(7), c=12.0640(6) Å, V=1660.01(16) ų, Z=8 at 100 K. The latter compound crystallizes in the triclinic space group P (No. 2) with a=5.4686(5), b=7.6861(8), c=9.9830(9) Å, α=85.320(8), β=82.060(7), γ=78.466(7)°, V=406.56(7) ų, Z=2 at 100 K. Both compounds contain the cation [Br₃]⁺, which has a bent structure and is coordinated by octahedron-like anions [MF₆]⁻ (M=Sb, Ir). Experimentally obtained cell parameters, bond lengths, and angles are confirmed by solid-state DFT calculations, which differ from the experimental values by less than 2 %. Relativistic effects on the structure of the tribromonium(1+) cation are studied computationally and found to be small. For the heaviest analogues containing At and Ts, however, pronounced relativistic effects are found, which lead to a linear structure of the polyhalogen cation.     

Superdiffusion and viscoelastic vortex flows in a two-dimensional complex plasma

Viscoelastic vortical fluid motion in a strongly coupled particle system has been observed experimentally. Optical tracking of particle motion in a complex plasma monolayer reveals high grain mobility and large scale vortex flows coexistent with partial preservation of the global hexagonal lattice structure. The transport of particles is superdiffusive and ascribed to Lévy statistics on short time scales and to memory effects on the longer scales influenced by cooperative motion. At these longer time scales, the transport is governed by vortex flows covering a wide spectrum of temporal and spatial scales.     

The Crystal Structure of MnF3 Revisited

We correct the crystal structure of MnF₃, of which the space group was reported as monoclinic C2/c (no. 15) with a = 8.9202, b = 5.0472, c = 13.4748 Å, β = 92.64°, V = 606.02 ų, Z = 12, mS48, T not given, likely 298 K. In the structure model proposed here, we use a unit cell of one third of the former volume. The ruby red crystals of MnF₃ were synthesized by a high-pressure/high-temperature method, where MnF₄ was used as a starting material. As determined on a single crystal, MnF₃ crystallizes in the monoclinic space group I2/a (no. 15) with a = 5.4964(11), b = 5.0084(10), c = 7.2411(14) Å, β = 93.00(3)°, V = 199.06(7) ų, Z = 4, mS16, T = 183(2) K. The crystal structure of MnF₃ is related by a direct group-subgroup transition to the VF₃ structure-type. We performed quantum chemical calculations on the crystal structure to allow the assignment of bands of the obtained vibrational spectra.     

Synthesis and Characterization of Manganese Tetrafluoride β-MnF4

The crystal structure of β-MnF₄ has finally been elucidated. It crystallizes in the non-centrosymmetric space group R3c, no. 161, hR360, with the lattice parameters a = 19.390(3), c = 12.940(3) Å, V = 4213.3(14) ų, Z = 72, T = 100 K. It is a 4a × 4a superstructure of the VF₃ (FeF₃) structure type. The Mn atoms are coordinated octahedron-like by F atoms, of which two are bound terminal, while the other act as μ-bridging F atoms to other Mn atoms forming a three-dimensional infinite network structure which can be described by the Niggli formula ³_∞[MnF_4/2F_2/1]. Voids on the metal sites, which are occupied in the VF₃ structure, are grouped together in the shape of a “star” with approximate D_3h symmetry. We prepared β-MnF₄ photochemically according to the literature and obtained a phase-pure powder as evidenced by X-ray diffraction at room temperature. The lattice parameters are a = 19.566(3), c = 12.984(2) Å, V = 4304(1) ų. IR and Raman spectra recorded on the powder show that β-MnF₄ has also been obtained free of moisture, HF, and O₂⁺ containing compounds, however MnF₃ is likely present as a magnetic impurity. We observe thermal decomposition of MnF₄ to MnF₂ and not MnF₃.     

Underbarrier interference

Quantum tunneling through a two-dimensional static barrier becomes unusual when a momentum of an electron has a tangent component with respect to a border of the prebarrier region. If the barrier is not homogeneous in the direction perpendicular to tunneling a fraction of the electron state is waves propagating away from the barrier. When the tangent momentum is zero a mutual interference of the waves results in an exponentially small outgoing flux. The finite tangent momentum destroys the interference due to formation of caustics by the waves. As a result, a significant fraction of the prebarrier density is carried away from the barrier providing a not exponentially small penetration even through an almost classical barrier. The total electron energy is well below the barrier.     

The role of negative ions in experiments with complex plasma

The influence of negative ions on the state of an rf gas-discharge dusty (complex) plasma containing electronegative gaseous impurities was investigated. A simple one-dimensional argon-discharge model allowing for the impurity-induced plasmachemical reactions was taken as an example to show that the addition of even a minor amount of molecular oxygen changes appreciably the plasma composition and plasma transport properties, as well as the microparticle charges. In turn, these changes have a strong effect on the microparticle force balance and on the formation of various dusty structures in the discharge.