Metastable modifications in mercury diiodide nanocrystals

The formation of the HgI₂ crystalline phase in pores of various porous matrices and on their surfaces was studied. Based on the analysis of the evolution of the HgI₂ optical spectra and electron and atomicforce microscopy data, it was shown that the formation of microcrystals of the stable red α modification is preceded by the formation and growth of particles of metastable yellow (β′) and orange modifications. The absorption edge of the β′ phase at T = 77 K is formed by excitonic transitions with an energy of ～2.7 eV. The Raman spectra of the β′ phase were compared to the spectra of known metastable yellow modifications.     

Interaction of counterpropagating discrete solitons in a nonlinear one-dimensional waveguide array

We experimentally investigate the interaction of counterpropagating discrete solitons in a one-dimensional waveguide array in photorefractive lithium niobate. While for low input powers only weak interaction and formation of counterpropagating vector solitons are observed, for higher input powers a growing instability results in discrete lateral shifting of the formed discrete solitons. Numerical modeling shows the existence of three different regimes: stable propagation of vector solitons at low power, instability for intermediate power levels leading to discrete shifting of the two discrete solitons, and an irregular temporal dynamic behavior of the two beams for high input power.     

Observation of higher-order solitons in defocusing waveguide arrays

We observe experimentally higher-order solitons in waveguide arrays with defocusing saturable nonlinearity. Such solitons can comprise several in-phase bright spots and are stable above a critical power threshold. We elucidate the impact of the nonlinearity saturation on the domains of existence and stability of the observed complex soliton states.     

Evidence of Vibrational-Induced Rotational Axis Switching for HD(12)C(16)O: New High-Resolution Analysis of the nu(5) and nu(6) Bands and First Analysis of the nu(4) Band (10-µm Region)

Using new high-resolution Fourier transform spectra recorded in Giessen in the 8-12 μm region, a more extended analysis of the nu(5) and nu(6) bands and the first high-resolution study of the nu(4) band of HDCO were performed. As pointed out previously [M. Allegrini, J. W. C. Johns, and A. R. W. McKellar, Can. J. Phys. 56, 859-864 (1978)], the energy levels of the 5(1) and 6(1) states are strongly coupled by A- and B-type Coriolis interactions. On the other hand, it appeared that weaker resonances involving the energy levels of the 4(1) state with those of the 5(1) and 6(1) states also had to be accounted for. Consequently, the calculation of the energy levels was performed taking into account the Coriolis-type resonances linking the energy levels of the {6(1), 5(1), 4(1)} resonating states. Because of the unusually strong Coriolis interaction between nu(5) and nu(6), a nonclassical behavior of the rotational levels of the 5(1) and 6(1) states was observed and it was necessary to use a new Hamiltonian matrix which possesses, as usual, both A- and B-type Coriolis operators in the 5(1) if 6(1) and 6(1) if 4(1) off diagonal blocks but differs from the classical reduced Hamiltonian which is used commonly for planar C(s)-type molecules. More precisely, it proved necessary to include non-orthorhombic terms in the expansion of the rotational Hamiltonian of the 5(1) and 6(1) states. According to the considerations developed by Watson [J. K. G. Watson, in "Vibrational Spectra and Structure," (J. Durig, Ed.), Chap. 1, Elsevier, Amsterdam, 1977], these non-orthorhombic operators which are not symmetry forbidden are usually removed for semirigid C(s)-type molecules by rotational contact transformations. In the present study, the occurrence of terms in {J(x), J(z)} in the expansions of the rotational Hamiltonians for the 5(1) and 6(1) states indicates that the inertial system of HDCO differs for each of the three {6(1), 5(1), 4(1)} resonating states. Therefore, HDCO becomes a good example of vibrational-induced rotational axis switching (VIRAS) which was already suggested as the mechanism responsible for the enhanced densities of coupled states observed in 2-fluoroethanol [H. Li, S. Erza, and L. A. Philips, J. Chem. Phys. 97, 5956-5963 (1992)]. Copyright 2000 Academic Press.     

Prospects for applications of electron beams in processing of gas and oil hydrocarbons

Physics of Atomic Nuclei - Waste-free processing of oil and oil gases can be based on electron-beam technologies. Their major advantage is an opportunity of controlled manufacturing of a wide range...     

Dissociative Excitation of the Even Quartet and Sextet Levels of the Manganese Atom by Collisions of Electrons with Manganese Diiodide Molecules

Dissociative excitation of even quartet and sextet levels of the manganese atom by electron collisions with manganese diiodide molecules was studied experimentally. Twelve excitation cross-sections for transitions from quartet levels and 23 cross-sections for transitions from sextet levels were measured at an incident electron energy of 100 eV. The optical excitation function (OEF) was recorded in the range of electron energies 0?100 eV for transitions originating at the 3d⁵4s4de⁶D_J levels. The potential channels of dissociative excitation in the range of low electron energies (E < 22 eV) were discussed.     

Observation of the Talbot effect for ultrasonic waves

The diffraction of ultrasonic radiation on an amplitude diffraction grating in the near-field area (Fresnel diffraction) has been studied. The effect of self-imaging of the grating (Talbot effect) has been detected for ultrasonic radiation at distances from the grating in the range from z = 0 to z = 2L _T, where L _T is the Talbot length. The fractional Talbot effect, i.e., the ultrasonic image of the grating with the period d/2, has been observed.     

Two-dimensional antiferromagnetic correlations in an La<Subscript>1.4</Subscript>Sr<Subscript>1.6</Subscript>(Mn<Subscript>0.9</Subscript>Co<Subscript>0.1</Subscript>)<Subscript>2</Subscript>O<Subscript>7</Subscript> single crystal

The temperature and field dependences of the magnetization, the electrical resistivity, and the magnetostriction of bilayer lanthanum manganite La_1.4Sr_1.6Mn₂O₇ single crystals and cobalt-doped La_1.4Sr_1.6(Mn_0.9Cu_0.1)₂O₇ are measured. The magnetostriction of the cobalt-doped compound increases as compared to the initial La_1.4Sr_1.6Mn₂O₇ compound, and the magnetization and the magnetoresistance of the former compound change substantially. Powder and single-crystal neutron diffraction patterns are used to detect ferromagnetic ordering in La_1.4Sr_1.6(Mn_0.9Co_0.1)₂O₇ at a temperature below T _C ~ 45(2) K, and this ordering coexists with antiferromagnetic correlations, which develop at temperatures below T _C ~ 80(5) K.     

Two-dimensional image magnification in an asymmetric-reflection X-ray microscope

The experimental results on the two-dimensional 20× magnification of an x-ray image obtained in an asymmetric-reflection x-ray microscope with the use of a laboratory source of x rays are discussed. The field of view is determined by the linear sizes of the detector and is equal to 0.5 × 0.5 mm in our experiment for an exposure time of 600 s.