X-ray photoelectron spectra and structure of polynuclear nickel complexes

Mono- and binuclear nickel complexes of different stoichiometry have been studied by X-ray photoelectron spectroscopy (XPS). The Ni2p, Ni3p, and N1s X-ray photoelectron spectra have been examined, and the role of a ligand in their formation has been determined. As distinct from a low-spin Ni(II) complex, the Ni2p spectra of high-spin Ni(II) compounds show strong satellite lines. For high-spin Ni(II) complexes, which have unpaired 3d electrons, the Ni2p _1/2-Ni2p _3/2 spin-orbit splitting is larger than that for a low-spin Ni(II) compound. The presence or absence of the satellite structure has made it possible to classify these complexes with regard to their magnetic properties. The difference between the Ni2p _3/2 and N1s binding energies has made it possible to estimate the covalence of the metal-ligand bond. The XPS results are consistent with X-ray crystallography data.     

Gas hydrates of argon and methane synthesized at high pressures: composition, thermal expansion, and self-preservation

For the first time, the compositions of argon and methane high-pressure gas hydrates have been directly determined. The studied samples of the gas hydrates were prepared under high-pressure conditions and quenched at 77 K. The composition of the argon hydrate (structure H, stable at 460-770 MPa) was found to be Ar.(3.27 +/- 0.17)H(2)O. This result shows a good agreement with the refinement of the argon hydrate structure using neutron powder diffraction data and helps to rationalize the evolution of hydrate structures in the Ar-H(2)O system at high pressures. The quenched argon hydrate was found to dissociate in two steps. The first step (170-190 K) corresponds to a partial dissociation of the hydrate and the self-preservation of a residual part of the hydrate with an ice cover. Presumably, significant amounts of ice Ic form at this stage. The second step (210-230 K) corresponds to the dissociation of the residual part of the hydrate. The composition of the methane hydrate (cubic structure I, stable up to 620 MPa) was found to be CH(4).5.76H(2)O. Temperature dependence of the unit cell parameters for both hydrates has been also studied. Calculated from these results, the thermal expansivities for the structure H argon hydrate are alpha(a) = 76.6 K(-1) and alpha(c) = 77.4 K(-1) (in the 100-250 K temperature range) and for the cubic structure I methane hydrate are alpha(a) = 32.2 K(-1), alpha(a) = 53.0 K(-1), and alpha(a) = 73.5 K(-1) at 100, 150, and 200 K, respectively.     

Infrared absorption and electron paramagnetic resonance studies of vinyl radical in noble-gas matrices

Vinyl radicals produced by annealing-induced reaction of mobilized hydrogen atoms with acetylene molecules in solid noble-gas matrices (Ar, Kr, and Xe) were characterized by Fourier transform infrared and electron paramagnetic resonance (EPR) spectroscopies. The hydrogen atoms were generated from acetylene by UV photolysis or fast electron irradiation. Two vibrational modes of the vinyl radical (nu7 and nu5) were assigned in IR absorption studies. The assignment is based on data for various isotopic substitutions (D and 13C) and confirmed by comparison with the EPR measurements and density-functional theory calculations. The data on the nu7 mode is in agreement with previous experimental and theoretical results whereas the nu5 frequency agrees well with the computational data but conflicts with the gas-phase IR emission results.     

Controlled diffractive optical elements containing a vanadium dioxide film

The principles of constructing optical devices on the basis of diffractive structures with a vanadium dioxide film for the control of radiation in the mid-IR range are analyzed. Methods are described for the practical implementation of such devices at λ=10.6 μm, and their response characteristics are calculated. It is shown that a contrast of 1:10⁷ can be attained in diffractive optical elements, and the actuation time of the elements when switched on by an intense laser beam can be shortened to tens of nanoseconds. Zh. Tekh. Fiz. 69, 91–96 (November 1999)     

Optimal recovery of linear functionals on sets of finite dimension

Suppose that X is a linear space and L ₁, …, L _n is a system of linearly independent functionals on P, where P ? X is a bounded set of dimension n + 1. Suppose that the linear functional L ₀ is defined in X. In this paper, we find an algorithm that recovers the functional L ₀ on the set P with the least error among all linear algorithms using the information L ₁ f, …, L _n f, f ∈ P.     

Nonlinear optical response from composites based on nanostructures consisting of an absorbing core and metallic shell near the plasmon resonance

The object of experimental study and numerical simulation is the nonlinear optical response from composites with nanoparticles consisting of a nonlinearly absorbing dielectric core and a metallic shell. It is shown that a small spread in nanoparticle sizes near the plasmon resonance may significantly change the dependence of the nonlinear optical response on the concentration of nanoparticles of each size.