Wave optics of Liesegang rings

Liesegang rings refract and reflect at the interface between the regions of the same gel but of different thickness. The incident and the refracted rings obey a refraction law analogous to the Snell's law of classical optics, with a reverse of the spacing coefficient being a counterpart of the refraction index. The wavelike behavior of the rings at the interface is explained by geometrical arguments derived from the Jablczynski's spacing principle, and is reproduced in numerical simulations based on a three-dimensional minimalistic version of the nucleation-growth model.     

Entropy of the Land Parcel Mosaic as a Measure of the Degree of Urbanization

Quantifying the urbanization level is an essential yet challenging task in urban studies because of the high complexity of this phenomenon. The urbanization degree has been estimated using a variety of social, economic, and spatial measures. Among the spatial characteristics, the Shannon entropy of the landscape pattern has recently been intensively explored as one of the most effective urbanization indexes. Here, we introduce a new measure of the spatial entropy of land that characterizes its parcel mosaic, the structure resulting from the division of land into cadastral parcels. We calculate the entropies of the parcel areas’ distribution function in different portions of the urban systems. We have established that the Shannon and Renyi entropies R0 and R1/2 are most effective at differentiating the degree of a spatial organization of the land. Our studies are based on 30 urban systems located in the USA, Australia, and Poland, and three desert areas from Australia. In all the cities, the entropies behave the same as functions of the distance from the center. They attain the lowest values in the city core and reach substantially higher values in suburban areas. Thus, the parcel mosaic entropies provide a spatial characterization of land to measure its urbanization level effectively.     

Gas-phase photofragmentation of tris(methyl vinyl ketone) tungsten(0) and the relationship to laser-assisted CVD of tungsten oxide thin films

The gas-phase laser-induced photofragmentation of tris(methyl vinyl ketone) tungsten(0) is studied, and the photoproducts are identified by time-of-flight mass spectroscopy. The initially populated excited electronic state of the complex is attributed to metal-to-ligand charge transfer by analysis of the electronic and preresonance Raman spectra. The major metal-containing photofragmentation products are W(+) and WO(+); smaller amounts of WC(+) and W(C(2)H(2))(+) are also observed. Intramolecular ligand coupling occurs, and dimeric products and their fragments are identified. Reaction pathways that explain the observed products are proposed. Thin films on silicon substrates are produced by laser-assisted chemical vapor deposition. The films consist of polycrystalline tungsten oxide with less than 10% tungsten carbide and are characterized by X-ray diffraction, SEM, and Auger electron spectroscopy. Relationships between the composition of the gas-phase photofragments and that of the solid films are discussed.     

Luminescence of the nonclassical homoleptic metal carbonyl complex [Rh(CO4]+

The nonclassical [Rh(CO)(4)](+) cation is luminescent at low temperature with a peak maximum at 19640 cm(-1) and a full-width at half-maximum of 2900 cm(-1). Both the solution absorption and low-temperature solid-state luminescence spectra of the [Rh(CO)(4)](1-Et-CB(11)F(11)) salt are reported. The cesium salt of the [1-Et-CB(11)F(11)](-) counterion is also luminescent (with a peak maximum at 22650 cm(-1)), but the emission maximum of [Rh(CO)(4)](+) is lower in energy. The Rh-C bond length changes of approximately 0.07 A in the excited state are calculated. The calculated bond length changes in the nonclassical [Rh(CO)(4)](+) ion are not very different from those in classical complexes.     

Effect of electron-ion bombardment on the growth of dielectric films in reactive sputtering

The mechanism by which electron — ion bombardment affects the growth of a silicon nitride film obtained by reactive sputtering in an apparatus based on a Penning discharge is investigated. The temperature and the degree of irradiation of the substrate are determined as functions of the distance from the substrate to the aperture in the anode. It is established that the presence or absence of bombardment leads to a difference in the formation of reactively sputtered silicon nitride films.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 12, pp. 11–15, December, 1976.The authors thank Yu. E. Kreindel' for his interest in the work and for useful discussions.     

Structures of photo-produced transient species

An overview of recent advances in the experimental measurements, theoretical interpretations, and practical applications of bond length and bond angle changes that occur after a molecule absorbs one or more photons is presented. “Gentle” changes are those in which the chemical bonds remain intact, but the lengths and angles increase or decrease. The bond length and bond angle changes that occur when a molecule absorbs a photon are measured by using a combination of electronic (emission and absorption) spectroscopy, resonance Raman spectroscopy, and the time-dependent theory of spectroscopy. “Catastrophic” changes are those in which multiple bonds are broken, leading to extensive photofragmentation. Luminescence spectroscopy is used to identify the transient fragments of metal-containing compounds that are precursors for laser assisted chemical vapor deposition.     

Amplification of changes of a thin film's macromolecular structure into macroscopic reaction-diffusion patterns

A reaction-diffusion process induced from a micronetwork geometry amplifies changes in the molecular structure of a thin gel film into macroscopic readout patterns. When the gel undergoes a helix-to-coil phase transition, the patterns formed by RD switch from symmetry-broken to symmetric ones. Theoretical analysis explains how the system reconfigures internally in response to mass transfer between the applied network and the probed film.