Long-range State Research Articles

HREELS INVESTIGATION OF CO AND POTASSIUM CO-ADSORPTION ON Fe(110)

Co-adsorption of CO and potassium on Fe(110) is investigated by HREELS. We find three CO adsorption states, with different C-O stretching frequencies. When θk=0.03, the three loss peaks are ascribed to three kinds of interactions i.e., short-range, medium-range and long-range interaction. When θk = 0.06, the long-range interaction adsorption state disappears, but the short-range state dominats. All C-O stretching frequencies shift to higher wavenum-ber with the increasing of CO exposure. CO-Fe loss peak disappears with the increasing of potassium atoms on the surface.

Electronic spectra of CH + involving “long-range” states

Previously reported “near-threshold” laser photofragment spectra of CH + near 540 nm are interpreted as arising from charge-transfer electronic transitions between levels lying just below the C + ( 2P)+H( 2 dissociation asymptote and a weakly bound long-range electronic state which correlates to the C ( 3P)+H + dissociation limit. The shallow well of the upper state is determined principally by the long-range attractive ion-induced-dipole and charge-quadrupole interactions between the carbon atom and the proton and shorter-range repulsive behaviour. In our interpretation, low-energy C + ions are detected following radiative decay of laser-excited CH + to continua just above the lowest dissociation limit. Experimental and theoretical evidence for this bound-bound-free process is presented. The characteristics of long-range weakly bound states and the role of non-adiabatic interactions near to dissociation are discussed. The possibility that previously observed laser photofragment spectra near 350 nm arise from a similar origin is considered.

New electronic transitions in the CH+molecule

The identification of new electronic transitions in the CH+ molecule is described. Laser photofragment spectra previously recorded near 540 nm arise from electronic transitions between triplet energy levels which lie just below the C+(2 P) + H(2 S) dissociation limit and a weakly-bound long-range triplet state which correlates to the C(3 P) + H+ dissociation asymptote. In addition, it is proposed that at least part of the reported CH+ photofragment spectrum near 350 nm is due to transitions between analogous near-threshold singlet levels and weakly-bound long-range singlet states which correlate to C(1 D) + H+. A bound-bound-free mechanism is invoked to explain the observations in which laser excitation is followed by radiative decay to the continua just above the lowest dissociation asymptote. This results in the formation of C+ ions which are detected

Occurrence of long-range helical spin ordering in Dy-Y multilayers (invited)

The magnetic ordering of highly perfect single-crystal multilayer films of alternate layers of magnetic Dy and nonmagnetic Y prepared by molecular beam epitaxy has been studied by neutron diffraction. Results on a series of films with Dy thicknesses of approximately 16 atomic planes (≊45 Å) and Y thicknesses ranging from 10 to 22 planes have confirmed the existence of long-range helimagnetic ordering of the Dy 4f spins which is propagated through the intervening Y layers in phase coherence. The propagation vectors in both Dy and Y layers have been calculated from the wave vector of the magnetic satellites and the intensity of the bilayer harmonics. The propagation vector for Dy decreases continuously with temperature, while that in the Y is temperature independent and equal to 0.31 Å−1. The nature of the ordering and the noninteger multiple of π for the phase change of the propagation wave vector across the Y, suggests that the mechanism of long-range coupling is a conduction band spin-density wave in both Y and Dy stabilized by the 4f spins of the Dy. No intrinsic ferromagnetic transition is observed due to the clamping effect of the Y layers on the Dy magnetostriction. The application of a field along basal plane directions destroys the helical order and produces a ferromagnetic state with all spins aligned along the field direction. The moment in the induced ferromagnetic state is 10 μB, while that calculated for the zero-field helical state ranges from 7.5μB to 9.5μB for different samples, suggesting a possible static disorder of some Dy spins superimposed on the intrinsic long-range helical state.

Long-range incommensurate spin state in dilute YGd alloys

Neutron diffraction measurements on single-crystal Y(2.2% Gd) reveal that the alloy orders ( T N = 6.64 K) with a long-range periodic incommensurate spin structure, with moments in the basal plane and a propagation vector of 0.28 c. The temperature dependence of the Gd moment derived from the integrated neutron intensities is similar to that of Gd metal.

Shape memory effect and phase transitions in TiNi alloys electron microscopy studies of the phase transitions after thermomechanical treatment

Diffuse scattering is observed in Ti–53 to 56 wt% Ni alloys after high-temperature treatment (within temperature range 650 to 800 °C) which can be explained as the result of the short-range order arrangement of the structural vacancies. During aging within the temperature range 400 to 650 °C this short-range order state transforms to a long-range order state which can be interpreted as a long-period superstructure with lattice constant a = 1.58 nm (x-phase). The orientation relationships between β-phase and x-phase are: {111} 〈321〉β ‖ {111} 〈110〉x. The quantity of the x-phase formed during aging at intermediate temperatures is limited (≈ 15%). The x-phase particles arrange in two to three directions and look like thin elongated lentiform plates coherent with the parent β-phase matrix. These particles are inherited partly by the martensite formed near room temperature. [Russian Text Ignored].

A cluster model for the transition from the short-range order to the long-range order state in f.c.c. based binary systems and its study by means of electron diffraction

The 'transition' state in binary f.c.c. based systems is assumed to be characterized by the repetition of interpenetrating polyhedral clusters of atoms occupying lattice sites and having the macroscopic composition. Its mathematical formulation leads to relations between the short-range order (SRO) coefficients, which in turn impose conditions on the distribution in reciprocal space of the diffuse intensity as observed in electron diffraction patterns. It follows that for a given cluster type the diffuse intensity can only differ from zero along certain surfaces or curves. The effect of deviations from the ideal composition of the clusters is briefly discussed. The theory allows an explanation of available diffraction data on certain binary alloys in the initial stages of ordering i.e. in the 'transition' state between the SRO state and the long-range order (LRO) state.

Irreversible effects on visible light on the retina: role of vitamin A.

Diffuse retinal irradiation by visible light produces in the rat the death of visual cells and pigment epithelium. Typically, cage illumination of 1500 lux from fluorescent light through a green filter leads to severe damage when continued for 40 hours. Vitamin A deficiency protects against this damage but experiments show that retinol released by light from rhodopsin is probably not the toxic agent. Protection against light damage depends on a long-range state of cell adaptation to light itself. The normal diurnal cycle of light and dark seems to be the essential factor in controlling visual cell viability and susceptibility.

Wisconsin's State Planning Program

Editor's Note. Comprehensive master planning is emerging as the goal of American municipal governments, large and small. But at the state level the same all-inclusive effort is still only a dream for most of the fifty state governments. A few noteworthy exceptions appear on the horizon as reflected in the current literature. One of them, Wisconsin, appears to be well launched on an ambitious, long-range state planning program which may prove to be a pioneer, pace-setting project. Land Economics has been giving considerable space to various city planning programs, also to discussions of the pros and cons of the economic base theories, and to allied factors essential to comprehensive planning. It seems appropriate that this journal, published on the campus of the University of Wisconsin, invite the State Planning Director to spell out the progress to date and prospects as he sees them for Wisconsin's comprehensive master planning program.

Short-Range Order Coexisting with Long-Range Order in Cu3Au

Diffuse x-ray scattering from a single crystal of Cu3Au was observed at T/Tc≅0.995 where the long-range order parameter S equals 0.85. By annealing at low temperatures, nearly perfect order was obtained. A difference curve yields the diffuse scattering attributable to short-range order coexisting with the long-range order state of S=0.85. Analysis of the diffuse intensity in absolute units gives values of the first three short-range order coefficients. The first coefficient is found to be close to the perfect order value: α1=0.33. Within experimental error the observed coefficients fit both the Cowley theory and a random long-range order model equally well.