Outermost Bands Research Articles

The influence of the bromine atom Cooper minimum on the photoelectron angular distributions and branching ratios of the four outermost bands of bromobenzene.

Angle resolved photoelectron spectra of the X̃(2)B1, Ã(2)A2, B̃(2)B2, and C̃(2)B1 states of bromobenzene have been recorded over the excitation range 20.5-94 eV using linearly polarized synchrotron radiation. The photoelectron anisotropy parameters and electronic branching ratios derived from these spectra have been compared to theoretical predictions obtained with the continuum multiple scattering approach. This comparison shows that ionization from the 8b2 orbital and, to a lesser extent, the 4b1 orbital is influenced by the Cooper minimum associated with the bromine atom. The 8b2 and 4b1 orbitals are nominally bromine lone-pairs, but the latter orbital interacts strongly with the π-orbitals in the benzene ring and this leads to a reduced atomic character. Simulations of the X̃(2)B1, B̃(2)B2, and C̃(2)B1 state photoelectron bands have enabled most of the vibrational structures appearing in the experimental spectra to be assigned. Many of the photoelectron peaks exhibit an asymmetric shape with a tail towards low binding energy. This asymmetry has been examined in the simulations of the vibrationally unexcited peak, due mainly to the adiabatic transition, in the X̃(2)B1 state photoelectron band. The simulations show that the asymmetric profile arises from hot-band transitions. The inclusion of transitions originating from thermally populated levels results in a satisfactory agreement between the experimental and simulated peak shapes.

Objective Analysis of Hyperreflective Outer Retinal Bands Imaged by Optical Coherence Tomography in Patients With Stargardt Disease.

To develop and apply an objective algorithm for analyzing outer retinal layers imaged by spectral-domain optical coherence tomography (SD-OCT) in patients with Stargardt disease (STGD1). Horizontal macular B-scans were acquired from 20 visually normal controls and 20 genetically confirmed stage 1 STGD1 patients. The number of outer retinal bands was quantified using a semiautomated algorithm that detected bands using the second derivative of longitudinal reflectivity profiles. The present analysis focused on the three outermost bands, currently associated with the ellipsoid zone (EZ), cone outer segment interdigitation zone (IZ), and retinal pigment epithelium (RPE) complex. The RPE complex and EZ bands were detected throughout the B-scan in all controls. The RPE complex was detected throughout the B-scan in all patients, but was atrophic appearing in some locations. The EZ band was detected only outside the central lesion. Interdigitation zone band detection varied as a function of eccentricity for both groups, with detection for controls being highest in the para- and perifovea and lowest in the fovea and near periphery. In patients, the IZ band was generally not present in the fovea or para- or perifovea due to the central lesion. Outside of the lesion, the IZ band was detected in 26% of patients (mean detection across the near periphery), which was approximately half of the detection in controls. An objective approach for quantifying the number of outer retinal OCT bands found reduced IZ detection in STGD1 patients. This occurred even outside the central lesion, demonstrating an inability to image the IZ, possibly due to enhanced RPE reflectivity or abnormal outer retinal structure.

Yes — Coral calcification rates have decreased in the last twenty-five years!

Outermost bands of corals were under-estimated in De'ath et al. (2009), and we have identified the cause of this problem as incomplete formation of some of the outermost bands. Correcting for this problem reduces our previous estimate of the decline in calcification over the period 1990–2005 from 14.2% to 11.4%. The claim that ontogenic effects account for part of the observed decline in calcification is false since (1) the hypothesised ontogenic effect was not present in colonies pre-1985, and (2) the decline in calcification is observable in the short cores that largely determine the decline, and are not subject to ontogenic effects. The adjusted decline of 11.4% (0.76% yr − 1 ) remains high and suggests a bleak future for corals of the GBR due to climate change.

Mineralogical, chemical, and crystallographic properties of supergene jarosite-group minerals from the Xitieshan Pb-Zn sulfide deposit, northern Tibetan Plateau, China

Supergene jarosite-group minerals are widespread in weathering profiles overlying Pb-Zn sulfide ores at Xitieshan, northern Tibetan Plateau, China. They consist predominantly of K-deficient natrojarosite, with lesser amounts of K-rich natrojarosite and plumbojarosite. Electron microprobe (EMP) analyses, scanning electron microcopy (SEM) investigation, and X-ray mapping reveal that the jarosite-group minerals are characterized by spectacular oscillatory zoning composed of alternating growth bands of K-deficient and K-bearing natrojarosite (K2O >1 wt.%). Plumbojarosite, whenever present, occurs as an overgrowth in the outermost bands, and its composition can be best represented by K0.29Na0.19Pb0.31Fe2.66Al0.22(SO4)1.65(PO4)0.31(AsO4)0.04(OH)7.37. The substitution of monovalent for divalent cations at the A site of plumbojarosite is charge balanced by the substitution of five-valent for six-valent anions in XO4 at the X site. Thermogravimetric analysis (TGA) of representative samples reveal mass losses of 11.46 wt.% at 446.6 °C and 21.42 wt.% at 683.4 °C due to dehydroxylation and desulfidation, respectively. TGA data also indicate that the natrojarosite structure collapses at 446.6 °C, resulting in the formation of NaFe(SO4)2 and minor hematite. The decomposition products of NaFe(SO4)2 are hematite and Na2SO4. Powder X-ray diffraction (XRD) analyses show that the jarosite-group minerals have mean unit-cell parameters of a = 7.315 A and c = 016.598 A. XRD and EMP data support the view that substitutions of Na for K in the A site and full Fe occupancy in the B site can considerably decrease the unit-cell parameter c, but only slightly increase a. The results from this study suggest that the observed oscillatory zoning of jarosite-group minerals at Xitieshan resulted mainly from substitutions of K for Na at the A site and P for S at the X site.

An experimental and theoretical study of the valence shell photoelectron spectrum of bromochlorofluoromethane

The complete valence shell photoelectron spectrum of bromochlorofluoromethane (CHFClBr), covering the binding energy range ∼10–50 eV, has been recorded using synchrotron radiation and the observed structure has been interpreted using ionization energies and relative spectral intensities computed using the third-order algebraic-diagrammatic-construction (ADC(3)) scheme for the one-particle Green's function and the outer valence Green's function (OVGF) method. The theoretical results demonstrate that the inner valence region of the photoelectron spectrum is dominated by satellite structure. Angle-resolved photoelectron spectra, recorded at selected excitation energies, have enabled the orbital assignments for the outer valence bands to be confirmed. The four outermost photoelectron bands, ascribed to the two pairs of orbitals associated with the nominally chlorine and bromine lone-pairs, exhibit characteristic angular distributions. The photon energy dependent variations in the relative photoelectron band intensities provide additional support for the orbital assignments.

Calcium fertilization increases the concentration of calcium in sapwood and calcium oxalate in foliage of red spruce

Calcium cycling plays a key role in the health and productivity of red spruce forests in the northeastern US. A portion of the flowpath of calcium within forests includes translocation as Ca 2+ in sapwood and accumulation as crystals of calcium oxalate in foliage. Concentrations of Ca in these tree tissues have been used as markers of environmental change due to acidic deposition or forest management practices. We compared the effects of Ca fertilization treatment on Ca concentration in wood and Ca and oxalate (Ox) concentration in foliage at two locations with different initial concentrations of Ca in the soil. We found greater amounts of Ca in wood from the high-Ca location than from the low-Ca location. Ca concentration was greater in wood formed in the 1970s than for wood formed in the 1980s, the outermost decadal band in these samples. The Ca-treatment was detected as an increased concentration of Ca in the 1970s and 1980s decadal bands. We also found that variation in Ca and Ox in foliage was essentially stoichiometric. The appearance and response to chemical tests of crystals in foliage were consistent with identification as calcium oxalate. The increased Ca in wood after Ca-treatment of the soil supports the use of dendrochemistry of base cations to investigate environmental change. However, differences in Ca concentration between the two outermost decadal bands of wood illustrate that internal processes of translocation and storage also affect Ca concentration. Calcium oxalate production in foliage diverts carbon from ordinary biosynthesis and energy-yielding processes. This sequestration, shedding, and decomposition of foliage may represent a significant and under-recognized contribution to carbon and Ca cycling.

Response of Bdellovibrio and Like Organisms (BALOs) to the Migration of Naturally Occurring Bacteria to Chemoattractants

A dual culture-based and non-culture-based approach was applied to characterize predator bacterial groups in surface water samples collected from Apalachicola Bay, Florida. Chemotaxis drop assays were performed on concentrated samples in an effort to isolate predator bacteria by their chemotactic ability. Yeast extract (YE) and casamino acids (CA) proved to be strong chemoattractants and resulted in three visibly distinct bands; however, dextrose, succinate, pyruvate, and concentrated cells of Vibrio parahaemolyticus P5 as prey did not elicit any response. The three distinct bands from YE and CA were separately collected to identify the chemotactic microbial assemblages. Plaque-forming unit assays from different chemotaxis bands with P5 as prey indicated 5- (CA) to 10-fold (YE) higher numbers of predator bacteria in the outermost chemotactic bands. Polymerase chain reaction-restriction fragment length polymorphism and 16S rDNA sequencing of clones from different chemotaxis bands resulted in identification of Pseudoalteromonas spp., Marinomonas spp., and Vibrio spp., with their numbers inversely proportional to the numbers of predators-i.e., Bdellovibrio spp. and Bacteriovorax spp-in the chemotaxis bands. This study indicates that predatorial bacteria potentially respond to high densities of microbial biomass in aquatic ecosystems and that chemotaxis drop assay may be an alternate culture-independent method to characterize predatorial bacterial guilds from the environment.

Methanol: A critical test of intensity models for molecular soft X-ray emission

We have used methanol as a critical test case for calculations of molecular soft X-ray emission spectra. Energies and intensities calculated from self-consistent multi-configurational wavefunctions optimized for each separate state have been used to theoretically analyze the emission spectra via the evaluation of dipole electronic transitions at different levels of approximation. The one-center intensity model is found to describe the X-ray intensities of methanol well. Results confirm that for main soft X-ray transitions the largest correction to the one-center model is given by the relaxation effect, while the effect of correlation does not change the overall results from ΔSCF calculations to any appreciable extent. A previously known ambiguity concerning the two outermost bands in the carbon spectrum is investigated here although the present results do not conclusively explain the discrepancy between the theoretical intensities corresponding to these transitions and the experimental data.

Skeletal growth markers in the deep-sea brittle starsOphiura ljungmani andOphiomusium lymani

Growth bands have been found in the calcitic vertebral arm ossicles of the commonly occurring deep-sea brittle starsOphiura ljungmani Wyville Thomson andOphiomusium lymani (Lyman) (Echinodermata: Ophiuroidea) trawled from the Rockall Trough (N.E. Atlantic) at 2 200 and 2 900 m depth from 1973 to 1982. InOphiura ljungmani, the study of ossicle microstructure by SEM shows that growth bands reflect differences in stereom porosity and surface relief, similar to that previously found amongst shallow-water brittle stars. The pattern inOphiomusium lymani was much less clear from the microstructure, but could be revealed by heating the ossicle to 450 °C and “clearing” in xylene. The bands showed up as fine, translucent rings separated by more opaque, wider zones, perhaps reflecting differences in organic material incorporated within the calcite. Both growth-banding patterns probably reflect an annual cycle in skeletal growth rate. On this assumption, the number and spacing of the banding in the two species indicates contrasting growth strategies. WithOphiura ljungmani, a rather regular annual growth increment and perhaps shorter lifespan (up to ca. 10 yr) thanOphiomusium lymani is indicated. The latter shows a relatively wide spacing of early bands, followed by tight clustering of the outermost bands corresponding to adult sizes. This growth pattern is characteristic of species “escaping” from predation by rapid growth to relatively large adult size. AdultO. lymani probably grow slowly, some perhaps reaching 20 yr of age. Growth curves were fitted to size-at-age corresponding to measurements of the size and ordering of growth bands. These corroborate age structure previously estimated from analysis of size frequencies in time series from the stations sampled in the present study. Such skeletal growth markers should be of value in analysis of the demography of deep-sea populations.

Vibronic and electronic states of doubly charged H2S studied by Auger and charge transfer spectroscopy and by a b i n i t i o calculations

Doubly ionic states of H2S are investigated by means of Auger and double charge transfer spectroscopy. From the kinetic energy distribution of H− ions arising from double charge-transfer of protons impinging on gaseous H2S several singlet state energies of H2S2+ have been resolved in the 30 to 50 eV energy region. The most intense experimental peak is narrow proving that the doubly ionized ground state is stable or quasi-stable. The LII,IIIVV Auger electron spectrum exhibits a number of well-defined structures which exhibit vibrational fine structure in the outermost bands. The assignments of the charge transfer states and of the Auger bands are given by ab initio MCSCF electronic structure calculations. We also present vertical double ionization energies, optimized geometries and normal coordinate analysis for the neutral, single and double ionized states. A vibrational analysis of the resolved Auger bands is carried out by employing a recently derived theory for vibrational decay of short-lived core hole states in polyatomic molecules.

Acquisition and processing of angle-resolved photoelectron spectra excited with focussed polarized resonance radiation

A system for the acquisition of angle-resolved photoelectron spectra is described. The sample gas is excited by VUV resonance radiation, which is polarized to about 95% using a fully rotatable fourfold reflection polarizer. One of the mirrors is toroidally shaped in order to focus the radiation into the sample gas cell. This design gives count rates comparable to those obtained by an unpolarized source, and at a greatly reduced background level. A computer controlled system has been developed to automate the recording procedure. It allows for simultaneous recordings of the spectra at the different angular settings, thus eliminating the effects of intensity drifts. Details of calibration procedures and data processing, including spectrum analysis, are given along with a discussion of the accuracy of the results. To illustrate the performance, measured β-values for the main components of the four outermost photoelectron bands in the Hel excited spectrum of CO 2 are presented.

Ultraviolet photoelectron spectroscopy of the valence bands of solid NH3, H2O, CO2, SO2and N2O4

A photoelectron study is presented for the outermost bands of the molecular solid phase of: NH3, H2O, CO2, SO2 and N2O4. Both gaseous and solid phase spectra were acquired with 40.81 eV ultraviolet photoelectron spectroscopy (UPS) techniques (except for gaseous N2O4). For the solids, charging effects were measured systematically and appropriate corrections made. Some valence band shifts were observed, as well as significant changes in valence band widths, between the gas and solid phase spectra, but the shifts were in general much less than those measured by previous workers. These results are interpreted in terms of molecular solid bonding and relaxation effects.

Electronic structure of the valence bands of SnCl 2 and SnBr 2 studied by ultraviolet photoelectron spectroscopy

A photoelectron study of the outermost bands of solid-phase SnCl 2 and SnBr 2 using 40.81 eV photons is reported. The main features of the spectra are successfully interpreted in terms of molecular orbital theory for the appropriate isolated molecules.

The electronic structure of the valence bands of solid NH 3 and H 2O studied by ultraviolet photoelectron spectroscopy

The results of a photoelectron study using ultraviolet 40.81 eV photons (UPS) of the outermost bands of the molecular solids NH 3 and H 2O are reported. The binding energies, the energy separation, the band widths and the branching ratio of the two outermost bands of solid NH 3 are found not to be significantly different from the 3a l and 1e molecular orbital states of the gaseous NH 3 UPS spectrum. This implies that hydrogen bonding has not produced any significant change in the electronic structure of the valence bands of solid NH 3. Because of a much smaller intermolecular hydrogen bond length in solid H 2O compared to that in solid NH 3, the hydrogen bond does, however, produce a significant change in the valence bands of H 2O on solidification, and because of the orbital geometry it predominantly affects the 3a l molecular orbital state.

Crystal-field splitting in strongly ionic solids studied by photoelectron spectroscopy

The splittings of the outermost 4d, 5d and 5p bands of some strongly ionic solids have been measured using 40.81 eV ultraviolet photoelectron spectroscopy. The level splitting of the solids with initial state metal ion configurations of 4d10 and 5p6 are interpreted in terms of crystal field effects on the final state 4d9 and 5p5 ions respectively. The level splitting for solids with an initial state metal ion configuration of 5d10 6s2 are found to agree with the free ion spin-orbit splitting and this is attributed to the screening of the crystal-field symmetry by the outer two 6s electrons.