Showing papers by "Environmental Molecular Sciences Laboratory published in 1999"
TL;DR: In this paper, a multiphoton microscopy based on coherent anti-Stokes Raman scattering with near-infrared ultrashort laser pulses is demonstrated for chemical and biological samples with high sensitivity, high spatial resolution, noninvasiveness, and three-dimensional sectioning capability.
Abstract: A multiphoton microscopy based on coherent anti-Stokes Raman scattering is accomplished with near-infrared ultrashort laser pulses. We demonstrate vibrational imaging of chemical and biological samples with high sensitivity, high spatial resolution, noninvasiveness, and three-dimensional sectioning capability. {copyright} {ital 1999} {ital The American Physical Society}
1,547 citations
Environmental Molecular Sciences Laboratory1, Yale University2, University of California, Davis3, Los Alamos National Laboratory4, University of Wyoming5, Texas A&M University6, École Polytechnique Fédérale de Lausanne7, Colorado State University8, California Institute of Technology9, Johns Hopkins University10, IBM11
TL;DR: This poster presents a probabilistic procedure to constrain the number of particles in the response of the immune system to the presence of Tau.
Abstract: Reference LPI-ARTICLE-1999-017View record in Web of Science Record created on 2006-02-21, modified on 2017-05-12
966 citations
TL;DR: In this article, a near-field fluorescence imaging using femtosecond laser pulses of proper polarization is presented. But the technique is not suitable for near field imaging, and the spatial resolution is limited to 20 nm.
Abstract: We present a new scheme for near-field fluorescence imaging using a metal tip illuminated with femtosecond laser pulses of proper polarization. The strongly enhanced electric field at the metal tip ( $\ensuremath{\approx}15\mathrm{nm}$ end diameter) results in a localized excitation source for molecular fluorescence. Excitation of the sample via two-photon absorption provides good image contrast due to the quadratic intensity dependence. The spatial resolution is shown to be better than that of the conventional aperture technique. We used the technique to image fragments of photosynthetic membranes, as well as $J$-aggregates with spatial resolutions on the order of 20 nm.
714 citations
TL;DR: In this paper, a spin-polarized DFT calculation was used to estimate the probability of an adsorbed O2 molecule following the molecular and dissociative channels in a 1:1 ratio with each vacancy site.
Abstract: vacancy population), presumably due to dissociative filling of the vacancy sites in a 1:1 ratio. Above a coverage of 4 10 13 molecules/cm 2 , a first-order O2 TPD peak appears at 410 K. Oxygen molecules in this peak do not scramble oxygen atoms with either the surface or with other coadsorbed oxygen molecules. Sequential exposures of 16 O2 and 18 O2 at 120 K indicate that each adsorbed O2 molecule, irrespective of its adsorption sequence, has equivalent probabilities with respect to its neighbors to follow the two channels (molecular and dissociative), suggesting that O 2 adsorption is not only precursor-mediated, as the sticking probability measurements indicate, but that all O2 molecules reside in this precursor state at 120 K. This precursor state may be associated with a weak 145 K O2 TPD state observed at high O2 exposures. ELS measurements suggest charge transfer from the surface to the O2 molecule based on disappearance of the vacancy loss feature at 0.8 eV, and the appearance of a 2.8 eV loss that can be assigned to an adsorbed O2 - species based on comparisons with Ti-O2 inorganic complexes in the literature. Utilizing results from recent spin-polarized DFT calculations in the literature, we propose a model where three O2 molecules are bound in the vicinity of each vacancy site at 120 K. For adsorption temperatures above 150 K, the dissociation channel completely dominates and the surface adsorbs oxygen in a 1:1 ratio with each vacancy site. ELS measurements indicate that the vacancies are filled, and the remaining oxygen adatom, which is apparent in TPD, is transparent in ELS. On the basis of the variety of oxygen adsorption states observed in this study, further work is needed in order to determine which oxygen-related species play important roles in chemical and photochemical oxidation processes on TiO2 surfaces.
452 citations
TL;DR: The morphology of amorphous solid water grown by vapor deposition was found to depend strongly on the angular distribution of the water molecules incident from the gas phase, and the ability to control its properties in the laboratory may shed light on some of the outstanding conflicts related to this important material.
Abstract: The morphology of amorphous solid water grown by vapor deposition was found to depend strongly on the angular distribution of the water molecules incident from the gas phase. Systematic variation of the incident angle during deposition using a collimated beam of water led to the growth of nonporous to highly porous amorphous solid water. The physical and chemical properties of amorphous solid water are of interest because of its presence in astrophysical environments. The ability to control its properties in the laboratory may shed light on some of the outstanding conflicts related to this important material.
379 citations
TL;DR: In this paper, the authors determined the diffusivity of amorphous ice by studying isotope intermixing in films less than 500 nanometres thick, which is consistent with the idea that the amorphus solid water melts into a deeply metastable extension of normal liquid water before crystallizing at 160.
Abstract: Supercooled water may offer clues to the anomalous properties of its normal liquid state1. The supercooled state also shows anomalous thermodynamic and transport properties at low temperatures2,3,4. Although there are several theoretical explanations for this behaviour, no consensus has emerged1,2,5,6,7,8,9,10,11,12. Some theories preclude the existence of the supercooled liquid below an apparent thermodynamic singularity at 228?K (refs 2, 7, 9); others are consistent with a continuous region of metastability from the melting point at 273?K to the glass transition temperature at 136?K (refs 6, 8, 13). But the data needed to distinguish between these possibilities have not yet been forthcoming. Here we determine the diffusivity of amorphous ice by studying isotope intermixing in films less than 500 nanometres thick. The magnitude and temperature dependence of the diffusivity is consistent with the idea that the amorphous solid water melts into a deeply metastable extension of normal liquid water before crystallizing at 160?K. This argues against the idea of a singularity in the supercooled regime at ambient pressure.
298 citations
TL;DR: In this paper, the authors investigated the mechanism of the bulk-assisted reoxidation of ion sputtered TiO 2 surfaces by monitoring the diffusion of oxygen and titanium in the 18 O and 46 Ti isotopically enriched surfaces of TiO2 (110).
265 citations
TL;DR: This work has monitored enzymatic turnovers of a few motor proteins and a few enzymes in real time and found that single-molecule sensitivities allow probing of conformational motions, which are otherwise masked in ensemble-averaged experiments.
259 citations
TL;DR: In this paper, the PES spectra from aluminum cluster anions were studied using ab initio molecular dynamics simulations and experimentally, and the calculated spectra, obtained via shifting of the simulated electronic densities of states by the self-consistently determined values of the asymptotic exchange-correlation potential, agree well with the measured ones, allowing reliable structural assignments and theoretical estimation of the clusters' temperatures.
Abstract: Photoelectron (PES) spectra from aluminum cluster anions, ${\mathrm{Al}}_{n}^{\ensuremath{-}}$ $(12l~nl~15),$ at various temperature regimes, were studied using ab initio molecular dynamics simulations and experimentally. The calculated PES spectra, obtained via shifting of the simulated electronic densities of states by the self-consistently determined values of the asymptotic exchange-correlation potential, agree well with the measured ones, allowing reliable structural assignments and theoretical estimation of the clusters' temperatures.
258 citations
TL;DR: In this paper, the potential energy curves of rare gas dimers He2, Ne2, and Ar2 have been computed using correlation consistent basis sets ranging from singly augmented aug-cc-pVDZ sets through triply augmented t-aug-c-pV6Z sets, with the augmented sextuple basis sets being reported herein.
Abstract: The potential energy curves of the rare gas dimers He2, Ne2, and Ar2 have been computed using correlation consistent basis sets ranging from singly augmented aug-cc-pVDZ sets through triply augmented t-aug-cc-pV6Z sets, with the augmented sextuple basis sets being reported herein. Several methods for including electron correlation were investigated, namely Moller—Plesset perturbation theory (MP2, MP3 and MP4) and coupled cluster theory [CCSD and CCSD(T)]. For He2 CCSD(T)/d-aug-cc-pV6Z calculations yield a well depth of 7.35 cm-1 (10.58 K), with an estimated complete basis set (CBS) limit of 7.40 cm-1 (10.65 K). The latter is smaller than the 'exact' well depth (Aziz, R. A., Janzen, A. R., and Moldover, M. R., 1995, Phys. Rev. Lett., 74, 1586) by about 0.2 cm-1 (0.35 K). The Ne2 well depth, computed with the CCSD(T)/d-aug-cc-pV6Z method, is 28.31 cm-1 and the estimated CBS limit is 28.4 cm-1, approximately 1 cm-1 smaller than the empirical potential of Aziz, R. A., and Slaman, M., J., 1989, Chem. Phys., 13...
255 citations
TL;DR: In this paper, the chemical structure and bonding of Al4C and al4C- have been studied by photoelectron spectroscopy and ab initio calculations. But the structure and the bonding of the two molecules are not known.
Abstract: The chemical structure and bonding of Al4C and Al4C- have been studied by photoelectron spectroscopy and ab initio calculations. While Al4C is known to be a tetrahedral molecule, the data reported ...
TL;DR: Progress is described in the development and initial application of the powerful combination of capillary isoelectric focusing (CIEF) and Fourier transform ion cyclotron resonance (FTICR) mass spectrometry for measurements of the proteome of the model system Escherichia coli.
Abstract: Unlike the genome, the proteome is exquisitely sensitive to cellular conditions and will consist of proteins having abundances dependent upon stage in the cell cycle, cell differentiation, response to environmental conditions (nutrients, temperature, stress, etc.), or disease state(s). Therefore, the study of proteomes under well-defined conditions can provide a better understanding of complex biological processes and inference of protein function. Thus, much faster, more sensitive, and precise capabilities for the characterization of cellular constituents are desired. We describe progress in the development and initial application of the powerful combination of capillary isoelectric focusing (CIEF) and Fourier transform ion cyclotron resonance (FTICR) mass spectrometry for measurements of the proteome of the model system Escherichia coli. Isotope depletion of the growth media has been used to improve mass measurement accuracy, and the comparison of CIEF-FTICR results for the analysis of cell lysates harv...
TL;DR: The authors have developed an approach utilizing organisms cultured in stable-isotope labeled media to provide effective internal calibrants for all detected proteins, thus enabling precise proteome-wide measurement of changes in protein abundances resulting from cellular perturbations.
Abstract: In contrast to a cell's virtually static genome, the proteome, the protein complement expressed by an organism, continually changes in response to external stimuli and internal processes. Global gene expression analysis at the mRNA level (i.e., transcriptome) has recently become feasible based on the serial analysis of gene expression and oligonucleotide micro-array assays. These techniques allow the activation states of thousands of genes to be polled simultaneously for a tissue or cell population. However, assays that measure mRNA abundances rather than the functional gene products (i.e., proteins) are uninformative with regard to protein modifications, and can poorly reflect protein abundances due to differences in stabilities, expression rates, etc., for both the mRNAs and proteins. The authors have developed an approach utilizing organisms cultured in stable-isotope labeled media (e.g., rare-isotope depleted and normal) to provide effective internal calibrants for all detected proteins, thus enabling precise proteome-wide measurement of changes in protein abundances resulting from cellular perturbations. The two (or more) isotopically distinctive cell populations are mixed prior to sample processing steps, eliminating all experimental variables associated with cell lysis, separation, and mass spectrometric analysis. Changes in relative protein abundances are thus precisely reflected by the ratio of two isotopically different andmore » resolvable versions of each protein.« less
Abstract: Bond dissociation energies (BDEs) of M+[c-(C2H4O)5] and M+[c-(C2H4O)6] for M = Na, K, Rb, and Cs are reported. The BDEs are determined experimentally by analysis of the thresholds for collision-induced dissociation of the cation−crown ether complexes by xenon measured by using guided ion beam mass spectrometry. In all cases, the primary and lowest energy dissociation channel observed experimentally is endothermic loss of the ligand molecule. The cross section thresholds are interpreted to yield 0 and 298 K BDEs after accounting for the effects of multiple ion−molecule collisions, internal energy of the complexes, and unimolecular decay rates. For both 18-crown-6 and 15-crown-5, the BDEs decrease monotonically with increasing cation size. These results indicate that the intrinsic affinity of c-(C2H4O)5 and c-(C2H4O)6 for M+ is determined principally by the charge density of the cation not by the ratio of the ionic radius to the cavity size. The BDEs reported here are in fair agreement with recent ab initio...
TL;DR: In this paper, the authors show that the addition of sulphonate groups to cyclic copper phthalocyanine (CuPc) increases the energy of the corresponding molecular orbitals, culminating in the highest occupied molecular orbital of the tetra-anion, [cuPc(SO3)4]4−, being unstable by 0.9
Abstract: In neutral atoms and molecules, electrons are kept within their orbitals by attractive electrostatic interactions with positively charged nuclei, with relatively few neutral molecules being able to bind more than one extra electron. For multiply charged molecular anions, dynamic stability plays an important role: the superposition of long-range Coulomb repulsion and short-range electron binding gives rise to a repulsive Coulomb barrier (RCB) that traps the excess electrons1. The RCB has profound effects on the physical and chemical properties of multiply charged anions in the gas phase1,2,3,4,5. For example, it has recently been shown to prevent the detachment of electrons from a doubly charged anion, even when the excitation energies exceed the electron binding energy6,7. Here we report photodetachment experiments which demonstrate that the RCB can even trap electrons in molecular orbitals characterized by a negative binding energy. We show that the addition of sulphonate groups (–SO3−) to cyclic copper phthalocyanine (CuPc; ref. 8) systematically increases the energy of the corresponding molecular orbitals, culminating in the highest occupied molecular orbital of the tetra-anion, [CuPc(SO3)4]4−, being unstable by 0.9 eV. The increase in molecular orbital energy and the negative electron binding energy we observe are due to charge localization in the sulphonate groups and the resultant RCB. The unusually large height of the repulsive barrier also ensures that the anion remains metastable, and continues to store 0.9 eV excess electrostatic energy, throughout the 400 seconds we are able to observe it.
TL;DR: The results suggest the potential for integration of such microfabricated devices with other sample manipulations for the rapid ESI-MS analysis of complex biological samples.
Abstract: A microfabricated dual-microdialysis device in a single integrated microfabricated platform was constructed using laser micromachining techniques for the rapid fractionation and cleanup of complex biological samples. On-line dual microdialysis and ESI-MS of biological samples was demonstrated using an ion trap mass spectrometer. The mass spectra obtained demonstrated the efficiency of dual microdialysis for removing both high-molecular-weight and low-molecular-weight species that interfere with effective ESI-MS analysis of target biopolymers. Signal-to-noise ratios were also greatly improved compared to direct sample infusion. In addition to its compactness, negligible dead volume, and robustness, the device can be used at a flow rate of only 200 nL/min, an order of magnitude lower than that obtained previously. This reduced sample consumption and improved sensitivity with ESI-MS. The results suggest the potential for integration of such microfabricated devices with other sample manipulations for the rapid ESI-MS analysis of complex biological samples.
TL;DR: In this article, correlated calculations of the benzene−water complex predict a geometry in which the water molecule sits above the aromatic ring with oxygen pointed away from the benene center of mass, or only 20% weaker than the water−water interaction.
Abstract: Very large basis set, correlated calculations of the benzene−water complex predict a geometry in which the water molecule sits above the aromatic ring with oxygen pointed away from the benzene center of mass. The purely electronic binding energy, in the complete basis set limit, was found to be −3.9 ± 0.2 kcal/mol, or only 20% weaker than the water−water interaction. When zero-point energies are included, the ΔE0(0 K) values are identical within their estimated uncertainties. Core/valence and higher-order correlation recovery via coupled cluster calculations were found to play a minor role. The present ΔE0(0 K) value of −2.9 ± 0.2 kcal/mol is in good agreement with a recent threshold photoionization experiment that yielded −2.4 ± 0.1 kcal/mol.
TL;DR: In this article, the authors presented an optimized geometries and binding energies for alkali-metal cation complexes with benzene at both the RHF and MP2 levels of theory with K+, Rb+, and Cs+ represented by relativistic ECPs and associated valence basis sets.
Abstract: We present optimized geometries and binding energies for alkali-metal cation complexes with benzene. Results are obtained for Li+ through Cs+ at the RHF/6-311G* and MP2/6-311+G* levels of theory with K+, Rb+, and Cs+ represented by relativistic ECPs and associated valence basis sets. RHF/6-311G* frequencies are used to verify the optimized geometries are minima and used to calculate binding enthalpies. The effects of basis-set superposition error (BSSE) are estimated at both the RHF and MP2 levels. We obtain BSSE-corrected MP2/6-311+G* binding enthalpies (in kcal/mol) of 35.0 (Li+), 21.0 (Na+), 16.0 (K+), 13.3 (Rb+), and 11.6 (Cs+). The distances (A) between the center of the benzene ring and the cation are 1.865 (Li+), 2.426 (Na+), 2.894 (K+), 3.165 (Rb+), and 3.414 (Cs+). Additional single-point CCSD(T)/6-311+G*//MP2/6-311+G* and CCSD(T)/6-311+G(2d,2p)//MP2/6-311+G* calculations indicate that the MP2/6-311+G* results are well converged with regard the extent of electron correlation, whereas small change...
TL;DR: In this paper, the authors discuss models of the dynamical disorder behavior and relate them to observables of single molecule experiments and compare simulations based on a discrete multistate model and a diffusive model with experiment data.
Abstract: Real-time observation of enzymatic turnovers of single molecules has revealed non-Markovian dynamical behavior. Although chemical kinetics (such as the Michaelis-Menten mechanism) are sufficient to describe the average behavior of an ensemble of molecules, statistical analysis of the single-molecule fluorescence time trace reveals fluctuations in the rate of the activation step. These fluctuations are attributed to slow fluctuations of protein conformations. In this paper, we discuss models of the dynamical disorder behavior and relate them to observables of single molecule experiments. Simulations based on a discrete multistate model and a diffusive model are compared with experiment data. The role of various correlation functions, including higher order time correlation functions, in the interpretation of the underlying dynamics is discussed.
TL;DR: An improved electrodynamic ion funnel for ion focusing at high pressure (> 1 Torr) has been developed for a triple quadrupole mass spectrometer and its performance compared with that of an earlier prototype previously reported.
Abstract: An improved electrodynamic ion funnel for ion focusing at high pressure (> 1 Torr) has been developed for a triple quadrupole mass spectrometer and its performance compared with that of an earlier prototype previously reported. The ion funnel consists of a series of ring electrodes of progressively smaller internal diameters to which rf and dc electric potentials are co-applied. The new design utilizes ring electrodes possessing larger internal diameters that taper down to a relatively larger exit aperture. In the 1-10 Torr pressure range, the new design provides significant improvement in low m/z ion transmission. Additionally, the overall ion transmission range is improved by linked scanning of the ion funnel's rf voltage concomitantly with the scanning of the quadrupole mass analyzer. Transmission of a noncovalent complex through the interface demonstrated that excessive ion heating was not problematic. Computer simulations of ion transport support the ion funnel design and help explain the relative performance of both designs. Both ion simulations and experimental results are in accord and indicate close to 100% ion transmission efficiency for electrosprayed biopolymer ions through the interface and into the mass analyzer.
TL;DR: In this paper, the heats of formation of CF3, its cation and anion, CF4, C2F4, and :CFCF3 have been calculated at high levels of ab initio molecular orbital theory.
Abstract: The heats of formation of CF3, its cation and anion, CF4, C2F4, and :CFCF3 have been calculated at high levels of ab initio molecular orbital theory. Geometries and frequencies were determined, in general, with second-order perturbation theory. Total energies based on coupled cluster calculations with perturbative triples were determined with basis sets up through augmented quadruple-ζ in quality and were subsequently extrapolated to the complete one-particle basis set limit, so as to further reduce the basis set truncation error. Due to its importance as a standard, CF4 was studied with even larger basis sets. Additional improvements in the atomization energy were achieved by applying corrections due to core/valence correlation, scalar relativistic, and atomic spin−orbit effects. Zero-point energies were based on the experimental fundamentals, when available, and harmonic frequencies obtained from MP2/cc-pVTZ calculations. Missing frequencies for :CFCF3 were calculated at the MP2/DZP level. The calculate...
TL;DR: In this article, the attachment of an electron to manganese tetroxide cluster is found to lower its total energy by as much as 5 eV, thus putting MnO 4 into the class of superhalogens.
TL;DR: In this article, a variational transition state theory is used to estimate the rate constants for cluster evaporation and condensation, which provides a consistent procedure for defining a unique value for the constraining volume of the physically consistent cluster.
Abstract: A new theoretical approach is presented for vapor-phase nucleation. In contrast to previous molecular approaches to nucleation that focus on evaluating equilibrium distributions of clusters, we evaluate rate constants for cluster evaporation and condensation that are the elementary kinetic steps in the nucleation mechanism. The use of variational transition state theory to estimate the rate constants provides a consistent procedure for defining a unique value for the constraining volume of the physically consistent cluster. The theory is applied to evaporation of small water clusters. {copyright} {ital 1999} {ital The American Physical Society}
TL;DR: In this article, the interplay between the ion−water and water−water interactions in determining the structures of halide ion-water clusters using infrared spectroscopy, interpreted with ab initio theory, was elucidated.
Abstract: We elucidate the interplay between the ion−water and water−water interactions in determining the structures of halide ion−water clusters using infrared spectroscopy, interpreted with ab initio theory. Vibrational predissociation spectra of the X-·(H2O)2·Arm (X = F, Cl, Br, I) clusters in the OH stretching region (2300−3800 cm-1) reveal a strongly halide-dependent pattern of bands. These spectra encode the incremental weakening of the interaction between the water molecules with the lighter halides, finally leading to their complete dissociation in the fluoride complex. A consequence of this is that the F-·(H2O)2 cluster is likely to be a floppy system with high amplitude zero point motion, in contrast to the pseudo-rigid behavior of the other halide hydrates.
TL;DR: In this article, the authors used coupled cluster theory with a perturbative treatment of triple excitations to obtain the theoretical and experimental 0 K values of SiH = 87.7 {+-} 0.6 kcal/mol at 0 K for nine small silicon-containing molecules.
Abstract: Heats of formation for nine small silicon-containing molecules were obtained from large basis set ab initio calculations using coupled cluster theory with a perturbative treatment of triple excitations. After adjusting the atomization energies for the finite basis set truncation error, core/valence correlation, scalar relativistic, higher order correlation, and atomic spin-orbit effects, the theoretical and experimental 0 K values of {Delta}H{sub f} values were in good agreement. Using 106.6 kcal/mol as the heat of formation of silicon, the authors obtain {Delta}H{sub f} values of SiH = 87.7 {+-} 0.4 vs 89.5 {+-} 0.7 (expt); SiH{sub 2}({sup 1}A{sub 1}) = 64.1 {+-} 0.4 vs 65.5 {+-} 0.7 (expt); SiH{sub 2}({sup 3}B{sub 1}{minus})= 85.4 {+-} 0.4 vs 86.5 {+-} 0.7 (expt); SiH{sub 3} = 47.3 {+-} 0.5 vs 47.7 {+-} 1.2 (expt); SiH{sub 4} = 8.7 {+-} 0.6 vs 9.5 {+-} 0.5 (expt); Si{sub 2} = 138.8 {+-} 0.4 vs 139.2 (expt); Si{sub 2}H{sub 6} = 19.7 {+-} 0.5 vs 20.9 {+-} 0.3 (expt); SiF = {minus}14.8 {+-} 0.4 vs {minus}5.2 {+-} 3 (expt); SiF{sub 2} = {minus}151.7 {+-} 0.5 vs {minus}140.3 {+-} 3 (expt); and SiF{sub 4} = {minus}384.5 {+-} 0.9 vs {minus}384.9 {+-} 0.2 (expt). Based on the present work, themore » authors suggest a number of revisions in the interpretation of the experimental data. Although a revision in {Delta}H{sub f}{degree}(Si) to 107.4 {+-} 0.6 kcal/mol at 0 K leads to improved agreement between theory and experiment for the SI{sub x}H{sub y} compounds, it worsens agreement for SiF{sub 4}. Given the remaining uncertainties in the theoretical approach, more definitive conclusions do not appear to be warranted.« less
TL;DR: In this paper, the surface structure of epitaxial α-Fe 2 O 3 (0001) grown on α-Al 2 O3 (0001), was determined using intermediate-energy X-ray photoelectron diffraction.
TL;DR: In this article, the reduction of chloroaurate and the incorporation of Au clusters in polyaniline, PANI, films have been investigated and the preliminary results indicate that Au cluster size distribution remains fairly constant regardless of the method used.
Abstract: The reduction of chloroaurate and the incorporation of Au clusters in polyaniline, PANI, films have been investigated. The chloroaurate complex is generated at the electrode surface during Cl- doping of Au/PANI. FTIR and UV/vis data indicate that chloroaurate interacts with PANI and that its reduction to metallic Au occurs preferentially at the nitrogen linkages. The voltammetric and XPS results show that the uptake of both protons and anions is suppressed by the formation of Au clusters due to this interaction. The ability to reduce chloroaurate in PANI films is also demonstrated for Pt electrodes coated with PANI in solutions containing KAuCl4. The preliminary results indicate that Au cluster size distribution remains fairly constant regardless of the method used.
TL;DR: In this article, it was shown that the surface of Fe3O4(001) exhibits a (1×1) surface net, in contrast to the assumption of a ( 2 × 2 ) R45 reconstruction.
TL;DR: In this article, the termination of epitaxial α-Fe 2 O 3 (0001) prepared by oxygen-plasma-assisted molecular beam epitaxy as grown was investigated, and it was shown that the Fe termination is the most stable surface structure to form, consistent with the predictions of the surface autocompensation model.
TL;DR: In this paper, an extensive experimental search for the smallest stable gaseous multiply charged anions (MCAs) was pursued, and four penta-atomic dianions were found to be the smallest observable using an electrospray ion source.
Abstract: An extensive experimental search for the smallest stable gaseous multiply charged anions (MCAs) was pursued. Four penta-atomic dianions, $\mathrm{Pt}{X}_{4}^{2\ensuremath{-}}$ and $\mathrm{Pd}{X}_{4}^{2\ensuremath{-}}$ $(X\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}\mathrm{Cl},\mathrm{Br})$, were found to be the smallest observable using an electrospray ion source. Photodetachment experiments revealed, however, that ${\mathrm{PtCl}}_{4}^{2\ensuremath{-}}$ and ${\mathrm{PtBr}}_{4}^{2\ensuremath{-}}$ are electronically metastable with negative electron-binding energies. ${\mathrm{PdCl}}_{4}^{2\ensuremath{-}}$ and ${\mathrm{PdBr}}_{4}^{2\ensuremath{-}}$ were found to be electronically stable, but thermodynamically unstable against fragmentation. Lifetimes were estimated using an ion-trap technique for the four observed metastable MCAs, providing further insight into their electronic and thermodynamic stability.