bluuebunny/crossref_metadata_2025 huggingface dataset:
Seasonal circulation on the western shelf of the Gulf of Mexico using a high‐resolution numerical model
Authors: Zavala‐Hidalgo Jorge , Morey Steven L. , O'Brien James J.
Published: December 2003

The seasonal circulation on the western shelf of the Gulf of Mexico is studied using a high‐resolution numerical simulation, historical hydrographic data, sea level data, and satellite images. Three regions are distinguished, the Tamaulipas‐Veracruz (TAVE) shelf, the Louisiana‐Texas (LATEX) shelf, and the western Campeche Bank. On the TAVE shelf there is a swift reversal of the along‐shelf current, downcoast from September to March and upcoast from May to August when there is upwelling due to offshore Ekman transport. Circulation on the western Campeche Bank is upcoast throughout the year. The LATEX shelf has a cyclonic circulation, except during summer months when the flow is eastward. During spring‐summer the upcoast current on the TAVE shelf reaches the southern Texas shelf where it encounters a downcoast coastal current favoring offshore transports. In the fall‐winter, the downcoast current reaches the southern Bay of Campeche where it meets an opposing along‐shelf current, generating seasonal offshore transports. During fall and winter, cool low‐salinity water from the Mississippi and Atchafalaya Rivers is advected westward along the LATEX shelf onto the TAVE shelf, developing along‐shelf fronts and temperature inversions commonly observed over the outer shelf and shelf break. The main forcing over the western shelf of the gulf is the along‐coast wind stress component. The existence of the cross‐shelf transports in the confluence regions is supported by chlorophyll a data. Up to 80% of the seasonal sea level variability is explained by the along shelf currents and the low‐frequency variability of the atmospheric sea level pressure.
A historical record of formate and acetate from a high‐elevation Alpine glacier: Implications for their natural versus anthropogenic budgets at the European scale
Authors: Legrand M. , Preunkert S. , Wagenbach D. , Cachier H. , Puxbaum H.
Published: December 2003

High‐resolution records of formate and acetate from a Col du Dôme (CDD, 4250 m elevation, French Alps) ice core were used to investigate the impact of man‐made activities on the midtropospheric levels of these species over Europe since 1925. Formate whose summer levels remained unchanged (80 ± 20 ng g−1) over the 1925–1995 time period is the major monocarboxylate present in summer CDD snow layers. In contrast, the acetate summer level being close to 15 ng g−1 prior to 1950 increased by a factor of 3 from 1950 to 1975 and declined during the 1980s. The difference in past changes of these monocarboxylates is due to recent acidification of the atmosphere which has lowered the scavenging efficiency in a larger extent for formate than for acetate. Formate levels corrected from effect of past acidity changes show a long‐term trend similar to the acetate one. These past changes are likely related to vehicle emissions (direct emissions and secondary production from alkenes) which strongly increased from 1950 to 1980. Because of improvement of engines and more stringent emission standards the CDD summer levels of monocarboxylates declined in the 1980s, and the 1990 levels are only slightly higher than their preindustrial levels. Therefore, except at the end of the 1970s when the anthropogenic input was as high as the natural one, natural sources appear to dominate the budget of the two monocarboxylates in the European midtroposphere. It is shown that natural sources include direct emissions by vegetation, oxidation of isoprene and monoterpenes, and possibly in‐cloud oxidation of formaldehyde into formic acid and gas phase oxidation of peroxyl acetyl radical into acetic acid.
Potential of observations from the Tropospheric Emission Spectrometer to constrain continental sources of carbon monoxide
Authors: Jones Dylan B. A. , Bowman Kevin W. , Palmer Paul I. , Worden John R. , Jacob Daniel J. , Hoffman Ross N. , Bey Isabelle , Yantosca Robert M.
Published: December 2003

We have conducted an observing system simulation experiment for the Tropospheric Emission Spectrometer (TES) satellite instrument to determine the potential of nadir retrievals of carbon monoxide (CO) from this instrument to constrain estimates of continental sources of CO. We use the GEOS‐CHEM global chemical transport model to produce a pseudoatmosphere in which the relationship between sources and concentrations of CO is known. Linear profile retrievals of CO are calculated by sampling this pseudoatmosphere along the orbit of TES. These retrievals are used as pseudo‐observations with a maximum a posteriori inverse algorithm to estimate the CO sources from the different continents. This algorithm accounts for the finite vertical resolution of the retrieval, instrument errors, and representation and transport errors in the GEOS‐CHEM simulation of CO. The structure of the transport error is estimated using the statistics of the difference between paired GEOS‐CHEM forecasts of CO, and this structure is then scaled to match the model error in the GEOS‐CHEM simulation of aircraft observations of Asian outflow over the NW Pacific. We show that with proper characterization of observation errors just 2 weeks of observations from TES have the potential to constrain estimates of continental sources of CO to within 10%.
Isotopic evidence for source changes of nitrate in rain at Bermuda
Authors: Hastings Meredith Galanter , Sigman Daniel M. , Lipschultz Fred
Published: December 2003

Rainwater collected on the island of Bermuda between January 2000 and January 2001 shows pronounced seasonal variation in the nitrogen and oxygen isotopic composition of nitrate. Higher 15N/14N and lower 18O/16O ratios are observed in the warm season (April–September) in comparison to the cool season (October–March): The mean δ15N of nitrate for the warm and cool seasons is −2.1‰ and −5.9‰ (versus air N2), respectively, while the mean δ18O is 68.6‰ and 76.9‰ (versus Vienna Standard Mean Ocean Water). The few cool season rain events that had high 15N/14N and low 18O/16O exhibited trajectory paths originating from the south, similar to those of warm season samples. Accordingly, the region from which air is transported to the island determines the 15N/14N and 18O/16O of the nitrate. The source region provides precursor nitrogen oxides (NOx), influencing the 15N/14N of nitrate, and contributes to the chemistry that produces nitrate from NOx, which determines the 18O/16O of nitrate. While the range in nitrate 15N/14N observed during the cool season is consistent with anthropogenic emissions from North America, the higher warm season 15N/14N suggests that lightning is a significant source of nitrate to Bermuda. The isotopic evidence for a significant southern source of nitrate to Bermuda helps to explain the previous observation of unexpectedly high nitrate concentrations in warm season rain. The 18O/16O of nitrate in rain at Bermuda is high throughout the year (δ18O = 60.3 to 86.5‰) as a result of interactions of precursor NOx with ozone, which has a high 18O/16O ratio. The lower nitrate 18O/16O in the warm season and in cool season air masses from the south is consistent with elevated concentrations of hydroxyl radical (OH), which dilutes the isotopic signal of ozone. Our limited data set suggests that the relative importance of the OH sink for NOx during the cool season varies spatially over as large a range as is observed between the warm and cool seasons.
Observed and modeled relationships among Arctic climate variables
Authors: Chen Yonghua , Miller James R. , Francis Jennifer A. , Russell Gary L. , Aires Filipe
Published: December 2003

The complex interactions among climate variables in the Arctic have important implications for potential climate change, both globally and locally. Because the Arctic is a data‐sparse region and because global climate models (GCMs) often represent Arctic climate variables poorly, significant uncertainties remain in our understanding of these processes. In addition to the traditional approach of validating individual variables with observed fields, we demonstrate that a comparison of covariances among interrelated parameters from observations and GCM output provides a tool to evaluate the realism of modeled relationships between variables. We analyze and compare a combination of conventional observations, satellite retrievals, and GCM simulations to examine some of these relationships. The three climate variables considered in this study are surface temperature, cloud cover, and downward longwave flux. Results show that the highest correlations between daily changes in pairs of variables for all three data sets occur between surface temperature and downward longwave flux, particularly in winter. There is less variability in GCM output, in part, because there is greater spatial averaging. Although the satellite products can be used to examine some of these relationships, additional work may be needed to ensure consistency between changes in radiative components of the energy budget and other retrieved quantities. The GCM's relationships between variables agree well with in situ observations, which provides some confidence that the GCM's representation of present‐day climate is reasonable in high northern latitudes.
Temperature and light dependence of β‐caryophyllene emission rates
Authors: Hansen Ute , Seufert Günther
Published: December 2003

Assessments of the overall release of reactive volatile organic compounds from vegetation require the knowledge of the effect of temperature and light intensity on emission rates. The aim of the study presented here was to investigate whether the rates of emission of the highly reactive sesquiterpene β‐Caryophyllene (BCAR) from foliage of orange trees (Citrus sinensis (L.) OSBECK, var. Navel and Navel Late), detected using branch enclosures in an orange orchard in Spain, were not only temperature but also light dependent. We used two algorithms to calculate the diurnal variation of BCAR emission rates from environmental data. One algorithm accounted exclusively for the known exponential relationship between emission rate and temperature, and the other for both temperature and light effects. Assuming a light and temperature dependence of BCAR emission rates led to a more precise prediction of the short‐term variation of BCAR emission rates than assuming that emissions are affected exclusively by temperature. The light dependence of BCAR emission rates could be due to a modulation of BCAR synthesis by light, or to an enhanced volatilization of BCAR from storage pools under high light exposure, or a combination of both. The data show that present assessments of the total release of reactive volatile organic compounds from vegetation, disregarding light effects on BCAR emission, are highly uncertain, if BCAR considerably contributes to total terpenoid emissions of the investigated plants.
Rock Abrasion Tool: Mars Exploration Rover mission
Authors: Gorevan S. P. , Myrick T. , Davis K. , Chau J. J. , Bartlett P. , Mukherjee S. , Anderson R. , Squyres S. W. , Arvidson R. E. , Madsen M. B. , Bertelsen P. , Goetz W. , Binau C. S. , Richter L.
Published: December 2003

The Rock Abrasion Tool (RAT) is an integral part of the Athena Science payload. Serving primarily as the geologist's rock hammer, the RAT will expose fresh surfaces of Martian rocks to other instruments on the payload. The RAT also brushes dust and debris from an excavated hole or unaltered rocks. To accomplish these tasks autonomously, the RAT, a sophisticated 3‐axis precision‐controlled device, was designed. Data products derived from RAT telemetry enable the RAT to also act as an important rock physical properties science instrument. The returned RAT grinding and penetration rate data will be inverted and compared to a rock library on the Earth. The design is also very compact and lightweight: the RAT is contained within a cylinder 128 mm long and 85 mm in diameter and has a mass of 687 g.
Athena Mars rover science investigation
Authors: Squyres Steven W. , Arvidson Raymond E. , Baumgartner Eric T. , Bell James F. , Christensen Philip R. , Gorevan Stephen , Herkenhoff Kenneth E. , Klingelhöfer Göstar , Madsen Morten Bo , Morris Richard V. , Rieder Rudolf , Romero Raul A.
Published: December 2003

Each Mars Exploration Rover carries an integrated suite of scientific instruments and tools called the Athena science payload. The primary objective of the Athena science investigation is to explore two sites on the Martian surface where water may once have been present, and to assess past environmental conditions at those sites and their suitability for life. The remote sensing portion of the payload uses a mast called the Pancam Mast Assembly (PMA) that provides pointing for two instruments: the Panoramic Camera (Pancam), and the Miniature Thermal Emission Spectrometer (Mini‐TES). Pancam provides high‐resolution, color, stereo imaging, while Mini‐TES provides spectral cubes at mid‐infrared wavelengths. For in‐situ study, a five degree‐of‐freedom arm called the Instrument Deployment Device (IDD) carries four more tools: a Microscopic Imager (MI) for close‐up imaging, an Alpha Particle X‐Ray Spectrometer (APXS) for elemental chemistry, a Mössbauer Spectrometer (MB) for the mineralogy of Fe‐bearing materials, and a Rock Abrasion Tool (RAT) for removing dusty and weathered surfaces and exposing fresh rock underneath. The payload also includes magnets that allow the instruments to study the composition of magnetic Martian materials. All of the Athena instruments have undergone extensive calibration, both individually and using a set of geologic reference materials that are being measured with all the instruments. Using a MER‐like rover and payload in a number of field settings, we have devised operations processes that will enable us to use the MER rovers to formulate and test scientific hypotheses concerning past environmental conditions and habitability at the landing sites.
Tropical sea‐surface temperature reconstruction for the early Paleogene using Mg/Ca ratios of planktonic foraminifera
Authors: Tripati Aradhna K. , Delaney Margaret L. , Zachos James C. , Anderson Linda D. , Kelly Daniel C. , Elderfield Harry
Published: December 2003

To understand the climate dynamics of hypothesized past greenhouse intervals, it is essential to constrain tropical sea‐surface temperatures (SST), yet existing proxy records give conflicting results. Here we present the first Mg/Ca‐based study of pre‐Quaternary SST and investigate early Paleogene (late Paleocene through late middle Eocene; 58.6–39.8 Ma) tropical temperatures, using planktonic foraminifera belonging to the genus Morozovella from Ocean Drilling Program Site 865 on Allison Guyot (western central equatorial Pacific Ocean). Calcification temperatures similar to or warmer than modern tropical SST are calculated using a range of assumptions regarding diagenesis, temperature calibration, and seawater Mg/Ca. Long‐term warming is observed into the early Eocene (54.8–49.0 Ma), with peak SST between 51 and 48 Ma and rapid cooling of 4°C beginning at 48 Ma. These findings are inconsistent with the δ18O‐based SST previously estimated for this site.
Effects of drainage salinity evolution on irrigation management
Authors: Kan Iddo
Published: December 2003

A soil physics theory of solute movement through a drained saturated zone underlying agricultural land is introduced into a long‐term economic analysis of farm‐level irrigation management; this is an alternative to the immediate, homogeneous blending assumption employed in previous studies as a base for calculating changes in drainage salinity over time. Using data from California, the effect of drainage salinity evolution is analyzed through a year‐by‐year profit optimization under the requirement of on‐farm drainage disposal. Paths of optimal land allocation among crop production with fresh surface water, saline drainage reuse and evaporation ponds appear to depend on the relative profitability of the first two; that of reuse is affected by the trend of drainage salinity. Tile spacing and environmental regulations associated with evaporation ponds affect the timing of evaporation pond construction. The system converges into a solution involving both drainage‐disposal activities; this solution includes an outlet for salts and is therefore sustainable. Following this strategy, the system is asymptotically approaching a steady state that possesses both hydrological and salt balances. Economic implications associated with land retirement programs in California are discussed.
Block‐effective macrodispersion in variably saturated heterogeneous formations
Authors: Russo David
Published: December 2003

Numerical models are frequently used in order to quantify the effect of the spatial heterogeneity in the formation hydraulic properties on field‐scale solute transport. Because of practical constraints it is common to discretize the flow domain into relatively large numerical cells, with characteristic length scales, ℓ1, ℓ2, ℓ3, comparable with those of the formation heterogeneity, I1, I2, I3, leading to a loss in the velocity variability, and, concurrently, in solute spreading. We analyzed block‐effective dispersion coefficients, D′ij (i, j = 1, 2, 3), required to compensate for this loss in three‐dimensional, variably saturated heterogeneous formations under conditions of steady state, gravity‐dominated, unsaturated flow. The results that the principal components of D′ij are controlled by the ratio ℓ′ = ℓ2/I2 = ℓ3/I3, that they may reach their ergodic limits if ℓ′ is sufficiently large, and that their tendency to their asymptotic limits with increasing scaled travel time, t′, is inversely related to ℓ′, are in agreement with previous results for saturated flow. New findings suggest that under unsaturated flow conditions, both the time required to reach the asymptotic limits of D′ij and the length scale needed to reach the ergodic limits of D′ij depend on soil stratification, soil texture, and mean soil water saturation and differ for the longitudinal and the transverse components of D′ij.
Serum IgM anti‐GM1 ganglioside antibodies in lower motor neuron syndromes
Authors: Niebroj‐Dobosz I. , Janik P. , Kwieciński H.
Published: December 2003

Lower motor neuron syndromes (LMNS) are heterogenous conditions, which include patients with progressive lower motor neuron disease (LMND) and cases with the clinical phenotype of motor neuropathy (MN). The aim of this study was to estimate the IgM anti‐GM1 ganglioside antibodies titer and the ratio of the light chains in order to define the presence of autoimmunity process in particular cases with LMNS. Twenty‐eight patients were diagnosed with LMND and 15 patients were diagnosed with MN (10 patients with multifocal motor neuropathy with conduction block, five patients with MN without conduction block). Total of 103 patients with classical amyotrophic lateral sclerosis (ALS) and 50 healthy, age‐matched persons were also tested. The IgM anti‐GM1 ganglioside titer and the ratio of lambda/kappa light chains in serum were determined using the ELISA technique. High titer of IgM anti‐GM1 antibodies were detected in serum of 46% LMND patients, 80% of MN patients, and 18% of the classical ALS cases. An elevated ratio of lambda/kappa light chains appeared in 18% of LMND patients, and in 67% of the MN cases. The lambda/kappa light chains ratio was normal in all ALS patients. The presence of elevated titer of IgM anti‐GM1 ganglioside antibodies and the changed ratio of the light chains supports the presence of autoimmune process in LMNS and may provide clues for their management.
Horizontal canal benign paroxysmal positioning vertigo with ipsilateral hearing loss
Authors: Rambold H. , Heide W. , Helmchen C.
Published: December 2003

The etiology of benign paroxysmal positioning vertigo (h‐BPPV) of the horizontal semicircular is unknown. Insight was obtained from two patients with h‐BPPV and associated hearing impairment. Based on the different inner ear lesion patterns in neurolabyrinthitis contrary to ischemic labyrinthine infarction we assessed multiple vestibulo‐cochlear functions for the first time in two patients who suffered from h‐BPPV with sudden unilateral hearing loss. While in patient no. 1 the lesion pattern (posterior canal paresis in addition to the sudden hearing loss) could possibly be caused by ischemia of the common cochlear artery, the lesion pattern of patient no. 2 (hearing loss and ipsilateral paresis of the posterior and horizontal semicircular canal) exceeds the typical vascular labyrinthine territories and may indicate viral neurolabyrinthitis.
Investigation of cytokine (tumor necrosis factor‐alpha, interleukin‐6, interleukin‐10) concentrations in the cerebrospinal fluid of female patients with multiple sclerosis and systemic lupus erythematosus
Authors: Baraczka K. , Nékám K. , Pozsonyi T. , Szüts I. , Ormos G.
Published: December 2003

Humoral immune response seems to play a role in the pathogenesis of multiple sclerosis (MS) and in the central nervous system (CNS) complications of systemic lupus erythematosus (SLE). The aim of the present study was to compare the levels of tumor necrosis factor‐alpha (TNF‐alpha), interleukin‐6 (IL‐6) and IL‐10 in the cerebrospinal fluid of female patients with several forms of MS (50 patients), and in female patients with several types of CNS complications in SLE (50 patients). Samples were investigated using an enzyme‐linked immunosorbent assay technique. Involvement of CNS in SLE patients seems to be characterized with elevated concentrations of all three cytokines in CNS and intrathecal synthesis of IL‐6. In MS patients, an intrathecal synthesis of TNF‐alpha (relapsing–remitting form) and IL‐6 (primary progressive form) were observed. Clinical forms of MS seem to be immunologically heterogeneous. The activation of cytokine network was observed in SLE patients with CNS complications, independent of the pathological process. Similarities between SLE and MS patients with the primary progressive form of the disease were demonstrated concerning the intrathecal synthesis of IL‐6. Only MS patients with the relapsing–remitting clinical form showed intrathecal TNF‐alpha synthesis.
The defect of the perforin granule system in cytotoxic T lymphocytes of atopic patients – are perforin reduction and hyperreleasability of clinical relevance?
Authors: Ambach Andreas , Bonnekoh Bernd , Gollnick Harald
Published: December 2003

Perforin‐containing lytic granules are secretory lysosomes of cytotoxic lymphocytes. They act as a negative regulator of activated T cells, control immunoglobulin production, contribute to the regulation of the TH1/TH2 balance, and occupy a central role in anti‐viral defense mechanisms. This review focuses on recent evidence for a fundamental defect in the lymphocytic perforin system of atopic patients, namely perforin reduction and the hyperreleasability of perforin granules. These findings are set in relation to the immune imbalance in atopy, which is characterized by a weakly restrained proliferation of allergen‐specific T and B cells, a predominance of Ttype‐2 cytokines, and an increased susceptibility to cutaneous infections. In the context of the well‐known defect of secretory lysosomes in mast cells and keratinocytes of atopic patients, the possibility of a cell type‐independent major pathological factor in atopy is discussed: pan‐cellular reduction and hyperreleasability of secretory lysosomes.
Die Extrakorporale Photopherese bei Progressiver Systemischer Sklerodermie: Unterscheidung von Respondern und Non‐Respondern
Authors: Reich Stefanie , Radenhausen Michael , Altmeyer Peter , Hoffmann Klaus
Published: December 2003

Hintergrund: Die Wirksamkeit der Extrakorporalen Photopherese (ExP) bei Progressiver Systemischer Sklerodermie (PSS) wird kontrovers diskutiert. Bisher bestehen nur wenige Erfahrungen zur Langzeitanwendung der ExP bei PSS. Ziel vorliegender Untersuchung war es, bei der Anwendung von ExP bei PSS Responder von Non‐Respondern zu unterscheiden und geeignete Verlaufsparameter zu evaluieren.

Patienten und Methodik: Es wurden 20 PSS‐Patienten während einer 12‐monatigen ExP‐Therapie (Intervall: 1x/Monat) als immunmodulatorische Mono‐ (11/20) oder Kombinationstherapie (9/20) beobachtet. Der Verlauf der PSS wurde mittels eines eigens für die einheitliche Beurteilung der PSS‐Patienten etablierten klinischen Scores und serologischen Parametern (CRP, ANA‐Titer, beta‐Galaktosidase, P‐III‐P, CD4/CD8‐Ratio, TNF‐alpha, Il‐2‐R, Il‐6) kontrolliert.

Ergebnisse: Nach 12‐monatiger ExP‐Therapie zeigten 30 % der PSS‐Patienten eine partielle Remission und 25 % einen stabilen Verlauf (55 % Responder), während 45 % eine Progression (Non‐Responder) aufwiesen. Zwar korrelierte der Krankheitsverlauf nicht mit den untersuchten laborchemischen Parametern, doch zeigte ein Anstieg der beta‐Galaktosidase unter Therapie bei den Non‐Respondern einen PSS‐Schub an. Bei den Respondern war ein kurzer Krankheitsverlauf vor ExP‐Beginn, moderat erhöhte ANA‐Titer, normwertige TNF‐alpha‐Spiegel sowie ein negativer Scl‐70‐Nachweis prognostisch günstig einzuschätzen.

Schlussfolgerungen: Etwa die Hälfte der PSS‐Patienten profitierten von einer langfristigen Wirksamkeit der ExP. Jedoch scheint die milde immunmodulatorische Wirkung der ExP nicht ausreichend, um stark progressive Verläufe der PSS zu kontrollieren.
Potential energy curves of diatomic molecular ions from high-resolution photoelectron spectroscopy. I. The first six electronic states of Ar2+
Authors: Wüest A. , Merkt F.
Published: December 2003

High-resolution photoelectron spectroscopic data have been used to determine the potential energy curves of the first six electronic states of Ar2+. The potential energy functions properly include the effects of the long-range interactions and of the spin–orbit interaction and are of spectroscopic accuracy (1–2 cm−1) over a wide range of internuclear distances. The total number of adjustable parameters could be reduced to only 12 by truncating the long-range interaction series after the R−6 term and assuming an R-independent spin–orbit coupling constant. This assumption was verified to be valid to an accuracy of ±2 cm−1 over the range of internuclear distances between 3.0 and 4.6 Å. The interaction potential proposed by Siska [P. E. Siska, J. Chem. Phys. 85, 7497 (1986)] was generalized to a form that is expected to be sufficiently flexible to describe chemical bonding in other diatomic molecular ions. The potential energy curves are more accurate than the best available ab initio curves by two orders of magnitude and provide quantitative information on dissociation energies and equilibrium internuclear distances. The local maximum between the two potential wells of the I(1/2g) state was determined to lie 62 cm−1 below the Ar(1S0)+Ar+(2P3/2) dissociation limit, and the II(1/2g) state is found to be significantly more bound (De=177 cm−1) than previously assumed.
Measurement and dynamics of the spatial distribution of an electron localized at a metal–dielectric interface
Authors: Bezel Ilya , Gaffney Kelly J. , Garrett-Roe Sean , Liu Simon H. , Miller André D. , Szymanski Paul , Harris Charles B.
Published: December 2003

The ability of time- and angle-resolved two-photon photoemission to estimate the size distribution of electron localization in the plane of a metal–adsorbate interface is discussed. It is shown that the width of angular distribution of the photoelectric current is inversely proportional to the electron localization size within the most common approximations in the description of image potential states. The localization of the n=1 image potential state for two monolayers of butyronitrile on Ag(111) is used as an example. For the delocalized n=1 state, the shape of the signal amplitude as a function of momentum parallel to the surface changes rapidly with time, indicating efficient intraband relaxation on a 100 fs time scale. For the localized state, little change was observed. The latter is related to the constant size distribution of electron localization, which is estimated to be a Gaussian with a 15±4 Å full width at half maximum in the plane of the interface. A simple model was used to study the effect of a weak localization potential on the overall width of the angular distribution of the photoemitted electrons, which exhibited little sensitivity to the details of the potential. This substantiates the validity of the localization size estimate.
The binding energies of the D2d and S4 water octamer isomers: High-level electronic structure and empirical potential results
Authors: Xantheas Sotiris S. , Aprà Edoardo
Published: December 2003

The MP2 complete basis set (CBS) limit for the binding energy of the two low-lying water octamer isomers of D2d and S4 symmetry is estimated at −72.7±0.4 kcal/mol using the family of augmented correlation-consistent orbital basis sets of double through quintuple zeta quality. The largest MP2 calculation with the augmented quintuple zeta (aug-cc-pV5Z) basis set produced binding energies of −73.70 (D2d) and −73.67 kcal/mol (S4). The effects of higher correlation, computed at the CCSD(T) level of theory, are estimated at <0.1 kcal/mol. The newly established MP2/CBS limit for the water octamer is reproduced quite accurately by the newly developed all atom polarizable, flexible interaction potential (TTM2-F). The TTM2-F binding energies of −73.21 (D2d) and −73.24 kcal/mol (S4) for the two isomers are just 0.5 kcal/mol (or 0.7%) larger than the MP2/CBS limit.
Phase behavior in thin films of cylinder-forming ABA block copolymers: Mesoscale modeling
Authors: Horvat A. , Lyakhova K. S. , Sevink G. J. A. , Zvelindovsky A. V. , Magerle R.
Published: December 2003

The phase behavior of cylinder-forming ABA block copolymers in thin films is modeled in detail using dynamic density functional theory and compared with recent experiments on polystyrene-block-polybutadiene-block-polystyrene triblock copolymers. Deviations from the bulk structure, such as wetting layer, perforated lamella, and lamella, are identified as surface reconstructions. Their stability regions are determined by an interplay between surface fields and confinement effects. Our results give evidence for a general mechanism governing the phase behavior in thin films of modulated phases.
A washboard with moment of inertia model of gas-surface scattering
Authors: Yan Tianying , Hase William L. , Tully John C.
Published: December 2003

A washboard with moment of inertia (WBMI) model for gas atom scattering from a flexible surface is proposed and applied. This model is a direct extension of the washboard model [J. Chem. Phys. 92, 680 (1990)] proposed for gas atom scattering from relatively rigid, corrugated surfaces. In addition, a moment of inertia is incorporated in the original washboard model to describe the flexibility of softer, more highly corrugated surfaces such as polymer or liquid surfaces. The moment of inertia of the effective surface object introduces a dependence of the efficiency of energy transfer on the position and direction of impact, a feature that has been shown to be critical by molecular dynamics simulations. The WBMI model is solved numerically by Monte Carlo integration, which makes the implementation of multiple impacts between a colliding atom and the surface very efficient. The model is applied to Ne and Ar atoms scattering from an alkylthiolate self-assembled monolayer surface and reproduces the major results obtained by classical trajectory simulation of the same system, i.e., a bimodal translation energy distribution P(Ef) with the low-energy component well-fit with a Boltzmann distribution, but with a temperature that may (Ar) or may not (Ne) be the same as the surface temperature. This indicates that the WBMI model, with well-motivated physical assumptions and simplified interaction, reveals many of the major aspects of the gas-surface collision dynamics, though it does not take into account the real-time dynamics explicitly.
Ferromagnetic dimer interactions in Cu2Cl4(CH3CN)2
Authors: Liu Chen , Talham Daniel R. , Park Ju-Hyun , Čižmár Erik , Meisel Mark W.
Published: December 2003

The magnetic properties of Cu2Cl4(CH3CN)2 are reported. Initially reported by Rundle and Willett [J. Chem. Phys. 40, 838, (1964)], the title compound consists of dimeric Cu(II) ions doubly bridged by two chloride ions. Each Cu(II) ion is further bonded to an additional nonbridging chloride ion and a nonbridging acetonitrile molecule. The dimers stack along the crystallographic a axis to form a ladder structure. Static magnetization measurements indicate the two Cu(II) ions within a dimer interact ferromagnetically with J/kB=40±2 K, while a weak ferromagnetic interaction, J′/kB=0.9±0.1 K, also exists between dimers. Ferromagnetic exchange is unusual for this structural motif and is attributed to the reduction of electronic density on the bridging ions due to the electron-accepting nature of the nitrile group in acetonitrile.
Dipole-bound anions of highly polar molecules: Ethylene carbonate and vinylene carbonate
Authors: Hammer Nathan I. , Hinde Robert J. , Compton Robert N. , Diri Kadir , Jordan Kenneth D. , Radisic Dunja , Stokes Sarah T. , Bowen Kit H.
Published: December 2003

Results of experimental and theoretical studies of dipole-bound negative ions of the highly polar molecules ethylene carbonate (EC, C3H4O3,μ=5.35 D) and vinylene carbonate (VC, C3H2O3,μ=4.55 D) are presented. These negative ions are prepared in Rydberg electron transfer (RET) reactions in which rubidium (Rb) atoms, excited to ns or nd Rydberg states, collide with EC or VC molecules to produce EC− or VC− ions. In both cases ions are produced only when the Rb atoms are excited to states described by a relatively narrow range of effective principal quantum numbers, n*; the greatest yields of EC− and VC− are obtained for nmax*=9.0±0.5 and 11.6±0.5, respectively. Charge transfer from low-lying Rydberg states of Rb is characteristic of a large excess electron binding energy (Eb) of the neutral parent; employing the previously derived empirical relationship Eb=23/nmax*2.8 eV, the electron binding energies are estimated to be 49±8 meV for EC and 24±3 meV for VC. Electron photodetachment studies of EC− show that the excess electron is bound by 49±5 meV, in excellent agreement with the RET results, lending credibility to the empirical relationship between Eb and nmax*. Vertical electron affinities for EC and VC are computed employing aug-cc-pVDZ atom-centered basis sets supplemented with a (5s5p) set of diffuse Gaussian primitives to support the dipole-bound electron; at the CCSD(T) level of theory the computed electron affinities are 40.9 and 20.1 meV for EC and VC, respectively.
The impact of the self-interaction error on the density functional theory description of dissociating radical cations: Ionic and covalent dissociation limits
Authors: Gräfenstein Jürgen , Kraka Elfi , Cremer Dieter
Published: December 2003

Self-interaction corrected density functional theory was used to determine the self-interaction error for dissociating one-electron bonds. The self-interaction error of the unpaired electron mimics nondynamic correlation effects that have no physical basis where these effects increase for increasing separation distance. For short distances the magnitude of the self-interaction error takes a minimum and increases then again for decreasing R. The position of the minimum of the magnitude of the self-interaction error influences the equilibrium properties of the one-electron bond in the radical cations H2+ (1), B2H4+ (2), and C2H6+ (3), which differ significantly. These differences are explained by hyperconjugative interactions in 2 and 3 that are directly reflected by the self-interaction error and its orbital contributions. The density functional theory description of the dissociating radical cations suffers not only from the self-interaction error but also from the simplified description of interelectronic exchange. The calculated differences between ionic and covalent dissociation for 1, 2, and 3 provide an excellent criterion for determining the basic failures of density functional theory, self-interaction corrected density functional theory, and other methods. Pure electronic, orbital relaxation, and geometric relaxation contributions to the self-interaction error are discussed. The relevance of these effects for the description of transition states and charge transfer complexes is shown. Suggestions for the construction of new exchange-correlation functionals are given. In this connection, the disadvantages of recently suggested self-interaction error-free density functional theory methods are emphasized.
A reinterpretation of the nature of the Fermi hole
Authors: Ludeña Eduardo V. , Ugalde Jesus M. , Lopez Xabier , Fernández-Rico Jaime , Ramı́rez Guillermo
Published: December 2003

A reinterpretation of the Boyd–Coulson [R. J. Boyd and C. A. Coulson, J. Phys. B 7, 1805 (1974)] definition of the Fermi hole is presented. Through this reinterpretation, which makes no reference to the hypothetical Hartree level, we are able to show the essentially identical character of the Boyd–Coulson definition with the one based on a conditional probability analysis. The basis-set dependence of the Fermi hole is emphasized and the effect of canonical, localized and delocalized Kohn–Sham and Hartree–Fock basis sets is examined for selected atoms and molecules.
Reaction of Cu+ with dimethoxyethane: Competition between association and multiple dissociation channels
Authors: Koizumi Hideya , Muntean Felician , Armentrout P. B.
Published: December 2003

The reaction of Cu+ with dimethoxyethane (DXE) is studied using kinetic-energy dependent guided ion beam mass spectrometry. The bimolecular reaction forms an associative Cu+(DXE) complex that is long-lived and dissociates into several competitive channels: C4H9O2++CuH, Cu+(C3H6O)+CH3OH, back to reactants, and other minor channels. The kinetic-energy dependences of the cross sections for the three largest product channels are interpreted with several different models (including rigorous phase space theory) to yield 0 K bond energies after accounting for the effects of multiple ion–molecule collisions, internal energy of the reactant ions, Doppler broadening, and dissociation lifetimes. These values are compared with bond energies obtained from collision-induced dissociation (CID) studies of the Cu+(DXE) complex and found to be self-consistent. Although all models provide reasonable thermochemistry, phase space theory reproduces the details of the cross sections most accurately. We also examine the dynamics of this reaction using time-of-flight methods and a retarding potential analysis. This provides additional insight into the unimolecular decay of the long-lived Cu+(DXE) association complex. Comparison of results from this study with those from the complementary CID study, thus forming the same energized Cu+(DXE) complex in two distinct ways, allows an assessment of the models used to interpret CID thresholds.
Mapped grid methods for long-range molecules and cold collisions
Authors: Willner K. , Dulieu O. , Masnou-Seeuws F.
Published: December 2003

The paper discusses ways of improving the accuracy of numerical calculations for vibrational levels of diatomic molecules close to the dissociation limit or for ultracold collisions, in the framework of a grid representation. In order to avoid the implementation of very large grids, Kokoouline et al. [J. Chem. Phys. 110, 9865 (1999)] have proposed a mapping procedure through introduction of an adaptive coordinate x subjected to the variation of the local de Broglie wavelength as a function of the internuclear distance R. Some unphysical levels (“ghosts”) then appear in the vibrational series computed via a mapped Fourier grid representation. In the present work the choice of the basis set is reexamined, and two alternative expansions are discussed: Sine functions and Hardy functions. It is shown that use of a basis set with fixed nodes at both grid ends is efficient to eliminate “ghost” solutions. It is further shown that the Hamiltonian matrix in the sine basis can be calculated very accurately by using an auxiliary basis of cosine functions, overcoming the problems arising from numerical calculation of the Jacobian J(x) of the R→x coordinate transformation.
Molecular dynamics simulation of liquid N2O4⇌2NO2 by orientation-sensitive pairwise potential. III. Reaction dynamics
Authors: Katō Toshiko
Published: December 2003

The dissociation and association dynamics of N2O4⇌2NO2 in liquid state are studied by classical molecular dynamics simulations of reactive liquid NO2. An OSPP+LJ potential between NO2 molecules, which is a sum of an orientation-sensitive pairwise potential (OSPP) between N–N atoms proposed in Paper I [J. Chem. Phys. 115, 10852 (2001)] and Lennard-Jones potentials between N–O and O–O atoms, has been used in the simulation. The reaction dynamics is studied as a function of well depth De and anisotropy factors of the OSPP potential: Aθ (0⩽Aθ⩽1) for the rocking angle and Aτ (0⩽Aτ⩽0.5) for the torsional angle of relative NO2–NO2 orientation. The lifetime τD of initially prepared NO2 dimers is found to increase as De increases, Aθ increases, and Aτ decreases. Dissociation and association dynamics are studied in detail around the extreme limit of pure NO2-dimer liquid: De=0.12×10−18 J, Aθ=0.5, and Aτ=0.1, which has been found to reproduce both the observed liquid phase equilibrium properties and Raman band shapes of the dissociation mode very well. The dissociation dynamics from microscopic reaction trajectories is compared with the potential of the mean force (PMF) as a function of the N–N distance R. The PMF of reactive liquid NO2 shows a transition state barrier at R=2.3–2.5 Å, and NO2-trimer structure is found to be formed at the barrier. Two types of dissociation of the NO2 dimer—the dissociation by collisional activation of the reactive mode to cross the dissociation limit and the NO2-mediated dissociation via bond transfer—are studied. The latter needs less free energy and is found to be much more probable. The dissociation trajectories and PMF in reactive liquid NO2 are compared with those of a reactive NO2 pair in inert solvent N2O4.
A new method for solving the quantum hydrodynamic equations of motion: Application to two-dimensional reactive scattering
Authors: Pauler Denise K. , Kendrick Brian K.
Published: December 2003

The de Broglie–Bohm hydrodynamic equations of motion are solved using a meshless method based on a moving least squares approach and an arbitrary Lagrangian–Eulerian frame of reference. A regridding algorithm adds and deletes computational points as needed in order to maintain a uniform interparticle spacing, and unitary time evolution is obtained by propagating the wave packet using averaged fields. The numerical instabilities associated with the formation of nodes in the reflected portion of the wave packet are avoided by adding artificial viscosity to the equations of motion. The methodology is applied to a two-dimensional model collinear reaction with an activation barrier. Reaction probabilities are computed as a function of both time and energy, and are in excellent agreement with those based on the quantum trajectory method.
Mode-specific photoelectron scattering effects on CO2+(C 2Σg+) vibrations
Authors: Rathbone G. J. , Poliakoff E. D. , Bozek John D. , Lucchese R. R. , Lin P.
Published: December 2003

Using high-resolution photoelectron spectroscopy, we have determined the energy dependent vibrational branching ratios for the symmetric stretch [v+=(100)], bend [v+=(010)], and antisymmetric stretch [v+=(001)], as well as several overtones and combination bands in the 4σg−1 photoionization of CO2. Data were acquired over the range from 20–110 eV, and this wide spectral coverage highlighted that alternative vibrational modes exhibit contrasting behavior, even over a range usually considered to be dominated by atomic effects. Alternative vibrational modes exhibit qualitatively distinct energy dependences, and this contrasting mode-specific behavior underscores the point that vibrationally resolved measurements reflect the sensitivity of the electron scattering dynamics to well-defined changes in molecular geometry. In particular, such energy-dependent studies help to elucidate the mechanism(s) responsible for populating the symmetry forbidden vibrational levels [i.e., v+=(010), (001), (030), and (110)]. This is the first study in which vibrationally resolved data have been acquired as a function of energy for all of the vibrational modes of a polyatomic system. Theoretical Schwinger variational calculations are used to interpret the experimental data, and they indicate that a 4σg→kσu shape resonance is responsible for most of the excursions observed for the vibrational branching ratios. Generally, the energy dependent trends are reproduced well by theory, but a notable exception is the symmetric stretch vibrational branching ratio. The calculated results display a strong peak in the vibrational branching ratio while the experimental data show a pronounced minimum. This suggests an interference mechanism that is not accounted for in the single-channel adiabatic-nuclei calculations. Electronic branching ratios were also measured and compared to the vibrational branching ratios to assess the relative contributions of interchannel (i.e., Herzberg–Teller) versus intrachannel (i.e., photoelectron-mediated) coupling.
The ground-state tunneling splitting of various carboxylic acid dimers
Authors: Tautermann Christofer S. , Voegele Andreas F. , Liedl Klaus R.
Published: December 2003

Carboxylic acid dimers in gas phase reveal ground-state tunneling splittings due to a double proton transfer between the two subunits. In this study we apply a recently developed accurate semiclassical method to determine the ground-state tunneling splittings of eight different carboxylic acid derivative dimers (formic acid, benzoic acid, carbamic acid, fluoro formic acid, carbonic acid, glyoxylic acid, acrylic acid, and N,N-dimethyl carbamic acid) and their fully deuterated analogs. The calculated splittings range from 5.3e-4 to 0.13 cm−1 (for the deuterated species from 2.8e-7 to 3.3e-4 cm−1), thus indicating a strong substituent dependence of the splitting, which varies by more than two orders of magnitude. One reason for differences in the splittings could be addressed to different barriers heights, which vary from 6.3 to 8.8 kcal/mol, due to different mesomeric stabilization of the various transition states. The calculated splittings were compared to available experimental data and good agreement was found. A correlation could be found between the tunneling splitting and the energy barrier of the double proton transfer, as the splitting increases with increased strength of the hydrogen bonds. From this correlation an empirical formula was derived, which allows the prediction of the ground-state tunneling splitting of carboxylic acid dimers at a very low cost and the tunneling splittings for parahalogen substituted benzoic acid dimers is predicted.
A different approach for calculating Franck–Condon factors including anharmonicity
Authors: Luis Josep M. , Bishop David M. , Kirtman Bernard
Published: December 2003

An efficient new procedure for calculating Franck–Condon factors, based on the direct solution of an appropriate set of simultaneous equations, is presented. Both Duschinsky rotations and anharmonicity are included, the latter by means of second-order perturbation theory. The critical truncation of basis set is accomplished by a build-up procedure that simultaneously removes negligible vibrational states. A successful test is carried out on ClO2 for which there are experimental data and other theoretical calculations.