Science.gov

Sample records for charge transfer chemistry

  1. Charge-displacement analysis via natural orbitals for chemical valence: Charge transfer effects in coordination chemistry

    NASA Astrophysics Data System (ADS)

    Bistoni, Giovanni; Rampino, Sergio; Tarantelli, Francesco; Belpassi, Leonardo

    2015-02-01

    We recently devised a simple scheme for analyzing on quantitative grounds the Dewar-Chatt-Duncanson donation and back-donation in symmetric coordination complexes. Our approach is based on a symmetry decomposition of the so called Charge-Displacement (CD) function quantifying the charge flow, upon formation of a metal (M)-substrate (S) bond, along the M-S interaction axis and provides clear-cut measures of donation and back-donation charges in correlation with experimental observables [G. Bistoni et al., Angew. Chem., Int. Ed. 52, 11599 (2013)]. The symmetry constraints exclude of course from the analysis most systems of interest in coordination chemistry. In this paper, we show how to entirely overcome this limitation by taking advantage of the properties of the natural orbitals for chemical valence [M. Mitoraj and A. Michalak, J. Mol. Model. 13, 347 (2007)]. A general scheme for disentangling donation and back-donation in the CD function of both symmetric and non-symmetric systems is presented and illustrated through applications to M-ethyne (M = Au, Ni and W) coordination bonds, including an explicative study on substrate activation in a model reaction mechanism.

  2. Revealing charge-transfer effects in gas-phase water chemistry.

    PubMed

    Cappelletti, David; Ronca, Enrico; Belpassi, Leonardo; Tarantelli, Francesco; Pirani, Fernando

    2012-09-18

    An understanding of the interactions involving water and other small hydrogenated molecules such as H(2)S and NH(3) at the molecular level is an important and elusive scientific goal with potential implications for fields ranging from biochemistry to astrochemistry. One longstanding question about water's intermolecular interactions, and notably hydrogen bonding, is the extent and importance of charge transfer (CT) , which can have important implications for the development of reliable model potentials for water chemistry, among other applications. The weakly bound adducts, commonly regarded as pure van der Waals systems, formed by H(2)O, H(2)S, and NH(3) with noble gases or simple molecules such as H(2), provide an interesting case study for these interactions. Their binding energies are approximately 1 or 2 kJ/mol at most, and CT effects in these systems are thought to be negligible. Our laboratory has performed high-resolution molecular-beam scattering experiments that probe the (absolute scale) intermolecular potential of various types of these gas-phase binary complexes with extreme sensitivity. These experiments have yielded surprising and intriguing quantitative results. The key experimental measurable is the "glory" quantum interference shift that shows a systematic, anomalous energy stabilization for the water complexes and clearly points to a significant role for CT effects. To investigate these findings, we have performed very accurate theoretical calculations and devised a simple approach to study the electron displacement that accompanies gas-phase binary intermolecular interactions in extreme detail. These calculations are based on a partial progressive integration of the electron density changes. The results unambiguously show that water's intermolecular interactions are not typical van der Waals complexes. Instead, these interactions possess a definite, strongly stereospecific CT component, even when very weak, where a water molecule may act as electron donor or acceptor depending on its orientation. CT is mediated by an asymmetric role played by the two hydrogen atoms, which causes strong orientation effects. The careful comparison of these calculations with the experimental results shows that the stabilization energy associated to CT is approximately 2-3 eV per electron transferred and may make up for a large portion of the total interaction energy. A simple electron delocalization model helps to validate and explain these findings. PMID:22775359

  3. Opposites Attract: Organic Charge Transfer Salts

    ERIC Educational Resources Information Center

    van de Wouw, Heidi L.; Chamorro, Juan; Quintero, Michael; Klausen, Rebekka S.

    2015-01-01

    A laboratory experiment is described that introduces second-year undergraduate organic chemistry students to organic electronic materials. The discovery of metallic conductivity in the charge transfer salt tetrathiafulvalene tetracyanoquinodimethane (TTF-TCNQ) is a landmark result in the history of organic electronics. The charge transfer

  4. Computational chemistry and aeroassisted orbital transfer vehicles

    NASA Technical Reports Server (NTRS)

    Cooper, D. M.; Jaffe, R. L.; Arnold, J. O.

    1985-01-01

    An analysis of the radiative heating phenomena encountered during a typical aeroassisted orbital transfer vehicle (AOTV) trajectory was made to determine the potential impact of computational chemistry on AOTV design technology. Both equilibrium and nonequilibrium radiation mechanisms were considered. This analysis showed that computational chemistry can be used to predict (1) radiative intensity factors and spectroscopic data; (2) the excitation rates of both atoms and molecules; (3) high-temperature reaction rate constants for metathesis and charge exchange reactions; (4) particle ionization and neutralization rates and cross sections; and (5) spectral line widths.

  5. Mechanochemical Synthesis of Two Polymorphs of the Tetrathiafulvalene-Chloranil Charge Transfer Salt: An Experiment for Organic Chemistry

    ERIC Educational Resources Information Center

    Wixtrom, Alex; Buhler, Jessica; Abdel-Fattah, Tarek

    2014-01-01

    Mechanochemical syntheses avoid or considerably reduce the use of reaction solvents, thus providing green chemistry synthetic alternatives that are both environmentally friendly and economically advantageous. The increased solid-state reactivity generated by mechanical energy imparted to the reactants by grinding or milling can offer alternative…

  6. Charge Transfer Reactions Induce Born-Oppenheimer Breakdown in Surface Chemistry: Applications of Double Resonance Spectroscopy in Molecule-Surface Scattering

    NASA Astrophysics Data System (ADS)

    Wodtke, Alec M.

    2013-06-01

    Atomic and molecular interactions constitute a many-body quantum problem governed fundamentally only by the Coulomb forces between many electrons and nuclei. While simple to state, computers are simply not fast enough to solve this problem by brute force, except for the simplest examples. Combining the Born-Oppenheimer Approximation (BOA) with Density Functional Theory (DFT), however, allows theoretical simulations of extraordinarily complex chemical systems including molecular interactions at solid metal surfaces, the physical basis of surface chemistry. This lecture describes experiments demonstrating the limits of the BOA/DFT approximation as it relates to molecules interacting with solid metal surfaces. One of the most powerful experimental tools at our disposal is a form of double resonance spectroscopy, which allows us to define the quantum state of the molecule both before and after the collision with the surface, providing a complete picture of the resulting energy conversion processes. With such data, we are able to emphasize quantitative measurements that can be directly compared to first principles theories that go beyond the Born-Oppenheimer approximation. One important outcome of this work is the realization that Born-Oppenheimer breakdown can be induced by simple charge transfer reactions that are common in surface chemistry. J. D. White, J. Chen, D. Matsiev, D. J. Auerbach and A. M. Wodtke Nature {433}(7025), 503-505 (2005) Y. H. Huang, C. T. Rettner, D. J. Auerbach and A. M. Wodtke Science {290}(5489), 111-114 (2000) R. Cooper, I. Rahinov, Z. S. Li, D. Matsiev, D. J. Auerbach and A. M. Wodtke Chemical Science {1}(1), 55-61 (2010) J. Larue, T. Schäfer, D. Matsiev, L. Velarde, N. H. Nahler, D. J. Auerbach and A. M. Wodtke PCCP {13}(1), 97-99 (2011).

  7. Charge Transfer Reactions in Porous Materials

    E-print Network

    Mitchell-Koch, Katie Rose

    2008-08-15

    REACTIONS IN POROUS MATERIALS BY Katie R. Mitchell-Koch Submitted to the graduate degree program in Chemistry and the Graduate Faculty of the University of Kansas in partial fulfillment of the requirements for the degree of Doctor of Philosophy. Committee...: Ward H. Thompson, Chairperson Mikhail V. Barybin Brian B. Laird Aaron M. Scurto Jon A. Tunge ii The Dissertation Committee for Katie R. Mitchell-Koch certifies that this is the approved version of the following dissertation: CHARGE TRANSFER REACTIONS...

  8. Contact charge-transfer lasers

    SciTech Connect

    Dharamsi, A.N.; Tulip, J.

    1981-07-01

    A mechanism for sustaining population inversions in contact charge-transfer complexes in which the ground electronic state is not bound is described. The mechanism relies on picosecond radiationless depletion of the lower laser state. This generates an inversion even when the ground-state potential curve, as plotted against the donor-acceptor distance, is not repulsive vertically below the excited state minimum. Contact charge-transfer lasers would offer high gain, high-energy density, and tunable sources of coherent radiation in the uv and visible. A method for pumping such a laser is examined and applied to the pyrrole-oxygen complex. A rate equation analysis is done and estimates for gain and energy density are presented.

  9. Charge-Transfer Versus Charge-Transfer-Like Excitations Revisited

    SciTech Connect

    Moore, Barry; Sun, Haitao; Govind, Niranjan; Kowalski, Karol; Autschbach, Jochen

    2015-07-14

    Criteria to assess charge-transfer (CT) and `CT-like' character of electronic excitations are examined. Time-dependent density functional theory (TDDFT) with non-hybrid, hybrid, and tuned long-range corrected (LC) functionals is compared with with coupled-cluster (CC) benchmarks. The test set includes an organic CT complex, two `push-pull' donor-acceptor chromophores, a cyanine dye, and several polycyclic aromatic hydrocarbons. Proper CT is easily identified. Excitations with significant density changes upon excitation within regions of close spatial proximity can also be diagnosed. For such excitations, the use of LC functionals in TDDFT sometimes leads to dramatic improvements of the singlet energies, similar to proper CT, which has led to the concept of `CT-like' excitations. However, `CT-like' excitations are not like charge transfer, and the improvements are not obtained for the right reasons. The triplet excitation energies are underestimated for all systems, often severely. For the `CT-like' candidates, when going from a non-hybrid to an LC functional the error in the singlet-triplet (S/T) separation changes from negative to positive, providing error compensation. For the cyanine, the S/T separation is too large with all functionals, leading to the best error compensation for non-hybrid functionals.

  10. Electron Transfer in Gaseous Positively Charged Peptides --

    E-print Network

    Simons, Jack

    CHAPTER 8 Electron Transfer in Gaseous Positively Charged Peptides -- Relation to Mass Spectrometry Jack Simons Contents 1. Introduction 164 1.1 The electron-capture event involves electron transfer 165 1.2 Intra-peptide electron transfer can also occur 166 2. The Theoretical Challenges and Examples

  11. Apparent Charge Transfer at Semiconductor Surfaces

    SciTech Connect

    Carpinelli, Joseph M.; Stumpf, Roland R.; Weitering, Hanno H.

    1999-05-11

    We investigate the apparent charge transfer between adatoms in the GeXPb[l.XjGe(lll) interface both experimentally and theoretically. Scanning tunneling microscopy and surface core level measurements suggest significant charge transfer from the Ge adatoms to the Pb adatoms. However, first-principles calculations unambiguously find that the total electronic displacement is negligibly small, and that the results of published experiments can be explained as a result of bond rearrangement.

  12. Charge Transfer during Alkali-Surface Collisions

    NASA Astrophysics Data System (ADS)

    Weare, Christopher Bruce

    The transfer of electrons between atoms and solid surfaces is the driving force behind ionic bond formation in adsorption and determines the final charge state in particle-surface collisions. Despite its importance, however, many aspects of charge transfer are not completely understood. The experiments presented in this dissertation use the scattering of ^7Li ^+ ions from surfaces to study several aspects of charge transfer. Primarily, the effects of alkali adsorption on the surface local electrostatic potential (LEP) are investigated via resonant charge transfer. In addition, the effects of charge promotion on the final charge state distributions of scattered ^7Li ^+ ions are determined. On metal surfaces, large differences in the final charge state distributions of ^7Li ^+ ions scattered from substrate and adsorbate sites are observed at low alkali coverages, which disappear at high coverages. The final charge state distribution of ^7Li^+ ions is determined primarily by resonant charge transfer, which is dependent on the LEP. Thus, there is a transition in the LEP from inhomogeneous to nearly homogeneous as the adsorbate coverage increases. The LEP is modeled as a collection of isolated dipoles positioned at the adsorbate sites. Calculations of the final charge state distributions of ions scattered from such model surfaces do an excellent job of reproducing the measured charge state distributions. From these calculations, it is shown that the inhomogeneous to homogeneous transition in the LEP is due to a coverage dependent depolarization of the adsorbate dipoles. For the alkali-covered Si(111)-7 x 7 surface, the final charge state distribution is independent of scattering site. This behavior is not attributed to a homogeneous LEP, rather, it is due to the dangling bonds of the Si(111) -7 x 7 surface, which allow resonant charge transfer to take place well above the surface. As a consequence, variations in the LEP near the adsorbate sites are not detected. During the Li-Al charge promotion process, a Li 1s hole is created, which later decays by electron emission. Because of this, the charge state distributions of promoted ions differ significantly from those of non-promoted ions. From a combination of charge state distributions and secondary electron spectra, it is shown that the lifetime of the hole is on the order of the ion-surface interaction time, i.e., 10 fs.

  13. Ultrafast charge transfer and atomic orbital polarization

    SciTech Connect

    Deppe, M.; Foehlisch, A.; Hennies, F.; Nagasono, M.; Beye, M.; Sanchez-Portal, D.; Echenique, P. M.; Wurth, W.

    2007-11-07

    The role of orbital polarization for ultrafast charge transfer between an atomic adsorbate and a substrate is explored. Core hole clock spectroscopy with linearly polarized x-ray radiation allows to selectively excite adsorbate resonance states with defined spatial orientation relative to the substrate surface. For c(4x2)S/Ru(0001) the charge transfer times between the sulfur 2s{sup -1}3p*{sup +1} antibonding resonance and the ruthenium substrate have been studied, with the 2s electron excited into the 3p{sub perpendicular}* state along the surface normal and the 3p{sub parallel}* state in the surface plane. The charge transfer times are determined as 0.18{+-}0.07 and 0.84{+-}0.23 fs, respectively. This variation is the direct consequence of the different adsorbate-substrate orbital overlap.

  14. Charge-transfer magnetoelectrics of polymeric multiferroics.

    PubMed

    Qin, Wei; Jasion, Daniel; Chen, Xiaomin; Wuttig, Manfred; Ren, Shenqiang

    2014-04-22

    The renaissance of multiferroics has yielded a deeper understanding of magneto-electric coupling of inorganic single-phase multiferroics and composites. Here, we report charge-transfer polymeric multiferroics, which exhibit external field-controlled magnetic, ferroelectric, and microwave response, as well as magneto-dielectric coupling. The charge-transfer-controlled ferroic properties result from the magnetic field-tunable triplet exciton which has been validated by the dynamic polaron-bipolaron transition model. In addition, the temperature-dependent dielectric discontinuity and electric-field-dependent polarization confirms room temperature ferroelectricity of crystalline charge-transfer polymeric multiferroics due to the triplet exciton, which allows the tunability of polarization by the photoexcitation. PMID:24654686

  15. Simulations of charge transfer in Electron Multiplying Charge Coupled Devices

    NASA Astrophysics Data System (ADS)

    Bush, N.; Stefanov, K.; Hall, D.; Jordan, D.; Holland, A.

    2014-12-01

    Electron Multiplying Charge Coupled Devices (EMCCDs) are a variant of traditional CCD technology well suited to applications that demand high speed operation in low light conditions. On-chip signal amplification allows the sensor to effectively suppress the noise introduced by readout electronics, permitting sub-electron read noise at MHz pixel rates. The devices have been the subject of many detailed studies concerning their operation, however there has not been a study into the transfer and multiplication process within the EMCCD gain register. Such an investigation has the potential to explain certain observed performance characteristics, as well as inform further optimisations to their operation. In this study, the results from simulation of charge transfer within an EMCCD gain register element are discussed with a specific focus on the implications for serial charge transfer efficiency (CTE). The effects of operating voltage and readout speed are explored in context with typical operating conditions. It is shown that during transfer, a small portion of signal charge may become trapped at the semiconductor-insulator interface that could act to degrade the serial CTE in certain operating conditions.

  16. Charge transfer complexes of certain aromatic polyimides

    NASA Technical Reports Server (NTRS)

    Gordina, T. A.; Kotov, B. V.; Kolninov, O. V.; Pravednikov, A. N.

    1985-01-01

    By electron spectroscopy it was shown that aromatic polyimides containing electron-donor residues of diamines -C6H4-X-C6H-(X=NH, NCH3, NC6H5, O, S, and CH2) form charge transfer complexes with low-molecular-weight electron acceptors. Based on the data obtained, the hypothesis was advanced that the coloration of the polyimides per se is due to the formation of charge transfer complexes between the electron-acceptor imide fragments and the electron-donor residues of the diamines.

  17. Chemistry Transfer Evaluations Before requesting a transfer evaluation, please look up your courses on the UO Transfer Credit

    E-print Network

    Cina, Jeff

    Chemistry Transfer Evaluations Before requesting a transfer evaluation, please look up your courses://registrar.uoregon.edu/current_students/transfer-articulation If your Chemistry courses have not been evaluated, or if you feel the evaluation is not correct, then fill out this form and bring it and the associated documents to a Chemistry advisor. Name

  18. Spacecraft Charging in Geostationary Transfer Orbit

    NASA Technical Reports Server (NTRS)

    Parker, Linda Neergaard; Minow, Joseph I.

    2014-01-01

    The 700 km x 5.8 Re orbit of the two Van Allen Probes spacecraft provide a unique opportunity to investigate spacecraft charging in geostationary transfer orbits. We use records from the Helium Oxygen Proton Electron (HOPE) plasma spectrometer to identify candidate surface charging events based on the "ion line" charging signature in the ion records. We summarize the energetic particle environment and the conditions necessary for charging to occur in this environment. We discuss the altitude, duration, and magnitude of events observed in the Van Allen Probes from the beginning of the mission to present time. In addition, we explore what information the dual satellites provide on the spatial and temporal variations in the charging environments.

  19. Building model systems to understand Proton-Coupled Electron Transfer in heme : spectroscopic investigation of charge transfer to axially bound diimide acceptors

    E-print Network

    Hanson, Christina J

    2013-01-01

    Proton-Coupled Electron Transfer (PCET) is an important mechanistic motif in chemistry, which allows for efficient charge transport in many biological systems. We seek to understand how the proton and electron motions are ...

  20. Charge transfer between carbon nanotubes on surfaces

    NASA Astrophysics Data System (ADS)

    Araujo, Karolline A. S.; Barboza, Ana P. M.; Fernandes, Thales F. D.; Shadmi, Nitzan; Joselevich, Ernesto; Mazzoni, Mario S. C.; Neves, Bernardo R. A.

    2015-10-01

    The charge transfer between neighboring single-walled carbon nanotubes (SWNTs) on a silicon oxide surface was investigated as a function of both the SWNT nature (metallic or semiconducting) and the anode/cathode distance using scanning probe techniques. Two main mechanisms were observed: a direct electron tunneling described by the typical Fowler-Nordheim model, and indirect electron transfer (hopping) mediated by functional groups on the supporting surface. Both mechanisms depend on the SWNT nature and on the anode/cathode separation: direct electron tunneling dominates the charge transfer process for metallic SWNTs, especially for large distances, while both mechanisms compete with each other for semiconducting SWNTs, prevailing one over the other depending on the anode/cathode separation. These mechanisms may significantly influence the design and operation of SWNT-based electronic devices.

  1. Dynamical Treatment of Charge Transfer through Duplex Nucleic Acids Containing Modified Adenines

    PubMed Central

    Brancolini, Giorgia; Migliore, Agostino; Corni, Stefano; Fuentes-Cabrera, Miguel; Luque, F. Javier; Di Felice, Rosa

    2014-01-01

    We address the issue of whether chemical alterations of nucleobases are an effective tool to modulate charge transfer through DNA molecules. Our investigation uses a multi-level computational approach based on classical molecular dynamics and quantum chemistry. We find yet another evidence that structural fluctuations are a key factor to determine the electronic structure of double-stranded DNA. We argue that the electronic structure and charge transfer ability of flexible polymers is the result of a complex intertwining of various structural, dynamical and chemical factors. Chemical intuition may be used to design molecular wires, but this is not the sole component in the complex charge transfer mechanism through DNA. PMID:24060008

  2. Charge transfer in tunnel-junction arrays

    NASA Astrophysics Data System (ADS)

    Kaplan, Daniel M. R.

    Numerical modeling was used to study charge transfer in tunnel junction arrays. The effects of various configurations of background charge were considered, with the ultimate goal of making predictions about the possibility of device design. First the uniform (no background charge) arrays were considered. In this case solitonantisoliton avalanches were observed. Though the time duration of any avalanche, and the total charge DeltaQ = ne transferred across the array during the avalanche, are always finite, in arrays with length N larger than certain critical value Lc and large width M >> f(N), the avalanche magnitude n may be exponentially large, resulting in particular in a giant increase of shot noise. Next a special distribution of background charge was found, such that the array's Coulomb blockade is completely suppressed and shot noise is reduced substantially at low applied voltages. In particular the Fano factor F can approach the minimum value Fmin = 1/N << 1 (where N is the array length). Finally, the effects of the fully random q = [-e/2; + e/2] background charge were studied. Density of states at zero energy was found to have a dramatically different dependence on the array size in 1D and 2D. Also, in 2D systems a soft Coulomb gap was observed, whit DoS value at low energy diminishing rapidly with the array size. The effects of background charge on shot noise were also studied. At zero temperature and low current in 2D systems a strong increase in shot noise was observed, while addition of moderately low (T < eVt/N) temperature suppresses the noise. Results are discussed in the context of their possible application to single-electron devices.

  3. Variable Charge Soils: Mineralogy and Chemistry

    SciTech Connect

    Qafoku, Nik; Van Ranst, Eric; Noble, Andrew; Baert, Geert

    2003-11-01

    Soils rich in particles with amphoteric surface properties in the Oxisols, Ultisols, Alfisols, Spodosols and Andisols orders (1) are considered variable charge soils (2). The term “variable charge” is used to describe organic and inorganic soil constituents with reactive surface groups whose charge varies with pH, ionic concentration and composition of the soil solution. Such groups are the surface carboxyl, phenolic and amino functional groups of organic materials in soils, and surface hydroxyl groups of Fe and Al oxides, allophane and imogolite. The hydroxyl surface groups are also present on edges of some phyllosilicate minerals such as kaolinite, mica, and hydroxyl-interlayered vermiculite. The variable charge is developed on the surface groups as a result of adsorption or desorption of ions that are constituents of the solid phase, i.e., H+, and the adsorption or desorption of solid-unlike ions that are not constituents of the solid. Highly weathered soils usually undergo isoeletric weathering and reach a “zero net charge” stage during their development. They have a slightly acidic to acidic soil solution pH, which is close to either point of zero net charge (PZNC) (3) or point of zero salt effect (PZSE) (3). They are characterized by high abundances of minerals with a point of zero net proton charge (PZNPC) (3) at neutral and slightly basic pHs; the most important being Fe and Al oxides and allophane. Under acidic conditions, the surfaces of these minerals are net positively charged. In contrast, the surfaces of permanent charge phyllosilicates are negatively charged regardless of ambient conditions. Variable charge soils therefore, are heterogeneous charge systems. The coexistence and interactions of oppositely charged surfaces or particles confers a different pattern of physical and chemical behavior on the soil, relatively to a homogeneously charged system of temperate regions. In some variable charge soils (Oxisols and some Ultisols developed on ferromagnesian-rich parent materials) the surfaces of phyllosilicates are coated to a lesser or greater extent by amorphous or crystalline, oppositely charged nanoparticles of Fe and Al oxides. These coatings exhibit a high reactive surface area and help cementing larger particles with one another. As a result of these electrostatic interactions, stable microaggregates that are difficult to disperse are formed in variable charge soils. Most of highly weathered soils have reached the “advanced stage” of Jackson-Sherman weathering sequence that is characterized by the removal of Na, K, Ca, Mg, and Fe(II), the presence of Fe and Al polymers, and very dilute soil solutions with an ionic strength (IS) of less than 1 mmol L-1. The inter-penetration or overlapping of the diffuse double layers on oppositely charged surfaces may occur in these dilute systems. These diffuse layer interactions may affect the magnitude of the effective charge, i.e., the counter-ion charge (4). In addition, salt adsorption, which is defined as the simultaneous adsorption in equivalent amounts of the cation and anion of an electrolyte with no net release of other ions into the soil solution, appears to be a common phenomenon in these soils. They act as cation- and anion-exchangers and as salt-sorbers. The magnitude of salt adsorption depends strongly on initial IS in the soil solution and the presence in appreciable amounts of oppositely charged surfaces. Among the authors that have made illustrious contributions towards a better understanding of these fascinating soil systems are S. Matson, R.K. Schofield, van Olphen, M.E. Sumner, G.W. Thomas, G.P. Gillman, G. Uehara, B.K.G. Theng, K. Wada, N.J. Barrow, J.W. Bowden, R.J. Hunter and G. Sposito. This entry is mainly based on publications by these authors.

  4. Pattern classification using charge transfer devices

    NASA Technical Reports Server (NTRS)

    1980-01-01

    The feasibility of using charge transfer devices in the classification of multispectral imagery was investigated by evaluating particular devices to determine their suitability in matrix multiplication subsystem of a pattern classifier and by designing a protype of such a system. Particular attention was given to analog-analog correlator devices which consist of two tapped delay lines, chip multipliers, and a summed output. The design for the classifier and a printed circuit layout for the analog boards were completed and the boards were fabricated. A test j:g for the board was built and checkout was begun.

  5. On the Acid-Base Chemistry of Permanently Charged Minerals

    E-print Network

    Morel, François M. M.

    On the Acid-Base Chemistry of Permanently Charged Minerals A N N E M . L . K R A E P I E L University, Princeton, New Jersey 08544 The acid-base properties of oxides are well described by the surface complexation model, which superposes a thermodynamic description of acid-base reactions

  6. Charge transfer processes: the role of optimized molecular orbitals.

    PubMed

    Meyer, Benjamin; Domingo, Alex; Krah, Tim; Robert, Vincent

    2014-08-01

    The influence of the molecular orbitals on charge transfer (CT) reactions is analyzed through wave function-based calculations. Characteristic CT processes in the organic radical 2,5-di-tert-butyl-6-oxophenalenoxyl linked with tetrathiafulvalene and the inorganic crystalline material LaMnO3 show that changes in the inner shells must be explicitly taken into account. Such electronic reorganization can lead to a reduction of the CT vertical transition energy up to 66%. A state-specific approach accessible through an adapted CASSCF (complete active space self-consistent field) methodology is capable of reaching good agreement with the experimental spectroscopy of CT processes. A partitioning of the relaxation energy in terms of valence- and inner-shells is offered and sheds light on their relative importance. This work paves the way to the intimate description of redox reactions using quantum chemistry methods. PMID:24781811

  7. Electrochemical charge transfer at a metallic electrode: a simulation study 

    E-print Network

    Pounds, Michael A.

    2010-01-01

    Part I Electrochemical charge transfer at a metallic electrode: a simulation study The factors which affect the rate of heterogeneous electron transfer at a metallic electrode in the context of Marcus theory are ...

  8. Photoinduced charge accumulation by metal ion-coupled electron transfer.

    PubMed

    Bonn, Annabell G; Wenger, Oliver S

    2015-10-01

    An oligotriarylamine (OTA) unit, a Ru(bpy)3(2+) photosensitizer moiety (Ru), and an anthraquinone (AQ) entity were combined to a molecular dyad (Ru-OTA) and a molecular triad (AQ-Ru-OTA). Pulsed laser excitation at 532 nm led to the formation of charge-separated states of the type Ru(-)-OTA(+) and AQ(-)-Ru-OTA(+) with lifetimes of ?10 ns and 2.4 ?s, respectively, in de-aerated CH3CN at 25 °C. Upon addition of Sc(OTf)3, very long-lived photoproducts were observed. Under steady-state irradiation conditions using a flux of (6.74 ± 0.21) × 10(15) photons per second at 450 nm, the formation of twofold oxidized oligotriarylamine (OTA(2+)) was detected in aerated CH3CN containing 0.02 M Sc(3+), as demonstrated unambiguously by comparison with UV-Vis absorption spectra obtained in the course of chemical oxidation with Cu(2+). Photodriven charge accumulation on the OTA unit of Ru-OTA and AQ-Ru-OTA is possible due to the lowering of the O2 reduction potential caused by the interaction of superoxide with the strong Lewis acid Sc(3+). The presence of the anthraquinone unit in AQ-Ru-OTA accelerates the rate-determining reaction step for charge accumulation by a factor of 10 compared to the Ru-OTA dyad. This is attributed to the formation of Sc(3+)-stabilized anthraquinone radical anion intermediates in the triad. Possible mechanistic pathways leading to charge accumulation are discussed. Photodriven charge accumulation is of key importance for solar fuels because their production will have to rely on multi-electron chemistry rather than single-electron reaction steps. Our study is the first to demonstrate that metal ion-coupled electron transfer (MCET) can be exploited to accumulate charges on a given molecular unit using visible light as an energy input. The approach of using a combination of intra- and intermolecular electron transfer reactions which are enabled by MCET is conceptually novel, and the fundamental insights gained from our study are relevant in the greater context of solar energy conversion. PMID:26312416

  9. Characterisation of a CMOS charge transfer device for TDI imaging

    NASA Astrophysics Data System (ADS)

    Rushton, J.; Holland, A.; Stefanov, K.; Mayer, F.

    2015-03-01

    The performance of a prototype true charge transfer imaging sensor in CMOS is investigated. The finished device is destined for use in TDI applications, especially Earth-observation, and to this end radiation tolerance must be investigated. Before this, complete characterisation is required. This work starts by looking at charge transfer inefficiency and then investigates responsivity using mean-variance techniques.

  10. PHOTOSENSITIVE CENTERS AND CHARGE TRANSFER PROCESSES IN BARIUM CALCIUM TITANATE

    E-print Network

    Malovichko, Galina

    PHOTOSENSITIVE CENTERS AND CHARGE TRANSFER PROCESSES IN BARIUM CALCIUM TITANATE G.MALOVICHKO, V@uos.de; vgrachev@uos.de; schirmer@uos.de Abstract The results of the study of charge transfer processes in barium of crystals from barium titanate (BT) family make them promising candidates for various applications

  11. The influence of optical light on the charge transfer efficiency

    E-print Network

    Barnstedt, Jürgen

    The influence of optical light on the charge transfer efficiency of the XMM EPIC pn­CCD camera J­CCD, the charge transfer efficiency (CTE) must be well known. Impurities in the wafer material act as traps. Electrons generated by optical light from the observed source or other optical sources may well saturate

  12. Ion momentum and energy transfer rates for charge exchange collisions

    NASA Technical Reports Server (NTRS)

    Horwitz, J.; Banks, P. M.

    1973-01-01

    The rates of momentum and energy transfer have been obtained for charge exchange collisions between ion and neutral gases having arbitrary Maxwellian temperatures and bulk transport velocities. The results are directly applicable to the F-region of the ionosphere where 0+ - 0 charge is the dominant mechanism affecting ion momentum and energy transfer.

  13. Transfer of Algebraic and Graphical Thinking between Mathematics and Chemistry

    ERIC Educational Resources Information Center

    Potgieter, Marietjie; Harding, Ansie; Engelbrecht, Johann

    2008-01-01

    Students in undergraduate chemistry courses find, as a rule, topics with a strong mathematical basis difficult to master. In this study we investigate whether such mathematically related problems are due to deficiencies in their mathematics foundation or due to the complexity introduced by transfer of mathematics to a new scientific domain. In the…

  14. Study of charges transferability for use in force fields

    NASA Astrophysics Data System (ADS)

    Maciel, Glauciete S.; Garcia, Edgardo

    2006-03-01

    This Letter examines the topological neighborhood effects on atomic partial charges and their transferability. To determine neighborhood effects, we used Breneman and Wiberg's CHELPG charges calculated at B3LYP/6-31G* theory level and AM1 geometries for a test set of 324 molecules of insecticides, ferroelectric liquid crystals (FLC) and antiinflammatories. The Qcode atomic descriptor was applied to represent topological neighborhood. Calculated molecular dipole moments using averaged charges with various neighbor numbers indicate that partial charges have a strong dependence with the molecular topology. Five or more neighbors are demonstrated to be typically needed for accurate partial charges transferability.

  15. Charge Transfer Nanocomposites: Advances in Organic Devices

    NASA Astrophysics Data System (ADS)

    Carroll, David

    2004-11-01

    Optically/electronically active blends of single walled carbon nanotubes (SWNTs) and conjugated polymers (MEH-PPV, PFO, PEDOT, P3OT, etc.), also known as charge transfer nanocomposites, exhibit a fascinating array of opto-electronic phenomena not found with the pure conducting polymers. Over the past two years, we have demonstrated that modifications to the conjugated polymer's transport properties and optical response can be interpreted directly from a simple band model with isolated gap states. These "donor-acceptor" states associated with the high aspect ratio nanotubes can be used to provide significant enhancements to the performance characteristics of organic devices. Specifically, enhanced electro-luminescence yields and resistance to photo-oxidation of the polymer has been observed for a variety of polymer systems. This resistance to photo-oxidation (and subsequent resistance to interfacial degradation) has also been observed in photovoltaic cells along with an increase in overall conversion efficiency for systems that form "shallow" trapping states with the SWNTs. While this is thought to be related to suppression of the triplet exciton in the polymer host, by the SWNT, the exact dynamics of the process remains unclear. Recent results examining photo-sensitive noise in electronic transport, injection dynamics, and exciton lifetimes coupled with the emergence of doped nanotubes suggest a much more complex model for the nature of the nanotube - electro-active polymer interface. Ultimately, a range of nanocomposite devices previously not considered viable in organics, may now be realized.

  16. Contributions of charge-density research to medicinal chemistry

    PubMed Central

    Dittrich, Birger; Matta, Chérif F.

    2014-01-01

    This article reviews efforts in accurate experimental charge-density studies with relevance to medicinal chemistry. Initially, classical charge-density studies that measure electron density distribution via least-squares refinement of aspherical-atom population parameters are summarized. Next, interaction density is discussed as an idealized situation resembling drug–receptor interactions. Scattering-factor databases play an increasing role in charge-density research, and they can be applied both to small-molecule and macromolecular structures in refinement and analysis; software development facilitates their use. Therefore combining both of these complementary branches of X-ray crystallography is recommended, and examples are given where such a combination already proved useful. On the side of the experiment, new pixel detectors are allowing rapid measurements, thereby enabling both high-throughput small-molecule studies and macromolecular structure determination to higher resolutions. Currently, the most ambitious studies compute intermolecular interaction energies of drug–receptor complexes, and it is recommended that future studies benefit from recent method developments. Selected new developments in theoretical charge-density studies are discussed with emphasis on its symbiotic relation to crystallography. PMID:25485126

  17. X-ray absorption structural study of a reversible, photoexcited charge-transfer state

    SciTech Connect

    Chen, L.X.; Bowman, M.K.; Norris, J.R. Univ. of Chicago, IL ); Montano, P.A. )

    1993-05-19

    Electron-transfer reactions can be accompanied by significant nuclear movements. Nuclear motion appears to be especially vital to the reversible, photoinduced charge-transfer chemistry of cyclopentadienylnickel nitrosyl (C[sub 5]H[sub 5]NiNO). Although extended X-ray absorption fine structure (EXAFS) spectroscopy has recorded photoinduced changes in the ligation of myoglobins, similar X-ray studies of electron-transfer chemistry have not been reported. Here we examine reversible, photoinduced structural changes in C[sub 5]H[sub 5]NiNO by EXAFS and propose a mechanism for the electron-transfer chemistry. This work demonstrates that EXAFS can measure distance changes accompanying photoinduced electron transfer to provide new details of the geometry of photoexcited state and suggests that electron transfer occurs in the transient, optically excited states of C[sub 5]H[sub 5]NiNO and C[sub 5]H[sub 5]NiNO[sup CT] as dictated by NO movement that produces either C[sub 5]H[sub 5]NiNO[sup CT] or C[sub 5]H[sub 5]NiNO[sup GS]. 14 refs., 2 figs.

  18. Improved Charge-Transfer Fluorescent Dyes

    NASA Technical Reports Server (NTRS)

    Meador, Michael

    2005-01-01

    Improved charge-transfer fluorescent dyes have been developed for use as molecular probes. These dyes are based on benzofuran nuclei with attached phenyl groups substituted with, variously, electron donors, electron acceptors, or combinations of donors and acceptors. Optionally, these dyes could be incorporated as parts of polymer backbones or as pendant groups or attached to certain surfaces via self-assembly-based methods. These dyes exhibit high fluorescence quantum yields -- ranging from 0.2 to 0.98, depending upon solvents and chemical structures. The wavelengths, quantum yields, intensities, and lifetimes of the fluorescence emitted by these dyes vary with (and, hence, can be used as indicators of) the polarities of solvents in which they are dissolved: In solvents of increasing polarity, fluorescence spectra shift to longer wavelengths, fluorescence quantum yields decrease, and fluorescence lifetimes increase. The wavelengths, quantum yields, intensities, and lifetimes are also expected to be sensitive to viscosities and/or glass-transition temperatures. Some chemical species -- especially amines, amino acids, and metal ions -- quench the fluorescence of these dyes, with consequent reductions in intensities, quantum yields, and lifetimes. As a result, the dyes can be used to detect these species. Another useful characteristic of these dyes is a capability for both two-photon and one-photon absorption. Typically, these dyes absorb single photons in the ultraviolet region of the spectrum (wavelengths < 400 nm) and emit photons in the long-wavelength ultraviolet, visible, and, when dissolved in some solvents, near-infrared regions. In addition, these dyes can be excited by two-photon absorption at near-infrared wavelengths (600 to 800 nm) to produce fluorescence spectra identical to those obtained in response to excitation by single photons at half the corresponding wavelengths (300 to 400 nm). While many prior fluorescent dyes exhibit high quantum yields, solvent-polarity- dependent fluorescence behavior, susceptibility to quenching by certain chemical species, and/or two-photon fluorescence, none of them has the combination of all of these attributes. Because the present dyes do have all of these attributes, they have potential utility as molecular probes in a variety of applications. Examples include (1) monitoring curing and deterioration of polymers; (2) monitoring protein expression; (3) high-throughput screening of drugs; (4) monitoring such chemical species as glucose, amines, amino acids, and metal ions; and (5) photodynamic therapy of cancers and other diseases.

  19. Phonons and charge-transfer excitations in HTS superconductors

    SciTech Connect

    Bishop, A.R.

    1989-01-01

    Some of the experimental and theoretical evidence implicating phonons and charge-transfer excitations in HTS superconductors is reviewed. It is suggested that superconductivity may be driven by a synergistic interplay of (anharmonic) phonons and electronic degrees of freedom (e.g., charge fluctuations, excitons). 47 refs., 5 figs.

  20. Charge transfer during individual collisions in ice growing by riming

    NASA Technical Reports Server (NTRS)

    Avila, Eldo E.; Caranti, Giorgio M.

    1991-01-01

    The charging of a target by riming in the wind was studied in the temperature range of (-10, -18 C). For each temperature, charge transfers of both signs are observed and, according to the environmental conditions, one of them prevails. The charge is more positive as the liquid water concentration is increased at any particular temperature. It is found that even at the low impact velocities used (5 m/s) there is abundant evidence of fragmentation following the collision.

  1. INTRAMOLECULAR CHARGE AND ENERGY TRANSFER IN MULTICHROMOPHORIC AROMATIC SYSTEMS

    SciTech Connect

    Edward C. Lim

    2008-09-09

    A concerted experimental and computational study of energy transfer in nucleic acid bases and charge transfer in dialkylaminobenzonitriles, and related electron donor-acceptor molecules, indicate that the ultrafast photoprocesses occur through three-state conical interactions involving an intermediate state of biradical character.

  2. Energetics of protein charge transfer and photosynthesis

    E-print Network

    Matyushov, Dmitry

    from redox chemistry: = 1 eV Do molecules present a dead case for solar energy conversion? Why does+ Electrostatics facts: Dipole moment ~ 2400 D Observables: #12; Gigantic reorganization energy of electron electron hops! #12; Energy loss to the phonon bath Moving electron with zero activation barrier requires

  3. Charge transfer reactions in nematic liquid crystals

    SciTech Connect

    Wiederrecht, G.P.; Wasielewski, M.R.; Galili, T.; Levanon, H.

    1998-07-01

    Ultrafast transient absorption studies of intramolecular photoinduced charge separation and thermal charge recombination were carried out on a molecule consisting of a 4-(N-pyrrolidino)naphthalene-1,8-imide donor (PNI) covalently attached to a pyromellitimide acceptor (PI) dissolved in the liquid crystal 4{prime}-(n-pentyl)-4-cyanobiphenyl (5CB). The temperature dependencies of the charge separation and recombination rates were obtained at temperatures above the nematic-isotropic phase transition of 5CB, where ordered microdomains exist and scattering of visible light by these domains is absent. The authors show that excited state charge separation is dominated by molecular reorientation of 5CB perpendicular to the director within the liquid crystal microdomains. They also show that charge recombination is adiabatic and is controlled by the comparatively slow collective reorientation of the liquid crystal microdomains relative to the orientation of PNI{sup +}-PI{sup {minus}}. They also report the results of time resolved electron paramagnetic resonance (TREPR) studies of photoinduced charge separation in a series of supramolecular compounds dissolved in oriented liquid crystal solvents. These studies permit the determination of the radical pair energy levels as the solvent reorganization energy increases from the low temperature crystalline phase, through the soft glass phase, to the nematic phase of the liquid crystal.

  4. Theoretical treatment of charge transfer processes of relevance to astrophysics

    SciTech Connect

    Krstic, P.S.; Stancil, P.C.; Schultz, D.R.

    1997-12-01

    Charge transfer is an important process in many astrophysical and atmospheric environments. While numerous experimental and theoretical studies exist for H and He targets, data on other targets, particularly metals and molecules, are sparse. Using a variety of theoretical methods and computational techniques the authors are developing methods to estimate the cross sections for electron capture (charge transfer) in slow collisions of low charge state ions with heavy (Mg, Ca, Fe, Co, Ni and Zn) neutrals. In this ongoing work particular attention is paid to ascertaining the importance of double electron capture.

  5. Coherent ultrafast charge transfer in an organic photovoltaic blend.

    PubMed

    Falke, Sarah Maria; Rozzi, Carlo Andrea; Brida, Daniele; Maiuri, Margherita; Amato, Michele; Sommer, Ephraim; De Sio, Antonietta; Rubio, Angel; Cerullo, Giulio; Molinari, Elisa; Lienau, Christoph

    2014-05-30

    Blends of conjugated polymers and fullerene derivatives are prototype systems for organic photovoltaic devices. The primary charge-generation mechanism involves a light-induced ultrafast electron transfer from the light-absorbing and electron-donating polymer to the fullerene electron acceptor. Here, we elucidate the initial quantum dynamics of this process. Experimentally, we observed coherent vibrational motion of the fullerene moiety after impulsive optical excitation of the polymer donor. Comparison with first-principle theoretical simulations evidences coherent electron transfer between donor and acceptor and oscillations of the transferred charge with a 25-femtosecond period matching that of the observed vibrational modes. Our results show that coherent vibronic coupling between electronic and nuclear degrees of freedom is of key importance in triggering charge delocalization and transfer in a noncovalently bound reference system. PMID:24876491

  6. The study of surface acoustic wave charge transfer device

    NASA Technical Reports Server (NTRS)

    Papanicolaou, N.; Lin, H. C.

    1978-01-01

    A surface acoustic wave-charge transfer device, consisting of an n-type silicon substrate, a thermally grown silicon dioxide layer, and a sputtered film of piezoelectric zinc oxide is proposed as a means of circumventing problems associated with charge-coupled device (CCD) applications in memory, signal processing, and imaging. The proposed device creates traveling longitudinal electric fields in the silicon and replaces the multiphase clocks in CCD's. The traveling electric fields create potential wells which carry along charges stored there. These charges may be injected into the wells by light or by using a p-n junction as in conventional CCD's.

  7. Charge Transfer and Support Effects in Heterogeneous Catalysis

    SciTech Connect

    Hervier, Antoine

    2011-12-21

    The kinetic, electronic and spectroscopic properties of two?dimensional oxide?supported catalysts were investigated in order to understand the role of charge transfer in catalysis. Pt/TiO{sub 2} nanodiodes were fabricated and used as catalysts for hydrogen oxidation. During the reaction, the current through the diode, as well as its I?V curve, were monitored, while gas chromatography was used to measure the reaction rate. The current and the turnover rate were found to have the same temperature dependence, indicating that hydrogen oxidation leads to the non?adiabatic excitation of electrons in Pt. A fraction of these electrons have enough energy to ballistically transport through Pt and overcome the Schottky barrier at the interface with TiO{sub 2}. The yield for this phenomenon is on the order of 10{sup ?4} electrons per product molecule formed, similar to what has been observed for CO oxidation and for the adsorption of many different molecules. The same Pt/TiO{sub 2} system was used to compare currents in hydrogen oxidation and deuterium oxidation. The current through the diode under deuterium oxidation was found to be greater than under hydrogen oxidation by a factor of three. Weighted by the difference in turnover frequencies for the two isotopes, this would imply a chemicurrent yield 5 times greater for D{sub 2} compared to H{sub 2}, contrary to what is expected given the higher mass of D{sub 2}. Reversible changes in the rectification factor of the diode are observed when switching between D{sub 2} and H{sub 2}. These changes are a likely cause for the differences in current between the two isotopes. In the nanodiode experiments, surface chemistry leads to charge flow, suggesting the possibility of creating charge flow to tune surface chemistry. This was done first by exposing a Pt/Si diode to visible light while using it as a catalyst for H{sub 2} oxidation. Absorption of the light in the Si, combined with the band bending at the interface, gives rise to a steady?state flow of hot holes to the surface. This leads to a decrease in turnover on the surface, an effect which is enhanced when a reverse bias is applied to the diode. Similar experiments were carried out for CO oxidation. On Pt/Si diodes, the reaction rate was found to increase when a forward bias was applied. When the diode was exposed to visible light and a reverse bias was applied, the rate was instead decreased. This implies that a flow of negative charges to the surface increases turnover, while positive charges decrease it. Charge flow in an oxide supported metal catalyst can be modified even without designing the catalyst as a solid state electronic device. This was done by doping stoichiometric and nonstoichiometric TiO{sub 2} films with F, and using the resulting oxides as supports for Pt films. In the case of stoichiometric TiO{sub 2}, F was found to act as an n?type dopant, creating a population of filled electronic states just below the conduction band, and dramatically increasing the conductivity of the oxide film. The electrons in those states can transfer to surface O, activating it for reaction with CO, and leading to increased turnover for CO oxidation. This reinforces the hypothesis that CO oxidation is activated by a flow of negative charges to the surface. The same set of catalysts was used for methanol oxidation. The electronic properties of the TiO{sub 2} films again correlated with the turnover rates, but also with selectivity. With stoichiometric TiO{sub 2} as the support, F?doping caused an increase in selectivity toward the formation of partial oxidation products, formaldehyde and methyl formate, versus the total oxidation product, CO{sub 2}. With non?stoichiometric TiO{sub 2}, F?doping had the reverse effect. Ambient Pressure X?Ray Photoelectron Spectroscopy was used to investigate this F?doping effect in reaction conditions. In O2 alone, and in CO oxidation conditions, the O1s spectrum showed a high binding energy peak that correlated in intensity with the activity of the different films: for stoichiomet

  8. Charge transfer in transition-metal alloying: Charge-tailing effects

    SciTech Connect

    Watson, R.E.; Weinert, M.; Fernando, G.W. )

    1991-01-15

    Charge transfer in alloys is normally discussed in terms of band hybridization, band filling, and screening, but at times experiment and theory yield apparently odd results where, for example, rare-earth actinides or elements from the Ti column apparently gain charge from electronegative transition metals such as Fe, Pt, or Au. Here it is observed that there are charge-tailing terms, due to tails of charge associated with an atom's nearest neighbors, which make substantial contributions to the change in charge count at a site in a compound. This is shown with linearized augmented Slater-type-orbital calculations for 5{ital d} transition-metal alloys in the ordered CsCl structure. That charge transfer that remains, {ital after} the tailing effects are subtracted out, is seen to be consistent with notions concerning electronegativity behavior (though indicating Pt rather than Au to be the most electronegative of the 5{ital d} elements). These findings have serious implications for understanding charge transfer and make it necessary to reexamine almost all the arguments relating charge transfer to the bonding of transition metals and, for that matter, of main group elements.

  9. Multiple-charge transfer and trapping in DNA dimers

    NASA Astrophysics Data System (ADS)

    Tornow, Sabine; Bulla, Ralf; Anders, Frithjof B.; Zwicknagl, Gertrud

    2010-11-01

    We investigate the charge transfer characteristics of one and two excess charges in a DNA base-pair dimer using a model Hamiltonian approach. The electron part comprises diagonal and off-diagonal Coulomb matrix elements such a correlated hopping and the bond-bond interaction, which were recently calculated by Starikov [E. B. Starikov, Philos. Mag. Lett. 83, 699 (2003)10.1080/0950083031000151374] for different DNA dimers. The electronic degrees of freedom are coupled to an ohmic or a superohmic bath serving as dissipative environment. We employ the numerical renormalization group method in the nuclear tunneling regime and compare the results to Marcus theory for the thermal activation regime. For realistic parameters, the rate that at least one charge is transferred from the donor to the acceptor in the subspace of two excess electrons significantly exceeds the rate in the single charge sector. Moreover, the dynamics is strongly influenced by the Coulomb matrix elements. We find sequential and pair transfer as well as a regime where both charges remain self-trapped. The transfer rate reaches its maximum when the difference of the on-site and intersite Coulomb matrix element is equal to the reorganization energy which is the case in a guanine/cytosine (GC)-dimer. Charge transfer is completely suppressed for two excess electrons in adenine/thymine (AT)-dimer in an ohmic bath and replaced by damped coherent electron-pair oscillations in a superohmic bath. A finite bond-bond interaction W alters the transfer rate: it increases as function of W when the effective Coulomb repulsion exceeds the reorganization energy (inverted regime) and decreases for smaller Coulomb repulsion.

  10. Photodissociation and charge transfer dynamics of negative ions studied with femtosecond photoelectron spectroscopy

    SciTech Connect

    Zanni, Martin T.

    1999-12-17

    This dissertation presents studies aimed at understanding the potential energy surfaces and dynamics of isolated negative ions, and the effects of solvent on each. Although negative ions play important roles in atmospheric and solution phase chemistry, to a large extent the ground and excited state potential energy surfaces of gas phase negative ions are poorly characterized, and solvent effects even less well understood. In an effort to fill this gap, the author's coworkers and the author have developed a new technique, anion femtosecond photoelectron spectroscopy, and applied it to gas phase photodissociation and charge transfer processes. Studies are presented that (1) characterize the ground and excited states of isolated and clustered anions, (2) monitor the photodissociation dynamics of isolated and clustered anions, and (3) explore the charge-transfer-to-solvent states of atomic iodide clustered with polar and non-polar solvents.

  11. Bioexcimers as Precursors of Charge Transfer and Reactivity in Photobiology

    SciTech Connect

    Serrano-Andres, Luis; Merchan, Manuela; Roca-Sanjuan, Daniel; Olaso-Gonzalez, Gloria; Rubio, Mercedes

    2007-11-29

    Accurate CASPT2//CASSCF calculations show that {pi}-stacked interactions in different biochromophores such as DNA nucleobases or porphyrin-quinone pairs yield excimer-like situations which behave as precursors of processes like charge transfer or photoreactivity. Examples are the transfer of charge between a reduced pheophytin and an accepting quinone molecule, process that trigger the sequence of electron transfer phenomena in photosynthetic photosystem II, the electron transfer between adjacent DNA nucleobases in a strand of oligonucleotides, and the photodimerization taking place in cytosine pairs leading to cyclobutanecytosine mutants. These processes take place through nonadiabatic photochemical mechanisms whose evolution is determined by the presence and accessibility of conical intersections and other surface crossings between different electronic states.

  12. Charge transfer to a semi-esterified bifunctional phenol

    NASA Astrophysics Data System (ADS)

    Brede, O.; Hermann, R.; Orthner, H.

    1996-03-01

    The charge transfer from solvent radical cations of n-butyl chloride and cyclohexane to 2-butyl-6(3'-t-butyl-2'-hydroxy-5'-methylbenzyl)-4-methyl-phenylacrylate (GM) yields in the first step phenoxyl radicals as well as acrylate radical cations of this semi-acrylated bifunctional phenol. Subsequently an intramolecular charge transfer from the acrylate radical cation to the phenol group takes place. Because of the instability of phenol radical cations, under our experimental conditions (nanosecond pulse radiolysis, non-polar solvents, room temperature) phenoxyl radicals are the only observable products of phenol ionization.

  13. Enhancing SERS by Means of Supramolecular Charge Transfer

    NASA Technical Reports Server (NTRS)

    Wong, Eric; Flood, Amar; Morales, Alfredo

    2009-01-01

    In a proposed method of sensing small quantities of molecules of interest, surface enhanced Raman scattering (SERS) spectroscopy would be further enhanced by means of intermolecular or supramolecular charge transfer. There is a very large potential market for sensors based on this method for rapid detection of chemical and biological hazards. In SERS, the Raman signals (vibrational spectra) of target molecules become enhanced by factors of the order of 108 when those molecules are in the vicinities of nanostructured substrate surfaces that have been engineered to have plasmon resonances that enhance local electric fields. SERS, as reported in several prior NASA Tech Briefs articles and elsewhere, has remained a research tool and has not yet been developed into a practical technique for sensing of target molecules: this is because the short range (5 to 20 nm) of the field enhancement necessitates engineering of receptor molecules to attract target molecules to the nanostructured substrate surfaces and to enable reliable identification of the target molecules in the presence of interferants. Intermolecular charge-transfer complexes have been used in fluorescence-, photoluminescence-, and electrochemistry-based techniques for sensing target molecules, but, until now, have not been considered for use in SERS-based sensing. The basic idea of the proposed method is to engineer receptor molecules that would be attached to nanostructured SERS substrates and that would interact with the target molecules to form receptor-target supramolecular charge-transfer complexes wherein the charge transfer could be photoexcited.

  14. CORRELATING ELECTRONIC AND VIBRATIONAL MOTIONS IN CHARGE TRANSFER SYSTEMS

    SciTech Connect

    Khalil, Munira

    2014-06-27

    The goal of this research program was to measure coupled electronic and nuclear motions during photoinduced charge transfer processes in transition metal complexes by developing and using novel femtosecond spectroscopies. The scientific highlights and the resulting scientific publications from the DOE supported work are outlined in the technical report.

  15. Primary cells utilize halogen-organic charge transfer complex

    NASA Technical Reports Server (NTRS)

    Gutmann, F.; Hermann, A. M.; Rembaum, A.

    1966-01-01

    Electrochemical cells with solid state components employ charge transfer complexes or donor-acceptor complexes in which the donor component is an organic compound and the acceptor component is a halogen. A minor proportion of graphite added to these composition helps reduce the resistivity.

  16. Charge transfer devices. Citations from the NTIS data base

    NASA Astrophysics Data System (ADS)

    Reed, W. E.

    1980-04-01

    The technology, design, fabrication, and applications of charge transfer devices are presented in the cited research reports. Applications include imaging, signal processing, detectors, filters, amplifiers, and memory devices. This updated bibliography contains 107 abstracts, all of which are new entries to the previous edition.

  17. Femtosecond direct observation of charge transfer between bases in DNA

    PubMed Central

    Wan, Chaozhi; Fiebig, Torsten; Schiemann, Olav; Barton, Jacqueline K.; Zewail, Ahmed H.

    2000-01-01

    Charge transfer in supramolecular assemblies of DNA is unique because of the notion that the ?-stacked bases within the duplex may mediate the transport, possibly leading to damage and/or repair. The phenomenon of transport through ?-stacked arrays over a long distance has an analogy to conduction in molecular electronics, but the mechanism still needs to be determined. To decipher the elementary steps and the mechanism, one has to directly measure the dynamics in real time and in suitably designed, structurally well characterized DNA assemblies. Here, we report our first observation of the femtosecond dynamics of charge transport processes occurring between bases within duplex DNA. By monitoring the population of an initially excited 2-aminopurine, an isomer of adenine, we can follow the charge transfer process and measure its rate. We then study the effect of different bases next to the donor (acceptor), the base sequence, and the distance dependence between the donor and acceptor. We find that the charge injection to a nearest neighbor base is crucial and the time scale is vastly different: 10 ps for guanine and up to 512 ps for inosine. Depending on the base sequence the transfer can be slowed down or inhibited, and the distance dependence is dramatic over the range of 14 ?. These observations provide the time scale, and the range and efficiency of the transfer. The results suggest the invalidity of an efficient wire-type behavior and indicate that long-range transport is a slow process of a different mechanism. PMID:11106376

  18. Attosecond snapshots: imaging charge transfer in molecules using EUV light

    NASA Astrophysics Data System (ADS)

    McCann, J. F.; McLaughlin, B. M.; Calvert, C. R.; King, R. B.; Bryan, W. A.; Newell, W. R.; Greenwood, J. B.; Williams, I. D.

    2012-11-01

    Electron dynamics underlie the charge and energy transfer processes in molecules. These processes, although extremely fast, can be resolved by sub-femtosecond light pulses and the electron motion can, to some extent, be controlled. A novel scheme for electron localization using intense IR lasers has recently been developed using phase-locked multiple pulses, in which the charge centre can be isolated. This process can be identified by the asymmetry in the dissociation products. We propose the use of an extreme ultraviolet probe of the molecular ion prior to dissociation to image the density and phase of the electron orbital. We hope this will provide rich insight into the charge transfer process in small molecules, which may be extended to larger systems.

  19. Infrared Spectroscopy of Charge Transfer Complexes of Purines and Pyrimidines

    SciTech Connect

    Rathod, Pravinsinh I.; Oza, A. T.

    2011-10-20

    The FTIR spectra of charge transfer complexes of purines and pyrimidines with organic acceptors such as TCNQ, TCNE, DDQ, chloranil and iodine are obtained and studied in the present work. Adenine, guanine, thymine, cytosine and uracil are the purines and pyrimidines which are found as constituent of DNA and RNA. Charge transfer induced hydrogen bonding is concluded on the basis of indirect transitions observed in the infrared range in these CTCs. Some CTCs show gaussian bands revealing delocalization of charge carriers. The CTCs show interband transition in three-dimensions rather than two-dimensions unlike CTCs of amino acids. There is no extended hydrogen bonded network spanning the whole crystal. This leads to indirect transition due to locally deformed lattice furnishing a phonon-assisted transition.

  20. Variational approach to charge transfer reactions in bridged triarylamine cations

    NASA Astrophysics Data System (ADS)

    Utz, Nadine; Koslowski, Thorsten

    2002-09-01

    In this work, we apply a recently proposed nonperturbative approach to the energetics of charge localization and charge transfer within molecules. The electronic structure of bridged organic donor-acceptor systems is described by a tight-binding Hamiltonian, which is extended by a nonretarded reaction field to account for the dielectric polarizability of the environment. The resulting Hamiltonian is solved self-consistently, and approximations to the potential energy curves for adiabatic self-exchange in the electronic ground state are obtained. The crossover from the localized (Day-Robin class I and II) to the delocalized (Day-Robin class IIIa) regime with decreasing bridge length is described. Kinetic parameters are computed by analyzing the potential energy curve of the charge transfer reaction. The limitations of the concept are discussed, and we give an outlook to its implementation for more elaborate electronic structure computations and advanced reaction fields.

  1. Photoinduced charge and energy transfer in molecular wires.

    PubMed

    Gilbert, Mélina; Albinsson, Bo

    2015-02-21

    Exploring charge and energy transport in donor-bridge-acceptor systems is an important research field which is essential for the fundamental knowledge necessary to develop future applications. These studies help creating valuable knowledge to respond to today's challenges to develop functionalized molecular systems for artificial photosynthesis, photovoltaics or molecular scale electronics. This tutorial review focuses on photo-induced charge/energy transfer in covalently linked donor-bridge-acceptor (D-B-A) systems. Of utmost importance in such systems is to understand how to control signal transmission, i.e. how fast electrons or excitation energy could be transferred between the donor and acceptor and the role played by the bridge (the "molecular wire"). After a brief description of the electron and energy transfer theory, we aim to give a simple yet accurate picture of the complex role played by the bridge to sustain donor-acceptor electronic communication. Special emphasis is put on understanding bridge energetics and conformational dynamics effects on the distance dependence of the donor-acceptor electronic coupling and transfer rates. Several examples of donor-bridge-acceptor systems from the literature are described as a support to the discussion. Finally, porphyrin-based molecular wires are introduced, and the relationship between their electronic structure and photophysical properties is outlined. In strongly conjugated porphyrin systems, limitations of the existing electron transfer theory to interpret the distance dependence of the transfer rates are also discussed. PMID:25212903

  2. A Gating Charge Transfer Center in Voltage Sensors

    SciTech Connect

    Tao, X.; Lee, A; Limapichat, W; Dougherty, D; MacKinnon, R

    2010-01-01

    Voltage sensors regulate the conformations of voltage-dependent ion channels and enzymes. Their nearly switchlike response as a function of membrane voltage comes from the movement of positively charged amino acids, arginine or lysine, across the membrane field. We used mutations with natural and unnatural amino acids, electrophysiological recordings, and x-ray crystallography to identify a charge transfer center in voltage sensors that facilitates this movement. This center consists of a rigid cyclic 'cap' and two negatively charged amino acids to interact with a positive charge. Specific mutations induce a preference for lysine relative to arginine. By placing lysine at specific locations, the voltage sensor can be stabilized in different conformations, which enables a dissection of voltage sensor movements and their relation to ion channel opening.

  3. Active pixel sensor with intra-pixel charge transfer

    NASA Technical Reports Server (NTRS)

    Fossum, Eric R. (Inventor); Mendis, Sunetra (Inventor); Kemeny, Sabrina E. (Inventor)

    2003-01-01

    An imaging device formed as a monolithic complementary metal oxide semiconductor integrated circuit in an industry standard complementary metal oxide semiconductor process, the integrated circuit including a focal plane array of pixel cells, each one of the cells including a photogate overlying the substrate for accumulating photo-generated charge in an underlying portion of the substrate, a readout circuit including at least an output field effect transistor formed in the substrate, and a charge coupled device section formed on the substrate adjacent the photogate having a sensing node connected to the output transistor and at least one charge coupled device stage for transferring charge from the underlying portion of the substrate to the sensing node.

  4. Active pixel sensor with intra-pixel charge transfer

    NASA Technical Reports Server (NTRS)

    Fossum, Eric R. (Inventor); Mendis, Sunetra (Inventor); Kemeny, Sabrina E. (Inventor)

    2004-01-01

    An imaging device formed as a monolithic complementary metal oxide semiconductor integrated circuit in an industry standard complementary metal oxide semiconductor process, the integrated circuit including a focal plane array of pixel cells, each one of the cells including a photogate overlying the substrate for accumulating photo-generated charge in an underlying portion of the substrate, a readout circuit including at least an output field effect transistor formed in the substrate, and a charge coupled device section formed on the substrate adjacent the photogate having a sensing node connected to the output transistor and at least one charge coupled device stage for transferring charge from the underlying portion of the substrate to the sensing node.

  5. Charge-transfer crystallites as molecular electrical dopants.

    PubMed

    Méndez, Henry; Heimel, Georg; Winkler, Stefanie; Frisch, Johannes; Opitz, Andreas; Sauer, Katrein; Wegner, Berthold; Oehzelt, Martin; Röthel, Christian; Duhm, Steffen; Többens, Daniel; Koch, Norbert; Salzmann, Ingo

    2015-01-01

    Ground-state integer charge transfer is commonly regarded as the basic mechanism of molecular electrical doping in both, conjugated polymers and oligomers. Here, we demonstrate that fundamentally different processes can occur in the two types of organic semiconductors instead. Using complementary experimental techniques supported by theory, we contrast a polythiophene, where molecular p-doping leads to integer charge transfer reportedly localized to one quaterthiophene backbone segment, to the quaterthiophene oligomer itself. Despite a comparable relative increase in conductivity, we observe only partial charge transfer for the latter. In contrast to the parent polymer, pronounced intermolecular frontier-orbital hybridization of oligomer and dopant in 1:1 mixed-stack co-crystallites leads to the emergence of empty electronic states within the energy gap of the surrounding quaterthiophene matrix. It is their Fermi-Dirac occupation that yields mobile charge carriers and, therefore, the co-crystallites-rather than individual acceptor molecules-should be regarded as the dopants in such systems. PMID:26440403

  6. Charge-transfer crystallites as molecular electrical dopants

    PubMed Central

    Méndez, Henry; Heimel, Georg; Winkler, Stefanie; Frisch, Johannes; Opitz, Andreas; Sauer, Katrein; Wegner, Berthold; Oehzelt, Martin; Röthel, Christian; Duhm, Steffen; Többens, Daniel; Koch, Norbert; Salzmann, Ingo

    2015-01-01

    Ground-state integer charge transfer is commonly regarded as the basic mechanism of molecular electrical doping in both, conjugated polymers and oligomers. Here, we demonstrate that fundamentally different processes can occur in the two types of organic semiconductors instead. Using complementary experimental techniques supported by theory, we contrast a polythiophene, where molecular p-doping leads to integer charge transfer reportedly localized to one quaterthiophene backbone segment, to the quaterthiophene oligomer itself. Despite a comparable relative increase in conductivity, we observe only partial charge transfer for the latter. In contrast to the parent polymer, pronounced intermolecular frontier-orbital hybridization of oligomer and dopant in 1:1 mixed-stack co-crystallites leads to the emergence of empty electronic states within the energy gap of the surrounding quaterthiophene matrix. It is their Fermi–Dirac occupation that yields mobile charge carriers and, therefore, the co-crystallites—rather than individual acceptor molecules—should be regarded as the dopants in such systems. PMID:26440403

  7. Charge-transfer crystallites as molecular electrical dopants

    NASA Astrophysics Data System (ADS)

    Méndez, Henry; Heimel, Georg; Winkler, Stefanie; Frisch, Johannes; Opitz, Andreas; Sauer, Katrein; Wegner, Berthold; Oehzelt, Martin; Röthel, Christian; Duhm, Steffen; Többens, Daniel; Koch, Norbert; Salzmann, Ingo

    2015-10-01

    Ground-state integer charge transfer is commonly regarded as the basic mechanism of molecular electrical doping in both, conjugated polymers and oligomers. Here, we demonstrate that fundamentally different processes can occur in the two types of organic semiconductors instead. Using complementary experimental techniques supported by theory, we contrast a polythiophene, where molecular p-doping leads to integer charge transfer reportedly localized to one quaterthiophene backbone segment, to the quaterthiophene oligomer itself. Despite a comparable relative increase in conductivity, we observe only partial charge transfer for the latter. In contrast to the parent polymer, pronounced intermolecular frontier-orbital hybridization of oligomer and dopant in 1:1 mixed-stack co-crystallites leads to the emergence of empty electronic states within the energy gap of the surrounding quaterthiophene matrix. It is their Fermi-Dirac occupation that yields mobile charge carriers and, therefore, the co-crystallites--rather than individual acceptor molecules--should be regarded as the dopants in such systems.

  8. Semiempirical and ab initio Calculations of Charged Species Used in the Physical Organic Chemistry Course.

    ERIC Educational Resources Information Center

    Gilliom, Richard D.

    1989-01-01

    Concentrates on the semiempirical methods MINDO/3, MNDO, and AMI available in the program AMPAC from the Quantum Chemistry Program Exchange at Indiana University. Uses charged ions in the teaching of computational chemistry. Finds that semiempirical methods are accurate enough for the general use of the bench chemist. (MVL)

  9. Theory of ultrafast heterogeneous electron transfer: Contributions of direct charge transfer excitations to the absorbance

    SciTech Connect

    Wang, Luxia; Willig, Frank; May, Volkhard

    2007-04-07

    Absorption spectra related to heterogeneous electron transfer are analyzed with the focus on direct charge transfer transition from the surface attached molecule into the semiconductor band states. The computations are based on a model of reduced dimensionality with a single intramolecular vibrational coordinate but a complete account for the continuum of conduction band states. The applicability of this model to perylene on TiO{sub 2} has been demonstrated in a series of earlier papers. Here, based on a time-dependent formulation, the absorbance is calculated with the inclusion of charge transfer excitations. A broad parameter set inspired by the perylene TiO{sub 2} systems is considered. In particular, the description generalizes the Fano effect to heterogeneous electron transfer reactions. Preliminary simulations of measured spectra are presented for perylene-catechol attached to TiO{sub 2}.

  10. Excited-state intramolecular charge transfer in 9-aminoacridine derivative.

    PubMed

    Pereira, Robson Valentim; Garcia Ferreira, Ana Paula; Gehlen, Marcelo Henrique

    2005-07-14

    A new fluorochromic dye was obtained from the reaction of 9-aminoacridine with ethyl-2-cyano-3-ethoxyacrylate. It displays complex fluorescence that is ascribed to normal emission from the acridine chromophore in addition to excited-state intramolecular charge transfer (ESICT) formed upon light excitation. The analysis of the fluorescence decays in different solvents reveals two short-lived components in the range of 80-450 ps and 0.7-3.2 ns, ascribed to the formation and decay of the intramolecular charge transfer (ICT) state, in addition to a third component of about 9.0 ns, which is related to the normal emission from the acridine singlet excited state, probably in an enol-imine tautomeric form. The ICT emission is readily quenched by water addition to polar solvents, and this effect is ascribed to changes in the keto-amine/enol-imine equilibrium of this fluorochromic dye. PMID:16833932

  11. Charge transfer magnetoexciton formation at vertically coupled quantum dots

    PubMed Central

    2012-01-01

    A theoretical investigation is presented on the properties of charge transfer excitons at vertically coupled semiconductor quantum dots in the presence of electric and magnetic fields directed along the growth axis. Such excitons should have two interesting characteristics: an extremely long lifetime and a permanent dipole moment. We show that wave functions and the low-lying energies of charge transfer exciton can be found exactly for a special morphology of quantum dots that provides a parabolic confinement inside the layers. To take into account a difference between confinement potentials of an actual structure and of our exactly solvable model, we use the Galerkin method. The density of energy states is calculated for different InAs/GaAs quantum dots’ dimensions, the separation between layers, and the strength of the electric and magnetic fields. A possibility of a formation of a giant dipolar momentum under external electric field is predicted. PMID:23092373

  12. Spectrophotometric determination of moclobemide by charge-transfer complexation.

    PubMed

    Adikwu, M U; Ofokansi, K C

    1997-11-01

    A simple and sensitive spectrophotometric method is described for the assay for the moclobemide. The method is based on the molecular interaction between the drug and chloranilic acid, to form a charge-transfer complex in which the drug acts as n-donor and chloranilic acid as pi-acceptor. Chloranilic acid was found to form a charge-transfer complex in a 1:1 stoichiometry with a maximum absorption band at 526 nm. Conformity with Beer's law was evident over the concentration range 4-36 mg 100 ml-1. A complete, detailed investigation of the complex formed was made with respect to its composition, association constant, molar absorptivity and free energy change. The method has been applied successfully to the analysis of commercially available moclobemide tablets with good recovery and reproducibility. PMID:9589413

  13. Charge Transfer Plasmons: Optical Frequency Conductances and Tunable Infrared Resonances.

    PubMed

    Wen, Fangfang; Zhang, Yue; Gottheim, Samuel; King, Nicholas S; Zhang, Yu; Nordlander, Peter; Halas, Naomi J

    2015-06-23

    A charge transfer plasmon (CTP) appears when an optical-frequency conductive pathway between two metallic nanoparticles is established, enabling the transfer of charge between nanoparticles when the plasmon is excited. Here we investigate the properties of the CTP in a nanowire-bridged dimer geometry. Varying the junction geometry controls its conductance, which modifies the resonance energies and scattering intensities of the CTP while also altering the other plasmon modes of the nanostructure. Reducing the junction conductance shifts this resonance to substantially lower energies in the near- and mid-infrared regions of the spectrum. The CTP offers both a high-information probe of optical frequency conductances in nanoscale junctions and a new, unique approach to controllably engineering tunable plasmon modes at infrared wavelengths. PMID:25986388

  14. Ultrafast Photo-Induced Charge Transfer Unveiled by Two-Dimensional Electronic Spectroscopy

    E-print Network

    Bixner, Oliver; Mancal, Tomas; Hauer, Juergen; Milota, Franz; Fischer, Michael; Pugliesi, Igor; Bradler, Maximilian; Schmid, Walther; Riedle, Eberhard; Kauffmann, Harald F; Christensson, Niklas

    2012-01-01

    The interaction of exciton and charge transfer (CT) states plays a central role in photo-induced CT processes in chemistry, biology and physics. In this work, we use a combination of two-dimensional electronic spectroscopy (2D-ES), pump-probe measurements and quantum chemistry to investigate the ultrafast CT dynamics in a lutetium bisphthalocyanine dimer in different oxidation states. It is found that in the anionic form, the combination of strong CT-exciton interaction and electronic asymmetry induced by a counter-ion enables CT between the two macrocycles of the complex on a 30 fs timescale. Following optical excitation, a chain of electron and hole transfer steps gives rise to characteristic cross-peak dynamics in the electronic 2D spectra, and we monitor how the excited state charge density ultimately localizes on the macrocycle closest to the counter-ion within 100 fs. A comparison with the dynamics in the radical species further elucidates how CT states modulate the electronic structure and tune fs-reac...

  15. Laboratory Studies of Thermal Energy Charge Transfer of Multiply Charged Ions in Astrophysical Plasmas

    NASA Technical Reports Server (NTRS)

    Kwong, Victor H. S.

    2003-01-01

    The laser ablation/ion storage facility at the UNLV Physics Department has been dedicated to the study of atomic and molecular processes in low temperature plasmas. Our program focuses on the charge transfer (electron capture) of multiply charged ions and neutrals important in astrophysics. The electron transfer reactions with atoms and molecules is crucial to the ionization condition of neutral rich photoionized plasmas. With the successful deployment of the Far Ultraviolet Spectroscopic Explorer (FUSE) and the Chandra X-ray Observatory by NASA high resolution VUV and X-ray emission spectra fiom various astrophysical objects have been collected. These spectra will be analyzed to determine the source of the emission and the chemical and physical environment of the source. The proper interpretation of these spectra will require complete knowledge of all the atomic processes in these plasmas. In a neutral rich environment, charge transfer can be the dominant process. The rate coefficients need to be known accurately. We have also extended our charge transfer measurements to KeV region with a pulsed ion beam. The inclusion of this facility into our current program provides flexibility in extending the measurement to higher energies (KeV) if needed. This flexibility enables us to address issues of immediate interest to the astrophysical community as new observations are made by high resolution space based observatories.

  16. Electrical properties of polyvinylpyridine — DDQ charge transfer complexes

    NASA Astrophysics Data System (ADS)

    Kang, E. T.; Ong, Y. K.

    1986-02-01

    The d.c. electrical conductivity of poly-2-vinylpyridine (P2VP) and poly-4-vinylridine (P4VP) charge transfer complexed with 2,3-dichloro-5,6-dicyano- p-benzoquinone (DDQ) is measured as a function of DDQ concentration and temperature. The conductivity data suggest two major current conduction processes separated by a characteristic temperature, Tc. Possible electronic conduction mechanisms involved are discussed.

  17. Energy and charge transfer in ionized argon coated water clusters.

    PubMed

    Ko?išek, J; Lengyel, J; Fárník, M; Slaví?ek, P

    2013-12-01

    We investigate the electron ionization of clusters generated in mixed Ar-water expansions. The electron energy dependent ion yields reveal the neutral cluster composition and structure: water clusters fully covered with the Ar solvation shell are formed under certain expansion conditions. The argon atoms shield the embedded (H2O)n clusters resulting in the ionization threshold above ?15 eV for all fragments. The argon atoms also mediate more complex reactions in the clusters: e.g., the charge transfer between Ar(+) and water occurs above the threshold; at higher electron energies above ~28 eV, an excitonic transfer process between Ar(+)* and water opens leading to new products Ar(n)H(+) and (H2O)(n)H(+). On the other hand, the excitonic transfer from the neutral Ar* state at lower energies is not observed although this resonant process was demonstrated previously in a photoionization experiment. Doubly charged fragments (H2O)(n)H2(2+) and (H2O)(n)(2+) ions are observed and Intermolecular Coulomb decay (ICD) processes are invoked to explain their thresholds. The Coulomb explosion of the doubly charged cluster formed within the ICD process is prevented by the stabilization effect of the argon solvent. PMID:24320381

  18. Energy and charge transfer in ionized argon coated water clusters

    NASA Astrophysics Data System (ADS)

    Ko?išek, J.; Lengyel, J.; Fárník, M.; Slaví?ek, P.

    2013-12-01

    We investigate the electron ionization of clusters generated in mixed Ar-water expansions. The electron energy dependent ion yields reveal the neutral cluster composition and structure: water clusters fully covered with the Ar solvation shell are formed under certain expansion conditions. The argon atoms shield the embedded (H2O)n clusters resulting in the ionization threshold above ?15 eV for all fragments. The argon atoms also mediate more complex reactions in the clusters: e.g., the charge transfer between Ar+ and water occurs above the threshold; at higher electron energies above ˜28 eV, an excitonic transfer process between Ar+* and water opens leading to new products ArnH+ and (H2O)nH+. On the other hand, the excitonic transfer from the neutral Ar* state at lower energies is not observed although this resonant process was demonstrated previously in a photoionization experiment. Doubly charged fragments (H2O)nH_2^{2+} and (H_{2 O})n^{2+} ions are observed and Intermolecular Coulomb decay (ICD) processes are invoked to explain their thresholds. The Coulomb explosion of the doubly charged cluster formed within the ICD process is prevented by the stabilization effect of the argon solvent.

  19. Energy and charge transfer in ionized argon coated water clusters

    SciTech Connect

    Ko?išek, J. E-mail: michal.farnik@jh-inst.cas.cz Lengyel, J.; Fárník, M. E-mail: michal.farnik@jh-inst.cas.cz; Slaví?ek, P. E-mail: michal.farnik@jh-inst.cas.cz

    2013-12-07

    We investigate the electron ionization of clusters generated in mixed Ar-water expansions. The electron energy dependent ion yields reveal the neutral cluster composition and structure: water clusters fully covered with the Ar solvation shell are formed under certain expansion conditions. The argon atoms shield the embedded (H{sub 2}O){sub n} clusters resulting in the ionization threshold above ?15 eV for all fragments. The argon atoms also mediate more complex reactions in the clusters: e.g., the charge transfer between Ar{sup +} and water occurs above the threshold; at higher electron energies above ?28 eV, an excitonic transfer process between Ar{sup +}* and water opens leading to new products Ar{sub n}H{sup +} and (H{sub 2}O){sub n}H{sup +}. On the other hand, the excitonic transfer from the neutral Ar* state at lower energies is not observed although this resonant process was demonstrated previously in a photoionization experiment. Doubly charged fragments (H{sub 2}O){sub n}H{sub 2}{sup 2+} and (H{sub 2}O){sub n}{sup 2+} ions are observed and Intermolecular Coulomb decay (ICD) processes are invoked to explain their thresholds. The Coulomb explosion of the doubly charged cluster formed within the ICD process is prevented by the stabilization effect of the argon solvent.

  20. Charge Transfer Channels in Formation of Exciplex in Polymer Blends

    NASA Astrophysics Data System (ADS)

    Dou, Fei; Zhang, Xin-Ping

    2011-09-01

    The strong dependence of photoluminescence of charge transfer excited states or exciplex in a blend film of poly(9,9'-dioctylfluorene-co-benzothiadiazole) (F8BT) and poly(9,9'-dioctylfluorene-co-bis-N,N'-(4-butylphenyl)-bis-N,N'-phenyl-1,4- phenylenediamine) (PFB) on the excitation wavelengths and morphology is investigated. The experimental results reveal that electron transfer in the LUMOs from PFB to F8BT is more efficient than hole transfer in the HOMOs from PFB to F8BT for the formation of exciplex at the interfacial junctions between these two types of molecules in the blend film. Furthermore, energy transfer from the blue-emitting PFB to the green-emitting F8BT at the interfaces introduces an additional two-step channel and thus enhances the formation of an exciplex. This is important for understanding of charge generation and separation in organic bulk heterojunctions and for design of optoelectronic devices.

  1. An Electronic Structure Approach to Charge Transfer and Transport in Molecular Building Blocks for Organic Optoelectronics

    NASA Astrophysics Data System (ADS)

    Hendrickson, Heidi Phillips

    A fundamental understanding of charge separation in organic materials is necessary for the rational design of optoelectronic devices suited for renewable energy applications and requires a combination of theoretical, computational, and experimental methods. Density functional theory (DFT) and time-dependent (TD)DFT are cost effective ab-initio approaches for calculating fundamental properties of large molecular systems, however conventional DFT methods have been known to fail in accurately characterizing frontier orbital gaps and charge transfer states in molecular systems. In this dissertation, these shortcomings are addressed by implementing an optimally-tuned range-separated hybrid (OT-RSH) functional approach within DFT and TDDFT. The first part of this thesis presents the way in which RSH-DFT addresses the shortcomings in conventional DFT. Environmentally-corrected RSH-DFT frontier orbital energies are shown to correspond to thin film measurements for a set of organic semiconducting molecules. Likewise, the improved RSH-TDDFT description of charge transfer excitations is benchmarked using a model ethene dimer and silsesquioxane molecules. In the second part of this thesis, RSH-DFT is applied to chromophore-functionalized silsesquioxanes, which are currently investigated as candidates for building blocks in optoelectronic applications. RSH-DFT provides insight into the nature of absorptive and emissive states in silsesquioxanes. While absorption primarily involves transitions localized on one chromophore, charge transfer between chromophores and between chromophore and silsesquioxane cage have been identified. The RSH-DFT approach, including a protocol accounting for complex environmental effects on charge transfer energies, was tested and validated against experimental measurements. The third part of this thesis addresses quantum transport through nano-scale junctions. The ability to quantify a molecular junction via spectroscopic methods is crucial to their technological design and development. Time dependent perturbation theory, employed by non-equilibrium Green's function formalism, is utilized to study the effect of quantum coherences on electron transport and the effect of symmetry breaking on the electronic spectra of model molecular junctions. The fourth part of this thesis presents the design of a physical chemistry course based on a pedagogical approach called Writing-to-Teach. The nature of inaccuracies expressed in student-generated explanations of quantum chemistry topics, and the ability of a peer review process to engage these inaccuracies, is explored within this context.

  2. Photochemistry and charge transfer chemistry of the platinum group elements

    SciTech Connect

    Eisenberg, R.

    1992-12-01

    During the past 3 years, progress was made in elucidating the excited state structures of Pt(diimine)(dithiolate) complexes, while more recent efforts focused on the photochemistry of these complexes and electronic structure of other dithiolate systems. A carbonyl-Ir-maleonitrile dithiolate complex is also studied.

  3. Efficient charge generation by relaxed charge-transfer states at organic interfaces

    NASA Astrophysics Data System (ADS)

    Vandewal, Koen; Albrecht, Steve; Hoke, Eric T.; Graham, Kenneth R.; Widmer, Johannes; Douglas, Jessica D.; Schubert, Marcel; Mateker, William R.; Bloking, Jason T.; Burkhard, George F.; Sellinger, Alan; Fréchet, Jean M. J.; Amassian, Aram; Riede, Moritz K.; McGehee, Michael D.; Neher, Dieter; Salleo, Alberto

    2014-01-01

    Interfaces between organic electron-donating (D) and electron-accepting (A) materials have the ability to generate charge carriers on illumination. Efficient organic solar cells require a high yield for this process, combined with a minimum of energy losses. Here, we investigate the role of the lowest energy emissive interfacial charge-transfer state (CT1) in the charge generation process. We measure the quantum yield and the electric field dependence of charge generation on excitation of the charge-transfer (CT) state manifold via weakly allowed, low-energy optical transitions. For a wide range of photovoltaic devices based on polymer:fullerene, small-molecule:C60 and polymer:polymer blends, our study reveals that the internal quantum efficiency (IQE) is essentially independent of whether or not D, A or CT states with an energy higher than that of CT1 are excited. The best materials systems show an IQE higher than 90% without the need for excess electronic or vibrational energy.

  4. A new technique for the study of charge transfer in multiply charged ion-ion collisions

    SciTech Connect

    Shinpaugh, J.L.; Meyer, F.W.; Datz, S.

    1994-12-31

    While large cross sections (>10{sup {minus}16} cm{sup 2}) have been predicted for resonant charge transfer in ion-ion collisions, no experimental data exist for multiply charged systems. A novel technique is being developed at the ORNL ECR facility to allow study of symmetric charge exchange in multiply charged ion-ion collisions using a single ion source. Specific intra-beam charge transfer collisions occurring in a well-defined interaction region labeled by negative high voltage are identified and analyzed by electrostatic analysis in combination with ion time-of-flight coincidence detection of the collision products. Center-of-mass collision energies from 400 to 1000 eV are obtained by varying source and labeling-cell voltages. In addition, by the introduction of a target gas into the high-voltage cell, this labeling-voltage method allows measurement of electron-capture and -loss cross sections for ion-atom collisions. Consequently, higher collision energies can be investigated without the requirement of placing the ECR source on a high-voltage platform.

  5. Metastable charge-transfer state of californium(iii) compounds.

    PubMed

    Liu, Guokui; Cary, Samantha K; Albrecht-Schmitt, Thomas E

    2015-06-28

    Among a series of anomalous physical and chemical properties of Cf(iii) compounds revealed by recent investigations, the present work addresses the characteristics of the optical spectra of An(HDPA)3·H2O (An = Am, Cm, and Cf), especially the broadband photoluminescence from Cf(HDPA)3·H2O induced by ligand-to-metal charge transfer (CT). As a result of strong ion-ligand interactions and the relative ease of reducing Cf(iii) to Cf(ii), a CT transition occurs at low energy (<3 eV) via the formation of a metastable Cf(ii) state. It is shown that the systematic trend in CT transitions of the lanthanide series is not paralleled by actinide elements lighter than Cf(iii), and californium represents a turning point in the periodicity of the actinide series. Analyses and modeling of the temperature-dependent luminescence dynamics indicate that the metastable Cf(ii) charge-transfer state undergoes radiative and non-radiative relaxations. Broadening of the CT transition arises from strong vibronic coupling and hole-charge interactions in the valence band. The non-radiative relaxation of the metastable CT state results from a competition between phonon-relaxation and thermal tunneling that populates the excited states of Cf(iii). PMID:26032575

  6. Super-iron Nanoparticles with Facile Cathodic Charge Transfer

    SciTech Connect

    M Farmand; D Jiang; B Wang; S Ghosh; D Ramaker; S Licht

    2011-12-31

    Super-irons contain the + 6 valence state of iron. One advantage of this is that it provides a multiple electron opportunity to store additional battery charge. A decrease of particle size from the micrometer to the nanometer domain provides a higher surface area to volume ratio, and opportunity to facilitate charge transfer, and improve the power, voltage and depth of discharge of cathodes made from such salts. However, super-iron salts are fragile, readily reduced to the ferric state, with both heat and contact with water, and little is known of the resultant passivating and non-passivating ferric oxide products. A pathway to decrease the super-iron particle size to the nano-domain is introduced, which overcomes this fragility, and retains the battery capacity advantage of their Fe(VI) valence state. Time and power controlled mechanosynthesis, through less aggressive, dry ball milling, leads to facile charge transfer of super-iron nanoparticles. Ex-situ X-ray Absorption Spectroscopy is used to explore the oxidation state and structure of these iron oxides during discharge and shows the significant change in stability of the ferrate structure to lower oxidation state when the particle size is in the nano-domain.

  7. Charge transfer between O6+ and atomic hydrogen

    NASA Astrophysics Data System (ADS)

    Wu, Y.; Stancil, P. C.; Liebermann, H. P.; Buenker, R. J.; Schultz, D. R.; Hui, Y.

    2011-05-01

    The charge exchange process has been found to play a dominant role in the production of X-rays and/or EUV photons observed in cometary and planetary atmospheres and from the heliosphere. Charge transfer cross sections, especially state-selective cross sections, are necessary parameters in simulations of X-ray emission. In the present work, charge transfer due to collisions of ground state O6+(1s2 1 S) with atomic hydrogen has been investigated theoretically using the quantum-mechanical molecular-orbital close-coupling method (QMOCC). The multi-reference single- and double-excitation configuration interaction approach (MRDCI) has been applied to compute the adiabatic potential and nonadiabatic couplings, and the atomic basis sets used have been optimized with the method proposed previously to obtain precise potential data. Total and state-selective cross sections are calculated for energies between 10 meV/u and 10 keV/u. The QMOCC results are compared to available experimental and theoretical data as well as to new atomic-orbital close-coupling (AOCC) and classical trajectory Monte Carlo (CTMC) calculations. A recommended set of cross sections, based on the MOCC, AOCC, and CTMC calculations, is deduced which should aid in X-ray modeling studies.

  8. Charge transfer efficiency in proton damaged CCD`s

    SciTech Connect

    Hardy, T.; Murowinski, R.; Deen, M.J.

    1998-04-01

    The authors have performed detailed measurements of the charge transfer efficiency (CTE) in a thinned, backside-illuminated imaging charge-coupled device (CCD). The device had been damaged in three separate sections by proton radiation typical of that which a CCD would receive in space-borne experiments, nuclear imaging, or particle detection. They examined CTE as a function of signal level, temperature, and radiation dose. The dominant factor affecting the CTE in radiation-damaged CCD`s is seen to be trapping by bulk states. They present a simple physical model for trapping as a function of transfer rate, trap concentration, and temperature. They have made calculations using this model and arrived at predictions which closely match the measured results. The CTE was also observed to have a nonlinear dependence on signal level. Using two-dimensional device simulations to examine the distribution of the charge packets in the CCD channel over a range of signal levels, they were able to explain the observed variation.

  9. Charge-transfer doping by fullerenes on oxidized Si surfaces

    SciTech Connect

    Tada, Tetsuya; Uchida, Noriyuki; Kanayama, Toshihiko; Hiura, Hidefumi; Kimoto, Kenji

    2007-10-01

    We have studied the charge transfer between various fullerenes (C{sub 60}, C{sub 78}, C{sub 84}, C{sub 60}F{sub 36}, and C{sub 60}F{sub 48}) and oxidized Si surfaces in order to evaluate their capability of charge-transfer doping to form ultrashallow junctions in Si. Although the lowest unoccupied molecular orbitals of these fullerene molecules in isolated states are higher in energy than the valence band maximum (VBM) of Si, the fullerenes C{sub 60}F{sub 36} and C{sub 60}F{sub 48}, which were deposited on oxidized Si substrates, captured electrons from the Si surfaces; this generated hole inversion layers. C{sub 60}, C{sub 78}, and C{sub 84} did not induce such electron transfer. From the densities of the generated holes, we estimated the acceptor levels of C{sub 60}F{sub 36} and C{sub 60}F{sub 48}, which were condensed on the oxidized Si surface, to be 5.6-5.7 and 5.2 eV below the vacuum level, respectively; these values are lower than the VBM of Si.

  10. Coupled electron-nuclear dynamics: Charge migration and charge transfer initiated near a conical intersection

    NASA Astrophysics Data System (ADS)

    Mendive-Tapia, David; Vacher, Morgane; Bearpark, Michael J.; Robb, Michael A.

    2013-07-01

    Coupled electron-nuclear dynamics, implemented using the Ehrenfest method, has been used to study charge migration with fixed nuclei, together with charge transfer when nuclei are allowed to move. Simulations were initiated at reference geometries of neutral benzene and 2-phenylethylamine (PEA), and at geometries close to potential energy surface crossings in the cations. Cationic eigenstates, and the so-called sudden approximation, involving removal of an electron from a correlated ground-state wavefunction for the neutral species, were used as initial conditions. Charge migration without coupled nuclear motion could be observed if the Ehrenfest simulation, using the sudden approximation, was started near a conical intersection where the states were both strongly coupled and quasi-degenerate. Further, the main features associated with charge migration were still recognizable when the nuclear motion was allowed to couple. In the benzene radical cation, starting from the reference neutral geometry with the sudden approximation, one could observe sub-femtosecond charge migration with a small amplitude, which results from weak interaction with higher electronic states. However, we were able to engineer large amplitude charge migration, with a period between 10 and 100 fs, corresponding to oscillation of the electronic structure between the quinoid and anti-quinoid cationic electronic configurations, by distorting the geometry along the derivative coupling vector from the D6h Jahn-Teller crossing to lower symmetry where the states are not degenerate. When the nuclear motion becomes coupled, the period changes only slightly. In PEA, in an Ehrenfest trajectory starting from the D2 eigenstate and reference geometry, a partial charge transfer occurs after about 12 fs near the first crossing between D1, D2 (N+-Phenyl, N-Phenyl+). If the Ehrenfest propagation is started near this point, using the sudden approximation without coupled nuclear motion, one observes an oscillation of the spin density - charge migration - between the N atom and the phenyl ring with a period of 4 fs. When the nuclear motion becomes coupled, this oscillation persists in a damped form, followed by an effective charge transfer after 30 fs.

  11. Coupled electron-nuclear dynamics: Charge migration and charge transfer initiated near a conical intersection

    SciTech Connect

    Mendive-Tapia, David; Vacher, Morgane; Bearpark, Michael J.; Robb, Michael A.

    2013-07-28

    Coupled electron-nuclear dynamics, implemented using the Ehrenfest method, has been used to study charge migration with fixed nuclei, together with charge transfer when nuclei are allowed to move. Simulations were initiated at reference geometries of neutral benzene and 2-phenylethylamine (PEA), and at geometries close to potential energy surface crossings in the cations. Cationic eigenstates, and the so-called sudden approximation, involving removal of an electron from a correlated ground-state wavefunction for the neutral species, were used as initial conditions. Charge migration without coupled nuclear motion could be observed if the Ehrenfest simulation, using the sudden approximation, was started near a conical intersection where the states were both strongly coupled and quasi-degenerate. Further, the main features associated with charge migration were still recognizable when the nuclear motion was allowed to couple. In the benzene radical cation, starting from the reference neutral geometry with the sudden approximation, one could observe sub-femtosecond charge migration with a small amplitude, which results from weak interaction with higher electronic states. However, we were able to engineer large amplitude charge migration, with a period between 10 and 100 fs, corresponding to oscillation of the electronic structure between the quinoid and anti-quinoid cationic electronic configurations, by distorting the geometry along the derivative coupling vector from the D{sub 6h} Jahn-Teller crossing to lower symmetry where the states are not degenerate. When the nuclear motion becomes coupled, the period changes only slightly. In PEA, in an Ehrenfest trajectory starting from the D{sub 2} eigenstate and reference geometry, a partial charge transfer occurs after about 12 fs near the first crossing between D{sub 1}, D{sub 2} (N{sup +}-Phenyl, N-Phenyl{sup +}). If the Ehrenfest propagation is started near this point, using the sudden approximation without coupled nuclear motion, one observes an oscillation of the spin density – charge migration – between the N atom and the phenyl ring with a period of 4 fs. When the nuclear motion becomes coupled, this oscillation persists in a damped form, followed by an effective charge transfer after 30 fs.

  12. Charge transfer in proton-hydrogen collisions under Debye plasma

    SciTech Connect

    Bhattacharya, Arka; Kamali, M. Z. M.; Ghoshal, Arijit; Ratnavelu, K.

    2015-02-15

    The effect of plasma environment on the 1s ? nlm charge transfer, for arbitrary n, l, and m, in proton-hydrogen collisions has been investigated within the framework of a distorted wave approximation. The effect of external plasma has been incorporated using Debye screening model of the interacting charge particles. Making use of a simple variationally determined hydrogenic wave function, it has been possible to obtain the scattering amplitude in closed form. A detailed study has been made to investigate the effect of external plasma environment on the differential and total cross sections for electron capture into different angular momentum states for the incident energy in the range of 20–1000?keV. For the unscreened case, our results are in close agreement with some of the most accurate results available in the literature.

  13. Enhancement of IR and VCD intensities due to charge transfer.

    PubMed

    Nicu, Valentin Paul; Autschbach, Jochen; Baerends, Evert Jan

    2009-03-14

    Donor-acceptor interactions such as the one between the Cl(-) base and the N-H sigma* acceptor orbitals encountered in the complexation of Cl(-) counterions to the [Co(en)(3)](3+) transition metal complex, have been shown to cause huge enhancement (between 1 and 2 orders of magnitude) of the VCD intensities of N-H stretching modes. This effect has been fully analyzed, and could be attributed to increased charge flow from the Cl(-) donors when the N-H bonds become stretched. The transfer of charge counteracts the movement of negative electronic charge that happens along with the motion of the H nuclei, effectively reversing the electronic part of the electric dipole transition moment (EDTM) in the direction of the charge flow (z, say), and of the magnetic transition dipole moment (MDTM) in the perpendicular direction. The consequences for the IR and VCD intensity follow: IR intensity is strongly increased if the EDTM is polarized in the z direction, e.g. in A(2) modes, but not so much if it is polarized in the xy plane (E modes), the VCD is strongly enhanced if the EDTM and MTDM are polarized in the xy plane (in E modes), but less so when they are polarized in the z direction (in A(2) modes). The explanation holds generally for complexation phenomena of this sort, including the donor-acceptor part of hydrogen bonding interactions, e.g. with solvent molecules. PMID:19240930

  14. Polarization and Charge Transfer in the Hydration of Chloride Ions

    E-print Network

    Zhen Zhao; David M. Rogers; Thomas L. Beck

    2009-12-14

    A theoretical study of the structural and electronic properties of the chloride ion and water molecules in the first hydration shell is presented. The calculations are performed on an ensemble of configurations obtained from molecular dynamics simulations of a single chloride ion in bulk water. The simulations utilize the polarizable AMOEBA force field for trajectory generation, and MP2-level calculations are performed to examine the electronic structure properties of the ions and surrounding waters in the external field of more distant waters. The ChelpG method is employed to explore the effective charges and dipoles on the chloride ions and first-shell waters. The Quantum Theory of Atoms in Molecules (QTAIM) is further utilized to examine charge transfer from the anion to surrounding water molecules. From the QTAIM analysis, 0.2 elementary charges are transferred from the ion to the first-shell water molecules. The default AMOEBA model overestimates the average dipole moment magnitude of the ion compared with the estimated quantum mechanical value. The average magnitude of the dipole moment of the water molecules in the first shell treated at the MP2 level, with the more distant waters handled with an AMOEBA effective charge model, is 2.67 D. This value is close to the AMOEBA result for first-shell waters (2.72 D) and is slightly reduced from the bulk AMOEBA value (2.78 D). The magnitude of the dipole moment of the water molecules in the first solvation shell is most strongly affected by the local water-water interactions and hydrogen bonds with the second solvation shell, rather than by interactions with the ion.

  15. Polarization and charge transfer in the hydration of chloride ions

    SciTech Connect

    Zhao Zhen; Rogers, David M.; Beck, Thomas L.

    2010-01-07

    A theoretical study of the structural and electronic properties of the chloride ion and water molecules in the first hydration shell is presented. The calculations are performed on an ensemble of configurations obtained from molecular dynamics simulations of a single chloride ion in bulk water. The simulations utilize the polarizable AMOEBA force field for trajectory generation and MP2-level calculations are performed to examine the electronic structure properties of the ions and surrounding waters in the external field of more distant waters. The ChelpG method is employed to explore the effective charges and dipoles on the chloride ions and first-shell waters. The quantum theory of atoms in molecules (QTAIM) is further utilized to examine charge transfer from the anion to surrounding water molecules. The clusters extracted from the AMOEBA simulations exhibit high probabilities of anisotropic solvation for chloride ions in bulk water. From the QTAIM analysis, 0.2 elementary charges are transferred from the ion to the first-shell water molecules. The default AMOEBA model overestimates the average dipole moment magnitude of the ion compared to the quantum mechanical value. The average magnitude of the dipole moment of the water molecules in the first shell treated at the MP2-level, with the more distant waters handled with an AMOEBA effective charge model, is 2.67 D. This value is close to the AMOEBA result for first-shell waters (2.72 D) and is slightly reduced from the bulk AMOEBA value (2.78 D). The magnitude of the dipole moment of the water molecules in the first solvation shell is most strongly affected by the local water-water interactions and hydrogen bonds with the second solvation shell, rather than by interactions with the ion.

  16. Photoinduced charge-transfer materials for nonlinear optical applications

    DOEpatents

    McBranch, Duncan W.

    2006-10-24

    A method using polyelectrolyte self-assembly for preparing multi-layered organic molecular materials having individual layers which exhibit ultrafast electron and/or energy transfer in a controlled direction occurring over the entire structure. Using a high molecular weight, water-soluble, anionic form of poly-phenylene vinylene, self-assembled films can be formed which show high photoluminescence quantum efficiency (QE). The highest emission QE is achieved using poly(propylene-imine) (PPI) dendrimers as cationic binders. Self-quenching of the luminescence is observed as the solid polymer film thickness is increased and can be reversed by inserting additional spacer layers of transparent polyelectrolytes between each active conjugated layer, such that the QE grows with thickness. A red shift of the luminescence is also observed as additional PPV layers are added. This effect persists as self-quenching is eliminated. Charge transfer superlattices can be formed by additionally incorporating C.sub.60 acceptor layers.

  17. Diamagnetism and charge transfer in graphite intercalation compounds

    NASA Technical Reports Server (NTRS)

    Tsang, T.; Resing, H. A.

    1984-01-01

    The magnetic susceptibilities at 300 K of the acceptor-type intercalation compounds of graphite with Br2 and ICl are calculated; the results are compared with published experimental measurements in graphs; and the charge-transfer parameter f is inferred using a rigid-band model (Loughin et al., 1978; Weinberger et al., 1978; Mattix et al., 1983). Assuming a screening length of 200 pm, the values determined are f = 0.3 for C(8N)Br2 and f = 0.09 for C(13N)ICl.

  18. Transfer-Student Performance in Upper-Division Chemistry Courses: Implications for Curricular Reform and Alignment

    ERIC Educational Resources Information Center

    Whitfield, Mary

    2005-01-01

    Using a statewide database of student records, the grades of students enrolled in organic chemistry and biochemistry at a large state university were analyzed to determine if there was a difference in performance between community college transfers and "native" students. Although only small differences were found for the organic chemistry

  19. Photoinduced Charge and Energy Transfer Processes in Molecular Aggregates

    SciTech Connect

    John F. Endicott

    2009-10-20

    This project involved the experimental probing of the electronic excited states generated by photoinduced (center-to-center) electron and energy transfer processes in several classes of transition metal donor/acceptor (D/A) complexes. Some of the general properties inferred from these studies should be useful in the design of new systems for energy conversion applications. Pursuit of the project goals has involved the determination of electron transfer efficiencies and the detailed study of variations in the electronic spectra of D/A complexes. This has resulted in the study of some very fundamental issues of photoinduced charge transfer and the identification of some of the constraints on its efficiency. The experimental studies of the competition between the degradative non-radiative unimolecular relaxation of transition metal excited states and their transfer of charge from these excited states to external acceptors have involved a range of techniques such as transient decay kinetics, photoacoustic calorimetry and transient or stationary state spectroscopy. The substrates synthesized for these studies were selected to provide model systems, or series of model systems to probe the validity of models of electronic excited states and their reactivity. The work during the last few years has focused largely, but not exclusively, on the use of emission spectral band shapes to probe the properties of charge transfer (CT) excited states. Bandshape variations are one of the very few approaches for systematically probing electronic excited states and good band shape resolution is necessary in order to gain information about the structural variations that correlate with excited state reactivity. Differences in molecular structure correlate with differences in chemical reactivity, and the variations in emission bandshapes are well known to relate to variations in the molecular structural differences between the excited and ground electronic states. However, it is has been rarely noticed that configurational mixing of the lowest energy excited state with other electronic states leads to unique distortions of the lowest energy excited state which result in modifications in the vibronic structure and bandshape of the emission. We have used the emission sideband shapes to evaluate patterns of ground state-excited state and excited state-excited state configurational mixing in some simple series of complexes.

  20. Electrochemical charge transfer at a metallic electrode: A simulation study

    NASA Astrophysics Data System (ADS)

    Reed, Stewart K.; Madden, Paul A.; Papadopoulos, Aristides

    2008-03-01

    The calculation of the Marcus free energy curves for electron transfer events between a redox species and a metallic electrode in an atomistic simulation designed to model the electrochemical interface with an ionic liquid is described. The calculation is performed on a system comprising a molten salt mixture confined between model metallic electrodes [Reed et al., J. Chem. Phys. 126, 084704 (2007)] which are maintained at a constant electrical potential. The calculation therefore includes a self-consistent description of the screening of the electrode potential by the liquid and the polarization of the electrode by the ions (image charge effects). The purpose of the study was to examine how the Marcus curves depend on the applied potential and on the distance of the redox species from an electrode. The pronounced oscillations in the mean electrical potential seen in molten salt systems in the "double-layer" region are not reflected in the reaction free energy for the electron transfer event. The reorganization energy depends markedly on the distance of the redox ion from the electrode surface because of image charge effects.

  1. Radiative charge transfer in cold and ultracold Sulfur atoms colliding with Protons

    E-print Network

    Shen, G; Wang, J G; McCann, J F; McLaughlin, B M

    2015-01-01

    Radiative decay processes at cold and ultra cold temperatures for Sulfur atoms colliding with protons are investigated. The MOLPRO quantum chemistry suite of codes was used to obtain accurate potential energies and transition dipole moments, as a function of internuclear distance, between low-lying states of the SH$^{+}$ molecular cation. A multi-reference configuration-interaction (MRCI) approximation together with the Davidson correction is used to determine the potential energy curves and transition dipole moments, between the states of interest, where the molecular orbitals (MO's) are obtained from state-averaged multi configuration-self-consistent field (MCSCF) calculations. The collision problem is solved approximately using an optical potential method to obtain radiative loss, and a fully two-channel quantum approach for radiative charge transfer. Cross sections and rate coefficients are determined for the first time for temperatures ranging from 10 $\\mu$ K up to 10,000 K. Results are obtained for all ...

  2. Axi-symmetric models of ultraviolet radiative transfer with applications to circumstellar disk chemistry

    E-print Network

    Zadelhoff, Gerd-Jan van

    Axi-symmetric models of ultraviolet radiative transfer with applications to circumstellar disk to calculate molecular lines profiles. The chemistry is driven by ultraviolet radiation and freeze-out of molecules CONCLUSIONS Radicals like CN and C¦ H need 2D UV radiative transfer for a correct abundance

  3. Nanocrystal/J-aggregate constructs : chemistry, energy transfer, and applications

    E-print Network

    Walker, Brian J. (Brian Jacob)

    2011-01-01

    The interaction of light with matter is one of the most central subjects to modern chemistry. Two types of materials, semiconductor nanocrystals and J-aggregates of cyanine dyes, have been developed chiefly due to their ...

  4. Quantum chemistry and charge transport in biomolecules with superconducting circuits

    E-print Network

    L. García-Álvarez; U. Las Heras; A. Mezzacapo; M. Sanz; E. Solano; L. Lamata

    2015-11-30

    We propose an efficient protocol for digital quantum simulation of quantum chemistry problems and enhanced digital-analog quantum simulation of transport phenomena in biomolecules with superconducting circuits. Along these lines, we prove that fermionic models of molecular structure can be optimally digitalized with single-qubit and two-qubit gates, by means of Trotter-Suzuki decomposition and Jordan-Wigner transformation. Furthermore, we address the modelling of system-environment interactions of biomolecules involving bosonic degrees of freedom with a digital-analog approach. Finally, we consider gate-truncated quantum algorithms to allow the study of environmental effects.

  5. Anion Exchange Chemistry of Middle Atlantic Soils: Charge Properties and Nitrate Retention Kinetics

    E-print Network

    Sparks, Donald L.

    Anion Exchange Chemistry of Middle Atlantic Soils: Charge Properties and Nitrate Retention Kinetics C. V. Toner, IV,* D. L. Sparks, and T. H. Carski ABSTRACT The negativeimpactof nitrate(NO3-flow reaction chamber and a first-order reaction best described the data. Nitrate adsorption was found

  6. Ab initio study of charge-transfer dynamics in collisions of C{sup 2+} ions with hydrogen chloride

    SciTech Connect

    Rozsalyi, E.; Vibok, A.; Bene, E.; Halasz, G. J.; Bacchus-Montabonel, M. C.

    2011-05-15

    Ab initio quantum chemistry molecular calculations followed by a semiclassical dynamical treatment in the keV collision energy range have been developed for the study of the charge-transfer process in collisions of C{sup 2+} ions with hydrogen chloride. The mechanism has been investigated in detail in connection with avoided crossings between states involved in the reaction. A simple mechanism driven by a strong nonadiabatic coupling matrix element has been pointed out for this process. A comparative analysis with the halogen fluoride target corresponding to a similar electronic configuration shows a quite different charge-transfer mechanism leading to a very different behavior of the cross sections. Such behavior may be correlated to specific nonadiabatic interactions observed in these collision systems.

  7. Charge transfer in model bioinspired carotene-porphyrin dyads.

    PubMed

    Orian, Laura; Carlotto, Silvia; Di Valentin, Marilena; Polimeno, Antonino

    2012-04-19

    We present a computational study based on accurate DFT and TD-DFT methods on model bioinspired donor-acceptor dyads, formed by a carotenoid covalently linked to a tetraphenylporphyrin (TPP) at the ortho position of one of the TPP phenyl rings. Dyadic systems can be used in the construction of organic solar cells and development of efficient photocatalytic systems for the solar energy conversion, due to the unique advantages they offer in terms of synthetic feasibility. This study aims to describe the influence of chemical modifications on the absorption spectra, in particular on the lowest energy charge transfer bands. Effects of different metals of biological interest, i.e., Mg, Fe, Ni, and Zn, and of H(2)O and histidine molecules coordinated to the metals in different axial positions are rationalized. PMID:22429261

  8. HST WFC3/UVIS: charge transfer efficiency monitoring and mitigation

    NASA Astrophysics Data System (ADS)

    Baggett, Sylvia M.; Sosey, Megan L.; Anderson, Jay; Gosmeyer, Catherine; Bourque, Matthew; Bajaj, Varun; Khandrika, Harish G.; Martlin, Catherine; Kozhurina-Platais, Vera; Sabbi, Elena; WFC3 Team

    2016-01-01

    The harsh low-earth orbit environment is known to damage CCD devices and the HST WFC3/UVIS camera is no exception. One consequence of the radiation damage is charge-transfer efficiency (CTE) loss over time. We summarize the level of the CTE losses, the effect on science data, and the pre- and post-observation mitigation options available. Among them is the pixel-based CTE correction, which has been incorporated into the HST automatic data processing pipeline. The pipeline now provides both standard and CTE-corrected data products; observers with older data can re-retrieve their images via the the Mikulski Archive for Space Telescopes (MAST) to obtain the new products.

  9. Switching effect in organic charge transfer complex crystals

    NASA Astrophysics Data System (ADS)

    Iwasa, Y.; Koda, T.; Tokura, Y.; Koshihara, S.; Iwasawa, N.

    1989-11-01

    In the past, the current-voltage characteristics of some organic substances have shown a current switching effect. In particular the switching effect in Cu-TCNQ(7,7,8,8-tetracyanoquinodimethane) thin films has been frequently referred to as a prototype to a molecular electronic device. Here, the observation is reported of a reproducible current switching effect in various mixed-stack organic charge transfer crystals whose ionicities are close to the neutral-ionic phase boundary. This effect appears to be related to the intrinsic nonlinear conductivity which has recently been reported in these crystals. This switching has a reasonably large delay time and the results indicate that this is a bulk property of the crystals. The possible mechanisms for this effect are discussed.

  10. Fingerprint of fractional charge transfer at metal/organic interface

    E-print Network

    Sabine-A. Savu; Giulio Biddau; Lorenzo Pardini; Rafael Bula; Holger F. Bettinger; Claudia Draxl; Thomas Chassé; M. Benedetta Casu

    2015-02-06

    Although physisorption is a widely occurring mechanism of bonding at the organic/metal interface, contradictory interpretations of this phenomenon are often reported. Photoemission and X-ray absorption spectroscopy investigations of nanorods of a substituted pentacene, 2,3,9,10-tetrafluoropentacene, deposited on gold single crystals reveal to be fundamental to identify the bonding mechanisms. We find fingerprints of a fractional charge transfer from the clean metal substrate to the physisorbed molecules. This phenomenon is unambiguously recognizable by a non-rigid shift of the core-level main lines while the occupied states at the interface stay mostly unperturbed, and the unoccupied states experience pronounced changes. The experimental results are corroborated by first-principles calculations.

  11. DFT charge transfer of hybrid molecular ferrocene/Si structures

    NASA Astrophysics Data System (ADS)

    Calborean, Adrian; Buimaga-Iarinca, Luiza; Graur, Florin

    2015-05-01

    The electrochemical behavior and electronic properties of redox-active ferrocenes grafted onto semiconductor Si(100) substrate were investigated theoretically by first-principles calculations. Organic molecules were attached via the formation of Si-C covalent bonds through two different linkers: vinyl (direct grafting), and N3(CH2)11 (indirect grafting). Redox energies and the electronic properties relating to different spacers in hybrid ferrocene Fc/Si and ferrocenium Fc+/Si structures were theoretically extracted and compared with experimental cyclic voltametry data. Electronic charge transfers are discussed through the alignment positions of the frontier orbitals of the molecule with respect to the Si substrate gap. Periodic boundary conditions were used to investigate the Si(100) as a slab surface and hybrid Fc/Si structures. The resulting projected density of states (PDOS) were compared with molecular results and discussed in the light of experimental data.

  12. Voltage Sensor Gating Charge Transfer in a hERG Potassium Channel Model

    PubMed Central

    Colenso, Charlotte K.; Cao, Yang; Sessions, Richard B.; Hancox, Jules C.; Dempsey, Christopher E.

    2014-01-01

    Relaxation of a hERG K+ channel model during molecular-dynamics simulation in a hydrated POPC bilayer was accompanied by transitions of an arginine gating charge across a charge transfer center in two voltage sensor domains. Inspection of the passage of arginine side chains across the charge transfer center suggests that the unique hydration properties of the arginine guanidine cation facilitates charge transfer during voltage sensor responses to changes in membrane potential, and underlies the preference of Arg over Lys as a mobile charge carrier in voltage-sensitive ion channels. PMID:25418316

  13. Photoinduced Charge Transfer from Titania to Surface Doping Site

    PubMed Central

    Inerbaev, Talgat; Hoefelmeyer, James D.; Kilin, Dmitri S.

    2013-01-01

    We evaluate a theoretical model in which Ru is substituting for Ti at the (100) surface of anatase TiO2. Charge transfer from the photo-excited TiO2 substrate to the catalytic site triggers the photo-catalytic event (such as water oxidation or reduction half-reaction). We perform ab-initio computational modeling of the charge transfer dynamics on the interface of TiO2 nanorod and catalytic site. A slab of TiO2 represents a fragment of TiO2 nanorod in the anatase phase. Titanium to ruthenium replacement is performed in a way to match the symmetry of TiO2 substrate. One molecular layer of adsorbed water is taken into consideration to mimic the experimental conditions. It is found that these adsorbed water molecules saturate dangling surface bonds and drastically affect the electronic properties of systems investigated. The modeling is performed by reduced density matrix method in the basis of Kohn-Sham orbitals. A nano-catalyst modeled through replacement defect contributes energy levels near the bottom of the conduction band of TiO2 nano-structure. An exciton in the nano-rod is dissipating due to interaction with lattice vibrations, treated through non-adiabatic coupling. The electron relaxes to conduction band edge and then to the Ru cite with faster rate than hole relaxes to the Ru cite. These results are of the importance for an optimal design of nano-materials for photo-catalytic water splitting and solar energy harvesting. PMID:23795229

  14. Metal-Organic Coordination Number Determined Charge Transfer Magnitude

    NASA Astrophysics Data System (ADS)

    Yang, Hung-Hsiang; Chu, Yu-Hsun; Lu, Chun-I.; Yang, Tsung-Han; Yang, Kai-Jheng; Kaun, Chao-Cheng; Hoffmann, Germar; Lin, Minn-Tsong

    2014-03-01

    By the appropriate choice of head groups and molecular ligands, various metal-organic coordination geometries can be engineered. Such metal-organic structures provide different chemical environments for molecules and give us templates to study the charge redistribution within the metal-organic interface. We created various metal-organic bonding environment by growing self-assembly nanostructures of Fe-PTCDA (3,4,9,10-perylene tetracarboxylic dianhydride) chains and networks on a Au(111) surface. Bonding environment dependent frontier molecular orbital energies are acquired by low temperature scanning tunneling microscopy and scanning tunneling spectroscopy. By comparing the frontier energies with the molecular coordination environments, we conclude that the specific coordination affects the magnitude of charge transfer onto each PTCDA in the Fe-PTCDA hybridization system. H.-H. Yang, Y.-H. Chu, C.-I Lu, T.-H. Yang, K.-J. Yang, C.-C. Kaun, G. Hoffmann, and M.-T. Lin, ACS Nano 7, 2814 (2013).

  15. Interface charge transfer in polypyrrole coated perovskite manganite magnetic nanoparticles

    NASA Astrophysics Data System (ADS)

    Pana, O.; Soran, M. L.; Leostean, C.; Macavei, S.; Gautron, E.; Teodorescu, C. M.; Gheorghe, N.; Chauvet, O.

    2012-02-01

    Different hybrid structures were obtained by coating magnetic nanoparticles of perovskite type manganite at optimal doping (La0.67Sr0.33MnO3,LSMO) with different quantities of polypyrrole (PPy). The amorphous layer of polypyrrole surrounding the crystalline magnetic core was observed by high resolution transmission electron microscopy (HRTEM) and analyzed by using X-ray photoelectron spectroscopy (XPS) and X-ray absorption spectroscopy (XAS) measurements in near edge structure (XANES) techniques. By analyzing the magnetic behavior of the samples one can observe that the surface modification of magnetic nanoparticles by PPy results in an increase in the saturation magnetization of the composites. The process is ascribed to paired electrons transferred from the delocalized ? states of the PPy into the outer disordered layers of the manganite. The analysis of pre-edge peak of the Mn K-edge XANES spectra in the case of PPy coated LSMO nanoparticles indicates that the charge transfer between polymer and nanoparticles is (directed) going to missing or distorted oxygen positions, hence increasing the 3d electrons' mobility and orbital hybridization between the neighboring manganese ion. As a consequence, within the surface layers of LSMO nanoparticles, both energy bands disrupted the structure, and the double exchange process between Mn ions was reestablished determining the saturation magnetizations and pre-edge features increase, respectively.

  16. Doping graphene films via chemically mediated charge transfer.

    PubMed

    Ishikawa, Ryousuke; Bando, Masashi; Morimoto, Yoshitaka; Sandhu, Adarsh

    2011-01-01

    Transparent conductive films (TCFs) are critical components of a myriad of technologies including flat panel displays, light-emitting diodes, and solar cells. Graphene-based TCFs have attracted a lot of attention because of their high electrical conductivity, transparency, and low cost. Carrier doping of graphene would potentially improve the properties of graphene-based TCFs for practical industrial applications. However, controlling the carrier type and concentration of dopants in graphene films is challenging, especially for the synthesis of p-type films. In this article, a new method for doping graphene using the conjugated organic molecule, tetracyanoquinodimethane (TCNQ), is described. Notably, TCNQ is well known as a powerful electron accepter and is expected to favor electron transfer from graphene into TCNQ molecules, thereby leading to p-type doping of graphene films. Small amounts of TCNQ drastically improved the resistivity without degradation of optical transparency. Our carrier doping method based on charge transfer has a huge potential for graphene-based TCFs. PMID:21711624

  17. Classical/quantum correspondence in state selective charge transfer and excitation reactions involving highly charged ions and hydrogen

    NASA Astrophysics Data System (ADS)

    Purkait, M.

    2009-11-01

    State selective charge transfer and excitation cross sections for collisions of Neq+ (q = 1-10) with atomic hydrogen are calculated within the framework of Classical Trajectory Monte Carlo (CTMC) method and Boundary Corrected Continuum Intermediate State (BCCIS) approximation.

  18. Conditions for Directional Charge Transfer in CdSe Quantum Dots Functionalized by Ru(II) Polypyridine Complexes.

    PubMed

    Kilina, Svetlana; Cui, Peng; Fischer, Sean A; Tretiak, Sergei

    2014-10-16

    Thermodynamic conditions governing the charge transfer direction in CdSe quantum dots (QD) functionalized by either Ru(II)-trisbipyridine or black dye are studied using density functional theory (DFT) and time-dependent DFT (TDDFT). Compared to the energy offsets of the isolated QD and the dye, QD-dye interactions strongly stabilize dye orbitals with respect to the QD states, while the surface chemistry of the QD has a minor effect on the energy offsets. In all considered QD/dye composites, the dyes always introduce unoccupied states close to the edge of the conduction band and control the electron transfer. Negatively charged ligands and less polar solvents significantly destabilize the dye's occupied orbitals shifting them toward the very edge of the valence band, thus, providing favorite conditions for the hole transfer. Overall, variations in the dye's ligands and solvent polarity can progressively adjust the electronic structure of QD/dye composites to modify conditions for the directed charge transfer. PMID:26278611

  19. Exciton harvesting, charge transfer, and charge-carrier transport in amorphous-silicon nanopillar/polymer hybrid solar cells

    E-print Network

    McGehee, Michael

    Exciton harvesting, charge transfer, and charge-carrier transport in amorphous-silicon nanopillar/polymer report on the device physics of nanostructured amorphous-silicon a-Si:H /polymer hybrid solar cells. Using two different polymers, poly 3-hexylthiophene P3HT and poly 2-methoxy-5- 2 -ethyl-hexyloxy -1

  20. Effect of solution physico-chemistry on the charge property of nanofiltration membranes.

    PubMed

    Tay, Joo-Hwa; Liu, Jianlin; Sun, Darren Delai

    2002-02-01

    Electrokinetic phenomenon is an important factor in pressure-driven membrane water filtration process. Zeta potential is a measurable and reliable parameter to characterize the charge property of membranes. This study investigated the effects of solution physico-chemistry on the zeta potential of nanofiltration membranes. A comprehensive semi-empirical mathematical model based on the Poisson-Boltzmann equation, Membrane Surface Charge model, was established. The correlations between the zeta potential, surface charge density and solution chemistry were well delineated by this new model. The empirical coefficients in the model are dependent on neither solution pH nor the ionic strength. They only reflect the characteristics of the electrokinetic property of the membrane--solution interface. The point of zero charge (PZC) can be calculated by combination of those empirical coefficients. The Membrane Surface Charge model also provides more information on understanding the charge interaction involved in membrane filtration system. The effects of potential determining ions, indifferent ions and specific adsorption of substances onto the membrane could be revealed by analyzing the coefficients of the model. PMID:11827320

  1. Charge transfer to the ionosphere and to the ground during thunderstorms

    E-print Network

    Pasko, Victor

    Charge transfer to the ionosphere and to the ground during thunderstorms Sotirios A. Mallios1 of the thunderstorm development. From these results, the charges that are transferred to the ionosphere thunderstorms, J. Geophys. Res., 117, A08303, doi:10.1029/2011JA017061. 1. Introduction [2] The Global Electric

  2. Charge Transfer and Chemisorption of Fullerene Molecules on Metal Surfaces: Application to Dynamics of Nanocars

    E-print Network

    Charge Transfer and Chemisorption of Fullerene Molecules on Metal Surfaces: Application to Dynamics Information ABSTRACT: It is widely believed that the dynamics of surface-bound fullerene molecules theoretical approach to describe charge transfer and chemisorption processes for fullerenes on gold surfaces

  3. Orbital Specific Charge Transfer Distances, Solvent Reorganization Energies, and Electronic Coupling Energies

    E-print Network

    Orbital Specific Charge Transfer Distances, Solvent Reorganization Energies, and Electronic: For the mixed-valent chromophore, (NC)5OsII-CN-RuIII(NH3)5 -, spin-orbit coupling and ligand-field asymmetry from an Os 5d orbital that is nominally orthogonal to the charge transfer axis. The lower energy

  4. ARCHITECTURE OF A CHARGE-TRANSFER STATE REGULATING LIGHT HARVESTING IN A PLANT ANTENNA PROTEIN

    SciTech Connect

    Fleming, Graham; Ahn, Tae Kyu; Avenson, Thomas J.; Ballottari, Matteo; Cheng, Yuan-Chung; Niyogi, Krishna K.; Bassi, Roberto; Fleming, Graham R.

    2008-04-02

    Energy-dependent quenching of excess absorbed light energy (qE) is a vital mechanism for regulating photosynthetic light harvesting in higher plants. All of the physiological characteristics of qE have been positively correlated with charge-transfer between coupled chlorophyll and zeaxanthin molecules in the light-harvesting antenna of photosystem II (PSII). In this work, we present evidence for charge-transfer quenching in all three of the individual minor antenna complexes of PSII (CP29, CP26, and CP24), and we conclude that charge-transfer quenching in CP29 involves a de-localized state of an excitonically coupled chlorophyll dimer. We propose that reversible conformational changes in CP29 can `tune? the electronic coupling between the chlorophylls in this dimer, thereby modulating the energy of the chlorophylls-zeaxanthin charge-transfer state and switching on and off the charge-transfer quenching during qE.

  5. Wire transfer of charge packets using a CCD-BBD structure for charge-domain signal processing

    NASA Technical Reports Server (NTRS)

    Fossum, Eric R.

    1991-01-01

    A structure for the virtual transfer of charge packets across metal wires is described theoretically and is experimentally verified. The structure is a hybrid of charge-coupled device (CCD) and bucket-brigade device (BBD) elements and permits the topological crossing of charge-domain signals in low power signal processing circuits. A test vehicle consisting of 8-, 32-, and 96-stage delay lines of various geometries implemented in a double-poly, double-metal foundry process is used to characterize the wire-transfer operation. Transfer efficiency ranging between 0.998 and 0.999 is obtained for surface n-channel devices with clock cycle times in the range from 40 ns to 0.3 ms. Transfer efficiency as high as 0.9999 is obtained for buried n-channel devices. Good agreement is found between experiment and simulation.

  6. Model-independent determination of the degree of charge transfer in molecular and metal complexes.

    PubMed

    Joo, Bora; Kim, Eung-Gun

    2015-09-29

    Quantifying charge transfer is a challenging task because it requires that the calculated degree of charge transfer be both consistent with chemical intuition and independent of charge analysis methods. Based on DFT results of molecular and transition metal complexes in organic electronics, we show that both requirements can be fulfilled by choosing a small active space of electrons for the analysis. Our findings hold for inter- and intramolecular processes whether in the ground state or during excitation. PMID:26324400

  7. Wire transfer of charge packets for on--chip CCD signal processing Eric R. Fossum

    E-print Network

    Fossum, Eric R.

    . The structure is a hybrid of charge-coupled device (CCD) and bucket-brigade device (BBD) elements and permits-domain. SPIE Vol. 1242 Charge-Coupled Devices and Solid State Optical Sensors (1990) / 179 #12;2. WIRE TRANSFER consideration in circuit design. Bucket-brigade devices (BBD5) also operate in the charge domain but have

  8. Molecular orbital (SCF-X-?-SW) theory of Fe2+-Mn3+, Fe3+-Mn2+, and Fe3+-Mn3+ charge transfer and magnetic exchange in oxides and silicates

    USGS Publications Warehouse

    Sherman, David M.

    1990-01-01

    Metal-metal charge-transfer and magnetic exchange interactions have important effects on the optical spectra, crystal chemistry, and physics of minerals. Previous molecular orbital calculations have provided insight on the nature of Fe2+-Fe3+ and Fe2+-Ti4+ charge-transfer transitions in oxides and silicates. In this work, spin-unrestricted molecular orbital calculations on (FeMnO10) clusters are used to study the nature of magnetic exchange and electron delocalization (charge transfer) associated with Fe3+-Mn2+, Fe3+-Mn3+, and Fe2+-Mn3+ interactions in oxides and silicates. 

  9. Ultrafast charge carrier relaxation and charge transfer processes in CdS/CdTe thin films.

    PubMed

    Pandit, Bill; Dharmadasa, Ruvini; Dharmadasa, I M; Druffel, Thad; Liu, Jinjun

    2015-07-14

    Ultrafast transient absorption pump-probe spectroscopy (TAPPS) has been employed to investigate charge carrier relaxation in cadmium sulfide/cadmium telluride (CdS/CdTe) nanoparticle (NP)-based thin films and electron transfer (ET) processes between CdTe and CdS. Effects of post-growth annealing treatments to ET processes have been investigated by carrying out TAPPS experiments on three CdS/CdTe samples: as deposited, heat treated, and CdCl2 treated. Clear evidence of ET process in the treated thin films has been observed by comparing transient absorption (TA) spectra of CdS/CdTe thin films to those of CdS and CdTe. Quantitative comparison between ultrafast kinetics at different probe wavelengths unravels the ET processes and enables determination of its rate constants. Implication of the photoinduced dynamics to photovoltaic devices is discussed. PMID:26033446

  10. Thermoelectric Properties of Organic Charge-Transfer Compounds

    NASA Astrophysics Data System (ADS)

    Itahara, H.; Maesato, M.; Asahi, R.; Yamochi, H.; Saito, G.

    2009-07-01

    We measured the thermoelectric (TE) properties of compressed pellets of various organic charge-transfer (CT) complexes, such as (TTF)(TCNQ), (BO)(TCNQ) and (ET)2(HCNAL), where TTF, TCNQ, BO, ET, and HCNAL represent tetrathiafulvalene, tetracyanoquinodimethane, bis(ethylenedioxy)-tetrathiafulvalene, bis(ethylenedithio)tetrathiafulvalene, and 2,5-dicyano- 3,6-dihydroxy- p-benzoquinone, respectively. The metallic (TTF)(TCNQ) and semiconducting (BO)(TCNQ) complexes showed Seebeck coefficients ( S) of -18 ?V/K and -30 ?V/K at 300 K, respectively. On the contrary, the Mott insulator (ET)2(HCNAL) was found to show a rather high absolute S (-116 ?V/K at 300 K), the magnitude of which is comparable to those of the conventional inorganic TE materials. With increasing temperature (170 K to 300 K), the electrical conductivity was increased about two orders of magnitude while the S value was nearly constant. These results suggest that S values could be determined mainly by spin entropy (configurations) of carriers in the Mott insulator (ET)2(HCNAL). The magnitude of the observed S value was compared with that derived from a theoretical model (generalized Heikes formula).

  11. Dynamic Peptide Library for the Discovery of Charge Transfer Hydrogels.

    PubMed

    Berdugo, Cristina; Nalluri, Siva Krishna Mohan; Javid, Nadeem; Escuder, Beatriu; Miravet, Juan F; Ulijn, Rein V

    2015-11-25

    Coupling of peptide self-assembly to dynamic sequence exchange provides a useful approach for the discovery of self-assembling materials. In here, we demonstrate the discovery and optimization of aqueous, gel-phase nanostructures based on dynamically exchanging peptide sequences that self-select to maximize charge transfer of n-type semiconducting naphthalenediimide (NDI)-dipeptide bioconjugates with various ?-electron-rich donors (dialkoxy/hydroxy/amino-naphthalene or pyrene derivatives). These gel-phase peptide libraries are characterized by spectroscopy (UV-vis and fluorescence), microscopy (TEM), HPLC, and oscillatory rheology and it is found that, of the various peptide sequences explored (tyrosine Y-NDI with tyrosine Y, phenylalanine F, leucine L, valine V, alanine A or glycine G-NH2), the optimum sequence is tyrosine-phenylalanine in each case; however, both its absolute and relative yield amplification is dictated by the properties of the donor component, indicating cooperativity of peptide sequence and donor/acceptor pairs in assembly. The methodology provides an in situ discovery tool for nanostructures that enable dynamic interfacing of supramolecular electronics with aqueous (biological) systems. PMID:26540455

  12. Quantum ferroelectricity in charge-transfer complex crystals

    PubMed Central

    Horiuchi, Sachio; Kobayashi, Kensuke; Kumai, Reiji; Minami, Nao; Kagawa, Fumitaka; Tokura, Yoshinori

    2015-01-01

    Quantum phase transition achieved by fine tuning the continuous phase transition down to zero kelvin is a challenge for solid state science. Critical phenomena distinct from the effects of thermal fluctuations can materialize when the electronic, structural or magnetic long-range order is perturbed by quantum fluctuations between degenerate ground states. Here we have developed chemically pure tetrahalo-p-benzoquinones of n iodine and 4–n bromine substituents (QBr4–nIn, n=0–4) to search for ferroelectric charge-transfer complexes with tetrathiafulvalene (TTF). Among them, TTF–QBr2I2 exhibits a ferroelectric neutral–ionic phase transition, which is continuously controlled over a wide temperature range from near-zero kelvin to room temperature under hydrostatic pressure. Quantum critical behaviour is accompanied by a much larger permittivity than those of other neutral–ionic transition compounds, such as well-known ferroelectric complex of TTF–QCl4 and quantum antiferroelectric of dimethyl–TTF–QBr4. By contrast, TTF–QBr3I complex, another member of this compound family, shows complete suppression of the ferroelectric spin-Peierls-type phase transition. PMID:26076656

  13. Charge transfer vibronic transitions in uranyl tetrachloride compounds

    SciTech Connect

    Liu, Guokui; Deifel, Nicholas P.; Cahill, Christopher L.; Zhurov, Vladimir V.; Pinkerton, A. Alan

    2012-01-01

    The electronic and vibronic interactions of uranyl (UO?)2+ in three tetrachloride crystals have been investigated with spectroscopic experiments and theoretical modeling. Analysis and simulation of the absorption and photoluminescence spectra have resulted in a quantitative understanding of the charge transfer vibronic transitions of uranyl in the crystals. The spectra obtained at liquid helium temperature consist of extremely narrow zero-phonon lines (ZPL) and vibronic bands. The observed ZPLs are assigned to the first group of the excited states formed by electronic excitation from the 3? ground state into the f?,? orbitals of uranyl. The Huang–Rhys theory of vibronic coupling is modified successfully for simulating both the absorption and luminescence spectra. It is shown that only vibronic coupling to the axially symmetric stretching mode is Franck–Condon allowed, whereas other modes are involved through coupling with the symmetric stretching mode. The energies of electronic transitions, vibration frequencies of various local modes, and changes in the O=U=O bond length of uranyl in different electronic states and in different coordination geometries are evaluated in empirical simulations of the optical spectra. Multiple uranyl sites derived from the resolution of a superlattice at low temperature are resolved by crystallographic characterization and time- and energy-resolved spectroscopic studies. The present empirical simulation provides insights into fundamental understanding of uranyl electronic interactions and is useful for quantitative characterization of uranyl coordination.

  14. Charge transfer vibronic transitions in uranyl tetrachloride compounds;

    SciTech Connect

    Liu, G. K.; Deifel, N. P.; Cahill, C. L.

    2012-01-01

    The electronic and vibronic interactions of uranyl (UO{sub 2}){sup 2+} in three tetrachloride crystals have been investigated with spectroscopic experiments and theoretical modeling. Analysis and simulation of the absorption and photoluminescence spectra have resulted in a quantitative understanding of the charge transfer vibronic transitions of uranyl in the crystals. The spectra obtained at liquid helium temperature consist of extremely narrow zero-phonon lines (ZPL) and vibronic bands. The observed ZPLs are assigned to the first group of the excited states formed by electronic excitation from the 3{sigma} ground state into the f{sub {delta}{phi}}, orbitals of uranyl. The Huang-Rhys theory of vibronic coupling is modified successfully for simulating both the absorption and luminescence spectra. It is shown that only vibronic coupling to the axially symmetric stretching mode is Franck-Condon allowed, whereas other modes are involved through coupling with the symmetric stretching mode. The energies of electronic transitions, vibration frequencies of various local modes, and changes in the O=U=O bond length of uranyl in different electronic states and in different coordination geometries are evaluated in empirical simulations of the optical spectra. Multiple uranyl sites derived from the resolution of a superlattice at low temperature are resolved by crystallographic characterization and time- and energy-resolved spectroscopic studies. The present empirical simulation provides insights into fundamental understanding of uranyl electronic interactions and is useful for quantitative characterization of uranyl coordination.

  15. Incorporation of charge transfer into the explicit polarization fragment method by grand canonical density functional theory

    NASA Astrophysics Data System (ADS)

    Isegawa, Miho; Gao, Jiali; Truhlar, Donald G.

    2011-08-01

    Molecular fragmentation algorithms provide a powerful approach to extending electronic structure methods to very large systems. Here we present a method for including charge transfer between molecular fragments in the explicit polarization (X-Pol) fragment method for calculating potential energy surfaces. In the conventional X-Pol method, the total charge of each fragment is preserved, and charge transfer between fragments is not allowed. The description of charge transfer is made possible by treating each fragment as an open system with respect to the number of electrons. To achieve this, we applied Mermin's finite temperature method to the X-Pol wave function. In the application of this method to X-Pol, the fragments are open systems that partially equilibrate their number of electrons through a quasithermodynamics electron reservoir. The number of electrons in a given fragment can take a fractional value, and the electrons of each fragment obey the Fermi-Dirac distribution. The equilibrium state for the electrons is determined by electronegativity equalization with conservation of the total number of electrons. The amount of charge transfer is controlled by re-interpreting the temperature parameter in the Fermi-Dirac distribution function as a coupling strength parameter. We determined this coupling parameter so as to reproduce the charge transfer energy obtained by block localized energy decomposition analysis. We apply the new method to ten systems, and we show that it can yield reasonable approximations to potential energy profiles, to charge transfer stabilization energies, and to the direction and amount of charge transferred.

  16. 46 CFR 153.957 - Persons in charge of transferring liquid cargo in bulk or cleaning cargo tanks.

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ...false Persons in charge of transferring liquid cargo in bulk or cleaning cargo tanks...DANGEROUS CARGOES SHIPS CARRYING BULK LIQUID, LIQUEFIED GAS, OR COMPRESSED GAS HAZARDOUS...957 Persons in charge of transferring liquid cargo in bulk or cleaning cargo...

  17. 46 CFR 153.957 - Persons in charge of transferring liquid cargo in bulk or cleaning cargo tanks.

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ...false Persons in charge of transferring liquid cargo in bulk or cleaning cargo tanks...DANGEROUS CARGOES SHIPS CARRYING BULK LIQUID, LIQUEFIED GAS, OR COMPRESSED GAS HAZARDOUS...957 Persons in charge of transferring liquid cargo in bulk or cleaning cargo...

  18. 46 CFR 153.957 - Persons in charge of transferring liquid cargo in bulk or cleaning cargo tanks.

    Code of Federal Regulations, 2012 CFR

    2012-10-01

    ...false Persons in charge of transferring liquid cargo in bulk or cleaning cargo tanks...DANGEROUS CARGOES SHIPS CARRYING BULK LIQUID, LIQUEFIED GAS, OR COMPRESSED GAS HAZARDOUS...957 Persons in charge of transferring liquid cargo in bulk or cleaning cargo...

  19. 46 CFR 153.957 - Persons in charge of transferring liquid cargo in bulk or cleaning cargo tanks.

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ...false Persons in charge of transferring liquid cargo in bulk or cleaning cargo tanks...DANGEROUS CARGOES SHIPS CARRYING BULK LIQUID, LIQUEFIED GAS, OR COMPRESSED GAS HAZARDOUS...957 Persons in charge of transferring liquid cargo in bulk or cleaning cargo...

  20. 46 CFR 153.957 - Persons in charge of transferring liquid cargo in bulk or cleaning cargo tanks.

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ...false Persons in charge of transferring liquid cargo in bulk or cleaning cargo tanks...DANGEROUS CARGOES SHIPS CARRYING BULK LIQUID, LIQUEFIED GAS, OR COMPRESSED GAS HAZARDOUS...957 Persons in charge of transferring liquid cargo in bulk or cleaning cargo...

  1. Investigation of charge transfer kinetics of Li-Intercalation in LiFePO4

    NASA Astrophysics Data System (ADS)

    Heubner, C.; Schneider, M.; Michaelis, A.

    2015-08-01

    Recent studies point out contradictions between classical Butler-Volmer kinetics and the charge transfer kinetics of lithium intercalation in host materials. In this work the charge transfer kinetics of lithium intercalation in LiFePO4 are investigated using current controlled electrochemical impedance spectroscopy with varying amplitudes. The results point out a significant impact of ohmic and diffusion contributions to the total overpotential which is normally extracted from constant current charging - discharging experiments to determine Tafel-plots, exchange currents and charge transfer coefficients. By the accurate separation of the activation overpotential from the total overpotential the authors are able to show that the charge transfer kinetics of lithium intercalation in LiFePO4 perfectly obey the Butler-Volmer equation.

  2. Charge and Energy Transfer in the Metal-free Indoline Dyes for Dye-sensitized Solar Cells

    NASA Astrophysics Data System (ADS)

    Diao, Li-ying; Gu, Wen-xiang; Chen, Yue-hui; Ma, Feng-cai

    2006-06-01

    Metal-free indoline dyes for dye-sensitized solar cells were studied by employing quantum chemistry methods. Comparative study of the properties of both ground and excited states of metal-free indoline dyes for dye- sensitized solar cells revealed: (i) as the number of rhodanine rings increases, the energy difference between HOMO and LUMO decreases and there is a red shift in the absorption spectrum with the binding energy increased, and the transition dipole moment decreased; (ii) Based on an analysis of charge differential density, we observed that the charge and energy are transfered from the phenylethenyl to the indoline and rhodanine rings; (iii) The electron-hole coherences are mainly on the indoline and rhodanine rings, and the exciton sizes are 30 and 40 atoms for indoline dyes with one and two rhodanline rings, respectively. These results serve as a good example of computer-aided design in metal-free indoline dyes for dye-sensitized solar cells.

  3. Probing charge transfer excitons in a MoSe2-WS2 van der Waals heterostructure

    NASA Astrophysics Data System (ADS)

    Ceballos, Frank; Bellus, Matthew Z.; Chiu, Hsin-Ying; Zhao, Hui

    2015-10-01

    We show that the van der Waals heterostructure formed by MoSe2 and WS2 provides a unique system with near degenerate interlayer and intralayer excitonic states. Photoluminescence measurements indicate that the charge transfer exciton states are approximately 50 meV below the MoSe2 exciton states, with a significant spectral overlap. The transient absorption of a femtosecond pulse was used to study the dynamics of the charge transfer excitons at room temperature. We found a lifetime of approximately 80 ps for the charge transfer excitons. A diffusion coefficient of about 14 cm2 s-1 was deduced, which is comparable to individual excitons in transition metal dichalcogenides.

  4. Direct observation of ion transfer in contact charging between a metal and a polymer

    NASA Astrophysics Data System (ADS)

    Mizes, H. A.; Conwell, E. M.; Salamida, D. P.

    1990-04-01

    Triboelectric charging between metals and insulators is usually thought to involve electron transfer. Doping some polymers with a small amount of salt can significantly change their charging properties, even reversing the sign to which they charge upon contact with a given metal. We show by means of secondary-ion mass spectrometry that ions of the salt are transferred across the interface in contacts between a doped polymer and a metal. Specifically, we observe a transfer of bromine ions when polystyrene doped with a small amount of the salt cetylpyridinium bromide is contacted to an indium surface.

  5. Reduced Charge Transfer Exciton Recombination in Organic Semiconductor Heterojunctions by Molecular Doping

    NASA Astrophysics Data System (ADS)

    Deschler, Felix; da Como, Enrico; Limmer, Thomas; Tautz, Raphael; Godde, Tillmann; Bayer, Manfred; von Hauff, Elizabeth; Yilmaz, Seyfullah; Allard, Sybille; Scherf, Ullrich; Feldmann, Jochen

    2011-09-01

    We investigate the effect of molecular doping on the recombination of electrons and holes localized at conjugated-polymer-fullerene interfaces. We demonstrate that a low concentration of p-type dopant molecules (<4% weight) reduces the interfacial recombination via charge transfer excitons and results in a favored formation of separated carriers. This is observed by the ultrafast quenching of photoluminescence from charge transfer excitons and the increase in photoinduced polaron density by ˜70%. The results are consistent with a reduced formation of emissive charge transfer excitons, induced by state filling of tail states.

  6. A bifurcated molecular pentad capable of sequential electronic energy transfer and intramolecular charge transfer.

    PubMed

    Harriman, Anthony; Stachelek, Patrycja; Sutter, Alexandra; Ziessel, Raymond

    2015-10-21

    An extended molecular array, comprising three distinct types of chromophores and two additional redox-active subunits, that harvests photons over most of the visible spectral range has been synthesized and characterised. The array exhibits a rich variety of electrochemical waves when examined by cyclic voltammetry but assignment can be made on the basis of control compounds and molecular orbital calculations. Stepwise electronic energy transfer occurs along the molecular axis, corresponding to a gradient of excitation energies, to populate the lowest-energy excited state of the ultimate acceptor. The latter species, which absorbs and emits in the far-red region, enters into light-induced charge transfer with a terminal amine group. The array is relatively stable under illumination with white light but degrades slowly via a series of well-defined steps, the first of which is autocatalytic. One of the main attributes of this system is the capability to harvest an unusually high fraction of sunlight while providing protection against exposure to UV light. PMID:26381219

  7. Charge-Transfer Induced Magnetic Field Effects of Nano-Carbon Heterojunctions

    E-print Network

    Qin, Wei; Gong, Maogang; Shastry, Tejas; Hersam, Mark C.; Ren, Shenqiang

    2014-08-22

    positive and negative polarons. Here, we demonstrate charge-transfer induced magnetic field effects in nano-carbon C60-SWCNT bulk heterojunctions at room temperature, where the mechanism of magnetic field effects is verified using excited state transition...

  8. Laser-assisted charge-transfer reactions (Li(3)(+)+H): Coupled dressed-quasimolecular-state approach

    E-print Network

    Ho, Tak-San; Laughlin, Cecil; Chu, Shih-I

    1985-07-01

    A semiclassical coupled dressed-quasimolecular-states (DQMS) approach is presented for nonperturbative treatment of multichannel charge-transfer reactions at low collision velocities and high laser intensities, incorporating ...

  9. Charge transfer polarisation wave and carrier pairing in the high T(sub c) copper oxides

    NASA Technical Reports Server (NTRS)

    Chakraverty, B. K.

    1990-01-01

    The High T(sub c) oxides are highly polarizable materials and are charge transfer insulators. The charge transfer polarization wave formalism is developed in these oxides. The dispersion relationships due to long range dipole-dipole interaction of a charge transfer dipole lattice are obtained in 3-D and 2-D. These are high frequency bosons and their coupling with carriers is weak and antiadiabatic in nature. As a result, the mass renormalization of the carriers is negligible in complete contrast to conventional electron-phonon interaction, that give polarons and bipolarons. Both bound and superconducting pairing is discussed for a model Hamiltonian valid in the antiadiabatic regime, both in 3-D and 2-D. The stability of the charge transfer dipole lattice has interesting consequences that are discussed.

  10. Charge transfer kinetics at the solid–solid interface in porous electrodes

    E-print Network

    Bai, Peng

    Interfacial charge transfer is widely assumed to obey the Butler–Volmer kinetics. For certain liquid–solid interfaces, the Marcus–Hush–Chidsey theory is more accurate and predictive, but it has not been applied to porous ...

  11. Low-energy charge transfer for collisions of Si3+ with atomic hydrogen

    E-print Network

    Savin, Daniel Wolf

    by charge transfer of solar wind ions, among them Si3+ , with neutrals in the cometary gas vapor 5 hydrogen oven as a target, were limited to collision energies above about 50 keV/u 7 . At these energetic

  12. Crystallography and Ellipsometry of Organic Charge Transfer Systems.

    NASA Astrophysics Data System (ADS)

    Lee, Wan-Jin

    Five crystal structures were determined. In the orange 1:1 complex between methyl-2-(2,4 -dinitroanilino)propanoate (MAP) and 2-methyl-4-nitroaniline (MNA) (space group P2_1, NR = 1783 unique reflections, reliability factor R = 4.1%, NP = 346 parameters), the MAP and MNA molecules stack above each other along (010) at van der Waals separations; there is a hydrogen bond between MAP and MNA. MNA, whose monoclinic structure MNA(M) is known (space group Ia), has a new triclinic polymorph, MNA(T) (P1, NR = 715, R = 6.5%, NP = 196): this structure is almost superimposable to MNA(M); three significant reflections are the difference between the structures. In the 1:1 complex between DPA and MNA (P2 _1, NR = 463, R = 13.9%, NP = 116) the DPA and MNA molecules do not overlap well, but are H-bonded. In bis-(N-methylene-2,5-bis-(2-thienyl)pyrrole) (P1, = 1583, R = 7.8%, NP = 145), half the molecule is unique; the two thiophenes have large dihedral angles with the middle pyrrole. Bis-(dimethylthienotetratellurafulvalene) (BDMT -TTeF) forms a black insulating 1:1 complex with buckminsterfullerene, C_{60}, and CS _2; (C2/c, NR = 1552, NP = 166, R = 9.8%). The C_{60} is disordered; BDMT-TTeF is bent. The complex index of refraction of MAP:MNA (ellipsometry, lambda = 632.8 nm) has principal values n_1-ik_1 = 1.5310-0.01959i; n_2-ik _2 = 1.7090-0.06752i; n_3 -ik_3 = 1.9561-0.02465i; {bf n_3}-i {bf k_3} is almost parallel to the c axis, and n1-i {bf k_1 } is along a. Disordered Langmuir-Blodgett multilayer films of C_{60} have (ellipsometry) n = 1.80(6) and a thickness of 19.0(1.2) A per "monolayer", i.e. about 2 C_{60} molecules per "monolayer". From published crystal structures of 179 TCNQ, 71 TTF + TMTTF, and 89 BEDT-TTF complexes and salts (electrical insulators, semiconductors, metals, or superconductors), one needs to know the degree of charge transfer rho, to understand their electrical conductivity. Eighty -two "reference" structures, with known rho , yield linear least-squares equations for rho as a function of molecular length, bond length ratio and bond length difference (coefficient of determination R^2 > 90%). These equations can then predict rho from bond length data for other structures.

  13. Integer versus Fractional Charge Transfer at Metal(/Insulator)/Organic Interfaces: Cu(/NaCl)/TCNE

    PubMed Central

    2015-01-01

    Semilocal and hybrid density functional theory was used to study the charge transfer and the energy-level alignment at a representative interface between an extended metal substrate and an organic adsorbate layer. Upon suppressing electronic coupling between the adsorbate and the substrate by inserting thin, insulating layers of NaCl, the hybrid functional localizes charge. The laterally inhomogeneous charge distribution resulting from this spontaneous breaking of translational symmetry is reflected in observables such as the molecular geometry, the valence and core density of states, and the evolution of the work function with molecular coverage, which we discuss for different growth modes. We found that the amount of charge transfer is determined, to a significant extent, by the ratio of the lateral spacing of the molecules and their distance to the metal. Therefore, charge transfer does not only depend on the electronic structure of the individual components but, just as importantly, on the interface geometry. PMID:25905769

  14. Topological Effects of Charge Transfer in Telomere G-Quadruplex Mechanism on Telomerase Activation and Inhibition

    NASA Astrophysics Data System (ADS)

    Wang, Xin; Liang, Shi-Dong

    2013-02-01

    We explore the charge transfer in the telomere G-Quadruplex (TG4) DNA theoretically by the nonequilibrium Green's function method, and reveal the topological effect of the charge transport in TG4 DNA. The consecutive TG4 (CTG4) is semiconducting with 0.2 0.3 eV energy gap. Charges transfer favorably in the CTG4, but are trapped in the nonconsecutive TG4 (NCTG4). The global conductance is inversely proportional to the local conductance for NCTG4. The topological structure transition from NCTG4 to CTG4 induces abruptly 3nA charge current, which provide a microscopic clue to understand the telomerase activated or inhibited by TG4. Our findings reveal the fundamental property of charge transfer in TG4 and its relationship with the topological structure of TG4.

  15. Topological effects of charge transfer in telomere G-quadruplex: Mechanism on telomerase activation and inhibition

    E-print Network

    Wang, Xin

    2015-01-01

    We explore charge transfer in the telomere G-Quadruplex (TG4) DNA theoretically by the nonequilibrium Green's function method, and reveal the topological effect of charge transport in TG4 DNA. The consecutive TG4(CTG4) is semiconducting with 0.2 ~ 0.3eV energy gap. Charges transfers favorably in the consecutive TG4, but are trapped in the non-consecutive TG4 (NCTG4). The global conductance is inversely proportional to the local conductance for NCTG4. The topological structure transition from NCTG4 to CTG4 induces abruptly ~ 3nA charge current, which provide a microscopic clue to understand the telomerase activated or inhibited by TG4. Our findings reveal the fundamental property of charge transfer in TG4 and its relationship with the topological structure of TG4.

  16. Radiative charge transfer in cold and ultracold Sulfur atoms colliding with Protons

    E-print Network

    G Shen; P C Stancil; J G Wang; J F McCann; B M McLaughlin

    2015-02-25

    Radiative decay processes at cold and ultra cold temperatures for Sulfur atoms colliding with protons are investigated. The MOLPRO quantum chemistry suite of codes was used to obtain accurate potential energies and transition dipole moments, as a function of internuclear distance, between low-lying states of the SH$^{+}$ molecular cation. A multi-reference configuration-interaction (MRCI) approximation together with the Davidson correction is used to determine the potential energy curves and transition dipole moments, between the states of interest, where the molecular orbitals (MO's) are obtained from state-averaged multi configuration-self-consistent field (MCSCF) calculations. The collision problem is solved approximately using an optical potential method to obtain radiative loss, and a fully two-channel quantum approach for radiative charge transfer. Cross sections and rate coefficients are determined for the first time for temperatures ranging from 10 $\\mu$ K up to 10,000 K. Results are obtained for all isotopes of Sulfur, colliding with H$^{+}$ and D$^{+}$ ions and comparison is made to a number of other collision systems.

  17. Intermolecular charge transfer and vibrational analysis of hydrogen bonding in acetazolamide

    NASA Astrophysics Data System (ADS)

    Chaturvedi, Deepika; Gupta, Vineet; Tandon, Poonam; Sharma, Anamika; Baraldi, C.; Gamberini, M. C.

    2012-12-01

    In the present work the structural and spectral characteristics of acetazolamide have been studied by methods of infrared, Raman spectroscopy and quantum chemistry. Electrostatic potential surface, optimized geometry, harmonic vibrational frequencies, infrared intensities and activities of Raman scattering were calculated by density functional theory (DFT) employing B3LYP with complete relaxation in the potential energy surface using 6-311++G(d,p) basis set. Based on these results, we have discussed the correlation between the vibrational modes and the structure of the dimers of acetazolamide. The calculated vibrational spectra of three dimers of acetazolamide have been compared with observed spectra, and the assignment of observed bands was carried out using potential energy distribution. The observed spectra agree well with the values computed from the DFT. A comparison of observed and calculated vibrational spectra clearly shows the effect of hydrogen bonding. The frequency shifts observed for the different dimers are in accord with the hydrogen bonding in acetazolamide. Natural bond orbital (NBO) analyses reflect the charge transfer interaction in the individual hydrogen bond units and the stability of different dimers of acetazolamide.

  18. Modeling Charge Transfer in Fullerene Collisions via Real-Time Electron Dynamics

    SciTech Connect

    Jakowski, Jacek; Irle, Stephan; Morokuma, Keiji; Sumpter, Bobby G

    2012-01-01

    An approach for performing real-time dynamics of electron transfer in a prototype redox reaction that occurs in reactive collisions between neutral and ionic fullerenes is discussed. The quantum dynamical simulations show that the electron transfer occurs within 60 fs directly preceding the collision of the fullerenes, followed by structural changes and relaxation of electron charge. The consequences of real-time electron dynamics are fully elucidated for the far from equilibrium processes of collisions between neutral and multiply charged fullerenes.

  19. Electronic reorganization triggered by electron transfer: the intervalence charge transfer of a Fe³?/Fe²? bimetallic complex.

    PubMed

    Domingo, Alex; Angeli, Celestino; de Graaf, Coen; Robert, Vincent

    2015-04-30

    The key role of the molecular orbitals in describing electron transfer processes is put in evidence for the intervalence charge transfer (IVCT) of a synthetic nonheme binuclear mixed-valence Fe(3+)/Fe(2+) compound. The electronic reorganization induced by the IVCT can be quantified by controlling the adaptation of the molecular orbitals to the charge transfer process. We evaluate the transition energy and its polarization effects on the molecular orbitals by means of ab initio calculations. The resulting energetic profile of the IVCT shows strong similarities to the Marcus' model, suggesting a response behaviour of the ensemble of electrons analogue to that of the solvent. We quantify the extent of the electronic reorganization induced by the IVCT process to be 11.74 eV, a very large effect that induces the crossing of states reducing the total energy of the transfer to 0.89 eV. PMID:25739890

  20. Electrospray Charging of Minerals: Surface Chemistry and Applications to High-Velocity Microparticle Impacts

    NASA Astrophysics Data System (ADS)

    Daly, T.; Call, S.; Austin, D. E.

    2010-12-01

    Electrospray is a soft ionization technique commonly used to charge large biomolecules; it has, however, also been applied to inorganic compounds. We are extending this technique to mineral microparticles. Electrospray-charged mineral microparticles are interesting in the context of surface science because surface chemistry dictates where and how charge carriers can bond to mineral surfaces. In addition, using electrospray to charge mineral particles allows these particles to be electrostatically accelerated as projectiles in high- and hyper-velocity impacts. Since current techniques for producing high- and hyper-velocity microparticle impacts are largely limited to metal or metal-coated projectiles, using minerals as projectiles is a significant innovation. Electrospray involves three steps: creation of charged droplets containing solute/particles, evaporation and bifurcation of droplets, and desolvation of the solute/particles. An acidified solution is slowly pumped through a needle in a strong DC field, which causes the solution to break into tiny, charged droplets laden with protons. Solvent evaporates from the electrosprayed droplets as they move through the electric field toward a grounded plate, causing the charge on the droplet to increase relative to its mass. When the electrosprayed droplet’s charge becomes such that the droplet is no longer stable, it bifurcates, and each of the resulting droplets carries some of the original droplet’s charge. Evaporation and bifurcation continues until the solute particle is completely desolvated. The result is a protonated solute molecule or particle. We built an instrument that electrosprays particles into vacuum and measures them using an image charge detector. Mineral microparticles were prepared by grinding natural mineral samples to ~2 µm diameter. These microparticles are then added to a 4:1 methanol:water solution to create a 0.005% w/v suspension. The suspension is electrosprayed into vacuum, where the charge detector measures the electrosprayed mineral particles’ speed and charge. Quartz microparticles have been successfully electrosprayed. Variation in quartz microparticles’ charge as a function of pH is being evaluated. In addition, we are studying how to completely desolvate electrosprayed mineral particles. Desolvation is not trivial and often requires more than the passive passage of the droplets from the needle to the grounded plate and into vacuum. We are testing two desolvation methods: a heated beam tube and a heated capillary. Preliminary data suggests we have achieved complete desolvation with a hot beam tube. Although quartz’s surface chemistry is rather unique, successful electrospray of quartz microparticles strongly suggests that other minerals may also be electrosprayed. We are preparing olivine samples for electrospray. In addition, an instrument that creates high-velocity microparticle impacts using electrospray-charged mineral microparticles is being developed. This instrument will not only permit minerals to be used as projectiles, but also allows direction characterization of chemical speciation occurring during microparticle impacts.

  1. Electronic and Nuclear Factors in Charge and Excitation Transfer

    SciTech Connect

    Piotr Piotrowiak

    2004-09-28

    We report the and/or state of several subprojects of our DOE sponsored research on Electronic and Nuclear Factors in Electron and Excitation Transfer: (1) Construction of an ultrafast Ti:sapphire amplifier. (2) Mediation of electronic interactions in host-guest molecules. (3) Theoretical models of electrolytes in weakly polar media. (4) Symmetry effects in intramolecular excitation transfer.

  2. Temperature dependence conductivity in organic charge transfer complexes: A theoretical view

    NASA Astrophysics Data System (ADS)

    Singh, Yadunath

    2013-06-01

    We propose a theoretical view of temperature dependent conductivity in organic charge transfer complexes and radical ion salts with symmetric and asymmetric donor molecules over a wide range of temperature. This phenomenon can be understand on the basis on the current carriers, 3-D effects, scattering by defects and impurities, formation of charge density waves (CDW) and soliton propagation etc.

  3. Competition between Covalent Bonding and Charge Transfer at Complex-Oxide Interfaces

    E-print Network

    Tennessee, University of

    Competition between Covalent Bonding and Charge Transfer at Complex-Oxide Interfaces Juan is observed. Model calculations rationalize the profile in terms of the competition between standard charge- (LCMO/YBCO) have attracted much attention. This system is a paradigmatic example of competition between

  4. Charge-Transfer Dynamics in Blue Copper Proteins: Experiment and Simulation

    E-print Network

    Scherer, Norbert F.

    Charge-Transfer Dynamics in Blue Copper Proteins: Experiment and Simulation N.F. Scherer,L.D. Book copper proteins are reported. Blue copper proteins function as mobile electron carriers in a wide variety absorption makes blue copper proteins suitable for ultrafast spectroscopic studies of electron transfer

  5. Charge-transfer electrostatic model of compositional order in perovskite alloys Zhigang Wu and Henry Krakauer

    E-print Network

    Wu, Zhigang

    Charge-transfer electrostatic model of compositional order in perovskite alloys Zhigang Wu transfer that is shown to account for the observed B-site ordering in Pb-based perovskite alloys. The model the long-range compositional order of both Pb- and Ba-based complex A(BB B )O3 perovskite alloys

  6. 33 CFR 127.301 - Persons in charge of shoreside transfer operations: Qualifications and certification.

    Code of Federal Regulations, 2014 CFR

    2014-07-01

    ... LNG may not use the services of any person, as a person in charge of shoreside transfer operations, unless that person— (1) Has at least 48 hours of LNG transfer experience; (2) Knows the hazards of LNG... at the waterfront facility handling LNG....

  7. 33 CFR 127.301 - Persons in charge of shoreside transfer operations: Qualifications and certification.

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... LNG may not use the services of any person, as a person in charge of shoreside transfer operations, unless that person— (1) Has at least 48 hours of LNG transfer experience; (2) Knows the hazards of LNG... at the waterfront facility handling LNG....

  8. 33 CFR 127.301 - Persons in charge of shoreside transfer operations: Qualifications and certification.

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ... LNG may not use the services of any person, as a person in charge of shoreside transfer operations, unless that person— (1) Has at least 48 hours of LNG transfer experience; (2) Knows the hazards of LNG... at the waterfront facility handling LNG....

  9. 33 CFR 127.301 - Persons in charge of shoreside transfer operations: Qualifications and certification.

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ... LNG may not use the services of any person, as a person in charge of shoreside transfer operations, unless that person— (1) Has at least 48 hours of LNG transfer experience; (2) Knows the hazards of LNG... at the waterfront facility handling LNG....

  10. 33 CFR 127.301 - Persons in charge of shoreside transfer operations: Qualifications and certification.

    Code of Federal Regulations, 2012 CFR

    2012-07-01

    ... LNG may not use the services of any person, as a person in charge of shoreside transfer operations, unless that person— (1) Has at least 48 hours of LNG transfer experience; (2) Knows the hazards of LNG... at the waterfront facility handling LNG....

  11. Incorporation of charge transfer into the explicit polarization fragment method by grand canonical density functional theory

    PubMed Central

    Isegawa, Miho; Gao, Jiali; Truhlar, Donald G.

    2011-01-01

    Molecular fragmentation algorithms provide a powerful approach to extending electronic structure methods to very large systems. Here we present a method for including charge transfer between molecular fragments in the explicit polarization (X-Pol) fragment method for calculating potential energy surfaces. In the conventional X-Pol method, the total charge of each fragment is preserved, and charge transfer between fragments is not allowed. The description of charge transfer is made possible by treating each fragment as an open system with respect to the number of electrons. To achieve this, we applied Mermin's finite temperature method to the X-Pol wave function. In the application of this method to X-Pol, the fragments are open systems that partially equilibrate their number of electrons through a quasithermodynamics electron reservoir. The number of electrons in a given fragment can take a fractional value, and the electrons of each fragment obey the Fermi–Dirac distribution. The equilibrium state for the electrons is determined by electronegativity equalization with conservation of the total number of electrons. The amount of charge transfer is controlled by re-interpreting the temperature parameter in the Fermi–Dirac distribution function as a coupling strength parameter. We determined this coupling parameter so as to reproduce the charge transfer energy obtained by block localized energy decomposition analysis. We apply the new method to ten systems, and we show that it can yield reasonable approximations to potential energy profiles, to charge transfer stabilization energies, and to the direction and amount of charge transferred. PMID:21895159

  12. An abnormally slow proton transfer reaction in a simple HBO derivative due to ultrafast intramolecular-charge transfer events.

    PubMed

    Alarcos, Noemí; Gutierrez, Mario; Liras, Marta; Sánchez, Félix; Douhal, Abderrazzak

    2015-07-01

    We report on the steady-state, picosecond and femtosecond time-resolved studies of a charge and proton transfer dye 6-amino-2-(2'-hydroxyphenyl)benzoxazole (6A-HBO) and its methylated derivative 6-amino-2-(2'-methoxyphenyl)benzoxazole (6A-MBO), in different solvents. With femtosecond resolution and comparison with the photobehaviour of 6A-MBO, we demonstrate for 6A-HBO in solution, the photoproduction of an intramolecular charge-transfer (ICT) process at S1 taking place in ?140 fs or shorter, followed by solvent relaxation in the charge transferred species. The generated structure (syn-enol charge transfer conformer) experiences an excited-state intramolecular proton-transfer (ESIPT) reaction to produce a keto-type tautomer. This subsequent proton motion occurs in 1.2 ps (n-heptane), 14 ps (DCM) and 35 ps (MeOH). In MeOH, it is assisted by the solvent molecules and occurs through tunneling for which we got a large kinetic isotope effect (KIE) of about 13. For the 6A-DBO (deuterated sample in CD3OD) the global proton-transfer reaction takes place in 200 ps, showing a remarkable slow KIE regime. The slow ESIPT reaction in DCM (14 ps), not through tunnelling as it is not sensitive to OH/OD exchange, has however to overcome an energy barrier using intramolecular as well as solvent coordinates. The rich ESIPT dynamics of 6A-HBO in the used solutions is governed by an ICT reaction, triggered by the amino group, and it is solvent dependent. Thus, the charge injection to a 6A-HBO molecular frame makes the ICT species more stable, and the phenol group less acidic, slowing down the subsequent ESIPT reaction. Our findings bring new insights into the coupling between ICT and ESIPT reactions on the potential-energy surfaces of several barriers. PMID:25870162

  13. Charge transfer at metal/solid polymer interfaces in the presence of liquids

    NASA Astrophysics Data System (ADS)

    Wasem, Joe; Langford, Steve; Dickinson, Tom

    2002-03-01

    Physical and chemical interactions can transfer charge between liquids and insulating surfaces with important consequences. We examine charge transfer across a metal stylus/solid polymer interface in the presence of liquid (here a perfluoropolyether lubricant, Fomblin Z-DOL--a common lubricant for magnetic hard disks--and water). Observations of transient currents to/from the metal stylus, near-surface bound charge, and free charge escaping from the surface provide direct evidence for the transfer of negative charge (electrons) from the metal (Al) to both the polymer (e.g., polyfluoroethylene--Teflon^TM) and the liquid. We report measurements of the resulting charge densities on the solid polymer surface and in the liquid, as well as the energy distributions of negative charge emitted into vacuum above the liquid layer. Finally, we discuss the potential impact of this charge on the physical manipulation of these liquids on the polymer surface as well as the possible role of negative charge in the decomposition of perfluoropolyether lubricants via electron attachment.

  14. Gating of single molecule junction conductance by charge transfer complex formation.

    PubMed

    Vezzoli, Andrea; Grace, Iain; Brooke, Carly; Wang, Kun; Lambert, Colin J; Xu, Bingqian; Nichols, Richard J; Higgins, Simon J

    2015-12-01

    The solid-state structures of organic charge transfer (CT) salts are critical in determining their mode of charge transport, and hence their unusual electrical properties, which range from semiconducting through metallic to superconducting. In contrast, using both theory and experiment, we show here that the conductance of metal |single molecule| metal junctions involving aromatic donor moieties (dialkylterthiophene, dialkylbenzene) increase by over an order of magnitude upon formation of charge transfer (CT) complexes with tetracyanoethylene (TCNE). This enhancement occurs because CT complex formation creates a new resonance in the transmission function, close to the metal contact Fermi energy, that is a signal of room-temperature quantum interference. PMID:26510687

  15. Charge transfer and band gap of ferrocene intercalated into TiSe 2

    NASA Astrophysics Data System (ADS)

    Titov, A. N.; Yarmoshenko, Yu. M.; Bazylewski, P.; Yablonskikh, M. V.; Kurmaev, E. Z.; Wilks, R.; Moewes, A.; Tsurin, V. A.; Fedorenko, V. V.; Suvorova, O. N.; Ketkov, S. Yu.; Neumann, M.; Chang, G. S.

    2010-09-01

    We have investigated the charge transfer characteristics and electronic structure of ferrocene-intercalated TiSe 2. The spectroscopic results revealed that an intercalation of metallocene molecules leads to changes in the ionic valence of Fe atom in ferrocene molecule and the band gap, which is in accordance with electrical resistivity measurements showing metallic conductivity. Our analysis of 57Fe Mössbauer and Fe 2 p XAS spectra suggested that the suppression of charge-density-wave state in TiSe 2 and an appearance of metallic conductivity are attributed to charge transfer of electrons from ferrocene intercalant to the dichalcogenide host material.

  16. Intrinsic charge trapping in organic and polymeric semiconductors: a physical chemistry perspective

    SciTech Connect

    Zhu, Xiaoyang; Barbara, Paul F.; Kaake, Loren

    2010-02-04

    We aim to understand the origins of intrinsic charge carrier traps in organic and polymeric semiconductor materials from a physical chemistry perspective. In crystalline organic semiconductors, we point out some of the inadequacies in the description of intrinsic charge traps using language and concepts developed for inorganic semiconductors. In ?-conjugated polymeric semiconductors, we suggest the presence of a two-tier electronic energy landscape, a bimodal majority landscape due to two dominant structural motifs and a minority electronic energy landscape from intrinsic charged defects. The bimodal majority electronic energy landscape results from a combination of amorphous domains and microcrystalline or liquid-crystalline domains. The minority tier of the electronic density of states is comprised of deep Coulomb traps embedded in the majority electronic energy landscape. This minority electronic energy landscape may dominate transport properties at low charge carrier densities, such as those expected for organic photovoltaic devices, while the bimodal majority electronic energy landscape becomes significant at high carrier densities, that is, in organic field effect transistors.

  17. Novel method for the fabrication of a charge-transfer complex crystal by photoirradiation.

    PubMed

    Matsuda, Masaki; Nishi, Miki; Koga, Shoko; Fujishima, Mika; Hoshino, Norihisa; Akutagawa, Tomoyuki; Hasegawa, Hiroyuki

    2014-09-01

    A novel method for the fabrication of a charge-transfer complex crystal was developed. Photoirradiation of a solution of TPP[Co(tbp)(CN)(2)] and TPP[Co(Pc)(CN)(2)] (tbp=tetrabenzoporphyrin, Pc=phthalocyanine, TPP=tetraphenylphosphonium) gave a molecular conducting crystal of a charge-transfer complex TPP[Co(tbp)(CN)(2)](2), which was produced by the process in which the photoexcited electron in tbp was transferred from the LUMO of tbp to that of Pc. PMID:25048397

  18. Controllable Quantum State Transfer Between a Josephson Charge Qubit and an Electronic Spin Ensemble

    NASA Astrophysics Data System (ADS)

    Yan, Run-Ying; Wang, Hong-Ling; Feng, Zhi-Bo

    2015-05-01

    We propose a theoretical scheme to implement controllable quantum state transfer between a superconducting charge qubit and an electronic spin ensemble of nitrogen-vacancy centers. By an electro-mechanical resonator acting as a quantum data bus, an effective interaction between the charge qubit and the spin ensemble can be achieved in the dispersive regime, by which state transfers are switchable due to the adjustable electrical coupling. With the accessible experimental parameters, we further numerically analyze the feasibility and robustness. The present scheme could provide a potential approach for transferring quantum states controllably with the hybrid system.

  19. On the relation between local and charge-transfer exciton binding energies in organic photovoltaic materials

    NASA Astrophysics Data System (ADS)

    de Gier, Hilde D.; Broer, Ria; Havenith, Remco W. A.

    2015-09-01

    In organic photovoltaic devices two types of excitons can be generated for which different binding energies can be defined: the binding energy of the local exciton generated immediately after light absorption on the polymer and the binding energy of the charge-transfer exciton generated through the electron transfer from polymer to PCBM. Lowering these two binding energies is expected to improve the efficiency of the devices. Using (time-dependent) density functional theory, we studied whether a relation exists between the two different binding energies. For a series of related co-monomers, we found that the local exciton binding energy on a monomer is not directly related to that of the chargetransfer exciton on a monomer-PCBM complex because the variation in exciton binding energy depends mainly on the variation in electron affinity, which does not affect in a direct way the charge-transfer exciton binding energy. Furthermore, for the studied co-monomers and their corresponding trimers, we provide detailed information on the amount of charge transfer upon excitation and on the charge transfer excitation length. This detailed study of the excitation process reveals that the thiophene unit that links the donor and acceptor fragments of the co-monomer actively participates in the charge transfer process.

  20. Sensing organic molecules by charge transfer through aptamer-target complexes: theory and simulation.

    PubMed

    Schill, Maria; Koslowski, Thorsten

    2013-01-17

    Aptamers, i.e., short sequences of RNA and single-stranded DNA, are capable of specificilly binding objects ranging from small molecules over proteins to entire cells. Here, we focus on the structure, stability, dynamics, and electronic properties of oligonucleotides that interact with aromatic or heterocyclic targets. Large-scale molecular dynamics simulations indicate that aromatic rings such as dyes, metabolites, or alkaloides form stable adducts with their oligonucleotide host molecules at least on the simulation time scale. From molecular dynamics snapshots, the energy parameters relevant to Marcus' theory of charge transfer are computed using a modified Su-Schrieffer-Heeger Hamiltonian, permitting an estimate of the charge transfer rates. In many cases, aptamer binding seriously influences the charge transfer kinetics and the charge carrier mobility within the complex, with conductivities up to the nanoampere range for a single complex. We discuss the conductivity properties with reference to potential applications as biosensors. PMID:23227783

  1. Conformationally Gated Charge Transfer in DNA Three-Way Junctions.

    PubMed

    Zhang, Yuqi; Young, Ryan M; Thazhathveetil, Arun K; Singh, Arunoday P N; Liu, Chaoren; Berlin, Yuri A; Grozema, Ferdinand C; Lewis, Frederick D; Ratner, Mark A; Renaud, Nicolas; Siriwong, Khatcharin; Voityuk, Alexander A; Wasielewski, Michael R; Beratan, David N

    2015-07-01

    Molecular structures that direct charge transport in two or three dimensions possess some of the essential functionality of electrical switches and gates. We use theory, modeling, and simulation to explore the conformational dynamics of DNA three-way junctions (TWJs) that may control the flow of charge through these structures. Molecular dynamics simulations and quantum calculations indicate that DNA TWJs undergo dynamic interconversion among "well stacked" conformations on the time scale of nanoseconds, a feature that makes the junctions very different from linear DNA duplexes. The studies further indicate that this conformational gating would control charge flow through these TWJs, distinguishing them from conventional (larger size scale) gated devices. Simulations also find that structures with polyethylene glycol linking groups ("extenders") lock conformations that favor CT for 25 ns or more. The simulations explain the kinetics observed experimentally in TWJs and rationalize their transport properties compared with double-stranded DNA. PMID:26266714

  2. The effects of charge transfer on the aqueous solvation of ions

    SciTech Connect

    Soniat, Marielle; Rick, Steven W.

    2012-07-28

    Ab initio-based charge partitioning of ionic systems results in ions with non-integer charges. This charge-transfer (CT) effect alters both short- and long-range interactions. Until recently, the effects of CT have been mostly neglected in molecular dynamics (MD) simulations. The method presented in this paper for including charge transfer between ions and water is consistent with ab initio charge partitioning and does not add significant time to the simulation. The ions of sodium, potassium, and chloride are parameterized to reproduce dimer properties and aqueous structures. The average charges of the ions from MD simulations (0.900, 0.919, and -0.775 for Na{sup +}, K{sup +}, and Cl{sup -}, respectively) are consistent with quantum calculations. The hydration free energies calculated for these ions are in agreement with experimental estimates, which shows that the interactions are described accurately. The ions also have diffusion constants in good agreement with experiment. Inclusion of CT results in interesting properties for the waters in the first solvation shell of the ions. For all ions studied, the first shell waters acquire a partial negative charge, due to the difference between water-water and water-ion charge-transfer amounts. CT also reduces asymmetry in the solvation shell of the chloride anion, which could have important consequences for the behavior of chloride near the air-water interface.

  3. 46 CFR 154.1831 - Persons in charge of transferring liquid cargo in bulk or preparing cargo tanks.

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ...false Persons in charge of transferring liquid cargo in bulk or preparing cargo tanks...1831 Persons in charge of transferring liquid cargo in bulk or preparing cargo tanks...on duty to safely conduct a transfer of liquid cargo in bulk or a cool-down,...

  4. 46 CFR 154.1831 - Persons in charge of transferring liquid cargo in bulk or preparing cargo tanks.

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ...false Persons in charge of transferring liquid cargo in bulk or preparing cargo tanks...1831 Persons in charge of transferring liquid cargo in bulk or preparing cargo tanks...on duty to safely conduct a transfer of liquid cargo in bulk or a cool-down,...

  5. Ultrafast Charge- and Energy-Transfer Dynamics in Conjugated Polymer: Cadmium Selenide Nanocrystal Blends

    PubMed Central

    2014-01-01

    Hybrid nanocrystal–polymer systems are promising candidates for photovoltaic applications, but the processes controlling charge generation are poorly understood. Here, we disentangle the energy- and charge-transfer processes occurring in a model system based on blends of cadmium selenide nanocrystals (CdSe-NC) with poly[2-methoxy-5-(3?,7?-dimethyloctyloxy)-1,4-phenylene vinylene] (MDMO-PPV) using a combination of time-resolved absorption and luminescence measurements. The use of different capping ligands (n-butylamine, oleic acid) as well as thermal annealing allows tuning of the polymer–nanocrystal interaction. We demonstrate that energy transfer from MDMO-PPV to CdSe-NCs is the dominant exciton quenching mechanism in nonannealed blends and occurs on ultrafast time scales (<1 ps). Upon thermal annealing electron transfer becomes competitive with energy transfer, with a transfer rate of 800 fs independent of the choice of the ligand. Interestingly, we find hole transfer to be much less efficient than electron transfer and to extend over several nanoseconds. Our results emphasize the importance of tuning the organic–nanocrystal interaction to achieve efficient charge separation and highlight the unfavorable hole-transfer dynamics in these blends. PMID:24490650

  6. Spectrophotometric study of the charge transfer complex between 2-amino-4-picoline with chloranilic acid

    NASA Astrophysics Data System (ADS)

    Alghanmi, Reem M.; Al-Attas, Amirah S.; Habeeb, Moustafa M.

    2013-02-01

    Charge transfer complex formation between 2-amino-4-picoline (2A4P) as the electron donor with chloranilic acid (CLA) as the electron acceptor has been studied spectrophotometrically in different polar solvents included acetone (AcN), ethanol (EtOH) and acetonitrile (AN). The molecular composition of the formed complex was recognized utilizing Job's, photometric and conductometric titration methods to be 1:1. The formation constants and molecular extinction coefficients were estimated using Benesi-Hildebrand equation; they recorded high values confirming high stability of the formed complex. Moreover, the results showed that the complex is more stable in acetone with lower electric permittivity compared with ethanol or acetonitrile of higher ones. The values of some spectroscopic physical parameters like oscillator strength f, transition dipole moment ?, resonance energy RN, charge transfer energy ECT, dissociation energy W, ionization potential IP and standard free energy ?Go were determined and evaluated. The solid complex was isolated and its molecular composition was determined by elemental analysis to be 1:1. Furthermore, the solid complex was characterized using FTIR and 1H NMR measurements. They confirmed the presence of proton transfer beside charge transfer in the obtained complex. Molecular orbital calculations utilizing GAMESS computations were carried out to predict infrared spectra. They also confirmed the presence of proton transfer beside charge transfer in the formed complex.

  7. Chemical Control of Charge Trapping and Charge Transfer Processes at the Organic-Inorganic Interface within Quantum Dot-Organic Complexes

    SciTech Connect

    Weiss, Emily A.

    2015-11-06

    Within the research program funded through the Early Career Research Award we designed complexes of colloidal semiconductor quantum dots (QDs) and organic molecules in which the interfacial chemistry controls the electronic structure and dynamics of the excitonic state of the QD. The program included two main projects; (1) investigation of the mechanisms by which organic surfactants control the quantum confinement of excitonic charge carriers; and (2) development of models for electron transfer between QDs and adsorbed molecules as a function of interfacial chemistry. This project was extremely successful in that our achievements in those two areas addressed the great majority of questions we outlined in the original proposal and answered questions I did not think to ask in that original proposal. Our work led to the discovery of “exciton delocalizing ligands”, which change the electronic structure of colloidal semiconductor nanocrystals by altering, with small synthetic modifications to their surfaces, their most defining characteristic – the quantum confinement of their excited states. It also led to detailed, quantitative descriptions of how the surface chemistry of a QD dictates, thermodynamically and kinetically, the probability of exchange of electrons between the QD and a small molecule. We used two of the three major techniques in the proposal (transient photoluminescence and transient absorption). Electrogenerated chemiluminescence was also proposed, but was too technically difficult with these systems to be useful. Instead, NMR spectroscopy emerged as a major analytical tool in our studies. With the fundamental advancements we made with this project, we believe that we can design QDs to be the next great class of visible-light photocatalysts.

  8. Investigations of Isoprene Oxidation Chemistry using Proton-Transfer Reaction Linear Ion Trap Mass Spectrometry

    NASA Astrophysics Data System (ADS)

    Xiong, F.; Pratt, K. A.; McAvey, K.; Rindelaub, J. D.; Mielke, L. H.; Prentice, B. M.; Hilger, R. T.; McLuckey, S. A.; Oglesbee, R. A.; Shepson, P. B.

    2011-12-01

    Isoprene, emitted primarily from forest ecosystems, comprises approximately one-third of all non-methane volatile organic compound emissions globally. However, uncertainties remain in our understanding of the atmospheric oxidation chemistry of isoprene, particularly with respect low-NOx conditions and the fate of oxidation products. Smog chamber studies allow oxidation products to be studied in detail in a controlled setting. The proton-transfer reaction linear ion trap mass spectrometer (PTR-LIT-MS) was developed to allow the differentiation and quantification of isomeric/isobaric compounds via MS/MS analysis. The PTR-LIT is used herein to examine changes in isoprene oxidation products with high temporal resolution during the photochemical reaction of isoprene and OH. In addition, using synthesized standards, the PTR-LIT is utilized to examine the OH-oxidation chemistry of first generation oxidation products, such as the primary isoprene nitrates. These measurements provide insights into the fates of isoprene oxidation products in the atmosphere.

  9. Charge Transfer Properties Through Graphene Layers in Gas Detectors

    E-print Network

    P. Thuiner; R. Hall-Wilton; R. B. Jackman; H. Müller; T. T. Nguyen; E. Oliveri; D. Pfeiffer; F. Resnati; L. Ropelewski; J. A. Smith; M. van Stenis; R. Veenhof

    2015-03-23

    Graphene is a single layer of carbon atoms arranged in a honeycomb lattice with remarkable mechanical, electrical and optical properties. For the first time graphene layers suspended on copper meshes were installed into a gas detector equipped with a gaseous electron multiplier. Measurements of low energy electron and ion transfer through graphene were conducted. In this paper we describe the sample preparation for suspended graphene layers, the testing procedures and we discuss the preliminary results followed by a prospect of further applications.

  10. Charge Transfer Properties Through Graphene Layers in Gas Detectors

    E-print Network

    Thuiner, P; Jackman, R B; Müller, H; Nguyen, T T; Oliveri, E; Pfeiffer, D; Resnati, F; Ropelewski, L; Smith, J A; van Stenis, M; Veenhof, R

    2015-01-01

    Graphene is a single layer of carbon atoms arranged in a honeycomb lattice with remarkable mechanical, electrical and optical properties. For the first time graphene layers suspended on copper meshes were installed into a gas detector equipped with a gaseous electron multiplier. Measurements of low energy electron and ion transfer through graphene were conducted. In this paper we describe the sample preparation for suspended graphene layers, the testing procedures and we discuss the preliminary results followed by a prospect of further applications.

  11. Charge transfer and momentum exchange in exospheric D-H(+) and H-D(+) collisions

    NASA Technical Reports Server (NTRS)

    Hodges, R. R., Jr.; Breig, E. L.

    1993-01-01

    Mechanisms that control the escape of deuterium from planetary exospheres include the acceleration of D(+) in the polar wind, and the production of suprathermal D atoms through nonthermal collisions. In this paper we examine the effects of neutral-ion interactions involving deuterium and hydrogen on the velocity distribution of neutral D. A two-center scattering approximation is used as the basis for calculations of the differential cross sections for charge transfer and elastic scatter in collision of H with D(+) and of D with H(+) for ionosphere-exosphere collision energies below 10 e V. These data are used to derive temperature dependent rate coefficients for the charge transfer branches of these interactions, and to determine the effects of ion-neutral temperature differences on the rate of generation of suprathermal D through charge transfer and elastic scatter.

  12. Emergent conductance and magnetism at metal oxide interfaces via internal charge transfer

    NASA Astrophysics Data System (ADS)

    Chen, Hanghui; Millis, Andrew; Marianetti, Chris

    2015-03-01

    Internal charge transfer across the interface of transition metal oxides is proven to be a powerful approach to induce new electronic structure in metamaterials (PRL 111, 116403 (2013); arXiv:1408.0217 (2014)). Here we use ab initio calculations to demonstrate that while SrVO3 is a paramagnetic metal and SrMnO3 is an antiferromagetic insulator, charge transfer in a SrVO3/SrMnO3 superlattice leads to both electronic and magnetic reconstructions on the Mn sites: the Mn eg states are electron doped and the Mn t2 g core spins are ferromagnetically aligned. As a result, net magnetic moments are expected to emerge in the superlattice. Our work shows that charge transfer is a robust route to the design of novel two dimensional half metallic ferromagnets. This research was supported by National Science Foundation under Grant No. DMR-1120296.

  13. Attosecond timing the ultrafast charge-transfer process in atomic collisions

    SciTech Connect

    Hu, S. X.

    2011-04-15

    By solving the three-dimensional, time-dependent Schroedinger equation, we have demonstrated that the ultrafast charge-transfer process in ion-atom collisions can be mapped out with attosecond extreme uv (xuv) pulses. During the dynamic-charge transfer from the target atom to the projectile ion, the electron coherently populates the two sites of both nuclei, which can be viewed as a 'short-lived' molecular state. A probing attosecond xuv pulse can instantly unleash the delocalized electron from such a ''transient molecule,'' so that the resulting photoelectron may exhibit a ''double-slit'' interference. On the contrary, either reduced or no photoelectron interference will occur if the attosecond xuv pulse strikes well before or after the collision. Therefore, by monitoring the photoelectron interference visibility, one can precisely time the ultrafast charge-transfer process in atomic collisions with time-delayed attosecond xuv pulses.

  14. Fermi level pinning and the charge transfer contribution to the energy of adsorption at semiconducting surfaces

    SciTech Connect

    Krukowski, Stanis?aw; Kempisty, Pawe?; Strak, Pawe?; Sakowski, Konrad

    2014-01-28

    It is shown that charge transfer, the process analogous to formation of semiconductor p-n junction, contributes significantly to adsorption energy at semiconductor surfaces. For the processes without the charge transfer, such as molecular adsorption of closed shell systems, the adsorption energy is determined by the bonding only. In the case involving charge transfer, such as open shell systems like metal atoms or the dissociating molecules, the energy attains different value for the Fermi level differently pinned. The Density Functional Theory (DFT) simulation of species adsorption at different surfaces, such as SiC(0001) or GaN(0001) confirms these predictions: the molecular adsorption is independent on the coverage, while the dissociative process adsorption energy varies by several electronvolts.

  15. Charge transfer in strongly correlated systems: An exact diagonalization approach to model Hamiltonians

    SciTech Connect

    Schöppach, Andreas; Gnandt, David; Koslowski, Thorsten

    2014-04-07

    We study charge transfer in bridged di- and triruthenium complexes from a theoretical and computational point of view. Ab initio computations are interpreted from the perspective of a simple empirical Hamiltonian, a chemically specific Mott-Hubbard model of the complexes' ? electron systems. This Hamiltonian is coupled to classical harmonic oscillators mimicking a polarizable dielectric environment. The model can be solved without further approximations in a valence bond picture using the method of exact diagonalization and permits the computation of charge transfer reaction rates in the framework of Marcus' theory. In comparison to the exact solution, the Hartree-Fock mean field theory overestimates both the activation barrier and the magnitude of charge-transfer excitations significantly. For triruthenium complexes, we are able to directly access the interruthenium antiferromagnetic coupling strengths.

  16. Ensemble density functional theory, the atom-in-molecule problem, and reactive charge transfer

    NASA Astrophysics Data System (ADS)

    Atlas, Susan; Valone, Steven

    2008-03-01

    A major challenge in large-scale simulations of complex biomolecular and materials systems is the ability to accurately describe reactive dynamics. We have previously described a new multiscale formalism, based on density functional theory and the embedded-atom method, that enables the rigorous encoding of quantum mechanical excitation effects such as charge polarization and charge transfer within a classical potential. Here we describe a new formulation of a key element of the theory: the deconstruction of molecular densities into subsystem atom-in-molecule components via ensemble constrained-search density functional theory. The method is implemented via the self-consistent solution of coupled sets of Kohn-Sham equations in conjunction with chemical potential equalization across subsystems. This leads to a natural interpretation of dynamical charge transfer and charge polarization in terms of an electronic entropy, thus extending the seminal work of Gross, Oliveira, and Kohn (1988).

  17. Charge transfer and mobility enhancement at CdO/SnTe heterointerfaces

    SciTech Connect

    Nishitani, Junichi; Yu, Kin Man; Walukiewicz, Wladek

    2014-09-29

    We report a study of the effects of charge transfer on electrical properties of CdO/SnTe heterostructures. A series of structures with variable SnTe thicknesses were deposited by RF magnetron sputtering. Because of an extreme type III band offset with the valence band edge of SnTe located at 1.5?eV above the conduction band edge of CdO, a large charge transfer is expected at the interface of the CdO/SnTe heterostructure. The electrical properties of the heterostructures are analyzed using a multilayer charge transport model. The analysis indicates a large 4-fold enhancement of the CdO electron mobility at the interface with SnTe. The mobility enhancement is attributed to reduction of the charge center scattering through neutralization of the donor-like defects responsible for the Fermi level pinning at the CdO/SnTe interface.

  18. Gating of single molecule junction conductance by charge transfer complex formation

    NASA Astrophysics Data System (ADS)

    Vezzoli, Andrea; Grace, Iain; Brooke, Carly; Wang, Kun; Lambert, Colin J.; Xu, Bingqian; Nichols, Richard J.; Higgins, Simon J.

    2015-11-01

    The solid-state structures of organic charge transfer (CT) salts are critical in determining their mode of charge transport, and hence their unusual electrical properties, which range from semiconducting through metallic to superconducting. In contrast, using both theory and experiment, we show here that the conductance of metal |single molecule| metal junctions involving aromatic donor moieties (dialkylterthiophene, dialkylbenzene) increase by over an order of magnitude upon formation of charge transfer (CT) complexes with tetracyanoethylene (TCNE). This enhancement occurs because CT complex formation creates a new resonance in the transmission function, close to the metal contact Fermi energy, that is a signal of room-temperature quantum interference.The solid-state structures of organic charge transfer (CT) salts are critical in determining their mode of charge transport, and hence their unusual electrical properties, which range from semiconducting through metallic to superconducting. In contrast, using both theory and experiment, we show here that the conductance of metal |single molecule| metal junctions involving aromatic donor moieties (dialkylterthiophene, dialkylbenzene) increase by over an order of magnitude upon formation of charge transfer (CT) complexes with tetracyanoethylene (TCNE). This enhancement occurs because CT complex formation creates a new resonance in the transmission function, close to the metal contact Fermi energy, that is a signal of room-temperature quantum interference. Electronic supplementary information (ESI) available: Synthesis of 1c; experimental details of conductance measurements, formation of charge transfer complexes of 1c and 2 in solution; further details of theoretical methods. See DOI: 10.1039/c5nr04420k

  19. Modelling electrified interfaces in quantum chemistry: constant charge vs. constant potential.

    PubMed

    Benedikt, Udo; Schneider, Wolfgang B; Auer, Alexander A

    2013-02-28

    The proper description of electrified metal/solution interfaces, as they occur in electrochemical systems, is a key component for simulating the unique features of electrocatalytic reactions using electronic structure calculations. While in standard solid state (plane wave, periodic boundary conditions) density functional theory (DFT) calculations several models for describing electrochemical environments exist, for cluster models in a quantum chemistry approach (atomic orbital basis, finite system) this is not straightforward. In this work, two different approaches for the theoretical description of electrified interfaces of nanoparticles, the constant charge and the constant potential model, are discussed. Different schemes for describing electrochemical reactions including solvation models are tested for a consistent description of the electrochemical potential and the local chemical behavior for finite structures. The different schemes and models are investigated for the oxygen reduction reaction (ORR) on a hemispherical cuboctahedral platinum nanoparticle. PMID:23329171

  20. Note: Charge transfer in a hydrated peptide group is determined mainly by its intrinsic hydrogen-bond energetics

    SciTech Connect

    Mirkin, Noemi G.; Krimm, Samuel

    2014-01-28

    Charge transfer in a hydrogen-bonded N-methylacetamide(H{sub 2}O){sub 3} system is obtained from ?B97X-D/6-31++G** and CHelpG atomic charge calculations of individual peptide-water interactions as well as that of the entire complex. In the latter, the electron transfer to water is 0.19 e, influenced primarily by the hydrogen bonds to the C=O group. The values of such charge transfer are paralleled by the corresponding intrinsic hydrogen-bond energies. These results support the desirability of incorporating charge transfer in molecular mechanics energy functions.

  1. Enhanced charge transfer by phenyl groups at a rubrene/C60 interface.

    PubMed

    Mou, Weiwei; Ohmura, Satoshi; Hattori, Shinnosuke; Nomura, Ken-ichi; Shimojo, Fuyuki; Nakano, Aiichiro

    2012-05-14

    Exciton dynamics at an interface between an electron donor, rubrene, and a C(60) acceptor is studied by nonadiabatic quantum molecular dynamics simulation. Simulation results reveal an essential role of the phenyl groups in rubrene in increasing the charge-transfer rate by an order-of-magnitude. The atomistic mechanism of the enhanced charge transfer is found to be the amplification of aromatic breathing modes by the phenyl groups, which causes large fluctuations of electronic excitation energies. These findings provide insight into molecular structure design for efficient solar cells, while explaining recent experimental observations. PMID:22583307

  2. Electronic memory switching in a new charge transfer-complex thin film

    NASA Astrophysics Data System (ADS)

    Wang, K. Z.; Xue, Z. Q.; Ouyang, M.; Zhang, H. X.; Huang, C. H.

    1995-11-01

    Charge transfer-complex thin films of 1,4-bis(2,2-dicyanovinyl)benzene(BDCB) with silver, sandwiched between two silver elctrodes, show current-controlled bistable electronic switching and memory behavior. The switching from a high to low impedance is believed to be associated with chemical phase change similar to that for charge transfer-complex thin films of TCNQ with either copper or silver. The films are analyzed by infrared, ultraviolet-visible spectroscopy, scanning electron microscopy (SEM) and X-ray diffraction.

  3. Computational approaches to charge transfer excitations in a zinc tetraphenylporphyrin and C70 complex.

    PubMed

    Ghosh, Prasenjit; Gebauer, Ralph

    2010-03-14

    Electronic charge transfer plays an important role in novel nanostructured photovoltaic materials. Standard density functional theory (DFT) as well as time-dependent DFT severely underestimate the excitation energies related to such transitions. For the paradigmatic case of a donor-acceptor dyad formed by a zinc-porphyrin donor and a C(70) fullerene acceptor these shortcomings are illustrated. A better quantitative estimate of the charge transfer energy is obtained from constrained DFT which is applied to this system in a novel implementation based on a penalty functional. PMID:20232942

  4. 46 CFR 153.957 - Persons in charge of transferring liquid cargo in bulk or cleaning cargo tanks.

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... charge of the transfer or the cleaning under Subpart C of 33 CFR part 155; (3) When cargo regulated under... safely transfer liquid cargo in bulk or to safely clean cargo tanks; (2) Each transfer of liquid cargo in... transfer will take place, the owner and operator of the vessel, and his or her agent, and each of...

  5. Evaluation of Bulk Charging in Geostationary Transfer Orbit and Earth Escape Trajectories Using the Numit 1-D Charging Model

    NASA Technical Reports Server (NTRS)

    Minow, Joseph I.; Coffey, Victoria N.; Parker, Linda N.; Blackwell, William C., Jr.; Jun, Insoo; Garrett, Henry B.

    2007-01-01

    The NUMIT 1-dimensional bulk charging model is used as a screening to ol for evaluating time-dependent bulk internal or deep dielectric) ch arging of dielectrics exposed to penetrating electron environments. T he code is modified to accept time dependent electron flux time serie s along satellite orbits for the electron environment inputs instead of using the static electron flux environment input originally used b y the code and widely adopted in bulk charging models. Application of the screening technique ts demonstrated for three cases of spacecraf t exposure within the Earth's radiation belts including a geostationa ry transfer orbit and an Earth-Moon transit trajectory for a range of orbit inclinations. Electric fields and charge densities are compute d for dielectric materials with varying electrical properties exposed to relativistic electron environments along the orbits. Our objectiv e is to demonstrate a preliminary application of the time-dependent e nvironments input to the NUMIT code for evaluating charging risks to exposed dielectrics used on spacecraft when exposed to the Earth's ra diation belts. The results demonstrate that the NUMIT electric field values in GTO orbits with multiple encounters with the Earth's radiat ion belts are consistent with previous studies of charging in GTO orb its and that potential threat conditions for electrostatic discharge exist on lunar transit trajectories depending on the electrical proper ties of the materials exposed to the radiation environment.

  6. Charge transfer and electronic doping in nitrogen-doped graphene.

    PubMed

    Joucken, Frédéric; Tison, Yann; Le Fèvre, Patrick; Tejeda, Antonio; Taleb-Ibrahimi, Amina; Conrad, Edward; Repain, Vincent; Chacon, Cyril; Bellec, Amandine; Girard, Yann; Rousset, Sylvie; Ghijsen, Jacques; Sporken, Robert; Amara, Hakim; Ducastelle, François; Lagoute, Jérôme

    2015-01-01

    Understanding the modification of the graphene's electronic structure upon doping is crucial for enlarging its potential applications. We present a study of nitrogen-doped graphene samples on SiC(000) combining angle-resolved photoelectron spectroscopy, scanning tunneling microscopy and spectroscopy and X-ray photoelectron spectroscopy (XPS). The comparison between tunneling and angle-resolved photoelectron spectra reveals the spatial inhomogeneity of the Dirac energy shift and that a phonon correction has to be applied to the tunneling measurements. XPS data demonstrate the dependence of the N 1s binding energy of graphitic nitrogen on the nitrogen concentration. The measure of the Dirac energy for different nitrogen concentrations reveals that the ratio usually computed between the excess charge brought by the dopants and the dopants' concentration depends on the latter. This is supported by a tight-binding model considering different values for the potentials on the nitrogen site and on its first neighbors. PMID:26411651

  7. Charge transfer and electronic doping in nitrogen-doped graphene

    PubMed Central

    Joucken, Frédéric; Tison, Yann; Le Fèvre, Patrick; Tejeda, Antonio; Taleb-Ibrahimi, Amina; Conrad, Edward; Repain, Vincent; Chacon, Cyril; Bellec, Amandine; Girard, Yann; Rousset, Sylvie; Ghijsen, Jacques; Sporken, Robert; Amara, Hakim; Ducastelle, François; Lagoute, Jérôme

    2015-01-01

    Understanding the modification of the graphene’s electronic structure upon doping is crucial for enlarging its potential applications. We present a study of nitrogen-doped graphene samples on SiC(000) combining angle-resolved photoelectron spectroscopy, scanning tunneling microscopy and spectroscopy and X-ray photoelectron spectroscopy (XPS). The comparison between tunneling and angle-resolved photoelectron spectra reveals the spatial inhomogeneity of the Dirac energy shift and that a phonon correction has to be applied to the tunneling measurements. XPS data demonstrate the dependence of the N 1s binding energy of graphitic nitrogen on the nitrogen concentration. The measure of the Dirac energy for different nitrogen concentrations reveals that the ratio usually computed between the excess charge brought by the dopants and the dopants’ concentration depends on the latter. This is supported by a tight-binding model considering different values for the potentials on the nitrogen site and on its first neighbors. PMID:26411651

  8. Charge transfer and electronic doping in nitrogen-doped graphene

    NASA Astrophysics Data System (ADS)

    Joucken, Frédéric; Tison, Yann; Le Fèvre, Patrick; Tejeda, Antonio; Taleb-Ibrahimi, Amina; Conrad, Edward; Repain, Vincent; Chacon, Cyril; Bellec, Amandine; Girard, Yann; Rousset, Sylvie; Ghijsen, Jacques; Sporken, Robert; Amara, Hakim; Ducastelle, François; Lagoute, Jérôme

    2015-09-01

    Understanding the modification of the graphene’s electronic structure upon doping is crucial for enlarging its potential applications. We present a study of nitrogen-doped graphene samples on SiC(000) combining angle-resolved photoelectron spectroscopy, scanning tunneling microscopy and spectroscopy and X-ray photoelectron spectroscopy (XPS). The comparison between tunneling and angle-resolved photoelectron spectra reveals the spatial inhomogeneity of the Dirac energy shift and that a phonon correction has to be applied to the tunneling measurements. XPS data demonstrate the dependence of the N 1s binding energy of graphitic nitrogen on the nitrogen concentration. The measure of the Dirac energy for different nitrogen concentrations reveals that the ratio usually computed between the excess charge brought by the dopants and the dopants’ concentration depends on the latter. This is supported by a tight-binding model considering different values for the potentials on the nitrogen site and on its first neighbors.

  9. Probing Electronic, Structural, and Charge Transfer Properties of Organic Semiconductor/Inorganic Oxide Interfaces Using Field-Effect Transistors

    NASA Astrophysics Data System (ADS)

    Spalenka, Josef Wade

    Interfaces between organic semiconductors and inorganic oxides provide the functionality for devices including field-effect transistors (FETs) and organic photovoltaics. Organic FETs are sensitive to the physical structure and electronic properties of the few molecular layers of material at the interface between the semiconducting channel and the gate dielectric, and provide quantitative information such as the field-effect mobility of charge carriers and the concentration of trapped charge. In this thesis, FET interfaces between organic small-molecule semiconductors and SiO2, and donor/acceptor interfaces between organic small-molecules and the wide bandgap semiconductor ZnO are studied using electrical measurements of field-effect transistor devices. Monolayer-scale films of dihexyl sexithiophene are shown to have higher hole mobility than other monolayer organic semiconductors, and the origin of the high mobility is discussed. Studies of the crystal structure of the monolayer using X-ray structural probes and atomic force microscopy reveal the crystal structure is different in the monolayer regime compared to thicker films and bulk crystals. Progress and remaining challenges are discussed for in situ X-ray diffraction studies of the dynamic changes in the local crystal structure in organic monolayers due to charge carriers generated during the application of electric fields from the gate electrode in working FETs. Studies were conducted of light sensitive organic/inorganic interfaces that are modified with organic molecules grafted to the surface of ZnO nanoparticles and thin films. These interfaces are models for donor/acceptor interfaces in photovoltaics. The process of exciton dissociation at the donor/acceptor interface was sensitive to the insulating or semiconducting molecules grafted to the ZnO, and the photoinduced charge transfer process is measured by the threshold voltage shift of FETs during illumination. Charge transfer between light sensitive donor molecules based on rhenium bipyridine complexes and ZnO thin films was measured using FETs, revealing the role of positive trapped charge in persistent photoconductivity in donor sensitized ZnO. The carboxylic acid attachment chemistry, used to anchor the donor molecules, is demonstrated to enhance the conductivity of ZnO thin films. The mechanism for the enhanced conductivity is linked to the passivation of defects on the surface of the ZnO.

  10. Computing intramolecular charge and energy transfer rates using optimal modes

    NASA Astrophysics Data System (ADS)

    Yang, Xunmo; Bittner, Eric R.

    2015-06-01

    In our recent work [X. Yang and E. R. Bittner, J. Phys. Chem. A 118, 5196 (2014)], we showed how to construct a reduced set of nuclear motions that capture the coupling between electronic and nuclear degrees of freedom over the course of an electronic transition. We construct these modes, referred to as "Lanczos modes," by applying a search algorithm to find linear combinations of vibrational normal modes that optimize the electronic/nuclear coupling operator. Here, we analyze the irreducible representations of the dominant contributions of these modes and find that for the cases considered here, these belong to totally symmetric irreducible representations of the donor and acceptor moieties. Upon investigating the molecular geometry changes following the transition, we propose that the electronic transition process can be broken into two steps, in the agreement of Born-Oppenheimer approximation: a fast excitation transfer occurs, facilitated by the "primary Lanczos mode," followed by slow nuclear relaxation on the final electronic diabatic surface.

  11. Charge Transfer Properties Through Graphene for Applications in Gaseous Detectors

    E-print Network

    S. Franchino; D. Gonzalez-Diaz; R. Hall-Wilton; R. B. Jackman; H. Muller; T. T. Nguyen; R. de Oliveira; E. Oliveri; D. Pfeiffer; F. Resnati; L. Ropelewski; J. Smith; M. van Stenis; C. Streli; P. Thuiner; R. Veenhof

    2015-12-16

    Graphene is a single layer of carbon atoms arranged in a honeycomb lattice with remarkable mechanical and electrical properties. Regarded as the thinnest and narrowest conductive mesh, it has drastically different transmission behaviours when bombarded with electrons and ions in vacuum. This property, if confirmed in gas, may be a definitive solution for the ion back-flow problem in gaseous detectors. In order to ascertain this aspect, graphene layers of dimensions of about 2x2cm$^2$, grown on a copper substrate, are transferred onto a flat metal surface with holes, so that the graphene layer is freely suspended. The graphene and the support are installed into a gaseous detector equipped with a triple Gaseous Electron Multiplier (GEM), and the transparency properties to electrons and ions are studied in gas as a function of the electric fields. The techniques to produce the graphene samples are described, and we report on preliminary tests of graphene-coated GEMs.

  12. Charge Transfer Properties Through Graphene for Applications in Gaseous Detectors

    E-print Network

    Franchino, S; Hall-Wilton, R; Jackman, R B; Muller, H; Nguyen, T T; de Oliveira, R; Oliveri, E; Pfeiffer, D; Resnati, F; Ropelewski, L; Smith, J; van Stenis, M; Streli, C; Thuiner, P; Veenhof, R

    2015-01-01

    Graphene is a single layer of carbon atoms arranged in a honeycomb lattice with remarkable mechanical and electrical properties. Regarded as the thinnest and narrowest conductive mesh, it has drastically different transmission behaviours when bombarded with electrons and ions in vacuum. This property, if confirmed in gas, may be a definitive solution for the ion back-flow problem in gaseous detectors. In order to ascertain this aspect, graphene layers of dimensions of about 2x2cm$^2$, grown on a copper substrate, are transferred onto a flat metal surface with holes, so that the graphene layer is freely suspended. The graphene and the support are installed into a gaseous detector equipped with a triple Gaseous Electron Multiplier (GEM), and the transparency properties to electrons and ions are studied in gas as a function of the electric fields. The techniques to produce the graphene samples are described, and we report on preliminary tests of graphene-coated GEMs.

  13. Charge transfer in a sharply nonuniform electric field mediated by swirling liquid flow with minimal hydraulic resistance

    NASA Astrophysics Data System (ADS)

    Nagorny, V. S.; Smirnovsky, A. A.; Chernyshev, A. S.; Kolodyazhny, D. Yu.

    2015-09-01

    A scheme of a fuel nozzle with "needle-plane" electrode system, the location of which enables one to minimize the imparted hydraulic resistance, is proposed. We consider the processes of charge transfer in a sharply inhomogeneous electric field in order to estimate the amount of charge coming out of the channel. For this purpose, we used the OpenFOAM software package, modified to account for the electrohydrodynamic effects. By using the k-? SST turbulence model within an axial-symmetrical RANS problem, the vortex liquid flow and charge transfer are calculated. The impact of vorticity degree on the processes of charge transfer is studied. It is found that the charge flowing out of the calculation domain is about 80% of the injected charge. The vorticity degree in the above range of values has little effect on the process of charge transfer.

  14. Quantum-Classical Path Integral Simulation of Ferrocene-Ferrocenium Charge Transfer in Liquid Hexane.

    PubMed

    Walters, Peter L; Makri, Nancy

    2015-12-17

    We employ the quantum-classical path integral methodology to simulate the outer sphere charge-transfer process of the ferrocene-ferrocenium pair in liquid hexane with unprecedented accuracy. Comparison of the simulation results to those obtained by mapping the solvent on an effective harmonic bath demonstrates the accuracy of linear response theory in this system. PMID:26673195

  15. Calculation of the cross section for charge transfer in fullerene-fullerene collisions

    SciTech Connect

    Iroshnikov, G. S.

    2006-11-15

    An expression for the charge transfer cross section in fullerene-fullerene collisions is derived by using an instanton approximation for the tunnel splitting of energy levels. The expression is valid in the adiabatic approximation and provides an accurate description of available experimental data.

  16. Doping single-walled carbon nanotubes through molecular charge-transfer: a theoretical study.

    PubMed

    Manna, Arun K; Pati, Swapan K

    2010-07-01

    We study the effect of the molecular charge transfer on the electronic structure of metallic (5,5) and semiconducting (8,0) single-walled carbon nanotubes (SWNTs) induced by surface adsorption of various organic donor-acceptor molecules of different affinities using ab initio density functional theory. Our results, obtained from first-principles spin-polarized calculations show that the adsorption of molecules with different affinities reflects the difference in interaction strength that measure the overall energy of adsorption. Moderate values of the binding energy of these surface adsorbed molecular charge-transfer complexes suggest that the nature of interaction is in the physisorption regime, and mainly governs by Coulombic forces. We also find that the large band gap of semiconducting (8,0) SWNT can be tuned through the surface adsorption of selective organic molecules which gives rise to mid-gap localized molecular levels near the Fermi energy with tuning of band gap region. Interestingly, we find that the metallic (5,5) SWNT and semiconducting (8,0) SWNT turn into semiconducting and metallic nanotubes respectively in presence of selective surface adsorbed molecules, corroborating recent experimental findings. We also suggest that these charge transfer effect can be probed through optical conductivity measurement, as the low-frequency profiles are affected by charge transfer. PMID:20648348

  17. Enhanced Charge-Transfer Kinetics by Anion Surface Modi cation of Kyu-Sung Park,,

    E-print Network

    Henkelman, Graeme

    /discharge rates desired for powering an electric vehicle. A LiFePO4 cathode has a theoretical capacity of 170 m barrier for charge transfer, but it can be stabilized by nitrogen or sulfur adsorption. The surface modi of the electrical energy generated from wind and radiant solar power. Moreover, rechargeable batteries that power

  18. Charge Transfer between Isomer Domains on n+ -Doped Si(111)-21: Energetic

    E-print Network

    Feenstra, Randall

    1 Charge Transfer between Isomer Domains on n+ -Doped Si(111)-2×1: Energetic Stabilization R. M- or positively-buckled isomers ­ have been previously observed on highly n-doped Si(111)-2×1 surfaces by angle, separate domains of the two isomer types are apparent in the data. It was argued in the prior work

  19. Molecular orbital (SCF-X?-SW) theory of metal-metal charge transfer processes in minerals

    USGS Publications Warehouse

    Sherman, David M.

    1987-01-01

    Electronic transitions between the Fe-Fe bonding and Fe-Fe antibonding orbitals results in the optically-induced intervalence charge transfer bands observed in the electronic spectra of mixed valence minerals. Such transitions are predicted to be polarized along the metal-metal bond direction, in agreement with experimental observations.

  20. Elastic, excitation, ionization and charge transfer cross sections of current interest in fusion energy research

    SciTech Connect

    Schultz, D.R.; Krstic, P.S.

    1996-12-31

    Due to the present interest in modeling and diagnosing the edge and divertor plasma regions in magnetically confined fusion devices, we have sought to provide new calculations regarding the elastic, excitation, ionization, and charge transfer cross sections in collisions among relevant ions, neutrals, and isotopes in the low- to intermediate-energy regime. We summarize here some of our recent work.

  1. Doping single-walled carbon nanotubes through molecular charge-transfer: a theoretical study

    NASA Astrophysics Data System (ADS)

    Manna, Arun K.; Pati, Swapan K.

    2010-07-01

    We study the effect of the molecular charge transfer on the electronic structure of metallic (5,5) and semiconducting (8,0) single-walled carbon nanotubes (SWNTs) induced by surface adsorption of various organic donor-acceptor molecules of different affinities using ab initio density functional theory. Our results, obtained from first-principles spin-polarized calculations show that the adsorption of molecules with different affinities reflects the difference in interaction strength that measure the overall energy of adsorption. Moderate values of the binding energy of these surface adsorbed molecular charge-transfer complexes suggest that the nature of interaction is in the physisorption regime, and mainly governs by Coulombic forces. We also find that the large band gap of semiconducting (8,0) SWNT can be tuned through the surface adsorption of selective organic molecules which gives rise to mid-gap localized molecular levels near the Fermi energy with tuning of band gap region. Interestingly, we find that the metallic (5,5) SWNT and semiconducting (8,0) SWNT turn into semiconducting and metallic nanotubes respectively in presence of selective surface adsorbed molecules, corroborating recent experimental findings. We also suggest that these charge transfer effect can be probed through optical conductivity measurement, as the low-frequency profiles are affected by charge transfer.

  2. Air-Stable Surface Charge Transfer Doping of MoS2 by Benzyl Daisuke Kiriya,,,

    E-print Network

    Javey, Ali

    Tosun,,,§ Peida Zhao,,,§ Jeong Seuk Kang,, and Ali Javey*,,,§ Electrical Engineering and Computer potentials of all electron- donor organic compounds, as a surface charge transfer donor for MoS2 flakes/drain contacts self- aligned with respect to the top gate. The device architecture, resembling

  3. Laboratory Measurements of Charge Transfer on Atomic Hydrogen at Thermal Energies

    NASA Technical Reports Server (NTRS)

    Havener, C. C.; Vane, C. R.; Krause, H. F.; Stancil, P. C.; Mroczkowski, T.; Savin, D. W.

    2002-01-01

    We describe our ongoing program to measure velocity dependent charge transfer (CT) cross sections for selected ions on atomic hydrogen using the ion-aloin merged-beams apparatus at Oak Ridge Natioiial Laboralory. Our focus is on those ions for which CT plays an important role in determining the ionization structure, line emis sion, and thermal structure of observed cosmic photoionized plasmas.

  4. Laser-assisted charge-transfer reactions (Li3++H): Coupled dressed-quasimolecular-state approach

    E-print Network

    Ho, Tak-San; Laughlin, Cecil; Chu, Shih-I

    1985-07-01

    . This yields a new set of coupled GVV-DQMS equations (neither adiabatic nor diabatic) which are particularly convenient for multichannel calculations. The method is applied to the study of the laser-assisted charge-transfer process: Li3++H(1s)+???Li2+(n= 3)+H...

  5. Underlying Spin-Orbit Coupling Structure of Intervalence Charge Transfer Bands in Dinuclear Polypyridyl Complexes of

    E-print Network

    Underlying Spin-Orbit Coupling Structure of Intervalence Charge Transfer Bands in Dinuclear that stereochemical effects lead to fundamental changes in the energy levels of the metal-based d orbitals, which are split by spin-orbit coupling and ligand-field asymmetry. An increase in the separation between the IC

  6. Effective Charge Transfer Distances in Cyanide-Bridged Mixed-Valence Transition Metal Complexes

    E-print Network

    Boxer, Steven G.

    in the effective charge-transfer distances for spin-orbit states in [(NC)5OsII-CN-RuIII(NH3)5]-, recently described are the same within experimental error for these spin-orbit states. These data provide informative examples

  7. Radiative charge-transfer lifetime of the excited state of (NaCa)+

    NASA Astrophysics Data System (ADS)

    Makarov, Oleg P.; Côté, R.; Michels, H.; Smith, W. W.

    2003-04-01

    New experiments were proposed recently to investigate the regime of cold atomic and molecular ion-atom collision processes in a special hybrid neutral-atom ion trap under high-vacuum conditions. We study the collisional cooling of laser precooled Ca+ ions by ultracold Na atoms. Modeling this process requires knowledge of the radiative lifetime of the excited singlet A 1?+ state of the (NaCa)+ molecular system. We calculate the rate coefficient for radiative charge transfer using a semiclassical approach. The dipole radial matrix elements between the ground and the excited states, and the potential curves were calculated using complete active space self-consistent field and Möller-Plesset second-order perturbation theory with an extended Gaussian basis, 6-311+G (3df). The semiclassical charge-transfer rate coefficient was averaged over a thermal Maxwellian distribution. In addition, we also present elastic collision cross sections and the spin-exchange cross section. The rate coefficient for charge transfer was found to be 2.3×10-16 cm3/sec, while those for the elastic and spin-exchange cross sections were found to be several orders of magnitude higher (1.1×10-8 cm3/sec and 2.3×10-9 cm3/sec, respectively). This confirms our assumption that the milli-Kelvin regime of collisional cooling of calcium ions by sodium atoms is favorable with the respect to low loss of calcium ions due to the charge transfer.

  8. Optimal control of charge transfer Jan Werschnika and Eberhard K.U. Grossa

    E-print Network

    Gross, E.K.U.

    Optimal control of charge transfer Jan Werschnika and Eberhard K.U. Grossa aFreie Universit is calculated with the help of quantum optimal control theory employing a time-dependent formulation for the control target. Within our two-dimensional (2D) model system we have successfully optimized laser fields

  9. CHANDRA OBSERVATIONS OF THE ``DARK'' MOON AND GEOCORONAL SOLAR WIND CHARGE TRANSFER

    E-print Network

    Wargelin, Bradford J.

    CHANDRA OBSERVATIONS OF THE ``DARK'' MOON AND GEOCORONAL SOLAR WIND CHARGE TRANSFER B. J. Wargelin-ray background, particularly in the ROSAT 3 4 keV band. Subject headings: atomic processes -- Moon -- solar wind of the Moon made by the Chandra X-Ray Observatory. In addition to obtaining a spectrum of the bright side

  10. CHANDRA OBSERVATIONS OF THE ``DARK'' MOON AND GEOCORONAL SOLAR WIND CHARGE TRANSFER

    E-print Network

    Wargelin, Bradford J.

    CHANDRA OBSERVATIONS OF THE ``DARK'' MOON AND GEOCORONAL SOLAR WIND CHARGE TRANSFER B. J. Wargelin of the Moon made by the Chandra X­Ray Observatory. In addition to obtaining a spectrum of the bright side­brightness regions of the sky. Over a decade ago, ROSAT also detected soft X­rays from the dark side of the Moon

  11. Interstellar Chemistry Gets More Complex With New Charged-Molecule Discovery

    NASA Astrophysics Data System (ADS)

    2007-07-01

    Astronomers using data from the National Science Foundation's Robert C. Byrd Green Bank Telescope (GBT) have found the largest negatively-charged molecule yet seen in space. The discovery of the third negatively-charged molecule, called an anion, in less than a year and the size of the latest anion will force a drastic revision of theoretical models of interstellar chemistry, the astronomers say. Molecule formation Formation Process of Large, Negatively-Charged Molecule in Interstellar Space CREDIT: Bill Saxton, NRAO/AUI/NSF Click on image for page of graphics and detailed information "This discovery continues to add to the diversity and complexity that is already seen in the chemistry of interstellar space," said Anthony J. Remijan of the National Radio Astronomy Observatory (NRAO). "It also adds to the number of paths available for making the complex organic molecules and other large molecular species that may be precursors to life in the giant clouds from which stars and planets are formed," he added. Two teams of scientists found negatively-charged octatetraynyl, a chain of eight carbon atoms and one hydrogen atom, in the envelope of gas around an old, evolved star and in a cold, dark cloud of molecular gas. In both cases, the molecule had an extra electron, giving it a negative charge. About 130 neutral and about a dozen positively-charged molecules have been discovered in space, but the first negatively-charged molecule was not discovered until late last year. The largest previously-discovered negative ion found in space has six carbon atoms and one hydrogen atom. "Until recently, many theoretical models of how chemical reactions evolve in interstellar space have largely neglected the presence of anions. This can no longer be the case, and this means that there are many more ways to build large organic molecules in cosmic environments than have been explored," said Jan M. Hollis of NASA's Goddard Space Flight Center (GSFC). Ultraviolet light from stars can knock an electron off a molecule, creating a positively-charged ion. Astronomers had thought that molecules would not be able to retain an extra electron, and thus a negative charge, in interstellar space for a significant time. "That obviously is not the case," said Mike McCarthy of the Harvard-Smithsonian Center for Astrophysics. "Anions are surprisingly abundant in these regions." Remijan and his colleagues found the octatetraynyl anions in the envelope of the evolved giant star IRC +10 216, about 550 light-years from Earth in the constellation Leo. They found radio waves emitted at specific frequencies characteristic of the charged molecule by searching archival data from the GBT, the largest fully-steerable radio telescope in the world. Another team from the Harvard-Smithsonian Center for Astrophysics (CfA) found the same characteristic emission when they observed a cold cloud of molecular gas called TMC-1 in the constellation Taurus. These observations also were done with the GBT. In both cases, preceding laboratory experiments by the CfA team showed which radio frequencies actually are emitted by the molecule, and thus told the astronomers what to look for. "It is essential that likely interstellar molecule candidates are first studied in laboratory experiments so that the radio frequencies they can emit are known in advance of an astronomical observation," said Frank Lovas of the National Institute of Standards and Technology (NIST). Both teams announced their results in the July 20 edition of the Astrophysical Journal Letters. "With three negatively-charged molecules now found in a short period of time, and in very different environments, it appears that many more probably exist. We believe that we can discover more new species using very sensitive and advanced radio telescopes such as the GBT, once they have been characterized in the laboratory," said Sandra Bruenken of the CfA. "Further detailed studies of anions, including astronomical observations, laboratory studies, and theo

  12. Charge and Heat Transfer Mechanism in Directly Coupled CdSe-Metal Nanohybrids

    NASA Astrophysics Data System (ADS)

    Augustine, Anju K.; Girijavallabhan, C. P.; Nampoori, V. P. N.; Kailasnath, M.

    2015-10-01

    The charge and heat energy transfer dynamics of directly coupled mixtures of CdSe quantum dots with metal nanoparticles have been studied using thermal lens and photoluminescence (PL) techniques, respectively. The PL of such nanohybrids is found to be quenched dramatically at a particular threshold. Fluorescence decay curves of the Au-CdSe nanohybrids and Ag-CdSe nanohybrids show distinct decay channels with the fastest one associated with transfer of electrons from the CdSe portion to the metal portion. A study on the influence of this charge transfer on the thermal diffusivity with respect to the emission wavelength of quantum dots has been carried out, which could lead to the design of modern photocatalysts and solar cells constructed from nanoscale metal-semiconductor hybrids.

  13. Charge-transfer dynamics in multilayered PbS and PbSe quantum dot architectures

    SciTech Connect

    Xu, F.; Ma, X.; Haughn, C. R.; Doty, M. F.; Cloutier, S. G.

    2014-02-03

    We demonstrate control of the charge transfer process in PbS and PbSe quantum dot assemblies. We first demonstrate efficient charge transfer from donor quantum dots to acceptor quantum dots in a multi-layer PbSe cascade structure. Then, we assemble type-I and type-II heterostructures using both PbS and PbSe quantum dots via careful control of the band alignment. In type-I structures, photo-generated carriers are transferred and localized in the smaller bandgap (acceptor) quantum dots, resulting in a significant luminescence enhancement. In contrast, a significant luminescence quenching and shorter emission lifetime confirms an efficient separation of photo-generated carriers in the type-II architecture.

  14. Charge-transfer dissociation of vibrationally cold HeH : Evidence for and lifetime of the a 3

    E-print Network

    Zajfman, Daniel

    Charge-transfer dissociation of vibrationally cold HeH¿ : Evidence for and lifetime of the a 3 beams, the kinetic-energy release after dissociative charge transfer of vibrationally cold He of controversy in previous dissociative recombination experiments. PACS number s : 34.50. s, 33.15. e, 34.70. e

  15. Hot charge-transfer excitons set the time limit for charge separation at donor/acceptor interfaces in organic photovoltaics.

    PubMed

    Jailaubekov, Askat E; Willard, Adam P; Tritsch, John R; Chan, Wai-Lun; Sai, Na; Gearba, Raluca; Kaake, Loren G; Williams, Kenrick J; Leung, Kevin; Rossky, Peter J; Zhu, X-Y

    2013-01-01

    Photocurrent generation in organic photovoltaics (OPVs) relies on the dissociation of excitons into free electrons and holes at donor/acceptor heterointerfaces. The low dielectric constant of organic semiconductors leads to strong Coulomb interactions between electron-hole pairs that should in principle oppose the generation of free charges. The exact mechanism by which electrons and holes overcome this Coulomb trapping is still unsolved, but increasing evidence points to the critical role of hot charge-transfer (CT) excitons in assisting this process. Here we provide a real-time view of hot CT exciton formation and relaxation using femtosecond nonlinear optical spectroscopies and non-adiabatic mixed quantum mechanics/molecular mechanics simulations in the phthalocyanine-fullerene model OPV system. For initial excitation on phthalocyanine, hot CT excitons are formed in 10(-13)?s, followed by relaxation to lower energies and shorter electron-hole distances on a 10(-12)?s timescale. This hot CT exciton cooling process and collapse of charge separation sets the fundamental time limit for competitive charge separation channels that lead to efficient photocurrent generation. PMID:23223125

  16. On charge transfer in the adsorbed molecules-graphene monolayer-SiC substrate system

    SciTech Connect

    Davydov, S. Yu.

    2011-05-15

    A step-by-step consideration of charge transfer in the molecule-single-layer graphene-SiC substrate system is presented. At the first step, a simple model of the density of states of a single graphene monolayer adsorbed on silicon carbide (the graphene-SiC system) is suggested, which allows the calculation of the corresponding occupation numbers of graphene atoms. It is shown that the graphene monolayer accumulates a negative charge. At the second step, the graphene-SiC system is considered as a substrate that adsorbs molecules with a high electron affinity. The charge of these molecules as a function of their surface concentration is calculated. It is shown that, in the case of a monolayer coating, the negative surface charge density of molecules in the molecule-graphene monolayer-SiC substrate system is considerably higher than the surface charge density transferring from the SiC substrate to the graphene layer. This suggests that it is possible to neutralize the excess charge in the graphene layer via adsorption of proper particles on the layer.

  17. Excitation transfer, charge transfer and hydrogen abstraction reaction, kinetic studies of modification of DNA components

    NASA Astrophysics Data System (ADS)

    Lin, N. Y.

    1996-02-01

    Laser induced acetone-sensitized excitation of DNA components offered, for the first time, T-T absorption spectra and direct measurement of triplet states kinetics of cytosine, cytidine, and dCMP, adenine, adenosine and dAMP and guanosine. Mechanisms and kinetics of electron transfer reactions between triplet acetone and purine bases and triplet thymine and electrophilic modifiers have been elucidated. Rapid electron transfer from hydroxycinnamic acid derivatives to oxidizing OH adducts of pyrimidines have been performed. Fast reduction and repair of oxidizing damage of pyrimidines have been achieved using pulse radiolysis techniques.

  18. Active pixel sensor having intra-pixel charge transfer with analog-to-digital converter

    NASA Technical Reports Server (NTRS)

    Fossum, Eric R. (Inventor); Mendis, Sunetra K. (Inventor); Pain, Bedabrata (Inventor); Nixon, Robert H. (Inventor); Zhou, Zhimin (Inventor)

    2000-01-01

    An imaging device formed as a monolithic complementary metal oxide semiconductor Integrated circuit in an industry standard complementary metal oxide semiconductor process, the integrated circuit including a focal plane array of pixel cells, each one of the cells including a photogate overlying the substrate for accumulating photo-generated charge in an underlying portion of the substrate, a readout circuit including at least an output field effect transistor formed in the substrate, and a charge coupled device section formed on the substrate adjacent the photogate having a sensing node connected to the output transistor and at least one charge coupled device stage for transferring charge from the underlying portion of the substrate to the sensing node and an analog-to-digital converter formed in the substrate connected to the output of the readout circuit.

  19. Enhanced Electron Transfer Dissociation of Peptides Modified at C-terminus with Fixed Charges

    NASA Astrophysics Data System (ADS)

    Ko, Byoung Joon; Brodbelt, Jennifer S.

    2012-11-01

    The impact of the conversion of carboxylates in peptides to basic or fixed charge sites on the outcome of electron transfer dissociation (ETD) is evaluated with respect to ETD efficiency and the number of diagnostic sequence ions. Four reagents, including benzylamine (BA), 1-benzylpiperazine (BZP), carboxymethyl trimethylammonium chloride hydrazide (GT), and (2-aminoethyl)trimethylammonium chloride hydrochloride (AETMA), were used for the carboxylate derivatization, with the first two replacing the acidic carboxylate groups with basic functionalities and the latter two introducing fixed charge sites. The ETD efficiencies and Xcorr scores were compared for both nonderivatized and derivatized tryptic and Glu-C peptides from cytochrome c. Derivatization of the carboxylate increases the average charge states, the number of fragment ions, and the dissociation efficiencies of peptides, especially for the fixed charge reagent, AETMA.

  20. Active pixel sensor having intra-pixel charge transfer with analog-to-digital converter

    NASA Technical Reports Server (NTRS)

    Fossum, Eric R. (Inventor); Mendis, Sunetra K. (Inventor); Pain, Bedabrata (Inventor); Nixon, Robert H. (Inventor); Zhou, Zhimin (Inventor)

    2003-01-01

    An imaging device formed as a monolithic complementary metal oxide semiconductor integrated circuit in an industry standard complementary metal oxide semiconductor process, the integrated circuit including a focal plane array of pixel cells, each one of the cells including a photogate overlying the substrate for accumulating photo-generated charge in an underlying portion of the substrate, a readout circuit including at least an output field effect transistor formed in the substrate, and a charge coupled device section formed on the substrate adjacent the photogate having a sensing node connected to the output transistor and at least one charge coupled device stage for transferring charge from the underlying portion of the substrate to the sensing node and an analog-to-digital converter formed in the substrate connected to the output of the readout circuit.

  1. Charge and energy transferred from a plasma jet to liquid and dielectric surfaces

    NASA Astrophysics Data System (ADS)

    Mussard, M. Dang Van Sung; Foucher, E.; Rousseau, A.

    2015-10-01

    A key parameter in using plasma jets for biomedical applications is the transferred energy to the living tissues. The objective of this paper is to understand which parameters control the energy transfer from the plasma jet to a liquid or a dielectric surface. The plasma jet is flown with helium and ignited by a 600?Hz ac high voltage (up to 15?kV). Capacitors are connected to two measurement electrodes placed in the plasma source region, and under the sample. Charge and energy transferred are estimated by plotting Lissajous cycles; the number of bullets and the charge probability density function are also calculated. It is shown that the applied voltage and the gap (distance between the end of the tube and the sample) have a dramatic influence on the energy deposition on the sample as well as on the charge probability density function. Surprisingly, both gap distance and voltage have very little influence on the number of bullets reaching the sample per cycle. It is also shown that the conductivity of the liquid sample has almost no influence on the energy deposition and charge probability density function.

  2. Unexpectedly similar charge transfer rates through benzo-annulated bicyclo[2.2.2]octanes.

    PubMed

    Goldsmith, Randall H; Vura-Weis, Josh; Scott, Amy M; Borkar, Sachin; Sen, Ayusman; Ratner, Mark A; Wasielewski, Michael R

    2008-06-18

    A 4-(pyrrolidin-1-yl)phenyl electron donor and 10-cyanoanthracen-9-yl electron acceptor are attached via alkyne linkages to the bridgehead carbon atoms of bicyclo[2.2.2]octane and all three benzo-annulated bicyclo[2.2.2]octanes. The sigma-system of bicyclo[2.2.2]octane provides a scaffold having nearly constant bridge geometry on which to append multiple, weakly interacting benzo pi-bridges, so that the effect of incrementally increasing numbers of pi-bridges on electron transfer rates can be studied. Surprisingly, photoinduced charge transfer rates measured by transient absorption spectroscopy in toluene show no benefit from increasing the number of bridge pi-systems, suggesting dominant transport through the sigma-system. Even more surprisingly, the significant changes in hybridization undergone by the sigma-system as a result of benzo-annulation also appear to have no effect on the charge transfer rates. Natural Bond Orbital analysis is applied to both sigma- and pi-communication pathways. The transient absorption spectra obtained in 2-methyltetrahydrofuran (MTHF) show small differences between the benzo-annulated molecules that are attributed to changes in solvation. All charge transfer rates increase significantly upon cooling the MTHF solutions to their glassy state. This behavior is rationalized using combined molecular dynamics/electronic structure trajectories. PMID:18500799

  3. Decellular biological scaffold polymerized with PEDOT for improving peripheral nerve interface charge transfer.

    PubMed

    Frost, Christopher M; Cederna, Paul S; Martin, David C; Bong Sup Shim; Urbanchek, Melanie G

    2014-08-01

    Regenerative peripheral nerve interfaces (RPNIs) are for signal transfer between peripheral nerves inside the body to controllers for motorized prosthetics external to the body. Within the residual limb of an amputee, surgical construction of a RPNI connects a remaining peripheral nerve and spare muscle. Nerve signals become concentrated within the RPNI. Currently metal electrodes implanted on the RPNI muscle transfer signals but scarring around metal electrodes progressively diminishes charge transfer. Engineered materials may benefit RPNI signal transfer across the neural interface if they lower the power and charge density of the biologically meaningful signals. Poly3,4-ethylenedioxythiophene (PEDOT) is known to mediate ionic potentials allowing excitation across a critical nerve gap. We hypothesize that the capacity of an interface material to conduct electron mediated current is significantly increased by polymerized coating of PEDOT. SIS was either used plain or after PEDOT coating by electrochemical polymerization. Muscle forces are a direct representation of stimulating current distribution within an RPNI. In situ muscle forces were measured for the same muscle by electrically stimulating: a) the muscle's innervating nerve, b) directly on the muscle, c) on plain SIS laid on the muscle, and d) on SIS polymerized with PEDOT laid on the muscle. Electro-chemically coating PEDOT on SIS resulted in a thin, flexible material. PEDOT coated SIS distributed electrical stimulation more efficiently than SIS alone. Conductive polymer containing biological material allowed ionic signal distribution within the RPNI like muscle at lower charge density. PMID:25569986

  4. Room-temperature ferroelectricity in supramolecular networks of charge-transfer complexes.

    PubMed

    Tayi, Alok S; Shveyd, Alexander K; Sue, Andrew C-H; Szarko, Jodi M; Rolczynski, Brian S; Cao, Dennis; Kennedy, T Jackson; Sarjeant, Amy A; Stern, Charlotte L; Paxton, Walter F; Wu, Wei; Dey, Sanjeev K; Fahrenbach, Albert C; Guest, Jeffrey R; Mohseni, Hooman; Chen, Lin X; Wang, Kang L; Stoddart, J Fraser; Stupp, Samuel I

    2012-08-23

    Materials exhibiting a spontaneous electrical polarization that can be switched easily between antiparallel orientations are of potential value for sensors, photonics and energy-efficient memories. In this context, organic ferroelectrics are of particular interest because they promise to be lightweight, inexpensive and easily processed into devices. A recently identified family of organic ferroelectric structures is based on intermolecular charge transfer, where donor and acceptor molecules co-crystallize in an alternating fashion known as a mixed stack: in the crystalline lattice, a collective transfer of electrons from donor to acceptor molecules results in the formation of dipoles that can be realigned by an external field as molecules switch partners in the mixed stack. Although mixed stacks have been investigated extensively, only three systems are known to show ferroelectric switching, all below 71 kelvin. Here we describe supramolecular charge-transfer networks that undergo ferroelectric polarization switching with a ferroelectric Curie temperature above room temperature. These polar and switchable systems utilize a structural synergy between a hydrogen-bonded network and charge-transfer complexation of donor and acceptor molecules in a mixed stack. This supramolecular motif could help guide the development of other functional organic systems that can switch polarization under the influence of electric fields at ambient temperatures. PMID:22914165

  5. Charge and Energy Transfer Dynamics in Molecular Systems, 2nd, Revised and Enlarged Edition

    NASA Astrophysics Data System (ADS)

    May, Volkhard; Kühn, Oliver

    2004-02-01

    This second edition is based on the successful concept of the first edition in presenting a unified perspective on molecular charge and energy transfer processes. The authors bridge the regimes of coherent and dissipative dynamics, thus establishing the connection between classic rate theories and modern treatments of ultrafast phenomena. The book serves as an introduction for graduate students and researchers. Among the new topics of this second edition are - semiclassical and quantum-classical hybrid formulations of molecular dynamics - the basics of femtosecond nonlinear spectroscopy - electron transfer through molecular bridges and proteins - multidimensional tunneling in proton transfer reactions - two-exciton states and exciton annihilation in biological and nonbiological chromophore complexes More illustrating examples as well as an enlarged reference list are added. A new chapter gives an introduction into the theory of laser pulse control of molecular transfer processes.

  6. Anomalous charge and negative-charge-transfer insulating state in cuprate chain compound KCuO2

    NASA Astrophysics Data System (ADS)

    Choudhury, D.; Rivero, P.; Meyers, D.; Liu, X.; Cao, Y.; Middey, S.; Whitaker, M. J.; Barraza-Lopez, S.; Freeland, J. W.; Greenblatt, M.; Chakhalian, J.

    2015-11-01

    Using a combination of x-ray absorption spectroscopy (XAS) experiments and first-principles calculations, we demonstrate that insulating KCuO2 contains Cu in an unusually high formal 3+ valence state, and the ligand-to-metal (O-to-Cu) charge-transfer energy is intriguingly negative (? ˜-1.5 eV) and has a dominant (˜60 % ) ligand-hole character in the ground state akin to the high Tc cuprate Zhang-Rice state. Unlike most other formal Cu3 + compounds, the Cu 2 p XAS spectra of KCuO2 exhibit pronounced 3 d8 (Cu3 +) multiplet structures, which account for ˜40 % of its ground state wave function. Ab initio calculations elucidate the origin of the band gap in KCuO2 as arising primarily from strong intracluster Cu 3 d -O 2 p hybridizations (tpd); the value of the band gap decreases with a reduced value of tpd. Further, unlike conventional negative-charge-transfer insulators, the band gap in KCuO2 persists even for vanishing values of Coulomb repulsion U , underscoring the importance of single-particle band-structure effects connected to the one-dimensional nature of the compound.

  7. Charge transfer tuning by chemical substitution and uniaxial pressure in the organic complex tetramethoxypyrene-tetracyanoquinodimethane

    NASA Astrophysics Data System (ADS)

    Rudloff, Milan; Ackermann, Kai; Huth, Michael; Jeschke, Harald O.; Tomic, Milan; Valentí, Roser; Wolfram, Benedikt; Bröring, Martin; Bolte, Michael; Chercka, Dennis; Baumgarten, Martin; Müllen, Klaus

    In the search for novel organic charge transfer salts with variable charge transfer degree we study the effects of two modifications to the recently synthesized donor-acceptor Tetramethoxypyrene (TMP)-Tetracyanoquinodimethane (TCNQ). One is of chemical nature by substituting the acceptor TCNQ molecules by F4TCNQ molecules. The second consists in simulating the application of uniaxial pressure along the stacking axis of the system. In order to test the chemical substitution, we have grown single crystals of TMP-F4TCNQ and analyzed its electronic structure via electronic transport measurements, ab initio density functional theory (DFT) calculations and UV/VIS/IR absorption spectroscopy. This system shows an almost ideal geometrical overlap of nearly planar molecules alternately stacked (mixed stack) and this arrangement is echoed by a semiconductor-like transport behavior with an increased conductivity along the stacking direction. This is in contrast to TMP-TCNQ which shows a less pronounced anisotropy and a smaller conductivity response. Our bandstructure calculations confirm the one-dimensional behavior of TMP-F4TCNQ with pro- nounced dispersion only along the stacking axis. Infrared measurements illustrating the CN vibration frequency shift in F4TCNQ suggest however no improvement on the degree of charge transfer in TMP-F4TCNQ with respect to TMP-TCNQ. In both complexes about 0.1 is transferred from TMP to the acceptor. Concerning the pressure effect, our DFT calculations on designed TMP-TCNQ and TMP-F4TCNQ structures under different pressure conditions show that application of uniaxial pressure along the stacking axis of TMP-TCNQ may be the route to follow in order to obtain a much more pronounced charge transfer.

  8. Charge transfer tuning by chemical substitution and uniaxial pressure in the organic complex tetramethoxypyrene-tetracyanoquinodimethane.

    PubMed

    Rudloff, Milan; Ackermann, Kai; Huth, Michael; Jeschke, Harald O; Tomic, Milan; Valentí, Roser; Wolfram, Benedikt; Bröring, Martin; Bolte, Michael; Chercka, Dennis; Baumgarten, Martin; Müllen, Klaus

    2015-02-14

    In the search for novel organic charge transfer salts with variable degrees of charge transfer we have studied the effects of two modifications of the recently synthesized donor-acceptor system [tetramethoxypyrene (TMP)]-[tetracyanoquinodimethane (TCNQ)]. One is of chemical nature by substituting the acceptor TCNQ molecules by F4TCNQ molecules. The second consists in simulating the application of uniaxial pressure along the stacking axis of the system. In order to test the chemical substitution, we have grown single crystals of the TMP-F4TCNQ complex and analyzed its electronic structure via electronic transport measurements, ab initio density functional theory (DFT) calculations and UV/VIS/IR absorption spectroscopy. This system shows an almost ideal geometrical overlap of nearly planar molecules stacked alternately (mixed stack) and this arrangement is echoed by a semiconductor-like transport behavior with an increased conductivity along the stacking direction. This is in contrast to TMP-TCNQ which shows a less pronounced anisotropy and a smaller conductivity response. Our band structure calculations confirm the one-dimensional behavior of TMP-F4TCNQ with pronounced dispersion only along the stacking axis. Infrared measurements illustrating the C?N vibration frequency shift in F4TCNQ suggest however no improvement in the degree of charge transfer in TMP-F4TCNQ with respect to TMP-TCNQ. In both complexes about 0.1e is transferred from TMP to the acceptor. Concerning the pressure effect, our DFT calculations on the designed TMP-TCNQ and TMP-F4TCNQ structures under different pressure conditions show that application of uniaxial pressure along the stacking axis of TMP-TCNQ may be the route to follow in order to obtain a much more pronounced charge transfer. PMID:25563213

  9. Nonadiabatic dynamics of charge transfer and singlet fission at the pentacene/C60 interface.

    PubMed

    Akimov, Alexey V; Prezhdo, Oleg V

    2014-01-29

    Charge carrier multiplication in organic heterojunction systems, a process known as singlet fission (SF), holds promise for development of solar cells with enhanced photon-to-electron yields, and therefore it is of substantial fundamental interest. The efficiency of photovoltaic devices based on this principle is determined by complex dynamics involving key electronic states coupled to particular nuclear motions. Extensive experimental and theoretical studies are dedicated to this topic, generating multiple opinions on the nature of such states and motions, their properties, and mechanisms of the competing processes, including electron-phonon relaxation, SF, and charge separation. Using nonadiabatic molecular dynamics, we identify the key steps and mechanisms involved in the SF and subsequent charge separation, and build a comprehensive kinetic scheme that is consistent with the existing experimental and theoretical results. The ensuing model provides time scales that are in excellent agreement with the experimental observations. We demonstrate that SF competes with the traditional photoinduced electron transfer between pentacene and C60. Efficient SF relies on the presence of intermediate dark states within the pentacene subsystem. Having multiexciton and charge transfer character, these states play critical roles in the dynamics, and should be considered explicitly when explaining the entire process from the photoexcitation to the final charge separation. PMID:24397723

  10. First-principles description of charge transfer in donor-acceptor compounds from self-consistent many-body perturbation theory

    NASA Astrophysics Data System (ADS)

    Caruso, Fabio; Atalla, Viktor; Ren, Xinguo; Rubio, Angel; Scheffler, Matthias; Rinke, Patrick

    2014-08-01

    We investigate charge transfer in prototypical molecular donor-acceptor compounds using hybrid density functional theory (DFT) and the GW approximation at the perturbative level (G0W0) and at full self-consistency (sc-GW). For the systems considered here, no charge transfer should be expected at large intermolecular separation according to photoemission experiments and accurate quantum-chemistry calculations. The capability of hybrid exchange-correlation functionals of reproducing this feature depends critically on the fraction of exact exchange ?, as for small values of ? spurious fractional charge transfer is observed between the donor and the acceptor. G0W0 based on hybrid DFT yields the correct alignment of the frontier orbitals for all values of ?. However, G0W0 has no capacity to alter the ground-state properties of the system because of its perturbative nature. The electron density in donor-acceptor compounds thus remains incorrect for small ? values. In sc-GW, where the Green's function is obtained from the iterative solution of the Dyson equation, the electron density is updated and reflects the correct description of the level alignment at the GW level, demonstrating the importance of self-consistent many-body approaches for the description of ground- and excited-state properties in donor-acceptor systems.

  11. Fermi level density of states modulation without charge transfer in nickelate superlattices.

    PubMed

    Han, Myung Joon; van Veenendaal, Michel

    2014-04-01

    By using first-principles density functional theory calculations for (LaNiO3)m/(SrTiO3)n superlattices, we report a systematic electronic response to the interface geometry. It is found that the density of states at the Fermi level of metallic nickelate layers is significantly reduced without charge transfer in the vicinity of the interface to the insulating SrTiO3. This type of electronic state redistribution is clearly distinctive from other interface phenomena such as charge and orbital reconstruction. Our result sheds new light on the understanding of the nickelates and other transition-metal oxide heterostructures. PMID:24637347

  12. Reversible Tuning of Interfacial and Intramolecular Charge Transfer in Individual MnPc Molecules.

    PubMed

    Zhong, Jian-Qiang; Wang, Zhunzhun; Zhang, Jia Lin; Wright, Christopher A; Yuan, Kaidi; Gu, Chengding; Tadich, Anton; Qi, Dongchen; Li, He Xing; Lai, Min; Wu, Kai; Xu, Guo Qin; Hu, Wenping; Li, Zhenyu; Chen, Wei

    2015-12-01

    The reversible selective hydrogenation and dehydrogenation of individual manganese phthalocyanine (MnPc) molecules has been investigated using photoelectron spectroscopy (PES), low-temperature scanning tunneling microscopy (LT-STM), synchrotron-based near edge X-ray absorption fine structure (NEXAFS) measurements, and supported by density functional theory (DFT) calculations. It is shown conclusively that interfacial and intramolecular charge transfer arises during the hydrogenation process. The electronic energetics upon hydrogenation is identified, enabling a greater understanding of interfacial and intramolecular charge transportation in the field of single-molecule electronics. PMID:26528623

  13. Polaron hopping in some biomolecular solids and their charge transfer complexes.

    PubMed

    Solanki, G K; Amin, Anand; Padhiyar, Ashvin; Ray, A K; Oza, A T

    2008-12-01

    The solid state spectroscopy of charge transfer complexes of biomolecules such as fatty acids, tripalmitin, lysozyme. folic acid, beta-carotene, cytochrome c, valinomycin and gramicidin has been carried out. The absorption coefficient is related with electronic conductivity. A half-power beta density is found common among these macromolecular solids, indicating photon-induced polaron hopping or hopping of a charge carrier between two branches of a polariton. Band gap vs full width at half-maximum of the mid-IR peak also reveals a linear relation. PMID:19239130

  14. Ultrafast processes of photoinduced charge and energy transfer in nanostructural fullerene-metal films

    SciTech Connect

    Chekalin, S. V.

    2006-11-15

    The primary stages of photoinduced processes in tin-doped C{sub 60} fullerene films have been studied using a femtosecond pump-probe technique with 150-fs laser excitation pulses ({lambda} = 400 nm) and differential transmission and reflection probing in the 1100-1700 nm range. The relaxation dynamics strongly depends both on the metal-to-fullerene ratio in the film and on the mutual distribution (packing) of components in the nanocomposite material. The observed response signal dynamics is related to features in the charge carrier generation, energy transfer between fullerene molecules, and charge transport between metal and fullerene.

  15. Excitation of the ligand-to-metal charge transfer band induces electron tunnelling in azurin

    NASA Astrophysics Data System (ADS)

    Baldacchini, Chiara; Bizzarri, Anna Rita; Cannistraro, Salvatore

    2014-03-01

    Optical excitation of azurin blue copper protein immobilized on indium-tin oxide, in resonance with its ligand-to-metal charge transfer absorption band, resulted in a light-induced current tunnelling within the protein milieu. The related electron transport rate is estimated to be about 105 s-1. A model based on resonant tunnelling through an azurin excited molecular state is proposed. The capability of controlling electron transfer processes through light pulses opens interesting perspectives for implementation of azurin in bio-nano-opto-electronic devices.

  16. Excitation of the ligand-to-metal charge transfer band induces electron tunnelling in azurin

    SciTech Connect

    Baldacchini, Chiara; Bizzarri, Anna Rita; Cannistraro, Salvatore

    2014-03-03

    Optical excitation of azurin blue copper protein immobilized on indium-tin oxide, in resonance with its ligand-to-metal charge transfer absorption band, resulted in a light-induced current tunnelling within the protein milieu. The related electron transport rate is estimated to be about 10{sup 5}?s{sup ?1}. A model based on resonant tunnelling through an azurin excited molecular state is proposed. The capability of controlling electron transfer processes through light pulses opens interesting perspectives for implementation of azurin in bio-nano-opto-electronic devices.

  17. Isotope effect in charge-transfer collisions of H with He{sup +}

    SciTech Connect

    Loreau, J.; Dalgarno, A.; Ryabchenko, S.

    2011-11-15

    We present a theoretical study of the isotope effect arising from the replacement of H by T in the charge-transfer collision H(n=2) + He{sup +}(1s) at low energy. Using a quasimolecular approach and a time-dependent wave-packet method, we compute the cross sections for the reaction including the effects of the nonadiabatic radial and rotational couplings. For H(2s) + He{sup +}(1s) collisions, we find a strong isotope effect at energies below 1 eV/amu for both singlet and triplet states. We find a much smaller isotopic dependence of the cross section for H(2p) + He{sup +}(1s) collisions in triplet states, and no isotope effect in singlet states. We explain the isotope effect on the basis of the potential energy curves and the nonadiabatic couplings, and we evaluate the importance of the isotope effect on the charge-transfer rate coefficients.

  18. Symmetry-Breaking Charge Transfer of Visible Light Absorbing Systems: Zinc Dipyrrins

    PubMed Central

    2015-01-01

    Zinc dipyrrin complexes with two identical dipyrrin ligands absorb strongly at 450–550 nm and exhibit high fluorescence quantum yields in nonpolar solvents (e.g., 0.16–0.66 in cyclohexane) and weak to nonexistent emission in polar solvents (i.e., <10–3, in acetonitrile). The low quantum efficiencies in polar solvents are attributed to the formation of a nonemissive symmetry-breaking charge transfer (SBCT) state, which is not formed in nonpolar solvents. Analysis using ultrafast spectroscopy shows that in polar solvents the singlet excited state relaxes to the SBCT state in 1.0–5.5 ps and then decays via recombination to the triplet or ground states in 0.9–3.3 ns. In the weakly polar solvent toluene, the equilibrium between a localized excited state and the charge transfer state is established in 11–22 ps. PMID:25270268

  19. Synthesis and spectroscopic studies of the charge transfer complexes of 2- and 3-aminopyridine

    NASA Astrophysics Data System (ADS)

    Mostafa, Adel; Bazzi, Hassan S.

    2009-09-01

    The interactions of the electron donors 2-aminopyridine (2APY) and 3-aminopyridine (3APY) with the ?-acceptors tetracyanoethylene (TCNE), 2,3-dichloro-5,6-dicyano-p-benzoquinone (DDQ), 2-chloro-1,3,5-trinitrobenzene (picryl chloride, PC), and 2,3,5,6-tetrachloro-1,4-benzoquinone (chloranil) were studied spectrophotometrically in chloroform at room temperature. The electronic and infrared spectra of the formed molecular charge transfer (CT) complexes were recorded. Photometric titration showed that the stoichiometries of the reactions were fixed and depended on the nature of both the donor and the acceptor. The molecular structures of the CT-complexes were, however, independent of the position of the amino group on the pyridine ring and were formulated as [(APY)(TCNE)], [(APY)(DDQ)], [(APY)(PC)], and [(APY) (chloranil)]. The formation constants ( KCT), charge transfer energy ( ECT) and molar extinction coefficients ( ?CT) of the formed CT-complexes were obtained.

  20. Charge transfer enhances two-photon absorption in transition metal porphyrins.

    PubMed

    Humphrey, Jonathan L; Kuciauskas, Darius

    2006-03-29

    Two-photon absorption processes were investigated in electropolymerized Fe(III), Mn(III), and Co(II) 5,10,15,20-tetrakis-(4-hydroxytetraphenyl)porphyrin films. Degenerate four wave mixing (DFWM) spectroscopy with 100 fs pulses in the near-IR spectral region was used. Metalloporphyrins with strong charge transfer (CT) transitions in the linear absorption spectra also show enhanced two-photon absorption. (Metalloporphyrin two-photon absorption cross section, delta, increases >10 times over that for the metal free porphyrin.) This effect was attributed to a two-photon induced charge transfer between the metal ion's d orbitals and the pi-system of the porphyrin. Correlation of one- and two-photon absorption properties of transition metal porphyrins suggests a new and simple approach to improve organic materials for photonic applications. PMID:16551085

  1. Specific features of the charge and mass transfer in a silver-intercalated hafnium diselenide

    NASA Astrophysics Data System (ADS)

    Pleshchev, V. G.; Selezneva, N. V.; Baranov, N. V.

    2013-07-01

    The specific features of the charge transfer in intercalated samples of Ag x HfSe2 have been studied for the first time by alternating current (ac) impedance spectroscopy. It has been found that relaxation processes in an ac field are accelerated with increasing silver content in the samples. The complex conductivity ( Y) shows a frequency dispersion described by power law Y ˜ ? s , which is characteristic of the hopping conductivity mechanism. The Ag x HfSe2 compounds demonstrate shorter relaxation times as compared to those observed in hafnium diselenide intercalated with copper atoms, and this fact indicates that the charge carrier mobility in the silver-intercalated compounds is higher. The possibility of silver ion transfer in Ag x HfSe2 is confirmed by the measurements performed by the method of electrochemical cell emf.

  2. Hydrogen-bonded charge-transfer complexes of TTFs containing nucleobase or imidazole moiety

    NASA Astrophysics Data System (ADS)

    Morita, Y.; Murata, T.; Miyazaki, E.; Maki, S.; Fukui, K.; Umemoto, Y.; Yamochi, H.; Saito, G.; Nakasuji, K.

    2004-04-01

    Novel electron-donor molecules based on tetrathiafulvalene (TTF) and imidazole skeleton with hydrogen-bonded (H-bonded) functionality 1 5 and 7 10 have been designed and synthesized. The cyclic voltammograms for TTF-based donors 1 5 exhibit two-stage one-electron reversible waves, while oligo(imidazole)s 7 10 show irreversible one. The room-temperature conductivities of their tetracyanoquinodimethane (TCNQ) complexes for 1, 2, 4, 5, 8 and 9 exhibit 0.11, 0.07, 2.3, 0.38, 0.16 and 0.10 Scm-1, respectively, revealing high electrical conductivity than those of known charge-transfer (CT) complexes derived from organic donors with amino or hydroxyl groups and organic acceptor molecules. Key words. TTF, nucleobase, imidazole, hydrogen-bonding, charge-transfer complex, conductivity.

  3. Charge transfer to solvent dynamics in iodide aqueous solution studied at ionization threshold.

    PubMed

    Kothe, Alexander; Wilke, Martin; Moguilevski, Alexandre; Engel, Nicholas; Winter, Bernd; Kiyan, Igor Yu; Aziz, Emad F

    2015-01-21

    We explore the early-time electronic relaxation in NaI aqueous solution exposed to a short UV laser pulse. Rather than initiating the charge transfer reaction by resonant photoexcitation of iodide, in the present time-resolved photoelectron spectroscopy study the charge-transfer-to-solvent (CTTS) states are populated via electronic excitation above the vacuum level. By analyzing the temporal evolution of electron yields from ionization of two transient species, assigned to CTTS and its first excited state, we determine both their ultrafast population and relaxation dynamics. Comparison with resonant-excitation studies shows that the highly excited initial states exhibit similar relaxation characteristics as found for resonant excitation. Implications for structure and dynamical response of the hydration cage are discussed. PMID:25474360

  4. Primary Side Power Flow Control of Wireless Power Transfer for Electric Vehicle Charging

    SciTech Connect

    Miller, John M; Onar, Omer C; Chinthavali, Madhu Sudhan

    2015-01-01

    Various noncontacting methods of plug-in electric vehicle charging are either under development or now deployed as aftermarket options in the light-duty automotive market. Wireless power transfer (WPT) is now the accepted term for wireless charging and is used synonymously for inductive power transfer and magnetic resonance coupling. WPT technology is in its infancy; standardization is lacking, especially on interoperability, center frequency selection, magnetic fringe field suppression, and the methods employed for power flow regulation. This paper proposes a new analysis concept for power flow in WPT in which the primary provides frequency selection and the tuned secondary, with its resemblance to a power transmission network having a reactive power voltage control, is analyzed as a transmission network. Analysis is supported with experimental data taken from Oak Ridge National Laboratory s WPT apparatus. This paper also provides an experimental evidence for frequency selection, fringe field assessment, and the need for low-latency communications in the feedback path.

  5. Measurement of the charge transfer efficiency of electrons clocked on superfluid helium

    SciTech Connect

    Sabouret, G.; Lyon, S.A.

    2006-06-19

    Electrons floating on the surface of liquid helium are possible qubits for quantum information processing. Varying electric potentials do not modify spin states, which allows their transport on helium using a charge-coupled device (CCD)-like array of underlying gates. This scheme depends on an efficient intergate electron transfer and on the absence of electron traps. We will present a measurement of the charge transfer efficiency (CTE) of electrons clocked back and forth above a short CCD-like structure. The CTE obtained at low clocking frequencies is 0.999 with an electron density of about 4 electrons/{mu}m{sup 2}. We find no evidence for deep electron trapping.

  6. Cross sections for charge transfer between mercury ions and other metals

    NASA Technical Reports Server (NTRS)

    Vroom, D. A.; Rutherford, J. A.

    1977-01-01

    Cross sections for charge transfer between several ions and metals of interest to the NASA electro propulsion program have been measured. Specifically, the ions considered were Hg(+), Xe(+) and Cs(+) and the metals Mo, Fe, Al, Ti, Ta, and C. Measurements were made in the energy regime from 1 to 5,000 eV. In general, the cross sections for charge transfer were found to be less than 10 to the minus 15 power sq cm for most processes over the total energy range. Exceptions are Hg(+) in collision with Ti and Ta. The results obtained for each reaction are given in both graphical and numerical form in the text. For quick reference, the data at several ion velocities are condensed into one table given in the summary.

  7. Forster Resonance Energy Transfer and Conformational Stability of Proteins: An Advanced Biophysical Module for Physical Chemistry Students

    ERIC Educational Resources Information Center

    Sanchez, Katheryn M.; Schlamadinger, Diana E.; Gable, Jonathan E.; Kim, Judy E.

    2008-01-01

    Protein folding is an exploding area of research in biophysics and physical chemistry. Here, we describe the integration of several techniques, including absorption spectroscopy, fluorescence spectroscopy, and Forster resonance energy transfer (FRET) measurements, to probe important topics in protein folding. Cytochrome c is used as a model…

  8. Controlling the charge transfer in phenylene-bridged borylene-amine pi-conjugated systems.

    PubMed

    Pro?, Agnieszka; Zhou, Gang; Norouzi-Arasi, Hassan; Baumgarten, Martin; Müllen, Klaus

    2009-08-20

    Novel boron-nitrogen-containing pi-conjugated compounds 3,3'- and 4,4'-((2,4,6-triisopropylphenyl)borylene)bis(N,N-diarylbenzenamine) (1-2), m- and p-phenylene bridged to the boron center, respectively, have been synthesized and characterized. Optical studies by means of UV-vis absorption and emission measurements as well as DFT calculations reveal a different charge transfer behavior between the para series and the meta series at ground and excited states. PMID:19719198

  9. On the crystal phases of /DEPE/ /TCNQ/4. [organic charge transfer salt

    NASA Technical Reports Server (NTRS)

    Coleman, L. B.; Hermann, A. M.; Williams, R.; Somoano, R. B.

    1977-01-01

    X-ray powder diffraction studies of two semiconducting crystal phases in the organic charge transfer salt (DEPE)(TCNQ) sub 4 has revealed almost identical electrical properties to those of metallic crystals. It is hypothesized that the similarity arises from the nature of the measurements themselves, i.e., electrode geometry. The possibility that a separate metallic phase for (DEPE)(TCNQ) sub 4 exists, is not, however, ruled out.

  10. Ink-jet printing of organic metal electrodes using charge-transfer compounds

    NASA Astrophysics Data System (ADS)

    Hiraoka, M.; Hasegawa, T.; Abe, Y.; Yamada, T.; Tokura, Y.; Yamochi, H.; Saito, G.; Akutagawa, T.; Nakamura, T.

    2006-10-01

    In this work the authors fabricated patterned thin films made of highly conductive organic charge-transfer complexes using the ink-jet printing technique. The overprinted films of BO9(C14-TCNQ)4 exhibit low sheet resistivity and are available for carrier injection and interconnection of organic field-effect transistors (FETs). The performance of pentacene thin film FETs, where the top contact and bottom contact are ink-jet-printed organic electrodes, demonstrates the potential of organic/organic heterointerfaces.

  11. Charge transfer and adsorption-desorption kinetics in carbon nanotube and graphene gas sensing

    NASA Astrophysics Data System (ADS)

    Liang, Sang-Zi; Chen, Gugang; Harutyunyan, Avetik; Cole, Milton; Sofo, Jorge

    2014-03-01

    Detection of molecules in the gas phase by carbon nanotube and graphene has great application potentials due to the high sensitivity and surface-to-volume ratio. In chemiresistor, the conductance of the materials has been proposed to change as a result of charge transfer from the adsorbed molecules. Due to self-interaction errors, calculations using LDA or GGA density functionals have an innate disadvantage in dealing with charge transfer situations. A model which takes into consideration the dielectric interaction between the graphene surface and the molecule is employed to estimate the distance where charge transfer becomes favorable. Adsorption-desorption kinetics is studied with a modified Langmuir model, including sites from which the molecules do not desorb within the experimental time. Assuming a constant mobility, the model reproduces existing experimental conductance data. Its parameters provide information about the microscopic process during the detection and varying them allows optimization of aspects of sensor performance, including sensitivity, detection limit and response time. This work is supported by Honda Research Institute USA, Inc.

  12. Charge transfer in photorechargeable composite films of TiO2 and polyaniline

    NASA Astrophysics Data System (ADS)

    Nomiyama, Teruaki; Sasabe, Kenichi; Sakamoto, Kenta; Horie, Yuji

    2015-07-01

    A photorechargeable battery (PRB) is a photovoltaic device having an energy storage function in a single cell. The photoactive electrode of PRB is a bilayer film consisting of bare porous TiO2 and a TiO2-polyaniline (PANi) mixture that work as a photovoltaic current generator and an electrochemical energy storage by ion dedoping, respectively. To study the charge transfer between TiO2 and PANi, the photorechargeable quantum efficiency QE ([electron count on discharge]/[incident photon count on photocharge]) was measured by varying the thickness LS of the TiO2-PANi mixture. The quantum efficiency QEuv for UV photons had a maximum of ˜7% at LS ˜ 7 µm. The time constant ?TP for the charge transfer was about 10-1 s, which was longer ten times or more than the lifetime of excited electrons within TiO2. These facts reveal that the main rate-limiting factor in the photocharging process is the charge transfer between TiO2 and PANi.

  13. Importance of Correctly Describing Charge-Transfer Excitations for Understanding the Chemical Effect in SERS

    SciTech Connect

    Moore, Justin E.; Morton, Seth M.; Jensen, Lasse

    2012-09-06

    The enhancement mechanism due to the molecule-surface chemical coupling in surface-enhanced Raman scattering (SERS) is governed to a large extent by the energy difference between the highest occupied molecular orbital (HOMO) of the metal and the lowest unoccupied molecular orbital (LUMO) of the molecule. Here, we investigate the importance of correctly describing charge-transfer excitations, using time dependent density functional theory (TDDFT), when calculating the chemical coupling in SERS. It is well-known that TDDFT, using traditional functionals, underestimates the position of charge-transfer excitations. Here, we show that this leads to a significant overestimation of the chemical coupling mechanism in SERS. Significantly smaller enhancements are found using long-range corrected (LC) functionals as compared with a traditional generalized gradient approximation (GGA) and hybrid functionals. Enhancement factors are found to be smaller than 530 and typically less than 50. Our results show that it is essential to correctly describe charge-transfer excitations for predicting the chemical enhancement in SERS.

  14. A study of different modes of charge transfer to ground in upward lightning

    NASA Astrophysics Data System (ADS)

    Zhou, Helin; Rakov, Vladimir A.; Diendorfer, Gerhard; Thottappillil, Rajeev; Pichler, Hannes; Mair, Martin

    2015-04-01

    We examined simultaneous measurements of currents and close electric field changes, as well as high-speed video images, associated with pulses superimposed on the initial continuous current (ICC pulses) and M-components following return strokes in upward flashes initiated from the Gaisberg Tower in Austria. For tower-initiated lightning, upward leaders often create multiple branches below the cloud base that can facilitate initiation of transients at relatively low heights along the grounded channel carrying ICC of some tens to hundreds of amperes. In this situation, a conducting channel is present, which is necessary for the M-component mode of charge transfer to ground, but the excitation wave (leader), after entering the channel, cannot form a long-front downward M-wave, because of the relatively short distance between the entry (junction) point and the strike-object top. Clearly, two parallel channels, one previously existing and the other newly formed (or rejuvenated) are involved in the charge transfer, and there is a common channel section between the junction point and the strike object. We use the term "mixed mode of charge transfer to ground", to indicate that in the case of low junction point the "classical" M-component mode is not possible, even though a conducting channel to ground (an attribute of the M-component mode) is present. The mixed mode scenario is also applicable to impulsive processes during continuing currents following return strokes in upward lightning.

  15. Charge Transfer-Induced Molecular Hole Doping into Thin Film of Metal-Organic Frameworks.

    PubMed

    Lee, Deok Yeon; Kim, Eun-Kyung; Shrestha, Nabeen K; Boukhvalov, Danil W; Lee, Joong Kee; Han, Sung-Hwan

    2015-08-26

    Despite the highly porous nature with significantly large surface area, metal-organic frameworks (MOFs) can be hardly used in electronic and optoelectronic devices due to their extremely poor electrical conductivity. Therefore, the study of MOF thin films that require electron transport or conductivity in combination with the everlasting porosity is highly desirable. In the present work, thin films of Co3(NDC)3DMF4 MOFs with improved electronic conductivity are synthesized using layer-by-layer and doctor blade coating techniques followed by iodine doping. The as-prepared and doped films are characterized using FE-SEM, EDX, UV/visible spectroscopy, XPS, current-voltage measurement, photoluminescence spectroscopy, cyclic voltammetry, and incident photon to current efficiency measurements. In addition, the electronic and semiconductor properties of the MOF films are characterized using Hall Effect measurement, which reveals that, in contrast to the insulator behavior of the as-prepared MOFs, the iodine doped MOFs behave as a p-type semiconductor. This is caused by charge transfer-induced hole doping into the frameworks. The observed charge transfer-induced hole doping phenomenon is also confirmed by calculating the densities of states of the as-prepared and iodine doped MOFs based on density functional theory. Photoluminescence spectroscopy demonstrates an efficient interfacial charge transfer between TiO2 and iodine doped MOFs, which can be applied to harvest solar radiations. PMID:26226050

  16. Lock-arm supramolecular ordering: a molecular construction set for cocrystallizing organic charge transfer complexes.

    PubMed

    Blackburn, Anthea K; Sue, Andrew C-H; Shveyd, Alexander K; Cao, Dennis; Tayi, Alok; Narayanan, Ashwin; Rolczynski, Brian S; Szarko, Jodi M; Bozdemir, Ozgur A; Wakabayashi, Rie; Lehrman, Jessica A; Kahr, Bart; Chen, Lin X; Nassar, Majed S; Stupp, Samuel I; Stoddart, J Fraser

    2014-12-10

    Organic charge transfer cocrystals are inexpensive, modular, and solution-processable materials that are able, in some instances, to exhibit properties such as optical nonlinearity, (semi)conductivity, ferroelectricity, and magnetism. Although the properties of these cocrystals have been investigated for decades, the principal challenge that researchers face currently is to devise an efficient approach which allows for the growth of high-quality crystalline materials, in anticipation of a host of different technological applications. The research reported here introduces an innovative design, termed LASO-lock-arm supramolecular ordering-in the form of a modular approach for the development of responsive organic cocrystals. The strategy relies on the use of aromatic electronic donor and acceptor building blocks, carrying complementary rigid and flexible arms, capable of forming hydrogen bonds to amplify the cocrystallization processes. The cooperativity of charge transfer and hydrogen-bonding interactions between the building blocks leads to binary cocrystals that have alternating donors and acceptors extending in one and two dimensions sustained by an intricate network of hydrogen bonds. A variety of air-stable, mechanically robust, centimeter-long, organic charge transfer cocrystals have been grown by liquid-liquid diffusion under ambient conditions inside 72 h. These cocrystals are of considerable interest because of their remarkable size and stability and the promise they hold when it comes to fabricating the next generation of innovative electronic and photonic devices. PMID:25369425

  17. Nonlinear optical properties of charge-transfer molecular systems with C60

    NASA Astrophysics Data System (ADS)

    Kajzar, Francois; Okada-Shudo, Yoshiko; Merritt, Charles D.; Kafafi, Zakya H.

    1997-11-01

    Second order nonlinear optical properties of C60 based multilayered charge transfer structures with TPP, TPD and TPN molecules, acting as electron donors, are studied by the transverse optical second harmonic generation. The studied structures are of ABABAB...and ABCABC...type, where layer A is made from electron accepting molecules, layer B from electron donating and layer C from neutral molecules. The typical thickness of individual layers is about 2 nm. A significant increase of SHG is observed in ABCABC...type structures, where an effective charge transfer is expected with creation of a noncentrosymmetry in the perpendicular direction tot eh layers. The largest (chi) (2) susceptibility is obtained with multilayers containing rubrene. The SHG generation experiments performed on thin films with different thicknesses show that the nonlinear optical response comes from the bulk material and not form the interfaces. A quadratic dependence of SHG intensity on input power is also observed, showing that the charge transfer takes place at the ground state.

  18. NIR and MIR charge transfer plasmons in wire-bridged antennas (Presentation Recording)

    NASA Astrophysics Data System (ADS)

    Zhang, Yue; Wen, Fangfang; Gottheim, Samuel; King, Nicholas S.; Zhang, Yu; Nordlander, Peter; Halas, Naomi J.

    2015-09-01

    We investigate optical properties of wire-bridged plasmonic nanoantennas. Here we found two spectral features: a dipolar plasmon in the visible and a Charge Transfer Plasmon (CTP) in the infrared. The CTP depends sensitively on the conductance of the junction wire, offering a controllable way for tuning the plasmon resonance to the desired wavelength regime via junction geometries. Here we use single-particle dark field spectroscopy from UV, visible to IR to identify plasmonic modes in different spectrum regimes. The simulations using Finite-difference time-domain (FDTD) method are in good agreement with experiment: Increasing the junction wire width and concurrently the junction conductance blue shifts resonance positions, and simultaneously modifies scattering strengths, the linewidth of CTP and dipolar plasmon. We notice that CTP in a much longer wavelength regime and preserving a narrow line width, an important implication for designing IR plasmons with a high quality factor for enhanced spectroscopy and sensing applications. We also extend the CTP to the IR regime by increasing the wire length to create IR plasmon while keeping the line width of the resonance. Our work offers a way for studying the charge transfer properties in plasmonic nanostructures. Not only it adds another degree in understanding the charge transfer properties in plasmonic nanostructures but also offers an optical platform for studying molecules transport at optical frequencies and related applications.

  19. Computational models of an inductive power transfer system for electric vehicle battery charge

    NASA Astrophysics Data System (ADS)

    Anele, A. O.; Hamam, Y.; Chassagne, L.; Linares, J.; Alayli, Y.; Djouani, K.

    2015-09-01

    One of the issues to be solved for electric vehicles (EVs) to become a success is the technical solution of its charging system. In this paper, computational models of an inductive power transfer (IPT) system for EV battery charge are presented. Based on the fundamental principles behind IPT systems, 3 kW single phase and 22 kW three phase IPT systems for Renault ZOE are designed in MATLAB/Simulink. The results obtained based on the technical specifications of the lithium-ion battery and charger type of Renault ZOE show that the models are able to provide the total voltage required by the battery. Also, considering the charging time for each IPT model, they are capable of delivering the electricity needed to power the ZOE. In conclusion, this study shows that the designed computational IPT models may be employed as a support structure needed to effectively power any viable EV.

  20. Ligand(s)-to-metal charge transfer as a factor controlling the equilibrium constants of late first-row transition metal complexes: revealing the Irving-Williams thermodynamical series.

    PubMed

    Varadwaj, Pradeep R; Varadwaj, Arpita; Jin, Bih-Yaw

    2015-01-14

    A unified relationship between the experimental formation constants and the ligand(s)-to-metal charge transfer values of versatile ligand complexes of late transition series first-row bivalent metal ions is uncovered. The latter property not only explicates the Irving-Williams series but also rationalizes quantitatively Pearson's concept of hard and soft acids and bases by correlating the gas-phase to aqueous solution-phase chemistry in a broad sense. PMID:25414118

  1. Charge constrained density functional molecular dynamics for simulation of condensed phase electron transfer reactions

    NASA Astrophysics Data System (ADS)

    Oberhofer, Harald; Blumberger, Jochen

    2009-08-01

    We present a plane-wave basis set implementation of charge constrained density functional molecular dynamics (CDFT-MD) for simulation of electron transfer reactions in condensed phase systems. Following the earlier work of Wu and Van Voorhis [Phys. Rev. A 72, 024502 (2005)], the density functional is minimized under the constraint that the charge difference between donor and acceptor is equal to a given value. The classical ion dynamics is propagated on the Born-Oppenheimer surface of the charge constrained state. We investigate the dependence of the constrained energy and of the energy gap on the definition of the charge and present expressions for the constraint forces. The method is applied to the Ru2+-Ru3+ electron self-exchange reaction in aqueous solution. Sampling the vertical energy gap along CDFT-MD trajectories and correcting for finite size effects, a reorganization free energy of 1.6 eV is obtained. This is 0.1-0.2 eV lower than a previous estimate based on a continuum model for solvation. The smaller value for the reorganization free energy can be explained by the fact that the Ru-O distances of the divalent and trivalent Ru hexahydrates are predicted to be more similar in the electron transfer complex than for the separated aqua ions.

  2. Transient negative photoconductance in a charge transfer double quantum well under optical intersubband excitation

    NASA Astrophysics Data System (ADS)

    Rüfenacht, M.; Tsujino, S.; Sakaki, H.

    1998-06-01

    Recently, it was shown that an electron-hole radiative recombination is induced by a mid-infrared light exciting an intersubband transition in a charge transfer double quantum well (CTDQW). This recombination was attributed to an upstream transfer of electrons from an electron-rich well to a hole-rich well. In this study, we investigated the electrical response of a CTDQW under intersubband optical excitation, and found that a positive photocurrent, opposite in sign and proportional to the applied electric field, accompanies the intersubband-transition-induced luminescence (ITIL) signal. A negative photocurrent component was also observed and attributed to heating processes. This work brings a further evidence of the ITIL process and shows that an important proportion of the carriers are consumed by the transfer of electrons.

  3. Energy transfer in binary collisions of two gyrating charged particles in a magnetic field

    SciTech Connect

    Nersisyan, H. B.; Zwicknagel, G.

    2010-08-15

    Binary collisions of the gyrating charged particles in an external magnetic field are considered within a classical second-order perturbation theory, i.e., up to contributions that are quadratic in the binary interaction, starting from the unperturbed helical motion of the particles. The calculations are done with the help of a binary collision treatment, which is valid for any strength of the magnetic field and involves all harmonics of the particles' cyclotron motion. The energy transfer is explicitly calculated for a regularized and screened potential, which is both of finite range and nonsingular at the origin. The validity of the perturbation treatment is evaluated by comparing with classical trajectory Monte Carlo (CTMC) calculations which also allow one to investigate the strong collisions with large energy and velocity transfer at low velocities. For large initial velocities, on the other hand, only small velocity transfers occur. There the nonperturbative numerical CTMC results agree excellently with the predictions of the perturbative treatment.

  4. Energy transfer in binary collisions of two gyrating charged particles in a magnetic field

    NASA Astrophysics Data System (ADS)

    Nersisyan, H. B.; Zwicknagel, G.

    2010-08-01

    Binary collisions of the gyrating charged particles in an external magnetic field are considered within a classical second-order perturbation theory, i.e., up to contributions that are quadratic in the binary interaction, starting from the unperturbed helical motion of the particles. The calculations are done with the help of a binary collision treatment, which is valid for any strength of the magnetic field and involves all harmonics of the particles' cyclotron motion. The energy transfer is explicitly calculated for a regularized and screened potential, which is both of finite range and nonsingular at the origin. The validity of the perturbation treatment is evaluated by comparing with classical trajectory Monte Carlo (CTMC) calculations which also allow one to investigate the strong collisions with large energy and velocity transfer at low velocities. For large initial velocities, on the other hand, only small velocity transfers occur. There the nonperturbative numerical CTMC results agree excellently with the predictions of the perturbative treatment.

  5. Studies of Photosynthetic Energy and Charge Transfer by Two-dimensional Fourier transform electronic spectroscopy

    NASA Astrophysics Data System (ADS)

    Ogilvie, Jennifer

    2010-03-01

    Two-dimensional (2D) Fourier transform electronic spectroscopy has recently emerged as a powerful tool for the study of energy transfer in complex condensed-phase systems. Its experimental implementation is challenging but can be greatly simplified by implementing a pump-probe geometry, where the two phase-stable collinear pump pulses are created with an acousto-optic pulse-shaper. This approach also allows the use of a continuum probe pulse, expanding the available frequency range of the detection axis and allowing studies of energy transfer and electronic coupling over a broad range of frequencies. We discuss several benefits of 2D electronic spectroscopy and present 2D data on the D1-D2 reaction center complex of Photosystem II from spinach. We discuss the ability of 2D spectroscopy to distinguish between current models of energy and charge transfer in this system.

  6. Molecular orbital (SCF-X?-SW) theory of metal-metal charge transfer processes in minerals - II. Application to Fe2+ --> Ti4+ charge transfer transitions in oxides and silicates

    USGS Publications Warehouse

    Sherman, David M.

    1987-01-01

    A molecular orbital description, based on X?-Scattered wave calculations on a (FeTiO10)14? cluster, is given for Fe2+ ? Ti4+ charge transfer transitions in minerals. The calculated energy for the lowest Fe2+ ? Ti4+ metal-metal charge transfer transition is 18040 cm?1 in reasonable agreement with energies observed in the optical spectra of Fe-Ti oxides and silicates. As in the case of Fe2+ ? Fe3+ charge transfer in mixed-valence iron oxides and silicates, Fe2+ ? Ti4+ charge transfer is associated with Fe-Ti bonding across shared polyhedral edges. Such bonding results from the overlap of the Fe(t 2g ) and Ti(t 2g ) 3d orbitals.

  7. Synergetic approach to many-body problems: From scattering charge transfer to arrays of quantum dots

    NASA Astrophysics Data System (ADS)

    Onufriev, Alexey Vlad

    We call synergetic an approach in which the use of analytical and numerical methods interweave, the results naturally complimenting each other. Analytical results improve numerical approximations and vice versa. We apply this philosophy to two particularly interesting many-body problems involving charge transfer. First, we consider charge transfer between alkali atoms and metallic scattering surfaces. The question is this: what is the final charge state of an atom scattered off a metal surface as a function of its initial state and other experimental parameters, such as atom's velocity and surface work function? We use a generalized time-dependent Newns-Anderson Hamiltonian which includes electron spin, multiple atomic orbitals with image shifted levels, intra-atomic Coulomb repulsion, and resonant exchange. A variational electronic many-body wave function solves the dynamical problem. The wave function consists of sectors with either zero, one, or two particle-hole pairs: the wave function ansatz is equivalent to a 1/N expansion (we set N = 2 for the physical case of electrons). The equations of motion are integrated numerically without further approximation. The solution shows loss-of-memory--the final charge state is independent of the initial one--in agreement with theoretical and experimental expectations. We develop a picture of probability flow between different sectors of the Hilbert space, and show that retaining sectors up to the second order in 1/N is sufficient for an accurate description of charge transfer. As further tests of the theory, we reproduce the experimentally observed peak in the excited neutral Li(2p) occupancy at intermediate work functions starting from different initial conditions. We include Auger processes by adding two-body interaction terms to the many-body Hamiltonian. Preliminary experimental evidence for an upturn in the Li(2p) occupancy at the lowest work-functions may be explained by Auger transitions. Next, we turn our attention to a different class of physical systems which involve charge transfer, namely arrays of semiconducting quantum dots. The physics of these structures is rich, as novel phases are attainable. We find conditions under which enhanced symmetry characterized by the group SU(4) occurs in isolated semiconducting quantum dots. A Hubbard model then describes a pillar array of coupled dots and at half-filling it can be mapped onto a SU(4) spin chain, which has a reach phase diagram. The chain spontaneously dimerizes which we confirm numerically by using a recent numerical technique--the Density Matrix Renormalization Group (DMRG). We suggest further improvements to the method. Our DMRG analysis also shows that this state is robust to perturbations which break SU(4) symmetry. We propose ways to experimentally verify the phases.

  8. Communication: CDFT-CI couplings can be unreliable when there is fractional charge transfer.

    PubMed

    Mavros, Michael G; Van Voorhis, Troy

    2015-12-21

    Constrained density functional theory with configuration interaction (CDFT-CI) is a useful, low-cost tool for the computational prediction of electronic couplings between pseudo-diabatic constrained electronic states. Such couplings are of paramount importance in electron transfer theory and transition state theory, among other areas of chemistry. Unfortunately, CDFT-CI occasionally fails significantly, predicting a coupling that does not decay exponentially with distance and/or overestimating the expected coupling by an order of magnitude or more. In this communication, we show that the eigenvalues of the difference density matrix between the two constrained states can be used as an a priori metric to determine when CDFT-CI are likely to be reliable: when the eigenvalues are near 0 or ±1, transfer of a whole electron is occurring, and CDFT-CI can be trusted. We demonstrate the utility of this metric with several illustrative examples. PMID:26696039

  9. Probing and Exploiting the Interplay between Nuclear and Electronic Motion in Charge Transfer Processes.

    PubMed

    Delor, Milan; Sazanovich, Igor V; Towrie, Michael; Weinstein, Julia A

    2015-04-21

    The Born-Oppenheimer approximation refers to the assumption that the nuclear and electronic wave functions describing a molecular system evolve and can be determined independently. It is now well-known that this approximation often breaks down and that nuclear-electronic (vibronic) coupling contributes greatly to the ultrafast photophysics and photochemistry observed in many systems ranging from simple molecules to biological organisms. In order to probe vibronic coupling in a time-dependent manner, one must use spectroscopic tools capable of correlating the motions of electrons and nuclei on an ultrafast time scale. Recent developments in nonlinear multidimensional electronic and vibrational spectroscopies allow monitoring both electronic and structural factors with unprecedented time and spatial resolution. In this Account, we present recent studies from our group that make use of different variants of frequency-domain transient two-dimensional infrared (T-2DIR) spectroscopy, a pulse sequence combining electronic and vibrational excitations in the form of a UV-visible pump, a narrowband (12 cm(-1)) IR pump, and a broadband (400 cm(-1)) IR probe. In the first example, T-2DIR is used to directly compare vibrational dynamics in the ground and relaxed electronic excited states of Re(Cl)(CO)3(4,4'-diethylester-2,2'-bipyridine) and Ru(4,4'-diethylester-2,2'-bipyridine)2(NCS)2, prototypical charge transfer complexes used in photocatalytic CO2 reduction and electron injection in dye-sensitized solar cells. The experiments show that intramolecular vibrational redistribution (IVR) and vibrational energy transfer (VET) are up to an order of magnitude faster in the triplet charge transfer excited state than in the ground state. These results show the influence of electronic arrangement on vibrational coupling patterns, with direct implications for vibronic coupling mechanisms in charge transfer excited states. In the second example, we show unambiguously that electronic and vibrational movement are coupled in a donor-bridge-acceptor complex based on a Pt(II) trans-acetylide design motif. Time-resolved IR (TRIR) spectroscopy reveals that the rate of electron transfer (ET) is highly dependent on the amount of excess energy localized on the bridge following electronic excitation. Using an adaptation of T-2DIR, we are able to selectively perturb bridge-localized vibrational modes during charge separation, resulting in the donor-acceptor charge separation pathway being completely switched off, with all excess energy redirected toward the formation of a long-lived intraligand triplet state. A series of control experiments reveal that this effect is mode specific: it is only when the high-frequency bridging C?C stretching mode is pumped that radical changes in photoproduct yields are observed. These experiments therefore suggest that one may perturb electronic movement by stimulating structural motion along the reaction coordinate using IR light. These studies add to a growing body of evidence suggesting that controlling the pathways and efficiency of charge transfer may be achieved through synthetic and perturbative approaches aiming to modulate vibronic coupling. Achieving such control would represent a breakthrough for charge transfer-based applications such as solar energy conversion and molecular electronics. PMID:25789559

  10. Synthesis of Stable Interfaces on SnO2 Surfaces for Charge-Transfer Applications

    NASA Astrophysics Data System (ADS)

    Benson, Michelle C.

    The commercial market for solar harvesting devices as an alternative energy source requires them to be both low-cost and efficient to replace or reduce the dependence on fossil fuel burning. Over the last few decades there has been promising efforts towards improving solar devices by using abundant and non-toxic metal oxide nanomaterials. One particular metal oxide of interest has been SnO2 due to its high electron mobility, wide-band gap, and aqueous stability. However SnO2 based solar cells have yet to reach efficiency values of other metal oxides, like TiO2. The advancement of SnO2 based devices is dependent on many factors, including improved methods of surface functionalization that can yield stable interfaces. This work explores the use of a versatile functionalization method through the use of the Cu(I)-catalyzed azide-alkyne cycloaddition (CuAAC) reaction. The CuAAC reaction is capable of producing electrochemically, photochemically, and electrocatalytically active surfaces on a variety of SnO2 materials. The resulting charge-transfer characteristics were investigated as well as an emphasis on understanding the stability of the resulting molecular linkage. We determined the CuAAC reaction is able to proceed through both azide-modified and alkyne-modified surfaces. The resulting charge-transfer properties showed that the molecular tether was capable of supporting charge separation at the interface. We also investigated the enhancement of electron injection upon the introduction of an ultra-thin ZrO2 coating on SnO2. Several complexes were used to fully understand the charge-transfer capabilities, including model systems of ferrocene and a ruthenium coordination complex, a ruthenium mononuclear water oxidation catalyst, and a commercial ruthenium based dye.

  11. Electronic and vibronic properties of a discotic liquid-crystal and its charge transfer complex

    SciTech Connect

    Haverkate, Lucas A.; Mulder, Fokko M.; Zbiri, Mohamed Johnson, Mark R.; Carter, Elizabeth; Kotlewski, Arek; Picken, S.

    2014-01-07

    Discotic liquid crystalline (DLC) charge transfer (CT) complexes combine visible light absorption and rapid charge transfer characteristics, being favorable properties for photovoltaic (PV) applications. We present a detailed study of the electronic and vibrational properties of the prototypic 1:1 mixture of discotic 2,3,6,7,10,11-hexakishexyloxytriphenylene (HAT6) and 2,4,7-trinitro-9-fluorenone (TNF). It is shown that intermolecular charge transfer occurs in the ground state of the complex: a charge delocalization of about 10{sup ?2} electron from the HAT6 core to TNF is deduced from both Raman and our previous NMR measurements [L. A. Haverkate, M. Zbiri, M. R. Johnson, B. Deme, H. J. M. de Groot, F. Lefeber, A. Kotlewski, S. J. Picken, F. M. Mulder, and G. J. Kearley, J. Phys. Chem. B 116, 13098 (2012)], implying the presence of permanent dipoles at the donor-acceptor interface. A combined analysis of density functional theory calculations, resonant Raman and UV-VIS absorption measurements indicate that fast relaxation occurs in the UV region due to intramolecular vibronic coupling of HAT6 quinoidal modes with lower lying electronic states. Relatively slower relaxation in the visible region the excited CT-band of the complex is also indicated, which likely involves motions of the TNF nitro groups. The fast quinoidal relaxation process in the hot UV band of HAT6 relates to pseudo-Jahn-Teller interactions in a single benzene unit, suggesting that the underlying vibronic coupling mechanism can be generic for polyaromatic hydrocarbons. Both the presence of ground state CT dipoles and relatively slow relaxation processes in the excited CT band can be relevant concerning the design of DLC based organic PV systems.

  12. Chandra Observations of the "Dark" Moon and Geocoronal Solar-Wind Charge Transfer

    E-print Network

    B. J. Wargelin; M. Markevitch; M. Juda; V. Kharchenko; R. Edgar; A. Dalgarno

    2004-02-11

    We have analyzed data from two sets of calibration observations of the Moon made by the Chandra X-ray Observatory. In addition to obtaining a spectrum of the bright side that shows several distinct fluorescence lines, we also clearly detect time-variable soft X-ray emission, primarily O VII Ka and O VIII Lya, when viewing the optically dark side. The apparent dark-side brightness varied by at least an order of magnitude, up to 2x10^-6 phot/s/arcmin^2/cm^2 between 500 and 900 eV, which is comparable to the typical 3/4-keV-band background emission measured in the ROSAT All-Sky Survey. The spectrum is also very similar to background spectra recorded by Chandra in low or moderate-brightness regions of the sky. Over a decade ago, ROSAT also detected soft X-rays from the dark side of the Moon, which were tentatively ascribed to continuum emission from energetic solar wind electrons impacting the lunar surface. The Chandra observations, however, with their better spectral resolution, combined with contemporaneous measurements of solar-wind parameters, strongly favor charge transfer between highly charged solar-wind ions and neutral hydrogen in the Earth's geocorona as the mechanism for this emission. We present a theoretical model of geocoronal emission and show that predicted spectra and intensities match the Chandra observations very well. We also model the closely related process of heliospheric charge transfer and estimate that the total charge transfer flux observed from Earth amounts to a significant fraction of the soft X-ray background, particularly in the ROSAT 3/4-keV band.

  13. An accurate and linear-scaling method for calculating charge-transfer excitation energies and diabatic couplings

    E-print Network

    Pavanello, Michele

    Quantum–mechanical methods that are both computationally fast and accurate are not yet available for electronic excitations having charge transfer character. In this work, we present a significant step forward towards this ...

  14. State-selective charge transfer and excitation in ion-ion interactions at intermediate and high energies

    NASA Astrophysics Data System (ADS)

    Samanta, R.; Purkait, M.

    2012-11-01

    Boundary Corrected Continuum Intermediate State (BCCIS) approximation and Classical Trajectory Monte Carlo (CTMC) methods are applied to calculate the charge transfer and excitation cross sections for ion-ion collisions.

  15. Photoexcitation and charge-transfer-to-solvent relaxation dynamics of the I(-)(CH3CN) complex.

    PubMed

    Mak, Chun C; Timerghazin, Qadir K; Peslherbe, Gilles H

    2013-08-15

    Photoexcitation of iodide-acetonitrile clusters, I(-)(CH3CN)n, to the charge-transfer-to-solvent (CTTS) state and subsequent cluster relaxation could result in the possible formation of cluster analogues of the bulk solvated electron. In this work, the relaxation process of the CTTS excited iodide-acetonitrile binary complex, [I(-)(CH3CN)]*, is investigated using rigorous ab initio quantum chemistry calculations and direct-dynamics simulations to gain insight into the role and motion of iodine and acetonitrile in the relaxation of CTTS excited I(-)(CH3CN)n. Computed potential energy curves and profiles of the excited electron vertical detachment energy for [I(-)(CH3CN)]* along the iodine-acetonitrile distance coordinate reveal for the first time significant dispersion effects between iodine and the excited electron, which can have a significant stabilizing effect on the latter. Results of direct-dynamics simulations demonstrate that [I(-)(CH3CN)]* undergoes dissociation to iodine and acetonitrile fragments, resulting in decreased stability of the excited electron. The present work provides strong evidence of solvent translational motion and iodine ejection as key aspects of the early time relaxation of CTTS excited I(-)(CH3CN)n that can also have a substantial impact on the subsequent electron solvation processes and further demonstrates that intricate details of the relaxation process of CTTS excited iodide-polar solvent molecule clusters make it heavily solvent-dependent. PMID:23819756

  16. Effects of partial charge-transfer solute -- solvent interactions in absorption spectra of aromatic hydrocarbons in aqueous and alcoholic solutions

    E-print Network

    I. A. Ar'ev; N. I. Lebovka; E. A. Solovieva

    2013-03-03

    A method for study of charge-transfer interactions between solute molecules and solvent based on the comparison of the ratios of spectral shifts of different electronic transitions in solute molecules in chemically inert solvent is proposed. The method is applicable to molecules that do not change their dipole moment on excitation. As an example, a presence of charge transfer interactions in higher electronic states of aromatic hydrocarbons (benzene, phenanthrene, and naphthalene) dissolved in water and alcohols was demonstrated.

  17. Effects of partial charge-transfer solute -- solvent interactions in absorption spectra of aromatic hydrocarbons in aqueous and alcoholic solutions

    E-print Network

    Ar'ev, I A; Solovieva, E A

    2013-01-01

    A method for study of charge-transfer interactions between solute molecules and solvent based on the comparison of the ratios of spectral shifts of different electronic transitions in solute molecules in chemically inert solvent is proposed. The method is applicable to molecules that do not change their dipole moment on excitation. As an example, a presence of charge transfer interactions in higher electronic states of aromatic hydrocarbons (benzene, phenanthrene, and naphthalene) dissolved in water and alcohols was demonstrated.

  18. Ultrafast Charge Transfer of a Valence Double Hole in Glycine Driven Exclusively by Nuclear Motion

    NASA Astrophysics Data System (ADS)

    Li, Zheng; Vendrell, Oriol; Santra, Robin

    2015-10-01

    We explore theoretically the ultrafast transfer of a double electron hole between the functional groups of glycine after K -shell ionization and subsequent Auger decay. Although a large energy gap of about 15 eV initially exists between the two electronic states involved and coherent electronic dynamics play no role in the hole transfer, we find that the double hole is transferred within 3 to 4 fs between both functional ends of the glycine molecule driven solely by specific nuclear displacements and non-Born-Oppenheimer effects. The nuclear displacements along specific vibrational modes are of the order of 15% of a typical chemical bond between carbon, oxygen, and nitrogen atoms and about 30% for bonds involving hydrogen atoms. The time required for the hole transfer corresponds to less than half a vibrational period of the involved nuclear modes. This finding challenges the common wisdom that nuclear dynamics of the molecular skeleton are unimportant for charge transfer processes at the few-femtosecond time scale and shows that they can even play a prominent role. It also indicates that in x-ray imaging experiments, in which ionization is unavoidable, valence electron redistribution caused by nuclear dynamics might be much faster than previously anticipated. Thus, non-Born-Oppenheimer effects may affect the apparent electron densities extracted from such measurements.

  19. Ultrafast Charge Transfer of a Valence Double Hole in Glycine Driven Exclusively by Nuclear Motion.

    PubMed

    Li, Zheng; Vendrell, Oriol; Santra, Robin

    2015-10-01

    We explore theoretically the ultrafast transfer of a double electron hole between the functional groups of glycine after K-shell ionization and subsequent Auger decay. Although a large energy gap of about 15 eV initially exists between the two electronic states involved and coherent electronic dynamics play no role in the hole transfer, we find that the double hole is transferred within 3 to 4 fs between both functional ends of the glycine molecule driven solely by specific nuclear displacements and non-Born-Oppenheimer effects. The nuclear displacements along specific vibrational modes are of the order of 15% of a typical chemical bond between carbon, oxygen, and nitrogen atoms and about 30% for bonds involving hydrogen atoms. The time required for the hole transfer corresponds to less than half a vibrational period of the involved nuclear modes. This finding challenges the common wisdom that nuclear dynamics of the molecular skeleton are unimportant for charge transfer processes at the few-femtosecond time scale and shows that they can even play a prominent role. It also indicates that in x-ray imaging experiments, in which ionization is unavoidable, valence electron redistribution caused by nuclear dynamics might be much faster than previously anticipated. Thus, non-Born-Oppenheimer effects may affect the apparent electron densities extracted from such measurements. PMID:26551809

  20. Ionic Charge Transfer Complex Induced Visible Light Harvesting and Photocharge Generation in Perovskite.

    PubMed

    Ng, Tsz-Wai; Thachoth Chandran, Hrisheekesh; Chan, Chiu-Yee; Lo, Ming-Fai; Lee, Chun-Sing

    2015-09-16

    Organometal trihalide perovskite has recently emerged as a new class of promising material for high efficiency solar cells applications. While excess ions in perovskites are recently getting a great deal of attention, there is so far no clear understanding on both their formation and relating ions interaction to the photocharge generation in perovskite. Herein, we showed that tremendous ions indeed form during the initial stage of perovskite formation when the organic methylammonium halide (MAXa, Xa=Br and I) meets the inorganic PbXb2 (Xb=Cl, Br, I). The strong charge exchanges between the Pb2+ cations and Xa- anions result in formation of ionic charge transfer complexes (iCTC). MAXa parties induce empty valence electronic states within the forbidden bandgap of PbXb2. The strong surface dipole provide sufficient driving force for sub-bandgap electron transition with energy identical to the optical bandgap of forming perovskites. Evidences from XPS/UPS and photoluminescence studies showed that the light absorption, exciton dissociation, and photocharge generation of the perovskites are closely related to the strong ionic charge transfer interactions between Pb2+ and Xa- ions in the perovskite lattices. Our results shed light on mechanisms of light harvesting and subsequent free carrier generation in perovskites. PMID:26305717

  1. Trifluoromethylmetallate anions as components of molecular charge transfer salts and superconductors.

    SciTech Connect

    Schlueter, J. A.

    1998-10-14

    Whereas polymeric and common inorganic anions frequently deprive the synthetic chemist of a chance to modify a charge transfer salt's structure through anion alterations, discrete organometallic anions provide a vast opportunity to probe the structure/property correlations of a material through rational synthetic methods. We have recently undertaken a research effort aimed at the crystallization of conducting charge transfer salts which possess modifiable, organometallic anions as the charge compensating entities. This research has been richly rewarded with the discovery of a new family of bis(ethylenedithio) tetrathiafulvalene (BEDT-TTF or ET) based molecular superconductors. Herein is presented a summary of over twenty {kappa}(ET){sub 2}M(CF{sub 3}){sub 4}(1,1,2-trihaloethane) (M = Cu, Ag, Au) superconducting salts. Three new related salts are also reported: (ET){sub 2} [trans-Ag(CF{sub 3}),(CN){sub 2}], {kappa}{sub L}(BEDT-TSF){sub 2}Ag(CF{sub 3}){sub 4}(TCE), and {kappa}{sub L}(ET){sub 2}Ag(CF{sub 3}){sub 3}Cl(TCE).

  2. Charge-transfer-based Gas Sensing Using Atomic-layer MoS2

    PubMed Central

    Cho, Byungjin; Hahm, Myung Gwan; Choi, Minseok; Yoon, Jongwon; Kim, Ah Ra; Lee, Young-Joo; Park, Sung-Gyu; Kwon, Jung-Dae; Kim, Chang Su; Song, Myungkwan; Jeong, Yongsoo; Nam, Kee-Seok; Lee, Sangchul; Yoo, Tae Jin; Kang, Chang Goo; Lee, Byoung Hun; Ko, Heung Cho; Ajayan, Pulickel M.; Kim, Dong-Ho

    2015-01-01

    Two-dimensional (2D) molybdenum disulphide (MoS2) atomic layers have a strong potential to be used as 2D electronic sensor components. However, intrinsic synthesis challenges have made this task difficult. In addition, the detection mechanisms for gas molecules are not fully understood. Here, we report a high-performance gas sensor constructed using atomic-layered MoS2 synthesised by chemical vapour deposition (CVD). A highly sensitive and selective gas sensor based on the CVD-synthesised MoS2 was developed. In situ photoluminescence characterisation revealed the charge transfer mechanism between the gas molecules and MoS2, which was validated by theoretical calculations. First-principles density functional theory calculations indicated that NO2 and NH3 molecules have negative adsorption energies (i.e., the adsorption processes are exothermic). Thus, NO2 and NH3 molecules are likely to adsorb onto the surface of the MoS2. The in situ PL characterisation of the changes in the peaks corresponding to charged trions and neutral excitons via gas adsorption processes was used to elucidate the mechanisms of charge transfer between the MoS2 and the gas molecules. PMID:25623472

  3. Non-Radiative Relaxation of Electronically Excited DNA Oligomers: Proton Coupled Charge Transfer

    NASA Astrophysics Data System (ADS)

    Lange, Adrian W.; Herbert, John M.

    2009-06-01

    We address possible relaxation mechanisms of electronically excited DNA oligomers with a combined quantum mechanics/molecular mechanics (QM/MM) approach. Using long-range corrected density functional theory (LRC-DFT), we show that charge transfer (CT) states between neighboring nucleobases appear at energies just above optically bright ^{1}??^{ast} excitonic states in aqueous solution. In double stranded DNA systems, both intrastrand and interstrand CT states are observed. It has been hypothesized that excitonic states may decay via a conical intersection into a CT state on a subpicosecond timescale. The proximity in energy of such states in out calculations appears consistent with this claim. Assuming that such a non-radiative mechanism occurs, we investigate subsequent relaxation of CT states by constructing and optimizing the geometry of model CT systems with constrained density functional theory (CDFT). We find that CT states relax in double stranded DNA through proton transfer across Watson-Crick base pairs with little to no energy barrier. Furthermore, the ground state energy shifts upwards along this reaction coordinate to nearly the same as that of the proton coupled charge transfer state, creating the possibility for a non-radiative pathway to the ground state. Q. Wu and T. Van Voorhis Phys. Rev. A (2005)

  4. Ambipolar Charge Photogeneration and Transfer at GaAs/P3HT Heterointerfaces.

    PubMed

    Panahandeh-Fard, Majid; Yin, Jun; Kurniawan, Michael; Wang, Zilong; Leung, Gle; Sum, Tze Chien; Soci, Cesare

    2014-04-01

    Recent work on hybrid photovoltaic systems based on conjugated polymers and III-V compound semiconductors with relatively high power conversion efficiency revived fundamental questions regarding the nature of charge separation and transfer at the interface between organic and inorganic semiconductors with different degrees of delocalization. In this work, we studied photoinduced charge generation and interfacial transfer dynamics in a prototypical photovoltaic n-type GaAs (111)B and poly(3-hexyl-thiophene) (P3HT) bilayer system. Ultrafast spectroscopy and density functional theory calculations indicate the coexistence of electron and hole transfer at the GaAs/P3HT interface, leading to the generation of long-lived species and photoinduced absorption upon creation of hybrid interfacial states. This opens up new avenues for the use of low-dimensional III-V compounds (e.g., nanowires or quantum dots) in hybrid organic/inorganic photovoltaics, where advanced bandgap and density of states engineering may also be exploited as design parameters. PMID:26274462

  5. Engineering interfacial photo-induced charge transfer based on nanobamboo array architecture for efficient solar-to-chemical energy conversion.

    PubMed

    Wang, Xiaotian; Liow, Chihao; Bisht, Ankit; Liu, Xinfeng; Sum, Tze Chien; Chen, Xiaodong; Li, Shuzhou

    2015-04-01

    Engineering interfacial photo-induced charge transfer for highly synergistic photocatalysis is successfully realized based on nanobamboo array architecture. Programmable assemblies of various components and heterogeneous interfaces, and, in turn, engineering of the energy band structure along the charge transport pathways, play a critical role in generating excellent synergistic effects of multiple components for promoting photocatalytic efficiency. PMID:25704499

  6. Axi-symmetric models of ultraviolet radiative transfer with applications to circumstellar disk chemistry

    E-print Network

    Gerd-Jan van Zadelhoff; Yuri Aikawa; M. R. Hogerheijde; Ewine F. van Dishoeck

    2002-11-01

    A new two-dimensional axi-symmetric ultraviolet radiative transfer code is presented, which is used to calculate photodissociation and ionization rates for use in chemistry models of flaring circumstellar disks. Scattering and absorption of photons from the central star and from the interstellar radiation field are taken into account. The molecules are effectively photodissociated in the surface layer of the disk, but can exist in the intermediate, moderately warm layers. A comparison has been made with an approximate 2D ray-tracing method and it was found that the latter underestimates the ultraviolet field and thus the molecular photodissociation rates below the disk surface. The full 2D results show significantly higher abundances of radicals such as CN and C2H than previous work, partly due to the fact that CO is dissociated to greater depths. Results for different stellar radiation fields are also presented. The CN/HCN ratio shows a strong dependence on the stellar spectrum, whereas other ratios such as HCO+/CO show only little variation.

  7. First Year Chemistry Laboratory Courses for Distance Learners: Development and Transfer Credit Acceptance

    ERIC Educational Resources Information Center

    Brewer, Sharon E.; Cinel, Bruno; Harrison, Michelle; Mohr, Christina L.

    2013-01-01

    In delivering chemistry courses by distance, a key challenge is to offer the learner an authentic and meaningful laboratory experience that still provides the rigour required to continue on in science. To satisfy this need, two distance general chemistry laboratory courses appropriate for Bachelor of Science (B.Sc.) students, including chemistry

  8. C-13 N.M.R. study of charge transfer in alkali metal-ammonia graphite compounds

    NASA Technical Reports Server (NTRS)

    Tsang, T.; Fronko, R. M.; Resing, H. A.; Qian, X. W.; Solin, S. A.

    1987-01-01

    The usefulness of C-13 NMR spectroscopy and chemical shift for the study of charge transfer in graphite intercalation compounds is demonstrated. A linear relationship is established between the chemical shifts and the square root of the absolute value of the electronic charge per carbon atom. The method is applied to the ternary alkali metal-ammonia-graphite compounds. Weak solvations of electronic charges by ammonia are observed.

  9. Charge transfer during low energy metal/semiconductor ion-surface interactions

    NASA Astrophysics Data System (ADS)

    Chen, Xiaojian

    Ion-surface charge exchange is a central process in many surface analysis techniques and technical processes. Previous ion scattering studies have extensively investigated the interactions between alkali/noble gas ions and surfaces. Investigations of the interactions between metal/semiconductor ions and metal surfaces have seldom been reported, although they are of central importance in understanding processes involving the removal material from metal/semiconductor surfaces. This dissertation uses low energy ion scattering and direct recoil to reveal charge transfer mechanisms between metal/semiconductor atomic particles and clean and adsorb ate-covered Al and Si surfaces. All involved experiments were performed in ultra-high vacuum. Charge transfer between an Al atom and an Al surface is studied by producing energetic recoiled Al from a Al(100) surface via Xe+ bombardment. The measured neutral fractions of the recoils show that resonant charge transfer (RCT) is a key mechanism. The ion formation of recoiled and sputtered atoms can be both described by RCT. The characteristic difference between recoiled and sputtered atoms is interpreted as due to different surface conditions at the time of ion emission. 1˜5 keV Si+ ions were incident on atomically clean Al(100) surface. All scattered Si was neutralized, while Al ions were found in multi-charged states. In contrast to the traditional sputtering studies, there is an abnormally high yield of Al2+ and Al3+. The multiply charged ions are attributed to the charge promotion of Al 2p level during the electronically nearly-symmetric Si-Al collision, and subsequent shake-off processes. This mechanism is supported by the energy dependence of Al ions as well as ion induced Auger electrons. Si+ ions were scattered from submonolayers of Cs deposited onto Al(100). Because of the high ionization energy of Si, resonant charge transfer would be expected to completely neutralize the scattered projectiles. In contrast, a considerable fraction of the Si scatters from the adatoms as positive and negative ions. Negative ions are produced by normal RCT when the work function is lowered. It is proposed that the positive ions are produced by the promotion of Si ionization level, which interacts with the I 5p level during the collision. The final ion fraction is then determined by RCT as the Si level crosses the Fermi energy along the exit trajectory. Similar ionization formation were observed for Si scattered from I adatoms on Al(100) and Si(111) surfaces. The promotion of the ionization level of Si is still invoked to explain the ion formation. The ion fractions, however, are lower than expected if only the surface potential and promotion are considered. This can be explained as a new neutralization channel resulting from the chemisorption states of the I adatom.

  10. Photoconductive response in organic charge transfer interfaces with high quantum efficiency

    NASA Astrophysics Data System (ADS)

    Alves, Helena; Pinto, Rui M.; Maçôas, Ermelinda S.

    2013-05-01

    Organic semiconductors have unique optical, mechanical and electronic properties that can be combined with customized chemical functionality. In the crystalline form, determinant features for electronic applications, such as molecular purity, the charge mobility or the exciton diffusion length, reveal a superior improved performance when compared with materials in a more disordered form. However, the use of organic single crystals in devices is still limited to a few applications, such as field-effect transistors. Here we report the first example of photoconductive behaviour of single-crystal charge-transfer interfaces. The system composed of rubrene and 7,7,8,8-tetracyanoquinodimethane presents a responsivity reaching 1?A?W-1, corresponding to an external quantum efficiency of nearly 100%. This result opens the possibility of using organic single-crystal interfaces in photonic applications.

  11. Photoconductive response in organic charge transfer interfaces with high quantum efficiency.

    PubMed

    Alves, Helena; Pinto, Rui M; Maçôas, Ermelinda S

    2013-01-01

    Organic semiconductors have unique optical, mechanical and electronic properties that can be combined with customized chemical functionality. In the crystalline form, determinant features for electronic applications, such as molecular purity, the charge mobility or the exciton diffusion length, reveal a superior improved performance when compared with materials in a more disordered form. However, the use of organic single crystals in devices is still limited to a few applications, such as field-effect transistors. Here we report the first example of photoconductive behaviour of single-crystal charge-transfer interfaces. The system composed of rubrene and 7,7,8,8-tetracyanoquinodimethane presents a responsivity reaching 1 AW(-1), corresponding to an external quantum efficiency of nearly 100%. This result opens the possibility of using organic single-crystal interfaces in photonic applications. PMID:23673627

  12. Doping Dependent Charge Transfer Gap and Realistic Electronic Model of n-type Cuprate Superconductors

    SciTech Connect

    Xiang, T.

    2010-05-03

    Based on the analysis of the measurement data of angle-resolved photoemission spectroscopy (ARPES) and optics, we show that the charge transfer gap is significantly smaller than the optical one and is reduced by doping in electron doped cuprate superconductors. This leads to a strong charge fluctuation between the Zhang-Rice singlet and the upper Hubbard bands. The basic model for describing this system is a hybridized two-band t-J model. In the symmetric limit where the corresponding intra- and inter-band hopping integrals are equal to each other, this two-band model is equivalent to the Hubbard model with an antiferromagnetic exchange interaction (i.e. the t-U-J model). The mean-field result of the t-U-J model gives a good account for the doping evolution of the Fermi surface and the staggered magnetization.

  13. Photophysics and charge transfer in donor-acceptor triblock copolymer photovoltaic materials

    NASA Astrophysics Data System (ADS)

    Schwarz, Kyra N.; Jones, David J.; Smith, Trevor A.; Ghiggino, Kenneth P.

    2014-10-01

    Efficient conversion of solar energy to electricity in low-cost organic photovoltaic (OPV) devices requires the complex interplay between multiple processes and components over various length and time scales. Optimizing device morphology to ensure efficient exciton diffusion and charge transport as well as ensuring efficient charge photogeneration is necessary to achieve optimum performance in new materials. The conjugated polymer electron donor PFM (poly(9,9-diocetyluorene-co-bis-N,N-(4-methylphenyl)-bis-N,N-phenyl-1,4-phenylenediamine)) and electron acceptor F8BT (poly[(9,9-di-n-octyluorenyl-2,7-diyl)-alt-(benzo[2,1,3]thiadiazol-4,8-diyl)), comprise the novel triblock copolymer PFM-F8BT-PFM. This copolymer is designed to phase separate on the 20-30 nm scale, a domain size ideal for maximizing exciton collection at the donor-acceptor interface. Using steady-state and ultrafast spectroscopic characterization including high repetition rate transient absorption spectroscopy, the dynamics of charge and energy transfer of the component polymers and the triblock co-polymer have been investigated. The results demonstrate that for the homopolymers solvent dependent exciton transport processes dominate, while in the triblock copolymer solutions transient spectroscopy provides evidence for interfacial charge separation.

  14. How well can charge transfer inefficiency be corrected? A parameter sensitivity study for iterative correction

    NASA Astrophysics Data System (ADS)

    Israel, Holger; Massey, Richard; Prod'homme, Thibaut; Cropper, Mark; Cordes, Oliver; Gow, Jason; Kohley, Ralf; Marggraf, Ole; Niemi, Sami; Rhodes, Jason; Short, Alex; Verhoeve, Peter

    2015-10-01

    Radiation damage to space-based charge-coupled device detectors creates defects which result in an increasing charge transfer inefficiency (CTI) that causes spurious image trailing. Most of the trailing can be corrected during post-processing, by modelling the charge trapping and moving electrons back to where they belong. However, such correction is not perfect - and damage is continuing to accumulate in orbit. To aid future development, we quantify the limitations of current approaches, and determine where imperfect knowledge of model parameters most degrades measurements of photometry and morphology. As a concrete application, we simulate 1.5 × 109 `worst-case' galaxy and 1.5 × 108 star images to test the performance of the Euclid visual instrument detectors. There are two separable challenges. If the model used to correct CTI is perfectly the same as that used to add CTI, 99.68 per cent of spurious ellipticity is corrected in our setup. This is because readout noise is not subject to CTI, but gets overcorrected during correction. Secondly, if we assume the first issue to be solved, knowledge of the charge trap density within ??/? = (0.0272 ± 0.0005) per cent and the characteristic release time of the dominant species to be known within ??/? = (0.0400 ± 0.0004) per cent will be required. This work presents the next level of definition of in-orbit CTI calibration procedures for Euclid.

  15. Energy transfer through a multi-layer liner for shaped charges

    DOEpatents

    Skolnick, Saul (Albuquerque, NM); Goodman, Albert (Albuquerque, NM)

    1985-01-01

    This invention relates to the determination of parameters for selecting materials for use as liners in shaped charges to transfer the greatest amount of energy to the explosive jet. Multi-layer liners constructed of metal in shaped charges for oil well perforators or other applications are selected in accordance with the invention to maximize the penetrating effect of the explosive jet by reference to four parameters: (1) Adjusting the explosive charge to liner mass ratio to achieve a balance between the amount of explosive used in a shaped charge and the areal density of the liner material; (2) Adjusting the ductility of each layer of a multi-layer liner to enhance the formation of a longer energy jet; (3) Buffering the intermediate layers of a multi-layer liner by varying the properties of each layer, e.g., composition, thickness, ductility, acoustic impedance and areal density, to protect the final inside layer of high density material from shattering upon impact of the explosive force and, instead, flow smoothly into a jet; and (4) Adjusting the impedance of the layers in a liner to enhance the transmission and reduce the reflection of explosive energy across the interface between layers.

  16. Collisions of fast multicharged ions in gas targets: charge transfer and ionization

    SciTech Connect

    Schlachter, A.S.

    1981-05-01

    Measurements of cross sections for charge transfer and ionization of H/sub 2/ and rare-gas targets have been made with fast, highly stripped projectiles in charge states as high as 59+. We have found an empirical scaling rule for electron-capture cross section in H/sub 2/ valid at energies above 275 keV/amu. Similar scaling might exist for other target gases. Cross sections are generally in good agreement with theory. We have found a scaling rule for electron loss from H in collisions with a fast highly stripped projectile, based on Olson's classical-trajectory Monte-Carlo calculations, and confirmed by measurements in an H/sub 2/ target. We have found a similar scaling rule for net ionization of rare-gas targets, based on Olson's CTMC calculations and the independent-electron model. Measurements are essentially consistent with the scaled cross sections. Calculations and measurements of recoil-ion charge-state spectra show large cross sections for the production of highly charged slow recoil ions.

  17. Charge-transfer complexes of 4-nitrocatechol with some amino alcohols.

    PubMed

    Baniyaghoob, Sahar; Najafpour, Mohammad Mahdi; Boghaei, Davar M

    2010-03-01

    Charge-transfer (CT) complexes formed from the reactions of 4-nitropyrocatechol (4-nCat) as an electron acceptor with four amino alcohols: 2-aminoethanol, 1-amino-2-propanol, 4-aminobutanol and N-(2-hydroxyethyl)-1,3-diaminopropane (NHEDAP) as electron donors, have been studied spectrophotometrically in H(2)O and H(2)O/EtOH at 20, 25, 30, 35 and 40 degrees C. The calculated values of the oscillator strength and transition moment confirm the formation of CT-complexes. The thermodynamic and spectroscopic parameters were also evaluated for the formation of CT-complexes. The equilibrium constants ranged from 9.00 to 2.20 l mol(-1) (M(-1)). These interactions are exothermic and have relatively large standard enthalpy and entropy changes (DeltaH values ranged from -15.58 to -3.10 kJ mol(-1); DeltaS ranged from 26.81 to -3.25 J K(-1)mol(-1)). The solid CT-complexes have been synthesized and characterized by IR, NMR, mass spectrometry and thermal analysis. The photometric titration curves and other spectrometric data for the reactions indicated that the data obtained refer to the formation of 1:1 charge-transfer complex of [(4-nCat) (NHEDAP)] and 1:2 charge-transfer complexes of other amino alcohols [(4-nCat) (amino alcohol)(2)]. The effect of alkali and alkaline earth metals on increasing the equilibrium constant of the CT-complexation was also investigated. PMID:20061181

  18. Theoretical Investigation of OCN(-) Charge Transfer Complexes in Condensed Phase Media: Spectroscopic Properties in Amorphous Ice

    NASA Technical Reports Server (NTRS)

    Park, Jin-Young; Woon, David E.

    2004-01-01

    Density functional theory (DFT) calculations of cyanate (OCN(-)) charge-transfer complexes were performed to model the "XCN" feature observed in interstellar icy grain mantles. OCN(-) charge-transfer complexes were formed from precursor combinations of HNCO or HOCN with either NH3 or H2O. Three different solvation strategies for realistically modeling the ice matrix environment were explored, including (1) continuum solvation, (2) pure DFT cluster calculations, and (3) an ONIOM DFT/PM3 cluster calculation. The model complexes were evaluated by their ability to reproduce seven spectroscopic measurements associated with XCN: the band origin of the OCN(-) asymmetric stretching mode, shifts in that frequency due to isotopic substitutions of C, N, O, and H, plus two weak features. The continuum solvent field method produced results consistent with some of the experimental data but failed to account for other behavior due to its limited capacity to describe molecular interactions with solvent. DFT cluster calculations successfully reproduced the available spectroscopic measurements very well. In particular, the deuterium shift showed excellent agreement in complexes where OCN(-) was fully solvated. Detailed studies of representative complexes including from two to twelve water molecules allowed the exploration of various possible solvation structures and provided insights into solvation trends. Moreover, complexes arising from cyanic or isocyanic acid in pure water suggested an alternative mechanism for the formation of OCN(-) charge-transfer complexes without the need for a strong base such as NH3 to be present. An extended ONIOM (B3LYP/PM3) cluster calculation was also performed to assess the impact of a more realistic environment on HNCO dissociation in pure water.

  19. Charge transfer fluorescence and 34 nm exciton diffusion length in polymers with electron acceptor end traps

    DOE PAGESBeta

    Zaikowski, Lori; Mauro, Gina; Bird, Matthew; Karten, Brianne; Asaoka, Sadayuki; Wu, Qin; Cook, Andrew R.; Miller, John R.

    2014-12-22

    Photoexcitation of conjugated poly-2,7-(9,9-dihexylfluorene) polyfluorenes with naphthylimide (NI) and anthraquinone (AQ) electron-acceptor end traps produces excitons that form charge transfer states at the end traps. Intramolecular singlet exciton transport to end traps was examined by steady state fluorescence for polyfluorenes of 17 to 127 repeat units in chloroform, dimethylformamide (DMF), tetrahydrofuran (THF), and p-xylene. End traps capture excitons and form charge transfer (CT) states at all polymer lengths and in all solvents. The CT nature of the end-trapped states is confirmed by their fluorescence spectra, solvent and trap group dependence and DFT descriptions. Quantum yields of CT fluorescence are asmore »large as 46%. This strong CT emission is understood in terms of intensity borrowing. Energies of the CT states from onsets of the fluorescence spectra give the depths of the traps which vary with solvent polarity. For NI end traps the trap depths are 0.06 (p-xylene), 0.13 (THF) and 0.19 eV (CHCl3). For AQ, CT fluorescence could be observed only in p-xylene where the trap depth is 0.27 eV. Quantum yields, emission energies, charge transfer energies, solvent reorganization and vibrational energies were calculated. Fluorescence measurements on chains >100 repeat units indicate that end traps capture ~50% of the excitons, and that the exciton diffusion length LD =34 nm, which is much larger than diffusion lengths reported in polymer films or than previously known for diffusion along isolated chains. As a result, the efficiency of exciton capture depends on chain length, but not on trap depth, solvent polarity or which trap group is present.« less

  20. Charge transfer fluorescence and 34 nm exciton diffusion length in polymers with electron acceptor end traps

    SciTech Connect

    Zaikowski, Lori; Mauro, Gina; Bird, Matthew; Karten, Brianne; Asaoka, Sadayuki; Wu, Qin; Cook, Andrew R.; Miller, John R.

    2014-12-22

    Photoexcitation of conjugated poly-2,7-(9,9-dihexylfluorene) polyfluorenes with naphthylimide (NI) and anthraquinone (AQ) electron-acceptor end traps produces excitons that form charge transfer states at the end traps. Intramolecular singlet exciton transport to end traps was examined by steady state fluorescence for polyfluorenes of 17 to 127 repeat units in chloroform, dimethylformamide (DMF), tetrahydrofuran (THF), and p-xylene. End traps capture excitons and form charge transfer (CT) states at all polymer lengths and in all solvents. The CT nature of the end-trapped states is confirmed by their fluorescence spectra, solvent and trap group dependence and DFT descriptions. Quantum yields of CT fluorescence are as large as 46%. This strong CT emission is understood in terms of intensity borrowing. Energies of the CT states from onsets of the fluorescence spectra give the depths of the traps which vary with solvent polarity. For NI end traps the trap depths are 0.06 (p-xylene), 0.13 (THF) and 0.19 eV (CHCl3). For AQ, CT fluorescence could be observed only in p-xylene where the trap depth is 0.27 eV. Quantum yields, emission energies, charge transfer energies, solvent reorganization and vibrational energies were calculated. Fluorescence measurements on chains >100 repeat units indicate that end traps capture ~50% of the excitons, and that the exciton diffusion length LD =34 nm, which is much larger than diffusion lengths reported in polymer films or than previously known for diffusion along isolated chains. As a result, the efficiency of exciton capture depends on chain length, but not on trap depth, solvent polarity or which trap group is present.

  1. [Solvent effect of europium (III) complex sensitized by charge transfer excited state of functional cation].

    PubMed

    Fu, Shi-rong; Shi, Meng; Han, Pei-gao; Zhang, Bei-bei; Yan, Ke-zhu

    2013-09-01

    Abstract In the novel europium (IIl) complex of the form [Eu(tta)4 . DEASPI], the sensitization of lanthanide luminescence is via functional cation The photophysical sensitization process of Eu(tta)4 . DEASPI involves an energy transfer from charge transfer excited state of hemicyanine (aminostyrylpyridinium) cation, and the sensitization mechanism follows Förster resonance energy mechanism. The solvent effect on this new kind of europium (III) complex was investigated in the present work. The europium (III) complex was dissolved in a variety of solvents, i.e., acetone, DMF, ethanol and acetonitrile, and the emission intensity of europium (III) complex in acetonitrile is much higher than in other solvents. The detailed discussion about solvent effect is provided in this paper. PMID:24369661

  2. Charge transfer fluorescence and f-f luminescence in ytterbium compounds

    NASA Astrophysics Data System (ADS)

    Kamenskikh, I. A.; Guerassimova, N.; Dujardin, C.; Garnier, N.; Ledoux, G.; Pedrini, C.; Kirm, M.; Petrosyan, A.; Spassky, D.

    2003-10-01

    Luminescence and excitation spectra as well as decay kinetics are presented for the charge transfer (CT) luminescence of Lu 3Al 5O 12, Y 3Ga 5O 12 and YAlO 3 crystals doped by Yb 3+ in various concentrations, the CT luminescence properties are compared to those of Y 3Al 5O 12-Yb. For the first time the excitation spectra of the intraconfigurational 2F 5/2 ? 2F 7/2 luminescence of Yb 3+ ions in YAG, LuAG and YAP in the region of the CT absorption band and in the fundamental absorption range up to 20 eV were measured, possible mechanisms of the energy transfer to Yb 3+ 4f states are discussed.

  3. Correlation between charge transfer exciton recombination and photocurrent in polymer/fullerene solar cells

    SciTech Connect

    Hallermann, Markus; Da Como, Enrico; Feldmann, Jochen; Izquierdo, Marta; Filippone, Salvatore; Martin, Nazario; Juechter, Sabrina; Hauff, Elizabeth von

    2010-07-12

    We correlate carrier recombination via charge transfer excitons (CTEs) with the short circuit current, J{sub sc}, in polymer/fullerene solar cells. Near infrared photoluminescence spectroscopy of CTE in three blends differing for the fullerene acceptor, gives unique insights into solar cell characteristics. The energetic position of the CTE is directly correlated with the open-circuit voltage, V{sub oc}, and more important J{sub sc} decreases with increasing CTE emission intensity. CTE emission intensity is discussed from the perspective of blend morphology. The work points out the fundamental role of CTE recombination and how optical spectroscopy can be used to derive information on solar cell performances.

  4. Charge Transfer in Single Chains of a Donor–Acceptor Conjugated Tri-Block Copolymer

    E-print Network

    Hooley, Emma N.; Jones, David J.; Greenham, Neil C.

    2014-11-24

    polarity (SI Figure 2 and SI Table 1). F8BT undergoes a red-shift of 37 nm (1300 cm-1), from 512 nm in cyclohexane to 549 nm in benzonitrile, whereas for PFM, a much larger shift of 95 nm (4100 cm-1) occurs on going from cyclohexane to dichloromethane... ) athe numbers in parentheses are the fractions of light emitted (as a %) attributable to each component. In addition to the formation of excited state complexes, donor-acceptor copolymers are capable of intra-molecular charge transfer...

  5. Trends in charge transfer and spin alignment of metallocene on graphene

    NASA Astrophysics Data System (ADS)

    Li, Yuanchang; Chen, Xiaobin; Zhou, Gang; Duan, Wenhui; Kim, Youngkuk; Kim, Minsung; Ihm, Jisoon

    2011-05-01

    By using the first-principles calculations, geometric, electronic, and magnetic properties of metallocene deposited on graphene are systematically investigated. Among all the metallocenes studied, only cobaltocene exhibits obvious charge transfer. Relatively delocalized e1 orbitals of cobaltocene are responsible for n-type doping of graphene or nanoribbons, as well as for the spin-polarized current along the cobaltocene chains. We also propose that, based on our total energy calculations, cobaltocene may be used as a sensor to detect pentagonal defects in graphene by taking advantage of the rotation of cobaltocene’s axis when located above pentagonal defects.

  6. Nanohydration of uracil: emergence of three-dimensional structures and proton-induced charge transfer.

    PubMed

    Bacchus-Montabonel, Marie-Christine; Calvo, Florent

    2015-04-21

    Stepwise hydration of uracil has been theoretically revisited using different methods ranging from classical force fields to quantum chemical approaches. Hydration initially begins within the uracil plane but proceeds at four molecules into three-dimensional configurations or even water clusters next to the nucleobase. The relative stability between the various structures is significantly affected by zero-point energy and finite temperature (entropy) effects and also gives rise to markedly different responses to an excitation by an impinging high-energy proton. In particular, charge transfer to the molecular complex is dramatically altered in collisions toward the coating cluster but barely modified for peripheral hydration patterns. PMID:25793649

  7. Molecular distortion and charge transfer effects in ZnPc/Cu(111)

    PubMed Central

    Amin, B.; Nazir, S.; Schwingenschlögl, U.

    2013-01-01

    The adsorption geometry and electronic properties of a zinc-phthalocyanine molecule on a Cu(111) substrate are studied by density functional theory. In agreement with experiment, we find remarkable distortions of the molecule, mainly as the central Zn atom tends towards the substrate to minimize the Zn-Cu distance. As a consequence, the Zn-N chemical bonding and energy levels of the molecule are significantly modified. However, charge transfer induces metallic states on the molecule and therefore is more important for the ZnPc/Cu(111) system than the structural distortions.

  8. Inner-Shell Charge-Transfer in Asymmetric Ion-Atom Collisions 

    E-print Network

    Reading, John F.; Ford, A. Lewis; Swafford, G. L.; Fitchard, A.

    1979-01-01

    (Received 10 February 1978) A method used previously for inner-shell ionization in asymmetric ion-atom collisions is extended to include charge transfer between the target inner shells and projectile E shell. We work in the energy rangeq'" = Rv/Z?e' & 1... consider R ?=(B, Z) =(5,vt), where B is the impact parameter and z, the velocity of the projectile, is assumed constant. The function V((r ?R(t)) is the interaction between the active electron and the projectile nu- cleus, and W(R) is a function...

  9. Temperature dependence of the phosphorescence of naphthalene-tetrachlorophthalic anhydride charge-transfer crystal complex

    SciTech Connect

    Avedeenko, A.A.; Karachevtsev, V.A.; Naboikin, Yu.V.

    1987-10-01

    In studying real crystals the presence of structural defects must always be taken into account. At the distorted nodes the donor-acceptor distance can differ from that in an undistorted crystal, which is reflected in the magnitude of the charge transfer. Since the electron-phonon interaction in such crystals depends on this magnitude, the spectrum of their triplet luminescence will contain not only structural phosphorescence, but also wide phosphorescence bands of various defects. This paper investigates the phosphorescence spectrum of the title crystal in the interval 1.4-77 K and the possible role of strong distortions in the crystal in the formation of excitation cells.

  10. Charge transfer in time-dependent density-functional theory via spin-symmetry breaking

    SciTech Connect

    Fuks, Johanna I.; Maitra, Neepa T.

    2011-04-15

    Long-range charge-transfer excitations pose a major challenge for time-dependent density-functional approximations. We show that spin-symmetry breaking offers a simple solution for molecules composed of open-shell fragments, yielding accurate excitations at large separations when the acceptor effectively contains one active electron. Unrestricted exact-exchange and self-interaction-corrected functionals are performed on one-dimensional models and on the real LiH molecule within the pseudopotential approximation to demonstrate our results.

  11. Organic Nano-transistors Wired by Oriented Charge Transfer Complex Crystal

    NASA Astrophysics Data System (ADS)

    Sakai, Masatoshi; Yajima, Eiji; Sakuma, Hirotaka; Iizuka, Masaaki; Nakamura, Masakazu; Kudo, Kazuhiro

    We have fabricated high conducting organic wires and self-wired nano-transistors of tetrathiafulvalene (TTF) and tetracyanoquinodimethane (TCNQ) charge transfer complex using co-evaporation method with an electric field. The conducting wires which directly bridge two gold electrodes indicated high-conductive ohmic contact with the gold electrode. Self-wired organic field effect transistor was formed at the connecting point of conductive wires. Field effect transistor characteristics of nano-transistor exhibited n-channel behavior with on/off ratio of 110. The length of active layer was estimated to be approximately a few nanometer.

  12. Estimation of instantaneous heat transfer coefficients for a direct-injection stratified-charge rotary engine

    NASA Technical Reports Server (NTRS)

    Lee, C. M.; Addy, H. E.; Bond, T. H.; Chun, K. S.; Lu, C. Y.

    1987-01-01

    The main objective of this report was to derive equations to estimate heat transfer coefficients in both the combustion chamber and coolant pasage of a rotary engine. This was accomplished by making detailed temperature and pressure measurements in a direct-injection stratified-charge rotary engine under a range of conditions. For each sppecific measurement point, the local physical properties of the fluids were calculated. Then an empirical correlation of the coefficients was derived by using a multiple regression program. This correlation expresses the Nusselt number as a function of the Prandtl number and Reynolds number.

  13. Estimation of instantaneous heat transfer coefficients for a direct-injection stratified-charge rotary engine

    SciTech Connect

    Lee, C.M.; Addy, H.E.; Bond, T.H.; Chun, K.S.

    1987-01-01

    The main objective of this report was to derive equations to estimate neat transfer coefficients in both the combustion chamber and coolant passage of a rotary engine. This was accomplished by making detailed temperature and pressure measurements in a direct-injection stratified-charge rotary engine under a range of conditions. For each specific measurement point, the local physical properties of the fluids were calculated. Then an empirical correlation of the coefficients was derived by using a multiple regression program. This correlation expresses the Nusselt number as a function of the Prandtl number and Reynolds number.

  14. Metallization and charge-transfer gap closure of transition-metal iodides under pressure

    SciTech Connect

    Chen, A. Li-Chung

    1993-05-01

    It is shown with resistivity and near-IR absorption measurements that NiI{sub 2}, CoI{sub 2}, and FeI{sub 2} metallize under pressure by closure of the charge-transfer energy gap at pressures of 17, 10, and 23 GPa, respectively, which is close to the antiferromagnetic-diamagnetic transition in NiI{sub 2} and CoI{sub 2}. Thus, the magnetic transitions probably are caused by the metallization; in NiI{sub 2} and CoI{sub 2}, the insulator-metal transitions are first order. Moessbauer and XRD data were also collected. Figs, 46 refs.

  15. On the charge transfer between single-walled carbon nanotubes and graphene

    SciTech Connect

    Rao, Rahul Pierce, Neal; Dasgupta, Archi

    2014-08-18

    It is important to understand the electronic interaction between single-walled carbon nanotubes (SWNTs) and graphene in order to use them efficiently in multifunctional hybrid devices. Here, we deposited SWNT bundles on graphene-covered copper and SiO{sub 2} substrates by chemical vapor deposition and investigated the charge transfer between them by Raman spectroscopy. Our results revealed that, on both copper and SiO{sub 2} substrates, graphene donates electrons to the SWNTs, resulting in p-type doped graphene and n-type doped SWNTs.

  16. Radical anion salts and charge transfer complexes based on tetracyanoquinodimethane and other strong ?-electron acceptors

    NASA Astrophysics Data System (ADS)

    Starodub, V. A.; Starodub, T. N.

    2014-05-01

    The unique properties of radical anion salts and charge transfer complexes formed by tetracyanoquinodimethane and other strong ?-electron acceptors are analyzed. Their ability to form fusible conductive materials and magnetically ordered structures, including ferromagnetic ones with high Curie temperatures, spin ladders and quasi-two-dimensional organic conductors and superconductors is considered. Particular attention is given to the possible areas of application of these radical anion salts in electronic industry as nanomaterials, materials for the fabrication of field effect transistors, photodiodes and ion selective electrodes. The bibliography includes 421 references.

  17. Spectroscopy of charge transfer complexes of four amino acids as organic two-dimensional conductors

    NASA Astrophysics Data System (ADS)

    Padhiyar, Ashvin; Patel, A. J.; Oza, A. T.

    2007-12-01

    It is found in this study that four amino acids, namely asparagine, arginine, histidine and glutamine form two-dimensional conducting systems which are charge transfer complexes (CTCs) with organic acceptors like TCNQ, TCNE, chloranil, DDQ, TNF and iodine. It is verified using optical absorption edges that these are 2d conductors like transition metal dichalcogenides obeying absorption functions different from 1d and 3d conductors. This 2d nature is related to the network of intermolecular H-bonding in these complexes, which leads to a global H-bonded network resulting in the absence of local deformation due to the relaxation of strain.

  18. 46 CFR 154.1831 - Persons in charge of transferring liquid cargo in bulk or preparing cargo tanks.

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... CFR 155.710; (3) On each foreign tankship, the person in charge of either a transfer of liquid cargo... required by 33 CFR 155.710; (4) When cargo regulated under this part is being transferred, the person in... in bulk or a cool-down, warm-up, gas-free, or air-out of each cargo tank; (2) Each transfer of...

  19. The influences of the transfer method and particle surface chemistry on the dispersion of nanoparticles in nanocomposites

    NASA Astrophysics Data System (ADS)

    Pravaz, Olivier; Droz, Benoît; Schurtenberger, Peter; Dietsch, Hervé

    2012-10-01

    The synthesis via in situ polymerization and characterization of nanocomposites (NCs) made from silica (SiO2) nanoparticles in a methyl methacrylate (MMA) monomer matrix is reported. We first investigate the transfer of well-defined spherical silica nanoparticles (NPs) (average radius R = 24.2 +/- 3.2 nm) into the monomer solvent. We study the influence of two transfer methods and different surface chemistries on the resulting colloidal stability. The first transfer method consists of drying the silica particles into powder before dispersing them via ultrasonication in the MMA matrix. The second is based on repetitive centrifugations to exchange NPs from their synthetic milieu to pure MMA, avoiding the dried powder state. These transfer methods are compared for two kinds of NP surface chemistry, natural silanol (Si-OH) groups of the silica NPs and an additional silane coupling agent, namely 3-(trimethoxysilyl)propyl methacrylate (TPM), which mimics the monomeric group of the MMA dispersing milieu. We then characterize the morphology of the resulting nanocomposites prepared via in situ polymerization at a fixed amount of dispersed NPs (2.2 wt%; 1 vol%) using a combination of transmission electron microscopy (TEM) from ultramicrotomed nanocomposite films, thermogravimetry (TGA) and small angle X-ray scattering (SAXS).The synthesis via in situ polymerization and characterization of nanocomposites (NCs) made from silica (SiO2) nanoparticles in a methyl methacrylate (MMA) monomer matrix is reported. We first investigate the transfer of well-defined spherical silica nanoparticles (NPs) (average radius R = 24.2 +/- 3.2 nm) into the monomer solvent. We study the influence of two transfer methods and different surface chemistries on the resulting colloidal stability. The first transfer method consists of drying the silica particles into powder before dispersing them via ultrasonication in the MMA matrix. The second is based on repetitive centrifugations to exchange NPs from their synthetic milieu to pure MMA, avoiding the dried powder state. These transfer methods are compared for two kinds of NP surface chemistry, natural silanol (Si-OH) groups of the silica NPs and an additional silane coupling agent, namely 3-(trimethoxysilyl)propyl methacrylate (TPM), which mimics the monomeric group of the MMA dispersing milieu. We then characterize the morphology of the resulting nanocomposites prepared via in situ polymerization at a fixed amount of dispersed NPs (2.2 wt%; 1 vol%) using a combination of transmission electron microscopy (TEM) from ultramicrotomed nanocomposite films, thermogravimetry (TGA) and small angle X-ray scattering (SAXS). Electronic supplementary information (ESI) available. See DOI: 10.1039/c2nr31846f

  20. EV Charging Through Wireless Power Transfer: Analysis of Efficiency Optimization and Technology Trends

    SciTech Connect

    Miller, John M; Rakouth, Heri; Suh, In-Soo

    2012-01-01

    This paper is aimed at reviewing the technology trends for wireless power transfer (WPT) for electric vehicles (EV). It also analyzes the factors affecting its efficiency and describes the techniques currently used for its optimization. The review of the technology trends encompasses both stationary and moving vehicle charging systems. The study of the stationary vehicle charging technology is based on current implementations and on-going developments at WiTricity and Oak Ridge National Lab (ORNL). The moving vehicle charging technology is primarily described through the results achieved by the Korean Advanced Institute of Technology (KAIST) along with on-going efforts at Stanford University. The factors affecting the efficiency are determined through the analysis of the equivalent circuit of magnetic resonant coupling. The air gap between both transmitting and receiving coils along with the magnetic field distribution and the relative impedance mismatch between the related circuits are the primary factors affecting the WPT efficiency. Currently the industry is looking at an air gap of 25 cm or below. To control the magnetic field distribution, Kaist has recently developed the Shaped Magnetic Field In Resonance (SMFIR) technology that uses conveniently shaped ferrite material to provide low reluctance path. The efficiency can be further increased by means of impedance matching. As a result, Delphi's implementation of the WiTricity's technology exhibits a WPT efficiency above 90% for stationary charging while KAIST has demonstrated a maximum efficiency of 83% for moving vehicle with its On Line Vehicle (OLEV) project. This study is restricted to near-field applications (short and mid-range) and does not address long-range technology such as microwave power transfer that has low efficiency as it is based on radiating electromagnetic waves. This paper exemplifies Delphi's work in powertrain electrification as part of its innovation for the real world program geared toward a safer, greener and more connected driving. Moreover, it draws from and adds to Dr. Andrew Brown Jr.'s SAE books 'Active Safety and the Mobility Industry', 'Connectivity and Mobility Industry', and 'Green Technologies and the Mobility Industry'. Magnetic resonant coupling is the foundation of modern wireless power transfer. Its efficiency can be controlled through impedance matching and magnetic field shaping. Current implementations use one or both of these control methods and enable both stationary and mobile charging with typical efficiency within the 80% and 90% range for an air gap up to 25 cm.

  1. Charge-transfer complex versus ?-complex formed between TiO2 and bis(dicyanomethylene) electron acceptors.

    PubMed

    Fujisawa, Jun-Ichi; Nagata, Morio; Hanaya, Minoru

    2015-10-14

    A novel group of organic-inorganic hybrid materials is created by the combination of titanium dioxide (TiO2) nanoparticles with bis(dicyanomethylene) (TCNX) electron acceptors. The TiO2-TCNX complex is produced by the nucleophilic addition reaction between a hydroxy group on the TiO2 surface and TCNX, with the formation of a ?-bond between them. The nucleophilic addition reaction generates a negatively-charged diamagnetic TCNX adsorbate that serves as an electron donor. The ?-bonded complex characteristically shows visible-light absorption due to interfacial charge-transfer (ICT) transitions. In this paper, we report on another kind of complex formation between TiO2 and TCNX. We have systematically studied the structures and visible-light absorption properties of the TiO2-TCNX complexes, with changing the electron affinity of TCNX. We found that TCNX acceptors with lower electron affinities form charge-transfer complexes with TiO2 without the ?-bond formation. The charge-transfer complexes show strong visible-light absorption due to interfacial electronic transitions with little charge-transfer nature, which are different from the ICT transitions in the ?-bond complexes. The charge-transfer complexes induce efficient light-to-current conversions due to the interfacial electronic transitions, revealing the high potential for applications to light-energy conversions. Furthermore, we demonstrate that the formation of the two kinds of complexes is selectively controlled by the electron affinity of TCNX. PMID:26418266

  2. TDDFT study of twisted intramolecular charge transfer and intermolecular double proton transfer in the excited state of 4'-dimethylaminoflavonol in ethanol solvent.

    PubMed

    Wang, Ye; Shi, Ying; Cong, Lin; Li, Hui

    2015-02-25

    Time-dependent density functional theory method at the def-TZVP/B3LYP level was employed to investigate the intramolecular and intermolecular hydrogen bonding dynamics in the first excited (S1) state of 4'-dimethylaminoflavonol (DMAF) monomer and in ethanol solution. In the DMAF monomer, we demonstrated that the intramolecular charge transfer (ICT) takes place in the S1 state. This excited state ICT process was followed by intramolecular proton transfer. Our calculated results are in good agreement with the mechanism proposed in experimental work. For the hydrogen-bonded DMAF-EtOH complex, it was demonstrated that the intermolecular hydrogen bonds can induce the formation of the twisted intramolecular charge transfer (TICT) state and the conformational twisting is along the C3-C4 bond. Moreover, the intermolecular hydrogen bonds can also facilitate the intermolecular double proton transfer in the TICT state. A stepwise intermolecular double proton transfer process was revealed. Therefore, the intermolecular hydrogen bonds can alter the mechanism of intramolecular charge transfer and proton transfer in the excited state for the DMAF molecule. PMID:25282020

  3. Tuning of intramolecular charge transfer properties and charge distributions in ferrocene-appended catechol derivatives by chemical substitution.

    PubMed

    Tahara, Keishiro; Akehi, Shogo; Akita, Tetsuhiro; Katao, Shohei; Kikuchi, Jun-Ichi; Tokunaga, Ken

    2015-09-01

    In this study, we report intramolecular charge transfer (ICT) properties and charge distributions in a series of FcC derivatives (FcC = 4-ferrocenylcatecholate where Fc = ferrocene and C = catecholate). This series consists of a previously reported complex FcV (4-ferrocenylveratrole) and newly synthesized complexes FcA (4-ferrocenylcatechol bis(acetate) and Pt((t)Bu2bpy)(FcC) ((t)Bu2bpy = 4,4'-di-tert-butyl-2,2'-dipyridyl). An electrochemical analysis of Pt((t)Bu2bpy)(FcC) using cyclic voltammetry revealed two well-defined, reversible waves which were assigned to the sequential oxidation of the Pt((t)Bu2bpy)(C) and Fc moieties. The potential splitting between the waves (524 mV) indicated that there was an electronic interaction between both moieties. ICT property and charge distribution of [Pt((t)Bu2bpy)(FcC)]?(+) were rationalized by comparison with the [FcV]?(+) and [FcA]?(+) (4-ferrocenylcatechol bis(acetate)). DFT calculations and UV-vis-NIR spectroscopy revealed that [Pt((t)Bu2bpy)(FcC)]?(+), [FcV]?(+), and [FcA]?(+) were ferrocenium (Fc(+))-centered rather than semiquinone ligand-centered and that these complexes exhibited ICT transition bands from the catechol-derivatized framework to the Fc(+) moiety in the near infrared (NIR) region. Both the electronic coupling parameter (HAB) and delocalization parameter (?) increased in value as the electron-donating strength of the substituent groups in the catechol-derivatized framework increased (OCOCH3 ([FcA]?(+)) < OCH3 ([FcV]?(+)) < O(-) ([Pt((t)Bu2bpy)(FcC)]?(+))). The electronic interactions between the organometallic center and the non-innocent framework were tuned by changing the substituents. The potential energy surfaces of the Fc(+) derivatives, obtained using two-state Marcus-Hush theory, can be modulated by changing the energy level of the molecular orbitals of the appended catechol-derivatized moieties. PMID:26212616

  4. Dependence of the direct electron transfer activity and adsorption kinetics of cytochrome c on interfacial charge properties.

    PubMed

    Wang, Gui-Xia; Wang, Min; Wu, Zeng-Qiang; Bao, Wen-Jing; Zhou, Yue; Xia, Xing-Hua

    2013-10-01

    With the advantages of in situ analysis and high surface sensitivity, surface-enhanced infrared absorption spectroscopy in attenuated total reflection mode (ATR-SEIRAS) combined with electrochemical methods has been employed to examine the interfacial direct electron transfer activity and adsorption kinetics of cytochrome c (cyt c). This work presents data on cyt c adsorption onto negatively charged mercaptohexanoic acid (MHA) and positively charged 6-amino-1-hexanethiol (MHN) self-assembled monolayers (SAMs) on gold nanofilm surfaces. The adsorbed cyt c displays a higher apparent electron transfer rate constant (33.5 ± 2.4 s(-1)) and apparent binding rate constant (73.1 ± 5.2 M(-1) s(-1)) at the MHA SAMs surface than those on the MHN SAMs surface. The results demonstrate that the surface charge density determines the protein adsorption kinetics, while the surface charge character determines the conformation and orientation of proteins assembled which in turn affects the direct electron transfer activity. PMID:23912152

  5. Ultrafast excited-state charge-transfer dynamics in laccase type I copper site.

    PubMed

    Delfino, Ines; Viola, Daniele; Cerullo, Giulio; Lepore, Maria

    2015-01-01

    Femtosecond pump-probe spectroscopy was used to investigate the excited state dynamics of the T1 copper site of laccase from Pleurotus ostreatus, by exciting its 600 nm charge transfer band with a 15-fs pulse and probing over a broad range in the visible region. The decay of the pump-induced ground-state bleaching occurs in a single step and is modulated by clearly visible oscillations. Global analysis of the two-dimensional differential transmission map shows that the excited state exponentially decays with a time constant of 375 fs, thus featuring a decay rate slower than those occurring in quite all the investigated T1 copper site proteins. The ultrashort pump pulse induces a vibrational coherence in the protein, which is mainly assigned to ground state activity, as expected in a system with fast excited state decay. Vibrational features are discussed also in comparison with the traditional resonance Raman spectrum of the enzyme. The results indicate that both excited state dynamics and vibrational modes associated with the T1 Cu laccase charge transfer have main characteristics similar to those of all the T1 copper site-containing proteins. On the other hand, the differences observed for laccase from P. ostreatus further confirm the peculiar hypothesized trigonal T1 Cu site geometry. PMID:25819432

  6. Charge Transfer in Single Chains of a Donor-Acceptor Conjugated Tri-Block Copolymer.

    PubMed

    Hooley, Emma N; Jones, David J; Greenham, Neil C; Ghiggino, Kenneth P; Bell, Toby D M

    2015-06-18

    The photophysics of a conjugated triblock copolymer comprising poly(9,9-dioctylfluorene-co-bis-N,N'-(4-methylphenyl)-bis-N,N'-phenyl-1,4-phenylenediamine) (PFM) electron donor and poly(4-(9,9-dioctyl-9H-fluoren-2-yl)benzo[c][1,2,5]-thiadiazole) (F8BT) electron acceptor blocks has been studied in solution, in films, and as single chains. While an additional long-wavelength emission apparent in neat films of the copolymer is attributed to interchain exciplex formation, no such long-wavelength emission is apparent in solution or from single molecules. However, in these cases, time-resolved fluorescence measurements indicate the presence of a delayed fluorescence. The kinetics of the delayed emission can be interpreted in terms of an equilibrium between a locally excited and a charge-transfer state at the interface of the copolymer block components. Rate constants and thermodynamic quantities associated with these processes have been evaluated. The single-molecule results allow the assignment of an intramolecular charge-transfer state in an isolated conjugated block copolymer chain. PMID:25417793

  7. Mixed-valence correlations in charge-transferring atom-surface collisions

    NASA Astrophysics Data System (ADS)

    Pamperin, M.; Bronold, F. X.; Fehske, H.

    2015-10-01

    Motivated by experimental evidence (He and Yarmoff 2010 Phys. Rev. Lett. 105 176806) for a mixed-valence state to occur in the neutralization of strontium ions on gold surfaces we analyze this type of charge-transferring atom-surface collision from a many-body theoretical point of view using quantum-kinetic equations together with a pseudo-particle representation for the electronic configurations of the atomic projectile. Particular attention is paid to the temperature dependence of the neutralization probability which—experimentally—seems to signal mixed-valence-type correlations affecting the charge-transfer between the gold surface and the strontium projectile. We also investigate the neutralization of magnesium ions on a gold surface which shows no evidence for a mixed-valence state. Whereas for magnesium excellent agreement between theory and experiment could be obtained, for strontium we could not reproduce the experimental data. Our results indicate mixed-valence correlations to be in principle present, but for the model mimicking most closely the experimental situation they are not strong enough to affect the neutralization process quantitatively.

  8. The charge transfer problem in density functional theory calculations of aqueously solvated molecules.

    PubMed

    Isborn, Christine M; Mar, Brendan D; Curchod, Basile F E; Tavernelli, Ivano; Martínez, Todd J

    2013-10-10

    Recent advances in algorithms and computational hardware have enabled the calculation of excited states with time-dependent density functional theory (TDDFT) for large systems of O(1000) atoms. Unfortunately, the aqueous charge transfer problem in TDDFT (whereby many spuriously low-lying charge transfer excited states are predicted) seems to become more severe as the system size is increased. In this work, we concentrate on the common case where a chromophore is embedded in aqueous solvent. We examine the role of exchange-correlation functionals, basis set effects, ground state geometries, and the treatment of the external environment in order to assess the root cause of this problem. We conclude that the problem rests largely on water molecules at the boundary of a finite cluster model, i.e., "edge waters." We also demonstrate how the TDDFT problem can be related directly to ground state problems. These findings demand caution in the commonly employed strategy that rests on "snapshot" cutout geometries taken from ground state dynamics with molecular mechanics. We also find that the problem is largely ameliorated when the range-separated hybrid functional LC-?PBEh is used. PMID:23964865

  9. Charge transfer and blue shifting of vibrational frequencies in a hydrogen bond acceptor.

    PubMed

    Wright, Ashley M; Howard, Austin A; Howard, J Coleman; Tschumper, Gregory S; Hammer, Nathan I

    2013-07-01

    A comprehensive Raman spectroscopic/electronic structure study of hydrogen bonding by pyrimidine with eight different polar solvents is presented. Raman spectra of binary mixtures of pyrimidine with methanol and ethylene glycol are reported, and shifts in ?1, ?3, ?6a, ?6b, ?8a, ?8b, ?9a, ?15, ?16a, and ?16b are compared to earlier results obtained for water. Large shifts to higher vibrational energy, often referred to as blue shifts, are observed for ?1, ?6b, and ?8b (by as much as 14 cm(-1)). While gradual blue shifts with increasing hydrogen bond donor concentration are observed for ?6b and ?8b, ?1 exhibits three distinct spectral components whose relative intensities vary with concentration. The blue shift of ?1 is further examined in binary mixtures of pyrimidine with acetic acid, thioglycol, phenylmethanol, hexylamine, and acetonitrile. Electronic structure computations for more than 100 microsolvated structures reveal a significant dependence of the magnitude of the ?1 blue shift on the local microsolvation geometry. Results from natural bond orbital (NBO) calculations also reveal a strong correlation between charge transfer and blue shifting of pyrimidine's normal modes. Although charge transfer has previously been linked to blue shifting of the X-H stretching frequency in hydrogen bond donors, here, a similar trend in a hydrogen bond acceptor is demonstrated. PMID:23679020

  10. Observation of excited state charge transfer with fs/ps-CARS

    SciTech Connect

    Blom, Alex Jason

    2009-08-01

    Excited state charge transfer processes are studied using the fs/ps-CARS probe technique. This probe allows for multiplexed detection of Raman active vibrational modes. Systems studied include Michler's Ketone, Coumarin 120, 4-dimethylamino-4{prime}-nitrostilbene, and several others. The vibrational spectrum of the para di-substituted benzophenone Michler's Ketone in the first excited singlet state is studied for the first time. It is found that there are several vibrational modes indicative of structural changes of the excited molecule. A combined experimental and theoretical approach is used to study the simplest 7-amino-4-methylcoumarin, Coumarin 120. Vibrations observed in FTIR and spontaneous Raman spectra are assigned using density functional calculations and a continuum solvation model is used to predict how observed modes are affected upon inclusion of a solvent. The low frequency modes of the excited state charge transfer species 4-dimethylamino-4{prime}-nitrostilbene are studied in acetonitrile. Results are compared to previous work on this molecule in the fingerprint region. Finally, several partially completed projects and their implications are discussed. These include the two photon absorption of Coumarin 120, nanoconfinement in cyclodextrin cavities and sensitization of titania nanoparticles.

  11. Visualization of Polymer Deformation Using Microcapsules Filled with Charge-Transfer Complex Precursors.

    PubMed

    Lavrenova, Anna; Farkas, Jacob; Weder, Christoph; Simon, Yoan C

    2015-10-01

    The visualization of polymer deformation using microcapsules filled with charge-transfer complex precursors is reported. Poly(urea-formaldehyde) microcapsules filled with toluene and either hexamethylbenzene as donor or chloranil as acceptor were prepared by in situ polymerization of an oil-in-water emulsion. The resulting microcapsules were incorporated in a poly(dimethylsiloxane) matrix by dispersing them in the monomer and subsequent curing. The microcapsules were shown to rupture when the polymer was placed under mechanical forces (i.e., tensile and compression) such that the donor and the acceptor are released into the polymeric matrix, where their combination to a charge-transfer complex results in a pronounced yellow-to-red color change. The factors influencing the extent of the color change (composition and mechanical strain) were investigated and a deformation threshold seems to be present. The new damage-sensing materials may be useful for a range of applications and the general concept applied seems to be readily applicable to other host polymers. PMID:26406316

  12. Ultrafast spin exchange-coupling torque via photo-excited charge-transfer processes

    PubMed Central

    Ma, X.; Fang, F.; Li, Q.; Zhu, J.; Yang, Y.; Wu, Y. Z.; Zhao, H. B.; Lüpke, G.

    2015-01-01

    Optical control of spin is of central importance in the research of ultrafast spintronic devices utilizing spin dynamics at short time scales. Recently developed optical approaches such as ultrafast demagnetization, spin-transfer and spin-orbit torques open new pathways to manipulate spin through its interaction with photon, orbit, charge or phonon. However, these processes are limited by either the long thermal recovery time or the low-temperature requirement. Here we experimentally demonstrate ultrafast coherent spin precession via optical charge-transfer processes in the exchange-coupled Fe/CoO system at room temperature. The efficiency of spin precession excitation is significantly higher and the recovery time of the exchange-coupling torque is much shorter than for the demagnetization procedure, which is desirable for fast switching. The exchange coupling is a key issue in spin valves and tunnelling junctions, and hence our findings will help promote the development of exchange-coupled device concepts for ultrafast coherent spin manipulation. PMID:26508587

  13. Ultrafast spin exchange-coupling torque via photo-excited charge-transfer processes.

    PubMed

    Ma, X; Fang, F; Li, Q; Zhu, J; Yang, Y; Wu, Y Z; Zhao, H B; Lüpke, G

    2015-01-01

    Optical control of spin is of central importance in the research of ultrafast spintronic devices utilizing spin dynamics at short time scales. Recently developed optical approaches such as ultrafast demagnetization, spin-transfer and spin-orbit torques open new pathways to manipulate spin through its interaction with photon, orbit, charge or phonon. However, these processes are limited by either the long thermal recovery time or the low-temperature requirement. Here we experimentally demonstrate ultrafast coherent spin precession via optical charge-transfer processes in the exchange-coupled Fe/CoO system at room temperature. The efficiency of spin precession excitation is significantly higher and the recovery time of the exchange-coupling torque is much shorter than for the demagnetization procedure, which is desirable for fast switching. The exchange coupling is a key issue in spin valves and tunnelling junctions, and hence our findings will help promote the development of exchange-coupled device concepts for ultrafast coherent spin manipulation. PMID:26508587

  14. Excited State Structural Dynamics of Carotenoids and ChargeTransfer Systems

    SciTech Connect

    Van Tassle, Aaron Justin

    2006-09-01

    This dissertation describes the development andimplementation of a visible/near infrared pump/mid-infrared probeapparatus. Chapter 1 describes the background and motivation ofinvestigating optically induced structural dynamics, paying specificattention to solvation and the excitation selection rules of highlysymmetric molecules such as carotenoids. Chapter 2 describes thedevelopment and construction of the experimental apparatus usedthroughout the remainder of this dissertation. Chapter 3 will discuss theinvestigation of DCM, a laser dye with a fluorescence signal resultingfrom a charge transfer state. By studying the dynamics of DCM and of itsmethyl deuterated isotopomer (an otherwise identical molecule), we areable to investigate the origins of the charge transfer state and provideevidence that it is of the controversial twisted intramolecular (TICT)type. Chapter 4 introduces the use of two-photon excitation to the S1state, combined with one-photon excitation to the S2 state of thecarotenoid beta-apo-8'-carotenal. These 2 investigations show evidencefor the formation of solitons, previously unobserved in molecular systemsand found only in conducting polymers Chapter 5 presents an investigationof the excited state dynamics of peridinin, the carotenoid responsiblefor the light harvesting of dinoflagellates. This investigation allowsfor a more detailed understanding of the importance of structuraldynamics of carotenoids in light harvesting.

  15. Ultrafast spin exchange-coupling torque via photo-excited charge-transfer processes

    NASA Astrophysics Data System (ADS)

    Ma, X.; Fang, F.; Li, Q.; Zhu, J.; Yang, Y.; Wu, Y. Z.; Zhao, H. B.; Lüpke, G.

    2015-10-01

    Optical control of spin is of central importance in the research of ultrafast spintronic devices utilizing spin dynamics at short time scales. Recently developed optical approaches such as ultrafast demagnetization, spin-transfer and spin-orbit torques open new pathways to manipulate spin through its interaction with photon, orbit, charge or phonon. However, these processes are limited by either the long thermal recovery time or the low-temperature requirement. Here we experimentally demonstrate ultrafast coherent spin precession via optical charge-transfer processes in the exchange-coupled Fe/CoO system at room temperature. The efficiency of spin precession excitation is significantly higher and the recovery time of the exchange-coupling torque is much shorter than for the demagnetization procedure, which is desirable for fast switching. The exchange coupling is a key issue in spin valves and tunnelling junctions, and hence our findings will help promote the development of exchange-coupled device concepts for ultrafast coherent spin manipulation.

  16. Study on the charge-transfer reaction between 7,7,8,8-tetracyanoquinodimethane and drugs.

    PubMed

    Feng-lin, Z; Bian-zhen, X; Zhi-quan, Z; Shen-yang, T

    1999-11-01

    The charge-transfer (CT) reaction between 7,7,8,8-tetracyanoquinodimethane (TCNQ) as a pi-electron acceptor and cinnarizine, analgin, norfloxacin as electron donors have been studied by spectrophotometric method. The charge transfer complexes between TCNQ and these drugs have stable blue color, therefore a simple, rapid, accurate and sensitive method for determination of these drugs has been developed. The optimization of the experimental conditions is described. Beer's law is obeyed in the ranges 2-18, 2-18 and 4-32 microg/ml for cinnarizine, analgin and norfloxacin, respectively. The apparent molar absorptivity of CT complexes at 743 nm is 1.58x10(4), 1.71x10(4) and 8.91x10(3) l/mol per cm, respectively. The composition of all these CT complexes are found to be 1:1 by different methods. The relative SDs are less than 3% (n = 10). The proposed method has been applied to the determination of these drugs in their each pharmaceutical dosage forms with satisfactory results. PMID:10703991

  17. Relation between Nonlinear Optical Properties of Push-Pull Molecules and Metric of Charge Transfer Excitations.

    PubMed

    List, Nanna Holmgaard; Zale?ny, Robert; Murugan, N Arul; Kongsted, Jacob; Bartkowiak, Wojciech; Ågren, Hans

    2015-09-01

    We establish the relationships between the metric of charge transfer excitation (?r) for the bright ??* state and the two-photon absorption probability as well as the first hyperpolarizability for two families of push-pull ?-conjugated systems. As previously demonstrated by Guido et al. (J. Chem. Theory Comput. 2013, 9, 3118-3126), ?r is a measure for the average hole-electron distance upon excitation and can be used to discriminate between short- and long-range electronic excitations. We indicate two new benefits from using this metric for the analyses of nonlinear optical properties of push-pull systems. First, the two-photon absorption probability and the first hyperpolarizability are found to be interrelated through ?r; if ? ? (?r)(k), then roughly, ?(TPA) ? (?r)(k+1). Second, a simple power relation between ?r and the molecular hyperpolarizabilities of push-pull systems offers the possibility of estimating properties for longer molecular chains without performing calculations of high-order response functions explicitly. We further demonstrate how to link the hyperpolarizabilities with the chain length of the push-pull ?-conjugated systems through the metric of charge transfer. PMID:26575913

  18. Modulation of the charge transfer and photophysical properties in non-fused tetrathiafulvalene-benzothiadiazole derivatives.

    PubMed

    Pop, Flavia; Seifert, Sabine; Hankache, Jihane; Ding, Jie; Hauser, Andreas; Avarvari, Narcis

    2015-01-28

    Bis(thiomethyl)- and bis(thiohexyl)-tetrathiafulvalene-bromo-benzothiadiazoles, containing electron donor tetrathiafulvalene (TTF) and electron acceptor benzothiadiazole (BTD) units, have been prepared by Stille coupling reactions between the TTF-SnMe3 precursors and BTD-Br2. In another series of experiments, TTF-acetylene-BTD compounds have been synthesized by Sonogashira coupling between either TTF-acetylenes and BTD-Br2 in low yields, or TTF-iodine and BTD-acetylene in moderate yields. In the compound TTF-C?C-BTD the TTF and BTD units are coplanar in the solid state, as shown by the single crystal X-ray structure, and there is segregation in the packing between the donor and acceptor units. All the derivatives have good electron donor properties, as determined by cyclic voltammetry measurements, and they can also be reversibly reduced thanks to the presence of the BTD moiety. UV-visible spectroscopy and photophysical investigations show the presence of an intramolecular charge transfer (ICT) band and an emission band originating from the charge transfer. Both the absorption and the emission are modulated by the substitution scheme and the insertion of the acetylenic bridge. PMID:25410315

  19. Momentum transfer theory of non-conservative charged particle transport in crossed electric and magnetic fields

    SciTech Connect

    Vrhovac, S.B.; Petrovic, Z.Lj.

    1995-12-31

    Momentum - transfer approximation is applied to momentum and energy balance equations describing reacting particle swarms in gases in crossed electric and magnetic fields. Transport coefficients of charged particles undergoing both inelastic and reactive, non-particle-conserving collisions with a gas of neutral molecules are calculated. Momentum - transfer theory (MTT) has been developed mainly by Robson and collaborators. It has been applied to a single reactive gas and mixtures of reactive gases in electric field only. MTT has also been applied in crossed electric and magnetic fields recently and independently of our work but the reactive collisions were not considered. Consider a swarm of electrons of charge e and mass m moving with velocity {rvec v} through a neutral gas under the influence of an applied electric {rvec E} and magnetic {rvec B} field. The collision processes which we shall investigate are limited to elastic, inelastic and reactive collisions of electrons with gas molecules. Here we interpret reactive collisions as collisions which produce change in number of the swarm particles. Reactive collisions involve creation (ionization by electron impact) or loss (electron attachment) of swarm particles. We consider only single ionization in approximation of the mass ratio m/m{sub 0}<1, where m and m{sub 0} are masses of electrons and neutral particles, respectively. We assume that the stage of evolution of the swarm is the hydrodynamic limit (HDL). In HDL, the space - time dependence of all properties is carried by the number density n of swarm particles.

  20. Colossal negative thermal expansion in BiNiO3 induced by intermetallic charge transfer

    PubMed Central

    Azuma, Masaki; Chen, Wei-tin; Seki, Hayato; Czapski, Michal; Olga, Smirnova; Oka, Kengo; Mizumaki, Masaichiro; Watanuki, Tetsu; Ishimatsu, Naoki; Kawamura, Naomi; Ishiwata, Shintaro; Tucker, Matthew G.; Shimakawa, Yuichi; Attfield, J. Paul

    2011-01-01

    The unusual property of negative thermal expansion is of fundamental interest and may be used to fabricate composites with zero or other controlled thermal expansion values. Here we report that colossal negative thermal expansion (defined as linear expansion charge-transfer transitions. BiNiO3 shows a 2.6% volume reduction under pressure due to a Bi/Ni charge transfer that is shifted to ambient pressure through lanthanum substitution for Bi. Changing proportions of coexisting low- and high-temperature phases leads to smooth volume shrinkage on heating. The crystallographic linear expansion coefficient for Bi0.95La0.05NiO3 is ?137×10?6 K?1 and a value of ?82×10?6 K?1 is observed between 320 and 380 K from a dilatometric measurement on a ceramic pellet. Colossal negative thermal expansion materials operating at ambient conditions may also be accessible through metal-insulator transitions driven by other phenomena such as ferroelectric orders. PMID:21673668

  1. Charge transfer of atomic and molecular rare-gas ions with mercury atoms at thermal energy

    NASA Astrophysics Data System (ADS)

    Johnsen, Rainer; Biondi, Manfred A.

    1980-11-01

    A drift tube-mass spectrometer apparatus has been used to determine thermal-energy rate coefficients for reactions of the type R++Hg?R+Hg+ and R2++Hg?2R+Hg+, where R denotes an atom of one of the rare gases. Except for He+ ions, charge transfer between atomic rare-gas ions and mercury was found to be immeasurably slow. Both He2+ and Xe2+ exhibited fast charge transfer with mercury; a moderately slow reaction also occurred in the case of Ne2+ ions. Formation of mercury dimer and trimer ions was observed to be quite efficient in xenon-mercury mixtures; rate coefficients for the reaction sequence Hg+?XeHg+?Hg2+?XeHg2+?Hg3+ were estimated to be on the order of 10-31 cm6/sec for the association steps 1 and 3, and about 10-10 cm3/sec for the two-body switching steps 2 and 4.

  2. Charge Density Quantification of Polyelectrolyte Polysaccharides by Conductometric Titration: An Analytical Chemistry Experiment

    ERIC Educational Resources Information Center

    Farris, Stefano; Mora, Luigi; Capretti, Giorgio; Piergiovanni, Luciano

    2012-01-01

    An easy analytical method for determination of the charge density of polyelectrolytes, including polysaccharides and other biopolymers, is presented. The basic principles of conductometric titration, which is used in the pulp and paper industry as well as in colloid and interface science, were adapted to quantify the charge densities of a…

  3. Bidirectional diffusion of ammonium and sodium cations in forward osmosis: role of membrane active layer surface chemistry and charge.

    PubMed

    Lu, Xinglin; Boo, Chanhee; Ma, Jun; Elimelech, Menachem

    2014-12-16

    Systematic fundamental understanding of mass transport in osmosis-driven membrane processes is important for further development of this emerging technology. In this work, we investigate the role of membrane surface chemistry and charge on bidirectional solute diffusion in forward osmosis (FO). In particular, bidirectional diffusion of ammonium (NH4(+)) and sodium (Na(+)) is examined using FO membranes with different materials and surface charge characteristics. Using an ammonium bicarbonate (NH4HCO3) draw solution, we observe dramatically enhanced cation fluxes with sodium chloride feed solution compared to that with deionized water feed solution for thin-film composite (TFC) FO membrane. However, the bidirectional diffusion of cations does not change, regardless of the type of feed solution, for cellulose triacetate (CTA) FO membrane. We relate this phenomenon to the membrane fixed surface charge by employing different feed solution pH to foster different protonation conditions for the carboxyl groups on the TFC membrane surface. Membrane surface modification is also carried out with the TFC membrane using ethylenediamine to alter carboxyl groups into amine groups. The modified TFC membrane, with less negatively charged groups, exhibits a significant decrease in the bidirectional diffusion of cations under the same conditions employed with the pristine TFC membrane. Based on our experimental observations, we propose Donnan dialysis as a mechanism responsible for enhanced bidirectional diffusion of cations in TFC membranes. PMID:25418020

  4. Collisions of highly stripped ions at MeV energies in gas targets: charge transfer and ionization

    SciTech Connect

    Schlachter, A.S.

    1980-01-01

    Cross sections have been measured for charge transfer and ionization in H/sub 2/ and rare-gas targets by fast, highly ionized carbon, iron, niobium, and lead ions in charge states +3 to +59, with energies in the range 0.1 to 4.8 MeV/amu. Experimental results are compared with classical-trajectory calculations; agreement is generally good. For a given target, the cross sections for net ionization reduce to a common curve when plotted as cross section divided by charge state versus energy per nucleon divided by charge state.

  5. Ion-pairing control of excited-state electron-transfer reactions. Quenching, charge recombination, and back electron transfer

    SciTech Connect

    Clark, C.D.; Hoffman, M.Z.

    1996-05-02

    The rate constants for the oxidative quenching of {sup *}Ru(bpy){sub 3}{sup 2+} by MV{sup 2+} (k{sub q}) and the charge recombination reaction between Ru(bpy){sub 3}{sup 3+} and MV{sup .+} in bulk solution (k{sub rec}) and the cage escape yields of the redox products ({eta}{sub ce}) were determined as a function of added electrolytes (Na{sup +} salts of oxyanions and halides) and temperature (10-60{degree}C) in aqueous solution. At 25{degree}C and constant [anion], k{sub q} and k{sub rec} are a function of the specific anion. Activation energies for k{sub q} and k{sub rec} for ClO{sub 4}{sup -} are nearly 30% lower than the average values for the other salts. Values of {eta}{sub ce} show anion-specific trends opposite to those for k{sub q} and k{sub rec}. The reactant cations are extensively ion-paired by the dominant anions in bulk solution, and a similar situation is proposed to exist within the quenching solvent cage. {Delta}H{sup dagger} (activation enthalpy) and {lambda} (solvent reorganization energy) were evaluated for k{sub ip} and back electron transfer within the solvent cage (k{sub bt}) and were found to be smallest for ClO{sub 4}{sup -} and I{sup -}. The correlation that exists between k{sub ip} or k{sub bt} and the standard free energy of hydration ({Delta} G{degree}{sub hyd}) of the anions indicates that the rates of electron transfer between the cationic reactants are greatest in the presence of anions that have the most weakly-held hydration sphere and the greatest ability to break the water structure. 33 refs., 7 figs., 3 tabs.

  6. Coarse-grained time-dependent density functional simulation of charge transfer in complex systems: application to hole transfer in DNA.

    PubMed

    Kubar, Tomás; Elstner, Marcus

    2010-09-01

    We present a coarse-grained tight-binding method based on density functional theory (DFT) for the simulation of charge transfer in complex materials. The charge-transfer parameters are computed using a fragment-orbital approach combined with the approximative DFT method self-consistent charge density functional tight binding (SCC-DFTB), which allows to follow the dynamics of excess charge along nanosecond MD trajectories, still accounting for the important impact of structural fluctuations and solvent effects. Since DFT suffers from the self-interaction error, which would lead to a delocalization of the hole charge over the entire system, we study the effect of an empirical self-interaction correction in detail. The wave function of the excess charge is propagated within the framework of time-dependent DFT, where the electron (hole) and the atomic system are propagated simultaneously according to the derived coupled equations of motion. In the case of DNA, the solvent polarization effects are a dominant factor affecting the hole transport. The hole charge polarizes the surrounding water, which in turn supports a localization of the hole charge--a water polaron is formed, extended dynamically over several nucleobases. As this polarization of water accompanies the migrating hole, the motion of hole is significantly slowed down due to the solvent reorganization energy involved. The estimated hopping rate between neighboring adenines in poly(A)-DNA is in the order of 100 ns(-1), and our simulations clearly show that the charge transfer occurs in a nonadiabatic fashion, due to the small average electronic coupling of around 0.06 eV. PMID:20687528

  7. The influences of the transfer method and particle surface chemistry on the dispersion of nanoparticles in nanocomposites.

    PubMed

    Pravaz, Olivier; Droz, Benoît; Schurtenberger, Peter; Dietsch, Hervé

    2012-11-01

    The synthesis via in situ polymerization and characterization of nanocomposites (NCs) made from silica (SiO(2)) nanoparticles in a methyl methacrylate (MMA) monomer matrix is reported. We first investigate the transfer of well-defined spherical silica nanoparticles (NPs) (average radius R = 24.2 ± 3.2 nm) into the monomer solvent. We study the influence of two transfer methods and different surface chemistries on the resulting colloidal stability. The first transfer method consists of drying the silica particles into powder before dispersing them via ultrasonication in the MMA matrix. The second is based on repetitive centrifugations to exchange NPs from their synthetic milieu to pure MMA, avoiding the dried powder state. These transfer methods are compared for two kinds of NP surface chemistry, natural silanol (Si-OH) groups of the silica NPs and an additional silane coupling agent, namely 3-(trimethoxysilyl)propyl methacrylate (TPM), which mimics the monomeric group of the MMA dispersing milieu. We then characterize the morphology of the resulting nanocomposites prepared via in situ polymerization at a fixed amount of dispersed NPs (2.2 wt%; 1 vol%) using a combination of transmission electron microscopy (TEM) from ultramicrotomed nanocomposite films, thermogravimetry (TGA) and small angle X-ray scattering (SAXS). PMID:23034718

  8. Microgravity and Charge Transfer in the Neuronal Membrane: Implications for Computational Neurobiology

    NASA Technical Reports Server (NTRS)

    Wallace, Ron

    1995-01-01

    Evidence from natural and artificial membranes indicates that the neural membrane is a liquid crystal. A liquid-to-gel phase transition caused by the application of superposed electromagnetic fields to the outer membrane surface releases spin-correlated electron pairs which propagate through a charge transfer complex. The propagation generates Rydberg atoms in the lipid bilayer lattice. In the present model, charge density configurations in promoted orbitals interact as cellular automata and perform computations in Hilbert space. Due to the small binding energies of promoted orbitals, their automata are highly sensitive to microgravitational perturbations. It is proposed that spacetime is classical on the Rydberg scale, but formed of contiguous moving segments, each of which displays topological equivalence. This stochasticity is reflected in randomized Riemannian tensor values. Spacetime segments interact with charge automata as components of a computational process. At the termination of the algorithm, an orbital of high probability density is embedded in a more stabilized microscopic spacetime. This state permits the opening of an ion channel and the conversion of a quantum algorithm into a macroscopic frequency code.

  9. Quantum effects in energy and charge transfer in an artificial photosynthetic complex

    SciTech Connect

    Ghosh, Pulak Kumar; Smirnov, Anatoly Yu.; Nori, Franco

    2011-06-28

    We investigate the quantum dynamics of energy and charge transfer in a wheel-shaped artificial photosynthetic antenna-reaction center complex. This complex consists of six light-harvesting chromophores and an electron-acceptor fullerene. To describe quantum effects on a femtosecond time scale, we derive the set of exact non-Markovian equations for the Heisenberg operators of this photosynthetic complex in contact with a Gaussian heat bath. With these equations we can analyze the regime of strong system-bath interactions, where reorganization energies are of the order of the intersite exciton couplings. We show that the energy of the initially excited antenna chromophores is efficiently funneled to the porphyrin-fullerene reaction center, where a charge-separated state is set up in a few picoseconds, with a quantum yield of the order of 95%. In the single-exciton regime, with one antenna chromophore being initially excited, we observe quantum beatings of energy between two resonant antenna chromophores with a decoherence time of {approx}100 fs. We also analyze the double-exciton regime, when two porphyrin molecules involved in the reaction center are initially excited. In this regime we obtain pronounced quantum oscillations of the charge on the fullerene molecule with a decoherence time of about 20 fs (at liquid nitrogen temperatures). These results show a way to directly detect quantum effects in artificial photosynthetic systems.

  10. Unravelling the mechanism of photoinduced charge transfer processes in lead iodide perovskite solar cells

    NASA Astrophysics Data System (ADS)

    Marchioro, Arianna; Teuscher, Joël; Friedrich, Dennis; Kunst, Marinus; van de Krol, Roel; Moehl, Thomas; Grätzel, Michael; Moser, Jacques-E.

    2014-03-01

    Lead halide perovskites have recently been used as light absorbers in hybrid organic-inorganic solid-state solar cells, with efficiencies as high as 15% and open-circuit voltages of 1 V. However, a detailed explanation of the mechanisms of operation within this photovoltaic system is still lacking. Here, we investigate the photoinduced charge transfer processes at the surface of the perovskite using time-resolved techniques. Transient laser spectroscopy and microwave photoconductivity measurements were applied to TiO2 and Al2O3 mesoporous films impregnated with CH3NH3PbI3 perovskite and the organic hole-transporting material spiro-OMeTAD. We show that primary charge separation occurs at both junctions, with TiO2 and the hole-transporting material, simultaneously, with ultrafast electron and hole injection taking place from the photoexcited perovskite over similar timescales. Charge recombination is shown to be significantly slower on TiO2 than on Al2O3 films.

  11. Competition between covalent bonding and charge transfer tendencies at complex-oxides interfaces

    NASA Astrophysics Data System (ADS)

    Salafranca, J.; Tornos, J.; García-Barriocanal, J.; León, C.; Santamaria, J.; Rincón, J.; Álvarez, G.; Pennycook, S. J.; Dagotto, E.; Varela, M.

    2013-03-01

    Interfaces alter the subtle balance among different degrees of freedom responsible for exotic phenomena in complex oxides, such as cuprate-manganite interfaces. We study these interfaces by means of scanning transmission electron microscopy and theoretical calculations. Microscopy and EEL spectroscopy indicate that the interfaces are sharp, and the chemical profile is symmetric with two equivalent interfaces. Spectroscopy also allows us to establish an oxidation state profile with sub-nanometer resolution. We find an anomalous charge redistribution: a non-monotonic behavior of the occupancy of d orbitals in the manganite layers as a function of distance to the interface. Relying on model calculations, we establish that this profile is a result of the competition between standard charge transfer tendencies involving materials with different chemical potentials and strong bonding effects across the interface. The competition can be tuned by different factors (temperature, doping, magnetic fields...). As examples, we report different charge distributions as a function of doping of the manganite layers. ACKNOWLEDGEMENTS ORNL:U.S. DOE-BES, Material Sciences and Engineering Division & ORNL's ShaRE. UCM:Juan de la Cierva, Ramon y Cajal, & ERC Starting Investigator Award programs.

  12. Unified approach to multipolar polarisation and charge transfer for ions: microhydrated Na+.

    PubMed

    Mills, Matthew J L; Hawe, Glenn I; Handley, Christopher M; Popelier, Paul L A

    2013-11-01

    Electrostatic effects play a large part in determining the properties of chemical systems. In addition, a treatment of the polarisation of the electron distribution is important for many systems, including solutions of monatomic ions. Typically employed methods for describing polarisable electrostatics use a number of approximations, including atom-centred point charges and polarisation methods that require iterative calculation on the fly. We present a method that treats charge transfer and polarisation on an equal footing. Atom-centred multipole moments describe the charge distribution of a chemical system. The variation of these multipole moments with the geometry of the surrounding atoms is captured by the machine learning method kriging. The interatomic electrostatic interaction can be computed using the resulting predicted multipole moments. This allows the treatment of both intra- and interatomic polarisation with the same method. The proposed method does not return explicit polarisabilities but instead, predicts the result of the polarisation process. An application of this new method to the sodium cation in a water environment is described. The performance of the method is assessed by comparison of its predictions of atomic multipole moments and atom-atom electrostatic interaction energies to exact results. The kriging models are able to predict the electrostatic interaction energy between the ion and all water atoms within 4 kJ mol(-1) for any of the external test set Na(+)(H2O)6 configurations. PMID:24064799

  13. Modeling the electrical conduction in DNA nanowires: Charge transfer and lattice fluctuation theories

    NASA Astrophysics Data System (ADS)

    Behnia, S.; Fathizadeh, S.

    2015-02-01

    An analytical approach is proposed for the investigation of the conductivity properties of DNA. The charge mobility of DNA is studied based on an extended Peyrard-Bishop-Holstein model when the charge carrier is also subjected to an external electrical field. We have obtained the values of some of the system parameters, such as the electron-lattice coupling constant, by using the mean Lyapunov exponent method. On the other hand, the electrical current operator is calculated directly from the lattice operators. Also, we have studied Landauer resistance behavior with respect to the external field, which could serve as the interface between chaos theory tools and electronic concepts. We have examined the effect of two types of electrical fields (dc and ac) and variation of the field frequency on the current flowing through DNA. A study of the current-voltage (I -V ) characteristic diagram reveals regions with a (quasi-)Ohmic property and other regions with negative differential resistance (NDR). NDR is a phenomenon that has been observed experimentally in DNA at room temperature. We have tried to study the affected agents in charge transfer phenomena in DNA to better design nanostructures.

  14. Quantum effects in energy and charge transfer in an artificial photosynthetic complex.

    PubMed

    Ghosh, Pulak Kumar; Smirnov, Anatoly Yu; Nori, Franco

    2011-06-28

    We investigate the quantum dynamics of energy and charge transfer in a wheel-shaped artificial photosynthetic antenna-reaction center complex. This complex consists of six light-harvesting chromophores and an electron-acceptor fullerene. To describe quantum effects on a femtosecond time scale, we derive the set of exact non-Markovian equations for the Heisenberg operators of this photosynthetic complex in contact with a Gaussian heat bath. With these equations we can analyze the regime of strong system-bath interactions, where reorganization energies are of the order of the intersite exciton couplings. We show that the energy of the initially excited antenna chromophores is efficiently funneled to the porphyrin-fullerene reaction center, where a charge-separated state is set up in a few picoseconds, with a quantum yield of the order of 95%. In the single-exciton regime, with one antenna chromophore being initially excited, we observe quantum beatings of energy between two resonant antenna chromophores with a decoherence time of ?100 fs. We also analyze the double-exciton regime, when two porphyrin molecules involved in the reaction center are initially excited. In this regime we obtain pronounced quantum oscillations of the charge on the fullerene molecule with a decoherence time of about 20 fs (at liquid nitrogen temperatures). These results show a way to directly detect quantum effects in artificial photosynthetic systems. PMID:21721608

  15. How well can Charge Transfer Inefficiency be corrected? A parameter sensitivity study for iterative correction

    E-print Network

    Israel, Holger; Prod'homme, Thibaut; Cropper, Mark; Cordes, Oliver; Gow, Jason; Kohley, Ralf; Marggraf, Ole; Niemi, Sami; Rhodes, Jason; Short, Alex; Verhoeve, Peter

    2015-01-01

    Radiation damage to space-based Charge-Coupled Device (CCD) detectors creates defects which result in an increasing Charge Transfer Inefficiency (CTI) that causes spurious image trailing. Most of the trailing can be corrected during post-processing, by modelling the charge trapping and moving electrons back to where they belong. However, such correction is not perfect -- and damage is continuing to accumulate in orbit. To aid future development, we quantify the limitations of current approaches, and determine where imperfect knowledge of model parameters most degrade measurements of photometry and morphology. As a concrete application, we simulate $1.5\\times10^{9}$ "worst case" galaxy and $1.5\\times10^{8}$ star images to test the performance of the Euclid visual instrument detectors. There are two separable challenges: If the model used to correct CTI is perfectly the same as that used to add CTI, $99.68$ % of spurious ellipticity is corrected in our setup. This is because readout noise is not subject to CTI,...

  16. Magneto-Dielectric Effects Induced by Optically-Generated Intermolecular Charge-Transfer States in Organic Semiconducting Materials

    PubMed Central

    Zang, Huidong; Yan, Liang; Li, Mingxing; He, Lei; Gai, Zheng; Ivanov, Ilia; Wang, Min; Chiang, Long; Urbas, Augustine; Hu, Bin

    2013-01-01

    Traditionally, magneto-dielectric effects have been developed by combining ferroelectric and magnetic materials. Here, we show a magneto-dielectric effect from optically-generated intermolecular charge-transfer states in an organic semiconducting donor:acceptor (PVK:TCNB) system. We observe in magnetic field effects of photoluminescence that a magnetic field can change singlet/triplet population ratio in intermolecular charge-transfer states. Furthermore, our theoretical analysis and experimental evidence indicate that the singlets and triplets in charge-transfer states have stronger and weaker electrical polarizations, respectively. Therefore, the observed magneto-dielectric effect can be attributed to magnetically-dependent singlet/triplet ratio in intermolecular charge-transfer states. In principle, a magneto-dielectric effect can be generated through two different channels based on magneto-polarization and magneto-current effects when the singlet/triplet ratio in intermolecular charge-transfer states is changed by a magnetic field. We find, from the simulation of dielectric effects, that magneto-polarization and magneto-current effects play primary and secondary roles in the generation of magneto-dielectric effect. PMID:24084983

  17. Regressed relations for forced convection heat transfer in a direct injection stratified charge rotary engine

    NASA Technical Reports Server (NTRS)

    Lee, Chi M.; Schock, Harold J.

    1988-01-01

    Currently, the heat transfer equation used in the rotary combustion engine (RCE) simulation model is taken from piston engine studies. These relations have been empirically developed by the experimental input coming from piston engines whose geometry differs considerably from that of the RCE. The objective of this work was to derive equations to estimate heat transfer coefficients in the combustion chamber of an RCE. This was accomplished by making detailed temperature and pressure measurements in a direct injection stratified charge (DISC) RCE under a range of conditions. For each specific measurement point, the local gas velocity was assumed equal to the local rotor tip speed. Local physical properties of the fluids were then calculated. Two types of correlation equations were derived and are described in this paper. The first correlation expresses the Nusselt number as a function of the Prandtl number, Reynolds number, and characteristic temperature ratio; the second correlation expresses the forced convection heat transfer coefficient as a function of fluid temperature, pressure and velocity.

  18. Regressed relations for forced convection heat transfer in a direct injection stratified charge rotary engine

    SciTech Connect

    Lee, C.M.; Schock, H.J.

    1988-01-01

    Currently, the heat transfer equation used in the rotary combustion engine (RCE) simulation model is taken from piston engine studies. These relations have been empirically developed by the experimental input coming from piston engines whose geometry differs considerably from that of the RCE. The objective of this work was to derive equations to estimate heat transfer coefficients in the combustion chamber of an RCE. This was accomplished by making detailed temperature and pressure measurements in a direct injection stratified charge (DISC) RCE under a range of conditions. For each specific measurement point, the local gas velocity was assumed equal to the local rotor tip speed. Local physical properties of the fluids were then calculated. Two types of correlation equations were derived and are described in this paper. The first correlation expresses the Nusselt number as a function of the Prandtl number, Reynolds number, and characteristic temperature ratio; the second correlation expresses the forced convection heat transfer coefficient as a function of fluid temperature, pressure and velocity. 10 references.

  19. Charge transfer and triplet states in OPV materials and devices (Presentation Recording)

    NASA Astrophysics Data System (ADS)

    Dyakonov, Vladimir

    2015-10-01

    Electron back transfer (EBT), potentially occurring after electron transfer from donor to acceptor may populate the lower lying donor or acceptor triplet state and serve as recombination channel.[1] Here we report on studies of charge transfer and triplet states in blends of highly efficient benzodithiophene PTB7 polymer in combination with the fullerene-derivative PC71BM using the spin sensitive optically detected magnetic resonance (ODMR) technique and compare the results with those obtained in P3HT (poly(3- hexylthiophene):PC61BM blends. Although PTB7:PC71BM absorbers yield much higher power conversion efficiencies in solar cells exceeding 7%, we found a significant increase of triplet exciton generation, which was absent in the P3HT based blends. We discuss this observation within the EBT scenario with the emphasis on the influence of morphology, fullerene load, HOMO/LUMO energy and presence of additives (DIO). Suppressing the EBT process by morphology and/or energetics of polymer and molecules is important to achieve the full potential of highly efficient OPV materials. [1] M. Liedtke, et al., JACS 133, 9088 (2011).

  20. Radiation-induced charge transfer inefficiency in charge-coupled devices: Sentinel-4 CCD pre-development as a case study

    NASA Astrophysics Data System (ADS)

    Prod'homme, T.; Belloir, J.-M.; Weber, H.; Bazalgette Courrèges-Lacoste, G.; Meynart, R.; Nowicki-Bringuier, Y.-R.; Caron, J.; Levillain, Y.; Woffinden, C.; Lord, B.; Mackie, R.

    2014-10-01

    Energetic particles in space damage electronic components, and in particular affect the capability of Charge-Coupled Devices (CCD) to transfer photo-generated charge packets to the output node. If not properly accounted for either during the instrument design process or in the mission data processing pipeline, radiation-induced Charge Transfer Inefficiency (CTI) causes image distortion, decreases the signal-to-noise ratio, and ultimately leads to bias in the measurement carried out. CTI is a well-identified error budget contributor for mission operating in the photon-starving regime like space telescopes dedicated to Astronomy, but is less studied in the context of Earth Observation missions. We present a study conducted during the Sentinel-4/UVN CCD pre-development to provide a first assessment of the CTI effects on the Sentinel-4 measurements.

  1. Interplay between the charge ordering, ground states and lattice potential in quasi-one-dimensional organic charge transfer salts

    NASA Astrophysics Data System (ADS)

    Zhang, Fan

    2007-12-01

    TMTTF (tetramethyltetrathiafulvalene) and TMTSF (tetramethyltetraselenafulvalene) based organic charge transfer salts are representatives of highly correlated quasi-1D electron systems which exhibit rich variety of ground states that can be easily tuned by pressure. They have been the top interests among researchers for the past few decades. Some concepts, such as the interplay between the magnetism and superconductivity, are believed to hold the key to the understanding of the mechanism of the high Tc superconductivity. How the repulsive Coulomb interactions U and V control the phases in these systems and how they evolve with pressure, become the major concern of numerous theories and experiments. Here we present the NMR and EPR studies on two compounds of this family, namely, (TMTTF) 2SbF6 and (TMTSF)2ClO4. The 121Sb and 19F NMR measurements reveal that at ambient pressure, the anion SbF6 will align along a preferred orientation below a crossover temperature, T ˜ 120 K. This unique property of the anion adds an additional degree of freedom to the system. The pressure studies of the (TMTTF)2SbF 6 show that this compound should be positioned in the lower pressure regime of the generic phase diagram. At ambient pressure, the charge ordering (CO) state at higher temperatures suppresses the spin-Peierls (SP) instabilities and an antiferromagnetic (AF) ground state is realized at low temperatures. Both the CO and the AF states are found to be suppressed by pressure very quickly and the ground states under intermediate and higher pressures are determined by how much disorder is introduced into the system. For the more disordered samples, the ground states resemble the familiar sequence of AF?SP?AF while for the more relaxed samples, no long range order is observed down to 1.8K. This is refreshing since a lot of the properties in this particular state are very similar to those observed in K-(BEDT-TTF) 2Cu2(CN)3, which is believed to have a spin liquid ground state. Interestingly enough, this shows the anions are participating in a certain way in the formation of different electronic ground states. The compound (TMTSF)2ClO4 shows another example of how the electronic state can be controlled by the lattice potential. The ordering of the perchlorate anions results in a unit cell doubling hence two bands crossing at the Fermi level. The NMR measurements show that the fluctuation in anion orientations directly controls the spin density distributions between the stacks.

  2. An Integrated Professional and Transferable Skills Course for Undergraduate Chemistry Students

    ERIC Educational Resources Information Center

    Ashraf, S. Salman; Marzouk, Sayed A. M.; Shehadi, Ihsan A.; Murphy, Brian M.

    2011-01-01

    Upon graduation, chemistry majors often find themselves inadequately prepared for the "real world" that awaits them when they join the workplace. Some employers find chemistry graduates lacking written- and oral-communication skills, critical-thinking skills, group-work skills, as well as the ability to efficiently analyze data and retrieve…

  3. Gas-Phase Chemical Separation of Phosphatidylcholine and Phosphatidylethanolamine Cations via Charge Inversion Ion/Ion Chemistry.

    PubMed

    Rojas-Betancourt, Stella; Stutzman, John R; Londry, Frank A; Blanksby, Stephen J; McLuckey, Scott A

    2015-11-17

    The [M + H](+) cations formed upon electrospray ionization of the glycerophospholipids phosphatidylcholine (PC) and phosphatidylethanolamine (PE) show distinct reactivities upon gas-phase reactions with doubly deprotonated 1,4-phenylenedipropionic acid (PDPA). PC cations undergo charge inversion via adduct formation with subsequent methyl cation and proton transfer to the acid to yield [PC - CH3](-) anions. These demethylated PC anions fragment upon ion trap collision-induced dissociation (CID) to yield products that reveal fatty acid chain lengths and degrees of unsaturation. PE cations, on the other hand, undergo charge inversion via double proton transfer to the two carboxylate moieties in doubly deprotonated PDPA to yield [PE - H](-) anions. These anions also fragment upon ion trap CID to yield product ions indicative of chain lengths and degrees of unsaturation in the fatty acyl moieties. Advantage is taken of this distinct reactivity to separate isomeric and isobaric PC and PE cations present in mass spectra of lipid mixtures. A cation precursor ion population containing a mixture of PE and PC cations is mass-selected and subjected to ion/ion charge inversion reactions that result in separation of PC and PE anions into different mass-to-charge ratios. Mass selection and subsequent ion trap CID of the lipid anions allows for the characterization of the isomeric lipids within each subclass. The charge inversion approach described here is demonstrated to provide increased signal-to-noise ratios for detection of PCs and PEs relative to the standard negative ionization approach as well as improved mixture analysis performance. PMID:26477819

  4. Charge transfer states as traps in organic solar cells (Presentation Recording)

    NASA Astrophysics Data System (ADS)

    Arndt, Andreas; Gerhard, Marina; Quintilla, Aina; Howard, Ian; Koch, Martin; Lemmer, Uli

    2015-10-01

    We investigate the NIR time-resolved photoluminescence of a series of P3HT:PC61BM solar cells with varying blend ratios after preferential excitation of the PC61BM and P3HT components respectively. Besides the rapid and diffusion-limited quenching of singlet excitons we resolve a weak emission feature in the near-infrared that our measurements confirm comes from interfacial charge-transfer (CT) states. This CT state emission becomes stronger for samples with an excess of PC61BM, and also after selective excitation of the PC61BM component. In this way, we show that these NIR time-resolved photoluminescence measurements provide an accurate method of observing subtle changes in the formation and dynamics of CT states at organic heterojunctions due to its high selectivity, and suggest that PC61BM excitons are more likely to lead to geminately recombining CT states than are the excitons created on P3HT. We also measure the temperature dependence of the transient NIR photoluminescence and find that while the intensity of the NIR emission is temperature dependent, its lifetime is not. This interesting observation suggests that the CT states we observe are formed through a precursor state which can either form separated charges or CT states, and that the relative yield of these two pools is temperature dependent. Furthermore, it indicates that charges within these relaxed CT states are trapped at the donor-acceptor interface and cannot contribute to free-charge generation via thermal activation anymore.

  5. The role of spin exchange in charge transfer in low-bandgap polymer: Fullerene bulk heterojunctions

    SciTech Connect

    Krinichnyi, V. I. Yudanova, E. I.; Denisov, N. N.

    2014-07-28

    Formation, relaxation and dynamics of polarons and methanofullerene anion radicals photoinitiated in poly[N-9?-hepta-decanyl-2,7-carbazole-alt-5,5-(4?,7?-di-2-thienyl-2?,1?, 3?-benzothiadiazole)]:-[6,6]-phenyl-C{sub 61}-butyric acid methyl ester (PCDTBT:PC{sub 61}BM) bulk heterojunctions were studied mainly by light-induced EPR (LEPR) spectroscopy in wide photon energy and temperature ranges. Some polarons are pinned by spin traps whose number and depth are governed by the composite morphology and photon energy. The proximity of the photon energy and the polymer bandgap reduces the number of such traps, inhibits recombination of mobile charge carriers, and facilitates their mobility in polymer network. Spin relaxation and charge carrier dynamics were studied by the steady-state saturation method at wide range of temperature and photon energy. These processes were shown to be governed by spin exchange as well as by the photon energy. Charge transfer in the composite is governed by the polaron scattering on the lattice phonons of crystalline domains embedded into amorphous polymer matrix and its activation hopping between polymer layers. The energy barrier required for polaron interchain hopping exceeds that of its intrachain diffusion. Anisotropy of polaron dynamics in the PCDTBT:PC61BM composite is less than that of poly(3-alkylthiophenes)-based systems that evidences for better ordering of the former. Lorentzian shape of LEPR lines of both charge carriers, lower concentration of spin traps as well as behaviours of the main magnetic resonance parameters were explained by layer ordered morphology of polymer matrix.

  6. Charge efficiency of Ni/H2 cells during transfer orbit of Telstar 4 satellites

    NASA Technical Reports Server (NTRS)

    Fang, W. C.; Maurer, Dean W.; Vyas, B.; Thomas, M. N.

    1994-01-01

    The TELSTAR 4 communication satellites being manufactured by Martin Marietta Astro Space (Astro Space) for AT&T are three axis stabilized spacecraft scheduled to be launched on expendable vehicles such as the Atlas or Ariane rockets. Typically, these spacecraft consist of a box that holds the electronics and supports the antenna reflectors and the solar array wings. The wings and reflectors are folded against the sides of the box during launch and the spacecraft is spun for attitude control in that phase; they are then deployed after achieving the final orbit. The launch phase and transfer orbits required to achieve the final geosynchronous orbit typically take 4 to 5 days during which time the power required for command, telemetry, attitude control, heaters, etc., is provided by two 50 AH nickel hydrogen batteries augmented by the exposed outboard solar panels. In the past, this situation has presented no problem since there was a considerable excess of power available from the array. In the case of large high powered spacecraft such as TELSTAR 4, however, the design power levels in transfer orbit approach the time-averaged power available from the exposed surface area of the solar arrays, resulting in a very tight power margin. To compound the difficulty, the array output of the spinning spacecraft in transfer orbit is shaped like a full wave rectified sine function and provides very low charging rates to the batteries during portions of the rotation. In view of the typically low charging efficiency of alkaline nickel batteries at low rates, it was decided to measure the efficiency during a simulation of the TELSTAR 4 conditions at the expected power levels and temperatures on three nickel hydrogen cells of similar design. The unique feature of nickel hydrogen cells that makes the continuous measurement of efficiency possible is that hydrogen is one of the active materials and thus, cell pressure is a direct measure of the state of charge or available capacity. The pressure is measured with a calibrated strain gage mounted on the outside of the pressurized cell.

  7. Synthesis, characterization, crystal structure and solution studies of a novel proton transfer (charge transfer) complex of 2,2?-dipyridylamine with 2,6-pyridine dicarboxylic acid

    NASA Astrophysics Data System (ADS)

    Ghasemi, Khaled; Rezvani, Ali Reza; Shokrollahi, Ardeshir; Zarghampour, Fereshteh; Moghimi, Abolghasem; García-Granda, Santiago; Mendoza-Meroño, Rafael

    2015-06-01

    Reaction between 2,2?-dipyridylamine (DPA) and 2,6-pyridine dicarboxylic acid (dipicolinic acid, dipicH2), in water results in the formation of a proton transfer or charge transfer (CT) complex, (DPAH)+(dipicH)-·H2O, 1. The characterization was performed using 1H NMR and FTIR spectroscopy, elemental analysis and X-ray crystallography. The crystal system is triclinic with space group P1. The structural investigations exhibit that the hydrogen bonds and ?-? stacking interactions stabilize the crystal structure of proton transfer complex. The protonation constants of 2,6-pyridine dicarboxylic acid, 2,2?-dipyridylamine and the equilibrium constants for dipic-DPA (1:1) proton transfer system were calculated by potentiometric pH titration method using Hyperquad2008 program. The stoichiometries of the proton transfer species in solution was in agreement with the solid state result.

  8. Preparation and spectroscopic studies on charge-transfer complexes of 2,2'-bipyridine with picric and chloranilic acids

    NASA Astrophysics Data System (ADS)

    Teleb, Said M.; Gaballa, Akmal S.

    2005-11-01

    Charge-transfer (CT) complexes formed on the reaction of 2,2'-bipyridine with some acceptors such as picric acid (HPA) and chloranilic acid (H 2CA) have been studied in CHCl 3 and MeOH at room temperature. Based on elemental analysis and IR spectra of the solid CT complexes along with the photometric titration curves for the reactions, the data obtained indicate the formation of 1:1 charge-transfer complexes [(bpyH)(PA)] and [(bpyH 2)(CA)], respectively. The infrared and 1H NMR spectroscopic data indicate a charge-transfer interaction associated with a proton migration from the acceptor to the donor followed by intramolecular hydrogen bonding. The formation constants ( KC) for the complexes were shown to be dependent on the structure of the electron acceptors used.

  9. Further perspectives on the charge transfer transitions of blue copper proteins and the ligand moieties in stellacyanin

    PubMed Central

    McMillin, David R.; Morris, Margaret C.

    1981-01-01

    The charge transfer spectra of plastocyanin and azurin are analyzed in detail, taking into account the structural information that is available. The number and relative energies of the low-lying charge transfer bands attributable to cysteine and methionine sulfur are considered with reference to the energy levels associated with the donor centers and to experimental work on relevant complexes. Two cysteine ? Cu(II) charge transfer transitions are assigned to bands that occur near 620 nm and near 770 nm. Energy considerations suggest that the methionine ? Cu(II) transition occurs in the vicinity of 550 nm for both plastocyanin and azurin. The existence of a disulfide linkage in stellacyanin is established by thiol titrations, and the possibility exists that the fourth ligand in stellacyanin may involve disulfide sulfur. If so, the cystine ? Cu(II) transition is also expected to appear around 550 nm. PMID:16593109

  10. Carbon-, sulfur-, and phosphorus-based charge transfer reactions in inductively coupled plasma-atomic emission spectrometry

    NASA Astrophysics Data System (ADS)

    Grindlay, Guillermo; Gras, Luis; Mora, Juan; de Loos-Vollebregt, Margaretha T. C.

    2016-01-01

    In this work, the influence of carbon-, sulfur-, and phosphorus-based charge transfer reactions on the emission signal of 34 elements (Ag, Al, As, Au, B, Ba, Be, Ca, Cd, Co, Cr, Cu, Fe, Ga, Hg, I, In, Ir, K, Li, Mg, Mn, Na, Ni, P, Pb, Pd, Pt, S, Sb, Se, Sr, Te, and Zn) in axially viewed inductively coupled plasma-atomic emission spectrometry has been investigated. To this end, atomic and ionic emission signals for diluted glycerol, sulfuric acid, and phosphoric acid solutions were registered and results were compared to those obtained for a 1% w w- 1 nitric acid solution. Experimental results show that the emission intensities of As, Se, and Te atomic lines are enhanced by charge transfer from carbon, sulfur, and phosphorus ions. Iodine and P atomic emission is enhanced by carbon- and sulfur-based charge transfer whereas the Hg atomic emission signal is enhanced only by carbon. Though signal enhancement due to charge transfer reactions is also expected for ionic emission lines of the above-mentioned elements, no experimental evidence has been found with the exception of Hg ionic lines operating carbon solutions. The effect of carbon, sulfur, and phosphorus charge transfer reactions on atomic emission depends on (i) wavelength characteristics. In general, signal enhancement is more pronounced for electronic transitions involving the highest upper energy levels; (ii) plasma experimental conditions. The use of robust conditions (i.e. high r.f. power and lower nebulizer gas flow rates) improves carbon, sulfur, and phosphorus ionization in the plasma and, hence, signal enhancement; and (iii) the presence of other concomitants (e.g. K or Ca). Easily ionizable elements reduce ionization in the plasma and consequently reduce signal enhancement due to charge transfer reactions.

  11. Exciton delocalization, charge transfer, and electronic coupling for singlet excitation energy transfer between stacked nucleobases in DNA: An MS-CASPT2 study

    SciTech Connect

    Blancafort, Lluís; Voityuk, Alexander A.

    2014-03-07

    Exciton delocalization and singlet excitation energy transfer have been systematically studied for the complete set of 16 DNA nucleobase dimers in their ideal, single-strand stacked B-DNA conformation, at the MS-CASPT2 level of theory. The extent of exciton delocalization in the two lowest (?,?{sup *}) states of the dimers is determined using the symmetrized one-electron transition density matrices between the ground and excited states, and the electronic coupling is calculated using the delocalization measure and the energy splitting between the states [see F. Plasser, A. J. A. Aquino, W. L. Hase, and H. Lischka, J. Phys. Chem. A 116, 11151–11160 (2012)]. The calculated couplings lie between 0.05 eV and 0.14 eV. In the B-DNA conformation, where the interchromophoric distance is 3.38 Å, our couplings deviate significantly from those calculated with the transition charges, showing the importance of orbital overlap components for the couplings in this conformation. The calculation of the couplings is based on a two-state model for exciton delocalization. However, in three stacks with a purine in the 5{sup ?} position and a pyrimidine in the 3{sup ?} one (AT, GC, and GT), there is an energetically favored charge transfer state that mixes with the two lowest excited states. In these dimers we have applied a three-state model that considers the two locally excited diabatic states and the charge transfer state. Using the delocalization and charge transfer descriptors, we obtain all couplings between these three states. Our results are important in the context of DNA photophysics, since the calculated couplings can be used to parametrize effective Hamiltonians to model extended DNA stacks. Our calculations also suggest that the 5{sup ?}-purine-pyrimidine-3{sup ?} sequence favors the formation of charge transfer excited states.

  12. Electron-molecule chemistry and charging processes on organic ices and Titan's icy aerosol surrogates

    NASA Astrophysics Data System (ADS)

    Pirim, C.; Gann, R. D.; McLain, J. L.; Orlando, T. M.

    2015-09-01

    Electron-induced polymerization processes and charging events that can occur within Titan's atmosphere or on its surface were simulated using electron irradiation and dissociative electron attachment (DEA) studies of nitrogen-containing organic condensates. The DEA studies probe the desorption of H- from hydrogen cyanide (HCN), acetonitrile (CH3CN), and aminoacetonitrile (NH2CH2CN) ices, as well as from synthesized tholin materials condensed or deposited onto a graphite substrate maintained at low temperature (90-130 K). The peak cross sections for H- desorption during low-energy (3-15 eV) electron irradiation were measured and range from 3 × 10-21 to 2 × 10-18 cm2. Chemical and structural transformations of HCN ice upon 2 keV electron irradiation were investigated using X-ray photoelectron and Fourier-transform infrared spectroscopy techniques. The electron-beam processed materials displayed optical properties very similar to tholins produced by conventional discharge methods. Electron and negative ion trapping lead to 1011 charges cm-2 on a flat surface which, assuming a radius of 0.05 ?m for Titan aerosols, is ?628 charges/radius (in ?m). The facile charge trapping indicates that electron interactions with nitriles and complex tholin-like molecules could affect the conductivity of Titan's atmosphere due to the formation of large negative ion complexes. These negatively charged complexes can also precipitate onto Titan's surface and possibly contribute to surface reactions and the formation of dunes.

  13. Photoinitiated charge separation in a carotenoid-porphyrin-diquinone tetra: enhanced quantum yields via multistep electron transfers

    SciTech Connect

    Gust, D.; Moore, T.A.; Moore, A.L.; Barrett, D.; Harding, L.O.; Makings, L.R.; Liddell, P.A.; De Schryver, F.C.; Van der Auweraer, M.; Bensasson, R.; Rougee, M.

    1988-01-06

    Photosynthesis converts light to chemical potential energy in the form of long-lived charge separation across a bilayer membrane. Recombination of the charge-separated state is prevented by the large distance between the final electron donor and acceptor. Because the quantum yield of a single long-range electron transfer across the bilayer would be vanishingly small, reaction centers employ a series of electron-transfer steps, each of which occurs over a short distance with high yield. Synthetic carotenoid-porphyrin-quinone triad molecules and other molecular systems which begin to model this approach have recently been reported. In photosynthetic bacteria, the charge separation sequence includes electron donation from a bacteriopheophytin to a quinone which then transfers an electron to a second quinone. An elegant molecule that models such electron transfer has been prepared, although it did not reproduce the long-lived charge separation characteristic of the natural system. The authors now report the synthesis of a tetrachromophoric molecule 1 consisting of a porphyrin (P) covalently linked to both a carotenoid polyene (C) and a rigid diquinone moiety (Q/sub A/-Q/sub B/), excitation of which produces a long-lived (460 ns in dichloromethane, 4 ..mu..s in acetonitrile charge-separated state C/sup .+/-P-Q/sub A/-Q/sub B//sup 0 -/ with a quantum yield of 0.23 at ambient temperatures and 0.50 at 240 K.

  14. Charge transfer in graphene oxide-dye system for photonic applications

    NASA Astrophysics Data System (ADS)

    Bongu, Sudhakara Reddy; Bisht, Prem B.; Thu, Tran V.; Sandhu, Adarsh

    2014-02-01

    The fluorescence of a standard dye Rhodamine 6G (R6G) in solution decreases on addition of reduced graphene oxide (rGO). The absorption spectra and lifetime measurements confirm that no excited-state but a ground-state complex formation is responsible for this effect. For silver decorated rGO (Ag-rGO), the quenching efficiency and ground state complex formation process is small. Z-scan measurements have been done to study the optical nonlinearity at 532 nm under ps time scale. Remarkable reduction in the saturable absorption (SA) effect of R6G indicates no nonlinear contribution from the ground state complex. The results have been explained with varying charge transfer rates and non-fluorescence nature of the complex.

  15. Engineering high charge transfer n-doping of graphene electrodes and its application to organic electronics.

    PubMed

    Sanders, Simon; Cabrero-Vilatela, Andrea; Kidambi, Piran R; Alexander-Webber, Jack A; Weijtens, Christ; Braeuninger-Weimer, Philipp; Aria, Adrianus I; Qasim, Malik M; Wilkinson, Timothy D; Robertson, John; Hofmann, Stephan; Meyer, Jens

    2015-08-14

    Using thermally evaporated cesium carbonate (Cs2CO3) in an organic matrix, we present a novel strategy for efficient n-doping of monolayer graphene and a ?90% reduction in its sheet resistance to ?250 Ohm sq(-1). Photoemission spectroscopy confirms the presence of a large interface dipole of ?0.9 eV between graphene and the Cs2CO3/organic matrix. This leads to a strong charge transfer based doping of graphene with a Fermi level shift of ?1.0 eV. Using this approach we demonstrate efficient, standard industrial manufacturing process compatible graphene-based inverted organic light emitting diodes on glass and flexible substrates with efficiencies comparable to those of state-of-the-art ITO based devices. PMID:26176814

  16. Optical charge transfer for the dope in GaAs

    SciTech Connect

    Vakulenko, O.V.; Skirda, A.S.; Skryshevskii, V.A.

    1984-05-01

    It is concluded that the chromium dope is amphoteric in behavior on the basis of the spectra, kinetics, and lux-ampere characteristics of the absorption and photoconductivity induced by 1.15-um IR laser radiation in high-resistance specimens of GaAs. It is assumed that the additional IR illumination produces optical charge transfer in the chromium in accordance with Cr/sup 3 +/3d/sup 3/ + h..nu.. ..-->.. Cr/sup 2 +/3d/sup 4/ + Cr/sup 4 +/3d/sup 2/. The photoneutralization of the Cr/sup 4 +/3d/sup 2/ centers is responsible for additional optical-absorption and photoconductivity bands appearing in the long-wave region. The kinetic equations for these centers are solved, which describes the experimental results satisfactorily. It is suggested that chromium may compensate not only shallow donors in GaAs but also shallow acceptors.

  17. Mechanisms for charge-transfer processes at electrode/solid-electrolyte interfaces.

    SciTech Connect

    Chueh, William; El Gabaly Marquez, Farid; Whaley, Josh A.; McCarty, Kevin F.; McDaniel, Anthony H.; Farrow, Roger L.

    2011-11-01

    This report summarizes the accomplishments of a Laboratory-Directed Research and Development (LDRD) project focused on developing and applying new x-ray spectroscopies to understand and improve electric charge transfer in electrochemical devices. Our approach studies the device materials as they function at elevated temperature and in the presence of sufficient gas to generate meaningful currents through the device. We developed hardware and methods to allow x-ray photoelectron spectroscopy to be applied under these conditions. We then showed that the approach can measure the local electric potentials of the materials, identify the chemical nature of the electrochemical intermediate reaction species and determine the chemical state of the active materials. When performed simultaneous to traditional impedance-based analysis, the approach provides an unprecedented characterization of an operating electrochemical system.

  18. Charge transfer in Fe-doped GaN: The role of the donor

    SciTech Connect

    Sunay, Ustun; Dashdorj, J.; Zvanut, M. E.; Harrison, J. G.; Leach, J. H.; Udwary, K.

    2014-02-21

    Several nitride-based device structures would benefit from the availability of high quality, large-area, freestanding semi-insulating GaN substrates. Due to the intrinsic n-type nature of GaN, however, the incorporation of compensating centers such as Fe is necessary to achieve the high resistivity required. We are using electron paramagnetic resonance (EPR) to explore charge transfer in 450 um thick GaN:Fe plates to understand the basic mechanisms related to compensation so that the material may be optimized for device applications. The results suggest that the simple model based on one shallow donor and a single Fe level is insufficient to describe compensation. Rather, the observation of the neutral donor and Fe3+ indicates that either the two species are spatially segregated or additional compensating and donor defects must be present.

  19. Direct observation of collective modes coupled to molecular orbital-driven charge transfer.

    PubMed

    Ishikawa, Tadahiko; Hayes, Stuart A; Keskin, Sercan; Corthey, Gastón; Hada, Masaki; Pichugin, Kostyantyn; Marx, Alexander; Hirscht, Julian; Shionuma, Kenta; Onda, Ken; Okimoto, Yoichi; Koshihara, Shin-ya; Yamamoto, Takashi; Cui, Hengbo; Nomura, Mitsushiro; Oshima, Yugo; Abdel-Jawad, Majed; Kato, Reizo; Miller, R J Dwayne

    2015-12-18

    Correlated electron systems can undergo ultrafast photoinduced phase transitions involving concerted transformations of electronic and lattice structure. Understanding these phenomena requires identifying the key structural modes that couple to the electronic states. We report the ultrafast photoresponse of the molecular crystal Me4P[Pt(dmit)2]2, which exhibits a photoinduced charge transfer similar to transitions between thermally accessible states, and demonstrate how femtosecond electron diffraction can be applied to directly observe the associated molecular motions. Even for such a complex system, the key large-amplitude modes can be identified by eye and involve a dimer expansion and a librational mode. The dynamics are consistent with the time-resolved optical study, revealing how the electronic, molecular, and lattice structures together facilitate ultrafast switching of the state. PMID:26680192

  20. Supramolecular fullerene/porphyrin charge transfer interaction studied by absorption spectrophotometric method

    NASA Astrophysics Data System (ADS)

    Mukherjee, Partha; Bhattacharya (Banerjee), Shrabanti; Nayak, Sandip K.; Chattopadhyay, Subrata; Bhattacharya, Sumanta

    2009-06-01

    A detailed UV-Vis spectrometric and thermodynamic studies were done to look insight into the nature of molecular interactions of the electron donor-acceptor complexes of C60 and C70 with 5,10,15,20-tetrakis(octadecyloxyphenyl)-21H,23H-porphyrin (1) in chloroform and toluene. Charge transfer (CT) absorption bands were located in the visible region and vertical ionization potential of 1 was determined utilizing CT transition energy. Low values of oscillator and transition dipole strengths suggested that the complexes were almost of neutral character in ground states. The high binding constant value for the C70-1 complex indicated high selectivity of 1 molecule towards C70. Experimental as well as theoretically determined of enthalpies of formation value substantiated the trend in K values for fullerene-1 complexes.

  1. Enhancement of thermal expansion of organic charge-transfer salts by strong electronic correlations

    NASA Astrophysics Data System (ADS)

    Kokalj, J.; McKenzie, Ross H.

    2015-05-01

    Organic charge-transfer salts exhibit thermal expansion anomalies similar to those found in other strongly correlated electron systems. The thermal expansion can be anisotropic and have a nonmonotonic temperature dependence. We show how these anomalies can arise from electronic effects and be significantly enhanced, particularly at temperatures below 100 K, by strong electronic correlations. For the relevant Hubbard model the thermal expansion is related to the dependence of the entropy on the parameters (t , t', and U ) in the Hamiltonian or the temperature dependence of bond orders and double occupancy. The latter are calculated on finite lattices with the finite-temperature Lanczos method. Although many features seen in experimental data, in both the metallic and Mott insulating phase, are described qualitatively, the calculated magnitude of the thermal expansion is smaller than that observed experimentally.

  2. Synthesis, characterization and biological studies of a charge transfer complex: 2-Aminopyridinium-4-methylbenzenesulfonate

    NASA Astrophysics Data System (ADS)

    Vadivelan, Ganesan; Saravanabhavan, Munusamy; Murugesan, Venkatesan; Sekar, Marimuthu

    2015-06-01

    A single crystal charge transfer (CT) complex, 2-aminopyridinium-4-methylbenzenesulfonate (APTS) was synthesized and recrystallized by slow solvent evaporation solution growth method at room temperature. The complex has been characterized with the elemental analysis, UV-visible, infrared (IR), 1H and 13C nuclear magnetic resonance (NMR) spectra. Thermogravimetric (TG) and differential thermal analysis (DTA) were reported the thermal behaviour of the complex. Single crystal XRD studies showed that the orthorhombic nature of the crystal with space group Pbca. The biological activities of CT complex, such as DNA binding and antioxidant activity has been carried out. The results indicated that the compound could interact with DNA through intercalation and show significant capacity of scavenging with 2,2-diphenyl-2-picryl-hydrazyl (DPPH).

  3. Symmetric charge-transfer cross sections of IIIa rare-earth-metal elements

    SciTech Connect

    Hashida, Masaki; Sakabe, Shuji; Izawa, Yasukazu

    2011-03-15

    Symmetric charge-transfer cross sections of IIIa rare-earth-metal elements (Sc, Y, and Gd) in the impact energy range of 30 to 1000 eV were measured for the first time. The experiments were performed with a crossed-beam apparatus that featured primary ion production by photoionization with a tunable dye laser. Comparing the cross sections of IIIa rare-earth-metal elements ({sigma}{sub Sc}, {sigma}{sub Y}, and {sigma}{sub Gd}) with those of alkali metals or helium {sigma}{sub 0}, we found that {sigma}{sub 0{approx_equal}{sigma}Sc}<{sigma}{sub Y}<{sigma}{sub Gd{approx_equal}}2{sigma}{sub 0}at an impact energy of 1000 eV.

  4. Raman study of the charge transfer C 60 complexes with tetraphenylphosphonium halides

    NASA Astrophysics Data System (ADS)

    Sauvajol, J. L.; Graja, A.; Firlej, L.; Król, S.

    1997-12-01

    Raman spectra are presented for single crystal charge-transfer complexes of fullerene and tetraphenylphosphonium halides, (Ph 4P) 2C 60Y (Y = Cl, Br, I). The Raman spectrum is found to be insensitive to the halogen ion indicating the intrinsic character of this spectrum. The spectra of complexes excited at 514.5 nm look very different from those excited at 647.1 nm; especially the low-frequency modes are stronger in the Raman spectrum excited at 647.1 nm. The 1469 cm -1 pentagonal pinch mode of C 60 is shifted and split in these complexes, a double-peak structure with components at 1462 and 1452 cm -1 is observed. All these results are understood as due to the presence of C -60 in crystalline sites of low symmetry.

  5. New measurement scheme to investigate low energy charge transfer in H + H 2 +

    NASA Astrophysics Data System (ADS)

    Andrianarijaona, V. M.

    2015-05-01

    The merged-beam apparatus at Oak Ridge National Laboratory (ORNL) in Oak Ridge, Tennessee, can reliably access low energy charge transfer in H + H2+ --> H+ + H2 and is able to benchmark the total cross section at 200 to under 0.1 eV/u, but is not equipped with a device that would provide the ro-vibrational state distribution of the primary molecular ions. A new experimental scheme, which will allow to upgrade the heretofore only total absolute cross section measurements to vibrationally resolved cross section measurements and will make comparison to state-to-state calculations possible, will be presented. Work supported by the National Science Foundation under Grant No. PHY-1068877.

  6. An Investigation of CCD Charge Transfer and Detector Anomalies for a Low Light Level Application

    NASA Astrophysics Data System (ADS)

    Dixon, Samantha; Aldering, Greg Scott; Domagalski, Rachel; Boone, Kyle; Fagrelius, Parker; Hayden, Brian; Perlmutter, Saul; Saunders, Clare; Sofiatti, Caroline

    2016-01-01

    The SuperNova Integral Field Spectrograph (SNIFS) is used to obtain spectra of nearby Type Ia supernovae as part of the Nearby Supernova Factory. Charge transfer inefficiency (CTI) in the CCD detectors used on SNIFS has the potential to cause distortions to spectra and increase noise. We present a study of the CTI in the SNIFS CCDs using trails from cosmic rays in dark frames. This study shows that the effect of CTI on supernova spectra is minimal, and additionally reveals a detector anomaly, a 1 e- undershoot, that is correlated with lower temperatures of the SDSU ARC electronics. We will also present plans for the characterization of new, lower noise, faster readout CCDs from Lawrence Berkeley National Laboratory as part of an upgrade of SNIFS.

  7. Bottom-up formation of endohedral mono-metallofullerenes is directed by charge transfer.

    PubMed

    Dunk, Paul W; Mulet-Gas, Marc; Nakanishi, Yusuke; Kaiser, Nathan K; Rodríguez-Fortea, Antonio; Shinohara, Hisanori; Poblet, Josep M; Marshall, Alan G; Kroto, Harold W

    2014-01-01

    An understanding of chemical formation mechanisms is essential to achieve effective yields and targeted products. One of the most challenging endeavors is synthesis of molecular nanocarbon. Endohedral metallofullerenes are of particular interest because of their unique properties that offer promise in a variety of applications. Nevertheless, the mechanism of formation from metal-doped graphite has largely eluded experimental study, because harsh synthetic methods are required to obtain them. Here we report bottom-up formation of mono-metallofullerenes under core synthesis conditions. Charge transfer is a principal factor that guides formation, discovered by study of metallofullerene formation with virtually all available elements of the periodic table. These results could enable production strategies that overcome long-standing problems that hinder current and future applications of metallofullerenes. PMID:25524825

  8. Spectrophotometric determination of some pharmaceutical amides through charge-transfer complexation reactions.

    PubMed

    Saleh, G A; Askal, H F

    1991-01-01

    A spectrophotometric method is described for the assay of fenpipramide hydrochloride, isopropamide iodide, trimethobenzamide hydrochloride, morphazinamide hydrochloride and tolazamide. The method is based on the formation of a charge-transfer complex between the drug as n-donor and iodine, a sigma-acceptor. The product exhibits absorption maxima at 295 and 365 nm; measurements are made at 365 nm for fenpipramide and at 295 nm for the other compounds. Beer's law is obeyed in a concentration range of 1-120 micrograms ml-1. The method is rapid, simple and sensitive and can be applied to the analysis of some commercial and laboratory prepared tablets without interference. A more detailed investigation of the complex was made with respect to its composition, association constant and free energy change. PMID:1678622

  9. Photoinduced charge transfer and acetone sensitivity of single-walled carbon nanotube-titanium dioxide hybrids.

    PubMed

    Ding, Mengning; Sorescu, Dan C; Star, Alexander

    2013-06-19

    The unique physical and chemical properties of single-walled carbon nanotubes (SWNTs) make them ideal building blocks for the construction of hybrid nanostructures. In addition to increasing the material complexity and functionality, SWNTs can probe the interfacial processes in the hybrid system. In this work, SWNT-TiO2 core/shell hybrid nanostructures were found to exhibit unique electrical behavior in response to UV illumination and acetone vapors. By experimental and theoretical studies of UV and acetone sensitivities of different SWNT-TiO2 hybrid systems, we established a fundamental understanding on the interfacial charge transfer between photoexcited TiO2 and SWNTs as well as the mechanism of acetone sensing. We further demonstrated a practical application of photoinduced acetone sensitivity by fabricating a microsized room temperature acetone sensor that showed fast, linear, and reversible detection of acetone vapors with concentrations in few parts per million range. PMID:23734594

  10. Single charge transfer in {{\\rm{C}}}^{6+} collisions with H and He atoms

    NASA Astrophysics Data System (ADS)

    Pindzola, M. S.; Fogle, M.

    2015-10-01

    A time-dependent lattice (TDL) method is used to calculate state selective charge transfer cross sections in {{{C}}}6+ collisions with H and He atoms. The {{{C}}}6+(nl) capture cross sections for energies of 2.7, 5.2, and 8.3 keV amu-1 are found to be in good agreement with recent atomic-orbital close-coupling (AOCC) calculations for H and somewhat larger than previous AOCC calculations for He. Using standard radiative transition rates, Lyman ?/? and ?/? line ratios are calculated using TDL and AOCC capture cross sections for both H and He. The theoretical line ratios for He are found to bracket recent experimental measurements.

  11. Low-energy charge transfer for collisions of Si3+ with atomic hydrogen

    NASA Astrophysics Data System (ADS)

    Bruhns, H.; Kreckel, H.; Savin, D. W.; Seely, D. G.; Havener, C. C.

    2008-06-01

    Cross sections of charge transfer for Si3+ ions with atomic hydrogen at collision energies of ?40-2500eV/u were carried out using a merged-beam technique at the Multicharged Ion Research Facility at Oak Ridge National Laboratory. The data span an energy range in which both molecular orbital close coupling (MOCC) and classical trajectory Monte Carlo (CTMC) calculations are available. The influence of quantum mechanical effects of the ionic core as predicted by MOCC is clearly seen in our results. However, discrepancies between our experiment and MOCC results toward higher collision energies are observed. At energies above 1000 eV/u good agreement is found with CTMC results.

  12. Low Energy Charge Transfer for Collisions of Si3+ with Atomic Hydrogen

    SciTech Connect

    Bruhns, H.; Kreckel, H.; Savin, D. W.; Seely, D. G.; Havener, Charles C

    2008-01-01

    Cross sections of charge transfer for Si{sup 3+} ions with atomic hydrogen at collision energies of {approx} 40-2500 eV/u were carried out using a merged-beam technique at the Multicharged Ion Research Facility at Oak Ridge National Laboratory. The data span an energy range in which both molecular orbital close coupling (MOCC) and classical trajectory Monte Carlo (CTMC) calculations are available. The influence of quantum mechanical effects of the ionic core as predicted by MOCC is clearly seen in our results. However, discrepancies between our experiment and MOCC results toward higher collision energies are observed. At energies above 1000 eV/u good agreement is found with CTMC results.

  13. Charge transfer behavior of graphene-titania photoanode in CO2 photoelectrocatalysis process

    NASA Astrophysics Data System (ADS)

    Hasan, Md. Rakibul; Hamid, Sharifah Bee Abd; Basirun, Wan Jeffrey

    2015-06-01

    In the present study, a graphene-titania composite photoelectrode was synthesized, characterized and examined for the photoelectrocatalytic (PEC) response. The charge transfer process on the semiconductor/electrolyte interface was investigated via electrochemical impedance spectroscopy (EIS) and voltammetry. In addition, the influence of pH toward the photoanode performance was also investigated and it was noticed that a high pH condition was favorable higher photocurrent response from the EIS measurements. The main reason could be attributed to the decrease of recombination process at the photoanode with fast quenching of the photogenerated holes with OH- ions at high pH. The experiment was also run for CO2 photoreduction and increased photocurrent was observed.

  14. The exact forces on classical nuclei in non-adiabatic charge transfer.

    PubMed

    Agostini, Federica; Abedi, Ali; Suzuki, Yasumitsu; Min, Seung Kyu; Maitra, Neepa T; Gross, E K U

    2015-02-28

    The decomposition of electronic and nuclear motion presented in Abedi et al. [Phys. Rev. Lett. 105, 123002 (2010)] yields a time-dependent potential that drives the nuclear motion and fully accounts for the coupling to the electronic subsystem. Here, we show that propagation of an ensemble of independent classical nuclear trajectories on this exact potential yields dynamics that are essentially indistinguishable from the exact quantum dynamics for a model non-adiabatic charge transfer problem. We point out the importance of step and bump features in the exact potential that are critical in obtaining the correct splitting of the quasiclassical nuclear wave packet in space after it passes through an avoided crossing between two Born-Oppenheimer surfaces and analyze their structure. Finally, an analysis of the exact potentials in the context of trajectory surface hopping is presented, including preliminary investigations of velocity-adjustment and the force-induced decoherence effect. PMID:25725727

  15. Charge transfer complex states in diketopyrrolopyrrole polymers and fullerene blends: Implications for organic solar cell efficiency

    NASA Astrophysics Data System (ADS)

    Moghe, D.; Yu, P.; Kanimozhi, C.; Patil, S.; Guha, S.

    2011-12-01

    The spectral photocurrent characteristics of two donor-acceptor diketopyrrolopyrrole (DPP)-based copolymers (PDPP-BBT and TDPP-BBT) blended with a fullerene derivative [6,6]-phenyl C61-butyric acid methyl ester (PCBM) were studied using Fourier-transform photocurrent spectroscopy (FTPS) and monochromatic photocurrent (PC) method. PDPP-BBT:PCBM shows the onset of the lowest charge transfer complex (CTC) state at 1.42 eV, whereas TDPP-BBT:PCBM shows no evidence of the formation of a midgap CTC state. The FTPS and PC spectra of P3HT:PCBM are also compared. The larger singlet state energy difference of TDPP-BBT and PCBM compared to PDPP-BBT/P3HT and PCBM obliterates the formation of a midgap CTC state resulting in an enhanced photovoltaic efficiency over PDPP-BBT:PCBM.

  16. Real time cumulant approach for charge-transfer satellites in x-ray photoemission spectra

    SciTech Connect

    Kas, Joshua J.; Vila, Fernando D.; Rehr, John J.; Chambers, Scott A.

    2015-03-01

    X-ray photoemission spectra generally exhibit satellite features in addition to quasi-particle peaks due to many-body excitations which have been of considerable theoretical and experimental interest. However, the satellites attributed to charge-transfer (CT) excitations in correlated materials have proved difficult to calculate from first principles. Here we report a real-time, real-space approach for such calculations based on a cumulant representation of the core-hole Green’s function and time-dependent density functional theory. This approach also yields an interpretation of CT satellites in terms of a complex oscillatory, transient response to a suddenly created core hole. Illustrative results for TiO2 and NiO are in good agreement with experiment.

  17. Second harmonic generation by charge-transfer excitons interacting with phonons

    SciTech Connect

    Reineker, P.; Yudson, V. I.

    2001-06-15

    Effects of exciton-phonon interaction on the nonlinear optical response of charge-transfer excitons (CTE) are studied in the framework of an exactly solvable model. It is found that the second order excitonic optical polarizability {beta} is modified due to the CTE-phonon interaction. For a nonresonant frequency range, where {beta} is relatively small, the change is not significant. On the contrary, in the vicinity of resonances (when the light frequency {omega}{approximately}{omega}{sub 0} or {omega}{approximately}{omega}{sub 0}/2, {omega}{sub 0} is the CTE transition frequency), the CTE-phonon interaction may remarkably diminish the value of {beta}. This should be taken into account when considering CTE systems in nonlinear optics.

  18. Charge-induced distortion and stabilization of surface transfer doped porphyrin films

    SciTech Connect

    Smets, Y.; Stark, C. B.; Wright, C. A.; Pakes, C. I.; Lach, S.; Schmitt, F.; Ziegler, C.; Wanke, M.; Ley, L.; Institut für Technische Physik, Universität Erlangen-Nürnberg, 91058 Erlangen

    2013-07-28

    The interaction between zinc-tetraphenylporphyrin (ZnTPP) and fullerenes (C{sub 60} and C{sub 60}F{sub 48}) are studied using ultraviolet photoelectron spectroscopy (UPS) and scanning tunneling microscopy (STM). Low temperature STM reveals highly ordered ZnTPP monolayers on Au(111). In contrast to C{sub 60}, a submonolayer coverage of C{sub 60}F{sub 48} results in long-range disorder of the underlying single ZnTPP layer and distortion of individual ZnTPP molecules. This is induced by substantial charge transfer at the organic-organic interface, revealed by the interface energetics from UPS. However, a second layer of ZnTPP prevents C{sub 60}F{sub 48} guests from breaking the self-assembled porphyrin template. This finding is important for understanding the growth behaviour of “bottom-up” functional nanostructures involving strong donor-acceptor heterojunctions in molecular electronics.

  19. Charge-induced distortion and stabilization of surface transfer doped porphyrin films

    NASA Astrophysics Data System (ADS)

    Smets, Y.; Stark, C. B.; Lach, S.; Schmitt, F.; Wright, C. A.; Wanke, M.; Ley, L.; Ziegler, C.; Pakes, C. I.

    2013-07-01

    The interaction between zinc-tetraphenylporphyrin (ZnTPP) and fullerenes (C60 and C60F48) are studied using ultraviolet photoelectron spectroscopy (UPS) and scanning tunneling microscopy (STM). Low temperature STM reveals highly ordered ZnTPP monolayers on Au(111). In contrast to C60, a submonolayer coverage of C60F48 results in long-range disorder of the underlying single ZnTPP layer and distortion of individual ZnTPP molecules. This is induced by substantial charge transfer at the organic-organic interface, revealed by the interface energetics from UPS. However, a second layer of ZnTPP prevents C60F48 guests from breaking the self-assembled porphyrin template. This finding is important for understanding the growth behaviour of "bottom-up" functional nanostructures involving strong donor-acceptor heterojunctions in molecular electronics.

  20. The exact forces on classical nuclei in non-adiabatic charge transfer

    SciTech Connect

    Agostini, Federica; Abedi, Ali; Suzuki, Yasumitsu; Min, Seung Kyu; Gross, E. K. U.; Maitra, Neepa T.

    2015-02-28

    The decomposition of electronic and nuclear motion presented in Abedi et al. [Phys. Rev. Lett. 105, 123002 (2010)] yields a time-dependent potential that drives the nuclear motion and fully accounts for the coupling to the electronic subsystem. Here, we show that propagation of an ensemble of independent classical nuclear trajectories on this exact potential yields dynamics that are essentially indistinguishable from the exact quantum dynamics for a model non-adiabatic charge transfer problem. We point out the importance of step and bump features in the exact potential that are critical in obtaining the correct splitting of the quasiclassical nuclear wave packet in space after it passes through an avoided crossing between two Born-Oppenheimer surfaces and analyze their structure. Finally, an analysis of the exact potentials in the context of trajectory surface hopping is presented, including preliminary investigations of velocity-adjustment and the force-induced decoherence effect.

  1. The synthesis and spectral properties of a stimuli-responsive D-?-A charge transfer dye

    NASA Astrophysics Data System (ADS)

    Kim, Sung-Hoon; Gwon, Seon-Yeong; Bae, Jin-Seok; Son, Young-A.

    2011-01-01

    A new donor-?-acceptor (D-?-A) type isophorone dye was synthesized by the condensation reaction between 2-(3,5,5-trimethylcyclohex-2-enylidene)-malononitrile and indole-3-carboxaldehyde. The chemical structure of the dye was characterized by 1H NMR, EA and MS. A novel, chromogenic, fluorescent dye based on indol as donor unit and isophorone as acceptor unit displayed marked UV-visible absorption changes and highly selective fluorescence quenching in the presence of fluoride ion. The dye also exhibited sizeable colour changes when used as a pH-induced molecular switch and as a detector for volatile organic compounds. The absorption and fluorescent intensity of the dye can be reversibly selected by protonation/deprotonation of the amine moiety via control of intramolecular charge transfer (ICT), leading to a molecular switch with "on" and "off" states.

  2. Spectroscopy of Photovoltaic Materials: Charge-Transfer Complexes and Titanium Dioxide

    NASA Astrophysics Data System (ADS)

    Dillon, Robert John

    The successful function of photovoltaic (PV) and photocatalytic (PC) systems centers primarily on the creation and photophysics of charge separated electron-hole pairs. The pathway leading to separate carriers varies by material; organic materials typically require multiple events to charge separate, whereas inorganic semiconductors can directly produce free carriers. In this study, time-resolved spectroscopy is used to provide insight into two such systems: 1) organic charge-transfer (CT) complexes, where electrons and holes are tightly bound to each other, and 2) Au-TiO2 core-shell nanostructures, where free carriers are directly generated. 1) CT complexes are structurally well defined systems consisting of donor molecules, characterized by having low ionization potentials, and acceptor molecules, characterized by having high electron affinities. Charge-transfer is the excitation of an electron from the HOMO of a donor material directly into the LUMO of the acceptor material, leading to an electron and hole separated across the donor:acceptor interface. The energy of the CT transition is often less than that of the bandgaps of donor and acceptor materials individually, sparking much interest if PV systems can utilize the CT band to generate free carriers from low energy photons. In this work we examine the complexes formed between acceptors tetracyanobenzene (TCNB) and tetracyanoquinodimethane (TCNQ) with several aromatic donors. We find excitation of the charge-transfer band of these systems leads to strongly bound electron-hole pairs that exclusively undergo recombination to the ground state. In the case of the TCNB complexes, our initial studies were flummoxed by the samples' generally low threshold for photo and mechanical damage. As our results conflicted with previous literature, a significant portion of this study was spent quantifying the photodegradation process. 2) Unlike the previous system, free carriers are directly photogenerated in TiO2, and the prime consideration is avoiding loss due to recombination of the electron and hole. In this study, four samples of core-shell Au-TiO 2 nanostructures are analyzed for their photocatalytic activity and spectroscopic properties. The samples were made with increasingly crystalline TiO2 shells. The more crystalline samples had higher photocatalytic activities, attributed to longer carrier lifetimes. The observed photophysics of these samples vary with excitation wavelength and detection method used. We find the time-resolved photoluminescence correlates with the samples' photocatalytic activities only when high energy, excitation wavelength less than or equal to 300 nm is used, while transient absorption experiments show no correlation regardless of excitation source. The results imply that photoexcitation with high energy photons can generate both reactive surface sites and photoluminescent surface sites in parallel. Both types of sites then undergo similar electron-hole recombination processes that depend on the crystallinity of the TiO2 shell. Surface sites created by low energy photons, as well as bulk TiO2 carrier dynamics that are probed by transient absorption, do not appear to be sensitive to the same dynamics that determine chemical reactivity.

  3. Charge transfer in some complexes of crown ether and of thiacrown ether with dihalogens: DFT study.

    PubMed

    Oftadeh, Mohsen; Kabiri, Ali

    2013-01-01

    The present study was carried out by focusing on the interaction between molecular complexes crown and thiacrown ethers such as 15-crown-5 (15C5), thia-15-crown-5 (T15C5), dithia-15-crown-5 (DT15C5) with homogeneous and heterogeneous dihalogens (XY) such as I2, IBr, ICl, Br2, Cl2 in the gas phase and in dichloromethane solvent through applying density function theory (DFT) as well as Gaussian 98 programs series. Characteristics such as frequency, enthalpy of reaction and energy have been totally specified. Special attention was placed on the study of electronegativity of outer halogen atom and polarization of bond between two halogens on the interaction. Results indicate that electronegativity of the external halogen atom and the polarization of dihalogen bond have remarkable effects on structure parameters, donor-acceptor effect, structural stabilization, and the enthalpy of the complex product. It is concluded that the charge transfer takes place in three complexes: 15C5, T15C5, and DT15C5; and the direction of charge transfer is from crown and thiacrown molecule to dihalogen. Stability of 15C5, T15C5 and DT15C5 complexes according to the energy is ICl > IBr > I2. The optimum condition for maximum stability of the molecular complex M…IY is optimized plane structure and the optimum level of polarization of dihalogen during complexation of 15C5, T15C5, and DT15C5 is ICl molecule. The study of the interaction in dichloromethane solvent has similar results to the gas phase. An analysis of the NBO confirms the obtained results. PMID:24362982

  4. Charge-transfer model for the electronic structure of layered ruthenates

    NASA Astrophysics Data System (ADS)

    Ro?ciszewski, Krzysztof; Ole?, Andrzej M.

    2015-04-01

    Motivated by the earlier experimental results and ab initio studies on the electronic structure of layered ruthenates (Sr2RuO4 and Ca2RuO4 ) we introduce and investigate the multiband d -p charge transfer model describing a single RuO4 layer, similar to the charge transfer model for a single CuO2 plane including apical oxygen orbitals in high Tc cuprates. The present model takes into account nearest-neighbor anisotropic ruthenium-oxygen d -p and oxygen-oxygen p -p hopping elements, crystal-field splittings, and spin-orbit coupling. The intraorbital Coulomb repulsion and Hund's exchange are defined not only at ruthenium but also at oxygen ions. Our results demonstrate that the RuO4 layer cannot be regarded to be a pure ruthenium t2 g system. We examine a different scenario in which ruthenium eg orbitals are partly occupied and highlight the significance of oxygen orbitals. We point out that the predictions of an idealized model based on ionic configuration (with n0=4 +4 ×6 =28 electrons per RuO4 unit) do not agree with the experimental facts for Sr2RuO4 which support our finding that the electron number in the d -p states is significantly smaller. In fact, we find the electron occupation of d and p orbitals for a single RuO4 unit n =28 -x , being smaller by at least 1-1.5 electrons from that in the ionic model and corresponding to self-doping with x ?1.5 .

  5. Spectrophotometric study of the charge transfer complexation of some porphyrin derivatives as electron donors with tetracyanoethylene

    NASA Astrophysics Data System (ADS)

    El-Zaria, Mohamed E.

    2008-01-01

    Charge transfer complexes (CTC) of 5,10,15,20-tetraphenylporphyrin (TPP), 5,10,15,20-tetra(4-tolyl)porphyrin (TTP), 5,10,15,20-tetra(4-methoxyphenyl)porphyrin (TMP), Zn-5,10,15,20-tetraphenylporphyrin (Zn-TPP), and Zn-5,10,15,20-tetra(4-tolyl)porphyrin (Zn-TTP) with tetracyanoethylene (TCNE) have been studied at various temperatures in CH 2Cl 2 and CCl 4. The data are discussed in terms of equilibrium constant ( KCT), molar extinction coefficient ( ?CT), thermodynamic standard reaction quantities (? G°, ? H° and ? S°), oscillator strength ( f), and transition dipole moment ( ?). The spectrum obtained for TPP/TCNE, TTP/TCNE, and TMP/TCNE systems shows two main absorption bands at 475 and 690 nm, which are not due to the absorption of any of the reactants. These bands are characteristic of an intermolecular charge transfer involving the overlap of the lowest unoccupied molecular orbital (LUMO) of the acceptor with the highest occupied molecular orbital (HOMO) of the donor. The results reveal that the interaction between the donors and acceptor is due to ?-? * transitions by the formation of radical ion pairs. The stoichiometry of the complexes was found to be 1:1 ratio by the Job and straight line methods between donors and acceptor with the maximum absorption bands at wavelengths of 475 and 690 nm. The observed data show salvation effects on the spectral and thermodynamics properties of CTC. The ionization potential of the donors and the dissociation energy of the CTC were also determined and are found to be constant.

  6. Theoretical Studies on the Structure and Spectrum of Imidazole-Chloranil Charge Transfer Complex

    NASA Astrophysics Data System (ADS)

    Wang, Hai-long; Lu, Tong-tong; He, Tian-jing; Chen, Dong-ming

    2008-12-01

    UV-Vis absorption spectra of the molecular complex formed by imidazole (Im) and chloranil (CA) were measured in chloroform. The stoichiometry of the imidazole-chloranil (Im-CA) complex was determined as 1:1 by applying Benesi-Hildebrand's equation and Job's continuous variation method. Density function theory (DFT) and MP2 calculations were performed to study the structures and the binding energies of the Im-CA complex. The calculations located four conformations (denoted as S1-S4) for the Im-CA complex, two edge(Im)-to-face(CA) linked and two edge(Im)-to-edge(CA) linked. It was found that the edge-to-face conformers are more stable than the edge-to-edge ones. The bonding characteristics of these conformers were investigated with natural population analysis (NPA), topological analysis of electron density, and natural bond orbital (NBO) analysis. It was revealed that the edge-to-face conformers are charge-transfer (CT) complexes whereas the edge-to-edge conformers are the hydrogen bond complexes. For the most stable conformation of the Im-CA complex (S1), the charge transfer interaction of the imidazole n(N15) lone pair orbital with the chloranil ?*(C1 = O7) orbital plays a crucial role in the Im-CA binding, and the binding is further strengthened by the O7 ... H20 hydrogen bond. The electronic excitation energies of the complex (S1) were calculated with time-dependent DFT (TDDFT), and the observed UV-Visible spectrum of the complex was analyzed based on the computed results.

  7. Engineering high charge transfer n-doping of graphene electrodes and its application to organic electronics

    NASA Astrophysics Data System (ADS)

    Sanders, Simon; Cabrero-Vilatela, Andrea; Kidambi, Piran R.; Alexander-Webber, Jack A.; Weijtens, Christ; Braeuninger-Weimer, Philipp; Aria, Adrianus I.; Qasim, Malik M.; Wilkinson, Timothy D.; Robertson, John; Hofmann, Stephan; Meyer, Jens

    2015-07-01

    Using thermally evaporated cesium carbonate (Cs2CO3) in an organic matrix, we present a novel strategy for efficient n-doping of monolayer graphene and a ~90% reduction in its sheet resistance to ~250 Ohm sq-1. Photoemission spectroscopy confirms the presence of a large interface dipole of ~0.9 eV between graphene and the Cs2CO3/organic matrix. This leads to a strong charge transfer based doping of graphene with a Fermi level shift of ~1.0 eV. Using this approach we demonstrate efficient, standard industrial manufacturing process compatible graphene-based inverted organic light emitting diodes on glass and flexible substrates with efficiencies comparable to those of state-of-the-art ITO based devices.Using thermally evaporated cesium carbonate (Cs2CO3) in an organic matrix, we present a novel strategy for efficient n-doping of monolayer graphene and a ~90% reduction in its sheet resistance to ~250 Ohm sq-1. Photoemission spectroscopy confirms the presence of a large interface dipole of ~0.9 eV between graphene and the Cs2CO3/organic matrix. This leads to a strong charge transfer based doping of graphene with a Fermi level shift of ~1.0 eV. Using this approach we demonstrate efficient, standard industrial manufacturing process compatible graphene-based inverted organic light emitting diodes on glass and flexible substrates with efficiencies comparable to those of state-of-the-art ITO based devices. Electronic supplementary information (ESI) available. See DOI: 10.1039/c5nr03246f

  8. An analytical model of radiation-induced Charge Transfer Inefficiency for CCD detectors

    NASA Astrophysics Data System (ADS)

    Short, A.; Crowley, C.; de Bruijne, J. H. J.; Prod'homme, T.

    2013-04-01

    The European Space Agency's Gaia mission is scheduled for launch in 2013. It will operate at L2 for 5 years, rotating slowly to scan the sky so that its two optical telescopes will repeatedly observe more than one billion stars. The resulting data set will be iteratively reduced to solve for the position, parallax and proper motion of every observed star. The focal plane contains 106 large area silicon CCDs continuously operating in a mode where the line transfer rate and the satellite rotation are in synchronization. One of the greatest challenges facing the mission is radiation damage to the CCDs which will cause charge deferral and image shape distortion. This is particularly important because of the extreme accuracy requirements of the mission. Despite steps taken at hardware level to minimize the effects of radiation, the residual distortion will need to be calibrated during the pipeline data processing. Due to the volume and inhomogeneity of data involved, this requires a model which describes the effects of the radiation damage which is physically realistic, yet fast enough to implement in the pipeline. The resulting charge distortion model was developed specifically for the Gaia CCD operating mode. However, a generalized version is presented in this paper and this has already been applied in a broader context, for example to investigate the impact of radiation damage on the Euclid dark-energy mission data.

  9. Charge transfer effects of ions at the liquid water/vapor interface

    SciTech Connect

    Soniat, Marielle; Rick, Steven W.

    2014-05-14

    Charge transfer (CT), the movement of small amounts of electron density between non-bonded pairs, has been suggested as a driving force for a variety of physical processes. Herein, we examine the effect of CT on ion adsorption to the water liquid-vapor interface. Using a CT force field for molecular dynamics, we construct a potential of mean force (PMF) for Na{sup +}, K{sup +}, Cl{sup ?}, and I{sup ?}. The PMFs were produced with respect to an average interface and an instantaneous interface. An analysis of the PMF relative to the instantaneous surface reveals that the area in which the anions experience a free energy minimum is quite narrow, and the cations feel a steeply repulsive free energy near the interface. CT is seen to have only minor effects on the overall free energy profiles. However, the long-ranged effects of ions are highlighted by the CT model. Due to CT, the water molecules at the surface become charged, even when the ion is over 15 Å away from the surface.

  10. Enhancement of Charge Transfer and Quenching of Photoluminescence of Capped CdS Quantum Dots

    PubMed Central

    Mehata, Mohan Singh

    2015-01-01

    Quantum dots (Q-dots) of cadmium sulfide (CdS) with three different capping ligands, 1-butanethiol (BT), 2-mercaptoethanol (ME) and benzyl mercaptan (BM) have been investigated. An external electric field of variable strength of 0.2–1.0?MV?cm?1 was applied to the sample of capped CdS Q-dots doped in a poly(methyl methacrylate) (PMMA) films. Field-induced changes in optical absorption of capped CdS Q-dots were observed in terms of purely the second-derivative of the absorption spectrum (the Stark shift), indicating an enhancement in electric dipole moment following transition to the first exciton state. The enhancement depends on the shape and size of the Q-dots prepared using different capping ligands. Field induced-change in photoluminescence (PL) reveals similar changes, an enhancement in charge-transfer (CT) character in exciton state. PL of capped CdS Q-dots is significantly quenched in presence of external electric field. The strong field-induced quenching occurs as a result of the increased charge separation resulting exciton dissociation. Thus, understanding the CT character and field-induced PL quenching of CdS Q-dots is important for photovoltaic, LEDs and biological applications. PMID:26166553

  11. Frequency dependent magneto-transport in charge transfer Co(II) complex

    NASA Astrophysics Data System (ADS)

    Shaw, Bikash Kumar; Saha, Shyamal K.

    2014-09-01

    A charge transfer chelated system containing ferromagnetic metal centers is the ideal system to investigate the magneto-transport and magneto-dielectric effects due to the presence of both electronic as well as magnetic properties and their coupling. Magneto-transport properties in materials are usually studied through dc charge transport under magnetic field. As frequency dependent conductivity is an essential tool to understand the nature of carrier wave, its spatial extension and their mutual interaction, in the present work, we have investigated frequency dependent magneto-transport along with magnetization behavior in [Co2(II)-(5-(4-PhMe)-1,3,4-oxadiazole-H+-2-thiolate)5](OAc)4 metal complex to elucidate the nature of above quantities and their response under magnetic field in the transport property. We have used the existing model for ac conduction incorporating the field dependence to explain the frequency dependent magneto-transport. It is seen that the frequency dependent magneto-transport could be well explained using the existing model for ac conduction.

  12. Single-crystal organic charge-transfer interfaces probed using Schottky-gated heterostructures.

    PubMed

    Gutiérrez Lezama, Ignacio; Nakano, Masaki; Minder, Nikolas A; Chen, Zhihua; Di Girolamo, Flavia V; Facchetti, Antonio; Morpurgo, Alberto F

    2012-09-01

    Organic semiconductors based on small conjugated molecules generally behave as insulators when undoped, but the heterointerfaces of two such materials can show electrical conductivity as large as in a metal. Although charge transfer is commonly invoked to explain the phenomenon, the details of the process and the nature of the interfacial charge carriers remain largely unexplored. Here we use Schottky-gated heterostructures to probe the conducting layer at the interface between rubrene and PDIF-CN(2) single crystals. Gate-modulated conductivity measurements demonstrate that interfacial transport is due to electrons, whose mobility exhibits band-like behaviour from room temperature to ~150 K, and remains as high as ~1 cm(2) V(-1) s(-1) at 30 K for the best devices. The electron density decreases linearly with decreasing temperature, an observation that can be explained quantitatively on the basis of the heterostructure band diagram. These results elucidate the electronic structure of rubrene/PDIF-CN(2) interfaces and show the potential of Schottky-gated organic heterostructures for the investigation of transport in molecular semiconductors. PMID:22820687

  13. Pseudocapacitive hausmannite nanoparticles with (101) facets: synthesis, characterization, and charge-transfer mechanism.

    PubMed

    Yeager, Matthew P; Du, Wenxin; Wang, Qi; Deskins, N Aaron; Sullivan, Matthew; Bishop, Brendan; Su, Dong; Xu, Wenqian; Senanayake, Sanjaya D; Si, Rui; Hanson, Jonathan; Teng, Xiaowei

    2013-10-01

    Hausmannite Mn3 O4 octahedral nanoparticles of 18.3 ± 7.0 nm with (101) facets have been prepared by an oxygen-mediated growth. The electrochemical properties of the Mn3 O4 particles as pseudocapacitive cathode materials were characterized both in half-cells and in button-cells. The Mn3 O4 nanoparticles exhibited a high mass-specific capacitance of 261 F g(-1), which was calculated from cyclic voltammetry analyses, and a capacitive retention of 78% after 10,000 galvanostatic charge-discharge cycles. The charge-transfer mechanisms of the Mn3 O4 nanoparticles were further studied by using synchrotron-based in situ X-ray absorption near edge spectroscopy and XRD. Both measurements showed concurrently that throughout the potential window of 0-1.2?V (vs. Ag/AgCl), a stable spinel structure of Mn3 O4 remained, and a reversible electrochemical conversion between tetrahedral [Mn(II) O4 ] and octahedral [Mn(III) O6 ] units accounted for the redox activity. Density functional theory calculations further corroborated this mechanism by confirming the enhanced redox stability afforded by the abundant and exposed (101) facets of Mn3 O4 octahedra. PMID:23650213

  14. A charge transfer complex nematic liquid crystalline gel with high electrical conductivity

    SciTech Connect

    Bhargavi, R.; Nair, Geetha G. E-mail: skpras@gmail.com; Krishna Prasad, S. E-mail: skpras@gmail.com; Majumdar, R.; Bag, Braja G.

    2014-10-21

    We describe the rheological, dielectric and elastic properties of a nematic liquid crystal gel created using an anthrylidene derivative of arjunolic acid, a chiral triterpenoid, obtained from the extracts of the wood of Terminalia arjuna. In this novel gel, having the electron-donor and acceptor components as minority constituents, the gelation and strengthening of charge-transfer complex (CTC) formation are seen to be occurring concomitantly. In addition to being mechanically strong with a large storage modulus, the gel with the maximized CTC exhibits Frank bend elastic constant values that approach nanonewton levels. The highlight of the study is the observation of 4–5 orders of magnitude increase in electrical conductivity for this gel, a value that is higher than even in the CT complexes of 2-d ordered columnar structures. A further important advantage of the present system over the columnar complex is that the high conductivity is seen for ac probing also, and owing to the nematic nature can be switched between its anisotropic limits. Some of these features are ascribed to a specific molecular packing architecture, which reduces the trapping of the charge carriers.

  15. Cellular and molecular analysis of mutagenesis induced by charged particles of defined linear energy transfer

    NASA Technical Reports Server (NTRS)

    Zhu, L. X.; Waldren, C. A.; Vannias, D.; Hei, T. K.; Chatterjee, A. (Principal Investigator)

    1996-01-01

    Mutation induction by charged particles of defined linear energy transfer (LET) and gamma rays was scored using human-hamster hybrid AL cells. The LET values for charged particles accelerated at the Radiological Research Accelerator Facility ranged from 10 keV/microm protons to 150 keV/microm 4He ions. The induced mutant fractions at both the S1 and HGPRT loci were dependent on the dose and LET. In addition, for each dose examined, the mutant yield at the S1 locus was 30-60 fold higher than at the corresponding HGPRT locus. To determine whether the mutation spectrum was comparably dependent on dose and LET, independent S1- and HGPRT- mutants induced by 150 keV/microm 4He ions and gamma rays were isolated, and their DNA was analyzed by both Southern blotting and multiplex PCR methods. While the majority of radiation-induced mutants showed deletions of varying sizes, the relative percentage of large deletions was found to be related to both the dose and LET of the radiation examined. Using a mutation system that can detect multilocus changes, results of the present study show that radiation-induced chromosomal loss can be in the millions of base pairs.

  16. The dynamics of energy and charge transfer in lead sulfide quantum dot solids

    SciTech Connect

    Lingley, Zachary; Lu, Siyuan; Madhukar, Anupam

    2014-02-28

    We report on a systematic time-resolved photoluminescence study of the competing energy and charge transfer rates in PbS QDs of differing sizes in the same QD solid as a function of both temperature and ligand-controlled different inter-QD average separations. This complements previous studies that typically varied only one parameter and reveals new aspects while also confirming some known features. For the smallest PbS QDs, the dominant decay process is nonradiative resonant energy transfer (NRET) to adjacent larger dots for all separations but at a rate that increases with decreasing temperature. For the largest QDs, NRET being forbidden, the decay is found to be exponential in the inter-QD separation consistent with carrier tunneling but, for each fixed tunneling distance, exhibiting a thermally activated tunneling carrier population with the activation energy dependent upon the ligand length controlling the inter-QD separation. A consistent understanding of this expanded and rich decay rate behavior of both large and small QDs, we show, can be obtained by accounting for the ligand length dependent (a) dielectric environment of the QD solid modeled using an effective medium description, (b) the energy cost of dissociating the exciton into electron and hole in neighboring QDs, and (c) the potential participation of midgap states. Implications of the findings for NRET based photovoltaics are discussed.

  17. Correlation between charge transfer and exchange coupling in carbon-based magnetic materials

    NASA Astrophysics Data System (ADS)

    Nguyen, Anh Tuan; Nguyen, Van Thanh; Pham, Thi Tuan Anh; Do, Viet Thang; Nguyen, Huy Sinh; Dam, Hieu Chi

    2015-10-01

    Several forms of carbon-based magnetic materials, i.e. single radicals, radical dimers, and alternating stacks of radicals and diamagnetic molecules, have been investigated using density-functional theory with dispersion correction and full geometry optimization. Our calculated results demonstrate that the C31H15 (R4) radical has a spin of ½. However, in its [R4]2 dimer structure, the net spin becomes zero due to antiferromagnetic spin-exchange between radicals. To avoid antiferromagnetic spin-exchange of identical face-to-face radicals, eight alternating stacks, R4/D2m/R4 (with m = 3-10), were designed. Our calculated results show that charge transfer (?n) between R4 radicals and the diamagnetic molecule D2m occurs with a mechanism of spin exchange (J) in stacks. The more electrons that transfer from R4 to D2m, the stronger the ferromagnetic spin-exchange in stacks. In addition, our calculated results show that ?n can be tailored by adjusting the electron affinity (Ea) of D2m. The correlation between ?n, Ea, m, and J is discussed. These results give some hints for the design of new ferromagnetic carbon-based materials.

  18. Ultrafast Charge Transfer in Nickel Phthalocyanine Probed by Femtosecond Raman-Induced Kerr Effect Spectroscopy

    PubMed Central

    2015-01-01

    The recently developed technique of femtosecond stimulated Raman spectroscopy, and its variant, femtosecond Raman-induced Kerr effect spectroscopy (FRIKES), offer access to ultrafast excited-state dynamics via structurally specific vibrational spectra. We have used FRIKES to study the photoexcitation dynamics of nickel(II) phthalocyanine with eight butoxy substituents, NiPc(OBu)8. NiPc(OBu)8 is reported to have a relatively long-lived ligand-to-metal charge-transfer (LMCT) state, an essential characteristic for efficient electron transfer in photocatalysis. Following photoexcitation, vibrational transitions in the FRIKES spectra, assignable to phthalocyanine ring modes, evolve on the femtosecond to picosecond time scales. Correlation of ring core size with the frequency of the ?10 (asymmetric C–N stretching) mode confirms the identity of the LMCT state, which has a ?500 ps lifetime, as well as that of a precursor d-d excited state. An even earlier (?0.2 ps) transient is observed and tentatively assigned to a higher-lying Jahn–Teller-active LMCT state. This study illustrates the power of FRIKES spectroscopy in elucidating ultrafast molecular dynamics. PMID:24841906

  19. Nanostructure and charge transfer in Bi2S3-TiO2 heterostructures.

    PubMed

    Yu, Haijing; Huang, Jing; Zhang, Hua; Zhao, Qingfei; Zhong, Xinhua

    2014-05-30

    Interfacial nanostructures in Bi2S3-TiO2 nanorod-nanoparticle heterostructures with a change of coupling mode have been engineered. The samples were characterized by x-ray diffraction, scanning electron microscopy, transmission electron microscopy, and ultraviolet-visual light absorption spectroscopy. By means of in situ growth of TiO2 nanoparticles on the surfaces of Bi2S3 nanorods in one pot, heterostructures with high-quality interfaces were obtained in which the {105} facet of anatase TiO2 selectively coupled with the {010} facet of orthorhombic Bi2S3 nanorods without any crystal defects, showing the epitaxial relationship of Bi2S3 {011} // TiO2 {101}. By means of a two-step method, TiO2 nanoparticles also could be grown on the {310} facet of the pre-prepared Bi2S3 nanorods to form heterostructures but with interfacial defects. Charge transfer in the interface-different heterostructures was evaluated by photodegradation of methyl orange under visible-light irradiation. The defect-free interfaces favored electron-hole separation and transfer, resulting in improved photocatalytic activity. The current structural characterization and interface engineering should be expanded to other heterostructures when studying the relationship between synthesis, interfacial structure, and photocatalytic or photovoltaic applications. PMID:24784772

  20. Hydrogenase/ferredoxin charge-transfer complexes: effect of hydrogenase mutations on the complex association.

    PubMed

    Long, Hai; King, Paul W; Ghirardi, Maria L; Kim, Kwiseon

    2009-04-23

    The [FeFe]-hydrogenases in the green alga Chlamydomonas reinhardtii utilize photogenerated electrons to reduce protons into hydrogen gas. The electrons are supplied from photosystem I and transferred to the [FeFe]-hydrogenase through specific hydrogenase-ferredoxin association. To understand how structural and kinetic factors control the association better, we used Brownian dynamics simulation methods to simulate the charge-transfer complex formation between both native and in silico mutants of the [FeFe]-hydrogenase HYDA2 and the [2Fe2S]-ferredoxin FDX1 from C. reinhardtii . The changes in binding free energy between different HYDA2 mutants and the native FDX1 were calculated by the free-energy perturbation method. Within the limits of our current models, we found that two HYDA2 mutations, T99K(H) and D102K(H), led to lower binding free energies and higher association rate with FDX1 and are thus promising targets for improving hydrogen production rates in engineered organisms. PMID:19317477

  1. Fullerol-titania charge-transfer-mediated photocatalysis working under visible light.

    PubMed

    Park, Yiseul; Singh, N Jiten; Kim, Kwang S; Tachikawa, Takashi; Majima, Tetsuro; Choi, Wonyong

    2009-10-19

    The development of visible-light-active photocatalysts is being investigated through various approaches. In this study, C(60)-based sensitized photocatalysis that works through the charge transfer (CT) mechanism is proposed and tested as a new approach. By employing the water-soluble fullerol (C(60)(OH)(x)) instead of C(60), we demonstrate that the adsorbed fullerol activates TiO(2) under visible-light irradiation through the "surface-complex CT" mechanism, which is largely absent in the C(60)/TiO(2) system. Although fullerene and its derivatives have often been utilized in TiO(2)-based photochemical conversion systems as an electron transfer relay, their successful photocatalytic application as a visible-light sensitizer of TiO(2) is not well established. Fullerol/TiO(2) exhibits marked visible photocatalytic activity not only for the redox conversion of 4-chlorophenol, I(-), and Cr(VI), but also for H(2) production. The photoelectrode of fullerol/TiO(2) also generates an enhanced anodic photocurrent under visible light as compared with the electrodes of bare TiO(2) and C(60)/TiO(2), which confirms that the visible-light-induced electron transfer from fullerol to TiO(2) is particularly enhanced. The surface complexation of fullerol/TiO(2) induced a visible absorption band around 400-500 nm, which was extinguished when the adsorption of fullerol was inhibited by fluorination of the surface of TiO(2). The transient absorption spectroscopic measurement gave an absorption spectrum ascribed to fullerol radical cations (fullerol(*+)) the generation of which should be accompanied by the proposed CT. The theoretical calculation regarding the absorption spectra for the (TiO(2) cluster+fullerol) model also confirmed the proposed CT, which involves excitation from HOMO (fullerol) to LUMO (TiO(2) cluster) as the origin of the visible-light absorption. PMID:19760729

  2. Localized surface plasmon mediated photochemistry and charge transfer in noble metal nanoparticles

    NASA Astrophysics Data System (ADS)

    Wu, Xiaomu

    This thesis addresses the fundamental physical and chemical processes of localized surface plasmon mediated photochemistry and charge transfer in noble metal nanoparticles. The first chapter introduces the theory and application of surface plasmons. It includes a discussion of propagating and localized surface plasmons, plasmon decay dynamics, factors governing plasmon excitation of metal nanoparticles, near-field enhanced photochemistry and plasmon mediated charge transfer. The second chapter presents a photovoltage mechanism for room light conversion of citrate stabilized silver nanocrystal seeds to large nanoprisms. The process relies on the excitation of silver surface plasmons and requires citrate and oxygen. The transformation rate is first-order in seed concentration. The mechanism involves oxidative etching of seeds and subsequent photoreduction of aqueous silver ions preferentially onto silver prisms that have a cathodic photovoltage resulting from plasmon hot hole citrate photo- oxidation. This idea also explains several previously reported experiments including single and dual wavelength irradiation and the core/shell synthesis of silver layers on gold seeds. The third chapter explores the photo-driven growth of citrate stabilized silver nanoparticles. Under plasmon excitation, particles that absorb/scatter light weakly reduce dioxygen and lose silver ions, whereas particles with resonant plasmons build up a high photovoltage due to citrate photo-oxidation and reduce silver ions. Overall, growth is favored for on-resonant particles. Compared to the borohydride reduction method, more monodisperse, round 10-20 nm diameter silver nanoparticles are obtained by plasmon mediated approaches. Adding a trace amount of potassium chloride can speed up the growth and inhibit the formation of Ag aggregates. The fourth chapter investigates the plasmon induced photochemical charge separation in gold nanoparticles on a transparent indium tin oxide (ITO) substrate. Photocurrent and photovoltage are directly measured under potentiostatic control in air. It is proposed that gold plasmon excitation causes hot electrons to inject into the ITO conduction band, while hot holes are scavenged by citrate and other solution redox species. A resonant increase in the photocurrent generated at more oxidizing potentials is observed.

  3. Memory loss and Auger processes in a many-body theory of charge transfer

    NASA Astrophysics Data System (ADS)

    Onufriev, A. V.; Marston, J. B.

    1996-05-01

    Charge transfer between hyperthermal alkali atoms and metallic scattering surfaces is an experimental and theoretical arena for many-body interactions. To model new facets, we use a generalized time-dependent Newns-Anderson Hamiltonian that includes electron spin, multiple atomic orbitals with image shifted levels, intra-atomic Coulomb repulsion, and resonant exchange. A variational electronic many-body wave function solves the dynamical problem. The wave function consists of sectors with zero and one particle-hole pair and goes beyond earlier work with the inclusion of amplitudes for a neutral atom plus an electron-hole pair. Higher-order sectors with more than one particle-hole pair are suppressed by powers of 1/N; hence the wave-function ansatz is equivalent to a 1/N expansion. The equations of motion are integrated numerically without further approximation. This solution shows improved loss of memory - the final charge state is independent of the initial one - in agreement with theoretical and experimental expectations. Understanding of this phenomenon is deepened through an analysis of entropy production. By studying the independent-particle approximation, and by examining the role played by different sectors of the Hilbert space in entropy production, we arrive at necessary and sufficient conditions for loss of memory to occur in the many-body solution. As further tests of the theory, we reproduce the experimentally observed peak in the excited neutral Li(2p) occupancy at intermediate work functions starting from different initial conditions. Next, we include Auger processes by adding two-body interaction terms to the many-body Hamiltonian. Several types of Auger processes are considered, and these are shown to affect the final-state occupancies at low work functions because phase space enlarges rapidly as the work function is lowered. Preliminary experimental evidence for an upturn in the Li(2p) occupancy at the lowest work functions thus may be explained by Auger transitions. Finally, we comment on the plausibility of observing a signature of the Kondo resonance in charge transfer experiments.

  4. Self-assembly of intramolecular charge-transfer compounds into functional molecular systems.

    PubMed

    Li, Yongjun; Liu, Taifeng; Liu, Huibiao; Tian, Mao-Zhong; Li, Yuliang

    2014-04-15

    Highly polarized compounds exhibiting intramolecular charge transfer (ICT) are used widely as nonlinear optical (NLO) materials and red emitters and in organic light emitting diodes. Low-molecular-weight donor/acceptor (D/A)-substituted ICT compounds are ideal candidates for use as the building blocks of hierarchically structured, multifunctional self-assembled supramolecular systems. This Account describes our recent studies into the development of functional molecular systems with well-defined self-assembled structures based on charge-transfer (CT) interactions. From solution (sensors) to the solid state (assembled structures), we have fully utilized intrinsic and stimulus-induced CT interactions to construct these functional molecular systems. We have designed some organic molecules capable of ICT, with diversity and tailorability, that can be used to develop novel self-assembled materials. These ICT organic molecules are based on a variety of simple structures such as perylene bisimide, benzothiadiazole, tetracyanobutadiene, fluorenone, isoxazolone, BODIPY, and their derivatives. The degree of ICT is influenced by the nature of both the bridge and the substituents. We have developed new methods to synthesize ICT compounds through the introduction of heterocycles or heteroatoms to the ?-conjugated systems or through extending the conjugation of diverse aromatic systems via another aromatic ring. Combining these ICT compounds featuring different D/A units and different degrees of conjugation with phase transfer methodologies and solvent-vapor techniques, we have self-assembled various organic nanostructures, including hollow nanospheres, wires, tubes, and ribbonlike architectures, with controllable morphologies and sizes. For example, we obtained a noncentrosymmetric microfiber structure that possessed a permanent dipole along its fibers' long axis and a transition dipole perpendicular to it; the independent NLO responses of this material can be separated and tuned spectroscopically and spatially. The ready processability and intrinsically high NLO efficiency of these microfibers offer great opportunities for applications in photonic devices. We have also designed molecular sensors based on changes in the efficiency of the ICT process upon complexation of an analyte with the D or A moieties in the ICT compounds. Such sensors, which display evident Stokes shifts or changes in quantum yields or fluorescence lifetimes, have promise for applications in chemical and biological recognition and sensing. In this Account, we shed light on the structure-function relationships of these functional molecular systems with well-defined self-assembled structures based on ICT interactions. The encouraging results that we have obtained suggest that such self-assembled ICT molecular materials can guide the design of new nanostructures and materials from organic systems, and that these materials, across a range of compositions, sizes, shapes, and functionalities, can potentially be applied in the fields of electronics, optics, and optoelectronics. PMID:24666347

  5. Optical absorption of electronic Fe-Ti charge-transfer transition in natural andalusite: the thermal stability of the charge-transfer band

    NASA Astrophysics Data System (ADS)

    Taran, Michail N.; Koch-Müller, Monika

    2011-03-01

    Differently colored natural Brazilian andalusite crystals heat-treated under reducing and oxidizing conditions were analyzed by optical spectroscopy. The intensity of a broad intense band at around 20,500 cm-1 in the optical absorption spectra of all color zones of the sample is proportional to the product of Ti- and Fe-concentrations and herewith proves its attribution to electronic Fe2+/Ti4+ IVCT transition. The band is strictly E|| c-polarized, causing an intense red coloration of the samples in this polarization. The polarization of the Fe2+/Ti4+ IVCT band in andalusite, E|| c, shows that the electronic charge-transfer process takes place in Al-O octahedral groups that share edges with neighbors on either side, forming chains parallel to the c-axis of the andalusite structure. Under thermal treatments in air, the first noticeable change is some intensification of the band at 800°C. However, at higher temperatures its intensity decreases until it vanishes at 1,000°C in lightly colored zones and 1,100°C in darkly colored ones. Under annealing in reducing conditions at 700 and 800°C, the band also slightly increases and maintains its intensity at treatments at higher temperatures up to 1,000°C. These results demonstrate that weakening and disappearance of the Fe2+/Ti4+ IVCT band in spectra of andalusite under annealing in air is caused by oxidization of Fe2+ to Fe3+ in IVCT Fe2+/Ti4+-pairs. Some intensification of the band at 800°C is, most probably, due to thermally induced diffusion of Fe2+ and Ti4+ in the structure that leads to aggregation of "isolated" Ti4+ and Fe2+ ions into Fe2+-Ti4+-pairs. At higher temperatures, the competing process of Fe2+ ? Fe3+ oxidation overcomes such "coupling" and the band continues to decrease. The different thermal stability of the band in lightly and darkly colored zones of the samples evidence some self-stabilization over an interaction of Fe2+/Ti4+-pairs involved in IVCT process.

  6. Collision of fast highly charged ions in gas targets: ionization, recoil-ion production, and charge transfer

    SciTech Connect

    Schalchter, A.S.; Berkner, K.H.; Beyer, H.F.

    1982-07-01

    Electron-capture, ionization, and recoil-ion-production cross sections are measured and calculated for fast highly charged projectiles in hydrogen and rare-gas targets. Recoil-ion-production cross sections are found to be large; the low energy and high charge states of the recoil ions make them useful for subsequent collision studies.

  7. Highly efficient nonradiative energy transfer using charged CdSe/ZnS nanocrystals for light-harvesting in solution

    E-print Network

    Demir, Hilmi Volkan

    Highly efficient nonradiative energy transfer using charged CdSe/ZnS nanocrystals for light; published online 20 July 2009 We propose and demonstrate highly efficient nonradiative Förster resonance propose and demonstrate optical excitation of RhB dye molecules in solution based on strong nonradiative

  8. Charge-transfer interactions of metoclopramide nausea drug against six kind of ?-acceptors: spectral and thermal discussions.

    PubMed

    El-Habeeb, Abeer A; Al-Saif, Foziah A; Refat, Moamen S

    2014-04-01

    The target of this paper is aimed to discuss the fast and newly techniques in order to assessment the metoclopramide (Mcp) nausea drug in pure form in solid and solution shape with different kind of ?-acceptors upon charge transfer interactions. Charge-transfer complexes (CTC) of metoclopramide with picric acid (PA), 2,3-dichloro-5,6-dicyano-p-benzoquinon (DDQ), tetracyanoquinodimethane (TCNQ), m-dinitrobenzene (DNB), p-nitrobenzoic acid (p-NBA) and tetrachloro-p-quinon (p-CL) have been studied spectrophotometrically in absolute methanol at room temperature. The stoichiometries of the complexes were found to be 1:1 ratio by the spectrophotometric titration between metoclopramide and represented ?-acceptors. The equilibrium constants, molar extinction coefficient (?CT) and spectroscopic-physical parameters (standard free energy (?G°), oscillator strength (ƒ), transition dipole moment (?), resonance energy (RN) and ionization potential (ID)) of the complexes were determined upon the modified Benesi-Hildebrand equation. The results indicate that the formation constants for the complexes depend on the nature of electron acceptors and configuration of drug donor, and also the spectral studies of the complexes were determined by (infrared, Raman, and (1)H NMR) spectra and X-ray powder diffraction (XRD). The charge-transfer complexes are formed during the interaction of electron-acceptors and electron-donors as result of partial or complete transfer of a negative charge from (D(+)-A(-)). PMID:24434200

  9. Ultrafast inter-ionic charge transfer of transition-metal complexes mapped by femtosecond X-ray powder diffraction

    SciTech Connect

    Freyer, Benjamin; Zamponi, Flavio; Juve, Vincent; Stingl, Johannes; Woerner, Michael; Elsaesser, Thomas; Chergui, Majed

    2013-04-14

    The transient electronic and molecular structure arising from photoinduced charge transfer in transition metal complexes is studied by X-ray powder diffraction with a 100 fs temporal and atomic spatial resolution. Crystals containing a dense array of Fe(II)-tris(bipyridine) ([Fe(bpy){sub 3}]{sup 2+}) complexes and their PF{sub 6}{sup -} counterions display pronounced changes of electron density that occur within the first 100 fs after two-photon excitation of a small fraction of the [Fe(bpy){sub 3}]{sup 2+} complexes. Transient electron density maps derived from the diffraction data reveal a transfer of electronic charge from the Fe atoms and-so far unknown-from the PF{sub 6}{sup -} counterions to the bipyridine units. Such charge transfer (CT) is connected with changes of the inter-ionic and the Fe-bipyridine distances. An analysis of the electron density maps demonstrates the many-body character of charge transfer which affects approximately 30 complexes around a directly photoexcited one. The many-body behavior is governed by the long-range Coulomb forces in the ionic crystals and described by the concept of electronic polarons.

  10. Room-Temperature Current Oscillation Based on Negative Differential Resistance in a One-Dimensional Organic Charge-Transfer Complex

    NASA Astrophysics Data System (ADS)

    Kishida, Hideo; Ito, Takafumi; Ito, Atsuya; Nakamura, Arao

    2011-03-01

    The one-dimensional organic charge-transfer complex potassium-tetracyanoquinodimethane shows negative differential resistance and a switching behavior between high- and low-resistance states. By controlling this switching behavior through the use of external circuit components, we achieved current oscillation at room temperature. Microscopic Raman measurements in the current oscillation indicate that the nonlinear conducting current flows throughout the crystal.

  11. Energy Dependence of the Ruthenium(II)-Bipyridine Metal-to-Ligand-Charge-Transfer Excited State Radiative Lifetimes: Effects of

    E-print Network

    Schlegel, H. Bernhard

    Energy Dependence of the Ruthenium(II)-Bipyridine Metal-to- Ligand-Charge-Transfer Excited State spectra of ruthenium- bipyridine (Ru-bpy) chromophores at 77 K have been postulated to arise from excited of ruthenium-(D)/polypyridyl ligand-(A) complex excited states that differ from expectation based on simple

  12. Metal-to-Ligand Charge-Transfer Emissions of Ruthenium(II) Pentaammine Complexes with Monodentate Aromatic Acceptor

    E-print Network

    Schlegel, H. Bernhard

    Metal-to-Ligand Charge-Transfer Emissions of Ruthenium(II) Pentaammine Complexes with Monodentate of pentaammine-MDA- ruthenium(II) ([Ru(NH3)5(MDA)]2+ ) complexes, where MDA is a monodentate aromatic ligand of different spin multiplicities. These issues are of considerable importance in [ruthenium

  13. Donor-substituted peralkynylated "radiaannulenes": novel all-carbon macrocycles with an intense intramolecular charge-transfer.

    PubMed

    Mitzel, Frieder; Boudon, Corinne; Gisselbrecht, Jean-Paul; Seiler, Paul; Gross, Maurice; Diederich, François

    2003-07-21

    A novel class of planar, highly conjugated all-carbon macrocycles, which we christened "radiaannulenes", have been prepared based on acetylenic scaffolding using tetraethynylethene (TEE) building blocks; these structures are powerful electron acceptors and, upon peripheral substitution with electron-donating N,N-dialkylanilino groups, display intense intramolecular charge-transfer. PMID:12877477

  14. THE JOURNAL OF CHEMICAL PHYSICS 134, 244103 (2011) Quantum effects in energy and charge transfer in an artificial

    E-print Network

    Nori, Franco

    2011-01-01

    -transduction process in natural photosystems begins with capturing sunlight photons by light-absorbing antenna complex in contact with a Gaussian heat bath. With these equations we can analyze the regime of strong the excitation energy to create a stable charge-separated state. Energy transfer in natural and artificial

  15. The role of charge-transfer interactions and delocalization in annelated nitronyl nitroxides

    NASA Astrophysics Data System (ADS)

    Dooley, Brynn Mary

    The design and synthesis of stable organic radicals with delocalized spin density distribution and low energy optical and redox processes is central to the development of magneto-conducting materials. Towards this end, a generalized synthetic methodology has been developed allowing for the synthesis of a series of annelated benzonitronyl nitroxide (BNN) radicals. The BNN radicals exhibited remarkably low reduction potentials (~0.0 V vs SCE) and a near-infrared absorption attributed to a HOMO--SOMO charge-transfer excitation. The annelated BNN radicals were found to be less stable than the closely related tetramethyl nitronyl nitroxide radicals, particularly in solution. A series of pi-delocalized and heteroaromatic radicals were synthesized to determine if the instability was due to the delocalization of electron density onto the carbon skeleton or the low reduction potential. DFT calculations with the EPR-II basis gave rise to calculated electronic structures that were consistent with EPR spectroscopy and suggested changes in spin density distribution are occurring with perturbation of the annelated ring. Cyclic voltammetry revealed the heteroaromatic and pi-delocalized radicals had reduction potentials lower than BNN, with some systems reducing at potentials of 0.2 V vs SCE, comparable to that of 7,7,8,8-tetracyanoquinodimethane. The distribution of spin throughout the molecular framework and the low reduction potential of the annelated nitronyl nitroxide radicals were both found to contribute to the lowered stability of the annelated nitronyl nitroxides relative to the far less redox active tetramethyl nitronyl nitroxides. The low reduction potential of the BNN radicals suggested that incorporation into acceptor--donor (A--D) systems would allow for investigation of the role of charge transfer interactions on the electronic structure and properties of neutral open-shell A--D radicals. Two D--A--D radicals were prepared using metal catalyzed coupling and furoxan condensation methodologies which resulted in incorporation of a second donor in the C5 position of the BNN moiety. The radical D1--A--D2 triads, where D1 = thiophene and D2 = thiophene or phenyl, exhibited three intramolecular charge-transfer excitations (lambdamax = 550, 580 and 1000 nm) that were investigated by variable temperature absorption spectroscopy. Structural characterization of the triads in the solid state by single crystal and powder X-ray diffraction revealed slipped pi stacks that arise from intermolecular pi-- pi and D--A interactions, providing pathways for antiferromagnetic (AFM) and ferromagnetic (FM) exchange. While the phenyl substituted triad (Th--BNN--Ph) exhibited antiferromagnetic interactions and a room temperature conductivity of sigmaRT = 10-7 S cm-1, the thienyl substituted derivative (Th--BNN--Th) exhibited short-range FM interactions and increased conductivity (sigmaRT = 10-5 S cm-1), giving rise to an organic semiconductor exhibiting FM exchange. The differences in conductivity and magnetic behavior were rationalized by the degree of slippage dictated by an interplay between pi-- pi and intermolecular D--A interactions. Finally, a series of BNN--D radicals were investigated where the donor ability of D was systematically varied from Eox = 2.30 V vs SCE (benzene) to 0.32 V vs SCE (tetrathiafulvalene). Calculations of the near-infrared charge transfer excitation suggested that the HOMO--SOMO gap could be significantly decreased with increasing donor ability, consistent with charge transfer theory. A subset of the series of BNN--D radicals with D = anisole, benzo[b]thiophene, N-methylindole, N-ethylcarbazole, and N,N-diphenylaniline were synthesized. Solution state spectroscopic studies of the series by EPR and electronic absorption spectroscopy revealed spin-delocalized structures with extremely low reduction potentials (~0 V vs SCE). The solid state properties of the BNN--D radicals were investigated by magnetometry and room temperature conductivity measurements. Due to primarily steric interactions, weak D--A coupling was observ

  16. Influence of Coherent Tunneling and Incoherent Hopping on the Charge Transfer Mechanism in Linear Donor-Bridge-Acceptor Systems.

    PubMed

    Li, Guangqi; Govind, Niranjan; Ratner, Mark A; Cramer, Christopher J; Gagliardi, Laura

    2015-12-17

    The mechanism of charge transfer has been observed to change from tunneling to hopping with increasing numbers of DNA base pairs in polynucleotides and with the length of molecular wires. The aim of this paper is to investigate this transition by examining the population dynamics using a tight-binding Hamiltonian with model parameters to describe a linear donor-bridge-acceptor (D-B-A) system. The model includes a primary vibration and an electron-vibration coupling at each site. A further coupling of the primary vibration with a secondary phonon bath allows the system to dissipate energy to the environment and reach a steady state. We apply the quantum master equation (QME) approach, based on second-order perturbation theory in a quantum dissipative system, to examine the dynamical processes involved in charge-transfer and follow the population transfer rate at the acceptor, ka, to shed light on the transition from tunneling to hopping. With a small tunneling parameter, V, the on-site population tends to localize and form polarons, and the hopping mechanism dominates the transfer process. With increasing V, the population tends to be delocalized and the tunneling mechanism dominates. The competition between incoherent hopping and coherent tunneling governs the mechanism of charge transfer. By varying V and the total number of sites, we also examine the onset of the transition from tunneling to hopping with increasing length. PMID:26554424

  17. Competition between diagonal and off-diagonal coupling gives rise to charge-transfer states in polymeric solar cells

    PubMed Central

    Yao, Yao; Zhou, Nengji; Prior, Javier; Zhao, Yang

    2015-01-01

    It has long been a puzzle on what drives charge separation in artificial polymeric solar cells as a consensus has yet to emerge among rivaling theories based upon electronic localization and delocalization pictures. Here we propose an alternative using the two-bath spin-boson model with simultaneous diagonal and off-diagonal coupling: the critical phase, which is born out of the competition of the two coupling types, and is neither localized nor delocalized. The decoherence-free feature of the critical phase also helps explain sustained coherence of the charge-transfer state. Exploiting Hamiltonian symmetries in an enhanced algorithm of density-matrix renormalization group, we map out boundaries of the critical phase to a precision previously unattainable, and determine the bath spectral densities inducive to the existence of the charge-transfer state. PMID:26412693

  18. Competition between diagonal and off-diagonal coupling gives rise to charge-transfer states in polymeric solar cells

    NASA Astrophysics Data System (ADS)

    Yao, Yao; Zhou, Nengji; Prior, Javier; Zhao, Yang

    2015-09-01

    It has long been a puzzle on what drives charge separation in artificial polymeric solar cells as a consensus has yet to emerge among rivaling theories based upon electronic localization and delocalization pictures. Here we propose an alternative using the two-bath spin-boson model with simultaneous diagonal and off-diagonal coupling: the critical phase, which is born out of the competition of the two coupling types, and is neither localized nor delocalized. The decoherence-free feature of the critical phase also helps explain sustained coherence of the charge-transfer state. Exploiting Hamiltonian symmetries in an enhanced algorithm of density-matrix renormalization group, we map out boundaries of the critical phase to a precision previously unattainable, and determine the bath spectral densities inducive to the existence of the charge-transfer state.

  19. Competition between diagonal and off-diagonal coupling gives rise to charge-transfer states in polymeric solar cells.

    PubMed

    Yao, Yao; Zhou, Nengji; Prior, Javier; Zhao, Yang

    2015-01-01

    It has long been a puzzle on what drives charge separation in artificial polymeric solar cells as a consensus has yet to emerge among rivaling theories based upon electronic localization and delocalization pictures. Here we propose an alternative using the two-bath spin-boson model with simultaneous diagonal and off-diagonal coupling: the critical phase, which is born out of the competition of the two coupling types, and is neither localized nor delocalized. The decoherence-free feature of the critical phase also helps explain sustained coherence of the charge-transfer state. Exploiting Hamiltonian symmetries in an enhanced algorithm of density-matrix renormalization group, we map out boundaries of the critical phase to a precision previously unattainable, and determine the bath spectral densities inducive to the existence of the charge-transfer state. PMID:26412693

  20. Charge-transfer matrix elements by FMO-LCMO approach: Hole transfer in DNA with parameter tuned range-separated DFT

    NASA Astrophysics Data System (ADS)

    Kitoh-Nishioka, Hirotaka; Ando, Koji

    2015-02-01

    A scheme for computing charge-transfer matrix elements with the linear combination of fragment molecular orbitals and the 'nonempirically tuned range-separated' density functional is presented. It takes account of the self-consistent orbital relaxation induced by environmental Coulomb field and the exchange interaction in fragment pairs at low computational scaling along the system size. The accuracy was confirmed numerically on benchmark systems of imidazole and furane homo-dimer cations. Applications to hole transfers in DNA nucleobase pairs and in a ?-stack adenine octomer highlight the effects of orbital relaxation.

  1. Photoinduced coupled twisted intramolecular charge transfer and excited-state proton transfer via intermolecular hydrogen bonding: A DFT/TD-DFT study

    NASA Astrophysics Data System (ADS)

    Wang, Dandan; Lü, Rui; Yuan, Minghu; Chen, Junsheng; Feng, Liqiang; Fu, Aiping; Tian, Fenghui; Varandas, António J. C.; Chu, Tianshu

    2014-08-01

    We discuss theoretically the geometric and electronic structure properties of the thiazolidinedione derivative A and its hydrogen-bonded complex in dimethylformamide (DMF) solution in the S0 and S1 states. To gain insight into the photoinduced coupled excited-state proton transfer (ESPT) and twisted intramolecular charge transfer (TICT) associated with intermolecular hydrogen bonding, the potential energy profiles are provided along the Osbnd H bond and the twisted angle. It is predicted that TICT in S1 can facilitate ESPT initiated by intermolecular hydrogen-bond strengthening in the S1 state. The coupling of ESPT and TICT is energetically preferable.

  2. Linear, third- and fifth-order nonlinear spectroscopy of a charge transfer system coupled to an underdamped vibration

    E-print Network

    Dijkstra, Arend G

    2015-01-01

    We study hole, electron and exciton transport in a charge transfer system in the presence of underdamped vibrational motion. We analyze the signature of these processes in the linear and third-, and fifth-order nonlinear electronic spectra. Calculations are performed with a numerically exact hierarchical equations of motion method for an underdamped Brownian oscillator spectral density. We find that combining electron, hole and exciton transfer can lead to non-trivial spectra with more structure than with excitonic coupling alone. Traces taken during the waiting time of a two-dimensional spectrum are dominated by vibrational motion and do not reflect the electron, hole, and exciton dynamics directly. We find that the fifth-order nonlinear response is particularly sensitive to the charge transfer process. While third-order 2D spectroscopy detects the correlation between two coherences, fifth-order 2D spectroscopy (2D population spectroscopy) is here designed to detect correlations between the excited states du...

  3. Theory of chemical kinetics and charge transfer based on nonequilibrium thermodynamics.

    PubMed

    Bazant, Martin Z

    2013-05-21

    Advances in the fields of catalysis and electrochemical energy conversion often involve nanoparticles, which can have kinetics surprisingly different from the bulk material. Classical theories of chemical kinetics assume independent reactions in dilute solutions, whose rates are determined by mean concentrations. In condensed matter, strong interactions alter chemical activities and create variations that can dramatically affect the reaction rate. The extreme case is that of a reaction coupled to a phase transformation, whose kinetics must depend not only on the order parameter but also on its gradients at phase boundaries. Reaction-driven phase transformations are common in electrochemistry, when charge transfer is accompanied by ion intercalation or deposition in a solid phase. Examples abound in Li-ion, metal-air, and lead-acid batteries, as well as metal electrodeposition-dissolution. Despite complex thermodynamics, however, the standard kinetic model is the Butler-Volmer equation, based on a dilute solution approximation. The Marcus theory of charge transfer likewise considers isolated reactants and neglects elastic stress, configurational entropy, and other nonidealities in condensed phases. The limitations of existing theories recently became apparent for the Li-ion battery material LixFePO4 (LFP). It has a strong tendency to separate into Li-rich and Li-poor solid phases, which scientists believe limits its performance. Chemists first modeled phase separation in LFP as an isotropic "shrinking core" within each particle, but experiments later revealed striped phase boundaries on the active crystal facet. This raised the question: What is the reaction rate at a surface undergoing a phase transformation? Meanwhile, dramatic rate enhancement was attained with LFP nanoparticles, and classical battery models could not predict the roles of phase separation and surface modification. In this Account, I present a general theory of chemical kinetics, developed over the past 7 years, which is capable of answering these questions. The reaction rate is a nonlinear function of the thermodynamic driving force, the free energy of reaction, expressed in terms of variational chemical potentials. The theory unifies and extends the Cahn-Hilliard and Allen-Cahn equations through a master equation for nonequilibrium chemical thermodynamics. For electrochemistry, I have also generalized both Marcus and Butler-Volmer kinetics for concentrated solutions and ionic solids. This new theory provides a quantitative description of LFP phase behavior. Concentration gradients and elastic coherency strain enhance the intercalation rate. At low currents, the charge-transfer rate is focused on exposed phase boundaries, which propagate as "intercalation waves", nucleated by surface wetting. Unexpectedly, homogeneous reactions are favored above a critical current and below a critical size, which helps to explain the rate capability of LFP nanoparticles. Contrary to other mechanisms, elevated temperatures and currents may enhance battery performance and lifetime by suppressing phase separation. The theory has also been extended to porous electrodes and could be used for battery engineering with multiphase active materials. More broadly, the theory describes nonequilibrium chemical systems at mesoscopic length and time scales, beyond the reach of molecular simulations and bulk continuum models. The reaction rate is consistently defined for inhomogeneous, nonequilibrium states, for example, with phase separation, large electric fields, or mechanical stresses. This research is also potentially applicable to fluid extraction from nanoporous solids, pattern formation in electrophoretic deposition, and electrochemical dynamics in biological cells. PMID:23520980

  4. Time-resolved spectroscopy of charge transfer phenomena in organic solar cells

    NASA Astrophysics Data System (ADS)

    Gerhard, Marina; Arndt, Andreas; Quintilla, Aina; Rahimi-Iman, Arash; Lemmer, Uli; Koch, Martin

    2015-03-01

    Geminate recombination of photo-generated excitons represents a considerable loss mechanism in polymer solar cells. We apply time-resolved photoluminescence (TRPL) to study the radiative recombination which accompanies the process of charge generation. A streak camera is used, which is sensitive for both the photoluminescence (PL) from the initially excited singlet excitons and the weaker emission from charge transfer (CT) states. The latter are formed at internal interfaces when the polymer is blended with a fullerene acceptor. We draw a comparison between our results for two polymers, P3HT and PTB7, respectively, which were studied in blends with the fullerene derivative PCBM. In addition, pristine films were investigated, allowing for the identification of interfacial features in the blends. For both polymers, the PL of the singlet states was rapidly quenched in blends with PCBM. In P3HT, time constants of about 40 ps were recorded for the singlet exciton decay and related to exciton diffusion, whereas the PL of PTB7 was almost completely quenched within the first 3 ps. The decay rates of the emissive CT excitons were 2-3 orders of magnitude smaller than those of the singlet state. Yet, due to their slower dynamics (~ 500 ps), they could be separated from the superimposed singlet emission. The CT decay times in blends with P3HT exhibited no significant temperature dependence, indicating that thermally driven dissociation of emissive excitons is unlikely. For blends with PTB7, however, a faster decay of the CT emission was obtained at room temperature.

  5. Influence of Self-Assembling Redox Mediators on Charge Transfer at Hydrophobic Electrodes.

    PubMed

    Smith, Timothy J; Wang, Chenxuan; Abbott, Nicholas L

    2015-10-01

    We report an investigation of the influence of reversible self-assembly of amphiphilic redox-mediators on interfacial charge transfer at chemically functionalized electrodes. Specifically, we employed (11-ferrocenylundecyl)-trimethylammonium bromide (FTMA) as a model self-assembling redox mediator and alkanethiol-modified gold films as hydrophobic electrodes. By performing cyclic voltammetry (CV, 10 mV/s) in aqueous solutions containing FTMA above its critical micellar concentration (CMC), we measured anodic (Ia) and cathodic (Ic) peak current densities of 18 ± 3 and 1.1 ± 0.1 ?A/cm(2), respectively, revealing substantial current rectification (Ia/Ic= 17) at the hydrophobic electrodes. In contrast, hydroxymethyl ferrocene (a non-self-assembling redox mediator) at hydrophobic electrodes and FTMA at bare gold electrodes, yielded relatively low levels of rectification (Ia/Ic= 1.7 and 2.3, respectively). Scan-rate-dependent measurements revealed Ia of FTMA to arise largely from the diffusion of FTMA from bulk solution to the hydrophobic electrode whereas Ic was dominated by adsorbed FTMA, leading to the proposal that current rectification observed with FTMA is mediated by interfacial assemblies of reduced FTMA that block access of oxidized FTMA to the hydrophobic electrode. Support for this proposal was obtained by using atomic force microscopy and quartz crystal microbalance measurements to confirm the existence of interfacial assemblies of reduced FTMA (1.56 ± 0.2 molecules/nm(2)). Additional characterization of a mixed surfactant system containing FTMA and dodecyltrimethylammonium bromide (DTAB) revealed that interfacial assemblies of DTAB also block access of oxidized FTMA to hydrophobic electrodes; this system exhibited Ia/Ic > 80. These results and others reported in this paper suggest that current rectification occurs in this system because oxidized FTMA does not mix with interfacial assemblies of reduced FTMA or DTAB formed at hydrophobic electrodes. More broadly, these results show that self-assembling redox mediators, when combined with chemically functionalized electrodes, offer the basis of new principles for controlling charge transfer at electrode/solution interfaces. PMID:26305703

  6. Charge versus Energy Transfer Effects in High-Performance Perylene Diimide Photovoltaic Blend Films.

    PubMed

    Singh, Ranbir; Shivanna, Ravichandran; Iosifidis, Agathaggelos; Butt, Hans-Jürgen; Floudas, George; Narayan, K S; Keivanidis, Panagiotis E

    2015-11-11

    Perylene diimide (PDI)-based organic photovoltaic devices can potentially deliver high power conversion efficiency values provided the photon energy absorbed is utilized efficiently in charge transfer (CT) reactions instead of being consumed in nonradiative energy transfer (ET) steps. Hitherto, it remains unclear whether ET or CT primarily drives the photoluminescence (PL) quenching of the PDI excimer state in PDI-based blend films. Here, we affirm the key role of the thermally assisted PDI excimer diffusion and subsequent CT reaction in the process of PDI excimer PL deactivation. For our study we perform PL quenching experiments in the model PDI-based composite made of poly[4,8-bis(5-(2-ethylhexyl)thiophen-2-yl)benzo[1,2-b;4,5-b']dithiophene-2,6-diyl-alt-(4-(2-ethylhexanoyl)-thieno[3,4-b]thiophene)-2-6-diyl] (PBDTTT-CT) polymeric donor mixed with the N,N'-bis(1-ethylpropyl)-perylene-3,4,9,10-tetracarboxylic diimide (PDI) acceptor. Despite the strong spectral overlap between the PDI excimer PL emission and UV-vis absorption of PBDTTT-CT, two main observations indicate that no significant ET component operates in the overall PL quenching: the PL intensity of the PDI excimer (i) increases with decreasing temperature and (ii) remains unaffected even in the presence of 10 wt % content of the PBDTTT-CT quencher. Temperature-dependent wide-angle X-ray scattering experiments further indicate that nonradiative resonance ET is highly improbable due to the large size of PDI domains. The dominance of the CT over the ET process is verified by the high performance of devices with an optimum composition of 30:70 PBDTTT-CT:PDI. By adding 0.4 vol % of 1,8-diiodooctane we verify the plasticization of the polymer side chains that balances the charge transport properties of the PBDTTT-CT:PDI composite and results in additional improvement in the device efficiency. The temperature-dependent spectral width of the PDI excimer PL band suggests the presence of energetic disorder in the PDI excimer excited state manifold. PMID:26480854

  7. Small-molecule activation chemistry catalyzed by proton-coupled electron transfer

    E-print Network

    Chang, Christopher J., 1974-

    2002-01-01

    Proton-coupled electron transfer (PCET) is the basic mechanism for bioenergetic conversion. Consummate examples include water oxidation in photosynthesis and oxygen reduction in respiration. Despite the importance of PCET ...

  8. Defect chemistry of a BaZrO3 ?3 (111) grain boundary by first principles calculations and space-charge theory.

    PubMed

    Polfus, Jonathan M; Toyoura, Kazuaki; Oba, Fumiyasu; Tanaka, Isao; Haugsrud, Reidar

    2012-09-21

    Defect calculations from density functional theory are implemented with space-charge theory models to describe the equilibrium defect chemistry of a ?3 (111) symmetric tilt boundary in BaZrO(3). As such, the space-charge potential and the concentrations of , , , NH and in the bulk, core and space-charge regions of the interface are calculated as a function of temperature and atmospheric conditions. Our results show that the core will be predominated by under hydrating conditions and that the space-charge potential increases with water vapor pressure. Under nitriding conditions, , NH and will predominate the core in different temperature regimes and effects of these defects on the space-charge properties are discussed. PMID:22864195

  9. Lithium adsorption on MgO(100) and its defects: Charge transfer, structure, and energetics

    NASA Astrophysics Data System (ADS)

    Farmer, J. A.; Ruzycki, N.; Zhu, J. F.; Campbell, Charles T.

    2009-07-01

    The adsorption energetics and growth of lithium vapor on MgO(100) at 300 K was studied using microcalorimetry, in combination with low-energy electron diffraction (LEED), low-energy ion scattering (ISS), Auger electron spectroscopy (AES), and work-function measurements. The MgO(100) samples were films of ˜4nm thickness grown on a Mo(100) single crystal. The initial sticking probability of lithium was ˜0.97 , reaching unity by 0.5 monolayer (ML). The AES and ISS signals vary with Li coverage up to 3 ML as expected if the Li atoms stay within the layer where they initially hit (i.e., with no interlayer transport). Initially, lithium adsorbs strongly at the intrinsic surface defects and as two-dimensional (2D) lithium clusters, with a heat of adsorption of 260 kJ/mol. The heat approaches the heat of sublimation of bulk Li (159 kJ/mol) by 0.4 ML, due to the growth of 2D and then three-dimensional (3D) Li islands. Argon-ion sputtering of the surface increases the defect density and the probability for adsorbing Li to find a defect, and thus the heat of adsorption at low coverages. When defects only are being populated, Li exhibits a heat of adsorption of 410 kJ/mol. Comparing heats with recent density functional theory (DFT) calculations suggests that the defect sites are under-coordinated O atoms at steps or kinks, or related structures at dislocations. The work function decreases by ˜1.8eV within the first 0.5 ML and then increases to near the value of bulk Li(solid), ˜2.6eV , by 3 ML. These results support recent DFT calculations predicting stronger electron transfer from Li to the MgO when at steps and kinks than at terraces, and decreasing charge transfer as 2D Li clusters grow. The work function starts to increase when the growth mode becomes dominated by growth of 3D Li(solid). In spite of a large amount of electron transfer from Li to MgO, Li adatoms have attractive interactions that lead to 2D clustering. For 1-nm-thick MgO films, the heat of adsorption was higher by 60-20 kJ/mol than for 4 nm films in the entire range from 0 to 0.7 ML, where adsorption in the first layer dominates.

  10. Dynamics of charge-transfer excited states relevant to photochemical energy conversion

    SciTech Connect

    Lim, E.C.

    1991-11-01

    The primary objective of the research program is to gain a fundamental understanding of the factors governing the efficiency of excited-state charge transfer CT interactions between two chromophores that are brought together in close proximity, either by a very short covalent linkage or by ground-state complex formation. CT and van der Walls (vdW), interactions in covalently bonded bichromophoric compounds in condensed phase, as well as those in vdW complexes in supersonic jets, are being investigated using laser-based techniques under a variety of experimental conditions. This progress report is divided into three parts, according to the class of molecular systems and the phase (liquid vs. gas) in which the excited-state interactions are probed. The first is concerned with the excited states of bridged diaryl compounds in the condensed phase. The second involves the excited states of vdW complexes in supersonic jets. Finally, the third, is concerned with the excited states of electron donor-acceptor (EDA) systems in both the condensed phase and supersonic jets. In each of these studies, we are concerned with the interchromophore interactions ranging from weak vdW forces to strong CT forces, and the factors determining whether the interaction forces are weak or strong in related molecules.

  11. Spectral modulation of charge transfer fluorescence probe encapsulated inside aqueous and non-aqueous ?-cyclodextrin nanocavities

    NASA Astrophysics Data System (ADS)

    Singh, Rupashree Balia; Mahanta, Subrata; Guchhait, Nikhil

    2010-01-01

    In this work, we report the spectral modulations of a intramolecular charge transfer (ICT) molecule ethyl ester of N, N-dimethylaminonaphthyl-(acrylic)-acid (EDMANA) when encapsulated in the water and N, N-dimethylformamide (DMF) solution of ?-CD nanocavities. From the nature of the Benesi-Hildebrand (B-H) plots, the stoichiometry of the host guest inclusion complexes are found to be 1:1 in water ?-CD solution and both 1:1 and 1:2 in DMF ?-CD solution. The preferential location and difference in orientation of EDMANA molecule inside the ?-CD cavity has been accessed by analysis of the effect of acid and metal cation Ni 2+ on the spectral characteristics in both the media. In case of 1:1 complex, the polar donor group prefers to expose to bulk aqueous phase capable of binding with H + and Ni 2+ ions and the acceptor to the hydrophobic interior. On the other hand, the acceptor group remains exposed to the non-polar bulk phase and the donor group is orientated preferentially inside the non-polar core in 1:2 inclusion complexes.

  12. Geometry and quadratic nonlinearity of charge transfer complexes in solution: A theoretical study

    NASA Astrophysics Data System (ADS)

    Mukhopadhyay, S.; Pandey, Ravindra; Das, Puspendu K.; Ramasesha, S.

    2011-01-01

    In this paper, we have computed the quadratic nonlinear optical (NLO) properties of a class of weak charge transfer (CT) complexes. These weak complexes are formed when the methyl substituted benzenes (donors) are added to strong acceptors like chloranil (CHL) or di-chloro-di-cyano benzoquinone (DDQ) in chloroform or in dichloromethane. The formation of such complexes is manifested by the presence of a broad absorption maximum in the visible range of the spectrum where neither the donor nor the acceptor absorbs. The appearance of this visible band is due to CT interactions, which result in strong NLO responses. We have employed the semiempirical intermediate neglect of differential overlap (INDO/S) Hamiltonian to calculate the energy levels of these CT complexes using single and double configuration interaction (SDCI). The solvent effects are taken into account by using the self-consistent reaction field (SCRF) scheme. The geometry of the complex is obtained by exploring different relative molecular geometries by rotating the acceptor with respect to the fixed donor about three different axes. The theoretical geometry that best fits the experimental energy gaps, ?HRS and macroscopic depolarization ratios is taken to be the most probable geometry of the complex. Our studies show that the most probable geometry of these complexes in solution is the parallel displaced structure with a significant twist in some cases.

  13. Carbene-dichlorosilylene stabilized phosphinidenes exhibiting strong intramolecular charge transfer transition.

    PubMed

    Roy, Sudipta; Stollberg, Peter; Herbst-Irmer, Regine; Stalke, Dietmar; Andrada, Diego M; Frenking, Gernot; Roesky, Herbert W

    2015-01-14

    The unstable species dichlorosilylene was previously stabilized by carbene. The lone pair of electrons on the silicon atom of (carbene)SiCl2 can form a coordinate bond with metal-carbonyls. Herein we report that (carbene)SiCl2 can stabilize a phosphinidene (Ar-P, a carbone analogue) with the general formula carbene?SiCl2?P-Ar (carbene = cyclic alkyl(amino) carbene (cAAC; 2) and N-heterocyclic carbene (NHC; 3)). Compounds 2 and 3 are stable, isolable, and storable at 0 °C (2) to room temperature (3) under an inert atmosphere. The crystals of 2 and 3 are dark blue and red, respectively. The intense blue color of 2 arises due to the strong intramolecular charge transfer (ICT) transition from ?Si?P??*cAAC. The electronic structure and bonding of 2, 3 were studied by theoretical calculations. The HOMO of the molecule is located on the ?Si?P bond, while the LUMO is located at the carbene moiety (cAAC or NHC). The dramatic change in color of these compounds from red (3, NHC) to blue (2, cAAC) is ascribed to the difference in energy of the LUMO within the carbenes (cAAC/NHC) due to a lower lying LUMO of cAAC. PMID:25539016

  14. Vibrational coherences in charge-transfer dyes: A non-adiabatic picture

    SciTech Connect

    Sissa, Cristina; Delchiaro, Francesca; Di Maiolo, Francesco

    2014-10-28

    Essential-state models efficiently describe linear and nonlinear spectral properties of different families of charge-transfer chromophores. Here, the essential-state machinery is applied to the calculation of the early-stage dynamics after ultrafast (coherent) excitation of polar and quadrupolar chromophores. The fully non-adiabatic treatment of coupled electronic and vibrational motion allows for a reliable description of the dynamics of these intriguing systems. In particular, the proposed approach is reliable even when the adiabatic and harmonic approximations do not apply, such as for quadrupolar dyes that show a multistable, broken-symmetry excited state. Our approach quite naturally leads to a clear picture for a dynamical Jahn-Teller effect in these systems. The recovery of symmetry due to dynamical effects is however disrupted in polar solvents where a static symmetry lowering is observed. More generally, thermal disorder in polar solvents is responsible for dephasing phenomena, damping the coherent oscillations with particularly important effects in the case of polar dyes.

  15. Antibacterial activity of large-area monolayer graphene film manipulated by charge transfer

    NASA Astrophysics Data System (ADS)

    Li, Jinhua; Wang, Gang; Zhu, Hongqin; Zhang, Miao; Zheng, Xiaohu; di, Zengfeng; Liu, Xuanyong; Wang, Xi

    2014-03-01

    Graphene has attracted increasing attention for potential applications in biotechnology due to its excellent electronic property and biocompatibility. Here we use both Gram-positive Staphylococcus aureus (S. aureus) and Gram-negative Escherichia coli (E. coli) to investigate the antibacterial actions of large-area monolayer graphene film on conductor Cu, semiconductor Ge and insulator SiO2. The results show that the graphene films on Cu and Ge can surprisingly inhibit the growth of both bacteria, especially the former. However, the proliferation of both bacteria cannot be significantly restricted by the graphene film on SiO2. The morphology of S. aureus and E. coli on graphene films further confirms that the direct contact of both bacteria with graphene on Cu and Ge can cause membrane damage and destroy membrane integrity, while no evident membrane destruction is induced by graphene on SiO2. From the viewpoint of charge transfer, a plausible mechanism is proposed here to explain this phenomenon. This study may provide new insights for the better understanding of antibacterial actions of graphene film and for the better designing of graphene-based antibiotics or other biomedical applications.

  16. Spectroscopy and dynamics of charge transfer excitons in type-II band aligned quantum confined heterostructures

    SciTech Connect

    Kushavah, Dushyant; Mohapatra, P. K.; Vasa, P.; Singh, B. P.; Rustagi, K. C.; Bahadur, D.

    2015-05-15

    We illustrate effect of charge transfer (CT) in type-II quantum confined heterostructure by comparing CdSe quantum dots (QDs), CdSe/CdTe heterostructure quantum dots (HQDs) and CdSe/CdTe/CdSe quantum well-quantum dots (QWQDs) heterostructures. CdSe core QDs were synthesized using a kinetic growth method where QD size depends on reaction time. For shell coating we used modified version of successive ionic layer adsorption and reaction (SILAR). Size of different QDs ?5 to 7 nm were measured by transmission electron microscopy (TEM). Strong red shift from ?597 to ?746 nm in photoluminescence (PL) spectra from QDs to QWQDs shows high tunability which is not possible with single constituent semiconductor QDs. PL spectra have been recorded at different temperatures (10K-300K). Room temperature time correlated single photon counting (TCSPC) measurements for QDs to QWQDs show three exponential radiative decay. The slowest component decay constant in QWQDs comes around eight fold to ?51 ns as compared to ?6.5 ns in HQD suggesting new opportunities to tailor the radiative carrier recombination rate of CT excitons.

  17. S-, N- and C-doped titanium dioxide nanoparticles: Synthesis, characterization and redox charge transfer study

    SciTech Connect

    Madhusudan Reddy, K.; Baruwati, Babita; Jayalakshmi, M.; Mohan Rao, M.; Manorama, Sunkara V . E-mail: manorama@iict.res.in

    2005-11-15

    Herein we report on the synthesis and characterization of TiO{sub 2} nanomaterials doped with anions like sulfur, carbon and nitrogen. Upon doping, the absorption extends well into the visible region. This shift in the absorption edge is accompanied by a concomitant narrowing of band gap. The resulting anion-doped TiO{sub 2} nanomaterials were characterized by XRD, XPS, elemental analysis, EDAX, TEM, UV-DRS, DC conductivity, AC impedance and cyclic voltammetric studies. XPS confirms the presence of the dopants and the elemental analysis determined the amount of dopants in TiO{sub 2}. Electrochemical characterization was carried out by cyclic voltammetry at pHs 2, 6.5 and 10. As against the response of undoped TiO{sub 2}, the doped samples show an active electrochemical response indicating an induced charge transfer across the titania/solution interface, thus forming two anodic peaks and a cathodic peak. This interesting and significant observation was understood in terms of band bending due to anion doping as well as to the pH changes in the experimental solutions.

  18. Conductive PVDF-HFP nanofibers with embedded TTF-TCNQ charge transfer complex.

    PubMed

    Gal-Oz, Reshef; Patil, Nilesh; Khalfin, Rafail; Cohen, Yachin; Zussman, Eyal

    2013-07-10

    Tetrathiafulvalene-tetracyanoquinodimethane charge-transfer complex (TTF-TCNQ CTC) represents a promising organic conductive system. However, application of this donor-acceptor pair is highly limited, because of its ultrafast crystallization kinetics and very low solubility. In this work, conductive organic nanofibers were generated via a coelectrospinning process of poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) with embedded TTF and TCNQ in the shell and core solutions, respectively. Upon supply of the polymer solutions, a core-shell droplet was formed at the exit of the spinneret. The electron donor TTF and the electron acceptor TCNQ migrated toward each other, within the compound droplet, to produce conductive CTC crystals. In the presence of a sufficiently strong electric field, jetting set in at the droplet tip, which yielded solidified PVDF-HFP nanofibers embedded with aligned CTC. Fiber diameters ranged between 100 and 500 nm. X-ray analysis showed strong equatorial reflections (110,200) of oriented copolymer PVDF-HFP crystals (?-phase) with copolymer chains oriented along the fiber axis, and of CTC (001), indicating that the CTC molecular planes were aligned parallel to the nanofiber axis. In addition, reflections of unreacted TCNQ (120,220) and TTF (110) crystals were observed. The electrospun nanofibers were collected to form a fiber mat, which was evaluated as a working electrode in a three-electrode cell system, exhibiting differential conductance of 5.23 ?mho. PMID:23745509

  19. Spectroscopy and dynamics of charge transfer excitons in type-II band aligned quantum confined heterostructures

    NASA Astrophysics Data System (ADS)

    Kushavah, Dushyant; Mohapatra, P. K.; Rustagi, K. C.; Bahadur, D.; Vasa, P.; Singh, B. P.

    2015-05-01

    We illustrate effect of charge transfer (CT) in type-II quantum confined heterostructure by comparing CdSe quantum dots (QDs), CdSe/CdTe heterostructure quantum dots (HQDs) and CdSe/CdTe/CdSe quantum well-quantum dots (QWQDs) heterostructures. CdSe core QDs were synthesized using a kinetic growth method where QD size depends on reaction time. For shell coating we used modified version of successive ionic layer adsorption and reaction (SILAR). Size of different QDs ˜5 to 7 nm were measured by transmission electron microscopy (TEM). Strong red shift from ˜597 to ˜746 nm in photoluminescence (PL) spectra from QDs to QWQDs shows high tunability which is not possible with single constituent semiconductor QDs. PL spectra have been recorded at different temperatures (10K-300K). Room temperature time correlated single photon counting (TCSPC) measurements for QDs to QWQDs show three exponential radiative decay. The slowest component decay constant in QWQDs comes around eight fold to ˜51 ns as compared to ˜6.5 ns in HQD suggesting new opportunities to tailor the radiative carrier recombination rate of CT excitons.

  20. Intramolecular charge transfer of ?-conjugated push-pull systems in terms of polarizability and electronegativity

    NASA Astrophysics Data System (ADS)

    Yong Lee, Jin; Kim, Kwang S.; Jin Mhin, Byung

    2001-11-01

    We have derived a simple expression to evaluate the amount of intramolecular charge transfer (ICT) of ?-conjugate push-pull systems from the properties of electronegativity (?) and polarizability (?) of the corresponding push and pull systems. This simple model is verified from ab initio calculations of disubstituted benzenes, stilbenes, and butadienes (push-pull systems) and their monosubstituted (push or pull) systems with various donors and acceptors. The bond length alternation (BLA) is often used as a good structural parameter to describe the amount of ICT; however, it is not a complete parameter because the amounts of ICT for the same sets of donor/acceptor pairs are different for different bridge systems. Here, we report a parameter composed of polarizability and electronegativity to give a consistent amount of ICT for different bridge systems. In particular, when a highly electropositive donor is used, the polarizability of an acceptor is the most determining factor for ICT. On the basis of this model, we find a very strong acceptor with large polarization effect, CH=C5H4, which gives a large nonlinear optical (NLO) response when a highly electropositive donor is used. The model would be a very useful utility to design various types of new functional molecular systems involving ICT optimization.

  1. Spectroscopic characterization of intramolecular charge transfer of sodium 4-( N, N-dimethylamino)naphthalene-1-sulfonate

    NASA Astrophysics Data System (ADS)

    Lin, Li-Rong; Yang, Wen-Liang; Zheng, Guang-Le; Jiang, Yun-Bao

    2004-08-01

    In this paper, a new dual fluorescent N, N-dimethylaminonaphthalene derivative, sodium 4-( N, N-dimethylamino)naphthalene-1-sulfonate (SDMDNS), was reported. It was found that SDMDNS emits dual fluorescence only in highly polar solvent water but not in organic solvents such as methanol, dioxane and acetonitrile. Only a single broad band emission at ca. 420 nm was observed in the short wavelength region in organic solvents. The dual fluorescence of SDMDNS in water was found at 423 and 520 nm, respectively. Introduction of organic solvent as ethanol into aqueous solution of SDMDNS leads to blue shift of the long-wavelength emission, and this was evidently supported by introduction of cyclodextrin or surfactant in the aqueous solution. It indicates that a highly polar solvent was required to bring out dual fluorescence; furthermore, the short wavelength fluorescence is emitted from locally excited (LE) state and the long wavelength fluorescence is emitted from charge transfer (CT) state. The pH dependence of the dual fluorescence of SDMDNS demonstrates that the neutral form of the molecular has a higher ratio of CT band intensity to LE band. Temperature effect on the excited state of SDMDNS was also examined and gave stabilization enthalpy (-? H ) of the CT reaction 8.7 kJ mol -1.

  2. Charge transfer complexes of fullerene[60] with porphyrins as molecular rectifiers. A theoretical study.

    PubMed

    Montiel, Filiberto; Fomina, Lioudmila; Fomine, Serguei

    2015-01-01

    Molecular diodes based on charge transfer complexes of fullerene[60] with different metalloporphyrins have been modeled. Their current-voltage characteristics and the rectification ratios (RR) were calculated using direct ab initio method at PBE/def2-SVP level of theory with D3 dispersion correction, for voltages ranging from -2 to +2?V. The highest RR of 32.5 was determined for the complex of fullerene[60] with zinc tetraphenylporphyrin at 0.8?V. Other molecular diodes possessed lower RR, however, all complexes showed RR higher than 1 at all bias voltages. The asymmetric evolutions and alignment of the molecular orbitals with the applied bias were found to be essential for generating the molecular diode rectification behavior. Metal nature of metalloporphyrins and the interaction porphyrin-electrode significantly affect RR of molecular diode. Large metal ions like Cd(2+) and Ag(2+) in metalloporphyrins disfavor rectification creating conducting channels in two directions, while smaller ions Zn(2+) and Cu(2+) favor rectification increasing the interaction between gold electrode and porphyrin macrocycle. PMID:25605605

  3. Charge transfer effects on the chemical reactivity of PdxCu1-x nanoalloys.

    PubMed

    Castegnaro, M V; Gorgeski, A; Balke, B; Alves, M C M; Morais, J

    2015-12-17

    This work reports on the synthesis and characterization of PdxCu1-x (x = 0.7, 0.5 and 0.3) nanoalloys obtained via an eco-friendly chemical reduction method based on ascorbic acid and trisodium citrate. The average size of the quasi-spherical nanoparticles (NPs) obtained by this method was about 4 nm, as observed by TEM. The colloids containing different NPs were then supported on carbon in order to produce powder samples (PdxCu1-x/C) whose electronic and structural properties were probed by different techniques. XRD analysis indicated the formation of crystalline PdCu alloys with a nanoscaled crystallite size. Core-level XPS results provided a fingerprint of a charge transfer process between Pd and Cu and its dependency on the nanoalloy composition. Additionally, it was verified that alloying was able to change the NP's reactivity towards oxidation and reduction. Indeed, the higher the amount of Pd in the nanoalloy, less oxidized are both the Pd and the Cu atoms in the as-prepared samples. Also, in situ XANES experiments during thermal treatment under a reducing atmosphere showed that the temperature required for a complete reduction of the nanoalloys depends on their composition. These results envisage the control at the atomic level of novel catalytic properties of such nanoalloys. PMID:26647173

  4. Antibacterial activity of large-area monolayer graphene film manipulated by charge transfer

    PubMed Central

    Li, Jinhua; Wang, Gang; Zhu, Hongqin; Zhang, Miao; Zheng, Xiaohu; Di, Zengfeng; Liu, Xuanyong; Wang, Xi

    2014-01-01

    Graphene has attracted increasing attention for potential applications in biotechnology due to its excellent electronic property and biocompatibility. Here we use both Gram-positive Staphylococcus aureus (S. aureus) and Gram-negative Escherichia coli (E. coli) to investigate the antibacterial actions of large-area monolayer graphene film on conductor Cu, semiconductor Ge and insulator SiO2. The results show that the graphene films on Cu and Ge can surprisingly inhibit the growth of both bacteria, especially the former. However, the proliferation of both bacteria cannot be significantly restricted by the graphene film on SiO2. The morphology of S. aureus and E. coli on graphene films further confirms that the direct contact of both bacteria with graphene on Cu and Ge can cause membrane damage and destroy membrane integrity, while no evident membrane destruction is induced by graphene on SiO2. From the viewpoint of charge transfer, a plausible mechanism is proposed here to explain this phenomenon. This study may provide new insights for the better understanding of antibacterial actions of graphene film and for the better designing of graphene-based antibiotics or other biomedical applications. PMID:24619247

  5. High pressure effect on charge transfer transition in Y2O2S:Eu3+

    NASA Astrophysics Data System (ADS)

    Behrendt, Miros?aw; Szczodrowski, Karol; Mahlik, Sebastian; Grinberg, Marek

    2014-08-01

    In this contribution, spectroscopic characterization of Y2O2S doped with 1 mol% of Eu3+ are presented. Steady state luminescence and luminescence excitation spectra, as well as the time resolved spectra and luminescence kinetics were measured. All experiments were performed at ambient and high hydrostatic pressure up to 240 kbar applied in diamond anvil cell (DAC). The excitation spectrum of the Eu3+ emission monitored at 5D0 ? 7F2 transition consists of two bands peaked at 262 nm and at 312 nm that can be attributed to host lattice absorption and to charge transfer (CT) transition (O2- ? Eu3+ and S2- ? Eu3+), respectively. At ambient pressure under excitation 325 nm the emission related to transitions from the 5D0,5D1 and 5D2 excited states of Eu3+, was observed. At pressure above 38 kbar additional lines related to the transitions from the 5D3 state appeared. We found that for all pressure the emission from the 5D0 was delayed in time after excitation pulse. Emission from the 5D1 and 5D2 appeared immediately after excitation at ambient pressure and for pressure higher than 40 and 80 kbar was delayed in time. Analysis of pressure induced changes in Eu3+ luminescence kinetics allowed to develop the quantitative configurational coordinated model of the Y2O2S:Eu3+ system.

  6. Transition from charge-transfer to largely locally excited exciplexes, from structureless to vibrationally structured emissions.

    PubMed

    Young, Ralph H; Feinberg, Adam M; Dinnocenzo, Joseph P; Farid, Samir

    2015-01-01

    Exciplexes of 9,10-dicyanoanthracene (DCA) with alkylbenzene donors in cyclohexane show structureless emission spectra, typical of exciplexes with predominantly charge-transfer (CT) character, when the donor has a relatively low oxidation potential (Eox ), e.g. hexamethylbenzene (HMB). With increasing Eox and stronger mixing with a locally excited (LE) state, vibrational structure begins to appear with 1,2,3,5-tetramethylbenzene and becomes prominent with p-xylene (p-Xy). A simple theoretical model reproduces the spectra and the radiative rate constants, and it reveals several surprises: Even in this nonpolar solvent, the fractional CT character of a highly mixed exciplex varies widely in response to fluctuations in the microscopic environment. Environments that favor the LE (or CT) state contribute more to the blue (or red) side of the overall spectrum. It is known that sparsely substituted benzene radical cations, e.g., p-Xy(•+) , are stabilized more in acetonitrile than the heavily substituted HMB(•+) . Remarkably, ion pairing with DCA(•-) in cyclohexane leads to even larger differences in the stabilization of these radical cations. The spectra of the low-Eox donors are almost identical except for displacements that approximately equal the differences in Eox , even though the exciplexes have varying degrees of CT character. These similarities result from compensation among several nonobvious, but quantified factors. PMID:25363042

  7. Charge-Transfer Induced High Efficient Hydrogen Evolution of MoS2/graphene Cocatalyst

    PubMed Central

    Li, Honglin; Yu, Ke; Li, Chao; Tang, Zheng; Guo, Bangjun; Lei, Xiang; Fu, Hao; Zhu, Ziqiang

    2015-01-01

    The MoS2 and reduced graphite oxide (rGO) composite has attracted intensive attention due to its favorable performance as hydrogen evolution reaction (HER) catalyst, but still lacking is the theoretical understanding from a dynamic perspective regarding to the influence of electron transfer, as well as the connection between conductivity and the promoted HER performance. Based on the first-principles calculations, we here clearly reveal how an excess of negative charge density affects the variation of Gibbs free energy (?G) and the corresponding HER behavior. It is demonstrated that the electron plays a crucial role in the HER routine. To verify the theoretical analyses, the MoS2 and reduced graphite oxide (rGO) composite with well defined 3-dimensional configuration was synthesized via a facile one-step approach for the first time. The experimental data show that the HER performance have a direct link to the conductivity. These findings pave the way for a further developing of 2-dimension based composites for HER applications. PMID:26688209

  8. Charge Transfer Molecular Rotor DCVJ Investigated by Coherent Anti-Stokes Raman Spectroscopy

    NASA Astrophysics Data System (ADS)

    Ujj, Laszlo; Miller, Scott; Welch, Jonathan; Amos, Charles; Prayaga, Chandra

    2009-05-01

    Coherent anti-Stokes Raman Spectroscopy (CARS) has been shown to be one of the most powerful experimental methodologies for obtaining vibrational information from both stable and transient molecular species^1. The electronically enhanced polarization sensitive version of CARS is even more effective for measuring molecular vibrational information not easily reachable by spontaneous Raman spectroscopy. Theoretical and experimental principles associated with CARS with an emphasis on points relevant to the interpretation of experimental spectra will be presented. The method is applied to measure the vibrational manifold of DCVJ for the first time. DCVJ is a charge transfer molecular rotor showing a viscosity dependent fluorescence quantum yield. Based upon the measured CARS spectra, the effect of inhibition of the internal rotation on the vibrational motion of the molecule will be discussed. The design and operation of an all solid-state broadband nanosecond CARS system will be also presented. An overview of applications of molecular rotors in biology and information technology will be outlined. Ref.: 1. L. Ujj and G. H. Atkinson, ``Coherent Anti-Stokes Raman Spectroscopy'', in Handbook of Vibr. Spect., Wiley & Sons, Ltd., (2002).

  9. Switching effect in Cu:TCNQ charge transfer-complex thin films by vacuum codeposition

    NASA Astrophysics Data System (ADS)

    Oyamada, Takahito; Tanaka, Haruo; Matsushige, Kazumi; Sasabe, Hiroyuki; Adachi, Chihaya

    2003-08-01

    We demonstrate the operation of an organic switching device using a uniform poly-crystalline Cu:7, 7, 8, 8-Tetracyanoquinodimethane (TCNQ) charge transfer (CT)-complex thin film that is prepared by vacuum vapor codeposition. Characteristic CT-absorption at ?=600-1200 nm was observed in the complex film in the UV-visible spectrum and the cyano stretching peak in the IR spectrum shifted to a higher (more than 29 cm-1) wave number than that of a pristine TCNQ film, suggesting the formation of a CT-complex in the evaporated thin film. Reproducible electrical switching characteristics were observed in the indium tin oxide/Al/(Al2O3)/Cu:TCNQ/Al structure. The device exhibited a clear threshold from low impedance to high impedance at an applied voltage of 10.0±2.0 V and a reverse phenomenon at a negative bias of -9.5±2.0 V. In this study, we demonstrate that a thin Al2O3 layer between the aluminum (Al) anode and Cu:TCNQ layers creates reproducible switching.

  10. Tuning the charge transfer plasmon in a metallic nanoparticle dimer bridged by a quantum dot

    NASA Astrophysics Data System (ADS)

    Kulkarni, Vikram; Manjavacas, Alejandro; Nordlander, Peter

    2015-03-01

    Localized surface plasmon resonances (LSPR) are a subject of intense experimental and theoretical research interest. LSPR have found applications in catalysis, solar energy, cancer therapy, and surface enhanced Raman spectroscopy (SERS). This is due to the exceptional light capturing and focusing capabilities of plasmonic nanostructures. An LSPR of particular interest is the charge transfer plasmon (CTP). This mode may be excited when two plasmonic nanoparticles are bridged by a conductive junction. The CTP is extraordinarily sensitive to the conductive properties of the junction. Here we perform a theoretical investigation of the CTP when two plasmonic nanoparticles are bridged by a quantum dot. All simulations are done using the time dependent density functional theory (TDDFT). By modulating the electronic structure of the quantum dot we are able to effectively turn the CTP on and off. Specifically, the CTP emerges only when a quantum dot energy level is resonant with the fermi energy of the plasmonic nanoparticles. We verify that the conductance through the junction is on the order of the quantum unit of conductance. This work is of great interest to the future design of plasmonic and molecular electronic systems. This work was supported in part by the Data Analysis and Visualization Cyberinfrastructure funded by NSF under Grant OCI-0959097.

  11. Role of direction of charge transfer on the nonlinear optical behavior of pyridine substituted chalcone derivatives

    NASA Astrophysics Data System (ADS)

    Menezes, Anthoni Praveen; Jayarama, A.

    2014-10-01

    High quality single crystals of an efficient novel nonlinear optical (NLO) chalcone derivative 3-(4-nitrophenyl)-1-(pyridine-3-yl) prop-2-en-1-one (4NP3AP) that are transparent in the entire visible and infrared region are grown by the slow evaporation solution growth method at ambient temperature. The single crystal XRD studies reveal that the crystal belongs to monoclinic system with the noncentrosymmetric space group P21. The presence of functional groups in the compound is confirmed by different spectroscopic techniques. The surface morphology of the crystal is studied by scanning electron microscopy. The second harmonic generation (SHG) efficiency of 4NP3AP determined by Perry and Kurtz method is 56% that of potassium dihydrogen phosphate (KDP) single crystals. The static and frequency dependent molecular hyperpolarizabilities were computed using MOPAC 2012. Thermal analysis confirms that the crystal is thermally stable up to 177 °C. The origin of nonlinearity and the role of charge transfer direction on the nonlinearity of the chalcone have been discussed in detail.

  12. The study of interaction and charge transfer at black phosphorus-metal interfaces

    NASA Astrophysics Data System (ADS)

    Zhu, Sicong; Ni, Yun; Liu, Juan; Yao, Kailun

    2015-11-01

    Using density-functional theory, we analyze the potential barrier, charge transfer and atomic orbital overlap at the metal-black phosphorus interface in an optimized structure to understand how efficiently carriers could be injected from a metal contact to the black phosphorus. We investigate a monolayer black phosphorus directly in contact with five representative metal substrates Ag(1?1?1), Au(1?1?1), Al(1?1?1), Cu(1?1?1) or Zn(0?0?0?1), having varying work functions but each with minimal lattice mismatch with the black phosphorus overlayer. We find that the contact nature is ohmic versus Schottky. For different kinds of contact, Cu and Al show better conductivity than the other metals. The dependence of the barrier height exhibits partial Fermi-level pinning character. These findings may prove to be instrumental in the future design of BP-based electronics, as well as in exploring novel catalysts for hydrogen production and related chemical processes.

  13. An internal charge transfer-dependent solvent effect in V-shaped azacyanines.

    PubMed

    Tasior, Mariusz; Bald, Ilko; Deperasi?ska, Irena; Cywi?ski, Piotr J; Gryko, Daniel T

    2015-12-28

    New V-shaped non-centrosymmetric dyes, possessing a strongly electron-deficient azacyanine core, have been synthesized based on a straightforward two-step approach. The key step in this synthesis involves palladium-catalysed cross-coupling of dibromo-N,N'-methylene-2,2'-azapyridinocyanines with arylacetylenes. The resulting strongly polarized ?-expanded heterocycles exhibit green to orange fluorescence and they strongly respond to changes in solvent polarity. We demonstrate that differently electron-donating peripheral groups have a significant influence on the internal charge transfer, hence on the solvent effect and fluorescence quantum yield. TD-DFT calculations confirm that, in contrast to the previously studied bis(styryl)azacyanines, the proximity of S1 and T2 states calculated for compounds bearing two 4-N,N-dimethylaminophenylethynyl moieties establishes good conditions for efficient intersystem crossing and is responsible for its low fluorescence quantum yield. Non-linear properties have also been determined for new azacyanines and the results show that depending on peripheral groups, the synthesized dyes exhibit small to large two-photon absorption cross sections reaching 4000 GM. PMID:26483360

  14. Nanoscale transport of charge-transfer states in organic donor-acceptor blends

    NASA Astrophysics Data System (ADS)

    Deotare, P. B.; Chang, W.; Hontz, E.; Congreve, D. N.; Shi, L.; Reusswig, P. D.; Modtland, B.; Bahlke, M. E.; Lee, C. K.; Willard, A. P.; Bulovi?, V.; van Voorhis, T.; Baldo, M. A.

    2015-11-01

    Charge-transfer (CT) states, bound combinations of an electron and a hole on separate molecules, play a crucial role in organic optoelectronic devices. We report direct nanoscale imaging of the transport of long-lived CT states in molecular organic donor-acceptor blends, which demonstrates that the bound electron-hole pairs that form the CT states move geminately over distances of 5-10 nm, driven by energetic disorder and diffusion to lower energy sites. Magnetic field dependence reveals a fluctuating exchange splitting, indicative of a variation in electron-hole spacing during diffusion. The results suggest that the electron-hole pair of the CT state undergoes a stretching transport mechanism analogous to an `inchworm’ motion, in contrast to conventional transport of Frenkel excitons. Given the short exciton lifetimes characteristic of bulk heterojunction organic solar cells, this work confirms the potential importance of CT state transport, suggesting that CT states are likely to diffuse farther than Frenkel excitons in many donor-acceptor blends.

  15. Charge transfer and ionization in collisions of Si3+ with H from low to high energy

    NASA Astrophysics Data System (ADS)

    Wang, J. G.; He, B.; Ning, Y.; Liu, C. L.; Yan, J.; Stancil, P. C.; Schultz, D. R.

    2006-11-01

    Charge transfer processes due to collisions of ground state Si3+(3sS1) ions with atomic hydrogen are investigated using the quantum-mechanical molecular-orbital close-coupling (MOCC) and classical-trajectory Monte Carlo (CTMC) methods. The MOCC calculations utilize ab initio adiabatic potentials and nonadiabatic radial coupling matrix elements obtained from Herrero [J. Phys. B 29, 5583 (1996)] which were calculated with a full configuration-interaction method. Total and state-selective single-electron capture cross sections are obtained for collision energies from 0.01eV/u to 1MeV/u . Total and state-selective rate coefficients are also presented for temperatures from 2×103K to 107K . Comparison with existing data reveals that the total CTMC cross sections are in good agreement with the experimental measurements at the higher considered energies and that previous Landau-Zener calculations underestimate the total rate coefficients by a factor of up to two. The CTMC calculations of target ionization are presented for high energies.

  16. Electrochemical performance of silver/molybdotungstate-amorphous-electrolyte cells with charge-transfer-complex cathodes

    NASA Astrophysics Data System (ADS)

    Sathya Sainath Prasad, P.; Radhakrishna, S.

    For the quaternary fast ion conducting system AgI?Ag 2O?MoO 3?WO 3, the highest ionic conductivity, 5.1 × 10 -2 (? cm) -1, was observed when using an amorphous electrolyte composition of 80%AgI-13.33%Ag 2O-6.66% (0.7MoO 3-0.3WO 3). This electrolyte was used in the fabrication of solid-state electrochemical cells with the configuration (anode)/(amorphous electrolyte)/(cathode). The anode consisted of silver while a variety of organic charge-transfer-complex materials was employed as cathodes. The latter included phenothiazene, pyrene, and 2-perylene·3I 2. Cell performance was assessed by studying open-circuit voltage (OCV), anodic and cathodic polarisation, current discharge capability, and load discharge characteristics. It was found that the cell with a 2-perylene·3I 2 cathode yielded the highest OCV (657 mV) without any anodic or cathodic polarisation. The cell exhibited an internal resistance of 32 ? and a short-circuit current of 10 mA with a rechargeability having marginal coulombic efficiency. The diffusion co-efficients of silver ion were evaluated from the time dependence of cell voltage as a function of current density. The optimum current density ( i.e., that giving no polarisation) was fixed and the load curves were recorded to evaluate the applicability of the cells to micropower sources and low-energy-density silver batteries.

  17. Influence of molecular conformations on the electronic structure of organic charge transfer salts

    NASA Astrophysics Data System (ADS)

    Guterding, Daniel; Valentí, Roser; Jeschke, Harald O.

    2015-08-01

    We report ab initio calculations for the electronic structure of organic charge transfer salts ? -(ET) 2Cu [N(CN) 2] Br , ? -(ET) 2Cu [N(CN) 2] I , ??-(ET) 2Cu [N(CN) 2] Cl , and ? -(ET) 2Cu2(CN) 3 . These materials show an ordering of the relative orientation of terminal ethylene groups in the bis-ethylenedithio-tetrathiafulvalene molecules at finite temperature and our calculations correctly predict the experimentally observed ground state molecular conformations (eclipsed or staggered). Further, it was recently demonstrated that the ethylene end group relative orientations can be used to reversibly tune ? -(ET) 2Cu [N(CN) 2] Br through a metal-insulator transition. Using a tight-binding analysis, we show that the molecular conformations of ethylene end groups are intimately connected to the electronic structure and significantly influence hopping and Hubbard repulsion parameters. Our results place ? -(ET) 2Cu [N(CN) 2] Br in eclipsed and staggered configurations on opposite sides of the metal-insulator transition.

  18. Resonant charge transfer at dielectric surfaces. Electron capture and release due to impacting metastable nitrogen molecules

    NASA Astrophysics Data System (ADS)

    Marbach, J.; Bronold, F. X.; Fehske, H.

    2012-04-01

    We report on the theoretical description of secondary electron emission due to resonant charge transfer occurring during the collision of metastable N2(3?+ u ) molecules with dielectric surfaces. The emission is described as a two step process consisting of electron capture to form an intermediate shape resonance N2 -(2? g ) and subsequent electron emission by decay of this ion, either due to its natural life time or its interaction with the surface. The electron capture is modeled using the Keldysh Green's function technique and the negative ion decay is described by a combination of the Keldysh technique and a rate equation approach. We find the resonant capture of electrons to be very efficient and the natural decay to be clearly dominating over the surface-induced decay. Secondary electron emission coefficients are calculated for Al2O3, MgO, SiO2, and diamond at several kinetic energies of the projectile. With the exception of MgO the coefficients turn out to be of the order of 10-1 over the whole range of kinetic energies. This rather large value is a direct consequence of the shape resonance acting as a relay state for electron emission.

  19. WFC3: Understanding and Mitigating UVIS Charge Transfer Efficiency Losses and IR Persistence Effects

    NASA Astrophysics Data System (ADS)

    Baggett, Sylvia M.; Anderson, J.; Long, K. S.; MacKenty, J. W.; Noeske, K.; Biretta, J. A.; WFC3 Team

    2014-01-01

    A panchromatic instrument, Wide Field Camera 3 (WFC3) contains a UVIS channel with a 4096x4096 pixel e2v CCD array as well as an IR channel with a 1014x1014 Rockwell Scientific HgCdTe focal plane array (FPA). Both detectors have been performing well on-orbit since the installation of the instrument in the Hubble Space Telescope (HST) in May 2009. However, as expected, the harsh low-earth orbit environment has been damaging the UVIS CCDs, resulting in a progressive loss of charge transfer efficiency (CTE) over time. We summarize the magnitude of the CTE losses, the effect on science data, and the pre- and post-observation mitigation options available. The IR FPA does not suffer from accumulating radiation damage but it does exhibit persistence i.e. an after-glow from sources in previous exposures, an anomaly commonly seen in these types of IR arrays. We summarize the characteristics of persistence in WFC3, suggest methods for reducing the effects during observation planning, and describe the calibration products which are available via the Mikulski Archive for Space Telescopes (MAST) for addressing persistence in IR science data.

  20. HST/WFC3 UVIS Detector: Dark, Charge Transfer Efficiency, and Point Spread Function Calibrations

    NASA Astrophysics Data System (ADS)

    Bourque, Matthew; Anderson, Jay; Baggett, Sylvia; Bowers, Ariel; MacKenty, John W.; Sahu, Kailash C.

    2015-08-01

    Wide Field Camera 3 (WFC3) is a fourth-generation imaging instrument on board the Hubble Space Telescope (HST) that was installed during Servicing Mission 4 in May 2009. As one of two channels available on WFC3, the UVIS detector is comprised of two e2v CCDs and is sensitive to ultraviolet and visible light. Here we provide updates to the characterization and monitoring of the UVIS performance and stability. We present the long-term growth of the dark current and the hot pixel population, as well as the evolution of Charge Transfer Efficiency (CTE). We also discuss updates to the UVIS dark calibration products, which are used to correct for dark current in science images. We examine the impacts of CTE losses and outline some techniques to mitigate CTE effects during and after observation by use of post-flash and pixel-based CTE corrections. Finally, we summarize an investigation of WFC3/UVIS Point Spread Functions (PSFs) and their potential use for characterizing the focus of the instrument.