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1

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

PubMed

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

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

2012-09-18

2

Charge Transfer Reactions  

NASA Astrophysics Data System (ADS)

Charge transfer, or charge exchange, describes a process in which an ion takes one or more electrons from another atom. Investigations of this fundamental process have accompanied atomic physics from its very beginning, and have been extended to astrophysical scenarios already many decades ago. Yet one important aspect of this process, i.e. its high efficiency in generating X-rays, was only revealed in 1996, when comets were discovered as a new class of X-ray sources. This finding has opened up an entirely new field of X-ray studies, with great impact due to the richness of the underlying atomic physics, as the X-rays are not generated by hot electrons, but by ions picking up electrons from cold gas. While comets still represent the best astrophysical laboratory for investigating the physics of charge transfer, various studies have already spotted a variety of other astrophysical locations, within and beyond our solar system, where X-rays may be generated by this process. They range from planetary atmospheres, the heliosphere, the interstellar medium and stars to galaxies and clusters of galaxies, where charge transfer may even be observationally linked to dark matter. This review attempts to put the various aspects of the study of charge transfer reactions into a broader historical context, with special emphasis on X-ray astrophysics, where the discovery of cometary X-ray emission may have stimulated a novel look at our universe.

Dennerl, Konrad

2010-12-01

3

Computational chemistry and aeroassisted orbital transfer vehicles  

NASA Technical Reports Server (NTRS)

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.

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

1985-01-01

4

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

ERIC Educational Resources Information Center

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…

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

2014-01-01

5

Biological Contexts for DNA Charge Transport Chemistry  

E-print Network

The double helical structure adopted by B-form DNA, where a negatively charged sugar phosphate backbone surrounds a ?-stacked array of heterocyclic aromatic basepairs, allows it to serve as an efficient medium for long-range charge transport (CT) (1). This chemistry has now been well established as a property of DNA. DNA CT can be

unknown authors

6

Facilely and efficiently tuning metal-organic nanostructures of a charge-transfer complex based on a water controlled nanoreaction and the chemistry of 7,7,8,8-tetracyanoquinodimethane (TCNQ)  

NASA Astrophysics Data System (ADS)

Metal-organic charge-transfer complexes based on 7,7,8,8-tetracyanoquinodimethane (TCNQ) have received considerable attention because of their unique solid-state physical properties for potential applications in nanoscale opto-electronic devices. To address the challenge in preparing novel metal-TCNQ (MTCNQ) nanostructures, here we introduce a facile and efficient way for synthesizing MTCNQ, taking Ni[TCNQ]2(H2O)2 as an example. By finely tuning the amount of water added into TCNQ solution, well-ordered and large-scale patterns of Ni[TCNQ]2(H2O)2 were successfully obtained in a controllable manner. This facile method will not only be beneficial for the tailored preparation of nanoscale MTCNQ complexes, but also enrich the chemistry of TCNQ.

Song, Jingyi; Ji, Zhuoyu; Nie, Qiong; Hu, Wenping

2014-02-01

7

Charge transfer states in alkali metals  

Microsoft Academic Search

The excitation spectra of halogen impurities in alkali metals was investigated throughout the photon energy range from 5 eV to 12 eV. The charge transfer configurations adopted by a variety of impurities in alkali metals were further investigated by measurements of the composition and temperature dependence of the electrical resistivity. Charge transfer effects observed to cause metal-to-insulator transitions at specific

R. Avci

1978-01-01

8

A monolithic SAW-charge transfer device  

NASA Technical Reports Server (NTRS)

Surface acoustic waves excited in a Si-SiO2-ZnO layered structure can produce a traveling electric field in the silicon substrate. Charges stored in the traveling potential wells can be transferred at high speed and density and with less complexity. The monolithic structure under investigation for the SAW-charge transfer device consists of a silicon substrate, a thin silicon dioxide insulating layer on top of which a ZnO piezoelectric film is deposited by sputtering. The surface acoustic waves are excited by interdigital transducers. The signal charge is injected into traveling potential wells that travel with the velocity of sound. Conditions for the transfer of the charges by the traveling wells are analyzed. A surface acoustic wave program was used to determine the optimum structure dimensions and transducer configuration which will produce the highest coupling in the excitation of the piezoelectric waves.

Papanicolaou, N. A.; Lin, H. C.

1978-01-01

9

Ultrafast charge transfer and atomic orbital polarization  

SciTech Connect

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.

Deppe, M.; Foehlisch, A.; Hennies, F.; Nagasono, M.; Beye, M.; Sanchez-Portal, D.; Echenique, P. M.; Wurth, W. [Institut fuer Experimentalphysik, Universitaet Hamburg, Luruper Chaussee 149, D-22761 Hamburg (Germany); MAX-Laboratory, Lund University, Ole Roemers vaeg 1, SE-22100 Lund (Sweden); Institut fuer Experimentalphysik, Universitaet Hamburg, Luruper Chaussee 149, D-22761 Hamburg (Germany); Centro de Fisica de Materiales, Universidad del Pais Vasco, Apdo. 1072, 20080 Donostia-San Sebastian (Spain); Centro Mixto CSIC-UPV/EHU, Universidad del Pais Vasco, Apdo. 1072, 20080 Donostia-San Sebastian (Spain); Donostia International Physics Center (DIPC), Universidad del Pais Vasco, Apdo. 1072, 20080 Donostia-San Sebastian (Spain) and Departamento de Fisica de Materiales, Universidad del Pais Vasco, Apdo. 1072, 20080 Donostia-San Sebastian (Spain); Institut fuer Experimentalphysik, Universitaet Hamburg, Luruper Chaussee 149, D-22761 Hamburg (Germany)

2007-11-07

10

Charge-transfer magnetoelectrics of polymeric multiferroics.  

PubMed

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

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

2014-04-22

11

Variable Charge Soils: Mineralogy and Chemistry  

SciTech Connect

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.

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

2003-11-01

12

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

E-print Network

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 ...

Hanson, Christina J

2013-01-01

13

Charge transfer in tunnel-junction arrays  

NASA Astrophysics Data System (ADS)

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.

Kaplan, Daniel M. R.

14

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

PubMed Central

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

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

2014-01-01

15

Charge Transfer Reactions and Solvation Dynamics  

Microsoft Academic Search

\\u000a In this article, we offer a perspective on solvation dynamics from the point of view of chemical reactions, and in particular\\u000a from an initial viewpoint of heavy particle charge transfer reactions. These reactions include SN2 nucleophilic displacements —, SN1 unimolecular ionizations —, dipolar isomerizations, and (with a certain elasticity of definition) ion pair interconversion.\\u000a Here the solvation dynamics act to

James T. Hynes

16

Transfer Guide: Chemistry -1 -Revised: 1 December 2009 TRANSFER GUIDE AND PLANNING WORKSHEET  

E-print Network

Transfer Guide: Chemistry - 1 - Revised: 1 December 2009 TRANSFER GUIDE AND PLANNING WORKSHEET-Certified Concentration This planning worksheet represents a guide for community college students transferring to Colorado, the planning worksheet serves as a "60+60" transfer guide. Under Colorado policy, students who complete

17

Charge transfer processes: the role of optimized molecular orbitals.  

PubMed

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

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

2014-08-01

18

Nonradiative charge transfer in collisions of protons with rubidium atoms  

NASA Astrophysics Data System (ADS)

The nonradiative charge-transfer cross sections for protons colliding with Rb(5s) atoms are calculated by using the quantum-mechanical molecularorbital close-coupling method in an energy range of 10-3 keV-10 keV. The total and state-selective charge-transfer cross sections are in good agreement with the experimental data in the relatively low energy region. The importance of rotational coupling for chargetransfer process is stressed. Compared with the radiative charge-transfer process, nonradiative charge transfer is a dominant mechanism at energies above 15 eV. The resonance structures of state-selective charge-transfer cross sections arising from the competition among channels are analysed in detail. The radiative and nonradiative charge-transfer rate coefficients from low to high temperature are presented.

Yan, Ling-Ling; Qu, Yi-Zhi; Liu, Chun-Hua; Zhang, Yu; Wang, Jian-Guo; Buenker, Robert J.

2012-06-01

19

Charge transfer excitons in codeposited organic films  

NASA Astrophysics Data System (ADS)

Charge transfer (CT) excitons play an important role in solar cells and organic light emitting devices. Such excitons are usually formed at the hetero-interfaces with an electron and hole residing in different materials. We studied the formation and recombination dynamics of CT excitons in co-deposited Alq3/PTCDA, TPD/Alq3, and TPD/PTCDA thin films that are grown by organic molecular beam deposition with various co-deposition ratios. (Alq3: Tris(8-hydroxyquinolinato)aluminium, PTCDA: perylene-3,4,9,10-tetracarboxylic-3,4,9,10-dianhydride, TPD: N,N'-Bis(3-methylphenyl)- N,N'-diphenylbenzidine.) The formation of CT excitons is associated with a quenching of the photoluminescence (PL) of the individual material. The PL spectrum shows a new emission peak at ˜750 nm for Alq3/PTCDA films and ˜700 nm for TPD/Alq3 which we tentatively attribute to the radiative recombination of CT excitons. The formation and decay time of the CT excitons is studied by time-resolved PL measurements using the technique of time-correlated single photon counting.

Wang, Xiaosheng; Milhan, Ajward; Wagner, Hans Peter

2010-03-01

20

Infrared Spectroscopy of Charge Transfer Complexes of Purines and Pyrimidines  

Microsoft Academic Search

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

Pravinsinh I. Rathod; A. T. Oza

2011-01-01

21

Mechanisms of proton transfer in proteins: Localized charge transfer versus delocalized soliton transfer  

PubMed Central

Proton translocation coupled to redox chemistry is ubiquitous for membrane enzymes involved in energy generation in cells. In such enzymes, proton transport occurs in special proton conducting channels, which consist of a series of protonatable groups of the protein connected by chains of mobile water molecules. Here we discuss two possible mechanisms of proton transport along such structures: diffusion of a localized charge and delocalized soliton transitions, in which several protons are collectively shifted along a chain of hydrogen bonds. PMID:19391991

Stuchebrukhov, Alexei A.

2010-01-01

22

Reaction filters. Charged-particle multiplicity and linear momentum transfer  

NASA Astrophysics Data System (ADS)

The relation between charged-particle multiplicity and linear momentum transfer to heavy reaction residues has been investigated with a 4? charged-particle detector for the reactions 36Ar+ 238U at {E}/{A}=35 MeV and 14N+ 238U at {E}/{A}=50 MeV. The multiplicity of charged particles at backward angles ( ? > 35°) incrreases linear momentum transfer while the multiplicity of charged particles in the forward direction is almost independent of the linear momentum transfer.

Tsang, M. B.; Kim, Y. D.; Carlin, N.; Chen, Z.; Fox, R.; Gelbke, C. K.; Gong, W. G.; Lynch, W. G.; Murakami, T.; Nayak, T. K.; Ronningen, R. M.; Xu, H. M.; Zhu, F.; Sobotka, L.; Stracener, D.; Sarantites, D. G.; Majka, Z.; Abenante, V.; Griffin, H.

1989-04-01

23

Transfer of Algebraic and Graphical Thinking between Mathematics and Chemistry  

ERIC Educational Resources Information Center

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…

Potgieter, Marietjie; Harding, Ansie; Engelbrecht, Johann

2008-01-01

24

Phase-transfer catalysis in analytical chemistry  

Microsoft Academic Search

Phase-transfer catalysis (PTC) has been a well-established technique on the synthesis of organic chemicals for more than three decades. Its scope and underlying mechanistic features have been the subject of numerous studies and appear to be recognized and understood.This review is intended to approach the subject by focusing on the extraction–preconcentration–derivatization\\/reaction prior to analysis and to chronicle recent progress made.

Yiannis C. Fiamegos; Constantine D. Stalikas

2005-01-01

25

Charge-shift bonding and its manifestations in chemistry.  

PubMed

Electron-pair bonding is a central chemical paradigm. Here, we show that alongside the two classical covalent and ionic bond families, there exists a class of charge-shift (CS) bonds wherein the electron-pair fluctuation has the dominant role. Charge-shift bonding shows large covalent-ionic resonance interaction energy, and depleted charge densities, and features typical to repulsive interactions, albeit the bond itself may well be strong. This bonding type is rooted in a mechanism whereby the bond achieves equilibrium defined by the virial ratio. The CS bonding territory involves, for example, homopolar bonds of compact electronegative and/or lone-pair-rich elements, heteropolar bonds of these elements among themselves and with other atoms (for example, the metalloids, such as silicon and germanium), hypercoordinated molecules, and bonds whose covalent components are weakened by exchange-repulsion strain (as in [1.1.1]propellane). Here, we discuss experimental manifestations of CS bonding in chemistry, and outline new directions demonstrating the portability of the new concept. PMID:21378912

Shaik, Sason; Danovich, David; Wu, Wei; Hiberty, Philippe C

2009-09-01

26

Oxidation and metal-insertion in molybdenite surfaces: evaluation of charge-transfer mechanisms and dynamics  

Microsoft Academic Search

Molybdenum disulfide (MoS2), a layered transition-metal dichalcogenide, has been of special importance to the research community of geochemistry, materials and environmental chemistry, and geotechnical engineering. Understanding the oxidation behavior and charge-transfer mechanisms in MoS2 is important to gain better insight into the degradation of this mineral in the environment. In addition, understanding the insertion of metals into molybdenite and evaluation

Chintalapalle V. Ramana; U. Becker; V. Shutthanandan; C. M. Julien

2008-01-01

27

Improved Charge-Transfer Fluorescent Dyes  

NASA Technical Reports Server (NTRS)

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.

Meador, Michael

2005-01-01

28

An Evaluation of 2-phase Charge Pump Topologies with Charge Transfer Switches for  

E-print Network

An Evaluation of 2-phase Charge Pump Topologies with Charge Transfer Switches for Green Mobile Technology Yan Chiew Wong1,2 , Nurul H. Noordin1,2 , Ahmed O. El-Rayis1,2 , Nakul Haridas1,2 , Ahmet T. The quality of the charge pump greatly depends on the effectiveness of switches to turn on and off

Arslan, Tughrul

29

Multistate continuum theory for multiple charge transfer reactions in solution  

E-print Network

be incorporated into the adiabatic free energy surfaces. The input quantities required for this theory are gas, such as Mar- cus theory,17 describe the charge transfer reaction in terms of a two-level system. Recently

Hammes-Schiffer, Sharon

30

Exciton/Charge-transfer Electronic Couplings in Organic Semiconductors  

E-print Network

Charge transfer (CT) states and excitons are important in energy conversion processes that occur in organic light emitting devices (OLEDS) and organic solar cells. An ab initio density functional theory (DFT) method for ...

Difley, Seth

31

Measurement techniques and applications of charge transfer to aerospace research  

NASA Technical Reports Server (NTRS)

A technique of developing high-velocity low-intensity neutral gas beams for use in aerospace research problems is described. This technique involves ionization of gaseous species with a mass spectrometer and focusing the resulting primary ion beam into a collision chamber containing a static gas at a known pressure and temperature. Equations are given to show how charge-transfer cross sections are obtained from a total-current measurement technique. Important parameters are defined for the charge-transfer process.

Smith, A.

1978-01-01

32

Screen charge transfer by grounded tip on ferroelectric surfaces.  

SciTech Connect

We have investigated polarization reversal and charge transfer effects by a grounded tip on 50 nm thick ferroelectric thin films using piezoelectric force microscopy and Kelvin force microscopy. We observed the polarization reversal in the center of written domains, and also identified another mechanism, which is the transfer of screen charges toward the grounded tip. In order to overcome these phenomena, we successfully applied a modified read/write scheme featuring a bias voltage.

Kim, Y.; Kim, J.; Buhlmann, S.; Hong, S.; Kim, Y. K.; Kim, S.-H.; No, K.; Materials Science Division; Korea Advanced Inst. of Science and Technology; Samsung Advanced Inst. of Technology; Inostek Inc.

2008-03-01

33

Charge transfer energies of tetraphenyl-porphyrin-fullerene dyads  

NASA Astrophysics Data System (ADS)

Porphyrin-fullerene dyads are extensively studied for their photoinduced charge transfer properties. They form a donor-acceptor pair where the fullerene is the acceptor. Accurate theoretical estimate of the charge transfer energies in such systems has proven to be a challenge. In this study we examine the charge transfer energetics for such dyads using our recently developed density functional based excited state method which can yield reliable estimates of charge transfer energetics. In this study the effect of varying both the donor and acceptor components are studied by changing the tetra-phenyl-porphyrin (TPP) to Zn-TPP. Similarly the acceptor component is changed from C60 to C70. The structures were optimized using DFT-D3 theory at the all-electron level. Among the donor-acceptor pairs studied, we find that the ZnTPP-C60 has the lowest charge transfer energy (1.69 eV) and the TPP-C70 (2.13 eV) has the highest charge transfer energy.

Zope, Rajendra; Olguin, Marco; Baruah, Tunna

2011-03-01

34

Phonons and charge-transfer excitations in HTS superconductors  

SciTech Connect

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.

Bishop, A.R.

1989-01-01

35

Charge Transfer Reactions in Porous Materials  

E-print Network

photoexcitation. The solute diffusion takes place on two timescales, fitting the expression ??d(t)? = D(1?B1e?t/?d1 ?B2e?t/?d2). [2.4] There is an initial, rapid motion with ?d1 ?1.4 ps, while ?d2 varies with cavity size, ranging from ?350 ps for the 10 ?A cavity.... In the ground state, the solute molecule is relatively nonpolar, with A having a charge +0.1 |e| and B a charge of ?0.1 |e|, giving ?=1.44 D. In the excited state, the dipole moment is sub- stantial: ?=7.1 D, with A/B charges of +0.5/-0.5 |e|. The solute...

Mitchell-Koch, Katie Rose

2008-08-15

36

INTRAMOLECULAR CHARGE AND ENERGY TRANSFER IN MULTICHROMOPHORIC AROMATIC SYSTEMS  

SciTech Connect

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.

Edward C. Lim

2008-09-09

37

The study of surface acoustic wave charge transfer device  

NASA Technical Reports Server (NTRS)

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.

Papanicolaou, N.; Lin, H. C.

1978-01-01

38

Charge Transfer and Support Effects in Heterogeneous Catalysis  

SciTech Connect

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

Hervier, Antoine

2011-12-21

39

Charge transfer and charge transport on the double helix N. P. Armitage*  

E-print Network

a ruthenium intercalator to end of a single DNA strand and a rhodium intercalator to a comple- mentary stand present a short review of various experiments that measure charge transfer and charge transport in DNA measurements performed by our group on the millimeter wave response of DNA. By measur- ing over a wide range

Gruner, George

40

Jahn-Teller effects and charge transfer in the positively charged triphenylene and coronene  

NASA Astrophysics Data System (ADS)

Vibronic interactions and Jahn-Teller effects in the monocations of triphenylene and coronene are discussed. The E' mode of 1634 cm -1 and the E2g mode of 1668 cm -1 afford large electron-phonon coupling constants in the monocations of triphenylene and coronene, respectively. The single charge transfer through the molecules in these positively charged species are discussed. The reorganization energies for elementary charge transfer are estimated to be 0.045 and 0.028 eV for triphenylene and coronene, respectively. The optimized structures of the monocations are discussed in terms of the frontier orbitals and the vibrational modes.

Kato, Takashi; Yamabe, Tokio

2005-02-01

41

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

SciTech Connect

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.

Zanni, Martin T.

1999-12-17

42

Oxidation and Metal-Insertion in Molybdenite Surfaces: Evaluation of Charge-Transfer Mechanisms and Dynamics  

SciTech Connect

Molybdenum sulfide (MoS2), an important representative member of the layered transition-metal dichalcogenides, has been of special importance to the research community of geochemistry, materials and environmental chemistry, and industrial science and technology. Understanding the oxidation behavior and charge-transfer mechanisms in MoS2 is important to gain better insight into the degradation of this mineral in the environment. On the other hand understanding the insertion of metals into molybdenite and evaluation of charge-transfer mechanism and dynamics is quite important to utilize these minerals in technological applications. Furthermore, such a detailed investigation of thermal oxidation behavior and intercalation process will provide a basis to further explore and model the mechanism of adsorption of metal ions on to geomedia. Therefore, the present work was performed to understand the oxidation and intercalation processes of molybdenite surfaces. The results obtained, using a wide variety of analytical techniques, are presented and discussed in this paper.

Ramana, Chintalapalle V.; Becker, U.; Shutthanandan, V.; Julien, C. M.

2008-06-05

43

Charge localization and charge transfer in the Bebq2 monomer and dimer.  

PubMed

The geometrical structure and electronic properties of bis(10-hydroxybenzo[h]quinolinato)beryllium (Bebq2) molecule and its dimer both in the neutral and in the positively and negatively charged states were studied using quantum-chemical calculations. It is found that the excess charge in the charged systems is localized on one of the hydroxybenzoquinoline ligands. Structural changes in charged Bebq2 are pronounced in the charged ligand and nearly negligible in the neutral ligand. Charge transfer from the charged ligand to a neutral one can proceed either within a single Bebq2 monomer molecule or between the different monomers in the Bebq2 dimer. The corresponding hopping integrals were estimated as half the excitation energy from the ground to the first excited state of either the monomer or the dimer calculated at the avoided crossing point. PMID:25107360

Safonov, Andrei A; Bagaturyants, Alexander A

2014-08-01

44

Mass and charge transfer within a floating water bridge  

NASA Astrophysics Data System (ADS)

When high voltage is applied to pure water filled into two beakers close to each other, a connection forms spontaneously, giving the impression of a floating water bridge 1-8. This phenomenon is of special interest, since it comprises a number of phenomena currently tackled in modern water science. In this work, the charge and mass transfer through the water bridge are investigated with schlieren visualization and laser interferometry. It can be shown that the addition of a pH dye increases the H+ and OH- production with subsequent electrolysis, whereas schlieren and interferometric methods reveal another mechanism where charge and mass transfer appear to be coupled. Whereas this mechanism seems to be responsible for the electrolysis-less charge and mass transfer in the water bridge, it is increasingly superseded by the electrochemical mechanism with rising conductivity. Thus it can be shown that a pH dye does only indirectly visualize the charge transfer in the water bridge since it is dragged along with the water flow like any other dye, and additionally promotes conventional electrochemical conduction mechanisms, thereby enhancing electrolysis and reducing the masscoupled charge transport and thus destabilizing the bridge.

Fuchs, Elmar C.; Agostinho, Luewton L. F.; Eisenhut, Mathias; Woisetschläger, Jakob

2010-11-01

45

PHOTOSENSITIVE CENTERS AND CHARGE TRANSFER PROCESSES IN BARIUM CALCIUM TITANATE  

E-print Network

PHOTOSENSITIVE CENTERS AND CHARGE TRANSFER PROCESSES IN BARIUM CALCIUM TITANATE G.MALOVICHKO, V calcium titanate crystals, Ba0.77Ca0.23TiO3, in the temperature range between 4.2 K and 300 K are reported of crystals from barium titanate (BT) family make them promising candidates for various applications

Malovichko, Galina

46

Charge transfer in triaryl pyrylium cations. Theoretical and experimental study  

NASA Astrophysics Data System (ADS)

The spectroscopic properties of 2,4,6-triaryl pyrylium cations bearing electron-donating groups (dialkylamino) are investigated. Calculations based on the CS-INDO-MRCI (conformations spectra - intermediate neglect of differential overlap - multi reference configuration interaction) method reveal that the two lower-lying singlet excited states have very different dipolar contributions. The corresponding electronic transitions are close in energy, polarized in the plane of the pyrylium core and orthogonal to one another. Their existence is confirmed by fluorescence anisotropy measurements leading to resolution of the visible absorption spectrum. Calculations show the formation of a non-fluorescent TICT (twisted intramolecular charge transfer) state involving rotation of the dialkylaminophenyl group without energy barrier; this formation is corroborated by the influence of the rotor size and the solvent viscosity on fluorescence properties. Photo-induced charge transfer is studied by second harmonic generation in solution using time-resolved non-degenerate six-wave mixing. It is shown that the charge transfer direction is parallel to the corresponding transition. The photo-induced variation of the dipole moment experimentally measured (18 D) is in good agreement with the calculated value (15.8 D). Comparison of the fluorescence decay and the second harmonic decay proves the formation of a non-fluorescent transient charge transfer state.

Markovitsi, Dimitra; Sigal, hervé; Ecoffet, Carole; Millié, Philippe; Charra, Fabrice; Fiorini, Céline; Nunzi, Jean-Michel; Strzelecka, Hélèna; Veber, Michèle; Jallabert, Colette

1994-04-01

47

Enhancing SERS by Means of Supramolecular Charge Transfer  

NASA Technical Reports Server (NTRS)

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.

Wong, Eric; Flood, Amar; Morales, Alfredo

2009-01-01

48

Space-charge transfer in hybrid inorganic-organic systems.  

PubMed

We discuss density functional theory calculations of hybrid inorganic-organic systems that explicitly include the global effects of doping (i.e., position of the Fermi level) and the formation of a space-charge layer. For the example of tetrafluoro-tetracyanoquinodimethane on the ZnO(0001[over ¯]) surface we show that the adsorption energy and electron transfer depend strongly on the ZnO doping. The associated work function changes are large, for which the formation of space-charge layers is the main driving force. The prominent doping effects are expected to be quite general for charge-transfer interfaces in hybrid inorganic-organic systems and important for device design. PMID:24329464

Xu, Yong; Hofmann, Oliver T; Schlesinger, Raphael; Winkler, Stefanie; Frisch, Johannes; Niederhausen, Jens; Vollmer, Antje; Blumstengel, Sylke; Henneberger, Fritz; Koch, Norbert; Rinke, Patrick; Scheffler, Matthias

2013-11-27

49

Infrared Spectroscopy of Charge Transfer Complexes of Purines and Pyrimidines  

NASA Astrophysics Data System (ADS)

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.

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

2011-10-01

50

Space-Charge Transfer in Hybrid Inorganic-Organic Systems  

NASA Astrophysics Data System (ADS)

We discuss density functional theory calculations of hybrid inorganic-organic systems that explicitly include the global effects of doping (i.e., position of the Fermi level) and the formation of a space-charge layer. For the example of tetrafluoro-tetracyanoquinodimethane on the ZnO(0001¯) surface we show that the adsorption energy and electron transfer depend strongly on the ZnO doping. The associated work function changes are large, for which the formation of space-charge layers is the main driving force. The prominent doping effects are expected to be quite general for charge-transfer interfaces in hybrid inorganic-organic systems and important for device design.

Xu, Yong; Hofmann, Oliver T.; Schlesinger, Raphael; Winkler, Stefanie; Frisch, Johannes; Niederhausen, Jens; Vollmer, Antje; Blumstengel, Sylke; Henneberger, Fritz; Koch, Norbert; Rinke, Patrick; Scheffler, Matthias

2013-11-01

51

Measurements of charge transfer efficiency in a proton-irradiated swept charge device  

NASA Astrophysics Data System (ADS)

Charged Coupled Devices (CCDs) have been successfully used in several low energy X-ray astronomical satellites over the past two decades. Their high energy resolution and high spatial resolution make them a perfect tool for low energy astronomy, such as observing the formation of galaxy clusters and the environment around black holes. The Low Energy X-ray Telescope (LE) group is developing a Swept Charge Device (SCD) for the Hard X-ray Modulation Telescope (HXMT) satellite. A SCD is a special low energy X-ray CCD, which can be read out a thousand times faster than traditional CCDs, simultaneously keeping excellent energy resolution. A test method for measuring the charge transfer efficiency (CTE) of a prototype SCD has been set up. Studies of the charge transfer inefficiency (CTI) with a proton-irradiated SCD have been performed at a range of operating temperatures. The SCD is irradiated by 3 × 108cm-2 10 MeV protons.

Wang, Yu-Sa; Yang, Yan-Ji; Chen, Yong; Liu, Xiao-Yan; Cui, Wei-Wei; Xu, Yu-Peng; Li, Cheng-Kui; Li, Mao-Shun; Han, Da-Wei; Chen, Tian-Xiang; Huo, Jia; Wang, Juan; Li, Wei; Hu, Wei; Zhang, Yi; Lu, Bo; Yin, Guo-He; Zhu, Yue; Zhang, Zi-Liang

2014-06-01

52

A model for charge transfer in buried-channel charge-coupled devices at low temperature  

Microsoft Academic Search

Charge transfer in buried-channel charge-coupled devices (CCDs) is explored with a one-dimensional numerical model which describes the capture and emission of electrons from a shallow donor level in silicon through the use of the Shockley-Read-Hall generation-recombination theory. Incorporated in the model are the three-dimensional Poole-Frenkel barrier lowering theory of A. K. Jonscher (1967) and J. L. Hartke (1968) and the

Edmund K. Banghart; James P. Lavine; Eugene A. Trabka; Edward T. Nelson; Bruce C. Burkey

1991-01-01

53

Product ion charge state determination via ion/ion proton transfer reactions  

SciTech Connect

Proton transfer from protonated pyridine to product anions derived from quadrupole ion trap collisional activation of the triply charged anion of the oligonucleotide 5`-d(AAAA)-3` and the 6{sup -} charge state of oxidized bovine insulin A-chain is shown to be a rapid and effective way to determine production charge states. The reactions are carried out in a quadrupole ion trap as part of a procedure involving three stages of mass analysis. It is demonstrated that the reactions can be driven at rates sufficiently high to convert 30-80% of the initial product anion population to second generation products in 50-200 ms. The use of ion/ion reactions enjoys significant advantages over the use of ion/molecule proton transfer chemistry. For example, ion/ion reactions are more universal than ion/molecule reactions due to their greater exothermicity, and ion/ion reactions allow for precise control over the timing of introduction and ejection of each reactant. Despite the high exothermicity of the reactions, no significant fragmentation of product ions derived from high-mass multiply charged anions is observed. 33 refs., 5 figs.

Herron, W.J.; Goeringer, D.E.; Mcluckey, S.A. [Oak Ridge National Lab., TN (United States)] [Oak Ridge National Lab., TN (United States)

1996-01-15

54

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

NASA Technical Reports Server (NTRS)

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.

Kwong, Victor H. S.

2003-01-01

55

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

E-print Network

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...

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

56

Ultrafast photo-induced charge transfer unveiled by two-dimensional electronic spectroscopy  

NASA Astrophysics Data System (ADS)

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-reaction dynamics. Our experiments demonstrate the unique capability of 2D-ES in combination with other methods to decipher ultrafast CT dynamics.

Bixner, Oliver; Lukeš, Vladimír; Man?al, Tomáš; Hauer, Jürgen; Milota, Franz; Fischer, Michael; Pugliesi, Igor; Bradler, Maximilian; Schmid, Walther; Riedle, Eberhard; Kauffmann, Harald F.; Christensson, Niklas

2012-05-01

57

Charge transfer magnetoexciton formation at vertically coupled quantum dots  

PubMed Central

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

2012-01-01

58

The charge transfer characteristic of porphyrin Langmuir-Blodgett films  

NASA Astrophysics Data System (ADS)

The ordered porphyrin Langmuir-Blodgett (LB) films were prepared under different surface pressures. The UV-vis absorption spectrum, infrared spectrum, cyclic voltammetry and constant potential jump were used for testing. UV-vis spectra showed that under the surface pressure of approx. 10 mN/m, the ordered porphyrin LB films formed were demonstrated by infrared spectra. With the order degree of LB films strengthened, the charge transfer and storage of porphyrin LB films enhanced. And it was measured by electrochemical method. IR spectrum proves that both the interaction of porphyrin rings (the rings can form the head-to-head structure) and that of hydroxyl groups (the groups can form the feet-to-feet structure) in porphyrin LB ordered films can affect the charge transfer characteristics of porphyrin films.

Qi, P.; Li, Z. H.; Zhou, Y.; Wang, F.; Du, Y.; Zhang, L. Q.; Li, G.; Zhang, H. Z.

2013-08-01

59

High Performance Blood Glucose Sensor using Charge Transfer Technique  

Microsoft Academic Search

The charge transfer type blood glucose sensor (CTTGS) has been proposed. The CTTGS is an accumulation method H+ ion (gluconic acid) perception system. As compared to cyclic-voltammetry and ISFET, the performance was found to be excellent with span and range of 1445 mV and 200 mmol\\/L respectively. The sensitivity obtained for blood glucose level of the person was 29.06 mV\\/mmol

Seung-Ro Lee; Takeshi Hizawa; Kazuaki Sawada; Hidekuni Takao; M. Ishida

2007-01-01

60

Momentum transfer in relativistic heavy ion charge-exchange reactions  

NASA Astrophysics Data System (ADS)

Relativistic heavy ion charge-exchange reactions yield fragments (Delta-Z = + 1) whose longitudinal momentum distributions are downshifted by larger values than those associated with the remaining fragments (Delta-Z = 1, -2,...). Kinematics alone cannot account for the observed downshifts; therefore, an additional contribution from collision dynamics must be included. In this work, an optical model description of collision momentum transfer is used to estimate the additional dynamical momentum downshift. Good agreement between theoretical estimates and experimental data is obtained.

Townsend, L. W.; Wilson, J. W.; Khan, F.; Khandelwal, G. S.

1991-07-01

61

Momentum transfer in relativistic heavy ion charge-exchange reactions.  

PubMed

Relativistic heavy ion charge-exchange reactions yield fragments (delta Z = +1) whose longitudinal momentum distributions are downshifted by larger values than those associated with the remaining fragments (delta Z = -1, -2, ...). Kinematics alone cannot account for the observed downshifts; therefore, an additional contribution from collision dynamics must be included. In this work, an optical model description of collision momentum transfer is used to estimate the additional dynamical momentum downshift. Good agreement between theoretical estimates and experimental data is obtained. PMID:9967432

Townsend, L W; Wilson, J W; Khan, F; Khandelwal, G S

1991-07-01

62

Spectrofluorometric determination of certain quinolone through charge transfer complex formation  

Microsoft Academic Search

A spectrofluorimetric method was developed for the determination of three fluoroquinolones antibacterials, namely, ofloxacin (OFL), levofloxacin (LEV), lomefloxacin (LOM), and pipemidic acid (PIP) through charge transfer (CT) complex formation with 7,7,8,8-tetracyanoquinodimethane (TCNQ). TCNQ was found to react with these drugs to produce stable complexes and the fluorescence intensity of the complexes was enhanced in 15–90 times higher than that of

Li Ming Du; Ya Qin Yang; Qing Mei Wang

2004-01-01

63

Energy and charge transfer in ionized argon coated water clusters  

SciTech Connect

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.

Ko?išek, J., E-mail: kocisek@jh-inst.cas.cz, E-mail: michal.farnik@jh-inst.cas.cz, E-mail: petr.slavicek@vscht.cz; Lengyel, J.; Fárník, M., E-mail: kocisek@jh-inst.cas.cz, E-mail: michal.farnik@jh-inst.cas.cz, E-mail: petr.slavicek@vscht.cz [J. Heyrovský Institute of Physical Chemistry v.v.i., Academy of Sciences of the Czech Republic, Dolejškova 3, 18223 Prague (Czech Republic); Slaví?ek, P., E-mail: kocisek@jh-inst.cas.cz, E-mail: michal.farnik@jh-inst.cas.cz, E-mail: petr.slavicek@vscht.cz [Department of Physical Chemistry, Institute of Chemical Technology, Technická 5, 16628 Prague 6 (Czech Republic)

2013-12-07

64

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

SciTech Connect

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}.

Wang, Luxia; Willig, Frank; May, Volkhard [Department of Physics, University of Science and Technology Beijing, Xueyuan Road 30, Haidian District, 100083 Beijing (China); Fritz-Haber-Institut der MPG, Faradayweg 4-6, 14195 Berlin (Germany); Institut fuer Physik, Humboldt-Universitaet zu Berlin, Newtonstrasse 15, D-12489 Berlin (Germany)

2007-04-07

65

Photochemistry and charge transfer chemistry of the platinum group elements  

SciTech Connect

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.

Eisenberg, R.

1992-12-01

66

Two-level system with a thermally fluctuating transfer matrix element: Application to the problem of DNA charge transfer  

E-print Network

donors intercalated in the DNA oligostrands. As the charge migrates towards the acceptor of DNA charge transfer Maria R. D'Orsogna and Joseph Rudnick Physics Department, University of California; published 10 October 2002 Charge transfer along the base-pair stack in DNA is modeled in terms of thermally

D'Orsogna, Maria Rita

67

Voltage and frequency dependence of prestin-associated charge transfer Sean X. Sun a,c  

E-print Network

Voltage and frequency dependence of prestin-associated charge transfer Sean X. Sun a,c , Brenda-diffusion model to reveal the frequency and voltage dependence of electric charge transfer by prestin to prestin. We found a voltage- and frequency-dependent phase shift between the transferred charge

Sun, Sean

68

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

SciTech Connect

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.

Mendive-Tapia, David; Vacher, Morgane; Bearpark, Michael J.; Robb, Michael A. [Department of Chemistry, Imperial College London, London SW7 2AZ (United Kingdom)] [Department of Chemistry, Imperial College London, London SW7 2AZ (United Kingdom)

2013-07-28

69

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

NASA Astrophysics Data System (ADS)

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.

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

2013-07-01

70

Enhancement of IR and VCD intensities due to charge transfer.  

PubMed

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

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

2009-03-14

71

Atypical charge redistribution over a charge-transfer monolayer on a metal  

NASA Astrophysics Data System (ADS)

We report an atypical charge distribution in a highly ordered monolayer of sodium (Na) and tetracyanoquinodimethane (TCNQ) on a Au(111) surface. Na atoms incorporated in the charge-transfer layer donate their 3s electron to the lowest unoccupied orbital of the TCNQ acceptor. A fingerprint of such a TCNQ anion is observed in scanning tunneling spectroscopy as a zero-bias peak characteristic of the Kondo effect. Spatial maps of the Kondo resonance surprisingly reveal that it appears most intense on top of the Na sites. Supported by density functional theory simulations, we interpret this peculiar charge distribution pattern as originating from the extension of the singly occupied molecular orbital beyond the molecular backbone, and cloaking the Na cations. We further suggest that this deformation of molecular orbitals is a consequence of the electrostatic potential landscape of the polar Na-TCNQ layer.

Umbach, T. R.; Fernández-Torrente, I.; Ruby, M.; Schulz, F.; Lotze, C.; Rurali, R.; Persson, M.; Pascual, J. I.; Franke, K. J.

2013-08-01

72

Energy transfer and charge separation kinetics in photosystem I  

PubMed Central

The energy transfer and charge separation kinetics of a photosystem I (PS I) core particle of an antenna size of 100 chlorophyll/P700 has been studied by combined fluorescence and transient absorption kinetics with picosecond resolution. This is the first combined picosecond study of transient absorption and fluorescence carried out on a PS I particle and the results are consistent with each other. The data were analyzed by both global lifetime and global target analysis procedures. In fluorescence major lifetime components were found to be 12 and 36 ps. The shorter-lived one shows a negative amplitude at long wavelengths and is attributed to an energy transfer process between pigments in the main antenna Chl pool and a small long-wavelength Chl pool emitting around 720 nm whereas the longer-lived component is assigned to the overall charge separation lifetime. The lifetimes resolved in transient absorption are 7-8 ps, 33 ps, and [unk]1 ns. The shortest-lived one is assigned to energy transfer between the same pigment pools as observed also in fluorescence kinetics, the middle component of 33 ps to the overall charge separation, and the long-lived component to the lifetime of the oxidized primary donor P700+. The transient absorption data indicate an even faster, but kinetically unresolved energy transfer component in the main Chl pool with a lifetime <3 ps. Several kinetic models were tested on both the fluorescence and the picosecond absorption data by global target analysis procedures. A model where the long-wave pigments are spatially and kinetically connected with the reaction center P700 is favored over a model where P700 is connected more closely with the main Chl pool. Our data show that the charge separation kinetics in these PS I particles is essentially trap limited. The relevance of our data with respect to other time-resolved studies on PS I core particles is discussed, in particular with respect to the nature and function of the long-wave pigments. From the transient absorption data we do not see any evidence for the occurrence of a reduced Chl primary electron acceptor, but we also can not exclude that possibility, provided that reoxidation of that acceptor should occur within a time <40 ps. PMID:19431900

Holzwarth, Alfred R.; Schatz, Gunther; Brock, Helmuth; Bittersmann, Edith

1993-01-01

73

Diamagnetism and charge transfer in graphite intercalation compounds  

NASA Technical Reports Server (NTRS)

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.

Tsang, T.; Resing, H. A.

1984-01-01

74

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

E-print Network

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

Sparks, Donald L.

75

Effect of solution chemistry on the surface charge of polymeric reverse osmosis and nanofiltration membranes  

Microsoft Academic Search

A streaming potential analyzer has been used to investigate the effect of solution chemistry on the surface charge of four commercial reverse osmosis and nanofiltration membranes. Zeta potentials of these membranes were analyzed for aqueous solutions of various chemical compositions over a pH range of 2 to 9. In the presence of an indifferent electrolyte (NaCl), the isoelectric points of

Amy E. Childress; Menachem Elimelech

1996-01-01

76

Charge transfer and charge localization in extended radical cations: Investigation of model molecules for peptides  

NASA Astrophysics Data System (ADS)

Molecules consisting of a flexible tail and an aromatic chromophore are used as model systems to understand the situation of a single chromophore in a small peptide. Their S0-S1 resonant multiphoton ionization (REMPI) spectra show, that in neutral molecules the tail-chromophore interaction is weak and electronic excitation is localized at the chromophore. For molecules, where the ionization energy of the tail is considerable higher than that of the chromophore, by high resolution REMPI photoelectron spectroscopy we find the charge to be localized on the aromatic chromophore. This scheme also in suitable peptides allows local ionization at the aromatic chromophore. An estimate for various charge positions in peptide chains, however, shows, that for most of the amino acids electron hole positions in the nitrogen and oxygen "lone pair" orbitals of the peptide bond are nearly degenerate. REMPI photoelectron spectra of phenylethylamine, which as a model system contains such two degenerate charge positions, show small energetic shift of the ionization energy but strong geometry changes upon electron removal. This result is interpreted as direct ionization into a mixed charge delocalized state. Consequences for the charge transfer mechanism in peptides are discussed.

Weinkauf, Rainer; Lehrer, Florian

1998-12-01

77

Spectrophotometric determination of boron based on charge transfer reaction.  

PubMed

Boron determination by a charge transfer spectrophotometric method is described. Accompanied the reaction, a charge transfer complex can be formed by lysine with sodium 1, 2-naphthoquinone-4-sulfonate and boron in alkaline solution (pH 12.00). Subsequently, a new reaction mechanism has been proposed and discussed. The absorbance at the maximal absorption wavelength is 574 nm and boron concentration agrees well with Beer's law in a range of 2.16-43.24 ?g mL(-1). The linear regression equation is A=-0.01867+0.01326C (?g mL(-1)), with a linearly correlation coefficient of 0.9935. The relative standard deviation (R.S.D.) of eleven parallel determinations is 2.1% with a detection limit (3?/k) of 2.00 ?g mL(-1). The recovery ranges from 96.4% to 104.5% with the satisfactory results. This method has been successfully applied to determine boron in pharmaceutical samples directly. PMID:21530377

Ma, Linjin; Zhang, Zhenxuan; Li, Quanmin

2011-08-01

78

Role of charge-transfer states in bacterial photosynthesis  

PubMed Central

Photon echo, photon-echo excitation, and “hole-burning” data recorded in the 800-990 nm region of Rhodobacter sphaeroides R26 and Rhodopseudomonas viridis reaction centers are reported. The primary process in these reaction centers, following excitation, was found to occur in ?25 fsec; the long-wavelength band of the primary electron donor (P) was largely homogeneously broadened. In accordance with our previous explanation of hole-burning and photon-echo measurements on Rb. sphaeroides [Meech, S. R., Hoff, A. J. & Wiersma, D. A. (1985) Chem. Phys. Lett. 121, 287-292], we interpret this as resulting from a dephasing of the excitation in P into a background of strongly coupled charge-transfer states. The previously reported picosecond lifetime of the excited P state is assigned to decay of these strongly mixed states. Further, a coupling between P and an adjacent bacteriochlorophyll was observed. The extent of this coupling and the role of charge-transfer states in the functioning of reaction centers is discussed. PMID:16593787

Meech, S. R.; Hoff, A. J.; Wiersma, D. A.

1986-01-01

79

Electronic energies for Neon dimer dication radiative charge transfer  

NASA Astrophysics Data System (ADS)

This research was conducted to find the shape of the potential energy surfaces for the Neon dimer dication, designated Ne2(+2), to include all symmetries which dissociate to two ground state Ne(+) ions or a ground state Ne atom and Ne(+2) ion. The motivation is to investigate whether there is a minimum in the upper level, the Ne(+2) and Ne level, located in such a way that populations of bound dimer molecules can be built up without dissociating or transitioning to the lower level other than by radiative charge transfer. It is also of interest to show that the ground state is dissociative, that is that its energy is monotonically decreasing with increasing nuclear separation. Calculations were completed using programs known as Gaussian-86, and Diatom. Diatom produced excellent results for the He2(+2)test case. Ne2(+2) calculations were not as accurate as He2(+2), but results did indicate that bound upper level states exist which can only undergo charge transfer radiatively. This research computed Neon dimer dication potential energies for nuclear separations from 0.9 to 20 a.u. of Ne2(+2) sigma, pi, and delta states.

Deemer, Roger Alan

1989-12-01

80

Electrochemical charge transfer at a metallic electrode: A simulation study  

SciTech Connect

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.

Reed, Stewart K.; Madden, Paul A. [School of Chemistry, University of Edinburgh, Edinburgh EH9 3JJ (United Kingdom); Papadopoulos, Aristides [Edinburgh Parallel Computer Centre, University of Edinburgh, Edinburgh EH9 3JZ (United Kingdom)

2008-03-28

81

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

E-print Network

cation improves greatly the charge transfer kinetics and the charge/discharge performance of a LiFePO4 for a Li-ion battery (LIB) that contains low-cost, environmentally benign materials, is safe, and hasEnhanced Charge-Transfer Kinetics by Anion Surface Modi cation of LiFePO4 Kyu-Sung Park,, Penghao

Henkelman, Graeme

82

The effect of potential obstacles on charge transfer in image sensors  

Microsoft Academic Search

Numerical methods are presented to investigate charge transfer in charge-coupled devices (CCDs) when potential barriers or wells occur. A Monte Carlo simulation of electron thermal diffusion and field-aided drift is used to determine the time scale for charge transfer. The Monte Carlo approach is useful for exploring new problems, but it requires considerable amounts of computer time. A quicker technique,

James P. Lavine; Edmund K. Banghart

1997-01-01

83

Transfer RNA: a dancer between charging and mis-charging for protein biosynthesis.  

PubMed

Transfer RNA plays a fundamental role in the protein biosynthesis as an adaptor molecule by functioning as a biological link between the genetic nucleotide sequence in the mRNA and the amino acid sequence in the protein. To perform its role in protein biosynthesis, it has to be accurately recognized by aminoacyl-tRNA synthetases (aaRSs) to generate aminoacyl-tRNAs (aa-tRNAs). The correct pairing between an amino acid with its cognate tRNA is crucial for translational quality control. Production and utilization of mis-charged tRNAs are usually detrimental for all the species, resulting in cellular dysfunctions. Correct aa-tRNAs formation is collectively controlled by aaRSs with distinct mechanisms and/or other trans-factors. However, in very limited instances, mis-charged tRNAs are intermediate for specific pathways or essential components for the translational machinery. Here, from the point of accuracy in tRNA charging, we review our understanding about the mechanism ensuring correct aa-tRNA generation. In addition, some unique mis-charged tRNA species necessary for the organism are also briefly described. PMID:23982864

Zhou, Xiaolong; Wang, Enduo

2013-10-01

84

Surface-assisted transient displacement charge technique. I. Photoinduced charge transfer in self-assembled monolayers.  

PubMed

Surface-assisted photoinduced transient displacement charge (SPTDC) technique was developed in order to study light-induced charge transfer in surface-bound molecules and applied to investigation of self-assembled monolayers of 7-diethylaminocoumarin and 2,4-dinitrophenylamine. The dipole moment change measured by SPTDC correlates reasonably well with that measured in solution by standard PTDC technique and with semiempirical calculations. Shortening of the excited-state lifetime of surface-immobilized coumarin due to stimulated emission was observed in both fluorescence and dipole measurements. The dipole signal decline in low-polarity solvents indicates the importance of dipole-dipole interaction that causes reorientation of molecules upon photoexcitation. PMID:16956284

Krasnoslobodtsev, Alexey V; Smirnov, Sergei N

2006-09-14

85

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

E-print Network

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 ...

Walker, Brian J. (Brian Jacob)

2011-01-01

86

Phase-transfer catalysis in the chemistry of heterocyclic compounds  

Microsoft Academic Search

Methods for the preparation of heterocyclic systems, the chemical transformations of heterocyclic compounds under conditions\\u000a of phase-transfer catalysis, and the use of quaternized heterocycles as phase-transfer catalysts are considered.

G. I. Koldobskii

2007-01-01

87

Intramolecular charge transfer effects on 4-hydroxy-3-methoxybenzaldehyde  

NASA Astrophysics Data System (ADS)

The absorption and fluorescence spectral characteristics of 4-hydroxy-3-methoxybenzaldehyde (HMB) have been studied in different solvents, pH and ?-cyclodextrin (?-CD) and compared with 4-hydroxy-3,5-dimethoxybenzaldehyde (HDMB). The inclusion complex of HMB with ?-CD is analysed by UV-vis, fluorimetry, FT-IR, 1H NMR, SEM and AM1 methods. In HMB, the normal emission (B band) is originates from a locally excited state and the longer emission (A band) is due to intramolecular charge transfer state (ICT). The OH group of HMB is present in the interior part of the ?-CD cavity and aldehyde group present in the upper part of the ?-CD cavity.

Rajendiran, N.; Balasubramanian, T.

2008-03-01

88

Charge-transfer complexes of some linear conjugated polyenes.  

PubMed Central

On adsorption of some electron-acceptor molecules on the solid films of all-trans-beta-carotene, beta-apo-8'-carotenal, astacene and methylbixin a new absorption band appears on the longer-wavelength side of the spectrum in addition to the original bands. The position of this new band is dependent on the electron affinity (EA) of the acceptor molecules, and the intensity of this band increases with the amount of adsorbed acceptor molecules. A linear relationship between the vmax. of the new band and EA was observed. The value of the ionization potential of the polyenes estimated from such linear relationship agrees satisfactorily with the value obtained by other methods. It has been concluded that the polyenes behave as electron donor and first form molecular charge-transfer complexes (of type [polyene . I2] with iodine) with electron acceptors, these finally dissociating to yield ionic complexes (of type [polyene . I+] with iodine). PMID:7213346

Mallik, B; Jain, K M; Misra, T N

1980-01-01

89

Intramolecular charge transfer dual fluorescence of p-dimethylaminobenzoates  

NASA Astrophysics Data System (ADS)

A series of ester, p- N, N-dimethylaminobenzoates ((CH 3) 2NC 6H 4COOR, R= n-C nH 2 n+1 , n=1,2,…,8), were synthesized and their fluorescence spectra were recorded. Intramolecular charge transfer (CT) dual fluorescence was found in common organic solvent or in water with cetyltrimethylammonium bromide (CTAB) micelle. The fluorescence intensity ratio of CT band to normal band ( ICT/ ILE) was decreased dramatically with the increasing of carbon number of R group when the carbon number of R group were 1-3, but the dependence was not obvious when the carbon number of R group were 4-8. Oppositely, the ICT/ ILE was increased with increasing of carbon number of R group in water with CTAB micelle.

Zhang, Cai-Hong; Chen, Zhao-Bin; Jiang, Yun-Bao

2004-10-01

90

Modeling charge transfer in the photosynthetic reaction center  

NASA Astrophysics Data System (ADS)

In this work, we present a model to elucidate the unidirectionality of the primary charge-separation process in the bacterial reaction centers. We have used a model of three sites/molecules with electron transfer beginning at site 1 with an option to proceed to site 2 or site 3. We used a stochastic model with arbitrary correlation functions. We get the quantum yields of electron escape via the sites 2,3 in two limiting cases that correspond to a spectral density of underdamped and overdamped Brownian oscillator. In the fast modulation limit of an overdamped regime we get the effect, which was named “fear of death,” in which for strong enough sink parameters the electron has a tendency to avoid the place with greater sink. The presented model was used to provide a plausible explanation of the temperature dependence of the quantum yields of the Rhodobacter sphaeroides photosynthetic reaction center in the high-temperature regime.

Pudlak, Michal; Pin?ak, Richard

2003-12-01

91

Photoinduced Charge Transfer from Titania to Surface Doping Site  

PubMed Central

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

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

2013-01-01

92

Simulation of the charge transfer inefficiency of column parallel CCDs  

NASA Astrophysics Data System (ADS)

Charge-Coupled Devices (CCDs) have been successfully used in several high-energy physics experiments over the past two decades. Their high spatial resolution and thin sensitive layer make them an excellent tool for studying short-lived particles. The Linear Collider Flavour Identification (LCFI) collaboration is developing Column Parallel CCDs (CPCCDs) for the vertex detector of the International Linear Collider (ILC). The CPCCDs can be read out many times faster than standard CCDs, significantly increasing their operating speed. The results of detailed simulations of the Charge Transfer Inefficiency (CTI) of a prototype CPCCD chip are reported. The effects of the radiation damage on the CTI of a Si-based CCD particle detector are studied by simulating the effects of two electron trap levels Ec-0.17 and Ec-0.44 eV at different concentrations and operating temperatures. The dependence of the CTI on different occupancy levels (percentage of hit pixels) and readout frequencies is also studied. The optimal operating temperature—where the effects of the trapping are at a minimum—is found to be ˜230 K for the range of readout speeds proposed for the ILC.

Maneuski, Dzmitry

2008-06-01

93

Doping graphene films via chemically mediated charge transfer  

PubMed Central

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

2011-01-01

94

Doping graphene films via chemically mediated charge transfer.  

PubMed

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

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

2011-01-01

95

Charge transfer between O^+ ions and oxygen atoms  

NASA Astrophysics Data System (ADS)

Absolute differential and integral cross sections are reported for charge-transfer scattering of 0.5-, 0.85-, 1.5-, 2.8-, and 5.0-keV O^+(^4S) and O^+(^2D, ^2P) ions by atomic oxygen at angles between 0.04^o and 2.9^o in the laboratory frame. The ground-state integral O^+ cross section is found to be approximately 50% greater than that for the metastable ion. These data suggest that the ion beam utilized in the early laboratory measurements of the O^+-O cross section was, as suspected at the time, contaminated by metastable ions and therefore call into question the subsequent use of those data for the interpretation of atmospheric phenomena. The O^+-O cross section is particularly important as it is directly related to the O^+-O momentum transfer collision frequency which is a critical parameter in models of the upper atmosphere. The present data suggest that the value of the O^+-O collision frequency appropriate to the upper atmosphere is close to that adopted as an interim standard by the CEDAR community.

Lindsay, B. G.; Sieglaff, D. R.; Smith, K. A.; Stebbings, R. F.

2000-06-01

96

Non-Markovian reduced dynamics of ultrafast charge transfer at an oligothiophene-fullerene heterojunction  

NASA Astrophysics Data System (ADS)

We extend our recent quantum dynamical study of the exciton dissociation and charge transfer at an oligothiophene-fullerene heterojunction interface (Tamura et al., 2012) [6] by investigating the process using the non-perturbative hierarchical equations of motion (HEOM) approach. Based upon an effective mode reconstruction of the spectral density the effect of temperature on the charge transfer is studied using reduced density matrices. It was found that the temperature had little effect on the charge transfer and a coherent dynamics persists over the first few tens of femtoseconds, indicating that the primary charge transfer step proceeds by an activationless pathway.

Hughes, Keith H.; Cahier, Benjamin; Martinazzo, Rocco; Tamura, Hiroyuki; Burghardt, Irene

2014-10-01

97

Laboratory Studies of Thermal Energy Charge Transfer of Silicon and Iron Ions in Astrophysical Plasmas  

NASA Technical Reports Server (NTRS)

Charge transfer at electron-volt energies between multiply charged atomic ions and neutral atoms and molecules is of considerable importance in astrophysics, plasma physics, and in particular, fusion plasmas. In the year covered by this report, several major tasks were completed. These include: (1) the re-calibration of the ion gauge to measure the absolute particle densities of H2, He, N2, and CO for our current measurements; (2) the analysis of data for charge transfer reactions of N(exp 2 plus) ion and He, H2, N2, and CO; (3) measurement and data analysis of the charge transfer reaction of (Fe(exp 2 plus) ion and H2; (4) charge transfer measurement of Fe(exp 2 plus) ion and H2; and (5) redesign and modification of the ion detection and data acquisition system for the low energy beam facility (reflection time of flight mass spectrometer) dedicated to the study of state select charge transfer.

Kwong, Victor H. S.

1996-01-01

98

Real-time Simulations of Photoinduced Coherent Charge Transfer and Proton-Coupled Electron Transfer.  

PubMed

Photoinduced electron transfer (ET) and proton-coupled electron transfer (PCET) are fundamental processes in natural phenomena, most noticeably in photosynthesis. Time-resolved spectroscopic evidence of coherent oscillatory behavior associated with these processes has been reported both in complex biological environments, as well as in biomimetic models for artificial photosynthesis. Here, we consider a few biomimetic models to investigate these processes in real-time simulations based on ab initio molecular dynamics and Ehrenfest dynamics. This allows for a detailed analysis on how photon-to-charge conversion is promoted by a coupling of the electronic excitation with specific vibrational modes and with proton displacements. The ET process shows a characteristic coherence that is linked to the nuclear motion at the interface between donor and acceptor. We also show real-time evidence of PCET in a benzimidazole-phenol redox relay. PMID:25224924

Eisenmayer, Thomas J; Buda, Francesco

2014-10-20

99

Bonding and Charge Transfer in Nitrogen-Donor Uranyl Complexes: Insights from NEXAFS Spectra.  

PubMed

We investigate the electronic structure of three newly synthesized nitrogen-donor uranyl complexes [(UO2)(H2bbp)Cl2], [(UO)2(Hbbp)(Py)Cl], and [(UO2)(bbp)(Py)2] using a combination of near-edge X-ray absorption fine structure (NEXAFS) spectroscopy experiments and simulations. The complexes studied feature derivatives of the tunable tridentate N-donor ligand 2,6-bis(2-benzimidazyl)pyridine (bbp) and exhibit discrete chemical differences in uranyl coordination. The sensitivity of the N K-edge X-ray absorption spectrum to local bonding and charge transfer is exploited to systematically investigate the evolution of structural as well as electronic properties across the three complexes. A thorough interpretation of the measured experimental spectra is achieved via ab initio NEXAFS simulations based on the eXcited electron and Core-Hole (XCH) approach and enables the assignment of spectral features to electronic transitions on specific absorbing sites. We find that ligand-uranyl bonding leads to a signature blue shift in the N K-edge absorption onset, resulting from charge displacement toward the uranyl, while changes in the equatorial coordination shell of the uranyl lead to more subtle modulations in the spectral features. Theoretical simulations show that the flexible local chemistry at the nonbinding imidazole-N sites of the bbp ligand is also reflected in the NEXAFS spectra and highlights potential synthesis strategies to improve selectivity. In particular, we find that interactions of the bbp ligand with solvent molecules can lead to changes in ligand-uranyl binding geometry while also modulating the K-edge absorption. Our results suggest that NEXAFS spectroscopy combined with first-principles interpretation can offer insights into the coordination chemistry of analogous functionalized conjugated ligands. PMID:25330350

Pemmaraju, C D; Copping, Roy; Wang, Shuao; Janousch, Markus; Teat, Simon J; Tyliszcak, Tolek; Canning, Andrew; Shuh, David K; Prendergast, David

2014-11-01

100

Nematic and spin-charge orders driven by hole-doping a charge-transfer insulator  

NASA Astrophysics Data System (ADS)

Recent experimental discoveries have brought a diverse set of broken symmetry states to the center stage of research on cuprate superconductors. Here, we focus on a thematic understanding of the diverse phenomenology by exploring a strong-coupling mechanism of symmetry breaking driven by frustration of antiferromagnetic (AFM) order. We achieve this through a variational study of a three-band model of the CuO2 plane with Kondo type exchange couplings between doped oxygen holes and classical copper spins. Two main findings from this strong-coupling multi-band perspective are (1) that the symmetry hierarchy of spin stripe, charge stripe, intra-unit-cell nematic order and isotropic phases are all accessible microscopically within the model, (2) many symmetry-breaking patterns compete with energy differences within a few meV per Cu atom to produce a rich phase diagram. These results indicate that the diverse phenomenology of broken-symmetry states in hole-doped AFM charge-transfer insulators may indeed arise from hole-doped frustration of antiferromagnetism.

Fischer, Mark H.; Wu, Si; Lawler, Michael; Paramekanti, Arun; Kim, Eun-Ah

2014-09-01

101

Charge remote fragmentation in electron capture and electron transfer dissociations  

PubMed Central

Secondary fragmentations of three synthetic peptides (human ?A crystallin peptide 1-11, the deamidated form of human ?B2 crystallin peptide 4-14, and amyloid ? peptide 25-35) were studied in both electron capture dissociation (ECD) and electron transfer dissociation (ETD) mode. In ECD, in addition to c and z• ion formations, charge remote fragmentations (CRF) of z• ions were abundant, resulting in internal fragment formation or partial/entire side chain losses from amino acids, sometimes several residues away from the backbone cleavage site, and to some extent multiple side chain losses. The internal fragments were observed in peptides with basic residues located in the middle of the sequences, which was different from most tryptic peptides with basic residues located at the C-terminus. These secondary cleavages were initiated by hydrogen abstraction at the ?-, ?-, or ?-position of the amino acid side chain. In comparison, ETD generates fewer CRF fragments than ECD. This secondary cleavage study will facilitate ECD/ETD spectra interpretation, and help de novo sequencing and database searching. PMID:20171118

Li, Xiaojuan; Lin, Cheng; Han, Liang; Costello, Catherine E.; O'Connor, Peter B.

2010-01-01

102

Intramolecular charge transfer effects on 3-aminobenzoic acid  

NASA Astrophysics Data System (ADS)

Effect of solvents, buffer solutions of different pH and ?-cyclodextrin on the absorption and fluorescence spectra of 3-aminobenzoic acid (3ABA) have been investigated. The solid inclusion complex of 3ABA with ?-CD is discussed by UV-Vis, fluorimetry, semiempirical quantum calculations (AM1), FT-IR, 1H NMR and Scanning Electron Microscope (SEM). The thermodynamic parameters (? H, ? G and ? S) of the inclusion process are also determined. The experimental results indicated that the inclusion processes is an exothermic and spontaneous. The large Stokes shift emission in solvents with 3ABA are correlated with different solvent polarity scales suggest that, 3ABA molecule is more polar in the S 1 state. Solvent, ?-CD studies and excited state dipole moment values confirms that the presence of intramolecular charge transfer (ICT) in 3ABA. Acidity constants for different prototropic equilibria of 3ABA in the S 0 and S 1 states are calculated. ?-Cyclodextrin studies shows that 3ABA forms a 1:1 inclusion complex with ?-CD. ?-CD studies suggest COOH group present in non-polar part and amino group present in hydrophilic part of the ?-CD cavity. A mechanism is proposed to explain the inclusion process.

Stalin, T.; Rajendiran, N.

2006-03-01

103

Pseudoparticle approach for charge-transferring molecule-surface collisions  

NASA Astrophysics Data System (ADS)

Based on a semiempirical generalized Anderson-Newns model, we construct a pseudoparticle description for electron emission due to deexcitation of metastable molecules at surfaces. The pseudoparticle approach allows us to treat resonant charge-transfer and Auger processes on an equal footing, as it is necessary when both channels are open. This is, for instance, the case when a metastable N2(3?u+) molecule hits a diamond surface. Using nonequilibrium Green functions and physically motivated approximations to the self-energies of the Dyson equations, we derive a system of rate equations for the probabilities with which the metastable N2(3?u+) molecule, the molecular ground state N2(1?g+), and the negative ion N2-(2?g) can be found in the course of the scattering event. From the rate equations, we also obtain the spectrum of the emitted electron and the secondary electron emission coefficient. Our numerical results indicate the resonant tunneling process undermining the source of the Auger channel, which therefore contributes only a few percent to the secondary electron emission.

Marbach, Johannes; Bronold, Franz Xaver; Fehske, Holger

2012-09-01

104

Charge transfer vibronic transitions in uranyl tetrachloride compounds;  

SciTech Connect

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.

Liu, G. K.; Deifel, N. P.; Cahill, C. L. (Chemical Sciences and Engineering Division); (George Washington University)

2012-01-01

105

Charge-transfer complexes of 4-methylpiperidine with ?- and ?-acceptors.  

PubMed

The solid charge-transfer (CT) molecular complexes formed in the reaction of the electron donor 4-methylpiperidine (4MP) with the ?-electron acceptor iodine and ?-acceptors 7,7,8,8-tetracyanoquinodimethane (TCNQ), 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) and 2,4,4,6-tetrabromo-2,5-cyclohexadienone (TBCHD) have been investigated spectrophotometrically in chloroform at 25°C. These were characterized through electronic and infrared spectra as well as elemental and thermal analysis. The obtained results showed that the formed solid CT-complexes have the formulas [(4MP) I](+)I(-)3, [(4MP)(DDQ)2] and [(4MP)(TBCHD)] and with TCNQ the adduct [TCMPQDM] is obtained through N-substitution reaction in full agreement with the known reaction stoichiometries in solution as well as the elemental measurements. The formation constant KCT, molar extinction coefficient ?CT, free energy change ?G(0), CT energy ECT and the ionization potential Ip have been calculated for the CT-complexes [(4MP) I](+)I(-)3, [(4MP)(DDQ)2] and [(4MP)(TBCHD)]. PMID:25123938

AlQaradawi, Siham Y; Mostafa, Adel; Bazzi, Hassan S

2015-01-25

106

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

107

Investigations of the kinetics of charge-transfer reactions in photoelectrochemical solar cells  

Microsoft Academic Search

Photoelectrochemical solar cells can be made on the basis of majority and minority carrier devices. Since the forward dark current limits the photovoltage, the kinetics of the charge transfer across the interface has been studied in detail. It is shown that the exchange current, and consequently the forward current, can be kinetically or diffusion controlled, depending on the charge transfer

Ruediger Memming; Rolf Reineke; Dieter Meissner

1992-01-01

108

Charge transfer to the ionosphere and to the ground during thunderstorms  

E-print Network

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

Pasko, Victor

109

An experimental TV ghost-suppressor circuit using charge-transfer devices  

Microsoft Academic Search

The rapid development of charge-transfer technology has fostered many new applications of charge-transfer devices (CTD's) in the field of analog-signal processing. In this paper, the realization of a TV ghost-suppressor circuit by means of a pair of 64-stage p-channel MOS bucket-brigade circuits is described and experimental results are reported.

W. J. Butler; C. M. Puckette; N. C. Gittinger

1975-01-01

110

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

NASA Astrophysics Data System (ADS)

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.

Fossum, Eric R.

1991-02-01

111

Reversible phase transfer of nanoparticles based on photoswitchable host-guest chemistry.  

PubMed

An azobenzene-containing surfactant was synthesized for the phase transfer of ?-cyclodextrin (?-CD)-capped gold nanoparticles between water and toluene phases by host-guest chemistry. With the use of the photoisomerization of azobenzene, the reversible phase transfer of gold nanoparticles was realized by irradiation with UV and visible light. Furthermore, the phase transfer scheme was applied for the quenching of a reaction catalyzed by gold nanoparticles, as well as the recovery and recycling of the gold nanoparticles from aqueous solutions. This work will have significant impact on materials transfer and recovery in catalysis and biotechnological applications. PMID:24524295

Peng, Lu; You, Mingxu; Wu, Cuichen; Han, Da; Öçsoy, Ismail; Chen, Tao; Chen, Zhuo; Tan, Weihong

2014-03-25

112

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

E-print Network

Wire transfer of charge packets for on--chip CCD signal processing Eric R. Fossum Department. The structure is a hybrid of charge-coupled device (CCD) and bucket-brigade device (BBD) elements and permits of the signal quantities is adequate. Charge-domain circuits, such as CCD5, have the added advantages

Fossum, Eric R.

113

Classical theory of charge transfer and ionization of hydrogen atoms by protons  

Microsoft Academic Search

The theory is presented for obtaining, by a Monte Carlo method, the classical cross sections for charge transfer and ionization of hydrogen atoms by protons, in which the atoms are chosen initially from a microcanonical ensemble. With minor modifications the theory applies to any collisions between three charged particles which do not all have charges of the same sign. Scaling

R. Abrines; I. C. Percival

1966-01-01

114

Charge transfer in NixPt1-x alloys studied by x-ray photoelectron spectroscopy  

Microsoft Academic Search

The charge transfer between Ni and Pt atoms in the Ni-Pt alloys is studied by the core-level shifts of Ni 2p3\\/2 and Pt 4f7\\/2 x-ray photoelectron spectra. From the analysis considering the final-state relaxation energy explicitly, we conclude that the amount of the charge transfer is, in general, very small for these alloys. We also find that the intra-atomic charge

Eunjip Choi; S.-J. Oh; M. Choi

1991-01-01

115

Charge-transfer excitons at organic semiconductor surfaces and interfaces.  

PubMed

When a material of low dielectric constant is excited electronically from the absorption of a photon, the Coulomb attraction between the excited electron and the hole gives rise to an atomic H-like quasi-particle called an exciton. The bound electron-hole pair also forms across a material interface, such as the donor/acceptor interface in an organic heterojunction solar cell; the result is a charge-transfer (CT) exciton. On the basis of typical dielectric constants of organic semiconductors and the sizes of conjugated molecules, one can estimate that the binding energy of a CT exciton across a donor/acceptor interface is 1 order of magnitude greater than k(B)T at room temperature (k(B) is the Boltzmann constant and T is the temperature). How can the electron-hole pair escape this Coulomb trap in a successful photovoltaic device? To answer this question, we use a crystalline pentacene thin film as a model system and the ubiquitous image band on the surface as the electron acceptor. We observe, in time-resolved two-photon photoemission, a series of CT excitons with binding energies < or = 0.5 eV below the image band minimum. These CT excitons are essential solutions to the atomic H-like Schrodinger equation with cylindrical symmetry. They are characterized by principal and angular momentum quantum numbers. The binding energy of the lowest lying CT exciton with 1s character is more than 1 order of magnitude higher than k(B)T at room temperature. The CT(1s) exciton is essentially the so-called exciplex and has a very low probability of dissociation. We conclude that hot CT exciton states must be involved in charge separation in organic heterojunction solar cells because (1) in comparison to CT(1s), hot CT excitons are more weakly bound by the Coulomb potential and more easily dissociated, (2) density-of-states of these hot excitons increase with energy in the Coulomb potential, and (3) electronic coupling from a donor exciton to a hot CT exciton across the D/A interface can be higher than that to CT(1s) as expected from energy resonance arguments. We suggest a design principle in organic heterojunction solar cells: there must be strong electronic coupling between molecular excitons in the donor and hot CT excitons across the D/A interface. PMID:19378979

Zhu, X-Y; Yang, Q; Muntwiler, M

2009-11-17

116

Molecular orbital (SCF-X??-SW) theory of Fe2+-Mn3+, Fe 3+-Mn 2+, and Fe3+-Mn3+ charge transfer and magnetic exchange in oxides and silicates  

USGS Publications Warehouse

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. -from Author

Sherman, D. M.

1990-01-01

117

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

NASA Astrophysics Data System (ADS)

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.

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

2010-12-01

118

The coordination and atom transfer chemistry of titanium porphyrin complexes  

SciTech Connect

Preparation, characterization, and reactivity of ({eta}{sup 2}- alkyne)(meso-tetratolylpoprphrinato)titanium(II) complexes are described, along with inetermetal oxygen atom transfer reactions involving Ti(IV) and Ti(III) porphyrin complexes. The {eta}{sup 2}- alkyne complexes are prepared by reaction of (TTP)TiCl{sub 2} with LiAlH{sub 4} in presence of alkyne. Structure of (OEP)Ti({eta}{sup 2}-Ph-C{triple_bond}C-Ph) (OEP=octaethylporphryin) was determined by XRD. The compounds undergo simple substitution to displace the alkyne and produce doubly substituted complexes. Structure of (TTP)Ti(4-picoline){sub 2} was also determined by XRD. Reaction of (TTP)Ti{double_bond}O with (OEP)Ti-Cl yields intermetal O/Cl exchange, which is a one-electron redox process mediated by O atom transfer. Also a zero-electron redox process mediated by atom transfer is observed when (TTP)TiCl{sub 2} is reacted with (OEP)Ti{double_bond}O.

Hays, J.A.

1993-11-05

119

A three-step kinetic model for electrochemical charge transfer in the hopping regime.  

PubMed

Single-step nonadiabatic electron tunneling models are widely used to analyze electrochemical rates through self-assembled monolayer films (SAMs). For some systems, such as nucleic acids, long-range charge transfer can occur in a "hopping" regime that involves multiple charge transfer events and intermediate states. This report describes a three-step kinetic scheme to model charge transfer in this regime. Some of the features of the three-step model are probed experimentally by changing the chemical composition of the SAM. This work uses the three-step model and a temperature dependence of the charge transfer rate to extract the charge injection barrier for a SAM composed of a 10-mer peptide nucleic acid that operates in the hopping regime. PMID:24813905

Yin, Xing; Wierzbinski, Emil; Lu, Hao; Bezer, Silvia; de Leon, Arnie R; Davis, Kathryn L; Achim, Catalina; Waldeck, David H

2014-09-01

120

Modulation of terrestrial ion escape flux composition /by low-altitude acceleration and charge exchange chemistry/  

NASA Technical Reports Server (NTRS)

Motivated by recent observations of highly variable hot plasma composition in the magnetosphere, control of the ionospheric escape flux composition by low-altitude particle dynamics and ion chemistry has been investigated for an e(-), H(+), O(+) ionosphere. It is found that the fraction of the steady state escape flux which is O(+) can be controlled very sensitively by the occurrence of parallel or transverse ion acceleration at altitudes below the altitude where the neutral oxygen density falls rapidly below the neutral hydrogen density and the ionospheric source of O(+) tends to be rapidly converted by charge exchange to H(+). The acceleration is required both to overcome the gravitational confinement of O(+) and to violate charge exchange equilibrium so that the neutral hydrogen atmosphere appears 'optically' thin to escaping O(+). Constraints are placed on the acceleration processes, and it is shown that O(+) escape is facilitated by observed ionospheric responses to magnetic activity.

Moore, T. E.

1980-01-01

121

Time-resolved studies of charge recombination in the pyrene/TCNQ charge-transfer crystal: evidence for tunneling.  

PubMed

Previous studies of solid-state tetracyanobenzene-based donor-acceptor complexes showed that these materials were highly susceptible to both laser and mechanical damage that complicated the analysis of their electron-transfer kinetics. In this paper, we characterize the optical properties of a pyrene/tetracyanoquinodimethane charge-transfer crystal that is much more robust than the tetracyanobenzene compounds. This donor-acceptor complex has a charge-transfer absorption that extends into the near-infrared, rendering the crystal black. We use time-resolved fluorescence and diffuse reflectance transient absorption to study its dynamics after photoexcitation. We show that the initially excited charge-transfer state undergoes a rapid, monoexponential decay with a lifetime of 290 ps at room temperature. There is no evidence for any long-lived intermediate or dark states; therefore, this decay is attributed to charge recombination back to the ground state. Fluorescence lifetime measurements demonstrate that this process becomes temperature-independent below 60 K, indicative of a thermally activated tunneling mechanism. The subnanosecond charge recombination makes this low-band-gap donor-acceptor material a poor candidate for generating long-lived electron-hole pairs. PMID:22591413

Dillon, Robert J; Bardeen, Christopher J

2012-05-31

122

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

Code of Federal Regulations, 2011 CFR

...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...

2011-10-01

123

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

Code of Federal Regulations, 2012 CFR

...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...

2012-10-01

124

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

Code of Federal Regulations, 2013 CFR

...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...

2013-10-01

125

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

...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...

2014-10-01

126

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

SciTech Connect

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.

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

2010-01-01

127

An evaluation of 2-phase charge pump topologies with charge transfer switches for green mobile technology  

Microsoft Academic Search

The development of charge pumps has been motivated by the power supply requirements of portable electronic devices. Charge pumps are inductorless DC-DC converters that are small size and high integration. The quality of the charge pump greatly depends on the effectiveness of switches to turn on and off at the designated clock phases. However, to date, no analysis has been

Yan Chiew Wong; Nurul H. Noordin; Ahmed O. El-Rayis; Nakul Haridas; Ahmet T. Erdogan; Tughrul Arslan

2011-01-01

128

Electron transfer dynamics and excited state branching in a charge-transfer platinum(ii) donor-bridge-acceptor assembly.  

PubMed

A linear asymmetric Pt(ii) trans-acetylide donor-bridge-acceptor triad designed for efficient charge separation, NAP[triple bond, length as m-dash]Pt(PBu3)2[triple bond, length as m-dash]Ph-CH2-PTZ (), containing strong electron acceptor and donor groups, 4-ethynyl-N-octyl-1,8-naphthalimide (NAP) and phenothiazine (PTZ) respectively, has been synthesised and its photoinduced charge transfer processes characterised in detail. Excitation with 400 nm, ?50 fs laser pulse initially populates a charge transfer manifold stemming from electron transfer from the Pt-acetylide centre to the NAP acceptor and triggers a cascade of charge and energy transfer events. A combination of ultrafast time-resolved infrared (TRIR) and transient absorption (TA) spectroscopies, supported by UV-Vis/IR spectroelectrochemistry, emission spectroscopy and DFT calculations reveals a self-consistent photophysical picture of the excited state evolution from femto- to milliseconds. The characteristic features of the NAP-anion and PTZ-cation are clearly observed in both the TRIR and TA spectra, confirming the occurrence of electron transfer and allowing the rate constants of individual ET-steps to be obtained. Intriguingly, has three separate ultrafast electron transfer pathways from a non-thermalised charge transfer manifold directly observed by TRIR on timescales ranging from 0.2 to 14 ps: charge recombination to form either the intraligand triplet (3)NAP with 57% yield, or the ground state, and forward electron transfer to form the full charge-separated state (3)CSS ((3)[PTZ(+)-NAP(-)]) with 10% yield as determined by target analysis. The (3)CSS decays by charge-recombination to the ground state with ?1 ns lifetime. The lowest excited state is (3)NAP, which possesses a long lifetime of 190 ?s and efficiently sensitises singlet oxygen. Overall, molecular donor-bridge-acceptor triad demonstrates excited state branching over 3 different pathways, including formation of a long-distant (18 Å) full charge-separated excited state from a directly observed vibrationally hot precursor state. PMID:25361227

Scattergood, Paul A; Delor, Milan; Sazanovich, Igor V; Bouganov, Oleg V; Tikhomirov, Sergei A; Stasheuski, Alexander S; Parker, Anthony W; Greetham, Gregory M; Towrie, Michael; Davies, E Stephen; Meijer, Anthony J H M; Weinstein, Julia A

2014-11-12

129

Undoing static correlation: Long-range charge transfer in time-dependent density-functional theory  

NASA Astrophysics Data System (ADS)

Long-range charge-transfer excited states are notoriously badly underestimated in time-dependent density-functional theory (TDDFT). We discuss how exact TDDFT captures charge transfer between open-shell species: in particular, the role of the step in the ground-state potential, and the severe frequency dependence of the exchange-correlation kernel. An expression for the latter is derived, that becomes exact in the limit that the charge-transfer excitations are well separated from other excitations. The exchange-correlation kernel has the task of undoing the static correlation in the ground state introduced by the step, in order to accurately recover the physical charge-transfer states.

Maitra, Neepa T.

2005-06-01

130

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

E-print Network

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 ...

Bai, Peng

131

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

E-print Network

Effective Charge Transfer Distances in Cyanide-Bridged Mixed-Valence Transition Metal Complexes theory (Oh; Boxer J. Am. Chem. Soc. 1990, 112, 8161). Stark spectra are reported for a series of cyanide

Boxer, Steven G.

132

Charge Transfer through Single-Stranded Peptide Nucleic Acid Composed of Thymine Nucleotides  

E-print Network

Charge Transfer through Single-Stranded Peptide Nucleic Acid Composed of Thymine Nucleotides Amit; In Final Form: February 18, 2008 Self-assembled monolayers (SAMs) of single-stranded peptide nucleic acids. Peptide nucleic acid (PNA) is an analo

Borguet, Eric

133

Charge transfer in time-dependent density-functional theory: Insights from the asymmetric Hubbard dimer  

NASA Astrophysics Data System (ADS)

We show that propagation with the best possible adiabatic approximation in time-dependent density-functional theory fails to properly transfer charge in an asymmetric two-site Hubbard model when beginning in the ground state. The approximation is adiabatic but exact otherwise, constructed from the exact ground-state exchange-correlation functional that we compute via constrained search. The model shares the essential features of charge-transfer dynamics in a real-space long-range molecule, so the results imply that the best possible adiabatic approximation, despite being able to capture nonlocal ground-state step features relevant to dissociation and charge-transfer excitations, cannot capture fully time-resolved charge-transfer dynamics out of the ground state.

Fuks, J. I.; Maitra, N. T.

2014-06-01

134

Charge-transfer interactions for the fabrication of multifunctional viral nanoparticles.  

PubMed

A facile strategy to fabricate multifunctional viral nanoparticles was described by introducing charge-transfer interactions between a pyrenyl motif with dinitrophenyl and pyridinium-contained guest molecules. PMID:25275634

Hu, Jun; Wang, Peiyi; Zhao, Xia; Lv, Lin; Yang, Song; Song, Baoan; Wang, Qian

2014-10-21

135

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

NASA Astrophysics Data System (ADS)

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.

Wang, Xin; Liang, Shi-Dong

2013-02-01

136

Electronic and Nuclear Factors in Charge and Excitation Transfer  

SciTech Connect

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.

Piotr Piotrowiak

2004-09-28

137

Chemistry and Radiative Transfer of Water in Cold, Dense Clouds  

E-print Network

The Herschel Space Observatory's recent detections of water vapor in the cold, dense cloud L1544 allow a direct comparison between observations and chemical models for oxygen species in conditions just before star formation. We explain a chemical model for gas phase water, simplified for the limited number of reactions or processes that are active in extreme cold ($water is removed from the gas phase by freezing onto grains and by photodissociation. Water is formed as ice on the surface of dust grains from O and OH and released into the gas phase by photodesorption. The reactions are fast enough with respect to the slow dynamical evolution of L1544 that the gas phase water is in equilibrium for the local conditions thoughout the cloud. We explain the paradoxical radiative transfer of the H$_2$O ($1_{10}-1_{01}$) line. Despite discouragingly high optical depth caused by the large Einstein A coefficient, the subcritical excitation in the cold, rarefied H$_2$ causes the line brightnes...

Keto, Eric; Caselli, Paola

2014-01-01

138

The role of charge-transfer states in energy transfer and dissipation within natural and artificial bacteriochlorophyll proteins.  

PubMed

Understanding how specific protein environments affect the mechanisms of non-radiative energy dissipation within densely assembled chlorophylls in photosynthetic protein complexes is of great interest to the construction of bioinspired solar energy conversion devices. Mixing of charge-transfer and excitonic states in excitonically interacting chlorophylls was implicated in shortening excited states' lifetimes, but its relevance to active control of energy dissipation in natural systems is under considerable debate. Here we show that the degree of fluorescence quenching in two similar pairs of excitonically interacting bacteriochlorophyll derivatives is directly associated with increasing charge-transfer character in the excited state, and that the protein environment may control non-radiative dissipation by affecting the mixing of charge-transfer and excitonic states. The capability of local protein environments to determine the fate of excited states, and thereby to confer different functionalities to excitonically coupled dimers substantiates the dimer as the basic functional element of photosynthetic enzymes. PMID:25342121

Wahadoszamen, Md; Margalit, Iris; Ara, Anjue Mane; van Grondelle, Rienk; Noy, Dror

2014-01-01

139

The role of charge-transfer states in energy transfer and dissipation within natural and artificial bacteriochlorophyll proteins  

NASA Astrophysics Data System (ADS)

Understanding how specific protein environments affect the mechanisms of non-radiative energy dissipation within densely assembled chlorophylls in photosynthetic protein complexes is of great interest to the construction of bioinspired solar energy conversion devices. Mixing of charge-transfer and excitonic states in excitonically interacting chlorophylls was implicated in shortening excited states' lifetimes, but its relevance to active control of energy dissipation in natural systems is under considerable debate. Here we show that the degree of fluorescence quenching in two similar pairs of excitonically interacting bacteriochlorophyll derivatives is directly associated with increasing charge-transfer character in the excited state, and that the protein environment may control non-radiative dissipation by affecting the mixing of charge-transfer and excitonic states. The capability of local protein environments to determine the fate of excited states, and thereby to confer different functionalities to excitonically coupled dimers substantiates the dimer as the basic functional element of photosynthetic enzymes.

Wahadoszamen, Md.; Margalit, Iris; Ara, Anjue Mane; van Grondelle, Rienk; Noy, Dror

2014-10-01

140

Mechanism of back electron transfer in an intermolecular photoinduced electron transfer reaction: solvent as a charge mediator.  

PubMed

Back electron transfer (BET) is one of the important processes that govern the decay of generated ion pairs in intermolecular photoinduced electron transfer reactions. Unfortunately, a detailed mechanism of BET reactions remains largely unknown in spite of their importance for the development of molecular photovoltaic structures. Here, we examine the BET reaction of pyrene (Py) and 1,4-dicyanobenzene (DCB) in acetonitrile (ACN) by using time-resolved near- and mid-IR spectroscopy. The Py dimer radical cation (Py2 (.+) ) and DCB radical anion (DCB(.-) ) generated after photoexcitation of Py show asynchronous decay kinetics. To account for this observation, we propose a reaction mechanism that involves electron transfer from DCB(.-) to the solvent and charge recombination between the resulting ACN dimer anion and Py2 (.+) . The unique role of ACN as a charge mediator revealed herein could have implications for strategies that retard charge recombination in dye-sensitized solar cells. PMID:25044892

Narra, Sudhakar; Nishimura, Yoshifumi; Witek, Henryk A; Shigeto, Shinsuke

2014-10-01

141

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

SciTech Connect

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.

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

2012-01-01

142

A quantative study of the charge-transfer between conjugated thiophene rings in vibrationally excited states  

NASA Astrophysics Data System (ADS)

The charge transfer integral (CTI) between monomers in polythiophene is important for the electrical properties of the polymer. Torsional oscillations of the monomers are thought to play a key role in reducing the CTI, but the present study shows that other out-of-plane vibrational modes may play an even more important role between 10 -12 and 10 -14 sec timescale on which charge-transfer occurs.

van Eijck, L.; Senthilkumar, K.; Siebbeles, L. D. A.; Kearley, G. J.

2004-07-01

143

Multiple Charge Transfer Bands in Complexes of Hexafluorobenzene with Aromatic Amines  

Microsoft Academic Search

HEXAFLUROBENZENE acts as an electron acceptor in forming charge transfer complexes with aromatic amines1. In complexes with certain of the amines the charge transfer absorption consists of two bands as shown in Fig. 1 for the hexafluorobenzene-N,N-dimethyl-p-toluidine (DMT) complex. Table 1 shows the positions of the two bands and the splitting between them for hexafluorobenzene complexes with DMT, N,N-dimethylaniline (DMA)

T. G. Beaumont; K. M. C. Davis

1968-01-01

144

Spectroscopy of equilibrium and nonequilibrium charge transfer in semiconductor quantum structures  

NASA Astrophysics Data System (ADS)

We investigate equilibrium and nonequilibrium charge-transfer processes by performing high-resolution transport spectroscopy. Using electrostatically defined quantum dots for energy-selective emission and detection, we achieved very high spectral resolution and a high degree of tunability of relevant experimental parameters. Most importantly, we observe that the spectral width of elastically transferred electrons can be substantially smaller than the linewidth of a thermally broadened Coulomb peak. This finding indicates that the charge-transfer process is fast compared to the electron-phonon interaction time. By drawing an analogy to double quantum dots, we argue that the spectral width of the elastic resonance is determined by the lifetime broadening h? of the emitter and detector states. Good agreement with the model is found also in an experiment in which the charge transfer is in the regime h??kBT. By performing spectroscopy below the Fermi energy, we furthermore observe elastic and inelastic transfer of holes.

Rössler, C.; Burkhard, S.; Krähenmann, T.; Röösli, M.; Märki, P.; Basset, J.; Ihn, T.; Ensslin, K.; Reichl, C.; Wegscheider, W.

2014-08-01

145

Charge Transfer between Uncharged Water Drops in Free Fall in an Electric Field  

Microsoft Academic Search

The charging of uncharged, equal or very nearly equal radius drops falling freely in an electric field has been observed to occur in two different modes. When the electric field exceeds a threshold value that is a function oœ drop size, the charge is transferred via a spark in the air between the near surfaces of approaching drops. Below this

J. Doyne Sartor; Charles E. Abbott

1968-01-01

146

Valence Topological Charge-Transfer Indices for Dipole Moments: Percutaneous Enhancers  

Microsoft Academic Search

Valence topological charge-transfer (CT) indices are applied to the calculation of dipole moments. The algebraic and vector semisum CT indices are defined. The combination of CT indices allows the estimation of the dipole moments. The model is generalized for molecules with heteroatoms. The ability of the indices for the description of the molecular charge distribution is established by comparing them

Francisco Torrens

2004-01-01

147

Potential curves for Na2/+/ and resonance charge transfer cross sections.  

NASA Technical Reports Server (NTRS)

A mode potential method, applied earlier to the positively charged diatomic lithium molecule Li2(+), is used to calculate the six lowest potential energy curves of Na2(+). Charge transfer cross sections are calculated for Li(+) on Li and for Na(+) on Na and found to be in reasonable agreement with experiment.

Bottcher, C.; Allison, A. C.; Dalgarno, A.

1971-01-01

148

Charge-Transfer Induced Dissociation in the H+ (H2O)3Ar collisions  

E-print Network

of the dissociation of the neutralized protonated water cluster. Thus, the present COINTOF method provides newCharge-Transfer Induced Dissociation in the H+ (H2O)3­Ar collisions observed with the COINTOF mass Nucléaire de Lyon ABSTRACT Electron-capture in collisions of singly charged protonated water cluster H+ (H2O

149

Chemistry  

NSDL National Science Digital Library

Finds ChemEd DL resources related to the sections of the General Chemistry textbook, Chemistry, by Kenneth W. Whitten, Raymond E. Davis, M. Larry Peck, George G. Stanley published by Brooks/Cole, 2010.

150

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

PubMed Central

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

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

2011-01-01

151

Differential charge-transfer cross sections for Na with Rb collisions at low energies  

E-print Network

on a theoretical and experimental study of state-selective differential single-electron transfer cross sectionsDifferential charge-transfer cross sections for Na¿ with Rb collisions at low energies T. G. Lee,1-electron capture amplitudes. By combining with the eikonal approximation, we calculated the angular differential

Lin, Chii-Dong

152

Simple charge-transfer model to explain the electrical response of hydrogen chains Adrienn Ruzsinszky,1  

E-print Network

-transfer model which explains both of these effects in analytic terms. In this model, charge is transferred semilocal density functionals like the local spin- density approximation LSD 8 and the generalized gradi that were proposed in Ref. 1 as exemplars of real polymer chains. In H14, for example, LSD overestimates

Csonka, Gábor István

153

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

E-print Network

-CNISM, Universita della Tuscia, I-01100 Viterbo, Italy 2 Institute of Agro-environmental and Forest Biology-tin oxide, in resonance with its ligand-to-metal charge transfer absorption band, resulted in a light. The capability of controlling electron transfer processes through light pulses opens interesting perspectives

Tuscia, Università Degli Studi Della

154

Charge-Transfer Transitions in the Vacuum-Ultraviolet of Protein Circular Dichroism Spectra  

E-print Network

of proteins. The vacuum UV region (below 190 nm), where charge-transfer transitions have an influence present calculations of the vacuum UV CD spectra of 71 proteins, for which experimental SRCD spectra and XCharge-Transfer Transitions in the Vacuum-Ultraviolet of Protein Circular Dichroism Spectra

Wallace, Bonnie Ann

155

Transferred Charge and Specific Energy Associated with Lightning Hitting Wind Turbines in Japan  

NASA Astrophysics Data System (ADS)

Cumulative distributions of charge amount and specific energy of upward winter lightning flashes, observed by Rogowski coils instrumented on wind turbines in the coastal area of the Sea of Japan, were analyzed. Among 284 current data recorded at 16 measuring sites, the transferred charge of 13 lightning flashes exceeded 300C, and the specific energy of 2 flashes exceeded 10MJ/?. The medians of transferred charge are about 60% higher than those observed at Nikaho wind farm in winter for the three types of current, negative, positive and bipolar. Importance of observation at multiple sites is manifest.

Ishii, Masaru; Saito, Mikihisa; Chihara, Masaaki; Natsuno, Daisuke

156

Using metal complex-labeled peptides for charge transfer-based biosensing with semiconductor quantum dots  

NASA Astrophysics Data System (ADS)

Luminescent colloidal semiconductor quantum dots (QDs) have unique optical and photonic properties and are highly sensitive to charge transfer in their surrounding environment. In this study we used synthetic peptides as physical bridges between CdSe-ZnS core-shell QDs and some of the most common redox-active metal complexes to understand the charge transfer interactions between the metal complexes and QDs. We found that QD emission underwent quenching that was highly dependent on the choice of metal complex used. We also found that quenching traces the valence or number of metal complexes brought into close proximity of the nanocrystal surface. Monitoring of the QD absorption bleaching in the presence of the metal complex provided insight into the charge transfer mechanism. The data suggest that two distinct charge transfer mechanisms can take place. One directly to the QD core states for neutral capping ligands and a second to surface states for negatively charged capping ligands. A basic understanding of the proximity driven charge-transfer and quenching interactions allowed us to construct proteolytic enzyme sensing assemblies with the QD-peptide-metal complex conjugates.

Medintz, Igor L.; Pons, Thomas; Trammell, Scott A.; Blanco-Canosa, Juan B.; Dawson, Philip E.; Mattoussi, Hedi

2009-02-01

157

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

PubMed

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

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

2014-09-01

158

Charge transfer and ionization in low-energy Ar/sup q/++Ne collisions  

SciTech Connect

A secondary-ion recoil source was used to study charge transfer and ionization in collisions of Ar/sup q/+ (2< or =q< or =9) on Ne at projectile energies between 100 and 1100 eV per projectile charge. Two experimental methods are presented. With the first one we measure cross sections for electron capture by detecting both the initial and final charge states of the Ar ions. With the second method we measure, in addition to those parameters, the charge state of the Ne ions after the reaction. This three-parameter method allows us to distinguish among various competing reaction mechanisms and to measure cross sections for single- and multiple-electron capture, ionization, and transfer ionization. We find that the cross sections for ionization without simultaneous capture are negligibly small, whereas those for transfer ionization are quite important in several cases.

Justiniano, E.; Cocke, C.L.; Gray, T.J.; DuBois, R.D.; Can, C.

1981-12-01

159

Ion/ion reactions in the gas phase: Proton transfer reactions involving multiply-charged proteins  

SciTech Connect

Multiply-charged cations derived from electrospray of bovine ubiquitin and horse skeletal muscle apomyoglobin have been subjected to reactions with anions derived from glow discharge ionization of perfluoro-1,3-dimethylcyclohexane. The results are compared with data obtained from proton transfer reactions with strong gaseous neutral bases. Ion/ion reaction rates are shown to be linearly related to the square of the charge on the protein ion, as expected based on a simple capture collision model. Cationic products with charge as low as +1 could be readily formed via ion/ion reactions, whereas efforts to produce such low charge states via ion/molecule reactions have proved unsuccessful. Ion/ion proton transfer reactions appear to be an effective means of reducing charge on highly charged proteins to arbitrarily low charge states. In addition to proton transfer, ion/ion recombination has also been observed. The propensity for proton transfer versus anion attachment to the cation is highly dependent upon the identity of the anion. 28 refs., 7 figs.

Stephenson, J.L. Jr.; MeLuckey, S.A. [Oak Ridge National Lab., TN (United States)] [Oak Ridge National Lab., TN (United States)

1996-08-07

160

Wire transfer of charge packets for on-chip CCD signal processing  

NASA Astrophysics Data System (ADS)

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 was used to characterize the wire-transfer operation. Transfer efficiency ranging between 0.998 and 0.999 was obtained for surface n-channel devices with clock cycle times in the range from 40 nsec to 0.3 msec. Transfer efficiency as high as 0.9999 was obtained for buried n-channel devices. Good agreement is found between experiment and simulation.

Fossum, Eric R.

161

Photochemistry and electron-transfer mechanism of transition metal oxalato complexes excited in the charge transfer band  

PubMed Central

The photoredox reaction of trisoxalato cobaltate (III) has been studied by means of ultrafast extended x-ray absorption fine structure and optical transient spectroscopy after excitation in the charge-transfer band with 267-nm femtosecond pulses. The Co–O transient bond length changes and the optical spectra and kinetics have been measured and compared with those of ferrioxalate. Data presented here strongly suggest that both of these metal oxalato complexes operate under similar photoredox reaction mechanisms where the primary reaction involves the dissociation of a metal–oxygen bond. These results also indicate that excitation in the charge-transfer band is not a sufficient condition for the intramolecular electron transfer to be the dominant photochemistry reaction mechanism. PMID:18832175

Chen, Jie; Zhang, Hua; Tomov, Ivan V.; Ding, Xunliang; Rentzepis, Peter M.

2008-01-01

162

A parametric study of shock jump chemistry, electron temperature, and radiative heat transfer models in hypersonic flows  

E-print Network

A PARAMETRIC STUDY OF SHOCK JUMP CHEMISTRY, ELECTRON TEMPERATURE, AND RADIATIVE HEAT TRANSFER MODELS IN HYPERSONIC FLOWS A Thesis by ROBERT BRIAN GREENDYKE Submitted to the Graduate College of Texas A&M University in partial fulfillment... of the requirements for the degree of MASTER OF SCIENCE August 1988 Major Subject: Aerospace Engineering A PARAMETRIC STUDY OF SHOCK JUMP CHEMISTRY, ELECTRON TEMPERATURE, AND RADIATIVE HEAT TRANSFER MODELS IN HYPERSONIC FLOWS A Thesis by ROBERT BRIAN...

Greendyke, Robert Brian

2012-06-07

163

Charge fluctuations, charge-transfer instabilities, and superconductivity in a three-band model of CuO2 planes  

Microsoft Academic Search

We apply a recently developed quasiparticle theory for strongly correlated systems to a three-band model of Cu-O planes. We allow for Cu-O hybridization, Cu-O intersite repulsion, and a large on-site repulsion at the Cu sites (which will be treated as infinite). We use the large spin degeneracy (1\\/N) expansion to study (i) the interplay between charge-transfer instabilities and phase separation

J. C. Hicks; Andrei E. Ruckenstein; Stefan Schmitt-Rink

1992-01-01

164

Ultrafast charge- and energy-transfer dynamics in conjugated polymer: cadmium selenide nanocrystal blends.  

PubMed

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

Morgenstern, Frederik S F; Rao, Akshay; Böhm, Marcus L; Kist, René J P; Vaynzof, Yana; Greenham, Neil C

2014-02-25

165

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

Code of Federal Regulations, 2013 CFR

...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,...

2013-10-01

166

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

...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,...

2014-10-01

167

Charge transfer in model peptides: obtaining Marcus parameters from molecular simulation.  

PubMed

Charge transfer within and between biomolecules remains a highly active field of biophysics. Due to the complexities of real systems, model compounds are a useful alternative to study the mechanistic fundamentals of charge transfer. In recent years, such model experiments have been underpinned by molecular simulation methods as well. In this work, we study electron hole transfer in helical model peptides by means of molecular dynamics simulations. A theoretical framework to extract Marcus parameters of charge transfer from simulations is presented. We find that the peptides form stable helical structures with sequence dependent small deviations from ideal PPII helices. We identify direct exposure of charged side chains to solvent as a cause of high reorganization energies, significantly larger than typical for electron transfer in proteins. This, together with small direct couplings, makes long-range superexchange electron transport in this system very slow. In good agreement with experiment, direct transfer between the terminal amino acid side chains can be dicounted in favor of a two-step hopping process if appropriate bridging groups exist. PMID:22260641

Heck, Alexander; Woiczikowski, P Benjamin; Kuba?, Tomáš; Giese, Bernd; Elstner, Marcus; Steinbrecher, Thomas B

2012-02-23

168

Solvent effect on bell-shaped energy gap dependence for charge transfer triplet exciplexes  

NASA Astrophysics Data System (ADS)

The decay kinetics of charge transfer triplet exciplexes—radical ion pairs formed by electron transfer from aromatic amines to the quinones in the triplet excited states in benzene, ethyl acetate and tert-amyl alcohol was studied by laser photolysis. The bell-shaped dependence for the intersystem electron transfer becomes more pronounced and narrow with the increasing polarity of the medium, which may be explained in terms of the single quantum mode approximation within the non-adiabatic multiphonon electron transfer theory by means of the decrease in the vibrational frequency of the quantum mode and in the quantum reorganization energy.

Levin, P. P.; Raghavan, P. K. N.

1991-08-01

169

Interstellar Chemistry Gets More Complex With New Charged-Molecule Discovery  

NASA Astrophysics Data System (ADS)

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

2007-07-01

170

A Novel Approach to Simulate a Charge Transfer in DNA Repair by an Anacystis nidulans Photolyase  

PubMed Central

An Anacystis nidulans photolyase enzyme containing two chromophore cofactors was simulated for a photoreaction DNA repairing process via molecular dynamics (MD) method. A novel approach has been introduced for the electron transfer between the FAD (flavin adenine dinucleotide; flavin) molecule and CPD (cyclobutane pyrimidine dimer). This approach involves four simulation stages with different charges for the FAD and CPD fragments and a role of a charged state of the active cofactor was qualified during the MD modeling. Observations show that flavin has actively participated in a charge transfer process, thereby involving the conformational changes of the DNA and CPD substrate fragment. The DNA conformation behavior has shown to correlate with the electron transfer from flavin to CPD. This is manifested on the similarities of the DNA repairing process by excision repair of the UV photoproducts. PMID:24772194

Dushanov, E.B.; Kholmurodov, Kh.T.

2014-01-01

171

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

NASA Astrophysics Data System (ADS)

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.

Schöppach, Andreas; Gnandt, David; Koslowski, Thorsten

2014-04-01

172

Relating Crystal Structure and the Charge-Transfer Nature of Excitons in Pentacene from First Principles  

NASA Astrophysics Data System (ADS)

The nature of low energy optical excitations within pentacene has been the subject of many experimental and theoretical studies, with much disagreement as to the degree of their charge-transfer character. Here, we use many-body perturbation theory to study singlet excitons within different solid phases of pentacene and demonstrate that inter-molecular interactions lead to delocalized, charge-transfer-like excitations in the bulk crystalline phase. Using the Bethe-Salpeter two-particle correlation function, we demonstrate that the interplay between intermolecular hybridization, local exchange interactions, and attractive electron/hole interactions controls the nature of the exciton. Additionally, we explore simple models to understand and predict the nature of the excitonic wavefunction, in particular whether it has charge-transfer character.

Sharifzadeh, Sahar; Darancet, Pierre; Kronik, Leeor; Neaton, Jeffrey

2013-03-01

173

Laboratory Studies of Thermal Energy Charge Transfer of Silicon and Iron Ions in Astrophysical Plasmas  

NASA Technical Reports Server (NTRS)

The laser ablation/ion storage facility at the UNLV Physics Department is dedicated to the study of atomic processes in low temperature plasmas. Our current program is directed to the study of charge transfer of multiply charged ions and neutrals that are of importance to astrophysics at energies less than 1 eV (about 10(exp 4) K). Specifically, we measure the charge transfer rate coefficient of ions such as N(2+), Si(3+), Si(3+), with helium and Fe(2+) with molecular and atomic hydrogen. All these ions are found in a variety of astrophysical plasmas. Their electron transfer reactions with neutral atoms can affect the ionization equilibrium of the plasma.

Kwong, Victor H. S.

1997-01-01

174

Charge transfer excited state energies by perturbative delta self consistent field method  

NASA Astrophysics Data System (ADS)

We use our recently outlined perturbative approach to compute the lowest charge transfer excitation energies for a set of tetracynoehylene (TCNE)-hydrocarbon complexes, C2H4-C2F4, NH3-F2, pentacene-C60, and tetraphenyl porphyrin-C60 complexes. Results show that the method can provide a reliable description of charge transfer excitation energies, which are comparable to that obtained by time-dependent density functional theory using specially optimized range-corrected functionals. As the calculation cost of excited state is comparable to the ground state and the calculation of each excited state is independent of others, the method can be easily used to describe the charge transfer excited states of large donor-acceptor complexes containing 200 or more atoms.

Baruah, Tunna; Olguin, Marco; Zope, Rajendra R.

2012-08-01

175

Differential Double Ionization of He by Compton Photons and Charged Particles at Large Energy Transfers  

Microsoft Academic Search

Double ionization of helium differential in energy transfer, ?, is studied for both high-energy Compton photons and charged particles. The ratios of double to single ionization, RC(?) for Compton scattering, and RZ(?) for charged particles, are found to display an unexpected behavior: For large ? up to the two-body binary encounter (BE) limit, ?BE, we find RC(?)=RZ(?)~=0.86% in good agreement

J. Wang; J. H. McGuire; J. Burgdoerfer; Y. Qiu

1996-01-01

176

Direct Observation of Charge Transfer in Double-Perovskite-Like RbMn[Fe(CN)6  

Microsoft Academic Search

The charge density distribution has been determined for a transition metal cyanide, RbMn[Fe(CN)6], by means of the maximum entropy Rietveld method combined with the highly angularly resolved synchrotron radiation x-ray powder diffraction at SPring-8 BL02B2. We directly observed a charge transfer from the Mn site to the Fe site in the low-temperature phase. On the basis of a local density

K. Kato; Y. Moritomo; M. Takata; M. Sakata; M. Umekawa; N. Hamada; S. Ohkoshi; H. Tokoro; K. Hashimoto

2003-01-01

177

Charge transfer during intracloud lightning from a time-dependent multidipole model  

Microsoft Academic Search

A time-dependent, multidipole (TDMD) model has been developed to show the charge transfer during intracloud (IC) flashes with high time and space resolution. This model combines high-speed electric field measurements from a balloon-borne instrument (Esonde) and three-dimensional lightning maps from the New Mexico Tech Lightning Mapping Array (LMA). The result is a time-varying spatial distribution of charge along lightning channels,

Gaopeng Lu; W. P. Winn; R. G. Sonnenfeld

2011-01-01

178

Modeling of charge transfer processes to understand photophysical signatures: The case of Rhodamine 110  

NASA Astrophysics Data System (ADS)

Photophysical signatures, namely absorption and emission energies, lifetime and quantum yields, have been computed through TD-DFT approaches and compared with experimental counterparts for the Rhodamine 110 dye in aqueous solution. Thanks to a new protocol of analysis, based on the use of very promising electronic based indices, it has been possible to investigate the interplay between Rhodamine 110 dye's structure, degree of charge transfer upon excitation, and fluorescence signatures. This combined analysis is very promising to support the understanding of charge transfer based mechanisms affecting dyes photophysics.

Savarese, Marika; Raucci, Umberto; Netti, Paolo A.; Adamo, Carlo; Ciofini, Ilaria; Rega, Nadia

2014-08-01

179

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

E-print Network

finite at the origin. A variety of other choices of W(R} have been used in first Born calculations of charge transfer. The well-known BK approximation of Brinkman and Kramers' uses no W(R). Halpern and Law" took W(R) to be the full projectile nucleus... finite at the origin. A variety of other choices of W(R} have been used in first Born calculations of charge transfer. The well-known BK approximation of Brinkman and Kramers' uses no W(R). Halpern and Law" took W(R) to be the full projectile nucleus...

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

1979-01-01

180

Delocalization and dielectric screening of charge transfer states in organic photovoltaic cells  

NASA Astrophysics Data System (ADS)

Charge transfer (CT) states at a donor-acceptor heterojunction have a key role in the charge photogeneration process of organic solar cells, however, the mechanism by which these states dissociate efficiently into free carriers remains unclear. Here we explore the nature of these states in small molecule-fullerene bulk heterojunction photovoltaics with varying fullerene fraction and find that the CT energy scales with dielectric constant at high fullerene loading but that there is a threshold C60 crystallite size of ~4?nm below which the spatial extent of these states is reduced. Electroabsorption measurements indicate an increase in CT polarizability when C60 crystallite size exceeds this threshold, and that this change is correlated with increased charge separation yield supported by CT photoluminescence transients. These results support a model of charge separation via delocalized CT states independent of excess heterojunction offset driving energy and indicate that local fullerene crystallinity is critical to the charge separation process.

Bernardo, B.; Cheyns, D.; Verreet, B.; Schaller, R. D.; Rand, B. P.; Giebink, N. C.

2014-02-01

181

Atomic polar tensor transferability and atomic charges in the fluoromethane series CH{sub x}F{sub 4-x}  

SciTech Connect

The atomic polar tensors (APT) of the fluorine and hydrogen atoms for the fluoromethanes are calculated and analyzed with respect to the charge, charge flux, and atomic and homopolar dipole fluxes. Their atomic and bonding contribution are used to discuss the transference of the fluorine and hydrogen APT among these molecules. The contributions of the APT can be written as the sum of a charge and a charge flux tensor leading to a charge-charge flux model. A novel expressive for the atomic charge is obtained on the basis of this proposed charge-charge flux model. The defined atomic charge a calculated for both atoms for this series of molecules. The calculated hydrogen atomic charges vary similarly to the respective equilibrium charges obtained experimentally but in the opposite direction of the Mulliken charges. 15 refs., 1 fig., 8 tabs.

Ferreira, M.M.C. [Universidade Estadual de Campinas (Brazil); Suto, E. [Universidade de Brasilia (Brazil)

1992-10-29

182

Intramolecular charge transfer photoemission of a silicon-based copolymer containing carbazole and divinylbenzene chromophores. Electron transfer across silicon bridges.  

PubMed

A new copolymer consisting of N-isopropylcarbazole/dimethylsilylene bridge/divinylbenzene units was synthesized and characterized. Dual fluorescence was observed in this copolymer in polar solvents. The absence of the second band at the lower transition energy of the two emission maxima in nonpolar solvents and the quantitative correlation of the lower-energy emission band maxima with solvent polarity indicate that the lower-energy emission band arises from an intramolecular charge transfer (ICT) state. A series of model compounds was synthesized to investigate the source of the charge transfer. It was found that the Si-bridged dyad with a single N-isopropylcarbazole and a single divinylbenzene was the minimum structure necessary to observe dual luminescence. The lack of dual luminescence in low-temperature glasses indicates that the ICT requires a conformation change in the copolymer. Analogous behavior in the Si-bridged dyad suggests that the ICT in the copolymer is across the silicon bridge. Results from time-resolved luminescence measurements with picosecond and subnanosecond excitation were used to support the thesis that twisted charge-transfer states are the likely source of the observed dual luminescence. PMID:24901805

Bayda, Malgorzata; Ludwiczak, Monika; Hug, Gordon L; Majchrzak, Mariusz; Marciniec, Bogdan; Marciniak, Bronislaw

2014-07-01

183

Camptothecins guanine interactions: mechanism of charge transfer reaction upon photoactivation  

NASA Astrophysics Data System (ADS)

The potent activity exhibited by the antitumoral camptothecin (CPT) and its analog irinotecan (CPT-11) is known to be related to a close contact between the drug and the nucleic acid base guanine. This specificity of interaction between these two chromophores was examined by following changes in the photophysical properties of the drug using steady-state as well as time-resolved absorption and fluorescence methods. The observed effects on absorption, fluorescence emission and singlet excited state lifetimes give evidence for the occurrence of a stacking complex formation restricted to the quinoline part of CPT or CPT-11 and the guanine base but also with the adenine base. The triplet excited state properties of the drugs have been also characterized in absence and in presence of guanosine monophosphate and reveal the occurrence of an electron transfer from the guanine base to the drug. Support for this conclusion was obtained from the studies of a set of biological targets of various oxido-reduction potentials, adenosine monophosphate, cytidine, cytosine, tryptophan, tyrosine and phenylalanine. This finding gives an interpretation of the CPT-induced guanine photolesions previously reported in the literature. These data taken together are discussed in connection with the drug activity. The stacking complex CPT/guanine is necessary but not sufficient to explain the role of the chirality and of the lactone structure in the function of the drug. A stereospecific interaction with the enzyme topoisomerase I seems necessary to stabilize the stacking complex. The first experiments using time-resolved fluorescence by two-photon excitation confirms that CPT does not bind to the isolated enzyme.

Steenkeste, K.; Guiot, E.; Tfibel, F.; Pernot, P.; Mérola, F.; Georges, P.; Fontaine-Aupart, M. P.

2002-01-01

184

Structure-property relationships for three indoline dyes used in dye-sensitized solar cells: TDDFT study of visible absorption and photoinduced charge-transfer processes.  

PubMed

The electronic structures of three D-A-?-A indoline dyes (WS-2, WS-6, and WS-11) used in dye-sensitized solar cells (DSSCs) were studied by performing quantum chemistry calculations. The coplanarity of the A-?-A segment and distinct noncoplanarity of the indoline donor part of each dye were confirmed by checking the calculated geometric parameters. The relationships between molecular modifications and the optical properties of the dyes were derived in terms of the partial density of states, absorption spectrum, frontier molecular orbital, and excited-state charge transfer. 3D real-space analysis of the transition density (TD) and charge difference density (CDD) was also performed to further investigate the excited-state features of the molecular systems, as they provide visualized physical pictures of the charge separation and transfer. It was found that modifying the alkyl chain of the bridge unit near the acceptor unit is an efficient way to decrease dye aggregation and improve DSSC efficiency. Inserting a hexylthiophene group next to the donor unit leads to a complicated molecular structure and a decrease in the charge-transfer ability of the system, which has an unfavorable impact on DSSC performance. PMID:24154611

Li, Huixing; Chen, Maodu

2013-12-01

185

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

SciTech Connect

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.

Iroshnikov, G. S. [Moscow Institute of Physics and Technology (Russian Federation)], E-mail: irosh@orc.ru

2006-11-15

186

Coherent Electronic and Nuclear Dynamics for Charge Transfer in 1-Ethyl-4-(carbomethoxy)pyridinium Iodide  

E-print Network

iodine. Nuclear relaxation of the acceptor induces sub-picosecond decay of the pump-probe polarization charge transfer between iodide and 1-ethyl-4-(carbomethoxy)- pyridinium ions. Pump-probe signal yields unique information on transient material resonances located outside the laser pulse spectrum

Scherer, Norbert F.

187

The synthesis of organic charge transfer hetero-microtubules by crack welding.  

PubMed

The strain-induced cracks in organic microtubules composed of an organic charge transfer (CT) complex of 1,2,4,5-tetracyanobenzene (TCNB) and naphthalene were selectively welded via the formation of secondary CT complexes; this process, in turn, led to the formation of organic hetero-microtubules consisting of multiple segments of two organic CT complexes. PMID:25054622

Kim, J; Chung, J; Hyon, J; Kwon, T; Seo, C; Nam, J; Kang, Y

2014-09-14

188

Vibrational state-to-state calculations of H(+) + O2 charge transfer collisions  

Microsoft Academic Search

Vibrational excitation and vibronic charge transfer in the H(+) + O2 collision at E(CM) = 23 eV are theoretically investigated. The vibronic semiclassical (VSC) and the quantal infinite order sudden (QIOS) descriptions of the quantum dynamics of nondiabatic vibronic processes are directly compared. VSC calculations of differential cross section for such processes are reported, which take into account both the

M. Sizun; D. Grimbert; V. Sidis; M. Baer

1992-01-01

189

Solvent Control of Vibronic Coupling upon Intervalence Charge Transfer Excitation of  

E-print Network

of the system. A polar solvent often largely controls the relative free energies of DA and D+A- in solution.1Solvent Control of Vibronic Coupling upon Intervalence Charge Transfer Excitation of (CN)5FeCNRu(NH3)5 - taken in several solvents show that the Franck-Condon activity of the different CN stretch

190

Second harmonic generation investigations of charge transfer at chemically-modified semiconductor interfaces  

E-print Network

advantages of high spatial and temporal resolution. We have investigated the use of self assembled monolayers. Similar effects were reported for the s-in/p- out polarization combination,2 for various oxide thicknesses-SHG to charge transfer across the Si­SiO2 interface, and trapping leading to a variation in the interfacial

Borguet, Eric

191

Ultrafast photoinduced electron transfer reactions in supramolecular arrays: From charge separation and storage to molecular switches  

SciTech Connect

Photoinduced charge separation reactions form the basis for energy storage processes in both natural and artificial photosynthesis. Moreover, rapid reversible photoinduced electron transfer reactions are a class of photophysical phenomena that can be exploited to develop schemes for optical switching. Examples from each of these fields are discussed.

Wasielewski, M.R.

1992-08-01

192

Ultrafast photoinduced electron transfer reactions in supramolecular arrays: From charge separation and storage to molecular switches  

SciTech Connect

Photoinduced charge separation reactions form the basis for energy storage processes in both natural and artificial photosynthesis. Moreover, rapid reversible photoinduced electron transfer reactions are a class of photophysical phenomena that can be exploited to develop schemes for optical switching. Examples from each of these fields are discussed.

Wasielewski, M.R.

1992-01-01

193

Transition-State Charge Transfer Reveals Electrophilic, Ambiphilic, and Nucleophilic Carbon-Hydrogen Bond Activation  

E-print Network

@scripps.edu To capture the powerful potential of metal-mediated carbon- hydrogen (C-H) bond activation, it is essentialTransition-State Charge Transfer Reveals Electrophilic, Ambiphilic, and Nucleophilic Carbon-Hydrogen Bond Activation Daniel H. Ess,*,, Robert J. Nielsen, William A. Goddard III,*, and Roy A. Periana

Goddard III, William A.

194

Surface modification and charge transfer studies at silicon and gallium arsenide interfaces  

NASA Astrophysics Data System (ADS)

This thesis describes chemical modifications of Si and GaAs surfaces, as a means of gaining control over the physical, chemical and electrical properties of these surfaces and of the interfaces formed from these surfaces. The Current-voltage properties of n-GaAs photoanodes were evaluated in KOH-Sesp{-/2-}(aq), CHsb3CN-ferrocene (Fc)sp{+/0}, and CHsb3CN-methyl viologen (MV)sp{2+/+} solutions. Chemisorption of transition-metal ions (Rhsp{III},\\ Rhsp{III},\\ Cosp{III},\\ Ossp{III}) onto GaAs has been shown previously to effect improved photoanode behavior for n-GaAs/KOH-Sesp{-/2-}(aq) contacts, but it is not clear whether the chemisorbed metal forms a buried semiconductor/metal (Schottky) junction or results in a "hybrid" semiconductor/metal/liquid contact. Metal ion treated n-GaAs photoanodes displayed different open circuit voltages in contact with each electrolyte solution investigated. The role of the chemisorbed metal in the n-GaAs/KOH-Sesp{-/2-}(aq) system is, therefore, best described as catalyzing interfacial charge transfer at the semiconductor/liquid interface, as opposed to forming a semiconductor/metal or semiconductor/insulator/metal contact. The ability to modify Si surface without partial oxidation or formation of electrical defects is potentially important. However, little is known about the chemistry of these surfaces under ambient temperature and pressure. A two-step halogenation/alkylation route to chemical functionalization of Si(111) surface is described, that allows covalent attachment of alkyl functionalities without concomitant oxidation of the silicon surface. In the first step, a hydrogen terminated silicon surface is chlorinated to obtain a chlorine terminated silicon surface. In the second step, the chlorinated surface is reacted with alkyl lithium or alkyl Grignard to obtain an alkyl terminated surface. The surface of silicon is extensively analyzed using a number of techniques such as XPS, HREELS, IRS, AES, TPD etc. The alkyl terminated surfaces are more resistant to oxidation in air and in contact with wet chemical environments than the H-terminated surface. Current-voltage and capacitance-voltage measurements of the alkyl terminated surfaces in CHsb3OH-Mesb2Fcsp{+/0} indicate that the electrical properties of these surfaces are very similar to those of a H-terminated surface. The alkyl overlayers provide a small resistance to charge transfer across the Si/liquid interface but do not shift the band edges or induce additional surface recombination. I-V characteristics of n-Si/alkyl/Au MIS devices indicate that these junctions behave largely like n-Si/Au Schottky junctions. The efficacy of alkyl overlayers in preventing photooxidation and photocorrosion of n-silicon surfaces was measured in contact with Fe(CN)sb6sp{3-/4-}(aq) and with CHsb3OH-Mesb2Fcsp{+/0} containing known amounts of water. The alkyl terminated surfaces consistently show better I-V characteristics and lower oxidation than the H-terminated surface, indicating that stability to oxidation had been achieved without any significant compromise in the electrical quality of the silicon surface.

Bansal, Ashish

195

Photoexcitation of electronic instabilities in one-dimensional charge-transfer systems  

NASA Astrophysics Data System (ADS)

We investigate the real-time dynamics of photoexcited electronic instabilities in a charge-transfer system model, using the time-dependent density matrix renormalization group method. The model of choice was the quarter-filled one-dimensional extended Peierls-Hubbard Hamiltonian interacting with classical few-cycle electromagnetic radiation. The results show that only one electronic instability drives the main features of the photogenerated time-dependent behavior. Indeed, the photoresponse of the system shows a large enhancement of the 4kF (bond and charge) instability whereas the 2kF state remains largely unaffected. This conclusion holds regardless of the nature of the optical excitations and whether the system is perturbed resonantly or not. Our results suggest potential applications of charge-transfer systems with slow phononic dynamics as optoelectronic switching devices.

Rincón, Julián; Al-Hassanieh, K. A.; Feiguin, Adrian E.; Dagotto, Elbio

2014-10-01

196

Pressure-induced charge transfer in lanthanum nickel ferrate (?) and analogies to composition-driven charge transfer in dilanthanum cuprate ?: an infrared study  

NASA Astrophysics Data System (ADS)

A reversible pressure-induced phase transition in lanthanum nickel ferrate 0953-8984/9/50/021/img8 manifests itself in the infrared spectrum of the transition metal - oxygen stretching 0953-8984/9/50/021/img9 modes by the emergence of new peaks at pressures greater than 0953-8984/9/50/021/img10. Analogies to this transition are made by considering charge transfer in dilanthanum cuprate 0953-8984/9/50/021/img11 and its modification by partial substitution of copper ions by chromium ions.

Mortimer, Richard; Powell, James G.; Vasanthacharya, Nagasampagi Y.

1997-12-01

197

Electric conductivity and phase diagram of a mixed-stack charge-transfer crystal: Tetrathiafulvalene-p-chloranil  

NASA Astrophysics Data System (ADS)

The electric conductivity has been measured on the mixed-stack charge-transfer crystal tetrathiafulvalene (TTF) -p-chloranil (CA) as a function of temperature (T>30 K) and pressure (P<11 kbar). On the basis of the experimental results, a P-T phase diagram is presented for the charge-transfer state in TTF-CA.

Mitani, T.; Kaneko, Y.; Tanuma, S.; Tokura, Y.; Koda, T.; Saito, G.

1987-01-01

198

Highly efficient nonradiative energy transfer using charged CdSe/ZnS nanocrystals for light-harvesting in solution  

E-print Network

Highly efficient nonradiative energy transfer using charged CdSe/ZnS nanocrystals for light 18.16 to 1.88 ns with FRET efficiencies 90% in solution. These strong modifications allow for light Förster resonance energy transfer FRET , enabled with the use of light-harvesting, positively charged Cd

Demir, Hilmi Volkan

199

Model for the charge-transfer probability in helium nanodroplets following electron-impact ionization  

SciTech Connect

A theoretical model has been developed to describe the probability of charge transfer from helium cations to dopant molecules inside helium nanodroplets following electron-impact ionization. The location of the initial charge site inside helium nanodroplets subject to electron impact has been investigated and is found to play an important role in understanding the ionization of dopants inside helium droplets. The model is consistent with a charge migration process in small helium droplets that is strongly directed by intermolecular forces originating from the dopant, whereas for large droplets (tens of thousands of helium atoms and larger) the charge migration increasingly takes on the character of a random walk. This suggests a clear droplet size limit for the use of electron-impact mass spectrometry for detecting molecules in helium droplets.

Ellis, Andrew M.; Yang Shengfu [Department of Chemistry, University of Leicester, University Road, Leicester LE1 7RH (United Kingdom)

2007-09-15

200

Lead methylammonium triiodide perovskite-based solar cells: an interfacial charge-transfer investigation.  

PubMed

This work reports on an investigation into interfacial charge transfer in CH3 NH3 PbI3 perovskite solar cells by using anatase TiO2 nanocuboids enclosed by active {100} and {001} facets. The devices show 6.0 and 8.0?% power conversion efficiency with and without hole-transport material. Transient photovoltage/photocurrent decay and charge extraction, as well as impedance spectroscopy measurements, reveal that carbon materials are effective counter electrodes in perovskite solar cells. The photogenerated charges are observed to be stored in mesoporous TiO2 film under illumination and in the CH3 NH3 PbI3 layer in the dark. The use of 2,2',7,7'-tetrakis(N,N-di-p-methoxyphenylamine)-9,9-spirobifluorene (spiro-MeOTAD) as a hole-transport material accelerates interfacial charge recombination between the photogenerated electrons and holes. PMID:25213607

Xu, Xiaobao; Zhang, Hua; Cao, Kun; Cui, Jin; Lu, Jianfeng; Zeng, Xianwei; Shen, Yan; Wang, Mingkui

2014-11-01

201

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

NASA Technical Reports Server (NTRS)

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.

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

2000-01-01

202

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

NASA Technical Reports Server (NTRS)

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.

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

2003-01-01

203

Monovalent counterion distributions at highly charged water interfaces: Proton-transfer and Poisson-Boltzmann theory  

SciTech Connect

Surface sensitive synchrotron-x-ray scattering studies reveal the distributions of monovalent ions next to highly charged interfaces. A lipid phosphate (dihexadecyl hydrogen phosphate) was spread as a monolayer at the air-water interface, containing CsI at various concentrations. Using anomalous reflectivity off and at the L{sub 3} Cs{sup +} resonance, we provide spatial counterion distributions (Cs{sup +}) next to the negatively charged interface over a wide range of ionic concentrations. We argue that at low salt concentrations and for pure water the enhanced concentration of hydroniums H{sub 3}O{sup +} at the interface leads to proton transfer back to the phosphate group by a high contact potential, whereas high salt concentrations lower the contact potential resulting in proton release and increased surface charge density. The experimental ionic distributions are in excellent agreement with a renormalized-surface-charge Poisson-Boltzmann theory without fitting parameters or additional assumptions.

Bu, W.; Vaknin, D.; Travesset, A. (Iowa State)

2010-07-13

204

Spectroscopic study of thermal transfer and charge transfer in an analytic high frequency plasma  

Microsoft Academic Search

The analysis of energy transfer mechanisms, the characterization of water and hydrogen effects on the excitation processes, and the determination of interferences between alkaline ions are described. An induction coupled plasma generator was used. The measurement system is implemented with ultrasonic aerosol flow, optical instruments and data processing. The results show that when the total excitation energy is similar to

Yong Qiu Tang

1986-01-01

205

Calculation of rates of exciton dissociation into hot charge-transfer states in model organic photovoltaic interfaces  

NASA Astrophysics Data System (ADS)

We investigate the process of exciton dissociation in ordered and disordered model donor/acceptor systems and describe a method to calculate exciton dissociation rates. We consider a one-dimensional system with Frenkel states in the donor material and states where charge transfer has taken place between donor and acceptor. We introduce a Green's function approach to calculate the generation rates of charge-transfer states. For disorder in the Frenkel states we find a clear exponential dependence of charge dissociation rates with exciton-interface distance, with a distance decay constant ? that increases linearly with the amount of disorder. Disorder in the parameters that describe (final) charge-transfer states has little effect on the rates. Exciton dissociation invariably leads to partially separated charges. In all cases final states are “hot” charge-transfer states, with electron and hole located far from the interface.

Vázquez, Héctor; Troisi, Alessandro

2013-11-01

206

Mass transfer within electrostatic precipitators: in-flight adsorption of mercury by charged suspended particulates.  

PubMed

Electrostatic precipitation is the dominant method of particulate control used for coal combustion, and varying degrees of mercury capture and transformation have been reported across ESPs. Nevertheless, the fate of gas-phase mercury within an ESP remains poorly understood. The present analysis focuses on the gas-particle mass transfer that occurs within a charged aerosol in an ESP. As a necessary step in gas-phase mercury adsorption or transformation, gas-particle mass transfer-particularly in configurations other than fixed beds-has received far less attention than studies of adsorption kinetics. Our previous analysis showed that only a small fraction of gas-phase mercury entering an ESP is likelyto be adsorbed by collected particulate matter on the plate electrodes. The present simplified analysis provides insight into gas-particle mass transfer within an ESP under two limiting conditions: laminar and turbulent fluid flows. The analysis reveals that during the process of particulate collection, gas-particle mass transfer can be quite high, easily exceeding the mass transfer to ESP plate electrodes in most cases. Decreasing particle size, increasing particle mass loading, and increasing temperature all result in increased gas-particle mass transfer. The analysis predicts significantly greater gas-particle mass transfer in the laminar limitthan in the turbulent limit; however, the differences become negligible under conditions where other factors, such as total mass of suspended particulates, are the controlling mass transfer parameters. Results are compared to selected pilot- and full-scale sorbent injection data. PMID:16786702

Clack, Herek L

2006-06-01

207

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

PubMed

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

Akimov, Alexey V; Prezhdo, Oleg V

2014-01-29

208

On the origin of ionicity in ionic liquids. Ion pairing versus charge transfer.  

PubMed

In this paper we show by using static DFT calculations and classical molecular dynamics simulations that the charge transfer between ionic liquid ions plays a major role in the observed discrepancies between the overall mobility of the ions and the observed conductivities of the corresponding ionic liquids, while it also directly suppresses the association of oppositely charged ions, thus the ion pairing. Accordingly, in electrochemical applications of these materials it is important to consider this reduction of the total charges on the ions, which can greatly affect the performance of the given process or device in which the ionic liquid is used. By slightly shifting from the salt-like to a molecular liquid-like system via the decreased charges, the charge transfer also fluidizes the ionic liquid. We believe that this vital information on the molecular level structure of ionic liquids offers a better understanding of these materials, and allows us to improve the a priori design of ionic liquids for any given purpose. PMID:25012230

Hollóczki, Oldamur; Malberg, Friedrich; Welton, Tom; Kirchner, Barbara

2014-08-28

209

Charge-dependent dissociation of insulin cations via ion/ion electron transfer  

NASA Astrophysics Data System (ADS)

The dissociation reactions of various charge states of insulin cations obtained directly from nano-electrospray were investigated as a result of ion/ion electron transfer from azobenzene anions. Data were collected with and without simultaneous ion trap collisional excitation of the first generation charge-reduced product during the ion/ion reaction period. Neither separation of the two constituent chains nor cleavages within the loop defined by the disulfide bridges were observed under normal electron transfer dissociation (ETD) conditions for any of the charge states studied. However, substantial sequence coverage (exocyclic region: 82.6%; entire protein: 38.8%) outside the ring structure was obtained for insulin +6, while only limited coverage (exocyclic: 43.5%; entire protein: 20.4%) was observed for insulin +5 and no dissociation, aside from low abundance side-chain losses, was noted for insulin +4 and +3 in the normal ETD spectra. When the first generation charge-reduced precursor ions were subjected to collisional activation during the ion/ion reaction period, higher sequence coverages were obtained for both insulin +5 (entire protein: 34.7%) and +4 (entire protein: 20.4%) with backbone cleavages occurring within the loop defined by the disulfide bonds. Dissociation of insulin +3 was not significantly improved by the additional activation. Separation of the two constituent chains resulting from cleavages of both of the two disulfide bridges that link the chains was observed for insulin +6, +5, and +4 when the charge-reduced species were activated. The dissociation of disulfide linkages in this study suggests that as the charge state decreases, disulfide bond cleavages dominate over N-C[alpha] bond cleavages in the electron transfer dissociation process.

Liu, Jian; Gunawardena, Harsha P.; Huang, Teng-Yi; McLuckey, Scott A.

2008-10-01

210

Boosting the efficiency of quantum dot sensitized solar cells through modulation of interfacial charge transfer.  

PubMed

The demand for clean energy will require the design of nanostructure-based light-harvesting assemblies for the conversion of solar energy into chemical energy (solar fuels) and electrical energy (solar cells). Semiconductor nanocrystals serve as the building blocks for designing next generation solar cells, and metal chalcogenides (e.g., CdS, CdSe, PbS, and PbSe) are particularly useful for harnessing size-dependent optical and electronic properties in these nanostructures. This Account focuses on photoinduced electron transfer processes in quantum dot sensitized solar cells (QDSCs) and discusses strategies to overcome the limitations of various interfacial electron transfer processes. The heterojunction of two semiconductor nanocrystals with matched band energies (e.g., TiO(2) and CdSe) facilitates charge separation. The rate at which these separated charge carriers are driven toward opposing electrodes is a major factor that dictates the overall photocurrent generation efficiency. The hole transfer at the semiconductor remains a major bottleneck in QDSCs. For example, the rate constant for hole transfer is 2-3 orders of magnitude lower than the electron injection from excited CdSe into oxide (e.g., TiO(2)) semiconductor. Disparity between the electron and hole scavenging rate leads to further accumulation of holes within the CdSe QD and increases the rate of electron-hole recombination. To overcome the losses due to charge recombination processes at the interface, researchers need to accelerate electron and hole transport. The power conversion efficiency for liquid junction and solid state quantum dot solar cells, which is in the range of 5-6%, represents a significant advance toward effective utilization of nanomaterials for solar cells. The design of new semiconductor architectures could address many of the issues related to modulation of various charge transfer steps. With the resolution of those problems, the efficiencies of QDSCs could approach those of dye sensitized solar cells (DSSC) and organic photovoltaics. PMID:22493938

Kamat, Prashant V

2012-11-20

211

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

NASA Astrophysics Data System (ADS)

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.

May, Volkhard; Kühn, Oliver

2004-02-01

212

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

SciTech Connect

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.

Chekalin, S. V. [Russian Academy of Sciences, Institute of Spectroscopy (Russian Federation)], E-mail: chekalin@isan.troitsk.ru

2006-11-15

213

Chiral selectivity in the charge-transfer bleaching of single-walled carbon-nanotube spectra  

NASA Astrophysics Data System (ADS)

Chiral selective reactivity and redox chemistry of carbon nanotubes are two emerging fields of nanoscience. These areas hold strong promise for producing methods for isolating nanotubes into pure samples of a single electronic type, and for reversible doping of nanotubes for electronics applications. Here, we study the selective reactivity of single-walled carbon nanotubes with organic acceptor molecules. We observe spectral bleaching of the nanotube electronic transitions consistent with an electron-transfer reaction occurring from the nanotubes to the organic acceptors. The reaction kinetics are found to have a strong chiral dependence, with rates being slowest for large-bandgap species and increasing for smaller-bandgap nanotubes. The chiral-dependent kinetics can be tuned to effectively freeze the reacted spectra at a fixed chiral distribution. Such tunable redox chemistry may be important for future applications in reversible non-covalent modification of nanotube electronic properties and in chiral selective separations.

O'Connell, Michael J.; Eibergen, Ezra E.; Doorn, Stephen K.

2005-05-01

214

TCD-IISc Symposium "Chemistry & Chemical Biology"  

E-print Network

. Valeria Nicolosi, ERC Research Professor. Research interest in the liquid-phase processing and atom and catalysis . Robert Baker, Assistant Professor in Chemistry. Research interest in fundamental and applied and photochemical reactions, with emphasis on radical chemistry and charge transfer at disordered carbons and oxide

O'Mahony, Donal E.

215

First-Principles Description of Charge Transfer in Donor-Acceptor Compounds from Self-Consistent Many-Body Perturbation Theory  

E-print Network

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 experiment and accurate quantum-chemistry calculations. The capability of hybrid exchange-correlation functionals of reproducing this feature depends critically on the fraction of exact exchange $\\alpha$, as for small values of $\\alpha$ 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 $\\alpha$. 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 $\\alpha$ values. In sc-GW, where the Gre...

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

2014-01-01

216

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

NASA Astrophysics Data System (ADS)

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.

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

2014-08-01

217

Problems of Rate Chemistry in the Flight Regimes of Aeroassisted Orbital Transfer Vehicles  

NASA Technical Reports Server (NTRS)

The dissociating and ionizing nonequilibrium flows behind a normal shock wave are calculated for the density and vehicle regimes appropriate for aeroassisted orbital transfer vehicles; the departure of vibrational and electron temperatures from the gas temperature as well as viscous transport phenomena are accounted for. From the thermodynamic properties so determined, radiative power emission is calculated using an existing code. The resulting radiation characteristics are compared with the available experimental data. Chemical parameters are varied to Investigate their effect on the radiation characteristics. It is concluded that the current knowledge of rate chemistry leads to a factor-of-4 uncertainty In nonequilibrium radiation intensities. The chemical parameters that must be studied to Improve the accuracy are identified.

Park, Chul

1985-01-01

218

Problems of rate chemistry in the flight regimes of aeroassisted orbital transfer vehicles  

NASA Technical Reports Server (NTRS)

The dissociating and ionizing nonequilibrium flows behind a normal shock wave are calculated for the density and vehicle regimes appropriate for aeroassisted orbital transfer vehicles; the departure of vibrational and electron temperatures from the gas temperature as well as viscous transport phenomena are accounted for. From the thermodynamic properties so determined, radiative power emission is calculated using an existing code. The resulting radiation characteristics are compared with the available experimental data. Chemical parameters are varied to investigate their effect on the radiation characteristics. It is concluded that the current knowledge of rate chemistry leads to a factor-of-4 uncertainty in nonequilibrium radiation intensities. The chemical parameters that must be studied to improve the accuracy are identified.

Park, C.

1984-01-01

219

Charge-transfer complexes of pyrimidine Schiff bases with aromatic nitro compounds  

NASA Astrophysics Data System (ADS)

Charge-transfer (CT) complexes of pyrimidine Schiff bases, derived from condensation of 2-aminopyrimidine and substituted benzaldehydes, with some aromatic polynitro compounds were prepared and investigated using IR, UV, visible and 1H NMR spectroscopy. For all solid complexes, the main interaction between the donor and acceptor molecules takes place through the ?-?* interaction. Strong and some weak acidic acceptors, in addition interact through proton transfer from the acceptor molecule to the basic centre of the electron donor. Also, an n-?* transition was detected in some complexes.

Issa, Yousry M.; El Ansary, A. L.; Sherif, O. E.; Hassib, H. B.

2011-08-01

220

2184 J . Phys. Chem. 1989, 93, 2184-2187 Other workers report charge transfer corresponding to a single  

E-print Network

transfers such as SN2 reaction^.^ With a few exception^,^" it is usually assumed that the force constant k for electron-transfer rate-reaction free energy gap behavior are discussed. Introduction In the presence; examples include electron-transfer reactions,' time-dependent fluorescence,*and heavy particle charge

Carter, Emily A.

221

Quantum confinement effects on charge-transfer between PbS quantum dots and 4-mercaptopyridine  

SciTech Connect

We obtain the surface enhanced Raman spectra of 4-mercaptopyridine on lead sulfide (PbS) quantum dots as a function of nanoparticle size and excitation wavelength. The nanoparticle radii are selected to be less than the exciton Bohr radius of PbS, enabling the observation of quantum confinement effects on the spectrum. We utilize the variation of nontotally symmetric modes of both b{sub 1} and b{sub 2} symmetry as compared to the totally symmetric a{sub 1} modes to measure the degree of charge-transfer between the molecule and quantum dot. We find both size dependent and wavelength dependent resonances in the range of these measurements, and attribute them to charge-transfer resonances which are responsible for the Raman enhancement.

Fu Xiaoqi [Department of Chemistry, City College of New York, New York, N.Y. 10031 (United States); Key Laboratory for Soft Chemistry and Functional Materials of Ministry Education, Nanjing University of Science and Technology, Nanjing 210094 (China); School of Chemistry and Chemical Engineering, Jiangsu University, Zhenjiang 212013 (China); Pan Yi; Lombardi, John R. [Department of Chemistry, City College of New York, New York, N.Y. 10031 (United States); Wang Xin [Key Laboratory for Soft Chemistry and Functional Materials of Ministry Education, Nanjing University of Science and Technology, Nanjing 210094 (China)

2011-01-14

222

Evaluating push-pull dye efficiency using TD-DFT and charge transfer indices.  

PubMed

The performances of different functionals in the prediction of Charge Transfer excitations (CT) have been assessed, both in terms of quantitative agreement with experimental absorption data and on the basis of a recently developed density based diagnostic index, for a family of 18 recently synthesized push-pull compounds, containing 4-5-dicyannoimidazole (DCI) as an acceptor moiety, six different bridges and three different donor groups. The index used also allows obtaining an estimate of the charge transferred upon excitation (qCT) and of the spatial extent associated with a given electronic transition (DCT). From the computed values of these indices an estimate of the transition energy considering a purely electrostatic model (wCT) can be computed and compared to that expected for an ideal CT between the donor and the acceptor, thus enabling us to estimate the efficiency of the CT transition for the different push-pull systems. PMID:24162782

García, Gregorio; Adamo, Carlo; Ciofini, Ilaria

2013-12-14

223

Cross sections for charge transfer between mercury ions and other metals  

NASA Technical Reports Server (NTRS)

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.

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

1977-01-01

224

WO3-reduced graphene oxide composites with enhanced charge transfer for photoelectrochemical conversion.  

PubMed

Hybrid structures between semiconducting metal oxides and carbon with rational synthesis represent unique device building blocks to optimize the light absorption and charge transfer process for the photoelectrochemical conversion. Here we demonstrate the realization of a WO3-reduced graphene oxide (RGO) nanocomposite via hydrothermal growth of ultrathin WO3 nanoplates directly on fluorine-doped tin oxide (FTO) substrates, followed by in situ photo-reduction to deposit RGO layers on WO3 nanoplate surface. Photoanodes made of the WO3-RGO nanocomposites have achieved a photocurrent density of 2.0 mA cm(-2) at 1.23 V vs. reversible hydrogen electrode (RHE), which is among the highest reported values for photoanodes based on hydrothermally grown WO3. Electrochemical impedance spectroscopy reveals that the increase of photoactivity is attributed to the enhanced charge transfer by the incorporation of RGO, thus suggesting a general approach for designing other metal oxide-RGO hybrid architectures. PMID:23986103

Wu, Haoyu; Xu, Ming; Da, Peimei; Li, Wenjie; Jia, Dingsi; Zheng, Gengfeng

2013-10-14

225

Dependence of charge transfer phenomena during solid-air two-phase flow on particle disperser  

NASA Astrophysics Data System (ADS)

An experimental investigation of the tribo-electrification of particles has been conducted during solid-air two-phase turbulent flow. The current induced in a metal plate by the impact of polymethylmethacrylate (PMMA) particles in a high-speed air flow was measured for two different plate materials. The results indicated that the contact potential difference between the particles and a stainless steel plate was positive, while for a nickel plate it was negative. These results agreed with theoretical contact charge transfer even if not only the particle size but also the kind of metal plate was changed. The specific charge of the PMMA particles during solid-air two-phase flow using an ejector, a stainless steel branch pipe, and a stainless steel straight pipe was measured using a Faraday cage. Although the charge was negative in the ejector, the particles had a positive specific charge at the outlet of the branch pipe, and this positive charge increased in the straight pipe. The charge decay along the flow direction could be reproduced by the charging and relaxation theory. However, the proportional coefficients in the theory changed with the particle size and air velocity. Therefore, an unexpected charge transfer occurred between the ejector and the branch pipe, which could not be explained solely by the contact potential difference. In the ejector, an electrical current in air might have been produced by self-discharge of particles with excess charge between the nickel diffuser in the ejector and the stainless steel nozzle or the stainless steel pipe due to a reversal in the contact potential difference between the PMMA and the stainless steel. The sign of the current depended on the particle size, possibly because the position where the particles impacted depended on their size. When dual coaxial glass pipes were used as a particle disperser, the specific charge of the PMMA particles became more positive along the particle flow direction due to the contact potential difference between the PMMA and the stainless steel. Furthermore, the current in air using the dual coaxial glass pipes was less than that using the ejector.

Tanoue, Ken-ichiro; Suedomi, Yuuki; Honda, Hirotaka; Furutani, Satoshi; Nishimura, Tatsuo; Masuda, Hiroaki

2012-12-01

226

Charge Transfer Between Polypyrrole Coated n-Si Electrodes And Solid Polymer Electrolytes  

Microsoft Academic Search

We have developed photoelectrochemical cells based on rectifying junctions between n-Si and thin film polymer solid electrolytes. We describe various surface modifications applied to the n-Si electrodes which overcome a high activation energy barrier for efficient charge transfer to redox ions in the polymer solid electrolytes.Solvent free solid polymer electrolytes represent an important new class of ionically conducting materials (1).

T. A. Skotheim; O. Inganas

1985-01-01

227

Spontaneous charge transfer at organic-organic homointerfaces to establish thermodynamic equilibrium  

NASA Astrophysics Data System (ADS)

The energy level alignment of ? ,?-dihexylsexithienyl (DH6T) mono- and multilayers on tetrafluorotetracyanoquinodimethane (F4-TCNQ) precovered Ag(111) and polycrystalline Au substrates was investigated with ultraviolet photoelectron spectroscopy. For certain F4-TCNQ precoverages molecular level pinning at DH6T monolayer-multilayer homointerfaces was observed. The pinning behavior shows that thermodynamic equilibrium can be established across hexyl chains via charge transfer, indicating the limited use of these short alkyl chains for insulation in the field of molecular electronics.

Duhm, S.; Glowatzki, H.; Rabe, J. P.; Koch, N.; Johnson, R. L.

2007-03-01

228

Spontaneous charge transfer at organic-organic homointerfaces to establish thermodynamic equilibrium  

Microsoft Academic Search

The energy level alignment of alpha,omega-dihexylsexithienyl (DH6T) mono- and multilayers on tetrafluorotetracyanoquinodimethane (F4-TCNQ) precovered Ag(111) and polycrystalline Au substrates was investigated with ultraviolet photoelectron spectroscopy. For certain F4-TCNQ precoverages molecular level pinning at DH6T monolayer-multilayer homointerfaces was observed. The pinning behavior shows that thermodynamic equilibrium can be established across hexyl chains via charge transfer, indicating the limited use of these

S. Duhm; H. Glowatzki; J. P. Rabe; N. Koch; R. L. Johnson

2007-01-01

229

Imidazole as a parent ?-conjugated backbone in charge-transfer chromophores  

PubMed Central

Summary Research activities in the field of imidazole-derived push–pull systems featuring intramolecular charge transfer (ICT) are reviewed. Design, synthetic pathways, linear and nonlinear optical properties, electrochemistry, structure–property relationships, and the prospective application of such D-?-A organic materials are described. This review focuses on Y-shaped imidazoles, bi- and diimidazoles, benzimidazoles, bis(benzimidazoles), imidazole-4,5-dicarbonitriles, and imidazole-derived chromophores chemically bound to a polymer chain. PMID:22423270

Kulhanek, Jiri

2012-01-01

230

Studies on Intramolecular Charge Transfer Fluorescence Probe and DNA Binding Characteristics  

Microsoft Academic Search

An intramolecular charge transfer fluorescence probe of 4?-N,N-dimethylamino-4-amino-chalcone(DMAC) exhibits characteristics clearly correlated with the polarity of solvents. The interaction of this fluorescence probe with calf thymus DNA has been investigated. Generally, DMAC bound to DNA shows marked changes in fluorescence and absorbance properties compared to the spectral characteristics of the free form in solution phase. In the presence of DNA

Xin Yang; Guo-Li Shen; Ru-Qin Yu

1999-01-01

231

Hydrogen bonding and charge transfer in some interactions involving methyl glyoxal and formamide  

Microsoft Academic Search

Summary  The possibility of hydrogen bonding between the nucleic-acid bases and methyl glyoxal or formamide is studied through an IEH\\u000a calculation; the charge transfer and hydrogen bond indices support this hypothesis. The CH...Y indices are similar to those\\u000a of usual hydrogen bonds. In six of the nine configurations previously proposed by other authors in order to analyse the H2S-formamide interactions, formamide

M. Giambiagi; C. Alarcon Chamarelli

1984-01-01

232

A charge-transfer amplifier and an encoded-bus architecture for low-power SRAM's  

Microsoft Academic Search

This paper proposes and reports a low-power SRAM using a charge-transfer (CT) pre-sense amplifier and a bus signal encoding scheme. The CT amplifier overcomes the Vth relative difference between the pair MOS transistors, and thus reduces the input offset voltage. The encoded-bus scheme reduces the number of signals being switched to cut the capacitive load. These read-path dynamic circuits have

Shoichiro Kawashima; Toshihiko Mori; Ryuhei Sasagawa; Makoto Hamaminato; Shigetoshi Wakayama; Kazuo Sukegawa; Isao Fukushi

1998-01-01

233

Low-distortion double-sampling ?? ADC using a direct-charge-transfer adder  

Microsoft Academic Search

A new double-sampling architecture is proposed for wideband low-power ?? ADC design. A direct-charge-transfer adder is used to reduce the bandwidth requirements for the adder, and the loop filter's linearity requirement is relaxed by using a low-distortion topology. To verify the proposed design methodology, a 2nd order double-sampling delta-sigma ADC using the proposed scheme has been designed and simulated.

Yan Wang; G. C. Temes

2009-01-01

234

Charge-transfer molecular complexes of 2-amino-1,3,4-thiadiazoles  

NASA Astrophysics Data System (ADS)

Charge-transfer molecular complexes of 2-amino-5-X-1,3,4-thiadiazole (D) (X = H, I; = CH 3, II; = phenyl, III) with some ?-electron acceptors (A) have been studied in methanol. It is concluded that these complexes are predominantly of the ?-? type. Solid 1:1 CT complexes of the donors I- III with ?-acceptors DDQ and TCNE have been synthesized and characterized.

Mahmoud, M. R.; Hamed, M. M. A.; Salman, H. M. A.

235

Ultrafast interfacial charge transfer dynamics in dye-sensitized and quantum dot solar cell  

NASA Astrophysics Data System (ADS)

Dye sensitized solar cell (DSSC) appeared to be one of the good discovery for the solution of energy problem. We have been involved in studying ultrafast interfacial electron transfer dynamics in DSSC using femtosecond laser spectroscopy. However it has been realized that it is very difficult to design and develop higher efficient one, due to thermodynamic limitation. Again in DSSC most of the absorbed photon energy is lost as heat within the cell, which apart from decreasing the efficiency also destabilizes the device. It has been realized that quantum dot solar cell (QDSC) are the best bet where the sensitizer dye molecules can be replaced by suitable quantum dot (QD) materials in solar cell. The quantum-confinement effect in semiconductors modifies their electronic structure, which is a very important aspect of these materials. For photovoltaic applications, a long-lived charge separation remains one of the most essential criteria. One of the problems in using QDs for photovoltaic applications is their fast charge recombination caused by nonradiative Auger processes, which occur predominantly at lower particle sizes due to an increase in the Coulomb interaction between electrons and holes. Various approaches, such as the use of metal-semiconductor composites, semiconductor-polymer composite, and semiconductor core-shell heterostructures, have been attempted to minimize the fast recombination between electrons and holes. To make higher efficient solar devices it has been realised that it is very important to understand charge carrier and electron transfer dynamics in QD and QD sensitized semiconductor nanostructured materials. In the present talk, we are going to discuss on recent works on ultrafast electron transfer dynamics in dye-sensitized TiO2 nanoparticles/film [1-12] and charge (electron/hole) transfer dynamics in quantum dot core-shell nano-structured materials [13-17].

Ghosh, Hirendra N.

2013-02-01

236

NMR study of partial charge transfer in N-methylphenazinium-tetracyanoquinodimethane (NMP-TCNQ)  

Microsoft Academic Search

The field dependence of the proton NMR second moment M2(H, T) of powder N-methylphenazinium-tetracyanoquinodimethane (NMP-TCNQ) and (DMP-TCNQ), the analogous material with a deuterated methyl, shows that at 4.2°K there are unpaired electrons localized on ~ 6% of the NMP sites. This strongly suggests partial (gamma=0.94) charge transfer in NMP+gamma-TCNQ-gamma, a room-temperature organic conductor previously thought to be fully ionic (gamma=1).

M. A. Butler; F. Wudl; Z. G. Soos

1975-01-01

237

Simulations of the Temperature Dependence of the Charge Transfer Inefficiency in a High-Speed CCD  

Microsoft Academic Search

Results of detailed simulations of the charge transfer inefficiency of a prototype serial readout CCD chip are reported. The effect of radiation damage on the chip operating in a particle detector at high frequency at a future accelerator is studied, specifically the creation of two electron trap levels, 0.17 eV and 0.44 eV below the bottom of the conduction band.

André Sopczak; Khaled Bekhouche; Chris Bowdery; Chris Damerell; Gavin Davies; Lakhdar Dehimi; Tim Greenshaw; Michal Koziel; Konstantin Stefanov; James Walder; Tim Woolliscroft; Steve Worm

2007-01-01

238

Study of charge transfer complexes of menadione (vitamin K 3) with a series of anilines  

Microsoft Academic Search

Menadione (vitamin K3) has been shown to form charge transfer complexes with N,N-dimethyl aniline, N,N-dimethyl p-toluidine and N,N-dimethyl m-toluidine in CCl4 medium. The CT transition energies are well correlated with the ionisation potentials of the anilines. The formation constants of the complexes have been determined at a number of temperatures from which the enthalpies and entropies of formation have been

Purnendu Pal; Avijit Saha; Asok K Mukherjee; Dulal C Mukherjee

2004-01-01

239

A fibre-optic oxygen sensor based on contact charge-transfer absorption  

Microsoft Academic Search

A fibre-optic oxygen (O2) sensor monitoring at a wavelength of 400 nm has been successfully developed for the determination of gaseous O2. Its working principle is based on the contact charge-transfer absorption of N,N-dimethyl-p-toluidine and O2. The response to changes in O2 concentrations is reversible and in good agreement with the Beer-Lambert law. The response and recovery times are 12

Ming Fat Choi; Peter Hawkins

1996-01-01

240

Hydroquinone–Benzonitrile System: Intramolecular Charge-Transfer and Computational Studies  

Microsoft Academic Search

A novel intramolecular donor–acceptor system of hydroquinone–benzonitrile was synthesized. Its photo-induced intramolecular\\u000a charge-transfer (ICT) transition was confirmed by (1) shift of its emission maximum with increasing solvent polarity, (2)\\u000a high dipole moment for the ICT excited state calculated from the Lippert equation, and (3) its HOMO and LUMO. According to\\u000a the extent of separation between HOMO and LUMO, it is

Kuangsen Sung; Pin-Mei Huang; Chi-Han Zhou

2007-01-01

241

Discotic charge transfer twins Structure and mesophase behaviour of covalently linked triphenylenes and trinitrofluorenones  

Microsoft Academic Search

Discotic charge transfer twins, a novel class of discotic liquid-crystalline compounds were studied. These compounds consist of triphenylene units (as donors) which are chemically linked via flexible spacers of various lengths to trinitrofluorenone units (acting as acceptor). They display a liquid-crystalline phase over a wide temperature range extending up to 240–260°C. Based on X-ray analysis a structural model is proposed

M. Möller; V. Tsukruk; J. H. Wendorff; H. Bengs; H. Ringsdorf

1992-01-01

242

Investigation of Charge Transfer and Degradation Features in Bilayer Zr-ZrO2  

NASA Astrophysics Data System (ADS)

The mechanism of charge transfer in bilayer system Zr-ZrO2 and its conductivity in the initial state and after degradation were investigated. The anodization parameter was calculated, permitting to set the thickness of the oxide layer at anodic oxidation of zirconium. The degradation mechanism of layer systems Zr-ZrO2, determined by increasing the oxide conductivity and accompanied by geometrical growth of oxide layer thickness, is outlined in this article.

Pugachov, A. T.; Starikov, V. V.; Taranukha, A. V.; Udovenko, L. M.; Mamalis, A. G.; Lavrynenko, S. N.

2012-04-01

243

Imidazole as a parent ?-conjugated backbone in charge-transfer chromophores.  

PubMed

Research activities in the field of imidazole-derived push-pull systems featuring intramolecular charge transfer (ICT) are reviewed. Design, synthetic pathways, linear and nonlinear optical properties, electrochemistry, structure-property relationships, and the prospective application of such D-?-A organic materials are described. This review focuses on Y-shaped imidazoles, bi- and diimidazoles, benzimidazoles, bis(benzimidazoles), imidazole-4,5-dicarbonitriles, and imidazole-derived chromophores chemically bound to a polymer chain. PMID:22423270

Kulhánek, Ji?í; Bureš, Filip

2012-01-01

244

Charge-transfer gap closure in transition-metal halides under pressure  

SciTech Connect

Insulator-to-metal transition induced by pressure has been studied in three transition metal iodides: NiI{sub 2}, CoI{sub 2} and FeI{sub 2} using optical absorption and resistivity measurements at room temperature. Comparisons between the results obtained by these two techniques suggested that the closure of the charge-transfer gap is the principal mechanism responsible for the insulator-to-metal transition in these materials.

Chen, A.L.; Yu, P.Y.

1995-01-01

245

Effects of Charge Transfer Agents on the Holographic Parameters of a Photopolymer  

NASA Astrophysics Data System (ADS)

The principle of charge transfer agents was investigated experimentally. There is a compensation effect between triethanolamine (TEA) and diphenyliodonium hexafluorophosphate (DPI) in the polymerization process of a photopolymer. The experimental results illustrate that TEA has a stronger effect in the initial stage of exposure, and DPI has a stronger effect during the propagation stage of the polymerization process. We explain the main contributions of DPI in the superadditive photopolymer kinetics that results in an obvious increase of sensitivity.

Yao, Hua-Wen; Huang, Ming-Ju; Chen, Zhong-Yu; Gan, Fu-Xi

2002-07-01

246

The Effects of Charge Transfer Inefficiency (CTI) on Galaxy Shape Measurements  

NASA Astrophysics Data System (ADS)

We examine the effects of charge transfer inefficiency (CTI) during CCD readout on the demanding galaxy shape measurements required by studies of weak gravitational lensing. We simulate a CCD readout with CTI such as that caused by charged particle radiation damage in space-based detectors. We verify our simulations on real data from fully depleted p-channel CCDs that have been deliberately irradiated in a laboratory. We show that only charge traps with time constants of the same order as the time between row transfers during readout affect galaxy shape measurements. We simulate deep astronomical images and the process of CCD readout, characterizing the effects of CTI on various galaxy populations. Our code and methods are general and can be applied to any CCDs, once the density and characteristic release times of their charge trap species are known. We baseline our study around p-channel CCDs that have been shown to have charge transfer efficiency up to an order of magnitude better than several models of n-channel CCDs designed for space applications. We predict that for galaxies furthest from the readout registers, bias in the measurement of galaxy shapes, ?e, will increase at a rate of (2.65±0.02)×10-4 yr-1 at L2 for accumulated radiation exposure averaged over the solar cycle. If uncorrected, this will consume the entire shape measurement error budget of a dark energy mission surveying the entire extragalactic sky within about 4 yr of accumulated radiation damage. However, software mitigation techniques demonstrated elsewhere can reduce this by a factor of ˜10, bringing the effect well below mission requirements. This conclusion is valid only for the p-channel CCDs we have modeled; CCDs with higher CTI will fare worse and may not meet the requirements of future dark energy missions. We also discuss additional ways in which hardware could be designed to further minimize the impact of CTI.

Rhodes, Jason; Leauthaud, Alexie; Stoughton, Chris; Massey, Richard; Dawson, Kyle; Kolbe, William; Roe, Natalie

2010-04-01

247

An improved correction method for charge transfer efficiency of XIS onboard Suzaku  

NASA Astrophysics Data System (ADS)

X-ray Imaging Spectrometer (XIS) onboard Suzaku is equipped with the Spaced-row Charge Injection (SCI) technique in order to suppress charge transfer inefficiency (CTI). The accuracy of the energy-scale has been getting worse. With the systematic analysis of the fiveyear data, we found that the accuracy deterioration is due to the unexpected behaviors of CTI: one is some discontinuous increases of CTI and the other is gradual time variation of its dependency on pulse heights of signal charges. By taking them into account, we upgraded the CTI correction method and achieved high accuracy of the energy scale both in the low and highenergy bands (<0.7% at ~1 keV and <0.1% at ~6 keV) over five years.

Sawada, Makoto; Nakashima, Shinya; Nobukawa, Masayoshi; Uchiyama, Hideki; XIS Team

2012-03-01

248

Charge transfer inefficiency in the Hubble Space Telescope since Servicing Mission 4  

NASA Astrophysics Data System (ADS)

We update a physically motivated model of radiation damage in the Hubble Space Telescope Advanced Camera for Surveys/Wide Field Channel, using data up to mid-2010. We find that charge transfer inefficiency increased dramatically before shuttle Servicing Mission 4, with ~1.3 charge traps now present per pixel. During detector readout, charge traps spuriously drag electrons behind all astronomical sources, degrading image quality in a way that affects object photometry, astrometry and morphology. Our detector readout model is robust to changes in operating temperature and background level, and can be used to iteratively remove the trailing by pushing electrons back to where they belong. The result is data taken in mid-2010 that recovers the quality of imaging obtained within the first six months of orbital operations.

Massey, Richard

2010-11-01

249

Effect of geometrical orientation on the charge transfer energetics of supramolecular (tetraphenyl)-porphyrin/fullerens dyads  

NASA Astrophysics Data System (ADS)

We present our study of several low lying charge-transfer (CT) excitation energies for a widely used donor-acceptor system composed of a porphyrin-fullerene pair. The dyad systems consist of C60 and C70 acceptor systems coupled to tetraphenyl-porphyrin (TPP) and tetraphenyl-(zinc)porphyrin (ZnTPP) donor systems in a co-facial orientation. We find that replacing C60 by C70 in a given dyad may increase the lowest charge transfer excitation energy by about 0.27 eV, whereas varying the donor in these complexes had marginal effect on the lowest charge transfer excitation energy. Additionally, we examined the effect of geometrical orientation on the CT energy by calculating several CT excited state energies for an end-on orientation of the porphyrin-fullerene dyads. The CT excitation energies are larger for the end-on orientation in comparison to the co-facial orientation by 0.6 eV - 0.75 eV. The difference is attributed to a reduced exciton binding energy in going from the co-facial to the end-on orientation.

Olguin, Marco; Zope, Rajendra; Baruah, Tunna

2013-03-01

250

Ab initio calculation of H + He$^+$ charge transfer cross sections for plasma physics  

E-print Network

The charge transfer in low energy (0.25 to 150 eV/amu) H($nl$) + He$^+(1s)$ collisions is investigated using a quasi-molecular approach for the $n=2,3$ as well as the first two $n=4$ singlet states. The diabatic potential energy curves of the HeH$^+$ molecular ion are obtained from the adiabatic potential energy curves and the non-adiabatic radial coupling matrix elements using a two-by-two diabatization method, and a time-dependent wave-packet approach is used to calculate the state-to-state cross sections. We find a strong dependence of the charge transfer cross section in the principal and orbital quantum numbers $n$ and $l$ of the initial or final state. We estimate the effect of the non-adiabatic rotational couplings, which is found to be important even at energies below 1 eV/amu. However, the effect is small on the total cross sections at energies below 10 eV/amu. We observe that to calculate charge transfer cross sections in a $n$ manifold, it is only necessary to include states with $n^{\\prime}\\leq n$, and we discuss the limitations of our approach as the number of states increases.

J. Loreau; K. Sodoga; D. Lauvergnat; M. Desouter-Lecomte; N. Vaeck

2010-06-02

251

Ferroelectric phase transition, ionicity condensation, and multicriticality in charge-transfer organic complexes  

NASA Astrophysics Data System (ADS)

To elucidate a pressure-temperature phase diagram of the quasi-one-dimensional mixed-stack charge-transfer complex tetrathiafulvalene-P-chloranil (TTF-CA), we study the quasi-one-dimensional spin-1 Blume-Emery-Griffiths model. In addition to the local charge-transfer energy (?) and the inter-stack polar (dipole-dipole) interaction (J?), we take account of the interstack electrostriction (Coulomb-lattice coupling). Using the self-consistent chain-mean-field theory, where the intra-stack degrees of freedom are exactly treated by the transfer-matrix method, we reproduce the gas-liquid-solid like phase diagram corresponding to the neutral (N), paraelectric ionic (Ipara), and ferroelectric ionic (Iferro) phases, respectively. Our classical model describes an essential point of the multicritical behavior of TTF-CA, i.e., the interchain electrostriction exclusively enhances the charge concentration (ionicity condensation), but does not affect the interchain ferroelectric coupling. This effect leads to appearance of the intermediate Ipara phase in between the N and Iferro phases on the ?-T phase diagram.

Kishine, Jun-Ichiro; Luty, Tadeusz; Yonemitsu, Kenji

2004-02-01

252

Semilocal and hybrid density embedding calculations of ground-state charge-transfer complexes.  

PubMed

We apply the frozen density embedding method, using a full relaxation of embedded densities through a freeze-and-thaw procedure, to study the electronic structure of several benchmark ground-state charge-transfer complexes, in order to assess the merits and limitations of the approach for this class of systems. The calculations are performed using both semilocal and hybrid exchange-correlation (XC) functionals. The results show that embedding calculations using semilocal XC functionals yield rather large deviations with respect to the corresponding supermolecular calculations. Due to a large error cancellation effect, however, they can often provide a relatively good description of the electronic structure of charge-transfer complexes, in contrast to supermolecular calculations performed at the same level of theory. On the contrary, when hybrid XC functionals are employed, both embedding and supermolecular calculations agree very well with each other and with the reference benchmark results. In conclusion, for the study of ground-state charge-transfer complexes via embedding calculations hybrid XC functionals are the method of choice due to their higher reliability and superior performance. PMID:23556714

Laricchia, S; Fabiano, E; Della Sala, F

2013-03-28

253

Organic photovoltaics: A charge transfer perspective in the study of donor-acceptor systems  

NASA Astrophysics Data System (ADS)

The present research involves the study of donor-acceptor (D/A) dyad complexes from a charge transfer energy perspective. The aim is to provide insight and predictive understanding into the charge transfer processes of the molecular-level components in donor-acceptor based organic solar cells using computational methods to describe photochemical processes at the quantum mechanical level within the Density Functional Theory (DFT) approximation. Predictive understanding is anchored in reproducing experimental results, wherein the present work a perturbative excited-state DFT method is described in detail and shown to give Charge Transfer (CT) energies in excellent agreement with benchmark experimental data. With an accurate excited state method for calculating CT excitation energies at hand, the present research applies the method to the study of D/A pairs employed in photovoltaic devices. An examination is made of the effect on the CT energetics of varying the donor and acceptor component in the dyad and the changes in the frontier orbital energy levels and CT energies with respect to a varying D/A distance and D/A relative orientation. The results of the perturbative excited state DFT calculations provide direct insight into photovoltaic device efficiency since the CT energy determines the achievable open circuit voltage of a donor-acceptor based organic solar cell device.

Olguin, Marco Augusto

254

The charge transfer characteristic of tetraphenylporphyrin iron chloride Langmuir-Blodgett films  

NASA Astrophysics Data System (ADS)

The charge transfer characteristic of tetraphenylporphyrin iron (III) chloride (FeP) Langmuir-Blodgett (LB) films on the surface of the ITO glass electrode was reported. When the cyclic voltammetry (CV) scanning was running, the charge transfer characteristic was controlled by the oxidation-reduction process of Fe(III)/Fe(II). The charge transfer characteristic was related to the following factors: the cross-sectional area, relative to the electrode, of FeP as the electron donor (or acceptor). The greater the cross-sectional area of the aggregation of FeP as the electron donor (or acceptor) was, the larger the number of the donated (or accepted) electrons was. The projected area of the cross-section on the ITO electrode. The greater the projected area was, the larger the number of the donated (or accepted) electrons was. The distance between the center of the electron donor (or acceptor) of FeP and the surface of ITO electrode. The smaller the distance was, the greater the rate of donating (or accepting) electrons was. The monolayer coverage, which formed because of the FeP lying on the ITO surface in the form of the monomer and aggregate, was more sensitive to detect oxygen.

Du, Y.; Li, Z. H.; Qi, P.; Wang, F.; Liu, D.

2013-11-01

255

Heme photolysis occurs by ultrafast excited state metal-to-ring charge transfer.  

PubMed Central

Ultrafast time-resolved resonance Raman spectra of carbonmonoxy hemoglobin (Hb), nitroxy Hb, and deoxy Hb are compared to determine excited state decay mechanisms for both ligated and unligated hemes. Transient absorption and Raman data provide evidence for a sequential photophysical relaxation pathway common to both ligated and unligated forms of Hb* (photolyzed heme), in which the excited state 1Q decays sequentially: 1Q-->Hb*I-->Hb*II-->Hb ground state. Consistent with the observed kinetics, the lifetimes of these states are <50 fs, approximately 300 fs, and approximately 3 ps for 1Q, Hb*I, and Hb*II, respectively. The transient absorption data support the hypothesis that the Hb*I state results from an ultrafast iron-to-porphyrin ring charge transfer process. The Hb*II state arises from porphyrin ring-to-iron back charge transfer to produce a porphyrin ground state configuration a nonequilibrium iron d-orbital population. Equatorial d-pi* back-bonding of the heme iron to the porphyrin during the lifetime of the Hb*II state accounts for the time-resolved resonance Raman shifts on the approximately 3 ps time scale. The proposed photophysical pathway suggests that iron-to-ring charge transfer is the key event in the mechanism of photolysis of diatomic ligands following a porphyrin ring pi-pi* transition. PMID:11325737

Franzen, S; Kiger, L; Poyart, C; Martin, J L

2001-01-01

256

Infrared photocurrent response of charge-transfer exciton in polymer bulk heterojunction  

SciTech Connect

We study the charge-transfer exciton absorption and photocurrent response in solution-processed bulk heterojunction based on poly(3-hexylthiophene) donor and (6,6)-phenyl-C{sub 61}-butyric acid methyl ester acceptor in the near-infrared wavelength region. While the exciton absorption exists only for wavelength below 650 nm, direct generation of charge-transfer exciton formed between the donor and acceptor extends the absorption wavelength to 950 nm. For films with micrometer thickness, the photon-to-electron conversion efficiency is about 60% at 750 nm wavelength under reverse voltage bias and the photocurrent to dark current ratio is about 8.6 at 900 nm and remains 3.6 even at 1000 nm. Photodetector with high sensitivity covering exclusively the 650-1000 nm near infrared region can therefore be made without a low bandgap material. The charge-transfer exciton absorption coefficient and photocurrent sensitivity depend on the annealing condition which controls the donor-acceptor morphology.

Yang, C.-M.; Tsai, P.-Y.; Horng, S.-F.; Lee, K.-C.; Tzeng, S.-R.; Meng, H.-F.; Shy, J.-T.; Shu, C.-F. [Department of Electric Engineering, National Tsing Hua University, Hsinchu 300, Taiwan (China); Institute of Electronic Engineering, National Chiao Tung University, Hsinchu 300, Taiwan (China); Institute of Physics, National Chiao Tung University, Hsinchu 300, Taiwan (China); Department of Physics, National Tsing Hua University, Hsinchu 300, Taiwan (China); Department of Applied Chemistry, National Chiao Tung University, Hsinchu 300, Taiwan (China)

2008-02-25

257

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

NASA Astrophysics Data System (ADS)

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 2O and H 2O/EtOH at 20, 25, 30, 35 and 40 °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 (? H values ranged from -15.58 to -3.10 kJ mol -1; ? S 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.

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

2010-03-01

258

Tuning the entanglement between orbital reconstruction and charge transfer at a film surface  

PubMed Central

The interplay between orbital, charge, spin, and lattice degrees of freedom is at the core of correlated oxides. This is extensively studied at the interface of heterostructures constituted of two-layer or multilayer oxide films. Here, we demonstrate the interactions between orbital reconstruction and charge transfer in the surface regime of ultrathin (La,Sr)MnO3, which is a model system of correlated oxides. The interactions are manipulated in a quantitative manner by surface symmetry-breaking and epitaxial strain, both tensile and compressive. The established charge transfer, accompanied by the formation of oxygen vacancies, provides a conceptually novel vision for the long-term problem of manganites—the severe surface/interface magnetization and conductivity deterioration. The oxygen vacancies are then purposefully tuned by cooling oxygen pressure, markedly improving the performances of differently strained films. Our findings offer a broad opportunity to tailor and benefit from the entanglements between orbit, charge, spin, and lattice at the surface of oxide films. PMID:24569650

Cui, B.; Song, C.; Li, F.; Wang, G. Y.; Mao, H. J.; Peng, J. J.; Zeng, F.; Pan, F.

2014-01-01

259

Chemistry control and corrosion mitigation of heat transfer salts for the fluoride salt reactor (FHR)  

SciTech Connect

The Molten Salt Reactor Experiment (MSRE) was a prototype nuclear reactor which operated from 1965 to 1969 at Oak Ridge National Laboratory. The MSRE used liquid fluoride salts as a heat transfer fluid and solvent for fluoride based {sup 235}U and {sup 233}U fuel. Extensive research was performed in order to optimize the removal of oxide and metal impurities from the reactor's heat transfer salt, 2LiF-BeF{sub 2} (FLiBe). This was done by sparging a mixture of anhydrous hydrofluoric acid and hydrogen gas through the FLiBe at elevated temperatures. The hydrofluoric acid reacted with oxides and hydroxides, fluorinating them while simultaneously releasing water vapor. Metal impurities such as iron and chromium were reduced by hydrogen gas and filtered out of the salt. By removing these impurities, the corrosion of reactor components was minimized. The Univ. of Wisconsin - Madison is currently researching a new chemical purification process for fluoride salts that make use of a less dangerous cleaning gas, nitrogen trifluoride. Nitrogen trifluoride has been predicted as a superior fluorinating agent for fluoride salts. These purified salts will subsequently be used for static and loop corrosion tests on a variety of reactor materials to ensure materials compatibility for the new FHR designs. Demonstration of chemistry control methodologies along with potential reduction in corrosion is essential for the use of a fluoride salts in a next generator nuclear reactor system. (authors)

Kelleher, B. C.; Sellers, S. R.; Anderson, M. H.; Sridharan, K.; Scheele, R. D. [Dept. of Engineering Physics, Univ.of Wisconsin - Madison, 1500 Engineering Drive, Madison, WI 53706 (United States)

2012-07-01

260

Photovoltaic charge generation in organic semiconductors based on long-range energy transfer.  

PubMed

For efficient charge generation in organic solar cells, photogenerated excitons must migrate to a donor/acceptor interface where they can be dissociated. This migration is traditionally presumed to be based on diffusion through the absorber material. Herein we study an alternative migration route--two-step exciton dissociation--whereby the exciton jumps from the donor to acceptor before charge creation takes place. We study this process in a series of multilayer donor/barrier/acceptor samples, where either poly(3-hexylthiophene) (P3HT) or copper phthalocyanine (CuPc) is the donor, fullerene (C60) is the acceptor, and N,N-diphenyl-N,N-bis(3-methylphenyl)-[1,1-bisphenyl]-4,4-diamine (TPD) acts as a barrier to energy transfer. By varying the thickness of the barrier layer, we find that energy transfer from P3HT to C60 proceeds over large distances (?50% probability of transfer across a 11 nm barrier), and that this process is consistent with long-range Förster resonance energy transfer (FRET). Finally, we demonstrate a fundamentally different architecture concept that utilizes the two-step mechanism to enhance performance in a series of P3HT/CuPc/C60 devices. PMID:20735062

Coffey, David C; Ferguson, Andrew J; Kopidakis, Nikos; Rumbles, Garry

2010-09-28

261

Interfacial charge transfer events of BODIPY molecules: single molecule spectroelectrochemistry and substrate effects.  

PubMed

We present single molecule fluorescence and spectroelectrochemistry characteristics of 4,4'-difluoro-4-bora-3a,4a-diaza-s-indacene (BODIPY) bearing two carboxylic acid groups at its 2 and 6 positions. Our study shows a heterogeneous half redox potential distribution for the BODIPY molecules embedded in polystyrene film because of the heterogeneity in their charge transfer rates. Single molecules adsorbed onto a TiO2 surface with ordered nanostructures show surprising fluorescence blinking activity with the shortest ON duration time in comparison to bare glass and indium-tin oxide (ITO) surfaces. Single molecule stability tests show longer ON duration time and a stable fluorescence feature when dispersed in polystyrene thin film than molecules exposed to air. Shorter ON times are observed for molecules. In intimate contact with ITO in comparison to glass substrates. Such a decrease in their fluorescence stability or intensity is explained by charge transfer activities from the dye molecules to the metal oxide surface. Electron transfer and back transfer rates are calculated to illustrate the substrate effects by using a well-established model. PMID:25252244

Liu, Jia; Hill, Caleb M; Pan, Shanlin; Liu, Haiying

2014-10-01

262

Investigation of ground state charge transfer complex between paracetamol and p-chloranil through DFT and UV-visible studies  

NASA Astrophysics Data System (ADS)

The present report deals with the theoretical investigation on ground state structure and charge transfer (CT) transitions in paracetamol (PA)/p-chloranil (CA) complex using Density Functional Theory (DFT) and Time Dependent Density Functional Theory (TD-DFT) method. It is found that Cdbnd O bond length of p-chloranil increases on complexation with paracetamol along with considerable amount of charge transfer from PA to CA. TD-DFT calculations have been performed to analyse the observed UV-visible spectrum of PA-CA charge transferred complex. Interestingly, in addition to expected CT transition, a weak symmetry relieved ?-?* transition in the chloranil is also observed.

Shukla, Madhulata; Srivastava, Nitin; Saha, Satyen

2012-08-01

263

Electron transfer in supercritical carbon dioxide: ultraexothermic charge recombination at the end of the "inverted region".  

PubMed

Charge-recombination rates in contact radical-ion pairs, formed between aromatic hydrocarbons and nitriles in supercritical CO(2) and heptane, decrease with the exothermicity of the reactions until they reach -70 kcal mol(-1), but from there on an increase is observed. The first decrease in rate is typical of the "inverted region" of electron-transfer reactions. The change to an increase in the rate for ultra-exothermic electron transfer indicates a new free-energy relationship. We show that the resulting "double-inverted region" is not due to a change in mechanism. It is an intrinsic property of electron-transfer reactions, and it is due to the increase of the reorganisation energy with the reaction exothermicity. PMID:16548016

Serpa, Carlos; Gomes, Paulo J S; Arnaut, Luis G; Formosinho, Sebastião J; Pina, João; de Melo, J Seixas

2006-06-23

264

Charge Transfer Dissociation (CTD) Mass Spectrometry of Peptide Cations Using Kiloelectronvolt Helium Cations.  

PubMed

A kiloelectronvolt beam of helium ions is used to ionize and fragment precursor peptide ions starting in the 1+ charge state. The electron affinity of helium cations (24.6 eV) exceeds the ionization potential of protonated peptides and can therefore be used to abstract an electron from-or charge exchange with-the isolated precursor ions. Kiloelectronvolt energies are used, (1) to overcome the Coulombic repulsion barrier between the cationic reactants, (2) to overcome ion-defocussing effects in the ion trap, and (3) to provide additional activation energy. Charge transfer dissociation (CTD) of the [M+H](+) precursor of Substance P gives product ions such as [M+H](2+•) and a dominant series of a ions in both the 1+ and 2+ charge states. These observations, along with the less-abundant a + 1 ions, are consistent with ultraviolet photodissociation (UVPD) results of others and indicate that C-C? cleavages are possible through charge exchange with helium ions. Although the efficiencies and timescale of CTD are not yet suitable for on-line chromatography, this new approach to ion activation provides an additional potential tool for the interrogation of gas phase ions. PMID:25231159

Hoffmann, William D; Jackson, Glen P

2014-11-01

265

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

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(t2 g) and Ti(t2 g) 3 d orbitals. ?? 1987 Springer-Verlag.

Sherman, D. M.

1987-01-01

266

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

NASA Astrophysics Data System (ADS)

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 10-2 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.

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

2014-01-01

267

Theoretical study of through-space and through-bond electron transfer within positively charged peptides in the gas phase  

NASA Astrophysics Data System (ADS)

As part of an on-going effort to probe mechanisms for disulfide and backbone N-C[alpha] cleavage under electron capture or electron-transfer dissociation mass spectroscopy conditions, theoretical simulations have been carried out to consider the probabilities that a. an electron initially attached to a protonated amine site on a side chain can migrate (through-bond or through-space) to an S-S [sigma]* orbital and thus cause disulfide cleavage; b. an electron initially attached to a protonated site might be transferred (through-bond or through-space) to another protonated site or to a fixed-charge positive site thus allowing the electron to migrate throughout charged sites in a multiply charged peptide. The primary findings of this work include: c. charged-site to S-S [sigma]* orbital through-bond electron transfer can occur at significant probabilities but only over ca. 5 intervening bonds covering up to ca. 15 Å; d. through-space electron transfer from protonated sites to protonated sites or from fixed-charge sites to fixed-charge sites can be facile, but between protonated and fixed-charge sites transfer is very slow; to effect the transfers between equivalent sites, the two sites must come within ca. 5 Å of one another; e. through-space electron transfer from a protonated or fixed-charge site to an S-S [sigma]* orbital can occur with reasonable probability but if the two sites come within ca. 5 Å of one another. Based on these findings, speculation is offered both to interpret recent findings of the McLuckey group on flexible, triply charged peptides and earlier data from the Marshall group on more rigid, helical, doubly charged peptides, both of which contain disulfide linkages that experiments find to be readily cleaved.

Sobczyk, Monika; Neff, Diane; Simons, Jack

2008-02-01

268

Mass transfer within electrostatic precipitators: in-flight adsorption of mercury by charged suspended particulates  

SciTech Connect

Electrostatic precipitation is the dominant method of particulate control used for coal combustion, and varying degrees of mercury capture and transformation have been reported across ESPs. Nevertheless, the fate of gas-phase mercury within an ESP remains poorly understood. The present analysis focuses on the gas-particle mass transfer that occurs within a charged aerosol in an ESP. As a necessary step in gas-phase mercury adsorption or transformation, gas-particle mass transfer - particularly in configurations other than fixed beds - has received far less attention than studies of adsorption kinetics. Our previous analysis showed that only a small fraction of gas-phase mercury entering an ESP is likely to be adsorbed by collected particulate matter on the plate electrodes. The present simplified analysis provides insight into gas-particle mass transfer within an ESP under two limiting conditions: laminar and turbulent fluid flows. The analysis reveals that during the process of particulate collection, gas-particle mass transfer can be quite high, easily exceeding the mass transfer to ESP plate electrodes in most cases. Decreasing particle size, increasing particle mass loading, and increasing temperature all result in increased gas-particle mass transfer. The analysis predicts significantly greater gas-particle mass transfer in the laminar limit than in the turbulent limit; however, the differences become negligible under conditions where other factors, such as total mass of suspended particulates, are the controlling mass transfer parameters. Results are compared to selected pilot- and full-scale sorbent injection data. 41 refs., 5 figs.

Herek L. Clack [Illinois Institute of Technology, Chicago, IL (United States). Department of Mechanical, Materials and Aerospace Engineering

2006-06-01

269

Charge transfer through single molecule contacts: How reliable are rate descriptions?  

PubMed Central

Summary Background: The trend for the fabrication of electrical circuits with nanoscale dimensions has led to impressive progress in the field of molecular electronics in the last decade. However, a theoretical description of molecular contacts as the building blocks of future devices is challenging, as it has to combine the properties of Fermi liquids in the leads with charge and phonon degrees of freedom on the molecule. Outside of ab initio schemes for specific set-ups, generic models reveal the characteristics of transport processes. Particularly appealing are descriptions based on transfer rates successfully used in other contexts such as mesoscopic physics and intramolecular electron transfer. However, a detailed analysis of this scheme in comparison with numerically exact solutions is still elusive. Results: We show that a formulation in terms of transfer rates provides a quantitatively accurate description even in domains of parameter space where strictly it is expected to fail, e.g., at lower temperatures. Typically, intramolecular phonons are distributed according to a voltage driven steady state that can only roughly be captured by a thermal distribution with an effective elevated temperature (heating). An extension of a master equation for the charge–phonon complex, to effectively include the impact of off-diagonal elements of the reduced density matrix, provides very accurate solutions even for stronger electron–phonon coupling. Conclusion: Rate descriptions and master equations offer a versatile model to describe and understand charge transfer processes through molecular junctions. Such methods are computationally orders of magnitude less expensive than elaborate numerical simulations that, however, provide exact solutions as benchmarks. Adjustable parameters obtained, e.g., from ab initio calculations allow for the treatment of various realizations. Even though not as rigorously formulated as, e.g., nonequilibrium Green’s function methods, they are conceptually simpler, more flexible for extensions, and from a practical point of view provide accurate results as long as strong quantum correlations do not modify the properties of the relevant subunits substantially. PMID:22003449

Kecke, L; Ankerhold, J

2011-01-01

270

Proton transfer assisted charge transfer phenomena in photochromic Schiff bases and effect of -NEt2 groups to the anil Schiff bases.  

PubMed

Photochromic Schiff bases 5-diethylamino-2-[(4-diethylamino-benzylidene)-hydrazonomethyl]-phenol (DDBHP) and N,N'-bis(4-N,N-diethylaminosalisalidene) hydrazine (DEASH) with both the proton and charge transfer moieties have been synthesized, and their photophysical properties such as excited state intramolecular charge transfer (ICT) and proton transfer (ESIPT) processes have been reported on the basis of steady-state and time-resolved spectral measurement in various solvents. The ground-state six-membered intramolecular hydrogen bonding network at the proton transfer site accelerates the ESIPT process for these compounds. Both the compounds show large Stokes-shifted emission bands for proton transfer and charge transfer processes. The hydrogen bonding solvents play a crucial role in these photophysical processes. Excited-state dipole moment of DDBHP and DEASH calculated by the solvatochromic method supports the polar character of the charge transfer excited state. Introduction of -NEt(2) groups to the reported salicylaldehyde azine (SAA) Schiff base results an increase in fluorescence lifetime from femtosecond to picosecond time scale for the proton transfer process. PMID:23098054

Jana, Sankar; Dalapati, Sasanka; Guchhait, Nikhil

2012-11-15

271

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

Code of Federal Regulations, 2010 CFR

...CERTAIN BULK DANGEROUS CARGOES SHIPS CARRYING BULK LIQUID, LIQUEFIED GAS, OR COMPRESSED GAS HAZARDOUS MATERIALS Operations...Procedures § 153.957 Persons in charge of transferring liquid cargo in bulk or cleaning cargo tanks. (a)...

2010-10-01

272

First principles investigation of water adsorption and charge transfer on III-V(110) semiconductor surfaces  

NASA Astrophysics Data System (ADS)

We report a DFT/GGA study of water adsorption and charge transfer at the relaxed (110) surfaces of several III-V binary semiconductors: GaAs, GaSb, and InAs. Our calculations are the first to show that adsorption of dissociated water changes the (110) surface structure. The characteristic III-V bond rotation through an angle of 30° is reversed. The buckled III-V bond at the semiconductor/water interface rotates into the surface through a new angle, which we calculate to be approximately 11° on all three binaries. Only dissociation of water - as opposed to chemisorption or physisorption - leads to this pseudo-unrelaxed configuration. We calculate geometries and reaction energies for several different adsorption mechanisms and find that molecular adsorption is the most favorable. We are able to reproduce binding configurations and energies for known adsorption sites on GaAs(110), but we also show new calculations for water on GaSb(110) and InAs(110). Lastly, we calculate the shift in electronic work function and induced surface dipole moment due to adsorbed water. We show that shifts in work function maximize at 1 ML of water, consistent with previous experimental works. Analysis of the partial charges and electron density reveals that adsorption of water polarizes the (110) surface, leading to local charge transfer across the semiconductor/water interface.

Williams, Kristen S.; Lenhart, Joseph L.; Andzelm, Jan W.; Bandara, Sumith V.; Baril, Neil F.; Henry, Nathan C.; Tidrow, Meimei Z.

2014-04-01

273

An improved model of Charge Transfer Inefficiency and correction algorithm for the Hubble Space Telescope  

E-print Network

Charge-Coupled Device (CCD) detectors, widely used to obtain digital imaging, can be damaged by high energy radiation. Degraded images appear blurred, because of an effect known as Charge Transfer Inefficiency (CTI), which trails bright objects as the image is read out. It is often possible to correct most of the trailing during post-processing, by moving flux back to where it belongs. We compare several popular algorithms for this: quantifying the effect of their physical assumptions and tradeoffs between speed and accuracy. We combine their best elements to construct a more accurate model of damaged CCDs in the Hubble Space Telescope's Advanced Camera for Surveys/Wide Field Channel, and update it using data up to early 2013. Our algorithm now corrects 98% of CTI trailing in science exposures, a substantial improvement over previous work. Further progress will be fundamentally limited by the presence of read noise. Read noise is added after charge transfer so does not get trailed - but it is incorrectly untr...

Massey, Richard; Cordes, Oliver; Marggraf, Ole; Israel, Holger; Miller, Lance; Hall, David; Cropper, Mark; Prod'homme, Thibaut; Niemi, Sami-Matias

2014-01-01

274

Jahn-Teller effects in transition-metal compounds with small charge-transfer energy  

NASA Astrophysics Data System (ADS)

We have studied Jahn-Teller effects in Cs2Au2Br6, ACu3Co4O12(A=Ca or Y), and IrTe2 in which the ligand p-to-transition-metal d charge-transfer energy is small or negative. The Au+/Au3+ charge disproportionation of Cs2Au2Br6 manifests in Au 4f photoemission spectra. In Cs2Au2Br6 with negative ? and intermediate U, the charge disproportionation can be described using effective d orbitals constructed from the Au 5d and Br 4p orbitals and is stabilized by the Jahn-Teller distortion of the Au3+ site with low-spin d8 configuration. In ACu3Co4O12, ?s for Cu3+ and Co4+ are negative and Us are very large. The Zhang-Rice picture is valid to describe the electronic state, and the valence change from Cu2+/Co4+ to Cu3+/Co3+ can be viewed as the O 2p hole transfer from Co to Cu or d9 + d6L ? d9L + d6. In IrTe2, both ? and U are small and the Ir 5d and Te 5p electrons are itinerant to form the multi-band Fermi surfaces. The ideas of band Jahn-Teller transition and Peierls transition are useful to describe the structural instabilities.

Mizokawa, Takashi

2013-04-01

275

Atomic dipole polarization in charge-transfer complexes with halogen bonding.  

PubMed

The polarization effects associated with halogen bonding for the series of charge-transfer complexes D(m)···X-Y, where donor molecules D(m) = NH(3), H(2)O, H(2)S, C(2)H(4), CO and X-Y = Cl(2), ClF, Br(2), BrCl, ICl, I(2), are characterized in terms of the quantum theory of atoms in molecules using the B3LYP/6-311** Kohn-Sham wave functions. We study the electrostatic potential features of separate donor and acceptor molecules, the change in atomic charges as well as the atomic electric dipole moments and their components, and the intra-atomic electron density dipole polarization and the bonding dipole moments resulting from the electron density redistribution between the molecules in the charge-transfer complexes. The equation linking the most negative electrostatic potential values in the donor molecules and the most positive values in dihalogen molecules with the stretching force constants was found using two-factor regression. It is demonstrated that the dipole polarization of the acceptor atom mirrors the strength of halogen bonding in complexes in a series of different donors and acceptors. An exponential relationship between the magnitude of the total atomic electric dipole moment of the acceptor atom and the intermolecular stretching force constant is established for weakly bounded complexes. PMID:23322002

Bartashevich, E V; Tsirelson, V G

2013-02-21

276

Ultrafast charge transfer in atomically thin MoS2/WS2 heterostructures  

NASA Astrophysics Data System (ADS)

Van der Waals heterostructures have recently emerged as a new class of materials, where quantum coupling between stacked atomically thin two-dimensional layers, including graphene, hexagonal-boron nitride and transition-metal dichalcogenides (MX2), give rise to fascinating new phenomena. MX2 heterostructures are particularly exciting for novel optoelectronic and photovoltaic applications, because two-dimensional MX2 monolayers can have an optical bandgap in the near-infrared to visible spectral range and exhibit extremely strong light-matter interactions. Theory predicts that many stacked MX2 heterostructures form type II semiconductor heterojunctions that facilitate efficient electron-hole separation for light detection and harvesting. Here, we report the first experimental observation of ultrafast charge transfer in photoexcited MoS2/WS2 heterostructures using both photoluminescence mapping and femtosecond pump-probe spectroscopy. We show that hole transfer from the MoS2 layer to the WS2 layer takes place within 50?fs after optical excitation, a remarkable rate for van der Waals coupled two-dimensional layers. Such ultrafast charge transfer in van der Waals heterostructures can enable novel two-dimensional devices for optoelectronics and light harvesting.

Hong, Xiaoping; Kim, Jonghwan; Shi, Su-Fei; Zhang, Yu; Jin, Chenhao; Sun, Yinghui; Tongay, Sefaattin; Wu, Junqiao; Zhang, Yanfeng; Wang, Feng

2014-09-01

277

Quantum dynamics of ultrafast charge transfer at an oligothiophene-fullerene heterojunction.  

PubMed

Following up on our recent study of ultrafast charge separation at oligothiophene-fullerene interfaces [H. Tamura, I. Burghardt, and M. Tsukada, J. Phys. Chem. C 115, 10205 (2011)], we present here a detailed quantum dynamical perspective on the charge transfer process. To this end, electron-phonon coupling is included non-perturbatively, by an explicit quantum dynamical treatment using the multi-configuration time-dependent Hartree (MCTDH) method. Based upon a distribution of electron-phonon couplings determined from electronic structure studies, a spectral density is constructed and employed to parametrize a linear vibronic coupling Hamiltonian. The diabatic coupling is found to depend noticeably on the inter-fragment distance, whose effect on the dynamics is here investigated. MCTDH calculations of the nonadiabatic transfer dynamics are carried out for the two most relevant electronic states and 60 phonon modes. The electron transfer process is found to be ultrafast and mediated by electronic coherence, resulting in characteristic oscillatory features during a period of about 100 fs. PMID:23249077

Tamura, Hiroyuki; Martinazzo, Rocco; Ruckenbauer, Matthias; Burghardt, Irene

2012-12-14

278

Charge-transfer complexes of bromine atoms with haloalkanes and alkanes  

SciTech Connect

Charge-transfer complexes of bromine atoms with haloalkanes and alkanes were produced by pulse radiolysis and by laser-flash photolysis in various organic solvents. Br atoms were produced by photolysis of Br[sub 2] (at 351 or 248 nm), by photolysis of bromoalkanes (at 248 nm), or by radiolysis of bromoalkanes (either in liquid form or in cyclohexane solutions). The transient spectra, monitored within microseconds after the pulse, had absorption maxima that varied between 300 and 500 nm and are ascribed to complexes of Br atoms with the various solvents or other solutes present. The absorption maxima for Br atom complexes with alkanes and chloroalkanes correlate with the ionization potential of these molecules, suggesting the existence of charge-transfer complexes. The correlation for the bromoalkanes was more complex. CBr[sub 4]Br and CHBr[sub 3][center dot]Br were observed to react rapidly (k = 10[sup 8]-10[sup 9] L mol[sup [minus]1] s[sup [minus]1]) with Br[sub 2] and with HBr to transfer their Br atom to these latter molecules. 16 refs., 5 figs., 2 tabs.

Alfassi, Z.B.; Huie, R.E.; Neta, P. (National Inst. of Standards and Technology, Gaithersburg, MD (United States)); Mittal, J.P.; Shoute, L.C.T. (Bhabha Atomic Research Centre, Bombay (India))

1993-09-09

279

New non-covalent charge–transfer complex of calix[4]pyrrole–chloranil: as a potential colorimetric anion sensor  

Microsoft Academic Search

Non-covalent calix[4]pyrrole–chloranil complex, a new class of supramolecular assembly, is reported. The formation of the complex is mainly attributed to the charge–transfer interactions between calix[4]pyrrole with electron-rich pyrrole rings and the electron-deficient chloranil subunit. As potential colorimetric anion sensors, the charge–transfer aggregation may be used for effective and selective detection of F? and H2PO4? by means of dramatic visual color

Shijun Shao; Yong Guo; Lijun He; Shengxiang Jiang; Xianda Yu

2003-01-01

280

Electron doping by charge transfer at LaFeO3/Sm2CuO4 epitaxial interfaces.  

PubMed

Using X-ray absorption spectroscopy and electron energy loss spectroscopy with atomic-scale spatial resolution, experimental evidence for charge transfer at the interface between the Mott insulators Sm2 CuO4 and LaFeO3 is obtained. As a consequence of the charge transfer, the Sm2 CuO4 is doped with electrons and thus epitaxial Sm2 CuO4 /LaFeO3 heterostructures become metallic. PMID:23292988

Bruno, Flavio Y; Schmidt, Rainer; Varela, Maria; Garcia-Barriocanal, Javier; Rivera-Calzada, Alberto; Cuellar, Fabian A; Leon, Carlos; Thakur, Pardeep; Cezar, Julio C; Brookes, Nicholas B; Garcia-Hernandez, Mar; Dagotto, Elbio; Pennycook, Stephen J; Santamaria, Jacobo

2013-03-13

281

Novel thin film titanium nitride micro-electrodes with excellent charge transfer capability for cell stimulation and sensing applications  

Microsoft Academic Search

Microelectrodes with high specific charge transfer capability are an important prerequisite for high resolution stimulation, and recording of neuronal and muscular tissue. Novel thin film titanium nitride (TiN) microelectrodes were fabricated onto a microelectrode array by reactive sputtering in a nitrogen\\/argon atmosphere. The electrodes showed excellent charge transfer capacity of 40 mC\\/cm2 and low ac-impedance along with high pulse stability.

M. Janders; U. Egert; M. Stelzle; W. Nisch

1996-01-01

282

Charge transfer, confinement, and ferromagnetism in LaMnO3/LaNiO3 (001) superlattices  

NASA Astrophysics Data System (ADS)

Using first-principles density functional theory calculations, we investigated the electronic structure and magnetic properties of (LaMnO3)m/(LaNiO3)n superlattices stacked along the (001) direction. The electrons are transferred from Mn to Ni, and the magnetic moments are induced at Ni sites that are paramagnetic in bulk and other types of superlattices. The size of the induced moment is linearly proportional to the amount of transferred electrons, but it is larger than the net charge transfer. The charge transfer and magnetic properties of the (m,n) superlattice can be controlled by changing the m/n ratio. Considering the ferromagnetic couplings between Mn and Ni spins and the charge-transfer characteristic, we propose the (2,1) superlattice as the largest moment superlattice. carrying ˜8?B per formula unit.

Lee, Alex Taekyung; Han, Myung Joon

2013-07-01

283

Energy transfer through a multi-layer liner for shaped charges  

DOEpatents

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.

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

1985-01-01

284

The role of charge transfer in the structure and dynamics of the hydrated proton  

PubMed Central

Although it has long been recognized that multiple water molecules strongly associate with an extra proton in bulk water, some models and conceptual frameworks continue to utilize the classical hydronium ion (H3O+) as a fundamental building block. In this work, the nature of the hydronium ion in aqueous systems is examined using an ab initio energy decomposition analysis (EDA) that evaluates both the magnitude of and energetic stabilization due to charge transfer among H3O+ and the surrounding water molecules. The EDA is performed on structures extracted from dynamical bulk-phase simulations, and used to determine how frequently the pure hydronium ion, where the excess charge is primarily localized on H3O+, occurs under dynamic conditions. The answer is essentially never. The energetic stabilization of H3O+ due to charge delocalization to neighboring water molecules is found to be much larger (16 to 49 kcal/mol) than for other ions (even Li+) and to constitute a substantial portion (20% to 52%) of the complex's binding energy. The charge defect is also shown to have intrinsic dynamical asymmetry and to display dynamical signatures that can be related to features appearing in IR spectra. PMID:19309128

Swanson, Jessica M.J.; Simons, Jack

2009-01-01

285

Charge transfer and polarization screening in organic thin films: phthalocyanines on Au(100)  

NASA Astrophysics Data System (ADS)

Core hole screening effects at organic/metal interfaces were studied by core level X-ray photoemission spectroscopy (XPS), X-ray excited Auger electron spectroscopy (XAES), and valence band ultraviolet photoemission spectroscopy (UPS). The comparison of energetic shifts in XPS and XAES enables the estimation of electronic relaxation energy (screening ability). Magnesium phthalocyanine (MgPc) and zinc phthalocyanine (ZnPc) evaporated on single crystalline Au(100) were used as model molecules. Two different features in the Mg KLL spectra can be clearly separated for (sub-)monolayer coverages, while only minor changes of the shape of Mg 1s are observed. Applying a dielectric continuum model, the major screening mechanism cannot be described sufficiently by polarization screening due to mirror charges, significant contributions by charge transfer screening have to be considered. In contrast, small screening effects in the bulk material can be explained by surface polarization.

Kolacyak, Daniel; Peisert, Heiko; Chassé, Thomas

2009-04-01

286

Adsorption of colloidal platinum nanoparticles to supports: charge transfer and effects of electrostatic and steric interactions.  

PubMed

Adsorption of colloidal nanoparticles to surfaces and supports is a convenient approach to heterogeneous catalysts, polymer additives, or wastewater treatment. We investigated the adsorption efficiency of laser-generated and initially ligand-free platinum nanoparticles to TiO2 supports as a function of pH, ionic strength, and ligand surface coverage. The nanoparticle adsorption is dominantly controlled by electrostatic interactions: if the pH of the suspension is between the isoelectric point of the nanoparticles and the support, nanoparticles are adsorbed and transfer a net charge to the support. This charge-driven adsorption is not affected by steric repulsion due to various ligands attached to the nanoparticle surface. In addition to electrostatic interactions, colloidal stability given by moderate ionic strengths and pH values above the isoelectric point of nanoparticles are prerequisites for colloidal deposition. PMID:25226205

Marzun, Galina; Streich, Carmen; Jendrzej, Sandra; Barcikowski, Stephan; Wagener, Philipp

2014-10-14

287

Spectroelectrochemical identification of charge-transfer excited states in transition metal-based polypyridyl complexes.  

PubMed

Identification of transient species is a necessary part of delineating the kinetics and mechanisms associated with chemical dynamics; when dealing with photo-induced processes, this can be an exceptionally challenging task due to the fact that spectra associated with excited state(s) sampled over the course of a photochemical event often cannot be uniquely identified nor readily calculated. Using Group 8 complexes of the general form [M(terpy)2](2+) and [M(bpy)3](2+) as a platform (where terpy is 2,2':6',2''-terpyridine and bpy is 2,2'-bipyridine), we demonstrate how spectroelectrochemical measurements can serve as an effective tool for identifying spectroscopic signatures of charge-transfer excited states of transition metal-based chromophores. Formulating the metal-to-ligand charge-transfer (MLCT) excited state(s) as M(3+)-L(-), the extent to which a linear combination of the spectra of the oxidized and reduced forms of the parent complexes can be used to simulate the characteristic absorptions of MLCT-based transient species is examined. Quantitative agreement is determined to be essentially unachievable due to the fact that certain transitions associated with the optically prepared excited states are either overcompensated for in the spectroelectrochemical data, or simply cannot be replicated through electrochemical means. Despite this limitation, it is shown through several illustrative examples that this approach can still be extremely useful as a qualitative if not semi-quantitative guide for interpreting time-resolved electronic absorption data of charge-transfer compounds, particularly in the ultrafast time domain. PMID:25321952

Brown, Allison M; McCusker, Catherine E; McCusker, James K

2014-11-12

288

Interfacial electronic charge transfer and density of states in short period Cu/Cr multilayers  

SciTech Connect

Nanometer period metallic multilayers are ideal structures to investigate electronic phenomena at interfaces between metal films since interfacial atoms comprise a large atomic fraction of the samples. The multilayers studied were fabricated by magnetron sputtering and consist of bilayers from 1.9 mn to 3.3 mn. X-ray diffraction, cross-section TEM and plan-view TEM show the Cu layers to have a BCC structure Cu in contrast to its equilibrium FCC structure. The electronic structure of the Cu and the Cr layers in several samples of thin Cu/Cr multilayers were studied using x-ray absorption spectroscopy (XAS). Total electron yield was measured and used to study the white lines at the Cu L{sub 2} and L{sub 3} absorption edges. The white lines at the Cu absorption edges are strongly related to the unoccupied d-orbitals and are used to calculate the amount of charge transfer between the Cr and Cu atoms in interfaces. Analysis of the Cu white lines show a charge transfer of 0.026 electrons/interfacial Cu atom to the interfacial Cr atoms. In the Cu XAS spectra we also observe a van Hove singularity between the L{sub 2} and L{sub 3} absorption edges as expected from the structural analysis. The absorption spectra are compared to partial density of states obtained from a full-potential linear muffin-tin orbital calculation. The calculations confirm the presence of charge transfer and indicate that it is localized to the first two interfacial layers in both Cu and Cr.

Bello, A.F.; Van Buuren, T.; Kepesis, J.E.; Barbee, T.W., Jr.

1998-04-01

289

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

SciTech Connect

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.

Hallermann, Markus; Da Como, Enrico; Feldmann, Jochen [Photonics and Optoelectronics Group, Department of Physics, CeNS Ludwig-Maximilians-University, 80799 Munich (Germany); Izquierdo, Marta; Filippone, Salvatore; Martin, Nazario [Department of Organic Chemistry, Universidad Complutense de Madrid, 28040 Madrid (Spain); Juechter, Sabrina; Hauff, Elizabeth von [Institute of Physics, Energy and Semiconductor Research Laboratory, University of Oldenburg, 26111 Oldenburg (Germany)

2010-07-12

290

Photoinduced charge transfer between fullerenes and TiO{sub 2} semiconductor colloids  

SciTech Connect

A photocatalytic method has been presented to carry out one-electron reduction of C{sub 60} and C{sub 70} in 50/50 (v/v) benzene/ethanol. The fullerene reduction was carried out in colloidal TiO{sub 2} suspension using UV excitation. The charge transfer between the excited TiO{sub 2} semiconductor colloid and fullerene molecule occurs with a quantum efficiency of 13% for C{sub 70} and 24% for C{sub 60}. Laser flash photolysis measurements have been carried out to elucidate the mechanism of photocatalytic reduction.

Kamat, P.V. [Univ. of Notre Dame, IN (United States). Radiation Lab.; Bedja, I.; Hotchandani, S. [Universite du Quebec a Trois Rivieres (Canada). Centre de Recherche en Photobiophysique

1994-10-01

291

Examination of charge transfer in Au/YSZ for high-temperature optical gas sensing  

SciTech Connect

Au-nanoparticle incorporated oxide thin film materials demonstrate significant promise as functionalsensor materials for high temperature optical gas sensing in severe environments relevant for fossil andnuclear based power generation. The Au/yttria-stabilized zirconia (YSZ) system has been extensivelystudied in the literature and serves as a model system for fundamental investigations that seek to betterunderstand the mechanistic origin of the plasmonic gas sensing response. In this work, X-ray photoelec-tron spectroscopy techniques are applied to Au/YSZ films in an attempt to provide further experimentalevidence for a proposed sensing mechanism involving a change in free carrier density of Au nanoparticles due to charge transfer.

Baltrus, John P. [U.S. DOE; Ohodnicki, Paul R. [U.S. DOE

2014-01-01

292

Charge transfer induced magnetism in sol-gel derived nanocrystalline BaTiO3  

NASA Astrophysics Data System (ADS)

Nanocrystalline BaTiO3 is prepared by sol-gel synthesis. The charge transfer and different state mixing effects are used in explaining the observed magnetism by the modified Stoner theory. The magnetic coercivity is found to decrease from 125 to 43 Oe as temperature increases from 5 K to 300 K. The optical absorption shows band narrowing arising from exchange-correlation and many-body effects of free carriers created on the surface of nanoparticles, as supported also by the non-adiabatic small polaron conductivity derived from impedance spectroscopy.

Ramakanth, S.; James Raju, K. C.

2014-06-01

293

Spontaneous charge transfer at organic-organic homointerfaces to establish thermodynamic equilibrium  

SciTech Connect

The energy level alignment of {alpha},{omega}-dihexylsexithienyl (DH6T) mono- and multilayers on tetrafluorotetracyanoquinodimethane (F4-TCNQ) precovered Ag(111) and polycrystalline Au substrates was investigated with ultraviolet photoelectron spectroscopy. For certain F4-TCNQ precoverages molecular level pinning at DH6T monolayer-multilayer homointerfaces was observed. The pinning behavior shows that thermodynamic equilibrium can be established across hexyl chains via charge transfer, indicating the limited use of these short alkyl chains for insulation in the field of molecular electronics.

Duhm, S.; Glowatzki, H.; Rabe, J. P.; Koch, N.; Johnson, R. L. [Institut fuer Physik, Humboldt-Universitaet zu Berlin, Newtonstr. 15, D-12489 Berlin (Germany); Institut fuer Experimentalphysik, Universitaet Hamburg, D-22761 Hamburg (Germany)

2007-03-19

294

Electric-Field Control of Solitons in a Ferroelectric Organic Charge-Transfer Salt  

NASA Astrophysics Data System (ADS)

The role of solitons in transport, dielectric, and magnetic properties has been revealed for the quasi-one-dimensional organic charge-transfer salt, TTF-QBrCl3 [tetrathiafulvalene (TTF)-2-bromo-3,5,6-trichloro-p-benzoquinone (QBrCl3)]. The material was found to be ferroelectric and hence the solitons should be located at the boundary of the segments with opposite electric polarization. This feature enabled the electric-field control of soliton density and hence the clear-cut detection of soliton contributions. The gigantic dielectric response in the ferroelectric phase is ascribed to the dynamical bound and creeping motions of spinless solitons.

Kagawa, F.; Horiuchi, S.; Matsui, H.; Kumai, R.; Onose, Y.; Hasegawa, T.; Tokura, Y.

2010-06-01

295

H-bonding assisted intramolecular charge transfer in 1-aminopyrene derivatives  

NASA Astrophysics Data System (ADS)

The electronic spectroscopy and photochemical properties of new derivatives of pyrene-1-aminovinylene containing strong electron withdrawing groups are reported. 2-((Pyren-8-ylamino)methylene) malononitrile (I) ethyl 2-cyano-3-(pyren-8-ylamino) acrylate (II), and diethyl 2-((pyren-8-ylamino)methylene) malonate (III) were prepared. These molecules show excited-state intramolecular charge transfer (ESICT). The carbonyl in II and III gives rise to a solvent dependent intramolecular H-bond interaction which not only enhances the mixing between ?-? ? and n-? ? states but also influences the ESICT dynamics.

Pereira, Robson Valentim; Gehlen, Marcelo Henrique

2006-08-01

296

Assessment of asymptotically corrected model potentials for charge-transfer-like excitations in oligoacenes.  

PubMed

We examine the performance of the asymptotically corrected model potential scheme on the two lowest singlet excitation energies of acenes with different numbers of linearly fused benzene rings (up to 5), employing both the real-time time-dependent density functional theory and the frequency-domain formulation of linear-response time-dependent density functional theory. The results are compared with the experimental data and those calculated using long-range corrected hybrid functionals and others. The long-range corrected hybrid scheme is shown to outperform the asymptotically corrected model potential scheme for charge-transfer-like excitations. PMID:25188860

Peng, Wei-Tao; Chai, Jeng-Da

2014-10-21

297

Transient Spectroscopy of Frenkel and Charge Transfer Excitons in {ital {alpha}} -Sexithienyl Films  

SciTech Connect

Photoexcitations dynamics are investigated in {alpha}-sexithienyl nanocrystalline films using transient photomodulation in a spectral range from 0.4 to 2.5eV and time domain from 200fs to 50ms. We identify intrachain and interchain excitations. The former are even parity excitons with ultrafast dynamics, whereas the latter are long-lived charge transfer excitons generated within 300fs, which separate into uncorrelated polaron pairs in the submicrosecond time domain. {copyright} {ital 1997} {ital The American Physical Society}

Lanzani, G. [Istituto di Matematica e Fisica, Universita di Sassari, Sassari 07100 Italy and Istituto Nazionale per la Fisica della Materia, Unita di Milano, Milano 20133 (Italy)] [Istituto di Matematica e Fisica, Universita di Sassari, Sassari 07100 Italy and Istituto Nazionale per la Fisica della Materia, Unita di Milano, Milano 20133 (Italy); Frolov, S.V.; Lane, P.A.; Vardeny, Z.V. [Department of Physics, University of Utah, Salt Lake City, Utah 84112 (United States)] [Department of Physics, University of Utah, Salt Lake City, Utah 84112 (United States); Nisoli, M.; De Silvestri, S. [Centro di Elettronica Quantistica e Strumentazione Elettronica Dipartimento di Fisica, Politecnico di Milano, Milano 20133 (Italy)] [Centro di Elettronica Quantistica e Strumentazione Elettronica Dipartimento di Fisica, Politecnico di Milano, Milano 20133 (Italy)

1997-10-01

298

Theoretical evidence of photo-induced charge transfer from DNA to intercalated ruthenium (II) organometallic complexes  

NASA Astrophysics Data System (ADS)

The absorption spectrum of two ruthenium (II) organometallic complexes intercalated into DNA is studied at the quantum mechanic/molecular mechanic level. The macromolecular environment is taken into account as to include geometric, electrostatic and polarization effects that can alter the excitation energy and oscillator strength. The inclusion of DNA base pairs into the quantum mechanic partition allows us for the first time to clearly evidence the presence of charge transfer excited states involving an electron withdraw from DNA base pairs to the organometallic complex.

Chantzis, Agisilaos; Very, Thibaut; Daniel, Chantal; Monari, Antonio; Assfeld, Xavier

2013-07-01

299

Reply to ‘Comment on “Four-body charge transfer processes in proton helium collisions”’  

NASA Astrophysics Data System (ADS)

Houamer and Popov have performed a first Born approximation calculation (FBA) for TTE (charge transfer with target excitation) for 300 keV proton-helium collisions. Their results are in reasonable agreement with the absolute measurements of Schöffler (2006 PhD thesis, University of Frankfurt am Main) whereas our FBA results yielded the shape of the experimental data reasonably well (except for small scattering angles) but with a magnitude that was a factor of 144 larger than experiment. Consequently, Houamer and Popov conclude that our results must have huge numerical errors. We have extensively tested our codes and we do not find any evidence to support this claim.

Chowdhury, U.; Harris, A. L.; Peacher, J. L.; Madison, D. H.

2013-01-01

300

Conjugated iminopyridine based Azo dye derivatives with efficient charge transfer for third order nonlinearities  

NASA Astrophysics Data System (ADS)

The third order nonlinearities of two azobenzene-iminopyridine molecular systems have been investigated employing the Z-scan technique at 532 nm, 30 ps. The objective of the work has been to study and to compare the nonlinearity of two iminopyridine based ligands substituted with one (NO2AzoIminoPy, A) and two azobenzene units ((NO2Azo)2IminoPy, B). The ligand B exhibits an extended conjugated structure and higher charge transfer within the molecule. Our results show high dependence of the nonlinearity on both the conjugation length within the molecule and on the number of the electron accepting units.

Kerasidou, A. P.; Khammar, F.; Iliopoulos, K.; Ayadi, A.; El-Ghayoury, A.; Zouari, N.; Mhiri, T.; Sahraoui, B.

2014-03-01

301

Manipulating the charge transfer at CuPc/graphene interface by O2 plasma treatments  

NASA Astrophysics Data System (ADS)

The manipulation of charge transfer at CuPc/graphene interface has been demonstrated by treating pristine graphene with O2 plasma. As revealed by in situ ultraviolet photoelectron spectroscopy measurements, a much stronger interfacial charge transfer occurs when the pristine graphene is exposed to O2 plasma prior to the growth of CuPc films, which is attributed to the increased work function of graphene after O2 plasma treatment. Moreover, the highest occupied molecular orbital leading edge of CuPc locates at ~0.80 eV below substrate Fermi level on O2 plasma treated graphene, whereas it locates at ~1.10 eV on pristine graphene. Our findings provide detailed information regarding the electronic structure at CuPc/graphene and CuPc/O2 plasma treated graphene interfaces. The increased work function in combination with the relatively smaller energy offset between the highest occupied molecular orbital of CuPc and Fermi level of O2 plasma treated graphene facilitates the extraction of holes at the interface, and hence paves the way for improving the performance of graphene-based organic photovoltaic cells.The manipulation of charge transfer at CuPc/graphene interface has been demonstrated by treating pristine graphene with O2 plasma. As revealed by in situ ultraviolet photoelectron spectroscopy measurements, a much stronger interfacial charge transfer occurs when the pristine graphene is exposed to O2 plasma prior to the growth of CuPc films, which is attributed to the increased work function of graphene after O2 plasma treatment. Moreover, the highest occupied molecular orbital leading edge of CuPc locates at ~0.80 eV below substrate Fermi level on O2 plasma treated graphene, whereas it locates at ~1.10 eV on pristine graphene. Our findings provide detailed information regarding the electronic structure at CuPc/graphene and CuPc/O2 plasma treated graphene interfaces. The increased work function in combination with the relatively smaller energy offset between the highest occupied molecular orbital of CuPc and Fermi level of O2 plasma treated graphene facilitates the extraction of holes at the interface, and hence paves the way for improving the performance of graphene-based organic photovoltaic cells. Electronic supplementary information (ESI) available. See DOI: 10.1039/c4nr02028f

Mao, Hongying; Hu, Fang; Ye, Quan-Lin; Xu, Yifeng; Yang, Xuxin; Lu, Bin

2014-06-01

302

Metallization and charge-transfer gap closure of transition-metal iodides under pressure  

SciTech Connect

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.

Chen, A. Li-Chung

1993-05-01

303

EV Charging Through Wireless Power Transfer: Analysis of Efficiency Optimization and Technology Trends  

SciTech Connect

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.

Miller, John M [ORNL; Rakouth, Heri [Delphi Automotive Systems, USA; Suh, In-Soo [Korea Advanced Institute of Science and Technology

2012-01-01

304

Intramolecular charge transfer, solvatochromism and hyperpolarizability of compounds bearing ethenylene or ethynylene bridges  

NASA Astrophysics Data System (ADS)

Emission or both absorption/emission solvatochromic effects induced by intramolecular charge transfer (ICT) have been used to determine the excited-state dipole moments of the locally excited ?e(LE) and the polar-solvent induced ?e(ICT) states and the first hyperpolarizability parameter ?CT of six asymmetric distyrylbenzene analogues, two 9,10-(diarylethynyl)anthracene derivatives and two 2,7-(diarylethynyl)fluorene analogues. The change in dipole moment under excitation (??eg) was also evaluated by theoretical calculations and compared with experimental data. All compounds display more or less remarkable positive solvatochromism which leads to relatively high hyperpolarizabilities and makes them interesting candidates for applications associated with photoinduced ICT. The structural effect on the transfer is also briefly discussed and related to the relaxation properties (previously investigated) of these compounds.

Carlotti, B.; Flamini, R.; Kikaš, I.; Mazzucato, U.; Spalletti, A.

2012-10-01

305

Short-lived charge-transfer excitons in organic photovoltaic cells studied by high-field magneto-photocurrent.  

PubMed

The main route of charge photogeneration in efficient organic photovoltaic cells based on bulk hetero-junction donor-acceptor blends involves short-lived charge-transfer excitons at the donor-acceptor interfaces. The cell efficiency is critically affected by the charge-transfer exciton recombination and dissociation processes. By measuring the magneto-photocurrent under ambient conditions at room temperature, we show here that magnetic field-induced spin-mixing among the charge-transfer exciton spin sublevels occurs in fields up to at least 8.5?Tesla. The resulting magneto-photocurrent increases at high fields showing non-saturating behaviour up to the highest applied field. We attribute the observed high-field spin-mixing mechanism to the difference in the donor-acceptor g-factors. The non-saturating magneto-photocurrent response at high field indicates that there exist charge-transfer excitons with lifetime in the sub-nanosecond time domain. The non-Lorentzian high-field magneto-photocurrent response indicates a dispersive decay mechanism that originates due to a broad distribution of charge-transfer exciton lifetimes. PMID:25073082

Devir-Wolfman, Ayeleth H; Khachatryan, Bagrat; Gautam, Bhoj R; Tzabary, Lior; Keren, Amit; Tessler, Nir; Vardeny, Z Valy; Ehrenfreund, Eitan

2014-01-01

306

Short-lived charge-transfer excitons in organic photovoltaic cells studied by high-field magneto-photocurrent  

NASA Astrophysics Data System (ADS)

The main route of charge photogeneration in efficient organic photovoltaic cells based on bulk hetero-junction donor-acceptor blends involves short-lived charge-transfer excitons at the donor-acceptor interfaces. The cell efficiency is critically affected by the charge-transfer exciton recombination and dissociation processes. By measuring the magneto-photocurrent under ambient conditions at room temperature, we show here that magnetic field-induced spin-mixing among the charge-transfer exciton spin sublevels occurs in fields up to at least 8.5?Tesla. The resulting magneto-photocurrent increases at high fields showing non-saturating behaviour up to the highest applied field. We attribute the observed high-field spin-mixing mechanism to the difference in the donor-acceptor g-factors. The non-saturating magneto-photocurrent response at high field indicates that there exist charge-transfer excitons with lifetime in the sub-nanosecond time domain. The non-Lorentzian high-field magneto-photocurrent response indicates a dispersive decay mechanism that originates due to a broad distribution of charge-transfer exciton lifetimes.

Devir-Wolfman, Ayeleth H.; Khachatryan, Bagrat; Gautam, Bhoj R.; Tzabary, Lior; Keren, Amit; Tessler, Nir; Vardeny, Z. Valy; Ehrenfreund, Eitan

2014-07-01

307

Dependence of the direct electron transfer activity and adsorption kinetics of cytochrome c on interfacial charge properties.  

PubMed

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

Wang, Gui-Xia; Wang, Min; Wu, Zeng-Qiang; Bao, Wen-Jing; Zhou, Yue; Xia, Xing-Hua

2013-10-01

308

Synthesis and characterization of highly conductive charge-transfer complexes using positron annihilation spectroscopy  

NASA Astrophysics Data System (ADS)

Molecular charge-transfer complexes of the tetramethylethylenediamine (TMEDA) with picric acid (Pi-OH), benzene-1,4-diol (QL), tin(IV) tetrachloride (SnCl4), iodine, bromine, and zinc chloride (ZnCl2) have been synthesized and investigated by elemental and thermal analysis, electronic, infrared, Raman and proton-NMR, energy-dispersive X-ray spectroscopy, X-ray powder diffraction and positron annihilation lifetime spectroscopy, and scanning electron microscopy. In this work, three types of acceptors ?-acceptors (Pi-OH and QL), ?-acceptors (iodine and bromine), and vacant orbital acceptors (SnCl4 and ZnCl2) were covered. The results of elemental analysis indicated that the CT complexes were formed with ratios 1:1 and 1:2 for QL, SnCl4, and ZnCl2 acceptors and iodine, Pi-OH, and Br2 acceptors, respectively. The type of chelating between the TMEDA donor and the mentioned acceptors depends upon the behavior of both items. The positron annihilation lifetime parameters were found to be dependent on the structure, electronic configuration, and the power of acceptors. The correlation between these parameters and the molecular weight and biological activities of studied complexes was also observed. Regarding the electrical properties, the AC conductivity and the dielectric coefficients were measured as a function of frequency at room temperature. The TMEDA charge-transfer complexes were screened against antibacterial (Escherichia coli, Staphylococcus aureus, Bacillus subtilis, and Pseudomonas aeruginosa) and antifungal (Aspergillus flavus and Candida albicans) activities.

Adam, Abdel Majid A.; Refat, Moamen S.; Sharshar, T.; Heiba, Z. K.

309

Excited State Structural Dynamics of Carotenoids and ChargeTransfer Systems  

SciTech Connect

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.

Van Tassle, Aaron Justin

2006-09-01

310

A two-state model of twisted intramolecular charge-transfer in monomethine dyes  

NASA Astrophysics Data System (ADS)

A two-state model Hamiltonian is proposed, which can describe the coupling of twisting displacements to charge-transfer behavior in the ground and excited states of a general monomethine dye molecule. This coupling may be relevant to the molecular mechanism of environment-dependent fluorescence yield enhancement. The model is parameterized against quantum chemical calculations on different protonation states of the green fluorescent protein chromophore, which are chosen to sample different regimes of detuning from the cyanine (resonant) limit. The model provides a simple yet realistic description of the charge transfer character along two possible excited state twisting channels associated with the methine bridge. It describes qualitatively different behavior in three regions that can be classified by their relationship to the resonant (cyanine) limit. The regimes differ by the presence or absence of twist-dependent polarization reversal and the occurrence of conical intersections. We find that selective biasing of one twisting channel over another by an applied diabatic biasing potential can only be achieved in a finite range of parameters near the cyanine limit.

Olsen, Seth; McKenzie, Ross H.

2012-10-01

311

Differential charge-transfer cross sections for systems with energetically degenerate or near-degenerate channels  

NASA Astrophysics Data System (ADS)

Resolution plays a vital role in spectroscopic studies. In the usual recoil-ion momentum spectroscopy (RIMS), Q-value resolution is relied upon to distinguish between different collision channels: The better the Q-value resolution, the better one is able to resolve energetically similar channels. Although traditional COLTRIMS greatly improves Q-value resolution by cooling the target and thus greatly reducing the initial target momentum spread, the resolution of the technique is still limited by target temperature. However, with the recent development in RIMS, namely, magneto-optical trap recoil ion momentum spectroscopy (MOTRIMS) superior recoil ion momentum resolution as well as charge transfer measurements with laser excited targets have become possible. Through MOTRIMS, methods for the measurements of target excited state fraction and kinematically complete relative charge transfer cross sections have been developed, even for some systems having energetically degenerate or nearly degenerate channels. In the present work, the systems of interest having energy degeneracies or near degeneracies are Rb+ , K+ , and Li+ colliding with trapped Rb(5l) , where l=s and p .

Nguyen, H.; Brédy, R.; Camp, H. A.; Awata, T.; Depaola, B. D.

2004-09-01

312

On the morphology of a discotic liquid crystalline charge transfer complex.  

PubMed

Discotic liquid crystalline (DLC) charge transfer (CT) complexes, which combine visible light absorption with rapid charge transfer characteristics within the CT complex, can have a great potential for photovoltaic applications when they can be made to self-assemble in a bulk heterojunction arrangement with separate channels for electron and hole conduction. However, the morphology of some liquid crystalline CT complexes has been under debate for many years. In particular, the liquid crystalline CT complex built from the electron acceptor 2,4,7-trinitro-9-fluorenone (TNF) and discotic molecules has been reported to have the TNF "sandwiched" either between the discotic molecules within the same column or between the columns within the aliphatic tails of the discotic molecules. We present a detailed structural study of the prototypic 1:1 mixture of the discotic 2,3,6,7,10,11-hexakis(hexyloxy)triphenylene (HAT6) and TNF. Nuclear magnetic resonance (NMR) line widths and cross-polarization rates are consistent with the picosecond time scale anisotropic thermal motions of the HAT6 and TNF molecules previously observed. By computational integration of Rietveld refinement analyses of neutron diffraction patterns with density experiments and short-range structural constraints from heteronuclear 2D NMR, we determine that the TNF molecules are vertically oriented between HAT6 columns. The data provide the insight that a morphology of separate hole conducting channels of HAT6 molecules can be realized in the liquid crystalline CT complex. PMID:23033895

Haverkate, Lucas A; Zbiri, Mohamed; Johnson, Mark R; Deme, Bruno; de Groot, Huub J M; Lefeber, Fons; Kotlewski, Arkadiusz; Picken, Stephen J; Mulder, Fokko M; Kearley, Gordon J

2012-11-01

313

Tuning the photoluminescence of graphene quantum dots through the charge transfer effect of functional groups.  

PubMed

The band gap properties of graphene quantum dots (GQDs) arise from quantum confinement effects and differ from those in semimetallic graphene sheets. Tailoring the size of the band gap and understanding the band gap tuning mechanism are essential for the applications of GQDs in opto-electronics. In this study, we observe that the photoluminescence (PL) of the GQDs shifts due to charge transfers between functional groups and GQDs. GQDs that are functionalized with amine groups and are 1-3 layers thick and less than 5 nm in diameter were successfully fabricated using a two-step cutting process from graphene oxides (GOs). The functionalized GQDs exhibit a redshift of PL emission (ca. 30 nm) compared to the unfunctionalized GQDs. Furthermore, the PL emissions of the GQDs and the amine-functionalized GQDs were also shifted by changes in the pH due to the protonation or deprotonation of the functional groups. The PL shifts resulted from charge transfers between the functional groups and GQDs, which can tune the band gap of the GQDs. Calculations from density functional theory (DFT) are in good agreement with our proposed mechanism for band gap tuning in the GQDs through the use of functionalization. PMID:23272894

Jin, Sung Hwan; Kim, Da Hye; Jun, Gwang Hoon; Hong, Soon Hyung; Jeon, Seokwoo

2013-02-26

314

Manipulating the charge transfer at CuPc/graphene interface by O? plasma treatments.  

PubMed

The manipulation of charge transfer at CuPc/graphene interface has been demonstrated by treating pristine graphene with O? plasma. As revealed by in situ ultraviolet photoelectron spectroscopy measurements, a much stronger interfacial charge transfer occurs when the pristine graphene is exposed to O? plasma prior to the growth of CuPc films, which is attributed to the increased work function of graphene after O? plasma treatment. Moreover, the highest occupied molecular orbital leading edge of CuPc locates at ?0.80 eV below substrate Fermi level on O? plasma treated graphene, whereas it locates at ?1.10 eV on pristine graphene. Our findings provide detailed information regarding the electronic structure at CuPc/graphene and CuPc/O? plasma treated graphene interfaces. The increased work function in combination with the relatively smaller energy offset between the highest occupied molecular orbital of CuPc and Fermi level of O? plasma treated graphene facilitates the extraction of holes at the interface, and hence paves the way for improving the performance of graphene-based organic photovoltaic cells. PMID:24921438

Mao, Hongying; Hu, Fang; Ye, Quan-Lin; Xu, Yifeng; Yang, Xuxin; Lu, Bin

2014-07-21

315

Differential charge-transfer cross sections for systems with energetically degenerate or near-degenerate channels  

SciTech Connect

Resolution plays a vital role in spectroscopic studies. In the usual recoil-ion momentum spectroscopy (RIMS), Q-value resolution is relied upon to distinguish between different collision channels: The better the Q-value resolution, the better one is able to resolve energetically similar channels. Although traditional COLTRIMS greatly improves Q-value resolution by cooling the target and thus greatly reducing the initial target momentum spread, the resolution of the technique is still limited by target temperature. However, with the recent development in RIMS, namely, magneto-optical trap recoil ion momentum spectroscopy (MOTRIMS) superior recoil ion momentum resolution as well as charge transfer measurements with laser excited targets have become possible. Through MOTRIMS, methods for the measurements of target excited state fraction and kinematically complete relative charge transfer cross sections have been developed, even for some systems having energetically degenerate or nearly degenerate channels. In the present work, the systems of interest having energy degeneracies or near degeneracies are Rb{sup +}, K{sup +}, and Li{sup +} colliding with trapped Rb(5l), where l=s and p.

Nguyen, H.; Bredy, R.; Camp, H.A.; DePaola, B.D. [J.R. Macdonald Laboratory, Department of Physics, Kansas State University, Manhattan, Kansas 66506-2601 (United States); Awata, T. [Department of Physics, Naruto University of Education, Naruto, Tokushima 772-8502 (Japan)

2004-09-01

316

Charge transfer and blue shifting of vibrational frequencies in a hydrogen bond acceptor.  

PubMed

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

Wright, Ashley M; Howard, Austin A; Howard, J Coleman; Tschumper, Gregory S; Hammer, Nathan I

2013-07-01

317

Charge transfer satellite in Pr@C82 metallofullerene observed using resonant x-ray emission spectroscopy  

NASA Astrophysics Data System (ADS)

Resonant x-ray emission spectroscopy (RXES) was performed on the metallofullerene Pr@C82 at the PrL3 absorption edge. We verify not only nearly three-electron charge transfers from the metal to the cage but also back-electron transfer observed as a charge transfer satellite. The results are compared to theoretical calculations with a single-impurity Anderson model. Theory shows that the electronic structure of endohedral atom in the cage is atomiclike. The satellite structure originates from the charge transfer, i.e., dynamical screening effect, induced by the core-hole potential in the final state rather than from the valence fluctuation of the rare-earth metal in the ground state. We also performed the RXES measurement of Pr2O3 for comparison.

Yamaoka, H.; Sugiyama, H.; Kubozono, Y.; Kotani, A.; Nouchi, R.; Vlaicu, A. M.; Oohashi, H.; Tochio, T.; Ito, Y.; Yoshikawa, H.

2009-11-01

318

Optically enhanced charge transfer between C60 and single-wall carbon nanotubes in hybrid electronic devices.  

PubMed

In this article we probe the nature of electronic interactions between the components of hybrid C60-carbon nanotube structures. Utilizing an aromatic mediator we selectively attach C60 molecules to carbon nanotube field-effect transistor devices. Structural characterization via atomic force and transmission electron microscopy confirm the selectivity of this attachment. Charge transfer from the carbon nanotube to the C60 molecules is evidenced by a blue shift of the Raman G(+) peak position and increased threshold voltage of the transistor transfer characteristics. We estimate this charge transfer to increase the device density of holes per unit length by up to 0.85 nm(-1) and demonstrate further optically enhanced charge transfer which increases the hole density by an additional 0.16 nm(-1). PMID:24241690

Allen, Christopher S; Liu, Guoquan; Chen, Yabin; Robertson, Alex W; He, Kuang; Porfyrakis, Kyriakos; Zhang, Jin; Briggs, G Andrew D; Warner, Jamie H

2014-01-01

319

Students' confidence in the ability to transfer basic math skills in introductory physics and chemistry courses at a community college  

NASA Astrophysics Data System (ADS)

The purpose of this study was to examine the confidence levels that community college students have in transferring basic math skills to science classes, as well as any factors that influence their confidence levels. This study was conducted with 196 students at a community college in central Mississippi. The study was conducted during the month of November after all of the students had taken their midterm exams and received midterm grades. The instrument used in this survey was developed and validated by the researcher. The instrument asks the students to rate how confident they were in working out specific math problems and how confident they were in working problems using those specific math skills in physics and chemistry. The instrument also provided an example problem for every confidence item. Results revealed that students' demographics were significant predictors in confidence scores. Students in the 18-22 year old range were less confident in solving math problems than others. Students who had retaken a math course were less confident than those who had not. Chemistry students were less confident in solving math problems than those in physics courses. Chemistry II students were less confident than those in Chemistry I and Principals of Chemistry. Students were least confident in solving problems involving logarithms and the most confident in solving algebra problems. In general, students felt that their math courses did not prepare them for the math problems encountered in science courses. There was no significant difference in confidence between students who had completed their math homework online and those who had completed their homework on paper. The researcher recommends that chemistry educators find ways of incorporating more mathematics in their courses especially logarithms and slope. Furthermore, math educators should incorporate more chemistry related applications to math class. Results of hypotheses testing, conclusions, discussions, and recommendations for future research are included.

Quinn, Reginald

320

Quantum effects in energy and charge transfer in an artificial photosynthetic complex  

SciTech Connect

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.

Ghosh, Pulak Kumar [Advanced Science Institute, RIKEN, Wako, Saitama 351-0198 (Japan); Smirnov, Anatoly Yu.; Nori, Franco [Advanced Science Institute, RIKEN, Wako, Saitama 351-0198 (Japan); Physics Department, University of Michigan, Ann Arbor, Michigan 41109-1040 (United States)

2011-06-28

321

A charge transfer inefficiency correction model for the Chandra advanced CCD imaging spectrometer  

NASA Astrophysics Data System (ADS)

Soon after launch, the Advanced CCD Imaging Spectrometer (ACIS), one of the focal plane instruments on the Chandra X-ray Observatory, suffered radiation damage from exposure to soft protons during passages through the Earth's radiation belts. The primary effect of the damage was to increase the charge transfer inefficiency (CTI) of the eight front illuminated CCDs by more than two orders of magnitude. The ACIS instrument team is continuing to study the properties of the damage with an emphasis on developing techniques to mitigate CTI and spectral resolution degradation. We will discuss the characteristics of the damage, the detector and the particle background and how they conspire to degrade the instrument performance. We have developed a model for ACIS CTI which can be used to correct each event and regain some of the lost performance. The correction uses a map of the electron trap distribution, a parameterization of the energy dependent charge loss and the fraction of the lost charge re-emitted into the trailing pixel to correct the pixels in the event island. This model has been implemented in the standard Chandra data processing pipeline. Some of the correction algorithm was inspired by the earlier work on ACIS CTI correction by Townsley and collaborators. The details of the CTI model and how each parameter improves performance will be discussed, as well as the limitations and the possibilities for future improvement.

Grant, Catherine E.; Bautz, Mark W.; Kissel, Steven E.; LaMarr, Beverly

2004-09-01

322

Unravelling the mechanism of photoinduced charge transfer processes in lead iodide perovskite solar cells  

NASA Astrophysics Data System (ADS)

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.

Marchioro, Arianna; Teuscher, Joël; Friedrich, Dennis; Kunst, Marinus; van de Krol, Roel; Moehl, Thomas; Grätzel, Michael; Moser, Jacques-E.

2014-03-01

323

Quantum effects in energy and charge transfer in an artificial photosynthetic complex  

NASA Astrophysics Data System (ADS)

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.

Ghosh, Pulak Kumar; Smirnov, Anatoly Yu.; Nori, Franco

2011-06-01

324

Competition between covalent bonding and charge transfer tendencies at complex-oxides interfaces  

NASA Astrophysics Data System (ADS)

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.

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

325

Simulation of charge transfer and orbital rehybridization in molecular and condensed matter systems  

NASA Astrophysics Data System (ADS)

The mixing and shifting of electronic orbitals in molecules, or between atoms in bulk systems, is crucially important to the overall structure and physical properties of materials. Understanding and accurately modeling these orbital interactions is of both scientific and industrial relevance. Electronic orbitals can be perturbed in several ways. Doping, adding or removing electrons from systems, can change the bond-order and the physical properties of certain materials. Orbital rehybridization, driven by either thermal or pressure excitation, alters the short-range structure of materials and changes their long-range transport properties. Macroscopically, during bond formation, the shifting of electronic orbitals can be interpreted as a charge transfer phenomenon, as electron density may pile up around, and hence, alter the effective charge of, a given atom in the changing chemical environment. Several levels of theory exist to elucidate the mechanisms behind these orbital interactions. Electronic structure calculations solve the time-independent Schrodinger equation to high chemical accuracy, but are computationally expensive and limited to small system sizes and simulation times. Less fundamental atomistic calculations use simpler parameterized functional expressions called force-fields to model atomic interactions. Atomistic simulations can describe systems and time-scales larger and longer than electronic-structure methods, but at the cost of chemical accuracy. In this thesis, both first-principles and phenomenological methods are addressed in the study of several encompassing problems dealing with charge transfer and orbital rehybridization. Firstly, a new charge-equilibration method is developed that improves upon existing models to allow next-generation force-fields to describe the electrostatics of changing chemical environments. Secondly, electronic structure calculations are used to investigate the doping dependent energy landscapes of several high-temperature superconducting materials in order to parameterize the apparently large nonlinear electron-phonon coupling. Thirdly, ab initio simulations are used to investigate the role of pressure-driven structural re-organization in the crystalline-to-amorphous (or, metallic-to-insulating) transition of a common binary phase-change material composed of Ge and Sb. Practical applications of each topic will be discussed. Keywords. Charge-equilibration methods, molecular dynamics, electronic structure calculations, ab initio simulations, high-temperature superconductors, phase-change materials.

Nistor, Razvan A.

326

Investigating photoinduced charge transfer in double- and single-emission PbS@CdS core@shell quantum dots.  

PubMed

We present for the first time detailed investigation of the charge transfer behavior of PbS@CdS core@shell quantum dots (QDs) showing either a single emission peak from the core or intriguing double emission peaks from the core and shell, respectively. A highly non-concentric core@shell structure model was proposed to explain the origin of double emissions from monodisperse QDs. Their charge transfer behavior was investigated by monitoring photoluminescence (PL) intensity variation with the introduction of electron or hole scavengers. It was found that the PL quenching of the PbS core is more efficient than that of the CdS shell, suggesting more efficient charge transfer from the core to scavengers, although the opposite was expected. Further measurements of the PL lifetime followed by wave function calculations disclosed that the time scale is the critical factor explaining the more efficient charge transfer from the core than from the shell. The charge transfer behavior was also examined on a series of single-emission core@shell QDs with either different core sizes or different shell thicknesses and dominant factors were identified. Towards photovoltaic applications, these PbS@CdS QDs were attached onto multi-walled carbon nanotubes (MWCNTs) and their charge transfer behavior was compared with that in the PbS-QD/MWCNT system. Results demonstrate that although the CdS shell serves as an electron transfer barrier, the electrons excited in the PbS cores can still be transferred into the MWCNTs efficiently when the shell thickness is ?0.7 nm. Considering their higher stability, these core@shell QDs are very promising for the development of highly efficient QD-based photovoltaic devices. PMID:24132400

Zhao, Haiguang; Liang, Hongyan; Gonfa, Belete Atomsa; Chaker, Mohamed; Ozaki, Tsuneyuki; Tijssen, Peter; Vidal, François; Ma, Dongling

2014-01-01

327

Empirical Corrections for Charge Transfer Inefficiency and Associated Centroid Shifts for STIS CCD Observations  

E-print Network

A variety of on-orbit imaging and spectroscopic observations are used to characterize the Charge Transfer Efficiency (CTE) of the Charge-Coupled Device (CCD) of the Space Telescope Imaging Spectrograph (STIS) aboard the Hubble Space Telescope. A set of formulae is presented to correct observations of point sources for CTE-related loss of signal. For data taken in imaging mode, the CTE loss is parametrized in terms of the location of the source on the CCD, the source signal level within the measurement aperture, the background level, and the time of observation. For spectroscopic data, it is found that one additional parameter is needed to provide an adequate calibration of the CTE loss, namely the signal in the point spread function located between the signal extraction box and the read-out amplifier. The effect of the latter parameter is significant for spectra taken using the G750L or G750M gratings of STIS. The algorithms presented here correct flux calibration inaccuracies due to CTE losses as large as 30% to within ~ 1.5% RMS throughout the wavelength range covered by the STIS CCD modes. This uncertainty is similar to the Poisson noise associated with a source detected at a signal level of about 2500 electrons per resolution element. Using bi-directional CCD readouts, centroid shifts incurred due to CTE loss are also derived. A tight correlation is found between the CTE loss and the centroid shift (both for imaging and spectroscopic modes), thus enabling one to correct for both effects of imperfect charge transfer to STIS CCD observations.

Paul Goudfrooij; Ralph C. Bohlin; Jesus Maiz-Apellaniz; Randy A. Kimble

2006-08-16

328

Photophysical investigations on supramolecular fullerene/phthalocyanine charge transfer interactions in solution  

NASA Astrophysics Data System (ADS)

The photophysical features of non-covalently linked fullerenes C60 and C70 with a designed free-base phthalocyanine, namely, 2,3,9,10,16,17,23,24-octakis-(octyloxy)-29H,31H-phthalocyanine (1) have been investigated employing various spectroscopic tools like UV-vis absorption spectrophotometry, steady state and time resolved fluorescence along with proton NMR measurements in toluene. The ground state interaction between fullerenes and 1 is nicely demonstrated with the appearance of well defined charge transfer absorption bands in the visible region of the electronic spectra. Steady state fluorescence experiment reveals efficient quenching of the excited singlet state of 1 in presence of both C60 and C70. The average values of binding constants for the non-covalent complexes of C60 and C70 with 1 are determined to be ?18,150 and ?32,000 dm3 mol-1, respectively. The magnitude of K suggests that 1 preferentially binds C70 in comparison to C60 although average value of selectivity in binding is measured to be low (?1.75). Time resolved emission measurements establish photoinduced energy transfer from the excited singlet state of 1 to fullerene in toluene. Measurements of free energy of electron transfer and free energy of radical ion-pair formation elicit that C70/1 complex is stabilized more in comparison to C60/1 complex regarding generation of charge-separated state. Proton NMR studies provide very good support in favor of effective ground state complexation between fullerenes and 1. Semi empirical theoretical calculations on fullerene/1 systems in vacuo substantiate the stronger binding between C70 and 1 in comparison to C60/1 system in terms of heat of formation value of the respective complexes, and determine the orientation of bound guest (here C70) towards the plane of 1 during complexation.

Ray, Anamika; Pal, Haridas; Bhattacharya, Sumanta

2014-01-01

329

Photophysical investigations on supramolecular fullerene/phthalocyanine charge transfer interactions in solution.  

PubMed

The photophysical features of non-covalently linked fullerenes C60 and C70 with a designed free-base phthalocyanine, namely, 2,3,9,10,16,17,23,24-octakis-(octyloxy)-29H,31H-phthalocyanine (1) have been investigated employing various spectroscopic tools like UV-vis absorption spectrophotometry, steady state and time resolved fluorescence along with proton NMR measurements in toluene. The ground state interaction between fullerenes and 1 is nicely demonstrated with the appearance of well defined charge transfer absorption bands in the visible region of the electronic spectra. Steady state fluorescence experiment reveals efficient quenching of the excited singlet state of 1 in presence of both C60 and C70. The average values of binding constants for the non-covalent complexes of C60 and C70 with 1 are determined to be ~18,150 and ~32,000 dm(3) mol(-1), respectively. The magnitude of K suggests that 1 preferentially binds C70 in comparison to C60 although average value of selectivity in binding is measured to be low (~1.75). Time resolved emission measurements establish photoinduced energy transfer from the excited singlet state of 1 to fullerene in toluene. Measurements of free energy of electron transfer and free energy of radical ion-pair formation elicit that C70/1 complex is stabilized more in comparison to C60/1 complex regarding generation of charge-separated state. Proton NMR studies provide very good support in favor of effective ground state complexation between fullerenes and 1. Semi empirical theoretical calculations on fullerene/1 systems in vacuo substantiate the stronger binding between C70 and 1 in comparison to C60/1 system in terms of heat of formation value of the respective complexes, and determine the orientation of bound guest (here C70) towards the plane of 1 during complexation. PMID:24128922

Ray, Anamika; Pal, Haridas; Bhattacharya, Sumanta

2014-01-01

330

Defect-Enhanced Charge Transfer by Ion-Solid Interactions in SiC using Large-Scale AbInitio Molecular Dynamics Simulations  

NASA Astrophysics Data System (ADS)

Large-scale ab initio molecular dynamics simulations of ion-solid interactions in SiC reveal that significant charge transfer occurs between atoms, and defects can enhance charge transfer to surrounding atoms. The results demonstrate that charge transfer to and from recoiling atoms can alter the energy barriers and dynamics for stable defect formation. The present simulations illustrate in detail the dynamic processes for charged defect formation. The averaged values of displacement threshold energies along four main crystallographic directions are smaller than those determined by empirical potentials due to charge-transfer effects on recoil atoms.

Gao, Fei; Xiao, Haiyan; Zu, Xiaotao; Posselt, Matthias; Weber, William J.

2009-07-01

331

Charge transfer structure-reactivity dependence of fullerene-single-walled carbon nanotube heterojunctions.  

PubMed

Charge transfer at the interface between single-walled carbon nanotubes (SWCNTs) of distinct chiral vectors and fullerenes of various molecular weights is of interest both fundamentally and because of its importance in emerging photovoltaic and optoelectronic devices. One approach for generating isolated, discretized fullerene-SWCNT heterojunctions for spectroscopic investigation is to form an amphiphile, which is able to disperse the latter at the single-SWCNT level in aqueous solution. Herein, we synthesize a series of methanofullerene amphiphiles, including derivatives of C60, C70, and C84, and investigated their electron transfer with SWCNT of specific chirality, generating a structure-reactivity relationship. In the cases of two fullerene derivatives, lipid-C61-polyethylene glycol (PEG) and lipid-C71-PEG, band gap dependent, incomplete quenching was observed across all SWCNT species, indicating that the driving force for electron transfer is small. This is further supported by a variant of Marcus theory, which predicts that the energy offsets between the nanotube conduction bands and the C61 and C71 LUMO levels are less than the exciton binding energy in SWCNT. In contrast, upon interfacing nanotubes with C85 methanofullerene, a complete quenching of all semiconducting SWCNT is observed. This enhancement in quenching efficiency is consistent with the deeper LUMO level of C85 methanofullerene in comparison with the smaller fullerene adducts, and suggests its promise as for SWCNT-fullerene heterojunctions. PMID:23848070

Hilmer, Andrew J; Tvrdy, Kevin; Zhang, Jingqing; Strano, Michael S

2013-08-14

332

Role of excited state intramolecular charge transfer in the photophysical properties of norfloxacin and its derivatives.  

PubMed

The photophysical properties of 1-ethyl-6-fluoro-7-(1-piperazinyl)-1,4-dihydro-4-oxoquinoline-3-carboxylic acid (norfloxacin, NFX) and some of its derivatives have been studied to evaluate the role of the free carboxylic acid and the nonprotonated piperazinyl group in the behavior of the 1,4-dihydro-4-oxoquinoline ring. Steady state and time-resolved fluorescence measurements at different pHs provide clear evidence in favor of singlet excited-state deactivation of NFX and its N(4')-methyl derivative pefloxacin (PFX) via intramolecular electron transfer from the N(4') atom of the piperazinyl ring to the fluoroquinolone (FQ) main system. This is a very efficient, energy-wasting pathway, which becomes dramatically enhanced in basic media. Acetylation at N(4') (as in ANFX) decreases the availability of the lone pair, making observable its fluorescence and the transient absorption spectrum of its triplet excited state even at high pH. It also reveals that the geometry of FQs changes from an almost sp3 hybridization of the N(1') of the piperazinyl substituent in the ground state to nearly sp2 in the singlet excited state (rehybridization accompanied by intramolecular charge transfer, RICT); accordingly, the singlet energy of ANFX is significantly lower than that of NFX and PFX. The fluorescence measurements using acetonitrile as a polar nonprotic organic solvent further support deactivation of the singlet excited state of nonacetylated NFX derivatives via intramolecular electron transfer from the N(4') atom. PMID:16494369

Cuquerella, M Consuelo; Miranda, Miguel A; Bosca, Francisco

2006-03-01

333

Mechanism of charge transfer/disproportionation in LnCu3Fe4O12 (Ln = lanthanides)  

NASA Astrophysics Data System (ADS)

The Fe-Cu intersite charge transfer and Fe charge disproportionation are interesting phenomena observed in some LnCu3Fe4O12 (Ln = lanthanides) compounds containing light and heavy Ln atoms, respectively. We show that a change in the spin state is responsible for the intersite charge transfer in the light Ln compounds. At the high-spin state, such systems prefer an unusual Cu d8 configuration, whereas at the low-spin state they retreat to the normal Cu d9 configuration through a charge transfer from Fe to the Cu 3dxy orbital. We find that the strength of the crystal-field splitting and the relative energy ordering between Cu 3dxy and Fe 3d states are the key parameters determining the intersite charge transfer (charge disproportionation) in light (heavy) Ln compounds. It is further proposed that the size of Ln affects the on-site interaction strength of Cu 3d states, leading to a strong modification of the Cu L3-edge spectrum, as observed by the x-ray-absorption spectroscopy.

Rezaei, N.; Hansmann, P.; Bahramy, M. S.; Arita, R.

2014-03-01

334

Charge and energy transfer in a bithiophene perylenediimide based donor-acceptor-donor system for use in organic photovoltaics.  

PubMed

The elementary charge and excitation energy transfer steps in a novel symmetric donor-acceptor-donor triad first described in Roland et al. Phys. Chem. Chem. Phys., 2012, 14, 273, consisting of a central perylenediimide moiety as a potential electron acceptor and two identical electron rich bithiophene compounds, have been investigated using quantum chemical methodology. These elementary processes determine the applicability of such systems in photovoltaic devices. The molecular structure, excited states and the photo-physical properties are investigated using smaller model systems and including solvation effects. The donor and acceptor ?-systems are separated by an ethyl bridge such that the molecular orbitals are either located on the donor or acceptor moiety making the identification of locally excited versus charge transfer states straightforward. Using excited state geometry optimizations, the mechanism of photo-initiated charge separation could be identified. Geometry relaxation in the excited donor state leads to a near-degeneracy with the locally excited acceptor state, entailing strong excitonic coupling and resonance energy transfer. This energy transfer process is driven by planarization and bond length alternation of the donor molecule. Geometry relaxation of the locally excited acceptor state in turn reveals a crossing with the energetically lowest charge transfer excited state. The energetic position of the latter depends in a sensitive fashion on the solvent. This provides an explanation of the sequential process observed in the experiment, favoring ultrafast (?130 fs) formation of the excited acceptor state followed by slower (?3 ps scale) formation of the charge separated state. PMID:23753008

Wenzel, Jan; Dreuw, Andreas; Burghardt, Irene

2013-07-28

335

Coupling between bulk- and surface chemistry in suspensions of charged colloids  

E-print Network

The ionic composition and pair correlations in fluid phases of realistically salt-free charged colloidal sphere suspensions are calculated in the primitive model. We obtain the number densities of all ionic species in suspension, including low-molecular weight microions, and colloidal macroions with acidic surface groups, from a self-consistent solution of a coupled physicochemical set of nonlinear algebraic equations and non-mean-field liquid integral equations. Here, we study suspensions of colloidal spheres with sulfonate or silanol surface groups, suspended in demineralized water that is saturated with carbon dioxide under standard atmosphere. The only input required for our theoretical scheme are the acidic dissociation constants pKa, and effective sphere diameters of all involved ions. Our method allows for an ab initio calculation of colloidal bare and effective charges, at high numerical efficiency.

Marco Heinen; Thomas Palberg; Hartmut Löwen

2013-10-28

336

Vibrational and electronic spectra of one-dimensional organic charge-transfer crystals: Model for a tetramerized cluster structure  

NASA Astrophysics Data System (ADS)

Recently synthesized organic charge-transfer crystals have been shown to display an interesting stack structure of the type ...DAADDAAD... (D denotes the donor molecule, A denotes the acceptor molecule), in which a self-charge-transfer interaction AA or DD alternates with a DA one. A theoretical model is developed for a tetrameric cluster DAAD or ADDA which can account for the coexistence of both types of interaction. The model is based on an electronic extended Hubbard Hamiltonian and also takes into account the interaction between electrons and molecular vibrations. A description of the optical and Raman spectra of the model system is achieved and used to study some complicated features observed in the spectra of the charge-transfer complex TTF-TCNE (TTF denotes tetrathiafulvalene, TCNE denotes tetracyanoethylene).

Meneghetti, M.; Pecile, C.

1989-12-01

337

Symmetric charge-transfer cross sections of IIIa rare-earth-metal elements  

SciTech Connect

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.

Hashida, Masaki; Sakabe, Shuji; Izawa, Yasukazu [ARCBS, Institute for Chemical Research, Kyoto University, Gokasho, Uji, Kyoto 611-0011 (Japan) and Department of Physics, Graduate School of Science, Kyoto University, Kitashirakawa, Sakyo, Kyoto 606-8502 (Japan); Institute of Laser Engineering, Osaka University, Suita, Osaka 565-0871 (Japan) and Institute for Laser Technology, 2-6 Yamadaoka, Suita, Osaka 565-0871 (Japan)

2011-03-15

338

Thermochemical hole burning performance of TCNQ-based charge transfer complexes with different electrical conductivities.  

PubMed

Thermochemical hole burning (THB) memory is an ultrahigh density data storage technique based on the scanning tunneling microscope (STM). It utilizes the STM current to induce localized thermochemical decomposition of TCNQ-based charge transfer (CT) complexes and sequentially create nanometer-sized holes as information bits. The writing reliability and hole size depend on many factors, including the properties of the storage materials and the STM tip, and the tip-sample distance and interaction. We have found here that for the high electrical conductivity CT complexes, the hole size (represented by volume) monotonically decreases with the tip displacement increasing in the direction of leaving the sample; but for low electrical conductivity samples, the hole size first increases and then decreases with the tip displacement increasing in the same direction. Subsequent experiments and analyses indicate that the surface deformation induced by the tip-sample interaction and the heat conduction of the metal tip account for such a unique phenomenon. PMID:21825786

Zhou, Wei; Lin, Feng; Ren, Liang; Huang, Xiaomin; Ran, Chunbo; Ding, Shuai; Peng, Hailin; Liu, Zhongfan

2008-06-11

339

Mechanisms for charge-transfer processes at electrode/solid-electrolyte interfaces.  

SciTech Connect

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.

Chueh, William; El Gabaly Marquez, Farid; Whaley, Josh A.; McCarty, Kevin F.; McDaniel, Anthony H.; Farrow, Roger L.

2011-11-01

340

Charge Transfer Between Ground-State Si(3+) and He at Electron-Volt Energies  

NASA Technical Reports Server (NTRS)

The charge-transfer rate coefficient for the reaction Si(3+)(3s(sup 2)S) + He yields products is measured by means of a combined technique of laser ablation and ion storage. A cylindrical radio-frequency ion trap was used to store Si(3+) ions produced by laser ablation of solid silicon targets. The rate coefficient of the reaction was derived from the decay rate of the ion signal. The measured rate coefficient is 6.27(exp +0.68)(sub -0.52) x 10(exp -10)cu cm/s at T(sub equiv) = 3.9 x 10(exp 3)K. This value is about 30% higher than the Landau-Zener calculation of Butler and Dalgarno and is larger by about a factor of 3 than the recent full quantal calculation of Honvault et al.

Fang, Z.; Kwong, Victor H. S.

1997-01-01

341

Optical switching of electric charge transfer pathways in porphyrin: a light-controlled nanoscale current router.  

PubMed

We introduce a novel molecular junction based on a thiol-functionalized porphyrin derivative with two almost energetically degenerate equilibrium configurations. We show that each equilibrium structure defines a pathway of maximal electric charge transfer through the molecular junction and that these two conduction pathways are spatially orthogonal. We further demonstrate computationally how to switch between the two equilibrium structures of the compound by coherent light. The optical switching mechanism is presented in the relevant configuration subspace of the compound, and the corresponding potential and electric dipole surfaces are obtained by ab initio methods. The laser-induced isomerization takes place in two steps in tandem, while each step is induced by a two-photon process. The effect of metallic electrodes on the electromagnetic irradiation driving the optical switching is also investigated. Our study demonstrates the potential for using thiol-functionalized porphyrin derivatives for the development of a light-controlled nanoscale current router. PMID:21832723

Thanopulos, Ioannis; Paspalakis, Emmanuel; Yannopapas, Vassilios

2008-11-01

342

Thermochemical hole burning performance of TCNQ-based charge transfer complexes with different electrical conductivities  

NASA Astrophysics Data System (ADS)

Thermochemical hole burning (THB) memory is an ultrahigh density data storage technique based on the scanning tunneling microscope (STM). It utilizes the STM current to induce localized thermochemical decomposition of TCNQ-based charge transfer (CT) complexes and sequentially create nanometer-sized holes as information bits. The writing reliability and hole size depend on many factors, including the properties of the storage materials and the STM tip, and the tip-sample distance and interaction. We have found here that for the high electrical conductivity CT complexes, the hole size (represented by volume) monotonically decreases with the tip displacement increasing in the direction of leaving the sample; but for low electrical conductivity samples, the hole size first increases and then decreases with the tip displacement increasing in the same direction. Subsequent experiments and analyses indicate that the surface deformation induced by the tip-sample interaction and the heat conduction of the metal tip account for such a unique phenomenon.

Zhou, Wei; Lin, Feng; Ren, Liang; Huang, Xiaomin; Ran, Chunbo; Ding, Shuai; Peng, Hailin; Liu, Zhongfan

2008-06-01

343

Experimental study of the asymmetric charge transfer reaction between Ar{sup +} ions and Fe atoms  

SciTech Connect

We investigate the Ar{sup +}-Fe asymmetric charge transfer (ACT) reaction using a combination of plasma diagnostics methods and a kinetic model of the afterglow plasma, which allow monitoring of the temporal evolution of the densities of different species. The iron vapor is created inside a discharge cell by cathode sputtering; its density is measured by atomic absorption spectroscopy. The rate coefficient of the reaction is evaluated from the emission intensity decay of Fe{sup +}* lines pumped by the ACT process in the He-Ar-Fe and Ar-Fe afterglow plasmas. The measurements yield a rate coefficient k= 7.6( {+-} 3.0) x 10{sup -9} cm{sup 3} s{sup -1} at T = 300 K.

Korolov, I.; Donko, Z.; Derzsi, A.; Hartmann, P. [Research Institute for Solid State Physics and Optics of the Hungarian Academy of Sciences, H-1525 Budapest, POB 49 (Hungary); Bano, G. [Research Institute for Solid State Physics and Optics of the Hungarian Academy of Sciences, H-1525 Budapest, POB 49 (Hungary); Department of Biophysics, P J Safarik University in Kosice, 04001 Jesenna 5, Kosice (Slovakia)

2011-02-14

344

Charge-induced distortion and stabilization of surface transfer doped porphyrin films  

SciTech Connect

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.

Smets, Y.; Stark, C. B.; Wright, C. A.; Pakes, C. I. [Department of Physics, La Trobe University, Bundoora, Victoria 3086 (Australia)] [Department of Physics, La Trobe University, Bundoora, Victoria 3086 (Australia); Lach, S.; Schmitt, F.; Ziegler, C. [Department of Physics and Research Center OPTIMAS, University of Kaiserslautern, 67663 Kaiserslautern (Germany)] [Department of Physics and Research Center OPTIMAS, University of Kaiserslautern, 67663 Kaiserslautern (Germany); Wanke, M. [Institut für Physik, Technische Universität Chemnitz, 09126 Chemnitz (Germany)] [Institut für Physik, Technische Universität Chemnitz, 09126 Chemnitz (Germany); Ley, L. [Department of Physics, La Trobe University, Bundoora, Victoria 3086 (Australia) [Department of Physics, La Trobe University, Bundoora, Victoria 3086 (Australia); Institut für Technische Physik, Universität Erlangen-Nürnberg, 91058 Erlangen (Germany)

2013-07-28

345

Temperature dependence of charge transfer inefficiency in Chandra X-ray CCDs  

NASA Astrophysics Data System (ADS)

Soon after launch, the Advanced CCD Imaging Spectrometer (ACIS), one of the focal plane instruments on the Chandra X-ray Observatory, suffered radiation damage from exposure to soft protons during passages through the Earth's radiation belts. The primary effect of the damage was to increase the charge transfer inefficiency (CTI) of the eight front illuminated CCDs by more than two orders of magnitude. The ACIS instrument team is continuing to study the properties of the damage with an emphasis on developing techniques to mitigate CTI and spectral resolution degradation. We present the initial temperature dependence of ACIS CTI from -120 to -60 degrees Celsius and the current temperature dependence after more than six years of continuing slow radiation damage. We use the change of shape of the temperature dependence to speculate on the nature of the damaging particles.

Grant, C. E.; Bautz, M. W.; Kissel, S. E.; LaMarr, B.; Prigozhin, G. Y.

2006-06-01

346

A theoretical study of the intramolecular charge transfer in 4-(dimethylamino)benzethyne.  

PubMed

We have investigated the non-adiabatic relaxation processes occurring in the singlet manifold of 4-(dimethylamino)benzethyne (DMABE), a molecule isoelectronic with 4-(dimethylamino)benzonitrile (DMABN) but lacking its characteristic dual fluorescence, using multireference perturbation theory methods. The results obtained point out to the existence of a two-fold decay mechanism in which the population of the initially accessed La state bifurcates towards a locally excited (LE) and a ??* state. Further relaxation to an emitting intramolecular charge transfer (ICT) state is impeded due to the presence of pronounced energy barriers along their associated potential energy surfaces. These results provide further evidence of the role of ??* states in the non-adiabatic relaxation processes of dialkylaminobenzonitriles. PMID:25351413

Segarra-Martí, Javier; Coto, Pedro B

2014-12-14

347

Charge-Transfer Excited States in Aqueous DNA: Insights from Many-Body Green's Function Theory  

NASA Astrophysics Data System (ADS)

Charge-transfer (CT) excited states play an important role in the excited-state dynamics of DNA in aqueous solution. However, there is still much controversy on their energies. By ab initio many-body Green's function theory, together with classical molecular dynamics simulations, we confirm the existence of CT states at the lower energy side of the optical absorption maximum in aqueous DNA as observed in experiments. We find that the hydration shell can exert strong effects (˜1 eV) on both the electronic structure and CT states of DNA molecules through dipole electric fields. In this case, the solvent cannot be simply regarded as a macroscopic screening medium as usual. The influence of base stacking and base pairing on the CT states is also discussed.

Yin, Huabing; Ma, Yuchen; Mu, Jinglin; Liu, Chengbu; Rohlfing, Michael

2014-06-01

348

Optoelectronic properties and charge transfer in donor-acceptor all-conjugated diblock copolymers.  

SciTech Connect

All-conjugated block copolymers, which can self-assemble into well-ordered morphologies, provide exciting opportunities to rationally design and control the nanoscale organization of electron-donor and electron-acceptor moieties in optoelectronic active layers. Here we report on the steady-state and time-resolved optical characterization of block copolymer films and solutions containing poly(3-hexylthiophene) as the donor block and poly(9,9-dioctylfluorene) with and without copolymerization with benzothiadiazole as the acceptor block. Transient absorption measurements suggest rapid charge transfer occurs in both systems, with higher efficiency observed in the latter composition. These results indicate that this class of materials has promise in preparing highly ordered bulk heterojunction all-polymer organic photovoltaic devices.

Botiz, I.; Schaller, R. D.; Verduzco, R.; Darling, S. B. (Center for Nanoscale Materials); (NWU); (Rice Univ.)

2011-05-12

349

Optical charge transfer for the dope in GaAs  

SciTech Connect

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.

Vakulenko, O.V.; Skirda, A.S.; Skryshevskii, V.A.

1984-05-01

350

Charge transfer dynamics in Cu-doped ZnO nanowires  

NASA Astrophysics Data System (ADS)

Time resolved photoluminescence (TRPL) and transient absorption (TA) spectroscopy reveal an ultrafast charge transfer (CT) process, with an electron localization time constant 39±9 ps, between the ZnO host and the Cu dopants in Cu-doped ZnO nanowires. This CT process effectively competes with the ZnO band edge emission, resulting in the quenching of the ZnO UV emission. TRPL measurements show that the UV decay dynamics coincides with the buildup of the Cu-related green emission. TA measurements probing the state-filling of the band edge and defect states provide further support to the CT model where the bleaching dynamics concur with the TRPL lifetimes.

Xing, Guozhong; Xing, Guichuan; Li, Mingjie; Sie, Edbert Jarvis; Wang, Dandan; Sulistio, Arief; Ye, Quan-lin; Huan, Cheng Hon Alfred; Wu, Tom; Sum, Tze Chien

2011-03-01

351

Spectroscopic studies of charge transfer complexes between colchicine and some pi acceptors.  

PubMed

Charge transfer complexes between colchicine as donor and pi acceptors such as tetracyanoethylene (TCNE), 2,3-dichloro-5,6-dicyano-p-benzoquinone (DDQ), p-chloranil (p-CHL) have been studied spectrophotometrically in dichloromethane at 21 degrees C. The stoichiometry of the complexes was found to be 1:1 ratio by the Job method between donor and acceptors with the maximum absorption band at a wavelength of 535, 585 and 515 nm. The equilibrium constant and thermodynamic parameters of the complexes were determined by Benesi-Hildebrand and van't Hoff equations. Colchicine in pure form and in dosage form was applied in this study. The formation constants for the complexes were shown to be dependent on the structure of the electron acceptors used. PMID:17029944

Arslan, Mustafa; Duymus, Hulya

2007-07-01

352

Charge-induced distortion and stabilization of surface transfer doped porphyrin films  

NASA Astrophysics Data System (ADS)

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.

Smets, Y.; Stark, C. B.; Lach, S.; Schmitt, F.; Wright, C. A.; Wanke, M.; Ley, L.; Ziegler, C.; Pakes, C. I.

2013-07-01

353

Charge-induced distortion and stabilization of surface transfer doped porphyrin films.  

PubMed

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. PMID:23901999

Smets, Y; Stark, C B; Lach, S; Schmitt, F; Wright, C A; Wanke, M; Ley, L; Ziegler, C; Pakes, C I

2013-07-28

354

Photoinduced intramolecular charge-transfer state in thiophene-?-conjugated donor–acceptor molecules  

Microsoft Academic Search

Novel thiophene-?-conjugated donor–acceptor molecules, 5-[2-(1,2,2,4-tetramethyl-1,2,3,4-tetrahydroquinolin-6-yl)-vinyl]-thiophene-2-carbaldehyde (QTC) and (1-cyano-2-{5-[2-(1,2,2,4-tetramethyl-1,2,3,4-tetrahydroquinolin-6-yl)-vinyl]-thiophen-2-yl}-vinyl)-phosphonic acid diethyl ester (QTCP), were designed and synthesized. Combined experimental and theoretical methods were performed to investigate the photoinduced intramolecular charge-transfer (ICT) processes of these compounds. Steady-state absorption and fluorescence measurements in different solvents indicate the photoinduced ICT characters of QTC and QTCP. Solvent dependency of the large Stokes shifts and high

Ruikui Chen; Guangjiu Zhao; Xichuan Yang; Xiao Jiang; Jifeng Liu; Haining Tian; Yan Gao; Xien Liu; Keli Han; Mengtao Sun; Licheng Sun

2008-01-01

355

Spectroscopy of Photovoltaic Materials: Charge-Transfer Complexes and Titanium Dioxide  

NASA Astrophysics Data System (ADS)

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.

Dillon, Robert John

356

Controlling the charge transfer in D-A-D chromophores based on pyrazine derivatives.  

PubMed

A series of symmetrical donor-acceptor-donor (D-A-D) chromophores bearing various electron-withdrawing groups, such as quinoxaline (Qx), benzo[g]quinoxaline (BQ), phenazine (Pz), benzo[b]phenazine (BP), thieno[3,4-b]pyrazine (TP), and thieno[3,4-b]quinoxaline (TQ), has been designed and synthesized. Intramolecular charge transfer (ICT) interactions can be found for all the chromophores due to the electron-withdrawing properties of the two imine nitrogens in the pyrazine ring and the electron-donating properties of the other two amine nitrogens in the two triphenylamines. Upon the fusion of either benzene or thiophene ring on the pyrazine acceptor unit, the ICT interactions are strengthened, which results in the bathochromically shifted ICT band. Moreover, the thiophene ring is superior to the benzene ring in enlarging the ICT interaction and expanding the absorption spectrum. Typically, when a thiophene ring is fused on the Qx unit in DQxD, a near-infrared dye is realized in simple chromophore DTQD, which displays the maximum absorption wavelength at 716 nm with the threshold over 900 nm. This is probably due to the enhanced charge density on the acceptor moiety and better orbital overlap, as revealed by theoretical calculation. These results suggest that extending the conjugation of a pyrazine acceptor in an orthogonal direction to the D-A-D backbone can dramatically improve the ICT interactions. PMID:24949892

Lu, Xuefeng; Fan, Suhua; Wu, Jinhong; Jia, Xiaowei; Wang, Zhong-Sheng; Zhou, Gang

2014-07-18

357

Cellular and molecular analysis of mutagenesis induced by charged particles of defined linear energy transfer  

NASA Technical Reports Server (NTRS)

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.

Zhu, L. X.; Waldren, C. A.; Vannias, D.; Hei, T. K.; Chatterjee, A. (Principal Investigator)

1996-01-01

358

Pseudocapacitive hausmannite nanoparticles with (101) facets: synthesis, characterization, and charge-transfer mechanism.  

PubMed

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

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

359

A charge transfer complex nematic liquid crystalline gel with high electrical conductivity  

NASA Astrophysics Data System (ADS)

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.

Bhargavi, R.; Nair, Geetha G.; Krishna Prasad, S.; Majumdar, R.; Bag, Braja G.

2014-10-01

360

Charge transfer effects of ions at the liquid water/vapor interface  

NASA Astrophysics Data System (ADS)

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+, K+, Cl-, and I-. 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.

Soniat, Marielle; Rick, Steven W.

2014-05-01

361

Tuning the hole injection barrier in the intermolecular charge-transfer compound DTBDT-F4TCNQ at metal interfaces  

NASA Astrophysics Data System (ADS)

Molecular monolayers of the charge-transfer salt dithienobenzodithiophene-tetrafluorotetracyanoquinodimethane (DTBDT-F4TCNQ) have been deposited on C(R15×3)/W(110), Co/W(110), and hcp Co(0001) using molecular beam epitaxy in an ultrahigh vacuum. The integrity of the deposited molecules has been confirmed by scanning tunneling microscopy. Scanning tunneling spectroscopy has been used to determine the energetic positions of the highest occupied (HOMO) and lowest unoccupied (LUMO) molecular orbital of acceptor and donor in the pure and in the mixed phase. The mixed charge transfer phase exhibits a new HOMO close to the Fermi edge depicting a charge transfer of less than one elementary charge. The total amount of the transferred charge depends on the underlying metal substrate. The binding energy of the HOMO decreases from 0.4 eV for C(R15×3)/W(110) to 0.16 eV for Co(0001), thus revealing the tunability of the hole injection barrier. The energy gap between HOMO and LUMO decreases from 0.96 eV (0.81 eV) for C(R15×3)/W(110) [ps-ML Co/W(110)] to 0.66 eV for Co(0001), demonstrating a strong reduction compared to the value of the pure moieties.

Bayer, D.; Diehl, S.; Baumgarten, M.; Muellen, K.; Methfessel, T.; Elmers, H. J.

2014-02-01

362

Ferroelectric nature and real-space observations of domain motions in the organic charge-transfer compound tetrathiafulvalene- p -chloranil  

NASA Astrophysics Data System (ADS)

Ferroelectricity in an organic charge-transfer compound, tetrathiafulvalene- p -chloranil (TTF-CA), originating from the one-dimensional valence and lattice instabilities, has been investigated by an electroreflectance (ER) method. Microscopic ER spectroscopy in the visible region enables real-space observations of both ferroelectric domain structures with a few hundred micrometers in size and depinning of the domain walls under strong electric fields. In addition, from ER spectroscopy in the infrared molecular-vibration region, we demonstrate that field-induced changes in the dimeric molecular displacement as well as charge transfer between TTF and CA molecules play an important role in the large dielectric response in TTF-CA.

Kishida, Hideo; Takamatsu, Hisashi; Fujinuma, Ken; Okamoto, Hiroshi

2009-11-01

363

From charge-transfer to a charge-separated state: a perspective from the real-time TDDFT excitonic dynamics.  

PubMed

In-chain donor/acceptor block copolymers comprised of alternating electron rich/poor moieties are emerging as promising semiconducting chromophores for use in organic photovoltaic devices. The mobilities of charge carriers in these materials are experimentally probed using gated organic field-effect transistors to quantify electron and hole mobilities, but a mechanistic understanding of the relevant charge diffusion pathways is lacking. To elucidate the mechanisms of electron and hole transport following excitation to optically accessible low-lying valence states, we utilize mean-field quantum electronic dynamics in the TDDFT formalism to explicitly track the evolution of these photo-accessible states. From the orbital pathway traversed in the dynamics, p- and n-type conductivities can be distinguished. The electronic dynamics of the studied polymers show the time-resolved transitions between the initial photoexcited state, a tightly-bound excitonic state that is dark to the ground state, and a partially charge separated state indicated by long-lived, out-of-phase charge oscillations along the polymer backbone. The frequency of these charge oscillations yields an insight into the characteristic mobilities of charge carriers in these materials. When the barycenters of the electron and hole densities are followed during the dynamics, a pseudo-classical picture for the translation of charge carrier densities along the polymer backbone emerges that clarifies a crucial aspect in the design of efficient organic photovoltaic materials. PMID:25306872

Petrone, Alessio; Lingerfelt, David B; Rega, Nadia; Li, Xiaosong

2014-10-21

364

Ultrafast Charge Transfer in Nickel Phthalocyanine Probed by Femtosecond Raman-Induced Kerr Effect Spectroscopy  

PubMed Central

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

Balakrishnan, Gurusamy; Soldatova, Alexandra V.; Reid, Philip J.; Spiro, Thomas G.

2014-01-01

365

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)

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.

Taran, Michail N.; Koch-Müller, Monika

2011-03-01

366

Photochemical and photophysical properties of ion-pair charge transfer complexes for all-optical information processing  

Microsoft Academic Search

The photochemical and photophysical properties of ion-pair charge transfer (IPCT) complexes comprising of 4,4?-bipyridinium and various counter ions have been reviewed. Quantum chemical and thermodynamic properties of IPCT complexes are summarized. IPCT complexes of 4,4?-bipyridinium with tetraphenylborate derivatives showed specific absorption and fluorescence properties. The photoinduced electron transfer from a counter anion to 4,4?-bipyridinium cation occurred within less than 100fs

Fuyuki Ito; Toshihiko Nagamura

2007-01-01

367

Optically enhanced charge transfer between C60 and single-wall carbon nanotubes in hybrid electronic devices  

NASA Astrophysics Data System (ADS)

In this article we probe the nature of electronic interactions between the components of hybrid C60-carbon nanotube structures. Utilizing an aromatic mediator we selectively attach C60 molecules to carbon nanotube field-effect transistor devices. Structural characterization via atomic force and transmission electron microscopy confirm the selectivity of this attachment. Charge transfer from the carbon nanotube to the C60 molecules is evidenced by a blue shift of the Raman G+ peak position and increased threshold voltage of the transistor transfer characteristics. We estimate this charge transfer to increase the device density of holes per unit length by up to 0.85 nm-1 and demonstrate further optically enhanced charge transfer which increases the hole density by an additional 0.16 nm-1.In this article we probe the nature of electronic interactions between the components of hybrid C60-carbon nanotube structures. Utilizing an aromatic mediator we selectively attach C60 molecules to carbon nanotube field-effect transistor devices. Structural characterization via atomic force and transmission electron microscopy confirm the selectivity of this attachment. Charge transfer from the carbon nanotube to the C60 molecules is evidenced by a blue shift of the Raman G+ peak position and increased threshold voltage of the transistor transfer characteristics. We estimate this charge transfer to increase the device density of holes per unit length by up to 0.85 nm-1 and demonstrate further optically enhanced charge transfer which increases the hole density by an additional 0.16 nm-1. Electronic supplementary information (ESI) available: AFM line scans of the substrate before and after functionalization; scheme for measuring amorphous carbon coverage from TEM images; diameter comparisons of ac-TEM image and simulation of C60 molecule; Raman spectra D peak comparison; optical response of transfer properties of pristine devices; comparison between swept and pulsed Vg measurements; functionalization effect and optical response of the transfer characteristics of a 550 nm and a 450 nm CNTFET device. See DOI: 10.1039/c3nr04314b

Allen, Christopher S.; Liu, Guoquan; Chen, Yabin; Robertson, Alex W.; He, Kuang; Porfyrakis, Kyriakos; Zhang, Jin; Briggs, G. Andrew D.; Warner, Jamie H.

2013-12-01

368

Modelling and Ni/Yttria-Stabilized-Zirconia pattern anode experimental validation of a new charge transfer reactions mechanism for hydrogen electrochemical oxidation on solid oxide fuel cell anodes  

NASA Astrophysics Data System (ADS)

Good understanding of the H2 electrochemical reaction mechanism helps optimize SOFC anode design and improve its performance. Controversies still exist regarding H2 oxidation mechanism despite extensive studies performed. In this work, a new charge transfer reactions mechanism proposed by Shishkin and Ziegler (2010) based on Density Functional Theory (DFT) study was investigated through kinetic modelling and pattern anode experimental validation. The new charge transfer reactions mechanism considers hydrogen oxidation at the interface of Ni and YSZ. It involves a hydrogen atom reacting with the oxygen ions bound to both Ni and YSZ to produce hydroxyl (Charge transfer reaction 1), the latter reacting with the other hydrogen atom to form water (Charge transfer reaction 2). The predictive capability of this reaction mechanism to represent our experimental results was evaluated. The simulated Tafel plots were compared with our experimental data for a wide range of H2 and H2O partial pressures and at different temperatures. Good agreements between simulation and experimental results were obtained. Charge transfer reaction 1 was found to dominate the overall charge transfer reaction under cathodic polarization. Under anodic polarization, a change in the dominating charge transfer reaction from charge transfer reaction 1 to charge transfer reaction 2 was found when increasing the H2O partial pressure.

Yao, Weifang; Croiset, Eric

2014-02-01

369

Influence of atomic layer deposition chemistry on high- k dielectrics for charge trapping memories  

NASA Astrophysics Data System (ADS)

In this work we report the performance of the SiO 2/Si 3N 4/HfO 2 and SiO 2/Si 3N 4/ZrO 2 stacks with emphasis on the influence of atomic layer deposition chemistry used for forming the HfO 2 and ZrO 2 blocking layers. Two Hf precursors were employed - tetrakis(ethylmethylamino)hafnium (TEMAH) and bis(methylcyclopentadienyl)methoxymethyl hafnium (HfD-04). For ZrO 2, tetrakis(ethylmethylamino)zirconium (TEMAZ) and bis(methylcyclopentadienyl)methoxymethyl zirconium (ZrD-04) were used as metal precursors. Ozone was used as the oxygen source. The structural characteristics of the stacks were examined by transmission electron microscopy and grazing incidence X-ray diffraction. The electrical properties of the stacks were studied using platinum-gated capacitor structures. The memory performance of the stacks was evaluated by write/erase (W/E) measurements, endurance and retention testing. Endurance measurements revealed the most important difference between the stacks. The films grown from TEMAH and TEMAZ could withstand a significantly higher number of W/E pulses (>3 × 10 5 in the 10 V/-11 V, 10 ms regime), in comparison to the stacks made from HfD-04 and ZrD-04 precursors (<5 × 10 3 W/E cycles). This difference in endurance characteristics is attributed mainly to the different deposition temperatures suited for these two precursors and the nature of the layer formed at the Si 3N 4/HfO 2 and the Si 3N 4/ZrO 2 interfaces.

Nikolaou, Nikolaos; Dimitrakis, Panagiotis; Normand, Pascal; Ioannou-Sougleridis, Vassilios; Giannakopoulos, Konstantinos; Mergia, Konstantina; Kukli, Kaupo; Niinistö, Jaakko; Ritala, Mikko; Leskelä, Markku

2012-02-01

370

Charge fluctuations, charge-transfer instabilities, and superconductivity in a three-band model of CuO sub 2 planes  

Microsoft Academic Search

We apply a recently developed quasiparticle theory for strongly correlated systems to a three-band model of Cu-O planes. We allow for Cu-O hybridization, Cu-O intersite repulsion, and a large on-site repulsion at the Cu sites (which will be treated as infinite). We use the large spin degeneracy (1\\/{ital N}) expansion to study (i) the interplay between charge-transfer instabilities and phase

J. C. Hicks; A. E. Ruckenstein; S. Schmitt-Rink

1992-01-01

371

Constructivist-Based Asynchronous Tutorial to Improve Transfer between Math and Chemistry Domains: Design, Implementation, and Analysis of the Impact of ReMATCH on General Chemistry Course Performance and Confidence  

E-print Network

and proportional reasoning ability on student performance, including tutorials to improve these ability in an undergraduate psychology course (Vass, et al., 2000) and physics course (Reif & et al., 1976; Reif & Heller, 1982a, 1982b). This research shows that many... Constructivist-Based Asynchronous Tutorial to Improve Transfer between Math and Chemistry Domains: Design, Implementation, and Analysis of the Impact of ReMATCH on General Chemistry Course Performance and Confidence...

Barker, M. Danielle

2011-12-31

372

Unimolecular reaction chemistry of a charge-tagged beta-hydroxyperoxyl radical.  

PubMed

?-Hydroxyperoxyl radicals are formed during atmospheric oxidation of unsaturated volatile organic compounds such as isoprene. They are intermediates in the combustion of alcohols. In these environments the unimolecular isomerization and decomposition of ?-hydroxyperoxyl radicals may be of importance, either through chemical or thermal activation. We have used ion-trap mass spectrometry to generate the distonic charge-tagged ?-hydroxyalkyl radical anion, ?CH2C(OH)(CH3)CH2C(O)O(-), and investigated its subsequent reaction with O2 in the gas phase under conditions that are devoid of complicating radical-radical reactions. Quantum chemical calculations and master equation/RRKM theory modeling are used to rationalize the results and discern a reaction mechanism. Reaction is found to proceed via initial hydrogen abstraction from the ?-methylene group and from the ?-hydroxyl group, with both reaction channels eventually forming isobaric product ions due to loss of either ?OH + HCHO or ?OH + CO2. Isotope labeling studies confirm that a 1,5-hydrogen shift from the ?-hydroxyl functionality results in a hydroperoxyalkoxyl radical intermediate that can undergo further unimolecular dissociations. Furthermore, this study confirms that the facile decomposition of ?-hydroxyperoxyl radicals can yield ?OH in the gas phase. PMID:25325244

So, Sui; Kirk, Benjamin B; Trevitt, Adam J; Wille, Uta; Blanksby, Stephen J; da Silva, Gabriel

2014-10-22

373

Calculation of the cross section for charge transfer in C{sub 70}{sup +} + C{sub 60} collisions  

SciTech Connect

Expressions for the charge transfer cross section in C{sub 60/70} fullerene-fullerene collisions are derived by using an instanton approximation for the tunnel splitting of energy levels. The resulting formulas are valid in the adiabatic approximation and provide an accurate description of available experimental data.

Iroshnikov, G. S. [Moscow Institute of Physics and Technology (State University) (Russian Federation)], E-mail: irosh@orc.ru

2007-10-15

374

Measuring Intramolecular Charge Transfer via Coherent Generation of THz Radiation Matthew C. Beard, Gordon M. Turner, and Charles A. Schmuttenmaer*  

E-print Network

ARTICLES Measuring Intramolecular Charge Transfer via Coherent Generation of THz Radiation Matthew of 10 ns.9,8 Two techniques closely related to this method are THz generation from biased semiconductors and the transient dc photocurrent (TDP) technique. THz generation from biased semiconductors utilizes the

375

Study of low energy Ytterbium atom-ion charge transfer collisions using a surface-electrode trap  

E-print Network

We demonstrate a new isotope-selective system to measure low energy charge transfer collisions between ytterbium ions and atoms in the range of collisional energy from 2.2x 10-5 eV to 4.3x 10-3 eV, corresponding to effective ...

Pruttivarasin, Thaned

2008-01-01

376

Electrically Active Magnetic Nanoparticles for Concentrating and Detecting Bacillus anthracis Spores in a Direct-Charge Transfer Biosensor  

Microsoft Academic Search

Bacillus anthracis, the causative agent of anthrax, is considered as one of the most important pathogens in the list of bioterrorism threats. This paper describes the synthesis of electrically active magnetic (EAM) nanoparticles and their application in a direct-charge transfer biosensor for detecting B. anthracis Sterne endospores. These EAM nanoparticles were synthesized from aniline monomer made electrically active by acid

Sudeshna Pal; Emma B. Setterington; Evangelyn C. Alocilja

2008-01-01

377

Charge transfer on the metallic atom-pair bond, and the crystal structures adopted by intermetallic compounds.  

PubMed

It has been argued in our recent papers that the heat of formation of intermetallic compounds is mostly concentrated in the nearest neighbor unlike atom-pair bonds, and that the positive term in Miedema's equation is associated with charge transfer on the bond to maintain electroneutrality. In this paper, taking examples of some well populated crystal-structure types such as MgCu(2), AsNa(3), AuCu(3), MoSi(2) and SiCr(3) types, the effect of such charge transfer on the crystal structures adopted by intermetallic compounds is examined. It is shown that the correlation between the observed size changes of atoms on alloying and their electronegativity differences is supportive of the idea of charge transfer between atoms. It is argued that the electronegativity and valence differences need to be of the required magnitude and direction to alter, through charge transfer, the elemental radius ratios R(A)/R(B) to the internal radius ratios r(A)/r(B) allowed by the structure types. Since the size change of atoms on alloying is highly correlated to how different R(A)/R(B) is from the ideal radius ratio for a structure type, the lattice parameters of intermetallic compounds can be predicted with excellent accuracy knowing R(A)/R(B). A practical application of the approach developed in our recent papers to superalloy design is presented. PMID:22186292

Rajasekharan, T; Seshubai, V

2012-01-01

378

Charge-transfer-featured materials-promising hosts for fabrication of efficient OLEDs through triplet harvesting via triplet fusion.  

PubMed

A charge-transfer-featured naphthalimide derivative with a small exchange energy but a lower lying (3)??* state than (3)CT state is found to contribute to triplet harvesting through a P-type rather than an E-type delayed fluorescence, and could act as a quite promising host to achieve highly efficient OLEDs. PMID:24796597

Zhou, Jie; Chen, Ping; Wang, Xu; Wang, Yan; Wang, Yi; Li, Feng; Yang, Minghui; Huang, Yan; Yu, Junsheng; Lu, Zhiyun

2014-07-21

379

New approach for evaluation optical absorption measurements of charge transfer complexes between dimethoxynaphthalenes and tetracyanoethylene: singular value decomposition method  

Microsoft Academic Search

Singular-value decomposition (SVD) method is a numerical multidimensional technique appropriate for evaluation of optical absorption measurements of 1:1 charge transfer complexes (CTCs). Matrix algebra of the absorption data for different solutions and wavenumbers is primarily used for evaluation of the equilibrium constant and to obtain some general expressions to illustrate physical significance of the results obtained. The influence of the

Maged A El-Kemary; Safaa El-Din H Etaiw; Hosney Y El-Baradie

2003-01-01

380

Theory of chemical kinetics and charge transfer based on nonequilibrium thermodynamics.  

PubMed

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

Bazant, Martin Z

2013-05-21

381

CoPc and CoPcF16 on gold: Site-specific charge-transfer processes  

PubMed Central

Summary Interface properties of cobalt(II) phthalocyanine (CoPc) and cobalt(II) hexadecafluoro-phthalocyanine (CoPcF16) to gold are investigated by photo-excited electron spectroscopies (X-ray photoemission spectroscopy (XPS), ultraviolet photoemission spectroscopy (UPS) and X-ray excited Auger electron spectroscopy (XAES)). It is shown that a bidirectional charge transfer determines the interface energetics for CoPc and CoPcF16 on Au. Combined XPS and XAES measurements allow for the separation of chemical shifts based on different local charges at the considered atom caused by polarization effects. This facilitates a detailed discussion of energetic shifts of core level spectra. The data allow the discussion of site-specific charge-transfer processes. PMID:24991487

Petraki, Fotini; Uihlein, Johannes; Aygul, Umut; Chasse, Thomas

2014-01-01

382

From evolution to green chemistry: rationalization of biomimetic oxygen-transfer cascades.  

PubMed

Thermodynamic electron-transfer potentials from biology textbooks elucidate the sequence of electron-transfer events in the respiratory chain in mitochondria. In this study, thermodynamic and kinetic oxygen-transfer potentials have been defined and predicted for oxidants and substrates using density functional theory, aiming to rationalize multiple oxygen-transfer events in chemical catalysis, particularly in current developments of the Sharpless dihydroxylation. Key transition states for competing mechanisms in a recent dihydroxylation method containing the olefin, osmium tetraoxide, methyltrioxorhenium(VII), a chiral tertiary amine, and the green terminal oxidant hydrogen peroxide have been investigated rigorously. The calculations show the amine to function as an oxygen-transfer mediator between rhenium peroxides and osma-2,5-dioxolanes, in addition to its role as a carrier of chiral information. Unique mechanistic and stereoelectronic patterns in this oxygen-transfer cascade explain the unexpected failure of reactivity predictions using simpler models such as Marcus theory. PMID:14746448

Deubel, Dirk V

2004-02-01

383

The recoil transfer chamber—An interface to connect the physical preseparator TASCA with chemistry and counting setups  

NASA Astrophysics Data System (ADS)

Performing experiments with transactinide elements demands highly sensitive detection methods due to the extremely low production rates (one -atom -at -a -time conditions). Preseparation with a physical recoil separator is a powerful method to significantly reduce the background in experiments with sufficiently long-lived isotopes ( t1/2?0.5 s). In the last years, the new gas-filled TransActinide Separator and Chemistry Apparatus (TASCA) was installed and successfully commissioned at GSI. Here, we report on the design and performance of a Recoil Transfer Chamber (RTC) for TASCA—an interface to connect various chemistry and counting setups with the separator. Nuclear reaction products recoiling out of the target are separated according to their magnetic rigidity within TASCA, and the wanted products are guided to the focal plane of TASCA. In the focal plane, they pass a thin Mylar window that separates the ˜1 mbar atmosphere in TASCA from the RTC kept at ˜1 bar. The ions are stopped in the RTC and transported by a continuous gas flow from the RTC to the ancillary setup. In this paper, we report on measurements of the transportation yields under various conditions and on the first chemistry experiments at TASCA—an electrochemistry experiment with osmium and an ion exchange experiment with the transactinide element rutherfordium.

Even, J.; Ballof, J.; Brüchle, W.; Buda, R. A.; Düllmann, Ch. E.; Eberhardt, K.; Gorshkov, A.; Gromm, E.; Hild, D.; Jäger, E.; Khuyagbaatar, J.; Kratz, J. V.; Krier, J.; Liebe, D.; Mendel, M.; Nayak, D.; Opel, K.; Omtvedt, J. P.; Reichert, P.; Runke, J.; Sabelnikov, A.; Samadani, F.; Schädel, M.; Schausten, B.; Scheid, N.; Schimpf, E.; Semchenkov, A.; Thörle-Pospiech, P.; Toyoshima, A.; Türler, A.; Vicente Vilas, V.; Wiehl, N.; Wunderlich, T.; Yakushev, A.

2011-05-01

384

Partial charge transfer in the shortest possible metallofullerene peapod, la@c82 ?[11]cycloparaphenylene.  

PubMed

[11]Cycloparaphenylene ([11]CPP) selectively encapsulates La@C82 to form the shortest possible metallofullerene-carbon nanotube (CNT) peapod, La@C82 ?[11]CPP, in solution and in the solid state. Complexation in solution was affected by the polarity of the solvent and was 16?times stronger in the polar solvent nitrobenzene than in the nonpolar solvent 1,2-dichlorobenzene. Electrochemical analysis revealed that the redox potentials of La@C82 were negatively shifted upon complexation from free La@C82 . Furthermore, the shifts in the redox potentials increased with polarity of the solvent. These results are consistent with formation of a polar complex, (La@C82 )(?-) ?[11]CPP(?+) , by partial electron transfer from [11]CPP to La@C82 . This is the first observation of such an electronic interaction between a fullerene pea and CPP pod. Theoretical calculations also supported partial charge transfer (0.07) from [11]CPP to La@C82 . The structure of the complex was unambiguously determined by X-ray crystallographic analysis, which showed the La atom inside the C82 near the periphery of the [11]CPP. The dipole moment of La@C82 was projected toward the CPP pea, nearly perpendicular to the CPP axis. The position of the La atom and the direction of the dipole moment in La@C82 ?[11]CPP were significantly different from those observed in La@C82 ?CNT, thus indicating a difference in orientation of the fullerene peas between fullerene-CPP and fullerene-CNT peapods. These results highlight the importance of pea-pea interactions in determining the orientation of the metallofullerene in metallofullerene-CNT peapods. PMID:25224281

Iwamoto, Takahiro; Slanina, Zdenek; Mizorogi, Naomi; Guo, Jingdong; Akasaka, Takeshi; Nagase, Shigeru; Takaya, Hikaru; Yasuda, Nobuhiro; Kato, Tatsuhisa; Yamago, Shigeru

2014-10-27

385

A new type of charge-transfer salts based on tetrathiafulvalene-tetracarboxylate coordination polymers and methyl viologen.  

PubMed

Although charge-transfer compounds based on tetrathiafulvalene (TTF) derivatives have been intensively studied, {[cation](n+)·[TTFs](n-)} ion pair charge-transfer (IPCT) salts have not been reported. The aim of this research is to introduce functional organic cations, such as photoactive methyl viologen (MV(2+)), into the negatively charged TTF-metal coordination framework to obtain this new type of IPCT complex. X-ray structural analysis of the four compounds (MV)2[Li4(L)2(H2O)6] (1), {(MV)(L)[Na2(H2O)8]·4H2O}n (2), {(MV)[Mn(L)(H2O)2]·2H2O}n (3), and {(MV)[Mn(L)(H2O)2]}n (4), reveals that the electron donor (D) TTF moiety and the electron acceptor (A) MV(2+) form a regular mixed-stack arrangement in alternating DADA fashion. The TTF moiety and the MV(2+) cation are essentially parallel stacked to form the column structures. The strong electrostatic interaction is a main force to shorten the distance between the cation and anion planes. Optical diffuse-reflection spectra indicate that charge transfer occurs in these complexes. The ESR and magnetic measurements confirm that there is strong charge-transfer-induced partial electron transfer. Compounds 2, 3, and 4 show an effective and repeatable photocurrent response. The current intensities of 3 and 4 are higher than that of 2, which reflects that the coordination center of the Mn(II) ion has a great effect on the increasing photocurrent response. PMID:24621401

Huang, Yu-De; Huo, Peng; Shao, Ming-Yan; Yin, Jing-Xue; Shen, Wei-Chun; Zhu, Qin-Yu; Dai, Jie

2014-04-01

386

Electron Doping by Charge Transfer at LaFeO3/Sm2CuO4 Epitaxial Interfaces  

NASA Astrophysics Data System (ADS)

We examine the interfacial charge transfer in epitaxial heterostructures formed between Mott insulating Sm2CuO4 (SCO) and charge transfer insulator LaFeO3 (LFO) in LFO/SCO superlattices. High resolution EELS measurements at the O-K edge have provided evidence for 0.09+/-0.01 extra electrons in the SCO d- band as revealed by a reduction of the Cu oxidation state. The transfer of electrons from LFO to SCO is further supported by the spectroscopic signature of Cu^1+ as obtained from XAS measurements. Transport measurements have evidenced a metallic state at the interface between two nominally insulating materials. Dielectric spectroscopy measurements have allowed ascribing the metallic state to the LFO/SCO interfaces, consistent with DC measurements. When lowering the temperature a metal to insulator transition occurs at 120 K, indicating, in accordance with the phase diagram, an insufficient doping level to enter a superconducting state.

Santamaria, Jacobo; Bruno, F. Y.; Varela, M.; Garcia-Barriocanal, J.; Rivera, A.; Schmidt, R.; Leon, C.; Thakur, P.; Cezar, J. C.; Brookes, N. B.; Garcia Hernandez, M.; Dagotto, E. R.; Pennycook, S. J.

2013-03-01

387

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)

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.

Wang, Dandan; Lü, Rui; Yuan, Minghu; Chen, Junsheng; Feng, Liqiang; Fu, Aiping; Tian, Fenghui; Varandas, António J. C.; Chu, Tianshu

2014-08-01

388

Investigating photoinduced charge transfer in double- and single-emission PbS@CdS core@shell quantum dots  

NASA Astrophysics Data System (ADS)

We present for the first time detailed investigation of the charge transfer behavior of PbS@CdS core@shell quantum dots (QDs) showing either a single emission peak from the core or intriguing double emission peaks from the core and shell, respectively. A highly non-concentric core@shell structure model was proposed to explain the origin of double emissions from monodisperse QDs. Their charge transfer behavior was investigated by monitoring photoluminescence (PL) intensity variation with the introduction of electron or hole scavengers. It was found that the PL quenching of the PbS core is more efficient than that of the CdS shell, suggesting more efficient charge transfer from the core to scavengers, although the opposite was expected. Further measurements of the PL lifetime followed by wave function calculations disclosed that the time scale is the critical factor explaining the more efficient charge transfer from the core than from the shell. The charge transfer behavior was also examined on a series of single-emission core@shell QDs with either different core sizes or different shell thicknesses and dominant factors were identified. Towards photovoltaic applications, these PbS@CdS QDs were attached onto multi-walled carbon nanotubes (MWCNTs) and their charge transfer behavior was compared with that in the PbS-QD/MWCNT system. Results demonstrate that although the CdS shell serves as an electron transfer barrier, the electrons excited in the PbS cores can still be transferred into the MWCNTs efficiently when the shell thickness is ~0.7 nm. Considering their higher stability, these core@shell QDs are very promising for the development of highly efficient QD-based photovoltaic devices.We present for the first time detailed investigation of the charge transfer behavior of PbS@CdS core@shell quantum dots (QDs) showing either a single emission peak from the core or intriguing double emission peaks from the core and shell, respectively. A highly non-concentric core@shell structure model was proposed to explain the origin of double emissions from monodisperse QDs. Their charge transfer behavior was investigated by monitoring photoluminescence (PL) intensity variation with the introduction of electron or hole scavengers. It was found that the PL quenching of the PbS core is more efficient than that of the CdS shell, suggesting more efficient charge transfer from the core to scavengers, although the opposite was expected. Further measurements of the PL lifetime followed by wave function calculations disclosed that the time scale is the critical factor explaining the more efficient charge transfer from the core than from the shell. The charge transfer behavior was also examined on a series of single-emission core@shell QDs with either different core sizes or different shell thicknesses and dominant factors were identified. Towards photovoltaic applications, these PbS@CdS QDs were attached onto multi-walled carbon nanotubes (MWCNTs) and their charge transfer behavior was compared with that in the PbS-QD/MWCNT system. Results demonstrate that although the CdS shell serves as an electron transfer barrier, the electrons excited in the PbS cores can still be transferred into the MWCNTs efficiently when the shell thickness is ~0.7 nm. Considering their higher stability, these core@shell QDs are very promising for the development of highly efficient QD-based photovoltaic devices. Electronic supplementary information (ESI) available: The PL and absorption spectra of PbS@CdS QDs in solution and in films with and without the combination of MWCNTs, Gaussian curve fit to the PL spectra of representative QD film samples, PL lifetime and charge transfer rate from QDs to electron or hole scavengers, radial distribution functions for 1s electron levels of the PbS@CdS core@shell QD with a different core size and constant shell thickness. See DOI: 10.1039/c3nr03691j

Zhao, Haiguang; Liang, Hongyan; Gonfa, Belete Atomsa; Chaker, Mohamed; Ozaki, Tsuneyuki; Tijssen, Peter; Vidal, François; Ma, Dongling

2013-12-01

389

Angle-resolved photoemission in doped charge-transfer Mott insulators  

NASA Astrophysics Data System (ADS)

A theory of angle-resolved photoemission (ARPES) in doped cuprates and other charge-transfer Mott insulators is developed taking into account the realistic (LDA+U) band structure, (bi)polaron formation due to the strong electron-phonon interaction, and a random-field potential. In most of these materials, the first band to be doped is the oxygen band inside the Mott-Hubbard gap. We derive the coherent part of the ARPES spectra with the oxygen hole spectral function calculated in the noncrossing (ladder) approximation and with the exact spectral function of a one-dimensional hole in a random potential. Some unusual features of ARPES, including the polarization dependence and spectral shape in YBa2Cu3O7 and YBa2Cu4O8, are described without any Fermi surface, large or small. The theory is compatible with the doping dependence of kinetic and thermodynamic properties of cuprates as well as with the d-wave symmetry of the superconducting order parameter.

Alexandrov, A. S.; Dent, C. J.

1999-12-01

390

Analysis of the association constants for charge-transfer complex formation  

NASA Astrophysics Data System (ADS)

The phenomenon of charge transfer (CT) complex formation has been of interest for more than 50 years and has led to the development of numerous applications. Even with the prolonged interest in these complexes the interactions responsible for complex formation have yet to be fully characterized and remain an area of sustained relevance. This report outlines the measurement of the association constants for CT complex formation of a series of methylated benzene donors with tetracyanoethylene, pyromellitic dianhydride, 2,3-dichloro-5,6-dicyano-p-benzoquinone, and 1,2,4,5-tetracyanobenzene acceptors in 1,2-dichloroethane solvent. The evaluation of the position of the CT absorption maximum and the magnitudes of the association constants within a theoretical model is described. The influence of solvent polarity on the magnitudes of the association constants was also discussed. These studies show that non-bonding interactions are important in most complexes while ion-pair interactions play a significant role in a select few of the complexes studied.

McKim, William D.; Ray, Jayanta; Arnold, Bradley R.

2013-02-01

391

Spectrophotometric Determination of Mycophenolate Mofetil as Its Charge-Transfer Complexes with Two ?-Acceptors.  

PubMed

Two simple, selective, and rapid spectrophotometric methods are described for the determination of mycophenolate mofetil (MPM) in pure form and in tablets. Both methods are based on charge-transfer complexation reaction of MPM with p-chloranilic acid (p-CA) or 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) in dioxane-acetonitrile medium resulting in coloured product measurable at 520 nm (p-CA) or 580?nm (DDQ). Beer's law is obeyed over the concentration ranges of 40-400 and 12-120??g?mL(-1) MPM for p-CA and DDQ, respectively, with correlation coefficients (r) of 0.9995 and 0.9947. The apparent molar absorptivity values are calculated to be 1.06 × 10(3) and 3.87 × 10(3)?L?mol(-1)?cm(-1), respectively, and the corresponding Sandell's sensitivities are 0.4106 and 0.1119??g?cm(-1). The limits of detection (LOD) and quantification (LOQ) are also reported for both methods. The described methods were successfully applied to the determination of MPM in tablets. Statistical comparison of the results with those of the reference method showed excellent agreement. No interference was observed from the common excipients present in tablets. Both methods were validated statistically for accuracy and precision. The accuracy and reliability of the methods were further ascertained by recovery studies via standard addition procedure. PMID:22567572

Vinay, K B; Revanasiddappa, H D; Raghu, M S; Abdulrahman, Sameer A M; Rajendraprasad, N

2012-01-01

392

Spectrophotometric Determination of Mycophenolate Mofetil as Its Charge-Transfer Complexes with Two ?-Acceptors  

PubMed Central

Two simple, selective, and rapid spectrophotometric methods are described for the determination of mycophenolate mofetil (MPM) in pure form and in tablets. Both methods are based on charge-transfer complexation reaction of MPM with p-chloranilic acid (p-CA) or 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) in dioxane-acetonitrile medium resulting in coloured product measurable at 520 nm (p-CA) or 580?nm (DDQ). Beer's law is obeyed over the concentration ranges of 40–400 and 12–120??g?mL?1 MPM for p-CA and DDQ, respectively, with correlation coefficients (r) of 0.9995 and 0.9947. The apparent molar absorptivity values are calculated to be 1.06 × 103 and 3.87 × 103?L?mol?1?cm?1, respectively, and the corresponding Sandell's sensitivities are 0.4106 and 0.1119??g?cm?1. The limits of detection (LOD) and quantification (LOQ) are also reported for both methods. The described methods were successfully applied to the determination of MPM in tablets. Statistical comparison of the results with those of the reference method showed excellent agreement. No interference was observed from the common excipients present in tablets. Both methods were validated statistically for accuracy and precision. The accuracy and reliability of the methods were further ascertained by recovery studies via standard addition procedure. PMID:22567572

Vinay, K. B.; Revanasiddappa, H. D.; Raghu, M. S.; Abdulrahman, Sameer. A. M.; Rajendraprasad, N.

2012-01-01

393

A zinc phthalocyanine based periodic mesoporous organosilica exhibiting charge transfer to fullerenes.  

PubMed

Periodic mesoporous organosilica (PMO) materials offer a strategy to position molecular semiconductors within a highly defined, porous network. We developed thin films of a new semiconducting zinc phthalocyanine-bridged PMO exhibiting a face-centered orthorhombic pore structure with an average pore diameter of 11?nm. The exceptional degree of order achieved with this PMO enabled us to create thin films consisting of a single porous domain throughout their entire thickness, thus providing maximal accessibility for subsequent incorporation of a complementary phase. The phthalocyanine building blocks inside the pore walls were found to be well-aggregated, enabling electronic conductivity and extending the light-harvesting capabilities to the near IR region. Ordered 3D heterojunctions capable of promoting photo-induced charge transfer were constructed by impregnation of the PMO with a fullerene derivative. When integrated into a photovoltaic device, the infiltrated PMO is capable of producing a high open-circuit voltage and a considerable photocurrent, which represents a significant step towards potential applications of PMOs in optoelectronics. PMID:25293365

Auras, Florian; Li, Yan; Löbermann, Florian; Döblinger, Markus; Schuster, Jörg; Peter, Laurence M; Trauner, Dirk; Bein, Thomas

2014-11-10

394

Charge Transfer Molecular Rotor DCVJ Investigated by Coherent Anti-Stokes Raman Spectroscopy  

NASA Astrophysics Data System (ADS)

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).

Ujj, Laszlo; Miller, Scott; Welch, Jonathan; Amos, Charles; Prayaga, Chandra

2009-05-01

395

Controlling the Conformational Changes in Donor-Acceptor [4]-Dendralenes through Intramolecular Charge-Transfer Processes  

PubMed Central

The synthesis of two [4]-dendralene compounds incorporating thiophene-(p-nitrophenyl) donor–acceptor units is presented. The dendralenes adopt two different conformers in solution and solid state and the transformation between the structures can be controlled by light and heat. The electron-donating components of the dendralenes are represented by bromothienyl (in 13) and ethylenedioxythiophene(EDOT)-thienyl (in 15) end-groups. The most facile transformation involves the isomerisation of donor–acceptor conjugated systems (a conformers) into structures in which only the thiophenes are conjugated (b conformers), and this process is driven by ambient light. The structures of the two conformers of compound 13 are confirmed by single-crystal X-ray diffraction studies and the structural changes in both compounds have been monitored by 1H NMR spectroscopy and absorption studies. The transformations were found to be first-order processes with rate constants of k = 0.0027 s?1 and k = 0.00022 s?1 for 13 and 15, respectively. Density functional theory calculations at the B3LYP/6-31G? level give credence to the proposed mechanism for the a?b conversion, which involves photoinduced intramolecular charge transfer (ICT) as the key step. The EDOT derivative (15) can be polymerised by electrochemical oxidation and a combination of cyclic voltammetry and UV/Vis spectroelectrochemical experiments indicate that the a conformer can be trapped and stabilised in the solid state. PMID:19760710

Kanibolotsky, Alexander L; Forgie, John C; McEntee, Greg J; Talpur, M Munsif A; Skabara, Peter J; Westgate, Thomas DJ; McDouall, Joseph JW; Auinger, Michael; Coles, Simon J; Hursthouse, Michael B

2009-01-01

396

Mixed-stack organic charge-transfer complexes with intercolumnar networks  

NASA Astrophysics Data System (ADS)

We report synthesis and examination of the electronic properties of an isomorphous series of mixed-stack organic charge-transfer complexes, composed of [bis(ethylenedithio)tetrathiafulvalene] (BEDT-TTF)-based electron donors and electron acceptors of halogen-substituted tetracyanoquinodimethanes (TCNQ's). Single crystals of (BEDT-TTF)(Me2TCNQ), (BEDT-TTF)(ClMeTCNQ), and (BEDO-TTF)(Cl2TCNQ) were investigated as to their crystal structures, and optical and magnetic properties. The intermolecular overlaps between the stacked columns were comparable to the face-to-face overlap between the donor and the acceptor molecules inside the stacks. As seen from the optical and magnetic measurements, the (BEDT-TTF)(Me2TCNQ) and (BEDT-TTF)(ClMeTCNQ) complexes were neutral, while the (BEDO-TTF)(Cl2TCNQ) complex was found to be ionic. Among these complexes, anomalous magnetic properties were observed in the ionic complex of (BEDO-TTF)(Cl2TCNQ). (BEDO-TTF)(Cl2TCNQ) is a magnetic insulator with Curie-Weiss behavior in magnetic susceptibility followed by a sharp drop at around 120 K, which is in sharp contrast to conventional ``spin-Peierls-type'' nonmagnetic mixed-stack ionic compounds.

Hasegawa, T.; Mochida, T.; Kondo, R.; Kagoshima, S.; Iwasa, Y.; Akutagawa, T.; Nakamura, T.; Saito, G.

2000-10-01

397

Conductive PVDF-HFP nanofibers with embedded TTF-TCNQ charge transfer complex.  

PubMed

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

Gal-Oz, Reshef; Patil, Nilesh; Khalfin, Rafail; Cohen, Yachin; Zussman, Eyal

2013-07-10

398

Bethe-Salpeter equation without empty electronic states applied to charge-transfer excitations  

NASA Astrophysics Data System (ADS)

We present an approach to compute optical absorption spectra of molecules and nanostructures from first principles, which is suitable for the study of large systems and gives access to spectra within a wide energy range. In this approach, the quantum Liouville equation is solved iteratively within first order perturbation theory, with a Hamiltonian containing a static self-energy operator. This is equivalent to solving the Bethe-Salpeter equation. Explicit calculations of single particle excited states and inversion of dielectric matrices are avoided using techniques based on Density Functional Perturbation Theory [1,2]. In this way, full absorption spectra may be obtained with a computational workload comparable to ground state Hartree-Fock calculations. Applications to the description of charge transfer excitations are presented. [1] D.Rocca, D.Lu and G.Galli (submitted) [2] H. Wilson, F. Gygi and G. Galli, Phys. Rev. B , 78, 113303, 2008;H. Wilson, D. Lu, F. Gygi and G. Galli, Phys. Rev. B, 79, 245106,2009.

Rocca, Dario; Lu, Deyu; Galli, Giulia

2010-03-01

399

Selective contacts drive charge extraction in quantum dot solids via asymmetry in carrier transfer kinetics  

NASA Astrophysics Data System (ADS)

Colloidal quantum dot solar cells achieve spectrally selective optical absorption in a thin layer of solution-processed, size-effect tuned, nanoparticles. The best devices built to date have relied heavily on drift-based transport due to the action of an electric field in a depletion region that extends throughout the thickness of the quantum dot layer. Here we study for the first time the behaviour of the best-performing class of colloidal quantum dot films in the absence of an electric field, by screening using an electrolyte. We find that the action of selective contacts on photovoltage sign and amplitude can be retained, implying that the contacts operate by kinetic preferences of charge transfer for either electrons or holes. We develop a theoretical model to explain these experimental findings. The work is the first to present a switch in the photovoltage in colloidal quantum dot solar cells by purposefully formed selective contacts, opening the way to new strategies in the engineering of colloidal quantum dot solar cells.

Mora-Sero, Ivan; Bertoluzzi, Luca; Gonzalez-Pedro, Victoria; Gimenez, Sixto; Fabregat-Santiago, Francisco; Kemp, Kyle W.; Sargent, Edward H.; Bisquert, Juan

2013-08-01

400

Photoelectrochemical and charge transfer properties of SnS/TiO2 heterostructure nanotube arrays  

NASA Astrophysics Data System (ADS)

SnS/TiO2 heterostructure nanotube arrays (NTAs) were synthesized through a successive ionic layer adsorption and reaction process. The photoelectrochemical (PEC) property of SnS/TiO2 heterostructure NTAs was evaluated in liquid junction PEC solar cells. The results revealed that SnS/TiO2 heterostructure NTAs exhibited PEC property with an open-circuit voltage of 1.08 V, a short-circuit current density of 1.55 mA/cm2, and a conversion efficiency of 0.75% under 1 sun illumination. These values are higher than those of pristine SnS nanoparticles and TiO2 NTAs. Surface photovoltage spectroscopy and phase spectroscopy measurements were conducted to verify the formation of heterojunction and probe charge transfer between SnS and TiO2 NTAs. The PEC property and surface photovoltaic response enhancement of SnS/TiO2 heterostructure NTAs can be attributed to the enhanced electron-hole separation due to the effect of interfacial electric field in SnS/TiO2 heterostructure NTAs.

Jia, Yongfang; Yang, Feng; Cai, Fanggong; Cheng, Cuihua; Zhao, Yong

2013-05-01

401

Bi and Cu valence characterization and charge transfer in single-phase Bi-2212 ceramics  

NASA Astrophysics Data System (ADS)

Samples with 0953-2048/11/1/023/img1 composition were synthesized by an original process based on the spray drying of a nitrate solution of Bi, Sr, Ca and Cu cations complexed with EDTA at pH > 6. After calcination at 0953-2048/11/1/023/img2 and grinding, the samples were sintered in the range 0953-2048/11/1/023/img3 in air and annealed between 0953-2048/11/1/023/img4 and 0953-2048/11/1/023/img5 in nitrogen. The relationships between critical temperature (0953-2048/11/1/023/img6 and 0953-2048/11/1/023/img7), Bi and Cu valences (determined by permanganate and iodometric titration) and cell parameter c were investigated. The relatively weak variation of Bi with respect to that of Cu as a function of the oxygen excess 0953-2048/11/1/023/img8 in the BiO planes provides evidence for a `buffer' effect in these planes induced by the charge transfer from the 0953-2048/11/1/023/img9 planes.

Duvigneaud, P. H.; DeBoeck, C.; Guo, Y. F.

1998-01-01

402

A gate controlled molecular switch based on picene-F4TCNQ charge-transfer material.  

PubMed

We show that the recently synthesized charge-transfer material picene-F4TCNQ can be used as a gate-voltage controlled molecular switch. The picene-F4TCNQ system is compared with the extensively characterized anthraquinone-based molecular system, which is known to exhibit large switching ratios due to quantum interference effects. In the case of picene-F4TCNQ we find switching ratios larger by one order of magnitude. Further, our calculations reveal that the picene-F4TCNQ system resembles remarkably well the I-V characteristics of a classical diode. The reverse-bias current of this molecular diode can be increased two orders of magnitude by an external gate voltage. Based on density-functional theory calculations we show that the hybrid states formed by the picene-F4TCNQ system play the key role in determining transport properties. We further conclude that the tuning of quantum transport properties through hybrid states is a general concept which opens a new route towards functional materials for molecular electronics. PMID:25347765

Hahn, Torsten; Liebing, Simon; Kortus, Jens

2014-11-01

403

Vibrational coherences in charge-transfer dyes: A non-adiabatic picture  

NASA Astrophysics Data System (ADS)

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.

Sissa, Cristina; Delchiaro, Francesca; Di Maiolo, Francesco; Terenziani, Francesca; Painelli, Anna

2014-10-01

404

Donor-acceptor substituted phenylethynyltriphenylenes – excited state intramolecular charge transfer, solvatochromic absorption and fluorescence emission  

PubMed Central

Summary Several 2-(phenylethynyl)triphenylene derivatives bearing electron donor and acceptor substituents on the phenyl rings have been synthesized. The absorption and fluorescence emission properties of these molecules have been studied in solvents of different polarity. For a given derivative, solvent polarity had minimal effect on the absorption maxima. However, for a given solvent the absorption maxima red shifted with increasing conjugation of the substituent. The fluorescence emission of these derivatives was very sensitive to solvent polarity. In the presence of strongly electron withdrawing (–CN) and strongly electron donating (–NMe2) substituents large Stokes shifts (up to 130 nm, 7828 cm?1) were observed in DMSO. In the presence of carbonyl substituents (–COMe and –COPh), the largest Stokes shift (140 nm, 8163 cm?1) was observed in ethanol. Linear correlation was observed for the Stokes shifts in a Lippert–Mataga plot. Linear correlation of Stokes shift was also observed with E T(30) scale for protic and aprotic solvents but with different slopes. These results indicate that the fluorescence emission arises from excited state intramolecular charge transfer in these molecules where the triphenylene chromophore acts either as a donor or as an acceptor depending upon the nature of the substituent on the phenyl ring. HOMO–LUMO energy gaps have been estimated from the electrochemical and spectral data for these derivatives. The HOMO and LUMO surfaces were obtained from DFT calculations. PMID:21085512

Nandy, Ritesh

2010-01-01

405

Structure and dynamics of a discotic liquid-crystalline charge-transfer complex.  

PubMed

The structure of the charge-transfer complex hexakis(n-hexyloxy)triphenylene-2,4,7-trinitro-9-fluorenone (HAT6-TNF) has been characterized by neutron scattering, X-ray diffraction (XRD), optical microscopy, and dielectric relaxation spectroscopy (DRS). On the basis of these data and the 1:1 stoichiometry, a consistent structure for the complex is proposed. This structure differs markedly from structures previously proposed for similar materials, because the TNF molecules are found to be situated between the discotic columns rather than sandwiched between the discotic molecules of a given column. The addition of TNF to HAT6 is found to stiffen the structure, and quasi-elastic neutron scattering shows that the local dynamics of the discotic molecules in HAT6-TNF is slowed by the presence of the TNF molecules. This scenario is consistent with the observation of two VFT-type (VFT=Vogel-Fulcher-Tamman) dielectric relaxation processes that relate to the columnar glass transition and a polyethylene-like hindered glass transition originating from the nano-phase-separated fraction of the aliphatic tails. PMID:17526037

Kruglova, Olga; Mendes, Eduardo; Yildirim, Zeynep; Wübbenhorst, Michael; Mulder, Fokko M; Stride, John A; Picken, Stephen J; Kearley, Gordon J

2007-06-25

406

Electron photodetachment from iodide in ionic liquids through charge-transfer-to-solvent band excitation.  

PubMed

Solvation of iodide and electrons in an ionic liquid (N,N,N-trimethyl-n-propylammonium bis(trifluoromethanesulfonyl)imide; TMPA-TFSI) was studied through the absorption spectra of the charge-transfer-to-solvent (CTTS) state of iodide and of solvated electrons. The interaction between the TMPA cation and iodide was strong, whereas electrons were weakly solvated in TMPA-TFSI. We followed electron photodetachment from iodide to the ionic liquid and formation of the solvated electrons by observing absorption in the visible and near-infrared regions using a nanosecond laser flash photolysis method. The quantum yield of the photodetachment in TMPA-TFSI was estimated to be 0.34, which is much higher than that in a high-concentration aqueous salt solution previously reported. We also examined a reaction of the solvated electrons with the ionic liquid 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide (Bmim-TFSI) as a solute in TMPA-TFSI. The reaction rate was determined to be 5.3 x 10(8) M(-1) s(-1). The electrons before full solvation (dry electrons) reacted with Bmim cations efficiently. These observations suggest that the electrons in TMPA-TFSI can move easily before solvation. PMID:17474702

Katoh, Ryuzi; Yoshida, Yoichi; Katsumura, Yosuke; Takahashi, Kenji

2007-05-10

407

Charge transfer in photoelectrochemical devices via interface states - unified model and comparison with experimental data  

SciTech Connect

A simple, unified model is presented for the mediation of charge transfer across the semiconductor/electrolyte interface by states localized in the bandgap of the semiconductor. These states are interpreted to arise from specific adsorption of anionic species from the electrolyte. The adsorbed ions could be either one of the components of a regenerative redox couple or comprise the constituent ions of the supporting electrolyte. The role of the interphasial layer in photoelectrochemical (PEC) devices is examined in the light of the above model. The key factor in determining the efficacy of energy conversion in the PEC system is identified as the competition between tunneling of photogenerated holes across the interphasial layer and their recombination with the majority carriers in the semiconductor conduction band. The extent of matching between the interface state and the reduced (filled) energy levels in the electrolyte is shown to be important in this regard. Experimental data on the n-GaAs/room temperature molten salt electrolyte and the n-CdSe/polysulfide interfaces are discussed in the light of this model. 28 refs.

Rajeshwar, K.

1982-05-01

408

Antibacterial activity of large-area monolayer graphene film manipulated by charge transfer.  

PubMed

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

Li, Jinhua; Wang, Gang; Zhu, Hongqin; Zhang, Miao; Zheng, Xiaohu; Di, Zengfeng; Liu, Xuanyong; Wang, Xi

2014-01-01

409

Antibacterial activity of large-area monolayer graphene film manipulated by charge transfer  

PubMed Central

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

Li, Jinhua; Wang, Gang; Zhu, Hongqin; Zhang, Miao; Zheng, Xiaohu; Di, Zengfeng; Liu, Xuanyong; Wang, Xi

2014-01-01

410

Role of direction of charge transfer on the nonlinear optical behavior of pyridine substituted chalcone derivatives  

NASA Astrophysics Data System (ADS)

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.

Menezes, Anthoni Praveen; Jayarama, A.

2014-10-01

411

Charge transfer interaction using quasiatomic minimal-basis orbitals in the effective fragment potential method  

SciTech Connect

The charge transfer (CT) interaction, the most time-consuming term in the general effective fragment potential method, is made much more computationally efficient. This is accomplished by the projection of the quasiatomic minimal-basis-set orbitals (QUAMBOs) as the atomic basis onto the self-consistent field virtual molecular orbital (MO) space to select a subspace of the full virtual space called the valence virtual space. The diagonalization of the Fock matrix in terms of QUAMBOs recovers the canonical occupied orbitals and, more importantly, gives rise to the valence virtual orbitals (VVOs). The CT energies obtained using VVOs are generally as accurate as those obtained with the full virtual space canonical MOs because the QUAMBOs span the valence part of the virtual space, which can generally be regarded as “chemically important.” The number of QUAMBOs is the same as the number of minimal-basis MOs of a molecule. Therefore, the number of VVOs is significantly smaller than the number of canonical virtual MOs, especially for large atomic basis sets. This leads to a dramatic decrease in the computational cost.

Xu, Peng; Gordon, Mark S. [Department of Chemistry, Iowa State University, Ames, Iowa 50011 (United States)] [Department of Chemistry, Iowa State University, Ames, Iowa 50011 (United States)

2013-11-21

412

Theoretical and experimental studies of the H+-N2 system: Differential cross sections for direct and charge-transfer scattering at kilo-electron-volt energies  

Microsoft Academic Search

Differential direct and charge-transfer scattering cross sections are calculated for collisions of H+ with N2 using the electron nuclear dynamics formalism. The calculated cross sections are compared to direct scattering measurements which are also reported here and to the experimental charge transfer data of Gao et al. [R. S. Gao, L. K. Johnson, C. L. Hakes, K. A. Smith, and

R. Cabrera-Trujillo; Y. Öhrn; E. Deumens; J. R. Sabin; B. G. Lindsay

2002-01-01

413

An experimental study on the heat transfer characteristics of a heat pipe heat exchanger with latent heat storage. Part II: Simultaneous charging\\/discharging modes  

Microsoft Academic Search

In this part of the paper, the performance of the simultaneous charging\\/discharging operation modes of the heat pipe heat exchanger with latent heat storage is experimentally studied. The experimental results show that the device may operate under either the fluid to fluid heat transfer with charging heat to the phase change material (PCM) or the fluid to fluid heat transfer

Zhongliang Liu; Zengyi Wang; Chongfang Ma

2006-01-01

414

Transfer and computation of optical topological charges via light pulse buffer memory in an electromagnetically-induced-transparency solid  

NASA Astrophysics Data System (ADS)

We verified that optical topological charges are conserved in a two-step light-pulse storage and retrieval process based on the electromagnetically-induced-transparency (EIT) effect in a Pr3+:Y2SiO5 crystal. Based on this conservation law, one could transfer topological charges from the interacting beams, which may not be overlapped in space and time domains, to the targeted output signal beam, and algebraic operations such as summation and subtraction of topological charges carried by the interacting beams were demonstrated via the EIT-assisted two-step light-pulse storage-retrieval process. The results may be useful for classical and quantum information processing based on optical topological charge buffer memory in EIT media.

Zhai, Zhaohui; Li, Zhixiang; Xu, Jingjun; Zhang, Guoquan

2013-09-01

415

The simplest equivalent circuit of a pulsed dielectric barrier discharge and the determination of the gas gap charge transfer  

SciTech Connect

The concept of the simplest equivalent circuit for a dielectric barrier discharge (DBD) is critically reviewed. It is shown that the approach is consistent with experimental data measured either in large-scale sinusoidal-voltage driven or miniature pulse-voltage driven DBDs. An expression for the charge transferred through the gas gap q(t) is obtained with an accurate account for the displacement current and the values of DBD reactor capacitance. This enables (i) the significant reduction of experimental error in the determination of q(t) in pulsed DBDs, (ii) the verification of the classical electrical theory of ozonizers about maximal transferred charge q{sub max}, and (iii) the development of a graphical method for the determination of q{sub max} from charge-voltage characteristics (Q-V plots, often referred as Lissajous figures) measured under pulsed excitation. The method of graphical presentation of q{sub max} is demonstrated with an example of a Q-V plot measured under pulsed excitation. The relations between the discharge current j{sub R}(t), the transferred charge q(t), and the measurable parameters are presented in new forms, which enable the qualitative interpretation of the measured current and voltage waveforms without the knowledge about the value of the dielectric barrier capacitance C{sub d}. Whereas for quantitative evaluation of electrical measurements, the accurate estimation of the C{sub d} is important.

Pipa, A. V.; Brandenburg, R.; Hoder, T. [Leibniz Institute for Plasma Science and Technology (INP Greifswald), Felix-Hausdorff-Str. 2, Greifswald 17489 (Germany); Koskulics, J. [Light and Life Laboratory, Department of Physics and Engineering Physics, Stevens Institute of Technology, Hoboken, New Jersey 07030 (United States)

2012-11-15

416

One-And-A-Half-Centered Expansion Method in Charge-Transfer Calculations of Proton-Hydrogen Scattering  

E-print Network

In this paper, we undertake a feasibility study of improving the one-and-a-half-centered expansion (OHCE) method of Reading, Ford, and Becker [J. Phys. B 14, 1995 (198 1)...15, 3257 (1982)]. We have explored the efficacy of an alternative method to evaluate the charge-transfer matrix elements and improved the estimated time dependence of the charge-transfer scattering amplitudes. More projectile states have been included in the calculations than used hitherto. A unitary matrix, U matrix, which can propagate the wave functions from -infinity to t, where t denotes time, has been constructed using the single-centered expansion (SCE) method. A complex basis set of nine radial s states and nine radial p states has been used in the expansion of trial wave functions for the target. Charge-transfer matrix elements have been evaluated by a Feynman integral technique...one numerical integral using Gaussian quadrature is needed. The radial parts of the matrix elements are stored on circles and used for all the impact parameters. In a OHCE calculation, we have to choose a function beta(m)(z) to modulate the charge...

Chen, Z. F.; Reading, John F.

1993-01-01

417

Elongation of lifetime of the charge-separated state of ferrocene-naphthalenediimide-[60]fullerene triad via stepwise electron transfer.  

PubMed

Photoinduced electron-transfer processes of a newly synthesized rodlike covalently linked ferrocene-naphthalenediimide-[60]fullerene (Fc-NDI-C(60)) triad in which Fc is an electron donor and NDI and C(60) are electron acceptors with similar first one-electron reduction potentials have been studied in benzonitrile. In the examined Fc-NDI-C(60) triad, NDI with high molar absorptivity is considered to be the chromophore unit for photoexcitation. Although the free-energy calculations verify that photoinduced charge-separation processes via singlet- and triplet-excited states of NDI are feasible, transient absorption spectra observed upon femtosecond laser excitation of NDI at 390 nm revealed fast and efficient electron transfer from Fc to the singlet-excited state of NDI ((1)NDI*) to produce Fc(+)-NDI(•-)-C(60). Interestingly, this initial charge-separated state is followed by a stepwise electron transfer yielding Fc(+)-NDI-C(60)(•-). As a result of this sequential electron-transfer process, the lifetime of the charge-separated state (?(CS)) is elongated to 935 ps, while Fc(+)-NDI(•-) has a lifetime of only 11 ps. PMID:22112188

Supur, Mustafa; El-Khouly, Mohamed E; Seok, Jai Han; Kay, Kwang-Yol; Fukuzumi, Shunichi

2011-12-22

418

Effects of electrostatic field on the phase properties of mixed-stack organic charge-transfer compounds  

NASA Astrophysics Data System (ADS)

We have studied the effects of an external electric field on the phase properties of mixed-stack organic charge-transfer complexes through illustrative calculations based on the ionic crystal model, paying special attention to the roles of electrostatic energy. The ground-state charge configurations of tetrathiafulvalene-p-chloranil (TTF-CA) under electric fields have been explored mainly by the Monte Carlo simulated annealing method in the cases of one-dimensional chain, three-dimensional bulk crystal, and thin film. It has been found for TTF-CA bulk crystals at room temperature and ambient pressure that the applied electric field beyond approximately 106 V/cm would induce a transition from the neutral phase to the charge-separated phase in which positively and negatively charged donor-acceptor pairs, D+A0 and D0A-, separately appear near both ends of DA stack chains. Investigating the phase structure of charge-transfer complexes through the variations in ionization energy, Madelung energy, and external field, we have also found that the applied field can cause a neutral-ionic transition of mixed-stack organic charge-transfer compounds in the close vicinity of neutral-ionic phase boundary. We then discuss the feasibility of this electric-field-induced neutral-ionic transition in actual organic-complex systems in terms of employing compounds other than TTF-CA or of varying temperature, pressure, and film thickness to approach the systems to the neutral-ionic phase boundary.

Tanaka, Shigenori; Aoki, Shinya; Nakayama, Toshio; Egusa, Syun

1995-07-01

419

The Complex Core Level Spectra of CeO2: An Analysis in Terms of Atomic and Charge Transfer Effects  

SciTech Connect

We present a rigorous parameter-free theoretical treatment of the Ce 4s and 5s photoelectron spectra of CeO2. In the currently accepted model the satellite structure in the photoelectron spectra is explained in terms of a mixed valence (Ce 4f0 O 2p6, Ce 4f1 O 2p5, and Ce 4f2 O 2p4) con?guration. We show that charge transfer (CT) into Ce 5d as well as con?gurations involving intra-atomic movement of charge must be considered in addition and compute their contributions to the spectra.

Bagus, Paul S.; Nelin, Constance J.; Ilton, Eugene S.; Baron, Martin; Abbott, Heather; Primorac, Elena; Kuhlenbeck, Helmut; Shaikhutdinov, Shamil; Freund, Hans-Joachim

2010-03-05

420

Intermolecular interactions and charge transfer transitions in aromatic hydrocarbon-tetracyanoethylene complexes.  

PubMed

A comprehensive theoretical study of the electronically excited states in complexes between tetracyanoethylene (TCNE) and three aromatic electron donors, benzene, naphthalene and anthracene, was performed with a focus on charge transfer (CT) transitions. The results show that the algebraic diagrammatic construction method to second order (ADC(2)) provides excellent possibilities for reliable calculations of CT states. Significant improvements in the accuracy of the computed transition energies are obtained by using the scaled opposite-spin (SOS) variant of ADC(2). Solvent effects were examined on the basis of the conductor-like screening model (COSMO) which has been implemented recently in the ADC(2) method. The dielectric constant and the refractive index of dichloromethane have been chosen in the COSMO calculations to compare with experimental solvatochromic effects. The computation of optimized ground state geometries and enthalpies of formation has been performed at the second-order Møller-Plesset perturbation theory (MP2) level. By comparison with experimental data and with high-level coupled-cluster methods including explicitly correlated (F12) wave functions, the importance of the SOS approach is demonstrated for the ground state as well. In the benzene-TCNE complex, the two lowest electronic excitations are of CT character whereas in the naphthalene and anthracene TCNE complexes three low-lying CT states are observed. As expected, they are strongly stabilized by the solvent. Geometry optimization in the lowest excited state allowed the calculation of fluorescence transitions. Solvent effects lead to a zero gap between S1 and S0 for the anthracene-TCNE complex. Therefore, in the series of benzene-TCNE to anthracene a change from a radiative