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1

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

2

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

3

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

NASA Astrophysics Data System (ADS)

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

Wodtke, Alec M.

2013-06-01

4

Non-Adiabatic Photoprocesses of Fundamental Importance toChemistry: From Electronic Relaxation of DNA Bases to IntramolecularCharge Transfer in Electron Donor-Acceptor Molecules  

Microsoft Academic Search

Substituent effects on ultrafast electronic relaxation (internal conversion) of nucleobases and intramolecular charge transfer\\u000a in electron donor-acceptor (EDA) molecules, containing benzonitrile and diphenylacetylene moieties, have been investigated\\u000a using laser spectroscopy and simple ab initio methods. The results demonstrate the central role biradical states play in the\\u000a nonadiabatic energy- and charge-transfer dynamics. Specifically, subpicosecond internal conversion characteristic of the naturally\\u000a occurring

Marek Z. Zgierski; Takashige Fujiwara; Edward C. Lim

5

Hostguest charge transfer states: CN doped Kr and Xe S. L. Fiedler  

E-print Network

Host­guest charge transfer states: CN doped Kr and Xe S. L. Fiedler Department of Chemistry; accepted 20 August 2002 The host­guest charge transfer absorption of CN doped krypton and xenon matrices/Kr charge transfer band at 193 nm leads to emission over CN(A(2 )X(2 )) transition, indicating

Apkarian, V. Ara

6

Charge transfer doping of silicon.  

PubMed

We demonstrate a novel doping mechanism of silicon, namely n-type transfer doping by adsorbed organic cobaltocene (CoCp2*) molecules. The amount of transferred charge as a function of coverage is monitored by following the ensuing band bending via surface sensitive core-level photoelectron spectroscopy. The concomitant loss of electrons in the CoCp2* adlayer is quantified by the relative intensities of chemically shifted Co2p components in core-level photoelectron spectroscopy which correspond to charged and neutral molecules. Using a previously developed model for transfer doping, the evolution in relative intensities of the two components as a function of coverage has been reproduced successfully. A single, molecule-specific parameter, the negative donor energy of -(0.50±0.15)??eV suffices to describe the self-limiting doping process with a maximum areal density of transferred electrons of 2×1013??cm-2 in agreement with the measured downward band bending. The advantage of this doping mechanism over conventional doping for nanostructures is addressed. PMID:24785050

Rietwyk, K J; Smets, Y; Bashouti, M; Christiansen, S H; Schenk, A; Tadich, A; Edmonds, M T; Ristein, J; Ley, L; Pakes, C I

2014-04-18

7

Detecting QGP with Charge Transfer Fluctuations  

Microsoft Academic Search

In this study, we analyze the recently proposed charge transfer fluctuations\\u000awithin a finite pseudo-rapidity space. As the charge transfer fluctuation is a\\u000ameasure of the local charge correlation length, it is capable of detecting\\u000ainhomogeneity in the hot and dense matter created by heavy ion collisions. We\\u000apredict that going from peripheral to central collisions, the charge transfer\\u000afluctuations

Sangyong Jeon; Lijun Shi; Marcus Bleicher

2005-01-01

8

Charge Transfer Fluctuations as a QGP Signal  

Microsoft Academic Search

In this study, we analyze the recently proposed charge transfer fluctuations\\u000awithin a finite pseudo-rapidity space. As the charge transfer fluctuation is a\\u000ameasure of the local charge correlation length, it is capable of detecting\\u000ainhomogeneity in the hot and dense matter created by heavy ion collisions. We\\u000apredict that going from peripheral to central collisions, the charge transfer\\u000afluctuations

Sangyong Jeon; Lijun Shi

2005-01-01

9

Charge Transfer Fluctuations as a QGP Signal  

E-print Network

In this study, we analyze the recently proposed charge transfer fluctuations within a finite pseudo-rapidity space. As the charge transfer fluctuation is a measure of the local charge correlation length, it is capable of detecting inhomogeneity in the hot and dense matter created by heavy ion collisions. We predict that going from peripheral to central collisions, the charge transfer fluctuations at midrapidity should decrease substantially while the charge transfer fluctuations at the edges of the observation window should decrease by a small amount. These are consequences of having a strongly inhomogeneous matter where the QGP component is concentrated around midrapidity. We also show how to constrain the values of the charge correlations lengths in both the hadronic phase and the QGP phase using the charge transfer fluctuations. Current manuscript is based on the preprints hep-ph/0503085 (to appear in Physical Review C) and nucl-th/0506025.

Sangyong Jeon; Lijun Shi

2005-11-24

10

Detecting QGP with Charge Transfer Fluctuations  

E-print Network

In this study, we analyze the recently proposed charge transfer fluctuations within a finite pseudo-rapidity space. As the charge transfer fluctuation is a measure of the local charge correlation length, it is capable of detecting inhomogeneity in the hot and dense matter created by heavy ion collisions. We predict that going from peripheral to central collisions, the charge transfer fluctuations at midrapidity should decrease substantially while the charge transfer fluctuations at the edges of the observation window should decrease by a small amount. These are consequences of having a strongly inhomogeneous matter where the QGP component is concentrated around midrapidity. We also show how to constrain the values of the charge correlations lengths in both the hadronic phase and the QGP phase using the charge transfer fluctuations.

Sangyong Jeon; Lijun Shi; Marcus Bleicher

2005-06-08

11

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

12

Charge transfer in cluster-atom collisions.  

SciTech Connect

Charge transfer in collisions Na{sub n}{sup +} + Cs {yields} Na{sub n} + Cs{sup +} (4 {<=} n {<=} 11) is investigated theoretically within a microscopic framework. It is shown that an understanding of the measured charge transfer cross-sections can be obtained only if the competing reaction channels (electronic excitations and fragmentation) are treated simultaneously and, in addition, if the initial temperature of the clusters in the beam is taken into account. The energy dependence of the cross-sections is predicted. An exotic charge transfer channel producing Cs{sup -} is found to have a finite probability.

Knospe, O.; Jellinek, J.; Saalmann, U.; Schmidt, R.; Chemistry; Max-Planck-Institut fur Physik Komplexer Systeme; Technical Univ. of Dresden

1999-01-01

13

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

14

Simulations of charge transfer in Electron Multiplying Charge Coupled Devices  

NASA Astrophysics Data System (ADS)

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

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

2014-12-01

15

Charge transfer complexes of certain aromatic polyimides  

NASA Technical Reports Server (NTRS)

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

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

1985-01-01

16

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

17

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

18

Biological charge transfer via flickering resonance  

PubMed Central

Biological electron-transfer (ET) reactions are typically described in the framework of coherent two-state electron tunneling or multistep hopping. However, these ET reactions may involve multiple redox cofactors in van der Waals contact with each other and with vibronic broadenings on the same scale as the energy gaps among the species. In this regime, fluctuations of the molecular structures and of the medium can produce transient energy level matching among multiple electronic states. This transient degeneracy, or flickering electronic resonance among states, is found to support coherent (ballistic) charge transfer. Importantly, ET rates arising from a flickering resonance (FR) mechanism will decay exponentially with distance because the probability of energy matching multiple states is multiplicative. The distance dependence of FR transport thus mimics the exponential decay that is usually associated with electron tunneling, although FR transport involves real carrier population on the bridge and is not a tunneling phenomenon. Likely candidates for FR transport are macromolecules with ET groups in van der Waals contact: DNA, bacterial nanowires, multiheme proteins, strongly coupled porphyrin arrays, and proteins with closely packed redox-active residues. The theory developed here is used to analyze DNA charge-transfer kinetics, and we find that charge-transfer distances up to three to four bases may be accounted for with this mechanism. Thus, the observed rapid (exponential) distance dependence of DNA ET rates over distances of ?15 Å does not necessarily prove a tunneling mechanism. PMID:24965367

Zhang, Yuqi; Liu, Chaoren; Balaeff, Alexander; Skourtis, Spiros S.; Beratan, David N.

2014-01-01

19

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.

20

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

21

Real-time observation of the charge transfer to solvent dynamics.  

PubMed

Intermolecular electron-transfer reactions have a crucial role in biology, solution chemistry and electrochemistry. The first step of such reactions is the expulsion of the electron to the solvent, whose mechanism is determined by the structure and dynamical response of the latter. Here we visualize the electron transfer to water using ultrafast fluorescence spectroscopy with polychromatic detection from the ultraviolet to the visible region, upon photo-excitation of the so-called charge transfer to solvent states of aqueous iodide. The initial emission is short lived (~60 fs) and it relaxes to a broad distribution of lower-energy charge transfer to solvent states upon rearrangement of the solvent cage. This distribution reflects the inhomogeneous character of the solvent cage around iodide. Electron ejection occurs from the relaxed charge transfer to solvent states with lifetimes of 100-400 fs that increase with decreasing emission energy. PMID:23820611

Messina, Fabrizio; Bräm, Olivier; Cannizzo, Andrea; Chergui, Majed

2013-01-01

22

Nucleic Acid Charge Transfer: Black, White and Gray  

PubMed Central

Theoretical studies of charge transport in deoxyribonucleic acid (DNA) and peptide nucleic acid (PNA) indicate that structure and dynamics modulate the charge transfer rates, and that different members of a structural ensemble support different charge transport mechanisms. Here, we review the influences of nucleobase geometry, electronic structure, solvent environment, and thermal conformational fluctuations on the charge transfer mechanism. We describe an emerging framework for understanding the diversity of charge transport mechanisms seen in nucleic acids. PMID:21528017

Venkatramani, Ravindra; Keinan, Shahar; Balaeff, Alexander; Beratan, David N.

2011-01-01

23

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@uos.de; vgrachev@uos.de; schirmer@uos.de Abstract The results of the study of charge transfer processes in barium of crystals from barium titanate (BT) family make them promising candidates for various applications

Malovichko, Galina

24

Ion momentum and energy transfer rates for charge exchange collisions  

NASA Technical Reports Server (NTRS)

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

Horwitz, J.; Banks, P. M.

1973-01-01

25

Charge transfer, surface charging, and overlayer-induced faceting J. G. Che* and C. T. Chan  

E-print Network

Charge transfer, surface charging, and overlayer-induced faceting J. G. Che* and C. T. Chan to analyze the change of surface energy of metallic surfaces upon surface charging. We then studied surface charging is main driving mechanism in view of such an empirical correlation. Our results show

Che, Jingguang

26

Proton Transfer Reactivity of Large Multiply Charged Ions  

PubMed Central

Charge-charge interactions dramatically influence the dissociation and proton transfer reactivity of large multiply protonated ions. In combination with tandem mass spectrometry, proton transfer reactions have been used to determine the charge state of an ion and to increase the effective mass resolution of electrospray ionization mass spectra. A model for the proton transfer reactivity of multiply protonated ions, in which protons are assigned to specific sites in an ion based on the intrinsic reactivity of the site and the sum of point-charge Coulomb interactions between charges, is discussed. In combination with experimentally measured rates of proton transfer to bases of known gas-phase basicity, information about the intramolecular electrostatic interactions, gas-phase ion conformation and maximum charge state of an ion produced by electrospray ionization can be obtained. PMID:8799309

Williams, Evan R.

2005-01-01

27

Charge transfer between reduced graphene oxide sheets on insulating substrates  

NASA Astrophysics Data System (ADS)

Understanding the electrical communications between graphene sheets placed on insulating substrates is of great value to rational design of functional graphene nanoelectronics. In this paper, we report charge transfer between reduced graphene oxide (rGO) sheets separated in hundreds of nanometers on insulating substrates. We found that the rGO sheet collects charges from the adjacent charged rGO sheet through the dielectric surfaces. The efficiency of charge transfer between the separated rGO sheets is dependent on their separation distance, gap length, and the substrate type. The findings suggest that the charge interflow should not be neglected in a graphene circuit.

Shen, Yue; Zhang, Xueqiang; Wang, Ying; Zhou, Xuejiao; Hu, Jun; Guo, Shouwu; Zhang, Yi

2013-07-01

28

Charge Transfer Fluctuations as a Signal for QGP  

Microsoft Academic Search

In this work, the charge transfer fluctuation which was previously used for\\u000a$pp$ collisions is proposed for relativistic heavy-ion collisions as a QGP\\u000aprobe. We propose the appearance of a local minimum at midrapidity for the\\u000acharge transfer fluctuation as a signal for a QGP. Within a two-component\\u000aneutral cluster model, we demonstrate that the charge transfer fluctuation can\\u000adetect

Lijun Shi; Sangyong Jeon

2005-01-01

29

Imaging charge transfer in iodomethane upon x-ray photoabsorption.  

PubMed

Studies of charge transfer are often hampered by difficulties in determining the charge localization at a given time. Here, we used ultrashort x-ray free-electron laser pulses to image charge rearrangement dynamics within gas-phase iodomethane molecules during dissociation induced by a synchronized near-infrared (NIR) laser pulse. Inner-shell photoionization creates positive charge, which is initially localized on the iodine atom. We map the electron transfer between the methyl and iodine fragments as a function of their interatomic separation set by the NIR-x-ray delay. We observe signatures of electron transfer for distances up to 20 angstroms and show that a realistic estimate of its effective spatial range can be obtained from a classical over-the-barrier model. The presented technique is applicable for spatiotemporal imaging of charge transfer dynamics in a wide range of molecular systems. PMID:25035485

Erk, Benjamin; Boll, Rebecca; Trippel, Sebastian; Anielski, Denis; Foucar, Lutz; Rudek, Benedikt; Epp, Sascha W; Coffee, Ryan; Carron, Sebastian; Schorb, Sebastian; Ferguson, Ken R; Swiggers, Michele; Bozek, John D; Simon, Marc; Marchenko, Tatiana; Küpper, Jochen; Schlichting, Ilme; Ullrich, Joachim; Bostedt, Christoph; Rolles, Daniel; Rudenko, Artem

2014-07-18

30

Contributions of charge-density research to medicinal chemistry.  

PubMed

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

Dittrich, Birger; Matta, Chérif F

2014-11-01

31

Charge transfer interaction in the effective fragment potential method  

NASA Astrophysics Data System (ADS)

An approximate formula is derived and implemented in the general effective fragment potential (EFP2) method to model the intermolecular charge transfer interaction. This formula is based on second order intermolecular perturbation theory and utilizes canonical molecular orbitals and Fock matrices obtained with preparative self-consistent field calculations. It predicts charge transfer energies that are in reasonable agreement with the reduced variational space energy decomposition analysis. The formulas for the charge transfer gradients with respect to EFP translational and rotational displacements are also derived and implemented.

Li, Hui; Gordon, Mark S.; Jensen, Jan H.

2006-06-01

32

A surface acoustic wave /SAW/ charge transfer imager  

NASA Technical Reports Server (NTRS)

An 80 MHz, 2-microsecond surface acoustic wave charge transfer device (SAW-CTD) has been fabricated in which surface acoustic waves are used to create traveling longitudinal electric fields in the silicon substrate and to replace the multiphase clocks of charge coupled devices. The traveling electric fields create potential wells which will carry along charges that may be stored in the wells; the charges may be injected into the wells by light. An optical application is proposed where the SAW-CTD structure is used in place of a conventional interline transfer design.

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

1981-01-01

33

Energy versus charge transfer in ?-conjugated polymer:fullerene blends  

NASA Astrophysics Data System (ADS)

The article is focused on the detailed elucidation of fluorescence quenching by charge and/or energy transfer in ?-conjugated polymers. The processes were studied in blends of MDMO-PPV, Tg-PPV, PCDTBT and PCBTDPP with fullerenes PC60BM and PC70BM in chlorobenzene. Fluorescence quenching was evaluated by the Perrin equation for static quenching and quenching sphere radiuses were calculated. These radiuses were found to be the same as the Förster critical distances for resonance energy transfer. It was concluded that energy transfer prevails over charge transfer under the conditions where the donor and acceptor are not in close contact.

Heinrichova, Patricie; Vala, Martin; Weiter, Martin

2014-01-01

34

Chemistry-dependent X-ray-induced surface charging.  

PubMed

Materials science in general, and surface/interface science in particular, have greatly benefited from the development of high energy synchrotron radiation facilities. Irradiation with intense ionizing beams can however influence relevant sample properties. Permanent radiation damage and irradiation-induced sample modifications have been investigated in detail during the last decades. Conversely, reversible sample alterations taking place only during irradiation are still lacking comprehensive in situ characterization. Irradiation-induced surface charging phenomena are particularly relevant for a wide range of interface science investigations, in particular those involving surfaces of solid substrates in contact with gaseous or liquid phases. Here, we demonstrate partially reversible radiation-induced surface charging phenomena, which extend far beyond the spatial dimensions of the X-ray beam mainly as a consequence of the interaction between the surface and ionized ambient molecules. The charging magnitude and sign are found to be surface chemistry specific and dependent on the substrates' bulk conductivity and grounding conditions. These results are obtained by combining a scanning Kelvin probe with a synchrotron surface diffractometer to allow simultaneous in situ work function measurements during precisely controlled hard X-ray micro-beam irradiation. PMID:25219347

Salg?n, Bekir; Pontoni, Diego; Vogel, Dirk; Schröder, Heiko; Keil, Patrick; Stratmann, Martin; Reichert, Harald; Rohwerder, Michael

2014-10-28

35

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

36

Frequency response of charge transfer in MOS inversion layers  

NASA Technical Reports Server (NTRS)

The dynamics of charge transfer from a reservoir into an MOS inversion layer, which limits the frequency response of an MOS transistor or a charge-coupled device, is investigated. Using Berman and Kerr's model of space-charge capacitance in the semiconductor, a small-signal distributed model is developed for an MOS structure which transfers charge in an inversion channel due to a variation in the gate voltage. The dynamics of the charge transfer is characterized by a time constant which is determined by the length of the inversion channel and its mobility. Experimental data of gate capacitance vs frequency, taken from a test structure with a diffused source/drain well, are satisfactorily fitted by theoretical curves derived from the model. The channel mobility is precisely determined from the adjusted time constant. The influence of interface states on the capacitance-frequency relationship is also briefly discussed.

Lieneweg, U.

1980-01-01

37

Multiferroicity of Carbon-Based Charge-Transfer Magnets.  

PubMed

A new type of carbon charge-transfer magnet, consisting of a fullerene acceptor and single-walled carbon nanotube donor, is demonstrated, which exhibits room temperature ferromagnetism and magnetoelectric (ME) coupling. In addition, external stimuli (electric/magnetic/elastic field) and the concentration of a nanocarbon complex enable the tunabilities of the magnetization and ME coupling due to the control of the charge transfer. PMID:25389110

Qin, Wei; Gong, Maogang; Chen, Xiaomin; Shastry, Tejas A; Sakidja, Ridwan; Yuan, Guoliang; Hersam, Mark C; Wuttig, Manfred; Ren, Shenqiang

2014-11-11

38

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

39

Femtochemistry of Intramolecular Charge and Proton Transfer Reactions in Solution  

SciTech Connect

We report on the first observation of ultrafast intramolecular charge- and proton-transfer reactions in 4'-dimethylaminoflavonol (DAMF) in solution. Upon femtosecond excitation of a non-planar structure of DMAF in apolar medium, the intramolecular charge transfer (ICT) does not occur, and a slow (2 ps) proton motion takes place. However, in polar solvents, the ICT is very fast (100-200 fs) and the produced structure is stabilized that proton motion takes place in few or tens of ps.

Douhal, Abderrazzak; Sanz, Mikel; Carranza, Maria Angeles; Organero, Juan Angel; Tormo, Laura [Departamento de Quimica Fisica, Seccion de Quimicas, Facultad de Ciencias del Medio Ambiente, Universidad de Castilla-La Mancha, Avda. Carlos III, S.N., 45071, Toledo (Spain)

2005-03-17

40

Charge transfer reactions in nematic liquid crystals  

SciTech Connect

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

Wiederrecht, G.P. [Argonne National Lab., IL (United States). Chemistry Div.; Wasielewski, M.R. [Argonne National Lab., IL (United States). Chemistry Div.; [Northwestern Univ., Evanston, IL (United States). Dept. of Chemistry; Galili, T.; Levanon, H. [Hebrew Univ. of Jerusalem (Israel). Dept. of Physical Chemistry

1998-07-01

41

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

42

Charge-transfer magnets: multiferroicity of carbon-based charge-transfer magnets (adv. Mater. 4/2015).  

PubMed

Carbon charge-transfer complexes offer great potential for next generation organic multiferroics. On page 734, S. Ren and co-workers demonstrate room temperature magnetoelectric coupling of nanocarbon charge-transfer magnets. In the image magnetic field effects on optoelectronic and dipole properties of nanocarbon complexes are shown, which would be critical for the development of all-organic multifunctional smart devices. PMID:25607918

Qin, Wei; Gong, Maogang; Chen, Xiaomin; Shastry, Tejas A; Sakidja, Ridwan; Yuan, Guoliang; Hersam, Mark C; Wuttig, Manfred; Ren, Shenqiang

2015-01-01

43

Charge Transfer Fluctuations as a Signal for QGP  

E-print Network

In this work, the charge transfer fluctuation which was previously used for $pp$ collisions is proposed for relativistic heavy-ion collisions as a QGP probe. We propose the appearance of a local minimum at midrapidity for the charge transfer fluctuation as a signal for a QGP. Within a two-component neutral cluster model, we demonstrate that the charge transfer fluctuation can detect the presence of a QGP as well as the size of the QGP in the rapidity space. We also show that the forward-backward correlation of multiplicity can be a similarly good measure of the presence of a QGP. Further, we show that the previously proposed net charge fluctuation is sensitive to the existence of the second phase only if the QGP phase occupies a large portion of the available rapidity space.

Lijun Shi; Sangyong Jeon

2005-03-08

44

Coherent ultrafast charge transfer in an organic photovoltaic blend.  

PubMed

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

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

2014-05-30

45

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

46

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

47

Reptation Quantum Monte Carlo calculation of charge transfer: The Na-Cl dimer  

NASA Astrophysics Data System (ADS)

The phenomenon of ion pairing in aqueous solutions is of widespread importance in chemistry and physics, and charge transfer between the ions plays a significant role. We examine the performance of quantum Monte Carlo (QMC) calculations for describing the charge transfer behavior in a NaCl dimer. The influence of the fermion nodes is investigated by obtaining the electron density using the reptation Monte Carlo approach. The fermion nodes are given by single-particle orbitals in Slater-Jastrow trial wavefunctions. We consider the single-particle orbitals from Hartree-Fock and density functional theory calculations with several exchange-correlation approximations. Appreciable dependence of the charge transfer on the fixed-node approximation was found although the total energy was found to be rather insensitive. Our work shows that a careful examination of the fixed-node approximation is necessary for quantifying charge transfer in QMC calculations even when other properties such as reaction energetics are insensitive to the approximation.

Yao, Yi; Kanai, Yosuke

2015-01-01

48

Analysis of charge transfer effects in molecular complexes based on absolutely localized molecular orbitals  

E-print Network

Analysis of charge transfer effects in molecular complexes based on absolutely localized molecular to measure the degree of intermolecular electron density delocalization charge transfer in molecular complexes. ALMO charge transfer analysis CTA enables separation of the forward and backward charge transfer

Bell, Alexis T.

49

Dynamics of charge transfer states on metal surfaces: The competition between reactivity and quenching  

E-print Network

Dynamics of charge transfer states on metal surfaces: The competition between reactivity by charge transfer is studied. Both negative and positive charge transfer processes are possible. In particular we are interested in positive charge transfer from a metal surface to molecular or atomic oxygen

Zeiri, Yehuda

50

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

51

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

52

Are hydrogen-bonded charge transfer crystals room temperature ferroelectrics?  

PubMed

We present a theoretical investigation of the anomalous ferroelectricity of mixed-stack charge transfer molecular crystals, based on the Peierls-Hubbard model, and first-principles calculations for its parametrization. This approach is first validated by reproducing the temperature-induced transition and the electronic polarization of TTF-CA, and then applied to a novel series of hydrogen-bonded crystals, for which room temperature ferroelectricity has recently been claimed. Our analysis shows that the hydrogen-bonded systems present a very low degree of charge transfer and hence support a very small polarization. A critical reexamination of experimental data supports our findings, shedding doubts on the ferroelectricity of these systems. More generally, our modeling allows the rationalization of general features of the ferroelectric transition in charge transfer crystals and suggests design principles for materials optimization. PMID:25526158

D'Avino, Gabriele; Verstraete, Matthieu J

2014-12-01

53

Are Hydrogen-Bonded Charge Transfer Crystals Room Temperature Ferroelectrics?  

NASA Astrophysics Data System (ADS)

We present a theoretical investigation of the anomalous ferroelectricity of mixed-stack charge transfer molecular crystals, based on the Peierls-Hubbard model, and first-principles calculations for its parametrization. This approach is first validated by reproducing the temperature-induced transition and the electronic polarization of TTF-CA, and then applied to a novel series of hydrogen-bonded crystals, for which room temperature ferroelectricity has recently been claimed. Our analysis shows that the hydrogen-bonded systems present a very low degree of charge transfer and hence support a very small polarization. A critical reexamination of experimental data supports our findings, shedding doubts on the ferroelectricity of these systems. More generally, our modeling allows the rationalization of general features of the ferroelectric transition in charge transfer crystals and suggests design principles for materials optimization.

D'Avino, Gabriele; Verstraete, Matthieu J.

2014-12-01

54

Bioexcimers as Precursors of Charge Transfer and Reactivity in Photobiology  

SciTech Connect

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

Serrano-Andres, Luis; Merchan, Manuela; Roca-Sanjuan, Daniel; Olaso-Gonzalez, Gloria [Institute de Ciencia Molecular, Universitat de Valencia Apartado de Correos 22085, ES-46071 Valencia (Spain); Rubio, Mercedes [Fundacio General, Universitat de Valencia, Plaza del Patriarca, 4, 1, ES-46002 Valencia (Spain)

2007-11-29

55

Charge transfer and in-cloud structure of large-charge-moment positive lightning strokes in a mesoscale convective system  

E-print Network

Charge transfer and in-cloud structure of large-charge-moment positive lightning strokes frequency magnetic fields are analyzed to investigate the charge transfer and in-cloud structure of eight were recorded, these strokes contained large charge moment changes (1500­3200 CÁkm) capable

Cummer, Steven A.

56

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

57

Surface Science Letters Surface to bulk charge transfer at  

E-print Network

Surface Science Letters Surface to bulk charge transfer at an alkali metal/metal oxide interface R and Medicine, Exhibition Road, London SW7 2AY, UK Received 19 June 2003; accepted for publication 8 October functional calculations; Synchrotron radiation photoelectron spectroscopy; Alkali metals; Titanium oxide; Low

58

Introduction to charge transfer device discrete time processing  

NASA Technical Reports Server (NTRS)

This tutorial paper reviews some of the advantages and disadvantages of a discrete time representation of a signal. Also reviewed are some of the recent theoretical advances in digital signal processing which can be implemented by the use of charge transfer signal processing devices. In particular, the design and implementation of transversal filters and spectrum analyzers will be discussed.

Brodersen, R. W.

1976-01-01

59

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

60

Infrared Spectroscopy of Charge Transfer Complexes of Purines and Pyrimidines  

SciTech Connect

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. [Department Of Physics, Sardar Patel University, Vallabh Vidyanagar, Gujarat, 388120 (India)

2011-10-20

61

Graphene nonvolatile memory prototype based on charge-transfer mechanism  

NASA Astrophysics Data System (ADS)

A graphene nonvolatile memory (GNVM) prototype based on charge transfer between the graphene layer and the NH2(CH2)3Si(OEt)3 (APTES) self-assembled monolayer (SAM) is demonstrated. Graphene was transferred to an APTES-SAM-engineered SiO2 substrate and patterned into bottom-gate transistors. Owing to the charge trapping/detrapping property of the nitrogen atoms in APTES, a significant and reproducible transfer curve hysteresis is observed. Memory performance metrics, including retention and endurance, are reported. Comparisons between vacuum and ambient environment test results indicate air absorbates’ detrimental effect. Loss of nonvolatile storage is explained on the basis of a two-layer tunneling junction model, which sheds light on further device improvement through aminosilane molecule structure optimization.

Lv, Hongming; Wu, Huaqiang; Huang, Can; Wang, Yuda; Qian, He

2014-04-01

62

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

ERIC Educational Resources Information Center

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

Gilliom, Richard D.

1989-01-01

63

Photoinduced charge and energy transfer in molecular wires.  

PubMed

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

Gilbert, Mélina; Albinsson, Bo

2015-02-10

64

Active pixel sensor with intra-pixel charge transfer  

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.

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

1995-01-01

65

Active pixel sensor with intra-pixel charge transfer  

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.

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

2004-01-01

66

Active pixel sensor with intra-pixel charge transfer  

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.

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

2003-01-01

67

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

68

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

69

Charge transfer magnetoexciton formation at vertically coupled quantum dots.  

PubMed

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

Gutiérrez, Willian; Marin, Jairo H; Mikhailov, Ilia D

2012-01-01

70

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

71

Strong electronic correlations in superconducting organic charge transfer salts  

Microsoft Academic Search

We review the role of strong electronic correlations in quasi-two-dimensional organic charge transfer salts such as (BEDT-TTF)2X, (BETS)2Y, and ??-[Pd(dmit)2]2Z. We begin by defining minimal models for these materials. It is necessary to identify two classes of material: the first class is strongly dimerized and is described by a half-filled Hubbard model; the second class is not strongly dimerized and

B. J. Powell; Ross H. McKenzie

2006-01-01

72

Partial charge transfer during anion adsorption. Methodological aspects  

NASA Astrophysics Data System (ADS)

Some problems of applying the Lippmann equation to ionic adsorption on solid electrodes are considered. The possibility of using a nonthermodynamic approach to certain thermodynamic problems (particularly, the role of elastic and plastic deformations of electrode surfaces in adsorption processes, the polarity of surface bonds during anion adsorption, and others) is discussed. The extremely thin electrode layer affected electrically and mechanically by adsorbate is considered to be free of dislocations because of volume discrepancy. The nearest structure-mechanical analogs of such layers are whiskers'-type crystals whose side surface could have point-, one- and two-dimensional defects, but not dislocations. Like whiskers, surface metal layers ought to possess an ultimate strength close to theoretical one (0.2 E) and a purely elastic deformation up to 0.04. The surface electrode layer (affected by adsorbate only) should be considered as an absolutely elastic body, whose plastic deformation is impossible. It means that the simple Lippmann equation and other equations containing terms of plastic deformation cannot be used in thermodynamics of the solid metal surface. Coefficients of the partial charge transfer and electrosorption valence of anions, as well as the role of electron tunneling in the formation of the contact electric resistance (CER) signal are considered. The relation between the charge transfer during adsorption of anions and the surface reconstruction of monocrystalline electrodes is analyzed. The beginning of the substantial charge transfer is proposed to be a trigger of the surface reconstruction process. The nature and adsorption of solvent molecules are shown to play a decisive role in the charge transfer during anion adsorption. The results are compared to the available literature data.

Marichev, V. A.

2005-03-01

73

Charge transfer at the antiscale composite layer-electrolyte interface  

Microsoft Academic Search

Properties of composite coatings based on oxide layers formed on a titanium surface using the plasmic electrolytic oxidation\\u000a method and processed using Forum® superdispersed polytetrafluorinethylene were investigated. A combination of electrochemical\\u000a impedance spectroscopy, differential thermal analysis, and thermal gravimetry methods allowed one to establish the change\\u000a of the surface state as a result of heating that determines the charge transfer

S. V. Gnedenkov; S. L. Sinebryukhov; D. V. Mashtalyar; V. S. Egorkin; A. K. Tsvetnikov; A. N. Minaev

2007-01-01

74

Charge transfer and atomic-level pressure in metallic glasses  

SciTech Connect

This paper presents a systematic study on the charge transfer and ionicity in various metallic-glass forming systems, as well as its relationship with other atomic-level structure indicators, using the Bader analysis method and molecular dynamics simulation. It is shown that in a binary or multicomponent system, the chemical effects (when more than one elements present) appear to play a more important role in setting the absolute level of the atomic-level pressure, compared to the topological fluctuation.

Ding, Jun, E-mail: ding@jhu.edu [Department of Materials Science and Engineering, Johns Hopkins University, Baltimore, Maryland 21218 (United States); Cheng, Yongqiang [Chemical and Engineering Materials Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831 (United States)

2014-02-03

75

Energy and charge transfer in ionized argon coated water clusters  

NASA Astrophysics Data System (ADS)

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

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

2013-12-01

76

Charge transfer in cold Yb++Rb collisions  

NASA Astrophysics Data System (ADS)

Charge-transfer cold Yb++ Rb collision dynamics is investigated theoretically using high-level ab initio potential energy curves, dipole moment functions, and nonadiabatic coupling matrix elements. Within the scalar-relativistic approximation, the radiative transitions from the entrance A1?+ to the ground X1?+ state are found to be the only efficient charge-transfer pathway. The spin-orbit coupling does not open other efficient pathways, but alters the potential energy curves and the transition dipole moment for the A-X pair of states. The radiative, as well as the nonradiative, charge-transfer cross sections calculated within the 10-3-10 cm-1 collision energy range exhibit all features of the Langevin ion-atom collision regime, including a rich structure associated with centrifugal barrier tunneling (orbiting) resonances. Theoretical rate coefficients for two Yb isotopes agree well with those measured by immersing Yb+ ions in an ultracold Rb ensemble in a hybrid trap. Possible origins of discrepancy in the product distributions and relations to previously studied similar processes are discussed.

Sayfutyarova, Elvira R.; Buchachenko, Alexei A.; Yakovleva, Svetlana A.; Belyaev, Andrey K.

2013-05-01

77

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

78

Charge Transfer Between Neutral Atoms and Highly Ionized Species: Implications for ISO Observations  

E-print Network

We estimate rate coefficients for charge transfer between neutral hydrogen and helium and moderate to highly ionized heavy elements. Although charge transfer does not have much influence on hot collisionally ionized plasmas, its effects on photoionized plasmas can be profound. We present several photoionization models which illustrate the significant effect of charge transfer on the far infrared lines detected by ISO.

G. J. Ferland; K. T. Korista; D. A. Verner; A. Dalgarno

1997-03-17

79

Nanocontact electrification: patterned surface charges affecting adhesion, transfer, and printing.  

PubMed

Contact electrification creates an invisible mark, overlooked and often undetected by conventional surface spectroscopic measurements. It impacts our daily lives macroscopically during electrostatic discharge and is equally relevant on the nanoscale in areas such as soft lithography, transfer, and printing. This report describes a new conceptual approach to studying and utilizing contact electrification beyond prior surface force apparatus and point-contact implementations. Instead of a single point contact, our process studies nanocontact electrification that occurs between multiple nanocontacts of different sizes and shapes that can be formed using flexible materials, in particular, surface-functionalized poly(dimethylsiloxane) (PDMS) stamps and other common dielectrics (PMMA, SU-8, PS, PAA, and SiO(2)). Upon the formation of conformal contacts and forced delamination, contacted regions become charged, which is directly observed using Kelvin probe force microscopy revealing images of charge with sub-100-nm lateral resolution. The experiments reveal chemically driven interfacial proton exchange as the dominant charging mechanism for the materials that have been investigated so far. The recorded levels of uncompensated charges approach the theoretical limit that is set by the dielectric breakdown strength of the air gap that forms as the surfaces are delaminated. The macroscopic presence of the charges is recorded using force-distance curve measurements involving a balance and a micromanipulator to control the distance between the delaminated objects. Coulomb attraction between the delaminated surfaces reaches 150 N/m(2). At such a magnitude, the force finds many applications. We demonstrate the utility of printed charges in the fields of (i) nanoxerography and (ii) nanotransfer printing whereby the smallest objects are ?10 nm in diameter and the largest objects are in the millimeter to centimeter range. The printed charges are also shown to affect the electronic properties of contacted surfaces. For example, in the case of a silicon-on-insulator field effect transistors are in contact with PDMS and subsequent delamination leads to threshold voltage shifts that exceed 500 mV. PMID:21526803

Cole, Jesse J; Barry, Chad R; Knuesel, Robert J; Wang, Xinyu; Jacobs, Heiko O

2011-06-01

80

Charge transfer and ionisation by intermediate-energy heavy ions.  

PubMed

The use of heavy ion beams for microbeam studies of mammalian cell response leads to a need to better understand interaction cross sections for collisions of heavy ions with tissue constituents. For ion energies of a few MeV u(-1) or less, ions capture electrons from the media in which they travel and undergo subsequent interactions as partially 'dressed' ions. For example, 16 MeV fluorine ions have an equilibrium charge of 7(+), 32 MeV sulphur ions have an equilibrium charge of approximately 11(+), and as the ion energies decrease the equilibrium charge decreases dramatically. Data for interactions of partially dressed ions are extremely rare, making it difficult to estimate microscopic patterns of energy deposition leading to damage to cellular components. Such estimates, normally obtained by Monte Carlo track structure simulations, require a comprehensive database of differential and total ionisation cross sections as well as charge transfer cross sections. To provide information for track simulation, measurement of total ionisation cross sections have been initiated at East Carolina University using the recoil ion time-of-flight method that also yields cross sections for multiple ionisation processes and charge transfer cross sections; multiple ionisation is prevalent for heavy ion interactions. In addition, measurements of differential ionisation cross sections needed for Monte Carlo simulation of detailed event-by-event particle tracks are under way. Differential, total and multiple ionisation cross sections and electron capture and loss cross sections measured for C(+) ions with energies of 100 and 200 keV u(-1) are described. PMID:17132666

Toburen, L H; McLawhorn, S L; McLawhorn, R A; Evans, N L; Justiniano, E L B; Shinpaugh, J L; Schultz, D R; Reinhold, C O

2006-01-01

81

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

PubMed

Interfaces between organic electron-donating (D) and electron-accepting (A) materials have the ability to generate charge carriers on illumination. Efficient organic solar cells require a high yield for this process, combined with a minimum of energy losses. Here, we investigate the role of the lowest energy emissive interfacial charge-transfer state (CT1) in the charge generation process. We measure the quantum yield and the electric field dependence of charge generation on excitation of the charge-transfer (CT) state manifold via weakly allowed, low-energy optical transitions. For a wide range of photovoltaic devices based on polymer:fullerene, small-molecule:C60 and polymer:polymer blends, our study reveals that the internal quantum efficiency (IQE) is essentially independent of whether or not D, A or CT states with an energy higher than that of CT1 are excited. The best materials systems show an IQE higher than 90% without the need for excess electronic or vibrational energy. PMID:24240240

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

2014-01-01

82

Super-iron Nanoparticles with Facile Cathodic Charge Transfer  

SciTech Connect

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

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

2011-12-31

83

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

84

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

85

Polarization and charge transfer in the hydration of chloride ions  

SciTech Connect

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

Zhao Zhen; Rogers, David M. [Department of Chemistry, University of Cincinnati, Cincinnati, Ohio 45221-0172 (United States); Beck, Thomas L. [Department of Chemistry and Department of Physics, University of Cincinnati, Cincinnati, Ohio 45221-0172 (United States)

2010-01-07

86

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, Günther; Brock, Helmuth; Bittersmann, Edith

1993-01-01

87

Local charge transfer doping in suspended graphene nanojunctions  

NASA Astrophysics Data System (ADS)

We report electronic transport measurements in nanoscale graphene transistors with gold and platinum electrodes whose channel lengths are shorter than 100 nm and compare them with transistors with channel lengths from 1 ?m to 50 ?m. We find a large positive gate voltage shift in charge neutrality point (NP) for transistors made with platinum electrodes but negligible shift for devices made with gold electrodes. This is consistent with the transfer of electrons from graphene into the platinum electrodes. As the channel length increases, the disparity between the measured NP using gold and platinum electrodes disappears.

Worne, Jeffrey H.; Gullapalli, Hemtej; Galande, Charudatta; Ajayan, Pulickel M.; Natelson, Douglas

2012-01-01

88

Dynamical Theory of Charge Transfer Between Complex Atoms and Surfaces  

NASA Astrophysics Data System (ADS)

An existing dynamical quantum many-body theory of charge transfer(A. V. Onufriev and J. B. Marston, Phys. Rev. B 53), 13340 (1996); J. Merino and J. B. Marston, Phys. Rev. B 58, 6982 (1998). describes atoms with simple s-orbitals, such as alkalis and alkaline-earths, interacting with metal surfaces. The many-body equations of motion (EOM) are developed systematically as an expansion in the number of surface particle-hole excitations. Here we generalize this theory to describe atoms with richer orbital structures, such as atomic oxygen. In the simplest version of the model, only the single-particle p_z-orbitals of the atom, the ones oriented perpendicular to the surface, participate directly in resonant charge transfer as they have the largest overlap with the metallic wavefunctions. However, as the several-electron Russell-Saunders eigenstates, labeled by total angular momenta quantum numbers J, L, and S, are built out of products of single-particle orbitals, non-trivial matrix elements must be incorporated into the many-body EOM's. Comparison to recent experimental results(A. C. Lavery, C. E. Sosolik, and B. H. Cooper, Nucl. Instrum. Meth. B 157), 42 (1999); A. C. Lavery et al. to appear in Phys. Rev. B. on the scattering of low-energy oxygen ions off Cu(001) surfaces is made.

Chaudhuri, Basudev; Marston, Brad

2000-03-01

89

Ultracold, radiative charge transfer in hybrid Yb ion-Rb atom traps  

NASA Astrophysics Data System (ADS)

Ultracold hybrid ion-atom traps offer the possibility of microscopic manipulation of quantum coherences in the gas using the ion as a probe. However, inelastic processes, particularly charge transfer can be a significant process of ion loss and has been measured experimentally for the Y{{b}^{+}} ion immersed in a Rb vapour. We use first-principles quantum chemistry codes to obtain the potential energy curves and dipole moments for the lowest-lying energy states of this complex. Calculations for the radiative decay processes cross sections and rate coefficients are presented for the total decay processes; Y{{b}^{+}}(6s{{\\;}^{2}}S)+Rb(5s{{\\;}^{2}}S)\\to Yb(6{{s}^{2}}{{\\;}^{1}}S)+R{{b}^{+}}(4{{p}^{6}}{{\\;}^{1}}S)+h\

McLaughlin, B. M.; Lamb, H. D. L.; Lane, I. C.; McCann, J. F.

2014-07-01

90

Is dipole moment a valid descriptor of excited state's charge-transfer character?  

PubMed

In the ongoing discussion on excited states of the pentacene crystal, dipole moment values have been recently invoked to gauge the CT admixture to excited states of Frenkel parentage in a model cluster. In the present paper, a simple dimer model is used to show that, in general, the dipole moment is not a valid measure of the CT contribution. This finding eliminates some apparent disagreement between the computational results published by different research groups. The implications of our results and other related aspects of cluster-type quantum chemistry calculations are discussed in the context of the standing literature dispute concerning the mechanism of singlet fission in the pentacene crystal, notably the role of charge transfer contributions vs the involvement of an excimer-like doubly excited intermediate (D state). PMID:24138489

Petelenz, Piotr; Pac, Barbara

2013-11-20

91

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

92

Surface Science 425 (1999) 114 Non-adiabatic charge transfer process of oxygen on  

E-print Network

Surface Science 425 (1999) 1­14 Non-adiabatic charge transfer process of oxygen on metal surfaces November 1998 Abstract The dynamics of charge transfer processes of oxygen on metal surfaces a different charged oxygen species. Empirical universal potential energy functions have been constructed

Zeiri, Yehuda

93

Charged particle energy transfer for parallel and concentric cylindrical nanotubes  

NASA Astrophysics Data System (ADS)

This dissertation is mainly concerned with three topics: (1) the separation of the particle-hole and plasmon excitation contributions to the energy transfer when a moving charged particle interacts with a cylindrical nanotube; (2) the demonstration of a plasmon instability for a multi-wall nanotube or a pair of parallel nanotubes; and (3) the image potential for multi-wall nanotubes. We consider nanotubes embedded in a dielectric material. The electrons on a single cylindrical nanotube form a free electron gas confined to the surface of an infinitely long cylinder. We employ self-consistent field theory given in terms of Laplace's equation along with the linear response formalism to calculate the collective plasma excitations on a single-wall nanotube. We obtain their frequency-dependence on the linear wave vector along the axis of the nanotube. The plasma dispersion relation is calculated for intrasubband and intersubband transitions, where each subband is labeled by an angular momentum quantum number. We generalize our formalism to coaxial and parallel tubules. In addition we determine the way in which the collective modes are affected by the electrostatic interaction between the tubules. Making use of these results, we calculate the rate of transfer of energy between the plasma modes and charged particle moving parallel to the axis of the tubule. The frictional force due to the electrostatic interaction of the charged particle with the electrons on the surface of the nanotube is calculated using the inverse dielectric function. The energy loss of the charged particle to single particle and plasmon excitations is calculated. We demonstrate that the plasmon excitations for coaxial and parallel tubules may become unstable and radiate energy. The velocities of the charged particle for which the instabilities occur are identified by examining the plasmon dispersion relating and matching where the phase velocity of a plasmon excitation equals the velocity of the impinging particle. We calculate the image potential for a single-wall and a double-wall nanotube. This image potential has bound states which depend on the angular momentum quantum number around the axis of the tubule. We examine the way in which these bound states can be influenced when there are two coaxial tubules.

Balassis, Antonios

94

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

95

New generation of fluorescence probes exhibiting charge-transfer reactions  

NASA Astrophysics Data System (ADS)

With the advent and development of time-resolved spectroscopic technique and substantial progress in understanding of photophysical and photochemical events in condensed phases, a new goal may be achieved: modeling of biochemical reaction or its elementary step by a photochemical event occurring within the probe, bound to protein molecule. The probe may be located in a well-determined site of the protein matrix and report on the modulation of the reaction rate by the matrix and by the surrounding solvent, or by interactions in multiprotein complexes and in biomembranes. The advantage of this approach is obvious: in contrast to ordinary biochemical reaction, the excited-state reaction may be started by a short light pulse, and its development may be observed directly with high resolution in time. If the reaction rate is influenced by the dynamics of the protein matrix, these dynamics may be studied simultaneously with the reaction, by the same or similar probe, and within the same time range. In this report we discuss shortly the prospects for application of probes exhibiting electron transfer, twisted intramolecular charge transfer, and isomerizations. In the studies of electron-transfer dynamics of bianthryl in the complex with albumin and anti-bianthryl antibodies we show that the reaction is controlled by the dynamics of protein matrix which is found to be slower than nanosecond. The general problem of photochemical modeling of biochemical reactions is discussed.

Demchenko, Alexander P.

1994-08-01

96

Electronic structure and charge transfer states of a multichromophoric heptad  

NASA Astrophysics Data System (ADS)

A multichromophoric Heptad molecule containing Zn-tetraphenyl porphyrin, BDPY dye, bisphenyl anthracene, and C60 attached to a hexaphenyl -benzene core was synthesized by Gust et al. (J. Phys. Chem. B, 113, 7147 (2009)). The snowflake like molecule behaves like an antenna capturing photons at different wavelengths and transferring the energy to the porphyrin. We present a DFT based study on the ground state of the complex and also on the lowest two charge transfer (CT) states of the complex carried out using a perturbative delta-SCF method. The calculations, done using a mixed all-electron and pseudo-potential approach, show that the ionization potential of porphyrin and the electron affinity of C60 in the complex changes significantly from isolated molecules. Our calculated value of the lowest CT state is within 0.2 eV of the experimental estimate. This CT state contains a hole on porphyrin HOMO and a particle on the C60 LUMO. A comparison of the energetics with experiment indicates that the process probably involves excitation from the HOMO-1 of porphyrin to the porphyrin LUMO followed by electron transfer and hole bubbling up resulting in a CT state with the hole on porphyrin HOMO and particle on C60 LUMO.

Basurto, Luis; Zope, Rajendra; Baruah, Tunna

2013-03-01

97

Molecular excited States: accurate calculation of relative energies and electronic coupling between charge transfer and non-charge transfer States.  

PubMed

We show for a series of six small donor-acceptor dyads that the energy difference between non-charge transfer (non-CT) and charge transfer (CT) excited states, as well as the squares of the electronic couplings between these states, can be predicted from first-principles using variational orbital adapted configuration interaction singles (VOA-CIS) theory. VOA-CIS correctly predicts the observed experimental trends in these values and provides quantitative accuracy roughly on par with a modern long-range corrected density functional, ?B97X. Using VOA-CIS and ?B97X, the experimental energy difference between the non-CT and CT excited states is predicted with root mean squared errors of 0.22 eV and 0.21 eV, respectively. The square of the electronic coupling between these states is predicted with root mean squared errors of 0.08 eV(2) and 0.07 eV(2), respectively. Orbital optimized CIS (OO-CIS) and CIS(D), two perturbative corrections to CIS, provide a significant correction to the errant relative energies predicted by CIS, but the correction is insufficient to recover the experimentally observed trend. PMID:25336192

Veldkamp, Brad S; Liu, Xinle; Wasielewski, Michael R; Subotnik, Joseph E; Ratner, Mark A

2015-01-15

98

Demonstration of interfacial charge transfer in an organic charge injection device  

NASA Astrophysics Data System (ADS)

We report the fabrication and testing of an organic charge injection device composed of two adjacent metal-insulator-semiconductor capacitors in which the active semiconductor is poly(3-hexylthiophene). One capacitor, C1, is biased into partial depletion and illuminated with 550 nm light. By applying higher depletion voltages to the second capacitor, C2, photogenerated electrons are induced to flow along the semiconductor-insulator interface from C1 to C2 where they are detected either by simultaneously measuring the C-V characteristic of C2 or the current flow into it. We estimate that the transfer efficiency is in excess of 40% but is capable of significant improvement.

Watson, C. P.; Taylor, D. M.

2011-11-01

99

Fluorescence spectroscopy determination of fluoroquinolones by charge-transfer reaction.  

PubMed

The charge-transfer (CT) reaction between chloranilic acid (CL) as a pi-electron acceptor and lomefloxacin (LOM), fleroxacin (FLX), ciprofloxacin (CPFX), norfloxacin (NOR) as electron donor have been studied by fluorimetry. The CT complexes have stable purple color in acetone solution and the fluorescence intensity of the CT complexes was enhanced in 4-14 fold higher than that of the four fluoroquinolones (FQS) itself, therefore a new spectrofluorimetric method with simple, rapid, accurate, high sensitivity and good selectivity for determination of the four FQS has been developed. The method was applied for determination of drugs (LOM, FLX, CPFX and NOR) in tablets with mean percentage accuracies 99.80+/-1.12, 99.93+/-0.92, 99.23+/-1.36 and 99.87+/-0.81, respectively. PMID:14623595

Liming, Du; Qingqin, Xu; Jianmei, Yuan

2003-11-24

100

Deuteron-proton charge exchange reaction at small transfer momentum  

E-print Network

The charge-exchange reaction pd -> npp at 1 GeV projectile proton energy is studied. This reaction is considered in a special kinematics, when the transfer momentum from the beam proton to fast outgoing neutron is close to zero. Our approach is based on the Alt-Grassberger-Sandhas formulation of the multiple-scattering theory for the three-nucleon system. The matrix inversion method has been applied to take account of the final state interaction (FSI) contributions. The differential cross section, tensor analyzing power $C_{0,yy}$, vector-vector $C_{y,y}$ and vector-tensor $C_{y,xz}$ spin correlation parameters of the initial particles are presented. It is shown, that the FSI effects play a very important role under such kinematical conditions. The high sensitivity of the considered observables to the elementary nucleon-nucleon amplitudes has been obtained.

N. B. Ladygina; A. V. Shebeko

2004-11-17

101

Fingerprint of fractional charge transfer at metal/organic interface  

E-print Network

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

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

2015-02-06

102

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

103

Experimental study of low-energy charge transfer in nitrogen  

NASA Technical Reports Server (NTRS)

Total charge transfer cross sections were obtained for the N2(+)-N2 system with relative translational ion energies between 9 and 441 eV. Data were obtained to examine the dependence of total cross section on ion energy. The effect of ion excitation on the cross sections was studied by varying the electron ionization energy in the mass spectrometer ion source over an electron energy range between 14.5 and 32.1 eV. The dependence of total cross section on the neutralization chamber gas pressure was examined by obtaining data at pressure values from 9.9 to 0.000199 torr. Cross section values obtained were compared with experimental and theoretical results of other investigations.

Smith, A.

1979-01-01

104

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

105

Charge transfer embedded-atom potentials for atomistic simulations of amino acids and proteins.  

E-print Network

??The dynamical simulation of biophysical systems requires force fields (interaction potentials) capable of describing bond formation and breaking and reactive charge transfer. Molecular motor proteins… (more)

Godwin, Amo-Kwao

2012-01-01

106

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

107

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

108

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

109

Signal and charge transfer efficiency of few electrons clocked on microscopic superfluid helium channels  

Microsoft Academic Search

Electrons floating on the surface of liquid helium are possible spin qubits for quantum information processing. Varying electric potentials are not expected to modify spin states, which allows their transport on helium using a charge-coupled device (CCD)-like array of underlying gates. This approach depends upon efficient intergate transfer of individual electrons. Measurements are presented here of the charge transfer efficiency

G. Sabouret; F. R. Bradbury; S. Shankar; J. A. Bert; S. A. Lyon

2008-01-01

110

Photoinduced Charge Transfer within Polyaniline-Encapsulated Quantum Dots Decorated on Graphene  

E-print Network

polyaniline/ QD/graphene hybrid. A testing electronic device was fabricated using the hybrid in order to investigate the photoinduced charge transfer between graphene and encapsulated QDs within the hybridPhotoinduced Charge Transfer within Polyaniline-Encapsulated Quantum Dots Decorated on Graphene Kim

Xiong, Qihua

111

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

112

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

SciTech Connect

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

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

2008-04-02

113

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

114

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

NASA Technical Reports Server (NTRS)

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.

1991-01-01

115

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

116

[Spectrophotometric determination of azithromycin by charge transfer reaction].  

PubMed

The charge transfer interactions of Azithromycin and 7,7,8,8-tetracyanoquinodimethane (TCNQ) or chloranilic acid (CL) were investigated by spectrophotometry. The apparent molar absorptivity of TCNQ complex is 2.7 x 10(4) L x mol(-1) x cm(-1) at 743 nm, and 5.0 x 10(4) L x mol(-1) x cm(-1) at 842 nm; and that of CL complex is 2.4 x 10(3) L x mol(-1) x cm(-1). Beers law is obeyed in the concentration range of 0-30 mg x L(-1) for TCNQ method, and 5-225 mg x L(-1) for CL method. The relative standard deviations of the two methods are 1.0% and 1.4% (n = 6), respectively. The composition of complex of Azithromycin with 7,7,8,8-tetracyanoquinodimethane or chloranilic acid is 1 : 2. This proposed method has been applied to the determination of Azithromycin in tablets with satisfactory results. PMID:16883867

Huang, Wei; Liu, Xue-Jing; Zhao, Feng-Lin

2006-05-01

117

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

NASA Astrophysics Data System (ADS)

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 ?G0, 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)].

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

2015-01-01

118

Density Functional Theory studies of Epitaxial Charge Transfer Salts  

NASA Astrophysics Data System (ADS)

Some of the fulvalene-based charge transfer salts (CTS) become superconducting in bulk. The basic physics and ways to control it has been explored by changing the intermolecular spacing using both chemical substitution and pressure, but the fixed stoichiometry limit the occupation of the filled states to what is naturally available. Recent experiments suggest growth of 2D epitaxial layers of CTS allowing stoichiometric and geometric control of the electronic structure, thereby leading to engineered superconducting interfaces. In a combined experiment and theory study, we provide new insight to understand the interplay between structure, stoichiometry and electronic-structure of epitaxially grown (ET)2SF5CH2CF2SO3 salt on Ag(111) surface. Density functional theory studies show that the cohesive energy of the 2D salts are very high, in spite of strong bonding to the underlying Ag surface via Ag-S metallic bonds, and provide a rationale for off-stoichiometric growth with different electronic structures as seen in our experiments, such as 3:1 and a 1:1 cation:anion stoichiometry, necessary for a monolayer coverage and different from the bulk 2:1 stoichiometry. We also explore the role of van der Waals interactions for structural stability. This research was conducted at the Center for Nanophase Materials Sciences, sponsored at ORNL by the Division of User Facilities, U.S. DOE.

Rojas, Geoffrey A.; Ganesh, P.; Kelly, Simon; Sumpter, Bobby J.; Schlueter, John A.; Maksymovich, Petro

2013-03-01

119

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

120

Fostering Analogical Transfer: The Multiple Components Approach to Algebra Word Problem Solving in a Chemistry Context  

ERIC Educational Resources Information Center

Holyoak and Koh (1987) and Holyoak (1984) propose four critical tasks for analogical transfer to occur in problem solving. A study was conducted to test this hypothesis by comparing a multiple components (MC) approach against worked examples (WE) in helping students to solve algebra word problems in chemistry classes. The MC approach incorporated…

Ngu, Bing Hiong; Yeung, Alexander Seeshing

2012-01-01

121

Charge Transfer Process During Collision of Riming Graupel Pellet with Small Ice Crystals within a Thundercloud  

NASA Technical Reports Server (NTRS)

A charge transfer process during the collision of a riming graupel pellet and an ice-crystal at low temperature is proposed. During riming, the surface structure of graupel deviates from perfect crystalline structure. A concept of quasi-solid layer (QSL) formation on the surface is introduced. This QSL contains defects formed during riming. In absence of impurities, positively charged X-defect abundance is considered in the outer layer. These defects are assumed to be the charge carriers during the charge transfer process. Some part of the QSL is stripped off by the colliding ice crystals, which thereby gain some positive charge, leaving the graupel pellet negatively charged. With the proposed model, fC to pC of charge transfer is observed per collision. A transition temperature between -10 C to -15 C is also noted beyond which the QSL concept does not hold. This transition temperature is dependent on the bulk liquid water content of the cloud.

Datta, Saswati; De, Utpal K.; Goswami, K.; Jones, Linwood

1999-01-01

122

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

123

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

124

'Tunable' positive and negative surface charges on a capillary wall: exploiting the Immobiline chemistry.  

PubMed

The Immobiline (weak acrylamido acids and bases) chemistry has been applied to the covalent attachment of a positively (or, if needed, negatively) charged layer onto the inner surface of the silica wall. In particular, the following basic Immobilines have been used: pK 6.2, pK 7.0, pK 8.5 and pK 9.3. In order to avoid pK changes, the charged Immobilines are mixed with neutral acrylamido derivatives (in particular the highly resistant and hydrophilic N-acryloyl aminoethoxyethanol) so as to form a co-polymer having a 1:5 molar ratio (charged to neutral). The mu(eo) vs. pH curves have a slope opposite to that of a naked capillary and fan out on the pH scale following the titration curves of the different weak bases. Such chemistry allows the covalent attachment of charged species having known pK values and offering controlled charged densities on the wall. However, with the atomic force microscope, it is found that such soft coatings (whether charged or neutral) do not seem to provide complete coverage of the surface: naked patches of fused silica are found interdispersed among the polymer-coated ones. A good solution is a hybrid bonded and dynamic coating, obtained by adding short chain linear polyacrylamides to the background electrolyte. Good separations of polycations [poly(L-histidine)] and of histones are reported up to pH 5.7. PMID:8796483

Capelli, L; Ermakov, S V; Righetti, P G

1996-05-14

125

Synergizing Noncovalent Bonding Interactions in the Self-Assembly of Organic Charge-Transfer Ferroelectrics and Metal-Organic Frameworks  

NASA Astrophysics Data System (ADS)

Contemporary supramolecular chemistry---chemistry beyond the molecule---seeks to leverage noncovalent bonding interactions to generate emergent properties and complexity. These aims extend beyond the solution phase and into the solid state, where crystalline organic materials have attracted much attention for their ability to imitate the physical properties of inorganic crystals. This Thesis outlines my efforts to understand the properties of the solid-state materials that are self-assembled with noncovalent bonding motifs which I have helped to realize. In the first five Chapters, I chronicle the development of the lock-arm supramolecular ordering (LASO) paradigm, which is a general molecular design strategy for amplifying the crystallization of charge transfer complexes that revolves around the synergistic action of hydrogen bonding and charge transfer interactions. In an effort to expand upon the LASO paradigm, I identify a two-point halogen-bonding motif which appears to operate orthogonally from the hydrogen bonding and charge transfer interactions. Since some of these single crystalline materials are ferroelectric at room temperature, I discuss the implications of these experimental observations and reconcile them with the centrosymmetric space groups assigned after X-ray crystallographic refinements. I conclude in the final two Chapters by recording my endeavors to control the assembly of metal-organic frameworks (MOFs) with noncovalent bonding interactions between [2]catenane-bearing struts. First of all, I describe the formation of syndiotactic pi-stacked 2D MOF layers before highlighting a two-component MOF that assembles with a magic number ratio of components that is independent of the molar proportions present in the crystallization medium.

Cao, Dennis

126

Ionicity and paramagnetism of strong organic charge-transfer complexes  

NASA Astrophysics Data System (ADS)

Ionic charge-transfer (CT) complexes were prepared by mixing neutral solutions of the potent electron acceptor TCNQF4 (7,7,8,8-tetracyano-2,3,5,6-tetrafluoroquinodimethane) with the strong donors M2P(5,10-dihydro-5,10-diemethylphenazine) and TMPD(N,N,N',N'-tetramethyl-p-phenylenediamine). M2P-TCNQF4 [complex (1)] and TMPD-TCNQF4 [complex (2)] were obtained as deep blue solids, the latter only in polycrystalline form. Complex (1) crystallizes in the triclinic space group P1¯ with a = 7.002 (2), b = 8.787(2), c = 9.551(3), ? = 108.53(2), ? = 99.68(2), ? = 91.88(2), and Z = 1. The planar M2P+? and TCNQF-4? radical ions form mixed regular stacks. The structure refinement gave R = 0.039 and Rw = 0.033 for 1044 counter data. The ionicity ? and structure of mixed ???D+?A-?D+?A-???? stacks are closely related to the paramagnetic susceptibility ?(T). The two TCNQF4 complexes are shown to be the first highly ionic (??0.9) systems. ?(T) for complex (1) follows a Heisenberg antiferromagnetic chain with J = 175 cm-1 for T?122 K, below which ?(T) decreases steeply as expected for a dimerization transition. ?(T) for complex (2) can be fit to a power law T-?, with ? = 0.75±0.10, and also indicates ??0.9. Both complexes (1) and (2) are on the paramagnetic side of the paramagnetic-diamagnetic interface, while the finite activation energy for paramagnetism in the less ionic M2P-TCNQ and TMPD-TCNQ complexes puts them on the diamagnetic side. The elementary excitations of these related CT complexes with different ionicities are modeled.

Soos, Z. G.; Keller, H. J.; Ludolf, K.; Queckbörner, J.; Wehe, D.; Flandrois, S.

1981-05-01

127

Breaking the simple proportionality between molecular conductances and charge transfer rates.  

PubMed

A theoretical framework is presented to describe and to understand the observed relationship between molecular conductances and charge transfer rates across molecular bridges as a function of length, structure, and charge transfer mechanism. The approach uses a reduced density matrix formulation with a phenomenological treatment of system-bath couplings to describe charge transfer kinetics and a Green's function based Landauer-Buttiker method to describe steady-state currents. Application of the framework is independent of the transport regime and includes bath-induced decoherence effects. This model shows that the relationship between molecular conductances and charge transfer rates follows a power-law. The nonlinear rate-conductance relationship is shown to arise from differences in the charge transport barrier heights and from differences in environmental decoherence rates for the two experiments. This model explains otherwise puzzling correlations between molecular conductances and electrochemical kinetics. PMID:25277465

Venkatramani, Ravindra; Wierzbinski, Emil; Waldeck, David H; Beratan, David N

2014-01-01

128

Interfacial charge transfer dynamics in small molecule-modified TiO2 nanoparticles  

NASA Astrophysics Data System (ADS)

Direct molecule-semiconductor interfacial charge transfer interactions have received considerable research attention for their applications in various fields. In this study, the dynamics of molecule-TiO2 interfacial charge transfer complexes is monitored with femtosecond fluorescence upconversion and transient absorption. Small molecules (catechol, dopamine, benzhydroxamic acid, acetyl acetonate and salicylate)-modified TiO2 nanoparticles are prepared and the complexation is followed with optical absorption measurements. Although little visible luminescence is observed from these molecule- TiO2 nanoparticles, ultrafast emission in broad range of wavelengths is detected with fluorescence upconversion which is ascribed to the interfacial charge transfer emission. The charge transfer emission arose out of the radiative recombination of the electrons in the conduction band of TiO2 with holes in the molecule. Femtosecond fluorescence anisotropy measurements have shown that the interfacial charge-transfer excitation is mostly a localized one for catechol, dopamine and benzhydroxamate modified TiO2 nanoparticles. However, the possibility of delocalized charge-transfer excitations is observed for salicylate and acetyl acetonate-TiO2 nanoparticles. The decay of the charge transfer emission is ascribed to the relaxation of the localized states to delocalized states in the TiO2 conduction band. Transient absorption measurements have shown long-lived charge separation in the case of surface-modified TiO2 nanoparticles. Further measurements on the influence of charge-transfer excitations on the interfacial electron transfer in surface-modified TiO2 nanoparticles are being carried out.

Varaganti, Shankar; Mghangha, Edwin; Hasan, Jameel A.; Ramakrishna, Guda

2010-08-01

129

Structural factors influencing the intramolecular charge transfer and photoinduced electron transfer in tetrapyrazinoporphyrazines.  

PubMed

A series of unsymmetrical tetrapyrazinoporphyrazines (TPyzPzs) from the group of azaphthalocyanines with one peripherally attached amino substituent (donor) were synthesized, and their photophysical properties (fluorescence quantum yield and singlet oxygen quantum yield) were determined. The synthesized TPyzPzs were expected to undergo intramolecular charge transfer (ICT) as the main pathway for deactivating their excited states. Several structural factors were found to play a critical role in ICT efficiency. The substituent in the ortho position to the donor center significantly influences the ICT, with tert-butylsulfanyl and butoxy substituents inducing the strongest ICTs, whereas chloro, methyl, phenyl, and hydrogen substituents in this position reduce the efficiency. The strength of the donor positively influences the ICT efficiency and correlates well with the oxidation potential of the amines used as the substituents on the TPyzPz as follows: n-butylamine < N,N-diethylamine < aniline < phenothiazine. The ICT (with conjugated donors and acceptors) in the TPyzPz also proved to be much stronger than a photoinduced electron transfer in which the donor and the acceptor are connected through an aliphatic linker. PMID:24509513

Novakova, Veronika; Hladík, Petr; Filandrová, Tereza; Zajícová, Ivana; Krepsová, Veronika; Miletin, Miroslav; Len?o, Juraj; Zimcik, Petr

2014-03-21

130

EnCOrE (Encyclopdie de Chimie Organique Electronique): an original way to represent and transfer Knowledge from freshmen to researchers in Organic Chemistry  

E-print Network

Knowledge from freshmen to researchers in Organic Chemistry EnCOrE (Encyclopédie de Chimie OrganiqueCOrE is an original proposal which is expected to allow to share and transfer knowledge in organic chemistry technology, GRIDs for chemistry. 1. ORGANIC CHEMISTRY EXPERIMENTS AND REPRESENTATION OF DATA Chemistry

Boyer, Edmond

131

Computational Insights into the Charge Relaying Properties of ?-Turn Peptides in Protein Charge Transfers.  

PubMed

Density functional theory calculations suggest that ?-turn peptide segments can act as a novel dual-relay elements to facilitate long-range charge hopping transport in proteins, with the N terminus relaying electron hopping transfer and the C terminus relaying hole hopping migration. The electron- or hole-binding ability of such a ?-turn is subject to the conformations of oligopeptides and lengths of its linking strands. On the one hand, strand extension at the C-terminal end of a ?-turn considerably enhances the electron-binding of the ?-turn N terminus, due to its unique electropositivity in the macro-dipole, but does not enhance hole-forming of the ?-turn C terminus because of competition from other sites within the ?-strand. On the other hand, strand extension at the N terminal end of the ?-turn greatly enhances hole-binding of the ?-turn C terminus, due to its distinct electronegativity in the macro-dipole, but does not considerably enhance electron-binding ability of the N terminus because of the shared responsibility of other sites in the ?-strand. Thus, in the ?-hairpin structures, electron- or hole-binding abilities of both termini of the ?-turn motif degenerate compared with those of the two hook structures, due to the decreased macro-dipole polarity caused by the extending the two terminal strands. In general, the high polarity of a macro-dipole always plays a principal role in determining charge-relay properties through modifying the components and energies of the highest occupied and lowest unoccupied molecular orbitals of the ?-turn motif, whereas local dipoles with low polarity only play a cooperative assisting role. Further exploration is needed to identify other factors that influence relay properties in these protein motifs. PMID:25430869

Zhang, Ru; Liu, Jinxiang; Yang, Hongfang; Wang, Shoushan; Zhang, Meng; Bu, Yuxiang

2015-02-01

132

Photo-induced charge transfer at heterogeneous interfaces: Dye-sensitized tin disulfide, the theory and the experiment  

Microsoft Academic Search

The study of photo-induced charge transfer is an endeavor that spans the entire industrial period of man`s history. Its great importance demands an ever greater understanding of its underlying principles. The work discussed here attempts to probe elementary aspects of the charge transfer process. Investigations into the theory of charge transfer reactions are made in an attempt to isolate the

Lanzafame

1993-01-01

133

Q-value measurements in charge-transfer collisions of highly charged ions with atoms by recoil longitudinal momentum spectroscopy  

Microsoft Academic Search

We report on the first Q-value measurements in charge-transfer collisions using recoil longitudinal momentum spectroscopy. This method is not limited to relatively low beam energies and is easily adaptable to captures involving any number of transferred electrons. A very monoenergetic beam is not necessary. For a 50-keV Ar15+ on Ar collision system, Q values coresponding to single through quintuple electron

R. Ali; V. Frohne; C. L. Cocke; M. Stockli; S. Cheng; M. L. A. Raphaelian

1992-01-01

134

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

2014-12-21

135

Unstable, metastable, or stable halogen bonding interaction involving negatively charged donors? A statistical and computational chemistry study.  

PubMed

The noncovalent halogen bonding could be attributed to the attraction between the positively charged ?-hole and a nucleophile. Quantum mechanics (QM) calculation indicated that the negatively charged organohalogens have no positively charged ?-hole on their molecular surface, leading to a postulation of repulsion between negatively charged organohalogens and nucleophiles in vacuum. However, PDB survey revealed that 24% of the ligands with halogen bonding geometry could be negatively charged. Moreover, 36% of ionizable drugs in CMC (Comprehensive Medicinal Chemistry) are possibly negatively charged at pH 7.0. QM energy scan showed that the negatively charged halogen bonding is probably metastable in vacuum. However, the QM calculated bonding energy turned negative in various solvents, suggesting that halogen bonding with negatively charged donors should be stable in reality. Indeed, QM/MM calculation on three crystal structures with negatively charged ligands revealed that the negatively charged halogen bonding was stable. Hence, we concluded that halogen bonding with negatively charged donors is unstable or metastable in vacuum but stable in protein environment, and possesses similar geometric and energetic characteristics as conventional halogen bonding. Therefore, negatively charged organohalogens are still effective halogen bonding donors for medicinal chemistry and other applications. PMID:25390886

Yang, Zhuo; Xu, Zhijian; Liu, Yingtao; Wang, Jinan; Shi, Jiye; Chen, Kaixian; Zhu, Weiliang

2014-12-11

136

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

137

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

138

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

139

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

E-print Network

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

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

2014-08-22

140

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

141

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

E-print Network

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

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

1985-07-01

142

Effect of bridge on energy transfer and photoinduced charge separation in perylene-diimide-naphthalene-bisimide-  

E-print Network

Effect of bridge on energy transfer and photoinduced charge separation in perylene-diimide-naphthalene-bisimide of a hexathiophene (6T) electron donor and a naphthalene bisimide (NDI)- perylene bisimide (PDI) dimer electron

Fleming, Graham R.

143

Charge transfer across transition-metal oxide interfaces: Emergent conductance and electronic structure  

NASA Astrophysics Data System (ADS)

We perform density functional theory plus dynamical mean-field theory calculations to investigate internal charge transfer in a superlattice composed of alternating layers of vanadate and manganite perovskite and Ruddlesden-Popper structure materials. We show that the electronegativity difference between vanadium and manganese causes moderate charge transfer from VO2 to MnO2 layers in both perovskite and Ruddlesden-Popper-based superlattices, leading to hole doping of the VO2 layer and electron doping of the MnO2 layer. Comparison of the perovskite and Ruddlesden-Popper-based heterostructures shows that apical oxygen motion in the perovskite superlattice enhances charge transfer. Our first principles simulations demonstrate that the combination of internal charge transfer and quantum confinement provided by heterostructuring is a powerful approach to engineering electronic structure and tailoring correlation effects in transition metal oxides.

Chen, Hanghui; Park, Hyowon; Millis, Andrew J.; Marianetti, Chris A.

2014-12-01

144

Anomalous small charge transfer in doped single wall carbon nanohorn aggregates with Li, K and Br  

NASA Astrophysics Data System (ADS)

Single wall carbon nanohorns (SWNHs) produced by CW CO2 laser vaporization of a carbon target are examined for their ability to undergo charge transfer reactions. A typical SWNH has been shown by HRTEM to be a short ( ~ 40 nm) ~ 2 nm diameter nanotube with a conical tip ( ~ 20 ^circ full cone angle). Charge transfer chemical doping of SWNHs with K and Br was examined by vapor phase reaction and studied by Raman scattering. Electrochemical Li ion doping was also carried out. All these experiments indicate that an anomalously small charge transfer occurs for SWNHs in sharp contrast to the behavior observed for single wall carbon nanotube bundles and graphite. This rather remarkable result is not understood at present. The Raman spectrum (488 nm excitation) exhibits a pair of surprisingly narrow bands at 1350 and 1580 cm -1 with nearly equal intensity. These bands shift due to charge transfer.

Bandow, S.; Iijima, S.; Rao, A. M.; Sumanasekera, G. U.; Eklund, P. C.; Kokai, F.; Takahashi, K.; Yudasaka, M.

2000-03-01

145

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

E-print Network

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

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

1985-07-01

146

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

147

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

E-print Network

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

Wang, Xin

2015-01-01

148

Charge transfer cross section calculation and evaluation for Beq++H collisions  

NASA Astrophysics Data System (ADS)

The charge transfer processes for the Beq++H(q = 1-4) collisions are investigated by the quantum-mechanical and semiclassical methods in wide energy ranges. The total, n-selective, nl-selective, singlet and triplet charge transfer cross sections are obtained and compared with other available theoretical data. The total and n-selective data are presented. The validity of different methods is discussed. The recommend cross section data are given for all collision systems.

Liu, C. H.; Liu, L.; Qu, Y. Z.; Wang, J. G.; Janev, R. K.

2013-07-01

149

Density of States, Charge Transfer, and Optical Properties of Magnesium Diboride  

Microsoft Academic Search

We performed ab-initio, local density functional calculations of the electronic structure, charge transfer, and optical properties of MgB2, using the LCAO formalism. The Fermi level of MgB2 cuts through relatively narrow electron bands which have a dominant contribution from B(2p) states. There is a substantial charge transfer from magnesium to boron atoms. We found the ionic formula for this material

D. Bagayoko; G. L. Zhao

2002-01-01

150

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

151

Charge Transfer Excited State Contributions to Polarity Dependent Ferromagnetism in ZnO Diluted Magnetic Semiconductors  

Microsoft Academic Search

A close link between the charge transfer electronic structures and polarity dependent high-TC ferromagnetism of TM2+:ZnO DMSs (TM2+ = 3d ions) is demonstrated. Trends in ferromagnetism across the 3d series of TM2+:ZnO DMSs predicted from their charge transfer energies reproduce experimental trends well. These results provide a unified basis for understanding both n- and p-type ferromagnetic oxide DMSs.

Kevin R. Kittilstved; William K. Liu; Daniel R. Gamelin

2005-01-01

152

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

153

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

154

Role of atomic charge transfer on sintering of TiO2 nanoparticles: Variable-charge molecular dynamics  

E-print Network

atomic diffusion at surfaces of the spherical nanoparticles at high temperatures; and ii creates in each nanosphere. The surface diffusion due to the charge transfer clearly distinguishes the two nanospheres with different underlying crystalline structures; the surface diffusion constant of the anatase

Southern California, University of

155

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

E-print Network

to step up or step down the voltage. This approach has the advantages of a simple control method, reduced electronic devices. Charge pumps are inductorless DC-DC converters that are small size and high integration common charge pump topologies are evaluated in terms of voltage drop due to on-resistance and charge loss

Arslan, Tughrul

156

Energy transfer through a multi-layer liner for shaped charges  

Microsoft Academic Search

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

Saul Skolnick; Albert Goodman

1985-01-01

157

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

NASA Astrophysics Data System (ADS)

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

Singh, Yadunath

2013-06-01

158

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

159

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

E-print Network

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

Wu, Zhigang

160

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

161

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.

162

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

163

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

PubMed

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

Schill, Maria; Koslowski, Thorsten

2013-01-17

164

Charge transfer fluctuations as a signal for quark-gluon plasma  

SciTech Connect

In this work, the charge transfer fluctuation that was previously used for pp collisions is proposed for relativistic heavy-ion collisions as a quark-gluon plasma (QGP) probe. We propose the appearance of a local minimum at midrapidity for the charge transfer fluctuation as a signal for a QGP. Within a two-component neutral cluster model, we demonstrate that the charge transfer fluctuation can detect the presence of a QGP as well as the size of the QGP in the rapidity space. We also show that the forward-backward correlation of multiplicity can be a similarly good measure of the presence of a QGP. Further, we show that the previously proposed net charge fluctuation is sensitive to the existence of the second phase only if the QGP phase occupies a large portion of the available rapidity space.

Shi Lijun; Jeon, Sangyong [Physics Department, McGill University, Montreal, Quebec, H3A 2T8 (Canada); Physics Department, McGill University, Montreal, Quebec, H3A 2T8 (Canada) and RIKEN-BNL Research Center, Upton, New York 11973 (United States)

2005-09-01

165

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

166

Picosecond dynamics of intramolecular charge-transfer processes of ?-substituted porphyrins adsorbed on the porous glass  

NASA Astrophysics Data System (ADS)

Intramolecular charge separation and charge recombination dynamics of 2,8,12,18-tetrakis(9-anthryl) substituted porphyrin (PA) adsorbed on porous glass were investigated. It was found that the porphyrin moiety adsorbed on the porous glass was protonated to form a dication which accepts an electron from the anthryl moiety. The application of picosecond transient absorption spectroscopy and time-resolved fluorescence measurements revealed that the charge transfer in the excited state of PA took place within 7 ps after the excitation even in the adsorbed system. The rapid intramolecular charge separation process in the adsorbed state without polar solvents was discussed by comparing the present result with those in solutions.

Kotani, Shoji; Miyasaka, Hiroshi; Itaya, Akira; Hamanaka, Yasushi; Mataga, Noboru; Nakajima, Satoshi; Osuka, Atsuhiro

1997-05-01

167

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

PubMed Central

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

2014-01-01

168

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

169

Q -value measurements in charge-transfer collisions of highly charged ions with atoms by recoil longitudinal momentum spectroscopy  

SciTech Connect

We report on the first {ital Q}-value measurements in charge-transfer collisions using recoil longitudinal momentum spectroscopy. This method is not limited to relatively low beam energies and is easily adaptable to captures involving any number of transferred electrons. A very monoenergetic beam is not necessary. For a 50-keV Ar{sup 15+} on Ar collision system, {ital Q} values coresponding to single through quintuple electron capture were measured and found to be in good agreement with the predictions of the molecular classical overbarrier model.

Ali, R.; Frohne, V.; Cocke, C.L.; Stockli, M.; Cheng, S.; Raphaelian, M.L.A. (J. R. Macdonald Laboratory, Department of Physics, Kansas State University, Manhattan, Kansas 66506-2604 (United States))

1992-10-26

170

Process techniques of charge transfer time reduction for high speed CMOS image sensors  

NASA Astrophysics Data System (ADS)

This paper proposes pixel process techniques to reduce the charge transfer time in high speed CMOS image sensors. These techniques increase the lateral conductivity of the photo-generated carriers in a pinned photodiode (PPD) and the voltage difference between the PPD and the floating diffusion (FD) node by controlling and optimizing the N doping concentration in the PPD and the threshold voltage of the reset transistor, respectively. The techniques shorten the charge transfer time from the PPD diode to the FD node effectively. The proposed process techniques do not need extra masks and do not cause harm to the fill factor. A sub array of 32 × 64 pixels was designed and implemented in the 0.18 ?m CIS process with five implantation conditions splitting the N region in the PPD. The simulation and measured results demonstrate that the charge transfer time can be decreased by using the proposed techniques. Comparing the charge transfer time of the pixel with the different implantation conditions of the N region, the charge transfer time of 0.32 ?s is achieved and 31% of image lag was reduced by using the proposed process techniques.

Zhongxiang, Cao; Quanliang, Li; Ye, Han; Qi, Qin; Peng, Feng; Liyuan, Liu; Nanjian, Wu

2014-11-01

171

Fragment orbital based description of charge transfer in peptides including backbone orbitals.  

PubMed

Charge transfer in peptides and proteins can occur on different pathways, depending on the energetic landscape as well as the coupling between the involved orbitals. Since details of the mechanism and pathways are difficult to access experimentally, different modeling strategies have been successfully applied to study these processes in the past. These can be based on a simple empirical pathway model, efficient tight binding type atomic orbital Hamiltonians or ab initio and density functional calculations. An interesting strategy, which allows an efficient calculations of charge transfer parameters, is based on a fragmentation of the system into functional units. While this works well for systems like DNA, where the charge transfer pathway is naturally divided into distinct molecular fragments, this is less obvious for charge transfer along peptide and protein backbones. In this work, we develop and access a strategy for an effective fragmentation approach, which allows one to compute electronic couplings for large systems along nanosecond time scale molecular dynamics trajectories. The new methodology is applied to a solvated peptide, for which charge transfer properties have been studied recently using an empirical pathway model. As could be expected, dynamical effects turn out to be important, which emphasizes the importance of using effective quantum approaches which allow for sufficient sampling. However, the computed rates are orders of magnitude smaller than experimentally determined, which indicates the shortcomings of present modeling approaches. PMID:24655342

Heck, Alexander; Woiczikowski, P Benjamin; Kuba?, Tomáš; Welke, Kai; Niehaus, Thomas; Giese, Bernd; Skourtis, Spiros; Elstner, Marcus; Steinbrecher, Thomas B

2014-04-24

172

Charge transfer dynamics in molecular solids and adsorbates driven by local and non-local excitations  

NASA Astrophysics Data System (ADS)

Charge transfer pathways and charge transfer times in molecular films and in adsorbate layers depend both on the details of the electronic structure as well as on the degree of the initial localization of the propagating excited electronic state. For C6F6 molecular adsorbate films on the Cu(111) surface we determined the interplay between excited state localization and charge transfer pathways. In particular we selectively prepared a free-particle-like LUMO band excitation and compared it to a molecularly localized core-excited C1s ? ?* C6F6 LUMO state using time-resolved two-photon photoemission (tr-2PPE) and core-hole-clock (CHC) spectroscopy, respectively. For the molecularly localized core-excited C1s ? ?* C6F6 LUMO state, we separate the intramolecular dynamics from the charge transfer dynamics to the metal substrate by taking the intramolecular dynamics of the free C6F6 molecule into account. Our analysis yields a generally applicable description of charge transfer within molecular adsorbates and to the substrate.

Föhlisch, A.; Vijayalakshmi, S.; Pietzsch, A.; Nagasono, M.; Wurth, W.; Kirchmann, P. S.; Loukakos, P. A.; Bovensiepen, U.; Wolf, M.; Tchaplyguine, M.; Hennies, F.

2012-06-01

173

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

NASA Astrophysics Data System (ADS)

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

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

2013-02-01

174

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

175

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

SciTech Connect

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, E-mail: koslowsk@uni-freiburg.de [Institut für Physikalische Chemie, Universität Freiburg, Albertstraße 23a, D-79104 Freiburg im Breisgau (Germany)] [Institut für Physikalische Chemie, Universität Freiburg, Albertstraße 23a, D-79104 Freiburg im Breisgau (Germany)

2014-04-07

176

Attosecond timing the ultrafast charge-transfer process in atomic collisions  

SciTech Connect

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

Hu, S. X. [Laboratory for Laser Energetics, University of Rochester, 250 East River Road, Rochester, New York 14623 (United States)

2011-04-15

177

Charge-transfer complexes and their role in exciplex emission and near-infrared photovoltaics.  

PubMed

Charge transfer and interactions at organic heterojunctions (OHJs) are known to have critical influences on various properties of organic electronic devices. In this Research News article, a short review is given from the electronic viewpoint on how the local molecular interactions and interfacial energetics at P/N OHJs contribute to the recombination/dissociation of electron-hole pairs. Very often, the P-type materials donate electrons to the N-type materials, giving rise to charge-transfer complexes (CTCs) with a P(?+) -N(?-) configuration. A recently observed opposite charge-transfer direction in OHJs is also discussed (i.e., N-type material donates electrons to P-type material to form P(?-) -N(?+) ). Recent studies on the electronic structures of CTC-forming material pairs are also summarized. The formation of P(?-) -N(?+) -type CTCs and their correlations with exciplex emission are examined. Furthermore, the potential applications of CTCs in NIR photovoltaic devices are reviewed. PMID:24799189

Ng, Tsz-Wai; Lo, Ming-Fai; Fung, Man-Keung; Zhang, Wen-Jun; Lee, Chun-Sing

2014-08-20

178

Horizontal versus vertical charge and energy transfer in hybrid assemblies of semiconductor nanoparticles  

PubMed Central

Summary We studied the photoluminescence and time-resolved photoluminescence from self-assembled bilayers of donor and acceptor nanoparticles (NPs) adsorbed on a quartz substrate through organic linkers. Charge and energy transfer processes within the assemblies were investigated as a function of the length of the dithiolated linker (DT) between the donors and acceptors. We found an unusual linker-length-dependency in the emission of the donors. This dependency may be explained by charge and energy transfer processes in the vertical direction (from the donors to the acceptors) that depend strongly on charge transfer processes occurring in the horizontal plane (within the monolayer of the acceptor), namely, parallel to the substrate. PMID:23019559

Gotesman, Gilad; Guliamov, Rahamim

2012-01-01

179

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

SciTech Connect

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

Krukowski, Stanis?aw, E-mail: stach@unipress.waw.pl [Institute of High Pressure Physics, Polish Academy of Sciences, Soko?owska 29/37, 01-142 Warsaw (Poland); Interdisciplinary Centre for Modelling, University of Warsaw, Pawi?skiego 5a, 02-106 Warsaw (Poland); Kempisty, Pawe?; Strak, Pawe?; Sakowski, Konrad [Institute of High Pressure Physics, Polish Academy of Sciences, Soko?owska 29/37, 01-142 Warsaw (Poland)

2014-01-28

180

Near resonant charge transfer in the reaction F(+) + CO - F + CO(+)  

NASA Astrophysics Data System (ADS)

Charge transfer reactions in the F(+) + CO system were investigated using a F(+) ion beam in the energy range 10-300 eVlab. The electronically excited product CO(+) A2Pi(i) was observed by the emission from the A-X transitions. At low collisional energy the dominant product is in the vibrational level v' = 5. The reaction cross section sigma(5) is about 1 A-sq at 12 eVc.m. and decreases with increasing collision energy. The large cross section at v' = 5 can be interpreted by near-resonant charge-transfer reactions. The rotational temperature of the product is about 300 K, which is the temperature of the reactant CO gas. For the resonant charge transfer, the translational energy is not effective, but the electronic and vibrational energy couple with each other strongly.

Kusunoki, I.; Ishikawa, T.

1985-06-01

181

Carbon-atom wires: charge-transfer doping, voltage drop, and the effect of distortions  

PubMed

We present first-principles calculations on electrical conduction through carbon atomic wires. The changes in charge distribution induced by a large bias exhibit the primary involvement of the wire's pi states. A significant fraction ( approximately 40%) of the voltage drops across the atomic wire itself. At zero bias, there is a large transfer of charge from the electrodes to the wire, effectively providing doping without introducing scattering centers. This transfer leads, however, to potential barriers at the wire-electrode junctions. Bending the wire reduces its conductance. PMID:11015910

Lang; Avouris

2000-01-10

182

Carbon-Atom Wires: Charge-Transfer Doping, Voltage Drop, and the Effect of Distortions  

NASA Astrophysics Data System (ADS)

We present first-principles calculations on electrical conduction through carbon atomic wires. The changes in charge distribution induced by a large bias exhibit the primary involvement of the wire's ? states. A significant fraction \\(~40%\\) of the voltage drops across the atomic wire itself. At zero bias, there is a large transfer of charge from the electrodes to the wire, effectively providing doping without introducing scattering centers. This transfer leads, however, to potential barriers at the wire-electrode junctions. Bending the wire reduces its conductance.

Lang, N. D.; Avouris, Ph.

2000-01-01

183

Charge transfer and excitation in high-energy ion-atom collisions  

SciTech Connect

Coincidence measurements of charge transfer and simultaneous projectile electron excitation provide insight into correlated two-electron processes in energetic ion-atom collisions. Projectile excitation and electron capture can occur simultaneously in a collision of a highly charged ion with a target atom; this process is called resonant transfer and excitation (RTE). The intermediate excited state which is thus formed can subsequently decay by photon emission or by Auger-electron emission. Results are shown for RTE in both the K shell of Ca ions and the L shell of Nb ions, for simultaneous projectile electron loss and excitation, and for the effect of RTE on electron capture.

Schlachter, A.S.; Berkner, K.H.; McDonald, R.J.; Stearns, J.W.; Bernstein, E.M.; Clark, M.W.; Tanis, J.A.; Graham, W.G.; McFarland, R.H.; Stockli, M.P.

1986-11-01

184

Charge Transfer Excited State Contributions to Polarity Dependent Ferromagnetism in ZnO Diluted Magnetic Semiconductors  

Microsoft Academic Search

A close link between the charge transfer electronic structures and polarity\\u000adependent high-TC ferromagnetism of TM2+:ZnO DMSs (TM2+ = 3d ions) is\\u000ademonstrated. Trends in ferromagnetism across the 3d series of TM2+:ZnO DMSs\\u000apredicted from their charge transfer energies reproduce experimental trends\\u000awell. These results provide a unified basis for understanding both n- and\\u000ap-type ferromagnetic oxide DMSs.

Kevin R. Kittilstved; William K. Liu; Daniel R. Gamelin

2005-01-01

185

Ion-atom charge-transfer reactions and a hot intercloud medium. [in interstellar space  

NASA Technical Reports Server (NTRS)

An investigation is conducted concerning the ionization equilibrium of carbon in a hot intercloud medium (ICM), taking into account various charge-transfer reactions. Attention is given to problems related to observations of carbon along the lines of sight to several unreddened stars. It is pointed out that the observed underabundance of C III and overabundance of C I can be consistent with the presence of a hot, partially ionized ICM, provided that two of the charge-transfer reactions considered are rapid at thermal energies.

Steigman, G.

1975-01-01

186

Switching to a reversible proton motion in a charge-transferred dye.  

PubMed

We report on the steady-state, pico- and femtosecond time-resolved emission studies of 6-amino-2-(2-methoxyphenyl)benzoxazole (6A-MBO) and 6-amino-2-(2-hydroxyphenyl)benzoxazole (6A-HBO) in different solvents. We observed an intramolecular charge transfer (ICT) reaction following by slow (relatively) solvent relaxation, which happened in the same time domain for both molecules. The ultrafast ICT reaction happens in 80-140 fs whereas the solvent relaxation occurs in 0.5-1.1 ps. In 6A-MBO the excited CT species has a lifetime of ?2.5 ns. However, in 6A-HBO and after the ICT reaction, a reversible excited-state intramolecular proton transfer (ESIPT) reaction takes place in the formed enol charge transfer (ECT*) species producing a keto (K*) type tautomer. Depending on the solvent, the forward ESIPT reaction (ECT* ? K*) happens in 40-175 ps while that of the reverse one (ECT* ? K*) occurs in 240-990 ps. Kinetic isotopic effect (OH/OD exchange) study in acetone shows that the reversible ESIPT reaction occurs via tunneling, while we suggest that in acetonitrile solution it evolves along the IHB and solvent coordinates. Our results show a reversible proton motion coupled to charge-transfer reactions opening the way to new explorations of charge- and proton-transfer dynamics and spectroscopy. PMID:25523413

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

2015-01-15

187

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

SciTech Connect

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

Mirkin, Noemi G.; Krimm, Samuel [LSA Biophysics, University of Michigan, 930 N. University Ave., Ann Arbor, Michigan 48109-1055 (United States)] [LSA Biophysics, University of Michigan, 930 N. University Ave., Ann Arbor, Michigan 48109-1055 (United States)

2014-01-28

188

Charge Transfer in Fullerene-Conducting Polymer Compositex: Electronic and Excitonic Properties  

Microsoft Academic Search

C60 doping into conducting polymer with highly extended ?-electron system in the main chain induces remarkable quenching of photoluminescence in conducting polymer and drastic enhancement of photoconductivity. These results can be explained in terms of photo-induced charge transfer between conducting polymer and C60. That is, photoexcited excitons or exciton-polarons on conducting polymer are effectively dissociated at C60 molecules transferring electrons

Katsumi Yoshino; Kazuya Tada; Akihiko Fujii; Kazuhisa Hosoda; Shin-ichi Kawabe; Hirotake Kajii; Masaharu Hirohata; Rahmat Hidayat; Hisashi Araki; Anvar A. Zakhidov; Ryu-ichi Sugmoto; Masahiko Iyoda; Mitsuo Ishikawa; Toshio Masuda

1997-01-01

189

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

NASA Technical Reports Server (NTRS)

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

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

2007-01-01

190

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

191

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

192

Charge-transfer energy in closed-shell ion-atom interactions. [for H and Li ions in He  

NASA Technical Reports Server (NTRS)

The importance of charge-transfer energy in the interactions between closed-shell ions and atoms is investigated. Ab initio calculations on H(plus)-He and Li(plus)-He are used as a guide for the construction of approximate methods for the estimation of the charge-transfer energy for more complicated systems. For many alkali ion-rate gas systems the charge-transfer energy is comparable to the induction energy in the region of the potential minimum, although for doubly charged alkaline-earth ions in rare gases the induction energy always dominates. Surprisingly, an empirical combination of repulsion energy plus asymptotic induction energy plus asymptotic dispersion energy seems to give a fair representation of the total interaction, especially if the repulsion energy is parameterized, despite the omission of any explicit charge-transfer contribution. More refined interaction models should consider the charge-transfer energy contribution.

Alvarez-Rizzatti, M.; Mason, E. A.

1975-01-01

193

Ionization and charge-transfer: basic data for track structure calculations.  

PubMed

It is widely accepted that an understanding of the detailed structure of charged particle tracks is essential for interpreting the mechanistic consequences of energy deposition by high linear energy transfer (LET) radiation. The spatial relationship of events along the path of a charged particle, including excitation, ionization, and charge-transfer, govern subsequent chemical, biochemical, and biological reactions that can lead to adverse biologic effects. The determination of spatial patterns of ionization and excitation relies on a broad range of cross-section data relating the interactions of charged particles to the molecular constituents of the absorbing medium. It is important that these data be absolute in magnitude, comprehensive in scope, and reliable if accurate assessment of track structure parameters is to be achieved. Great strides have been made in the development of this database, understanding the underlying theory, and developing analytic models, particularly for interactions involving electrons and protons with atoms and molecules. The database is less comprehensive for interactions involving heavier charged particles, especially those that carry bound electrons, and for interactions in condensed phase media. Although there has been considerable progress in understanding the physical mechanisms for interactions involving fast heavy ions and atomic targets during the past few years, we still lack sufficient understanding to confidently predict cross-sections for these ions with biologically relevant material. In addition, little is known of the interaction cross-sections for heavy charged particles as they near the end of their track, i.e., for low velocity ions where collision theory is less well developed and where the particle's net charge fluctuates owing to electron capture and loss processes. This presentation focuses on the current status of ionization and charge-transfer data. Compilations, reviews, Internet sources, theoretical models, and recent data applicable to track structure calculations are discussed. PMID:10052672

Toburen, L H

1998-12-01

194

Computing the energetic component of the charge-transfer symmetry factor  

E-print Network

-transfer symmetry factor (UI: 0.47; MT: 0.49). The latter is larger than its energetic (TPS: 0.39; UI: 0.23; MT: 0.38) and entropic (UI: 0.25; MT: 0.13) components, given by the variation of the activation energy and entropy with the reaction free energy. The charge...

Drechsel-Grau, Christof

195

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

E-print Network

1 Charge Transfer between Isomer Domains on n+ -Doped Si(111)-2Ã?1: Energetic Stabilization R. M to negative ones leads to an energetic stabilization of the negative isomers. The model predicts a dependence of this buckling since the relevant energetics require very high precision in the computations. More recent results

Feenstra, Randall

196

Laboratory Measurements of Charge Transfer on Atomic Hydrogen at Thermal Energies  

NASA Technical Reports Server (NTRS)

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

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

2002-01-01

197

Classical model for electronic degrees of freedom: charge transfer in Na + I collisions  

NASA Astrophysics Data System (ADS)

Charge transfer in Na + I collisions is treated with the classical analog hamiltonian developed previously by Miller, McCurdy and Meyer. Purely classical trajectories are shown to describe the energy dependence of the ionization cross section reasonably well. A semiclassical perturbation theory analysis, valid at high energies, is also given.

Gray, S. K.; Miller, W. H.

1982-12-01

198

Photoluminescence and Charge-Transfer Complexes of Calixarenes Grafted on TiO2 Nanoparticles  

E-print Network

Photoluminescence and Charge-Transfer Complexes of Calixarenes Grafted on TiO2 Nanoparticles Justin nanoparticles up to a geometrical maximum surface density of 0.30 nm-2. Grafted calixarenes are hydrolytically synthesized by grafting preformed calixarene-Ti complexes. Individually, protonated calixarenes and TiO2

Iglesia, Enrique

199

Comparison of laser-assisted charge transfer of symmetric and asymmetric colliding systems  

NASA Astrophysics Data System (ADS)

We study the effect of an intense, ultra-short, and ultra-fast (1 and 2 fs) pulse with the aim to manipulate the charge transfer process of symmetric and asymmetric colliding systems. We report the total and state-selective cross section for charge transfer for the symmetric H+ + H and for the asymmetric He2+ + H system by means of the Crank-Nicolson method in the energy collision range for 1-10 keV/amu and 0.25-10 keV/amu, respectively. In this work, we show that the laser assistance do minimal contribution to charge transfer process in the symmetric system and that the laser pulse increases the charge transfer process at low impact energies for asymmetric system up to an order of magnitude. To asses the validity of our results, we compare our numerical results for the case of collisions with no laser to available experimental data in the literature showing good agreement for both systems.

Domíguez-Gutiérrez, F. J.; Cabrera-Trujillo, R.

2014-05-01

200

Spectrophotometric determination of ciprofloxacin, enrofloxacin and pefloxacin through charge transfer complex formation.  

PubMed

A spectrophotometric method was described for the determination of the antibacterial quinolone derivatives, ciprofloxacin, enrofloxacin and pefloxacin through charge transfer complex formation with three different acceptors. Chloranilic acid (CL) was utilized for their determination, forming charge transfer complex with lambdamax 520 nm. The proposed method was applied for determination of Ciprocin tablets, Enroxil oral solution, Peflacin ampoules and Peflacin tablets, with mean percentage accuracies, 99.58+/-1.25,99.94+/-0.96,100.91+/-1.59 and 99.86+/-1.003. Also, tetracyanoethylene (TCNE) was utilized in the determination of the concerned compounds forming charge transfer complexes with maximum absorbances at lambdamax 335 nm for ciprofloxacin and at lambdamax 290 nm for both enrofloxacin and pefloxacin. The procedure was applied for determination of Ciprocin tablets, Enroxil 10% oral solution, Peflacine tablets and Peflacine ampoules with mean percentage accuracies 99.40+/-1.27,99.95+/-0.90,98.98+/-1.565 and 99.88+/-0.998, respectively. Also, 2,3-dichloro-5,6-dicyano-p-benzoquinone (DDQ) was utilized for determination of pefloxacin forming charge transfer complex with maximum absorbance at lambdamax 460 nm. The procedure was applied for determination of peflacine tablets and peflacine ampoules with mean percentage accuracies 100.40+/-0.76 and 99.91+/-0.623, respectively. Statistical analysis of the obtained results showed no significant difference between the proposed method and other official and reported methods as evident from the t-test and variance ratio. PMID:11682219

Mostafa, Samia; El-Sadek, Mohamed; Alla, Esmail Awad

2002-01-01

201

Interfacial Charge Transfer and Colloidal Semiconductor Dye-Sensitization: Mechanism Assessment via Stark Emission Spectroscopy  

E-print Network

element of many photoelectrochemical solar energy conversion (light to electricity) schemes.1,2 Typically) charge-transfer complex. Examples include catechol,3 thiocy- anate,4 and ferrocyanide5-7 on titanium Preparation. Titanium dioxide14 and zirconium dioxide15 colloids (10 nm diameter) were prep

202

Application of charge transfer devices and surface acoustic wave devices to analog signal processing. III  

Microsoft Academic Search

The capabilities of charge transfer devices and surface acoustic wave devices are compared with attention to frequency and time delay ranges, insertion loss and dynamic ranges, temperature sensitivity, and compatibility in technology with other processing techniques. The performance of the two systems is analyzed in applications involving delay lines, digital memories, band pass filters, matched filters, correlators, oscillators, and global

C. Lardat; C. Legay; P. Tournois

1977-01-01

203

Polarization and Charge-Transfer Effects in Aqueous Solution via Ab Initio QM/MM Simulations  

E-print Network

Polarization and Charge-Transfer Effects in Aqueous Solution via Ab Initio QM/MM Simulations Yirong, acetate and methylammonium ions in aqueous solution. Calculations reveal that the electronic polarization, the polarization effect is dominated by the solvent (water) polarization. Introduction Computer simulation offers

Minnesota, University of

204

A bio-implantable platform for inductive data and power transfer with integrated battery charging  

Microsoft Academic Search

This paper describes a mixed signal subsystem for the inductive transfer of power and data to a fully-implantable medical device. The design includes circuits for the inductive power recovery and energy storage (charging), in addition to data recovery and demodulation. The data link is used to upload (at a data rate of up to 180Kbps) calibration and configuration data to

Michael Sole; Ayodele Sanni; Antonio Vilchesy; Christofer Toumazou; Timothy G. Constandinou

2011-01-01

205

Charge transfer at surfaces on femtosecond timescales: New information from electron spectroscopies  

Microsoft Academic Search

Charge transfer (CT) between an adsorbed atom or molecule and its substrate is of direct importance for the understanding of photochemical surface processes and more generally of the adsorbate-substrate coupling. A direct measurement of its timescales is difficult as it is extremely fast (from less than a fs to some or some tens of fs, as deduced from indirect evidence).

D. Menzel; W. Wurth

2000-01-01

206

Charge-transfer inclusion complex formation of tropylium cation with pillar[6]arenes.  

PubMed

The complexation behavior of pillar[6]arene hosts towards a carbonium ion, tropylium tetrafluoroborate (T·BF4), and the formation of novel charge-transfer (CT) inclusion complexes are described. In contrast, smaller pillar[5]arenes and larger pillar[7]arenes cannot form such complexes due to the unsuitable cavity dimensions. PMID:23749258

Fan, Jiazeng; Deng, Hongmei; Li, Jian; Jia, Xueshun; Li, Chunju

2013-07-18

207

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.

208

46 CFR 35.35-35 - Duties of person in charge of transfer-TB/ALL.  

Code of Federal Regulations, 2011 CFR

...SECURITY TANK VESSELS OPERATIONS Cargo Handling § 35.35-35 Duties of person in charge of transfer—TB/ALL. ...observe rate of loading to avoid overflow of tanks. (f) Comply with 33 CFR 156.120 and 156.150....

2011-10-01

209

46 CFR 35.35-35 - Duties of person in charge of transfer-TB/ALL.  

Code of Federal Regulations, 2013 CFR

...SECURITY TANK VESSELS OPERATIONS Cargo Handling § 35.35-35 Duties of person in charge of transfer—TB/ALL. ...observe rate of loading to avoid overflow of tanks. (f) Comply with 33 CFR 156.120 and 156.150....

2013-10-01

210

46 CFR 35.35-35 - Duties of person in charge of transfer-TB/ALL.  

Code of Federal Regulations, 2010 CFR

...SECURITY TANK VESSELS OPERATIONS Cargo Handling § 35.35-35 Duties of person in charge of transfer—TB/ALL. ...observe rate of loading to avoid overflow of tanks. (f) Comply with 33 CFR 156.120 and 156.150....

2010-10-01

211

46 CFR 35.35-35 - Duties of person in charge of transfer-TB/ALL.  

...SECURITY TANK VESSELS OPERATIONS Cargo Handling § 35.35-35 Duties of person in charge of transfer—TB/ALL. ...observe rate of loading to avoid overflow of tanks. (f) Comply with 33 CFR 156.120 and 156.150....

2014-10-01

212

46 CFR 35.35-35 - Duties of person in charge of transfer-TB/ALL.  

Code of Federal Regulations, 2012 CFR

...SECURITY TANK VESSELS OPERATIONS Cargo Handling § 35.35-35 Duties of person in charge of transfer—TB/ALL. ...observe rate of loading to avoid overflow of tanks. (f) Comply with 33 CFR 156.120 and 156.150....

2012-10-01

213

Solvent Control of Vibronic Coupling upon Intervalence Charge Transfer Excitation of  

E-print Network

CNRu(NH3)5 - as Revealed by Resonance Raman and Near-Infrared Absorption Spectroscopies Chengfei WangVersity EVanston, Illinois 60208 ReceiVed October 24, 1997 The charge-transfer resonance Raman spectra of (CN)5Fe among these modes, and resonance Raman spectra are particularly useful for extracting specific mode

214

Charge transfer activation energy for alkali atoms on Re and Ta  

Microsoft Academic Search

Ion and atom desorption energies for five alkali metals on Re and Ta were determined using the ion thermal emission noise method. The activation energies for the charge transfer process in the adsorbed state were calculated using a special energetic balance equation, which describes the surface ionization and thermal desorption effect.

Longin Gladyszewski

1993-01-01

215

The Influence of Internal Charge Transfer on Nonradiative Decay in Substituted Terthiophenes  

NASA Astrophysics Data System (ADS)

Photophysical data for a series of end substitued 3',4'-dibutyl-2,2':5',2''-terthiophenes are reported. Static absorption and fluorescence, quantum yields, time-resolved fluorescence, and time- and frequency-resolved pump-probe spectra are applied to investigate excited state relaxation in bromo, nitro, and tricyanovinyl substituted species in a variety of solvents. The effect of solvent polarizability and end-group substitution is discussed in the context of charge transfer in the excited state and its impact on nonradiative decay rates. In solution at room temperature, both symmetric and asymmetric addition of electron withdrawing end groups generate an excited state with substantial charge transfer character. Solvent polarizability has a significant influence on the excited state dynamics in the charge transfer compounds. Examples include a 20-fold reduction in the intersystem crossing rate going from hexane to toluene and an order of magnitude increase in the internal conversion rate between toluene and acetone. The results demonstrate that the impact of the substituents on intramolecular charge transfer, and the resulting amplification of the interactions between the excited state(s) and the local molecular environment, can dramatically change the excited state relaxation dynamics in substituted terthiophenes.

Huss, Adam S.; Pappenfus, Ted; Bohnsack, Jon; Burand, Michael; Mann, Kent R.; Blank, David A.

2009-09-01

216

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

217

Spectroscopy of Equilibrium and Non-Equilibrium Charge Transfer in Semiconductor Quantum Structures  

E-print Network

We investigate equilibrium and non-equilibrium charge-transfer processes by performing high-resolution transport spectroscopy. Using electrostatically defined quantum dots for energy-selective emission and detection, we achieved unprecedented 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 $h\\it{\\Gamma}$ 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 $h\\it{\\Gamma}\\gg k_{\\rm{B}}T$. By performing spectroscopy below the Fermi energy, we furthermore observe elastic and inelastic transfer of holes.

Clemens Rössler; Simon Burkhard; Tobias Krähenmann; Marc Röösli; Peter Märki; Julien Basset; Thomas Ihn; Klaus Ensslin; Christian Reichl; Werner Wegscheider

2014-03-17

218

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

219

Interaction and charge transfer between isolated thylakoids and multi-walled carbon nanotubes.  

PubMed

Charge separation in photosynthetic light reactions has gained much interest in an attempt to fabricate biological photovoltaic devices through integration of photosynthetic material and conducting electrodes. Direct interaction between thylakoids, as representatives of photosynthetic materials, and multi-walled carbon nanotubes (MWCNTs) is expected to increase charge transfer. Thylakoids are isolated from spinach leaf chloroplasts and pristine MWCNTs are dispersed in Triton X-100 (TX-100) as a surfactant to retain their electronic properties through non-covalent interactions. The Raman and UV-Vis spectra suggest close interactions between the thylakoids and the MWCNTs. Stable thylakoids including the embedded protein subunits and light harvesting antennas can be detected from the non-shifted 680 nm absorbance peak. The 50% fluorescence quenching in the MWCNTs-thylakoids preparation as compared to thylakoids alone using single wavelength excitation suggests charge transfer between the thylakoids and the MWCNTs. PMID:25531101

Dewi, Herlina Arianita; Sun, Gengzhi; Zheng, Lianxi; Lim, Sierin

2015-02-01

220

Temperature dependence of positronium reactivities with charge transfer molecules in bilayer membranes  

NASA Astrophysics Data System (ADS)

Rate constants for positronium atoms reacting chemically with charge-transfer molecules such as p-benzoquinone, nitrobenzene, and coenzyme Q-10 in a model bilayer membrane, dipalmitoylphosphatidylcholine (DPPC), have been measured at temperatures between 23 and 65 °C. A strong variation of the positronium chemical reactivities, kPs was observed in these systems: kPs increases with increasing temperature until the pretransition temperature of the membrane reaches a maximum value near the main transition temperature and decreases at temperatures higher than the main transition temperature. This variation is interpreted in terms of fluidity and permeability changes associated with the phase transitions of membranes and in terms of charge-transfer-complex formation between the solubilized molecules and the polar head of the membrane. These results demonstrate that positronium and its annihilation characteristics can be employed to investigate charge transport phenomena and microstructural changes of real biological membranes.

Jean, Y. C.; Yu, C.; Wang, Y. Y.; Yeh, Y. Y.

1984-02-01

221

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

SciTech Connect

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

Xu, F.; Ma, X. [Department of Electrical and Computer Engineering, University of Delaware, 140 Evans Hall, Newark, Delaware 19716 (United States); Haughn, C. R.; Doty, M. F. [Department of Materials Science and Engineering, University of Delaware, 201 DuPont Hall, Newark, Delaware 19716 (United States); Cloutier, S. G., E-mail: sylvaing.cloutier@etsmtl.ca [Department of Electrical and Computer Engineering, University of Delaware, 140 Evans Hall, Newark, Delaware 19716 (United States); Department of Electrical Engineering, École de Technologie Supérieure, 1100 rue Notre-Dame Ouest, Montréal, Québec H3C 1K3 (Canada)

2014-02-03

222

Charge transfer dynamics from adsorbates to surfaces with single active electron and configuration interaction based approaches  

NASA Astrophysics Data System (ADS)

We employ wavepacket simulations based on many-body time-dependent configuration interaction (TD-CI), and single active electron theories, to predict the ultrafast molecule/metal electron transfer time scales, in cyano alkanethiolates bonded to model gold clusters. The initial states represent two excited states where a valence electron is promoted to one of the two virtual ?? molecular orbitals localized on the cyanide fragment. The ratio of the two time scales indicate the efficiency of one charge transfer channel over the other. In both our one-and many-electron simulations, this ratio agree qualitatively with each other as well as with the previously reported experimental time scales (Blobner et al., 2012), measured for a macroscopic metal surface. We study the effect of cluster size and the description of electron correlation on the charge transfer process.

Ramakrishnan, Raghunathan; Nest, Mathias

2015-01-01

223

Reaction dynamics and proton coupled electron transfer: studies of tyrosine-based charge transfer in natural and biomimetic systems.  

PubMed

In bioenergetic reactions, electrons are transferred long distances via a hopping mechanism. In photosynthesis and DNA synthesis, the aromatic amino acid residue, tyrosine, functions as an intermediate that is transiently oxidized and reduced during long distance electron transfer. At physiological pH values, oxidation of tyrosine is associated with a deprotonation of the phenolic oxygen, giving rise to a proton coupled electron transfer (PCET) reaction. Tyrosine-based PCET reactions are important in photosystem II, which carries out the light-induced oxidation of water, and in ribonucleotide reductase, which reduces ribonucleotides to form deoxynucleotides. Photosystem II contains two redox-active tyrosines, YD (Y160 in the D2 polypeptide) and YZ (Y161 in the D1 polypeptide). YD forms a light-induced stable radical, while YZ functions as an essential charge relay, oxidizing the catalytic Mn?CaO? cluster on each of four photo-oxidation reactions. In Escherichia coli class 1a RNR, the ?2 subunit contains the radical initiator, Y122O•, which is reversibly reduced and oxidized in long range electron transfer with the ?2 subunit. In the isolated E. coli ?2 subunit, Y122O• is a stable radical, but Y122O• is activated for rapid PCET in an ?2?2 substrate/effector complex. Recent results concerning the structure and function of YD, YZ, and Y122 are reviewed here. Comparison is made to recent results derived from bioengineered proteins and biomimetic compounds, in which tyrosine-based charge transfer mechanisms have been investigated. This article is part of a Special Issue entitled: Vibrational spectroscopies and bioenergetic systems. PMID:25260243

Barry, Bridgette A

2015-01-01

224

Substituent and Solvent Effects on Excited State Charge Transfer Behavior of Highly Fluorescent Dyes Containing Thiophenylimidazole-Based Aldehydes  

NASA Technical Reports Server (NTRS)

The excited state charge transfer for a series of highly fluorescent dyes containing thiophenylimidazole moiety was investigated. These systems follow the Twisted Intramolecular Charge Transfer (TICT) model. Dual fluorescence was observed for each substituted dye. X-ray structures analysis reveals a twisted ground state geometry for the donor substituted aryl on the 4 and 5 position at the imidazole ring. The excited state charge transfer was modeled by a linear solvation energy relationship using Taft's pi and Dimroth's E(sub T)(30) as solvent parameters. There is linear relation between the energy of the fluorescence transition and solvent polarity. The degree of stabilization of the excited state charge transfer was found to be consistent with the intramolecular molecular charge transfer. Excited dipole moment was studied by utilizing the solvatochromic shift method.

Santos, Javier; Bu, Xiu R.; Mintz, Eric A.

2001-01-01

225

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

226

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

PubMed

This work reports on an investigation into interfacial charge transfer in CH3NH3PbI3 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 CH3NH3PbI3 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

227

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

228

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

229

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

230

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

231

Charge Transfer and Triplet States in High Efficiency OPV Materials and Devices  

NASA Astrophysics Data System (ADS)

The advantage of using polymers and molecules in electronic devices, such as light-emitting diodes (LED), field-effect transistors (FET) and, more recently, solar cells (SC) is justified by the unique combination of high device performance and processing of the semiconductors used. Power conversion efficiency of nanostructured polymer SC is in the range of 10% on lab scale, making them ready for up-scaling. Efficient charge carrier generation and recombination in SC are strongly related to dissociation of the primary singlet excitons. The dissociation (or charge transfer) process should be very efficient in photovoltaics. The mechanisms governing charge carrier generation, recombination and transport in SC based on the so-called bulk-heterojunctions, i.e. blends of two or more semiconductors with different electron affinities, appear to be very complex, as they imply the presence of the intermediate excited states, neutral and charged ones [1-3]. Charge transfer states, or polaron pairs, are the intermediate states between free electrons/holes and strongly bound excitons. Interestingly, the mostly efficient OLEDs to date are based on the so-called triplet emitters, which utilize the triplet-triplet annihilation process. In SC, recent investigations indicated that on illumination of the device active layer, not only mobile charges but also triplet states were formed [4]. With respect to triplets, it is unclear how these excited states are generated, via inter-system crossing or via back transfer of the electron from acceptor to donor. Triplet formation may be considered as charge carrier loss channel; however, the fusion of two triplets may lead to a formation of singlet excitons instead. In such case, a generation of charges by utilizing of the so far unused photons will be possible. The fundamental understanding of the processes involving the charge transfer and triplet states and their relation to nanoscale morphology and/or energetics of blends is essential for the optimization of the performance of molecular photovoltaic devices. I will present the state of the art in this field and discuss the mechanisms of polaron pair generation and recombination in the novel low band gap polymer-fullerene blends as well as in high-efficiency SC.[4pt] [1] C. Deibel, T. Strobel, V. Dyakonov, Phys. Rev. Lett. 103, 036402 (2009).[0pt] [2] C. Deibel, T. Strobel, and V. Dyakonov, Adv. Mater. 22, 4097 (2010).[0pt] [3] C. Deibel, and V. Dyakonov, Rep. Prog. Phys. 73, 096401 (2010).[0pt] [4] M. Liedtke, et al., JACS 133, 9088 (2011).

Dyakonov, Vladimir

2013-03-01

232

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

PubMed

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

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

2012-08-23

233

[Fluorescence spectroscopy determination of lomefloxacin by charge transfer complex formation with chloranilic acid].  

PubMed

Charge-transfer complex was formed between LMX as the donor and Chloranilic Acid (CL) as the acceptor has been studied by fluorimetry. It was shown that the n-pi complex can be formed at ambient temperature, which can emit, which strong fluorescence. Different variables and parameters affecting the reactions were studied and optimized. Based on this, a simple and reliable fluorescence spectroscopy method for the determination of Lomefloxacin (LMX) has been developed. Interference from some co-formulated drugs was also studied. No interference was observed due to additives commonly present in the pharmaceutical preparations. The proposed methods could be applied successfully to the investigated pure compounds and pharmaceutical dosage forms with good accuracy and precision. The linear range is 0.04-0.8 mg x L(-1), the detection limit is 0.04 mg x L(-1), the recoveries of LMX are 97.4%-99.3%, and RSD is 1.3%-2.6%. Finally, the charge-transfer reaction mechanism was discussed. The composition of the change-transfer complex was found to be 1:1 by Bent-French and curved intersection methods. This ratio may be due to the presence of the fluorine atom acting as an electron drawing group in the molecule of lomefloxacin. The benzene ring has lower electron density, but nitrogen atom in 4' of piperazingl has higher electron density and is less sterically hindered. So n-pi charge transfer complexes were formed. PMID:15828343

Du, Li-ming; Zhou, Jing; Yuan, Jian-mei

2004-12-01

234

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

PubMed

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

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

2008-06-18

235

Metal-organic charge transfer can produce biradical states and is mediated by conical intersections  

PubMed Central

The present paper illustrates key features of charge transfer between calcium atoms and prototype conjugated hydrocarbons (ethylene, benzene, and coronene) as elucidated by electronic structure calculations. One- and two-electron charge transfer is controlled by two sequential conical intersections. The two lowest electronic states that undergo a conical intersection have closed-shell and open-shell dominant configurations correlating with the 4s2 and 4s13d1 states of Ca, respectively. Unlike the neutral-ionic state crossing in, for example, hydrogen halides or alkali halides, the path from separated reactants to the conical intersection region is uphill and the charge-transferred state is a biradical. The lowest-energy adiabatic singlet state shows at least two minima along a single approach path of Ca to the ? system: (i) a van der Waals complex with a doubly occupied highest molecular orbital, denoted , and a small negative charge on Ca and (ii) an open-shell singlet (biradical) at intermediate approach (Ca?C distance ?2.5–2.7 ?) with molecular orbital structure ?1?2, where ?2 is an orbital showing significant charge transfer form Ca to the ?-system, leading to a one-electron multicentered bond. A third minimum (iii) at shorter distances along the same path corresponding to a closed-shell state with molecular orbital structure has also been found; however, it does not necessarily represent the ground state at a given Ca?C distance in all three systems. The topography of the lowest adiabatic singlet potential energy surface is due to the one- and two-electron bonding patterns in Ca-? complexes. PMID:21037111

Tishchenko, Oksana; Li, Ruifang; Truhlar, Donald G.

2010-01-01

236

Charge transfer excitations from excited state Hartree-Fock subsequent minimization scheme.  

PubMed

Photoinduced charge-transfer processes play a key role for novel photovoltaic phenomena and devices. Thus, the development of ab initio methods that allow for an accurate and computationally inexpensive treatment of charge-transfer excitations is a topic that nowadays attracts a lot of scientific attention. In this paper we extend an approach recently introduced for the description of single and double excitations [M. Tassi, I. Theophilou, and S. Thanos, Int. J. Quantum Chem. 113, 690 (2013); M. Tassi, I. Theophilou, and S. Thanos, J. Chem. Phys. 138, 124107 (2013)] to allow for the description of intermolecular charge-transfer excitations. We describe an excitation where an electron is transferred from a donor system to an acceptor one, keeping the excited state orthogonal to the ground state and avoiding variational collapse. These conditions are achieved by decomposing the space spanned by the Hartree-Fock (HF) ground state orbitals into four subspaces: The subspace spanned by the occupied orbitals that are localized in the region of the donor molecule, the corresponding for the acceptor ones and two more subspaces containing the virtual orbitals that are localized in the neighborhood of the donor and the acceptor, respectively. Next, we create a Slater determinant with a hole in the subspace of occupied orbitals of the donor and a particle in the virtual subspace of the acceptor. Subsequently we optimize both the hole and the particle by minimizing the HF energy functional in the corresponding subspaces. Finally, we test our approach by calculating the lowest charge-transfer excitation energies for a set of tetracyanoethylene-hydrocarbon complexes that have been used earlier as a test set for such kind of excitations. PMID:24784248

Theophilou, Iris; Tassi, M; Thanos, S

2014-04-28

237

Charge transfer excitations from excited state Hartree-Fock subsequent minimization scheme  

SciTech Connect

Photoinduced charge-transfer processes play a key role for novel photovoltaic phenomena and devices. Thus, the development of ab initio methods that allow for an accurate and computationally inexpensive treatment of charge-transfer excitations is a topic that nowadays attracts a lot of scientific attention. In this paper we extend an approach recently introduced for the description of single and double excitations [M. Tassi, I. Theophilou, and S. Thanos, Int. J. Quantum Chem. 113, 690 (2013); M. Tassi, I. Theophilou, and S. Thanos, J. Chem. Phys. 138, 124107 (2013)] to allow for the description of intermolecular charge-transfer excitations. We describe an excitation where an electron is transferred from a donor system to an acceptor one, keeping the excited state orthogonal to the ground state and avoiding variational collapse. These conditions are achieved by decomposing the space spanned by the Hartree-Fock (HF) ground state orbitals into four subspaces: The subspace spanned by the occupied orbitals that are localized in the region of the donor molecule, the corresponding for the acceptor ones and two more subspaces containing the virtual orbitals that are localized in the neighborhood of the donor and the acceptor, respectively. Next, we create a Slater determinant with a hole in the subspace of occupied orbitals of the donor and a particle in the virtual subspace of the acceptor. Subsequently we optimize both the hole and the particle by minimizing the HF energy functional in the corresponding subspaces. Finally, we test our approach by calculating the lowest charge-transfer excitation energies for a set of tetracyanoethylene-hydrocarbon complexes that have been used earlier as a test set for such kind of excitations.

Theophilou, Iris, E-mail: i.theophilou@fz-juelich.de [Peter Grunberg Institut (PGI) Forschungszentrum Jülich, D-52425 Jülich (Germany)] [Peter Grunberg Institut (PGI) Forschungszentrum Jülich, D-52425 Jülich (Germany); Tassi, M.; Thanos, S. [Institute for Advanced Materials, Physicochemical Processes, Nanotechnology and Microsystems, ‘Demokritos’ National Center for Scientific Research, 15310 Athens (Greece)] [Institute for Advanced Materials, Physicochemical Processes, Nanotechnology and Microsystems, ‘Demokritos’ National Center for Scientific Research, 15310 Athens (Greece)

2014-04-28

238

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

239

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

240

Impact of distributions and mixtures on the charge transfer properties of graphene nanoflakes  

NASA Astrophysics Data System (ADS)

Many of the promising new applications of graphene nanoflakes are moderated by charge transfer reactions occurring between defects, such as edges, and the surrounding environment. In this context the sign and value of properties such as the ionization potential, electron affinity, electronegativity and chemical hardness can be useful indicators of the efficiency of graphene nanoflakes for different reactions, and can help identify new application areas. However, as samples of graphene nanoflakes cannot necessarily be perfectly monodispersed, it is necessary to predict these properties for polydispersed ensembles of flakes, and provide a statistical solution. In this study we use some simple statistical methods, in combination with electronic structure simulations, to predict the charge transfer properties of different types of ensembles where restrictions have been placed on the diversity of the structures. By predicting quality factors for a variety of cases, we find that there is a clear motivation for restricting the sizes and suppressing certain morphologies to increase the selectivity and efficiency of charge transfer reactions; even if samples cannot be completely purified.Many of the promising new applications of graphene nanoflakes are moderated by charge transfer reactions occurring between defects, such as edges, and the surrounding environment. In this context the sign and value of properties such as the ionization potential, electron affinity, electronegativity and chemical hardness can be useful indicators of the efficiency of graphene nanoflakes for different reactions, and can help identify new application areas. However, as samples of graphene nanoflakes cannot necessarily be perfectly monodispersed, it is necessary to predict these properties for polydispersed ensembles of flakes, and provide a statistical solution. In this study we use some simple statistical methods, in combination with electronic structure simulations, to predict the charge transfer properties of different types of ensembles where restrictions have been placed on the diversity of the structures. By predicting quality factors for a variety of cases, we find that there is a clear motivation for restricting the sizes and suppressing certain morphologies to increase the selectivity and efficiency of charge transfer reactions; even if samples cannot be completely purified. Electronic supplementary information (ESI) available: Details of computational simulations and specific results. Comparison of the expectation values of quality factors for ensemble properties based on different statistical distributions. See DOI: 10.1039/c4nr06123c

Shi, Hongqing; Rees, Robert J.; Per, Manolo C.; Barnard, Amanda S.

2015-01-01

241

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

ERIC Educational Resources Information Center

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

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

2008-01-01

242

Resonant transfer and excitation: Dependence on projectile charge state and target-electron momentum distribution  

SciTech Connect

Resonant transfer and excitation (RTE) involving simultaneous electron capture and projectile K-shell excitation has been measured for calcium ions in charge states ranging from neon-like to hydrogen-like incident on molecular hydrogen over an energy range 100--370 MeV. The results establish a projectile charge-state dependence for RTE and provide a detailed test of theoretical calculations. The effect of the target-electron momentum distribution on the RTE process is demonstrated by comparing with previous results for calcium ions incident on helium.

Tanis, J.A.; Bernstein, E.M.; Clark, M.W.; Graham, W.G.; McFarland, R.H.; Morgan, T.J.; Mowat, J.R.; Mueller, D.W.; Mueller, A.; Stockli, M.P.

1986-09-01

243

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

NASA Astrophysics Data System (ADS)

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 electrodes. Here we report a simple method to extract the charge transfer rates in carbon-coated LiFePO4 porous electrodes from chronoamperometry experiments, obtaining curved Tafel plots that contradict the Butler-Volmer equation but fit the Marcus-Hush-Chidsey prediction over a range of temperatures. The fitted reorganization energy matches the Born solvation energy for electron transfer from carbon to the iron redox site. The kinetics are thus limited by electron transfer at the solid-solid (carbon-LixFePO4) interface rather than by ion transfer at the liquid-solid interface, as previously assumed. The proposed experimental method generalizes Chidsey’s method for phase-transforming particles and porous electrodes, and the results show the need to incorporate Marcus kinetics in modelling batteries and other electrochemical systems.

Bai, Peng; Bazant, Martin Z.

2014-04-01

244

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

SciTech Connect

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

Baldacchini, Chiara [Biophysics and Nanoscience Centre, DEB-CNISM, Università della Tuscia, I-01100 Viterbo (Italy); Institute of Agro-environmental and Forest Biology, National Research Council, I-05010 Porano (Italy); Bizzarri, Anna Rita; Cannistraro, Salvatore, E-mail: cannistr@unitus.it [Biophysics and Nanoscience Centre, DEB-CNISM, Università della Tuscia, I-01100 Viterbo (Italy)

2014-03-03

245

Energy and charge transfer dynamics between Alq3 and CdSeS nanocrystals.  

PubMed

The photoluminescence properties of the blend films consisting of organic small molecules and nanocrystals (NCs)--Alq3 and CdSeS NCs--were studied by steady-state and time-resolved photoluminescence (PL) spectroscopy with different excited wavelengths. Both the fluorescence intensity and lifetime are intensively dependent on the NC concentration. The detailed analysis of experiment data proves that Forster energy transfer from the Alq3 to the NCs exists simultaneously with the charge transfer and both compete with each other in the blend films. PMID:20355648

Zhang, Shuping; Liu, Yuqiang; Yang, Yanqiang

2010-03-01

246

Charge transfer in cold collisions of rubidium atoms with calcium and ytterbium ions  

NASA Astrophysics Data System (ADS)

Low-energy collisions of the Ca and Yb cations with Rb atoms are investigated theoretically using accurate ab initio potential energy curves and coupling matrix elements to elucidate the dominant charge transfer mechanisms. The cross sections calculated at collision energies above 10?5 cm?1 exhibit the features typical to Langevin ion-atom collision regime, including a rich structure associated with the centrifugal barrier tunnelling (orbiting) resonances. It is shown that the dominant process in Yb+ + Rb collisions is the radiative charge transfer, while in the case of Ca+ + Rb collisions nonadiabatic transitions due to spin-orbit coupling dominate. Theoretical results are in a good agreement with available experimental data.

Yakovleva, S. A.; Belyaev, A. K.; Buchachenko, A. A.

2014-12-01

247

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

PubMed

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

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

2015-01-21

248

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

SciTech Connect

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

Loreau, J.; Dalgarno, A. [Institute for Theoretical Atomic, Molecular and Optical Physics, Harvard-Smithsonian Center for Astrophysics, Cambridge, Massachusetts 02138 (United States); Ryabchenko, S. [Northern (Arctic) Federal University, 17 Severnaya Dvina Emb., 163002 Arkhangelsk (Russian Federation); Laboratoire de Chimie Quantique et Photophysique, Universite Libre de Bruxelles (ULB), CP160/09, 1050 Bruxelles (Belgium); Vaeck, N. [Laboratoire de Chimie Quantique et Photophysique, Universite Libre de Bruxelles (ULB), CP160/09, 1050 Bruxelles (Belgium)

2011-11-15

249

Spectrophotometric and some thermodynamic parameters of the charge transfer complexation between chloranilic acid and chlorpheniramine.  

PubMed

The principle of charge transfer complexation involving a pi-acceptor (chloranilic acid) and an n-donor (chlorpheniramine) was utilized in the assay of the later in its pure form and in its tablet dosage forms. Some thermodynamic parameters of the complex such as association constant (Kc), molar absorptivity (epsilon c), free energy change (delta G degree), enthalpy (delta H degree) and entropy (delta S degree) changes were determined to establish the stability of the complex and the optimum conditions for the complex formation. The values obtained for these thermodynamic parameters indicated that the complex formed between this two chemical entities is highly stable. Assay of chlorpheniramine in its pure form and in its tablet dosage forms gave high percentage recoveries. The principle of charge transfer complexation could therefore be employed in the colorimetric assay of chlorpheniramine in its tablet dosage forms. PMID:11680092

Ofoefule, S I; Ajali, U

2001-01-01

250

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

251

Competition between covalent bonding and charge transfer at complex-oxide interfaces.  

PubMed

Here we study the electronic properties of cuprate-manganite interfaces. By means of atomic resolution electron microscopy and spectroscopy, we produce a subnanometer scale map of the transition metal oxidation state profile across the interface between the high Tc superconductor YBa2Cu3O7-? and the colossal magnetoresistance compound (La,Ca)MnO3. A net transfer of electrons from manganite to cuprate with a peculiar nonmonotonic charge profile is observed. Model calculations rationalize the profile in terms of the competition between standard charge transfer tendencies (due to band mismatch), strong chemical bonding effects across the interface, and Cu substitution into the Mn lattice, with different characteristic length scales. PMID:24877959

Salafranca, Juan; Rincón, Julián; Tornos, Javier; León, Carlos; Santamaria, Jacobo; Dagotto, Elbio; Pennycook, Stephen J; Varela, Maria

2014-05-16

252

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

253

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

254

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

PubMed Central

Room temperature magnetic field effects have not been definitively observed in either single-walled carbon nanotubes (SWCNTs) or C60 under a small magnetic field due to their weak hyperfine interaction and slight difference of g-factor between positive and negative polarons. Here, we demonstrate charge-transfer induced magnetic field effects in nano-carbon C60-SWCNT bulk heterojunctions at room temperature, where the mechanism of magnetic field effects is verified using excited state transition modeling. By controlling SWCNT concentrations and interfacial interactions, nano-carbon heterojunctions exhibit tunability of charge-transfer density and room temperature magnetoconductance of 2.8% under 100?mT external magnetic field. External stimuli, such as electric field and photoexcitation, also play an important role in controlling the magnetic field effects of nano-carbon heterojunctions, which suggests that these findings could enable the control of optoelectronic properties of nano-carbon heterojunctions. PMID:25146555

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

2014-01-01

255

Resonant hot charge-transfer excitations in fullerene-porphyrin complexes: Many-body Bethe-Salpeter study  

NASA Astrophysics Data System (ADS)

We study the neutral singlet excitations of the zinc-tetraphenylporphyrin and C70-fullerene donor-acceptor complex within the many-body Green's-function GW and Bethe-Salpeter approaches. The lowest transition is a charge-transfer excitation between the donor and the acceptor with an energy in excellent agreement with recent constrained density functional theory calculations. Beyond the lowest charge-transfer state, which can be determined with simple electrostatic models that we validate, the Bethe-Salpeter approach provides the full excitation spectrum. We evidence the existence of hot electron-hole states which are resonant in energy with the lowest donor intramolecular excitation and show a hybrid intramolecular and charge-transfer character, favoring the transition towards charge separation. Such findings, and the ability to describe accurately both low-lying and excited charge-transfer states, are important steps in the process of discriminating “cold” versus “hot” exciton dissociation processes.

Duchemin, Ivan; Blase, Xavier

2013-06-01

256

Tuning the charge-transfer energy in hole-doped cuprates  

NASA Astrophysics Data System (ADS)

Chemical substitution, combined with strain, allows the charge-transfer energy in hole-doped cuprates to be broadly tuned. We theoretically characterize the structural and electronic properties of the family of compounds R2CuO2S2, constructed by sulfur replacement of the apical oxygens and rare-earth substitutions in the parent cuprate La2CuO4. Additionally, the enthalpies of formation for possible synthesis pathways are determined.

Yee, Chuck-Hou; Kotliar, Gabriel

2014-03-01

257

Study of deuteron-proton charge exchange reaction at small transfer momentum  

E-print Network

The charge-exchange reaction pd->npp at 1 GeV projectile proton energy is studied in the multiple-scattering expansion technique. This reaction is considered in a special kinematics, when the transfer momentum from the beam proton to fast neutron is close to zero. The differential cross section and a set of polarization observables are calculated. It was shown that contribution of the final state interaction between two protons is very significant.

N. B. Ladygina; A. V. Shebeko

2004-04-15

258

Charge-transfer excitations steer the Davydov splitting and mediate singlet exciton fission in pentacene.  

PubMed

Quantum-chemical calculations are combined to a model Frenkel-Holstein Hamiltonian to assess the nature of the lowest electronic excitations in the pentacene crystal. We show that an admixture of charge-transfer excitations into the lowest singlet excited states form the origin of the Davydov splitting and mediate instantaneous singlet exciton fission by direct optical excitation of coherently coupled single and double exciton states, in agreement with recent experiments. PMID:23767738

Beljonne, D; Yamagata, H; Brédas, J L; Spano, F C; Olivier, Y

2013-05-31

259

Charge-Transfer Excitations Steer the Davydov Splitting and Mediate Singlet Exciton Fission in Pentacene  

NASA Astrophysics Data System (ADS)

Quantum-chemical calculations are combined to a model Frenkel-Holstein Hamiltonian to assess the nature of the lowest electronic excitations in the pentacene crystal. We show that an admixture of charge-transfer excitations into the lowest singlet excited states form the origin of the Davydov splitting and mediate instantaneous singlet exciton fission by direct optical excitation of coherently coupled single and double exciton states, in agreement with recent experiments.

Beljonne, D.; Yamagata, H.; Brédas, J. L.; Spano, F. C.; Olivier, Y.

2013-05-01

260

TOPICAL REVIEW: Strong electronic correlations in superconducting organic charge transfer salts  

Microsoft Academic Search

We review the role of strong electronic correlations in quasi-two-dimensional organic charge transfer salts such as (BEDT-TTF)2X, (BETS)2Y, and beta'-[Pd(dmit)2]2Z. We begin by defining minimal models for these materials. It is necessary to identify two classes of material: the first class is strongly dimerized and is described by a half-filled Hubbard model; the second class is not strongly dimerized and

B. J. Powell; Ross H. McKenzie

2006-01-01

261

Excited state intramolecular charge transfer reaction in nonaqueous electrolyte solutions: Temperature dependence  

Microsoft Academic Search

Temperature dependence of the excited state intramolecular charge transfer reaction of 4-(1-azetidinyl)benzonitrile (P4C) in ethyl acetate (EA), acetonitrile (ACN), and ethanol at several concentrations of lithium perchlorate (LiClO4) has been investigated by using the steady state and time resolved fluorescence spectroscopic techniques. The temperature range considered is 267-343 K. The temperature dependent spectral peak shifts and reaction driving force (-DeltaGr)

Tuhin Pradhan; Harun Al Rasid Gazi; Ranjit Biswas

2009-01-01

262

Electrodeposition of magnesium from halide melts—charge transfer and diffusion kinetics  

Microsoft Academic Search

Electrodeposition of magnesium from molten MgCl2 and MgCl2-MgF2 (78-22 mol%) mixtures was studied by electrochemical techniques. The process was found to be quasi-reversible with a cathodic electrochemical rate constant for the total charge transfer reaction of about 10?3 cm\\/s at 780 °C. Underpotential deposition of an adsorbed layer of reduced Mg(II)-species was observed during cyclic voltammetry and potential step measurements.

B. Børresen; G. M. Haarberg; R. Tunold

1997-01-01

263

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

264

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

265

Impact of distributions and mixtures on the charge transfer properties of graphene nanoflakes.  

PubMed

Many of the promising new applications of graphene nanoflakes are moderated by charge transfer reactions occurring between defects, such as edges, and the surrounding environment. In this context the sign and value of properties such as the ionization potential, electron affinity, electronegativity and chemical hardness can be useful indicators of the efficiency of graphene nanoflakes for different reactions, and can help identify new application areas. However, as samples of graphene nanoflakes cannot necessarily be perfectly monodispersed, it is necessary to predict these properties for polydispersed ensembles of flakes, and provide a statistical solution. In this study we use some simple statistical methods, in combination with electronic structure simulations, to predict the charge transfer properties of different types of ensembles where restrictions have been placed on the diversity of the structures. By predicting quality factors for a variety of cases, we find that there is a clear motivation for restricting the sizes and suppressing certain morphologies to increase the selectivity and efficiency of charge transfer reactions; even if samples cannot be completely purified. PMID:25521251

Shi, Hongqing; Rees, Robert J; Per, Manolo C; Barnard, Amanda S

2015-01-22

266

N+ charge transfer and N+2 dissociation in N2 at swarm energies.  

PubMed

This paper reports a drift-tube-mass-spectrometer measurement of the relative abundances of N+ and N+2 in pure nitrogen, over a ratio of electric field to gas density, E/N, from 800 to 7200 Td [1 townsend (Td)=10(-17) V cm(2)]. A proposed charge transfer dissociation scheme between the above two ions and N2 allowed us to obtain spatial rate coefficients for charge transfer and dissociation over the E/N range 800-2800 Td. Using previously measured cross sections for the above processes, and assuming a Maxwellian distribution of ion velocities, we calculated the reaction coefficients, which were found to be in good agreement with our measured values. In particular, the present results support the trend toward fairly high charge transfer cross section values for N+ energies above 10 eV. In the overlap range between 2.4 and 7.2 kTd, our concentration ratio [N(+)/N(+)(2)] is about five times smaller than that measured previously from a diffuse Townsend discharge in which electron impact is involved in addition to N+2 collisional dissociation with N2, but has the same trend. Thus it seems that, besides N+2 dissociation by electron impact, collisional dissociation becomes important at elevated values of E/N. In connection with previous discharge work in nitrogen, the present study may help explain the enhanced cathode yields observed. PMID:11304365

Basurto, E; de Urquijo, J; Cisneros, C; Alvarez, I

2001-01-01

267

Ultrafast intramolecular charge transfer of formyl perylene observed using femtosecond transient absorption spectroscopy.  

PubMed

The excited-state photophysics of formylperylene (FPe) have been investigated in a series of nonpolar, polar aprotic, and polar protic solvents. A variety of experimental and theoretical methods were employed including femtosecond transient absorption (fs-TA) spectroscopy with 130 fs temporal resolution. We report that the ultrafast intramolecular charge transfer from the perylene unit to the formyl (CHO) group can be facilitated drastically by hydrogen-bonding interactions between the carbonyl group oxygen of FPe and hydrogen-donating solvents in the electronically excited state. The excited-state absorption of FPe in methanol (MeOH) is close to the reported perylene radical cation produced by bimolecular quenching by an electron acceptor. This is a strong indication for a substantial charge transfer in the S(1) state in protic solvents. The larger increase of the dipole moment change in the protic solvents than that in aprotic ones strongly supports this observation. Relaxation mechanisms including vibrational cooling and solvation coupled to the charge-transfer state are also discussed. PMID:20886856

Mohammed, Omar F

2010-11-01

268

Excited Charge Transfer States in Donor-Acceptor Fluorescent Phenanthroimidazole Derivatives.  

PubMed

Solvent-dependent electronic structure of the selected donor (D) acceptor (A) derivatives of phenanthroimidazole derivatives containing fluoro substituent as an electron acceptor fragment in the fluorescent charge transfer (CT) states has been investigated. The mechanism of the radiative charge recombination CT???S0 is discussed in terms of the Mulliken-Murrell model of the CT complexes and the Marcus theory of photoinduced electron transfer (ET). Solvatochromic effects on the spectral position and profile of the stationary fluorescence spectra clearly indicate the CT character of the emitting singlet states of all of the compounds studied both in a polar and a non polar environment. An analysis of the CT fluorescence leads to the quantities relevant for the electron transfer in the Marcus inverted region. The values of the fluorescence rate constants (k r ) and corresponding transition dipole moments (M) and their solvent polarity dependence indicate that the electronic coupling between the emitting (1)CT state and the ground state is a governing factor of the radiative transitions. The relatively large values of M indicate a nonorthogonal geometry of the donor and acceptor subunits in the fluorescent states. It is shown that Marcus theory can be applied for the quantitative description of the radiationless charge recombination processes in the cases when an intersystem crossing to the excited triplet states can be neglected. PMID:24142304

Jayabharathi, J; Thanikachalam, V; Sathishkumar, R

2013-10-20

269

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

270

Double-charge-transfer cross sections in inelastic collisions of bare ions with helium atoms  

SciTech Connect

Double-charge-transfer cross sections into singly and doubly excited states for collisions of {alpha} particles with helium atoms have been studied in the energy range of 50 to 500 keV/amu. We have also studied the double electron capture cross sections into ground states for collisions of {sup 7}Li{sup 3+} and {sup 10}B{sup 5+} with helium atoms. In our study we have applied the four-body boundary corrected continuum intermediate state approximation. The intermediate continuum states of each electron and static correlations of the electrons have been taken into account in this formalism. Present calculated results for total charge transfer cross sections for the reaction {alpha}+He and Li{sup 3+}+He compare favorably well with the existing experimental and other theoretical predictions. Due to the nonavailability of any theoretical and experimental finding for the reaction B{sup 5+}+He, the energy variation of capture cross sections into the ground state of B{sup 5+} ion has been shown within the same energy range. However, charge transfer cross sections into singly and doubly excited states of He are compared with the available theoretical observations only due to nonavailability of any experimental result. In this case as well, agreement is very encouraging.

Purkait, M. [Department of Physics, Ramakrishna Mission Residential College, Narendrapur, Kolkata-700 103 (India); Sounda, S.; Dhara, A.; Mandal, C. R. [Department of Physics, Jadavpur University, Kolkata-700 032 (India)

2006-10-15

271

pH Dependence of charge transfer between tryptophan and tyrosine in dipeptides.  

PubMed

Time-resolved absorption spectroscopy has been employed to study the directionality and rate of charge transfer in W-Y and Ac-W-Y dipeptides as a function of pH. Excitation with 266-nm nanosecond laser pulses produces both W (or [WH](+), depending on pH) and Y. Between pH 6 and 10, W to was found to oxidize Y with k(X)=9.0x10(4) s(-1) and 1.8x10(4) s(-1) for the W-Y and Ac-W-Y dipeptide systems, respectively. The intramolecular charge transfer rate increases as the pH is lowered over the range 6>pH>2. For 10W-Y(-) (Y(-), tyrosinate anion), with a rate constant of k(X)=1.2x10(5) s(-1). The dependence of charge transfer directionality between W and Y on pH is important to the enzymatic function of several model and natural biological systems as discussed here for ribonucleotide reductase. PMID:15694351

Reece, Steven Y; Stubbe, Joanne; Nocera, Daniel G

2005-02-17

272

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

273

Structure and Electronic Spectra of Purine-Methyl Viologen Charge Transfer Complexes  

PubMed Central

The structure and properties of the electron donor-acceptor complexes formed between methyl viologen (MV) and purine nucleosides and nucleotides in water and the solid state have been investigated using a combination of experimental and theoretical methods. Solution studies were performed using UV-vis and 1H NMR spectroscopy. Theoretical calculations were performed within the framework of density functional theory (DFT). Energy decomposition analysis indicates that dispersion and induction (charge-transfer) interactions dominate the total binding energy, whereas electrostatic interactions are largely repulsive. The appearance of charge transfer bands in the absorption spectra of the complexes are well described by time-dependent (TD) DFT and are further explained in terms of the redox properties of purine monomers and solvation effects. Crystal structures are reported for complexes of methyl viologen with the purines 2?-deoxyguanosine 3?-monophosphate GMP (DAD?DAD? type) and 7-deazaguanosine zG (DAD?ADAD? type). Comparison of the structures determined in the solid state and by theoretical methods in solution provides valuable insights into the nature of charge-transfer interactions involving purine bases as electron donors. PMID:24294996

Jalilov, Almaz S.; Patwardhan, Sameer; Singh, Arunoday; Simeon, Tomekia; Sarjeant, Amy A.; Schatz, George C.; Lewis, Frederick D.

2014-01-01

274

Application of double-hybrid density functionals to charge transfer in N-substituted pentacenequinones  

NASA Astrophysics Data System (ADS)

A set of N-heteroquinones, deriving from oligoacenes, have been recently proposed as n-type organic semiconductors with high electron mobilities in thin-film transistors. Generally speaking, this class of compounds self-assembles in neighboring ?-stacks linked by weak hydrogen bonds. We aim at theoretically characterizing here the sequential charge transport (hopping) process expected to take place across these arrays of molecules. To do so, we need to accurately address the preferred packing of these materials simultaneously to single-molecule properties related to charge-transfer events, carefully employing dispersion-corrected density functional theory methods to accurately extract the key molecular parameters governing this phenomenon at the nanoscale. This study confirms the great deal of interest around these compounds, since controlled functionalization of model molecules (i.e., pentacene) allows to efficiently tune the corresponding charge mobilities, and the capacity of modern quantum-chemical methods to predict it after rationalizing the underlying structure-property relationships.

Sancho-García, J. C.

2012-05-01

275

Inhomogeneous charge transfer within monolayer zinc phthalocyanine absorbed on TiO{sub 2}(110)  

SciTech Connect

The d-orbital contribution from the transition metal centers of phthalocyanine brings difficulties to understand the role of the organic ligands and their molecular frontier orbitals when it adsorbs on oxide surfaces. Here we use zinc phthalocyanine (ZnPc)/TiO{sub 2}(110) as a model system where the zinc d-orbitals are located deep below the organic orbitals leaving room for a detailed study of the interaction between the organic ligand and the substrate. A charge depletion from the highest occupied molecular orbital is observed, and a consequent shift of N1s and C1s to higher binding energy in photoelectron spectroscopy (PES). A detailed comparison of peak shifts in PES and near-edge X-ray absorption fine structure spectroscopy illustrates a slightly uneven charge distribution within the molecular plane and an inhomogeneous charge transfer screening between the center and periphery of the organic ligand: faster in the periphery and slower at the center, which is different from other metal phthalocyanine, e.g., FePc/TiO{sub 2}. Our results indicate that the metal center can substantially influence the electronic properties of the organic ligand at the interface by introducing an additional charge transfer channel to the inner molecular part.

Yu Shun; Ahmadi, Sareh; Adibi, Pooya Tabib Zadeh; Chow, Winnie; Goethelid, Mats [Materials Physics, ICT, Royal Institute of Technology, Electrum 229, SE-16440 Stockholm (Sweden); Sun, Chenghua [University of Queensland, ARC Centre of Excellence for Functional Nanomaterials and Centre for Computational Molecular Science, Australia Institute for Bioengineering and Nanotechnology, University of Queensland, Qld 4072 (Australia); Pietzsch, Annette [Max-lab, Lund University, Box 118, SE- 22100 Lund (Sweden)

2012-04-21

276

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

277

Inhomogeneous charge transfer within monolayer zinc phthalocyanine absorbed on TiO2(110)  

NASA Astrophysics Data System (ADS)

The d-orbital contribution from the transition metal centers of phthalocyanine brings difficulties to understand the role of the organic ligands and their molecular frontier orbitals when it adsorbs on oxide surfaces. Here we use zinc phthalocyanine (ZnPc)/TiO2(110) as a model system where the zinc d-orbitals are located deep below the organic orbitals leaving room for a detailed study of the interaction between the organic ligand and the substrate. A charge depletion from the highest occupied molecular orbital is observed, and a consequent shift of N1s and C1s to higher binding energy in photoelectron spectroscopy (PES). A detailed comparison of peak shifts in PES and near-edge X-ray absorption fine structure spectroscopy illustrates a slightly uneven charge distribution within the molecular plane and an inhomogeneous charge transfer screening between the center and periphery of the organic ligand: faster in the periphery and slower at the center, which is different from other metal phthalocyanine, e.g., FePc/TiO2. Our results indicate that the metal center can substantially influence the electronic properties of the organic ligand at the interface by introducing an additional charge transfer channel to the inner molecular part.

Yu, Shun; Ahmadi, Sareh; Sun, Chenghua; Adibi, Pooya Tabib Zadeh; Chow, Winnie; Pietzsch, Annette; Göthelid, Mats

2012-04-01

278

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

279

Dynamic structural effects and ultrafast biomolecular kinetics in photoinduced charge transfer reactions  

SciTech Connect

During the first budget significant progress was made in three areas: (1) assessment of dynamic structural effects accompanying charge transfer, (2) electrochemical assessment of site-to-site electronic coupling in simple inorganic systems, and (3) direct observation of intramolecular electron transfer kinetics in mixed-valence systems. In area 1 the most significant finding was that Franck-Condon parameters for electron transfer (i.e. normal coordinate displacements, vibrational frequencies, and single-mode vibrational reorganizational energy components) could be obtained for weakly interacting (ion-paired) redox systems (J.Phys.Chem., 1991, 95, 10535). Studies in area 3 have yielded results in both the ultrafast (femtosecond/picosecond) time regime (J.Phys.Chem. 1991, 95, 5712) and the intermediate (microsecond/millisecond) time regime (J.Am.Chem. Soc., submitted).

Hupp, J.T.

1992-01-01

280

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

NASA Astrophysics Data System (ADS)

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

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

1998-06-01

281

33 CFR 155.715 - Contents of letter of designation as a person-in-charge of the transfer of fuel oil.  

Code of Federal Regulations, 2010 CFR

...person-in-charge of the transfer of fuel oil. 155.715 Section 155.715...person-in-charge of the transfer of fuel oil. The letter of instruction required...person-in-charge of the transfer of fuel oil and state that the holder...

2010-07-01

282

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

283

Chemistry  

NSDL National Science Digital Library

These sites willhelp you gain greater understanding of Chemistry! Weather is also available Three areas to be on the test. STUDY HARD!!!! Equations Types of Equations Types of Equations text/htmlMichigan Teacher Network Matter Density of solids Density of solids text/htmlICSD ScienceZone Metals Kidneys and Metals Problem Set Kidneys and Metals Problem Set image/tiffCenter for Digital Curriculum Research POTENTIAL SURROGATE METALS FOR INCINERATOR TRIAL BURNS POTENTIAL SURROGATE METALS FOR INCINERATOR TRIAL BURNS text/html Let it snow Interactive Weather Maker Interactive Weather Maker urlexample ...

Riley

2006-04-22

284

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

NASA Astrophysics Data System (ADS)

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

Onufriev, Alexey Vlad

285

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

286

Assessing carbon-based anodes for lithium-ion batteries: a universal description of charge-transfer binding.  

PubMed

Many key performance characteristics of carbon-based lithium-ion battery anodes are largely determined by the strength of binding between lithium (Li) and sp(2) carbon (C), which can vary significantly with subtle changes in substrate structure, chemistry, and morphology. Here, we use density functional theory calculations to investigate the interactions of Li with a wide variety of sp(2) C substrates, including pristine, defective, and strained graphene, planar C clusters, nanotubes, C edges, and multilayer stacks. In almost all cases, we find a universal linear relation between the Li-C binding energy and the work required to fill previously unoccupied electronic states within the substrate. This suggests that Li capacity is predominantly determined by two key factors-namely, intrinsic quantum capacitance limitations and the absolute placement of the Fermi level. This simple descriptor allows for straightforward prediction of the Li-C binding energy and related battery characteristics in candidate C materials based solely on the substrate electronic structure. It further suggests specific guidelines for designing more effective C-based anodes. The method should be broadly applicable to charge-transfer adsorption on planar substrates, and provides a phenomenological connection to established principles in supercapacitor and catalyst design. PMID:25062244

Liu, Yuanyue; Wang, Y Morris; Yakobson, Boris I; Wood, Brandon C

2014-07-11

287

Assessing Carbon-Based Anodes for Lithium-Ion Batteries: A Universal Description of Charge-Transfer Binding  

NASA Astrophysics Data System (ADS)

Many key performance characteristics of carbon-based lithium-ion battery anodes are largely determined by the strength of binding between lithium (Li) and sp2 carbon (C), which can vary significantly with subtle changes in substrate structure, chemistry, and morphology. Here, we use density functional theory calculations to investigate the interactions of Li with a wide variety of sp2 C substrates, including pristine, defective, and strained graphene, planar C clusters, nanotubes, C edges, and multilayer stacks. In almost all cases, we find a universal linear relation between the Li-C binding energy and the work required to fill previously unoccupied electronic states within the substrate. This suggests that Li capacity is predominantly determined by two key factors—namely, intrinsic quantum capacitance limitations and the absolute placement of the Fermi level. This simple descriptor allows for straightforward prediction of the Li-C binding energy and related battery characteristics in candidate C materials based solely on the substrate electronic structure. It further suggests specific guidelines for designing more effective C-based anodes. The method should be broadly applicable to charge-transfer adsorption on planar substrates, and provides a phenomenological connection to established principles in supercapacitor and catalyst design.

Liu, Yuanyue; Wang, Y. Morris; Yakobson, Boris I.; Wood, Brandon C.

2014-07-01

288

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

PubMed

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. PMID:24410238

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

2014-01-01

289

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

SciTech Connect

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

Haverkate, Lucas A.; Mulder, Fokko M. [Reactor Institute Delft, Faculty of Applied Sciences, Delft University of Technology, Mekelweg 15, 2629JB Delft (Netherlands)] [Reactor Institute Delft, Faculty of Applied Sciences, Delft University of Technology, Mekelweg 15, 2629JB Delft (Netherlands); Zbiri, Mohamed, E-mail: zbiri@ill.fr; Johnson, Mark R. [Institut Laue Langevin, 38042 Grenoble Cedex 9 (France)] [Institut Laue Langevin, 38042 Grenoble Cedex 9 (France); Carter, Elizabeth [Vibrational Spectroscopy Facility, School of Chemistry, The University of Sydney, NSW 2008 (Australia)] [Vibrational Spectroscopy Facility, School of Chemistry, The University of Sydney, NSW 2008 (Australia); Kotlewski, Arek; Picken, S. [ChemE-NSM, Faculty of Chemistry, Delft University of Technology, 2628BL/136 Delft (Netherlands)] [ChemE-NSM, Faculty of Chemistry, Delft University of Technology, 2628BL/136 Delft (Netherlands); Kearley, Gordon J. [Bragg Institute, Australian Nuclear Science and Technology Organisation, Menai, NSW 2234 (Australia)] [Bragg Institute, Australian Nuclear Science and Technology Organisation, Menai, NSW 2234 (Australia)

2014-01-07

290

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

ERIC Educational Resources Information Center

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

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

2013-01-01

291

Complexation of polyaniline and graphene for efficient counter electrodes in dye-sensitized solar cells: Enhanced charge transfer ability  

NASA Astrophysics Data System (ADS)

With an aim of significantly enhancing charge-transfer ability of counter electrodes and therefore photovoltaic performances of dye-sensitized solar cells (DSSCs), here we pioneerly report the complexation of polyaniline (PANi) and graphene as well as their employment as counter electrodes (CEs) in efficient DSSCs. Owing to the covalent bond between PANi (N atoms) and graphene (C atoms), charge transfer kinetics is dramatically elevated, which can be confirmed by the enhancement on electrocatalytic activity toward triiodides and a decrease in charge-transfer resistance. A power conversion efficiency of 7.70% is determined from DSSC using PANi-8 wt‰ graphene complex CE in comparison with 6.40% from pure PANi CE-based DSSC. The high conversion efficiency, facile charge-transfer in combination with simple preparation, relatively low cost, and scalability demonstrates the potential use of PANi-graphene complexes in robust DSSCs.

He, Benlin; Tang, Qunwei; Wang, Min; Ma, Chunqing; Yuan, Shuangshuang

2014-06-01

292

The Proton Transfer Reaction-Mass Spectrometer for Atmospheric Chemistry Tracers of Diesel Exhaust Emissions and Measurements of Trace gas and Aerosol properties.  

E-print Network

The Proton Transfer Reaction-Mass Spectrometer for Atmospheric Chemistry Tracers of Diesel Exhaust the use of a technique referred to as the Dynamic Dilution System. The use of a Proton Transfer ReactionL/hr) Thermometers (Centigrade) Ionicon Analytik Proton Transfer Reaction-Mass Spectrometer (PTR-MS) Procedure The N2

Collins, Gary S.

293

Reduction of charge transfer resistance at the lithium phosphorus oxynitride\\/lithium cobalt oxide interface by thermal treatment  

Microsoft Academic Search

An all-solid-state thin-film battery consisting of a c-axis-oriented LiCoO2 thin-film and a lithium phosphorus oxynitride (LiPON) glass electrolyte was fabricated. Thermal treatment at 473K after fabrication of the LiPON\\/LiCoO2 interface decreased the charge transfer resistance at the interface, and the resistance was further reduced by prolonging the thermal treatment time. The charge transfer resistance per unit electrode area (interfacial resistivity)

Yasutoshi Iriyama; Tomonori Kako; Chihiro Yada; Takeshi Abe; Zempachi Ogumi

2005-01-01

294

Charge-Transfer States and Upper Limit of the Open-Circuit Voltage in Polymer:Fullerene Organic Solar Cells  

Microsoft Academic Search

The power conversion efficiency of polymer:fullerene bulk heterojunction solar cells depends on the generated photocurrent and photovoltage. Here we show, using the thermodynamic theory of detailed balance, that the photovoltage in particular is limited by the presence of polymer:fullerene material interaction, resulting in the formation of a weak donor-acceptor charge transfer complex (CTC). Excited CTCs, or charge transfer (CT) states,

Koen Vandewal; Kristofer Tvingstedt; Jean V. Manca; Olle Inganas

2010-01-01

295

Radiative and nonradiative charge transfer in He{sub +} + H{sub 2} Collisions in the meV regime  

SciTech Connect

Schauer et al. recently measured absolute rate constants at ultra-low energy in an experiment for dissociative charge transfer (DCT) of He{sup +} ions on hydrogen molecules, and radiative charge transfer (RCT) between the same particles at T=15K. The authors proposed that exoergic inelastic processes proceed via tunneling for DCT and dipole coupling for RCT. The present findings are in reasonable accord with the measurements.

Kimura, M.; Lane, N.F. [Argonne National Lab., IL (United States)]|[Rice Univ., Houston, TX (United States)

1992-12-01

296

Synthesis and electrochemical studies of charge-transfer complexes of thiazolidine-2,4-dione with ? and ? acceptors  

NASA Astrophysics Data System (ADS)

In the present work, we report the synthesis and characterization of novel charge-transfer complexes of thiazolidine-2,4-dione (TZD) with sigma acceptor (iodine) and pi acceptors (chloranil, dichlorodicyanoquinone, picric acid and duraquinone). We also evaluated their thermal and electrochemical properties and we conclude that these complexes are frequency dependent. Charge-transfer complex between thiazolidine-2,4-dione and iodine give best conductivity. In conclusion, complex with sigma acceptors are more conducting than with pi acceptors.

Singh, Prashant; Kumar, Pradeep; Katyal, Anju; Kalra, Rashmi; Dass, Sujata K.; Prakash, Satya; Chandra, Ramesh

2010-03-01

297

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

PubMed

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

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

2015-01-01

298

Theoretical Investigation of Charge Transfer between N6+ and atomic Hydrogen  

SciTech Connect

Charge transfer due to collisions of ground-state N{sup 6+}(1s{sup 2} S) with atomic hydrogen has been investigated theoretically using the quantum-mechanical molecular-orbital close-coupling (QMOCC) method, in which the adiabatic potentials and nonadiabatic couplings were obtained using the multireference single- and double-excitation configuration-interaction (MRDCI) approach. Total, n-, l-, and S-resolved cross sections have been obtained for energies between 10 meV/u and 10 keV/u. The QMOCC results were compared to available experimental and theoretical data as well as to merged-beams measurements and atomic-orbital close-coupling and classical trajectory Monte Carlo calculations. The accuracy of the QMOCC charge-transfer cross sections was found to be sensitive to the accuracy of the adiabatic potentials and couplings. Consequently, we developed a method to optimize the atomic basis sets used in the MRDCI calculations for highly charged ions. Since cross sections, especially those that are state selective, are necessary input for x-ray emission simulation of heliospheric and Martian exospheric spectra arising from solar wind ion-neutral gas collisions, a recommended set of state-selective cross sections, based on our evaluation of the calculations and measurements, is provided.

Wu, Y. [University of Georgia, Athens, GA; Stancil, P C [University of Georgia, Athens, GA; Liebermann, H. P. [Bergische Universitaet Wuppertal, Germany; Funke, P. [Bergische Universitaet Wuppertal, Germany; Rai, S. N. [Bergische Universitaet Wuppertal, Germany; Buenker, R. J. [Bergische Universitaet Wuppertal, Germany; Schultz, David Robert [ORNL; Hui, Yawei [ORNL; Draganic, Ilija N [ORNL; Havener, Charles C [ORNL

2011-01-01

299

Dipole polarization and charge transfer effects in the lattice dynamics and dielectric properties of ionic crystals  

NASA Astrophysics Data System (ADS)

We extend our formalism of an ab initio description of electronic screening in solids with a strong ionic component of bonding by introducing electronic density polarization effects of dipole type in addition to charge transfer polarization processes. The latter have been found earlier to be very important for the lattice dynamics and the electron-phonon interaction in the high-temperature superconductors. The dipole deformations are calculated with the Sternheimer method and the influence on the polarizability induced by the crystalline environment and by self-interaction corrections is studied. We further derive detailed expressions for the various coupling coefficients appearing in the dynamical matrix in our formalism and apply this theory in a first step in view of the ultimate goal, namely, the high-temperature superconductors, to the calculation of complete dispersion curves for the alkali halide NaCl and the alkaline-earth oxide MgO taking into account for the first time dipole polarization and charge transfer effects together. The agreement of our calculated results with the experiments is good. As a main effect we find a renormalization of the LO modes and a reduction of the LO-TO splitting by both types of polarization processes. The dipole polarization, however, dominates the electronic screening by far. Finally, we investigate the macroscopic dielectric constant and the transverse effective charges and discuss the results in context with the Clausius-Mossotti relation.

Falter, Claus; Klenner, Michael; Hoffmann, Georg A.; Schnetgöke, Frank

1999-11-01

300

Fowler-Nordheim tunneling induced charge transfer plasmons between nearly touching nanoparticles.  

PubMed

Reducing the gap between two metal nanoparticles down to atomic dimensions uncovers novel plasmon resonant modes. Of particular interest is a mode known as the charge transfer plasmon (CTP). This mode has been experimentally observed in touching nanoparticles, where charges can shuttle between the nanoparticles via a conductive path. However, the CTP mode for nearly touching nanoparticles has only been predicted theoretically to occur via direct tunneling when the gap is reduced to ~0.4 nm. Because of challenges in fabricating and characterizing gaps at these dimensions, experiments have been unable to provide evidence for this plasmon mode that is supported by tunneling. In this work, we consider an alternative tunneling process, that is, the well-known Fowler-Nordheim (FN) tunneling that occurs at high electric fields, and apply it for the first time in the theoretical investigation of plasmon resonances between nearly touching nanoparticles. This new approach relaxes the requirements on gap dimensions, and intuitively suggests that with a sufficiently high-intensity irradiation, the CTP can be excited via FN tunneling for a range of subnanometer gaps. The unique feature of FN tunneling induced CTP is the ability to turn on and off the charge transfer by varying the intensity of an external light source, and this could inspire the development of novel quantum devices. PMID:23215253

Wu, Lin; Duan, Huigao; Bai, Ping; Bosman, Michel; Yang, Joel K W; Li, Erping

2013-01-22

301

Physical adsorption and charge transfer of molecular Br2 on graphene.  

PubMed

We present a detailed study of gaseous Br2 adsorption and charge transfer on graphene, combining in situ Raman spectroscopy and density functional theory (DFT). When graphene is encapsulated by hexagonal boron nitride (h-BN) layers on both sides, in a h-BN/graphene/h-BN sandwich structure, it is protected from doping by strongly oxidizing Br2. Graphene supported on only one side by h-BN shows strong hole doping by adsorbed Br2. Using Raman spectroscopy, we determine the graphene charge density as a function of pressure. DFT calculations reveal the variation in charge transfer per adsorbed molecule as a function of coverage. The molecular adsorption isotherm (coverage versus pressure) is obtained by combining Raman spectra with DFT calculations. The Fowler-Guggenheim isotherm fits better than the Langmuir isotherm. The fitting yields the adsorption equilibrium constant (?0.31 Torr(-1)) and repulsive lateral interaction (?20 meV) between adsorbed Br2 molecules. The Br2 molecule binding energy is ?0.35 eV. We estimate that at monolayer coverage each Br2 molecule accepts 0.09 e- from single-layer graphene. If graphene is supported on SiO2 instead of h-BN, a threshold pressure is observed for diffusion of Br2 along the (somewhat rough) SiO2/graphene interface. At high pressure, graphene supported on SiO2 is doped by adsorbed Br2 on both sides. PMID:24528378

Chen, Zheyuan; Darancet, Pierre; Wang, Lei; Crowther, Andrew C; Gao, Yuanda; Dean, Cory R; Taniguchi, Takashi; Watanabe, Kenji; Hone, James; Marianetti, Chris A; Brus, Louis E

2014-03-25

302

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

PubMed Central

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

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

2015-01-01

303

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

304

Ultrafast charge transfer in atomically thin MoS?/WS? heterostructures.  

PubMed

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. PMID:25150718

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

2014-09-01

305

Thermal and Quantum Peierls Transitions in Organic Charge-Transfer Salts  

NASA Astrophysics Data System (ADS)

The choice of donors (D) and acceptors (A) governs the charge-transfer ? in organic CT salts with mixed one-dimensional DADA stacks. Strong D and A yield ? ˜ 0.9 stacks of radical ions with thermally accessible spin and charge degrees of freedom whose Peierls transition can be described by a Hubbard model with site energies. The same microscopic model describes CT salts with smaller and variable ? ˜ 0.5 in which neutral-ionic and/or Peierls transitions occur in the ground electronic state. Quantum transitions are driven by volume changes, with negligible thermal population of excite states. CT salts with thermal or quantum Peierls transitions are identified. Conflicting magnetic, vibrational and structural data in several CT salts are resolved in terms of mobile spin solitons, a dimerized ground state and a Peierls transition beyond the crystal's thermal stability.

Bewick, Sharon; Soos, Zoltan

2006-03-01

306

Compton scattering and charge transfer in Er substituted DyAl2  

NASA Astrophysics Data System (ADS)

A unique applicability of Compton spectroscopy in probing the electronic states of rare earth aluminides using high energy (662 keV) ?-rays is reported. We have measured first-ever Compton profiles of Dy1-xErxAl2 (x=0, 0.2) using 20Ci 137Cs Compton spectrometer. The charge reorganization in Dy1-xErxAl2 (x=0, 0.2), on the formation of compound, has been discussed using the valence band Compton profile data. The experimental Compton profile data unambiguously establish charge transfer from Al to Dy (Dy and Er) on formation of x=0.0 (0.2) compound, which is in tune with spin polarized relativistic Korringa-Kohn-Rostoker (SPR-KKR) calculations. A reasonable agreement between SPR-KKR based Compton profiles and the experimental data show applicability of the Green function method in predicting the electronic properties of rare earth compounds.

Ahuja, B. L.; Mohammad, F. M.; Mohammed, S. F.; Sahariya, Jagrati; Mund, H. S.; Heda, N. L.

2015-02-01

307

Visualizing interfacial charge transfer in dye sensitized nanoparticles using x-ray transient absorption spectroscopy.  

SciTech Connect

A molecular level understanding of the structural reorganization accompanying interfacial electron transfer is important for rational design of solar cells. Here we have applied XTA (X-ray transient absorption) spectroscopy to study transient structures in a heterogeneous interfacial system mimicking the charge separation process in dye-sensitized solar cell (DSSC) with Ru(dcbpy){sub 2}(NCS){sub 2} (RuN3) dye adsorbed to TiO{sub 2} nanoparticle surfaces. The results show that the average Ru-NCS bond length reduces by 0.06 {angstrom}, whereas the average Ru-N(dcbpy) bond length remains nearly unchanged after the electron injection. The differences in bond-order change and steric hindrance between two types of ligands are attributed to their structural response in the charge separation. This study extends the application of XTA into optically opaque hybrid interfacial systems relevant to the solar energy conversion.

Zhang, X. Y.; Smolentsev, G.; Guo, J.; Attenkofer, K.; Kurtz, C.; Jennings, G.; Lockard, J. V.; Stickrath, A. B.; Chen, L. X. (X-Ray Science Division); (Southern Federal Univ.); (Lund Univ.); (Northwestern Univ.)

2011-01-01

308

Polarization anisotropy of charge transfer absorption and emission of aligned polymer:fullerene blend films  

NASA Astrophysics Data System (ADS)

An improved understanding of the electronic structure of interfacial charge transfer (CT) states is of importance due to their crucial role in charge carrier generation and recombination in organic donor-acceptor (DA) solar cells. DA combinations with a small difference between the energy of the CT state (ECT) and energy of the donor exciton (ED*) are of special interest since energy losses due to electron transfer are minimized, resulting in an optimized open-circuit voltage. In that case, the CT state can be considered as a resonance mixture, containing character of a fully ionic state (D+A-) and of the local polymer excited state (D*A). We show that the D*A contribution to the overall CT state wave function can be determined by measurements of the polarization anisotropy of CT absorption and emission of polymer:fullerene blends with aligned polymer chains. We study two donor polymers, P3HT and TQ1, blended with fullerene acceptors with different ionization potentials, allowing variation of the ED*-ECT difference. We find that, upon decreasing ED*-ECT, the local excitonic D*A character of the CT state increases, resulting in a decreased fraction of charge transferred and an increased transition dipole moment. For typical polymer:fullerene systems, this effect is expected to become detrimental for device performance if ED*-ECT<0.1 eV. This however, depends on the electronic coupling between D*A and D+A-, which we experimentally estimate to be ˜6 meV for the TQ1:PCBM system.

Vandewal, Koen; Tvingstedt, Kristofer; Inganäs, Olle

2012-07-01

309

Control of Adsorbate\\/Substrate Charge Transfer Through Coadsorption in the CO\\/S\\/Cu(111) System  

Microsoft Academic Search

The nature of the charge transfer between an adsorbate and a metal surface determines the various energy transfer processes which are important for thermal and photoinduced surface reactions. Coadsorbate sytems provide an environment enabling the modification of these processes. We present FTIR data of an annealed OCS\\/Cu(111) surface. We find through isotope and TPD studies that this sytem can be

R. Verma; Z.-J. Sun; J. P. Culver; R. M. Hochstrasser; A. G. Yodh

1996-01-01

310

Atom-scale surface reactivity mediated by long-ranged equilibrium charge transfer  

NASA Astrophysics Data System (ADS)

The observation of reaction outcomes at the bulk scale provides an average view of chemical processes, obscuring potentially significant differences in the behavior of matter at the atom scale. Through a series of atom-resolved scanning tunneling microscopy experiments, the inhomogeneous reactivity of silicon surface dangling bond states is revealed. The differences in reactivity provide evidence for the coexistence of neutral and negative surface states on these surfaces. It is shown that reactivity can be modulated through the density of surface states and by the bulk dopant level. These findings demonstrate that site-specific surface reactivity at the atom scale can be modulated by nonlocal charge allocation and provide opportunities for controlling chemistry at this scale.

Piva, Paul G.; DiLabio, Gino A.; Livadaru, Lucian; Wolkow, Robert A.

2014-10-01

311

Class IV charge models: a new semiempirical approach in quantum chemistry.  

PubMed

We propose a new criterion for defining partial charges on atoms in molecules, namely that physical observables calculated from those partial charges should be as accurate as possible. We also propose a method to obtain such charges based on a mapping from approximate electronic wave functions. The method is illustrated by parameterizing two new charge models called AM1-CM1A and PM3-CM1P, based on experimental dipole moments and, respectively, on AM1 and PM3 semiempirical electronic wave functions. These charge models yield rms errors of 0.30 and 0.26 D, respectively, in the dipole moments of a set of 195 neutral molecules consisting of 103 molecules containing H, C, N and O, covering variations of multiple common organic functional groups, 68 fluorides, chlorides, bromides and iodides, 15 compounds containing H, C, Si or S, and 9 compounds containing C-S-O or C-N-O linkages. In addition, partial charges computed with this method agree extremely well with high-level ab initio calculations for both neutral compounds and ions. The CM1 charge models provide a more accurate point charge representation of the dipole moment than provided by most previously available partial charges, and they are far less expensive to compute. PMID:7751872

Storer, J W; Giesen, D J; Cramer, C J; Truhlar, D G

1995-02-01

312

Electron Transfer Dissociation: Effects of Cation Charge State on Product Partitioning in Ion/Ion Electron Transfer to Multiply Protonated Polypeptides  

PubMed Central

The effect of cation charge state on product partitioning in the gas-phase ion/ion electron transfer reactions of multiply protonated tryptic peptides, model peptides, and relatively large peptides with singly charged radical anions has been examined. In particular, partitioning into various competing channels, such as proton transfer (PT) versus electron transfer (ET), electron transfer with subsequent dissociation (ETD) versus electron transfer with no dissociation (ET,noD), and fragmentation of backbone bonds versus fragmentation of side chains, was measured quantitatively as a function of peptide charge state to allow insights to be drawn about the fundamental aspects of ion/ion reactions that lead to ETD. The ET channel increases relative to the PT channel, ETD increases relative to ET,noD, and fragmentation at backbone bonds increases relative to side-chain cleavages as cation charge state increases. The increase in ET versus PT with charge state is consistent with a Landau-Zener based curve-crossing model. An optimum charge state for ET is predicted by the model for the ground state-to-ground state reaction. However, when the population of excited product ion states is considered, it is possible that a decrease in ET efficiency as charge state increases will not be observed due to the possibility of the population of excited electronic states of the products. Several factors can contribute to the increase in ETD versus ET,noD and backbone cleavage versus side-chain losses. These factors include an increase in reaction exothermicity and charge state dependent differences in precursor and product ion structures, stabilities, and sites of protonation. PMID:23264749

Liu, Jian; McLuckey, Scott A.

2012-01-01

313

Charge transfer processes and ultraviolet induced absorption in Yb:YAG single crystal laser materials  

NASA Astrophysics Data System (ADS)

Charge transfer (CT) transitions and UV induced color centers in Yb:YAG single crystals have been investigated. A simultaneous pair formation of a stable Yb2+ ion and a hole related (O-) color center (hole polaron) are observed through a CT-process. Slightly different types of hole related color centers are formed in Yb:YAG crystals containing small levels of iron impurities. Furthermore, excitation spectroscopy on the UV irradiated Yb:YAG samples could confirm an energy transfer process between Yb3+ and Yb2+ ions. The findings are important for an increased knowledge of the physical loss mechanisms observed in Yb-doped laser materials, such as the nonlinear decay process in Yb:YAG crystals as well as the photodarkening phenomenon in Yb-doped fiber lasers.

Rydberg, S.; Engholm, M.

2013-06-01

314

Multi-state charge transfer dynamics and trapping of hyperthermal and low energy alkali ions  

NASA Astrophysics Data System (ADS)

Experimental and theoretical studies were performed of the scattering of hyperthermal and keV energy Lisp+ and Nasp+ ions from Cu(001) surfaces. Chapter one presents measurements of relative total Li(2p) and Na(3p) yields, for 400 eV Lisp+ and 1320 eV Nasp+ scattering from clean and alkali-covered Cu(001). These excited-state yields were measured because they provide a sensitive test of multi-state models of resonant charge transfer, that is, models that are capable of treating more than two atomic states. Chapter two presents a detailed conceptual analysis of two multi-state models: a rate-equation model and the Marston model. The rate-equation model fails to reproduce the measured Li(2p) and Na(3p) yields, whereas the Marston model reproduces the primary trends in the yields. The different behaviors of these models are explained by physical reasoning. The rate-equation model is a fundamentally flawed description of resonant charge transfer, because it includes neither hybridization nor non-adiabatic excitations. Both aspects of resonant charge transfer are required to explain the Li(2p) and Na(3p) yields. These aspects are included in the Marston model, which describes the atom-metal system quantum-mechanically. The quantum mechanics of the atom-metal system can be understood from a physical viewpoint by the use of a few basic principles-principles which are broadly applicable to resonant charge transfer. A key principle is the tendency of the atom-metal system to electronically equilibrate throughout the scattering trajectory of an atom. Additional principles follow from an examination of the many-electron basis states of the atom-metal system. Chapter three presents measurements of the probability that 5 to 600 eV Nasp+ ions incident on Cu(001) become trapped on top of the surface. At a near-normal incident geometry the on-top trapping probability decreased monotonically as the incident energy was decreased. At 45sp° incidence along the < 100> azimuth, a surprising trend was observed in the on-top trapping probability: the probability initially decreased to zero as the incident energy was increased to 20 eV, but then increased as the energy was increased above 20 eV. Classical trajectory simulations show that the nonmonotonic trend in the on-top trapping probability is due to the increase in the surface corrugation at higher incident energies.

Dahl, Eric Brian

315

Quasidiabatic states for intramolecular charge transfer. Application to the protonation of NH3  

NASA Astrophysics Data System (ADS)

We have constructed ab initio adiabatic and quasidiabatic surfaces for the description of the protonation of NH3. For the diabatic states, we applied a recently developed method which is based on the propagation along the reaction coordinate, starting from the dissociation region, of the maximized nonorthonormal overlap between diabatic states calculated at successive geometries. In agreement with earlier calculations [Kaldor et al., J. Chem. Phys. 90, 6395 (1989)], it was found that the adiabatic surfaces cannot explain this charge-transfer process. On the contrary, a single diabatic potential curve correlates smoothly the ground state of NH+4 with the NH3+H+ limit.

Petsalakis, I. D.; Theodorakopoulos, G.; Nicolaides, C. A.

1994-04-01

316

Scale-model charge-transfer technique for measuring enhancement factors  

NASA Technical Reports Server (NTRS)

Determination of aircraft electric field enhancement factors is crucial when using airborne field mill (ABFM) systems to accurately measure electric fields aloft. SRI used the scale model charge transfer technique to determine enhancement factors of several canonical shapes and a scale model Learjet 36A. The measured values for the canonical shapes agreed with known analytic solutions within about 6 percent. The laboratory determined enhancement factors for the aircraft were compared with those derived from in-flight data gathered by a Learjet 36A outfitted with eight field mills. The values agreed to within experimental error (approx. 15 percent).

Kositsky, J.; Nanevicz, J. E.

1991-01-01

317

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

NASA Astrophysics Data System (ADS)

Menadione (vitamin K 3) 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 CCl 4 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 obtained. The formation constants exhibit a very good linear free energy relationship (Hammett) at all the temperatures studied.

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

2004-01-01

318

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

E-print Network

. Experimental: A central poly-(4-(9,9-dioctyl-9H-fluoren-2-yl)benzo[c][1,2,5]-thiadiazole) (F8BT) electron- accepting block was synthesised by Suzuki condensation, followed by endcapping with trimethylsilylpheny groups and reaction with ICl. The block size... to theoretical patterns calculated as described elsewhere.29,30 Results and discussion: Donor-acceptor block copolymers must have appropriate energy levels and redox properties to allow for effective charge transfer; in this case from the electron donor...

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

2014-11-24

319

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

320

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

321

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

322

Direct observation of charge transfer region at interfaces in graphene devices  

SciTech Connect

Nanoscale spectromicroscopic characterizing technique is indispensable for realization of future high-speed graphene transistors. Highly spatially resolved soft X-ray photoelectron microscopy measurements have been performed using our '3D nano-ESCA' (three-dimensional nanoscale electron spectroscopy for chemical analysis) equipment in order to investigate the local electronic states at interfaces in a graphene device structure. We have succeeded in detecting a charge transfer region at the graphene/metal-electrode interface, which extends over {approx}500 nm with the energy difference of 60 meV. Moreover, a nondestructive depth profiling reveals the chemical properties of the graphene/SiO{sub 2}-substrate interface.

Nagamura, Naoka [Department of Applied Chemistry, Graduate School of Engineering, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656 (Japan) [Department of Applied Chemistry, Graduate School of Engineering, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656 (Japan); Synchrotron Radiation Research Organization, The University of Tokyo, 1-1-1 Kouto, Sayo-cho, Sayo-gun, Hyogo 679-5198 (Japan); Horiba, Koji; Oshima, Masaharu [Department of Applied Chemistry, Graduate School of Engineering, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656 (Japan) [Department of Applied Chemistry, Graduate School of Engineering, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656 (Japan); Synchrotron Radiation Research Organization, The University of Tokyo, 1-1-1 Kouto, Sayo-cho, Sayo-gun, Hyogo 679-5198 (Japan); Core Research for Evolutional Science and Technology, Japan Science and Technology Agency, 5-7, Goban-cho, Chiyoda-ku, Tokyo, 102-0076 (Japan); Toyoda, Satoshi [Synchrotron Radiation Research Organization, The University of Tokyo, 1-1-1 Kouto, Sayo-cho, Sayo-gun, Hyogo 679-5198 (Japan) [Synchrotron Radiation Research Organization, The University of Tokyo, 1-1-1 Kouto, Sayo-cho, Sayo-gun, Hyogo 679-5198 (Japan); Core Research for Evolutional Science and Technology, Japan Science and Technology Agency, 5-7, Goban-cho, Chiyoda-ku, Tokyo, 102-0076 (Japan); Kurosumi, Shodai; Shinohara, Toshihiro [Department of Applied Chemistry, Graduate School of Engineering, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656 (Japan)] [Department of Applied Chemistry, Graduate School of Engineering, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656 (Japan); Fukidome, Hirokazu; Suemitsu, Maki [Research Institute of Electrical Communication, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai 980-8577 (Japan)] [Research Institute of Electrical Communication, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai 980-8577 (Japan); Nagashio, Kosuke; Toriumi, Akira [Department of Materials Engineering, Graduate School of Engineering, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656 (Japan)] [Department of Materials Engineering, Graduate School of Engineering, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656 (Japan)

2013-06-17

323

Direct observation of charge transfer region at interfaces in graphene devices  

NASA Astrophysics Data System (ADS)

Nanoscale spectromicroscopic characterizing technique is indispensable for realization of future high-speed graphene transistors. Highly spatially resolved soft X-ray photoelectron microscopy measurements have been performed using our "3D nano-ESCA" (three-dimensional nanoscale electron spectroscopy for chemical analysis) equipment in order to investigate the local electronic states at interfaces in a graphene device structure. We have succeeded in detecting a charge transfer region at the graphene/metal-electrode interface, which extends over ˜500 nm with the energy difference of 60 meV. Moreover, a nondestructive depth profiling reveals the chemical properties of the graphene/SiO2-substrate interface.

Nagamura, Naoka; Horiba, Koji; Toyoda, Satoshi; Kurosumi, Shodai; Shinohara, Toshihiro; Oshima, Masaharu; Fukidome, Hirokazu; Suemitsu, Maki; Nagashio, Kosuke; Toriumi, Akira

2013-06-01

324

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

SciTech Connect

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

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

1987-10-01

325

A new method for recycling asymmetric catalysts via formation of charge transfer complexes.  

PubMed

[reaction: see text]. A new concept for recycling asymmetric bis(oxazoline)-type catalysts is reported. The formation of charge-transfer complexes between the chiral ligand and trinitrofluorenone and their subsequent precipitation and reuse by addition of new substrate solutions is described. The efficiency of this procedure is demonstrated in a Diels-Alder reaction to reach the expected endo product as major isomer (up to 97% de and 94% ee): the catalyst was used up to 12 times without loss of either activity or selectivity. PMID:16435879

Chollet, Guillaume; Rodriguez, Fernand; Schulz, Emmanuelle

2006-02-01

326

Competition between charge-transfer exciton dissociation and direct photocarrier generation in molecular donor-acceptor compounds.  

PubMed

The interfacial charge-separation and photovoltaic characteristics of a molecular donor-acceptor charge-transfer compound were examined. Measurements of laser beam-induced currents on the single crystals allowed selective detection of hole and electron photocurrents through the metal-semiconductor interfaces. This method also reveals the exceptionally long diffusion length of 20???m in the crystal. The transition from charge-transfer exciton dissociation to direct photocarrier generation is discussed on the basis of the photon-energy-dependent diffusion length and photon-to-current conversion spectrum. PMID:21231409

Tsutsumi, Jun'ya; Yamada, Toshikazu; Matsui, Hiroyuki; Haas, Simon; Hasegawa, Tatsuo

2010-11-26

327

Bidirectional diffusion of ammonium and sodium cations in forward osmosis: role of membrane active layer surface chemistry and charge.  

PubMed

Systematic fundamental understanding of mass transport in osmosis-driven membrane processes is important for further development of this emerging technology. In this work, we investigate the role of membrane surface chemistry and charge on bidirectional solute diffusion in forward osmosis (FO). In particular, bidirectional diffusion of ammonium (NH4(+)) and sodium (Na(+)) is examined using FO membranes with different materials and surface charge characteristics. Using an ammonium bicarbonate (NH4HCO3) draw solution, we observe dramatically enhanced cation fluxes with sodium chloride feed solution compared to that with deionized water feed solution for thin-film composite (TFC) FO membrane. However, the bidirectional diffusion of cations does not change, regardless of the type of feed solution, for cellulose triacetate (CTA) FO membrane. We relate this phenomenon to the membrane fixed surface charge by employing different feed solution pH to foster different protonation conditions for the carboxyl groups on the TFC membrane surface. Membrane surface modification is also carried out with the TFC membrane using ethylenediamine to alter carboxyl groups into amine groups. The modified TFC membrane, with less negatively charged groups, exhibits a significant decrease in the bidirectional diffusion of cations under the same conditions employed with the pristine TFC membrane. Based on our experimental observations, we propose Donnan dialysis as a mechanism responsible for enhanced bidirectional diffusion of cations in TFC membranes. PMID:25418020

Lu, Xinglin; Boo, Chanhee; Ma, Jun; Elimelech, Menachem

2014-12-16

328

Charge Density Quantification of Polyelectrolyte Polysaccharides by Conductometric Titration: An Analytical Chemistry Experiment  

ERIC Educational Resources Information Center

An easy analytical method for determination of the charge density of polyelectrolytes, including polysaccharides and other biopolymers, is presented. The basic principles of conductometric titration, which is used in the pulp and paper industry as well as in colloid and interface science, were adapted to quantify the charge densities of a…

Farris, Stefano; Mora, Luigi; Capretti, Giorgio; Piergiovanni, Luciano

2012-01-01

329

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

330

TDDFT study of twisted intramolecular charge transfer and intermolecular double proton transfer in the excited state of 4?-dimethylaminoflavonol in ethanol solvent  

NASA Astrophysics Data System (ADS)

Time-dependent density functional theory method at the def-TZVP/B3LYP level was employed to investigate the intramolecular and intermolecular hydrogen bonding dynamics in the first excited (S1) state of 4?-dimethylaminoflavonol (DMAF) monomer and in ethanol solution. In the DMAF monomer, we demonstrated that the intramolecular charge transfer (ICT) takes place in the S1 state. This excited state ICT process was followed by intramolecular proton transfer. Our calculated results are in good agreement with the mechanism proposed in experimental work. For the hydrogen-bonded DMAF-EtOH complex, it was demonstrated that the intermolecular hydrogen bonds can induce the formation of the twisted intramolecular charge transfer (TICT) state and the conformational twisting is along the C3-C4 bond. Moreover, the intermolecular hydrogen bonds can also facilitate the intermolecular double proton transfer in the TICT state. A stepwise intermolecular double proton transfer process was revealed. Therefore, the intermolecular hydrogen bonds can alter the mechanism of intramolecular charge transfer and proton transfer in the excited state for the DMAF molecule.

Wang, Ye; Shi, Ying; Cong, Lin; Li, Hui

2015-02-01

331

Interplay between excited-state intramolecular proton transfer and charge transfer in flavonols and their use as protein-binding-site fluorescence probes  

SciTech Connect

A comparative study is presented of competitive fluorescences of three flavonols, 3-hydroxyflavone, 3,3[prime],4[prime],7-tetrahydroxyflavone (fisetin), and 4[prime]-diethylamino-3-hydroxyflavone (DHF). The normal fluorescence S[sub 1] [yields] S[sub 0] (400-nm region) is largely replaced by the proton-transfer tautomer fluorescence S[prime][sub 1] [yields] S[prime][sub 0] in the 550-nm region for all three of the flavonols in aprotic solvents at room temperature. For DHF in polar solvents the normal fluorescence becomes a charge-transfer fluorescence (460-500 nm) which competes strongly with the still dominant proton-transfer fluorescence (at 570 nm). In protic solvents, and at 77 K, the interference with intramolecular hydrogen bonding gives rise to greatly enhanced normal fluorescence, lowering the quantum yield of proton-transfer fluorescence. The utility of DHF as a discriminating fluorescence probe for protein binding sites is suggested by the strong dependence of the charge-transfer fluorescence on polarity of the environment and by various static and dynamic parameters of the charge-transfer and proton-transfer fluorescence which can be determined. 49 refs., 6 figs., 1 tab.

Sytnik, A.; Gormin, D.; Kasha, M. (Florida State Univ., Tallahassee, FL (United States))

1994-12-06

332

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

333

Charge transfer satellites in x-ray spectra of transition metal oxides  

NASA Astrophysics Data System (ADS)

Strongly correlated materials such as transition metal oxides (TMOs) often exhibit large satellites in their x-ray photoemission (XPS) and x-ray absorption spectra (XAS). These satellites arise largely from localized charge transfer excitations that accompany the sudden creation of a core hole. Here we use a two-step approach to treat such excitations in a localized system embedded in a condensed-matter environment and coupled to a photoelectron. The total XAS is then given by a convolution of an energy-dependent spectral function representing the localized excitations coupled to the photoelectron and the XAS of the extended system. The local system is modeled roughly in terms of a simplified three-level model, leading to a double-pole approximation for the spectral function that represents dynamically weighted contributions from the dominant neutral and charge transfer excitations. This method is implemented using a resolvent approach, with potentials, radial wave functions, and matrix elements from the real-space Green's function code feff9, and parameters fitted to XPS experiments. Representative calculations for several TMOs are found to be in reasonable agreement with experiment and with other calculations.

Klevak, E.; Kas, J. J.; Rehr, J. J.

2014-02-01

334

Spectrophotometric analysis of some guanidino drugs by acid-dye and charge-transfer complexation methods.  

PubMed

Two spectrophotometric methods are described for the determination of guanethidine sulphate (I), guanfacine hydrochloride (II), guanoclor sulphate (III), guanoxan sulphate (IV) and debrisoquine sulphate (V). The first method involves ion-pair formation of the selected compounds (I-V) with bromocresol purple at pH 3.8. The yellow ion pair is extracted with chloroform and the absorbance is measured at about 415 nm. The second method is based on the reaction of the basic guanidino compounds (I, III-V) with iodine in chloroform to give molecular charge-transfer complexes with maximum absorbance at 292 and 345 nm. Beer's law was obeyed for both methods and the relative standard deviations were found to be less than 2%. The apparent molar absorptivities were found to be 2.1 x 10(4) to 6.9 x 10(4) l mol-1 cm-1 using bromocresol purple and 0.7 x 10(4) to 2.4 x 10(4) l mol-1 cm-1 using iodine. The investigated drugs were assayed in tablets. The mean percentage recoveries were found to be 99.8-100.8% by the acid-dye method and around 100.4% by the charge-transfer complexation method. PMID:8257728

Wahbi, A A; Bedair, M M; Galal, S M; Gazy, A A

1993-08-01

335

Spectrophotometric determination of flunarizine dihydrochloride through the formation of charge-transfer complex with iodine.  

PubMed

A spectrophotometric method is described for the assay of flunarizine dihydrochloride. The method is based on the molecular interaction between the drug and iodine, to form a charge-transfer complex in which the drug acts as n-donor and iodine as sigma-acceptor. The iodine was found to form charge-transfer complex in a 1:1 stoichiometry with absorption bands at 295 and 355 nm. The concentrations were linear over 8-13 micrograms ml-1 at both 295 and 355 nm, respectively. A complete, detailed investigation of the formed complex was made with respect to its composition, associated constant and free energy change. The method has been applied successfully to the analysis of commercially available flunarizine dihydrochloride capsules without interference from the capsules excipient. To validate the proposed method, its accuracy and precision, the results were statistically compared with a newly developed reversed-phase HPLC procedure using Student-t and F-ratio tests. PMID:7718634

el Walily, A F; el Gindy, A; Wahbi, A A

1995-01-01

336

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

337

Spectrophotometric and electrical studies of charge-transfer complexes of sodium flucloxacillin with ?-acceptors  

NASA Astrophysics Data System (ADS)

The present study is interested to develop a simple, rapid and accurate spectrophotometric method for determination of sodium flucloxacillin (fluc) in pure form and pharmaceutical formulations. The charge-transfer (CT) interactions between sodium flucloxacillin as electron donor and chloranilic acid (CLA), dichloroquinone 4-chloroimide (DCQ), 2,3-dichloro-5,6-dicyano- p-benzoquinone (DDQ) and 7,7,8,8 tetracyano- p-quinodimethane (TCNQ), as ?-electron acceptors have been investigated spectrophotometrically. Different variables affecting the reaction were studied and optimized. Under the optimum conditions, linear relationships with good correlation coefficients (0.9979-0.9995) were found between the absorbance and the concentration of the drug in the range 16-880 ?g ml -1. The proposed methods were applied successfully to the determination of the examined drug either in pure or pharmaceutical dosage forms with good accuracy and precision. The formation of the CT-complexes and the sites of interaction were confirmed by elemental analysis CHN, UV-vis, IR, 1H NMR and mass spectra techniques. Based on Job's method of continuous variation plots, the obtained results indicate the formation of 1:1 charge-transfer complexes with the general formula [(fluc)(acceptor)]. Statistical analysis of the obtained results showed no significant difference between the proposed method and official method.

Refat, Moamen S.; El-Didamony, Akram M.

2006-11-01

338

Spectrophotometric and electrical studies of charge-transfer complexes of sodium flucloxacillin with pi-acceptors.  

PubMed

The present study is interested to develop a simple, rapid and accurate spectrophotometric method for determination of sodium flucloxacillin (fluc) in pure form and pharmaceutical formulations. The charge-transfer (CT) interactions between sodium flucloxacillin as electron donor and chloranilic acid (CLA), dichloroquinone 4-chloroimide (DCQ), 2,3-dichloro-5,6-dicyano-p-benzoquinone (DDQ) and 7,7,8,8 tetracyano-p-quinodimethane (TCNQ), as pi-electron acceptors have been investigated spectrophotometrically. Different variables affecting the reaction were studied and optimized. Under the optimum conditions, linear relationships with good correlation coefficients (0.9979-0.9995) were found between the absorbance and the concentration of the drug in the range 16-880 microg ml(-1). The proposed methods were applied successfully to the determination of the examined drug either in pure or pharmaceutical dosage forms with good accuracy and precision. The formation of the CT-complexes and the sites of interaction were confirmed by elemental analysis CHN, UV-vis, IR, (1)H NMR and mass spectra techniques. Based on Job's method of continuous variation plots, the obtained results indicate the formation of 1:1 charge-transfer complexes with the general formula [(fluc)(acceptor)]. Statistical analysis of the obtained results showed no significant difference between the proposed method and official method. PMID:16527531

Refat, Moamen S; El-Didamony, Akram M

2006-11-01

339

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

PubMed

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. PMID:23126722

Olsen, Seth; McKenzie, Ross H

2012-10-28

340

Colossal negative thermal expansion in BiNiO3 induced by intermetallic charge transfer  

PubMed Central

The unusual property of negative thermal expansion is of fundamental interest and may be used to fabricate composites with zero or other controlled thermal expansion values. Here we report that colossal negative thermal expansion (defined as linear expansion charge-transfer transitions. BiNiO3 shows a 2.6% volume reduction under pressure due to a Bi/Ni charge transfer that is shifted to ambient pressure through lanthanum substitution for Bi. Changing proportions of coexisting low- and high-temperature phases leads to smooth volume shrinkage on heating. The crystallographic linear expansion coefficient for Bi0.95La0.05NiO3 is ?137×10?6 K?1 and a value of ?82×10?6 K?1 is observed between 320 and 380 K from a dilatometric measurement on a ceramic pellet. Colossal negative thermal expansion materials operating at ambient conditions may also be accessible through metal-insulator transitions driven by other phenomena such as ferroelectric orders. PMID:21673668

Azuma, Masaki; Chen, Wei-tin; Seki, Hayato; Czapski, Michal; Olga, Smirnova; Oka, Kengo; Mizumaki, Masaichiro; Watanuki, Tetsu; Ishimatsu, Naoki; Kawamura, Naomi; Ishiwata, Shintaro; Tucker, Matthew G.; Shimakawa, Yuichi; Attfield, J. Paul

2011-01-01

341

Utilizing Metal to Ligand Charge Transfer States of MM Quadruply Bonded Complexes for Photovoltaic Applications  

NASA Astrophysics Data System (ADS)

In this contribution, we report two examples of our efforts to develop MM quadruply bonded complexes for photovoltaic applications. In the first example, evidence, based on femtosecond transient absorption and time resolved infrared spectroscopy, is presented for photoinduced charge transfer from the Mo_{2}? orbital of the quadruply bonded molecule trans-Mo_{2}(TiPB)_{2}BTh)_{2}, where TiPB = 2,4,6-triisopropyl benzoate and BTh = 2,2'-bithienylcarboxylate, to di-n-octyl perylene diimide and di-n-hexylheptyl perylene diimide in thin films and solutions of the mixtures. In the second example, the structural and photophysical properties of the new compounds trans-M_{2}(TiPB)_{2}(L)_{2} and trans-M_{2}(TiPB)_{2}(L')_{2}, where M=Mo or W and L and L' are triphenylamine-cyanoacrylate ligands are presented. These ligands promote intense metal to ligand charge transfer transitions that span the range 550 to 1100 nm. The excited states have been studied by transient absorption and time resolved infrared spectroscopy

Lewis, Sharlene A.; Brown-Xu, Samantha E.; Chisholm, Malcolm H.; Epstein, Arthur J.

2013-06-01

342

Modulation of the charge transfer and photophysical properties in non-fused tetrathiafulvalene-benzothiadiazole derivatives.  

PubMed

Bis(thiomethyl)- and bis(thiohexyl)-tetrathiafulvalene-bromo-benzothiadiazoles, containing electron donor tetrathiafulvalene (TTF) and electron acceptor benzothiadiazole (BTD) units, have been prepared by Stille coupling reactions between the TTF-SnMe3 precursors and BTD-Br2. In another series of experiments, TTF-acetylene-BTD compounds have been synthesized by Sonogashira coupling between either TTF-acetylenes and BTD-Br2 in low yields, or TTF-iodine and BTD-acetylene in moderate yields. In the compound TTF-C[triple bond, length as m-dash]C-BTD the TTF and BTD units are coplanar in the solid state, as shown by the single crystal X-ray structure, and there is segregation in the packing between the donor and acceptor units. All the derivatives have good electron donor properties, as determined by cyclic voltammetry measurements, and they can also be reversibly reduced thanks to the presence of the BTD moiety. UV-visible spectroscopy and photophysical investigations show the presence of an intramolecular charge transfer (ICT) band and an emission band originating from the charge transfer. Both the absorption and the emission are modulated by the substitution scheme and the insertion of the acetylenic bridge. PMID:25410315

Pop, Flavia; Seifert, Sabine; Hankache, Jihane; Ding, Jie; Hauser, Andreas; Avarvari, Narcis

2015-01-28

343

Label-Free Acetylcholine Image Sensor Based on Charge Transfer Technology for Biological Phenomenon Tracking  

NASA Astrophysics Data System (ADS)

A 32 ×32 charge-transfer enzyme-type acetylcholine (ACh) image sensor array was produced for label-free tracking of images of ACh distribution and its performance in repeatable measurements without enzyme deactivation was examined. The proposed sensor was based on a charge-transfer-type pH image sensor, which was modified using an enzyme membrane (acetylcholine esterase, AChE) for each pixel. The ACh image sensor detected hydrogen ions generated by the ACh-AChE reaction. A polyion complex membrane composed of poly(L-lysine) and poly(4-styrenesulfonate) was used to immobilize the enzyme on the sensor. The improved uniformity and adhesion of the polyion complex membrane were evaluated in this study. As a result, temporal and spatial fluctuations of the ACh image sensor were successfully minimized using this approach. The sensitivity of the sensor was 4.2 mV/mM, and its detection limit was 20 µM. In five repeated measurements, the repeatability was 8.8%.

Takenaga, Shoko; Tamai, Yui; Okumura, Koichi; Ishida, Makoto; Sawada, Kazuaki

2012-02-01

344

Near-resonant versus nonresonant chemiluminescent charge-transfer reactions of atomic ions with HCl  

NASA Astrophysics Data System (ADS)

Charge-transfer reactions of C+, O+, F+, Ar+ and some other atomic ions with hydrogen chloride were investigated at collision energies between <1 eV and 1 keV. The electronically excited products HCl+ (A 2?+) were detected by means of the A 2?+?X 2?i optical emission. In some cases the spectra showed, at low collision energies, an enhanced excitation of specific vibrational HCl+(A,v') levels: for C+, v'=1; for O+, v'=3 as well as v'=1; and for F+, v'=6. These levels are populated in near-resonant, slightly exothermic processes. Their rotational temperature was on the order of 600-700 K. For the other vibrational levels the excitation is off-resonance, mostly endothermic, and here the rotational temperature was 1000-4000 K. Corresponding data are also given for DCl. The selectivity for certain vibrational states is explained by crossings between the vibronic entrance and exit state energy surfaces, calculated from classical electrostatic multipole potentials. The cross sections for the near-resonant reactions decrease monotonically with increasing collision energy, while for the endothermic channels they rise steeply from threshold to a plateau. With argon ions the excitation function exhibits an unusual shape. Here the charge-transfer cross sections for all vibrational levels go through a maximum just above threshold, which is followed by a distinct minimum at about 10 eVc.m.. This may be due to formation of a long-lived collision complex (Ar-HCl)+.

Glenewinkel-Meyer, Th.; Ottinger, Ch.

1994-01-01

345

Defect-enhanced charge transfer by ion-solid interactions in SiC using large-scale ab initio molecular dynamics simulations.  

PubMed

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. PMID:19659244

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

2009-07-10

346

Spontaneous redox synthesis of the charge transfer material TTF4[SVMo11O40].  

PubMed

The charge-transfer material TTF-SV(IV)Mo(11)O(40) (TTF = tetrathiafulvalene) was prepared by a spontaneous redox reaction between TTF and the vanadium-substituted polyoxometalate (n-Bu(4)N)(3)[SV(V)Mo(11)O(40)] in both solution and solid state phases. Single crystal X-ray diffraction gave the stoichiometry TTF(4)[SVMo(11)O(40)]·2H(2)O·2CH(2)Cl(2), with the single V atom positionally disordered with eight Mo atoms over the whole ?-Keggin polyanion [SVMo(11)O(40)](4-). Raman spectra support the 1+ charge assigned to the oxidized TTF deduced from bond lengths, and elemental and voltammetric analysis also are consistent with this formulation. Scanning electron microscopy images showed a rod-type morphology for the new charge-transfer material. The conductivity of the solid at room temperature is in the semiconducting range. The TTF and (n-Bu(4)N)(3)[SV(V)Mo(11)O(40)] solids also undergo a rapid interfacial reaction, as is the case with TTF and TCNQ (TCNQ = tetracyanoquinodimethane) solids. EPR spectra at temperatures down to 2.6 K confirm the presence of two paramagnetic species, V(IV) and the oxidized TTF radical. Spectral evidence shows that the TTF-SV(IV)Mo(11)O(40) materials prepared from either solution or solid state reactions are equivalent. The newly isolated TTF-SV(IV)Mo(11)O(40) material represents a new class of TTF-polyoxometalate compound having dual electrical and magnetic functionality derived from both the cationic and anionic components. PMID:23146046

Li, Qi; Lu, Jinzhen; Boas, John F; Traore, Daouda A K; Wilce, Matthew C J; Huang, Fuzhi; Martin, Lisandra L; Ueda, Tadaharu; Bond, Alan M

2012-12-01

347

Microgravity and Charge Transfer in the Neuronal Membrane: Implications for Computational Neurobiology  

NASA Technical Reports Server (NTRS)

Evidence from natural and artificial membranes indicates that the neural membrane is a liquid crystal. A liquid-to-gel phase transition caused by the application of superposed electromagnetic fields to the outer membrane surface releases spin-correlated electron pairs which propagate through a charge transfer complex. The propagation generates Rydberg atoms in the lipid bilayer lattice. In the present model, charge density configurations in promoted orbitals interact as cellular automata and perform computations in Hilbert space. Due to the small binding energies of promoted orbitals, their automata are highly sensitive to microgravitational perturbations. It is proposed that spacetime is classical on the Rydberg scale, but formed of contiguous moving segments, each of which displays topological equivalence. This stochasticity is reflected in randomized Riemannian tensor values. Spacetime segments interact with charge automata as components of a computational process. At the termination of the algorithm, an orbital of high probability density is embedded in a more stabilized microscopic spacetime. This state permits the opening of an ion channel and the conversion of a quantum algorithm into a macroscopic frequency code.

Wallace, Ron

1995-01-01

348

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

349

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

350

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

351

Interplay between the charge ordering, ground states and lattice potential in quasi-one-dimensional organic charge transfer salts  

NASA Astrophysics Data System (ADS)

TMTTF (tetramethyltetrathiafulvalene) and TMTSF (tetramethyltetraselenafulvalene) based organic charge transfer salts are representatives of highly correlated quasi-1D electron systems which exhibit rich variety of ground states that can be easily tuned by pressure. They have been the top interests among researchers for the past few decades. Some concepts, such as the interplay between the magnetism and superconductivity, are believed to hold the key to the understanding of the mechanism of the high Tc superconductivity. How the repulsive Coulomb interactions U and V control the phases in these systems and how they evolve with pressure, become the major concern of numerous theories and experiments. Here we present the NMR and EPR studies on two compounds of this family, namely, (TMTTF) 2SbF6 and (TMTSF)2ClO4. The 121Sb and 19F NMR measurements reveal that at ambient pressure, the anion SbF6 will align along a preferred orientation below a crossover temperature, T ˜ 120 K. This unique property of the anion adds an additional degree of freedom to the system. The pressure studies of the (TMTTF)2SbF 6 show that this compound should be positioned in the lower pressure regime of the generic phase diagram. At ambient pressure, the charge ordering (CO) state at higher temperatures suppresses the spin-Peierls (SP) instabilities and an antiferromagnetic (AF) ground state is realized at low temperatures. Both the CO and the AF states are found to be suppressed by pressure very quickly and the ground states under intermediate and higher pressures are determined by how much disorder is introduced into the system. For the more disordered samples, the ground states resemble the familiar sequence of AF?SP?AF while for the more relaxed samples, no long range order is observed down to 1.8K. This is refreshing since a lot of the properties in this particular state are very similar to those observed in K-(BEDT-TTF) 2Cu2(CN)3, which is believed to have a spin liquid ground state. Interestingly enough, this shows the anions are participating in a certain way in the formation of different electronic ground states. The compound (TMTSF)2ClO4 shows another example of how the electronic state can be controlled by the lattice potential. The ordering of the perchlorate anions results in a unit cell doubling hence two bands crossing at the Fermi level. The NMR measurements show that the fluctuation in anion orientations directly controls the spin density distributions between the stacks.

Zhang, Fan

2007-12-01

352

Mechanism of Redox-Active Ligand-Assisted Nitrene-Group Transfer in a Zr(IV) Complex: Direct Ligand-to-Ligand Charge Transfer Preferred.  

PubMed

The mechanism of the nitrene-group transfer reaction from an organic azide to isonitrile catalyzed by a Zr(IV) d(0) complex carrying a redox-active ligand was studied by using quantum chemical molecular-modeling methods. The key step of the reaction involves the two-electron reduction of the azide moiety to release dinitrogen and provide the nitrene fragment, which is subsequently transferred to the isonitrile substrate. The reducing equivalents are supplied by the redox-active bis(2-iso-propylamido-4-methoxyphenyl)-amide ligand. The main focus of this work is on the mechanism of this redox reaction, in particular, two plausible mechanistic scenarios are considered: 1)?the metal center may actively participate in the electron-transfer process by first recruiting the electrons from the redox-active ligand and becoming formally reduced in the process, followed by a classical metal-based reduction of the azide reactant. 2)?Alternatively, a non-classical, direct ligand-to-ligand charge-transfer process can be envisioned, in which no appreciable amount of electron density is accumulated at the metal center during the course of the reaction. Our calculations indicate that the non-classical ligand-to-ligand charge-transfer mechanism is much more favorable energetically. Utilizing a series of carefully constructed putative intermediates, both mechanistic scenarios were compared and contrasted to rationalize the preference for ligand-to-ligand charge-transfer mechanism. PMID:25470137

Ghosh, Soumya; Baik, Mu-Hyun

2014-12-01

353

Magneto-Dielectric Effects Induced by Optically-Generated Intermolecular Charge-Transfer States in Organic Semiconducting Materials  

PubMed Central

Traditionally, magneto-dielectric effects have been developed by combining ferroelectric and magnetic materials. Here, we show a magneto-dielectric effect from optically-generated intermolecular charge-transfer states in an organic semiconducting donor:acceptor (PVK:TCNB) system. We observe in magnetic field effects of photoluminescence that a magnetic field can change singlet/triplet population ratio in intermolecular charge-transfer states. Furthermore, our theoretical analysis and experimental evidence indicate that the singlets and triplets in charge-transfer states have stronger and weaker electrical polarizations, respectively. Therefore, the observed magneto-dielectric effect can be attributed to magnetically-dependent singlet/triplet ratio in intermolecular charge-transfer states. In principle, a magneto-dielectric effect can be generated through two different channels based on magneto-polarization and magneto-current effects when the singlet/triplet ratio in intermolecular charge-transfer states is changed by a magnetic field. We find, from the simulation of dielectric effects, that magneto-polarization and magneto-current effects play primary and secondary roles in the generation of magneto-dielectric effect. PMID:24084983

Zang, Huidong; Yan, Liang; Li, Mingxing; He, Lei; Gai, Zheng; Ivanov, Ilia; Wang, Min; Chiang, Long; Urbas, Augustine; Hu, Bin

2013-01-01

354

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

355

The role of spin exchange in charge transfer in low-bandgap polymer: Fullerene bulk heterojunctions  

NASA Astrophysics Data System (ADS)

Formation, relaxation and dynamics of polarons and methanofullerene anion radicals photoinitiated in poly[N-9?-hepta-decanyl-2,7-carbazole-alt-5,5-(4',7'-di-2-thienyl-2',1',3'-benzothiadiazole)]:-[6,6]-phenyl-C61-butyric acid methyl ester (PCDTBT:PC61BM) bulk heterojunctions were studied mainly by light-induced EPR (LEPR) spectroscopy in wide photon energy and temperature ranges. Some polarons are pinned by spin traps whose number and depth are governed by the composite morphology and photon energy. The proximity of the photon energy and the polymer bandgap reduces the number of such traps, inhibits recombination of mobile charge carriers, and facilitates their mobility in polymer network. Spin relaxation and charge carrier dynamics were studied by the steady-state saturation method at wide range of temperature and photon energy. These processes were shown to be governed by spin exchange as well as by the photon energy. Charge transfer in the composite is governed by the polaron scattering on the lattice phonons of crystalline domains embedded into amorphous polymer matrix and its activation hopping between polymer layers. The energy barrier required for polaron interchain hopping exceeds that of its intrachain diffusion. Anisotropy of polaron dynamics in the PCDTBT:PC61BM composite is less than that of poly(3-alkylthiophenes)-based systems that evidences for better ordering of the former. Lorentzian shape of LEPR lines of both charge carriers, lower concentration of spin traps as well as behaviours of the main magnetic resonance parameters were explained by layer ordered morphology of polymer matrix.

Krinichnyi, V. I.; Yudanova, E. I.; Denisov, N. N.

2014-07-01

356

Charge efficiency of Ni/H2 cells during transfer orbit of Telstar 4 satellites  

NASA Technical Reports Server (NTRS)

The TELSTAR 4 communication satellites being manufactured by Martin Marietta Astro Space (Astro Space) for AT&T are three axis stabilized spacecraft scheduled to be launched on expendable vehicles such as the Atlas or Ariane rockets. Typically, these spacecraft consist of a box that holds the electronics and supports the antenna reflectors and the solar array wings. The wings and reflectors are folded against the sides of the box during launch and the spacecraft is spun for attitude control in that phase; they are then deployed after achieving the final orbit. The launch phase and transfer orbits required to achieve the final geosynchronous orbit typically take 4 to 5 days during which time the power required for command, telemetry, attitude control, heaters, etc., is provided by two 50 AH nickel hydrogen batteries augmented by the exposed outboard solar panels. In the past, this situation has presented no problem since there was a considerable excess of power available from the array. In the case of large high powered spacecraft such as TELSTAR 4, however, the design power levels in transfer orbit approach the time-averaged power available from the exposed surface area of the solar arrays, resulting in a very tight power margin. To compound the difficulty, the array output of the spinning spacecraft in transfer orbit is shaped like a full wave rectified sine function and provides very low charging rates to the batteries during portions of the rotation. In view of the typically low charging efficiency of alkaline nickel batteries at low rates, it was decided to measure the efficiency during a simulation of the TELSTAR 4 conditions at the expected power levels and temperatures on three nickel hydrogen cells of similar design. The unique feature of nickel hydrogen cells that makes the continuous measurement of efficiency possible is that hydrogen is one of the active materials and thus, cell pressure is a direct measure of the state of charge or available capacity. The pressure is measured with a calibrated strain gage mounted on the outside of the pressurized cell.

Fang, W. C.; Maurer, Dean W.; Vyas, B.; Thomas, M. N.

1994-01-01

357

Preparation and spectroscopic studies on charge-transfer complexes of 2,2'-bipyridine with picric and chloranilic acids  

NASA Astrophysics Data System (ADS)

Charge-transfer (CT) complexes formed on the reaction of 2,2'-bipyridine with some acceptors such as picric acid (HPA) and chloranilic acid (H 2CA) have been studied in CHCl 3 and MeOH at room temperature. Based on elemental analysis and IR spectra of the solid CT complexes along with the photometric titration curves for the reactions, the data obtained indicate the formation of 1:1 charge-transfer complexes [(bpyH)(PA)] and [(bpyH 2)(CA)], respectively. The infrared and 1H NMR spectroscopic data indicate a charge-transfer interaction associated with a proton migration from the acceptor to the donor followed by intramolecular hydrogen bonding. The formation constants ( KC) for the complexes were shown to be dependent on the structure of the electron acceptors used.

Teleb, Said M.; Gaballa, Akmal S.

2005-11-01

358

Preparation and spectroscopic studies on charge-transfer complexes of 2,2'-bipyridine with picric and chloranilic acids.  

PubMed

Charge-transfer (CT) complexes formed on the reaction of 2,2'-bipyridine with some acceptors such as picric acid (HPA) and chloranilic acid (H(2)CA) have been studied in CHCl(3) and MeOH at room temperature. Based on elemental analysis and IR spectra of the solid CT complexes along with the photometric titration curves for the reactions, the data obtained indicate the formation of 1:1 charge-transfer complexes [(bpyH)(PA)] and [(bpyH(2))(CA)], respectively. The infrared and (1)H NMR spectroscopic data indicate a charge-transfer interaction associated with a proton migration from the acceptor to the donor followed by intramolecular hydrogen bonding. The formation constants (K(C)) for the complexes were shown to be dependent on the structure of the electron acceptors used. PMID:16257705

Teleb, Said M; Gaballa, Akmal S

2005-11-01

359

The low-energy, charge-transfer excited states of 4-amino-4-prime-nitrodiphenyl sulfide  

NASA Technical Reports Server (NTRS)

Absorption and emission spectra of 4-amino-4-prime-nitrodiphenyl sulfide in polar and nonpolar solvents were used to characterize and assign the low-energy excited states of the molecule. Fluorescence-excitation anisotropy spectra and fluorescence quantum yields were also used to characterize the photophysics of these states. The lowest-energy fluorescent singlet state was determined to be an intramolecular charge transfer (ICT) state involving transfer of a full electron charge from the amino to the nitro group yielding a dipole moment of about 50 D. A low-energy, intense absorption band is assigned as a transition to a different ICT state involving a partial electron charge transfer from sulfur to the nitro group.

O'Connor, Donald B.; Scott, Gary W.; Tran, Kim; Coulter, Daniel R.; Miskowski, Vincent M.; Stiegman, Albert E.; Wnek, Gary E.

1992-01-01

360

On the maximum charge state and proton transfer reactivity of peptide and protein ions formed by electrospray ionization.  

PubMed

A relatively simple model for calculation of the energetics of gas-phase proton transfer reactions and the maximum charge state of multiply protonated ions formed by electrospray ionization is presented. This model is based on estimates of the intrinsic proton transfer reactivity of sites of protonation and point charge Coulomb interactions. From this model, apparent gas-phase basicities (GB(app)) of multiply protonated ions are calculated. Comparison of this value to the gas-phase basicity of the solvent from which an ion is formed enables a maximum charge state to be calculated. For 13 commonly electrosprayed proteins, our calculated maximum charge states are within an average of 6% of the experimental values reported in the literature. This indicates that the maximum charge state for proteins is determined by their gas-phase reactivity. Similar results are observed for peptides with many basic residues. For peptides with few basic residues, we find that the maximum charge state is better correlated to the charge state in solution. For low charge state ions, we find that the most basic sites Arg, Lys, and His are preferentially protonated. A significant fraction of the less basic residues Pro, Trp, and Gln are protonated in high charge state ions. The calculated GB(app) of individual protonation sites varies dramatically in the high charge state ions. From these values, we calculate a reduced cross section for proton transfer reactivity that is significantly lower than the Langevin collision frequency when the GB(app) of the ion is approximately equal to the GB of the neutral base. PMID:24214055

Schnier, P D; Gross, D S; Williams, E R

1995-11-01

361

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

362

Spectrophotometric determination of three anti-ulcer drugs through charge-transfer complexation.  

PubMed

A simple charge-transfer complexation method is described for the spectrophotometric assay of nizatidine, ranitidine, and famotidine. This method is based on interaction of these drugs, as n-electron donors, with 7,7,8,8-tetracyanoquinodimethane, as the pi-acceptor, in acetonitrile to give highly colored green radical anions that are measured at 840 nm. Calibration graphs for the 3 compounds are linear over the concentration ranges of 1-6 microg/mL for nizatidine and ranitidine and 1-7 microg/mL for famotidine, with correlation coefficients (n = 6) of >0.999. The conditioned stability constants and the free energy changes were measured; the values obtained were generally high and negative, respectively, suggesting highly stable complexes. The proposed method was successfully applied to the determination of the drugs in pharmaceutical preparations. The assay results were in accordance with those obtained by using reference methods. PMID:12374395

Al-Ghannam, Sheikha; Belal, Fathalla

2002-01-01

363

Photoinduced charge transfer and acetone sensitivity of single-walled carbon nanotube-titanium dioxide hybrids.  

PubMed

The unique physical and chemical properties of single-walled carbon nanotubes (SWNTs) make them ideal building blocks for the construction of hybrid nanostructures. In addition to increasing the material complexity and functionality, SWNTs can probe the interfacial processes in the hybrid system. In this work, SWNT-TiO2 core/shell hybrid nanostructures were found to exhibit unique electrical behavior in response to UV illumination and acetone vapors. By experimental and theoretical studies of UV and acetone sensitivities of different SWNT-TiO2 hybrid systems, we established a fundamental understanding on the interfacial charge transfer between photoexcited TiO2 and SWNTs as well as the mechanism of acetone sensing. We further demonstrated a practical application of photoinduced acetone sensitivity by fabricating a microsized room temperature acetone sensor that showed fast, linear, and reversible detection of acetone vapors with concentrations in few parts per million range. PMID:23734594

Ding, Mengning; Sorescu, Dan C; Star, Alexander

2013-06-19

364

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

365

Quantitative determination of famotidine through charge-transfer complexation with chloranilic acid.  

PubMed

Quantitative determination of famotidine and its dosage forms was carried out spectrophotometrically, analysing the coloured complex resulting from a charge-transfer interaction between the drug as an electron-donor and chloranilic acid as an electron-acceptor. Famotidine-Chloranilic acid complex displayed l-max at 5 25 nm. Conditions and time for complex formation have been optimized. The stoichiometry of the complex is 3:2 donor to acceptor mole ratio. Calibration graph of the complex was found to be linear at a working concentration range of 1.60-11.g% (w/v). Excellent quantitative recoveries (99.01-100.71%) was obtained for the drugs in both its pure and standard dosage forms. PMID:11680091

Chukwurah, B K; Ajali, U

2001-01-01

366

Spectrophotometric determination of nikethamide by charge--transfer complexation with chloranilic acid.  

PubMed

A Spectrophotometric method is described for assay of nikethamide which was based on charge transfer complexation between it and chloranilic acid. They form a complex with stoichiometric ratio of 1:1 and showed l-max at 535 nm. Maximum complexation occurred 30 min after mixing the reactants and was stable for 12 hr. The molar absorptivity, association constant and free energy for the complex were 1.05 x 1.0(2), 4.40 x 10(-2) litre mole-1 and 1819.02 kcal respectively. Conformity to Beer's Law was within the concentration range of 1-2.5 x 10(-4), which enabled the assay of dosage forms of the drug at microquantities. PMID:12426818

Okide, G B; Odoh, U E; Ajali, U

2002-01-01

367

Ultrafast twisting dynamics of thioflavin-T: spectroscopy of the twisted intramolecular charge-transfer state.  

PubMed

Understanding the excited-state properties of thioflavin-T (ThT) has been of immense importance, because of its efficient amyloid-sensing ability related to neurodegenerative disorders. The excited-state dynamics of ThT is studied by using sub-pico- and nanosecond time-resolved transient absorption techniques as well as density functional theory (DFT)/time-dependent DFT calculations. Barrierless twisting around the central C?C bond between two aromatic moieties is the dominant process that contributes to the ultrafast dynamics of the S1 state. The spectroscopic properties of the intramolecular charge-transfer state are characterized for the first time. The energetics of the S0 and S1 states has also been correlated with the experimentally observed spectroscopic parameters and structural dynamics. A longer-lived transient state populated with a very low yield has been characterized as the triplet state. PMID:25251013

Ghosh, Rajib; Palit, Dipak K

2014-12-15

368

Spectroscopic evidence of hydrogen bonding and intramolecular charge transfer cooperation in polar m-aminophenol crystal  

NASA Astrophysics Data System (ADS)

The polarized infrared (IR) and Raman spectra of the m-aminophenol ( m-AP) single crystal and the vibrational spectra of its solutions and powders in the 200-4000 cm -1 and 5000-7000 cm -1 regions as well as the electronic spectra were measured. on the basis of previous data and the oriented gas-model calculations, assignments of the internal vibrations are proposed. Discrepancies from the model relative intensities are explained with the help of quantum chemical INDO calculations by vibronic couplings and by the delocalization of charge through the chain of molecules connected by intermolecular O?H⋯N bonding. The possibility of proton transfer in the excited state was excluded. The findings were considered in view of the non-linear electrooptic properties of the m-AP crystal.

Gierma?ska, J.; Szostak, M. M.; Kowala, W. W.

1990-05-01

369

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

370

Molecular structure and vibrational spectral investigation of charge transfer NLO crystal naphthalene picrate for THz application.  

PubMed

Molecular structure and the vibrational spectra of Naphthalene Picrate have been calculated using density functional theoretical computation and compared with the experimental. The dipole moments (?), polarizability (?), first hyperpolarizabilities (?) second hyperpolarizability (?) and frontier molecular orbital energies are computed at the DFT level. The frontier molecular orbital calculation shows the inverse relationship of HOMO-LUMO gap with the total static hyperpolarizability. The hyperpolarizability value reveals that these classes of organic compounds show very large non-linear optical properties. Natural Bond Orbital analysis confirms the presence of intramolecular charge transfer and the hydrogen bonding interaction. Terahertz time-domain spectroscopy has been used to detect the absorption spectra in the frequency range from 0.2 to 1.5 THz. PMID:23501937

Amalanathan, M; Hubert Joe, I; Rastogi, V K

2013-05-01

371

Charge-transfer interaction mediated organogels from 18?-glycyrrhetinic acid appended pyrene  

PubMed Central

Summary We describe herein the two-component charge-transfer (CT) interaction induced organogel formation with 18?-glycyrrhetinic acid appended pyrene (GA-pyrene, 3) as the donor, and 2,4,7-trinitrofluorenone (TNF, 4) as the acceptor. The use of TNF (4) as a versatile electron acceptor in the formation of CT gels is demonstrated through the formation of gels in a variety of solvents. Thermal stability, stoichiometry, scanning electron microscopy (SEM), optical micrographs, and circular dichroism (CD) are performed on these CT gels to investigate their thermal and assembly properties. UV–vis, fluorescence, mass spectrometric as well as variable-temperature 1H NMR experiments on these gels suggest that the CT interaction is one of the major driving forces for the formation of these organogels. PMID:24367453

Hu, Jun; Wu, Jindan

2013-01-01

372

Bottom-up formation of endohedral mono-metallofullerenes is directed by charge transfer.  

PubMed

An understanding of chemical formation mechanisms is essential to achieve effective yields and targeted products. One of the most challenging endeavors is synthesis of molecular nanocarbon. Endohedral metallofullerenes are of particular interest because of their unique properties that offer promise in a variety of applications. Nevertheless, the mechanism of formation from metal-doped graphite has largely eluded experimental study, because harsh synthetic methods are required to obtain them. Here we report bottom-up formation of mono-metallofullerenes under core synthesis conditions. Charge transfer is a principal factor that guides formation, discovered by study of metallofullerene formation with virtually all available elements of the periodic table. These results could enable production strategies that overcome long-standing problems that hinder current and future applications of metallofullerenes. PMID:25524825

Dunk, Paul W; Mulet-Gas, Marc; Nakanishi, Yusuke; Kaiser, Nathan K; Rodríguez-Fortea, Antonio; Shinohara, Hisanori; Poblet, Josep M; Marshall, Alan G; Kroto, Harold W

2014-01-01

373

Bottom-up formation of endohedral mono-metallofullerenes is directed by charge transfer  

NASA Astrophysics Data System (ADS)

An understanding of chemical formation mechanisms is essential to achieve effective yields and targeted products. One of the most challenging endeavors is synthesis of molecular nanocarbon. Endohedral metallofullerenes are of particular interest because of their unique properties that offer promise in a variety of applications. Nevertheless, the mechanism of formation from metal-doped graphite has largely eluded experimental study, because harsh synthetic methods are required to obtain them. Here we report bottom-up formation of mono-metallofullerenes under core synthesis conditions. Charge transfer is a principal factor that guides formation, discovered by study of metallofullerene formation with virtually all available elements of the periodic table. These results could enable production strategies that overcome long-standing problems that hinder current and future applications of metallofullerenes.

Dunk, Paul W.; Mulet-Gas, Marc; Nakanishi, Yusuke; Kaiser, Nathan K.; Rodríguez-Fortea, Antonio; Shinohara, Hisanori; Poblet, Josep M.; Marshall, Alan G.; Kroto, Harold W.

2014-12-01

374

Identifying the magnetoconductance responses by the induced charge transfer complex states in pentacene-based diodes  

NASA Astrophysics Data System (ADS)

We investigate the magnetoconductance (MC) responses in photocurrent, unipolar injection, and bipolar injection regimes in pentacene-based diodes. Both photocurrent and bipolar injection contributed MC responses show large difference in MC line shape, which are attributed to triplet-polaron interaction modulated by the magnetic field dependent singlet fission and the intersystem crossing of the polaron pair, respectively. By blending 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane into pentacene, all the MC responses are suppressed but the MC response at unipolar injection regime is enhanced, which is attributed to the induced charge transfer complex states (CT complex states). This work identify the MC responses between single carrier contributed MC and exciton related MC by the induced CT complex states.

Huang, Wei-Shun; Lee, Tsung-Hsun; Guo, Tzung-Fang; Huang, J. C. A.; Wen, Ten-Chin

2012-07-01

375

Charge transfer in graphene oxide-dye system for photonic applications  

SciTech Connect

The fluorescence of a standard dye Rhodamine 6G (R6G) in solution decreases on addition of reduced graphene oxide (rGO). The absorption spectra and lifetime measurements confirm that no excited-state but a ground-state complex formation is responsible for this effect. For silver decorated rGO (Ag-rGO), the quenching efficiency and ground state complex formation process is small. Z-scan measurements have been done to study the optical nonlinearity at 532 nm under ps time scale. Remarkable reduction in the saturable absorption (SA) effect of R6G indicates no nonlinear contribution from the ground state complex. The results have been explained with varying charge transfer rates and non-fluorescence nature of the complex.

Bongu, Sudhakara Reddy, E-mail: bisht@iitm.ac.in; Bisht, Prem B., E-mail: bisht@iitm.ac.in [Department of Physics, Indian Institute of Technology Madras, Chennai, 600036 (India); Thu, Tran V.; Sandhu, Adarsh [EIIRIS, Toyohashi University of Technology, 1-1 Hibarigaoka, Tempaku, Toyohashi 441-8580 (Japan)

2014-02-20

376

Charge transfer in Fe-doped GaN: The role of the donor  

SciTech Connect

Several nitride-based device structures would benefit from the availability of high quality, large-area, freestanding semi-insulating GaN substrates. Due to the intrinsic n-type nature of GaN, however, the incorporation of compensating centers such as Fe is necessary to achieve the high resistivity required. We are using electron paramagnetic resonance (EPR) to explore charge transfer in 450 um thick GaN:Fe plates to understand the basic mechanisms related to compensation so that the material may be optimized for device applications. The results suggest that the simple model based on one shallow donor and a single Fe level is insufficient to describe compensation. Rather, the observation of the neutral donor and Fe3+ indicates that either the two species are spatially segregated or additional compensating and donor defects must be present.

Sunay, Ustun; Dashdorj, J.; Zvanut, M. E.; Harrison, J. G. [Department of Physics, University of Alabama at Birmingham, 1300 University Blvd., CH 310, Birmingham, Alabama 35294-1170 (United States); Leach, J. H.; Udwary, K. [Kyma Technologies, 8829 Midway West Rd., Raleigh, North Carolina 27617 (United States)

2014-02-21

377

Effect of. gamma. -cyclodextrin on the intramolecular charge transfer processes in aminocoumarin laser dyes  

SciTech Connect

Steady-state and time-resolved studies on the emission properties of three 7-(diethylamino)coumarin laser dyes (I-III) in aqueous {gamma}-cyclodextrin ({gamma}-CD) solutions are reported. On addition of {gamma}-CD, fluorescence maxima of all the three dyes shift to higher energy, with a huge enhancement of the yield of intramolecular charge transfer (ICT) emission for the flexible ones (I and II) and a very slight enhancement for the rigid analogue III. The results are explained in terms of the concept of polarity-dependent twisted ICT rates. It is proposed that twisted ICT, the main nonradiative process in the excited ICT states of these dyes, is severely restricted inside the {gamma}-cyclodextrin cavity because of the reduced polarity. This is responsible for the enhancement of fluorescence from the ICT state.

Nag, A.; Chakrabarty, T.; Bhattacharyya, K. (Indian Association for the cultivation of Science, Calcutta (India))

1990-05-17

378

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

379

Charge Exchange Processes for Highly Charged Ion -Atom, Molecule  

E-print Network

) Charge Exchange Processes of HCI's are very important for understanding the edge plasma behavior process are greatly concerned with the cooling of the plasma. We paid attention to the following thing of Chemistry and Physics #12;The detail of electron transfer process by HCI's-Atom collision has been made

Princeton Plasma Physics Laboratory

380

Photoinduced intramolecular charge transfer in an electronically modified flavin derivative: roseoflavin.  

PubMed

The photophysical properties of a push-pull flavin derivative, roseoflavin (RoF), are investigated in different surroundings at the molecular level, with focus on intramolecular charge transfer (ICT). Time-dependent density functional theory (TD-DFT, CAM-B3LYP functional) and DFT-based multireference configuration interaction (DFT/MRCI) are used to compute excited-state energies and one-electron properties of a truncated RoF model, roseolumiflavin (RoLF). Solvent effects are taken into account implicitly by the conductor-like polarizable continuum model and explicitly through a microsolvation scheme. In the gas phase, the calculations predict no crossing between the lowest locally excited (LE) and charge-transfer (CT) states upon twisting the dimethylamine donor group relative to the plane of the isoalloxazine acceptor moiety, whereas this crossing is found to be facile in solution (i.e., in water or benzene). Crossing of the LE and CT states facilitates ICT, which is the main cause of the fluorescence quenching and dual fluorescence character experimentally observed for roseoflavin in solution. The barrier for the ICT process is computed to be lower in water than in benzene, consistent with the enhanced ICT rates observed in more polar solvents. We present a detailed study of the molecular mechanism of the photoinduced ICT process in RoLF. For a typical donor-acceptor chromophore, three such mechanisms are discussed in the literature, which differ in the alignment of the donor and acceptor planes, namely, planar ICT (PICT), perpendicular-twisted ICT (TICT), and wagging ICT (WICT). Our theoretical results suggest that the TICT mechanism is favored in RoLF. PMID:25214319

Karasulu, Bora; Thiel, Walter

2015-01-22

381

Exciton delocalization, charge transfer, and electronic coupling for singlet excitation energy transfer between stacked nucleobases in DNA: An MS-CASPT2 study  

SciTech Connect

Exciton delocalization and singlet excitation energy transfer have been systematically studied for the complete set of 16 DNA nucleobase dimers in their ideal, single-strand stacked B-DNA conformation, at the MS-CASPT2 level of theory. The extent of exciton delocalization in the two lowest (?,?{sup *}) states of the dimers is determined using the symmetrized one-electron transition density matrices between the ground and excited states, and the electronic coupling is calculated using the delocalization measure and the energy splitting between the states [see F. Plasser, A. J. A. Aquino, W. L. Hase, and H. Lischka, J. Phys. Chem. A 116, 11151–11160 (2012)]. The calculated couplings lie between 0.05 eV and 0.14 eV. In the B-DNA conformation, where the interchromophoric distance is 3.38 Å, our couplings deviate significantly from those calculated with the transition charges, showing the importance of orbital overlap components for the couplings in this conformation. The calculation of the couplings is based on a two-state model for exciton delocalization. However, in three stacks with a purine in the 5{sup ?} position and a pyrimidine in the 3{sup ?} one (AT, GC, and GT), there is an energetically favored charge transfer state that mixes with the two lowest excited states. In these dimers we have applied a three-state model that considers the two locally excited diabatic states and the charge transfer state. Using the delocalization and charge transfer descriptors, we obtain all couplings between these three states. Our results are important in the context of DNA photophysics, since the calculated couplings can be used to parametrize effective Hamiltonians to model extended DNA stacks. Our calculations also suggest that the 5{sup ?}-purine-pyrimidine-3{sup ?} sequence favors the formation of charge transfer excited states.

Blancafort, Lluís, E-mail: lluis.blancafort@udg.edu [Institut de Química Computacional i Catàlisi (IQCC) and Departament de Química, Universitat de Girona, Campus de Montilivi, 17071 Girona (Spain)] [Institut de Química Computacional i Catàlisi (IQCC) and Departament de Química, Universitat de Girona, Campus de Montilivi, 17071 Girona (Spain); Voityuk, Alexander A., E-mail: alexander.voityuk@icrea.cat [Institut de Química Computacional i Catàlisi (IQCC) and Departament de Química, Universitat de Girona, Campus de Montilivi, 17071 Girona (Spain); Institució Catalana de Recerca i Estudis Avançats (ICREA), Barcelona 08010 (Spain)

2014-03-07

382

Diverse photoinduced dynamics in an organic charge-transfer complex having strong electron-phonon interactions.  

PubMed

Conspectus Phenomena that occur in nonequilibrium states created by photoexcitation differ qualitatively from those that occur at thermal equilibrium, and various physical theories developed for thermal equilibrium states can hardly be applied to such phenomena. Recently it has been realized that understanding phenomena in nonequilibrium states in solids is important for photoenergy usage and ultrafast computing. Consequently, much effort has been devoted to revealing such phenomena by developing various ultrafast observation techniques and theories applicable to nonequilibrium states. This Account describes our recent studies of diverse photoinduced dynamics in a strongly correlated organic solid using various ultrafast techniques. Solids in which the electronic behavior is affected by Coulomb interactions between electrons are designated as strongly correlated materials and are known to exhibit unique physical properties even at thermal equilibrium. Among them, many organic charge-transfer (CT) complexes have low dimensionality and flexibility in addition to strong correlations; thus, their physical properties change sensitively in response to changes in pressure or electric field. Photoexcitation is also expected to drastically change their physical properties and would be useful for ultrafast photoswitching devices. However, in nonequilibrium states, the complicated dynamics due to these characteristics prevents us from understanding and using these materials for photonic devices. The CT complex (EDO-TTF)2PF6 (EDO-TTF = 4,5-ethylenedioxytetrathiafulvalene) exhibits unique photoinduced dynamics due to strong electron-electron and electron-phonon interactions. We have performed detailed studies of the dynamics of this complex using transient electronic spectroscopy at the 10 and 100 fs time scales. These studies include transient vibrational spectroscopy, which is sensitive to the charges and structures of constituent molecules, and transient electron diffraction, which provides direct information on the crystal structure. Photoexcitation of the charge-ordered low-temperature phase of (EDO-TTF)2PF6 creates a new photoinduced phase over 40 fs via the Franck-Condon state, in which electrons and vibrations are coherently and strongly coupled. This new photoinduced phase is assigned to an insulator-like state in which the charge order differs from that of the initial state. In the photoinduced phase, translations of component molecules proceed before the rearrangements of intramolecular conformations. Subsequently, the charge order and structure gradually approach those of the high-temperature phase over 100 ps. This unusual two-step photoinduced phase transition presumably originates from steric effects due to the bent EDO-TTF as well as strong electron-lattice interactions. PMID:25340327

Onda, Ken; Yamochi, Hideki; Koshihara, Shin-Ya

2014-12-16

383

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

SciTech Connect

Charge transfer (CT), the movement of small amounts of electron density between non-bonded pairs, has been suggested as a driving force for a variety of physical processes. Herein, we examine the effect of CT on ion adsorption to the water liquid-vapor interface. Using a CT force field for molecular dynamics, we construct a potential of mean force (PMF) for Na{sup +}, K{sup +}, Cl{sup ?}, and I{sup ?}. The PMFs were produced with respect to an average interface and an instantaneous interface. An analysis of the PMF relative to the instantaneous surface reveals that the area in which the anions experience a free energy minimum is quite narrow, and the cations feel a steeply repulsive free energy near the interface. CT is seen to have only minor effects on the overall free energy profiles. However, the long-ranged effects of ions are highlighted by the CT model. Due to CT, the water molecules at the surface become charged, even when the ion is over 15 Å away from the surface.

Soniat, Marielle; Rick, Steven W., E-mail: srick@uno.edu [Department of Chemistry, University of New Orleans, New Orleans, Louisiana 70148 (United States)

2014-05-14

384

Lattice theory of ultrafast excitonic and charge-transfer dynamics in DNA.  

PubMed

We propose a lattice fermion model suitable for studying the ultrafast photoexcitation dynamics of ordered chains of deoxyribonucleic acid (DNA) polymers. The model includes both parallel (intrachain) and perpendicular (cross-chain) terms as well as diagonal cross-chain terms coupling neighboring bases. The general form of our Hamiltonian is borrowed from lattice fermion models of quantum chromodynamics. The band structure for this model can be determined analytically, and we use this as a basis for computing the singly excited states of the poly(dA)poly(dT) DNA duplex using configuration interaction singles. Parameters for the model are taken from various literature sources and our own ab initio calculations. Results indicate that the excited states consist of a low energy band of dark charge-separated states followed by separate bands of delocalized excitonic states which have weak mixing between the thymidine and adenosine sides of the DNA chain. We then propose a lattice exciton model based upon the transition dipole-dipole couplings between bases and compare the analytical results for the survival probability of an initially localized exciton to exact numerical results. The results herein underscore the competing role of excitonic and charge-transfer dynamics in these systems. PMID:16965121

Bittner, Eric R

2006-09-01

385

Single-crystal organic charge-transfer interfaces probed using Schottky-gated heterostructures  

NASA Astrophysics Data System (ADS)

Organic semiconductors based on small conjugated molecules generally behave as insulators when undoped, but the heterointerfaces of two such materials can show electrical conductivity as large as in a metal. Although charge transfer is commonly invoked to explain the phenomenon, the details of the process and the nature of the interfacial charge carriers remain largely unexplored. Here we use Schottky-gated heterostructures to probe the conducting layer at the interface between rubrene and PDIF-CN2 single crystals. Gate-modulated conductivity measurements demonstrate that interfacial transport is due to electrons, whose mobility exhibits band-like behaviour from room temperature to ~150?K, and remains as high as ~1?cm2?V-1?s-1 at 30?K for the best devices. The electron density decreases linearly with decreasing temperature, an observation that can be explained quantitatively on the basis of the heterostructure band diagram. These results elucidate the electronic structure of rubrene/PDIF-CN2 interfaces and show the potential of Schottky-gated organic heterostructures for the investigation of transport in molecular semiconductors.

Lezama, Ignacio Gutiérrez; Nakano, Masaki; Minder, Nikolas A.; Chen, Zhihua; di Girolamo, Flavia V.; Facchetti, Antonio; Morpurgo, Alberto F.

2012-09-01

386

The dynamics of energy and charge transfer in lead sulfide quantum dot solids  

SciTech Connect

We report on a systematic time-resolved photoluminescence study of the competing energy and charge transfer rates in PbS QDs of differing sizes in the same QD solid as a function of both temperature and ligand-controlled different inter-QD average separations. This complements previous studies that typically varied only one parameter and reveals new aspects while also confirming some known features. For the smallest PbS QDs, the dominant decay process is nonradiative resonant energy transfer (NRET) to adjacent larger dots for all separations but at a rate that increases with decreasing temperature. For the largest QDs, NRET being forbidden, the decay is found to be exponential in the inter-QD separation consistent with carrier tunneling but, for each fixed tunneling distance, exhibiting a thermally activated tunneling carrier population with the activation energy dependent upon the ligand length controlling the inter-QD separation. A consistent understanding of this expanded and rich decay rate behavior of both large and small QDs, we show, can be obtained by accounting for the ligand length dependent (a) dielectric environment of the QD solid modeled using an effective medium description, (b) the energy cost of dissociating the exciton into electron and hole in neighboring QDs, and (c) the potential participation of midgap states. Implications of the findings for NRET based photovoltaics are discussed.

Lingley, Zachary [Mork Family Department of Chemical Engineering and Materials Science, University of Southern California, Los Angeles, California 90089 (United States); Lu, Siyuan [Department of Physics and Astronomy, University of Southern California, Los Angeles, California 90089 (United States); Madhukar, Anupam, E-mail: madhukar@usc.edu [Mork Family Department of Chemical Engineering and Materials Science, University of Southern California, Los Angeles, California 90089 (United States); Department of Physics and Astronomy, University of Southern California, Los Angeles, California 90089 (United States)

2014-02-28

387

Nanostructure and charge transfer in Bi2S3-TiO2 heterostructures.  

PubMed

Interfacial nanostructures in Bi2S3-TiO2 nanorod-nanoparticle heterostructures with a change of coupling mode have been engineered. The samples were characterized by x-ray diffraction, scanning electron microscopy, transmission electron microscopy, and ultraviolet-visual light absorption spectroscopy. By means of in situ growth of TiO2 nanoparticles on the surfaces of Bi2S3 nanorods in one pot, heterostructures with high-quality interfaces were obtained in which the {105} facet of anatase TiO2 selectively coupled with the {010} facet of orthorhombic Bi2S3 nanorods without any crystal defects, showing the epitaxial relationship of Bi2S3 {011} // TiO2 {101}. By means of a two-step method, TiO2 nanoparticles also could be grown on the {310} facet of the pre-prepared Bi2S3 nanorods to form heterostructures but with interfacial defects. Charge transfer in the interface-different heterostructures was evaluated by photodegradation of methyl orange under visible-light irradiation. The defect-free interfaces favored electron-hole separation and transfer, resulting in improved photocatalytic activity. The current structural characterization and interface engineering should be expanded to other heterostructures when studying the relationship between synthesis, interfacial structure, and photocatalytic or photovoltaic applications. PMID:24784772

Yu, Haijing; Huang, Jing; Zhang, Hua; Zhao, Qingfei; Zhong, Xinhua

2014-05-30

388

Nanostructure and charge transfer in Bi2S3-TiO2 heterostructures  

NASA Astrophysics Data System (ADS)

Interfacial nanostructures in Bi2S3-TiO2 nanorod-nanoparticle heterostructures with a change of coupling mode have been engineered. The samples were characterized by x-ray diffraction, scanning electron microscopy, transmission electron microscopy, and ultraviolet-visual light absorption spectroscopy. By means of in situ growth of TiO2 nanoparticles on the surfaces of Bi2S3 nanorods in one pot, heterostructures with high-quality interfaces were obtained in which the {105} facet of anatase TiO2 selectively coupled with the {010} facet of orthorhombic Bi2S3 nanorods without any crystal defects, showing the epitaxial relationship of Bi2S3 {011} // TiO2 {101}. By means of a two-step method, TiO2 nanoparticles also could be grown on the {310} facet of the pre-prepared Bi2S3 nanorods to form heterostructures but with interfacial defects. Charge transfer in the interface-different heterostructures was evaluated by photodegradation of methyl orange under visible-light irradiation. The defect-free interfaces favored electron-hole separation and transfer, resulting in improved photocatalytic activity. The current structural characterization and interface engineering should be expanded to other heterostructures when studying the relationship between synthesis, interfacial structure, and photocatalytic or photovoltaic applications.

Yu, Haijing; Huang, Jing; Zhang, Hua; Zhao, Qingfei; Zhong, Xinhua

2014-05-01

389

Computational Confirmation of the Carrier for the "XCN" Interstellar Ice Bank: OCN(-) Charge Transfer Complexes  

NASA Technical Reports Server (NTRS)

Recent experimental studies provide evidence that carrier for the so-called XCN feature at 2165 cm(exp -1) (4.62 micron) in young stellar objects is an OCN(-)/NH4(+) charge transfer (CT) complex that forms in energetically processed interstellar icy grain mantles. Although other RCN nitriles and RCN iosonitriles have been considered, Greenberg's conjecture that OCN(-) is associated with the XCN feature has persisted for over 15 years. In this work we report a computational investigation that thoroughly confirms the hypothesis that the XCN feature observed in laboratory studies can result from OCN(-)/NH4(+) CT complexes arising from HNCO and NH3, in a water ice environment. Density functional theory calculations with theory calculations with HNCO, NH3, and up to 12 waters reproduce seven spectroscopic measurements associated with XCN: the band origin of the asymmetric stretching mode of OCN(-), shifts due to isotopic substitutions of C, N, O, and H, and two weak features. However, very similar values are also found for the OCN(-)/NH4(+) CT complex arising from HOCN and NH3. In both cases, the complex forms by barrierless proton transfer from HNCO or HOCN to NH3 during the optimization of the solvated system. Scaled B3LYP/6-31+G** harmonic frequencies for HNCO and HOCN cases are 2181 and 2202 cm(exp -1), respectively.

Park, J.-Y.; Woon, D. E.

2004-01-01

390

Novel Approaches in Energy Conversion by Molecular Charge Transfer from Diamond Surfaces  

NASA Astrophysics Data System (ADS)

Vacuum thermionic energy conversion is based on electron transfer from a hot emitter across a vacuum gap to the collector. Our approach for an efficient emitter utilizes nanostructured, negative electron affinity doped diamond films. With a low effective work function of less than 1.3 eV thermionic emission commences at 260 C and observes the law of Richardson -- Dushman with a significant emission current > 5 mA at 500 C. Pairing this emitter with a similar collector results in a potential across the gap and introduction of an ohmic load establishes a current indicative of energy conversion. Utilizing ionization processes of gaseous species at the emitter surface can enhance inter-electrode charge transfer and increase output power. In the ionization process an electron is trapped in an occupied molecular orbital establishing a negative ion state. The electron affinity and negative ion binding energy determines stability of the transient negative species, and we present results for H2 and CH4. As these species are introduced in the inter-electrode gap an increase in output power is observed with a concurrent shift of maximum output power to lower load resistance.

Koeck, Franz A. M.; Sharp, Jeff; Nemanich, Robert J.

2011-03-01

391

Ruthenium cation substitutional doping for efficient charge carrier transfer in organic/inorganic hybrid solar cells  

NASA Astrophysics Data System (ADS)

Solution-processed organic/inorganic hybrid solar cells have emerged as a new platform for low-cost optoelectronics. At the heart of photovoltaic devices lies the matching of a junction, which requires the suitable energy level alignment of n-type and p-type semiconductors. Incorporating foreign ions into bulk semiconductors has been largely employed for many decades, yet electronically active doping in energy level control of the hybrid bulk heterojunctions has been rarely involved and the demonstration of robust functional optoelectronic devices had thus far been elusive. Herein, we introduce Ru ions into TiO2 to decorate the energy level of the acceptor to gain better energy level alignment between the donor and acceptor. By reducing the 'excess' energy offset between the n-type and p-type semiconductors, the electron transfer becomes faster, thus leading to a notable enhancement in power conversion efficiency, i.e., from 2.20% to 2.89%. The results demonstrate that the energy level can be controlled effectively by the versatile Ru dopants. This work opens an effective route for accelerating the charge carrier transfer at the interface and achieving high-performance organic/inorganic hybrid optoelectronic devices.

Kong, Degui; Jin, Xiao; Sun, Weifu; Du, Jiaxing; Tong, Jifeng; Chen, Changyong; Yang, Xuwei; Cheng, Yuanyuan; Li, Qinghua

2015-01-01

392

Ultrafast solvation dynamics and charge transfer reactions in room temperature ionic liquids.  

PubMed

Room temperature ionic liquids (ILs) are a new type of solvent with peculiar properties. ILs are usually composed of an anion and a bulky cation with one or more alkyl chains to decrease the melting point. These structural peculiarities lead to the high viscosity and the heterogeneity of ILs, which could affect chemical reactions. In the present perspective, we will first introduce the experimentally observed nature of the heterogeneous liquid structure and then introduce recent developments in the study on electron transfer (ET) and charge transfer (CT) reactions in relation with the solvation and the heterogeneity of ILs. Because of the high viscosity of ILs, diffusive solvation is expected to be slow which could be the rate-limiting factor for ET and CT processes. However, ILs could provide a unique reaction field depending on the location of the solute within the heterogeneous liquid structure and the reaction could be faster than that expected from the bulk viscosity due to the fast fluctuation of the local environment. PMID:24879120

Nagasawa, Yutaka; Miyasaka, Hiroshi

2014-07-14

393

First-principles study of the interaction and charge transfer between graphene and metals  

NASA Astrophysics Data System (ADS)

Measuring the transport of electrons through a graphene sheet necessarily involves contacting it with metal electrodes. We study the adsorption of graphene on metal substrates using first-principles calculations at the level of density-functional theory. The bonding of graphene to Al, Ag, Cu, Au, and Pt (111) surfaces is so weak that its unique “ultrarelativistic” electronic structure is preserved. The interaction does, however, lead to a charge transfer that shifts the Fermi level by up to 0.5 eV with respect to the conical points. The crossover from p -type to n -type doping occurs for a metal with a work function ˜5.4eV , a value much larger than the work function of free-standing graphene, 4.5 eV. We develop a simple analytical model that describes the Fermi-level shift in graphene in terms of the metal substrate work function. Graphene interacts with and binds more strongly to Co, Ni, Pd, and Ti. This chemisorption involves hybridization between graphene pz states and metal d states that opens a band gap in graphene, and reduces its work function considerably. The supported graphene is effectively n -type doped because in a current-in-plane device geometry the work-function lowering will lead to electrons being transferred to the unsupported part of the graphene sheet.

Khomyakov, P. A.; Giovannetti, G.; Rusu, P. C.; Brocks, G.; van den Brink, J.; Kelly, P. J.

2009-05-01

394

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

PubMed

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. PMID:24697478

Heinen, M; Palberg, T; Löwen, H

2014-03-28

395

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

2014-03-12

396

Localized surface plasmon mediated photochemistry and charge transfer in noble metal nanoparticles  

NASA Astrophysics Data System (ADS)

This thesis addresses the fundamental physical and chemical processes of localized surface plasmon mediated photochemistry and charge transfer in noble metal nanoparticles. The first chapter introduces the theory and application of surface plasmons. It includes a discussion of propagating and localized surface plasmons, plasmon decay dynamics, factors governing plasmon excitation of metal nanoparticles, near-field enhanced photochemistry and plasmon mediated charge transfer. The second chapter presents a photovoltage mechanism for room light conversion of citrate stabilized silver nanocrystal seeds to large nanoprisms. The process relies on the excitation of silver surface plasmons and requires citrate and oxygen. The transformation rate is first-order in seed concentration. The mechanism involves oxidative etching of seeds and subsequent photoreduction of aqueous silver ions preferentially onto silver prisms that have a cathodic photovoltage resulting from plasmon hot hole citrate photo- oxidation. This idea also explains several previously reported experiments including single and dual wavelength irradiation and the core/shell synthesis of silver layers on gold seeds. The third chapter explores the photo-driven growth of citrate stabilized silver nanoparticles. Under plasmon excitation, particles that absorb/scatter light weakly reduce dioxygen and lose silver ions, whereas particles with resonant plasmons build up a high photovoltage due to citrate photo-oxidation and reduce silver ions. Overall, growth is favored for on-resonant particles. Compared to the borohydride reduction method, more monodisperse, round 10-20 nm diameter silver nanoparticles are obtained by plasmon mediated approaches. Adding a trace amount of potassium chloride can speed up the growth and inhibit the formation of Ag aggregates. The fourth chapter investigates the plasmon induced photochemical charge separation in gold nanoparticles on a transparent indium tin oxide (ITO) substrate. Photocurrent and photovoltage are directly measured under potentiostatic control in air. It is proposed that gold plasmon excitation causes hot electrons to inject into the ITO conduction band, while hot holes are scavenged by citrate and other solution redox species. A resonant increase in the photocurrent generated at more oxidizing potentials is observed.

Wu, Xiaomu

397

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

2014-11-28

398

Coupled quantum treatment of vibrationally inelastic and vibronic charge transfer in proton-O sub 2 collisions  

SciTech Connect

A three-dimensional quantum-mechanical study of vibrational, state-resolved differential cross sections (DCS) for the direct inelastic and for the charge-transfer scattering channels has been carried out for the H{sup +}+O{sub 2} system. The collision energy considered was {ital E}{sub c.m.}=23.0 eV, which is the same as that examined by Noll and Toennies in their experiments (J. Chem. Phys. 85, 3313 (1986)). The scattering treatment employed was the charge-transfer infinite-order sudden approximation (CT IOSA) with the vibrational states correctly expanded over the relevant adiabatic basis for each of the two electronic channels. The state-to-state DCS are found to follow closely the behavior of the experimental quantities, both in the inelastic and the charge-transfer channels. Moreover, a careful comparison between the measured relative probabilities and computed values allows us to test in minute detail the efficiency of the scattering model and the reliability of the potential-energy surfaces employed. It is found that vibrational energy transfer is overestimated in the vibrational inelastic channels while in the charge-transfer inelastic channels the same energy transfer is slightly underestimated by the calculations. The total flux distribution, however, is found to be in very good accord with experiments. Angular distributions are also well reproduced both by the DCS and by the average energy-transfer values. The study of some of the CT IOSA quantities also allows us to establish clearly the importance of nonadiabatic transitions in enhancing vibrational inelasticity in the present system.

Gianturco, F.A. (Department of Chemistry, The University of Rome, Citta Universitaria, 00185 Rome (Italy)); Palma, A.; Semprini, E.; Stefani, F. (Instituto Teoria e Structure Elettronica, Consiglio Nazionale delle Ricerche, Area della Ricerca di Roma, Monterotondo Scalo, 00016 Rome (Italy)); Baer, M. (Department of Theoretical Physics and Applied Mathematics, Soreq Nuclear Research Centre, Yavne (Israel))

1990-10-01

399

Intermolecular hydrogen bond complexes by in situ charge transfer complexation of o-tolidine with picric and chloranilic acids.  

PubMed

A two new charge transfer complexes formed from the interactions between o-tolidine (o-TOL) and picric (PA) or chloranilic (CA) acids, with the compositions, [(o-TOL)(PA)(2)] and [(o-TOL)(CA)(2)] have been prepared. The (13)C NMR, (1)H NMR, (1)H-Cosy, and IR show that the charge-transfer chelation occurs via the formation of chain structures O-H?N intermolecular hydrogen bond between 2NH(2) groups of o-TOL molecule and OH group in each PA or CA units. Photometric titration measurements concerning the two reactions in methanol were performed and the measurements show that the donor-acceptor molar ratio was found to be 1:2 using the modified Benesi-Hildebrand equation. The spectroscopic data were discussed in terms of formation constant, molar extinction coefficient, oscillator strength, dipole moment, standard free energy, and ionization potential. Thermal behavior of both charge transfer complexes showed that the complexes were more stable than their parents. The thermodynamic parameters were estimated from the differential thermogravimetric curves. The results indicated that the formation of molecular charge transfer complexes is spontaneous and endothermic. PMID:21531618

Refat, Moamen S; Saad, Hosam A; Adam, Abdel Majid A

2011-08-01

400

Intermolecular hydrogen bond complexes by in situ charge transfer complexation of o-tolidine with picric and chloranilic acids  

NASA Astrophysics Data System (ADS)

A two new charge transfer complexes formed from the interactions between o-tolidine (o-TOL) and picric (PA) or chloranilic (CA) acids, with the compositions, [(o-TOL)(PA) 2] and [(o-TOL)(CA) 2] have been prepared. The 13C NMR, 1H NMR, 1H-Cosy, and IR show that the charge-transfer chelation occurs via the formation of chain structures O-H⋯N intermolecular hydrogen bond between 2NH 2 groups of o-TOL molecule and OH group in each PA or CA units. Photometric titration measurements concerning the two reactions in methanol were performed and the measurements show that the donor-acceptor molar ratio was found to be 1:2 using the modified Benesi-Hildebrand equation. The spectroscopic data were discussed in terms of formation constant, molar extinction coefficient, oscillator strength, dipole moment, standard free energy, and ionization potential. Thermal behavior of both charge transfer complexes showed that the complexes were more stable than their parents. The thermodynamic parameters were estimated from the differential thermogravimetric curves. The results indicated that the formation of molecular charge transfer complexes is spontaneous and endothermic.

Refat, Moamen S.; Saad, Hosam A.; Adam, Abdel Majid A.

2011-08-01

401

Interlayer charge-transfer in impacting the second hyperpolarizabilities: Radical and cation species of hexathiophenalenylium and its nitro dimers.  

PubMed

Hexathiophenalenylium (HTPLY) has gained increasing attention for its interesting and potentially useful optical properties as a result of the enhancement in spin delocalization and charge-transfer of phenalenyl radicals, occasioned by the attachment of successive three disulfide linkages. Herein, we performed density functional theory to calculate the binding interactions, electronic absorption spectra and the second hyperpolarizabilities of cation and radical dimers of HTPLY and its nitro derivatives. It is found that the equilibrium structures of the ? dimers at fully staggered position are most stable. Among these ? dimers, radical dimers exhibit stronger binding interactions with respect to cation dimers. In addition, obvious red shifts in electronic spectra of radical dimers are dependent on the large interlayer charge-transfers. More importantly, radical dimers [4]dim3 and [5]dim1 exhibit a significant increase in the second hyperpolarizabilities as compared to cation dimers, which is due to lower excitation energies and larger interlayer charge-transfers. We believe that the results presented in this article shall provide important evidence for the large interlayer charge-transfers in enhancing the NLO properties of the ? dimers. PMID:25424657

Wang, Li; Wang, Wen-Yong; Ma, Na-Na; Tian, Dong-Mei; Wang, Jiao; Qiu, Yong-Qing

2014-11-01

402

Charge transfer interactions of a Ru(II) dye complex and related ligand molecules adsorbed on Au(111)  

SciTech Connect

The interaction of the dye molecule, N3 (cis-bis(isothiocyanato)bis(2,2{sup '}-bipyridyl-4,4{sup '}-dicarboxylato) -ruthenium(II)), and related ligand molecules with a Au(111) surface has been studied using synchrotron radiation-based electron spectroscopy. Resonant photoemission spectroscopy (RPES) and autoionization of the adsorbed molecules have been used to probe the coupling between the molecules and the substrate. Evidence of charge transfer from the states near the Fermi level of the gold substrate into the lowest unoccupied molecular orbital (LUMO) of the molecules is found in the monolayer RPES spectra of both isonicotinic acid and bi-isonicotinic acid (a ligand of N3), but not for the N3 molecule itself. Calibrated x-ray absorption spectroscopy and valence band spectra of the monolayers reveals that the LUMO crosses the Fermi level of the surface in all cases, showing that charge transfer is energetically possible both from and to the molecule. A core-hole clock analysis of the resonant photoemission reveals a charge transfer time of around 4 fs from the LUMO of the N3 dye molecule to the surface. The lack of charge transfer in the opposite direction is understood in terms of the lack of spatial overlap between the {pi}*-orbitals in the aromatic rings of the bi-isonicotinic acid ligands of N3 and the gold surface.

Britton, Andrew J.; Weston, Matthew; O'Shea, James N. [School of Physics and Astronomy, University of Nottingham, Nottingham NG7 2RD (United Kingdom); Nottingham Nanotechnology and Nanoscience Centre (NNNC), University of Nottingham, Nottingham NG7 2RD (United Kingdom); Taylor, J. Ben; Rienzo, Anna; Mayor, Louise C. [School of Physics and Astronomy, University of Nottingham, Nottingham NG7 2RD (United Kingdom)

2011-10-28

403

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

404

Impact of exact exchange in the description of the electronic structure of organic charge-transfer molecular crystals  

NASA Astrophysics Data System (ADS)

We evaluate the impact that the amount of nonlocal Hartree-Fock (%HF) exchange included in a hybrid density functional has on the microscopic parameters (transfer integrals, band gaps, bandwidths, and effective masses) describing charge transport in high-mobility organic crystals. We consider both crystals based on a single molecule, such as pentacene, and crystals based on mixed-stack charge-transfer systems, such as dibenzo-TTF-TCNQ. In the pentacene crystal, the band gap decreases and the effective masses increase linearly with an increase in the amount of %HF exchange. In contrast, in the charge-transfer crystals, while the band gap increases linearly, the effective masses vary only slightly with an increase in %HF exchange. We show that the superexchange nature of the electronic couplings in charge-transfer systems is responsible for this peculiar evolution of the effective masses. We compare the density functional theory results with results obtained within the G0W0 approximation as a way of benchmarking the optimal amount of %HF exchange needed in a given functional.

Fonari, Alexandr; Sutton, Christopher; Brédas, Jean-Luc; Coropceanu, Veaceslav

2014-10-01

405

Assessment of space proton radiation-induced charge transfer inefficiency in the CCD204 for the Euclid space observatory  

Microsoft Academic Search

Euclid is a medium class European Space Agency mission candidate for launch in 2019 with a primary goal to study the dark universe using the weak lensing and baryonic acoustic oscillations techniques. Weak lensing depends on accurate shape measurements of distant galaxies. Therefore it is beneficial that the effects of radiation-induced charge transfer inefficiency (CTI) in the Euclid CCDs over

J P D Gow; N J Murray; A D Holland; D J Hall; M Cropper; D Burt; G Hopkinson; L Duvet

2012-01-01

406

Ultrafast inter-ionic charge transfer of transition-metal complexes mapped by femtosecond X-ray powder diffraction  

SciTech Connect

The transient electronic and molecular structure arising from photoinduced charge transfer in transition metal complexes is studied by X-ray powder diffraction with a 100 fs temporal and atomic spatial resolution. Crystals containing a dense array of Fe(II)-tris(bipyridine) ([Fe(bpy){sub 3}]{sup 2+}) complexes and their PF{sub 6}{sup -} counterions display pronounced changes of electron density that occur within the first 100 fs after two-photon excitation of a small fraction of the [Fe(bpy){sub 3}]{sup 2+} complexes. Transient electron density maps derived from the diffraction data reveal a transfer of electronic charge from the Fe atoms and-so far unknown-from the PF{sub 6}{sup -} counterions to the bipyridine units. Such charge transfer (CT) is connected with changes of the inter-ionic and the Fe-bipyridine distances. An analysis of the electron density maps demonstrates the many-body character of charge transfer which affects approximately 30 complexes around a directly photoexcited one. The many-body behavior is governed by the long-range Coulomb forces in the ionic crystals and described by the concept of electronic polarons.

Freyer, Benjamin; Zamponi, Flavio; Juve, Vincent; Stingl, Johannes; Woerner, Michael; Elsaesser, Thomas [Max-Born-Institut fuer Nichtlineare Optik und Kurzzeitspektroskopie, Max-Born-Strasse 2 A, 12489 Berlin (Germany); Chergui, Majed [Ecole Polytechnique Federale de Lausanne, Laboratoire de Spectroscopie Ultrarapide, Faculte des Sciences de Base, ISIC-BSP, CH-1015 Lausanne (Switzerland)

2013-04-14

407

Ultrafast inter-ionic charge transfer of transition-metal complexes mapped by femtosecond X-ray powder diffraction.  

PubMed

The transient electronic and molecular structure arising from photoinduced charge transfer in transition metal complexes is studied by X-ray powder diffraction with a 100 fs temporal and atomic spatial resolution. Crystals containing a dense array of Fe(II)-tris(bipyridine) ([Fe(bpy)3](2 +)) complexes and their [Formula: see text] counterions display pronounced changes of electron density that occur within the first 100 fs after two-photon excitation of a small fraction of the [Fe(bpy)3](2 +) complexes. Transient electron density maps derived from the diffraction data reveal a transfer of electronic charge from the Fe atoms and-so far unknown-from the [Formula: see text] counterions to the bipyridine units. Such charge transfer (CT) is connected with changes of the inter-ionic and the Fe-bipyridine distances. An analysis of the electron density maps demonstrates the many-body character of charge transfer which affects approximately 30 complexes around a directly photoexcited one. The many-body behavior is governed by the long-range Coulomb forces in the ionic crystals and described by the concept of electronic polarons. PMID:24981537

Freyer, Benjamin; Zamponi, Flavio; Juvé, Vincent; Stingl, Johannes; Woerner, Michael; Elsaesser, Thomas; Chergui, Majed

2013-04-14

408

Do fluorescence and transient absorption probe the same intramolecular charge transfer state of 4-(dimethylamino)benzonitrile?  

SciTech Connect

We present here the results of time-resolved absorption and emission experiments for 4-(dimethylamino)benzonitrile in solution, which suggest that the fluorescent intramolecular charge transfer (ICT) state may differ from the twisted ICT (TICT) state observed in transient absorption.

Gustavsson, Thomas [Laboratoire Francis Perrin, CEA/DSM/DRECAM/SPAM-CNRS URA 2453, CEA/Saclay, 91 191 Gif-sur-Yvette Cedex (France); Coto, Pedro B.; Serrano-Andres, Luis [Molecular Science Institute, University of Valencia, P.O. Box 22085, ES-46071 Valencia (Spain); Fujiwara, Takashige; Lim, Edward C. [Department of Chemistry and Center for Laser and Optical Spectroscopy, University of Akron, Akron, Ohio 44325-3601 (United States)

2009-07-21

409

State-selective preparation of NO2+ and the effects of NO2+ vibrational mode on charge transfer with NO.  

PubMed

Two color resonance-enhanced multiphoton ionization (REMPI) scheme of NO(2) through the E (2)Sigma(u)(+) (3psigma) Rydberg state was used to prepare NO(2)(+) in its ground and (100), (010), (02(0)0), (02(2)0), and (001) vibrational states. Photoelectron spectroscopy was used to verify >96% state selection purity, in good agreement with results of Bell et al. for a similar REMPI scheme. The effects of NO(2)(+) vibrational excitation on charge transfer with NO have been studied over the center-of-mass collision energy (E(col)) range from 0.07 to 2.15 eV. Charge transfer is strongly suppressed by collision energy at E(col) < approximately 0.25 eV but is independent of E(col) at higher energies. Mode-specific vibrational effects are observed for both the integral and differential cross-sections. The NO(2)(+) bending vibration strongly enhances charge transfer, with enhancement proportional to the bending quantum number, and is not dependent on the bending angular momentum. The enhancement results from increased charge transfer probability in large impact parameter collisions that lead to small deflection angles. The symmetric stretch also enhances reaction at low collision energies, albeit less efficiently than the bend. The asymmetric stretch has virtually no effect, despite being the highest-energy mode. A model is proposed to account for both the collision energy and the vibrational state dependence. PMID:16435788

Uselman, Brady; Liu, Jianbo; Boyle, Jason; Anderson, Scott

2006-02-01

410

Mössbauer effect of 129I in n-? and ?-? charge-transfer complexes of iodine in the frozen solution  

NASA Astrophysics Data System (ADS)

The Mössbauer effect of 129I was applied to investigate charge-transfer complexes of the n-? and ?-? types in the carbon disulfide frozen solution at 16 K. In the case of n-? type complexes such as triethylamine-iodine and pyridine-iodine, two chemical species of iodine, which correspond to the bridging and terminal iodines, were observed in the Mössbauer spectra. It is elucidated that a charge-transfer bond is described as a mixture of a four-electron three-center bond and a covalent bond involving d?p? hybrid orbitals in the bridging iodine. On the other hand, for the ?-? type complexes such as benzene-iodine and methylated benzene-iodine the Mössbauer spectra show only one chemical species of iodine. The acceptor orbital of iodine is thought to be described by an spd hybrid orbital. That is, a small amount of s and d characters contributes to the formation of the charge-transfer bond. From the Mössbauer parameters the charge densities and the charge distributions of iodine in these complexes were obtained.

Sakai, H.; Maeda, Y.; Ichiba, S.; Negita, H.

1980-06-01

411

Full-electron calculation of effective electronic couplings and excitation energies of charge transfer states: Application to hole transfer in DNA ?-stacks  

PubMed Central

In this work I develop and apply a theoretical method for calculating effective electronic couplings (or transfer integrals) between redox sites involved in hole or electron transfer reactions. The resulting methodology is a refinement and a generalization of a recently developed approach for transfer integral evaluation. In fact, it holds for any overlap between the charge-localized states used to represent charge transfer (CT) processes in the two-state model. The presented theoretical and computational analyses show that the prototype approach is recovered for sufficiently small overlaps. The method does not involve any empirical parameter. It allows a complete multielectron description, therefore including electronic relaxation effects. Furthermore, its theoretical formulation holds at any value of the given reaction coordinate and yields a formula for the evaluation of the vertical excitation energy (i.e., the energy difference between the adiabatic ground and first-excited electronic states) that rests on the same physical quantities used in transfer integral calculation. In this paper the theoretical approach is applied to CT in B-DNA base dimers within the framework of Density Functional Theory (DFT), although it can be implemented in other computational schemes. The results of this work, as compared with previous Hartree–Fock (HF) and post-HF evaluations, support the applicability of the current implementation of the method to larger ?-stacked arrays, where post-HF approaches are computationally unfeasible. PMID:19778106

Migliore, Agostino

2009-01-01

412

Ab initio Evaluation of the Charge-Transfer Integrals and Band Structures of Phenanthroline-based Molecular Crystals  

NASA Astrophysics Data System (ADS)

Ab initio calculations are carried out to study the charge-transport properties of phenanthroline-based molecular crystals, BCP and Bphen. The charge-transfer integrals in the two crystalline structures and in a quasi-1D chain model for BCP are evaluated based on: (i) a tight-binding approximation for dimers; (ii) the band structures of the periodic systems. In these compounds, the LUMO/LUMO+1energies of the isolated molecules are very close, which results in the LUMO and LUMO+1orbitals both having significant contributions to the LUMO level in the dimer. In this case, the usual definition based on the electronic coupling between the two LUMO orbitals from each molecule cannot be applied to describe the charge-transfer characteristics in the dimer. A new definition of ``effective transfer integrals'' based on ``mixed states'' was proposed (H. Li, J.L. Bredas, and C. Lennartz, J. Chem. Phys. 126 (2007) 164704) to address this problem. Within the tight-binding approximation, the ``effective transfer integrals'' for both hole and electron transfers are found to be in very good agreement with the valence and conduction band dispersions obtained from plane-wave DFT calculations. We acknowledge many stimulating discussions with Veaceslav Coropceanu and Demetrio da Silva Filho.

Li, H.; Bredas, J.-L.; Lennartz, C.

2008-03-01

413

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; Aygül, Umut; Chassé, Thomas

2014-01-01

414

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

415

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

416

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

417

Proton Irradiation Experiment for X-ray Charge-Coupled Devices of the Monitor of All-Sky X-ray Image Mission Onboard the International Space Station: I. Experimental Setup and Measurement of the Charge Transfer Inefficiency  

Microsoft Academic Search

We have investigated the radiation damage effects on a charge-cloupled device (CCD) to be employed in the Japanese X-ray astronomy mission including the monitor of all-sky X-ray image (MAXI) onboard the international space station (ISS). Since low-energy protons release their energy mainly at the charge transfer channel, resulting in a decrease of the charge transfer efficiency, we focused on low-energy

Emi Miyata; Tomoyuki Kamazuka; Hirohiko Kouno; Mitsunori Fukuda; Mototsugu Mihara; Kensaku Matsuta; Hiroshi Tsunemi; Kanenobu Tanaka; Tadanori Minamisono; Hiroshi Tomida; Kazuhisa Miyaguchi

2002-01-01

418

Towards time-dependent, non-equilibrium charge-transfer force fields. Contact electrification and history-dependent dissociation limits  

NASA Astrophysics Data System (ADS)

Force fields uniquely assign interatomic forces for a given set of atomic coordinates. The underlying assumption is that electrons are in their quantum-mechanical ground state or in thermal equilibrium. However, there is an abundance of cases where this is unjustified because the system is only locally in equilibrium. In particular, the fractional charges of atoms, clusters, or solids tend to not only depend on atomic positions but also on how the system reached its state. For example, the charge of an isolated solid — and thus the forces between atoms in that solid — usually depends on the counterbody with which it has last formed contact. Similarly, the charge of an atom, resulting from the dissociation of a molecule, can differ for different solvents in which the dissociation took place. In this paper we demonstrate that such charge-transfer history effects can be accounted for by assigning discrete oxidation states to atoms. With our method, an atom can donate an integer charge to another, nearby atom to change its oxidation state as in a redox reaction. In addition to integer charges, atoms can exchange "partial charges" which are determined with the split charge equilibration method.

Dapp, Wolf B.; Müser, Martin H.

2013-07-01

419

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

420

Effects of Charge Transfer on the ESIPT Process in Methyl 5-R-Salicylates.  

PubMed

The fluorescent behavior of the methyl-5-R-salicylates is analyzed in media of negligible acidity and basicity so that the methyl-5-R-salicylates may undergo solvent dipolarity changes or not in a controlled manner based on the following guidelines: (i) The molecular forms of these methyl-5-R-salicylates possessing an intramolecular hydrogen bond (IMHB) between their hydroxyl group and ether type oxygen (rotated tautomer) undergo no excited-state intramolecular proton transfer (ESIPT) in their first excited electronic state; (ii) on the other hand, the molecular species with an IMHB between its hydroxyl group and carbonyl oxygen (normal tautomer) exhibits both ESIPT and normal emission when charge transfer (CT) from the R-substituent to the phenol group is slight to moderate, but only normal emission is monitored when CT is strong. The special insensitivity of the first UV absorption band for the normal tautomer of methylsalicylate (MS, with R = H) to the polarity of the solvent is not echoed by the normal forms of methyl-5-R-salicylates containing substituents R with a substantial effect of CT in the IMHB of the compound. These solvatochromic features of MS are shared by the emissions of its derivatives. The photophysical evidence found for the methyl-5-R-salicylates confirms the photophysical model recently reported (Phys. Chem. Chem. Phys. 2012, 14, 8903-8909), which assigns three fluorescent emissions to the methyl-5-R-salicylates: two of them coming from the IMHB normal tautomer, which undergoes ESIPT, and another from the IMHB rotated tautomer, which cannot undergo ESIPT. PMID:24967729

Catalán, J

2015-02-12

421

Hydrogen-bond interaction in organic conductors: redox activation, molecular recognition, structural regulation, and proton transfer in donor-acceptor charge-transfer complexes of TTF-imidazole.  

PubMed

Hydrogen-bond interaction in donor-acceptor charge-transfer complexes of TTF-imidazole demonstrated the electronic effects in terms of control of component ratio and redox activation. These unprecedented effects of hydrogen bonds renewed the criteria giving "a high probability of being organic metals" and produced a number of highly conductive complexes with various acceptors having a wide range of electron-accepting ability. In p-chloranil complex, both molecules were linked by hydrogen bonds and formed a D-A-D triad, regulating the donor-acceptor composition to be 2:1. Theoretical calculations have revealed that the polarizability of hydrogen bonds controls the redox ability of the donor and p-benzoquinone-type acceptors and afforded different ionicity in complexes from those expected by the difference of redox potentials between donor and acceptors. In the p-chloranil complex, this electronic and structural regulation by hydrogen bond realized the first metallic donor-acceptor charge-transfer complex based on hydrogen bond functionalized TTF. Hydrogen bonds controlled also molecular arrangements in charge-transfer complexes, giving diverse and highly ordered assembled structures, D-A-D triad in the p-chloranil complex, one-dimensional zigzag chain in I(5) salt, alternating donor-acceptor chain in chloranilic acid complex, and D-A-D-A cyclic tetramer in nitranilic acid complex. Furthermore, TTF-imidazole acted as electron donor as well as proton acceptor in anilic acid complexes and realized the simultaneous charge- and proton-transfer complexes. These investigations demonstrated the new and intriguing potentials of the hydrogen bond in the development of organic conductors and multifunctional molecular materials. PMID:17696346

Murata, Tsuyoshi; Morita, Yasushi; Yakiyama, Yumi; Fukui, Kozo; Yamochi, Hideki; Saito, Gunzi; Nakasuji, Kazuhiro

2007-09-01

422

Molecular orbital (SCF-X??-SW) theory of metal-metal charge transfer processes in minerals - I. application to Fe2+???Fe3+ charge transfer and "electron delocalization" in mixed-valence iron oxides and silicates  

USGS Publications Warehouse

A number of mixed valence iron oxides and silicates (e.g., magnetite, ilvaite) exhibit thermally induced electron delocalization between adjacent Fe2+ and Fe3+ ions and optically induced electronic transitions which are assigned to Fe2+???Fe3+ intervalence charge transfer. In this paper, the mechanism of electron delocalization (i.e., polarons versus itinerant electrons) and the nature of optically induced intervalence charge-transfer in minerals are investigated using molecular orbital theory. SCF-X??-SW molecular orbital calculations were done for several mixed-valence (Fe2O10)15- clusters corresponding to edgesharing Fe2+ and Fe3+ coordination polyhedra. A spinunrestricted formalism was used so that the effect of ferromagnetic versus antiferromagnetic coupling of adjacent Fe2+ and Fe3+ cations could be determined. The molecular orbital results can be related to the polaron theory of solid state physics and the perturbation theory formalism used by Robin and Day (1967) and others to describe electron transfer in mixed valence compounds. Intervalence charge-transfer results from the overlap of Fe(3d) orbitals across the shared edges of adjacent FeO6 polyhedra to give weak Fe-Fe bonds. Electron delocalization, however, requires that adjacent Fe cations be ferromagnetically coupled. Antiferromagnetic coupling results in distinguishable Fe2+ and Fe3+ cations. Electronic transitions between the Fe-Fe bonding and Fe-Fe antibonding orbitals results in the optically-induced intervalence charge transfer bands observed in the electronic spectra of mixed valence minerals. Such transitions are predicted to be polarized along the metal-metal bond direction, in agreement with experimental observations. ?? 1987 Springer-Verlag.

Sherman, D.M.

1987-01-01

423

A Theoretical Investigation of the Charge Transfer System TCNQ-F4 and Alpha-Sexithiophene  

NASA Astrophysics Data System (ADS)

The electronic and geometrical structures of the charge-transfer system of alpha-sexihiophene and tetrafluorotetracyanoquinodimethane are calculated self-consistently from first principles. By means of density functional theory (DFT) methods several configurations of the free molecules are calculated within LDA and B3LYP employing a plane wave basis and different atomic orbital sets. The combined system exhibits preferential binding of the center of the TCNQ-F4 on top of a c-c bond of the sexithiophene, thereby the central configuration having the lowest energy. As opposed to the periodic arrangement in a crystal of the related system dimethylquaterthiophene and TCNQ-F4, the free system exhibits a strong interaction going along with a substantial polarization of both molecules. For comparison with scanning tunneling spectroscopy results, the molecules were adsorbed in a parallel geometry on a Au(111) slab. To take into account the voltage applied to the STM tip the system was finally calculated within an electric field. This work is financially supported by the US-DOE grant no. DE-FG02-02ER46012.

Braun, Kai-Felix

2005-03-01

424

Two-photon circular dichroism of an axially dissymmetric diphosphine ligand with strong intramolecular charge transfer.  

PubMed

In this article we report on the study of the polarization dependent two-photon absorption (TPA) of (S)-(+)-(1,1'-binaphthalene-2,2'-diyl)bis(diphenylphosphine) (S-BINAP) in solution, and the theoretical-experimental analysis of its two-photon circular dichroism (TPCD) spectrum. The comparative examination of the following two correlation functionals, using the 6-31G* basis set, showed that the Coulomb attenuated method variant of the Becke's three-parameter exchange and the Lee-Yang-Parr (CAM-B3LYP) is more reliable than B3LYP in molecules such as S-BINAP, a heteroaromatic diphosphine chiral ligand with strong intramolecular charge transfer. To access the theoretical TPCD spectra, we employed time dependent density functional theory (TD-DFT) at the mentioned level of theory and over the first 40 electronic excited states including solvent effects by means of the polarizable continuum model (PCM). The extended calculation on twice as many electronic excited states in vacuo proved to be crucial for the correct assignment of the experimental bands. TPA measurements were performed in the femtosecond regime and over a broad spectral range using the double L-scan technique. PMID:24446721

Díaz, Carlos; Echevarria, Lorenzo; Rizzo, Antonio; Hernández, Florencio E

2014-02-01

425

Charge transfer interaction using quasiatomic minimal-basis orbitals in the effective fragment potential method  

NASA Astrophysics Data System (ADS)

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.

2013-11-01

426

Determination of some psychotropic phenothiazine drugs by charge-transfer complexation reaction with chloranilic acid.  

PubMed

A spectrophotometric method is described for the determination of four commonly used psychotropic phenothiazine drugs. The method is based on the measurement of the intensely coloured charge-transfer complex formed by the interaction of these drugs as n-electron donors with chloranilic acid as the pi-acceptor. The coloured species measured exhibits maximum absorption at 535 nm. The molar-combining ratio and optimum assay conditions are reported. Beer's law is obeyed over the range, 25-250 microg ml(-1) with apparent molar absorptivity in the range, 0.93 x 10(3)-1.45 x 10(3) l mol(-1) cm(-1). The limits of detection and quantification are reported. The proposed method was applied to the determination of these psychotropics in pharmaceutical formulations and the results demonstrated that the method is equally accurate, precise and reproducible as the official methods. The validity of method was established by recovery studies via standard-addition technique with satisfactory results. PMID:15081349

Basavaiah, K

2004-04-01

427