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1

Photoinduced Charge Transfer Process  

NASA Astrophysics Data System (ADS)

The photoinduced charge transfer process is the fundamental process in a photovoltaic system. Organic photovoltaics contain a donor-acceptor molecular system which undergoes photoinduced charge transfer leading to a large dipole moment. Often the charge transfer properties of such donor-acceptor systems are measured in solution. The dipole moments on the solvent molecules creates a reaction field. To simulate this reaction field we adopt an approach similar to the explicit solvent model proposed by Washel and co-workers. We use Monte Carlo simulations to determine various possible solvent structures. We use a carotenoid-porphyrin-C60 molecular triad as the light-harvesting system. This molecular triad has a very large dipole moment (153 Debye) in the charge separated state. The resulting solvent structures and the reaction field as a function of temperature will be presented.

Basurto, Luis; Baruah, Tunna; Zope, Rajendra; Rodriguez, Jose

2011-10-01

2

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

3

Electronic Structure of 1 to 2 nm Diameter Silicon Core/Shell Nanocrystals: Surface Chemistry, Optical Spectra, Charge Transfer, and Doping  

SciTech Connect

Static and time-dependent density functional calculations, geometrically optimized and including all electrons, are described for silicon nanocrystals as large as Si??H??, which contains 163 atoms. We explore and predict the effect that different sp³ passivation schemessF or H termination, thin oxide shell, or alkane terminationshave on the HOMO and LUMO, on the optical spectra, and on electron transfer properties. Electronegativity comparisons are a useful guide in understanding the observed deviation from the simple quantum size effect model. Nanocrystals containing Al or P impurity atoms, either on the surface or in the interior, are explored to understand electrical doping in strongly quantum-confined nanocrystals. Surface dangling bonds are found to participate in internal charge transfer with P atom dopant electrons.

Zhou, Zhiyong; Friesner, Richard A.; Brus, Louis

2003-12-17

4

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

5

Charge Transfer Doping of Silicon  

NASA Astrophysics Data System (ADS)

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.

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

2014-04-01

6

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

NASA Astrophysics Data System (ADS)

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

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

2014-02-01

7

Charge Transfer and Transport in DNA  

Microsoft Academic Search

We explore charge migration in DNA, advancing two distinct mechanisms of charge separation in a donor (d)-bridge ({Bj})-acceptor (a) system, where {Bj} = B1,B2,\\\\cdots ,BN are the N-specific adjacent bases of B-DNA: (i) two-center unistep superexchange induced charge transfer, d*{Bj}a -> dmp{Bj}a±, and (ii) multistep charge transport involves charge injection from d* (or d+) to {Bj}, charge hopping within {Bj},

Joshua Jortner; Mordechai Bixon; Thomas Langenbacher; Maria E. Michel-Beyerle

1998-01-01

8

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

Microsoft Academic Search

Electron-transfer reactions can be accompanied by significant nuclear movements. Nuclear motion appears to be especially vital to the reversible, photoinduced charge-transfer chemistry of cyclopentadienylnickel nitrosyl (C[sub 5]H[sub 5]NiNO). Although extended X-ray absorption fine structure (EXAFS) spectroscopy has recorded photoinduced changes in the ligation of myoglobins, similar X-ray studies of electron-transfer chemistry have not been reported. Here we examine reversible, photoinduced

Lin X. Chen; Michael K. Bowman; J. R. Norris; P. A. Montano

1993-01-01

9

Photoswitching Intramolecular Energy and Charge Transfer  

Microsoft Academic Search

Light controlled on- and off-switching of intramolecular energy and charge transfer is demonstrated in donor-switch-acceptor (D-S-A) supermolecules. The supermolecules are designed based on our experience on donor-bridge-acceptor (D-B-A) systems. Switching function is achieved by incorporating optically bistable photochromic fulgides and diarylethenes and proved via fs transient absorption. For both transfer processes, the transfer function is suppressed in the closed form

H. Port; A. Hartschuh; M. Hennrich; H. C. Wolf; J. M. Endtner; F. Effenberger

2000-01-01

10

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

11

Charge-transfer magnetoelectrics of polymeric multiferroics.  

PubMed

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

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

2014-04-22

12

Variable Charge Soils: Mineralogy and Chemistry  

SciTech Connect

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

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

2003-11-01

13

Charge transfer efficiency in proton damaged CCD's  

Microsoft Academic Search

We have performed detailed measurements of the charge transfer efficiency (CTE) in a thinned, backside-illuminated imaging charge-coupled device (CCD). The device had been damaged in three separate sections by proton radiation typical of that which a CCD would receive in space-borne experiments, nuclear imaging, or particle detection. We examined CTE as a function of signal level, temperature, and radiation dose.

Tim Hardy; R. Murowinski; M. J. Deen

1998-01-01

14

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

15

Charge transfer reactions on semiconductor surfaces  

Microsoft Academic Search

A survey is given of semiconductor electronic structures which are related to surface atom geometric structures (“relaxation”)\\u000a and\\/or adsorption properties of foreign particles. Results obtained on two characteristic “model surfaces”, Si (111) and \\u000a ZnO (10[`<\\/font\\u000a>1]0)ZnO (10\\\\bar 10)\\u000a , are discussed. Examples are given for kinetically controlled charge transfer reactions during irreversible formation of\\u000a interfaces and for reversible charge transfer

Wolfgang Göpel

1980-01-01

16

Dynamical treatment of charge transfer through duplex nucleic acids containing modified adenines.  

PubMed

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 multilevel computational approach based on classical molecular dynamics and quantum chemistry. We find yet another piece of 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

2013-10-22

17

Charge transfer reactions in Xe plasma expansion  

SciTech Connect

Charge transfer reactions of fast Xe ions with hydrocarbons including methane (CH{sub 4}), ethene (C{sub 2}H{sub 4}), and propane (C{sub 3}H{sub 8}) are studied by adding these hydrocarbon gases into a cross flowing Xe plasma expansion. Branching ratios and relative reaction rates for the charge transfers of fast Xe{sup +} with each of the three hydrocarbon gases are measured under different rf powers of the inductively coupled Xe discharge. For CH{sub 4}/Xe system, we find that fast Xe{sup +} reacts readily with CH{sub 4} generating CH{sub 4}{sup +} and CH{sub 3}{sup +} in a ratio of 1:0.56, with an estimated rate coefficient of (2.3{+-}0.3)x10{sup -10} cm{sup 3}/s at 75 W rf power which slowly increases to (2.9{+-}0.3)x10{sup -10} cm{sup 3}/s at 250 W (error bars reflect only the uncertainties due to the unknown extent of the ion recombination that follows the charge transfer reaction). These observed charge transfer reactions are made possible by the kinetically excited Xe ions produced by free expansion of the plasma. For the C{sub 2}H{sub 4}/Xe system product ions C{sub 2}H{sub 4}{sup +} and C{sub 2}H{sub 2}{sup +} are observed, and for C{sub 3}H{sub 8}/Xe, C{sub 2}H{sub 4}{sup +} and C{sub 2}H{sub 5}{sup +} and minor product ions including C{sub 2}H{sub 2}{sup +} and C{sub 3}H{sub 7}{sup +} are observed.

Jiao, C. Q.; Garscadden, A.; Ganguly, B. N. [Innovative Scientific Solutions Inc., Dayton, Ohio 45440-3638 (United States); Air Force Research Laboratory, Wright-Patterson AFB, Ohio 45433-7251 (United States)

2007-04-15

18

Charge Transfer Nanocomposites: Advances in Organic Devices  

Microsoft Academic Search

Optically\\/electronically active blends of single walled carbon nanotubes (SWNTs) and conjugated polymers (MEH-PPV, PFO, PEDOT, P3OT, etc.), also known as charge transfer nanocomposites, exhibit a fascinating array of opto-electronic phenomena not found with the pure conducting polymers. Over the past two years, we have demonstrated that modifications to the conjugated polymer's transport properties and optical response can be interpreted directly

David Carroll

2004-01-01

19

Pattern classification using charge transfer devices  

NASA Technical Reports Server (NTRS)

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

1980-01-01

20

Charge transfer processes: the role of optimized molecular orbitals.  

PubMed

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

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

2014-08-01

21

Students' understanding of the transfer of charge between conductors  

NSDL National Science Digital Library

Investigates students' understanding of the transfer of charge between two charged conductors. Findings indicate that a considerable number of students from eighth grade to college in advanced physics courses were unable to predict the transfer of charge correctly from one conductor to another. Discusses implications for instruction.

Guruswamy, Chitra

2005-10-20

22

Charge transfer in positron-hydrogen collisions  

SciTech Connect

The nonperturbative approach developed recently by Tripathy and Rao for the study of charge transfer in proton-hydrogen collisions has been applied to the problem of positronium formation in positron-hydrogen collisions. The cross section for capture into the ground state has been calculated by partially taking into account the Coulomb distortions but neglecting the polarization effect of the target atom. The calculated cross section has a maximum at an incident energy of 10.2 eV, and as the incident positron energy increases it approaches the results of the first Born approximation (FBA) of Massey and Mohr. The calculated results for capture cross sections and differential scattering cross sections for various incident energies have been compared with those from the FBA and other theoretical calculations.

Satapathy, U.C.; Tripathy, D.N.; Rao, B.K.

1982-03-01

23

Luminescence of charge transfer sensitizers anchored to metal oxide nanoparticles  

Microsoft Academic Search

The photoluminescence (PL) properties of inorganic charge transfer sensitizers anchored to nanometer sized metal oxide particles are presented. The charge transfer sensitizers are inorganic coordination compounds such as ruthenium tribipyridine, Ru(bpy)2+3, which have long lived metal-to-ligand charge transfer (MLCT) excited states. The metal oxides are insulators or semiconductor materials in the form of powders, colloidal solutions, and porous nanocrystalline films.

Todd A. Heimer; Gerald J. Meyer

1996-01-01

24

Graphene\\/substrate charge transfer characterized by inverse photoelectron spectroscopy  

Microsoft Academic Search

Wave vector-resolved inverse photoelectron spectroscopy (IPES) measurements demonstrate that there is a large variation of interfacial charge transfer between graphene and various substrates. IPES measurements of CVD single layer graphene on BN(0001)\\/Ru(0001), Ru, Ni(poly), and Cu(poly) indicate a substrate-to-graphene charge transfer of approximately 0.07, 0.06, 0.03 e- per carbon atom respectively and a charge transfer of 0.02 e- from graphene

Lingmei Kong; Cameron Bjelkevig; Sneha Gaddam; Mi Zhou; Younghee Lee; Ganghee Han; Haekyung Jeong; Ning Wu; Zhengzheng Zhang; Jie Xiao; Peter Dowben; Jeffry Kelber

2011-01-01

25

Transfer ionization processes in charge-transfer reactions between slowly moving, highly charged ions and atoms  

NASA Astrophysics Data System (ADS)

We study charge-transfer reactions between slowly moving, highly charged ions and neutral atoms using an energy-loss spectroscopy method. In this study, Xeq+ (q = 4-11) ions (incident energy: 5.0 keV) are used as the incident ions and Ar as the target atom. Transfer-ionization (TI) processes are identified for one-electron capture reactions by application of a coincidence technique. We find that the TI process represents approximately 25% of the total one-electron capture reaction for q\\geqq 8 . The measured energy gains agree well with theoretical predictions for one-electron capture, but the agreement between the measured and theoretical energy gains is not as good for two-electron capture processes.

Nakajima, Yusuke; Koizumi, Tetsuo

2013-09-01

26

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

27

Charge transfer between a superconductor and a hopping insulator  

Microsoft Academic Search

We develop a theory of the low-temperature charge transfer between a superconductor and a hopping insulator. We show that the charge transfer is governed by the coherent two-electron -- Cooper pair conversion process, time reversal reflection, where electrons tunnel into superconductor from the localized states in the hopping insulator located near the interface, and calculate the corresponding interface resistance. This

V. I. Kozub; A. A. Zyuzin; Y. M. Galperin; V. Vinokur

2004-01-01

28

Charge-transfer transitions and optical spectra of chromites  

NASA Astrophysics Data System (ADS)

Specific features of charge-transfer states and charge-transfer transitions of the O2 p ? Cr3 d type in octahedral complexes (CrO6)9- have been considered in the cluster approximation. Reduced matrix elements of the electric-dipole moment operator on many-electron wave functions, which are the initial and final states for charge-transfer transitions, are calculated. The results are parameterized, and the relative intensities of different allowed charge-transfer transitions in the absence of mixing of different charge-transfer configurations with identical symmetry are calculated. This mixing is taken into account within the Tanabe-Sugano theory, and the true energies and intensities of many-electron charge-transfer transitions are obtained. The Coulomb interaction between 2 p electrons of O2- ligands and 3 d electrons of the central Cr3+ ion in (CrO6)9- cluster is considered. The influence of this interaction on the optical spectra is found to be insignificant. Simulation of the optical spectra of chromium oxides has shown the presence of a band of complex charge-transfer transitions composed of 33 lines with a total width of about 8 eV. The model spectrum is in adequate agreement with the experimental data, which indicates limited applicability of the widespread view that charge-transfer transition spectra have a simple structure.

Zenkov, A. V.

2013-04-01

29

Charge Transfer Nanocomposites: Advances in Organic Devices  

NASA Astrophysics Data System (ADS)

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

Carroll, David

2004-11-01

30

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.

Williams, Evan R.

2005-01-01

31

Charge Transfer to MEMS Pressure Sensors By Glow Discharge Plasmas  

Microsoft Academic Search

Electrical charging resulting in temporary performance degradation of automotive MEMS pressure sensors has been observed. A method of charge transfer from the outside of a statically charged hose, along the inside the hose, through the module port, to a sensor inside the module is proposed. Specifically, the existence of a glow discharge plasma through the hose, is analyzed with respect

T. M. Betzner

2006-01-01

32

Charge transfer reactions in nematic liquid crystals.  

National Technical Information Service (NTIS)

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 pyromellit...

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

1998-01-01

33

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

34

Marcus wins nobel prize in chemistry for electron transfer theory  

SciTech Connect

This article describes the work of Rudolf Marcus of Caltech leading to his receipt of the 1992 Nobel Prize in Chemistry [open quotes]for his contributions to the theory of electron transfer reactions in chemical systems.[close quotes] Applications of Marcus' theory include such diverse phenomena as photosynthesis, electrically conducting polymers, chemiluminescence, and corrosion. Historical aspects of his career are given. 10 refs., 1 fig.

Levi, B.G.

1993-01-01

35

Charge-transfer states in dense hydrogenCharge-transfer states in dense hydrogen  

NASA Astrophysics Data System (ADS)

THE electronic properties of hydrogen, from the gas phase to the solid state, are fundamental to our understanding of the chemical bond1. The strong covalent bond of diatomic hydrogen persists in low-density condensed phases, where the molecules interact very weakly through van der Waals forces2. At very high densities, molecular bonding has long been predicted to give way to a mon-atomic and presumably metallic lattice3. At intermediate densities, intermolecular interactions are expected to increase; however, the relative strengths of the intermolecular and intramolecular interactions, and their effect on physical and chemical properties, have received comparatively little attention theoretically. Recent diamond-anvil-cell studies have revealed a range of unexpected phenomena in solid hydrogen at these densities4. Here we show that marked changes in the infrared and Raman spectra of the intramolecular stretching modes (vibrons)5 with increasing pressure can be interpreted in a manner analogous to the behaviour of organic charge-transfer salts at ambient pressure, including those exhibiting pressure-induced neutral-to-ionic transitions6,7. Increased molecular overlap in dense hydrogen leads to symmetry breaking, which makes possible charge-transfer states between adjacent H2 molecules. The consequent changes in bond strength and in vibron frequencies are evident in the spectra. These findings present a new picture of dense hydrogen and highlight the advantages of a localized, 'chemical' description of the bonding.

Hemley, Russell J.; Soos, Zoltan G.; Hanfland, Michael; Mao, Ho-Kwang

1994-06-01

36

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

37

Non-adiabatic interactions in charge transfer collisions  

NASA Astrophysics Data System (ADS)

An analysis of the charge transfer mechanism in the collision of multiply charged ions with molecular and biomolecular targets is performed, considering the non-adiabatic interactions between the molecular states involved. Collisions of doubly charged C 2+ ions on small molecular targets, CO and OH, have been investigated, together with the analysis of charge transfer between C 4+ ions on uracil and halouracil biomolecular targets. The process is studied theoretically by means of ab-initio molecular calculations followed by a semi-classical treatment of the collision dynamics. The influence of rotational couplings is discussed with regard to the collision energy. Strong anisotropic and vibration effects are pointed out.

Bacchus-Montabonel, Marie-Christine; Rozsályi, Emese; Bene, Erika; Halász, Gábor J.; Vibók, Ágnes

2013-09-01

38

Improved Charge-Transfer Fluorescent Dyes  

NASA Technical Reports Server (NTRS)

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

Meador, Michael

2005-01-01

39

Non-reversible charge transfer and mass transfer: Methodology for experimental characterization without theoretical models  

Microsoft Academic Search

An extension of the methodology based on the concept of mass transfer operator to non-reversible (i.e. quasi-reversible or irreversible) charge transfer is proposed. We show how it is possible to characterize the charge and mass transfer steps, without postulating a modelling equation to describe the behaviour (except a very general assumption of first-order kinetics). The concept of mass transfer operator,

E. Vieil; F. Miomandre

1995-01-01

40

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

41

Induced-charge errors in charge-transfer measurement: Brush discharges between charged, insulating discs and earthed, conductive spheres  

Microsoft Academic Search

Charge-transfer measurements made with fast-response, unshielded probes will, in principle, underestimate charge-transfers because of induced-charge errors. It is, however, difficult to know when the degree of underestimation is significant or to allow for it quantitatively because information on the magnitude of these errors is fragmented. Consequently, when measurements are done for electrostatic hazard assessment, unsafe equipment could wrongly be classified

Harold L. Walmsley

2010-01-01

42

Charge-Transfer Complexes of Purines and Pyrimidines.  

National Technical Information Service (NTIS)

The spectra of 20 purines and pyrimidines with chloranil, bromanil, and p-benzoquinone in dimethyl sulphoxide were studied. Most of the systems exhibited absorption bands which were concluded to be charge transfer in nature. The ionization energies of the...

A. Fulton L. E. Lyons

1968-01-01

43

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

44

Charge Transfer between a Superconductor and a Hopping Insulator  

Microsoft Academic Search

We develop a theory of the low-temperature charge transfer between a superconductor and a hopping insulator. We show that the charge transfer is governed by the coherent two-electron Cooper pair conversion process time-reversal reflection, where electrons tunnel into a superconductor from the localized states in the hopping insulator located near the interface, and calculate the corresponding interface resistance. A specific

Yuri Galperin; Veniamin Kozub; Alexander Zyuzin; Valerii Vinokur

2006-01-01

45

Photon-induced charge transfer and surface emission  

Microsoft Academic Search

Experimental measurements have been made of photon-induced charge transfer between plane-parallel electrodes. X-rays from a pulsed X-ray source were directed at near-normal incidence onto plane-parallel electrodes, and the current which flowed between the electrodes during the X-ray pulse was measured. Quantities obtained include bulk charge transfer in several dielectric materials; forward and reverse electron emission from Al, Cu, and Au

R. H. Barlett; G. A. Fulk; W. W. Hofer; D. J. Meeker; R. S. Lee; R. C. Weingart

1974-01-01

46

D/sup -/ production by charge transfer in metal vapors  

SciTech Connect

Fast D/sup -/ ions can be produced from D/sup +/ by multiple charge-transfer collisions in a metal-vapor target. Experimental cross sections and thick-target D/sup -/ yields are presented and discussed. The high D/sup -/ yield experimentally observed from charge transfer in cesium vapor is consistent with recent low-energy cross-section calculations and measurements.

Schlachter, A.S.

1980-10-01

47

Resonant inelastic charge transfer in short alanine bridges  

NASA Astrophysics Data System (ADS)

We investigate theoretically the effect of atomic vibrations on the electron tunneling in polyalanine bridges. The inelastic-scattering processes in the bridge are included using a nonequilibrium Green’s function formalism with the density-functional Hamiltonian. With this method we analyze the inelastic charge transfer in polyalanine. We find that electron tunneling across alanine exhibits a resonant behavior and that atomic vibrations substantially change the charge-transfer rate across the bridge by providing additional scattering channels.

Sergueev, Nikolai; Demkov, Alexander A.

2010-01-01

48

Charge transfer reactions in nematic liquid crystals  

NASA Astrophysics Data System (ADS)

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'-(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. We show that excited state charge separation is non-adiabatic, and obtain the unexpected result that charge separation is dominated by molecular reorientation of 5CB perpendicular to the director within the liquid crystal microdomains relative to the orientation of PNI+-PI-. We also report the result of time resolved electron paramagnetic resonance 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 increase from the low temperature crystalline phase, through the soft glass phase, to the nematic phase of the liquid crystal.

Wiederrecht, Gary P.; Wasielewski, Michael R.; Galili, Tamar; Levanon, Haim

1998-10-01

49

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

50

Charge transfer excitations in cofacial fullerene-porphyrin complexes  

NASA Astrophysics Data System (ADS)

Porphyrin and fullerene donor-acceptor complexes have been extensively studied for their photo-induced charge transfer characteristics. We present the electronic structure of ground states and a few charge transfer excited states of four cofacial porphyrin-fullerene molecular constructs studied using density functional theory at the all-electron level using large polarized basis sets. The donors are base and Zn-tetraphenyl porphyrins and the acceptor molecules are C60 and C70. The complexes reported here are non-bonded with a face-to-face distance between the porphyrin and the fullerene of 2.7 to 3.0 A?. The energies of the low lying excited states including charge transfer states calculated using our recent excited state method are in good agreement with available experimental values. We find that replacing C60 by C70 in a given dyad may increase the lowest charge transfer excitation energy by about 0.27 eV. Variation of donor in these complexes has marginal effect on the lowest charge transfer excitation energy. The interfacial dipole moments and lowest charge transfer states are studied as a function of face-to-face distance.

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

2012-08-01

51

Charge transfer energies of tetraphenyl-porphyrin-fullerene dyads  

NASA Astrophysics Data System (ADS)

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

Zope, Rajendra; Olguin, Marco; Baruah, Tunna

2011-03-01

52

Super-iron nanoparticles with facile cathodic charge transfer  

Microsoft Academic Search

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

Maryam Farmand; Dianlu Jiang; Baohui Wang; Susanta Ghosh; D. E. Ramaker; Stuart Licht

2011-01-01

53

Charge prediction machine: tool for inferring precursor charge states of electron transfer dissociation tandem mass spectra.  

PubMed

Electron transfer dissociation (ETD) can dissociate highly charged ions. Efficient analysis of ions dissociated with ETD requires accurate determination of charge states for calculation of molecular weight. We created an algorithm to assign the charge state of ions often used for ETD. The program, Charge Prediction Machine (CPM), uses Bayesian decision theory to account for different charge reduction processes encountered in ETD and can also handle multiplex spectra. CPM correctly assigned charge states to 98% of the 13,097 MS2 spectra from a combined data set of four experiments. In a comparison between CPM and a competing program, Charger (ThermoFisher), CPM produced half the mistakes. PMID:19203245

Carvalho, Paulo C; Cociorva, Daniel; Wong, Catherine C L; Carvalho, Maria da Gloria da C; Barbosa, Valmir C; Yates, John R

2009-03-01

54

Resolving vibration in H++H2 charge transfer collisions  

NASA Astrophysics Data System (ADS)

We measure the vibrational distribution of Hj ions issued from charge transfer in H+ + H2 collisions to probe the details of the electron transfer mechanism from low to high impact energies. The experiments are accompanied by theoretical calculations. This joint experimental-theoretical study allows us to elicit the adequacy and accuracy of widely used assumptions in the description of molecular collisions.

Urbain, X.; Andrianarijaona, V. M.; de Ruette, N.; Errea, L. F.; Méndez, L.; Rabadán, I.; Fernández, L.; Pons, B.

2014-04-01

55

XAFS study of charge transfer in intercalation compounds  

Microsoft Academic Search

An intercalation process is a reversible topotactic reaction in which a guest species occupies empty sites in a solid structure. A charge transfer is always observed between the guest and the host. An accurate knowledge of this electronic exchange, i.e. how many electrons are transferred and on which electronic level, can only be obtained from precise electronic band structure calculations.

Guy Ouvrard; Ziyu Wu

1997-01-01

56

Theoretical treatment of charge transfer processes of relevance to astrophysics  

SciTech Connect

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

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

1997-12-01

57

Charge transfer reactions in multiply charged ion-atom collisions. [in interstellar clouds  

NASA Technical Reports Server (NTRS)

Charge-transfer reactions in collisions between highly charged ions and neutral atoms of hydrogen and/or helium may be rapid at thermal energies. If these reactions are rapid, they will suppress highly charged ions in H I regions and guarantee that the observed absorption features from such ions cannot originate in the interstellar gas. A discussion of such charge-transfer reactions is presented and compared with the available experimental data. The possible implications of these reactions for observations of the interstellar medium, H II regions, and planetary nebulae are outlined.

Steigman, G.

1975-01-01

58

Atomic and Molecular Charge Transfer Processes.  

National Technical Information Service (NTIS)

Differential scattering techniques have been used to study the resonant charge exchange in Ar2(+) and Xe2(+). Particular emphasis was given to understanding the scattering interference patterns that result when spin-orbit (J,J) coupling is dominant. In th...

D. C. Lorents G. M. Conklin P. R. Jones R. E. Olson

1973-01-01

59

Frenkel versus charge-transfer exciton dispersion in molecular crystals  

NASA Astrophysics Data System (ADS)

By solving the many-body Bethe-Salpeter equation at finite momentum transfer, we characterize the exciton dispersion in two prototypical molecular crystals, picene and pentacene, in which localized Frenkel excitons compete with delocalized charge-transfer excitons. We explain the exciton dispersion on the basis of the interplay between electron and hole hopping and electron-hole exchange interaction, unraveling a simple microscopic description to distinguish Frenkel and charge-transfer excitons. This analysis is general and can be applied to other systems in which the electron wave functions are strongly localized, as in strongly correlated insulators.

Cudazzo, Pierluigi; Gatti, Matteo; Rubio, Angel; Sottile, Francesco

2013-11-01

60

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

61

IR spectroscopic studies of charge transfer in organic semiconductors  

NASA Astrophysics Data System (ADS)

Charge transfer (CT) mechanisms are crucial for device performance in organic electronics, but they are still not understood on a fundamental level. Here we want to show that in situ IR spectroscopy is very well suited to investigate CT effects in organic semiconductors in a qualitative and quantitative way. We study the ambipolar transport material 4,4´-bis(N-carbazolyl)-1,1´-biphenyl (CBP) as matrix and cesium carbonate (Cs2CO3) as n-dopant. To achieve doped layers, both materials were evaporated simultaneously. The system is one of the rare ones for n-doping of organic layers. In the spectra of the doped layers, additional absorption bands appear in the mid IR range. These can be assigned to the negatively charged matrix molecules that indicate electron transfer. The charged molecules exhibit these different absorption bands, as the charge transfer leads to a change in bond length and bond strength of the molecules. Our results very well agree with density functional theory calculations of the vibrational spectra of both, charged and non-charged molecules. By fitting the spectra of the doped layers as a superposition of the vibrational oscillators of neutral and charged species, we were able to quantify the amount of charged matrix molecules and to determine the doping efficiency of the investigated systems. For CBP n-doped with Cs2CO3 a hindrance of the CT due to air exposure could be observed.

Beck, Sebastian; Gerbert, David; Krekeler, Christian; Glaser, Tobias; Pucci, Annemarie

2014-05-01

62

Correlation between stick-slip frictional sliding and charge transfer  

NASA Astrophysics Data System (ADS)

A decade ago, Budakian and Putterman [Phys. Rev. Lett. 85, 1000 (2000)]10.1103/PhysRevLett.85.1000 ascribed friction to the formation of bonds arising from contact charging when a gold tip of a surface force apparatus was dragged on polymethylmethacrylate surface. We propose a stick-slip model that captures the observed correlation between stick-slip events and charge transfer, and the lack of dependence of the scale factor connecting the force jumps and charge transfer on normal load. Here, stick-slip dynamics arises as a competition between the viscoelastic and plastic deformation time scales and that due to the pull speed with contact charging playing a minor role. Our model provides an alternate basis for explaining most experimental results without ascribing friction to contact charging.

Ananthakrishna, G.; Kumar, Jagadish

2010-08-01

63

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

64

Charge transfer in collisions of doubly charged ions of iron and nickel with hydrogen atoms  

Microsoft Academic Search

The Landau-Zener approximation is used to compute the charge-transfer recombination rate coefficients of Fe(2+) and Ni(2+) in hydrogen at thermal energies. The energy separations of the adiabatic potential-energy curves of the quasi-molecules FeH(2+) and NiH(2+) are obtained from one-electron calculations. The rate coefficients are of the order of 10 to the -9th cu cm\\/s or greater. Charge transfer of Fe(2+)

David A. Neufeld; A. Dalgarno

1987-01-01

65

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

66

Charge transfer in helium-rich supernova plasma  

NASA Technical Reports Server (NTRS)

Charge transfer rate coefficients are estimated using Landau-Zener and modified Demkov approximations. The coefficients, augmented by those available from the literature, are used in statistical equilibrium equations describing the state of helium-rich supernova plasma. Such a plasma may describe both Type Ib and Type Ic supernova ejecta. The hypothesis that extensive mixing of metals with helium in Type Ic supernovae may provide a catalyst for rapid charge transfer that weakens the helium line emission by altering the excitation balance is tested. It is shown that charge transfer as a mechanism for suppressing helium line emission is ineffective unless the metal abundance is comparable to or larger than the helium abundance. This result supports an earlier conclusion that Type Ic supernovae must be helium poor relative to Type Ib events.

Swartz, Douglas A.

1994-01-01

67

Charge-transfer water potential for solvated protein dynamics  

NASA Astrophysics Data System (ADS)

Water plays a critical role in simulations of complex structure-function relationships such as the mechanochemistry of molecular motor proteins, wherein solvating water molecules interact with divalent cations such as Mg^+2, salt bridges, and polar or charged amino acids. Existing fixed-charge and fluctuating charge water models are inadequate in these environments, since they do not support reactive charge transfer with proper long-range dissociation behavior. The charge-transfer embedded atom method (CT-EAM) potential of Valone and Atlas was developed to address these challenges. It includes charge-polarized and ionic embedding terms that describe many-body atomistic interactions as a statistical ensemble of integer-charge excitations; background embedding densities are functions of local pseudoatom electron density distributions that integrate to non-integer charges and evolve dynamically under chemical potential equalization. Here we report first results from simulations of water using the CT-EAM potential of [1] and compare with characteristic properties of the liquid as determined via conventional force fields. [1] K. Muralidharan, S. M. Valone, and S.R. Atlas. arXiv:cond-mat/0705.0857v1, submitted.

Janardhanam, Vijay; Amo-Kwao, Godwin; Atlas, Susan R.

2010-03-01

68

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

69

Abinitio study of charge-transfer dynamics in collisions of C2+ ions with hydrogen chloride  

NASA Astrophysics Data System (ADS)

Ab initio quantum chemistry molecular calculations followed by a semiclassical dynamical treatment in the keV collision energy range have been developed for the study of the charge-transfer process in collisions of C2+ ions with hydrogen chloride. The mechanism has been investigated in detail in connection with avoided crossings between states involved in the reaction. A simple mechanism driven by a strong nonadiabatic coupling matrix element has been pointed out for this process. A comparative analysis with the halogen fluoride target corresponding to a similar electronic configuration shows a quite different charge-transfer mechanism leading to a very different behavior of the cross sections. Such behavior may be correlated to specific nonadiabatic interactions observed in these collision systems.

Rozsályi, E.; Bene, E.; Halász, G. J.; Vibók, Á.; Bacchus-Montabonel, M. C.

2011-05-01

70

Multiple-charge transfer and trapping in DNA dimers  

NASA Astrophysics Data System (ADS)

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

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

2010-11-01

71

Quasi-resonant K-K charge transfer  

Microsoft Academic Search

The impact parameter dependence, P(b), of single and double K to K charge transfer have been deduced from the coincidences between K-Auger electrons and scattered particles for F\\/sup 9 +\\/ + Ne and F\\/sup 9 +\\/ + Ne collisions at 10 MeV and 4.4 MeV. The 4.4 MeV single K-K transfer probability exhibits oscillations with b. The P(b) for delta-electron

S. Hagmann; C. L. Cocke; P. Richard; A. Skutlartz; S. Kelbch; H. Schmidt-Boecking; R. Schuch

1983-01-01

72

Filter functions for reversible charge transfer reactions in pulse techniques  

Microsoft Academic Search

A filter function is a mode of pulse voltammetry that removes completely the current response for a reversible charge transfer reaction for all values of potential or gives a constant response (?0) for all values of E. These modes will be designated as filter functions of the first and second class, respectively. With both kinds of functions it is a

Jesús Gálvez

2002-01-01

73

Electronic Structure, Charge Transfer Excitations and High Temperature Superconductivity.  

National Technical Information Service (NTIS)

High precision local density electronic band structure results (for YBa sub 2 Cu sub 3 O sub 7 , YBa sub 2 Cu sub 3 O sub 6 and GdBa sub 2 Cu sub 3 O sub 7 ) lead to the possibly important role of charge transfer excitations as the mechanism of high T/sub...

A. J. Freeman J. Yu S. Massidda D. D. Koelling

1987-01-01

74

Classical Trajectory Monte Carlo Simulations for Charge Transfer Processes  

Microsoft Academic Search

I have calculated electron transfer cross sections for slow, highly charged ion-atomic hydrogen collisions by using the classical trajectory Monte Carlo method. Similar calculations for alkaline metal targets are also carried out using a simple one-electron model. I compare the results to predictions by the extended classical over barrier model and available experimental data. The calculated cross sections are in

YAMADA Ichihiro

2004-01-01

75

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

76

Space-charge transfer in hybrid inorganic-organic systems.  

PubMed

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

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

2013-11-27

77

Infrared Spectroscopy of Charge Transfer Complexes of Purines and Pyrimidines  

NASA Astrophysics Data System (ADS)

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

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

2011-10-01

78

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

79

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

80

Multistep hopping and extracellular charge transfer in microbial redox chains.  

PubMed

Dissimilatory metal-reducing bacteria are microorganisms that gain energy by transferring respiratory electrons to extracellular solid-phase electron acceptors. In addition to its importance for physiology and natural environmental processes, this form of metabolism is being investigated for energy conversion and fuel production in bioelectrochemical systems, where microbes are used as biocatalysts at electrodes. One proposed strategy to accomplish this extracellular charge transfer involves forming a conductive pathway to electrodes by incorporating redox components on outer cell membranes and along extracellular appendages known as microbial nanowires within biofilms. To describe extracellular charge transfer in microbial redox chains, we employed a model based on incoherent hopping between sites in the chain and an interfacial treatment of electrochemical interactions with the surrounding electrodes. Based on this model, we calculated the current-voltage (I-V) characteristics and found the results to be in good agreement with I-V measurements across and along individual microbial nanowires produced by the bacterium Shewanella oneidensis MR-1. Based on our analysis, we propose that multistep hopping in redox chains constitutes a viable strategy for extracellular charge transfer in microbial biofilms. PMID:22797729

Pirbadian, Sahand; El-Naggar, Mohamed Y

2012-10-28

81

Proteins as specific polar media for charge transfer processes  

NASA Astrophysics Data System (ADS)

A great many of biological processes involve the transfer of charged particles: electrons and protons. The electrostatic interaction of a moving charge with its surroundings, primarily with protein, is tbe major factor determining the thermodynamics and kinetics involved. This paper treats protein as a pre-organized highly-polar low-dielectric medium that posseses a pre-existent intraprotein electric field, a low reorganization energy, and a wide range of dielectric relaxation times. These specific protein features are the factors controlling the catalytic acceleration of biochemical reactions. Methods for quantitatively calculating the energetics of a number of typical processes are considered, and examples of their application are given.

Krishtalik, Lev I.

2012-12-01

82

Theoretical study of charge transfer dynamics in collisions of C6+ carbon ions with pyrimidine nucleobases  

NASA Astrophysics Data System (ADS)

A theoretical approach of the charge transfer dynamics induced by collision of C6+ ions with biological targets has been performed in a wide collision energy range by means of ab-initio quantum chemistry molecular methods. The process has been investigated for the target series thymine, uracil and 5-halouracil corresponding to similar molecules with different substituent on carbon C5. Such a study may be related to hadrontherapy treatments by C6+carbon ions and may provide, in particular, information on the radio-sensitivity of the different bases with regard to ion-induced radiation damage. The results have been compared to a previous analysis concerning the collision of C4+ carbon ions with the same biomolecular targets and significant charge effects have been pointed out.

Bacchus-Montabonel, M. C.

2012-07-01

83

Photochemistry and charge transfer chemistry of the platinum group elements  

SciTech Connect

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

Eisenberg, R.

1992-12-01

84

Charge transfer and charge broadening of GEM structures in high magnetic fields  

Microsoft Academic Search

We report on the measurements of charge transfer in Gas Electron Multipliers (GEM) structures in high magnetic fields. These were performed in the framework of the R&D work for a Time Projection Chamber at a future Linear Collider. A small test chamber has been installed in the aperture of a superconducting magnet with the GEM structures mounted perpendicular to the

M. Killenberg; S. Lotze; J. Mnich; A. Münnich; S. Roth; F. Sefkow; M. Tonutti; M. Weber; P. Wienemann

2004-01-01

85

CHEMISTRY NOBEL: Getting a Charge Out of Plastics.  

PubMed

This year's Nobel Prize in chemistry was awarded to a trio of researchers--Alan Heeger of the University of California, Santa Barbara; Alan MacDiarmid of the University of Pennsylvania in Philadelphia; and Hideki Shirakawa of the University of Tsukuba in Japan--for discovering that plastics can be made electrically conductive. The discovery paved the way for revolutionary applications such as full-color displays for cellular phones and plastic electronics for computerized merchandise. PMID:17844278

Service, R F

2000-10-20

86

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.

2012-01-01

87

Charge-transfer complexes of phenylephrine with nitrobenzene derivatives  

NASA Astrophysics Data System (ADS)

The molecular charge-transfer complexes of phenylephrine with picric acid and m-dinitrobenzene have been studied and investigated by IR, 1H NMR electronic spectra in organic solvents and buffer solutions, respectively. Simple and selective methods are proposed for the determination of phenylephrine hydrochloride in bulk form and in tablets. The two methods are based on the formation of charge-transfer complexes between drug base as a n-donor (D) and picric acid, m-dinitrobenzene as ?-acceptor (A). The products exhibit absorption maxima at 497 and 560 nm in acetonitrile for picric acid and m-dinitrobenzene, respectively. The coloured product exhibits an absorption maximum at 650 nm in dioxane. The sensitive kinetic methods for the determination phynylephrine hydrochloride are described. The method is based upon a kinetic investigation of the oxidation reaction of the drug with alkaline potassium permanganate at room temperature for a fixed time at 20 min.

El-Mossalamy, E. H.

2004-04-01

88

Fully differential cross section for four body charge transfer process  

NASA Astrophysics Data System (ADS)

Recently experimental fully differential cross sections (FDCS) have been reported for double capture in proton helium collisions which disagree with existing theoretical calculations by two orders of magnitude. We introduce here a theoretical model for charge transfer processes which is fully quantum mechanical and takes all post collision interactions (PCI) between the particles into account exactly. The results of this model are in much better agreement with experimental data.

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

2012-11-01

89

Charge Transfer in Collisions of S^4+ with He  

Microsoft Academic Search

Charge transfer processes due to collisions of ground state S^4+ ions with atomic helium were investigated for energies between 0.1 meV\\/u and 10 MeV\\/u. Total and state-selective cross sections and rate coefficients were obtained utilizing the quantum-mechanical molecular-orbital close-coupling (MOCC), atomic-orbital close-coupling, classical trajectory Monte Carlo (CTMC), and continuum distorted wave methods. The MOCC calculations utilized ab initio adiabatic potentials

J. G. Wang; P. C. Stancil; A. R. Turner; D. L. Cooper; D. R. Schultz; M. J. Rakovic; W. Fritsch; B. Zygelman

2001-01-01

90

Vibrationally resolved charge transfer of O3+ with molecular hydrogen  

Microsoft Academic Search

Charge transfer due to collisions of ground state O3+ (2 s2 2p 2 Po ) ions with molecular hydrogen are investigated using the quantum-mechanical molecular-orbital (QMO) coupled-channel method. The QMO calculations utilize ab initio adiabatic potentials and nonadiabatic radial coupling matrix elements obtained with the spin-coupled valence-bond approach for a representative range of orientation angles and diatom internuclear separations. Vibrationally

J. G. Wang; P. C. Stancil; A. R. Turner; D. L. Cooper

2004-01-01

91

Charge Transfer in Collisions of S^4+ with H  

Microsoft Academic Search

Charge transfer processes due to collisions of ground state S^4+ ions with atomic hydrogen were investigated for energies between 1 meV\\/u and 10 MeV\\/u using the quantum-mechanical molecular-orbital close-coupling (MOCC), atomic-orbital close-coupling, classical trajectory Monte Carlo (CTMC), and continuum distorted wave methods. The MOCC calculations utilized ab initio adiabatic potentials and nonadiabatic radial coupling matrix elements obtained with the spin-coupled

P. C. Stancil; A. R. Turner; D. L. Cooper; D. R. Schultz; M. J. Rakovic; W. Fritsch; B. Zygelman

2001-01-01

92

Charge-transfer excitations in the cuprate superconductors  

SciTech Connect

First-principles calculations of the dielectric matrix of the key structural element of the copper-oxide superconductors show a weakly damped resonance at 3.5 eV which contains most of the oscillator strength in charge-transfer excitations. Such excitations have been proposed as a mediating boson for superconductive pairing. Although this mode is a well-developed and robust excitation, we find its energy to be too large to give high superconducting transition temperatures.

Dadachanji, Z.; Godby, R.W.; Needs, R.J. [Cavendish Laboratory, University of Cambridge, Cambridge CB3 0HE (United Kingdom)] [Cavendish Laboratory, University of Cambridge, Cambridge CB3 0HE (United Kingdom); Littlewood, P.B. [AT& T Bell Laboratories, Murray Hill, New Jersey 07974 (United States)] [AT& T Bell Laboratories, Murray Hill, New Jersey 07974 (United States)

1995-12-01

93

Energy and Charge Transfer in Hyperthermal Ion - Scattering  

Microsoft Academic Search

I have investigated the energy and charge transfer between hyperthermal (10 eV to 500 eV) alkali ions and copper surfaces, using a combination of theoretical and experimental techniques. Experiments were performed with a monochromatic, well-collimated ion beam incident on a single crystal copper surface maintained in an ultra-high -vacuum scattering chamber. Energy- and angle-resolved scattering spectra were taken for K^+

David Martin Goodstein

1990-01-01

94

Electron transfer and decay processes of highly charged iodine ions  

Microsoft Academic Search

In the present experimental work we have investigated multi-electron transfer processes in Iq+ (q = 10, 15, 20 and 25) + Ne, Ar, Kr and Xe collisions at 1.5q keV energy. Using the coincidence technique between charge-selected projectile and recoil ions, the branching ratios between Auger and radiative decay channels have been measured in decay processes of multiply excited states

Hiroyuki A. Sakaue; Atsunori Danjo; Kazumoto Hosaka; Daiji Kato; Masahiro Kimura; Atsushi Matsumoto; Nobuyuki Nakamura; Shunsuke Ohtani; Makoto Sakurai; Hiroyuki Tawara; Ichihiro Yamada; Masuhiro Yoshino

2004-01-01

95

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

PubMed

Molybdenum disulfide (MoS2), a layered transition-metal dichalcogenide, has been of special importance to the research community of geochemistry, materials and environmental chemistry, and geotechnical engineering. Understanding the oxidation behavior and charge-transfer mechanisms in MoS2 is important to gain better insight into the degradation of this mineral in the environment. In addition, understanding the insertion of metals into molybdenite and evaluation of charge-transfer mechanism and dynamics is important to utilize these minerals in technological applications. Furthermore, a detailed investigation of thermal oxidation behavior and metal-insertion will provide a basis to further explore and model the mechanism of adsorption of metal ions onto geomedia.The present work was performed to understand thermal oxidation and metal-insertion processes of molybdenite surfaces. The analysis was performed using atomic force microscopy (AFM), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Rutherford backscattering spectrometry (RBS), and nuclear reaction analysis (NRA).Structural studies using SEM and TEM indicate the local-disordering of the structure as a result of charge-transfer process between the inserted lithium and the molybdenite layer. Selected area electron diffraction measurements indicate the large variations in the diffusivity of lithium confirming that the charge-transfer is different along and perpendicular to the layers in molybdenite. Thermal heating of molybenite surface in air at 400 degrees C induces surface oxidation, which is slow during the first hour of heating and then increases significantly. The SEM results indicate that the crystals formed on the molybdenite surface as a result of thermal oxidation exhibit regular thin-elongated shape. The average size and density of the crystals on the surface is dependent on the time of annealing; smaller size and high density during the first one-hour and significant increase in size associated with a decrease in density with further annealing. PMID:18534025

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

2008-01-01

96

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

PubMed Central

Molybdenum disulfide (MoS2), a layered transition-metal dichalcogenide, has been of special importance to the research community of geochemistry, materials and environmental chemistry, and geotechnical engineering. Understanding the oxidation behavior and charge-transfer mechanisms in MoS2 is important to gain better insight into the degradation of this mineral in the environment. In addition, understanding the insertion of metals into molybdenite and evaluation of charge-transfer mechanism and dynamics is important to utilize these minerals in technological applications. Furthermore, a detailed investigation of thermal oxidation behavior and metal-insertion will provide a basis to further explore and model the mechanism of adsorption of metal ions onto geomedia. The present work was performed to understand thermal oxidation and metal-insertion processes of molybdenite surfaces. The analysis was performed using atomic force microscopy (AFM), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Rutherford backscattering spectrometry (RBS), and nuclear reaction analysis (NRA). Structural studies using SEM and TEM indicate the local-disordering of the structure as a result of charge-transfer process between the inserted lithium and the molybdenite layer. Selected area electron diffraction measurements indicate the large variations in the diffusivity of lithium confirming that the charge-transfer is different along and perpendicular to the layers in molybdenite. Thermal heating of molybenite surface in air at 400°C induces surface oxidation, which is slow during the first hour of heating and then increases significantly. The SEM results indicate that the crystals formed on the molybdenite surface as a result of thermal oxidation exhibit regular thin-elongated shape. The average size and density of the crystals on the surface is dependent on the time of annealing; smaller size and high density during the first one-hour and significant increase in size associated with a decrease in density with further annealing.

Ramana, CV; Becker, U; Shutthanandan, V; Julien, CM

2008-01-01

97

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

98

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

99

Energy and charge transfer in ionized argon coated water clusters.  

PubMed

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

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

2013-12-01

100

Importance of post collision interactions for charge transfer process  

NASA Astrophysics Data System (ADS)

Recently experimental fully differential cross sections (FDCS) have been reported for double capture, single capture and transfer excitation in proton helium collisions. In case of double capture, the proton captures both of the electrons from helium and leaves the collision as a H- ion. For single capture, the proton captures one electron from helium and leaves the other electron in the ground state. Transfer excitation is similar to single capture except the target is excited to an excited state. Recently experiments performed for proton energies ranging from 25keV to 300keV. We introduce here a theoretical model for charge transfer processes which is fully quantum mechanical and takes all post collision interactions (PCI) between the particles into account exactly. Numerically, this requires a full nine-dimensional integral which is computationally expensive. The theoretical results will be compared with absolute experimental measurements.

Chowdhury, Uttam; Harris, Allison; Peacher, Jerry; Madison, Don

2012-06-01

101

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

Microsoft Academic Search

Electrokinetic phenomenon is an important factor in pressure-driven membrane water filtration process. Zeta potential is a measurable and reliable parameter to characterize the charge property of membranes. This study investigated the effects of solution physico-chemistry on the zeta potential of nanofiltration membranes. A comprehensive semi-empirical mathematical model based on the Poisson–Boltzmann equation, Membrane Surface Charge model, was established. The correlations

Joo-Hwa Tay; Jianlin Liu; Darren Delai Sun

2002-01-01

102

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

103

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

104

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

105

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

106

The Nature of the Intramolecular Charge Transfer State in Peridinin  

PubMed Central

Experimental and theoretical evidence is presented that supports the theory that the intramolecular charge transfer (ICT) state of peridinin is an evolved state formed via excited-state bond-order reversal and solvent reorganization in polar media. The ICT state evolves in <100 fs and is characterized by a large dipole moment (?35 D). The charge transfer character involves a shift of electron density within the polyene chain, and it does not involve participation of molecular orbitals localized in either of the ?-rings. Charge is moved from the allenic side of the polyene into the furanic ring region and is accompanied by bond-order reversal in the central portion of the polyene chain. The electronic properties of the ICT state are generated via mixing of the “11Bu+” ionic state and the lowest-lying “21Ag–” covalent state. The resulting ICT state is primarily 1Bu+-like in character and exhibits not only a large oscillator strength but an unusually large doubly excited character. In most solvents, two populations exist in equilibrium, one with a lowest-lying ICT ionic state and a second with a lowest-lying “21Ag–” covalent state. The two populations are separated by a small barrier associated with solvent relaxation and cavity formation.

Wagner, Nicole L.; Greco, Jordan A.; Enriquez, Miriam M.; Frank, Harry A.; Birge, Robert R.

2013-01-01

107

Raman scattering studies of organic semiconducting charge-transfer compounds  

NASA Astrophysics Data System (ADS)

Organic semiconductors offer the possibility of devices with greater mechanical flexibility and lower production costs compared to existing materials. Reports of carrier mobilities in monomolecular organic semiconductors in the 10-50 cm^2/V-s range and success in fabricating electronic devices from organic materials has increased the interest in their properties for electronic applications. However, the range of properties displayed by the monomolecular crystals is rather narrow. Charge-transfer compounds composed of two different organic molecules in which one acts as a donor and the other as an acceptor may represent the next generation of organic semiconductors. Control of their properties by modification of the molecules or changes in stoichiometry and crystalline structure makes them particularly attractive for a wide range of applications provided that the relationship between the structure and constituents of the compounds and their physical properties can be elucidated. Raman scattering studies of single crystals of two representative charge-transfer compounds, perylene-TCNQ and anthracene-TCNQ, will be presented. Theoretical calculations suggest that these materials have the potential for ambipolar charge transport, and so intermolecular interactions in these compounds are of particular interest.

McNeil, Laurie; Kloc, Christian

2011-03-01

108

Charge-transfer doping by fullerenes on oxidized Si surfaces  

SciTech Connect

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

Tada, Tetsuya; Uchida, Noriyuki; Kanayama, Toshihiko; Hiura, Hidefumi; Kimoto, Kenji [Advanced Semiconductor Research Center, National Institute of Advanced Industrial Science and Technology (AIST), 1-1-1 Higashi, Tsukuba, Ibaraki 305-8562 (Japan); Fundamental and Environmental Research Laboratories, NEC Corporation, 34 Miyukigaoka, Tsukuba, Ibaraki 305-8501 (Japan); MIRAI, Association of Super-Advanced Electronics Technologies (ASET), AIST, 1-1-1 Higashi, Tsukuba, Ibaraki 305-8562 (Japan)

2007-10-01

109

Localized state and charge transfer in nitrogen-doped graphene  

NASA Astrophysics Data System (ADS)

Nitrogen-doped epitaxial graphene grown on SiC(0001¯) was prepared by exposing the surface to an atomic nitrogen flux. Using scanning tunneling microscopy and scanning tunneling spectroscopy (STS), supported by density functional theory (DFT) calculations, the simple substitution of carbon with nitrogen atoms has been identified as the most common doping configuration. High-resolution images reveal a reduction of local charge density on top of the nitrogen atoms, indicating a charge transfer to the neighboring carbon atoms. Local STS spectra clearly evidenced the energy levels associated with the chemical doping by nitrogen, localized in the conduction band. Various other nitrogen-related defects have been observed. The bias dependence of their topographic signatures demonstrates the presence of structural configurations more complex than substitution as well as hole doping.

Joucken, Frédéric; Tison, Yann; Lagoute, Jérôme; Dumont, Jacques; Cabosart, Damien; Zheng, Bing; Repain, Vincent; Chacon, Cyril; Girard, Yann; Botello-Méndez, Andrés Rafael; Rousset, Sylvie; Sporken, Robert; Charlier, Jean-Christophe; Henrard, Luc

2012-04-01

110

Charge transfer of slow highly charged xenon ions in collisions with magnesium atoms  

NASA Astrophysics Data System (ADS)

We report an experimental study of the charge-transfer process in collisions of Xeq+ ions (16?q?20) with magnesium atoms at an energy of 5.5q keV. With charge-selective and time-coincidence techniques, we separated the pure capture and capture accompanied by transfer-ionization processes. The experimental data indicate that the magnesium target is around two times more likely to lose two electrons than one in the collision. This finding is very different compared to the calculation based on the extended classic over-the-barrier model. The Xeq+-Mg collision also behaves very differently from “traditional” collisions between highly charged ions and noble gases. We suggest a one-step dielectronic mechanism for the capture process. The data also show that autoionization dominates the relaxation process after the capture, and fluctuation of the autoionization fraction versus the projectile charge state indicates that for the relaxation processes, the projectile core structure plays a more important role than the detailed characteristics of the projectile states where the target electrons are initially captured.

Chen, W.; Vorobyev, G.; Guo, D.; Hillenbrand, P.-M.; Herfurth, F.; Hagmann, S.; Spillmann, U.; Trotsenko, S.; Gumberidze, A.; Stöhlker, Th.

2013-11-01

111

Charge-transfer transitions and optical properties of cobaltites  

Microsoft Academic Search

Specific features of the charge-transfer states and transitions of the O 2p ? Co 3d type in octahedral complexes (CoO6)9? and (CoO6)10? are considered in the cluster approach. The reduced matrix elements of the electric dipole transition operator are calculated\\u000a on the many-electron wave functions of the complexes corresponding to the initial (high-or low-spin) state and the final state\\u000a at

A. V. Zenkov

2005-01-01

112

Electron solvation in water clusters following charge transfer from iodide.  

PubMed

The dynamics following charge transfer to solvent from iodide to a water cluster are studied using time-resolved photoelectron imaging of I-(H2O)n and I-(D2O)n clusters with n< or =28. The results show spontaneous conversion, on a time scale of approximately 1 ps, from water cluster anions with surface-bound electrons to structures in which the excess electron is more strongly bound and possibly more internalized within the solvent network. The resulting dynamics provide valuable insight into the electron solvation dynamics in water clusters and the relative stabilities between recently observed isomers of water cluster anions. PMID:16392904

Verlet, Jan R R; Kammrath, Aster; Griffin, Graham B; Neumark, Daniel M

2005-12-15

113

Photochromic charge transfer processes in natural pink and brown diamonds.  

PubMed

Natural pink and brown diamonds exhibit surprising photochromic phenomena when optically pumped with ultraviolet light of photon energy ? ? 4.1 eV, including a subsequent sensitivity to infrared pumps, which is not evident prior to UV exposure. In this study, we observe the dependence of photochromism on pump photon energy and intensity, for both UV and IR pumps. From these observations, we propose a model of several distinct charge transfer processes between multiple species of optically active defect centres. We show it is likely that the UV-induced behaviour of pink diamond photochromism is linked to the vacancy clusters responsible for brown colouration in diamonds. PMID:24351435

Byrne, K S; Chapman, J G; Luiten, A N

2014-01-22

114

Diamagnetism and charge transfer in graphite intercalation compounds  

NASA Technical Reports Server (NTRS)

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

Tsang, T.; Resing, H. A.

1984-01-01

115

Charge transfer kinetics from surface plasmon resonance voltammetry.  

PubMed

On the basis of a quantitative relationship between surface plasmon resonance signal and electrochemical current in the electrochemical surface plasmon resonance (EC-SPR), EC-SPR signal measures the semi-integral of faradaic current. We theoretically discussed the electrode potential and charge transfer kinetics to be determined from surface plasmon resonance voltammetry (or potential sweep EC-SPR) signals for the fully reversible, quasi-reversible, and irreversible redox reactions. The results indicated that the electroanalysis of EC-SPR signal is more straightforward than conventional electrochemical current. Then, we studied two model redox reactions of hexaammineruthenium chloride and 4-nitrotoluene, to obtain half wave potential of quasi-reversible redox reaction, transfer coefficient, and standard rate constant of irreversible redox reaction from EC-SPR signals. PMID:24654883

Lu, Jin; Li, Jinghong

2014-04-15

116

A collection of fullerenes for synthetic access toward oriented charge-transfer cascades in triple-channel photosystems.  

PubMed

The development of synthetic methods to build complex functional systems is a central and current challenge in organic chemistry. This goal is important because supramolecular architectures of highest sophistication account for function in nature, and synthetic organic chemistry, contrary to high standards with small molecules, fails to deliver functional systems of similar complexity. In this report, we introduce a collection of fullerenes that is compatible with the construction of multicomponent charge-transfer cascades and can be placed in triple-channel architectures next to stacks of oligothiophenes and naphthalenediimides. For the creation of this collection, modern fullerene chemistry-methanofullerenes and 1,4-diarylfullerenes-is combined with classical Nierengarten-Diederich-Bingel approaches. PMID:24692344

Bolag, Altan; López-Andarias, Javier; Lascano, Santiago; Soleimanpour, Saeideh; Atienza, Carmen; Sakai, Naomi; Martín, Nazario; Matile, Stefan

2014-05-01

117

Spectrophotometric determination of boron based on charge transfer reaction.  

PubMed

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

Ma, Linjin; Zhang, Zhenxuan; Li, Quanmin

2011-08-01

118

Spectrophotometric determination of boron based on charge transfer reaction  

NASA Astrophysics Data System (ADS)

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

Ma, Linjin; Zhang, Zhenxuan; Li, Quanmin

2011-08-01

119

Electronic energies for Neon dimer dication radiative charge transfer  

NASA Astrophysics Data System (ADS)

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

Deemer, Roger Alan

1989-12-01

120

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

121

A nanocomposite superstructure of metal oxides with effective charge transfer interfaces  

NASA Astrophysics Data System (ADS)

The alignment of nanoparticle building blocks into ordered superstructures is one of the key topics in modern colloid and material chemistry. Metal oxide mesocrystals are superstructures of assembled nanoparticles of metal oxides and have potentially tunable electronic, optical and magnetic properties, which would be useful for applications ranging from catalysis to optoelectronics. Here we report a facile and general approach for synthesizing metal oxide mesocrystals and developing them into new nanocomposite materials containing two different metals. The surface and internal structures of the mesocrystals were fully characterized by electron microscopy techniques. Single-particle confocal fluorescence spectroscopy, electron paramagnetic resonance spectroscopy and time-resolved diffuse reflectance spectroscopy measurements revealed that efficient charge transfer occurred between n-type and p-type semiconductor nanoparticles in the composite mesocrystals. This behaviour is desirable for their applications ranging from catalysis, optoelectronics and sensing, to energy storage and conversion.

Bian, Zhenfeng; Tachikawa, Takashi; Zhang, Peng; Fujitsuka, Mamoru; Majima, Tetsuro

2014-01-01

122

Charge Transfer in bar PP Reactions at 22.4 GeV\\/c  

Microsoft Academic Search

Charge transfer is investigated between c.m. hemispheres and across the largest rapidity gap in an event. The latter method is found to give a larger contribution to zero charge transfer than the former. The rapidity gap size is noted to be bigger for a separation into groups with an odd number of charged particles than into groups with an even

M. Dzhanbusinova; D. I. Ermilova; V. V. Filippova; B. V. Batyunya; I. V. Boguslavsky; I. M. Gramenitsky; R. Lednicky; L. A. Tikhonova; T. Topuriya; A. Valkàrovà; V. Vrba; J. Zàcek; Z. Zlatanov; J. Ervanne; E. Hannula; S. Ljung; H. Villanen; P. Villanen; R. K. Dementiev; V. E. Grechko; I. A. Korzhavina; E. M. Leikin; V. I. Rud; M. Suk; J. Cvach; I. Herynek; P. Reimer; V. Simàk

1978-01-01

123

Ion-ion proton transfer reactions of multiply-charged oligonucleotide cations  

NASA Astrophysics Data System (ADS)

Multiply-charged cations derived from the positive ion electrospray of the oligonucleotide 5'-d(CTTAGCGCTAAG)-3' were subjected to reactions with the (M - CF3-)- and (M - F-)- anions derived from perfluoro-1,3-dimethylcyclohexane in a quadrupole ion trap. Both single strand ions and double strand ions formed from the self-complementary oligonucleotide were studied. In analogy with the reactions of multiply-protonated proteins with the same anions, no adduct formation was observed and the data were consistent with exclusive proton transfer. No evidence for fragmentation was observed for either the single strand ions or the double strand ions, although a small degree of fragmentation of the latter species could not be precluded based on these results alone. The simple and well-defined chemistry associated with the ion-ion reactions of oligonucleotide cations with anions derived from PDCH is desirable for the charge-state manipulation of moderately-sized oligomers (up to roughly 100 residues) because PDCH anions possess a number of desirable characteristics for the production and storage of ion/ion reaction products with mass-to-charge ratios in the tens of thousands.

Stephenson, James L.; McLuckey, Scott A.

1997-11-01

124

Charge Prediction Machine: A tool for inferring precursor charge states of Electron Transfer Dissociation tandem mass spectra  

PubMed Central

Electron Transfer Dissociation (ETD) can dissociate highly charged ions. Efficient analysis of ions dissociated with ETD requires accurate determination of charge states for calculation of molecular weight. We created an algorithm to assign the charge state of ions often used for ETD. The program, Charge Prediction Machine (CPM), uses Bayesian decision theory to account for different charge reduction processes encountered in ETD, and can also handle multiplex spectra. CPM correctly assigned charge states to 98% of the 13,097 MS2 spectra from a combined dataset of four experiments. In a comparison between CPM and a competing program, Charger (ThermoFisher), CPM produced half the mistakes.

Carvalho, Paulo C; Cociorva, Daniel; Wong, Catherine; Carvalho, Maria da Gloria da C; Barbosa, Valmir C; Yates, John R

2010-01-01

125

Filter functions in pulse techniques: application to the study of a slow charge transfer reaction  

Microsoft Academic Search

A first class filter function is a mode of pulse voltammetry that removes completely the current response for a reversible charge transfer reaction without modifying the corresponding signal for a slow charge transfer reaction. Therefore, the application of these modes permits study without interferences of the response for an irreversible electron transfer in those cases where reversible processes are also

Jesús Gálvez

2004-01-01

126

Space charge segregation at grain boundaries in titanium dioxide: 1. Relationship between lattice defect chemistry and space charge potential  

SciTech Connect

The electrical potential difference between the interface and the bulk in TiO[sub 2] is obtained as a function of temperature, oxygen pressure, and acceptor or donor doping from a space charge model that explicitly includes the high-temperature lattice defect chemistry. Using defect equilibrium constants for TiO[sub 2] from previous literature studies, it is shown that for a space charge determined by ionic defect equilibrium with the interface, the potential is negative in undoped and acceptor-doped TiO[sub 2] and positive at high donor concentrations. The isoelectric point lies in the donor-doped regime at high temperatures due to the contribution of defects from reduction, even for fairly oxidizing ambients.

Ikeda, J.A.S.; Yetming Chiang (Massachusetts Inst. of Tech., Cambridge, MA (United States). Dept. of Materials Science and Engineering)

1993-10-01

127

Electrostatic interactions of colloidal particles in nonpolar solvents: role of surface chemistry and charge control agents.  

PubMed

We study the electrostatic and hydrodynamic interactions of colloidal particles in nonpolar solvents. Using blinking optical tweezers, we can extract the screening length, kappa-1, the effective surface potential, |ezeta*|, and the hydrodynamic radius, ah, in a single measurement. We apply this technique to suspensions of polystyrene and poly(methyl methacrylate) particles in hexadecane with soluble charge control agents, aerosol sodium di-2-ethylhexylsulfosuccinate (AOT) and polyisobutylene succinimide (OLOA-1200). We find that the electrostatic interactions of these particles depend sensitively on surface composition as well as on the concentration and chemistry of the charge control agent. PMID:18062711

Sainis, Sunil K; Germain, Vincent; Mejean, Cecile O; Dufresne, Eric R

2008-02-19

128

Charge-transfer complexes of some linear conjugated polyenes.  

PubMed Central

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

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

1980-01-01

129

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

130

Direct observation of intramolecular charge transfer on photoexcitation  

SciTech Connect

The authors construct a model for determining photostimulated charge transfer in organic macromolecules based on molecules with a high value of photoexcitation and a sufficiently long lifetime of the photoexcited state owing to intersystem crossing to the triplet state. In this connection the change in the dipole moment of the molecules during the transition from the ground state to the photoexcited state was determined using measurements of the Stark effect for isotropic polymeric solutions. In addition a long hydrocarbon tail was fastened to the molecules to make it possible to use the Blodgett-Langmuir technique to prepare solid multimolecular layers with a given molecular orientation. The multilayer is placed between two semitransparent aluminium electrodes in order to record the electrical signal during exposure to light along with the photoelectromotive force.

Blinov, L.M.; Lazareva, V.T.; Mikhnev, L.V.; Yudin, S.G.

1986-09-01

131

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

NASA Astrophysics Data System (ADS)

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

Rajendiran, N.; Balasubramanian, T.

2008-03-01

132

Octahedral engineering of orbital polarizations in charge transfer oxides  

NASA Astrophysics Data System (ADS)

Negative charge transfer ABO3 oxides may undergo electronic metal-insulator transitions (MIT) concomitant with a dilation and contraction of nearly rigid octahedra. On both sides of the MIT are in-phase or out-of-phase (or both) rotations of adjacent octahedra that buckle the B-O-B bond angle away from 180?. Using density functional theory with the PBEsol +U approach, we describe an octahedral engineering avenue to control the B 3d and O 2p orbital polarization through enhancement of the BO6 rotation “sense” rather than solely through conventional changes to the B-O bond lengths, i.e., crystal field distortions. Using CaFeO3 as a prototypical material, we show the flavor of the octahedral rotation pattern when combined with strain-rotation coupling and thin film engineering strategies offers a promising avenue to fine tune orbital polarizations near electronic phase boundaries.

Cammarata, Antonio; Rondinelli, James M.

2013-04-01

133

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.

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

2013-01-01

134

Simulation of the charge transfer inefficiency of column parallel CCDs  

NASA Astrophysics Data System (ADS)

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

Maneuski, Dzmitry

2008-06-01

135

Correcting for the Temperature Dependence of ACIS Charge Transfer Inefficiency  

NASA Astrophysics Data System (ADS)

The spectral resolution of the ACIS CCDs is substantially improved by a charge transfer inefficiency (CTI) correction algorithm included in acis_process_events. However, the behavior of the charge traps that cause CTI is temperature dependent: warmer-than-nominal focal plane temperatures reduce the effectiveness of the correction algorithm. As the insulation on the exterior of the SIM and the ACIS radiator shade have aged, the surfaces around the ACIS focal plane and radiator have become warmer, leading to FP temperatures which are sometimes a few degrees warmer than desired, particularly for observations done at spacecraft pitch angles greater than 140 degrees. The ACIS team successfully reduced average focal plane temperatures by shutting off the detector housing heater in April 2008 and a heater on the SIM was turned off in August 2009 providing additional margin, but many warm observations exist in the archive, and observations done at "tail-Sun" attitudes still often have warm focal plane temperatures. Here we review the temperature dependence of ACIS performance and present a temperature-dependent CTI correction algorithm, which we have implemented as contributed software designed to work with current CALDB products and CIAO tools. We show examples using this software to CTI-correct warm ACIS observations.

Posson-Brown, Jennifer; Grant, C.; Allen, G.; Plucinsky, P.; Edgar, R.

2010-02-01

136

Power dissipation in frame-transfer charge-coupled devices  

NASA Astrophysics Data System (ADS)

The power dissipation for large-area high-speed charge-coupled device (CCD) arrays is analyzed. The four mechanisms responsible for power dissipation in a CCD are carried lift and fraction within the CCD channel, load currents through the on-chip output amplifiers, capacitive charge and discharge currents through the epitaxial layer or substrate, and currents flowing through the polysilicon clock register electrodes. These processes are easily calculated for small or slow devices. For large high-speed devices, on the other hand, the conventional analytical techniques are inadequate. The large device area leads to high resistive-capacitive constants in the parallel clock registers, causing clock pulses to degrade in shape as they travel along a clock electrode. A distributed system analysis based on lumped circuit parameters for each pixel is necessary to calculate the current and thus the power dissipated at each point on the surface of the CCD. A computer simulation of a standard frame-transfer CCD was performed using SPICE software. The results of the simulation indicate a much lower power dissipation than previously assumed and also point out various problems with conventional device architectures for large-area high-speed CCDs.

Graeve, Thorsten; Dereniak, Eustace L.

1993-05-01

137

Influence of surface chemistry and charge on mineral-RNA interactions.  

PubMed

We present the results of large-scale molecular simulations, run over several tens of nanoseconds, of 25-mer sequences of single-stranded ribonucleic acid (RNA) in bulk water and at the surface of three hydrated positively charged MgAl layered double hydroxide (LDH) minerals. The three LDHs differ in surface charge density, through varying the number of isomorphic Al substitutions. Over the course of the simulations, RNA adsorbs tightly to the LDH surface through electrostatic interactions between the charged RNA phosphate groups and the alumina charge sites present in the LDH sheet. The RNA strands arrange parallel to the surface with the base groups aligning normal to the surface and exposed to the bulk aqueous region. This templating effect makes LDH a candidate for amplifying the population of a known RNA sequence from a small number of RNAs. The structure and interactions of RNA at a positively charged, hydroxylated LDH surface were compared with those of RNA at a positively charged calcium montmorillonite surface, allowing us to establish the comparative effect of complexation and water structure at hydroxide and silicate surfaces. The systems were studied by computing radial distribution functions, atom density plots, and radii of gyration, as well as visualization. An observation pertinent to the role of these minerals in prebiotic chemistry is that, for a given charge density on the mineral surface, different genetic sequences of RNA adopt different configurations. PMID:23302032

Swadling, Jacob B; Suter, James L; Greenwell, H Christopher; Coveney, Peter V

2013-02-01

138

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.

2011-01-01

139

Revealing photoinduced charge transfer mechanism across ?-conjugated heterojunctions  

NASA Astrophysics Data System (ADS)

The adapted Su-Schrieffer-Heeger (aSSH) model is extended to the ?-conjugated bulk heterojunction system. The New aSSH Hamiltonian incorporated interchain ?-? stacking and dynamic electron-phonon coupling effects. Excellent agreements are found between the computed photoadsorption and photoinduced adsorption spectra and their corresponding experimental measurements. It is found that excitons generated in the bulk poly-(p-phenylene vinylene) (PPV) phase must overcome an energy barrier of 0.23 eV to reach heterojunction interface. These interfacial excitons show clear charge separations, with their electron states leaning towards the interface. Therefore, electron transfers from the D1^* state of PPV to the t1u^* state of C60 follow non-adiabatic mechanisms, which are accelerated by the 0.97 eV energy drop, close vicinity of the D1^* state to the C60 phase, and suppressed inversion symmetry that doubles the number of electron-accepting states. After non-adiabatic electron transfers, the hole D1 states are screened by the optical phonons in PPV, forming self-localized hole polarons and moving further away from heterojunction interface.

Shin, Yongwoo; Lin, Xi

2013-03-01

140

Interface charge transfer in polypyrrole coated perovskite manganite magnetic nanoparticles  

NASA Astrophysics Data System (ADS)

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

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

2012-02-01

141

Doping graphene films via chemically mediated charge transfer  

NASA Astrophysics Data System (ADS)

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.

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

2011-12-01

142

Charge Transfer Characteristics and Initiation Mechanisms of Long Delayed Sprites  

NASA Astrophysics Data System (ADS)

Simultaneous measurements of high altitude optical emissions and the magnetic field produced by sprite-associated lightning discharges enable a close examination of the link between low altitude lightning process and high altitude sprite process. In this work, we report results of the coordinated analysis of high speed (1000--10000 frames per second) sprite video and wideband (0.1 Hz to 30 kHz) magnetic field measurements made simultaneously at the Yucca Ridge Field Station and Duke University during the June through August 2005 campaign period. During the observation period, the high speed camera detected 83 sprite events in 67 TLE sequences, which are caused by the same number of +CGs. 46% of these sprite events are delayed more than 10 ms after the lightning return stroke. With the estimated lightning source current moment waveform, we computed the continuing current amplitude and total charge transfer characteristics of the long delayed sprites (>10 ms delay). Our calculation shows the total charge moment change of the long delayed sprites can vary from several hundred C km to more than ten thousand C km. All the long delayed sprites are related with intense continuing current bigger than 2 kA. This continuing current provides about 50% to 90% of the total charge transfer. However, a bigger continuing current does not necessarily mean a shorter time delay. This indicates that other processes also involved in the sprite initiation for long delayed sprites. In our observations, the sferic burst, a high frequency noise caused by intra-cloud activity, is always accompanied by a slow intensification in the lightning source current before the time of sprite initiation. Thus we used the lightning source current as an input and employed a 2-D FDTD model to numerically simulate the electric field at different altitudes and compare it with the breakdown field. Including the effect of the electron mobility dependence on electric field, the simulation results showed that the slow intensification itself plays an important role in sprite initiation. For events analyzed, the predicted altitude from the FDTD simulation agree well with the measurement from high speed video images. Both the measurements and the simulations indicate that sprites with long time delay tend to initiate at a lower altitude comparing to short delayed sprites.

Li, J.; Cummer, S. A.; Lyons, W. A.; Nelson, T. E.

2007-12-01

143

Experimental evidence of state-selective charge transfer in inductively coupled plasma-atomic emission spectrometry  

NASA Astrophysics Data System (ADS)

State-selective charge-transfer behavior was observed for Fe, Cr, Mn and Cu in inductively coupled plasma (ICP)-atomic emission spectrometry. Charge transfer from Ar + to Fe, Cr and Mn is state-selective because of inefficient collisional mixing of the quasiresonant charge-transfer energy levels with nearby levels. This low efficiency is the consequence of differences in electronic configuration of the core electrons. The reason for state-selective charge-transfer behavior to Cu is not clear, although a tentative explanation based on efficiency of intramultiplet and intermultiplet mixing for this special case is offered.

Chan, George C.-Y.; Hieftje, Gary M.

2004-07-01

144

Intramolecular energy transfer through charge transfer state in lanthanide compounds: A theoretical approach  

NASA Astrophysics Data System (ADS)

A theoretical approach for the intramolecular energy transfer process involving the ligand-to-metal charge transfer (LMCT) state in lanthanide compounds is developed. Considering a two-electron interaction, both the direct Coulomb and exchange interactions are taken into account, leading to expressions from which selection rules may be derived and transfer rates may be calculated. These selection rules show that the direct Coulomb and exchange mechanisms are complementary, in the same way as obtained in previous works for the case of ligand-lanthanide ion energy transfer processes. An important result from numerical estimates is that the channel ligand-LMCT state is by far the dominant case, leading to transfer rates higher than for the channel lanthanide ion-LMCT state by several orders of magnitude. The analysis of the emission quantum yield as a function of the relative energy position of the LMCT state in a typical Eu3+ compound allows the identification of two quenching regions, the most pronounced one occurring close to the lower ligand triplet level.

Faustino, W. M.; Malta, O. L.; de Sá, G. F.

2005-02-01

145

Eliminating the Reverse Charge Sharing Effect in the Charge-Transfer-Switch (CTS) Converter  

NASA Astrophysics Data System (ADS)

A novel voltage level controller for low-power charge pump converters will be presented in this paper. The proposed voltage level controller would react according to the pumped voltage in the charge-transfer-switch (CTS) converter. For the CTS circuit, the pumping operation would be degraded by the charge sharing effect in the auxiliary switch path. In this study, a voltage shifter was used as the voltage level controller to overcome this serious problem without consuming too much chip area. The simulation results showed that the converter can accept a rated input of 1.5V and generated an output up to 8V based on the TSMC 0.35-µm CMOS technology. The layout consumed an area of 125*160µm2. The highest output obtained in measuring the real chip was 5.5V which is primarily due to the limitation that the transistor could tolerated. The largest load was estimated as high as 6mW which is large enough for on-chip application.

Shiau, Miin-Shyue; Liu, Don-Gey; Liao, Shry-Sann

146

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

147

On the role of solvent electronic polarization in charge transfer reactions  

Microsoft Academic Search

The effect of a solvent’s electronic polarization on the rate of a charge transfer reaction is studied in both continuum and discrete solvent models. An effective system Hamiltonian that contains the equilibrium solvation from the solvent electronic polarization is obtained, and leads to an effective matrix element Veff coupling the charge transfer states that is smaller than the gas phase

Jianjun Zhu; R. I. Cukier

1995-01-01

148

Ultrafast charge transfer processes in ordered molecular systems  

NASA Astrophysics Data System (ADS)

Using ultrafast emission and absorption spectroscopies, rates of DNA-mediated electron-transfer reactions have been established between a series of metal complex donors and acceptors bound by intercalation to the DNA double helix. In the presence of intercalating rhodium(III) acceptors, a substantial fraction of photoexcited (M(phen)2dppz) 2+ (M = Ru, Os) exhibits fast oxidative quenching (k q > 3 × 1010 s-1), while the remaining excited-state species exhibit a range of quenching constants less than 108 s-1. Transient-absorption experiments on the picosecond timescale indicate that, for all donors bound to mixed sequence DNA, the majority of back electron transfer is also very fast (ca. 1010 s-1) and its rate constant is independent of the loading of Rh complexes on the helix. We report a Monte Carlo simulation combined with an electron-tunneling kinetics program to model transient- absorption and emission data monitoring reactions between a series of metallointercalators on a variety of DNA. Our simplistic model simulates sub-ns transient absorption, sub-ns TCSPC and ns luminescence spectroscopy remarkably well. The apparent simple first-order kinetics are reproduced by an electron tunneling mechanism with a ? value near 1.0 A-1. The extent of reaction is reproduced by assuming a preferential binding of acceptors near donors. (Ru(phen)2dppz) 2+ (phen = 1,10- phenanthroline, dppz = dipyridophenazine) and closely related complexes have previously been observed to have an undetectably small quantum yield of photoluminescence in water but a moderate emission yield when bound to DNA. This so-called 'light-switch' effect is a critical factor in the utility of these complexes as spectroscopic probes for DNA. Here we describe a detailed investigation of the photophysics of (Ru(phen)2dppz) 2+ in aqueous solution, and in mixtures of acetonitrile and water, by time-resolved absorption and emission spectroscopies. Atomic force microscopy (AFM) and near-field scanning optical microscopy (NSOM) are used in conjunction with bulk absorption and fluorescence measurements to correlate the morphological and photophysical properties of titanyl phthalocyanine/perylene phenethylimide (TiOPc/PPEI) bilayer systems. Steady-state fluorescence intensity and fluorescence lifetime measurements are used as a measure of interfacial charge-transfer quenching efficiencies.

Olson, Eric James Crane

1998-11-01

149

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

150

Fundamental studies of interfacial excited-state charge transfer in molecularly tethered semiconductor nanoassemblies  

NASA Astrophysics Data System (ADS)

The research presented in this dissertation focuses on elucidating the parameters affecting dynamics and yield of electron transfer reactions in semiconducting nanoparticle assemblies through the use of time-resolved spectroscopy. In particular, the dissertation focuses on photoinduced electron injection in assemblies of CdSe, CdS, or PbS quantum dots covalently bound to either metal oxide films or each other through the use of bifunctional molecular linkers. Chapter 2 elucidates the influence of electronic coupling on excited-state electron transfer from CdS quantum dots to TiO2 nanoparticles via molecular linkers with phenylene bridges. We establish that the efficiency of electron injection from CdS quantum dots to TiO2 nanoparticle varies dramatically with electronic coupling, which can be controlled by tuning the properties of molecular linkers. Chapter 3 presents the role of excitation energy on interfacial electron transfer in tethered assemblies of CdSe quantum dots and TiO2 nanoparticles. Through this work, we determined that injection efficiency from band-edge states is independent of excitation energy. However, the efficiency of injection from trap-states decreases at lower-energy excitation. We attribute the decrease to a lower energy distribution of emissive trap-states from which injection is less efficient. Chapter 4 presents the observation of multiphasic electron injection dynamics from photoexcited PbS quantum dots to TiO2 nanoparticles. In this collaborative study with Dr. Masumoto from the University of Tsukuba we observed electron injection on multiple timescales. We determined that electron injection occurred in this system through two different mechanisms. The first involved injection from thermalized PbS excited states and the second through injection of hot electrons through Auger recombination of biexcitons that creates high lying excitonic states. Chapter 5 investigates charge transfer in covalently bound quantum dot assemblies. We utilize established carbodiimide chemistry to tether quantum dots to each other through covalent bonds between capping groups. As a result of our controlled-covalent quantum dot attachment, we observe evidence of interfacial charge transfer from photoexcited CdS quantum dots to covalently-bound CdSe quantum dots.

Youker, Diane Greer

151

Low-energy charge transfer excitations in NiO  

NASA Astrophysics Data System (ADS)

Comparative analysis of photoluminescence (PL) and photoluminescence excitation (PLE) spectra of NiO poly- and nanocrystals in the spectral range 2-5.5 eV reveals two PLE bands peaked near 3.7 and 4.6 eV with a dramatic rise in the low-temperature PLE spectral weight of the 3.7 eV PLE band in the nanocrystalline NiO as compared with its polycrystalline counterpart. In frames of a cluster model approach we assign the 3.7 eV PLE band to the low-energy bulk-forbidden p-d (t1g(?)-eg) charge transfer (CT) transition which becomes the allowed one in the nanocrystalline state while the 4.6 eV PLE band is related to a bulk allowed d-d (eg-eg) CT transition scarcely susceptible to the nanocrystallization. The PLE spectroscopy of the nanocrystalline materials appears to be a novel informative technique for inspection of different CT transitions.

Sokolov, V. I.; Pustovarov, V. A.; Churmanov, V. N.; Ivanov, V. Yu; Yermakov, A. Ye; Uimin, M. A.; Gruzdev, N. B.; Sokolov, P. S.; Baranov, A. N.; Moskvin, A. S.

2012-08-01

152

Pseudoparticle approach for charge-transferring molecule-surface collisions  

NASA Astrophysics Data System (ADS)

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

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

2012-09-01

153

Phase separation in ternary charge-transfer-complexes  

NASA Astrophysics Data System (ADS)

Mixing of different organic charge-transfer-complexes (CT-complexes) might allow the adjustment of the optical and morphological properties of the resulting material system. In this work, a study of two CT-complexes, mixed by thermal coevaporation at different concentrations by substituting only the acceptor molecules, is presented. Electron diffraction patterns, which were collected on samples of the ternary system of the prototypical CT-complexes DBTTF-TCNQ and DBTTF-F4TCNQ do not show any indication of a mixed crystalline phase or novel crystalline order. X-ray diffraction measurements additionally confirm the phase separation in the ternary system. However, upon mixing of the complexes, the degree of crystallinity of the individual phases is reduced. This effect correlates with the mixing ratio of the CT-complexes in the ternary compound. Furthermore, we do not observe a shift or the appearance of new peaks in the infrared spectra of (DBTTF-TCNQ) x :(DBTTF-F4TCNQ)1- x . Hence, there is no indication for a pronounced or novel chemical interaction between the individual CT-complexes in the mixed compound.

Nanova, Diana; Beck, Sebastian; Alt, Milan; Glaser, Tobias; Pucci, Annemarie; Schultheiß, Katrin; Dieterle, Levin; Schröder, Rasmus R.; Pflaum, Jens; Kowalsky, Wolfgang; Kroeger, Michael

2013-09-01

154

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

155

Charge transfer in alkali-metal-doped polymeric fullerenes  

SciTech Connect

We present room-temperature Raman measurements of pressure-polymerized C{sub 60} and compare them with the spectra of RbC{sub 60} in the orthorhombic phase. Although both materials were prepared according to two completely different routes the spectra show a surprising similarity with respect to mode positions and line splitting. We concluded from this that both materials, the uncharged pressure-polymerized C{sub 60} and the rubidium-doped orthorhombic compound, have the same overall structure and the {ital A}C{sub 60} compounds can be considered as the doped species of the C{sub 60}, polymerized using moderate low pressure and high temperatures. From a detailed comparison between both spectra mode shifting and line broadening as a consequence of the charge transfer was determined and electron-phonon coupling constants were estimated for the high-frequency {ital H}{sub {ital g}}(7) and {ital H}{sub {ital g}}(8) modes. The low values for the coupling constants compared to the ones in the K{sub 3}C{sub 60} can explain the lack of superconductivity in the {ital A}C{sub 60} compounds. {copyright} {ital 1996 The American Physical Society.}

Winter, J.; Kuzmany, H. [Institut fuer Materialphysik, Universitaet Wien Strudlhofgasse 4, A-1090 Wien (Austria)] [Institut fuer Materialphysik, Universitaet Wien Strudlhofgasse 4, A-1090 Wien (Austria); Soldatov, A.; Persson, P.; Jacobsson, P.; Sundqvist, B. [Department of Experimental Physics, Umea University, S-901 87 Umea (Sweden)] [Department of Experimental Physics, Umea University, S-901 87 Umea (Sweden)

1996-12-01

156

Charge transfer vibronic transitions in uranyl tetrachloride compounds.  

PubMed

The electronic and vibronic interactions of uranyl (UO(2))(2+) in three tetrachloride crystals have been investigated with spectroscopic experiments and theoretical modeling. Analysis and simulation of the absorption and photoluminescence spectra have resulted in a quantitative understanding of the charge transfer vibronic transitions of uranyl in the crystals. The spectra obtained at liquid helium temperature consist of extremely narrow zero-phonon lines (ZPL) and vibronic bands. The observed ZPLs are assigned to the first group of the excited states formed by electronic excitation from the 3? ground state into the f(?,?) orbitals of uranyl. The Huang-Rhys theory of vibronic coupling is modified successfully for simulating both the absorption and luminescence spectra. It is shown that only vibronic coupling to the axially symmetric stretching mode is Franck-Condon allowed, whereas other modes are involved through coupling with the symmetric stretching mode. The energies of electronic transitions, vibration frequencies of various local modes, and changes in the O?U?O bond length of uranyl in different electronic states and in different coordination geometries are evaluated in empirical simulations of the optical spectra. Multiple uranyl sites derived from the resolution of a superlattice at low temperature are resolved by crystallographic characterization and time- and energy-resolved spectroscopic studies. The present empirical simulation provides insights into fundamental understanding of uranyl electronic interactions and is useful for quantitative characterization of uranyl coordination. PMID:22148434

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

2012-01-19

157

[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

158

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

159

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

160

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

161

Charge transfer hysteresis in graphene dual-dielectric memory cell structures  

NASA Astrophysics Data System (ADS)

We report controlled charge transfer between large-area graphene and a dual-dielectric, silicon nitride/silicon oxide substrate. Graphene was grown on copper by chemical vapour deposition, transferred to the nitride substrates, and patterned into test structures. Hysteresis in conductance with varying gate voltage is easily understood in terms of electron transfer between graphene and nitride traps. Increased hysteresis with temperature suggests thermally activated charge transfer of a Poole-Frenkel or Schottky nature. A 7.3× change in graphene sheet resistance is observed at room temperature with the nitride in a charged and discharged state.

Imam, S. A.; Deshpande, T.; Guermoune, A.; Siaj, M.; Szkopek, T.

2011-08-01

162

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

163

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

164

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

NASA Technical Reports Server (NTRS)

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

Moore, T. E.

1980-01-01

165

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.

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

2011-01-01

166

Three-centered model of ultrafast photoinduced charge transfer: Continuum dielectric approach  

SciTech Connect

A theoretical description of photoinduced charge transfer involves explicit treating both the optical formation of the nuclear wave packet on the excited free energy surface and its ensuing dynamics. The reaction pathway constitutes two-stage charge transfer between three centers. Manifestations of fractional charge transfer at first stage are explored. An expression for time dependent rate constant of photoinduced charge transfer is found in the framework of the linear dielectric continuum model of the medium. The model involves both the intramolecular vibrational reorganization and the Coulombic interaction of the transferred charge with the medium polarization fluctuations and allows to express the rate in terms of intramolecular reorganization parameters and complex dielectric permittivity. The influence of the vibrational coherent motion in the locally excited state on the charge transfer dynamics has been explored. The dependence of the ultrafast photoinduced charge transfer dynamics on the excitation pulse carrier frequency (spectral effect) has been investigated. The spectral effect has been shown to depend on quantity of the fractional charge.

Khohlova, Svetlana S.; Mikhailova, Valentina A.; Ivanov, Anatoly I. [Department of Physics, Volgograd State University, University Avenue 100, Volgograd 400062 (Russian Federation)

2006-03-21

167

Role of the charge transfer state in organic donor-acceptor solar cells.  

PubMed

Charge transfer complexes are interfacial charge pairs residing at the donor-acceptor heterointerface in organic solar cell. Experimental evidence shows that it is crucial for the photovoltaic performance, as both photocurrent and open circuit voltage directly depend on it. For charge photogeneration, charge transfer complexes represent the intermediate but essential step between exciton dissotiation and charge extraction. Recombination of free charges to the ground state is via the bound charge transfer state before being lost to the ground state. In terms of the open circuit voltage, its maximum achievable value is determined by the energy of the charge transfer state. An important question is whether or not maximum photocurrent and maximum open circuit voltage can be achieved simultaneously. The impact of increasing the CT energy-in order to raise the open circuit voltage, but lowering the kinetic excess energy of the CT complexes at the same time-on the charge photogeneration will accordingly be discussed. Clearly, the fundamental understanding of the processes involving the charge transfer state is essential for an optimisation of the performance of organic solar cells. PMID:20803527

Deibel, Carsten; Strobel, Thomas; Dyakonov, Vladimir

2010-10-01

168

Association function of conjugated polymer charge-transfer complex.  

PubMed

The donor-acceptor ground-state charge-transfer complex (CTC) formed in solution between a conjugated polymer, poly[methoxy-5-(2'-ethylhexyloxy)-1,4-phenylene-vinylene] (MEH-PPV), and a low-molecular-weight organic acceptor, 2,4,7-trinitrofluorenone (TNF), is studied by optical absorption and Raman spectroscopy. The CTC absorption as a function of TNF content shows a threshold increase that is in conflict with the model commonly used for optical characterization of low-molecular-weight CTCs. The shift of MEH-PPV characteristic Raman band at 1585 cm(-1) also exhibits a threshold dependence upon TNF addition. We assign the threshold in both the absorption and Raman data to the CTC concentration. To describe the threshold in the terms of the common model, we extend it by introducing an association function instead of a constant. The association function of acceptor concentration has been calculated to be K(a) approximately 1.5-3 M(-1) below the threshold, to increase steeply up to K(a) approximately 6-7.5 M(-1) just after the threshold, and then to grow gradually up to K(a) approximately 40 M(-1). The CTC molar absorption coefficient has been found to be epsilon(CTC) = (12.7 +/- 0.6) x 10(3) M(-1) cm(-1) at 635 nm. We explain the threshold as a result of the positive feedback: the CTC formation induces planarizaton of conjugated polymer segments that in turn facilitates further CTC formation. PMID:20396825

Parashchuk, Olga D; Bruevich, Vladimir V; Paraschuk, Dmitry Yu

2010-06-21

169

Experimental and theoretical studies of charge transfer and deuterium ion transfer between D2O+ and C2H4  

NASA Astrophysics Data System (ADS)

The charge transfer and deuterium ion transfer reactions between D2O+ and C2H4 have been studied using the crossed beam technique at relative collision energies below one electron volt and by density functional theory (DFT) calculations. Both direct and rearrangement charge transfer processes are observed, forming C2H4+ and C2H3D+, respectively. Independent of collision energy, deuterium ion transfer accounts for approximately 20% of the reactive collisions. Between 22 and 36 % of charge transfer collisions occur with rearrangement. In both charge transfer processes, comparison of the internal energy distributions of products with the photoelectron spectrum of C2H4 shows that Franck-Condon factors determine energy disposal in these channels. DFT calculations provide evidence for transient intermediates that undergo H/D migration with rearrangement, but with minimal modification of the product energy distributions determined by long range electron transfer. The cross section for charge transfer with rearrangement is approximately 103 larger than predicted from the Rice-Ramsperger-Kassel-Marcus isomerization rate in transient complexes, suggesting a nonstatistical mechanism for H/D exchange. DFT calculations suggest that reactive trajectories for deuterium ion transfer follow a pathway in which a deuterium atom from D2O+ approaches the ?-cloud of ethylene along the perpendicular bisector of the C-C bond. The product kinetic energy distributions exhibit structure consistent with vibrational motion of the D-atom in the bridged C2H4D+ product perpendicular to the C-C bond. The reaction quantitatively transforms the reaction exothermicity into internal excitation of the products, consistent with mixed energy release in which the deuterium ion is transferred in a configuration in which both the breaking and the forming bonds are extended.

Liu, Li; Cai, Xiaohui; Li, Yue; Richards O'Grady, Elizabeth; Farrar, James M.

2004-08-01

170

Experimental and theoretical studies of charge transfer and deuterium ion transfer between D2O+ and C2H4.  

PubMed

The charge transfer and deuterium ion transfer reactions between D(2)O(+) and C(2)H(4) have been studied using the crossed beam technique at relative collision energies below one electron volt and by density functional theory (DFT) calculations. Both direct and rearrangement charge transfer processes are observed, forming C(2)H(4) (+) and C(2)H(3)D(+), respectively. Independent of collision energy, deuterium ion transfer accounts for approximately 20% of the reactive collisions. Between 22 and 36 % of charge transfer collisions occur with rearrangement. In both charge transfer processes, comparison of the internal energy distributions of products with the photoelectron spectrum of C(2)H(4) shows that Franck-Condon factors determine energy disposal in these channels. DFT calculations provide evidence for transient intermediates that undergo H/D migration with rearrangement, but with minimal modification of the product energy distributions determined by long range electron transfer. The cross section for charge transfer with rearrangement is approximately 10(3) larger than predicted from the Rice-Ramsperger-Kassel-Marcus isomerization rate in transient complexes, suggesting a nonstatistical mechanism for H/D exchange. DFT calculations suggest that reactive trajectories for deuterium ion transfer follow a pathway in which a deuterium atom from D(2)O(+) approaches the pi-cloud of ethylene along the perpendicular bisector of the C-C bond. The product kinetic energy distributions exhibit structure consistent with vibrational motion of the D-atom in the bridged C(2)H(4)D(+) product perpendicular to the C-C bond. The reaction quantitatively transforms the reaction exothermicity into internal excitation of the products, consistent with mixed energy release in which the deuterium ion is transferred in a configuration in which both the breaking and the forming bonds are extended. PMID:15303914

Liu, Li; Cai, Xiaohui; Li, Yue; Richards O'Grady, Elizabeth; Farrar, James M

2004-08-22

171

Ligand dissociation mediated charge transfer observed at colloidal W18O49 nanoparticle interfaces.  

PubMed

Understanding charge transfer dynamics through the ligand shell of colloidal nanoparticles has been an important pursuit in solar energy conversion. While charge transport through ligand shells of nanoparticle films has been studied intensely in static dry and electrochemical systems, its influence on charge transfer kinetics in dispersed colloidal systems has received relatively less attention. This work reports the oxidation of amine passivated tungsten oxide nanoparticles by an organically soluble tris-(1,10-phenanthroline) iron(III) derivative. By following the rate of this oxidation optically via the production of the ferroin derivative under various reaction conditions and particle derivatizations, we are able to show that the fluxional ligand shells on dispersed, colloidal nanoparticles provide a separate and more facile pathway for charge transfer, in which the rate-limiting step for charge transfer is the ligand dissociation. Since such ligand shells are frequently required for nanoparticle stability, this observation has significant implications for colloidal nanoparticle photocatalysis. PMID:24564847

Grauer, David C; Alivisatos, A Paul

2014-03-11

172

Coherence in charge and energy transfer in molecular junctions  

NASA Astrophysics Data System (ADS)

We consider the effects of dephasing on field-induced coherent charge and energy transport in molecular junctions. Within generic models we show that dephasing controls the relative intensities of energy and charge fluxes, and that the dependence of the energy flux on the dephasing rate is nonmonotonic. We further demonstrate the possibility for laser-controlled charge-energy separation in multiterminal molecular junctions, a prerequisite for engineering low-heating stable nanoscale devices.

White, Alexander J.; Peskin, Uri; Galperin, Michael

2013-11-01

173

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

PubMed

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

Dillon, Robert J; Bardeen, Christopher J

2012-05-31

174

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

175

Molecular rotors of coronene in charge-transfer solids.  

PubMed

Ten types of neutral charge transfer (CT) complexes of coronene (electron donor; D) were obtained with various electron acceptors (A). In addition to the reported 7,7,8,8-tetracyanoquinodimethane (TCNQ) complex of 1:1 stoichiometry with a DA-type alternating ? column, TCNQ also afforded a 3:1 complex, in which a face-to-face dimer of parallel coronenes (Cor-As) is sandwiched between TCNQs to construct a DDA-type alternating ? column flanked by another coronene (Cor-B). Whereas solid-state (2)H?NMR spectra of the 1:1 TCNQ complex formed with deuterated coronene confirmed the single in-plane 6-fold flipping motion of the coronenes, two unsynchronized motions were confirmed for the 3:1 TCNQ complex, which is consistent with a crystallographic study. Neutral [Ni(mnt)2] (mnt: maleonitriledithiolate) as an electron acceptor afforded a 5:2 complex with a DDA-type alternating ? column flanked by another coronene, similar to the 3:1 TCNQ complex. The fact that the Cor-As in the [Ni(mnt)2] complex arrange in a non-parallel fashion must cause the fast in-plane rotation of Cor-A relative to that of Cor-B. This is in sharp contrast to the 3:1 TCNQ complex, in which the dimer of parallel Cor-As shows inter-column interactions with neighboring Cor-As. The solid-state (1)H?NMR signal of the [Ni(mnt)2] complex suddenly broadens at temperatures below approximately 60?K, indicating that the in-plane rotation of the coronenes undergoes down to approximately 60?K; the rotational rate reaches the gigahertz regime at room temperature. Rotational barriers of these CT complexes, as estimated from variable-temperature spin-lattice relaxation time (T1) experiments, are significantly lower than that of pristine coronene. The investigated structure-property relationships indicate that the complexation not only facilitates the molecular rotation of coronenes but also provides a new solid-state rotor system that involves unsynchronized plural rotators. PMID:23897669

Yoshida, Yukihiro; Shimizu, Yasuhiro; Yajima, Takeshi; Maruta, Goro; Takeda, Sadamu; Nakano, Yoshiaki; Hiramatsu, Takaaki; Kageyama, Hiroshi; Yamochi, Hideki; Saito, Gunzi

2013-09-01

176

Percolation Treatment of Charge Transfer in Humidified Smectite Clays  

Microsoft Academic Search

Bulk electrical conductivity of soil is generally assumed to be domi- nated by the electrical conductivity of the soil solution, with perhaps a small contribution from surface charges associated with soil solids. Soils high in smectites often exhibit high electrical conductivity due to water associated with the clays. These charges are either associated with the exchangeable cations or with proton

Allen G. Hunt; Sally D. Logsdon; David A. Laird

2006-01-01

177

Charge transfer interactions between conjugated block copolymers and reduced graphene oxides.  

PubMed

The charge transfer interactions between reduced graphene oxides and conjugated block copolymers were confirmed by various spectroscopic methods, giving rise to manipulation of the electrical properties of the former. PMID:21858330

Choi, Bong Gill; Hong, Won Hi; Jung, Young Mee; Park, HoSeok

2011-10-01

178

The mechanisms of delayed fluorescence in charge-transfer crystal of tetracyanobenzene-hexamethylbenzene  

NASA Astrophysics Data System (ADS)

Fluorescence, phosphorescence and delayed fluorescence emission characteristics of tetracyanobenzene-hexamethylbenzene (TCNB-HMB) charge-transfer crystal have been studied in the 1.7-340 K temperature range. Delayed fluorescence, originating from heterogeneous triplet-triplet annihilation indicates the presence of mobile charge-transfer triplet excitons at a temperature as low as 1.7 K. However, the behaviour of triplet excitons in TCNB-HMB crystal is strongly controlled by a very efficient trapping process in the whole temperature range investigated. It was found that thermally activated delayed fluorescence, which is a dominating emission of the crystal at elevated temperatures (>60 K), has a different origin (a different initial state) at different temperatures. These observations were analysed and interpreted in terms of a photokinetic model, which is considered to be typical for charge-transfer crystals with high charge-transfer character of triplet excitons.

Kozankiewicz, B.; Prochorow, J.

1989-08-01

179

Charge Transfer Reactions in Alkane and Cycloalkane Systems. Estimated Ionization Potentials.  

National Technical Information Service (NTIS)

This paper reports the results of a quantitative investigation of charge transfer reactions in alkane mixtures, carried out in an ion cyclotron resonance mass spectrometer. The study was undertaken in order to elucidate the influence of such factors as re...

S. G. Lias P. Ausloos Z. Horvath

1976-01-01

180

Product distributions for some thermal energy charge transfer reactions of rare gas ions  

NASA Technical Reports Server (NTRS)

Ion cyclotron resonance methods were used to measure the product distributions for thermal-energy charge-transfer reactions of He(+), Ne(+), and Ar(+) ions with N2, O2, CO, NO, CO2, and N2O. Except for the He(+)-N2 reaction, no molecular ions were formed by thermal-energy charge transfer from He(+) and Ne(+) with these target molecules. The propensity for dissociative ionization channels in these highly exothermic charge-transfer reactions at thermal energies contrasts with the propensity for formation of parent molecular ions observed in photoionization experiments and in high-energy charge-transfer processes. This difference is explained in terms of more stringent requirements for energy resonance and favorable Franck-Condon factors at thermal ion velocities.

Anicich, V. G.; Laudenslager, J. B.; Huntress, W. T., Jr.; Futrell, J. H.

1977-01-01

181

The Near-adiabatic Criterion in Charge Transfer Collisions  

Microsoft Academic Search

Coulomb and polarization enrgy corrections to the near-adiabatic criterion have been calculated for the available cross section function data on one- and two-electron transfer collisions. In the `adiabatic maximum rule' the product of adiabatic parameter and number of electrons transferred is found to have a mean value of 7 Å, the probable errors being reduced. The recombination energies of the

J. B. Hasted; A. R. Lee

1962-01-01

182

Picosecond spectroscopy of charge-transfer processes. Photochemistry of anthracene-tetranitromethane EDA complexes  

NASA Astrophysics Data System (ADS)

The temporal sequence of events that follow 532 nm excitation of electron donor-acceptor, EDA, complexes of several substituted anthracenes with tetranitromethane is monitored by means of picosecond spectroscopy. Excitation of the charge-transfer band of these EDA complexes produces high yields of 1 : 1 adducts. Absorption spectra and kinetics of the transient species involved in these photochemical reactions provide the basis for elucidation of the reaction mechanism following charge-transfer excitation to the ion pairs.

Masnovi, J. M.; Huffman, J. C.; Kochi, J. K.; Hilinski, E. F.; Rentzepis, P. M.

1984-04-01

183

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

184

Multiple Charge Transfer Bands in Complexes of Hexafluorobenzene with Aromatic Amines  

Microsoft Academic Search

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

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

1968-01-01

185

Simultaneous Determination of Several Charge-transfer Complex Association Constants using Nuclear Magnetic Resonance  

Microsoft Academic Search

A METHOD for determining the association constants of organic charge-transfer complexes in solution using nuclear magnetic resonance has recently been described1,2. For a series of solutions containing an electron donor species (D) and an electron acceptor species (A) which interact by a very fast reversible process to form a 1 : 1 charge-transfer complex (DA), if one of the reactants,

R. Foster; C. A. Fyfe

1967-01-01

186

Interfacial charge transfer dynamics in small molecule-modified TiO2 nanoparticles  

Microsoft Academic Search

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.

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

2010-01-01

187

Architecture of a Charge-Transfer State Regulating Light Harvesting in a Plant Antenna Protein  

Microsoft Academic Search

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). We found evidence for charge-transfer quenching in all three of the individual

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

2008-01-01

188

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

Microsoft Academic Search

We study the charge-transfer exciton absorption and photocurrent response in solution-processed bulk heterojunction based on poly(3-hexylthiophene) donor and (6,6)-phenyl-C61-butyric acid methyl ester acceptor in the near-infrared wavelength region. While the exciton absorption exists only for wavelength below 650 nm, direct generation of charge-transfer exciton formed between the donor and acceptor extends the absorption wavelength to 950 nm. For films with

Chia-Ming Yang; Pei-Yu Tsai; Sheng-Fu Horng; Kuan-Chen Lee; Shin-Rong Tzeng; Hsin-Fei Meng; Jow-Tsong Shy; Ching-Fong Shu

2008-01-01

189

Reflection time-of-flight mass spectrometer for charge-transfer cross section measurements  

Microsoft Academic Search

A new method is described that combines the production of ions by laser ablation with a reflection time-of-flight mass spectrometer for charge-transfer cross section measurements. This method allows a specific charge-transfer channel of an ion-neutral pair to be measured at energies of about 0.1 keV\\/amu. The metastable state ion fraction in the laser ablation ion beam is shown to be

Jiebing Wang; Victor H. S. Kwong

1997-01-01

190

High Pressure Optical Studies of the Thallous Halides and of Charge-Transfer Complexes  

NASA Astrophysics Data System (ADS)

High pressure was used to study the insulator -to-metal transition in sulfur and the thallous halides and to study the intermolecular interactions in charge -transfer complexes. The approach to the band overlap insulator -to-metal transition was studied in three thallous halides and sulfur by optical absorption measurements of the band gap as a function of pressure. The band gap of sulfur continuously decreases with pressure up to the insulator -to-metal transition which occurs between 450 and 485 kbars. The results on the thallous halides indicate that the indirect gap decreases more rapidly than the direct gap; the closing of the indirect gap is responsible for the observed insulator -to-metal transitions. High pressure electronic and vibrational spectroscopic measurements on the solid-state complexes of HMB-TCNE were used to study the intermolecular interactions of charge -transfer complexes. The vibrational frequency shifts indicate that the degree of charge transfer increases with pressure which is independently confirmed by an increase in the molar absorptivity of the electronic charge-transfer peak. Induction and dispersion forces contribute towards a red shift of the charge-transfer peak; however, charge-transfer resonance contributes toward a blue shift and this effect is dominant for the HMB-TCNE complexes. High pressure electronic spectra were used to study the effect of intermolecular interactions on the electronic states of TCNQ and its complexes. The red shifts with pressure of the electronic spectra of TCNQ and (TCNQ)(' -) in polymer media and of crystalline TCNQ can be understood in terms of Van der Waals interactions. None of the calculations which considered intradimer distance obtained the proper behavior for either the charge-transfer of the locally excited states of the complexes. The qualitative behavior of both states can be interpreted as the effect of increased mixing of the locally excited and charge transfer states.

Jurgensen, Charles Willard

191

Influence of laser radiation on charge transfer in proton--alkali-metal-atom collisions  

Microsoft Academic Search

The atomic-eigenfunction-expansion method is used to investigate the influence of laser radiation on charge-transfer processes in proton--alkali-metal-atom collisions. The radiation is treated classically. The cross sections for charge transfer into the ground state of hydrogen in collisions between a proton and any of the atoms sodium, potassium, rubidium, and cesium in the presence of radiation of wavelengths varying between 3000

Keka Choudhury; D. P. Sural

1986-01-01

192

Influence of laser radiation on charge transfer in proton-alkali-metal-atom collisions  

Microsoft Academic Search

The atomic-eigenfunction-expansion method is used to investigate the influence of laser radiation on charge-transfer processes in proton-alkali-metal-atom collisions. The radiation is treated classically. The cross sections for charge transfer into the ground state of hydrogen in collisions between a proton and any of the atoms sodium, potassium, rubidium, and cesium in the presence of radiation of wavelengths varying between 3000

Keka Basu Choudhury; D. P. Sural

1986-01-01

193

Reflection and absorption spectra of singlet charge transfer excitons in anthracene-PMDA crystals  

Microsoft Academic Search

The polarized reflection spectra of single crystals of the weak charge transfer (CT) complex anthracene-pyromellitic dianhydride (A-PMDA) have been measured at 2 K. The oscillator strengths and energies of the singlet charge transfer transitions have been determined from the frequency dependent dielectric function derived from the reflection spectrum by means of a Kramers-Kronig transformation. A theory of exciton-phonon coupling appropriate

Aldo Brillante; Michael R. Philpott

1980-01-01

194

Charge Transfer Interaction and Hydrogen Bonding between Vitamine K1 and Dihydrovitamine K1  

NASA Astrophysics Data System (ADS)

We studied visible and infrared spectra, in particular their temperature dependence, of Vitamine K1 oil dissolving dihydrovitamine K1. Vitamine K1 and dihydrovitamine K1 were found to form charge transfer complexes and hydrogen bonds in the mixture. A co-crystal of Dihydrovitamine K1 and Vitamine K1 with charge transfer interaction and hydrogen bonding was shown to grow in a narrow temperature range near -20°C.

Nagahira, Yukio; Matsuki, Kazunori; Fukutome, Hideo

1981-01-01

195

Laser and isotope effects in charge transfer processes in atomic collisions  

NASA Astrophysics Data System (ADS)

Charge transfer processes are fundamental to the understanding of matter neutralization in atomic and molecular processes. Due to the polarizability of the material, charge transfer can be enhanced or suppressed during the interaction with electromagnetic radiation. Furthermore, charge transfer has different contributions arising from the radial and rotational regions of the potential interaction in the collision, which depend on the mass of the target and projectile. Since these effects appear in a very short time (femtoseconds), the dynamics must be carried out outside the Born-Oppenheimer approximation. In this work, we present charge transfer results for He2+ ions colliding with atomic hydrogen and tritium atoms for collision energies from 100 eV/amu up to 1.5 keV/amu, assisted by a fast, short laser pulses of intensity 3.5×1012 W/cm2 and wave length of 790 nm by means of an electron-nuclear dynamic treatment. We find large isotope effects in the low-energy region up to one order of magnitude in the charge transfer cross-section in the absence of the laser pulse. In the presence of the laser pulse, the isotope effect is negligible and the charge transfer cross-section is enhanced up to two orders of magnitude in the low-energy region.

Cabrera-Trujillo, R.

196

Estimitation of Charge-Transfer Resistivity of Pt Cathode on YSZ Electrolyte Using Patterned Electrodes  

SciTech Connect

YSZ Electrolyte discs with patterned LSM electrodes having different three phase boundary (TPB) lengths but the same electrode-electrolyte interface area, were prepared using photomicrolithography. Impedance spectra for half-cells were obtained under oxygen partial pressures, ranging from 10-3 to 1 atm and temperatures from 650 to 800oC. Area specific charge transfer resistance was found to vary inversely. While the charge transfer resistance is inversely proportional to consistent with the charge transfer reaction occurring mainly at the TPB, at 800oC some transport through LSM also appears to occur. The estimated value of charge transfer resistivity corresponding to the charge transfer reaction occurring at TPB, in air at 800oC is in good agreement with that estimated from actual fuel cell tests using quantitative stereological analysis of LSM-YSZ composite electrodes and were found to decrease with increasing and with increasing temperature. The activation energy for the overall charge transfer reaction was estimated to be ~1.5 eV.

Radhakrishnan, Rajesh; Virkar, Anil V.; Singhal, Subhash C.

2005-04-01

197

Charge transfer reductive doping of single crystal TiO 2 anatase  

Microsoft Academic Search

Electrochemical reductive doping and oxidative de-doping was employed to modify anatase photoelectrochemical properties in situ. Spectroelectrochemical (Raman) and surface analysis (XPS, STM) revealed that changes in surface composition are responsible for variations in the course of both dark and photoassisted charge transfer processes including sub-bandgap photoeffects. The amount of charge passed during electrochemical reduction and oxidation of the electrode served

Hana Pelouchova; Pavel Janda; Jan Weber; Ladislav Kavan

2004-01-01

198

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

Microsoft Academic Search

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

Xiaomu Wu

2010-01-01

199

Collisions of Fast Multicharged Ions in Gas Targets: Charge Transfer and Ionization.  

National Technical Information Service (NTIS)

Measurements of cross sections for charge transfer and ionization of H sub 2 and rare-gas targets have been made with fast, highly stripped projectiles in charge states as high as 59+. We have found an empirical scaling rule for electron-capture cross sec...

A. S. Schlachter

1981-01-01

200

Comparison of charge transfer device and photomultiplier tube performance for extremely low photon fluxes  

Microsoft Academic Search

New solid state silicon arrays which outperform photon counting photomultiplier tubes (PMTs) under extreme low light fluxes are described. The results of the evaluation of the spectroscopically pertinent characteristics of several charge transfer device (CTD) detectors are presented. The characteristics of these multichannel detectors include peak quantum efficiencies exceeding 80 percent, read noises of approximately ten charge carriers and virtually

Jonathan V. Sweedler; M. B. Denton

1988-01-01

201

Evaluating charge transfer in epicocconone analogues: toward a targeted design of fluorophores.  

PubMed

Through-space charge transfers upon photon absorption in aminated epicocconone analogues, which serve as promising proteins markers, are investigated within time-dependent density functional theory using total densities differences and various point-charge models (with a special emphasis on Bader's atoms-in-molecules theory). In particular, the distances and the amounts of charge transfer, as well as the transition dipole moments, are discussed from a methodological point of view, and their values are subsequently linked with the chemical structures of these efficient fluorophores. Finally, on the basis of these theoretical findings, several hints for the future improvement of the photochemical properties of these analogues are advanced. PMID:24446675

Syzgantseva, Olga A; Tognetti, Vincent; Boulangé, Agathe; Peixoto, Philippe A; Leleu, Stéphane; Franck, Xavier; Joubert, Laurent

2014-01-30

202

Charge transfer hysteresis in graphene dual-dielectric memory cell structures  

Microsoft Academic Search

We report controlled charge transfer between large-area graphene and a dual-dielectric, silicon nitride\\/silicon oxide substrate. Graphene was grown on copper by chemical vapour deposition, transferred to the nitride substrates, and patterned into test structures. Hysteresis in conductance with varying gate voltage is easily understood in terms of electron transfer between graphene and nitride traps. Increased hysteresis with temperature suggests thermally

S. A. Imam; T. Deshpande; A. Guermoune; M. Siaj; T. Szkopek

2011-01-01

203

Palm size charging platform with uniform wireless power transfer  

Microsoft Academic Search

In this paper, the design of wireless inductive charger for portable electronic devices is present. There are two main parts have been included. The first part is the exciting circuit in which to provide sufficient input power to the primary charging platform. The exciting circuit is comprised by oscillator circuit and power amplifier circuit. Both of the two circuits have

Yun You; Boon-Hee Soong; Selvakumaran Ramachandran; Wei Liu

2010-01-01

204

Study of charge transfer effects using ballistic method  

Microsoft Academic Search

The ballistic probe principle is applied in this experimental study. Lead pellets were fired from a modified CO2 powered gun and charged by triboelectrification; characteristics of the discharge to a metal target were measured. Preliminary results suggest a dependence of discharge characteristics on speed of approach.

William D Greason; Zdenek Kucerovsky; Cezar Zaharia

2002-01-01

205

Charge transfer in spinel Co3O4 at high pressures.  

PubMed

Charge transfer in cobalt oxide Co(3)O(4) in the spinel structure is evidenced by experimental results using x-ray diffraction (XRD), x-ray absorption near edge structure (XANES) spectroscopy, and Raman scattering at high pressures up to 42.1, 24.6 and 35.1 GPa, respectively. While the cubic structure was found to persist under pressure up to 42.1 GPa based on the XRD and Raman results, the mode Grüneisen parameter was calculated according to our Raman measurements. Our structural data refinement revealed a structural transition from the normal spinel structure at low pressures to a partially inverse spinel structure at pressures above 17.7 GPa. This transition may be caused by the interaction of charges between tetrahedral and octahedral sites via a charge transfer process. Evidence for the charge transfer process is further supported by changes of the pre-edge features in the XANES data. PMID:23032302

Bai, Ligang; Pravica, Michael; Zhao, Yusheng; Park, Changyong; Meng, Yue; Sinogeikin, Stas V; Shen, Guoyin

2012-10-31

206

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

SciTech Connect

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

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

1996-08-07

207

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

208

Chemically intuitive indices for charge-transfer excitation based on SAC-CI and TD-DFT calculations.  

PubMed

A recently proposed charge-transfer (CT) index and some related quantities aimed to the description of CT excitations in push-pull donor-acceptor model systems were computed in vacuum and in ethanol by the direct symmetry-adapted cluster-configuration interaction (SAC-CI) method including solvent effects by means of the nonequilibrium state-specific approach. The effects of both solvation and electron correlations on these quantities were found to be significant. The present results are also in line with previous time-dependent (TD) density functional theory calculations and they demonstrate that SAC-CI provides a description of the excitation character close to that of TD-PBE0. Indeed, CT indices evaluated by the SAC-CI and TD-PBE0 would be useful in the field of materials chemistry, for the design and development of novel molecular materials. PMID:24037799

Ehara, Masahiro; Fukuda, Ryoichi; Adamo, Carlo; Ciofini, Ilaria

2013-11-01

209

Photophysics of charge transfer in a polyfluorene/violanthrone blend  

NASA Astrophysics Data System (ADS)

We present a study of the photophysical and photovoltaic properties of blends of violanthrone in poly[9, 9-bis (2-ethylhexyl)-fluorene-2, 7-diyl ] (PF2/6) . Photoluminescence quenching and photocurrent measurements show moderate efficiencies for charge generation, characteristic of such polymer/dye blends. Pump-probe measurements on blend films suggest that while ˜47% of the total exciton population dissociates within 4ps of photoexcitation, only ˜32% subsequently results in the formation of dye anions. We attribute the discrepancy to the likely formation of complex species with long lifetimes, such as stabilized interface charge pairs or exciplexes. This conclusion is supported by the appearance of a long lifetime component of 2.4ns in the dynamics of the photoinduced absorption signal associated to polarons in photoinduced absorption bands centered at 560nm .

Cabanillas-Gonzalez, J.; Virgili, T.; Lanzani, G.; Yeates, S.; Ariu, M.; Nelson, J.; Bradley, D. D. C.

2005-01-01

210

Chemistry  

NSDL National Science Digital Library

Chemistry is the scientific study of matter and its interaction with other matter and with energy. It is the branch of natural science that deals with the composition of substances and their properties and reactions.

K-12 Outreach,

211

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.

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

2008-01-01

212

A CMOS Image Sensor With In-Pixel Two-Stage Charge Transfer for Fluorescence Lifetime Imaging  

Microsoft Academic Search

A CMOS image sensor for time-resolved fluorescence lifetime imaging with subnanosecond time resolution is presented. In order to analyze the fluorescence lifetime, the proposed CMOS image sensor has two charge transfer stages using a pinned photodiode structure in which the first charge transfer stage is for the time-resolved sifting of fluorescence in all the pixels simultaneously and the second charge

Hyung-June Yoon; Shinya Itoh; Shoji Kawahito

2009-01-01

213

Electrostatic sensors applied to the measurement of electric charge transfer in gas solids pipelines  

NASA Astrophysics Data System (ADS)

This paper describes the development of a number of electric charge sensors. The sensors have been developed specifically to investigate triboelectric charge transfer which takes place between particles and the pipeline wall, when powdered materials are conveyed through a pipeline using air. A number of industrial applications exist for such gas solids pipelines, including pneumatic conveyors, vacuum cleaners and dust extraction systems. The build-up of electric charge on pipelines and powdered materials can lead to electrostatic discharge and so is of interest from a safety viewpoint. The charging of powders can also adversely affect their mechanical handling characteristics and so is of interest to handling equipment engineers. The paper presents the design of the sensors, the design of the electric charge test rig and electric charge measurement test results.

Woodhead, S. R.; Denham, J. C.; Armour-Chelu, D. I.

2005-01-01

214

Grain-boundary chemistry of barium titanate and strontium titanate. Part 1; High temperature equilibrium space charge  

SciTech Connect

This paper reports on direct observations using scanning transmission electron microscopy (STEM) of the grain-boundary chemistry of selectively doped SrTiO{sub 3} and BaTiO{sub 3} that show the predominant solute segregation in both systems to be that of acceptors (negative effective charge). Appreciable donor segregation is not observed even at lattice concentrations as high as 10 mol%. Donor and acceptor codoped materials show segregation of the acceptor only. The results are consistent with a grain-boundary space-charge distribution consisting of a positive boundary and negative space charge. All grain boundaries examined also show an excess of Ti relative to the A-site cations, suggesting that the positive boundary charge is at least partially accommodated by an excess of Ti ions. The sign and magnitude of the electrostatic potential appear to be remarkably insensitive to changes in lattice defect structure with solute doping. Grain-boundary chemistry appears dominated by space-charge segregation, in contrast with the predictions of recent atomistic simulations which neglect the space-charge potential.

Chiang, Y.M.; Takagi, T. (Dept. of Materials Science and Engineering, Massachusetts Inst. of Technology, Cambridge, MA (US))

1990-11-01

215

SF4: electron affinity determination by charge-transfer reactions  

NASA Astrophysics Data System (ADS)

A selected-ion flow drift tube was used to conduct an extensive study of the negative ion/molecule reaction of SF4 and SF-4. Thirteen reactions proceed by electron transfer. Data from these reactions, and information from systems that do not react at all, are used to determine the electron affinity of SF4, EA(SF4) = 1.5 ± 0.2 eV. Additional thermochemical data are used to determine the fluoride affinity of SF3, D(SF3-F-) = 1.8 ± 0.3 eV.

Viggiano, A. A.; Miller, Thomas M.; Stevens Miller, Amy E.; Morris, Robert A.; van Doren, Jane M.; Paulson, John F.

1991-11-01

216

Continuum electrostatic investigations of charge transfer processes in biological molecules using a microstate description.  

PubMed

Charge transfer through biological macromolecules is essential for many biological processes such as for instance photosynthesis and respiration. In these processes, protons or electrons are transferred between titratable residues or redox-active cofactors, respectively. Often their transfer is tightly coupled. Computational methods based on continuum electrostatics are widely used in theoretical biochemistry to analyze the function of even very complex biochemical systems. These methods allow one to consider the pH and the redox potential of the solution as well as explicitly considering membrane potentials in the calculations. Combining continuum electrostatic calculations with a statistical thermodynamic analysis, it is possible to calculate equilibrium parameters such as protonation or oxidation probabilities. Moreover, it is also possible to simulate reaction kinetics by using parameters calculated from continuum electrostatics. One needs to consider that the transfer rate between two sites depends on the current charge configuration of neighboring sites. We formulate the kinetics of charge transfer systems in a microstate formalism. A unique transfer rate constant can be assigned to the interconversion of microstates. Mutual interactions between sites participating in the transfer reactions are naturally taken into account. This formalism is applied to the kinetics of electron transfer in the tetraheme-subunit and the special pair of the reaction center of Blastochloris viridis. It is shown that continuum electrostatic calculations can be used in combination with an existing rate law to obtain electron transfer rate constants. The relaxation electron transfer kinetics after photo-oxidation of the special pair of photosynthetic reaction center is simulated by a microstate formalism and it is shown to be in good agreement with experimental data. A flux analysis is used to follow the individual electron transfer steps. This method of simulating the complex kinetics of biomolecules based on structural data is a first step on the way from structural biology to systems biology. PMID:21322484

Bombarda, Elisa; Ullmann, G Matthias

2011-01-01

217

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

PubMed

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. PMID:24712774

Schöppach, Andreas; Gnandt, David; Koslowski, Thorsten

2014-04-01

218

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

NASA Astrophysics Data System (ADS)

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

Schöppach, Andreas; Gnandt, David; Koslowski, Thorsten

2014-04-01

219

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

220

Excited-state proton coupled charge transfer modulated by molecular structure and media polarization.  

PubMed

Charge and proton transfer reactions in the excited states of organic dyes can be coupled in many different ways. Despite the complementarity of charges, they can occur on different time scales and in different directions of the molecular framework. In certain cases, excited-state equilibrium can be established between the charge-transfer and proton-transfer species. The interplay of these reactions can be modulated and even reversed by variations in dye molecular structures and changes of the surrounding media. With knowledge of the mechanisms of these processes, desired rates and directions can be achieved, and thus the multiple emission spectral features can be harnessed. These features have found versatile applications in a number of cutting-edge technological areas, particularly in fluorescence sensing and imaging. PMID:23169387

Demchenko, Alexander P; Tang, Kuo-Chun; Chou, Pi-Tai

2013-02-01

221

A Molecular Switch Made of Charge Transfer Complexes on Au (111)  

NASA Astrophysics Data System (ADS)

A low temperature scanning tunneling microscope (STM) and spectroscopy study of organic charge transfer complexes is presented. The complexes are formed by self assembly of the electron donor ?- sexithiophene (6T) and the electron acceptor tetrafluro-tetracyano-quinodimethane (F4TCNQ) on Au (111) surface. The formation of new hybrid molecular orbitals in CTCs is evident by STM imaging at different bias voltages as well as by differential conductance spectra. The charge transfer lead to the shift of HOMO and LUMO orbitals of the molecules in complexes with respect to the pure molecular orbitals. Finally, we use a voltage dependent resonance-tunneling scheme to demonstrate a molecular switch made of F4TCNQ/6T charge transfer complexes. This work is financially supported by the US-DOE grant DE-FG02-02ER46012.

Perera, U. G. E.; Jäckel, F.; Iancu, V.; Braun, K.-F.; Koch, N.; Rabe, J. P.; Hla, S.-W.

2008-03-01

222

Spectrophotometric study of the charge-transfer complexes of iodine with antipyrine in organic solvents  

NASA Astrophysics Data System (ADS)

The charge-transfer complex formation of iodine with antipyrine has been studied spectrophotometrically in chloroform, dichloromethane (DCM) and 1,2-dichloroethane (DCE) solutions at 25 °C. The results indicate the formation of 1:1 charge-transfer complexes. The observed time dependence of the charge-transfer band and subsequent formation of I 3- in solution were related to the slow transformation of the initially formed 1:1 antipyrine:I 2 outer complex to an inner electron donor-acceptor (EDA) complex, followed by fast reaction of the inner complex with iodine to form a triiodide ion. The values of the equilibrium constant, K, are calculated for each complex and the influence of the solvent properties on the formation of EDA complexes and the rates of subsequent reaction is evaluated.

Hasani, Masoumeh; Rezaei, Alireza

2006-12-01

223

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

PubMed

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

Dushanov, E B; Kholmurodov, Kh T

2014-01-01

224

Evidences For Charge Transfer-Induced Conformational Changes In Carbon Nanostructure-Protein Corona.  

PubMed

The binding of proteins to a nanostructure often alters protein secondary and tertiary structures. However, the main physical mechanisms that elicit protein conformational changes in the presence of the nanostructure have not yet been fully established. Here we performed a comprehensive spectroscopic study to probe the interactions between bovine serum albumin (BSA) and carbon-based nanostructures of graphene and single-walled carbon nanotubes (SWNTs). Our results showed that the BSA "corona" acted as a weak acceptor to facilitate charge transfer from the carbon nanostructures. Notably, we observed that charge transfer occurred only in the case of SWNTs but not in graphene, resulting from the sharp and discrete electronic density of states of the former. Furthermore, the relaxation of external ?-helices in BSA secondary structure increased concomitantly with the charge transfer. These results may help guide controlled nanostructure-biomolecular interactions and prove beneficial for developing novel drug delivery systems, biomedical devices and engineering of safe nanomaterials. PMID:23243478

Podila, R; Vedantam, P; Ke, P C; Brown, J M; Rao, A M

2012-10-18

225

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

PubMed Central

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

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

2014-01-01

226

Interpenetrating network hydrogels via simultaneous "click chemistry" and atom transfer radical polymerization.  

PubMed

Simultaneous interpenetrating polymer networks (sIPNs) from concurrent copper(I)-catalyzed azide-alkyne cycloaddition "click chemistry" and atom transfer radical polymerization (ATRP) are described. Semi-sIPN of poly(ethylene glycol)/poly(2-hydroxyethyl methacrylate) (semi-PEG/PHEMA-sIPN) was first prepared via simultaneous "click chemistry" and ATRP from a mixture of poly(ethylene glycol)-diazide (N3-PEG-N3, Mn=4000 g/mol), tetrakis(2-propynyloxymethyl)methane (TPOM), ethyl-2-bromobutyrate (EBB), CuBr, pentamethyldiethylenetriamine (PMDETA), and 2-hydroxyethyl methacrylate (HEMA) in dimethylformamide (DMF). Full sIPN of PEG/PHEMA (full-PEG/PHEMA-sIPN) was then prepared via simultaneous "click chemistry" and ATRP from a mixture of N3-PEG-N3 (Mn=4000 g/mol), TPOM, EBB, CuBr, PMDETA, HEMA, and poly(ethylene glycol) diacrylate) (PEGDA, Mn=575) in DMF. Both the semi- and full-sIPNs exhibit a fast gelation rate and high gel yield. The sIPNs also exhibit high swelling ratios and good mechanical and antifouling properties. The morphology and thermal behavior of the sIPNs were studied by scanning electron microscopy (SEM), thermogravimetric analysis (TGA), and differential scanning calorimetry (DSC). These sIPNs could find applications as biomaterials for contact lenses, biomedical materials, artificial organs, and drug delivery systems. PMID:20518556

Xu, L Q; Yao, F; Fu, G D; Kang, E T

2010-07-12

227

Photoswitching of dipole moments, charge-transfer and spectroscopic properties  

NASA Astrophysics Data System (ADS)

The photoswitching of the dipole moment, absorption spectra and oxidation/reduction potentials of donor-acceptor-substituted dihydropyrene-[2,2]metacyclophanediene photochromic systems has been studied theoretically. Two types of basic structures can be formulated for the closed-ring dihydropyrene photoisomers: a conjugated betaine dye type and a merocyanine type structure, respectively. The thermodynamically less stable [2,2]metacyclophanediene forms have significantly larger dipole moments (>40 D) and longer wavelength absorption (CT transition in NIR region) in relation to the closed-ring dihydropyrene structures (<20 D and absorption in visible region). The reason for the strong changing of these properties is that the [2,2]metacyclophanediene fragment acts as a ?-electron conjugation barrier which gives rise to a charge separation of the donor and acceptor substituents, respectively.

Dietz, F.; Olbrich, G.; Karabunarliev, S.; Tyutyulkov, N.

2003-09-01

228

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

229

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

Microsoft Academic Search

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

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

2003-01-01

230

Observation of slow charge redistribution preceding excited-state proton transfer.  

PubMed

The photoacid 8-hydroxy-N,N,N',N',N',N'-hexamethylpyrene-1,3,6-trisulfonamide (HPTA) and related compounds are used to investigate the steps involved in excited-state deprotonation in polar solvents using pump-probe spectroscopy and time correlated single photon counting fluorescence spectroscopy. The dynamics show a clear two-step process leading to excited-state proton transfer. The first step after electronic excitation is charge redistribution occurring on a tens of picoseconds time scale followed by proton transfer on a nanosecond time scale. The three states observed in the experiments (initial excited state, charge redistributed state, and proton transfer state) are recognized by distinct features in the time dependence of the pump-probe spectrum and fluorescence spectra. In the charge redistributed state, charge density has transferred from the hydroxyl oxygen to the pyrene ring, but the OH sigma bond is still intact. The experiments indicate that the charge redistribution step is controlled by a specific hydrogen bond donation from HPTA to the accepting base molecule. The second step is the full deprotonation of the photoacid. The full deprotonation is clearly marked by the growth of stimulated emission spectral band in the pump-probe spectrum that is identical to the fluorescence spectrum of the anion. PMID:18052436

Spry, D B; Fayer, M D

2007-11-28

231

Charge-transfer cross section measurements using laser ablation ion source and reflection time-of-flight mass spectrometer  

Microsoft Academic Search

A new method is developed that combines the production of ions by laser ablation with a reflection time-of-flight mass spectrometer (RTOFMS) for charge-transfer cross section measurements. This method allows a specific charge-transfer channel of an ion-neutral pair to be measured at energies of about 0.1 KeV\\/amu. The charge- transfer cross section is determined by measuring the intensity ratio of the

Jiebing Wang

1997-01-01

232

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

NASA Astrophysics Data System (ADS)

Transient electron density maps are derived from x-ray diffraction patterns of photoexcited [Fe(bpy)3]2+(PF6-)2 powder. Upon photoexcitation, the 5T2 quintet state reveals a charge transfer from the PF6- ions and from the Fe atoms to neighboring bpy units. The charge transfer from the Fe points to a partial and weak charge-transfer character of this state.

Zamponi, F.; Freyer, B.; Juvé, V.; Stingl, J.; Woerner, M.; Chergui, M.; Elsaesser, T.

2013-03-01

233

Charge Transfer in Collisions of C+ with H and H+ with C  

NASA Astrophysics Data System (ADS)

Charge transfer rate coefficients for collisions of C+ with H and H+ with C are presented for temperatures from 30,000 to 107 K and from 10 to 107 K, respectively. The rate coefficients were calculated from recommended cross sections deduced in a recent theoretical and experimental investigation that took into account previous measurements. Nonadiabatic radial coupling is the dominant mechanism for both reactions above ~50,000 K, but for lower temperatures the reaction of H+ with C proceeds primarily by radiative charge transfer. Implications, due to the magnitude of the rate coefficients, for various astrophysical environments are discussed.

Stancil, P. C.; Havener, C. C.; Krsti?, P. S.; Schultz, D. R.; Kimura, M.; Gu, J.-P.; Hirsch, G.; Buenker, R. J.; Zygelman, B.

1998-08-01

234

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

NASA Astrophysics Data System (ADS)

Exciton dynamics at an interface between an electron donor, rubrene, and a C60 acceptor is studied by nonadiabatic quantum molecular dynamics simulation. Simulation results reveal an essential role of the phenyl groups in rubrene in increasing the charge-transfer rate by an order-of-magnitude. The atomistic mechanism of the enhanced charge transfer is found to be the amplification of aromatic breathing modes by the phenyl groups, which causes large fluctuations of electronic excitation energies. These findings provide insight into molecular structure design for efficient solar cells, while explaining recent experimental observations.

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

2012-05-01

235

Enhanced charge transfer by phenyl groups at a rubrene/C{sub 60} interface  

SciTech Connect

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

Mou Weiwei; Hattori, Shinnosuke; Nomura, Ken-ichi; Nakano, Aiichiro [Collaboratory for Advanced Computing and Simulations, Department of Physics and Astronomy, Department of Computer Science, Department of Chemical Engineering and Materials Science, University of Southern California, Los Angeles, California 90089-0242 (United States); Ohmura, Satoshi; Shimojo, Fuyuki [Collaboratory for Advanced Computing and Simulations, Department of Physics and Astronomy, Department of Computer Science, Department of Chemical Engineering and Materials Science, University of Southern California, Los Angeles, California 90089-0242 (United States); Department of Physics, Kumamoto University, Kumamoto 860-8555 (Japan)

2012-05-14

236

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

PubMed

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

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

2012-05-14

237

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

NASA Astrophysics Data System (ADS)

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.

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

2014-05-01

238

Charge transfer and association of protons colliding with potassium from very low to intermediate energies  

Microsoft Academic Search

The nonradiative charge-transfer process for H{sup +}+K(4s) collision is investigated using the quantum-mechanical molecular-orbital close-coupling method for collision energies from 1 eV to 10 keV. The radiative-decay and radiative charge transfer cross sections are calculated using the optical potential approach and the fully quantal method, respectively, for the energy range of 10-10 eV. The radiative-association cross sections are obtained by

C. H. Liu; Y. Z. Qu; J. G. Wang; Y. Li; R. J. Buenker

2010-01-01

239

Charge transfer and association of protons colliding with potassium from very low to intermediate energies  

Microsoft Academic Search

The nonradiative charge-transfer process for H++K(4s) collision is investigated using the quantum-mechanical molecular-orbital close-coupling method for collision energies from 1 eV to 10 keV. The radiative-decay and radiative charge transfer cross sections are calculated using the optical potential approach and the fully quantal method, respectively, for the energy range of 10-5-10 eV. The radiative-association cross sections are obtained by subtracting

C. H. Liu; Y. Z. Qu; J. G. Wang; Y. Li; R. J. Buenker

2010-01-01

240

Charge transfer and dissociation in collisions of metal clusters with atoms.  

PubMed

We present a combined theoretical and experimental study of charge transfer and dissociation in collisions of slow Li31(2+) clusters with Cs atoms. We provide a direct quantitative comparison between theory and experiment and show that good agreement is found only when the exact experimental time of flight and initial cluster temperature are taken into account in the theoretical modeling. We demonstrate the validity of the simple physical image that consists in explaining evaporation as resulting from a collisional energy deposit due to cluster electronic excitation during charge transfer. PMID:12398598

Bréchignac, C; Cahuzac, Ph; Concina, B; Leygnier, J; Ruiz, L F; Zarour, B; Hervieux, P A; Hanssen, J; Politis, M F; Martín, F

2002-10-28

241

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

Microsoft Academic Search

Pump-probe and classical dynamics simulation results for electron transfer in blue copper proteins are reported. Blue copper proteins function as mobile electron carriers in a wide variety of biological systems.(l) In oxidized form, their active sites have a strong ligand-to-metal charge transfer transition between the copper atom and a cysteine sulfur ligand in the region of 595-630 nm.(2) This strong

N. F. Scherer; L. W. Ungar; D. C. Amett; H. Hu; G. A. Voth

242

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

243

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

NASA Astrophysics Data System (ADS)

Charge transfer in a hydrogen-bonded N-methylacetamide(H2O)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

2014-01-01

244

Charge state dependent top-down characterisation using electron transfer dissociation.  

PubMed

The dissociation of protein ions (5-30? kDa) as a function of charge state has been explored in order to suggest the optimal charge state range for top-down sequencing. Proteins were generated under denaturing conditions and their charge states were modified via ion/ion proton transfer reactions prior to dissociation. Electron transfer dissociation (ETD) data suggested optimal sequence coverage for charge states in the m/z range from 700 to 950 while limited sequence coverage was noted when the precursor m/z was above 1000. Sequence coverage from ETD data was found to be dependent on protein size, with smaller proteins having better sequence coverage. An observed depletion in sequence-related information was mainly attributed to limited instrument (ion trap) performance (m/z range and resolution). For a combined ETD/collision-induced dissociation (CID) approach it is difficult to propose an optimal m/z range since good sequence coverage for CID is at intermediate charge states and the optimal m/z range increases with protein size. When only one charge state can be analysed in a combined ETD/CID approach, a range around 950? m/z is suggested as a starting point. Alternatively, two charge states should be explored, each optimal for either ETD or CID. Overall, these suggestions should be useful to achieve enhanced characterisation of smaller proteins/large protein fragments (generated from denaturing solutions) in minimal analysis times. PMID:22223314

Rožman, Marko; Gaskell, Simon J

2012-02-15

245

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

PubMed

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

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

2014-07-01

246

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

PubMed

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

Li, Huixing; Chen, Maodu

2013-12-01

247

Camptothecins guanine interactions: mechanism of charge transfer reaction upon photoactivation  

NASA Astrophysics Data System (ADS)

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

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

2002-01-01

248

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

National Technical Information Service (NTIS)

The charge-transfer rate coefficient for the reaction Si(3+)(3s(sup 2)S) + He yields products is measured by means of a combined technique of laser ablation and ion storage. A cylindrical radio-frequency ion trap was used to store Si(3+) ions produced by ...

Z. Fang V. H. S. Kwong

1997-01-01

249

Dynamic instability of an excited cylindrical interface supporting surface charges and admitting mass and heat transfer  

Microsoft Academic Search

The linear stability of two dielectric inviscid fluids separated by a cylindrical interface is investigated. The interface allows mass and heat transfer. The system is stressed by a radial periodic electric field that allows the presence of surface charges at the interface. The standard normal-modes approach is utilized. A general dispersion equation valid for all (axisymmetric and non-axisymmetric) modes of

G. M. Moatimid

1994-01-01

250

Nanowire labeled direct-charge transfer biosensor for detecting Bacillus species  

Microsoft Academic Search

A direct-charge transfer (DCT) biosensor was developed for the detection of the foodborne pathogen, Bacillus cereus. The biosensor was fabricated using antibodies as the sensing element and polyaniline nanowire as the molecular electrical transducer. The sensor design consisted of four membrane pads, namely, sample application, conjugate, capture and absorption pads. Two sets of polyclonal antibodies, secondary antibodies conjugated with polyaniline

Sudeshna Pal; Evangelyn C. Alocilja; Frances P. Downes

2007-01-01

251

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

252

Dynamic self-assembly of charge-transfer nanofibers of tetrathiafulvalene derivatives with F4TCNQ.  

PubMed

One-dimensional charge-transfer nanostructures were constructed by the supramolecular coassembly of amphiphilic (Amph-TTF) and hydrophobic (TDD-TTF) tetrathiafulvalene (TTF) donor derivatives with the acceptor 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F(4)TCNQ), in appropriate solvent composition mixtures. Microscopic analyses show that TDD-TTF retains its self-assembled fibrillar morphology even in the charge-transfer state, whereas Amph-TTF undergoes a spherical to nanorod transition upon coassembly. Time-dependent optical spectroscopy studies have shown a spontaneous change in molecular organization in TDD-TTF-based donor-acceptor costacks, which suggests a dynamic behavior, in contrast to the kinetically stable amphiphilic TTF assemblies. We have also tried to get an insight into the observed time-dependent change in molecular packing of these nanostructures through spectroscopic analyses by commenting on whether the TTF-TCNQ pair is cofacially arranged or present in the classical herringbone (orthogonal) fashion. Furthermore, our two-probe electrical measurements showed that these charge-transfer fibers are conducting. A supramolecular approach that yields 1D charge-transfer nanostructures of donor and acceptor molecules will be an alternative to existing crystalline substances with high conductivity and hence can be a viable tool for nanoelectronics. PMID:21922580

Jain, Ankit; Rao, K Venkata; Mogera, Umesha; Sagade, Abhay A; George, Subi J

2011-10-24

253

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

254

The effect of charge mixture ratio and particle size on igniter plume heat transfer characteristics  

Microsoft Academic Search

Investigation of the heat transfer characteristics of igniter output plumes, first reported at the Fourteenth International Pyrotechnics Seminar in 1989, has continued, using two types of igniter to determine the effect of charge mixture ratio and fuel particle size on performance. While both of these igniters had the same metallic closure disc (scored Hastelloy with a capture cone), the bridgewire

N. A. Evans; C. F. Brezowski

1990-01-01

255

Oscillatory Behavior of Relaxation of Hot Electrons in a Biased Charge Transfer Double Quantum Well  

Microsoft Academic Search

The relaxation of hot electrons and holes is investigated at 8.5 K in a charge transfer double quantum well (CTDQW) structure. In a CTDQW, the middle barrier BM is lowered to allow confined levels above it. Photoluminescence measurements showed that the relaxation of electrons optically excited above BM alternated between the two wells when a reverse bias applied normally to

M. Rüfenacht; H. Sakaki

1997-01-01

256

Nonlinear optical properties of fullerenes and charge-transfer complexes of fullerenes  

SciTech Connect

The authors present results on the second- and third-order nonlinear optical properties of fullerenes and some of their derivatives. This is part of their effort to study general nonlinear properties of clusters. Polarizability measurements in fullerenes and in N,N-diethylaniline charge transfer complexes are reported.

Wang, Ying; Cheng, Lap-Tak [Du Pont Co., Wilmington, DE (United States)

1992-02-20

257

Preparation and characterization of DABCO ?+x-C ?-60( y) charge transfer complex  

NASA Astrophysics Data System (ADS)

A stable complex of C 60 with an organic donor (tertiary amine, DABCO) has been prepared in the solid state at room temperature. The charge transfer complex, DABCO ?+x-C ?-60( y) is characterised by powder X-ray diffraction and FTIR methods. The complex is soluble in an aqueous medium and shows weak paramagnetic properties.

Priyadarsini, K. I.; Mohan, H.; Tyagi, A. K.; Mittal, J. P.

1994-12-01

258

Thermal vibrational disorder of a conjugated polymer in charge-transfer complex.  

PubMed

Temperature dependences of optical absorption and Raman spectra of ground-state charge-transfer complex (CTC) formed in blends of a conjugated polymer, poly[2-methoxy-5-(2(')-ethylhexyloxy)-p-phenylenevinylene] (MEH-PPV), and low-molecular-weight acceptor, 2,4,7-trinitrofluorenone, were studied. Upon cooling from 320 to 120 K, the polymer strongest Raman band shows a 0.5 cm(-1) low-frequency shift while it demonstrates a 0.5 cm(-1) high-frequency shift in the CTC. This behavior is explained by the temperature dependence of polymer-acceptor charge transfer in the CTC: The amount of transferred charge decreases by 25% upon cooling. At the same time, both the pristine polymer and CTC demonstrate a 0.05-0.1 eV redshift of the absorption edge. To account for these temperature shifts, we propose a model that relates temperature variations in the effective conjugation length with thermal torsion vibrations of the conjugated chains. Comparison of the model and experimental data reveals that the torsion rigidity of conjugated chains involved in the CTC is 30% stronger than that of the pristine ones. This enhanced rigidity increases the conjugation length of MEH-PPV chains in the CTC by 20%. However, the major contribution to the MEH-PPV absorption edge shift in the CTC is assigned to a local built-in electric field effect induced by the ground-state charge transfer. PMID:19739872

Osotov, M O; Bruevich, V V; Paraschuk, D Yu

2009-09-01

259

Charge-transfer range for photoexcitations in conjugated polymer/fullerene bilayers and blends  

SciTech Connect

Time-resolved photoinduced absorption was measured on bilayers of poly-[2-methoxy,5-(2{sup {prime}}-ethylhexoxy)-1,4-phenylenevinylene] (MEH-PPV) and fullerene (C{sub 60}), and on MEH-PPV/C{sub 60} composite films of various concentrations. We find that even in the picosecond regime, charge transfer from the conjugated polymer to C{sub 60} slows down the decay dynamics relative to the decay in the pure samples. The fact that charge transfer occurs in the picosecond time scale in bilayer structure (thickness{approx}200 {Angstrom}) implies that diffusion of localized excitations to the interface is not the dominant mechanism; the charge-transfer range is a significant fraction of the film thickness. From an analysis of the excited-state decay curves, we estimate the charge-transfer range to be 80 {Angstrom} and interpret that range as resulting from quantum delocalization of the photoexcitations. {copyright} {ital 1997} {ital The American Physical Society}

Vacar, D. [Institute for Polymers and Organic Solids, University of California, Santa Barbara, California 93106 (United States)] [Institute for Polymers and Organic Solids, University of California, Santa Barbara, California 93106 (United States); Maniloff, E.S.; McBranch, D.W. [Chemical Science and Technology Division, Mail Stop J585, Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States)] [Chemical Science and Technology Division, Mail Stop J585, Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States); Heeger, A.J. [Institute for Polymers and Organic Solids, University of California, Santa Barbara, California 93106 (United States)] [Institute for Polymers and Organic Solids, University of California, Santa Barbara, California 93106 (United States)

1997-08-01

260

Oxygen-assisted charge transfer between ZnO quantum dots and graphene.  

PubMed

Efficient charge transfer between ZnO quantum dots (QDs) and graphene is demonstrated by decorating ZnO QDs on top of graphene, with the assistance of oxygen molecules from the air. The electrical response of the device to UV light is greatly enhanced, and a photoconductive gain of up to 10(7) can be obtained. PMID:23520196

Guo, Wenhao; Xu, Shuigang; Wu, Zefei; Wang, Ning; Loy, M M T; Du, Shengwang

2013-09-23

261

Spectroscopic Study of Thermal Transfer and Charge Transfer in an Analytic High Frequency Plasma.  

National Technical Information Service (NTIS)

The analysis of energy transfer mechanisms, the characterization of water and hydrogen effects on the excitation processes, and the determination of interferences between alkaline ions are described. An induction coupled plasma generator was used. The mea...

Y. Q. Tang

1986-01-01

262

Probing Transient Structures during interfacial charge transfer mimicking solar cells and heterogeneous catalysis  

NASA Astrophysics Data System (ADS)

Photoinduced charge transfer at interfaces is a key process in photocatalysis and dye sensitized solar cells (DSSCs). Using X-ray transient absorption (XTA) spectroscopy, we extracted metal center surrounding transient structural information in a DSSC mimic, namely the RuN3 dye on the TiO2 nanoparticle surfaces. Structural evolution of the adsorbed dye sensitizer and the rearrangement of the nanocrystal surface associated with the electron density shift during and after the interfacial charge injection were investigated. The other interfacial charge transfer system is a suspension of Pt nanoparticles on TiO2 where the photoexcitation induces redox reactions and generate hydrogen fuel. The preliminary XTA results demonstrate the feasibility of the method in probing heterogeneous catalytic systems.

Chen, Lin; Zhang, Xiaoyi; Smolentsev, Grigory; Guo, Jianchang; Attenkofer, Klaus; Stickrath, Andrew B.; Liu, Di-Jia; Gothard, Nosheen

2011-03-01

263

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

SciTech Connect

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

Davydov, S. Yu., E-mail: sergei_davydov@mail.ru [Russian Academy of Sciences, Ioffe Physical Technical Institute (Russian Federation)

2011-05-15

264

Mechanism of charge separation in DNA by hole transfer through consecutive adenines.  

PubMed

To investigate the mechanism of charge separation in DNA with consecutive adenines adjacent to a photosensitizer (Sens), a series of naphthalimide (NI) and 5-bromouracil ((br)U)-modified DNAs were prepared, and the quantum yields of formation of the charge-separated states (Phi) upon photo-excitation of the Sens NI in DNA were measured. The Phi was modulated by the incorporation site of (br)U, which changes the oxidation potential of its complementary A through hydrogen bonding and the hole-transfer rates between adenines. The results were interpreted as charge separation by means of the initial charge transfer between NI in the singlet excited state and the second- and third-nearest adenine to the NI. In addition, the oxidation of the A nearest to NI leads to the rapid charge recombination within a contact ion pair. This suggests that the charge-separation process can be refined to maximize the Phi by putting a redox-inactive spacer base pair between a photosensitizer and an A-T stretch. PMID:18318023

Kawai, Kiyohiko; Osakada, Yasuko; Fujitsuka, Mamoru; Majima, Tetsuro

2008-01-01

265

Charge transfer to the ionosphere and to the ground during thunderstorms  

NASA Astrophysics Data System (ADS)

The Global Electric Circuit (GEC) is a circuit that is formed between the Earth's surface, which is a good conductor, and the ionosphere, weakly - ionized plasma at region starting at approximately 80 km altitude [e.g., Rycroft et al., Space Sci. Rev., 137, 83-105, 2008]. It is accepted that thunderstorms are the main generators in the global electric circuit (GEC) [e.g., Williams, Atmospheric Research, 91, 140, 2009; Mareev, Physics Uspekhi, 53, 504, 2010]. For the quantification of the contribution of the thunderstorms in the GEC an efficiency term has been introduced, which is defined as the ratio of the total charge transferred to the ionosphere to the net charge neutralized during the lightning [Mareev et al., GRL, 35, L15810, 2008]. In the current work, we examine the current that is driven to the ionosphere and to the ground before, during and after single negative cloud-to-ground (CG) and intracloud (IC) flashes. A numerical model has been developed, that calculates the quasi-electrostatic fields and the charge that is induced in the atmosphere before the flashes, due to the slow accumulation of the charge in the thundercloud, and after the flashes by taking into account the Maxwellian relaxation of the charges in conducting atmosphere. From these results, the induced charges that are transferred to the ionosphere and to the ground are derived. Using a more realistic profile for modeling the conductivity inside the thundercloud we demonstrate the significance of considering the pre-lightning slow charge accumulation stage, we show that the efficiency depends mainly on the altitudes of the charges inside the thundercloud and their spatial separation, and we show also that the amount of charge that is transferred to the ground is negligible compared to the amount of charge that is transferred to the ionosphere. Finally, we show that typical efficiencies for the pre-lightning phase range between 23-60%, for the negative CG case range between 11-50% and for the IC case range between 20-60% and we compare our results with those published recently by Mareev et al. [GRL, 35, L15810, 2008].

Mallios, S. A.; Pasko, V. P.

2011-12-01

266

Experimental and theoretical studies of charge transfer and hydride transfer in the reactions of OD+ and C2H4  

NASA Astrophysics Data System (ADS)

We present a crossed beam and density functional theory (DFT) study of the dynamics of charge transfer and hydride transfer in collisions of OD+ with C2H4 at relative collision energies between 19.3 and 102 kJ mol-1 (0.20-1.06 eV). Charge transfer to form C2H4+ is a direct process occurring through large impact parameters. A comparison of the internal energy distributions of reaction products with the photoelectron spectrum of C2H4 is consistent with a Franck-Condon picture for long distance electron transfer. Charge transfer with H/D rearrangement to form C2H3D+ + OH does not occur, unlike the related system D2O+ + C2H4, in which comparable amounts of C2H4+ and C2H3D+ are observed. This difference is accounted for by the significantly smaller proton affinity of OH relative to H2O. Reactive processes are initiated by the formation of a protonated oxirane triplet diradical, which undergoes intersystem crossing to the singlet manifold. Formation of C2H3+ + HOD, nominally a hydride transfer reaction, is shown to occur at the lowest collision energy through transient singlet intermediates in which the timescale for rate-limiting hydrogen atom migration corresponds to a significant fraction of a rotational period. Formation of hydride transfer products is sufficiently exothermic ([Delta]H = -489 kJ mol-1) that a fraction of the C2H3+ products may be formed above the dissociation threshold to C2H2+. Increasing collision energy results in enhanced yields of C2H2+ relative to C2H3+, consistent with unimolecular decay of the most highly excited C2H3+ products. However, the very small translational energy releases at all collision energies also require significant vibrational excitation in the HOD products; the most probable internal excitation in HOD is approximately 60 kJ mol-1 at all collision energies.

Cai, Xiaohui; Li, Yue; O'Grady, Elizabeth Richards; Farrar, James M.

2005-03-01

267

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

268

Nonanalytic enhancement of the charge transfer from adatom to one-dimensional semiconductor superlattice and optical absorption spectrum  

Microsoft Academic Search

The charge transfer from an adatom to a semiconductor substrate of one-dimensional quantum dot array is evaluated theoretically. Due to the Van Hove singularity in the density of electron states at the band edges, the charge transfer decay rate is enhanced nonanalytically in terms of the coupling constant g as g4\\/3 . The optical absorption spectrum for the ionization of

Satoshi Tanaka; Sterling Garmon; Tomio Petrosky

2006-01-01

269

Impact of a single base pair substitution on the charge transfer rate along short DNA hairpins  

PubMed Central

Numerical studies of hole migration along short DNA hairpins were performed with a particular emphasis on the variations of the rate and quantum yield of the charge separation process with the location of a single guanine:cytosine (G:C) base pair. Our calculations show that the hole arrival rate increases as the position of the guanine:cytosine base pair shifts from the beginning to the end of the sequence. Although these results are in agreement with recent experimental findings, the mechanism governing the charge migration along these sequences is revisited here. Instead of the phenomenological two-step hopping mechanism via the guanine base, the charge propagation occurs through a delocalization of the hole density along the base pair stack. Furthermore, the variations of the charge transfer with the position of the guanine base are explained by the impact of the base pair substitutions on the delocalized conduction channels.

Renaud, Nicolas; Berlin, Yuri A.; Ratner, Mark A.

2013-01-01

270

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

SciTech Connect

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

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

2010-07-13

271

Characteristic features of charge transfer in the interaction between sensitizer molecules and AgCl(I) molecules  

NASA Astrophysics Data System (ADS)

We have used flash luminescence stimulation and photoinduced emission methods to study deep impurity states of AgCl(I) microcrystals with adsorbed organic cationic and anionic dye molecules. We have observed that when these molecules interact with the crystal, charge transfer occurs simultaneously from different orbitals and the transfer occurs differently from each orbital: some orbitals of the molecule pick up a negative charge, others at the same time give up a negative charge. We hypothesize that the type of transfer is determined by the overall charge.

Latyshev, A. N.; Chung, Nguyen Thi Kim; Suvorova, T. I.; Ovchinnikov, O. V.; Smirnov, M. S.; Egorushina, E. A.

2011-07-01

272

Suppression of Electron Transfer to Dioxygen by Charge Transfer and Electron Transfer Complexes in the FAD-dependent Reductase Component of Toluene Dioxygenase*  

PubMed Central

The three-component toluene dioxygenase system consists of an FAD-containing reductase, a Rieske-type [2Fe-2S] ferredoxin, and a Rieske-type dioxygenase. The task of the FAD-containing reductase is to shuttle electrons from NADH to the ferredoxin, a reaction the enzyme has to catalyze in the presence of dioxygen. We investigated the kinetics of the reductase in the reductive and oxidative half-reaction and detected a stable charge transfer complex between the reduced reductase and NAD+ at the end of the reductive half-reaction, which is substantially less reactive toward dioxygen than the reduced reductase in the absence of NAD+. A plausible reason for the low reactivity toward dioxygen is revealed by the crystal structure of the complex between NAD+ and reduced reductase, which shows that the nicotinamide ring and the protein matrix shield the reactive C4a position of the isoalloxazine ring and force the tricycle into an atypical planar conformation, both factors disfavoring the reaction of the reduced flavin with dioxygen. A rapid electron transfer from the charge transfer complex to electron acceptors further reduces the risk of unwanted side reactions, and the crystal structure of a complex between the reductase and its cognate ferredoxin shows a short distance between the electron-donating and -accepting cofactors. Attraction between the two proteins is likely mediated by opposite charges at one large patch of the complex interface. The stability, specificity, and reactivity of the observed charge transfer and electron transfer complexes are thought to prevent the reaction of reductaseTOL with dioxygen and thus present a solution toward conflicting requirements.

Lin, Tzong-Yuan; Werther, Tobias; Jeoung, Jae-Hun; Dobbek, Holger

2012-01-01

273

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

274

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

275

Prediction of remarkable ambipolar charge-transport characteristics in organic mixed-stack charge-transfer crystals.  

PubMed

We have used density functional theory calculations and mixed quantum/classical dynamics simulations to study the electronic structure and charge-transport properties of three representative mixed-stack charge-transfer crystals, DBTTF-TCNQ, DMQtT-F(4)TCNQ, and STB-F(4)TCNQ. The compounds are characterized by very small effective masses and modest electron-phonon couplings for both holes and electrons. The hole and electron transport characteristics are found to be very similar along the stacking directions; for example, in the DMQtT-F(4)TCNQ crystal, the hole and electron effective masses are as small as 0.20 and 0.26 m(0), respectively. This similarity arises from the fact that the electronic couplings of both hole and electron are controlled by the same superexchange mechanism. Remarkable ambipolar charge-transport properties are predicted for all three crystals. Our calculations thus provide strong indications that mixed-stack donor-acceptor materials represent a class of systems with high potential in organic electronics. PMID:22239171

Zhu, Lingyun; Yi, Yuanping; Li, Yuan; Kim, Eung-Gun; Coropceanu, Veaceslav; Brédas, Jean-Luc

2012-02-01

276

Phosphopeptide Anion Characterization via Sequential Charge Inversion and Electron Transfer Dissociation  

PubMed Central

Sequential ion/ion reactions have been used to characterize phosphopeptides present in relatively simple peptide mixtures, including one generated from the tryptic digestion of ?-casein. The phosphopeptides in these mixtures gave rise to either low or no signals via positive ion electrospray ionization. Strong signals, however, were generated in the negative ion mode. An initial ion/ion reaction that employed multiply-protonated amino-terminated dendrimers converted phosphopeptide anions to the doubly protonated species. The doubly charged cations were then subjected to ion/ion electron transfer to induce dissociation. Electron transfer dissociation of doubly positive charged phosphopeptides yields characteristic c- and z-type fragment ions by dissociation of the N-C? bond along the peptide backbone while preserving the labile post-translational modifications. These results illustrate the ability to alter ion charge after ion formation and prior to structural interrogation. Phosphopeptides provide an example where it can be difficult to form strong doubly charged cation signals directly when they are present in mixtures, which, as a result, precludes the use of electron transfer dissociation as a structural probe. The sequential ion/ion reaction process described here, therefore, can provide a new capability for structural interrogation in phosphoproteomics.

Gunawardena, Harsha P.; Emory, Joshua F.; McLuckey, Scott A.

2008-01-01

277

Charge transfer between alkali cluster ions and atoms in the 1 to 10 keV collisional energy range  

Microsoft Academic Search

:   The cross-sections for collisional charge transfer between singly charged free clusters M\\u000a n\\u000a \\u000a + (M = Li, Na; n=1...50) and atomic targets A (cesium, potassium) have been measured as a function of collisional relative velocity in laboratory\\u000a energy range 1–10 keV. For each cluster size, the experimental values of the charge transfer cross-section are fitted with an universal parametric

C. Bréchignac; Ph. Cahuzac; B. Concina; J. Leygnier; I. Tignères

2000-01-01

278

Evidence for a near-resonant charge transfer mechanism for double-stranded peptide nucleic acid.  

PubMed

We present evidence for a near-resonant mechanism of charge transfer in short peptide nucleic acid (PNA) duplexes obtained through electrochemical, STM break junction (STM-BJ), and computational studies. A seven base pair (7-bp) PNA duplex with the sequence (TA)(3)-(XY)-(TA)(3) was studied, in which XY is a complementary nucleobase pair. The experiments showed that the heterogeneous charge transfer rate constant (k(0)) and the single-molecule conductance (?) correlate with the oxidation potential of the purine base in the XY base pair. The electrochemical measurements showed that the enhancement of k(0) is independent, within experimental error, of which of the two PNA strands contains the purine base of the XY base pair. 7-bp PNA duplexes with one or two GC base pairs had similar measured k(0) and conductance values. While a simple superexchange model, previously used to rationalize charge transfer in single stranded PNA (Paul et al. J. Am. Chem. Soc. 2009, 131, 6498-6507), describes some of the experimental observations, the model does not explain the absence of an enhancement in the experimental k(0) and ? upon increasing the G content in the duplexes from one to two. Moreover, the superexchange model is not consistent with other studies (Paul et al. J. Phys. Chem. B 2010, 114, 14140), that showed a hopping charge transport mechanism is likely important for PNA duplexes longer than seven base pairs. A quantitative computational analysis shows that a near-resonant charge transfer regime, wherein a mix of superexchange and hopping mechanisms are expected to coexist, can rationalize all of the experimental results. PMID:21141966

Venkatramani, Ravindra; Davis, Kathryn L; Wierzbinski, Emil; Bezer, Silvia; Balaeff, Alexander; Keinan, Shahar; Paul, Amit; Kocsis, Laura; Beratan, David N; Achim, Catalina; Waldeck, David H

2011-01-12

279

Relationship between surface dipole, work function and charge transfer:??Some exceptions to an established rule  

NASA Astrophysics Data System (ADS)

Local-density-functional calculations are used to study the change of work functions induced by a layer of adsorbates. We investigated and compared the work function of a monolayer of Mo, Ag, Au, Fe, Co, Ni, Nb, Li, N, and O on W(100), W(110), W(211), and W(111) surfaces. While many systems obey the commonly accepted rule that electronegative adsorbates increase the work function of the surface, we find some exceptions. For example, overlayers of Fe, Co, and Ni increase the work function of W(100), W(211), and W(111), but decrease the work function of the W(110) surface, although the charge transfer is the same in all orientations. We found that even a layer of oxygen can decrease the work function of W(100), although there are always electrons transferred from the W substrate to the oxygen adsorbates. In order to understand these results, we established the relationship between surface dipole density and work function within the framework of local-density formalism. It turns out that subtle details of the charge transfer can determine the sign and magnitude of surface dipole change, leading to a strong dependence on the orientation of the substrate, with the consequence that the work-function changes are not always governed by the sign and quantity of adsorbate induced charge transfer.

Leung, T. C.; Kao, C. L.; Su, W. S.; Feng, Y. J.; Chan, C. T.

2003-11-01

280

[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

281

Additive, nanoscale patterning of metal films with a stamp and a surface chemistry mediated transfer process: Applications in plastic electronics  

Microsoft Academic Search

We describe a method for contact printing metal patterns with nanometer features over large areas. This nanotransfer printing (nTP) technique relies on tailored surface chemistries to transfer metal films from the raised regions of a stamp to a substrate when these two elements are brought into intimate physical contact. The printing is purely additive, fast (<15 s contact time), and

Yueh-Lin Loo; Robert L. Willett; Kirk W. Baldwin; John A. Rogers

2002-01-01

282

Charge Transfer Inefficiency effect for high-precision radial velocity measurements  

NASA Astrophysics Data System (ADS)

Charge Transfer Inefficiency (CTI) is a well known effect of charge-coupled devices (CCD). The charge transfer from one pixel to the next is not perfect and is quantified by the fraction of charge successfully moved (clocked) between adjacent pixels. The amplitude of this effect depends on the signal level inside the pixel. In the context of high-precision radial velocity measurements using cross-dispersed echelle spectrograph, this CTI effect on a CCD recording spectral orders may introduce associated spectral lines shifts. Indeed if the signal level recorded on the spectra is changing, the CTI amplitude will change affecting the associated centroid of all spectral lines. Such effect may introduced radial velocity shifts of several m s-1. We describe here CTI effect which is affecting the SOPHIE spectrograph installed on the 1.93-m telescope of Observatoire de Haute Provence (OHP). We calibrated the effect thanks to the Thorium-Argon lines and we applied a software correction on the spectra in order to assess the charge lost during the readout process on all pixels.

Bouchy, F.; Isambert, J.; Lovis, C.; Boisse, I.; Figueira, P.; Hébrard, G.; Pepe, F.

283

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

284

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

NASA Astrophysics Data System (ADS)

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; Tassi, M.; Thanos, S.

2014-04-01

285

Molecular control of photoexcited charge transfer and recombination at a quaterthiophene/zinc oxide interface  

SciTech Connect

Nonadiabatic quantum molecular dynamics simulations are performed to study photoexcited charge transfer (CT) and charge recombination (CR) at an interface between a conjugated oligomer donor, quaterthiophene (QT), and an inorganic acceptor (ZnO). Simulations reveal a detrimental effect of static disorder in QT conformation on the efficiency of hybrid QT/ZnO solar cells due to increased CR. On the contrary, dynamic disorder (i.e., fluctuation of carbon-hydrogen bonds in QT) is essential for high efficiency by assisting CT. The separate controllability of CT and CR at the molecular level has impacts on molecular design for efficient solar cells and explains recent experimental observations.

Mou Weiwei; Nakano, Aiichiro [Collaboratory for Advanced Computing and Simulations, Department of Physics and Astronomy, Department of Computer Science, Department of Chemical Engineering and Materials Science, University of Southern California, Los Angeles, California 90089-0242 (United States); Ohmura, Satoshi; Shimojo, Fuyuki [Collaboratory for Advanced Computing and Simulations, Department of Physics and Astronomy, Department of Computer Science, Department of Chemical Engineering and Materials Science, University of Southern California, Los Angeles, California 90089-0242 (United States); Department of Physics, Kumamoto University, Kumamoto 860-8555 (Japan)

2012-05-14

286

Charge Transfer and Evaporation in Low Energy Collisions of Metal Clusters and Fullerenes with Atomic Targets  

NASA Astrophysics Data System (ADS)

We have studied theoretically charge transfer and fragmentation in collisions of positively charged metal clusters (Na9+, Li312+) and C60 with various atomic targets (Cs and He2+). We show that the relative abundance of different fragments depends critically on cluster temperature and the spectrometer time of flight window (TOF). We have found good agreement with recent experimental results. For C60q+ species (q = 0, 1, 2) produced in collisions with He2+ projectiles, dissociation energies for dimer evaporation have been calculated within DFT. A very good agreement between theoretical estimates and available measurements is found.

Hervieux, P.-A.; Ruiz, L. F.; Diaz-Tendero, S.; Alcami, M.; Zarour, B.; Politis, M. F.; Hanssen, J.; MartA~­n, F.

287

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

288

Aspects of artificial photosynthesis. Photosensitized electron transfer and charge separation in redox active surfactant aggregates  

Microsoft Academic Search

Photosensitized electron transfer and charge separation have been demonstrated by steady-state and nanosecond laser flash photolysis in the presence of redox active surfactant aggregates prepared from CHâ==C(CHâ)-COO(CHâ)ââ(CâHâN\\/sup +\\/)âCHâ,Br⁻,I⁻ (RMV\\/sup 2 +\\/). Tris(2,2'-bipyridine)ruthenium chloride (Ru(bpy)â\\/sup 2 +\\/) has been used as a sensitizer. Forward electron transfer from excited Ru(bpy)â\\/sup 2 +\\/ to RMV\\/sup 2 +\\/ aggregates has been shown to be

Kazue Kurihara; Pietro Tundo; Janos H. Fendler

1983-01-01

289

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

290

Peptides-assisted charge transfers in proteins: relay mechanism and its controllability  

Microsoft Academic Search

This feature article addresses several novel aspects regarding the peptide-mediated charge migrations, including: i) radical\\u000a exchanges with tunable radical types (?-radical versus ?-radical) and electron-transfer (ET)-channel-tunable cooperative proton-coupled\\u000a ET (PCET) mechanism, including hydrogen-atom transfer (HAT), single ET-channel PCET, double ET channel PCET, and channel-type-tunable\\u000a (?-channel versus ?-channel) PCET; ii) hole hopping migration between the active groups in the side-chains and

Yuxiang Bu

2010-01-01

291

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

NASA Astrophysics Data System (ADS)

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

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

2013-07-01

292

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

293

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 YBa_{2}Cu_{3}O_{7-?} and the colossal magnetoresistance compound (La,Ca)MnO_{3}. 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

294

Charge-transfer complexes of Cu(II)/HD analogue in sol gel sensors  

NASA Astrophysics Data System (ADS)

An optically transparent xerogel encapsulating Cu(II) acetate is fabricated to detect mustard gas (HD) analogues via a charge-transfer mechanism. A fast response (color change from sky blue to canary yellow) is observed for the chlorinated sulfide, and is accompanied by an absorption band at 370-420 nm. MO calculations revealed that the chlorinated HD analogue displays a charge-transfer transition extended from sulfur to chlorine atom. A 1:1 complex of Cu(II)/HD analogue is preferred. For a colorimetric sol-gel detector prepared at pH 3, the detection limit of HD analogue is calibrated at 0.03 ?l per 1.5 ml sensor volume.

Brinkley, J. F.; Kirkey, M. L.; Marques, A. D. S.; Lin, C. T.

2003-01-01

295

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

NASA Astrophysics Data System (ADS)

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

Mostafa, Adel; Bazzi, Hassan S.

2009-09-01

296

Investigation of charge transfer in low energy D2+ + H collisions using merged beams  

NASA Astrophysics Data System (ADS)

(H2-H)+ is the most fundamental ion-molecule two-electron system. This temporary complex which is formed during charge transfer collisions of H2+ + H proceeds through dynamically coupled electronic, vibrational, and rotational degrees of freedom. Using the upgraded ion-atom merged-beams apparatus at Oak Ridge National Laboratory, absolute direct charge transfer cross sections for D2+ + H are measured from keV/u collision energies where the collision is considered "ro-vibrationally frozen" to meV/u energies where collision times are long enough to sample vibrational and rotational modes. The measurements presented here are the first to benchmark high energy theory and vibrationally specific adiabatic theory.

Andrianarijaona, V. M.; Rada, J. J.; Rejoub, R.; Havener, C. C.

2009-11-01

297

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

298

Charge transfer complex in diketopyrrolopyrrole polymers and fullerene blends: Implication for organic solar cell efficiency  

NASA Astrophysics Data System (ADS)

Copolymers based on diketopyrrolopyrrole (DPP) have recently gained potential in organic photovoltaics. When blended with another acceptor such as PCBM, intermolecular charge transfer occurs which may result in the formation of charge transfer (CT) states. We present here the spectral photocurrent characteristics of two donor-acceptor DPP based copolymers, PDPP-BBT and TDPP-BBT, blended with PCBM to identify the CT states. The spectral photocurrent measured using Fourier-transform photocurrent spectroscopy (FTPS) and monochromatic photocurrent (PC) methods are compared with P3HT:PCBM, where the CT state is well known. PDPP-BBT:PCBM shows a stable CT state while TDPP-BBT does not. Our analysis shows that the larger singlet state energy difference between TDPP-BBT and PCBM along with the lower optical gap of TDPP-BBT obliterates the formation of a midgap CT state resulting in an enhanced photovoltaic efficiency over PDPP-BBT:PCBM.

Moghe, D.; Yu, P.; Kanimozhi, C.; Patil, S.; Guha, S.

2012-02-01

299

Charge-transfer processes in coupled semiconductor systems. Photochemistry and photoelectrochemistry of the colloidal CdS-ZnO system  

Microsoft Academic Search

Picosecond laser flash photolysis and photoelectrochemical studies have been carried out to elucidate the charge-transfer processes in CdS-ZnO coupled semiconductor systems. Charge injection from excited CdS into ZnO occurs within the laser pulse duration of 18 ps. Long-lived trapped charge carriers demonstrate the improved charge separation in CdS-ZnO coupled semiconductor systems. The feasibility of employing a colloidal CdS-ZnO system in

S. Hotchandani; P. V. Kamat

1992-01-01

300

Aspects of artificial photosynthesis. Photosensitized electron transfer and charge separation in cationic surfactant vesicles  

Microsoft Academic Search

Electron transfer and charge separation have been investigated in cationic dioctadecyldimethylammonium chloride (DODAC) vesicles by laser spectroscopy. h-Methylphenothiazine (MPTH) and its long-chain analogue, N-dodecylphenothiazine (DPTH), were used as electron donors, while a surfactant derivative of tris(2,2'-bipyridine)ruthenium perchlorate, RuCââ(bpy)â\\/sup 2 +\\/, acted as the photoactive electron acceptor, DODAC vesicles organized these donor and acceptor molecules. RuCââ(bpy)â\\/sup 2 +\\/ molecules were anchored

Pierre P. Infelta; Michael Graetzel; Janos H. Fendler

1980-01-01

301

A role of charge-transfer complex with iodine in the modification of coal tar pitch  

Microsoft Academic Search

Iodine introduced into coal tar pitch (CTP) can drastically alter its reology and carbonization behavior. Here, the mechanism of interaction between iodine and CTP has been investigated by using various spectroscopic methods such as 127I-NMR, EPR and FT–IR. It is shown that some iodine molecules infiltrated into the CTP and form charge transfer complexes with the relative large aromatic components

N Miyajima; T Akatsu; T Ikoma; O Ito; B Rand; Y Tanabe; E Yasuda

2000-01-01

302

Photo-induced charge transfer in fullerene-oligothiophene dyads - A quantum-chemical study  

NASA Astrophysics Data System (ADS)

The excited states of fullerene-oligothiophene dyads were studied by quantum-chemical methods in respect of their theoretical suitability as solar-cell materials. Compared to the constituents a significant extension of the absorption spectra to the red has been found caused by optically excitable charge transfer states. These states seem to be responsible for the low energy conversion efficiency of fullerene-oligothiophene dyads in photovoltaic devices.

Beenken, Wichard J. D.

2009-02-01

303

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

Microsoft Academic Search

We study the effect of the molecular charge transfer on the electronic structure of metallic (5,5) and semiconducting (8,0) single-walled carbon nanotubes (SWNTs) induced by surface adsorption of various organic donor-acceptor molecules of different affinities using ab initio density functional theory. Our results, obtained from first-principles spin-polarized calculations show that the adsorption of molecules with different affinities reflects the difference

Arun K. Manna; Swapan K. Pati

2010-01-01

304

Vibrationally resolved charge transfer of O{sup 3+} with molecular hydrogen  

Microsoft Academic Search

Charge transfer due to collisions of ground state O{sup 3+}(2s²2p ²P{sup o}) ions with molecular hydrogen are investigated using the quantum-mechanical molecular-orbital (QMO) coupled-channel method. The QMO calculations utilize ab initio adiabatic potentials and nonadiabatic radial coupling matrix elements obtained with the spin-coupled valence-bond approach for a representative range of orientation angles and diatom internuclear separations. Vibrationally resolved cross sections

J. G. Wang; P. C. Stancil; A. R. Turner; D. L. Cooper

2004-01-01

305

Charge transfer of O{sup 3+} ions with atomic hydrogen  

Microsoft Academic Search

Charge transfer processes due to collisions of ground state O{sup 3+}(2s²2p ²P) ions with atomic hydrogen are investigated using the quantum-mechanical molecular-orbital close-coupling (MOCC) method. The MOCC calculations utilize ab initio adiabatic potentials and nonadiabatic radial and rotational coupling matrix elements obtained with the spin-coupled valence-bond approach. Total and state-selective cross sections and rate coefficients are presented. Comparison with existing

J. G. Wang; P. C. Stancil; A. R. Turner; D. L. Cooper

2003-01-01

306

Investigating Molecular Charge Transfer Complexes with a Low Temperature Scanning Tunneling Microscope  

Microsoft Academic Search

Electron donor-acceptor molecular charge transfer complexes (CTCs) formed by alpha-sexithiophene (6T) and tetrafluoro-tetracyano-quinodimethane (F4TCNQ) on a Au(111) surface are investigated by scanning tunneling microscopy, spectroscopy, and spectroscopic imaging at 6 K. New hybrid molecular orbitals are formed in the CTCs, and the highest occupied molecular orbital of the CTC is mainly located on the electron accepting F4TCNQ while the lowest

F. Jäckel; U. G. E. Perera; V. Iancu; K.-F. Braun; N. Koch; J. P. Rabe; S.-W. Hla

2008-01-01

307

A Molecular Switch Made of Charge Transfer Complexes on Au (111)  

Microsoft Academic Search

A low temperature scanning tunneling microscope (STM) and spectroscopy study of organic charge transfer complexes is presented. The complexes are formed by self assembly of the electron donor alpha- sexithiophene (6T) and the electron acceptor tetrafluro-tetracyano-quinodimethane (F4TCNQ) on Au (111) surface. The formation of new hybrid molecular orbitals in CTCs is evident by STM imaging at different bias voltages as

U. G. E. Perera; F. Jäckel; V. Iancu; K.-F. Braun; N. Koch; J. P. Rabe; S.-W. Hla

2008-01-01

308

Peculiarity of Hexamethylenetetratellurafulvalene (HMTTeF) Charge Transfer Complexes of Donor-Acceptor (DA) Type  

Microsoft Academic Search

The complex formation of hexamethylenetetratellurafulvalene (HMTTeF) with 28 kinds of organic electron acceptors yielded 31 charge transfer (CT) complexes. The infrared and ultra-violet–visible–near-infrared spectra of the complexes were examined to study the ionicity of their ground states in solid. A plot of CT transition energies and the difference of redox potentials; ?E(DA) of donor (D) and acceptor (A) molecules indicated

Sang-Soo Pac; Gunzi Saito

2002-01-01

309

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

Microsoft Academic Search

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

Ming Fat Choi; Peter Hawkins

1996-01-01

310

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

Microsoft Academic Search

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

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

2004-01-01

311

Charge-Transfer Spectra of Iodine with Hydrogen Sulfide and Benzene in Low-Temperature Matrices  

Microsoft Academic Search

The absorption spectrum of benzene–iodine and hydrogen sulfide–iodine was studied at 20°K in argon, krypton, xenon, methane, nitrogen, and sulfur hexafluoride in the spectral range of 2300 to 4500 Å. In addition to the component spectra, strong bands were observed around 2800 Å in all solvents. They are assigned to the electronic charge-transfer transitions of the electron donor-acceptor systems benzene–iodine

E. M. Voigt; Beat Meyer

1968-01-01

312

Electrochemically Controllable Reversible Formation of Cucurbit[8]uril-Stabilized Charge-Transfer Complex on Surface  

Microsoft Academic Search

The reversible formation of cucurbit[8]uril (CB[8])-stabilized charge-transfer (CT) complex on gold, which can be regulated by electrochemical stimuli, is reported. A viologen-based thread molecule with a thiol terminus was designed to synthesise a stable CB[8]-threaded [2]pseudorotaxane (5 ). A mixed self-assembled monolayer (SAM) of 5 and 3-mercaptopropionic acid (3-MPA) on gold was prepared and characterised by reflectance FT-IR spectroscopy. The

Jin-Koo Kang; Ilha Hwang; Young Ho Ko; Woo Sung Jeon; Hee-Joon Kim; Kimoon Kim

2008-01-01

313

Charge-transfer mediated photochemistry in alkene-O2 complexes  

Microsoft Academic Search

The photochemistry of a series of alkene-O2 complexes was studied in a supersonic expansion using a resonance enhanced multiphoton ionization probe of the O(3Pj) photoproduct at 226 nm. The relative yield of oxygen atoms from each complex was correlated to the ionization potential of the alkene species and indicates that initial excitation of an intermolecular charge-transfer state mediates the subsequent

Gary Deboer; Amy Preszler Prince; Mark A. Young

2001-01-01

314

Time-dependent picture of the charge-transfer contributions to surface enhanced Raman spectroscopy  

Microsoft Academic Search

We reexamine the Herzberg-Teller theory of charge-transfer contributions to the theory of surface enhanced Raman scattering (SERS). In previous work, the Kramers-Heisenberg-Dirac framework was utilized to explain many of the observed features in SERS. However, recent experimental and theoretical developments suggest that we revise the theory to take advantage of the time-dependent picture of Raman scattering. Results are obtained for

John R. Lombardi; Ronald L. Birke

2007-01-01

315

Probing Transient Structures during interfacial charge transfer mimicking solar cells and heterogeneous catalysis  

Microsoft Academic Search

Photoinduced charge transfer at interfaces is a key process in photocatalysis and dye sensitized solar cells (DSSCs). Using X-ray transient absorption (XTA) spectroscopy, we extracted metal center surrounding transient structural information in a DSSC mimic, namely the RuN3 dye on the TiO2 nanoparticle surfaces. Structural evolution of the adsorbed dye sensitizer and the rearrangement of the nanocrystal surface associated with

Lin Chen; Xiaoyi Zhang; Grigory Smolentsev; Jianchang Guo; Klaus Attenkofer; Andrew B. Stickrath; Di-Jia Liu; Nosheen Gothard

2011-01-01

316

Correlations between Photoinduced EPR and Photoconductivity in TCNE-THF Solution Charge-Transfer Complex  

Microsoft Academic Search

Reversible photoinduced electron paramagnetic resonance (EPR) signals and photoconductivity were observed when a solution of tetracyanoethylene (TCNE) in tetrahydrofuran (THF) was irradiated in the charge-transfer band of the complex formed between these two compounds. The eleven-line hyperfine structure of the EPR spectrum which was obtained demonstrated the presence of TCNE negative-ion radical. The concentration of this radical was found to

David F. Ilten; Melvin Calvin

1965-01-01

317

Charge transfer properties and photoelectrocatalytic activity of TiO 2\\/MWCNT hybrid  

Microsoft Academic Search

The vertically aligned multiwalled carbon nanotube (MWCNT) arrays on tantalum foils were successfully coated with TiO2 nanoparticles by a hydrothermal process. The prepared TiO2\\/MWCNT hybrid was characterized by scanning electron microscopy and transmission electron microscopy. The charge transfer properties and photocatalytic degradation of rhodamine B with and without bias potential under UV irradiation were investigated. The MWCNTs promoted the separation

Liao-Chuan Jiang; Wei-De Zhang

2010-01-01

318

Photophysical properties of fullerenes and fullerene/N,N-diethylaniline charge-transfer complexes  

SciTech Connect

The author reports fluorescence and phosphorescence measurements of C{sub 60} and C{sub 70} in methylcyclohexane, and photophysical parameters inferred from these measurements. Fluorescence quantum yields are found to depend on the excitation wavelength. The addition of N,N-diethylaniline results in the formation of charge-transfer complexes, and luminescene from both singlet and triplet excited states are observed for C{sub 70}.

Wang, Y. [E.I. du Pont de Nemours and Company, Wilmington, DE (United States)

1992-01-23

319

Theoretical modeling of thermally activated luminescence quenching through charge transfer states in lanthanide complexes  

NASA Astrophysics Data System (ADS)

A theoretical approach for the luminescence thermal quenching through ligand-to-metal charge transfer (LMCT) states in lanthanide compounds is developed. Considering single configurational coordinate models for both LMCT and intra-ligand states, expressions for the spectral overlap integrals involving a donor state, 4f-state (case 1) or an intra-ligand state (case 2), and the LMCT, were obtained. Comparison between theoretical and experimental results of quantum efficiencies for some coordination compounds is quite satisfactory.

Faustino, W. M.; Malta, O. L.; de Sá, G. F.

2006-10-01

320

Radiative charge-transfer lifetime of the excited state of (NaCa){sup +}  

SciTech Connect

New experiments were proposed recently to investigate the regime of cold atomic and molecular ion-atom collision processes in a special hybrid neutral-atom-ion trap under high-vacuum conditions. We study the collisional cooling of laser precooled Ca{sup +} ions by ultracold Na atoms. Modeling this process requires knowledge of the radiative lifetime of the excited singlet A {sup 1}{sigma}{sup +} state of the (NaCa){sup +} molecular system. We calculate the rate coefficient for radiative charge transfer using a semiclassical approach. The dipole radial matrix elements between the ground and the excited states, and the potential curves were calculated using complete active space self-consistent field and Moeller-Plesset second-order perturbation theory with an extended Gaussian basis, 6-311+G (3df). The semiclassical charge-transfer rate coefficient was averaged over a thermal Maxwellian distribution. In addition, we also present elastic collision cross sections and the spin-exchange cross section. The rate coefficient for charge transfer was found to be 2.3x10{sup -16} cm{sup 3}/sec, while those for the elastic and spin-exchange cross sections were found to be several orders of magnitude higher (1.1x10{sup -8} cm{sup 3}/sec and 2.3x10{sup -9} cm{sup 3}/sec, respectively). This confirms our assumption that the milli-Kelvin regime of collisional cooling of calcium ions by sodium atoms is favorable with the respect to low loss of calcium ions due to the charge transfer.

Makarov, Oleg P.; Cote, R.; Michels, H.; Smith, W.W. [Department of Physics, University of Connecticut, Storrs, Connecticut 06269-3046 (United States)

2003-04-01

321

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

PubMed Central

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

Kulhanek, Jiri

2012-01-01

322

M-component mode of charge transfer to ground in lightning discharges  

Microsoft Academic Search

The M-component mode of charge transfer to ground is examined using (1) multiple-station measurements of electric and magnetic fields at distances ranging from 5 to ~500 m from triggered-lightning channels and (2) measured currents at the channel base. Data have been obtained in 1997, 1999, and 2000 at the International Center for Lightning Research and Testing at Camp Blanding, Florida,

Vladimir A. Rakov; David E. Crawford; Keith J. Rambo; George H. Schnetzer; Martin A. Uman; Rajeev Thottappillil

2001-01-01

323

Formation of an intermolecular charge-transfer compound in UHV codeposited tetramethoxypyrene and tetracyanoquinodimethane  

Microsoft Academic Search

Ultrahigh vacuum (UHV)-deposited films of the mixed phase of tetramethoxypyrene and tetracyanoquinodimethane (TMP1-TCNQ1) on gold have been studied using ultraviolet photoelectron spectroscopy (UPS), x-ray diffraction (XRD), infrared (IR) spectroscopy, and scanning tunneling spectroscopy (STS). The formation of an intermolecular charge-transfer (CT) compound is evident from the appearance of new reflexes in XRD ( d1=0.894nm and d2=0.677nm ). A softening of

K. Medjanik; S. Perkert; S. Naghavi; M. Rudloff; V. Solovyeva; D. Chercka; M. Huth; S. A. Nepijko; T. Methfessel; C. Felser; M. Baumgarten; K. Müllen; H. J. Elmers; G. Schönhense

2010-01-01

324

Charge transfer in collisions of Be3+ ions with H atoms  

NASA Astrophysics Data System (ADS)

The nonradiative charge-transfer processes for the Be3+(1s)+H(1s) collisions are investigated by the quantum-mechanical molecular orbital close-coupling method in the energy range of 0.01-10 keV/u. The radiative charge-transfer cross sections are calculated by the optical potential and semiclassical methods in the energy range 10-6-103 eV/u. The needed molecular data are obtained by the ab initio multireference single- and double-excitation configuration interaction method. Total and state-selective cross sections are presented and compared with other available theoretical data. Our calculation agrees well with the atomic orbital close-coupling results of Liu [L. Liu, D. Jakimovski, J. G. Wang, and R. K. Janev, J. Phys. BJPAPEH0953-407510.1088/0953-4075/43/14/144005 43, 144005 (2010)], but there exist some discrepancies with the semiclassical molecular orbital close-coupling results of Shimakura [N. Shimakura, J. Phys. BJPAMA40953-407510.1088/0953-4075/21/13/015 21, 2485 (1988)]. The present results show that the capture to Si2+(1s3l) states is dominant in the whole energy range with the exception of a narrow range of 2-4 keV/u. Rotational couplings play an important role not only in the state-selective cross sections, but also in the total charge-transfer results. At energies below 40 eV/u, the radiative charge transfer exceeds the nonradiative process.

Liu, C. H.; Wang, J. G.

2013-04-01

325

Dual fluorescence and fast intramolecular charge transfer with 4-(diisopropylamino)benzonitrile in alkane solvents  

Microsoft Academic Search

Dual fluorescence and fast intramolecular charge transfer (ICT) is observed with 4-(diisopropylamino)benzonitrile (DIABN) in alkane solvents. The rate constant ka for the reaction from the locally excited (LE) to the ICT state has a value of 3.4×1011 s?1 in n-hexane at 25°C, with an activation energy Ea of 6 kJ mol?1. Efficient intersystem crossing with a yield of 0.94 takes

Attila Demeter; Sergey Druzhinin; Mathew George; Edwin Haselbach; Jean-Luc Roulin; Klaas A. Zachariasse

2000-01-01

326

Charge transfer, electronic quantum processes, and dissociation dynamics in molecule-surface collisions  

Microsoft Academic Search

In this paper some fundamental processes in molecule-surface dynamics are addressed; charge transfer from a metal surface to an incident or adsorbed particle, non-adiabatic electronic processes, and bond breaking dynamics. These processes are illustrated and discussed by referring to two recent experiments and the associated theories.The first example is Cl2 molecules impinging on a clean potassium surface [L. Hellberg, J.

Bengt Kasemo

1996-01-01

327

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

NASA Astrophysics Data System (ADS)

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

Ghosh, Hirendra N.

2013-02-01

328

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

Microsoft Academic Search

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

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

1975-01-01

329

Charge-Transfer Complexation for Spectrophotometric Assay of Certain Imidazole Antifungal Drugs  

Microsoft Academic Search

A spectrophotometric method is described for the assay of some antifungal agents containing an imidazole ring: clotrimazole, econazole, ketoconazole and miconazole. The method is based on the formation of a charge-transfer complex between the drug as n-electron donor and iodine as [sgrave]-acceptor. The product exhibited two absorption maxima at 290 and 377 nm; measurements are made at 290 nm. Beer's

Salwa R. El-Shabouri; Kamla M. Emara; Pakinaz Y. Khashaba; Ashraf M. Mohamed

1998-01-01

330

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

NASA Technical Reports Server (NTRS)

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

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

1977-01-01

331

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

NASA Astrophysics Data System (ADS)

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

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

2010-04-01

332

Charge transfer through DNA/DNA duplexes and DNA/RNA hybrids: complex theoretical and experimental studies.  

PubMed

Oligonucleotides conduct electric charge via various mechanisms and their characterization and understanding is a very important and complicated task. In this work, experimental (temperature dependent steady state fluorescence spectroscopy, time-resolved fluorescence spectroscopy) and theoretical (Density Functional Theory) approaches were combined to study charge transfer processes in short DNA/DNA and RNA/DNA duplexes with virtually equivalent sequences. The experimental results were consistent with the theoretical model - the delocalized nature of HOMO orbitals and holes, base stacking, electronic coupling and conformational flexibility formed the conditions for more effective short distance charge transfer processes in RNA/DNA hybrids. RNA/DNA and DNA/DNA charge transfer properties were strongly connected with temperature affected structural changes of molecular systems - charge transfer could be used as a probe of even tiny changes of molecular structures and settings. PMID:23968861

Kratochvílová, Irena; Vala, Martin; Weiter, Martin; Špérová, Miroslava; Schneider, Bohdan; Páv, Ond?ej; Šebera, Jakub; Rosenberg, Ivan; Sychrovský, Vladimír

2013-01-01

333

Ion-Pair Charge Transfer Photochemistry in Rhenium(I) Borate Salts.  

PubMed

The photophysics and photochemistry of the salt [(bpy)Re(CO)(3)(py)(+)][BzBPh(3)(-)] (ReBo, where bpy = 2,2'-bipyridine, py = pyridine, Bz = C(6)H(5)CH(2) and Ph = C(6)H(5)) has been investigated in THF and CH(3)CN solutions. UV-visible absorption and steady-state emission spectroscopy indicates that in THF ReBo exists primairly as an ion-pair. A weak absorption band is observed for the salt in THF solution that is assigned to an optical ion-pair charge transfer transition. Stern-Volmer emission quenching studies indicate that BzBPh(3)(-) quenches the luminescent dpi (Re) --> pi (bpy) metal-to-ligand charge transfer excited state of the (bpy)Re(CO)(3)(py)(+) chromophore. The quenching is attributed to electron transfer from the benzylborate anion to the photoexcited Re(I) complex, (bpy(-)(*))Re(II)(CO)(3)(py)(+) + BzBPh(3)(-) --> (bpy(-)(*))Re(I)(CO)(3)(py) + BzBPh(3)(*). Laser flash photolysis studies reveal that electron transfer quenching leads to irreversible reduction of the Re(I) cation to (bpy(-)(*))Re(I)(CO)(3)(py). Photoinduced electron transfer is irreversible owing to rapid C-B bond fragmentation in the benzylboranyl radical, PhCH(2)BPh(3)(*) --> PhCH(2)(*) + BPh(3)(*). Quantitative laser flash photolysis experiments show that the quantum efficiency for production of the reduced complex (bpy(-)(*))Re(I)(CO)(3)(py) is unity, suggesting that C-B bond fragmentation in the benzylboranyl radical occurs more rapidly than return electron transfer within the geminate radical pair that is formed by photoinduced electron transfer. PMID:11666846

McCosar, Bruce H.; Schanze, Kirk S.

1996-11-01

334

A Mobile Tryptophan is the Intrinsic Charge Transfer Donor in a Flavoenzyme Essential for Nikkomycin Antibiotic Biosynthesis†  

PubMed Central

The flavoenzyme nikD is required for the biosynthesis of nikkomycin antibiotics. NikD exhibits an unusual long wavelength absorption band attributed to a charge transfer complex of FAD with an unknown charge transfer donor. NikD crystals contain an endogenous active site ligand. At least four different compounds are detected in nikD extracts, including variable amounts of two ADP derivatives that bind to the enzyme’s dinucleotide binding motif in competition with FAD, picolinate (0.07 mol/mol nikD) and an unknown picolinate-like compound. Picolinate, the product of the physiological catalytic reaction, matches the properties deduced for the active site ligand in nikD crystals. The charge transfer band is eliminated upon mixing nikD with excess picolinate but not by a reversible unfolding procedure that removes the picolinate-like compound, ruling out both compounds as the intrinsic charge transfer donor. Mutation of Trp355 to Phe eliminates the charge transfer band, accompanied by a 30-fold decrease in substrate binding affinity. The results provide definitive evidence for Trp355 as the intrinsic charge transfer donor. The indole ring of Trp355 is coplanar with or perpendicular to the flavin ring in “open” or “closed” crystalline forms of nikD, respectively. Importantly, a coplanar configuration is required for charge transfer interaction. Absorption in the long wavelength region therefore constitutes a valuable probe to monitor conformational changes in solution that are likely to be important in nikD catalysis.

Bruckner, Robert C.; Zhao, Gouhua; Ferreira, Patricia; Jorns, Marilyn Schuman

2008-01-01

335

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

NASA Astrophysics Data System (ADS)

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

Massey, Richard

2010-11-01

336

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

NASA Astrophysics Data System (ADS)

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

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

2012-03-01

337

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

338

Excitation and charge transfer in p+H(2s) collisions  

SciTech Connect

Excitation and charge transfer cross sections for proton collisions with 2s excited state hydrogen are calculated using time-dependent lattice, atomic-orbital close-coupling with pseudostates, and classical trajectory Monte Carlo methods. The time-dependent lattice calculation yields {delta}n=1 excitation and {delta}n=0 and {delta}n=1 charge transfer cross sections at 5, 10, and 15 keV incident energy. The atomic-orbital close-coupling with pseudostates calculation yields excitation cross sections to n=3-5 and charge transfer cross sections to n=1-5 at a number of incident energies between 1 and 100 keV. The time-dependent lattice and close-coupling pseudostates calculations are found to be in good agreement with previous standard close-coupling results. The close-coupling with pseudostates calculations are used to benchmark the classical trajectory Monte Carlo calculations, which are widely used in astrophysical and laboratory plasma modelling.

Pindzola, M. S.; Lee, T. G.; Minami, T.; Schultz, D. R. [Department of Physics, Auburn University, Auburn, Alabama 36849 (United States); Physics Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831 (United States)

2005-12-15

339

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

NASA Astrophysics Data System (ADS)

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

Olguin, Marco; Zope, Rajendra; Baruah, Tunna

2013-03-01

340

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

341

Environmental and Structural Effects on Intramolecular Charge Transfer Exhibited by 4-Aminobenzoic Acid and its Derivatives  

NASA Astrophysics Data System (ADS)

This study inspected intramolecular charge transfer in a variety of conditions by methodically adjusting the parent compound structure and solvent properties under spectroscopic analysis. 4-aminobenzoic acid and its derivatives were analyzed in three buffers of varying pH (2, 7, 10). The various compounds were used to study structural effects, while the placement in buffers allowed control of the protonation states of the molecules. The samples were each scanned for absorbance to determine excitation wavelengths which were used for subsequent fluorescent spectroscopic analysis. The charge transfer, when exhibited, is recognized by dual fluorescence. Varying the temperature of the scans allowed analysis of the thermodynamic driving forces for the reaction while the particular solvent-solute combinations that exhibited the phenomenon lend insight to the conditions conducive to charge transfer. To study what controlled the extent of the phenomenon, titrations were carried out to determine the amine pKa and computational models were generated to inspect hybridization and its influence on photophysical behavior.

Thayer, Mitchell; Schmidtke, Sarah

2009-10-01

342

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

NASA Astrophysics Data System (ADS)

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

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

2004-02-01

343

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

PubMed Central

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

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

2001-01-01

344

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

SciTech Connect

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

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

2008-02-25

345

Charge transfer in metal catalysts supported on doped TiO{sub 2}: A theoretical approach based on metal - semiconductor contact theory  

SciTech Connect

The authors developed mathematical models for charge transfer in supported metal catalysts. The electronic structure of supported metal crystallites under the conditions of charge transfer is presented. 53 refs., 5 figs., 3 tabs.

Ioannides, T.; Verykios, X.E. [Univ. of Patras (Greece)] [Univ. of Patras (Greece)

1996-07-01

346

Characteristics of charge density waves on the surfaces of quasi-one-dimensional charge-transfer complex layered organic crystals  

NASA Astrophysics Data System (ADS)

We performed scanning tunneling microscope (STM) studies to observe the surface electronic structure of the following semiconducting charge-transfer complexes: dipropylamine-tetracyanoquinodimethane [DPA(TCNQ)2], triethylammonium [TEA (TCNQ)2], and N-ethylmorpholinium [HEM(TCNQ)2], which all possess the molecularly flat bc surface terminated predominately with the quasi-one-dimensional (1D) TCNQ-0.5 anion chains or the corresponding DPA+, TEA+, and HEM+ cations contributing a lesser fraction. On the bc surfaces terminated with TCNQ-0.5 anions for all crystals, the 4kF[DPA(TCNQ)2] or 2kF [TEA(TCNQ)2 and HEM(TCNQ)2] charge density wave (CDW) driven by the spin-Peierls or Peierls instability for the quasi-1D TCNQ-0.5 chains, respectively, which occur already within the bulk, were probed by use of STM on the crystal surfaces. In that the surface lattice constants obtained from CDW are in good agreement with the bulk ones obtained by x-ray diffraction, such CDWs are commensurate. This modulation of the electric structure is so distinct that the geometric corrugation of individual TCNQ anions was hardly traced during our STM measurements. On the bc surfaces terminated with DPA+, TEA+, and HEM+ cations, the STM images with submolecular resolution represent the geometric corrugation of individual molecular cations, and the surface lattice constants obtained deviate greatly from that of the x-ray crystal structures, indicating self-reassembling of the surface cations.

Lin, Feng; Huang, Xiaoming; Qu, Shengchun; Fang, Zheyu; Huang, Shan; Song, Wentong; Zhu, Xing; Liu, Zhongfan

2011-03-01

347

Dissecting the kinetics of the NADP(+)-FADH2 charge transfer complex and flavin semiquinones in neuronal nitric oxide synthase.  

PubMed

Electron flow within the neuronal nitric oxide synthase reductase domain (nNOSrd) includes hydride transfer from NADPH to FAD followed by two one-electron transfer reactions from FAD to FMN. We have used stopped flow spectrometry to closely monitor these electron transfer steps for both the wild type and the ?G810 mutant of nNOSrd using a protocol involving both global analyses of the photodiode array spectral scans and curve fittings of single wavelength kinetic traces. The charge transfer complex and interflavin electron transfer events recorded at 750nm and 600nm, respectively, show the kinetics in different time frames. All electron transfer events are slow enough at 4°C to enable measurements of rate constants even for the fast charge transfer event. To our knowledge this is the first time the rate constants for the charge transfer between NADP(+) and FADH2 have been determined for NOS. These procedures allow us to conclude that (1) binding of the second NADPH is necessary to drive the full reduction of FMN and; (2) charge transfer and the subsequent interflavin electron transfer have distinct spectral features that can be monitored separately with stopped flow spectroscopy. These studies also enable us to conclude that interflavin electron transfer reported at 600nm is not limiting in NOS catalysis. PMID:23567464

Li, Huiying; Jamal, Joumana; Chreifi, Georges; Venkatesh, Vikram; Abou-Ziab, Hoda; Poulos, Thomas L

2013-07-01

348

Gas-Phase Chemistry of Multiply Charged Bioions in Analytical Mass Spectrometry  

PubMed Central

Ion chemistry has long played an important role in molecular mass spectrometry (MS), as it is central to the use of MS as a structural characterization tool. With the advent of ionization methods capable of producing gaseous ions from large biomolecules, the chemistry of gaseous bioions has become a highly active area of research. Gas-phase biomolecule-ion reactions are usually driven by interactions with neutral molecules, photons, electrons, ions, or surfaces. Ion dissociation or transformation into different ion types can be achieved. The types of reaction products observed depend on the characteristics of the ions, the transformation methods, and the time frame of observation. This review focuses on the gas-phase chemistries of ions derived from the electrospray ionization of peptides, proteins, and oligonucleotides, with particular emphasis on their utility in bioanalysis. Various ion-transformation strategies, which further facilitate structural interrogation by converting ions from one type to another, are also summarized.

Huang, Teng-Yi; McLuckey, Scott A.

2011-01-01

349

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

350

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

PubMed

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

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

2010-09-28

351

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

352

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

353

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

NASA Astrophysics Data System (ADS)

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

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

2014-01-01

354

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

PubMed

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

Kast, Denis; Kecke, L; Ankerhold, J

2011-01-01

355

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

PubMed Central

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

Kecke, L; Ankerhold, J

2011-01-01

356

Enhanced intersystem crossing via a high energy charge transfer state in a perylenediimide-perylenemonoimide dyad.  

PubMed

The electronic relaxation processes of a photoexcited linear perylenediimide-perylenemonoimide (PDI-PMI) acceptor-donor dyad were studied. PDI-PMI serves as a model compound for donor-acceptor systems in photovoltaic devices and has been designed to have a high-energy PDI (-*)-PMI (+*) charge transfer (CT) state. Our study focuses on the minimal Gibbs free energy (Delta G ET) required to achieve quantitative CT and on establishing the role of charge recombination to a triplet state. We used time-resolved photoluminescence and picosecond photoinduced absorption (PIA) to investigate excited singlet (S 1) and CT states and complemented these experiments with singlet oxygen ( (1)Delta g) luminescence and PIA measurements on longer timescales to study the population of triplet excited states (T 1). In an apolar solvent like cyclohexene (CHX), photoinduced electron transfer does not occur, but in more polar solvents such as toluene (TOL) and chlorobenzene (CB), photoexcitation is followed by a fast electron transfer, populating the PDI (-*)-PMI (+*) CT state. We extract rate constants for electron transfer (ET; S 1-->CT), back electron transfer (BET; S 1<--CT), and charge recombination (CR) to lower-energy states (CT-->S 0 and CT-->T 1). Temperature-dependent measurements yield the barriers for the transfer reactions. For ET and BET, these correspond to predictions from Marcus-Jortner theory and show that efficient, near quantitative electron transfer ( k ET/ k BET >or= 100) can be obtained when Delta G ET approximately -120 meV. With respect to triplet state formation, we find a relatively low triplet quantum yield (Phi T < 25%) in CHX but much higher values (Phi T = 30-98%) in TOL and CB. We identify the PDI (-*)-PMI (+*) state as a precursor to the T 1 state. Recombination to T 1, rather than to the ground-state S 0, is required to rationalize the experimental barrier for CR. Finally, we discuss the relevance of these results for electron donor-acceptor films in photovoltaic devices. PMID:18729442

Veldman, Dirk; Chopin, Stéphanie M A; Meskers, Stefan C J; Janssen, René A J

2008-09-18

357

Experimental observation of sub-femtosecond charge transfer in a model water splitting dye-sensitized solar cell.  

PubMed

Charge transfer from photoexcited dye molecules to a semiconductor substrate forms the basis of dye sensitized solar cells (DSCs); the overall effectiveness of a DSC device is critically dependent upon the efficiency of this process due to competition with other de-excitation channels. In this paper, we experimentally derive timescales for the charge transfer process in model water splitting DSCs. We studied two organometallic dye complexes adsorbed onto a rutile TiO(2)(110) substrate, the dye molecules were deposited in ultra-high vacuum using electrospray deposition. DFT simulations were used to calculate the spatial distribution of orbitals relevant to the charge transfer process. The core-hole clock implementation of resonant photoemission spectroscopy was used to determine upper limits on charge transfer timescales for previously unoccupied orbitals, which were found to be in the low-femtosecond regime apart from one orbital found to have an upper limit in the sub-femtosecond regime. PMID:23249025

Weston, Matthew; Handrup, Karsten; Reade, Thomas J; Champness, Neil R; O'Shea, James N

2012-12-14

358

41 CFR 102-36.285 - May we charge for personal property transferred to another federal agency?  

Code of Federal Regulations, 2013 CFR

41 Public Contracts and Property Management 3 2013-07-01 ...false May we charge for personal property transferred to another federal agency...102-36.285 Public Contracts and Property Management Federal Property...

2013-07-01

359

Dynamic structural effects and ultrafast biomolecular kinetics in photoinduced charge transfer reactions. Progress report, September 15, 1990--March 14, 1992.  

National Technical Information Service (NTIS)

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...

J. T. Hupp

1992-01-01

360

Intermetallic charge transfer in A-site-ordered double perovskite BiCu3Fe4O12.  

PubMed

An A-site-ordered double perovskite BiCu(3)Fe(4)O(12) was synthesized at high-pressure and high-temperature conditions. Similar to the isostructural LaCu(3)Fe(4)O(12), the temperature-induced intermetallic charge transfer between the A'-site Cu and the B-site Fe ions occurs but at higher temperature (428 K) than LaCu(3)Fe(4)O(12) (393 K) does. This charge transfer causes an isostructural phase transition with volume contraction by 0.6% as well as semiconductor-to-metal and antiferromagnetism-to-paramagnetism transitions. Although the Bi cation at the A site does not take part in the charge transfer, it appears to enhance the charge-transfer temperature by stabilizing the square-planar coordinated Cu(3+). PMID:19655792

Long, Youwen; Saito, Takashi; Tohyama, Takenori; Oka, Kengo; Azuma, Masaki; Shimakawa, Yuichi

2009-09-01

361

Reduction of charge injection into PECVD SiNxHy by control of deposition chemistry  

Microsoft Academic Search

The high rate of charge trapping in thin-film silicon nitride causes its electrical properties to change with stressing level and time. The rate of shift of the high-frequency CV curves of Al\\/SiNxHy\\/cSi capacitors was used here to measure nitride charging rate and to compare PECVD nitrides deposited under various conditions of plasma power and gas mixture in the same parallel-plate

Donald L. Smith; Andrew S. Alimonda; Chau-Chen Chen; Hsing C. Tuan

1990-01-01

362

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

NASA Astrophysics Data System (ADS)

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

Mizokawa, Takashi

2013-04-01

363

Charge transfer spectra and photoreactivity of ( E)-1-ferrocenyl-2-(1-methyl-4-pyridiniumyl)ethylene cation  

Microsoft Academic Search

The electronic spectrum of (E)-1-ferrocenyl-2-(1-methyl-4-pyridiniumyl)ethylene (E-fmpe+) cation shows two long-wavelength absorptions near 570 and 370 nm which are assigned to metal-to-ligand charge transfer (MLCT) and intraligand charge transfer (ILCT) transitions, respectively. The complex displays a strong negative solvatochromism. MLCT as well as ILCT excitation leads to a trans\\/cis isomerization at the olefinic double bond. The complex is photochromic since the

Horst Kunkely; Arnd Vogler

2001-01-01

364

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

365

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

366

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

PubMed

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. PMID:20080059

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

2010-03-01

367

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

Microsoft Academic Search

A relatively simple model for calculation of the energetics of gas-phase proton transfer reactions and the maximum charge\\u000a state of multiply protonated ions formed by electrospray ionization is presented. This model is based on estimates of the\\u000a intrinsic proton transfer reactivity of sites of protonation and point charge Coulomb interactions. From this model, apparent\\u000a gas-phase basicities (GBapp) of multiply protonated

Paul D. Schnier; Deborah S. Gross; Evan R. Williams

1995-01-01

368

Influence of charge state and amino acid composition on hydrogen transfer in electron capture dissociation of peptides  

Microsoft Academic Search

Although conventional N-C? bond cleavage in electron capture dissociation (ECD) of multiply-charged peptides generates a complementary\\u000a c? and z? fragment pair, the N-C? cleavage followed by hydrogen transfer from c? to z? fragments produces other fragments,\\u000a namely c? and z?. In this study, the influence of charge state and amino acid composition on hydrogen transfer in ECD is described\\u000a using

Takashi Nishikazea; Mitsuo Takayama

2010-01-01

369

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

Microsoft Academic Search

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

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

1996-01-01

370

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

NASA Astrophysics Data System (ADS)

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

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

2012-12-01

371

Theoretical perspectives on electron transfer and charge separation events in photochemical water cleavage systems  

SciTech Connect

We study in this paper the dynamics induced by models for photochemical water cleavage systems, focusing on the spatial and temporal factors influencing electron transfer and charge separation processes in such systems. The reaction-diffusion theory is formulated in full generality and the consequences explored in a number of spatio-temporal regimes, viz. the spatially homogeneous system in the long-time limit (i.e. the steady state for a well-stirred system), the spatially homogeneous system in evolution, and the spatially inhomogeneous system in evolution (where, in the latter study, we consider electron transfer at the cluster surface to be governed by a rate constant that reflects the localized nature of such processes). The results of numerical simulations are presented for all three cases and used to highlight the importance of heterogeneous environments in enhancing the cage escape yield of charge separated species, and to demonstrate the dependence of the hydrogen yield on the localization of electron-transfer processes in the vicinity of the microcatalyst surface.

Kozak, J.J.; Lenoir, P.M.; Musho, M.K.; Tembe, B.L.

1984-01-01

372

Creation of ternary multicomponent crystals by exploitation of charge-transfer interactions.  

PubMed

Four new ternary crystalline molecular complexes have been synthesised from a common 3,5-dinitrobenzoic acid (3,5-dnda) and 4,4'-bipyridine (bipy) pairing with a series of amino-substituted aromatic compounds (4-aminobenzoic acid (4-aba), 4-(N,N-dimethylamino)benzoic acid (4-dmaba), 4-aminosalicylic acid (4-asa) and sulfanilamide (saa)). The ternary crystals were created through the application of complementary charge transfer and hydrogen-bonding interactions. For these systems a dimer was created through a charge-transfer interaction between two of the components, while hydrogen bonding between the third molecule and this dimer completed the construction of the ternary co-crystal. All resulting structures display the same acid???pyridine interaction between 3,5-dnba and bipy. However, changing the third component causes the proton of this bond to shift from neutral OH???N to a salt form, O(-) ???HN(+) , as the nature of the group hydrogen bonding to the carboxylic acid was changed. This highlights the role of the crystal environment on the level of proton transfer and the utility of ternary systems for the study of this process. PMID:23794534

Seaton, Colin C; Blagden, Nicholas; Munshi, Tasnim; Scowen, Ian J

2013-08-01

373

The influences of the transfer method and particle surface chemistry on the dispersion of nanoparticles in nanocomposites  

NASA Astrophysics Data System (ADS)

The synthesis via in situ polymerization and characterization of nanocomposites (NCs) made from silica (SiO2) nanoparticles in a methyl methacrylate (MMA) monomer matrix is reported. We first investigate the transfer of well-defined spherical silica nanoparticles (NPs) (average radius R = 24.2 +/- 3.2 nm) into the monomer solvent. We study the influence of two transfer methods and different surface chemistries on the resulting colloidal stability. The first transfer method consists of drying the silica particles into powder before dispersing them via ultrasonication in the MMA matrix. The second is based on repetitive centrifugations to exchange NPs from their synthetic milieu to pure MMA, avoiding the dried powder state. These transfer methods are compared for two kinds of NP surface chemistry, natural silanol (Si-OH) groups of the silica NPs and an additional silane coupling agent, namely 3-(trimethoxysilyl)propyl methacrylate (TPM), which mimics the monomeric group of the MMA dispersing milieu. We then characterize the morphology of the resulting nanocomposites prepared via in situ polymerization at a fixed amount of dispersed NPs (2.2 wt%; 1 vol%) using a combination of transmission electron microscopy (TEM) from ultramicrotomed nanocomposite films, thermogravimetry (TGA) and small angle X-ray scattering (SAXS).The synthesis via in situ polymerization and characterization of nanocomposites (NCs) made from silica (SiO2) nanoparticles in a methyl methacrylate (MMA) monomer matrix is reported. We first investigate the transfer of well-defined spherical silica nanoparticles (NPs) (average radius R = 24.2 +/- 3.2 nm) into the monomer solvent. We study the influence of two transfer methods and different surface chemistries on the resulting colloidal stability. The first transfer method consists of drying the silica particles into powder before dispersing them via ultrasonication in the MMA matrix. The second is based on repetitive centrifugations to exchange NPs from their synthetic milieu to pure MMA, avoiding the dried powder state. These transfer methods are compared for two kinds of NP surface chemistry, natural silanol (Si-OH) groups of the silica NPs and an additional silane coupling agent, namely 3-(trimethoxysilyl)propyl methacrylate (TPM), which mimics the monomeric group of the MMA dispersing milieu. We then characterize the morphology of the resulting nanocomposites prepared via in situ polymerization at a fixed amount of dispersed NPs (2.2 wt%; 1 vol%) using a combination of transmission electron microscopy (TEM) from ultramicrotomed nanocomposite films, thermogravimetry (TGA) and small angle X-ray scattering (SAXS). Electronic supplementary information (ESI) available. See DOI: 10.1039/c2nr31846f

Pravaz, Olivier; Droz, Benoît; Schurtenberger, Peter; Dietsch, Hervé

2012-10-01

374

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

NASA Astrophysics Data System (ADS)

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

Quinn, Reginald

375

Modification of electronic structure by charge transfer and molecular motion in titanium disulfide-ethylenediamine intercalation compound  

Microsoft Academic Search

An attempt at modifying the electronic conduction mechanism by guest-host charge transfer and thermally excited molecular motion is reported. Ethylenediamine was intercalated into a semiconducting layered material, titanium disulfide, and a significant increase in charge carriers was evidenced by metallic conductivity, Pauli paramagnetism, and conduction electron spin resonance. Rotational motion of the guest molecule was evidenced by the proton spin-lattice

Hironori Ogata; Hiroki Fujimori; Seiichi Miyajima; Kazuhisa Kobashi; Takehiko Chiba; Robert E. Taylor; Kazuhiro Endo

1997-01-01

376

Photoconductive response in organic charge transfer interfaces with high quantum efficiency  

NASA Astrophysics Data System (ADS)

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

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

2013-05-01

377

Energy and charge transfer in polymers as seen by spectrally resolved thermoluminescence  

NASA Astrophysics Data System (ADS)

Several applications of the thermoluminescence (TL) technique for investigations of mechanisms of charge carrier trapping and recombination in electroluminescent polymers which are used for construction of various opto-electronic devices are described. The presented TL studies were focused on polymers emitting blue light, because such emissive materials are requested to realize the white-light-emitting OLEDs or RGB-displays. We have investigated wide band-gap conjugated polymers and also non-conjugated polymers: series of polyfluorenes (homo- and copolymers) and poly(9- vinylcarbazole), neat and doped with low-molecular-weight dopants. The dopants were introduced in order to improve the charge carrier transport and also the to modify the recombination processes. It is shown, that the spectrally resolved thermoluminescence studies, especially when performed in a broad temperature range allow to characterise the nature of the trapping sites and of the recombination centres and to identify the mechanisms responsible for transfer of energy in the investigated materials.

Glowacki, Ireneusz; Luszczynska, Beata; Dobruchowska, Ewa; Ulanski, Jacek

2009-09-01

378

Stability of the staging structure of charge-transfer complexes showing a neutral-ionic transition  

NASA Astrophysics Data System (ADS)

The stability of staging states has been investigated for mixed-stack charge-transfer complexes, TMB-TCNQ [ (3,3',5,5') -tetramethylbenzidine-(7,7,8,8)tetracyanoquinodimethane], DMTTF-CA (dimethyltetrathiafulvalene- p -chloranil), and TTF-CA (tetrathiafulvalene- p -chloranil) crystals, by the calculation of their electrostatic energies considering intramolecular charge distributions. The staging state, a superstructure consisting of an alternative sequence of the ionic and neutral domains, is supposed to be advantageous for reducing the repulsive interaction between neighboring chains in the ionic phase. However, our calculations indicate that the electrostatic interchain interaction is attractive, implying that the staging state is disadvantageous. Nevertheless, a staging state can be marginally stabilized around the neutral-ionic transition in TMB-TCNQ although the energy difference between the staging state and the uniform ionic state is quite small.

Iizuka-Sakano, Takako; Kawamoto, Tohru; Shimoi, Yukihiro; Abe, Shuji

2004-08-01

379

Charge transfer equilibria in ambient-exposed epitaxial graphene on (0001) 6 H-SiC  

NASA Astrophysics Data System (ADS)

The transport properties of electronic materials have been long interpreted independently from both the underlying bulk-like behavior of the substrate or the influence of ambient gases. This is no longer the case for ultra-thin graphene whose properties are dominated by the interfaces between the active material and its surroundings. Here, we show that the graphene interactions with its environments are critical for the electrostatic and electrochemical equilibrium of the active device layers and their transport properties. Based on the prototypical case of epitaxial graphene on (0001) 6 H-SiC and using a combination of in-situ thermoelectric power and resistance measurements and simulations from first principles, we demonstrate that the cooperative occurrence of an electrochemically mediated charge transfer from the graphene to air, combined with the peculiar electronic structure of the graphene/SiC interface, explains the wide variation of measured conductivity and charge carrier type found in prior reports.

Sidorov, Anton N.; Gaskill, Kurt; Buongiorno Nardelli, Marco; Tedesco, Joseph L.; Myers-Ward, Rachel L.; Eddy, Charles R.; Jayasekera, Thushari; Kim, Ki Wook; Jayasingha, Ruwantha; Sherehiy, Andriy; Stallard, Robert; Sumanasekera, Gamini U.

2012-06-01

380

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

381

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

NASA Technical Reports Server (NTRS)

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

Park, Jin-Young; Woon, David E.

2004-01-01

382

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

SciTech Connect

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

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

1998-04-01

383

Solvent-Mediated Electron Leapfrogging: Charge Transfer in IBr^-(CO_2) Photodissociation  

NASA Astrophysics Data System (ADS)

In this work, we investigate the time-resolved photoelectron spectra of IBr^-(CO_2). In the photodetachment studies performed by Lineberger and co-workers,^a IBr^-(CO_2) is prepared in its electronic ground state (^2?1/2^+) whereupon it is excited to its ~A'^ (^2?3/2) excited state, before electron photodetachment/photoionization and dissociation on the Ctilde (^1?_1) excited state of IBr. Previous experimental work showed that dissociation of bare IBr^- yields only I^- + Br products. However in IBr^-(CO_2), a small fraction (˜ 3%) of the dissociating molecules undergo an electron transfer from I to Br at 350 fs after the initial excitation. Thus a single solvent molecule can initiate a non-adiabatic transition from the ~A' state to either the lower ~A or ~X state, thereby producing I + Br^- (+ CO_2) prior to photoionization. To study the dynamics, we perform high level ab initio calculations (MR-SO-CISD/aug-cc-pVTZ(-PP)) as well as classical molecular dynamics (MD) simulations. The MD simulations capture much of the dynamics of the photodissociation but underestimate the charge-transfer channel. Results of the ab initio calculations show how CO_2 bend vibrational excitation could increase the percentage of non-adiabatic transitions and how the CO_2 modifies the charge distribution of IBr^- to make the charge transfer accessible. The proposed mechanism and timescales are consistent with the observed Br^- products. L. Sheps, E. M. Miller, S. Horvath, M. A. Thompson, R. Parson, A. B. McCoy, and W. C. Lineberger, Science, 2010, in press R. Mabbs, K. Pichugin, and A. Sanov, J. Chem. Phys., 2005, 122, 174305.

Horvath, Samantha; McCoy, Anne B.; Sheps, Leonid; Miller, Elisa M.; Thompson, Matthew A.; Parson, Robert; Lineberger, W. Carl

2010-06-01

384

Synthesis of a novel restricted access chiral stationary phase based on atom transfer radical polymerization and click chemistry for the analysis of chiral drugs in biological matrices  

Microsoft Academic Search

A novel chiral restricted access material was synthesized via a combination of atom transfer radical polymerization (ATRP) and click chemistry. Poly(2-methyl-3-butyn-2-ol methacrylate) (pMBMA) was grafted onto porous silica gel by a surface-initiated ATRP in order to synthesize an inner layer for ?-cyclodextrin (?-CD) immobilization. The azide-modified ?-CD was bound to pMBMA by click chemistry. The results demonstrate that click chemistry

Huaisong Wang; Ping Jiang; Min Zhang; Xiangchao Dong

2011-01-01

385

Observation of Frenkel and charge transfer excitons in pentacene single crystals using spectroscopic generalized ellipsometry  

NASA Astrophysics Data System (ADS)

We report on the emerging and admixture of Frenkel and charge transfer (CT) excitons near the absorption onset in pentacene single crystals. Using high energy-resolution spectroscopic generalized ellipsometry with in-plane polarization dependence, the excitonic nature of three lowest lying excitations is discussed. Their distinct polarization dependence strongly indicates the presence of both Frenkel and CT types of excitons near the excitation onset. In particular, the peculiar polarization behavior of the second excitation can only be rationalized by taking into account the inherent CT transition dipole moment. This observation has important implications for the pentacene-based optoelectronic devices.

Qi, Dongchen; Su, Haibin; Bastjan, M.; Jurchescu, O. D.; Palstra, T. M.; Wee, Andrew T. S.; Rübhausen, M.; Rusydi, A.

2013-09-01

386

Thin films and surface patterning with BEDT-TTF based charge transfer salts.  

SciTech Connect

Densely covered (ET)X{sub 2} thin films can be selectively electrodeposited on gold electrodes. The insulating (ET)X{sub 2} films are converted to (ET){sub 2}X conductive films through a novel conproportionation reaction. Both ET and ET salt patterns can be prepared with the PDMS stamping technique with use of an ET derivative with a dodecanethiol chain for surface derivatization. These solution procedures open up the possibility to prepare conductive and superconductive charge-transfer salt thin films as well as patterns.

Wang, H. H.; Han, C. Y.; Noh, D.-Y.; Shin, K.-S.; Willing, G. A.; Geiser, U.

2002-08-21

387

Charge transfer induced magnetism in sol–gel derived nanocrystalline BaTiO3  

NASA Astrophysics Data System (ADS)

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

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

2014-06-01

388

Investigating molecular charge transfer complexes with a low temperature scanning tunneling microscope.  

PubMed

Electron donor-acceptor molecular charge transfer complexes (CTCs) formed by alpha-sexithiophene (6T) and tetrafluoro-tetracyano-quinodimethane (F4TCNQ) on a Au(111) surface are investigated by scanning tunneling microscopy, spectroscopy, and spectroscopic imaging at 6 K. New hybrid molecular orbitals are formed in the CTCs, and the highest occupied molecular orbital of the CTC is mainly located on the electron accepting F4TCNQ while the lowest unoccupied molecular orbital is predominantly positioned on the electron donating 6T. We observed the conductance switching of F4TCNQ inside CTCs, which may find potential applications in novel molecular device operations. PMID:18517888

Jäckel, F; Perera, U G E; Iancu, V; Braun, K-F; Koch, N; Rabe, J P; Hla, S-W

2008-03-28

389

Investigating Molecular Charge Transfer Complexes with a Low Temperature Scanning Tunneling Microscope  

NASA Astrophysics Data System (ADS)

Electron donor-acceptor molecular charge transfer complexes (CTCs) formed by ?-sexithiophene (6T) and tetrafluoro-tetracyano-quinodimethane (F4TCNQ) on a Au(111) surface are investigated by scanning tunneling microscopy, spectroscopy, and spectroscopic imaging at 6 K. New hybrid molecular orbitals are formed in the CTCs, and the highest occupied molecular orbital of the CTC is mainly located on the electron accepting F4TCNQ while the lowest unoccupied molecular orbital is predominantly positioned on the electron donating 6T. We observed the conductance switching of F4TCNQ inside CTCs, which may find potential applications in novel molecular device operations.

Jäckel, F.; Perera, U. G. E.; Iancu, V.; Braun, K.-F.; Koch, N.; Rabe, J. P.; Hla, S.-W.

2008-03-01

390

Orbital Localization, Charge Transfer, and Band Gaps in Semilocal Density-Functional Theory  

NASA Astrophysics Data System (ADS)

We derive an exchange energy functional of generalized gradient form with a corresponding potential that changes discontinuously at integer particle numbers. The functional is semilocal, yet incorporates key features that are connected to the derivative discontinuity of Kohn-Sham density-functional theory. We validate our construction for several paradigm systems and explain how it addresses central well-known deficiencies of antecedent semilocal methods, i.e., the description of charge transfer, properly localized orbitals, and band gaps. We find, e.g., an improved shell structure for atoms, eigenvalues that more closely correspond to ionization energies, and an improved description of band structure where localized states are lowered in energy.

Armiento, R.; Kümmel, S.

2013-07-01

391

Study of charge transfer complexes of menadione (vitamin K3) with a series of anilines.  

PubMed

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. PMID:14670474

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

2004-01-01

392

Double exchange in the charge-transfer states of [Cr 2(OH) 3(tmtame) 2] 3+  

NASA Astrophysics Data System (ADS)

The exchange splittings in the ground and ligand-to-metal charge transfer (LMCT) states of the dimer [Cr 2(OH) 3(tmtame) 2] 3+ (tmtame=1,1,1-tris(aminomethyl)ethane) are derived from optical absorption spectroscopy. The ground-state splitting is antiferromagnetic, whereas the energy ordering of the lowest observed LMCT states is ferromagnetic. This is a new situation. It is due to the dominant direct interactions between metal-centered orbitals, which leads to a double-exchange situation in the LMCT electron configurations.

Schenker, Ralph; Weihe, Høgni; Güdel, Hans U.

1999-04-01

393

Phosphorescent ligand-to-metal charge-transfer excited states in the group IVB metallocene triad  

NASA Astrophysics Data System (ADS)

Long-lived ligand-to-metal charge transfer (LMCT) excited states based on a zirconium complex (ca. 2000 ?s) and a hafnium complex (ca. 300 ?s) are first characterised with use of the Cp 2Zr(IV)Cl 2 and Cp 2Hf(IV)Cl 2. The tendency in the observed photophysics (absorption and phosphorescence spectra, lifetimes, and quantum yields) in the homologous group IVB metallocenes Cp 2M(IV)Cl 2 is discussed in view of the nature of the unique metal (Ti, Zr or Hf)-ligand ?-bonding character.

Loukova, G. V.; Smirnov, V. A.

2000-10-01

394

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

SciTech Connect

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

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

1997-10-01

395

Spectroscopy of charge transfer complexes of four amino acids as organic two-dimensional conductors  

NASA Astrophysics Data System (ADS)

It is found in this study that four amino acids, namely asparagine, arginine, histidine and glutamine form two-dimensional conducting systems which are charge transfer complexes (CTCs) with organic acceptors like TCNQ, TCNE, chloranil, DDQ, TNF and iodine. It is verified using optical absorption edges that these are 2d conductors like transition metal dichalcogenides obeying absorption functions different from 1d and 3d conductors. This 2d nature is related to the network of intermolecular H-bonding in these complexes, which leads to a global H-bonded network resulting in the absence of local deformation due to the relaxation of strain.

Padhiyar, Ashvin; Patel, A. J.; Oza, A. T.

2007-12-01

396

Radical anion salts and charge transfer complexes based on tetracyanoquinodimethane and other strong ?-electron acceptors  

NASA Astrophysics Data System (ADS)

The unique properties of radical anion salts and charge transfer complexes formed by tetracyanoquinodimethane and other strong ?-electron acceptors are analyzed. Their ability to form fusible conductive materials and magnetically ordered structures, including ferromagnetic ones with high Curie temperatures, spin ladders and quasi-two-dimensional organic conductors and superconductors is considered. Particular attention is given to the possible areas of application of these radical anion salts in electronic industry as nanomaterials, materials for the fabrication of field effect transistors, photodiodes and ion selective electrodes. The bibliography includes 421 references.

Starodub, V. A.; Starodub, T. N.

2014-05-01

397

A new charge-transfer complex in UHV co-deposited tetramethoxypyrene and tetracyanoquinodimethane  

Microsoft Academic Search

UHV-deposited films of the mixed phase of tetramethoxypyrene and\\u000atetracyanoquinodimethane (TMP1-TCNQ1) on gold have been studied using\\u000aultraviolet photoelectron spectroscopy (UPS), X-ray-diffraction (XRD), infrared\\u000a(IR) spectroscopy and scanning tunnelling spectroscopy (STS). The formation of\\u000aan intermolecular charge-transfer (CT) compound is evident from the appearance\\u000aof new reflexes in XRD (d1= 0.894 nm, d2= 0.677 nm). A softening of the CN

K. Medjanik; S. Perkert; S. Naghavi; M. Rudloff; V. Solovyeva; D. Chercka; M. Huth; S. A. Nepijko; T. Methfessel; C. Felser; M. Baumgarten; K. Müllen; H. J. Elmers; G. Schönhense

2010-01-01

398

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

NASA Astrophysics Data System (ADS)

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

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

2013-01-01

399

Strong charge-transfer excitonic effects and the Bose-Einstein exciton condensate in graphane.  

PubMed

Using first principles many-body theory methods (GW+Bethe-Salpeter equation) we demonstrate that the optical properties of graphane are dominated by localized charge-transfer excitations governed by enhanced electron correlations in a two-dimensional dielectric medium. Strong electron-hole interaction leads to the appearance of small radius bound excitons with spatially separated electron and hole, which are localized out of plane and in plane, respectively. The presence of such bound excitons opens the path towards an excitonic Bose-Einstein condensate in graphane that can be observed experimentally. PMID:20867194

Cudazzo, Pierluigi; Attaccalite, Claudio; Tokatly, Ilya V; Rubio, Angel

2010-06-01

400

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

401

Theoretical fully differential cross sections for double-charge-transfer collisions  

SciTech Connect

We present a four-body model for double charge transfer, called the four-body double-capture model. This model explicitly treats all four particles in the collision, and we apply it here to fully differential cross sections (FDCSs) for proton+helium collisions. The effects of initial- and final-state electron correlations are studied, as well as the role of the projectile-nucleus interaction. We also present results for proton+helium single capture, as well as single-capture:double-capture ratios of FDCSs.

Harris, A. L.; Peacher, J. L.; Madison, D. H. [Physics Department, Missouri University of Science and Technology, Rolla, Missouri 65401 (United States)

2010-08-15

402

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

NASA Astrophysics Data System (ADS)

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

Pereira, Robson Valentim; Gehlen, Marcelo Henrique

2006-08-01

403

The Yb-doped aluminosilicate fibers photodarkening mechanism based on the charge-transfer state excitation  

NASA Astrophysics Data System (ADS)

We have studied the photodarkening effect in fiber preforms with an ytterbium-doped aluminosilicate glass core. The room-temperature stable Yb2+ ions formation in the glass matrix under both UV- and NIR-pumping irradiation was revealed by the method of absorption spectra analysis and the fluorescence spectroscopy technique. Comparative studies of preforms and crystals samples luminescence spectra, obtained under UV-excitation, were performed. A general mechanism of Yb2+ ions and aluminium oxygen-hole centers (Al-OHC) formation as a result of photoinduced process of Yb3+ ions excitation to "charge-transfer state" (CTS) was found for both Yb:YAG crystal and aluminosilicate glass.

Rybaltovsky, A. A.; Bobkov, K. K.; Velmiskin, V. V.; Umnikov, A. A.; Shestakova, I. A.; Guryanov, A. N.; Likhachev, M. E.; Bubnov, M. M.; Dianov, E. M.

2014-03-01

404

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

PubMed Central

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

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

2013-01-01

405

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

406

The influence of substrate charge and molecular structure on interphase transfer in cloud point extraction systems.  

PubMed

The specificity of interphase transfer of organic reagents of different types between water and the nonionic-surfactant-rich phases at the cloud point temperature was investigated. In contrast to organic solvents, the ability of the micellar phases to extract highly charged ions of organic reagents was shown. Further evidence of the specificity of interphase transfer in micellar-extraction systems is independent and cooperative influence of substrate molecular structure and hydrophobicity on their distribution. The appearance of host-guest phenomenon in cloud point extraction systems that is inherent in organized systems with molecules of the receptors was established. The possibility of describing reagent distribution using regressions that consider substrate hydrophobicity and molecular structure in the cloud point extraction systems was shown. PMID:15972216

Doroschuk, V O; Kulichenko, S A; Lelyushok, S O

2005-11-01

407

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

408

Charge Transfer Processes in Collisions of Si4+ Ions with He Atoms at Intermediate Energies  

NASA Astrophysics Data System (ADS)

Charge transfer in collisions of Si4+ ions with He atoms below 100 keV/u is studied by using a molecular orbital representation within both the semiclassical and quantal representations. Single transfer reaction Si4++He ?Si3++He+ has been studied by a number of theoretical investigations. In addition to the reaction (1), the first semiclassical MOCC calculations are performed for the double transfer channel Si4++HE?Si2++He2+ Nine molecular states that connect both with single and double electron transfer processes are considered in the present model. Electronic states and corresponding couplings are determined by the multireference single- and double- excitation configuration interaction method. The present cross sections tie well with the earlier calculations of Stancil et al., Phys. Rev. A 55, 1064 (1997) at lower energies, but show a rather different magnitude from those of Bacchus-Montabonel and Ceyzeriat, Phys. Rev. A 58, 1162 (1998). The present rate constant is found to be significantly different from the experimental finding of Fang and Kwong, Phys. Rev. A 59, 342 (1996) at 4,600 K, and hence does not support the experiment.

Suzuki, R.; Watanabe, A.; Sato, H.; Gu, J. P.; Hirsch, G.; Buenker, R. J.; Kimura, M.; Stancil, P. C.

409

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

PubMed

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

2012-12-15

410

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.

Liu, Jian; McLuckey, Scott A.

2012-01-01

411

The influences of the transfer method and particle surface chemistry on the dispersion of nanoparticles in nanocomposites.  

PubMed

The synthesis via in situ polymerization and characterization of nanocomposites (NCs) made from silica (SiO(2)) nanoparticles in a methyl methacrylate (MMA) monomer matrix is reported. We first investigate the transfer of well-defined spherical silica nanoparticles (NPs) (average radius R = 24.2 ± 3.2 nm) into the monomer solvent. We study the influence of two transfer methods and different surface chemistries on the resulting colloidal stability. The first transfer method consists of drying the silica particles into powder before dispersing them via ultrasonication in the MMA matrix. The second is based on repetitive centrifugations to exchange NPs from their synthetic milieu to pure MMA, avoiding the dried powder state. These transfer methods are compared for two kinds of NP surface chemistry, natural silanol (Si-OH) groups of the silica NPs and an additional silane coupling agent, namely 3-(trimethoxysilyl)propyl methacrylate (TPM), which mimics the monomeric group of the MMA dispersing milieu. We then characterize the morphology of the resulting nanocomposites prepared via in situ polymerization at a fixed amount of dispersed NPs (2.2 wt%; 1 vol%) using a combination of transmission electron microscopy (TEM) from ultramicrotomed nanocomposite films, thermogravimetry (TGA) and small angle X-ray scattering (SAXS). PMID:23034718

Pravaz, Olivier; Droz, Benoît; Schurtenberger, Peter; Dietsch, Hervé

2012-11-01

412

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

PubMed

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

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

2014-01-01

413

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

SciTech Connect

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

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

2004-09-01

414

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

NASA Astrophysics Data System (ADS)

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

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

415

WFC3/UVIS Charge-Transfer-Efficiency Losses: Mitigation and Correction  

NASA Astrophysics Data System (ADS)

WFC3/UVIS was installed on HST in 2009 and has been subjected to the harsh radiation environment of space for the past five years. One consequence of radiation damage is charge-transfer-efficiency (CTE) losses, and these losses became apparent much more quickly than expected for WFC3/UVIS because of its low dark current and the low backgrounds in the ultraviolet. Several years ago, we developed a pixel-based model to describe the WFC3/UVIS charge-transfer process, similar to the model that was developed for ACS/WFC. This model showed us that a low-level of post-flash (12 electrons) significantly improves CTE, and many observations now take advantage of this preventative strategy. We have recently taken some calibration data to allow us to improve the pixel-based CTE-correction model in anticipation for the model's inclusion in the WFC3 pipeline. This poster will report on the latest model and CTE-losses.

Anderson, Jay

2014-06-01

416

Reversible Switching Between Molecular and Charge Transfer Phases in a Liquid Crystalline Organic Semiconductor  

SciTech Connect

We report the first experimental example, to our knowledge, of reversible switching between a molecular and a charge transfer phase in an organic semiconductor. An oriented film of liquid crystal perylene diimide molecules reversibly switches between a red phase with narrow conduction and valence bands and a large bandwidth black phase as the {pi}-stacked chromophores shift just 1.6 {angstrom} relative to their neighbors. This shift causes a substantial change in the intermolecular electronic overlap between molecules. The polarization of maximum absorbance rotates {approx} 90{sup o}, from an apparently molecule centered transition to an intermolecular charge transfer (CT) transition polarized along the {pi}-{pi} stacking axis. The experimental results are further explored via density functional theory calculations on a dimer model that demonstrate the variations in energy and oscillator strength of the molecular (Frenkel) and CT transitions as the longitudinal molecular offset is varied. These results demonstrate the exquisite sensitivity of the electrical properties of organic semiconductors to slight variations in molecular stacking.

Gregg, B. A.; Kose, M. E.

2008-01-01

417

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.

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

418

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

NASA Astrophysics Data System (ADS)

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

Olsen, Seth; McKenzie, Ross H.

2012-10-01

419

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

2013-05-24

420

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

PubMed

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. PMID:24921438

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

2014-06-26

421

Charge Transfer Inefficiency Over The History Of The ACS WFC Instrument Of The HST  

NASA Astrophysics Data System (ADS)

We have examined multiple epochs of data extending from April 2002, up through June 2010, from the Hubble Space Telescope's (HST) Advanced Camera for Surveys (ACS) Wide Field Channel (WFC), in effort to determine the charge transfer efficiency loss, (also known as charge transfer inefficiency: CTI), during the time this instrument has spent on-orbit. With special attention paid to the calibration data of the post Servicing Mission 4 (SM4) period, and in lieu of the gross abundance of calibration darks taken throughout the history of the ACS WFC, there existed a large and conclusive database of information as to the development of these notorious trails arising from CTI. The CTI trails extend from warm pixels much the same, and as reproducibly predictable, as the bleeding flux from point sources, with which we are all unfortunately so well acquainted. The growth and evolution of these trails, that proceed from, and downstream to, these recurrent warm pixels, has grown in a nonlinear fashion in both magnitude and shape relative to time elapsed on-orbit. We present an archive of CTI trails found throughout eight and a half years of ACS WFC orbit time, along with the chronological trends found therein.

Ferguson, Brian A.; Smith, L.; Grogin, N.; Golimowski, D.

2011-01-01

422

Time-resolved fluorescence of intramolecular charge-transfer systems: experimental results and theoretical predictions  

NASA Astrophysics Data System (ADS)

The time-resolved emission spectrum of dual fluorescent pyrrolidino-benzonitrile in glycerol acetate is interpreted by employing a stochastic model. The model system is made up of an internal coordinate describing the intramolecular adiabatic charge-transfer reaction and a polarization coordinate describing the dynamic behaviour of the polar solvent. The time evolution of the system is governed by a coupled Smoluchowski equation plus source and sink terms to account for the excitation from the ground state and subsequent decay. The model reproduces the dynamic Stokes shift of the frequency maximum of the emission band related to the charge-transfer (CT) state towards the red region, and it provides interpretation of the kinetic behaviour manifested by the system after pulse excitation at the short-wavelength absorption band, corresponding to the locally excited (LE) state. The observation of a dynamic Stokes shift accompanying the time evolution of the CT band implies a kinetic pathway which deviates from steepest descent to the CT state, the rate-determining step being the solvent relaxation.

Braun, David; Nordio, Pier Luigi; Polimeno, Antonino; Saielli, Giacomo

1996-07-01

423

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

PubMed

The interactions of the electron donors 2-aminopyridine (2APY) and 3-aminopyridine (3APY) with the pi-acceptors tetracyanoethylene (TCNE), 2,3-dichloro-5,6-dicyano-p-benzoquinone (DDQ), 2-chloro-1,3,5-trinitrobenzene (picryl chloride, PC), and 2,3,5,6-tetrachloro-1,4-benzoquinone (chloranil) were studied spectrophotometrically in chloroform at room temperature. The electronic and infrared spectra of the formed molecular charge transfer (CT) complexes were recorded. Photometric titration showed that the stoichiometries of the reactions were fixed and depended on the nature of both the donor and the acceptor. The molecular structures of the CT-complexes were, however, independent of the position of the amino group on the pyridine ring and were formulated as [(APY)(TCNE)], [(APY)(DDQ)], [(APY)(PC)], and [(APY) (chloranil)]. The formation constants (K(CT)), charge transfer energy (E(CT)) and molar extinction coefficients (epsilon(CT)) of the formed CT-complexes were obtained. PMID:19574089

Mostafa, Adel; Bazzi, Hassan S

2009-09-15

424

Charge-transfer complexes of sulfamethoxazole drug with different classes of acceptors  

NASA Astrophysics Data System (ADS)

The charge-transfer complexes of the donor sulfamethoxazole (SZ) with iodine (I 2), 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ), p-chloranil (CHL) and picric acid (PA) have been studied spectrophotometrically in chloroform or methanol at room temperature using absorption spectrophotometer. The results indicate that formation of CT-complexes in case of four acceptors. The stoichiometry of the complexes was found to be 1:1 ratio by molar ratio method between donor and acceptor with maximum absorption bands (CT band). The data are discussed in terms of formation constant ( KCT), molar extinction coefficient ( ?CT), standard free energy (? G°), oscillator strength (ƒ), transition dipole moment ( ?), resonance energy ( RN) and ionization potential ( ID). The results indicate that the formation constant ( KCT) for the complexes were shown to be dependent upon the nature of electron acceptor, donor and polarity of solvents which were used. IR, 1H NMR, mass spectra, UV-Vis techniques, elemental analyses (CHN) and TG-DTG investigation were used to characterize the four sulfamethoxazole charge-transfer complexes.

Refat, Moamen S.; El-Korashy, Sabry A.; El-Deen, Ibrahim M.; El-Sayed, Shaima M.

2010-09-01

425

Resolving photo-induced twisted intramolecular charge transfer with vibrational anisotropy and TDDFT.  

PubMed

The interplay between reaction environment and photochemical outcome has wide ranging implications for designing and directing light driven chemical conversions. We present a detailed mechanistic description of photoisomerization in julolidine malononitrile (JDMN) as the first step to characterizing this interplay between reaction pathways and reaction environment. We have used polarization resolved UV pump-mid-IR probe spectroscopy and time dependent DFT calculations to investigate the dynamics of charge transfer induced intramolecular rotation in JDMN. We have probed the mechanism and dynamics of photoisomerization with the symmetric and antisymmetric CN-stretch of the malononitrile group. These measurements show the S1 electronic excited state relaxes with a 12.3 ps time constant by isomerizing around both the C-C single and C-C double bond of the malononitrile group with a branching ratio of 1:5. Isomerization around the single bond leads to the formation of a metastable twisted excited state, while isomerization around the double bond leads to excited state quenching via a conical intersection between the S1 and S0 electronic states. We have characterized the electronic and nuclear structure of the long-lived excited state with pump-probe anisotropy measurements and time dependent DFT calculations using the CAM-B3LYP functional and the 6-31G(d,p) basis set. These calculations further confirm that isomerization around the malononitrile single bond forms a twisted intermolecular charge transfer excited state. PMID:22934677

Zhang, Wenkai; Lan, Zhenggang; Sun, Zheng; Gaffney, Kelly J

2012-09-20

426

Electric-field-induced charge-transfer phase transition: a promising approach toward electrically switchable devices.  

PubMed

Much research has been directed toward the development of electrically switchable optical materials for applications in memory and display devices. Here we present experimental evidence for an electric-field-induced charge-transfer phase transition in two cyanometalate complexes: Rb(0.8)Mn[Fe(CN)(6)](0.93).1.62H(2)O and Co(3)[W(CN)(8)](2)(pyrimidine)(4).6H(2)O, involving changes in their magnetic, optical, and electronic properties as well. Application of an electric field above a threshold value and within the thermal hysteresis region leads to a transition from the high- to the low-temperature phase in these compounds. A model is proposed to explain the main observations on the basis of a para-ferroelectric transition. Our observations suggest that this new concept of electrical switching, based on materials exhibiting charge-transfer phase transitions with large thermal hysteresis loops, may open up doors for novel electro-optical devices. PMID:19788300

Mahfoud, Tarik; Molnár, Gábor; Bonhommeau, Sébastien; Cobo, Saioa; Salmon, Lionel; Demont, Philippe; Tokoro, Hiroko; Ohkoshi, Shin-Ichi; Boukheddaden, Kamel; Bousseksou, Azzedine

2009-10-21

427

Ligand-ligand charge-transfer excited states of Os(II) complexes  

SciTech Connect

This paper examines the photophysics of metal-to-ligand charge-transfer (MLCT) and ligand-to-ligand charge-transfer (LLCT) excited states in a series of ((bpy){sub 2}Os{sup II}(CO)L){sup 2+} (Os-L) complexes. For each of the complexes studied, the d{pi}(Os) {yields} {pi}*(bpy) absorption band is the lowest energy transition that is apparent. For L = pyridine and benzonitrile, only long-lived, highly luminescent MLCT states are observed. However, when L = an electron-donor aminobenzonitrile (ABN) species (DMABN, TMABN, or CMI; see text), MLCT emission is quenched and in < 30 ps LLCT excited states are formed, *((bpy{sup {sm bullet}{minus}})-(bpy)OS{sup II}(CO)ABN{sup {sm bullet}+}){sup 2+}. The observed, weight-average radiationless decays of the LLCT excited states in acetonitrile and dichloromethane follow the squence Os-DMABN < Os-TMABN < Os-CMI in each solvent, and the calculated energies of the LLCT states for these complexes are in inverse order to the decay rates as expected if an energy gap law is followed. Finally, multiexponential relaxations of the LLCT states are pronounced in the nonpolar solvent dichloromethane. The dependence of these relaxations on the concentration of added electrolyte suggests that they may be due to ion-pair structure and dynamics.

Perkins, T.A.; Schanze, K.S. (Univ. of Florida, Gainesville (USA)); Pourreau, D.B.; Netzel, T.L. (Amoco Research Corp., Naperville, IL (USA))

1989-06-01

428

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

429

Kinetic Energy Dependence of Endothermic Charge Transfer (KEDECT) in Xenon Ion -- Hydrocarbon Collisions  

NASA Astrophysics Data System (ADS)

KEDECT has been studied by Fisher and Armentrout (ref 1) who showed clearly the strong influence of modest rare gas ion kinetic energy in opening up dissociative charge transfer channels in silane. Charge transfers of fast xenon ions with CH4, C2H4 and C3H8 are studied using xenon plasma expansion through a small nozzle into low-pressure hydrocarbon gas. Branching ratios and relative reaction rates creating the parent ion and smaller molecular ions are measured under selected power levels of an rf coupled discharge. Xe^+ reacts with CH4 to produce CH4^+ (I) and CH3^+ (II) in the ratio 1: 0.56 and an estimated rate coefficient 2.6 x 10-10 cm^3/s. The Xe^+(^2P1/2) reaction I with CH4 is exothermic by 0.83 eV while reaction II is endothermic by 0.88 eV. The Xe^+ (^2P3/2) reactions with CH4 are endothermic by 0.48 and 2.19 eV respectively, however mass-spectrometry of the interaction region shows that the reactions do occur. The xenon plasma expansion can add up to 3 KTe kinetic energy to the ion, permitting the reactions to occur. Results for the other collision partners C2H4 and C3H8 are discussed. [1] Ellen R. Fisher and P.B. Armentrout, J. Chem. Phys., 93, 4858 (1990).

Jiao, Charles; Ganguly, Biswa; Garscadden, Alan

2006-10-01

430

Density functional approximations for charge transfer excitations with intermediate spatial overlap.  

PubMed

Density functional theory is now the method of choice for calculating the electronic structure of complex systems, and time-dependent density functional theory (TDDFT) is now the preferred method for calculating spectroscopic properties of large molecules. The validity of the theory depends mainly on the quality of the approximation to the unknown exchange-correlation energy. In the present paper we consider TDDFT calculations of electronic excitation energies and oscillator strengths. We show that the M06-2X and M08-HX density functionals perform as well as and better than the range-separated CAM-B3LYP functional for charge transfer excitations with intermediate spatial overlap but have better performance for bond energies, noncovalent interactions, and chemical reaction barrier heights for representative systems; we conclude that M06-2X and M08-HX should be preferred for studies requiring the exploration of potential energy surfaces as well as electronic excitation energies, provided that those excitations with the longest-range charge transfer are excluded. PMID:20733991

Li, Ruifang; Zheng, Jingjing; Truhlar, Donald G

2010-10-21

431

Spectroscopic study of polyphenylquinolines—materials with efficient intramolecular charge transfer  

NASA Astrophysics Data System (ADS)

The energy structure and nature of intramolecular charge transfer have been determined for a series of synthesized 2,6-polyphenylquinolines (PPQs) containing resorcinol, oxygen, and phenylamine bridging groups between phenylquinoline cycles and possessing an arylene radical in the form of alkylated derivatives of carbazole or indolo[3,2-b]carbazole, as well as arylated derivatives of carbazole with nitro- and fluorine substituents. The analysis was based on data on their absorption spectra, photosensitivity, carrier photogeneration quantum efficiency, and luminescence. It is shown that the PPQ monomeric unit is a composite intramolecular charge-transfer complex (ICTC) between the donor arylene fragment and the acceptor quinoline cycle; the latter, in turn, is an ICTC between the donor bridging group and quinoline ring (when acceptor fluorine or nitro substituents are introduced into the carbazole structure, the complex becomes ternary), and the narrowest band gap (2.3 eV) corresponds to the PPQ having a phenylamine bridging group and a fragment of indolo[3,2-