Note: This page contains sample records for the topic triplet state spectra from Science.gov.
While these samples are representative of the content of Science.gov,
they are not comprehensive nor are they the most current set.
We encourage you to perform a real-time search of Science.gov
to obtain the most current and comprehensive results.
Last update: November 12, 2013.
1

The Triplet State  

NASA Astrophysics Data System (ADS)

Preface; List of participants; Part I. Spin-orbit Coupling and Intersystem Crossing: 1. Spin-orbit interactions in organic molecules; 2. Singlet-triplet transitions in organic molecules; 3. Triplet decay and intersystem crossing in aromatic hydrocarbons; 4. Statistical aspects of resonance energy transfer; Discussion; Part II. Magnetic Resonance and Magnetic Interactions: 5. Magnetic resonance spectra of organic molecules in triplet states in single crystals; 6. Magnetic interactions related to phosphorescence; 7. ESR investigations of naphthalene-d8:Naphthalene-h8 mixed crystals; 8. Biradicals and polyradicals in the nitroxide series; 9. Changes induced in the phosphorescent radiation of aromatic molecules by paramagnetic resonance in their metastable triplet states; 10. Paramagnetic resonance of the triplet state of tetramethylpyrazine; 11. On magnetic dipole contributions to the intrinsic S0 = T1 transition in simple aromatics; Discussion; Part III. Photochemistry: 12. The kinetics of energy transfer from the triplet state in rigid solutions; 13. Triplet states in gas-phase photochemistry; 14. Biphotonic photochemistry, involving the triplet state: polarisation of the effective T-T transition and solvent effects; 15. Direct and sensitised photo-oxidation of aromatic hydrocarbons in boric acid glass; Discussion; Part IV. Radiationless Transitions: 16. Radiationless transitions in gaseous benzene; 17. Low-lying excited triplet states and intersystem crossing in aromatic hydrocarbons; 18. De-excitation rates of triplet states in condensed media; 19. Lifetimes of the triplet state of aromatic hydrocarbons in the vapour phase; Discussion; Part V. Triplet Excitons: 20. Some comments on the properties of triplet excitons in molecular crystals; 21. Exact treatment of coherent and incoherent triplet exciton migration; 22. Magnetic susceptibility of a system of triplet excitons: Würster's Blue Perchlorate; 23. A study of triplet excitons in anthracene crystals under laser excitation; 24. The electronic states in crystaline anthracene; Discussion; Part VI. Delayed Fluorescent and Phosphorescence: 25. Delayed fluorescence of solutions; 26. The kinetics of the excited states of anthracene and phenanthrene vapor; 27. Optical investigations of the triplet states of naphthalene in different crystalline environments; 28. Excitation of the triplet states of organic molecules; 29. The delayed luminescence and triplet quantum yields of pyrene solutions; 30. Triplet state studies of some polyphenyls in rigid glasses; 31. Decay time of delayed fluorescence of anthracene as a function of temperature (2-30ºK); 32. Energy transfer between benzene and biacetyl and the lifetime of triplet benzene in the gas phase; 33. Charge transfer triplet state of molecular complexes. 34. Flash-photolytic detection of triplet acridine formed by energy transfer from biacetyl; 35. Extinction coefficients of triplet-triplet transitions between 3000 and 8800 A in anthracene; 36. Anthracene triplet-triplet annihilation rate constant; Discussion; Part VII. Triplet State Related to Biology: 37. ESR and optical studies of some triplet states of biological interest; 38. The triplet state of DNA; 39. Some characteristics of the triplet states of the nucleic bases; Discussion; Indexes.

Zahlan, A. B.

2010-01-01

2

Singlet oxygen generation and triplet excited-state spectra of brominated BODIPY.  

PubMed

The excited triplet-, singlet-, and ground-state properties as well as singlet oxygen generation capability of four brominated BODIPY dyes were measured in toluene with laser flash photolysis, fluorescence spectroscopy, time-correlated single-photon counting, and absorption spectroscopy. The triplet-triplet (T1-Tn) absorption spectra were identified for four dyes 1B, 2B, 4B, and 6B substituted with one, two, four, and six Br atoms, respectively. The triplet quantum yield (?T) of a usual BODIPY dye is negligible and has rarely been studied. So is the case for the parent compound 0B (8-phenyl boron-dipyrromethene), in which no Br atom is present. The substitution of the first Br atom into the ? ring of BODIPY allowed a dramatic increase of ?T from 0.0 of 0B to 0.39 for 1B. The further addition of Br number increased ?T to 0.46, 0.50, and 0.66 for 2B, 4B, and 6B, respectively. The triplet lifetimes ?T are also fairly long, which is 43, 39, 36, and 26 ?s, for 1B, 2B, 4B, and 6B, respectively. The brominated BODIPY dyes are therefore efficient singlet oxygen photosensitizers with the formation quantum yield of 0.39, 0.45, 0.49, and 0.64 for 1B, 2B, 4B, and 6B, respectively. The result indicates their potential application in photodynamic therapy of cancer. The fluorescence properties of the dyes were also measured. PMID:23574359

Zhang, Xian-Fu; Yang, Xudong

2013-04-26

3

Resonance Raman Spectra of a Perylene Bis(dicarboximide) Chromophore in Ground and Lowest Triplet States.  

PubMed

Resonance Raman spectroscopy is employed to probe the ground (S0) and lowest triplet (T1) excited states of a perylene bis(dicarboximide) (PDI) dimer. Four bands at ?1324, 1507, ?1535, and 1597 cm(-1) are signatures of the T1 excited state; a fifth band at ?1160 cm(-1) is tentatively assigned. Density functional calculations of an asymmetrically substituted PDI monomer match the experimental bands of the PDI dimer in both S0 and T1 states. The match supports a T1 excited state that is localized on a single PDI moiety of the dimer. The normal modes of the asymmetrically substituted PDI are correlated with ones calculated for the unsubstituted PDI in the D2h point group. Patterns in the Raman intensities are consistent with an A-term mechanism of enhancement. The positions of six bands are predicted for the resonance Raman spectrum of unsubstituted PDI in its T1 excited state. The spectra and normal-mode analysis reported here are expected to facilitate future studies of singlet fission in PDI crystals or other assemblies. PMID:24070416

Angelella, Maria; Wang, Chen; Tauber, Michael J

2013-09-11

4

Assignments of Lowest Triplet State in Ir Complexes by Observation of Phosphorescence Excitation Spectra at 6 K  

NASA Astrophysics Data System (ADS)

We tried the assignment of the origin of phosphorescent bands in Ir complexes. It is important to elucidate the luminescent mechanism in order to design organic light-emitting devices (OLEDs) besed on new materials. The Stokes shift between the phosphorescence and phosphorescence excitation spectra of Ir complexes such as fac-tris(2-phenylpyridine) iridium(III) [Ir(ppy)3], fac-tris(2-(2-thienyl)pyridine) iridium(III) [Ir(thpy)3], bis(2-phenylpyridine) iridium(III)benzo[h]quinoline [Ir(ppy)2bzq], fac-tris(benzo[h]quinoline) iridium(III) [Ir(bzq)3] and bis[(4,6-difluorophenyl)pyridinato](picolinato) iridium(III) [FIrpic] was measured in a solution and (phenyl)4Sn at 6 K. The amount of Stokes shift corresponds to the nature of the lowest triplet state. We discovered that the amount of Stokes shift clearly differs depending on whether the lowest triplet state of each Ir complex is triplet metal-to-ligand charge transfer (3MLCT) or 3?-?*. Namely, the case of 3MLCT shows a large shift, while the case of 3?-?* shows a small shift. We also present the resolved phosphorescence and phosphorescence excitation spectra of Ir complexes in (phenyl)4Sn. The sharp bands were assigned to the 3?-?* transition, and the broad bands were assigned to the 3MLCT state. The nature of the lowest triplet state is also discussed on the basis of resolved spectra.

Kodate, Satoshi; Suzuka, Isamu

2006-01-01

5

Jahn-Teller triplet excited state structures and spectra of zinc complexes of porphyrin and phthalocyanine: A density functional theory study  

NASA Astrophysics Data System (ADS)

Density functional theory (DFT) electronic structure calculations were carried out to predict the triplet Jahn-Teller distorted structures and energetics for zinc complexes of porphyrin (ZnP), tetraazaporphyrin, tetrabenzoporphyrin, and phthalocyanine. The D4h square planar structures in the ground state are found to distort along the b1g mode leading to the D2h rectangle structures in the lowest triplet state. Time-dependent DFT calculations were also carried out to interpret the observed triplet-triplet spectra and to quantify the effects of meso-tetraaza substitutions and tetrabenzo annulations on ZnP. The computed triplet-triplet excitation energies and oscillator strengths are in good agreement with experiment. The effects of meso-tetraaza substitutions and tetrabenzo annulations on the triplet excited state structures and spectra are discussed in detail.

Nguyen, Kiet A.; Pachter, Ruth

2003-04-01

6

Triplet-Triplet Absorption and Polarization Spectra of Trans-Stilbene and Some of Its Derivatives.  

National Technical Information Service (NTIS)

The triplet-triplet absorption spectra of organic molecules having short triplet state lifetimes, such as trans-stilbene, 4,4'-dihydroxy stilbene, 4,4'-diaminodisodium disulfonate, and 4,4'-diphenyl stilbene, were measured. Ultraviolet cw lasers were used...

T. G. Pavlopoulos D. G. Taylor

1985-01-01

7

Steady-state and time-resolved direct detection EPR spectra of fullerene triplets in liquid solution and glassy matrices. Evidence for a dynamic Jahn-Teller effect in triplet C{sub 60}  

SciTech Connect

Steady-state and time-resolved EPR spectroscopy of UV-irradiated C{sub 60}-methylcyclohexane solutions reveal evidence of a dynamic Jahn-Teller effect in triplet C{sub 60} in this paper. This is attributed to a very rapid interchange of the magnetic axes by pseudorotation. This is supported by other spectra of methylcyclohexane glasses and the different behavior of C{sub 70}. 14 refs., 4 figs., 1 tab.

Closs, G.L.; Gautam, P.; Zhang, D. [Univ. of Chicago, IL (United States)] [and others

1992-06-25

8

Triplet States of Liquid Benzene and Toluene.  

National Technical Information Service (NTIS)

The sensitization of biacetyl phosphorescence has been used to study the triplet states of benzene and toluene in the undiluted (neat) liquids. The results are not consistent with the expected triplet-triplet transfer and suggest that the transferring spe...

J. W. van Loben Sels J. T. Dubois

1966-01-01

9

Organic triplet sensitizer library derived from a single chromophore (BODIPY) with long-lived triplet excited state for triplet-triplet annihilation based upconversion.  

PubMed

Triplet-triplet annihilation (TTA) based upconversions are attractive as a result of their readily tunable excitation/emission wavelength, low excitation power density, and high upconversion quantum yield. For TTA upconversion, triplet sensitizers and acceptors are combined to harvest the irradiation energy and to acquire emission at higher energy through triplet-triplet energy transfer (TTET) and TTA processes. Currently the triplet sensitizers are limited to the phosphorescent transition metal complexes, for which the tuning of UV-vis absorption and T(1) excited state energy level is difficult. Herein for the first time we proposed a library of organic triplet sensitizers based on a single chromophore of boron-dipyrromethene (BODIPY). The organic sensitizers show intense UV-vis absorptions at 510-629 nm (? up to 180,000 M(-1) cm(-1)). Long-lived triplet excited state (?(T) up to 66.3 ?s) is populated upon excitation of the sensitizers, proved by nanosecond time-resolved transient difference absorption spectra and DFT calculations. With perylene or 1-chloro-9,10-bis(phenylethynyl)anthracene (1CBPEA) as the triplet acceptors, significant upconversion (?(UC) up to 6.1%) was observed for solution samples and polymer films, and the anti-Stokes shift was up to 0.56 eV. Our results pave the way for the design of organic triplet sensitizers and their applications in photovoltaics and upconversions, etc. PMID:21786760

Wu, Wanhua; Guo, Huimin; Wu, Wenting; Ji, Shaomin; Zhao, Jianzhang

2011-08-09

10

Theory of Optical Spectra of Photosystem II Reaction Centers: Location of the Triplet State and the Identity of the Primary Electron Donor  

PubMed Central

Based on the structural analysis of photosystem II of Thermosynechococcus elongatus, a detailed calculation of optical properties of reaction-center (D1–D2) complexes is presented applying a theory developed previously. The calculations of absorption, linear dichroism, circular dichroism, fluorescence spectra, all at 6 K, and the temperature-dependence of the absorption spectrum are used to extract the local optical transition energies of the reaction-center pigments, the so-called site energies, from experimental data. The site energies are verified by calculations and comparison with seven additional independent experiments. Exciton relaxation and primary electron transfer in the reaction center are studied using the site energies. The calculations are used to interpret transient optical data. Evidence is provided for the accessory chlorophyll of the D1-branch as being the primary electron donor and the location of the triplet state at low temperatures.

Raszewski, Grzegorz; Saenger, Wolfram; Renger, Thomas

2005-01-01

11

Triplet--Triplet Absorption Spectra of Organic Molecules in Condensed Phases  

SciTech Connect

We present a compilation of spectral parameters associated with triplet--triplet absorption of organic molecules in condensed media. The wavelengths of maximum absorbance and the corresponding extinction coefficients, where known, have been critically evaluated. Other data, for example, lifetimes, energies and energy transfer rates, relevant to the triplet states of these molecules are included by way of comments but have not been subjected to a similar scrutiny. Work in the gas phase has been omitted, as have theoretical studies. We provide an introduction to triplet state processes in solution and solids, developing the conceptual background and offering an historical perspective on the detection and measurement of triplet state absorption. Techniques employed to populate the triplet state are reviewed and the various approaches to the estimation of the extinction coefficient of triplet--triplet absorption are critically discussed. A statistical analysis of the available data is presented and recommendations for a hierarchical choice of extinction coefficients are made. Data collection is expected to be complete through the end of 1984. Compound name, molecular formula and author indexes are appended.

Carmichael, I.; Hug, G.L.

1986-01-01

12

Assignments of Lowest Triplet State in Ir Complexes by Observation of Phosphorescence Excitation Spectra at 6 K  

Microsoft Academic Search

We tried the assignment of the origin of phosphorescent bands in Ir complexes. It is important to elucidate the luminescent mechanism in order to design organic light-emitting devices (OLEDs) besed on new materials. The Stokes shift between the phosphorescence and phosphorescence excitation spectra of Ir complexes such as fac-tris(2-phenylpyridine) iridium(III) [Ir(ppy)3], fac-tris(2-(2-thienyl)pyridine) iridium(III) [Ir(thpy)3], bis(2-phenylpyridine) iridium(III)benzo[h]quinoline [Ir(ppy)2bzq], fac-tris(benzo[h]quinoline) iridium(III) [Ir(bzq)3

Satoshi Kodate; Isamu Suzuka

2006-01-01

13

Investigation of the Triplet State of Chlorophylls.  

National Technical Information Service (NTIS)

Our research program has utilized triplet state of chlorophyll as a (nondestructive) probe into the structural and dynamical nature of the photosynthetic unit. Using primarily zero-field optically detected magnetic resonance spectroscopy, supplemented by ...

R. H. Clarke

1982-01-01

14

Triplet state radiationless transitions in polycyclic hydrocarbons  

Microsoft Academic Search

The zero-field EPR transitions and spin sublevel intersystem crossing rates for the lowest triplet states of tetracene, perdeuterotetracene, 1,2-benzanthracene, and 1,2,3,4-dibenzanthracene have been measured in n-alkane solvents at 2°K by optical detection of magnetic resonance techniques. The rates of spin sublevel intersystem crossing are primarily nonradiative, and an analysis of these molecules, as well as the triplet state dynamics of

Richard H. Clarke; Harry A. Frank

1976-01-01

15

Molecular packing effects on the optical spectra and triplet dynamics in oligofluorene films.  

PubMed

We report on the triplet spectra and dynamics in two types of oligomeric films deposited by two different techniques: thermal evaporation and spin coating. The different molecular arrangement in both films is manifested in a red shift of the absorption, PL, and T1-Tn absorption spectra of the sublimated film relative to the spin-coated one. Triplet recombination dynamics studied with steady-state photoinduced absorption (PA) spectroscopy follow a dispersive bimolecular recombination model away from the trap filling regime. We obtained values for the triplet bimolecular recombination ratio (beta) of 3.4 x 10 (-14) and 1.1 x 10 (-15) cm3 s (-1) for evaporated and spin-coated film, respectively, the difference being attributed to diverse molecular arrangement in both films. PMID:18712907

Cabanillas-Gonzalez, Juan; Sciascia, Calogero; Lanzani, Guglielmo; Toffanin, Stefano; Capelli, Raffaella; Ramon, Miguel C; Muccini, Michele; Gierschner, Johannes; Hwu, Tsyr-Yuan; Wong, Ken-Tsung

2008-08-20

16

Confined helium: Excited singlet and triplet states  

NASA Astrophysics Data System (ADS)

Energies for the first four singlet and triplet S states of a helium atom confined at the center of an impenetrable sphere are reported. All calculations used explicitly correlated Hylleraas basis sets. The first triplet state is shown to lie below the first excited singlet state only when the confinement radius is greater than 0.988a0. A simple configuration interaction calculation was performed in parallel with Hylleraas calculation. The one-electron atomic orbitals of the configuration treatment provide insight into the physical concepts behind the numerical results of the Hylleraas treatment. This was particularly helpful in understanding the level crossing and avoided crossings observed with changing confinement radius.

Montgomery, H. E.; Pupyshev, Vladimir I.

2013-11-01

17

Ab initio Studies of Triplet-State Properties for Organic Semiconductor Molecules.  

PubMed

Triplet-triplet annihilation (TTA) leads to a reduced efficiency of organic light emitting diodes (OLEDs) at high current densities. Spacial confinement of the triplet excitons, which is mainly dependent on triplet energy differences, can reduce the TTA rate. Thus, a deliberate choice of the organic semiconductor materials with particular attention to their triplet energies can help to considerably increase the device efficiency. Organic solid-state lasers are on the other hand efficiently quenched by singlet-triplet annihilation (STA), which is closely related to the triplet-triplet absorption of the organic semiconductors. To establish a useful set of parameters related to the processes in organic semiconducting devices, we provide theoretical estimates for the triplet energy of 31 organic semiconductor molecules using state-of-the art ab initio quantum chemical methods. For a subset of 22 molecules the triplet-triplet absorption spectra were calculated, as well. We also discuss related features like localizations of excitations to molecular fragments, driven by the structural changes of the molecules in the excited triplet state. The calculated excited-state properties can assist experimentalists and serve as input parameters in simulations of organic electronics. PMID:22734677

Pabst, Mathias; Sundholm, Dage; Koehn, Andreas

2012-06-26

18

Triplet-state monitoring by fluorescence correlation spectroscopy  

Microsoft Academic Search

The effects of high excitation intensities in fluorescence correlation spectroscopy (FCS) in terms of saturation and triplet-state build-up have been studied for the case of Rh6G in aqueous solution. It was found that FCS provides a powerful means for the determination of intersystem crossing and triplet-state depopulation rates of fluorophores in solution.

Jerker Widengren; Rudolf Rigler; Ülo Mets

1994-01-01

19

Room-temperature long-lived triplet excited states of naphthalenediimides and their applications as organic triplet photosensitizers for photooxidation and triplet-triplet annihilation upconversions.  

PubMed

Naphthalenediimide (NDI) derivatives with 2,6- or 2,3,6,7-tetrabromo or amino substituents were prepared. N,N'-dialkyl-2,6-dibromo NDI (compound 2) and N,N'-dialkyl-2,3,6,7-tetrabromo NDI (compound 4) show phosphorescence emission at 610 or 667 nm, respectively. Phosphorescence was never observed for NDI derivatives. Conversely, N,N'-dialkyl-2,6-dibromo-3,7-diamino NDI (compound 5) shows strong absorption at 526 nm and fluorescence at 551 nm, and no phosphorescence was observed. However, nanosecond time-resolved transient difference absorption spectroscopy confirmed that the triplet excited state of 5 was populated upon photoexcitation. 2,3,6,7-Tetraamino NDI (6) shows fluorescence, and no triplet excited state was populated upon excitation. The compounds were used as singlet oxygen ((1)O(2)) photosensitizers for the photooxidation of 1,5-dihydroxylnaphthalene (DHN). We found that 5 is more efficient than the conventional photosensitizer, such as Ir(ppy)(2)(bpy)[PF(6)]. The compounds were also used as organic triplet photosensitizers for triplet-triplet annihilation based upconversions. An upconversion quantum yield up to 18.5% was observed. PMID:22439855

Guo, Song; Wu, Wanhua; Guo, Huimin; Zhao, Jianzhang

2012-04-02

20

The missing link between molecular triplets and spin-polarized free radicals: room temperature triplet states of nanocrystalline radical pairs.  

PubMed

Photochemical reactions of organic molecules in the solid state have an excellent potential in green chemistry technologies as they often proceed in high yields to give a single product without generating volatile organic solvent waste. While recent synthetic applications highlight the need for a better understanding of reaction mechanisms and kinetics, spectroscopic observations of excited states and short-lived intermediates in single crystals and powdered samples have been extremely challenging due to the high optical density and scattering power of single crystals and powdered samples. In this communication, we report the first direct observation of a radical pair triplet state by time-resolved electron paramagnetic resonance (TREPR) with nanocrystals of 4,4'-dimethoxy-dicumyl ketone (1OMe) suspended in water. Steady state irradiation of 1OMe had previously shown that reactions in dry powders and nanocrystalline suspensions proceed with high efficiency and chemoselectivity to generate 4,4'-dimethoxy-dicumene 2OMe by decarbonylation and radical coupling. The nanocrystalline suspensions were excited with an 25 ns laser pulse at 308 nm using a flow system within the cavity of a time-resolved EPR spectrometer. The resulting TREPR spectra showed strong spin polarization with enhanced absorption A and emission E signals in an AAAEEE pattern characteristic of a randomly oriented triplet with zero-field splitting parameters D = 243 G and E = 11 G as well as an isotropic exchange integral J = -45,000 G. The assignment of this spectrum to a radical pair triplet state was supported by measurements carried out in fluid solution and in frozen glasses, which allowed for the characterization of the free radical and the triplet excited molecular state of the starting ketone 1OMe. PMID:20000762

Lebedeva, Natalia V; Tarasov, Valery F; Resendiz, Marino J E; Garcia-Garibay, Miguel A; White, Ryan C; Forbes, Malcolm D E

2010-01-13

21

Singlet-Triplet Exciton Absorption Spectra in Naphthalene and Pyrene Crystals  

Microsoft Academic Search

Singlet—triplet exciton absorption spectra have been measured in naphthalene and pyrene single crystals at room temperature by observing the dependence of the ``anti-Stokes'' emission intensity resulting from mutual annihilation of triplet pairs on the wavelength of exciting light. The origin of the naphthalene spectrum is at 21 170 cm?1, and the most prominent intervals in the vibrational structure are 490

P. Avakian; E. Abramson

1965-01-01

22

The EPR of the triplet state of aryl cations in crystals of diazonium salts  

Microsoft Academic Search

The spectra of the electron paramagnetic resonance (EPR) of aryl cations possessing a principle triplet ground-state and orientated in a monocrystal of diazonium salts is studied. It is shown that two nonequivalent paramagnetic centers, which differ in orientation are formed within the crystal. A theoretic description of experimental results is possible only when allowing for the effect of low symmetry.

P. A. Kondratenko; E. V. Shrubovich; S. Z. Shulga

1989-01-01

23

Optically detected magnetic resonance (ODMR) of photoexcited triplet states  

Microsoft Academic Search

Optically Detected Magnetic Resonance (ODMR) is a double resonance technique which combines optical measurements (fluorescence,\\u000a phosphorescence, absorption) with electron spin resonance spectroscopy. After the first triplet-state ODMR experiments in\\u000a zero magnetic field reported in 1968 by Schmidt and van der Waals, the number of double resonance studies on excited triplet\\u000a states grew rapidly. Photosynthesis has proven to be a fruitful

Donatella Carbonera

2009-01-01

24

Eosin Y triplet state as a probe of spatial heterogeneity in microcrystalline cellulose.  

PubMed

The photophysical behavior of eosin Y adsorbed onto microcrystalline cellulose was evaluated by reflectance spectroscopy, steady-state fluorescence spectroscopy and laser induced time-resolved luminescence. On increasing the concentration of the dye, small changes in absorption spectra, fluorescence redshifts and fluorescence quenching are observed. Changes in absorption spectra point to the occurrence of weak exciton interactions among close-lying dye molecules, whereas fluorescence is affected by reabsorption and excitation energy trapping. Phosphorescence decays are concentration independent as a result of the negligible exciton interaction of dye pairs in the triplet state. Lifetime distribution and bilinear regression analyses of time-resolved phosphorescence and delayed fluorescence spectra reveal the existence of two different environments: long-lived, more energetic triplet states arise from dyes tightly entrapped within the cellulose chains, while short-lived, less-energetic states result from dyes in more flexible environments. Stronger hydrogen bond interactions between the dye and cellulose hydroxyl groups lead in the latter case to a lower triplet energy and faster radiationless decay. These effects, observed also at low temperatures, are similar to those encountered in several amorphous systems, but rather than being originated in changes in the environment during the triplet lifetime, they are ascribed in this case to spatial heterogeneity. PMID:22462536

Rodríguez, Hernán B; San Román, Enrique; Duarte, Paulo; Machado, Isabel Ferreira; Ferreira, Luis F Vieira

2012-05-10

25

Flash photolysis of flavins. IV. Some properties of the lumiflavin triplet state  

Microsoft Academic Search

Analysis of lumiflavin triplet-state decay kinetics in aqueous solution has given the following results:k1 (first-order decay)=670 sec-1,k2 (triplet-triplet quenching)=8·9×108 M-1 sec-1,k3 (triplet-ground-state quenching)=3·7×108 M-1 sec-1. The FMN triplet decays mainly via intramolecular quenching by the ribityl side chain and triplet-groundstate quenching. Ferricyanide and phenols are shown to be excellent quenchers of the flavin triplet (comparable to KI and O2). In

Shiv P. Vaish; Gordon Tollin

1970-01-01

26

The triplet state of indigo: Electronic structure calculations  

NASA Astrophysics Data System (ADS)

The electronic structure of indigo was determined using B3LYP functional and different basis sets. The first triplet 3A u ( C2h) state of indigo is characterized by the singlet-triplet gaps of ? ET-S(vertical) = 1.23 eV and ? ET-S(adiabatic) = 0.95 eV (recent experiment: 1.04 ± 0.1 eV). The vertical S 1-T 1 gap amounts to 1.0 eV (exptl: 0.91 ± 0.1 eV). The electron localization function (ELF) and spin density analysis show that the singlet-triplet excitation is accompanied by a migration of electrons from the C dbnd C bond and N-atoms to the adjacent C-C and C-N bonds. A low ionization energy is confirmed for indigo IE a = 6.9 eV.

Ngan, Vu Thi; Gopakumar, G.; Hue, Tran Thanh; Nguyen, Minh Tho

2007-11-01

27

Probing preferential solvation and ion aggregation with charge transfer triplet states of aromatic amino-nitro compounds  

Microsoft Academic Search

The charge transfer triplet states of p-aminonitroterphenyl (PANT) p-aminonitrobiphenyl (PANB) and aminonitrofluorene (ANF) were used as probes of preferential solvation and ion clustering in a variety of binary media. The excited states of the above molecules are characterized by very large static dipole moments (“giant dipoles”). As a result, the corresponding transient absorption spectra are highly sensitive to the local

Timothy R. Schatz; Renata Kobetic; Piotr Piotrowiak

1997-01-01

28

Time-resolved high-frequency EPR studies on magnesium and zinc tetraphenylporphines in their lowest excited triplet states.  

PubMed

The lowest excited triplet (T(1)) states of magnesium and zinc tetraphenylporphines (MgTPP and ZnTPP) were studied by time-resolved (TR) high-frequency/high-field W-band electron paramagnetic resonance (hf-EPR) spectroscopy in rigid glasses at low temperatures. Inspections of the TR-hf-EPR spectra of the spin-polarized triplets revealed that the zero field splitting (ZFS) parameters, D and E, for MgTPP and ZnTPP triplets were nearly the same. At the same time, their g-tensors were found to be different. These results are interpreted quantitatively in terms of spin-orbit couplings (SOCs) and angular momenta among the excited states, giving a magnitude of SOC in the T(1) state of ZnTPP. For the first time, both the TR-hf-EPR spectra and corresponding time profiles were acquired on the ZnTPP's triplet at room temperature in liquid paraffin solution with the populations of the electron spin states being in Boltzmann equilibrium. Because of relatively fast paramagnetic relaxation in rotating triplet at room temperature, the spectra and time profiles were free from the effects of microwave saturation that allowed for the direct measurement of the absolute intersystem crossing ratios P(x):P(y):P(z) 0.085:0.085:0.83. All of these results have demonstrated advantages and new perspectives of the W-band EPR spectroscopy. PMID:20527941

Yamauchi, Seigo; Takahashi, Katsuaki; Islam, Saiful S M; Ohba, Yasunori; Tarasov, Valery

2010-06-09

29

Novel mechanism for triplet state formation in short distance covalently linked radical ion pairs.  

SciTech Connect

We report on a series of electron donor-acceptor (D-A) dyads that undergo singlet-initiated charge separation to produce a strongly spin coupled radical ion pair that subsequently undergoes charge recombination to produce a triplet state with unusual spin polarization. The molecules consist of either a 4-(N-piperidinyl)naphthalene-1,8-imide (6P) or 4-(N-pyrrolidinyl)naphthalene-1,8-imide (5P) donor and a 1,8:4,5-naphthalenediimide (NI) or pyromellitimide (PI) acceptor. Selective photoexcitation of D within D- -A produces the radical ion pair {sup 1}[D{sup {sm_bullet}+}-A{sup {sm_bullet}-}] quantitatively. This is followed by the formation of {sup 3}[D{sup {sm_bullet}+}-A{sup {sm_bullet}-}] via singlet-triplet mixing within the radical pair. Radical pair intersystem crossing (RP-ISC) leads to charge recombination to yield [D-{sup 3*}A] or [{sup 3*}D-A]. Time-resolved optical absorption and emission spectroscopy is coupled with EPR spectroscopy to characterize the mechanism of the nearly quantitative initial charge separation reaction and the subsequent radical ion pair recombination reaction leading to the unusually spin polarized triplet state. These radical pairs also possess charge transfer emission bands that aid in the data analysis. The small number of previously reported covalent donor-acceptor systems that yield a triplet state from radical ion pair recombination use multistep charge separation reactions to achieve a {>=}20 {angstrom} spacing between the oxidized donor and reduced acceptor. These examples have small exchange couplings, J, within the radical pair, so that S-T0 mixing between the radical pair energy levels occurs. In the strongly coupled systems described here, we show that the triplet states are formed by means of both S-T{sub 0} and S-T{sub -1} mixing, producing novel spin-polarized EPR spectra characterized by anisotropic spin lattice relaxation.

Weiderrecht, G. P.; Svec, W. A.; Wasielewski, M. R.; Galili, T.; Levanon, H.; Chemistry; Northwestern Univ.; Hebrew Univ. of Jerusalem

2000-10-11

30

Optically Detected Magnetic Resonance (ODMR) of Triplet States in Photosynthesis  

Microsoft Academic Search

The triplet state of aromatic molecules and of polyenes is a versatile probe of molecular structure and of the interactions\\u000a with the environment, through the zero-field splitting (ZFS) parameters and the sublevel decay rates. These tripletproperties\\u000a can be determined accurately with magnetic resonance. Optical detection of magnetic resonance (ODMR) is often advantageous\\u000a because it pairs the frequency resolution of magnetic

Arnold J. Hoff

31

Intersystem Crossing Rate and Triplet State Lifetime for a Lasing Dye  

Microsoft Academic Search

Triplet state kinetics for rhodamine 6G in alcohol have been studied. The singlet-to-triplet intersystem crossing rate kST and triplet lifetime ?T have been determined in air-saturated alcohol, where the spin-forbidden decay from the triplet manifold into the singlet ground state is enhanced by collision with oxygen molecules dissolved in the solution. Values of the kinetic parameters for air-saturated ethanol solutions

J. P. Webb; W. C. McColgin; O. G. Peterson; D. L. Stockman; J. H. Eberly

1970-01-01

32

Pulse ESR of triplet states of large molecular ? systems  

NASA Astrophysics Data System (ADS)

We report on the electronic properties of flat, disc-type molecules with extended ? systems, which are designed as well-defined graphite subunit molecules by a new synthetic route. In our contribution, we have investigated the excited states of three benzenoid hydrocarbons-namely hexa-peri-hexabenzocoronene and two higher homologues-with time-resolved electron spin resonance (ESR) and optical techniques. After applying a laser flash to shock-frozen solutions of these molecules, we find excited states with lifetimes in the range of seconds. We have examined the fine-structure parameters of the triplet states in two molecules and furthermore observed the luminescence in the third one.

Knorr, S.; Grupp, A.; Mehring, M.; Wehmeier, M.; Herwig, P.; Iyer, V. S.; Müllen, K.

1998-08-01

33

Combined effect of Stark and singlet-triplet mixing on photon-yield spectra of singly excited helium  

NASA Astrophysics Data System (ADS)

We present a theoretical framework for the calculation of photon-yield spectra from radiative-cascade decays of photoexcited helium atoms in a static electric field for incident photon energies below the first (N=1) ionization threshold. The present theory takes full account of the singlet-triplet mixing among the singly excited states with principal quantum numbers n?10. The model predicts the enhancement of transition probabilities to triplet final states due to the field-induced mixing. In particular, for a field strength of 9.17 kV/cm, polarization of incident photons perpendicular to the field, and a 4 meV broad excitation function tuned to the 1s6p1P states, the 1s6??1s2p3P and 1s5??1s2p3P emitted photon yields are predicted to be about 70 times and 20 times lower, respectively, than the photon yields for transitions to the corresponding singlet final states.

Miheli?, A.; Žitnik, M.; Prince, K. C.; Coreno, M.; Richter, R.

2012-02-01

34

Photoexcited triplet state of porphycene, a novel porphin isomer. Time-resolved electron paramagentic resonance spectroscopy  

SciTech Connect

The photoexcited triplet state of free-base porphycene and its tetra-n-propyl derivatives, oriented in a uniaxial liquid crystal, was investigated by laser photoexcitation - EPR diode detection. By monitoring the transient behavior of the magnetization, time-dependent CW spectra were obtained and examined. The results yield (a) positive values for the zero-field splitting parameters D; (b) the location of the fine structure tensor axes in the molecular frame (x and y lie in-plane and cross the bridges between the pyrrole rings, and z is perpendicular to the porphycene plane.

Ofir, H.; Regev, A.; Levanon, H.; Vogel, E.; Koecher, M.; Balci, M.

1987-05-21

35

Effects of optical pumping in the photo-excitation of organic triplet states  

NASA Astrophysics Data System (ADS)

Upon the application of laser and microwave pulses, non-zero magnetic moment of a photo-excited triplet state of organic molecules is generated in zero-field (ZF). The time evolution of the transient magnetic moments can be measured by free induction decay (FID) in ZF. The observed ZF spectra become broadened and ZF transition shifted to lower frequencies when the repetition rate of laser excitation is increased, which are attributed to the optical pumping of nuclear polarization (ONP) effect and the associated nuclear spin lattice relaxation processes. The observed ONP effect is discussed in terms of the local field effect and spin diffusion processes in optical pumping.

Lin, Tien-Sung; Yang, Tran-Chin; Sloop, David J.

2013-08-01

36

Ultrafast entangling gates between nuclear spins using photoexcited triplet states  

NASA Astrophysics Data System (ADS)

The representation of information within the spins of electrons and nuclei has been a powerful method in the ongoing development of quantum computers. Although nuclear spins are advantageous as quantum bits (qubits) because of their long coherence lifetimes (exceeding seconds), they exhibit very slow spin interactions and have weak thermal polarization. A coupled electron spin can be used to polarize the nuclear spin and create fast single-qubit gates, however, the permanent presence of electron spins is a source of nuclear decoherence. Here we show how a transient electron spin, arising from the optically excited triplet state of C60, can be used to hyperpolarize, manipulate and measure two nearby nuclear spins. Implementing a scheme that uses the spinor nature of the electron, we performed an entangling gate in hundreds of nanoseconds: five orders of magnitude faster than the liquid-state J coupling. This approach can be widely applied to systems comprising an electron spin coupled to multiple nuclear spins, such as nitrogen-vacancy centres in diamond, while the successful use of a transient electron spin motivates the design of new molecules able to exploit photoexcited triplet states.

Filidou, Vasileia; Simmons, Stephanie; Karlen, Steven D.; Giustino, Feliciano; Anderson, Harry L.; Morton, John J. L.

2012-08-01

37

A triplet ground state for cationic polyaromatic hydrocarbons after hydrogen loss  

NASA Astrophysics Data System (ADS)

i-system into the empty ?-orbital, although this compromises the aromaticity of the system and leads to a triplet state. While a singlet state has now been firmly established for the phenyl cation, the stability of the triplet in larger polyaromatic species increases as result of the growing %B i-system, thus reducing the energy required to transfer an electron to the empty ?-orbital. Observation of the triplet state of isolated naphthyl+, phenanthyl+ and pyrenyl+ systems is undertaken by IR multiple-photon dissociation (IRMPD) spectroscopy using a tunable free electron laser. The establishment of a triplet ground state for these PAH species possibly invokes new scenarios to be considered, such as regarding the triplet-state chemistry of PAH molecules and the altered optical properties. After reviewing the experimental aspects of this work, possible consequences of a triplet ground state of PAH species are briefly outlined.

Galue, H. A.; Oomens, J.

2011-05-01

38

Triplet-state formation of porphycenes. Intersystem crossing versus sensitization mechanisms  

SciTech Connect

The authors report on a study of the photoexcited triplet state, in the liquid phase, of the following free-base porphycenes: parent porphycene (H/sub 2/PCl), 2,7,12,17-tetra-n-propylporphycene (H/sub 2/PC2), and 9,10,19,20-tetra-n-propylporphycene (H/sub 2/PC3). The triplet states are produced by two independent experimental methods: (i) singlet-triplet intersystem crossing following laser excitation; (ii) triplet-triplet sensitization, following pulse radiolysis of the same solutions as in (i) and the sensitizer, ..beta..-acetonaphthone. The latter method produces comparable yields of the photoexcited triplet, at room temperature, independent of the substitution site, whereas in the former method, the triplet yield of H/sub 2/PC3 is negligible at room temperature. The triplet-triplet absorption of the alkyl-substituted free-base porphycene, H/sub 2/PC3/sup T/, starts to show a reasonable signal-to-noise ratio only at temperatures below approx. 240 K. This temperature dependence is interpreted in terms of a thermally activated excited state in the singlet manifold, approx. 1000 cm/sup -1/ above S/sub 1/. Supporting evidence for such a mechanism is provided by the similarity of the temperature dependence of the triplet-triplet absorption and fluorescence intensity of H/sub 2/PC3.

Levanon, H.; Toporowicz, M.; Ofir, H.; Fessenden, R.W.; Das, P.K.; Vogel, E.; Koecher, M.; Pramod, K.

1988-05-05

39

Time-resolved resonance Raman study of the triplet states of p-hydroxyacetophenone and the p-hydroxyphenacyl diethyl phosphate phototrigger compound.  

PubMed

Pico- and nanosecond time-resolved resonance Raman (TR3) spectroscopy have been utilized to study the dynamics and structure of p-hydroxyacetophenone (HA) and the p-hydroxyphenacyl-caged phototrigger compound p-hydroxyphenacyl diethyl phosphate (HPDP) in acetonitrile solution. Transient intermediates were detected and attributed to the triplet states of HA and HPDP. Nanosecond-TR3 measurements were done for two isotopically substituted HA molecules to help better assign the triplet state carbonyl C=O stretching and the ring related vibrational modes. The dynamics of formation and the spectral characteristics for the triplet states were found to be similar for the HA and HPDP. The temporal evolution at very early picosecond time scale indicates there is rapid intersystem crossing (ISC) conversion and subsequent relaxation of the excess energy of the initially produced energetic triplet state. B3LYP/6-311G** density functional theory (DFT) calculations were done to determine the structures and vibrational frequencies for both the triplet and ground states of HA and HPDP. The calculated spectra reproduce the experimental spectra and the observed isotopic shifts reasonably well and were used to make tentative assignments to all the experimentally observed features. The triplet states were found to have extensive conjugated pipi* nature with a single-bond-like carbonyl CO bond. We briefly compare the triplet structure and formation dynamics of HA and HPDP as well as the conformational changes upon going from the ground state to the triplet state. We discuss our present results in relation to the initial pathway for the p-hydroxyphenacyl photodeprotection process. We also compare and discuss the properties of the HA pipi* triplet state relative to the published results of other aromatic carbonyl compounds. PMID:15387586

Ma, Chensheng; Zuo, Peng; Kwok, Wai Ming; Chan, Wing Sum; Kan, Jovi Tze Wai; Toy, Patrick H; Phillips, David Lee

2004-10-01

40

Intersystem Crossing to Excited Triplet State of Aza Analogues of Nucleic Acid Bases in Acetonitrile  

NASA Astrophysics Data System (ADS)

Excited state characteristics of aza analogues of nucleic acid bases, 8-azaadenine (8AA), 5-azacytosine (5AC), 8-azaguanine (8AG), and 6-azauracil (6AU), in acetonitrile solution were comprehensively investigated with steady state absorption and emission spectra, transient absorption measurements, emission measurements for the singlet oxygen molecule, and time-dependent density functional theory (TD-DFT) calculations. The triplet-triplet absorption spectrum of 8AA whose peak was 455 nm was observed for the first time. Sensitized singlet oxygen formation of 8AA was also observed in O2-saturated acetonitrile with quantum yields of 0.15 ± 0.02. It was concluded that there were two kinds of aza analogues of nucleic acid bases: type A had substantial quantum yield for the intersystem crossing and potential of O2 (1?g) formation (8AA and 6AU), and type B did not (5AC and 8AG). TD-DFT calculations indicated that type A molecules had a dark 1n?* state below the first allowed 1??* state, while both S1 and S2 states for type B molecules had a ??* character. It strongly suggested that the dark 1n?* state below the 1??* state would play an important role in the ISC process of aza analogues of nucleic acid bases.

Kobayashi, Takashi; Kuramochi, Hikaru; Harada, Yosuke; Suzuki, Tadashi; Ichimura, Teijiro

2009-10-01

41

Maleimides as electron-transfer photoinitiators: quantum yields of triplet states and radical-ion formation  

Microsoft Academic Search

The knowledge of quantum yields of triplet states and, moreover, of initiating radicals is a crucial prerequisite to evaluate any novel photoinitiator system. This work provides triplet quantum yields of N-methylmaleimide (0.03±0.01), N-ethylmaleimide (0.07±0.01) and N-propylmaleimide (0.05±0.02) determined by relative actinometry using laser flash photolysis and acetone sensitisation. Unsubstituted maleimide on the other hand shows rapid triplet state tautomerisation, not

Justus von Sonntag; Wolfgang Knolle

2000-01-01

42

Molecular Adaptation of Photoprotection: Triplet States in Light-Harvesting Proteins  

PubMed Central

The photosynthetic light-harvesting systems of purple bacteria and plants both utilize specific carotenoids as quenchers of the harmful (bacterio)chlorophyll triplet states via triplet-triplet energy transfer. Here, we explore how the binding of carotenoids to the different types of light-harvesting proteins found in plants and purple bacteria provides adaptation in this vital photoprotective function. We show that the creation of the carotenoid triplet states in the light-harvesting complexes may occur without detectable conformational changes, in contrast to that found for carotenoids in solution. However, in plant light-harvesting complexes, the triplet wavefunction is shared between the carotenoids and their adjacent chlorophylls. This is not observed for the antenna proteins of purple bacteria, where the triplet is virtually fully located on the carotenoid molecule. These results explain the faster triplet-triplet transfer times in plant light-harvesting complexes. We show that this molecular mechanism, which spreads the location of the triplet wavefunction through the pigments of plant light-harvesting complexes, results in the absence of any detectable chlorophyll triplet in these complexes upon excitation, and we propose that it emerged as a photoprotective adaptation during the evolution of oxygenic photosynthesis.

Gall, Andrew; Berera, Rudi; Alexandre, Maxime T.A.; Pascal, Andrew A.; Bordes, Luc; Mendes-Pinto, Maria M.; Andrianambinintsoa, Sandra; Stoitchkova, Katerina V.; Marin, Alessandro; Valkunas, Leonas; Horton, Peter; Kennis, John T.M.; van Grondelle, Rienk; Ruban, Alexander; Robert, Bruno

2011-01-01

43

Molecular adaptation of photoprotection: triplet states in light-harvesting proteins.  

PubMed

The photosynthetic light-harvesting systems of purple bacteria and plants both utilize specific carotenoids as quenchers of the harmful (bacterio)chlorophyll triplet states via triplet-triplet energy transfer. Here, we explore how the binding of carotenoids to the different types of light-harvesting proteins found in plants and purple bacteria provides adaptation in this vital photoprotective function. We show that the creation of the carotenoid triplet states in the light-harvesting complexes may occur without detectable conformational changes, in contrast to that found for carotenoids in solution. However, in plant light-harvesting complexes, the triplet wavefunction is shared between the carotenoids and their adjacent chlorophylls. This is not observed for the antenna proteins of purple bacteria, where the triplet is virtually fully located on the carotenoid molecule. These results explain the faster triplet-triplet transfer times in plant light-harvesting complexes. We show that this molecular mechanism, which spreads the location of the triplet wavefunction through the pigments of plant light-harvesting complexes, results in the absence of any detectable chlorophyll triplet in these complexes upon excitation, and we propose that it emerged as a photoprotective adaptation during the evolution of oxygenic photosynthesis. PMID:21843485

Gall, Andrew; Berera, Rudi; Alexandre, Maxime T A; Pascal, Andrew A; Bordes, Luc; Mendes-Pinto, Maria M; Andrianambinintsoa, Sandra; Stoitchkova, Katerina V; Marin, Alessandro; Valkunas, Leonas; Horton, Peter; Kennis, John T M; van Grondelle, Rienk; Ruban, Alexander; Robert, Bruno

2011-08-17

44

ATOMIC AND MOLECULAR PHYSICS: Scattering properties of the ultracold 133Cs2 triplet state  

NASA Astrophysics Data System (ADS)

The elastic scattering properties of ultracold 133Cs2 triplet state are investigated in detail. We construct a potential curve of the 133Cs2 triplet state, based on the latest ab initio molecular potential data and show how the scattering parameters are obtained by using three methods: the Numerov method, the semiclassical method and the variable phase method, where the scattering lengths of the 133Cs2 triplet state, i.e. 301.79a0, 300.67a0 and 310.81a0 are obtained respectively, with a0 being the Bohr radius. We also calculate the effective range and the number of bound states for the 133Cs2 triplet state. Our results are in agreement with the recent experimental data and the theoretical calculations. This confirms that the results of the scattering properties of the ultracold 133Cs2 triplet state, calculated by using these three methods, are reliable.

Sun, Jin-Feng; Du, Bing-Ge; Zhang, Ji-Cai; Li, Wei; Zhu, Zun-Lue

2009-03-01

45

Triplet and fluorescing states of the CP47 antenna complex of photosystem II studied as a function of temperature.  

PubMed Central

Fluorescence emission and triplet-minus-singlet (T-S) absorption difference spectra of the CP47 core antenna complex of photosystem II were measured as a function of temperature and compared to those of chlorophyll a in Triton X-100. Two spectral species were found in the chlorophyll T-S spectra of CP47, which may arise from a difference in ligation of the pigments or from an additional hydrogen bond, similar to what has been found for Chl molecules in a variety of solvents. The T-S spectra show that the lowest lying state in CP47 is at approximately 685 nm and gives rise to fluorescence at 690 nm at 4 K. The fluorescence quantum yield is 0.11 +/- 0.03 at 4 K, the chlorophyll triplet yield is 0.16 +/- 0.03. Carotenoid triplets are formed efficiently at 4 K through triplet transfer from chlorophyll with a yield of 0.15 +/- 0.02. The major decay channel of the lowest excited state in CP47 is internal conversion, with a quantum yield of about 0.58. Increase of the temperature results in a broadening and blue shift of the spectra due to the equilibration of the excitation over the antenna pigments. Upon increasing the temperature, a decrease of the fluorescence and triplet yields is observed to, at 270 K, a value of about 55% of the low temperature value. This decrease is significantly larger than of chlorophyll a in Triton X-100. Although the coupling to low-frequency phonon or vibration modes of the pigments is probably intermediate in CP47, the temperature dependence of the triplet and fluorescence quantum yield can be modeled using the energy gap law in the strong coupling limit of Englman and Jortner (1970. J. Mol. Phys. 18:145-164) for non-radiative decays. This yields for CP47 an average frequency of the promoting/accepting modes of 350 cm-1 with an activation energy of 650 cm-1 for internal conversion and activationless intersystem crossing to the triplet state through a promoting mode with a frequency of 180 cm-1. For chlorophyll a in Triton X-100 the average frequency of the promoting modes for non-radiative decay is very similar, but the activation energy (300 cm-1) is significantly smaller. Images FIGURE 3 FIGURE 5 FIGURE 6

Groot, M L; Peterman, E J; van Stokkum, I H; Dekker, J P; van Grondelle, R

1995-01-01

46

Effect of quenching of molecular triplet states in organic dye lasers  

Microsoft Academic Search

The effect of quenching of metastable triplet states upon the efficiency of organic dye lasers is considered in detail by solving the coupled differential equations describing the laser process. It is shown that specific quenching agents for excited triplet states can 1) cause a dramatic increase in the laser efficiency, 2) negate the previous requirements of very fast pumping sources,

R. Keller

1970-01-01

47

Experimental confirmation of photon-induced spin-flip transitions in helium via triplet metastable yield spectra  

Microsoft Academic Search

Doubly excited states below the N=2 ionization threshold are populated by exciting helium atoms in a supersonic beam with monochromatized synchrotron radiation. The fluorescence decay of these states triggers a radiative cascade back to the ground state with large probability to populate long lived singlet and triplet helium metastable states. The yield of metastables is measured using a multichannel plate

Jan-Erik Rubensson; Angelica Moise; Andrej Mihelic; Klemen Bucar; Matjaz Zitnik; Robert Richter

2010-01-01

48

Experimental confirmation of photon-induced spin-flip transitions in helium via triplet metastable yield spectra  

NASA Astrophysics Data System (ADS)

Doubly excited states below the N=2 ionization threshold are populated by exciting helium atoms in a supersonic beam with monochromatized synchrotron radiation. The fluorescence decay of these states triggers a radiative cascade back to the ground state with large probability to populate long lived singlet and triplet helium metastable states. The yield of metastables is measured using a multichannel plate detector after the beam has passed a singlet-quenching discharge lamp. The variation of the yield observed with the lamp switched on or off is related to the triplet-singlet mixing of the doubly excited states.

Rubensson, Jan-Erik; Moise, Angelica; Miheli?, Andrej; Bu?ar, Klemen; Žitnik, Matjaž; Richter, Robert

2010-06-01

49

Experimental confirmation of photon-induced spin-flip transitions in helium via triplet metastable yield spectra  

SciTech Connect

Doubly excited states below the N=2 ionization threshold are populated by exciting helium atoms in a supersonic beam with monochromatized synchrotron radiation. The fluorescence decay of these states triggers a radiative cascade back to the ground state with large probability to populate long lived singlet and triplet helium metastable states. The yield of metastables is measured using a multichannel plate detector after the beam has passed a singlet-quenching discharge lamp. The variation of the yield observed with the lamp switched on or off is related to the triplet-singlet mixing of the doubly excited states.

Rubensson, Jan-Erik [Department of Physics and Astronomy, Box 530, S-75121 Uppsala (Sweden); Moise, Angelica; Richter, Robert [Sincrotrone Trieste, in Area Science Park, I-34149 Basovizza, Trieste (Italy); Mihelic, Andrej; Bucar, Klemen; Zitnik, Matjaz [Jozef Stefan Institute, Jamova cesta 39, SI-1000 Ljubljana (Slovenia)

2010-06-15

50

Excited-state properties and physiological functions of biological polyenes: the triplet-excited region of retinoids and carotenoids  

NASA Astrophysics Data System (ADS)

Both experimental and theoretical results which indicate the presence of the triplet-excited region in retinoids and carotenoids are reviewed. The triplet- excited region is defined as a region where changes in the bond order take place, upon triplet excitation, toward its inversion, i.e., a double bond becomes more signal bond-like and a single bond becomes more double bond-like. (1) It has a span of approximately six conjugated double bonds, (2) it is localized in the central part of a conjugated chain, and (3) it triggers `cis' to `trans' isomerization in the T1 state. The experimental and theoretical results include: (1) the T1 Raman spectra of all-trans-retinal and its homologues; (2) the T1-state isomerization of isomeric retinal; (3) the T1-state isomerization of isomeric (beta) -carotene; (4) the PPP-SD-CI calculations of the bond orders of the carbon-carbon bonds in a set of model polyenes; and (5) the normal-coordinate analysis of the T1 Raman lines of undeuterated and deuterated all-trans-retinal. Finally, (6) the biological implication of 'the triplet-excited region' is discussed in relation to the photo-protective function of a 15-cis carotenoid bound to the bacterial photoreaction center.

Koyama, Y.; Mukai, Yumiko; Kuki, Michitaka

1993-06-01

51

The structure of strongly additive states and Markov triplets on the CAR algebra  

NASA Astrophysics Data System (ADS)

We find a characterization of states satisfying equality in strong subadditivity of entropy and of Markov triplets on the CAR algebra. For even states, a more detailed structure of the density matrix is given.

Jen?ová, Anna

2010-11-01

52

Electron paramagnetic resonance and optical evidence for two distinct porphyrin triplet states in linked porphyrin-quinone molecules  

SciTech Connect

The authors have carried out a spectroscopic and photophysical study of the triplet states of a series of meso-tetratolylporphyrins to which certain molecular moieties have been covalently attached via diamide linkages, the two amides being separated by n methylene groups (n = 2-4). The attached end groups include methyl-p-benzoquinone, the corresponding hydroquinone, and dimethoxybenzene. At low temperatures (approx.90 K) in frozen solvent matrices, the authors have found electron paramagnetic resonance (EPR) spectral evidence of two triplet states with different zero-field splitting parameters. The authors attribute this behavior to conformational heterogeneity in the linked molecules. The data are best interpreted as arising from perturbed (i.e., complexed) or normal (i.e., extended) porphyrin triplets. This is consistent with the previous interpretations of the absorption and fluorescence properties of these molecules. The EPR intensities also exhibit spectra photoselection on excitation in red-shifted and broadened porphyrin Soret band. Over the temperature range 80-300 K, laser flash photolysis experiments with time resolved detection of optical absorption show decay kinetics for these same linked porphyrin molecules which confirm the existence of two porphyrin triplets with different lifetimes in the complexed and extended conformers, respectively. Kinetic analysis of the transient absorbance profiles suggest that interconversion of the two molecular forms is slow on the time scale of a few hundred microseconds, even at room temperature.

McIntosh, A.R.; Bolton, J.R.; Connolly, J.S.; Marsh, K.L.; Cook, D.R.; Ho, T.F.; Weedon, A.C.

1986-10-23

53

Spectroscopy of triplet states of Rb{sub 2} by femtosecond pump-probe photoionization of doped helium nanodroplets  

SciTech Connect

The dynamics of vibrational wave packets in triplet states of rubidium dimers (Rb{sub 2}) formed on helium nanodroplets are studied using femtosecond pump-probe photoionization spectroscopy. Due to fast desorption of the excited Rb{sub 2} molecules off the droplets and due to their low internal temperature, wave-packet oscillations can be followed up to very long pump-probe delay times > or approx. 1.5 ns. In the first-excited triplet state (1){sup 3}{sigma}{sub g}{sup +}, full and fractional revivals are observed with high contrast. Fourier analysis provides high-resolution vibrational spectra which are in excellent agreement with ab initio calculations.

Mudrich, M.; Heister, Ph.; Hippler, T.; Giese, Ch.; Stienkemeier, F. [Physikalisches Institut, Universitaet Freiburg, 79104 Freiburg (Germany); Dulieu, O. [Laboratoire Aime Cotton, CNRS, Universite Paris-Sud, Batiment 505, 91405 Orsay (France)

2009-10-15

54

Mimicry of the radical pair and triplet states in photosynthetic reaction centers with a synthetic model.  

National Technical Information Service (NTIS)

Results are presented on a photosynthetic model system that closely mimics the spin dynamics of triplet state formation found in photosynthetic reaction centers. This research will make it possible to design new models to probe the mechanism of the primar...

M. R. Wasielewski S. R. Greenfield W. A. Svec

1997-01-01

55

Coherent storage of photoexcited triplet states using 29Si nuclear spins in silicon.  

PubMed

Pulsed electron paramagnetic resonance spectroscopy of the photoexcited, metastable triplet state of the oxygen-vacancy center in silicon reveals that the lifetime of the m(s)=±1 sublevels differs significantly from that of the m(s)=0 state. We exploit this significant difference in decay rates to the ground singlet state to achieve nearly ~100% electron-spin polarization within the triplet. We further demonstrate the transfer of a coherent state of the triplet electron spin to, and from, a hyperfine-coupled, nearest-neighbor (29)Si nuclear spin. We measure the coherence time of the (29)Si nuclear spin employed in this operation and find it to be unaffected by the presence of the triplet electron spin and equal to the bulk value measured by nuclear magnetic resonance. PMID:22463668

Akhtar, Waseem; Filidou, Vasileia; Sekiguchi, Takeharu; Kawakami, Erika; Itahashi, Tatsumasa; Vlasenko, Leonid; Morton, John J L; Itoh, Kohei M

2012-02-27

56

Pulsed Transient Nutation Experiments of the Photo-Excited Triplet State  

Microsoft Academic Search

Pulsed transient nutation (TN) techniques have been employed to investigate the transient spin dynamics of the photo-excited triplet state of pentacene inp-terphenyl crystals using an X-band pulsed EPR spectrometer. The time evolution of the longitudinal magnetization of the triplet state is monitored in the electron-spin-echo-detected TN experiments. Different transient responses have been observed in the low-field and the high-field transitions.

VLADIMIR KOUSKOV; DAVID J. SLOOP; SHANG-BIN LIU; TIEN-SUNG LIN

1995-01-01

57

New excited state intramolecular proton transfer (ESIPT) dyes based on naphthalimide and observation of long-lived triplet excited states.  

PubMed

A new excited state intramolecular proton transfer chromophore of naphthalimide (NI) conjugated 2-(2-hydroxyphenyl) benzothiazole (HBT) was prepared which shows red shifted absorption and long-lived triplet excited states. PMID:22914845

Ma, Jie; Zhao, Jianzhang; Yang, Pei; Huang, Dandan; Zhang, Caishun; Li, Qiuting

2012-10-01

58

Photodissociation and Radiative Association of HeH(+) in the Metastable Triplet State.  

PubMed

We investigate the photodissociation of HeH(+) in the metastable triplet state as well as its formation through the inverse process, radiative association. In models of astrophysical plasmas, HeH(+) is assumed to be present only in the ground state, and the influence of the triplet state has not been explored. It may be formed by radiative association during collisions between a proton and metastable helium, which are present in significant concentrations in nebulae. The triplet state can also be formed by association of He(+) and H, although this process is less likely to occur. We compute the cross sections and rate coefficients corresponding to the photodissociation of the triplet state by UV photons from a central star using a wave packet method. We show that the photodissociation cross sections depend strongly on the initial vibrational state and that the effects of excited electronic states and nonadiabatic couplings cannot be neglected. We then calculate the cross section and rate coefficient for the radiative association of HeH(+) in the metastable triplet state. PMID:23437906

Loreau, J; Vranckx, S; Desouter-Lecomte, M; Vaeck, N; Dalgarno, A

2013-02-25

59

Photodissociation and Radiative Association of HeH+ in the Metastable Triplet State  

NASA Astrophysics Data System (ADS)

We investigate the photodissociation of HeH+ in the metastable triplet state as well as its formation through the inverse process, radiative association. In models of astrophysical plasmas, HeH+ is assumed to be present only in the ground state, and the influence of the triplet state has not been explored. It may be formed by radiative association during collisions between a proton and metastable helium, which are present in significant concentrations in nebulae. The triplet state can also be formed by association of He+ and H, although this process is less likely to occur. We compute the cross sections and rate coefficients corresponding to the photodissociation of the triplet state by UV photons from a central star using a wave packet method. We show that the photodissociation cross sections depend strongly on the initial vibrational state and that the effects of excited electronic states and nonadiabatic couplings cannot be neglected. We then calculate the cross section and rate coefficient for the radiative association of HeH+ in the metastable triplet state.

Loreau, J.; Vranckx, S.; Desouter-Lecomte, M.; Vaeck, N.; Dalgarno, A.

2013-10-01

60

Effects of spin transitions degeneracy in pulsed EPR of the fullerene C70 triplet state produced by continuous light illumination.  

PubMed

X-band echo-detected electron paramagnetic resonance (ED EPR) spectra of triplet state of fullerene C(70) generated by continuous light illumination were found to correspond below 30K to a non-equilibrium electron spin polarization. Above 30K spectra are characteristic of Boltzmann equilibrium. Spectra were simulated fairly well with zero-field splitting parameters D=153 MHz and E and distributed within the range of 6-42 MHz. The origin of E distribution is attributed to the Jahn-Teller effect, which in glassy matrix is expected to depend on the local surrounding of a fullerene molecule (a so-called E-strain). In the center of ED EPR spectra a narrow hole was observed. With increase of the microwave pulse turning angle this hole transforms into a single narrow absorptive line. Numerical simulations by density matrix formalism confirm that central hole originates from a simultaneous excitation of both allowed electron spin transitions of the triplet (T(0)?T(+) and T(0)?T(-)), because of their degeneracy at this spectral position. Also explanations are given why this hole has not been observed in the previously reported experiments on continuous wave EPR and on ED EPR under laser pulse excitation. PMID:21339084

Uvarov, Mikhail N; Kulik, Leonid V; Pichugina, Tatiana I; Dzuba, Sergei A

2011-02-02

61

Generic nodeless Larkin-Ovchinnikov states due to singlet-triplet mixing in organic superconductors  

NASA Astrophysics Data System (ADS)

Larkin-Ovchinnikov (LO) states typically have a singlet gap that vanishes along real-space lines. These real-space nodes lead to Andreev midgap states which can serve as a signature of LO pairing. We show that at these nodes, an odd-parity, spin-triplet component is always induced, leading to a nodeless LO phase. We find the two-dimensional weak coupling, clean limit s wave phase diagram when this spin-triplet part is included. The triplet component is large and increases the stability of the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) phase. We also show that the spin-triplet contribution pushes the midgap states away from zero energy. Finally, we show how our results can be explained phenomenologically though Lifshitz invariants. These invariants provide a simple approach to understand the role of unconventional pairing states, spin-orbit coupling, and inhomogeneous mixed singlet-triplet states that are not due to an FFLO instability. We discuss our results in the context of organic superconductors.

Zheng, Z.; Agterberg, D. F.

2010-07-01

62

Accessing the long-lived triplet excited states in bodipy-conjugated 2-(2-hydroxyphenyl) benzothiazole/benzoxazoles and applications as organic triplet photosensitizers for photooxidations.  

PubMed

Bodipy derivatives containing excited state intramolecular proton transfer (ESIPT) chromophores 2-(2-hydroxyphenyl) benzothiazole and benzoxazole (HBT and HBO) subunits were prepared (7-10). The compounds show red-shifted UV-vis absorption (530-580 nm; ? up to 50000 M(-1) cm(-1)) and emission compared to both HBT/HBO and Bodipy. The new chromophores show small Stokes shift (45 nm) and high fluorescence quantum yields (?(F) up to 36%), which are in stark contrast to HBT and HBO (Stokes shift up to 180 nm and ?(F) as low as 0.6%). On the basis of steady state and time-resolved absorption spectroscopy, as well as DFT/TDDFT calculations, we propose that 7-9 do not undergo ESIPT upon photoexcitation. Interestingly, nanosecond time-resolved transient absorption spectroscopy demonstrated that Bodipy-localized triplet excited states were populated for 7-10 upon photoexcitation; the lifetimes of the triplet excited states (?(T)) are up to 195 ?s. DFT calculations confirm the transient absorptions are due to the triplet state. Different from the previous report, we demonstrated that population of the triplet excited states is not the result of ESIPT. The compounds were used as organic triplet photosensitizers for photooxidation of 1,5-dihydroxylnaphthalene. One of the compounds is more efficient than the conventional [Ir(ppy)(2)(phen)][PF(6)] triplet photosensitizer. Our result will be useful for design of new Bodipy derivatives, ESIPT compounds, and organic triplet photosensitizers, as well as for applications of these compounds in photovoltaics, photocatalysis and luminescent materials, etc. PMID:22742957

Yang, Pei; Zhao, Jianzhang; Wu, Wanhua; Yu, Xuerong; Liu, Yifan

2012-07-12

63

2-(3,5-Dinitrophenyl)-1,3-dithiane carbanion: a benzylic anion with a low energy triplet state.  

PubMed

Calculations at the DFT level predict that benzyl anions with strong ?-electron-withdrawing groups in the meta position(s) have low energy diradical or triplet electronic states. Specifically, the 2-(3,5-dinitrophenyl)-1,3-dithiane carbanion is predicted to have nearly degenerate singlet and triplet states at the (U)B3LYP level as a free anion. Its lithium ion pair is predicted to be a ground-state triplet with a substantial (26 kcal/mol) singlet-triplet energy gap. Experiments on this anion using chemical trapping, NMR, and the Evans method strongly suggest that this anion is either a triplet or a ground-state singlet with a very low energy triplet state. PMID:21870822

Perrotta, Raffaele R; Winter, Arthur H; Coldren, William H; Falvey, Daniel E

2011-09-12

64

Non-adiabatic charge state transitions in singlet–triplet qubits  

NASA Astrophysics Data System (ADS)

In double quantum dot singlet–triplet qubits, the exchange interaction is used in both quantum gate operation and the measurement of the state of the qubit. The exchange can be controlled electronically by applying gate voltage pulses. We simulate the exchange induced charge state transitions in one and two singlet–triplet qubit systems using the exact diagonalization method. We find that fast detuning pulses may result in leakage between different singlet charge states. The leakage could cause measurement errors and hinder quantum gate operation for example in the case of the two-qubit Coulomb gate.

Hiltunen, Tuukka; Ritala, Juha; Siro, Topi; Harju, Ari

2013-10-01

65

Canonical Watson-Crick base pair interactions in ?* type triplet states  

NASA Astrophysics Data System (ADS)

Ground state and triplet ? ? ?* states of canonical Watson-Crick base pairs have been studied at the B3LYP level of theory. Excited states were found to be localized at either of the monomers forming the base pair (guanine, cytosine, adenine and thymine), geometry relaxation of the excited base pair being similar to that occurring in the isolated nucleobase. For thymine and cytosine, triplet ? ? ?* excitation produces a significant elongation of the C5-C6 bond whereas for guanine and adenine there is a significant increase of the N3-C2 bond and pyramidalization of the NH2 group. Adenine-thymine energy pairing remains almost unaffected by triplet excitation. However, for guanine-cytosine, with excitation localized at the guanine moiety, base pairing energy decreases about 5 kcal/mol due to pyramidalization of the amino group of guanine.

Noguera, M.; Blancafort, L.; Sodupe, M.; Bertran, J.

2006-03-01

66

Studies of energy transfer processes in triplet states using optically detected magnetic resonance  

SciTech Connect

The techniques of both continuous wave and pulsed-coherent optically detected magnetic resonance spectroscopy are used to study energy transfer processes in the lowest triplet states of two aromatic molecular crystals (1,2,4,5-tetrachlorobenzene and pyrimidine). Of particular interest are the effects of crystal dimensionality and isotopic trap states on the efficiency of the transfer process in these systems.

Lewellyn, M.T.

1977-06-01

67

Investigation of the triplet state of chlorophylls. Technical progress report, May 1, 1979-April 30, 1980  

SciTech Connect

The triplet state of chlorophyll has been utilized as a nondestructive probe into the structural and dynamical nature of the photosynthetic apparatus, both in vitro and in isolated in vivo subunits. During the past year, using zero-field triplet state optically detected magnetic resonance spectroscopy, the research program has examined triplet energy transfer between photosynthetic pigments in solution; has isolated and studied subchloroplast particles enriched with photo-system I and the light harvesting chlorophyll protein (antenna) system; and has examined model chlorophyll-protein systems, specifically chlorophyll protein 668 and the reconstituted myoglobins. The overall aim of the research program has been to detail the physical features and interactions of the photosynthetic pigment systems through examination of structural subunits of the photosynthetic apparatus and model systems which represent them.

Clarke, R.H.

1980-01-01

68

Red-light-absorbing diimine Pt(ii) bisacetylide complexes showing near-IR phosphorescence and long-lived (3)IL excited state of Bodipy for application in triplet-triplet annihilation upconversion.  

PubMed

Bodipy is used for the preparation of Pt(ii) bisacetylide complexes which show strong absorption of visible light and long-lived triplet state. Room temperature (RT) near-IR phosphorescence of Bodipy was observed. The ?-conjugation framework of visible light-harvesting Bodipy ligand was connected to the Pt(ii) center by the C[triple bond, length as m-dash]C bond. The complexes were used as triplet photosensitizers for triplet-triplet annihilation (TTA) upconversion. PMID:24008767

Wu, Wanhua; Liu, Lianlian; Cui, Xiaoneng; Zhang, Caishun; Zhao, Jianzhang

2013-09-24

69

Nonradiative deactivation of the lowest excited triplet state of the dibenzo- p-dioxin molecule  

NASA Astrophysics Data System (ADS)

In the nonadiabatic approximation, we study how intramolecular interactions affect the nonradiative energy degradation T {1/ s } ? S 0 of triplet sublevels s of the lowest triplet state of the dibenzo- p-dioxin molecule. We consider the role played in the degradation by the shape of promoting high- and low-frequency vibrational modes and by spin-orbit interactions separately in the carbon backbone of the molecule and in heteroatoms (oxygen). We find that ?-electrons of oxygen that correspond to the lone pair and to valence electrons play different roles in the nonadiabatic interaction.

Gastilovich, E. A.; Klimenko, V. G.; Volkova, L. V.; Nurmukhametov, R. N.

2011-11-01

70

The luminescent triplet state of VO3-4 in YPO4  

Microsoft Academic Search

The electronic structure of the lowest excited triplet state of the vanadate ion is investigated by determining the polarization of the emission from the individual spin sublevels with optically detected magnetic resonance techniques in zero field at 1·3 K. In addition, the polarization of the total emission is determined as a function of temperature between 7 and 530 K. An

J. van Tol; J. A. van Hulst; J. H. van der Waals

1992-01-01

71

Singlet and triplet excited-state interactions and photochemical reactivity of phenyleneethynylene oligomers.  

PubMed

The rigid rodlike character of phenyleneethynylenes and their ability to communicate charge/excitation energy over long distances have made them useful as molecular linkers in the light energy harvesting assemblies and molecular electronics devices. These linker molecules themselves possess rich photochemistry as evident from the relatively large yields of the excited singlet (0.5-0.66) and triplet (0.4-0.5) states of two model oligomers, 1,4-bis(phenylethynyl)-2,5-bis(hexyloxy)benzene (OPE-1) and 1,4-bis((4-phenylethynyl)phenylethynyl)-2,5-bis(hexyloxy)benzene (OPE-2). In particular, the long-lived triplet excited state is capable of undergoing deactivation by self-quenching processes such as ground-state quenching and triplet-triplet (T-T) annihilation. The T-T annihilation occurs with a nearly diffusion-controlled rate (approximately 2 x 10(9) M(-1) s(-1)), and ground-state quenching occurs with a rate constant of approximately 6 x 10(7) M(-1) s(-1). The electron transfer from the excited OPE-1 and OPE-2 to benzoquinone as characterized from the transient absorption spectroscopy illustrates the ability of these molecules to shuttle the electrons to acceptor moieties. In addition, pulse radiolysis experiments confirm the spectroscopic fingerprint of the cation radical (or "trapped hole") with absorption bands in the 500-600 nm region. PMID:16640358

Sudeep, P K; James, P V; Thomas, K George; Kamat, Prashant V

2006-05-01

72

Triplet State Geometry of Hexachlorobenzene in Different Hosts at 1.6K.  

National Technical Information Service (NTIS)

The zerofield parameters of the triplet state of hexachlorobenzene (HCB) in HCB x-traps and in hexamethylbenzene (HMB) are determined using PMDR methods. In HCB, D and E are found to be 4.66 and 0.89 GHz, respectively. The corresponding values in HMB are ...

M. A. El-Sayed A. A. Gwaiz C. T. Lin

1972-01-01

73

Triplet-singlet conversion in ultracold Cs{sub 2} and production of ground-state molecules  

SciTech Connect

We propose a process to convert ultracold metastable Cs{sub 2} molecules in their lowest triplet state into (singlet) ground-state molecules in their lowest vibrational levels. Molecules are first pumped into an excited triplet state, and the triplet-singlet conversion is facilitated by a two-step spontaneous decay through the coupled A {sup 1{Sigma}}{sub u}{sup +}-b {sup 3{Pi}}{sub u} states. Using spectroscopic data and accurate quantum chemistry calculations for Cs{sub 2} potential curves and transition dipole moments, we show that this process competes favorably with the single-photon decay back to the lowest triplet state. In addition, we demonstrate that this conversion process represents a loss channel for vibrational cooling of metastable triplet molecules, preventing an efficient optical pumping cycle down to low vibrational levels.

Bouloufa, Nadia; Aymar, Mireille; Dulieu, Olivier [Laboratoire Aime Cotton, CNRS, Universite Paris-Sud, Bat. 505, F-91405 Orsay (France); Pichler, Marin [Physics Department, Goucher College, Baltimore, Maryland 21204 (United States)

2011-02-15

74

The triplet excited state of the bioactive compound thiabendazole. Characterization and suitability as reporter for cyclodextrin complexation  

NASA Astrophysics Data System (ADS)

Fluorescence spectroscopy, laser flash photolysis (LPF), and density functional theory calculations have been performed to characterize the photobehavior of thiabendazole (1). Direct LFP of 1 results in the generation of a transient absorbing at ?max = 570 nm identified as the triplet excited state (31?). The intersystem crossing quantum yield is 0.91, and the triplet energy is 288 kJ mol-1. The singlet-triplet energy gap is 84 kJ mol-1.The behavior of thiabendazole within CDs results in a marked enhancement of the triplet lifetime, this change is attributed to the mobility restrictions of included 1 imposed by the cyclodextrin cavities.

Bartovský, Pavel; Domingo, Luis R.; Jornet, Dolors; Tormos, Rosa; Miranda, Miguel A.

2012-02-01

75

Quantum hall states and boson triplet condensate for rotating spin-1 bosons.  

PubMed

We propose and analyze two series of clustered quantum Hall states for rotating systems of spin-1 bosons. The first series [labeled SU(4)(k)] includes the exact ground states of a model Hamiltonian at large angular momentum L, and also for N=3k particles at L=N. The latter is a spin-singlet boson-triplet condensate. The second series, labeled SO(5)(k), includes exact ground states at large L for different parameter values. PMID:12225073

Reijnders, J W; Van Lankvelt, F J M; Schoutens, K; Read, N

2002-08-30

76

Rotational autoionization and energy levels of triplet nf, v=0 Rydberg states of H2s  

Microsoft Academic Search

We have measured the energy levels and purely rotational autoionization rates of 25 different triplet Rydberg states of the H2 molecule with quantum numbers n=14-29, L=3, v=0, and R=2-4. Electron impact excites the ground-state molecules in a beam to the metastable c(2p) 3 Piu states. Two-color laser excitation from two counterpropagating single-mode cw dye laser beams excites the metastable molecules

M. D. Lindsay; F. M. Pipkin

1997-01-01

77

Measurements and Analysis of Helium-Like Triplet Ratios in the X-Ray Spectra of O-Type Stars  

SciTech Connect

We discuss new methods of measuring and interpreting the forbidden-to-intercombination line ratios of helium-like triplets in the X-ray spectra of O-type stars, including accounting for the spatial distribution of the X-ray emitting plasma and using the detailed photospheric UV spectrum. Measurements are made for four O stars using archival Chandra HETGS data. We assume an X-ray emitting plasma spatially distributed in the wind above some minimum radius R{sub 0}. We find minimum radii of formation typically in the range of 1.25 < R{sub 0}/R{sub *} < 1.67, which is consistent with results obtained independently from line profile fits. We find no evidence for anomalously low f/i ratios and we do not require the existence of X-ray emitting plasmas at radii that are too small to generate sufficiently strong shocks.

Leutenegger, Maurice A.; Paerels, Frits B.S.; /Columbia U., Astron. Astrophys.; Kahn, Steven M.; /SLAC; Cohen, David H.; /Swarthmore Coll.

2006-06-19

78

Quenching of ??* triplet states of vaporous polycyclic aromatic compounds by oxygen  

NASA Astrophysics Data System (ADS)

The oxygen quenching rate constants k T O2 of the triplet state T 1 of vapors of polycyclic aromatic hydrocarbons (PAHs) with strongly different oxidation potentials 0.44 eV < E OX < 1.61 eV and energies of the triplet levels 14800 cm-1 < E T < 24500 cm-1 (anthracene, 2-aminoanthracene, 9-nitroanthracene, chrysene, phenanthrene, fluoranthene, and carbazole) are estimated from the measured dependences of the decay rates and intensities of delayed fluorescence on the oxygen pressure P O2. It is found that the rate constants k T O2 vary from 4 × 103 (9-nitroanthracene) to 4 × 105 s-1 Torr-1 (2-aminoanthracene) and increase with decreasing oxidation potentials E OX of PAHs. The rate constants k T O2 for vapors and solutions are compared. The dependences of k T O2 on the free energy of two intermolecular processes, namely, triplet energy transfer to oxygen and electron transfer, are analyzed. It is shown that the rate constants k T O2 increase with decreasing electron transfer free energy, which proves that, along with energy transfer, charge-transfer interactions contribute to the quenching of the triplet states of PAH vapors.

Zalesskaya, G. A.; Kuchinski?, A. V.

2007-05-01

79

Geometry of the Lowest Triplet State of Benzene.  

National Technical Information Service (NTIS)

The paper begins by giving a brief theoretical background to the problem of nonhexagonal benzene. Optical experiments are then described that show the lowest excited states of benzene in the crystalline state to be nonhexagonal.

G. C. Nieman D. S. Tinti

1966-01-01

80

Ligand-localized triplet-state photophysics in a platinum(II) terpyridyl perylenediimideacetylide.  

PubMed

The synthesis, electrochemistry, and photophysical behavior of a Pt(II) terpyridyl perylenediimide (PDI) acetylide (1) charge-transfer complex is reported. The title compound exhibits strong (? ? 5 × 10(4) M(-1)cm(-1)) low-energy PDI acetylide-based ?-?* absorption bands in the visible range extending to 600 nm, producing highly quenched singlet fluorescence (? = 0.014 ± 0.001, ? = 109 ps) with respect to a nonmetalated PDI model chromophore. Nanosecond transient absorption spectroscopy revealed the presence of a long excited-state lifetime (372 ns in 2-methyltetrahydrofuran) with transient features consistent with the PDI-acetylide triplet state, ascertained by direct comparison to a model Pt(II) PDI-acetylide complex lacking low-energy charge-transfer transitions. For the first time, time-resolved step-scan FT-IR spectroscopy was used to characterize the triplet excited state of the PDI-acetylide sensitized in the title compound and its associated model complex. The observed red shifts (?30-50 cm(-1)) in the C?O and C?C vibrations of the two Pt(II) complexes in the long-lived excited state are consistent with formation of the (3)PDI acetylide state and found to be in excellent agreement with the expected change in the relevant DFT-calculated IR frequencies in the nonmetalated PDI model chromophore (ground singlet state and lowest triplet excited state). Formation of the PDI triplet excited state in the title chromophore was also supported by sensitization of the singlet oxygen photoluminescence centered at ?1275 nm in air-saturated acetonitrile solution, ?((1)O(2)) = 0.52. In terms of light emission, only residual PDI-based red fluorescence could be detected and no corresponding PDI-based phosphorescence was observed in the visible or NIR region at 298 or 77 K in the Pt(II) terpyridyl perylenediimideacetylide. PMID:22808997

Prusakova, Valentina; McCusker, Catherine E; Castellano, Felix N

2012-07-18

81

Magnetic intragap states and mixed parity pairing at the edge of spin-triplet superconductors.  

PubMed

We show that a spontaneous magnetic moment may appear at the edge of a spin-triplet superconductor if the system allows for pairing in a subdominant channel. To unveil the microscopic mechanism behind such an effect, we combine numerical solution of the Bogoliubov-de Gennes equations for a tight-binding model with nearest-neighbor attraction, and the symmetry based Ginzburg-Landau approach. We find that a potential barrier modulating the electronic density near the edge of the system leads to a nonunitary superconducting state close to the boundary where spin-singlet pairing coexists with the dominant triplet superconducting order. We demonstrate that the spin polarization at the edge appears due to the inhomogeneity of the nonunitary state and originates in the lifting of the spin degeneracy of the Andreev bound states. PMID:23848911

Romano, Alfonso; Gentile, Paola; Noce, Canio; Vekhter, Ilya; Cuoco, Mario

2013-06-26

82

Magnetic Intragap States and Mixed Parity Pairing at the Edge of Spin-Triplet Superconductors  

NASA Astrophysics Data System (ADS)

We show that a spontaneous magnetic moment may appear at the edge of a spin-triplet superconductor if the system allows for pairing in a subdominant channel. To unveil the microscopic mechanism behind such an effect, we combine numerical solution of the Bogoliubov-de Gennes equations for a tight-binding model with nearest-neighbor attraction, and the symmetry based Ginzburg-Landau approach. We find that a potential barrier modulating the electronic density near the edge of the system leads to a nonunitary superconducting state close to the boundary where spin-singlet pairing coexists with the dominant triplet superconducting order. We demonstrate that the spin polarization at the edge appears due to the inhomogeneity of the nonunitary state and originates in the lifting of the spin degeneracy of the Andreev bound states.

Romano, Alfonso; Gentile, Paola; Noce, Canio; Vekhter, Ilya; Cuoco, Mario

2013-06-01

83

On the triplet ground state of tetrahedral X4 clusters (X = Li, Na, K, Cu).  

PubMed

The lowest electronic state of distorted tetrahedral X(4) clusters (with X = Li, Na, K, Cu) is studied at coupled-cluster level using high-quality atomic basis sets. The ground state is found to have a triplet spin symmetry for this kind of geometry and for all the considered atomic species. The equilibrium geometries correspond to Jahn-Teller-distorted oblate tetrahedra having D(2d) symmetry, and tetrahedric structures are local minima on the potential-energy surfaces for the triplet states. Their energies lie between 0.2 eV (for the K(4) cluster) and 0.9 eV (for Cu(4)) above the absolute minimum of the corresponding systems, which is a spin singlet having a rhombus geometry. PMID:22401434

Verdicchio, Marco; Evangelisti, Stefano; Leininger, Thierry; Monari, Antonio

2012-03-01

84

Synthesis and transient absorption spectra of derivatives of 1,8-naphthalic anhydrides and naphthalimides containing 2,2,6,6-tetramethylpiperidine; triplet route of deactivation  

Microsoft Academic Search

Novel probes represented 4-substituted 1,8-naphtalic anhydride and 1,8-naphthalimide as a chromophore and sterically hindered amine in the form of parent amine as well as stable nitroxyl radical form were synthesized. Laser flash photolysis was used to examine the triplet route of deactivation. The formation of the triplet state occurred at 355nm laser excitation exhibiting the absorption in the range 360–700nm.

J. Kollár; P. Hrdlovi?; Š. Chmela; M. Sarakha; G. Guyot

2005-01-01

85

DERIVING METALLICITIES FROM THE INTEGRATED SPECTRA OF EXTRAGALACTIC GLOBULAR CLUSTERS USING THE NEAR-INFRARED CALCIUM TRIPLET  

SciTech Connect

The Ca II triplet (CaT) feature in the near-infrared has been employed as a metallicity indicator for individual stars as well as integrated light of Galactic globular clusters (GCs) and galaxies with varying degrees of success, and sometimes puzzling results. Using the DEIMOS multi-object spectrograph on Keck we obtain a sample of 144 integrated light spectra of GCs around the brightest group galaxy NGC 1407 to test whether the CaT index can be used as a metallicity indicator for extragalactic GCs. Different sets of single stellar population models make different predictions for the behavior of the CaT as a function of metallicity. In this work, the metallicities of the GCs around NGC 1407 are obtained from CaT index values using an empirical conversion. The measured CaT/metallicity distributions show unexpected features, the most remarkable being that the brightest red and blue GCs have similar CaT values despite their large difference in mean color. Suggested explanations for this behavior in the NGC 1407 GC system are (1) the CaT may be affected by a population of hot blue stars, (2) the CaT may saturate earlier than predicted by the models, and/or (3) color may not trace metallicity linearly. Until these possibilities are understood, the use of the CaT as a metallicity indicator for the integrated spectra of extragalactic GCs will remain problematic.

Foster, Caroline; Forbes, Duncan A.; Proctor, Robert N.; Spitler, Lee R. [Centre for Astrophysics and Supercomputing, Swinburne University, Hawthorn, VIC 3122 (Australia); Strader, Jay [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States); Brodie, Jean P. [UCO/Lick Observatory, University of California, Santa Cruz, CA 95064 (United States)], E-mail: cfoster@astro.swin.edu.au

2010-04-15

86

Anisotropic pseudorotation of the photoexcited triplet state of fullerene C60 in molecular glasses studied by pulse EPR.  

PubMed

Spin-polarized echo-detected electron paramagnetic resonance (EPR) spectra and the transversal relaxation rate T2(-1) of the photoexcited triplet state of fullerene C60 molecules were studied in o-terphenyl, 1-methylnaphthalene, and decalin glassy matrices. The model is composed of a fast (correlation time approximately 10(-12) s) pseudorotation of (3)C60 in a local anisotropic potential created by interaction of the fullerene molecule with the surrounding matrix molecules. In simulations, this potential is assumed to be axially symmetric around some axis of a preferable orientation in a matrix cage. The fitted value of the potential was found to depend on the type of glass and to decrease monotonically with a temperature increase. A sharp increase of the T2(-1) temperature dependence was found near 240 K in glassy o-terphenyl and near 100 K in glassy 1-methylnaphthalene and decalin. This increase probably is related to the influence on the pseudorotation of the onset of large-amplitude vibrational molecular motions (dynamical transition in glass) that are known for glasses from neutron scattering and molecular dynamics studies. The obtained results suggest that molecular and spin dynamics of the triplet fullerene are extremely sensitive to molecular motions in glassy materials. PMID:18298102

Uvarov, Mikhail N; Kulik, Leonid V; Bizin, Mikhail A; Ivanova, Valentina N; Zaripov, Ruslan B; Dzuba, Sergei A

2008-02-26

87

Quenching of triplet states of aromatic ketones by sulfur-containing amino acids in solution. Evidence for electron transfer  

SciTech Connect

The mechanism for quenching triplet states of benzophenones by sulfur-containing amino acids in water/acetonitrile solution was investigated by laser flash photolysis. The amino acids in the study were methionine, S-methylcysteine, and S-carboxymethylcysteine, and the eight aromatic triplets were those of benzophenone and its derivatives possessing electron-withdrawing or electron-donating groups. The presence of radical ions in the transient spectra and correlations of the quenching rate constants with the free energy change for electron transfer are strong indications that the process involves an electron transfer. These correlations were displayed as Rehm-Weller plots (logarithm of quenching rate vs free energy). Classical theoretical formulations of the Rehm-Weller correlations were used to estimate the intrinsic barriers and the transmission coefficients for the electron-transfer processes. Applying both [open quotes]quadratic[close quotes] Marcus and [open quotes]asymptotic[close quotes] Agmon-Levine free energy relationships led to the values of intrinsic barriers lower than the solvent reorganization energy calculated within the framework of the dielectric continuum model. These relationships also led to low electronic transmission coefficients. The low values of the intrinsic barriers for electron transfer were also obtained using the recently developed Tachiya approach. 58 refs., 5 figs., 2 tabs.

Marciniak, B.; Bobrowski, K.; Hug, G.L. (Univ. of Notre Dame, IN (United States))

1993-11-18

88

Investigation of the triplet state of chlorophylls. Progress report, May 1, 1980-April 30, 1981  

SciTech Connect

The triplet state of chlorophyll has been utilized as a nondestructive probe into the structural and dynamical nature of the photosynthetic apparatus. During the past year, using zero-field triplet state optically detected magnetic resonance spectroscopy, chlorophyll aggregates were examined in both their natural environment in vivo and in model complexes in vitro. Research efforts have focused on subchloroplast particles extracted from green plants, on chlorophyll monolayers, and on isolated chlorophyll molecules bound to both simple ligands and to complete proteins. The overall aim of the research program is to detail the physical features and interactions of the photosynthetic pigment systems through examination of structural subunits of the photosynthetic apparatus and model systems which represent them.

Clarke, R.H.

1980-12-22

89

Electronic structure of the lowest excited triplet state of 5,12-naphthacenequinone.  

PubMed

Continuous-wave time-resolved EPR (cw-TREPR) and pulsed electron nuclear double resonance (ENDOR) studies have been carried out to clarify the electronic structure of the lowest excited triplet (Tl) state of 5,12-naphthacenequinone (5,12-NpQ) as well as 1,4-anthraquinone (1,4-AQ) and 6,13-pentacenequinone (6,13-PeQ). The Tl energy level and the D value of the zero-field splitting (ZFS) parameters only slightly decreased with the increasing pi-conjugated system. The Tl states of these linear para-acenequinones were assigned to the pi pi* character. In triplet 5,12-naphthacenequinone, more than 80% of the unpaired electron spins are localized on the naphthalene aromatic sub-system. PMID:11993468

Shimokage, Takuji; Ikoma, Tadaaki; Akiyama, Kimio; Tero-Kubota, Shozo

2002-04-01

90

An electron-spin-echo study of the nonradiative triplet state of polyenals  

Microsoft Academic Search

The lowest triplet state T0 of the all-trans isomers of dodecapentaenal, decatetraenal, octatrienal, and hexadienal dissolved in polyethylene films has been investigated by electron–spin–echo spectroscopy in combination with pulsed laser excitation. Microwave transitions between the spin sublevels have been observed both in magnetic field and in zero field. For these polyenals T0 is found to be of ??* character. The

Marianne Ros; Edgar J. J. Groenen

1991-01-01

91

Laser photolysis study of the triplet states of fulvic acids in aqueous solutions  

Microsoft Academic Search

The spectral and kinetic characteristics of short-lived intermediates formed during the photolysis of aqueous and alkaline\\u000a (0.1 mol l?1 NaOH) solutions of fulvic acids (FA) were studied by the nanosecond laser photolysis technique. Laser photolysis of FA at\\u000a 337 nm leads to the formation of short-lived triplet states of FA (3FA) with a quantum yield of about 1% and different

N. B. Sul’timova; P. P. Levin; O. N. Chaikovskaya; I. V. Sokolova

2008-01-01

92

Quenching of the triplet state of certain porphyrins by cyanocobalamin and co-phthalocyanine  

NASA Astrophysics Data System (ADS)

The bimolecular exchange-resonance energy transfer efficiency from the triplet level of a number of Pd porphyrins to cyanocobalamin (vitamin B-12) is much lower in ethanol than in aqueous solutions. This is explained by a change in a cyanocobalamin-molecule geometry in ethanol from that in aqueous solutions. This change can be the detachment of the nucleotide from the cobalt ion or a change in the cyanocobalamin-molecule conformation. As a result, stearic hindrance of intermolecular energy transfer arises, or the mobility of the cyanocobalamin molecules decreases. No quenching of the triplet state of tetraphenyl tetrahydroporphin by cyanocobalamine is detected, whereas quenching of Co-phthalocyanine occurs with a high rate constant.

Sapunov, V. V.

1992-10-01

93

The rotational spectrum of HC8N, a linear molecule with a triplet ground state  

NASA Astrophysics Data System (ADS)

By means of Fourier transform microwave spectroscopy of a supersonic molecular beam, we report here the laboratory detection of HC8N, a carbon chain with a triplet electronic ground state. A total of 71 hyperfine components from six rotational transitions between 8 and 13 GHz were measured to an uncertainty of 5 kHz or better. Eight spectroscopic constants, including six fine and hyperfine coupling constants, were determined to high accuracy, despite a complex spectrum which consists of many closely spaced lines. Like the shorter HC2nN chains, the linear triplet isomer detected here is highly polar and is almost certainly the ground state of HC8N; in our molecular beam discharge source, it is 10 times less abundant than triplet HC6N, but more than 100 times less abundant than the well-studied closed-shell cyanopolyyne HC7N. Owing to the collapse of the hyperfine structure with increasing chain length, still longer chains may be detectable.

McCarthy, M. C.; Thaddeus, P.

2005-08-01

94

Communication: Orbital instabilities and triplet states from time-dependent density functional theory and long-range corrected functionals  

NASA Astrophysics Data System (ADS)

Long-range corrected hybrids represent an increasingly popular class of functionals for density functional theory (DFT) that have proven to be very successful for a wide range of chemical applications. In this Communication, we examine the performance of these functionals for time-dependent (TD)DFT descriptions of triplet excited states. Our results reveal that the triplet energies are particularly sensitive to the range-separation parameter; this sensitivity can be traced back to triplet instabilities in the ground state coming from the large effective amounts of Hartree-Fock exchange included in these functionals. As such, the use of standard long-range corrected functionals for the description of triplet states at the TDDFT level is not recommended.

Sears, John S.; Koerzdoerfer, Thomas; Zhang, Cai-Rong; Brédas, Jean-Luc

2011-10-01

95

Singlet and triplet excited-state dynamics study of the keto and enol tautomers of cytosine.  

PubMed

The photoinduced excited-state dynamics of the keto and enol forms of cytosine have been investigated by using ab initio surface-hopping to gain an understanding of the outcome of molecular beam femtosecond pump-probe photoionisation spectroscopy experiments. Both singlet and triplet states were included in the dynamics. The results show that triplet states play a significant role in the relaxation of the keto tautomer, whereas they are less important in the enol tautomer. In both forms, the T1 state minimum was found to be too low in energy to be detected in standard photoionisation spectroscopy experiments and therefore experimental decay times should arise from simultaneous relaxation to the ground state and additional intersystem crossing followed by internal conversion to the T1 state. In agreement with available experimental lifetimes, we observed three decay constants of 7, 270 and 1900 fs, the first two coming from the keto tautomer and the third from the enol form. Deactivation of the enol tautomer is due to internal conversion to the ground state through two ethylenic-type S1/S0 conical intersections. PMID:23893944

Mai, Sebastian; Marquetand, Philipp; Richter, Martin; González-Vázquez, Jesús; González, Leticia

2013-07-25

96

Characterization of the triplet state of hybridization-sensitive DNA probe by using fluorescence correlation spectroscopy.  

PubMed

The nonradiative relaxation mechanism of the newly synthesized hybridized-sensitive DNA probe has not been fully understood until now. In this study, the transient dark state of the probe, which is a double fluorescent dye attached to a specific DNA sequence, was investigated using a fluorescence correlation spectroscopy (FCS). The transient dark state was measured in various solvents that are known to affect the intersystem crossing or photoisomerization of the DNA probe. On the basis of the experimental results, a simplified two energy state model of the probe was constructed, and this model provides an insight into the nonradiative relaxation mechanism of the fluorophore and the applications for DNA and RNA detection. The transient dark state that was measured in a time scale of a few microseconds is a triplet state and is related to photoisomerization, viscosity, oxygen concentration, and hybridization, all of which are important parameters for cellular microscopy. The transient dark state in a time scale of a sub-microseconds is sensitively changed after the addition of target DNA. The characterization can improve the probe's capability to identify target DNA/RNA by using FCS since the triplet state that occurred after hybridization is distinctive in the time scale with that occurred before hybridization. PMID:23210598

Shin, Hyo-Sup; Okamoto, Akimitsu; Sako, Yasushi; Kim, Sok Won; Kim, Soo Yong; Pack, Chan-Gi

2012-12-21

97

Radiative properties and charge-transfer character of the phosphorescent triplet state in mixed rhodium chelates  

Microsoft Academic Search

The kinetics of the lowest excited [sup 3][pi]-[pi]* states of the complex cations [Rh(thpy)[sub 2](bpy)][sup +] and [Rh(thpy)(phpy)(bpy)][sup +] (thpy = 2,2[prime]-thienylpyridine, phpy = 2-phenylpyridine, bpy = bipyridine), co-doped in a single crystal of [Rh(phpy)[sub 2](bpy)]PF[sub 6], has been studied by means of optically detected microwave recovery and adiabatic rapid passage experiments. The population decay of the ligand-localized triplet-state sublevels

Claudia Giesbergen; Max Glasbeek

1993-01-01

98

Responses of Phycomyces indicating optical excitation of the lowest triplet state of riboflavin.  

PubMed Central

Phototropic and light growth responses of the sporangiophore of Phycomyces have been elicited using tunable laser stimulation from 575 to 630 nm. The growth response shows additional components of the action spectrum with a sharp peak at 595 nm, a sharp cut-off at 585 nm, and a tail extending beyond 630 nm. The integral over the electronic transition (f-value) is 1.5 X 10(-9) times that at 455 nm. These parameters indicate a direct transition from the ground state to the lowest triplet state of riboflavin.

Delbruck, M; Katzir, A; Presti, D

1976-01-01

99

Laser flash photolysis study of 2,6-dimethyl-3,5-diphenyl-4-pyrone and related chromones. Evidence for triplet state structural relaxation from quenching behaviors  

SciTech Connect

The 308- or 337.1-nm laser excitation of 2,6-dimethyl-3,5-diphenyl-4-pyrone (1), 2-phenylchromone (2), and 2,3-diphenylchromone (3) results in the formation of short-lived triplets (tau/sub 0//sup T/ = 1-5 ..mu..s, lambda/sub max//sup T/ = 330-365 nm) in high yields (0.5-1.0 in benzene). From phosphorescence spectra at 77 K, the spectroscopic triplet energies of these aromatic enones are estimated at 69, 62, and 67 kcal mol/sup -1/, respectively. However, in fluid solutions at room temperature, the triplets are poorly quenched by 1-methylnaphthalene (E/sub T/ = 59.6 kcal mol/sup -1/), dienes (E/sub T/ approx. = 59 kcal mol/sup -1/), and ferrocene (E/sub T/ approx. = 40 kcal mol/sup -1/). In spite of the apparent exothermicity, the energy-transfer processes are inefficient; this suggests geometric distortion in these triplets, very probably in the form of partial twisting about the ene double bonds, causing a lowering of vertical energy (at relaxed geometry) by approx.30 kcal mol/sup -1/. The quenching behavior of the triplet of 2, however, is normal, the rate constants for quenching by the above-mentioned quenchers being in the limit of diffusion control. A major reason for the excited-state torsional distortion in 1 and 3 appears to be the steric interaction between adjacent substituents (phenyl and methyl) on the carbon atoms of the ene double bond.

Bhattacharyya, K.; Ramaiah, D.; Das, P.K.; George, M.V.

1986-10-23

100

Excited states of tryptophan in cod parvalbumin. Identification of a short-lived emitting triplet state at room temperature.  

PubMed Central

The fluorescence and phosphorescence spectra of model indole compounds and of cod parvalbumin III, a protein containing a single tryptophan and no tyrosine, were examined in the time scale ranging from subnanoseconds to milliseconds at 25 degrees C in aqueous buffer. For both Ca- bound and Ca-free parvalbumin and for model indole compounds that contained a proton donor, a phosphorescent species emitting at 450 nm with a lifetime of approximately 20-40 ns could be identified. A longer-lived phosphorescence is also apparent; it has approximately the same absorption and emission spectrum as the short-lived triplet molecule. For Ca parvalbumin, the decay of the long-lived triplet tryptophan is roughly exponential with a lifetime of 4.7 ms at 25 degrees C whereas for N-acetyltryptophanamide in aqueous buffer the decay lifetime was 30 microseconds. In contrast, the lifetime of the long-lived tryptophan species is much shorter in the Ca-free protein compared with Ca parvalbumin, and the decay shows complex nonexponential kinetics over the entire time range from 100 ns to 1 ms. It is concluded that the photochemistry of tryptophan must take into account the existence of two excited triplet species and that there are quenching moieties within the protein matrix that decrease the phosphorescence yield in a dynamic manner for the Ca-depleted parvalbumin. In contrast, for Ca parvalbumin, the tryptophan site is rigid on the time scale of milliseconds.

Sudhakar, K; Phillips, C M; Williams, S A; Vanderkooi, J M

1993-01-01

101

Resonance Raman scattering of the excited triplet (/sup 3/B/sup +//sub 2u/ ) electronic state of naphthalene in fluid media  

SciTech Connect

Resonance Raman spectra of the photoexcited lowest triplet (/sup 3/B/sup +//sub 2u/) state of naphthalene (N-h/sub 8/ and N-d/sub 8/), observed in solution by time-resolved technique, are reported. Eight Raman bands (396, 496, 741, 958, 1337, 1395, 1440, and 2676 cm/sup -1/) have been observed in N-h/sub 8/ and ten (479, 690, 754, 1005, 1142, 1281, 1356, 2491, 2638, and 2714 cm/sup -1/) in N-d/sub 8/. Vibrational assignments are briefly discussed.

Fisher, M.R.; Tripathi, G.N.R.

1985-05-15

102

Photofunctional triplet excited states of cyclometalated Ir(III) complexes: beyond electroluminescence.  

PubMed

The development of cyclometalated Ir(III) complexes has enabled important breakthroughs in electroluminescence because such complexes permit the efficient population of triplet excited states that give rise to luminescent transitions. The triplet states of Ir(III) complexes are advantageous over those of other transition metal complexes in that their electronic transitions and charge-transfer characteristics are tunable over wide ranges. These favorable properties suggest that Ir(III) complexes have significant potential in a variety of photofunctions other than electroluminescence. In this critical review, we describe recent photonic applications of novel Ir(III) complexes. Ir(III) complexes have been shown to affect the exciton statistics in the active layers of organic photovoltaic cells, thereby improving the photon-to-current conversion efficiencies. Nonlinear optical applications that take advantage of the strong charge-transfer properties of triplet transitions are also discussed. The tunability of the electrochemical potentials facilitates the development of efficient photocatalysis in the context of water photolysis or organic syntheses. The photoredox reactivities of Ir(III) complexes have been employed in studies of charge migration along DNA chains. The photoinduced cytotoxicity of Ir(III) complexes on live cells suggests that the complexes may be useful in photodynamic therapy. Potential biological applications of the complexes include phosphorescence labeling and sensing. Intriguing platforms based on cyclometalated Ir(III) complexes potentially provide novel protein tagging and ratiometric detection. We envision that future research into the photofunctionality of Ir(III) complexes will provide important breakthroughs in a variety of photonic applications. PMID:22797418

You, Youngmin; Nam, Wonwoo

2012-07-16

103

Dynamical processes in the lowest-excited triplet metal-to-ligand charge transfer states of ruthenium and osmium diimine complexes in crystals  

NASA Astrophysics Data System (ADS)

This review presents a detailed description of the lowest-excited states in ruthenium(II) and osmium(II) diimine complexes, based on extensive studies of their optical spectra in crystalline environments. Deuteration, and Zeeman and Stark effects provide a wealth of incisive results. The transferred charge in the lowest-excited triplet metal-to-ligand charge transfer states is localized on a single ligand in ruthenium(II) diimine complexes and the excitation exchange interaction between equivalent metal-ligand subunits is 0 5 cm . Localization gives rise to subtle effects, such as small Stokes shifts, in spectra. The lowest-excited states of osmium(II) diimine complexes in crystals with low inhomogeneous broadening are well described as coherent intramolecular excitons with excitation exchange interactions in the range from 2 to 30 cm .

Riesen, Hans; Wallace, Lynne; Krausz, Elmars

104

Photophysical processes of triplet states and radical ions in pure and molecularly doped polymers. Final report  

SciTech Connect

Both the past and current objectives are to learn how to control the rate and direction of triplet exciton migration in both pure and molecularly doped polymer systems. Since triplet excimers are efficient traps for migrating excitons, a secondary objective has been to characterize these excimers with a view toward their use as rate modifiers or excited state quenchers. Further objectives included those stated above as past and current objectives but with an additional goal. The authors learned that fluid solutions of many of the nitrogen containing chromophores with which they work produce both radical cations and anions upon excimer laser excitation. They also learned that a phosphorus analogue behaves similarly. At this time the mechanism of charge generation in these systems is not well established but they do know that the electronically excited states and radical ions can potentially interconvert. They wanted to find out whether or not the pure or molecularly doped polymer systems could be used in a step-wise sequence involving light absorption followed by charge generation. All of their activities are oriented toward the potential end use of polymeric systems in the conversion of light energy to perform various types of useful work.

Burkhart, R.D.

1998-01-01

105

Triplet excited state characters and photosensitization mechanisms of alpha-terthienyl: a theoretical study.  

PubMed

The triplet excited (T(1)) state characters of alpha-terthienyl (alpha-T) have been investigated using density functional theory calculations, based on which, its photosensitization mechanisms were explored. Primarily, the direct oxidation to the DNA bases by the T(1) state alpha-T through the electron transfer is not thermodynamically feasible. Secondly, 1O2 can be photogenerated both in benzene and water through the direct energy transfer from the T(1) state alpha-T to 3O2, while O2(.-) can only be formed in water through the electron transfer from the T(1) state alpha-T or alpha-T(-) to 3O2. PMID:18990584

Ji, Hong-Fang; Shen, Liang

2008-10-07

106

Relativistic potential energy surfaces of initial oxidations of Si(100) by atomic oxygen: The importance of surface dimer triplet state  

NASA Astrophysics Data System (ADS)

The non-relativistic and relativistic potential energy surfaces (PESs) of the symmetric and asymmetric reaction paths of Si(100)-2×1 oxidations by atomic oxygen were theoretically explored. Although only the singlet PES turned out to exist as a major channel leading to ``on-dimer'' product, both the singlet and triplet PESs leading to ``on-top'' products are attractive. The singlet PESs leading to the two surface products were found to be the singlet combinations (open-shell singlet) of the low-lying triplet state of surface silicon dimer and the ground 3P state of atomic oxygen. The triplet state of the ``on-top'' product can also be formed by the ground singlet state of the surface silicon dimer and the same 3P oxygen. The attractive singlet PESs leading to the ``on-dimer'' and ``on-top'' products made neither the intersystem crossings from triplet to singlet PES nor high energy 1D of atomic oxygen necessary. Rather, the low-lying triplet state of surface silicon dimer plays an important role in the initial oxidations of silicon surface.

Kim, Tae-Rae; Shin, Seokmin; Choi, Cheol Ho

2012-06-01

107

Local CC2 response method for triplet states based on Laplace transform: excitation energies and first-order properties.  

PubMed

A new multistate local CC2 response method for calculating excitation energies and first-order properties of excited triplet states in extended molecular systems is presented. The Laplace transform technique is employed to partition the left/right local CC2 eigenvalue problems as well as the linear equations determining the Lagrange multipliers needed for the properties. The doubles part in the equations can then be inverted on-the-fly and only effective equations for the singles part must be solved iteratively. The local approximation presented here is adaptive and state-specific. The density-fitting method is utilized to approximate the electron-repulsion integrals. The accuracy of the new method is tested by comparison to canonical reference values for a set of 12 test molecules and 62 excited triplet states. As an illustrative application example, the lowest four triplet states of 3-(5-(5-(4-(bis(4-(hexyloxy)phenyl)amino)phenyl)thiophene-2-yl)thiophene-2-yl)-2-cyanoacrylic acid, an organic sensitizer for solar-cell applications, are computed in the present work. No triplet charge-transfer states are detected among these states. This situation contrasts with the singlet states of this molecule, where the lowest singlet state has been recently found to correspond to an excited state with a pronounced charge-transfer character having a large transition strength. PMID:21197979

Freundorfer, Katrin; Kats, Daniel; Korona, Tatiana; Schütz, Martin

2010-12-28

108

Photoinduced electron transfer between sulfur-containing carboxylic acids and the 4-carboxybenzophenone triplet state in aqueous solution  

SciTech Connect

The mechanism of photoinduced electron transfer was investigated using laser flash photolysis and steady-state photolysis techniques. Bimolecular rate constants for quenching of the CB triplet state by six sulfur-containing acids, with varying numbers of COO[sup [minus

Marciniak, B. (Univ. of Notre Dame, IN (United States) A. Mickiewicz Univ., Poznan (Poland)); Bobrowski, K.; Hug, G.L. (Univ. of Notre Dame, IN (United States)); Rozwadowski, J. (A. Mickiewicz Univ., Poznan (Poland))

1994-05-05

109

Role of the triplet state in the green emission peak of polyfluorene films: A time evolution study  

NASA Astrophysics Data System (ADS)

The blue emission of ethyl-hexyl substituted polyfluorene (PF2/6) films is accompanied by a low energy green emission peak around 500 nm in inert atmosphere. The intensity of this 500 nm peak is large in electroluminescence (EL) compared to photoluminescence (PL) measurements. Furthermore, the green emission intensity reduces dramatically in the presence of molecular oxygen. To understand this, we have modeled various nonradiative processes by time dependent quantum many body methods. These are (i) intersystem crossing to study conversion of excited singlets to triplets leading to a phosphorescence emission, (ii) electron-hole recombination (e-hR) process in the presence of a paramagnetic impurity to follow the yield of triplets in a polyene system doped with paramagnetic metal atom, and (iii) quenching of excited triplet states in the presence of oxygen molecules to understand the low intensity of EL emission in ambient atmosphere, when compared with that in nitrogen atmosphere. We have employed the Pariser-Parr-Pople Hamiltonian to model the molecules and have invoked electron-electron repulsions beyond zero differential approximation while treating interactions between the organic molecule and the rest of the system. Our time evolution methods show that there is a large cross section for triplet formation in the e-hR process in the presence of paramagnetic impurity with degenerate orbitals. The triplet yield through e-hR process far exceeds that in the intersystem crossing pathway, clearly pointing to the large intensity of the 500 nm peak in EL compared to PL measurements. We have also modeled the triplet quenching process by a paramagnetic oxygen molecule which shows a sizable quenching cross section especially for systems with large sizes. These studies show that the most probable origin of the experimentally observed low energy EL emission is the triplets.

Mukhopadhyay, S.; Ramasesha, S.; Guha, S.

2010-01-01

110

Quenching Rate Constants for the Ar(triplet P(0)), Ar(triplet P92)), and Xe(triplet P(2)) States.  

National Technical Information Service (NTIS)

The measurement of total quenching cross sections and identification of product channels from the interaction of the metastable states of the rare-gas atoms with simple molecules have been the goals of the research program. The total quenching cross secti...

D. W. Setser L. G. Piper J. E. Velazco

1974-01-01

111

Dynamics of C[sub 70] in the lowest excited triplet state at low temperatures  

SciTech Connect

The dynamic behavior of C[sub 70] in the lowest excited triplet state is investigated by the time-resolved EPR (TREPR) method in methylcyclohexane at low temperatures. From the line width of the TREPR spectrum, the distributions of the shortest and middle radii of the distorted rugby ball shape are revealed to be inhomogeneously broadened although the longest radius is relatively constant. The observing time dependence of the spectrum after the laser excitation is examined on the basis of the model involving pseudorotation and molecular rotation. The time dependence calculated based on the pseudorotation around the longest axis fits the observed one well. The activation energy of the dynamic deformation is determined. 16 refs., 4 figs.

Terazima, Masahide; Sakurada, Keita; Hirota, Noboru (Kyoto Univ. (Japan)); Shinohara, Hisanori; Saito, Yahachi (Mi'e Univ., Tsu (Japan))

1993-05-27

112

Spin filtering neutrons with a proton target dynamically polarized using photo-excited triplet states  

NASA Astrophysics Data System (ADS)

In a test of principle a neutron spin filter has been built, which is based on dynamic nuclear polarization (DNP) using photo-excited triplet states. This DNP method has advantages over classical concepts as the requirements for cryogenic equipment and magnets are much relaxed: the spin filter is operated in a field of 0.3 T at a temperature of about 100 K and has performed reliably over periods of several weeks.The neutron beam was also used to analyze the polarization of the target employed as a spin filter. We obtained an independent measurement of the proton spin polarization of ?0.13 in good agreement with the value determined with NMR. Moreover, the neutron beam was used to measure the proton spin polarization as a function of position in the naphthalene sample. The polarization was found to be homogeneous, even at low laser power, in contradiction to existing models describing the photo-excitation process.

Haag, M.; van den Brandt, B.; Eichhorn, T. R.; Hautle, P.; Wenckebach, W. Th.

2012-06-01

113

The Electronic Investigation of Singlet and Triplet States of Oxyhemoglobin by Hartree-Fock Procedure and Associated Hyperfine Interaction.  

NASA Astrophysics Data System (ADS)

The observation of paramagnetic susceptibility [1] in Oxy-Hb from measurements over a broad temperature range has stimulated interest in the occurrence of a low-lying excited triplet state close to the ground singlet state of Oxy-Hb. An earlier theoretical investigation [2] has shown the existence of such a triplet state providing support to the interpretation of the susceptibility data [1]. Support for the low-lying excited triplet state has been augmented recently [3] from microscopic relaxation rate measurements for muon attached to the heme group of Oxy-Hb. We are studying by first principles Hartree-Fock procedure the energies and the electronic wave functions of the ground and triplet states and the quantitative theoretical prediction of muon magnetic hyperfine interaction in room temperature ?SR measurements on Oxy-Hb. Results will be presented for hyperfine interactions of muon and other nuclei in Oxy-Hb [1] M.Cerdonio etal. Proc. Nat. Acad. Sci USA 75, 4916(1978). [2] Zalek S. Herman and Gilda H Loew JACS 102, 1815(1980).[ 3] K. Nagamine etal Proc. Jpn. Acad.Ser.B 83,120(2007).

Dubey, Archana; Badu, S. R.; Scheicher, R. H.; Sahoo, N.; Pink, R. H.; Schulte, A.; Saha, H. P.; Chow, Lee; Nagamine, K.; Das, T. P.

2008-03-01

114

Symmetry analysis of the vibronic States in the upper conical potential (2(3)A') of triplet.  

PubMed

The symmetry properties of the rovibronic resonance states (Slonczewski resonances) supported by an upright conical potential are investigated. These symmetry properties lead to a useful correlation between states calculated with and without consideration of the geometrical phase, which can assist in the assignment of those states. The vibronic resonance states of triplet H3(+) (2(3)A'), which had been studied by us before, have now been assigned to spectroscopic quantum numbers. PMID:16833663

Viegas, Luis P; Alijah, Alexander; Varandas, António J C

2005-04-21

115

Deuteration effect on the spin dynamics of the photo-excited triplet state of pentacene in p-terphenyl crystals  

NASA Astrophysics Data System (ADS)

The kinetic parameters of the photo-excited triplet state of pentacene in p-terphenyl crystals have been calculated from the electron spin echo (ESE) decay curves in the temperature range of 5-300 K. The results suggest the calculated decay parameters depend strongly on guest deuteration, especially from the long-axis T x spin substate which can be explained in terms of the isotope effect on the non-radiative transitions arising mainly from the Franck-Condon factor. The relative populations of the triplet sublevels and spin-lattice relaxation show little or no dependence on the deuteration of the pentacene molecule.

Ong, Jui-Lin; Sloop, David J.; Lin, Tien-Sung

1995-08-01

116

Two-dimensional (2+n) resonance enhanced multiphoton ionization of HCl: State interactions and photorupture channels via low-energy triplet Rydberg states  

NASA Astrophysics Data System (ADS)

Mass spectra were recorded for (2+n) resonance enhanced multiphoton ionization (REMPI) of HCl as a function of resonance excitation energy in the 81 710-82 870 cm-1 region to obtain two-dimensional REMPI data. Small but significant fragmentations and H+, Cl+, as well as HCl+ formations are found to occur after resonance excitations to the triplet Rydberg states f 3?2(v'=0), f 3?1(v'=0), and g 3?+(1)(v'=0). Whereas insignificant rotational line shifts could be observed, alterations in relative ion signal intensities, due to perturbations, clearly could be seen, making such data ideal for detecting and analyzing weak state interactions. Model analysis of relative ion signal intensities, taking account of the major ion formation channels following excitations to Rydberg states, its near-resonance interactions with ion-pair states as well as dissociations and/or photodissociations were performed. These allowed verification of the existence of all these major channels as well as quantifications of the relative weights of the channels and estimates of state interaction strengths. The proposed mechanisms were supported by ion signal power dependence studies.

Kvaran, Ágúst; Matthiasson, Kristján; Wang, Huasheng

2009-07-01

117

Optimization of Triplet Excited State and Singlet Oxygen Quantum Yields of Picolylamine-Porphyrin Conjugates through Zinc Insertion.  

PubMed

We synthesized a new class of picolylamine-porphyrin conjugates 1-3 and have investigated the effect of heavy atom insertion on their intersystem crossing efficiency through spin-orbit perturbations. By incorporating zinc ions in the core as well as periphery positions of the porphyrin ring, we have successfully optimized their triplet excited state quantum yields and their efficiency to generate singlet oxygen. Uniquely, the picolylamine-porphyrin conjugate 3 having five zinc ions exhibited a triplet excited state quantum yield of ca. 0.97 and a sensitized singlet oxygen generation yield of ca. 0.92. In contrast, the free base porphyrin derivative 1 exhibited ca. 0.64 and 0.5 of the triplet excited state and singlet oxygen quantum yields, respectively. Our results demonstrate that the insertion of zinc metal ions in the picolylamine-porphyrin conjugates not only quantitatively enhances the triplet excited state and singlet oxygen yields but also imparts hydrophilicity, thereby their potential use as sensitizers in photodynamic therapy and green photooxygenation reactions. PMID:24063545

Marydasan, Betsy; Nair, Akhil K; Ramaiah, Danaboyina

2013-10-10

118

Conical intersections in triplet excited states of methylene from the anti-Hermitian contracted Schrödinger equation  

NASA Astrophysics Data System (ADS)

A conical intersection in triplet excited states of methylene is computed through the direct calculation of two-electron reduced density matrices (2-RDMs) from solutions of the anti-Hermitian contracted Schrödinger equation (ACSE). The study synthesizes recent extensions of the ACSE method for the treatment of excited states [G. Gidofalvi and D. A. Mazziotti, Phys. Rev. A 80, 022507 (2009)] and arbitrary-spin states [A. E. Rothman, J. J. Foley, and D. A. Mazziotti, Phys. Rev. A 80, 052508 (2009)]. We compute absolute energies of the 1 3B1, 1 3A2, and 2 3B1 states of methylene (CH2) and the location of the conical intersection along the 1 3A2-2 3B1 potential-energy surfaces. To treat multireference correlation, we seed the ACSE with an initial 2-RDM from a multiconfiguration self-consistent field (MCSCF) calculation. The ACSE produces energies that significantly improve upon those from MCSCF and second-order multireference many-body perturbation theory, and the 2-RDMs from the ACSE nearly satisfy necessary N-representability conditions. Comparison of the results from augmented double-zeta and triple-zeta basis sets demonstrates the importance of augmented (or diffuse) functions for determining the location of the conical intersection.

Snyder, James W.; Mazziotti, David A.

2010-04-01

119

Conical intersections in triplet excited states of methylene from the anti-Hermitian contracted Schrödinger equation.  

PubMed

A conical intersection in triplet excited states of methylene is computed through the direct calculation of two-electron reduced density matrices (2-RDMs) from solutions of the anti-Hermitian contracted Schrodinger equation (ACSE). The study synthesizes recent extensions of the ACSE method for the treatment of excited states [G. Gidofalvi and D. A. Mazziotti, Phys. Rev. A 80, 022507 (2009)] and arbitrary-spin states [A. E. Rothman, J. J. Foley, and D. A. Mazziotti, Phys. Rev. A 80, 052508 (2009)]. We compute absolute energies of the 1 (3)B(1), 1 (3)A(2), and 2 (3)B(1) states of methylene (CH(2)) and the location of the conical intersection along the 1 (3)A(2)-2 (3)B(1) potential-energy surfaces. To treat multireference correlation, we seed the ACSE with an initial 2-RDM from a multiconfiguration self-consistent field (MCSCF) calculation. The ACSE produces energies that significantly improve upon those from MCSCF and second-order multireference many-body perturbation theory, and the 2-RDMs from the ACSE nearly satisfy necessary N-representability conditions. Comparison of the results from augmented double-zeta and triple-zeta basis sets demonstrates the importance of augmented (or diffuse) functions for determining the location of the conical intersection. PMID:20423170

Snyder, James W; Rothman, Adam E; Foley, Jonathan J; Mazziotti, David A

2010-04-21

120

Analysis of photosystem II triplet states in thylakoids by fluorescence detected magnetic resonance in relation to the redox state of the primary quinone acceptor Q A  

NASA Astrophysics Data System (ADS)

The dependence of PSII triplet populations as a function of the primary quinone acceptor Q A redox state has been investigated by means of the fluorescence detected magnetic resonance (FDMR) technique in isolated thylakoid membranes. The results show that the population level of a microsecond decaying component having zero field splitting parameters | D|=0.0292 cm -1 and | E|=0.0037 cm -1 is inversely correlated to that of the recombination triplet (| D|=0.0285 cm -1 | E|=0.045 cm -1). The results could be interpreted in terms of the fast (50-150 ?s) decaying population being either the recombination triplet when the primary quinone Q A is singly reduced or a triplet located on a chlorophyll which is in tight singlet transfer coupling with the primary donor.

Santabarbara, S.; Jennings, R. C.; Carbonera, D.

2003-11-01

121

Triplet state properties of the OLED emitter Ir(btp)2(acac): characterization by site-selective spectroscopy and application of high magnetic fields.  

PubMed

The well-known red emitting complex Ir(btp)2(acac) (bis(2-(2'-benzothienyl)-pyridinato-N,C3')iridium(acetylacetonate)), frequently used as emitter material in OLEDs, has been investigated in a polycrystalline CH2Cl2 matrix. The studies were carried out under variation of temperature down to 1.2 K and at magnetic fields up to B=10 T. Highly resolved emission and excitation spectra of several specific sites are obtained by site-selective spectroscopy. For the preferentially investigated site (I-->0 at 16268 cm-1), the three substates I, II, and III of the T1 triplet state are separated by DeltaEII-I=2.9 cm-1 and DeltaEIII-I=25.0 cm-1, respectively. DeltaEIII-I represents the total zero-field splitting (ZFS). The individual decay times of these substates are tauI=150 micros, tauII=58 micros, and tauIII=2 micros, respectively. The long decay time of the lowest substate I indicates its almost pure triplet character. The time for relaxation from state II to state I (spin-lattice relaxation, SLR) is as long as 22 micros at T=1.5 K, while the thermalization between the two lower lying substates and substate III is fast. Application of a magnetic field induces Zeeman mixing of the substates of T1, resulting in an increased splitting between the two lower lying substates from 2.9 cm-1 at zero field to, for example, 6.8 cm-1 at B=10 T. Further, the decay time of the B-field perturbed lowest substate IB decreases by a factor of about 7 up to 10 T. The magnetic field properties clearly show that the three investigated states belong to the same triplet parent term of one single site. Other sites show a similar behavior, though the values of ZFS vary between 15 and 27 cm-1. Since the amount of ZFS reflects the extent of MLCT (metal-to-ligand charge transfer) parentage, it can be concluded that the emitting state T1 is a 3LC (ligand centered) state with significant admixtures of 1,3MLCT (metal-to-ligand charge transfer) character. Interestingly, the results show that the MLCT perturbation is different for the various sites. An empirical correlation between the amount of ZFS and the compound's potential for its use as emitter material in an OLED is presented. As a rule of thumb, a triplet emitter is considered promising for application in OLEDs, if it has a ZFS larger than about 10 cm-1. PMID:17488070

Finkenzeller, Walter J; Hofbeck, Thomas; Thompson, Mark E; Yersin, Hartmut

2007-05-09

122

Triplet-state bound-free transitions of alkali dimers (Na2 , K2, and Rb2) by electron-beam excitation  

Microsoft Academic Search

Amplified spontaneous emissions (ASEs) of the Na2 violet, K2 yellow, and Rb2 orange diffuse bands, which are potentially important in the development of continuously tunable high-power laser sources, were observed from electron-beam-excited mixtures of Na-Na2, K-K2, or Rb-Rb2 vapor with argon buffer gas. The continuum spectra centered at 436, 574, and 604 nm were attributed to triplet-triplet Na 2, K2,

Da Xing; Qi Wang; Shici Tan; Ken-ichi Ueda

1998-01-01

123

Triplet excimers of fluoroquinolones in aqueous media.  

PubMed

Generation of triplet eximers of 6-fluoro-7-piperazinyl-quinolone-3-carboxylic acids (FQs) have been detected in aqueous media using laser flash photolysis (LFP). These transient species (SS) are generated by self-quenching reactions of FQ triplet excited states such as pefloxacin (PFX), norfloxacin (NFX), the N-acetylated form of NFX (ANFX), and its methyl ester (EANFX) with their ground states. In this context, self-quenching rate constants in the range of (1-7) × 10(8) M(-1) s(-1) were determined. The triplet excimers show transient absorption spectra with ?(max) ca. 710 nm for SS(NFX), 740 nm for SS(PFX), and 620 nm for SS(ANFX) and E(ANFX), which are red-shifted with respect to their predecessors triplet excited states. These excimers can be also observed in the presence of phosphate buffer (PB). Experiments performed with NFX and ANFX at different PB concentrations showed that deprotonation processes are not involved in the generation of SS. The triplet multiplicity of the FQ excimers was confirmed by energy transfer reactions with naproxen. The correlation between fluorescence, intersystem crossing, excimer and photodegradation quantum yields of (A)NFX indicated that FQ self-quenching reactions are mainly a deactivation pathway. On the other hand, generation of FQ radical anions absorbing at ?(max) ca. 620 nm has been observed by an efficient electron transfer reaction from Trp to NFX, PFX, and ANFX (rate constants ca. 1 × 10(9) M(-1) s(-1)). PMID:22548526

Cuquerella, M Consuelo; Andreu, Inmaculada; Soldevila, Sonia; Bosca, Francisco

2012-05-17

124

Calculation of electron-photon coincidence parameters for singlet-triplet mixed 4F states of helium  

NASA Astrophysics Data System (ADS)

We present the theoretical formalism required to interpret the electron-photon coincidence measurements of the helium 4F state by Cvejanovi? and Crowe [Phys. Rev. Lett. 80, 3033 (1998)]. The results of the convergent close-coupling theory are compared with experiment and found to be in good qualitative agreement. We demonstrate that the singlet-triplet mixing in the 4F states does not affect the calculated results significantly.

Fursa, Dmitry V.; Bray, Igor

1999-02-01

125

Theory of enhanced proximity effect by midgap Andreev resonant state in diffusive normal-metal\\/triplet superconductor junctions  

Microsoft Academic Search

Enhanced proximity effect by the midgap Andreev resonant state (MARS) in a diffusive normal-metal\\/insulator\\/triplet superconductor (DN\\/TS) junction is studied based on the Keldysh-Nambu quasiclassical Green's-function formalism. By choosing a p -wave superconductor as a typical example of the TS, conductance of the junction and the spatial variation of the quasiparticle local density of states (LDOS) in the DN are calculated

Y. Tanaka; S. Kashiwaya; T. Yokoyama

2005-01-01

126

Triplet-Charge Annihilation versus Triplet-Triplet Annihilation in Organic Semiconductors  

SciTech Connect

A triplet can annihilate with a charge or a triplet, generating triplet-charge annihilation (TCA) or triplet-triplet annihilation (TTA) in organic semiconductors. On one hand, the TCA and TTA are critical issues to improve optoelectronic responses by using triplet states. On the other hand, the TCA and TTA are important spin-dependent processes to generate magneto-optoelectronic responses. Our experimental studies find that the TCA is a dominant process over TTA in organic semiconductors. Specifically, we separately confine triplets with charges or with triplets towards the generation of TCA and TTA by adjusting triplet density, charge confinement, and charge/exciton ratio based on organic light-emitting diodes. We then use magnetic field effects of electroluminescence (MFEEL), as an experimental tool, to study the generation of TCA and TTA. We observe that the electroluminescence can show negative response to applied magnetic field, generating a negative MFEEL, when triplets and charges are simultaneously confined within close proximity by using interfacial confinement with unbalanced charge/exciton ratio. On contrast, the electroluminescence only exhibits a positive MFEEL when triplets are confined within close proximity by using interfacial confinement without unbalanced charge/exciton ratio. Therefore, it can be concluded from our MFEEL results that the TCA is a major process to annihilate triplets over than TTA. Clearly, this experimental finding provides a new understanding on controlling triplets-related optoelectronic and magneto-optoelectronic processes in organic semiconductors.

Shao, Ming [ORNL; Yan, Liang [ORNL; Li, Mingxing [ORNL; Ivanov, Ilia N [ORNL; Hu, Bin [ORNL

2013-01-01

127

Search for ?/2 state in large-area spin-triplet ferromagnetic Josephson junctions  

NASA Astrophysics Data System (ADS)

The current-phase relationship of ferromagnetic spin-triplet Josephson junctions was predicted to be tuned by the magnetization orientations of different magnetic layers [1]. Given the random domain structure in large-area ferromagnetic junctions, the possibility of a random distribution of 0 or ? sub-junctions across the area could lead to a global ?/2 junction [2]. Critical current measurements as a function of area provide indirect evidence for ?/2 coupling [3], but they do not provide phase-sensitive information. Unfortunately there are technical difficulties faced by a direct current-phase measurement, especially for large area junctions. We are currently working toward a SQUID-based experiment that should be able to distinguish the ?/2 state from either the 0 or ? states. In this talk we will report our progress toward this goal. [1] A.F. Volkov, F.S. Bergeret, and K.B. Efetov, Phys. Rev. Lett. 90, 117006 (2003). [2] A. Zyuzin, B. Spivak, Phys. Rev. B 61 5902 (2000). [3] Y Wang, W. P. Pratt Jr., N. O. Birge, Phys. Rev. B 85 214522 (2012).

Wang, Yixing; Birge, Norman O.; Pratt, William P., Jr.

2013-03-01

128

A triplet of differently shaped spin-zero states in the atomic nucleus 186Pb  

PubMed

Understanding the fundamental excitations of many-fermion systems is of significant current interest. In atomic nuclei with even numbers of neutrons and protons, the low-lying excitation spectrum is generally formed by nucleon pair breaking and nuclear vibrations or rotations. However, for certain numbers of protons and neutrons, a subtle rearrangement of only a few nucleons among the orbitals at the Fermi surface can result in a different elementary mode: a macroscopic shape change. The first experimental evidence for this phenomenon came from the observation of shape coexistence in 16O (ref. 4). Other unexpected examples came with the discovery of fission isomers and super-deformed nuclei. Here we find experimentally that the lowest three states in the energy spectrum of the neutron deficient nucleus 186Pb are spherical, oblate and prolate. The states are populated by the alpha-decay of a parent nucleus; to identify them, we combine knowledge of the particular features of this decay with sensitive measurement techniques (a highly efficient velocity filters with strong background reduction, and an extremely selective recoil-alpha-electron coincidence tagging methods). The existence of this apparently unique shape triplet is permitted only by the specific conditions that are met around this particular nucleus. PMID:10839532

Andreyev; Huyse; Van Duppen P; Weissman; Ackermann; Gerl; Hessberger; Hofmann; Kleinbohl; Munzenberg; Reshitko; Schlegel; Schaffner; Cagarda; Matos; Saro; Keenan; Moore; O'Leary; Page; Taylor; Kettunen; Leino; Lavrentiev; Wyss; Heyde

2000-05-25

129

Spin-Triplet Pairing State of Sr2RuO4 in the c-Axis Magnetic Field  

NASA Astrophysics Data System (ADS)

We investigate the spin-triplet superconducting state of Sr2RuO4 in the magnetic field along the c-axis on the basis of the four-component Ginzburg--Landau (GL) model with a weak spin--orbit coupling. We consider superconducting states described by the d-vector parallel to the ab-plane (\\mbi{d}\\parallel ab), and find that three spin-triplet pairing states are stabilized in the magnetic field--temperature (H--T) phase diagram. Although a helical state is stable at low magnetic fields, a chiral II state is stabilized at high magnetic fields. A non-unitary spin-triplet pairing state appears near the transition temperature owing to the coupling of magnetic field and chirality. We elucidate synergistic and/or competing roles of the magnetic field, chirality, and spin--orbit coupling. It is shown that a fractional vortex lattice is stabilized in the chiral II phase owing to the spin--orbit coupling.

Takamatsu, Shuhei; Yanase, Youichi

2013-06-01

130

Laser flash photolysis study of triplet states in aligned liquid crystalline media  

SciTech Connect

A simple method for the laser flash photolysis study of aligned liquid crystals is reported. The formation of triplets of zinc tetraphenylporphyrin and 2-piperidinoanthraquinone in aligned nematic and isotropic phases of some commercially available cyanobiphenyl liquid crystals was studied. An observed increase in triplet-triplet absorption intensity in the nematic phase compared to the isotropic phase is entirely due to improved alignment and absorption of the polarized laser emission and contradicts a previously reported finding of enhancement of intersystem crossing efficiency. The variation of triplet lifetimes with temperature indicates that the microviscosity unlike the measured macroviscosity does not change drastically at the nematic-isotropic transition temperatures. At high laser intensities local melting of the nematic-to-isotropic phase was observed because of internal conversion-radiationless decay.

Das, S.; Lenoble, C.; Becker, R.S.

1987-07-08

131

A TDDFT study on the singlet and triplet excited-state hydrogen bonding and proton transfer of 10-hydroxybenzo[ h]quinoline (HBQ) and 7,9-diiodo-10-hydroxybenzo[ h]quinoline (DIHBQ)  

NASA Astrophysics Data System (ADS)

The singlet and triplet excited state as well as the influence of an iodine on the steady-spectra of 10-hydroxybenzo[ h]quinoline (HBQ) and 7,9-diiodo-10-hydroxybenzo[ h]quinoline (DIHBQ) were investigated using theoretical approach. For the HBQ and DIHBQ, only enol conformation exists in the singlet excited state, whereas there are two hydrogen bonded conformations in the triplet excited state: enol- and keto-tautomer conformation. The enol phosphorescence peak of HBQ which has not been detected in experiments is at 669 nm. The phosphorescence spectrum of DIHBQ ( ?max = 692 nm) may be the enol phosphorescence, which was assigned as keto-tautomer phosphorescence in the previous study.

Zhao, Xiaohong; Chen, Maodu

2011-08-01

132

Singlet and triplet energy levels in pi-conjugated polymers  

Microsoft Academic Search

In the first part of this talk I will discuss singlet and triplet energy levels in PPV, focusing on the optical exciton, singlet states observed in nonlinear spectroscopy, the lowest triplet, and the final triplet state reached by optical excitation from the lowest triplet. Lower and upper bounds to the energies of the two triplet states can be obtained this

Sumit Mazumdar

2000-01-01

133

The lifetime and efficiency of triplet-triplet fluorescence from the excited state of a TMM biradical determined using transient emission spectroscopy by two-color two-laser flash photolysis.  

PubMed

The single laser flash photolysis (FP) of 2-(4-benzoylphenyl)-2-phenyl-1-methylenecyclopropane gave rise to a ground state trimethylenemethane (TMM) biradical with absorption bands at 362 and 545 nm and an excited state of this biradical that displays triplet-triplet fluorescence at 580 nm. The excited biradical is likely formed via an expected two-photon process as well as an unexpected one-photon process. The fluorescence quantum yield of the excited biradical, 0.021, was successfully determined by employing a two-color two-laser FP technique. PMID:23576242

Matsui, Yasunori; Kawahara, Daisuke; Ohta, Eisuke; Ikeda, Hiroshi

2013-05-21

134

Photoinduced charge separation and charge recombination to a triplet state in a carotene-porphyrin-fullerene triad  

SciTech Connect

A molecular triad consisting of a diarylporphyrin (P) covalently linked to a carotenoid polyene (C) and a fullerene (C{sub 60}) has been prepared and studied using time-resolved spectroscopic methods. In 2-methyltetrahydrofuran solution, the triad undergoes photoinduced electron transfer to yield C-P{sup .+}-C{sub 60}{sup .-}, which evolves into C{sup .+}-P-C{sub 60}{sup .-} with an overall quantum yield of 0.14. This state decays by charge recombination to yield the carotenoid triplet state with a time constant of 170 ns. Even in a glass at 77 K, C{sup .+}-P-C{sub 60}{sup .-} is formed with a quantum yield of nearly 0.10 and again decays mainly by charge recombination to give {sup 3}C-P-C{sub 60}. The fullerene triplet, formed through normal intersystem crossing, is also observed at 77K. the generation in the triad of a long-lived charge separated state by photoinduced electron transfer, the low-temperature electron transfer behavior, and the formation of a triplet state by charge recombination are phenomena previously observed mostly in photosynthetic reaction centers. 36 refs., 5 figs.

Liddell, P.A.; Kuciauskas, D.; Sumida, J.P.; Nash, B.; Nguyen, D.; Moore, A.L.; Moore, T.A.; Gust, D. [Arizona State Univ. Tempe, AZ (United States)

1997-02-12

135

J-state interference signatures in the second solar spectrum. Modeling the Cr i triplet at 5204-5208 Å  

NASA Astrophysics Data System (ADS)

The scattering polarization in the solar spectrum is traditionally modeled with each spectral line treated separately, but this is generally inadequate for multiplets where J-state interference plays a significant role. Through simultaneous observations of all the 3 lines of a Cr i triplet, combined with realistic radiative transfer modeling of the data, we show that it is necessary to include J-state interference consistently when modeling lines with partially interacting fine structure components. Polarized line formation theory that includes J-state interference effects together with partial frequency redistribution for a two-term atom is used to model the observations. Collisional frequency redistribution is also accounted for. We show that the resonance polarization in the Cr i triplet is strongly affected by the partial frequency redistribution effects in the line core and near wing peaks. The Cr i triplet is quite sensitive to the temperature structure of the photospheric layers. Our complete frequency redistribution calculations in semi-empirical models of the solar atmosphere cannot reproduce the observed near wing polarization or the cross-over of the Stokes Q/I line polarization about the continuum polarization level that is due to the J-state interference. When however partial frequency redistribution is included, a good fit to these features can be achieved. Further, to obtain a good fit to the far wings, a small temperature enhancement of the FALF model in the photospheric layers is necessary.

Smitha, H. N.; Nagendra, K. N.; Stenflo, J. O.; Bianda, M.; Sampoorna, M.; Ramelli, R.; Anusha, L. S.

2012-05-01

136

Lowest triplet (n, ?*) electronic state of acrolein: Determination of structural parameters by cavity ringdown spectroscopy and quantum-chemical methods  

NASA Astrophysics Data System (ADS)

The cavity ringdown absorption spectrum of acrolein (propenal, CH2=CH--CH=O) was recorded near 412 nm, under bulk-gas conditions at room temperature and in a free-jet expansion. The measured spectral region includes the 000 band of the T1(n, ?*) <-- S0 system. We analyzed the 000 rotational contour by using the STROTA computer program [R. H. Judge et al., J. Chem. Phys. 103, 5343 (1995)], which incorporates an asymmetric rotor Hamiltonian for simulating and fitting singlet-triplet spectra. We used the program to fit T1(n, ?*) inertial constants to the room-temperature contour. The determined values (cm-1), with 2? confidence intervals, are A = 1.662 +/- 0.003, B = 0.1485 +/- 0.0006, C = 0.1363 +/- 0.0004. Linewidth analysis of the jet-cooled spectrum yielded a value of 14 +/- 2 ps for the lifetime of isolated acrolein molecules in the T1(n, ?*), v = 0 state. We discuss the observed lifetime in the context of previous computational work on acrolein photochemistry. The spectroscopically derived inertial constants for the T1(n, ?*) state were used to benchmark a variety of computational methods. One focus was on complete active space methods, such as complete active space self-consistent field (CASSCF) and second-order perturbation theory with a CASSCF reference function (CASPT2), which are applicable to excited states. We also examined the equation-of-motion coupled-cluster and time-dependent density function theory excited-state methods, and finally unrestricted ground-state techniques, including unrestricted density functional theory and unrestricted coupled-cluster theory with single and double and perturbative triple excitations. For each of the above methods, we or others [O. S. Bokareva et al., Int. J. Quantum Chem. 108, 2719 (2008)] used a triple zeta-quality basis set to optimize the T1(n, ?*) geometry of acrolein. We find that the multiconfigurational methods provide the best agreement with fitted inertial constants, while the economical unrestricted Perdew-Burke-Ernzerhof exchange-correlation hybrid functional (UPBE0) technique performs nearly as well.

Hlavacek, Nikolaus C.; McAnally, Michael O.; Drucker, Stephen

2013-02-01

137

Lowest triplet (n, ?*) electronic state of acrolein: determination of structural parameters by cavity ringdown spectroscopy and quantum-chemical methods.  

PubMed

The cavity ringdown absorption spectrum of acrolein (propenal, CH(2)=CH-CH=O) was recorded near 412 nm, under bulk-gas conditions at room temperature and in a free-jet expansion. The measured spectral region includes the 0(0)(0) band of the T(1)(n, ?*) ? S(0) system. We analyzed the 0(0)(0) rotational contour by using the STROTA computer program [R. H. Judge et al., J. Chem. Phys. 103, 5343 (1995)], which incorporates an asymmetric rotor Hamiltonian for simulating and fitting singlet-triplet spectra. We used the program to fit T(1)(n, ?*) inertial constants to the room-temperature contour. The determined values (cm(-1)), with 2? confidence intervals, are A = 1.662 ± 0.003, B = 0.1485 ± 0.0006, C = 0.1363 ± 0.0004. Linewidth analysis of the jet-cooled spectrum yielded a value of 14 ± 2 ps for the lifetime of isolated acrolein molecules in the T(1)(n, ?*), v = 0 state. We discuss the observed lifetime in the context of previous computational work on acrolein photochemistry. The spectroscopically derived inertial constants for the T(1)(n, ?*) state were used to benchmark a variety of computational methods. One focus was on complete active space methods, such as complete active space self-consistent field (CASSCF) and second-order perturbation theory with a CASSCF reference function (CASPT2), which are applicable to excited states. We also examined the equation-of-motion coupled-cluster and time-dependent density function theory excited-state methods, and finally unrestricted ground-state techniques, including unrestricted density functional theory and unrestricted coupled-cluster theory with single and double and perturbative triple excitations. For each of the above methods, we or others [O. S. Bokareva et al., Int. J. Quantum Chem. 108, 2719 (2008)] used a triple zeta-quality basis set to optimize the T(1)(n, ?*) geometry of acrolein. We find that the multiconfigurational methods provide the best agreement with fitted inertial constants, while the economical unrestricted Perdew-Burke-Ernzerhof exchange-correlation hybrid functional (UPBE0) technique performs nearly as well. PMID:23425467

Hlavacek, Nikolaus C; McAnally, Michael O; Drucker, Stephen

2013-02-14

138

Spin-lattice relaxation of the quinoxaline triplet state in n-alkane matrices measured in zero magnetic field  

Microsoft Academic Search

The individual spin-lattice relaxation (SLR) rate constants (Wij) between the sublevels of the lowest triplet state of quinoxaline in n-pentane and in n-hexane Sphol’skii hosts over the temperature range of 1.2 to 4.2 K have been measured in zero applied magnetic field. The anisotropy pattern for the Wij for quinoxaline in these n-alkane hosts differs from that observed in a

Sanjib Ghosh; Michael Petrin; August H. Maki

1987-01-01

139

Twist conformational effects on the excited triplet states of aromatic ketones studied by multifrequency TREPR and pulsed EPR spectroscopy  

Microsoft Academic Search

Employing X- and Q-band time-resolved EPR and pulsed EPR techniques, we have investigated effects of twist conformation on the electronic structures and magnetic properties of the lowest excited triplet states of alkyl phenyl ketones. The conformational variation due to steric hindrance of a bulky substituent on the alpha-position drastically leads to a decrease of the zerofield splitting constant of D

Tadaaki Ikoma; KIMIO AKIYAMA; SHOZO TERO-KUBOTA

1999-01-01

140

Deuteration effect on the spin dynamics of the photo-excited triplet state of pentacene in p-terphenyl crystals  

Microsoft Academic Search

The kinetic parameters of the photo-excited triplet state of pentacene in p-terphenyl crystals have been calculated from the electron spin echo (ESE) decay curves in the temperature range of 5–300 K. The results suggest the calculated decay parameters depend strongly on guest deuteration, especially from the long-axis Tx spin substate which can be explained in terms of the isotope effect

Jui-Lin Ong; David J. Sloop; Tien-Sung Lin

1995-01-01

141

Lasing action in a family of perylene derivatives: Singlet absorption and emission spectra, triplet absorption and oxygen quenching constants, and molecular mechanics and semiempirical molecular orbital calcuations  

SciTech Connect

The authors present experimental and computational determination of the excited-state properties in several perylene dyestuffs that are potential candidates for use as laser dyes. Attention is focused on the following species derived from 3,4,9,10-perylenetetracarboxylic acid dianhydride: the bis ((2,6-dimethylphenyl)imide) (1b, DXP); the bis(methylimide) (1c, DMP); both 1,6,7,12-tetrachloro- (1d, Cl{sub 4}DMP) and 1,2,5,6,7,8,11,12-octachloro- (1e, Cl{sub 8}DMP) derivatives. Soluble derivatives of seven-ringed or larger aromatic systems are produced by the introduction of relatively rigid out-of-plane substituents that prevent intermolecular close packing. Chiral distortions in ring-chlorinated perylene derivatives significantly alter the shape of the absorption bands, a consequence of symmetry breaking. Triplet-triplet absorptions and oxygen-quenching rates are observed under the conditions found in a dye laser cavity. Semiempirical molecular orbital calculations (INDO/S) provide detailed mapping of the singlet and triplet excited state manifolds of DMP, Cl{sub 4}DMP, and Cl{sub 8}DMP. Computed transition energies and intensities are used in the interpretation of the spectral features, in particular the observed T{sub 1} {yields} T{sub n} and potential S{sub 1} {yields} S{sub n} absorptions. The authors conclude the perylene-3,4,9,10-tetracarboxylic acid diimide chromophores may be solubilized and utilized in laser materials exhibiting superior performance in terms of power output, tuning range, and light stability. 42 refs., 5 figs., 7 tabs.

Sadrai, M.; Hadel, L.; Sauers, R.R. [State Univ. of New Jersey, New Brunswick, NJ (United States)] [and others

1992-10-01

142

On the role of singlet versus triplet excited states in the uncaging of ortho-nitrobenzyl caged compounds.  

PubMed

ortho-Nitrobenzylacetate (oNBA) is one of the smallest caged-compounds utilizing the famous ortho-nitrobenzyl caging group and thus serves here as a proto-typical example. Crucial for efficient uncaging of, here, acetate from oNBA is the formation of the aci-form of the nitro-group, which can be formed via excited-state intramolecular hydrogen transfer (ESIHT) in the lowest excited singlet S1 or the triplet T1 state. Using state-of-the-art quantum chemical methods, the efficiency of singlet and triplet ESIHT in aci-formation is investigated and the results are discussed in comparison to previous calculations on related caged-compounds as well as with respect to recent experimental findings. It is shown that the majority of the excited molecules undergo singlet ESIHT, which is generally inefficient with respect to aci-formation and subsequent uncaging, while only a minority of excited molecules undergo intersystem crossing and triplet ESIHT, which eventually leads to kinetically stable aci-isomers of oNBA resulting in final uncaging. Our computational results explain all existing experimental findings on ortho-nitrobenzylic caging groups conclusively and general synthetic strategies for their improvement are suggested. PMID:23487251

Mewes, Jan-Michael; Dreuw, Andreas

2013-03-13

143

The role played by some factors of intramolecular interaction in nonradiative deactivation of the lowest triplet state of octachlorodibenzo- p-dioxin  

NASA Astrophysics Data System (ADS)

We have studied how intramolecular interactions, such as vibronically induced spin-orbit (VISO) and nonadiabatic interactions, which are governed by different structural elements of the octachlorodibenzo- p-dioxin (OCDD) molecule, affect the deactivation of its lowest triplet state. In the nonadiabatic approximation, taking into account out-of-plane vibrational modes as promoting ones, we have estimated the values of rate constant K {dg/s} of the nonradiative energy deactivation of in-plane triplet sublevels ( s = z, y) of the triplet state of the OCDD molecule.

Gastilovich, E. A.; Klimenko, V. G.; Volkova, L. V.; Nurmukhametov, R. N.

2012-11-01

144

Calculated photoexcitation spectra of positronium Rydberg states  

NASA Astrophysics Data System (ADS)

Calculations of the photoexcitation spectra of ortho-positronium Rydberg states with principal quantum numbers between 10 and 30 are presented. The effects of Doppler broadening and saturation of the corresponding electric-dipole transitions are studied, together with the role of static and motionally induced electric fields. This is done in the context of recent measurements reported by Cassidy [Phys. Rev. Lett.PRLTAO0031-900710.1103/PhysRevLett.108.043401 108, 043401 (2012)], and with regard to experiments involving the production of antihydrogen by charge-exchange between Rydberg positronium and cold antiprotons.

Hogan, S. D.

2013-06-01

145

Zero-field magnetic resonance of the photo-excited triplet state of pentacene at room temperature  

NASA Astrophysics Data System (ADS)

The pulsed EPR free induction decay (FID) signals of the photo-excited pentacene triplet state are reported for three mixed crystals at room temperature: pentacene-h14 in p-terphenyl, pentacene-h14 in benzoic acid, and pentacene-d14 in p-terphenyl. The recorded FID signals have relatively long decay times of about four microseconds, presumably due to the reduced hyperfine interactions in the zero magnetic field. The time domain FID signals transform to spectral components typically narrower than 500 kHz, allowing us to determine the pentacene triplet zero field splitting parameters to better accuracy than previously reported. Further, a new experimental technique using the high speed magnetic field jumping capability enables us to examine the anisotropic hyperfine and quadrupole interactions.

Yang, Tran-Chin; Sloop, David J.; Weissman, S. I.; Lin, Tien-Sung

2000-12-01

146

Complete assignment of spin sublevels in the lowest excited triplet state of corrole compounds by time-resolved EPR spectroscopy  

NASA Astrophysics Data System (ADS)

The lowest excited triplet state of free-base 5,10,15-trispentafluorophenylcorrole (H3Cor) was studied in rigid glass by time-resolved electron paramagnetic resonance (TR-EPR) spectroscopy. Triplet sublevels were experimentally determined by using magnetophotoselection and liquid crystal. Quantum chemical calculations of zero-field splitting parameters D and E were used for the sublevel assignment. The out-of-plane sublevel Tz was found to be the lowest; namely, D is positive for H3Cor, in contrast to previous reports. The origin of the difference is discussed in detail. Preliminary TR-EPR experiments on rhodium corrole, accompanied by the quantum chemical calculations, emphasize the important contribution of spin-orbit couplings.

Yamauchi, Seigo; Tanabe, Mana; Ohba, Yasunori; Sugisaki, Kenji; Toyota, Kazuo; Sato, Kazunobu; Takui, Takeji; Saltsman, Irena

2012-01-01

147

Spin triplet excitations for a valence bond solid on the kagome lattice  

NASA Astrophysics Data System (ADS)

One of the most promising candidate ground states for the quantum antiferromagnetic Heisenberg model on the kagome lattice is the valence bond solid (VBS) with a 36-site unit cell. We present a theory of triplet excitation spectra about this ground state using bond operator formalism. In particular we obtain dispersions of all 18 triplet modes in the reduced Brillouin zone. In the bond operator mean-field theory, it is found that a large number of triplet modes are nondispersive. In particular, the lowest triplet excitation is nondispersive and degenerate with a dispersive mode at the zone center. Away from the zone center, the lowest triplet is separated from two other flat modes by a small energy gap. Quantum fluctuations are considered by taking into account scattering processes of two triplets and their bound-state formation, which leads to a downward renormalization of the lowest spin triplet gap. The dispersion of the lowest triplet excitation in the VBS state is compared with the dispersive lower bound of the triplet continuum expected in competing spin liquid phases. Implications to future neutron-scattering experiments are discussed.

Yang, Bohm-Jung; Kim, Yong Baek; Yu, Jaejun; Park, Kwon

2008-06-01

148

High resolution infrared-infrared double resonance spectroscopy study of the triplet ground state of the rubidium dimer  

NASA Astrophysics Data System (ADS)

This thesis consists of two parts. The first part is focused on the high resolution infrared-infrared (IRIR) double resonance spectroscopy study of the Rubidium dimer triplet ground state a3Sigma u+. We have observed fluorescence to this state for J=30, 50 and 70 rotational quantum numbers. We have used a perturbed pair of rovibrational levels in the a3Sigmau + ˜ b3piu electronic states as an intermediate excitation step to the higher lying 2 3pig state to get access by fluorescence decay to thea3Sigmau+ state. This allowed us to calculate the term values and the potential energy curve for the triplet ground state. The second part of the thesis is a computational study of lifetimes and transition dipole moment matrix elements for the sodium dimer ion pair states of 1Sigmag+ symmetry. These calculated parameters will be helpful for the design of a quadruple resonance based Autler-Townes spectroscopic probe of the transition dipole moments between these states and the A1Sigma u+ state. The calculated lifetime values compare well with results from literature when available. This work was supported by the National Science Foundation through awards PHY 0245311, PHY 0555608 and PHY 0855502.

Beser, Bediha

149

A time-resolved electron nuclear double resonance study of the photoexcited triplet state of P680 in isolated reaction centers of photosystem II  

NASA Astrophysics Data System (ADS)

A time-resolved ENDOR spectrum of the triplet state of the primary donor of photosystem II in isolated reaction centers has been obtained at cryogenic temperatures. Selective excitation of donor molecules, which have their z triplet axes parallel to the magnetic field, has permitted the measurement of the Azz component of the hyperfine coupling tensor of protons, in the reference frame of the zero field splitting tensor. For comparison, measurements have also been made on the photoexcited triplet state of monomeric chlorophyll a in vitro. The results indicate that in the temperature range 10-20 K the triplet state of the primary donor of photosystem II is largely located on a monomeric chlorophyll a molecule.

Di Valentin, M.; Kay, C. W. M.; Giacometti, G.; Möbius, K.

1996-01-01

150

Spin—lattice relaxation in a guest triplet state is induced by proton tunneling in a benzoic acid host crystal  

NASA Astrophysics Data System (ADS)

Spin—lattice relaxation (SLR) of the triplet state of pentacene-6,13-quinone (PQ) in n-C 11H 24, and as a guest impurity in benzoic acid, BA- h2 and the acid deuterated host, BA- d2, has been measured at temperatures near 4 K. Enhanced SLR in the BA hosts relative to n-C 11H 24 is a thermally activated process which we attribute to a phonon-assisted tunneling transition between local BA tautomer states.

Chaudhuri, D.; Schlyer, B. D.; Maki, A. H.

1991-03-01

151

Gaussian Markov Triplets  

NASA Astrophysics Data System (ADS)

The Markov property of states of algebras of the canonical commutation relation is studied and in the case of Gaussian states several equivalent properties are obtained. The detailed description is given in terms of a block matrix. The relation to classical multivariate Gaussian Markov triplets is also described. The minimizer of relative entropy with respect to a Gaussian markov state has the Markov property.

Petz, Dénes; Pitrik, József

2010-01-01

152

Internal heavy atom effect on the triplet spin sublevels of the lowest triplet state of naphthalene. I. Radiative and nonradiative decays of the spin sublevels of 1-halonaphthalenes  

Microsoft Academic Search

The mechanism of the internal heavy atom effect is discussed from the viewpoints of the dynamic and spectral properties of the triplet spin sublevels of 1-halonaphthalenes. The heavy atom effect on the radiative rate constant for phosphorescence emission in the O-O band is most prominent in the Tx emission, somewhat less in the Ty emission, and is small in the

Hiroyuki Saigusa; Tohru Azumi

1979-01-01

153

Pulsed electron nuclear double resonance studies of the photoexcited triplet state of pentacene in p-terphenyl crystals at room temperature  

Microsoft Academic Search

Pulsed electron nuclear double resonance (ENDOR) using a modified Davies-type [Phys. Lett. 47A, 1 (1974)] sequence is employed to study the hyperfine (HF) structure of the photoexcited triplet state of pentacene dispersed in protonated and deuterated p-terphenyl single crystals. The strong electron spin polarization and long phase memory time of triplet pentacene enable us to perform the ENDOR measurements on

Tomoaki Yago; Gerhard Link; Gerd Kothe; Tien-Sung Lin

2007-01-01

154

Spectrum of the Autoionizing Triplet Gerade Rydberg States of H2 and its Analysis Using Multichannel Quantum-Defect Theory  

NASA Astrophysics Data System (ADS)

A new spectrum of the autoionizing triplet states of gerade symmetry of H2 has been recorded from the -- = 1-4, N- = 1-3 rovibrational levels of the metastable c 3-u- state in a supersonic beam. The spectrum consists of overlapping ns and nd Rydberg series with n in the range between 4 and 45 converging to the -+ = 1-4, N+ = 0-5 levels of the X+ 2?g+ ground state of H2+. Numerous perturbations caused by s-d and rovibrational channel interactions are revealed in the spectrum and were fully assigned by combining double-resonance experiments and ab initio multichannel quantum-defect theory (MQDT). The energy- and internuclear-distance-dependent eigenquantum-defect parameters of MQDT were derived from available ab initio calculations of the low-lying electronic states of H2 and the ground state of H2+ and were subsequently refined in a global fit to experimental data. The positions of 552 triplet ns and nd Rydberg levels of H2 (361 of which were measured in the present study) could be reproduced with a root-mean-square deviation of 0.2 cm-1.

Sprecher, Daniel; Jungen, Christian; Merkt, Frédéric

2013-10-01

155

Calculating electron paramagnetic resonance g-matrices for triplet state molecules from multireference spin-orbit configuration interaction wave functions.  

PubMed

We present a way to calculate electron paramagnetic resonance (EPR) g-matrices from variationally optimized spin-orbit coupled wave functions. Our method constructs a triangular g-matrix from the matrix representation of the total electron magnetic moment in the basis of the spin-orbit coupled wave functions by means of a projection technique. Principal g-values are obtained in the standard fashion by forming from the triangular matrix g the tensor G=gg(t) and diagonalizing it. In principle, the scheme allows to calculate the spin-orbit orbital Zeeman cross term which usually gives the dominating contribution to the EPR g-shifts for any multiplicity. We have implemented this approach into a multireference spin-orbit configuration interaction (MRSOCI) program [M. Kleinschmidt et al., J. Chem. Phys. 124, 124101 (2006)]. Test applications are carried out for various triplet state sytems. The g-shifts of several of main group diatomics with X (3)Sigma(g)(-) ground state are investigated at the level of ab initio MRSOCI. We obtain perpendicular g-shifts which underestimate experimental Delta g(perpendicular) values from literature by approximately 13% on the average. For a set of organic triplet state molecules we employ the combined density functional theory/multireference configuration interaction (DFT/MRCI) technique [S. Grimme and M. Waletzke, J. Chem. Phys. 111, 5645 (1999)] to reduce the computational costs of the spin-free correlation problem. This approach yields principal g-values that match experiment well in many cases. Due to the small absolute g-shifts, a rigorous comparison will require the inclusion of first-order contributions such as the relativistic mass correction and gauge correction terms which have not been included here. For the triplet state dication trans-(CNSSS)(2)(2+) the principal g-shifts Delta g(a)=-0.3 ppt, Delta g(b)=17.5 ppt, and Delta g(c)=26.6 ppt are significantly larger and compare rather well to the experimental values Delta g(1)=-0.1+/-0.2 ppt, Delta g(2)=14.8+/-0.2 ppt, and Delta g(3)=24.8+/-0.1 ppt [A. Berces et al., Magn. Reson. Chem. 37, 353 (1999)]. In comparison to conventional truncated sum-over state techniques based on Rayleigh-Schrodinger perturbation theory, our new variational approach shows, in practice, robust and advantageous convergence characteristics with respect to the size of the many-particle basis set. We demonstrate that the DFT/MRSOCI technology is a very feasible means to compute reliable g-shifts for large organic triplet systems at low computational cost. PMID:19388735

Tatchen, Jörg; Kleinschmidt, Martin; Marian, Christel M

2009-04-21

156

Involvement of triplet excited states in the electron transfer photodegradation of cinnamic acids using pyrylium and thiapyrylium salts as photocatalysts.  

PubMed

The mechanistic pathway for degradation of cinnamic acids using 2,4,6-triphenylpyrylium as well as 2,4,6-triphenyl(thia)pyrylium salts (,) as solar photocatalysts has been unambiguously established. Results obtained in steady-state experiments have been correlated with time-resolved photophysical studies. High percentages of photodegradation (60-70%) were achieved when aqueous solutions of caffeic and ferulic acids (,) as model pollutants were submitted to irradiation in the presence of ,. Electron-transfer quenching of both the singlet and triplet excited states of , by , has been proved, and the quenching rate constants (close to diffusion control) have been determined. However, the percentages of singlet quenching by ,, even at relatively high concentrations of the model pollutants, is lower than 5%. In addition to this, growth of the signal corresponding to the pyranyl radical occurs in the microsecond timescale, incompatible with the singlet state as precursor. Thus, photodegradation of , mainly involves the triplet state of the photocatalysts. PMID:17668114

Marín, M Luisa; Miguel, Ana; Santos-Juanes, Lucas; Arques, Antonio; Amat, Ana M; Miranda, Miguel A

2007-06-04

157

Singlet and triplet excited state behaviors of C[sub 60] in nonreactive and reactive polymer films  

SciTech Connect

The excited state behavior of C[sub 60] has been investigated in polystyrene (PS) and poly(9-vinylcarbazole) (PVCz) polymer films. Picosecond and nanosecond laser flash photolysis techniques are employed to probe the transient absorption properties of singlet and triplet excited states in nonreactive (PS) and reactive (PVCz) microenvironments. In PS film, the absorption properties and lifetimes of these excited states are very similar to those observed in solutions. Encapsulation of C[sub 60] with PS results in the suppression of excited state self-quenching processes. Excited state charge transfer complex formation dominates in PVCz film. The absence of long-lived electron transfer products indicates that the charge separation in PVCz film is short-lived. 40 refs., 6 figs.

Sauve, G.; Dimitrijevic, N.M.; Kamat, P.V. (Univ. of Notre Dame, IN (United States))

1995-01-26

158

Carbon Monoxide Triplet Rydberg Series in the f Complex Region.  

PubMed

Using a multistep state-selective excitation scheme, fluorescence-dip spectra of carbon monoxide have been recorded in the energy region between 106 100 and 112 200 cm(-1). Prominent groups of bands were tentatively identified as transitions into the 6f em leader10f (v=0) and 9psigma em leader11psigma (v=0) triplet Rydberg series. For the f complex states, molecular constants have been calculated. The triplet f levels show an unusually large rotational constant and are located at higher energies than their singlet counterparts. Copyright 2001 Academic Press. PMID:11281691

Mellinger, Axel; Rohwer, Erich G.; Vidal, Carl Rudolf

2001-04-01

159

Triplet state sensitization of covalently linked hybrid porphyrin dimers. Evidence for intramolecular triplet energy transfer. [Free base tetraphenylporphyrin and zinc tetraphenylporphyrin  

SciTech Connect

Triplet sensitization of covalently linked hybrid porphyrin dimers, in pulsed radiolysis solutions, allows monitoring intramolecular triplet energy transfer. Results for two dimers are reported: the para-para and ortho-ortho of Zn(-CH/sub 2/-)/sub 3/H/sub 2/, where the Zn and H/sub 2/ are the tetratosyl, zinc, and free base, porphyrin chromophores. The results for the intramolecular rates are k/sub et//sup para-para/ = (2.6-10) x 10/sup 5/ s/sup -1/ and k/sub et//sup ortho-ortho/ > 10 x 10/sup 5/ s/sup -1/. The pseudo-first-order rates for sensitization are k/sup ortho-ortho/ = 1.8 x 10/sup 5/ s/sup -1/ and k/sup para-para/ > 1.8 x 10/sup 5/ s/sup -1/.

Levanon, H.; Regev, A.; Das, P.K.

1987-01-01

160

An apparatus for pulsed ESR and DNP experiments using optically excited triplet states down to liquid helium temperatures.  

PubMed

In standard Dynamic Nuclear Polarization (DNP) electron spins are polarized at low temperatures in a strong magnetic field and this polarization is transferred to the nuclear spins by means of a microwave field. To obtain high nuclear polarizations cryogenic equipment reaching temperatures of 1 K or below and superconducting magnets delivering several Tesla are required. This equipment strongly limits applications in nuclear and particle physics where beams of particles interact with the polarized nuclei, as well as in neutron scattering science. The problem can be solved using short-lived optically excited triplet states delivering the electron spin. The spin is polarized in the optical excitation process and both the cryogenic equipment and magnet can be simplified significantly. A versatile apparatus is described that allows to perform pulsed dynamic nuclear polarization experiments at X-band using short-lived optically excited triplet sates. The efficient (4)He flow cryostat that cools the sample to temperatures between 4 K and 300 K has an optical access with a coupling stage for a fiber transporting the light from a dedicated laser system. It is further designed to be operated on a neutron beam. A combined pulse ESR/DNP spectrometer has been developed to observe and characterize the triplet states and to perform pulse DNP experiments. The ESR probe is based on a dielectric ring resonator of 7 mm inner diameter that can accommodate cubic samples of 5mm length needed for neutron experiments. NMR measurements can be performed during DNP with a coil integrated in the cavity. With the presented apparatus a proton polarization of 0.5 has been achieved at 0.3 T. PMID:23838526

Eichhorn, T R; Haag, M; van den Brandt, B; Hautle, P; Wenckebach, W Th; Jannin, S; van der Klink, J J; Comment, A

2013-06-22

161

An apparatus for pulsed ESR and DNP experiments using optically excited triplet states down to liquid helium temperatures  

NASA Astrophysics Data System (ADS)

In standard Dynamic Nuclear Polarization (DNP) electron spins are polarized at low temperatures in a strong magnetic field and this polarization is transferred to the nuclear spins by means of a microwave field. To obtain high nuclear polarizations cryogenic equipment reaching temperatures of 1 K or below and superconducting magnets delivering several Tesla are required. This equipment strongly limits applications in nuclear and particle physics where beams of particles interact with the polarized nuclei, as well as in neutron scattering science. The problem can be solved using short-lived optically excited triplet states delivering the electron spin. The spin is polarized in the optical excitation process and both the cryogenic equipment and magnet can be simplified significantly. A versatile apparatus is described that allows to perform pulsed dynamic nuclear polarization experiments at X-band using short-lived optically excited triplet sates. The efficient 4He flow cryostat that cools the sample to temperatures between 4 K and 300 K has an optical access with a coupling stage for a fiber transporting the light from a dedicated laser system. It is further designed to be operated on a neutron beam. A combined pulse ESR/DNP spectrometer has been developed to observe and characterize the triplet states and to perform pulse DNP experiments. The ESR probe is based on a dielectric ring resonator of 7 mm inner diameter that can accommodate cubic samples of 5 mm length needed for neutron experiments. NMR measurements can be performed during DNP with a coil integrated in the cavity. With the presented apparatus a proton polarization of 0.5 has been achieved at 0.3 T.

Eichhorn, T. R.; Haag, M.; van den Brandt, B.; Hautle, P.; Wenckebach, W. Th.; Jannin, S.; van der Klink, J. J.; Comment, A.

2013-09-01

162

A 240 GHz high-field transient EPR study of the primary donor triplet state g-tensor in photosynthetic reaction centers of Rhodobacter sphaeroides R-26.  

NASA Astrophysics Data System (ADS)

We report time-resolved 240 GHz EPR spectra of the primary donor triplet state ^3P from photosynthetic reaction centers of Rhodobacter sphaeroides R26.1 as a function of temperature in the range 10-230K. The data allow the determination of the principal g-tensor values and the principal axes directions of the ^3P g-tensor with respect to its zero-field axes. The g-tensor measured at 240 GHz differs appreciably from previous measurements of ^3P at lower frequencies and also differs from that of the cation radical state P^+, which has previously been characterized at high frequencies. In contrast to P^+, the ^3P state exhibits significant temperature dependence in its g-tensor, particularly in the direction of the principal axes. The ^3P yield anisotropy first observed by Boxer and coworkers at high field using photoselection methods is also evident in the high-field EPR spectrum as a significant variation of intensity across the spectrum. This variation is analyzed in terms of a radical pair and a yield ratio model.

van Tol, Johan; Budil, David; Zeng, Ronghui; Frank, Harry; Deal, Amanda

2003-03-01

163

Autler–Townes triplet spectroscopy  

Microsoft Academic Search

We study the effects of quantum interference in the spontaneous emission spectrum of a four-level driven atomic system. We use three strong laser fields to drive the atom and a weak laser field to prepare the initial state of the atom. The atomic system exhibits Autler–Townes triplet in the spectrum. The single Lorentzian peak splits into triplet and their widths

Fazal Ghafoor; Sajid Qamar; Shi-Yao Zhu; M. Suhail Zubairy

2007-01-01

164

Light-harvesting fullerene dyads as organic triplet photosensitizers for triplet-triplet annihilation upconversions.  

PubMed

Visible light-harvesting C(60)-bodipy dyads were devised as universal organic triplet photosensitizers for triplet-triplet annihilation (TTA) upconversion. The antennas in the dyad were used to harvest the excitation energy, and then the singlet excited state of C(60) will be populated via the intramolecular energy transfer from the antenna to C(60) unit. In turn with the intrinsic intersystem crossing (ISC) of the C(60), the triplet excited state of the C(60) will be produced. Thus, without any heavy atoms, the triplet excited states of organic dyads are populated upon photoexcitation. Different from C(60), the dyads show strong absorption of visible light at 515 nm (C-1, ? = 70400 M(-1) cm(-1)) or 590 nm (C-2, ? = 82500 M(-1) cm(-1)). Efficient intramolecular energy transfer from the bodipy moieties to C(60) unit and localization of the triplet excited state on C(60) were confirmed by steady-state and time-resolved spectroscopy as well as DFT calculations. The dyads were used as triplet photosensitizers for TTA upconversion, and an upconversion quantum yield up to 7.0% was observed. We propose that C(60)-organic chromophore dyads can be used as a general molecular structural motif for organic triplet photosensitizers, which can be used for photocatalysis, photodynamic therapy, and TTA upconversions. PMID:22616881

Wu, Wanhua; Zhao, Jianzhang; Sun, Jifu; Guo, Song

2012-05-30

165

Triplet sublevels of metal organic complexes – temperature dependence of spin–lattice relaxation  

Microsoft Academic Search

Triplets of transition metal complexes with organic chelate ligands can act as important pathways in photo-redox processes. Detailed information on these states is available from highly resolved optical spectra and time-resolved investigations. The lowest triplets are often zero-field split into sublevels by several cm?1 (zero-field splitting, ZFS) due to spin–orbit interactions. Interestingly, the relaxation between these sublevels can be very

Johann Strasser; Herbert H. H. Homeier; Hartmut Yersin

2000-01-01

166

More on the catalysis of internal conversion in chlorophyll a by an adjacent carotenoid in light-harvesting complex (Chl a/ b LHCII) of higher plants: time-resolved triplet-minus-singlet spectra of detergent-perturbed complexes  

NASA Astrophysics Data System (ADS)

Wavelength-selective photo-excitation of samples containing a detergent and LHCII (the main light-harvesting complex pertaining to photosystem II of green plants) is used for recording time-resolved triplet-minus-singlet (TmS) difference spectra, with a view to probing interactions between chlorophyll a (Chl a) and chlorophyll b (Chl b), and between Chl a and lutein (Lut). Once the detergent concentration ( CD) exceeds a threshold, C©, the TmS spectrum becomes sensitive to ??, the wavelength of excitation, and to t, the delay between excitation and observation. Each increment in CD brings about a diminution in the efficiency of a†? x† transfer (triplet-triplet transfer from Chl a to Lut) and a rise in both the triplet formation yield and the fluorescence yield of Chl a. What is more, b*? a* transfer (singlet-singlet transfer from Chl b to Chl a) slackens to such an extent that Chl b*?Chl b† intersystem crossing, negligible when CD is below C©, begins to vie with transfer, for the deactivation of Chl b* (in the foregoing an asterisk/dagger denotes singlet/triplet excitation). The reduction in the efficiencies of the two transfers is easily understood by: (i) invoking the Kühlbrandt-Wang-Fujiyoshi model of LHCII, which posits each Chl b in contact with a Chl a and each Chl a in contact with a Lut, and (ii) assuming that the detergent severs contact between adjacent chromophores. That a growth in the triplet yield of Chl a* accompanies the detergent-induced decrease in the efficiency of a†? x† transfer becomes intelligible if one assumes, further, that internal conversion in Chla* is faster than that in overlineChla * , where under or over lining betokens the presence or absence of a carotenoid neighbour. When CD is close to C©, most Chl a molecules are adjacent to a Lut, internal conversion dominates, and the overall triplet yield is low. As CD is gradually raised the Chla ? overlineChla transformation sets in, causing concomitant drops in the efficiencies of a†? x† transfer and internal conversion, and a consequent rise in the overall yields of Chl a fluorescence and formation of Chl a triplets.

Naqvi, K. Razi; Jávorfi, Tamás; Melø, T. B.; Garab, Gyözö

1998-12-01

167

First principles electronic structure investigation of order of singlet and triplet states of oxyhemoglobin and analysis of possible influence of muon trapping  

NASA Astrophysics Data System (ADS)

Interest in the possibility of magnetic character for oxyhemoglobin (OxyHb) has been recently stimulated by the observations of muon spin-lattice relaxation effects studied (Nagamine et al., Proc Jpn Acad Ser B Phys Biol Sci 83:120-126, 2007) with the muon-spin rotation ( ?SR) technique. In view of this, we have carried out first-principles electronic structure investigations involving Hartree-Fock theory combined with many body perturbation effects for the singlet and triplet states of OxyHb. Our results indicate that using two recent x-ray structural data (Paoli et al., J Mol Biol 256:775, 1996; Park et al., J Mol Biol 360:690, 2006) for OxyHb, for only Hartree-Fock theory without many-body effects included, the singlet state lies above the triplet state by energies of about 0.08 and 0.13 a.u. for the two structures in Paoli et al. (J Mol Biol 256:775, 1996) and Park et al. (J Mol Biol 360:690, 2006). Incorporation of many-body effects by the perturbation method reverses the order, with the triplet state located 0.18 and 0.14 a.u. above the singlet state for the structures in Paoli et al. (J Mol Biol 256:775, 1996) and Park et al. (J Mol Biol 360:690, 2006). Physical reasons for these relative orderings of the singlet and triplet states will be discussed. It is clear that OxyHb by itself would be in a singlet state at room temperature or below, since from our calculation, the triplet state lies about KT above the singlet state with T having the value of 44,098 K and 56,449 K for the two structural data in Paoli et al. (J Mol Biol 256:775, 1996) and Park et al. (J Mol Biol 360:690, 2006). As regards the muon spin-lattice relaxation effects obtained by recent ?SR measurements (by Nagamine et al., Proc Jpn Acad Ser B Phys Biol Sci 83:120-126, 2007) at room temperature, the sensitive dependence of the singlet-triplet separation on many-body effects in our investigation suggests that it is possible that the singlet-triplet separation could be reversed or reduced significantly when a muon is trapped near an oxygen atom of the oxygen molecule, allowing the triplet to be occupied at room temperature and lead to significant muon spin-lattice relaxation.

Badu, S. R.; Pink, R. H.; Scheicher, R. H.; Dubey, Archana; Sahoo, N.; Nagamine, K.; Das, T. P.

2010-04-01

168

Spin-triplet paired state induced by Hund’s rule coupling and correlations: a fully statistically consistent Gutzwiller approach  

NASA Astrophysics Data System (ADS)

The intrasite and intersite spin-triplet pairing gaps induced by interband Hund’s rule coupling and their correlations are analyzed in the doubly degenerate Hubbard Hamiltonian. To include the effect of correlations, the statistically consistent Gutzwiller approximation is used. In this approach the consistency means that the averages calculated from the self-consistent equations and those determined variationally coincide with each other. Emphasis is put on the solution for which the average particle number is conserved when carrying out the Gutzwiller projection. This method leads to a stable equal-spin paired state in the so-called repulsive interactions limit (U > 3J) in the regime of moderate correlations. The interband hybridization introduces an inequivalence of the bands which, above a critical magnitude, suppresses the paired state due to both the Fermi-wavevector mismatch for the Cooper pair and the interband hopping allowed by the Pauli principle.

Spa?ek, J.; Zegrodnik, M.

2013-10-01

169

Spin-triplet paired state induced by Hund's rule coupling and correlations: a fully statistically consistent Gutzwiller approach.  

PubMed

The intrasite and intersite spin-triplet pairing gaps induced by interband Hund's rule coupling and their correlations are analyzed in the doubly degenerate Hubbard Hamiltonian. To include the effect of correlations, the statistically consistent Gutzwiller approximation is used. In this approach the consistency means that the averages calculated from the self-consistent equations and those determined variationally coincide with each other. Emphasis is put on the solution for which the average particle number is conserved when carrying out the Gutzwiller projection. This method leads to a stable equal-spin paired state in the so-called repulsive interactions limit (U > 3J) in the regime of moderate correlations. The interband hybridization introduces an inequivalence of the bands which, above a critical magnitude, suppresses the paired state due to both the Fermi-wavevector mismatch for the Cooper pair and the interband hopping allowed by the Pauli principle. PMID:24097123

Spa?ek, J; Zegrodnik, M

2013-10-04

170

Time-resolved electron paramagnetic resonance and phosphorescence studies of the lowest excited triplet states of Rh(III) corrole complexes.  

PubMed

The lowest excited triplet (T(1)) ??* states of gallium (Ga) and various rhodium (Rh) 5,10,15-trispentafluorophenyl corroles (Cors) were studied in the liquid crystal (LC) E-7 and in rigid glasses by time-resolved electron paramagnetic resonance (TR-EPR) spectroscopy. The triplet sublevel energies were experimentally determined by the alignment of the molecules in the LC and by magnetophotoselection in the glass. The sublevel scheme of GaCor was determined by calculating the zero field splitting (ZFS) parameters. Axial ligand effects and quantum chemical calculations were used for the sublevel assignment of RhCors. The anisotropic EPR parameters were used to determine the important higher excited states and the magnitudes of their spin-orbit coupling (SOC) contributions were evaluated. On the basis of these results and analyses, the EPR parameters and triplet lifetime were discussed for each RhCor complex. PMID:22946766

Tanabe, Mana; Matsuoka, Hideto; Ohba, Yasunori; Yamauchi, Seigo; Sugisaki, Kenji; Toyota, Kazuo; Sato, Kazunobu; Takui, Takeji; Goldberg, Israel; Saltsman, Irena; Gross, Zeev

2012-09-24

171

Triplet State of the Semiquinone-Rieske Cluster as an Intermediate of Electronic Bifurcation Catalyzed by Cytochrome bc1.  

PubMed

Efficient energy conversion often requires stabilization of one-electron intermediates within catalytic sites of redox enzymes. While quinol oxidoreductases are known to stabilize semiquinones, one of the famous exceptions includes the quinol oxidation site of cytochrome bc1 (Qo), for which detection of any intermediate states is extremely difficult. Here we discover a semiquinone at the Qo site (SQo) that is coupled to the reduced Rieske cluster (FeS) via spin-spin exchange interaction. This interaction creates a new electron paramagnetic resonance (EPR) transitions with the most prominent g = 1.94 signal shifting to 1.96 with an increase in the EPR frequency from X- to Q-band. The estimated value of isotropic spin-spin exchange interaction (|J0| = 3500 MHz) indicates that at a lower magnetic field (typical of X-band) the SQo-FeS coupled centers can be described as a triplet state. Concomitantly with the appearance of the SQo-FeS triplet state, we detected a g = 2.0045 radical signal that corresponded to the population of unusually fast-relaxing SQo for which spin-spin exchange does not exist or is too small to be resolved. The g = 1.94 and g = 2.0045 signals reached up to 20% of cytochrome bc1 monomers under aerobic conditions, challenging the paradigm of the high reactivity of SQo toward molecular oxygen. Recognition of stable SQo reflected in g = 1.94 and g = 2.0045 signals offers a new perspective on understanding the mechanism of Qo site catalysis. The frequency-dependent EPR transitions of the SQo-FeS coupled system establish a new spectroscopic approach for the detection of SQo in mitochondria and other bioenergetic systems. PMID:23941428

Sarewicz, Marcin; Dutka, Ma?gorzata; Pintscher, Sebastian; Osyczka, Artur

2013-09-04

172

First Principles Electronic Structure Investigation of Singlet and Triplet States of Oxyhemoglobin by Hartree-Fock Procedure Combined with Many-Body Perturbation Theory  

NASA Astrophysics Data System (ADS)

Interest in the possibility of magnetic character of oxyhemoglobin has been recently stimulated by spin-lattice relaxation effects studied [1] by the muon-spin rotation technique. In view of this, we have carried out first-principles electronic structure investigations involving Hartree-Fock theory combined with many body perturbation effects on the singlet and triplet states of oxyhemoglobin. Our results indicates using two recent x-ray structural data [2,3] for oxyhemoglobin that, using only Hartree-Fock theory without correlation effects included, the singlet state lies above the triplet state by about 0.08a.u.[2] and 0.13a.u.[3]. Incorporation of many body effects by perturbation methods reverses the order with the triplet state located 0.18a.u.[2] and 0.14a.u.[3] respectively above the singlet state. Physical reasons for these relative orderings of the singlet and triplet states will be discussed.[4pt] [1] K. Nagamine etal. Proc. Acad.Ser.B 83,120(2007).[0pt] [2] Massimo Paoli etal. J.Mol. Biol. 256,775(1996).[0pt] [3] Sam-Yong Park etal. J.Mol. Biol. 360,690(2006)

Badu, S. R.; Dubey, Archana; Scheicher, R. H.; Sahoo, N.; Pink, R. H.; Schulte, A.; Saha, H. P.; Chow, Lee; Nagamine, K.; Das, T. P.

2010-03-01

173

Organic Luminescent Molecule with Energetically Equivalent Singlet and Triplet Excited States for Organic Light-Emitting Diodes  

NASA Astrophysics Data System (ADS)

We demonstrate an organic molecule with an energy gap between its singlet and triplet excited states of almost zero (?EST˜0eV). Such separation was realized through proper combination of an electron-donating indolocarbazole group and a diphenyltriazine electron-accepting moiety. Calculated and measured ?EST were 0.003 and 0.02 eV, respectively. A total photoluminescence efficiency of 59%±2% with 45%±2% from a delayed component and 14%±2% from a prompt component was obtained for a doped film. Organic light emitting diodes containing this molecule as an emitting dopant exhibited an unexpectedly high external electroluminescence efficiency of ?EQE=14%±1%.

Sato, Keigo; Shizu, Katsuyuki; Yoshimura, Kazuaki; Kawada, Atsushi; Miyazaki, Hiroshi; Adachi, Chihaya

2013-06-01

174

Flow Rate and Fluence Rate Dependences of the Triplet-State Lifetime of Talaporfin Sodium Photochemical Reaction in Flowing Solution  

NASA Astrophysics Data System (ADS)

The flow rate and fluence rate dependences of the triplet-state lifetime (?T) and singlet oxygen (1O2) luminescence intensity of a Talaporfin sodium (mono-l-aspartyl chlorin e6, Laserphyrin\\textregistered) photochemical reaction in a flowing solution were studied. The oxygen consumption rate constant (k) did not proportionally increase as the fluence rate increased. The relationship between the static oxygen concentration in the flowing solution and ?T was estimated. ?T at the fluence rate of 0.8× 104 W/m2 was 16% longer than that at 0.2× 104 W/m2 at the same oxygen concentration. The ?T increase at the high-fluence rate is attributed to local and temporal oxygen depletion. The local and temporal oxygen depletion might cause the fluence-rate dependence nonproportionality of the measured k.

Ohmori, Sayaka; Hakomori, Shiho; Arai, Tsunenori

2007-03-01

175

Phase transitions of dense neutron matter with generalized Skyrme interaction to superfluid states with triplet pairing in strong magnetic field  

NASA Astrophysics Data System (ADS)

A generalized non-relativistic Fermi-liquid approach was used to find analytical formulas for temperatures Tc1(n, H) and Tc2(n, H) (which are functions nonlinear of density n and linear of magnetic field H) of phase transitions in spatially uniform dense pure neutron matter from normal to superfluid states with spin-triplet p-wave pairing (similar to anisotropic superfluid phases 3He-A1 and 3He-A2) in steady and homogeneous strong magnetic field (but |?n| H ll Ec < ?F(n), where ?n is the magnetic dipole moment of a neutron, Ec is the cutoff energy and ?F(n) is the Fermi energy in neutron matter). General formulas for Tc1, 2 (n, H) (valid for arbitrary parameterization of the effective Skyrme interaction in neutron matter) are specified here for generalized BSk18 parameterization of the Skyrme forces (with additional terms dependent on density n) on the interval 0.3 n0 < n < nc (BSk18) ? 2.7952 · n0, where n0 = 0.17 fm-3 is nuclear density and at critical density nc(BSk18) triplet superfluidity disappears, Tc0(n, cH = 0) = 0. Expressions for phase transition temperatures Tc0(n)<0.09MeV (at Ec = 10MeV) and Tc1, 2(n, H) are realistic non-monotone functions of density n for BSk18 parameterization of the Skyrme forces (contrary to their monotone increase for all previous BSk parameterizations). Phase transitions to superfluid states of such type might occur in liquid outer core of magnetars (strongly magnetized neutron stars).

Tarasov, A. N.

2012-12-01

176

Energy Landscapes of Dynamic Ensembles of Rolling Triplet Repeat Bulge Loops: Implications for DNA Expansion Associated with Disease States  

PubMed Central

DNA repeat domains can form ensembles of canonical and noncanonical states, including stable and metastable DNA secondary structures. Such sequence-induced structural diversity creates complex conformational landscapes for DNA processing pathways, including those triplet expansion events that accompany replication, recombination, and/or repair. Here we demonstrate further levels of conformational complexity within repeat domains. Specifically, we show that bulge loop structures within an extended repeat domain can form dynamic ensembles containing a distribution of loop positions, thereby yielding families of positional loop isomers, which we designate as “rollamers”. Our fluorescence, absorbance, and calorimetric data are consistent with loop migration/translocation between sites within the repeat domain (“rollamerization”). We demonstrate that such “rollameric” migration of bulge loops within repeat sequences can invade and disrupt previously formed base-paired domains via an isoenthalpic, entropy-driven process. We further demonstrate that destabilizing abasic lesions alter the loop distributions so as to favor “rollamers” with the lesion positioned at the duplex/loop junction, sites where the flexibility of the abasic “universal hinge” relaxes unfavorable interactions and/or facilitates topological accommodation. Another strategic siting of an abasic site induces directed loop migration toward denaturing domains, a phenomenon that merges destabilizing domains. In the aggregate, our data reveal that dynamic ensembles within repeat domains profoundly impact the overall energetics of such DNA constructs as well as the distribution of states by which they denature/renature. These static and dynamic influences within triplet repeat domains expand the conformational space available for selection and targeting by the DNA processing machinery. We propose that such dynamic ensembles and their associated impact on DNA properties influence pathways that lead to DNA expansion.

2012-01-01

177

Theory of enhanced proximity effect by midgap Andreev resonant state in diffusive normal-metal/triplet superconductor junctions  

NASA Astrophysics Data System (ADS)

Enhanced proximity effect by the midgap Andreev resonant state (MARS) in a diffusive normal-metal/insulator/triplet superconductor (DN/TS) junction is studied based on the Keldysh-Nambu quasiclassical Green’s-function formalism. By choosing a p -wave superconductor as a typical example of the TS, conductance of the junction and the spatial variation of the quasiparticle local density of states (LDOS) in the DN are calculated as the function of the magnitudes of the resistance Rd , Thouless energy in the DN, and the transparency of the insulating barrier. The resulting conductance spectrum has a zero-bias conductance peak (ZBCP) and the LDOS has a zero energy peak (ZEP) except for ?=?/2 (0????/2) , where ? denotes the angle between the lobe direction of the p -wave pair potential and the normal to the interface. The widths of the ZBCP and the ZEP are reduced with the increase of Rd while their heights are drastically enhanced. These peaks are revealed to be suppressed by applying a magnetic field. When the magnitude of Rd / R0 is sufficiently large, the total zero voltage resistance of the junction is almost independent of the Rd for ???/2 . The extreme case is ?=0 , where total zero voltage resistance is always R0 /2 . We also studied the charge transport in px +i py -wave junctions, where only the quasiparticles with perpendicular injection feel the MARS. Even in this case, the resulting LDOS in the DN has a ZEP. Thus the existence of the ZEP in the LDOS of the DN region is a remarkable feature for DN/TS junctions which have never been expected for the DN/singlet superconductor junctions where the MARS and proximity effect compete with each other. Based on these results, a crucial test to identify triplet pairing superconductors based on tunneling experiments is proposed.

Tanaka, Y.; Kashiwaya, S.; Yokoyama, T.

2005-03-01

178

Energy landscapes of dynamic ensembles of rolling triplet repeat bulge loops: implications for DNA expansion associated with disease states.  

PubMed

DNA repeat domains can form ensembles of canonical and noncanonical states, including stable and metastable DNA secondary structures. Such sequence-induced structural diversity creates complex conformational landscapes for DNA processing pathways, including those triplet expansion events that accompany replication, recombination, and/or repair. Here we demonstrate further levels of conformational complexity within repeat domains. Specifically, we show that bulge loop structures within an extended repeat domain can form dynamic ensembles containing a distribution of loop positions, thereby yielding families of positional loop isomers, which we designate as "rollamers". Our fluorescence, absorbance, and calorimetric data are consistent with loop migration/translocation between sites within the repeat domain ("rollamerization"). We demonstrate that such "rollameric" migration of bulge loops within repeat sequences can invade and disrupt previously formed base-paired domains via an isoenthalpic, entropy-driven process. We further demonstrate that destabilizing abasic lesions alter the loop distributions so as to favor "rollamers" with the lesion positioned at the duplex/loop junction, sites where the flexibility of the abasic "universal hinge" relaxes unfavorable interactions and/or facilitates topological accommodation. Another strategic siting of an abasic site induces directed loop migration toward denaturing domains, a phenomenon that merges destabilizing domains. In the aggregate, our data reveal that dynamic ensembles within repeat domains profoundly impact the overall energetics of such DNA constructs as well as the distribution of states by which they denature/renature. These static and dynamic influences within triplet repeat domains expand the conformational space available for selection and targeting by the DNA processing machinery. We propose that such dynamic ensembles and their associated impact on DNA properties influence pathways that lead to DNA expansion. PMID:22397401

Völker, Jens; Gindikin, Vera; Klump, Horst H; Plum, G Eric; Breslauer, Kenneth J

2012-03-23

179

Pulsed electron nuclear double resonance studies of the photoexcited triplet state of pentacene in p-terphenyl crystals at room temperature  

NASA Astrophysics Data System (ADS)

Pulsed electron nuclear double resonance (ENDOR) using a modified Davies-type [Phys. Lett. 47A, 1 (1974)] sequence is employed to study the hyperfine (HF) structure of the photoexcited triplet state of pentacene dispersed in protonated and deuterated p-terphenyl single crystals. The strong electron spin polarization and long phase memory time of triplet pentacene enable us to perform the ENDOR measurements on the S=1 spin system at room temperature. Proton HF tensor elements and spin density values of triplet pentacene are extracted from a detailed angular-dependent study in which the orientation of the magnetic field is varied systematically in two different pentacene planes. Analysis reveals that the pentacene molecule is no longer planar in the p-terphenyl host lattice. The distortion is more pronounced in the deuterated crystal where the unit cell dimensions are slightly smaller than those of the protonated crystal.

Yago, Tomoaki; Link, Gerhard; Kothe, Gerd; Lin, Tien-Sung

2007-09-01

180

Pulsed electron nuclear double resonance studies of the photoexcited triplet state of pentacene in p-terphenyl crystals at room temperature.  

PubMed

Pulsed electron nuclear double resonance (ENDOR) using a modified Davies-type [Phys. Lett. 47A, 1 (1974)] sequence is employed to study the hyperfine (HF) structure of the photoexcited triplet state of pentacene dispersed in protonated and deuterated p-terphenyl single crystals. The strong electron spin polarization and long phase memory time of triplet pentacene enable us to perform the ENDOR measurements on the S=1 spin system at room temperature. Proton HF tensor elements and spin density values of triplet pentacene are extracted from a detailed angular-dependent study in which the orientation of the magnetic field is varied systematically in two different pentacene planes. Analysis reveals that the pentacene molecule is no longer planar in the p-terphenyl host lattice. The distortion is more pronounced in the deuterated crystal where the unit cell dimensions are slightly smaller than those of the protonated crystal. PMID:17887853

Yago, Tomoaki; Link, Gerhard; Kothe, Gerd; Lin, Tien-Sung

2007-09-21

181

Excited-State Dynamics of Nitrated Push-Pull Molecules: The Importance of the Relative Energy of the Singlet and Triplet Manifolds  

NASA Astrophysics Data System (ADS)

We present a study of the dynamics following photoexcitation in the first electronic band of NO2-para-substituted nitronaphthalenes. Our main goal was to determine the interplay between the nitro group, electron-donating substituents, and the solvent in defining the relative excited-state energies and their photoinduced pathways. We studied 4-nitro-1-naphthylamine and 1-methoxy-4-nitronaphthalene in solution samples through femtosecond fluorescence up-conversion and transient absorption techniques. In all solvents, both compounds have ultrafast fluorescence decays, showing that, similarly to the parent compound 1-nitronaphthalene, these molecules have highly efficient S1 decay channels. The evolution of the transient absorption signals in the visible region reveals that for the methoxy-substituted compound, independently of solvent polarity, the photophysical pathways are the same as in 1-nitronaphthalene, namely, ultrafast intersystem crossing to an upper triplet state (receiver Tn state) followed by relaxation into the lowest energy phosphorescent triplet T1. In contrast, for the amino-substituted nitronaphthalene, the excited-state evolution shows a strong solvent dependence: In nonpolar solvents, the same type of intersystem crossing through an upper receiver triplet state dictates the photochemistry. However, in methanol, where the first singlet excited state shows an important solvent-induced stabilization, we observed typical signals of the repopulation of the electronic ground state in the time scale of less than 1 ps followed by vibrational cooling within S0. Excited-state calculations at the time-dependent density functional level with the PBE0 functional give an approximate characterization of the states involved and appear to correlate well with the experimental results as they show that the S1 state of the amino compound is stabilized with respect to upper triplet states only in the polar solvent. These findings sustain and illustrate the recent view that the intersystem crossing channel so prevalent in nitroaromatic compounds is related to an energy coincidence between the ?-?* first singlet excited state and upper triplet states with n-?* character. Our results indicate through direct observations that if the S1 state is sufficiently stabilized, other rapid decay channels like internal conversion to the ground state will minimize the transfer of population to the triplet manifold.

Collado-Fregoso, Elisa; Zugazagoitia, Jimena S.; Plaza-Medina, Eddy F.; Peon, Jorge

2009-10-01

182

Excited-state dynamics of nitrated push-pull molecules: the importance of the relative energy of the singlet and triplet manifolds.  

PubMed

We present a study of the dynamics following photoexcitation in the first electronic band of NO(2)-para-substituted nitronaphthalenes. Our main goal was to determine the interplay between the nitro group, electron-donating substituents, and the solvent in defining the relative excited-state energies and their photoinduced pathways. We studied 4-nitro-1-naphthylamine and 1-methoxy-4-nitronaphthalene in solution samples through femtosecond fluorescence up-conversion and transient absorption techniques. In all solvents, both compounds have ultrafast fluorescence decays, showing that, similarly to the parent compound 1-nitronaphthalene, these molecules have highly efficient S(1) decay channels. The evolution of the transient absorption signals in the visible region reveals that for the methoxy-substituted compound, independently of solvent polarity, the photophysical pathways are the same as in 1-nitronaphthalene, namely, ultrafast intersystem crossing to an upper triplet state (receiver T(n) state) followed by relaxation into the lowest energy phosphorescent triplet T(1). In contrast, for the amino-substituted nitronaphthalene, the excited-state evolution shows a strong solvent dependence: In nonpolar solvents, the same type of intersystem crossing through an upper receiver triplet state dictates the photochemistry. However, in methanol, where the first singlet excited state shows an important solvent-induced stabilization, we observed typical signals of the repopulation of the electronic ground state in the time scale of less than 1 ps followed by vibrational cooling within S(0). Excited-state calculations at the time-dependent density functional level with the PBE0 functional give an approximate characterization of the states involved and appear to correlate well with the experimental results as they show that the S(1) state of the amino compound is stabilized with respect to upper triplet states only in the polar solvent. These findings sustain and illustrate the recent view that the intersystem crossing channel so prevalent in nitroaromatic compounds is related to an energy coincidence between the pi-pi* first singlet excited state and upper triplet states with n-pi* character. Our results indicate through direct observations that if the S(1) state is sufficiently stabilized, other rapid decay channels like internal conversion to the ground state will minimize the transfer of population to the triplet manifold. PMID:19839627

Collado-Fregoso, Elisa; Zugazagoitia, Jimena S; Plaza-Medina, Eddy F; Peon, Jorge

2009-12-01

183

Optical Determination of the Electron Spin-Lattice Relaxation Mechanisms Between the Zero-Field Levels of the Lowest Triplet State.  

National Technical Information Service (NTIS)

Very little work has been carried out on the mechanism of the spin lattice relaxation (SLR) processes between the Zeeman levels of the lowest triplet state of molecular impurity in molecular solids. Studies in zero field (zf) on the temperature dependence...

L. H. Hall M. A. El-Sayed

1971-01-01

184

An ab initio mechanism for efficient population of triplet states in cytotoxic sulfur substituted DNA bases: the case of 6-thioguanine.  

PubMed

The deactivation mechanism of the cytotoxic 6-thioguanine, the 6-sulfur-substituted analogue of the canonical DNA base, is unveiled by ab initio calculations. Oxygen-by-sulfur substitution leads to efficient population of triplet states-the first step for generating singlet oxygen-which is responsible for its cytotoxicity. PMID:22245861

Martínez-Fernández, Lara; González, Leticia; Corral, Inés

2012-01-16

185

First-order properties for triplet excited states in the approximated coupled cluster model CC2 using an explicitly spin coupled basis  

NASA Astrophysics Data System (ADS)

An implementation is reported for first-order properties of excited triplet states within the approximate coupled cluster model CC2 using an explicitly spin coupled basis for the triplet excitation manifold and the resolution of the identity (RI) approximation for the electron repulsion integrals. Results are presented for the change of the second moment of charge upon excitation in the ??* valence and n=3 Rydberg states of benzene. Employing large basis sets with up to 828 functions, we obtain results close to the CC2 basis set limit and are able to resolve an uncertainty in the assignment of the lowest 1E1u states. It is found that the often used %T1 measure for the single excitation contribution to excited states is not reliable for a comparison across different excitation operator manifolds. An alternative diagnostic is proposed which provides a unique measure for the single excitation contribution that is independent of the chosen representation of the excitation operator manifold.

Hättig, Christof; Köhn, Andreas; Hald, Kasper

2002-04-01

186

Vibrational relaxation and the statistics of triplet states and matrix elements in methylglyoxal  

Microsoft Academic Search

Quantum beat spectroscopy is presently the only direct probe of intramolecular couplings and spacings between individual highly exicted states of polyatomic molecules with state densities of the order of 1000 states per wave number. We have applied this method to methylglyoxal in an attempt to discover if there are preferred pathways of intramolecular energy flow and if it is possible,

M. Gurnick; J. Chaiken; J. D. McDonald

1981-01-01

187

A new graphical version of STROTAB: The analysis and fitting of singlet triplet spectra of asymmetric top molecules in the prolate or oblate limits  

NASA Astrophysics Data System (ADS)

The original version of STROTAB has been modified to run under Microsoft Windows using the C++ programming language. The new version takes full advantage of the Microsoft Foundation Classes available within the Microsoft Visual C++ Version 6 development environment. Specifically, windows can be created that edit the input file, summarize the results of the least-squares fit, display the calculated and observed spectra, display whole or partial sections of the calculated spectra as a stick or Gaussian de-convoluted spectrum. A listing of the rotational quantum numbers in the cases (a) and (b) limits for each of the displayed lines is provided. A branch annotating routine provides a quick visual guide to the assignment of the spectrum. A new eigenvalue sorting method has been added as an option that complements the existing method based on the eigenvector coefficients. The new sorting method has eliminated some difficulties that may arise using the existing “Least Ambiguous Method”. The program has been extended to handle near-oblate asymmetric tops using a type IIIr representation.New version summaryTitle of program: STROTAB Version number: 2 Catalogue identifier:ADCA_v2_0 Program summary URL:http://cpc.cs.qub.ac.uk/summaries/ADCA_v2_0 Program obtainable from:CPC Program Library, Queen's University of Belfast, N. Ireland Reference in CPC to previous version: 93 (1996) 241 264 Catalog identifier of previous version: ADCA Authors of previous version: R.H. Judge, E.D. Womeldorf, R.A. Morris, D.E. Shimp, D.J. Clouthier, D.L. Joo, D.C. Moule Does the new version supersede the original program: Yes Computers for which the program is designed and others on which it has been tested: Pentium Xenon, Pentium Pro and Later Operating systems or monitors under which program has been tested: Windows 98, Windows 2000, Windows XP Programming language used in the new version: ANSI C, C++, Microsoft Foundation Class (MFC) No. of lines in distributed program, including test data, etc.:11?913 No. of bytes in distributed program, including test data, etc.: 2?816?652 Memory required to execute with typical data: 7 Meg No of bits in a word: 16 No of processors used: 1 Has the code been vectorized or parallelized?: No No. of bytes in distributed program, including test data, etc.: ˜3.2 MB (compressed) Distribution format: zip file Additional keywords:near oblate top, bootstrap eigenvalue sorting, graphical environment, band contour Nature of physical problem: The least-squares/band contour fitting of the singlet triplet spectra of asymmetric tops of orthorhombic symmetry using a basis set appropriate to the symmetric top limit (prolate or oblate) of the molecule in either Hund's case (a) or case (b) coupling situations. Method of solution: The calculation of the eigenvectors and eigenvalues remains unchanged from the earlier version. An option to sort the eigenvalues of the current J by fitting them to regular progressions formed from earlier J values (bootstrap method) can be used as an option in place of the existing method based on eigenvector coefficients. Reasons for the new version: The earlier version can only handle oblate tops by diagonalizing using the prolate limit. This has turned out to be unacceptable. An improved method of sorting eigenvalues under certain conditions is also needed. A graphical interface has been added to ease the use of the program. Summary of revisions: The Hamiltonian can now be constructed in a limit appropriate the representation for of the molecule. Sorting by an alternate method is now offered. Numerous graphical features have been added. Restrictions on complexity of the problem: The rotational quantum number restrictions are J?255 and K (or P) ?127. The allowed transition frequency minus the band origin frequency must be in the range of ±10?000 cm-1. Up to five decimal places may be reported. The number of observed lines is limited by the dynamic memory and the amount of disk space available. Only molecules of symmetry D2h, D2 and C2v can be accommodated in this version. Only constants of

Kodet, John; Judge, Richard H.

2007-05-01

188

Laser-induced fluorescence of rhodamine 6G cations in the gas phase: a lower bound to the lifetime of the first triplet state.  

PubMed

We have studied the gas-phase laser-induced fluorescence of an ensemble of buffer gas-cooled Rhodamine 6G cations (R6G(+)) stored in a quadrupole ion trap at 90 K. The fluorescence resulting from excitation with continuous-wave 488 nm radiation was observed to disappear almost completely on a time scale of seconds, dependent in detail on the excitation laser fluence. Such decay can be explained by the accumulation of R6G(+) in a dark triplet state. This in turn facilitates the first lifetime determination of the lowest triplet state of free R6G(+) by direct ground-state recovery measurements. A lower bound for the half-life was found to be approximately 2 s. Adding oxygen in a volume fraction of 1% to the buffer gas leads to efficient quenching of the triplet state and correspondingly to complete suppression of the fluorescence intensity decay. Different rare gases were applied as buffers for collisional cooling, but no significant changes in the fluorescence properties were found. PMID:20392060

Kordel, Mattias; Schooss, Detlef; Neiss, Christian; Walter, Lars; Kappes, Manfred M

2010-05-01

189

Dependence of the triplet state properties on the orientation of metal ion perturbers in naphthalene-crown ether metal ion complexes. I. External heavy atom effect  

Microsoft Academic Search

The lowest excited triplet state and the sublevel dynamics have been studied in 1, 5-naphtho-22-crown-6 (I), 1,8-naphtho-21-crown-6 (II), and 2, 3-naphtho-20-crown-6 (III) and their complexes with various metal ions (Na+, K+,Cs+, Tl+) using optical detection of magnetic resonance at 1.2 K in zero applied magnetic field. The results indicate that the orientation of the heavy ion perturber with respect to

Sanjib Ghosh; Michael Petrin; August H. Maki; Lynn R. Sousa

1987-01-01

190

Water-soluble polystyrene latexes as photoredox media. 1. Interfacial fluorescence quenching and triplet-state electron transfer from pyrene and 1-pyrenebutyric acid  

Microsoft Academic Search

Aromatic chromophores (pyrene and 1-pyrenebutyric acid) have been adsorbed on water-soluble polystyrene latex particles (commercially referred to as microspheres) from the aqueous phase. The fluorescence properties and quenching efficiencies of these chromophores have been measured using a zwitterionic viologen SPV (4,4[prime]-bipyridino-l,l[prime]-bis(propanesulfonate)). The quenching mechanism has been found to be diffusion controlled. The electron-transfer quenching of the triplet state by SPV

Jiunn Shyong Hsiao; S. E. Webber

1993-01-01

191

Series of singlet and triplet S-wave doubly-excited states of B3+ below the N=2 threshold of B4+  

NASA Astrophysics Data System (ADS)

We determined the doubly-excited-state resonances of both the singlet and triplet S-wave series of B3+ at energy below the N=2 threshold of B4+ using an accurate Harris-Nesbet variational calculation of electron-B4+ scattering. The widths of many of these resonances were obtained for the first time by us. Graphical presentation of these resonances were also given.

Gien, T. T.

2012-11-01

192

Study of triplet state of the primary electron donor on preparations of reaction centers of photosynthetic bacteria using magnetooptical absorbance difference spectroscopy  

SciTech Connect

The authors use magneto-optical absorbance difference spectroscopy based on fluorescence determination to investigate the photosynthetic membrane reaction centers of two photosynthetic bacteria, the blue-green mutant of Rps. sphaeroides R-26 and the cytoplasmatic membrane from C. aurantiacus, and their primary electron donors. The mechanism of triplet state excitation under the action of continuous irradiation and a modulating magnetic field is described in detail. Data are also given on hyperfine structure determined by computer processing of the spectral image.

Elfimov, E.I.; Voznyak, V.M.; Shkuropatov, A.Ya.; Shuvalov, V.A.

1987-11-01

193

Hot band transitions to the triplet state in anthracene and pyrene crystals  

Microsoft Academic Search

The low energy end of the S0?T1 absorption spectrum has been measured in anthracene and pyrene crystals from 220 to 330°K. A transition is found in both of these systems at an energy approximately 400 cm?1 below the 0–0 energy. The temperature dependence of this absorption reveals it to be excitation of a hot vibrational level of the ground state.

W. B. Whitten; S. Arnold; C. E. Swenberg

1974-01-01

194

Hot band transitions to the triplet state in anthracene and pyrene crystals  

Microsoft Academic Search

The low energy end of the S0-->T1 absorption spectrum has been measured in anthracene and pyrene crystals from 220 to 330°K. A transition is found in both of these systems at an energy approximately 400 cm-1 below the 0-0 energy. The temperature dependence of this absorption reveals it to be excitation of a hot vibrational level of the ground state.

W. B. Whitten; S. Arnold; C. E. Swenberg

1974-01-01

195

Phonon coupling in optical transitions for singlet-triplet pairs of bound excitons in semiconductors  

NASA Astrophysics Data System (ADS)

A model is presented for the observed strong difference in selection rules for coupling of phonons in the one-phonon sideband of optical spectra related to bound excitons in semiconductors. The present treatment is specialized to the case of a closely spaced pair of singlet-triplet character as the lowest electronic states, as is common for bound excitons associated with neutral complexes in materials like GaP and Si. The optical transition for the singlet bound-exciton state is found to couple strongly only to symmetric A1 modes. The triplet state has a similar coupling strength to A1 modes, but in addition strong contributions are found for replicas corresponding to high-density-of-states phonons TAX, LAX, and TOX. This can be explained by a treatment of particle-phonon coupling beyond the ordinary adiabatic approximation. A weak mixing between the singlet and triplet states is mediated by the phonon coupling, as described in first-order perturbation theory. The model derived in this work, for such phonon-induced mixing of closely spaced electronic states, is shown to explain the observed phonon coupling for several bound-exciton systems of singlet-triplet character in GaP. In addition, the observed oscillator strength of the forbidden triplet state may be explained as partly derived from phonon-induced mixing with the singlet state, which has a much larger oscillator strength.

Pistol, M. E.; Monemar, B.

1986-05-01

196

Hyperfine-structure splitting in the triplet states of carbon muonic ions  

SciTech Connect

Hyperfine-structure splittings in the 2{sup 3}S(L=0) state of the six-body carbon muonic {sup 11}C{sup 6+}mu{sup -}e{sub 4}{sup -}, {sup 12}C{sup 6+}mu{sup -}e{sub 4}{sup -}, {sup 13}C{sup 6+}mu{sup -}e{sub 4}{sup -}, and {sup 14}C{sup 6+}mu{sup -}e{sub 4}{sup -} ions are determined numerically with the use of variational wave functions. The variational wave functions for each of these carbon muonic ions are constructed with the use of six-body Gaussoids which explicitly depend upon all 15 relative coordinates r{sub 12},r{sub 13},...,r{sub 56} defined in an arbitrary six-body system.

Frolov, Alexei M.; Wardlaw, David M. [Department of Chemistry, University of Western Ontario, London, Ontario, N6A 5B7 (Canada)

2009-12-15

197

Long-lived charge-separated species observed on flash photolysis of peptide conjugates. Interplay of local and radical ion pair triplet states  

SciTech Connect

Peptides composed of alanine (Ala) and tryptophan (Trp), modified with the (nitro)pyrenesulfonyl chromophore (Pyr and NPyr) at the N-terminus have been examined by nanosecond laser flash photolysis. A common phototransient for Pyr-AlaOEt and Pyr-Ala-TrpOEt was observed that exhibited broad absorption at 410--550 nm and decay time constants in the range {tau}{sub 1/2} = 20--40 {micro}s. This species was assigned to the triplet excited state that is local to the pyrene chromophore ({sup 3}Pyr). For the conjugates having a stronger electron acceptor group at the N-terminus, NPyr-Ala-TrpOEt and NPyr-Ala-Ala-TrpOEt, the local triplet was replaced with a phototransient whose principal feature is a sharp band at 440 nm. The radical ion transients for the NPyr peptide derivatives were assigned to intermediates that result from the intramolecular electron transfer quenching of NP excited species by pendant groups. The lifetimes observed for the radical ion transients associated with the NPyr series were relatively long and depended in an interesting way on the structure of the peptide linkage. A mechanism of electron transfer in the singlet manifold and recombination yielding a local Pyr triplet state is important for the Pyr series.

Jones, G. II; Lu, L.N. [Boston Univ., MA (United States)

1998-11-27

198

Photofragmentations, state interactions, and energetics of Rydberg and ion-pair states: Two-dimensional resonance enhanced multiphoton ionization of HBr via singlet-, triplet-, ? = 0 and 2 states  

NASA Astrophysics Data System (ADS)

Mass spectra were recorded for one-colour resonance enhanced multiphoton ionization (REMPI) of HiBr (i = 79, 81) for the two-photon resonance excitation region 79 040-80 300 cm-1 to obtain two-dimensional REMPI data. The data were analysed in terms of rotational line positions, intensities, and line-widths. Quantitative analysis of the data relevant to near-resonance interactions between the F1?2(v' = 1) and V1?+(v' = m + 7) states gives interaction strengths, fractional state mixing, and parameters relevant to dissociation of the F state. Qualitative analysis further reveals the nature of state interactions between ion-pair states and the E1?+ (v' = 1) and H1?+(v' = 0) Rydberg states in terms of relative strengths and J' dependences. Large variety in line-widths, depending on electronic states and J' quantum numbers, is indicative of number of different predissociation channels. The relationship between line-widths, line-shifts, and signal intensities reveals dissociation mechanisms involving ion-pair to Rydberg state interactions prior to direct or indirect predissociations of Rydberg states. Quantum interference effects are found to be important. Moreover, observed bromine atom (2 + 1) REMPI signals support the importance of Rydberg state predissociation channels. A band system, not previously observed in REMPI, was observed and assigned to the k3?0(v' = 0) <--<-- X transition with band origin 80 038 cm-1 and rotational parameter Bv'=7.238 cm-1.

Long, Jingming; HróÐmarsson, Helgi Rafn; Wang, Huasheng; Kvaran, Ágúst

2012-06-01

199

Synthesis and solid state absorption spectra of some aminonaphthoquinone dyes  

Microsoft Academic Search

The 2,6- and 4,8-bisarylamino-1,5-naphthoquinone derivatives 3b-d and 6a-e were synthesized by the amination of naphthazarin (1) and naphthazarin intermediate (4), respectively. Their chromophoric systems were evaluated by the PPP MO method, and their absorption spectra in solution and the solid state were investigated to evaluate the intermolecular ?-? interactions of the dye molecules in the solid state. In the case

Jae Hong Kim; Masaru Matsuoka; Koushi Fukunishi

1996-01-01

200

Determination of the individual spin-lattice relaxation rates between the spin levels of phosphorescent triplet-state molecules  

NASA Astrophysics Data System (ADS)

It is shown how one can determine the individual spir-lattice relaxation rates of a phosphorescent triplet-stale molecule from analysis of the recovery curve in the phosphorescence intensity upon a microwave sweep through one of the zero-field transitions.

Van Noort, H. M.; Wirnitzer, B.; Schmidt, J.

1982-01-01

201

Electronic excited states and electronic spectra of biphenyl: a study using many-body wavefunction methods and density functional theories.  

PubMed

The low-lying electronic excited states of biphenyl were studied using the symmetry-adapted cluster-configuration interaction (SAC-CI), complete active space self-consistent field (CASSCF), complete active space perturbation theory of the second-order (CASPT2), and the time-dependent density functional theory (TDDFT). The molecular geometries in the ground and excited states were optimized using the SAC-CI and TDDFT for singlet and triplet states. The energies of vertical excitations, emissions, and adiabatic transitions were calculated. The TDDFT calculations significantly underestimated the excitation energy of the 1(1)B1 state, while the SAC-CI and CASPT2 provided essentially similar results. The present SAC-CI and CASPT2 calculations concluded that the lowest singlet state of isolated biphenyl is the 1(1)B3 state that takes a planar geometry and the second lowest state is the 1(1)B2 state with a twisted geometry. The present results were consistent with the previous experimental findings. The 1(1)B1 state that has a charge-separated biracial character in the vertical excitation relaxed into a planar quinoid structure in which bond alternations were emphasized. The other states took a benzenoid structure. The ultraviolet (UV) absorption and circular dichroism (CD) spectra below 7 eV were calculated with the SAC-CI method. The valence-Rydberg mixings were found to be significant in the second and higher series of excited states. PMID:24022338

Fukuda, Ryoichi; Ehara, Masahiro

2013-09-25

202

Photoprocesses in diphenylpolyenes. Oxygen and heavy-atom enhancement of triplet yeilds  

SciTech Connect

Results, obtained by nanosecond laser flash photolysis (337.1 nm) and fluorescence measurements, are presented concerning triplet-triplet spectra and excited-state dynamics of three all-trans ..cap alpha..,..omega..-diphenyl-substituted polyenes, Ph(CH=CH)/sub n/Ph (n = 2-4), in various solvents and in the presence of oxygen and heavy-atom-containing molecules. The spectra of triplets generated by both direct excitation and energy transfer, display the characteristics of an intense Franck-Condon allowed transition with vibrational spacings in the range 1200-1600 cm/sup -1/ and show solvent-effect and chain-length dependence very similar to those observed for the strongly allowed band system in ground-state absorption. The quantum yields of occupation of lowest triplet are small (0.5-3%) in deaerated solvents such as cyclohexane, methanol, and benzene, but become significantly enhanced in heavy-atom-containing solvents (e.g., ethyl bromide and bromobenzene) and in the presence of oxygen and heavy-atom species. The intersystem crossing rate constants for T/sub 1/reverse arrowS/sub 1/ and S/sub 0/reverse arrowT/sub 1/ are in the ranges 7 x 10/sup 5/ - 9 x 10/sup 7/ and 2 x 10/sup 4/ - 7 x 10/sup 5/ s/sup -1/, respectively, and exhibit a decreasing trend as the polyene chain length is increased. Based on kinetic data concerning singlet quenching and triplet yield enhancement by O/sub 2/ and ethyl iodide in methanol and cyclohexane, the fraction of the singlet quenching events that result in triplet generation is found to range from 0.1 to 0.8. The correlation (or lack of it) between intersystem crossing rate constants and those for bimolecular quenching of singlet and triplet is discussed in the context of the energy gap law observed in similar studies for aromatic hydrocarbons.

Chattopadhyay, S.K. (Univ. of Notre Dame, IN); Das, P.K.; Hug, G.L.

1982-08-25

203

Zero-field electron spin resonance and theoretical studies of light penetration into single crystal and polycrystalline material doped with molecules photoexcitable to the triplet state via intersystem crossing  

Microsoft Academic Search

A theory is presented to calculate the penetration depth of light in single crystal or polycrystalline material doped with the molecule whose electronic state can be excited by photoabsorption from the ground state to the excited singlet state, and transferred by intersystem crossing into the triplet state. An experimental study on the penetration depth is also reported, which is made

Kazuyuki Takeda; K. Takegoshi; Takehiko Terao

2002-01-01

204

Improvement of photovoltaic response based on enhancement of spinorbital coupling and triplet states in organic solar cells  

SciTech Connect

This article reports an improvement of photovoltaic response by dispersing phosphorescent Irppy3 molecules in an organic solar cell of poly2-methoxy-5-2-ethylhexyloxy-1 4-phenylenevinylene MEH-PPV blended with surface-functionalized fullerene 1-3-methyloxycarbonylpropy1-phenyl 6,6 C61 PCBM. The magnetic field dependent photocurrent indicates that the dispersed Irppy3 molecules increase the spin-orbital coupling strength with the consequence of changing the singlet and triplet ratios through intersystem crossing due to the penetration of the delocalized electrons of MEH-PPV into the large orbital magnetic field of Irppy3 dopants. The tuning of singlet and triplet exciton ratios can lead to an enhancement of photovoltaic response due to their different contributions to the two different photocurrent generation channels: exciton dissociation and exciton-charge reaction in organic materials. In addition, the photoluminescence temperature dependence reveals that the dispersed Irppy3 reduces the recombination of dissociated charge carriers in the PCBM doped MEH-PPV. As a result, adjusting singlet and triplet ratios by introducing heavy-metal complex Irppy3 provides a mechanism to improve the photovoltaic response through controlling exciton dissociation, exciton-charge reaction, and recombination of dissociated charge carriers in organic bulk-heterojunction solar cells.

Xu, Zhihua [University of Tennessee, Knoxville (UTK); Hu, Bin [University of Tennessee, Knoxville (UTK); Howe, Jane Y [ORNL

2008-01-01

205

First-principles Calculation of Excited State Spectra in QCD  

SciTech Connect

Recent progress at understanding the excited state spectra of mesons and baryons is described. I begin by outlining the application of the variational method to compute the spectrum of QCD, and then present results for the excited meson spectrum, with continuum quantum numbers of the states clearly delineated. I emphasise the need to extend the calculation to encompass multi-hadron contributions, and describe a recent calculation of the I = 2{pi}{pi} energy-dependent phase shifts as a precursor to the study of channels with resonant behavior. I conclude with recent results for the low lying baryon spectrum, and the prospects for future calculations.

Dudek, Jozef J. [Jefferson Laboratory, 12000 Jefferson Avenue Suite 1, Newport News, VA 23606 (United States); Department of Physics, Old Dominion University, Norfolk, VA 23529 (United States); Edwards, Robert G.; Richards, David G.; Thomas, Christopher E. [Jefferson Laboratory, 12000 Jefferson Avenue Suite 1, Newport News, VA 23606 (United States); Peardon, Michael J. [School of Mathematics, Trinity College, Dublin 2 (Ireland)

2011-05-24

206

Total and Radiative Triplet-Triplet Exciton-Annihilation Rate Constant in Pyrene Crystals  

Microsoft Academic Search

The total and the radiative rate constants for triplet-triplet exciton annihilation have been determined in pyrene single crystals. The values are gammatot=(7.5+\\/-4.0)×10-12 cm3 sec-1 and gammarad=(2.0+\\/-1)×10-12 cm3 sec-1, respectively. The fraction of triplet fusions leading to singlets is 0.19 × 0.02. A simple procedure is presented which allows the determination of the product alphagammatot where alpha is the ground-state-singlet-first-excited-triplet absorption

V. Ern; H. Bouchriha; M. Bisceglia; S. Arnold; M. Schott

1973-01-01

207

Hund's rule and singlet-triplet energy differences for the lowest n pi-asterisk states of formaldehyde, H2CO  

NASA Astrophysics Data System (ADS)

Multireference single and double substitution configuration interaction calculations have been carried out for the 1 Alpha double prime and 3 Alpha double prime arising from the lowest n to pi-asterisk excitation of formaldehyde. In order to provide a fundamental basis for the interpretation of Hund's rule in a polyatomic molecule, vertical and adiabatic differences of the total energy and its components have been computed from the wave functions. For a vertical comparison of the two states near their equilibrium geometries, it is shown that electron-electron repulsion is less in the triplet state than in the singlet state, in contrast with the corresponding results for the 1B1 and 3B1 states of methylene.

Darvesh, Katherine Valenta; Boyd, Russell J.

1989-05-01

208

Infrared absorption spectra of various doping states in cuprate superconductors  

SciTech Connect

Doping states in a two-dimensional three-band extended Peierls-Hubbard model was investigated within inhomogeneous Hartree-Fock and random phase approximation. They are very sensitive to small changes of interaction parameters and their distinct vibrational and optical absorption spectra can be used to identify different doping states. For electronic parameters relevant to cuprate superconductors, as intersite electron-phonon interaction strength increases, the doping state changes from a Zhang-Rice state to a covalent molecular singlet state accompanied by local quenching of the Cu magnetic moment and large local lattice distortion in an otherwise undistorted antiferromagnetic background. In a region where both intersite electron-phonon interaction and on-site electron-electron repulsion are large, we obtain new stable global phases including a bond-order-wave state and a mixed state of spin-Peierls bonds and antiferromagnetic Cu spins, as well as many metastable states. Doping in the bond-order-wave region induces separation of spin and charge. 9 refs.

Yonemitsu, K.; Bishop, A.R. (Los Alamos National Lab., NM (United States)); Lorenzana, J. (International School of Advanced Studies, Trieste (Italy))

1992-01-01

209

Infrared absorption spectra of various doping states in cuprate superconductors  

SciTech Connect

Doping states in a two-dimensional three-band extended Peierls-Hubbard model was investigated within inhomogeneous Hartree-Fock and random phase approximation. They are very sensitive to small changes of interaction parameters and their distinct vibrational and optical absorption spectra can be used to identify different doping states. For electronic parameters relevant to cuprate superconductors, as intersite electron-phonon interaction strength increases, the doping state changes from a Zhang-Rice state to a covalent molecular singlet state accompanied by local quenching of the Cu magnetic moment and large local lattice distortion in an otherwise undistorted antiferromagnetic background. In a region where both intersite electron-phonon interaction and on-site electron-electron repulsion are large, we obtain new stable global phases including a bond-order-wave state and a mixed state of spin-Peierls bonds and antiferromagnetic Cu spins, as well as many metastable states. Doping in the bond-order-wave region induces separation of spin and charge. 9 refs.

Yonemitsu, K.; Bishop, A.R. [Los Alamos National Lab., NM (United States); Lorenzana, J. [International School of Advanced Studies, Trieste (Italy)

1992-02-01

210

Crossing behavior of the singlet and triplet State of the negatively charged magneto-exciton in a GaAs/AlGaAs quantum well  

SciTech Connect

Polarized magneto-photoluminescence (MPL) measurements on a high mobility {delta}-doped GaAs/AlGaAs single quantum well from 0--60 T at temperatures between 0.37--2.1 K are reported. In addition to the neutral heavy hole magneto-exciton (X{sup 0}), the singlet (X {sub s}{sup {minus}}) and triplet (X {sub t}{sup {minus}}) states of the negatively charged magneto-exciton are observed in both polarizations. The energy dispersive and time-resolved MPL data suggest that their development is fundamentally related to the formation of the neutral magneto-exciton. At a magnetic field of 40 T the singlet and the triplet states cross as a result of the role played by the higher Landau levels and higher energy subbands in their energetic evolution, confirming theoretical predictions. The authors also observed the formation of two higher energy peaks. One of them is completely right circularly polarized and its appearance can be considered a result of the electron-hole exchange interaction enhancement with an associated electron g-factor of 3.7 times the bulk value. The other peak completely dominates the MPL spectrum at fields around 30 T. Its behavior with magnetic field and temperature indicates that it may be related to previous anomalies observed in the integer and fractional quantum Hall regimes.

MUNTEANU,F.M.; KIM,YONGMIN; PERRY,C.H.; RICKEL,D.G.; SIMMONS,JERRY A.; RENO,JOHN L.

2000-01-27

211

Abrupt enhancement of noncentrosymmetry and appearance of a spin-triplet superconducting state in Li2(Pd1-xPtx)3B beyond x=0.8  

NASA Astrophysics Data System (ADS)

We report synthesis, 195Pt, 11B, and 7Li NMR measurements, and first-principles band calculations for noncentrosymmetric superconductors Li2(Pd1-xPtx)3B (x=0, 0.2, 0.5, 0.8, 0.84, 0.9, and 1). For 0?x?0.8, the spin-lattice relaxation rate 1/T1 shows a clear coherence peak just below Tc, decreasing exponentially at low temperature, and the Knight shift 195K decreases below Tc. For x=0.9 and 1.0, in contrast, 1/T1 shows no coherence peak but a T3 variation and 195K remains unchanged across Tc. These results indicate that the superconducting state changes drastically from a spin-singlet dominant to a spin-triplet dominant state at x=0.8. We find that the distortion of B(Pt,Pd)6 increases abruptly above x=0.8, which leads to an abrupt enhancement of the asymmetric spin-orbit coupling as confirmed by band calculation. Such structure distortion that enhances the extent of inversion-symmetry breaking is primarily responsible for the pairing symmetry evolution. The insight obtained here provides a guideline for searching for noncentrosymmetric superconductors with a large spin-triplet component.

Harada, S.; Zhou, J. J.; Yao, Y. G.; Inada, Y.; Zheng, Guo-qing

2012-12-01

212

Quasiclassical asymptotics and coherent states for bounded discrete spectra  

SciTech Connect

We consider discrete spectra of bound states for nonrelativistic motion in attractive potentials V{sub {sigma}}(x)=-|V{sub 0}| |x|{sup -}{sigma}, 0<{sigma}{<=}2. For these potentials the quasiclassical approximation for n{yields}{infinity} predicts quantized energy levels e{sub {sigma}}(n) of a bounded spectrum varying as e{sub {sigma}}(n){approx}-n{sup -}2{sigma}/(2-{sigma}). We construct collective quantum states using the set of wavefunctions of the discrete spectrum assuming this asymptotic behavior. We give examples of states that are normalizable and satisfy the resolution of unity, using explicit positive functions. These are coherent states in the sense of Klauder and their completeness is achieved via exact solutions of Hausdorff moment problems, obtained by combining Laplace and Mellin transform methods. For {sigma} in the range 0 < {sigma}{<=} 2/3 we present exact implementations of such states for the parametrization {sigma}= 2(k-l)/(3k-l) with k and l positive integers satisfying k>l.

Gorska, K. [Nicolaus Copernicus University, Institute of Physics, ul. Grudziadzka 5/7, PL 87-100 Torun (Poland); Laboratoire de Physique Theorique de la Matiere Condensee, Universite Pierre et Marie Curie, CNRS UMR 7600, Tour 13 - 5ieme et., B.C. 121, 4 pl. Jussieu, F 75252 Paris Cedex 05 (France); Penson, K. A. [Laboratoire de Physique Theorique de la Matiere Condensee, Universite Pierre et Marie Curie, CNRS UMR 7600, Tour 13 - 5ieme et., B.C. 121, 4 pl. Jussieu, F 75252 Paris Cedex 05 (France); Horzela, A.; Blasiak, P. [H. Niewodniczanski Institute of Nuclear Physics, Polish Academy of Sciences, ul. Eliasza-Radzikowskiego 152, PL 31342 Krakow (Poland); Duchamp, G. H. E. [Universite Paris XIII, LIPN, Institut Galilee, CNRS UMR 7030, 99 Av. J.-B. Clement, F 93430 Villetaneuse (France); Solomon, A. I. [Laboratoire de Physique Theorique de la Matiere Condensee, Universite Pierre et Marie Curie, CNRS UMR 7600, Tour 13 - 5ieme et., B.C. 121, 4 pl. Jussieu, F 75252 Paris Cedex 05 (France); Physics and Astronomy Department, The Open University, Milton Keynes MK7 6AA (United Kingdom)

2010-12-15

213

Intramolecular energy transfer between the triplet of ancillary ligand and the metal to ligand charge transfer state existed in heterocyclometalated iridium (III) complexes  

NASA Astrophysics Data System (ADS)

Higher efficiency red organic light emitting devices (OLEDs) were obtained by employing Ir (III) complexes with 1-phenylbutane-1, 3-dione (ba) as the second ligand than that with acetylacetone (acac) as the second ligand, which were attributed to the intramolecular energy transfer existed in these complexes. The reason were attributed to the intramolecular energy transfer existed in these complexes and were approved by their photoluminescence characteristics at 77 K, as well the phosphorescence decay lifetime. Because of the lower triplet energy level of ba (Tba,19 230 cm-1) whose energy was suitable to transfer to the triplet of the metal to ligand charge transfer (MLCT) (3MLCT,16 260 cm-1) state compared to Tacac (25 500 cm-1), more efficient OLEDs were obtained (7.0 cd/A) using Ir[2-(4'-methanoxy-styryl)-benzothiazole]2ba (ba-2) than Ir[2-(4'-methanoxy-styryl)-benzothiazole]2acac acac-2 (6.1 cd/A).

Han, Liangliang; Yang, Dongfang; Li, Wenlian; Chu, Bei; Chen, Yiren; Su, Zisheng; Zhang, Dongyu; Yan, Fei; Wu, Shuanghong; Wang, Junbo; Hu, Zhizhi; Zhang, Zhiqiang

2009-04-01

214

Phenol transformation and dimerisation, photosensitised by the triplet state of 1-nitronaphthalene: A possible pathway to humic-like substances (HULIS) in atmospheric waters  

NASA Astrophysics Data System (ADS)

The nitroderivatives of polycyclic aromatic hydrocarbons are potentially important photosensitisers in the atmospheric condensed phase. Here we show that the triplet state of 1-nitronaphthalene (31NN*) is able to directly react with phenol, causing its transformation upon irradiation of 1NN in aqueous solution. Additional but less important processes of phenol degradation are reactions with OH and 1O2, both photogenerated by irradiated 1NN. Dihydroxybiphenyls and phenoxyphenols were detected as main phenol transformation intermediates, likely formed by dimerisation of phenoxy radicals that would be produced upon phenol oxidation by 31NN*. Very interestingly, irradiation with 1NN shifted the fluorescence peaks of phenol (Ex/Em = 220-230/280-320 nm and 250-275/280-320 nm, with Ex/Em = excitation and emission wavelengths) to a region that overlaps with "M-like" fulvic substances (Ex/Em = 250-300/330-400 nm). Moreover, at longer irradiation times a further peak appeared (Ex/Em = 300-450/400-450 nm), which is in the region of HULIS fluorescence. Irradiated material was also able to photoproduce 1O2, thus showing photosensitisation properties. Therefore, compounds with fluorescence properties that closely resemble those of HULIS (they would be identified as HULIS by fluorescence if present in environmental samples) can be formed upon triplet-sensitised transformation of phenol by 1NN.

De Laurentiis, Elisa; Sur, Babita; Pazzi, Marco; Maurino, Valter; Minero, Claudio; Mailhot, Gilles; Brigante, Marcello; Vione, Davide

2013-05-01

215

Quenching of triplet states of organic compounds by copper(II) and nickel(II) 1,3-diketonates in acetonitrile solution. Energy and/or electron transfer  

SciTech Connect

Rate constants for quenching of the triplet states of 15 organic compounds by copper(II) bis(2,4-pentanedionate), Cu(acac)[sub 2], copper(II) bis(1,1,1,5,5,5-hexafluoro-2,4-pentanedionate), Cu(hfac)[sub 2], Ni(II) bis(2,4-pentanedionate), Ni(acac)[sub 2], and Ni(II) bis(1,1,1,5,5,5-hexafluoro-2,4-pentanedionate), Ni(hfac)[sub 2], in acetonitrile solution have been measured using the nanosecond laser flash photolysis technique. The quenching data were interpreted in terms of energy or electron transfer alone or in terms of both as competitive processes. With a classical framework for energy and electron transfer, the correlations of the quenching rate constants with the standard free energy changes for energy and electron transfer were used to evaluate appropriate intrinsic barriers and transmission coefficients for both processes. In acetonitrile, quenching by Cu(acac)[sub 2] was suggested to occur mainly by electron transfer, whereas quenching by Cu(hfac)[sub 2] was shown to involve energy transfer to the ligand-localized triplet in combination with electron transfer. 58 refs., 4 figs., 5 tabs.

Hug, G.L. (Univ. of Notre Dame, IN (United States)); Marciniak, B. (Univ. of Notre Dame, IN (United States) A. Mickiewicz Univ., Poznan (Poland))

1994-08-04

216

The Predicted Spectrum and Singlet-Triplet Interaction of the Hypermetallic Molecule SrOSr  

NASA Astrophysics Data System (ADS)

In accordance with previous studies in our group on Be, Mg, and Ca hypermetallic oxides, we find that SrOSr has a linear X-1?g+ ground electronic state and a very low lying first excited -3?u+ triplet electronic state. No gas-phase spectrum of this molecule has been assigned yet, and to encourage and assist in its discovery we present a complete ab initio simulation, with absolute intensities, of the infrared absorption spectrum for both electronic states. The three-dimensional potential energy surfaces and the electric dipole moment surfaces of the X-1?g+ and -3?u+ electronic states are calculated using a multireference configuration interaction (MRCISD) approach in combination with internally contracted multireference perturbation theory (RS2C) based on complete active space self-consistent field (CASSCF) wave functions applying a Sadlej pVTZ basis set for both O and Sr and the Stuttgart relativistic small-core effective core potential for Sr. The infrared spectra are simulated using the MORBID program system. We also calculate vertical excitation energies and transition moments for several excited singlet and triplet electronic states in order to predict the positions and intensities of the most prominent singlet and triplet electronic absorption bands. Finally, for this heavy molecule, we calculate the singlet-triplet interaction matrix elements between close-lying vibronic levels of the X- and - electronic states and find them to be very small.

Ostoji?, B.; Jensen, Per; Schwerdtfeger, P.; Bunker, P. R.

2013-10-01

217

The importance of a hot-sequential mechanism in triplet-state formation by charge recombination in reaction centers of bacterial photosynthesis  

NASA Astrophysics Data System (ADS)

In photosynthesis, pigment-excitation energies in the antenna system produced by light harvesting are transferred among antenna pigments toward the core antenna, where they are captured by the reaction center and initially fixed in the form of a charge separation. Primary charge separation between an oxidized special pair (P+) and a reduced bacteriopheohytin (H-) is occasionally intervened by recombination, and a spin-triplet state (3P*) is formed on P in the bacterial reaction center. The 3P* state is harmful to bio-organisms, inducing the formation of the highly damaging singlet oxygen species. Therefore, understanding the 3P*-formation mechanism is important. The 3P* formation is mediated by a state |m> of intermediate charge separation between P and the accessory chlorophyll, which is located between P and H. It will be shown theoretically in the present work that at room temperature, not only the mechanism of superexchange by quantum-mechanical virtual mediation at |m>, but also a hot-sequential mechanism contributes to the mediation. In the latter, although |m> is produced as a real state, the final state 3P* is quickly formed during thermalization of phonons in the protein matrix in |m>. In the former, the final state is formed more quickly before dephasing-thermalization of phonons in |m>. 3P* is unistep formed from the charge-separated state in the both mechanisms.

Saito, K.; Mukai, K.; Sumi, H.

2006-07-01

218

Singlet--Triplet Excitations and High-Field Magnetization in CuTe2O5  

NASA Astrophysics Data System (ADS)

By measuring the THz electron spin resonance (ESR) transmission spectra and high-field magnetization on the spin-gapped system CuTe2O5, we identified the singlet--triplet excitations in the dimerized non-magnetic ground state. The determined spin-gap value of h?0=4.94 meV at the ? point (Q?0) is significantly smaller than the strongest antiferromagnetic exchange interaction between the Cu ions predicted by theoretical investigations. We also observed the critical field Hc1a^{*}=37.6 T for H\\perpbc-plane and Hc1bc=40.6 T for H\\parallelbc-plane at the onset of non-zero magnetization, consistent with the gap value and corresponding anisotropic g-factors determined previously. The observed singlet--triplet excitations in Faraday and Voigt configurations suggest a mixing of the singlet state with the Sz=0 triplet state and the Sz=± 1 triplet states, respectively, due to the Dzyaloshinskii--Moriya (DM) interaction with a DM vector perpendicular to the crystalline bc-plane.

Wang, Zhe; Schmidt, Michael; Goncharov, Yurii; Skourski, Yurii; Wosnitza, Joachim; Berger, Helmuth; Nidda, Hans-Abrecht Krug von; Loidl, Alois; Deisenhofer, Joachim

2011-12-01

219

Excited state absorption spectra and intersystem crossing kinetics in diazanaphthalenes  

NASA Astrophysics Data System (ADS)

Picosecond time-resolved, excited state absorption spectra in the visible following excitation at 355 nm are discussed for room temperature solutions of four diazanaphthalenes (DN)-quinoxaline (1,4-DN), quinazoline (1,3-DN), cinnoline (1,2-DN), and phthalazine (2,3-DN). Kinetics of singlet state decay are obtained by monitoring the decay of Sn<--S1 bands. The intersystem crossing rate constant (kisc) is found to vary as kisc(1,4-DN)>~kisc(1,3-DN)>~kisc(1,2-DN). The kisc in phthalazine could not be determined from the weak, visible Sn<--S1 absorption. Assuming rapid singlet vibrational relaxation and only minor effects due to energy gap variations, these experimental results agree with statistical limit predictions for the relative nonradiative rate. Calculations of the spin-orbit coupling matrix element ?el= , using INDO wave functions, give the ordering ?el(1,4-DN)>~?el(2,3-DN)>~?el(1,3-@qL DN) >~?el(1,2-DN).

Scott, Gary W.; Talley, Larry D.; Anderson, Robert W.

1980-05-01

220

Triplet Exciton Dynamics. An Investigation Using Electron Spin Echo Techniques Combined with Laser Flash Excitation.  

National Technical Information Service (NTIS)

Results are presented of electron spin echo experiments combined with laser flash excitation on triplet states of aromatic molecules. Some of the theoretical and experimental aspects of the photoexcited triplet state are discussed in detail and the electr...

A. J. van Strien

1981-01-01

221

A Simple Procedure for Computing Density of States Spectra in Solid State Physics  

Microsoft Academic Search

The histogram method for computing density of states spectra is simplified considerably for the cubic lattices. As an example we treat the fcc lattice by randomly sampling a cube in k space (composed of octants from two adjacent Wigner-Seitz cells of the reciprocal lattice). Graphical results for the magnitude of the group velocity are used to locate the critical points

M. Buchheit; P. D. Loly

1972-01-01

222

Far infrared spectra of solid state aliphatic amino acids in different protonation states  

Microsoft Academic Search

Far infrared spectra of zwitterionic, cationic, and anionic forms of aliphatic amino acids in solid state have been studied experimentally. Measurements were done on glycine, L-alanine, L-valine, L-leucine, and L-isoleucine powder samples and film samples obtained from dried solutions prepared at pH ranging from 1 to 13. Solid state density functional theory calculations were also performed, and detailed potential energy

Aurélien Trivella; Thomas Gaillard; Roland H. Stote; Petra Hellwig

2010-01-01

223

Molecular orbitals of the oxocarbons (CO)n, n = 2-6. Why does (CO)4 have a triplet ground state?  

PubMed

Cyclobutane-1,2,3,4-tetrone has been both predicted and found to have a triplet ground state, in which a b(2g) ? MO and an a(2u) ? MO are each singly occupied. The nearly identical energies of these two orbitals of (CO)(4) can be attributed to the fact that both of these MOs are formed from a bonding combination of C-O ?* orbitals in four CO molecules. The intrinsically stronger bonding between neighboring carbons in the b(2g) ? MO compared to the a(2u) ? MO is balanced by the fact that the non-nearest-neighbor, C-C interactions in (CO)(4) are antibonding in b(2g), but bonding in a(2u). Crossing between an antibonding, b(1g) combination of carbon lone-pair orbitals in four CO molecules and the b(2g) and a(2u) bonding combinations of ?* MOs is responsible for the occupation of the b(2g) and a(2u) MOs in (CO)(4). A similar orbital crossing occurs on going from two CO molecules to (CO)(2), and this crossing is responsible for the triplet ground state that is predicted for (CO)(2). However, such an orbital crossing does not occur on formation of (CO)(2n+1) from 2n + 1 CO molecules, which is why (CO)(3) and (CO)(5) are both calculated to have singlet ground states. Orbital crossings, involving an antibonding, b(1), combination of lone-pair MOs, occur in forming all (CO)(2n) molecules from 2n CO molecules. Nevertheless, (CO)(6) is predicted to have a singlet ground state, in which the b(2u) ? MO is doubly occupied and the a(2u) ? MO is left empty. The main reason for the difference between the ground states of (CO)(4) and (CO)(6) is that interactions between 2p AOs on non-nearest-neighbor carbons, which stabilize the a(2u) ? MO in (CO)(4), are much weaker in (CO)(6), due to the much larger distances between non-nearest-neighbor carbons in (CO)(6) than in (CO)(4). PMID:22687146

Bao, Xiaoguang; Zhou, Xin; Flener Lovitt, Charity; Venkatraman, Amruth; Hrovat, David A; Gleiter, Rolf; Hoffmann, Roald; Borden, Weston Thatcher

2012-06-11

224

Fluorescence and phosphorescence resulting from electrochemical generation of triplet excitations  

NASA Astrophysics Data System (ADS)

The biexcitonic annihilation of triplet products of ion recombination is incorporated in the kinetic description of electrochemiluminescence. This process resulting in excitation and fluorescencence of singlets is the dominant mechanism of the initial quenching of triplets, while their concentration is still high. Therefore, the contribution of triplets in subsequent phosphorescence is never as high as expected even at a large exergonicity of inter-ion electron transfer when the recombination to the triplet state prevails on recombination to the ground state of neutral products. The kinetics and quantum yields of fluorescence and phosphorescence are calculated by means of integral encounter theory.

Burshtein, A. I.; Neufeld, A. A.; Ivanov, K. L.

2001-12-01

225

Dynamics of p-terphenyl crystals at the phase transition temperature: a zero-field EPR study of the photoexcited triplet state of pentacene in p-terphenyl crystals.  

PubMed

Pulsed zero-field electron paramagnetic resonance free induction decay (ZF EPR FID) techniques are employed to study the phase transition of p-terphenyl crystals (Tc = 193 K) by measuring selectively populated photoexcited triplet ZF transitions of dilute pentacene molecules in p-terphenyl single crystals. The sensitivity of ZF spectroscopy to small shifts in local magnetic fields enables the studies of guest-host configuration changes over a wide temperature range. Here we report the observation of guest pentacene (-h(14) and -d(14)) triplet ZF EPR FID spectra that disappear abruptly at Tc and of spectral broadening and shift below Tc. We interpret these spectral changes as evidence for guest couplings to host phenyl rings. Further, these data allow assignments of spectroscopic sites to crystallographic sites that occur in the phase transition. PMID:17497761

Lang, Jun; Sloop, David J; Lin, Tien-Sung

2007-05-11

226

Reactive photoinduced species in estuarine waters. Characterization of hydroxyl radical, singlet oxygen and dissolved organic matter triplet state in natural oxidation processes.  

PubMed

This paper describes the reactive photo-induced species (RPS) hydroxyl radical (HO*), singlet oxygen ((1)O(2)) and chromophoric dissolved organic matter triplet state ((3)CDOM*) in fresh water (Canal Fumemorte) and estuarine water (Vaccarès), sampled in the Camargue region, southern France. Experiments were conducted with a medium-pressure Hg lamp in a glass photoreactor (lambda > 290 nm, 220 W m(-2) irradiance between 290 and 400 nm). Steady-state concentration and initial production rate of RPS were determined for HO* and for (1)O(2). HO* and (1)O(2) were indirectly identified in the presence of benzene and furfuryl alcohol, respectively, as specific probes. The steady-state measured concentration of HO* was (1.72 +/- 0.01) x 10(-16) M and (9.41 +/- 0.12) x 10(-17) M for Vaccarès and Canal waters samples, respectively, and the respective concentrations of (1)O(2) was (2.06 +/- 0.22) x 10(-13) M and (5.44 +/- 0.04) x 10(-14) M. The interference of (3)CDOM* or other species in the determination of (1)O(2) with furfuryl alcohol, and of (1)O(2) in the quantification of (3)CDOM* with 2,4,6-trimethylphenol was also quantitatively assessed. We developed a kinetic model describing the solar photo-transformation of xenobiotic organic compounds induced by the three different photooxidants HO*, (1)O(2) and (3)CDOM*. PMID:20062847

al Housari, Fadi; Vione, Davide; Chiron, Serge; Barbati, Stéphane

2009-12-02

227

Triplet-triplet energy transfer between luminescent probes bound to albumins  

NASA Astrophysics Data System (ADS)

The interaction of polar and nonpolar luminescent probes with human blood serum albumins is studied by absorption and luminescence spectroscopy. It is found that the probes (polar eosin and nonpolar anthracene) can efficiently bind to proteins. The radii of the quenching spheres of energy-donor (eosin) triplet states in the presence of an acceptor (anthracene) in the process of the triplet-triplet energy transfer in proteins are determined for homogeneous and inhomogeneous distributions of acceptor molecules over the solution volume. It is shown that a decrease in the radius of the quenching sphere observed upon the addition of sodium dodecylsulfate surfactant is caused by structural changes in the protein.

Mel'Nikov, A. G.; Saletskii, A. M.; Kochubey, V. I.; Pravdin, A. B.; Kurchatov, I. S.; Mel'Nikov, G. V.

2010-08-01

228

A benchmark theoretical study of the electronic ground state and of the singlet-triplet split of benzene and linear acenes.  

PubMed

A benchmark theoretical study of the electronic ground state and of the vertical and adiabatic singlet-triplet (ST) excitation energies of benzene (n=1) and n-acenes (C(4n+2)H(2n+4)) ranging from naphthalene (n=2) to heptacene (n=7) is presented, on the ground of single- and multireference calculations based on restricted or unrestricted zero-order wave functions. High-level and large scale treatments of electronic correlation in the ground state are found to be necessary for compensating giant but unphysical symmetry-breaking effects in unrestricted single-reference treatments. The composition of multiconfigurational wave functions, the topologies of natural orbitals in symmetry-unrestricted CASSCF calculations, the T1 diagnostics of coupled cluster theory, and further energy-based criteria demonstrate that all investigated systems exhibit a (1)A(g) singlet closed-shell electronic ground state. Singlet-triplet (S(0)-T(1)) energy gaps can therefore be very accurately determined by applying the principles of a focal point analysis onto the results of a series of single-point and symmetry-restricted calculations employing correlation consistent cc-pVXZ basis sets (X=D, T, Q, 5) and single-reference methods [HF, MP2, MP3, MP4SDQ, CCSD, CCSD(T)] of improving quality. According to our best estimates, which amount to a dual extrapolation of energy differences to the level of coupled cluster theory including single, double, and perturbative estimates of connected triple excitations [CCSD(T)] in the limit of an asymptotically complete basis set (cc-pVinfinityZ), the S(0)-T(1) vertical excitation energies of benzene (n=1) and n-acenes (n=2-7) amount to 100.79, 76.28, 56.97, 40.69, 31.51, 22.96, and 18.16 kcal/mol, respectively. Values of 87.02, 62.87, 46.22, 32.23, 24.19, 16.79, and 12.56 kcal/mol are correspondingly obtained at the CCSD(T)/cc-pVinfinityZ level for the S(0)-T(1) adiabatic excitation energies, upon including B3LYP/cc-PVTZ corrections for zero-point vibrational energies. In line with the absence of Peierls distortions, extrapolations of results indicate a vanishingly small S(0)-T(1) energy gap of 0 to approximately 4 kcal/mol (approximately 0.17 eV) in the limit of an infinitely large polyacene. PMID:20001050

Hajgató, B; Szieberth, D; Geerlings, P; De Proft, F; Deleuze, M S

2009-12-14

229

Excitons and excess electrons in nanometer size molecular polyoxotitanate clusters: electronic spectra, exciton dynamics, and surface states.  

PubMed

The behavior of excitons and excess electrons in the confined space of a molecular polyoxotitanate cluster Ti17(?4-O)4(?3-O)16(?2-O)4(OPr(i))20 (in short Ti17) was studied using femtosecond pump-probe transient absorption, pulse radiolysis, and fluorescence spectroscopy. Due to pronounced quantum size effects, the electronic spectra of the exciton, Ti17*, and the excess electron carrying radical anion, Ti17(•-), are blue-shifted in comparison with bulk TiO2 and have maxima at 1.91 and 1.24 eV, respectively. The 0.7 eV difference in the position of the absorption maxima of Ti17* and Ti17(•-) indicates the presence of strong Coulomb interaction between the conduction band electron and the valence band hole in the ?1 nm diameter cluster. Ground state Raman spectra and the vibronic structure of the fluorescence spectrum point to the importance of the interfacial ligand modes in the stabilization and localization of the fully relaxed exciton. Four pentacoordinate Ti sites near the surface of the cluster appear to play a special role in this regard. Solvent polarity has only a minor influence on the spectral behavior of Ti17*. Exciton recombination in Ti17 is faster than in anatase nanoparticles or mesoporous films. The kinetics exhibits three components, ranging from less than 1 ps to 100 ps, which are tentatively assigned to the geminate recombination within the core of the cluster and to the decay of the surface stabilized charge transfer exciton. A persistent long-lived component with ? > 300 ps may indicate the involvement of intraband dark states, i.e., triplet excitons (3)Ti17*. PMID:23113586

Bao, Jianhua; Yu, Zhihao; Gundlach, Lars; Benedict, Jason B; Coppens, Philip; Chen, Hung Cheng; Miller, John R; Piotrowiak, Piotr

2012-11-12

230

Incompatible quartets, triplets, and characters  

PubMed Central

We study a long standing conjecture on the necessary and sufficient conditions for the compatibility of multi-state characters: There exists a function f(r) such that, for any set C of r-state characters, C is compatible if and only if every subset of f(r) characters of C is compatible. We show that for every r?2, there exists an incompatible set C of ?(r2)r-state characters such that every proper subset of C is compatible. This improves the previous lower bound of f(r)?r given by Meacham (1983), and f(4)?5 given by Habib and To (2011). For the case when r=3, Lam, Gusfield and Sridhar (2011) recently showed that f(3)=3. We give an independent proof of this result and completely characterize the sets of pairwise compatible 3-state characters by a single forbidden intersection pattern. Our lower bound on f(r) is proven via a result on quartet compatibility that may be of independent interest: For every n?4, there exists an incompatible set Q of ?(n2) quartets over n labels such that every proper subset of Q is compatible. We show that such a set of quartets can have size at most 3 when n=5, and at most O(n3) for arbitrary n. We contrast our results on quartets with the case of rooted triplets: For every n?3, if R is an incompatible set of more than n?1 triplets over n labels, then some proper subset of R is incompatible. We show this bound is tight by exhibiting, for every n?3, a set of n?1 triplets over n taxa such that R is incompatible, but every proper subset of R is compatible.

2013-01-01

231

A ruthenium(II) arene complex showing emission enhancement and photocleavage activity towards DNA from singlet and triplet excited states respectively.  

PubMed

The emission enhancement behavior and photocleavage activity of a ruthenium(II) arene complex, [(?(6)-p-cymene)Ru(dppn)(py)](2+) (1) (dppn = 4,5,9,16-tetraaza-dibenzo[a,c]naphthacene, py = pyridine), towards DNA were compared with [(?(6)-p-cymene)Ru(bpy)(py)](2+) (2), [Ru(bpy)2(dppz)](2+) (3) and [Ru(bpy)2(dppn)](2+) (4) (bpy = 2,2'-bipyridine, dppz = dipyrido-[3,2-a:2',3'-c]phenazine). It was found that 1 emits fluorescence from the dppn-based ligand-centered (LC) singlet excited state and generates singlet oxygen ((1)O2) from the dppn-based LC triplet excited state. As a result, 1 displays emission enhancement behavior and photocleavage activity towards DNA simultaneously. In contrast, 3 is the most classical DNA light switch but shows poor DNA photocleavage activity, while 4 is an efficient DNA photocleaver but cannot report DNA binding by luminescence enhancement. An increased cytotoxicity against human lung carcinoma cells A549 by about 10-fold was also observed for 1 upon visible light activation. These intriguing properties result from the unique combination of the Ru(II) arene and dppn subunits. PMID:23459918

Chen, Yongjie; Lei, Wanhua; Jiang, Guoyu; Zhou, Qianxiong; Hou, Yuanjun; Li, Chao; Zhang, Baowen; Wang, Xuesong

2013-04-28

232

Bond shortening (1.4 Å) in the singlet and triplet excited states of [Ir2(dimen)4]2+ in solution determined by time-resolved X-ray scattering.  

PubMed

Ground- and excited-state structures of the bimetallic, ligand-bridged compound Ir2(dimen)4(2+) are investigated in acetonitrile by means of time-resolved X-ray scattering. Following excitation by 2 ps laser pulses at 390 nm, analysis of difference scattering patterns obtained at eight different time delays from 250 ps to 300 ns yields a triplet excited-state distance between the two Ir atoms of 2.90(2) Å and a triplet excited-state lifetime of 410(70) ns. A model incorporating the presence of two ground-state structures differing in Ir–Ir separation is demonstrated to fit the obtained data very well, in agreement with previous spectroscopic investigations. Two ground-state isomers with Ir–Ir separations of 3.60(9) and 4.3(1) Å are found to contribute equally to the difference scattering signal at short time delays. Further studies demonstrate the feasibility of increasing the effective time resolution from the 100 ps probe width down to the 10 ps regime by positioning the laser pump pulse at selected points in the X-ray probe pulse. This approach is used to investigate the structures of both the singlet and the triplet excited states of Ir2(dimen)4(2+). PMID:21823573

Haldrup, Kristoffer; Harlang, Tobias; Christensen, Morten; Dohn, Asmus; van Driel, Tim Brandt; Kjær, Kasper Skov; Harrit, Niels; Vibenholt, Johan; Guerin, Laurent; Wulff, Michael; Nielsen, Martin Meedom

2011-08-08

233

Zero-field electron spin resonance and theoretical studies of light penetration into single crystal and polycrystalline material doped with molecules photoexcitable to the triplet state via intersystem crossing  

NASA Astrophysics Data System (ADS)

A theory is presented to calculate the penetration depth of light in single crystal or polycrystalline material doped with the molecule whose electronic state can be excited by photoabsorption from the ground state to the excited singlet state, and transferred by intersystem crossing into the triplet state. An experimental study on the penetration depth is also reported, which is made by measuring the amplitude of the zero-field electron spin resonance (ESR) signal of the photoexcited triplet electron spins in single crystal and polycrystalline pentacene-doped p-terphenyl and naphthalene samples at room temperature. The samples were irradiated by a pulsed laser beam, and the zero-field ESR signals were observed for various sample thicknesses. In single crystals of 0.053 mol % pentacene-doped p-terphenyl, the pentacene molecule within ca. 1 mm from the surface of the sample was found to undergo intersystem crossing to the triplet state by the laser irradiation with a pulse duration of 1 mus and a beam intensity of 9.2 x108 W m-2. This result could be well reproduced by the calculation using the reported kinetic parameters, and the limit depth of photoexcitation to the triplet state is shown to coincide with the penetration depth of light when the effect of the stimulated emission is negligible. For polycrystalline 0.099 mol % pentacene-doped p-terphenyl, the penetration depth under an incident beam intensity of 2.9 x109 W m-2 was determined to be ca. 0.7 mm, which could be reproduced by taking account of the laser beam attenuation due to multiple scattering at the crystallite boundaries in the calculations. For pentacene-doped naphthalene, the experimental results were reproduced by the simulations using the intersystem crossing yield of 40%, which is much higher than the value (2%) reported at 1.4 K.

Takeda, Kazuyuki; Takegoshi, K.; Terao, Takehiko

2002-09-01

234

Spin accumulation in triplet Josephson junction.  

PubMed

We employ a Hamiltonian method to study the equal-spin pairing triplet Josephson junction with different orbital symmetries of pair potentials. Both the spin/charge supercurrent and possible spin accumulation at the interface of the junction are analyzed by means of the Keldysh Green's function. It is found that a spontaneous angle-resolved spin accumulation can form at the junction's interface when the orbital symmetries of Cooper pairs in two triplet superconductors are different, the physical origin is the combined effect of the different orbital symmetries and different spin states of Cooper pairs due to the misalignment of two d vectors in triplet leads. An abrupt current reversal effect induced by misalignment of d vectors is observed and can survive in a strong interface barrier scattering because the zero-energy state appears at the interface of the junction. These properties of the p-wave Josephson junction may be helpful for identifying the order parameter symmetry. PMID:21411901

Yang, Zhi Hong; Wang, J; Chan, K S

2011-02-08

235

Far infrared spectra of solid state aliphatic amino acids in different protonation states  

NASA Astrophysics Data System (ADS)

Far infrared spectra of zwitterionic, cationic, and anionic forms of aliphatic amino acids in solid state have been studied experimentally. Measurements were done on glycine, L-alanine, L-valine, L-leucine, and L-isoleucine powder samples and film samples obtained from dried solutions prepared at pH ranging from 1 to 13. Solid state density functional theory calculations were also performed, and detailed potential energy distributions were obtained from normal mode results. A good correspondence between experimental and simulated spectra was achieved and this allowed us to propose an almost complete band assignment for the far infrared spectra of zwitterionic forms. In the 700-50 cm-1 range, three regions were identified, each corresponding to a characteristic set of normal modes. A first region between 700 and 450 cm-1 mainly contained the carboxylate bending, rocking, and wagging modes as well as the ammonium torsional mode. The 450-250 cm-1 region was representative of backbone and sidechain skeletal bending modes. At last, the low wavenumber zone, below 250 cm-1, was characteristic of carboxylate and skeletal torsional modes and of lattice modes. Assignments are also proposed for glycine cationic and anionic forms, but could not be obtained for all aliphatic amino acids due to the lack of structural data. This work is intended to provide fundamental information for the understanding of peptides vibrational properties.

Trivella, Aurélien; Gaillard, Thomas; Stote, Roland H.; Hellwig, Petra

2010-03-01

236

Discrimination among States of Consciousness Using EEG Spectra.  

National Technical Information Service (NTIS)

EEG recordings were made during waking (W) and the five sleep stages (REM, 1, 2, 3, and 4) on thirteen young adult males. For each stage, one-minute sections of the parietal EEG trace were digitized and subjected to Fourier analysis. The resulting spectra...

A. Lubin L. C. Johnson M. T. Austin

1969-01-01

237

Triplet State Formation in Photoexcited Slip-Stacked Perylene-3,4:9,10-bis(dicarboximide) Dimers on a Xanthene Scaffold.  

PubMed

Two covalent perylene-3,4:9,10-bis(dicarboximide) (PDI) dimers in which the PDI molecules are attached to a xanthene (Xan) scaffold in which the long axes of the two ?-? stacked PDI molecules are slipped by 4.3 and 7.9 Å were prepared. These dimers are designed to mimic J-aggregates and provide insights into the photophysics of triplet state formation in PDI aggregates that target organic electronics. Using ultrafast transient absorption and stimulated Raman spectroscopy, the mechanism of (3)*PDI formation was found to depend strongly on a competition between the rate of Xan(•+)-PDI(•-) formation involving the spacer group and the rate of excimer-like state formation. Which mechanism is favored depends on the degree of electronic coupling between the two PDI molecules and/or solvent polarity. Singlet exciton fission to produce (3)*PDI does not compete kinetically with these processes. The excimer-like state decays relatively slowly with ? = 28 ns to produce (3)*PDI, while charge recombination of Xan(•+)-PDI(•-) yields (3)*PDI more than an order of magnitude faster. The perpendicular orientation between the ? orbitals of PDI and the Xan bridge provides a large enough orbital angular momentum change to greatly increase the intersystem crossing rate via Xan(•+)-PDI(•-) ? (3)*PDI charge recombination. These results highlight the importance of understanding inter-chromophore electronic coupling in a wide range of geometries as well as the active role that molecular spacers can play in the photophysics of covalent models for self-assembled chromophore aggregates. PMID:24032482

Lefler, Kelly M; Brown, Kristen E; Salamant, Walter A; Dyar, Scott M; Knowles, Kathryn E; Wasielewski, Michael R

2013-09-27

238

N2 triplet band emissions in the dayglow of Venus, Mars, and Titan  

NASA Astrophysics Data System (ADS)

Vegard-Kaplan (VK) and Second Positive emissions of N_2 are common features in the terrestrial dayglow and aurora and have been studied extensively. Recent discoveries of N_2 triplet band emissions on Mars by SPICAM/Mars-Express and on Titan by Cassini UVIS have led planetary scientists to look for the processes governing the N_2 triplet band emissions in different planetary atmospheres. Present work deals with the modeling of N_2 triplet band emission on Mars, Venus, and Titan. A model for N_2 triplet band emissions has been developed and used to explain the recent observations of N_2 Vegard-Kaplan (VK) (A^3?_u^+ - X^1?^+_g ) band on Mars and Titan. Steady state photoelectron fluxes and volume excitation rates have been calculated using the Analytical Yield Spectra technique. Since interstate cascading is important for triplet states of N_2, the population of any given level of N_2 triplet states is calculated under statistical equilibrium considering direct excitation, cascading, and quenching effects. Relative population of all vibrational levels of each triplet state is calculated in the model. Line of sight intensities and height-integrated overhead intensities have been calculated for VK, First Positive ( B^3?_g - A^3?^+_u ), Second Positive ( C^3?_u - B^3?_g ), Wu-Benesch (W^3?_u - B^3?_g), Reverse First Positive, Herman--Kaplan (E ? A), E ? B, and E ? C bands of N_2. The N_2 VK band span wavelength range from far ultraviolet to visible, and some transitions even originate at wavelength more than 1000 nm . Our calculations show that the overhead intensity of VK bands in the wavelength range 400--800, 300--190, 200--300, and 150--200 nm are 22%, 39%, 35%, and 4% of the total VK band emission. Emissions between 600 and 800 nm wavelength consist of about 50% of the total First Positive band system. Major portion of Second Positive band emissions lie in wavelengths between 300 and 400 nm, which is more than 90% of the total Second Positive band overhead intensity. On Mars, a reduction in the N_2 density by a factor of 3 in the Mars thermospheric general circulation model is required to obtain agreement between calculated limb profiles of VK (0-6) and the SPICAM/MEX observation. On Titan, the calculated intensity of N_2 VK band in 150--190 nm wavelength range is in good agreement with the Cassini-UVIS observation. Calculations are also carried out on Venus using this model. Calculated intensities on Venus are about factor of 10 higher than that on Mars. The results will be presented and discussed.

Jain, Sonal Kumar; Bhardwaj, Anil

2012-07-01

239

Efficient organic light-emitting diodes through up-conversion from triplet to singlet excited states of exciplexes  

NASA Astrophysics Data System (ADS)

Enhanced electroluminescence efficiency is achieved in organic light-emitting diodes through delayed fluorescence of the exciplex state formed between 4,4',4''-tris[3-methylphenyl(phenyl)amino]-triphenylamine (m-MTDATA) as an electron-donating material and 2,8-bis(diphenylphosphoryl)dibenzo-[b,d]thiophene (PPT) as an electron-accepting material. The devices exhibited maximum external electroluminescence quantum and power efficiencies of 10.0% and 47.0 lm/W, respectively.

Goushi, Kenichi; Adachi, Chihaya

2012-07-01

240

Bose-Einstein condensation of the triplet states in the magnetic insulator TlCuCl3  

Microsoft Academic Search

Bose-Einstein condensation denotes the formation of a collective quantum ground state of identical particles with integer spin or intrinsic angular momentum. In magnetic insulators, the magnetic properties are due to the unpaired shell electrons that have half-integer spin. However, in some such compounds (KCuCl3 and TlCuCl3), two Cu2+ ions are antiferromagnetically coupled to form a dimer in a crystalline network:

Ch. Rüegg; N. Cavadini; A. Furrer; H.-U. Güdel; K. Krämer; H. Mutka; A. Wildes; K. Habicht; P. Vorderwisch

2003-01-01

241

Ground-state features in the THz spectra of molecular clusters of ?-HMX.  

PubMed

We present calculations of absorption spectra arising from molecular vibrations at THz frequencies for molecular clusters of the explosive HMX using density functional theory (DFT). The features of these spectra can be shown to follow from the coupling of vibrational modes. In particular, the coupling among ground-state vibrational modes provides a reasonable molecular-level interpretation of spectral features associated with the vibrational modes of molecular clusters. THz excitation from the ground state is associated with frequencies that characteristically perturb molecular electronic states, in contrast to frequencies, which are usually substantially above the mid-infrared (mid-IR) range, that can induce appreciable electronic-state transition. Owing to this characteristic of THz excitation, one is able to make a direct association between local oscillations about ground-state minima of molecules, either isolated or comprising a cluster, and THz absorption spectra. The DFT software program GAUSSIAN was used for the calculations of the absorption spectra presented here. PMID:23031709

Huang, Lulu; Shabaev, Andrew; Lambrakos, Samuel G; Massa, Lou

2012-10-01

242

The Discovery of a Prolate-Oblate Shape Triplet of Spin 0+ States in the Atomic Nucleus 186PB  

NASA Astrophysics Data System (ADS)

The fundamental excitations in many-fermion systems remain one of the most exciting subjects of today's physics. In even-even atomic nuclei, pair breaking, vibrations and rotations generally form the low-lying excitation spectrum. However, for specific numbers of protons and neutrons, a subtle rearrangement of only a few nucleons among the orbitals at the Fermi surface can result in a different elementary mode: a macroscopic shape change [1,2]. We have identified for the first time in a nucleus (186Pb) three different shapes (spherical - oblate - prolate) as the lowest three states in the energy spectrum [3]. The parent 190Po nuclei were produced in the 142Nd(52Cr,4n)190Po complete fusion reaction, studied with the velocity filter SHIP [4] at the UNILAC heavy ion accelerator (GSI, Darmstadt). Nuclei of interest after separation were implanted into a position-sensitive silicon detector (PSSD), where their subsequent a decays were measured. In front of the PSSD six similar silicon detectors were mounted (Si-box), facing the PSSD, which were used to detect conversion electrons in prompt coincidence with ?-particles. A 4-fold segmented Ge Clover detector was installed behind the PSSD to record prompt ?-X and ?-? coincidences. The whole set-up has been optimized to observe fine structure in the ? decay that leads, as studied for the heavier even-even Pb nuclei [5], to the identification of low-lying 0+ band heads, which will decay predominantly by E0 conversion electron transitions to the ground state. Further details on the experimental method can be found in [3,6,7]...

Andreyev, A. N.; Huyse, M.; van Duppen, P.; Weissman, L.; Ackermann, D.; Gerl, J.; He?BERGER, F. P.; Hofmann, S.; Kleinböhl, A.; Münzenberg, G.; Reshitko, S.; Schlegel, C.; Schaffner, H.; Cagarda, P.; Matos, M.; Saro, S.; Keenan, A.; Moore, C.; O'Leary, C. D.; Page, R. D.; Taylor, M.; Kettunen, H.; Leino, M.; Lavrentiev, A.; Wyss, R.; Heyde, K.

2001-11-01

243

Degenerate discrete energy spectra and associated coherent states  

NASA Astrophysics Data System (ADS)

Generalized and Gaussian coherent states constructed for quantum system with degeneracies in the energy spectrum are compared with respect to some minimal definitions and fundamental properties they have to satisfy. The generalized coherent states must be eigenstates of a certain annihilation operator that has to be properly defined in the presence of degeneracies. The Gaussian coherent states are, in the particular harmonic oscillator case, an approximation of the generalized coherent states and so the localizability in phase space of the particle in those states is very good. For other quantum systems, this last property serves as a definition of those Gaussian coherent states. The example of a particle in a two-dimensional square box is thus revisited having in mind the preceding definitions of generalized and Gaussian coherent states and also the preservation of the important property known as the resolution of the identity operator.

Dello Sbarba, L.; Hussin, V.

2007-01-01

244

Degenerate discrete energy spectra and associated coherent states  

SciTech Connect

Generalized and Gaussian coherent states constructed for quantum system with degeneracies in the energy spectrum are compared with respect to some minimal definitions and fundamental properties they have to satisfy. The generalized coherent states must be eigenstates of a certain annihilation operator that has to be properly defined in the presence of degeneracies. The Gaussian coherent states are, in the particular harmonic oscillator case, an approximation of the generalized coherent states and so the localizability in phase space of the particle in those states is very good. For other quantum systems, this last property serves as a definition of those Gaussian coherent states. The example of a particle in a two-dimensional square box is thus revisited having in mind the preceding definitions of generalized and Gaussian coherent states and also the preservation of the important property known as the resolution of the identity operator.

Dello Sbarba, L.; Hussin, V. [Centre de Recherches Mathematiques et Departement de Mathematiques et de Statistique, Universite de Montreal, C.P. 6128, Succursale Centre-ville, Montreal, (Quebec) H3C 3J7 (Canada)

2007-01-15

245

Quenching of the cascade reaction between triplet and photochrome probes by nitroxide radicals  

Microsoft Academic Search

A cascade of photochemical reactions between the triplet sensitizer Erythrosin B and the photochrome stilbene-derivative probe exhibiting the phenomenon of cis–trans photoisomerization has been investigated. The cascade triplet cis–trans photoisomerization of the excited stilbene chromophore is sensitized with the excited triplet Erythrosin B and depressed with nitroxide radicals quenching the excited triplet state of sensitizer. The rate of the cascade

V. Papper; G. I. Likhtenshtein; N. Medvedeva; D. V. Khoudyakov

1999-01-01

246

Substituent effect on reactivity of triplet excited state of 2,3-diazabicyclo[2.2.1]hept-2-enes, DBH derivatives: ? C-N bond cleavage versus ? C-C bond cleavage.  

PubMed

The photoreaction of a series of 2,3-diazabicyclo[2.2.1]hept-2-ene (DBH) derivatives, in which various substituents (X) were introduced at the methano bridge carbon of C(7), was investigated under direct (>290 nm) and triplet-sensitized (Ph2CO, >370 nm) irradiation conditions of the azo chromophore (?C?–C?–N?N–C?–C??). The azo compounds offered a unique opportunity to see the substituent X effect at the remote position of the azo chromophore on the reactivity of the triplet excited state of bicyclic azoalkanes. The present study led to the first observation of the unusual C?–C? bond-cleavage reaction without the ring stiffness, that is, the structural rigidity, in the triplet state of the cyclic azoalkanes. The stereoelectronic effects were found to play an important role in lowering the activation energy of the C?–C? bond-cleavage reaction. NBO analyses at the M06-2X/cc-PVDZ level of theory confirmed the stereoelectronic effect. PMID:22985271

Abe, Manabu; Watanabe, Shinji; Tamura, Hiroshi; Boinapally, Srikanth; Kanahara, Kousei; Fujiwara, Yoshihisa

2012-10-01

247

Methylcarbene: The singlet-triplet energy separation  

SciTech Connect

Ab initio molecular electronic structure theory is used to examine the energy separation between the ground triplet and lowest lying singlet states of methylcarbene. Zero-point corrections to the singlet-triplet energy separation are considered. Correlation methods, specifically configuration interaction, are employed in this study. The structures of the above-mentioned electronic states are optimized with a Gaussian basis set of double {zeta} plus polarization quality, DZP. Single-point energies are determined at the DZP optimized structures with a much larger basis set, TZ+2P+f, which takes into account the effects of carbon atom f functions and is otherwise of triple {zeta} plus double polarization quality. Harmonic vibrational frequencies are determined for both methylcarbene electronic states with the double {zeta} plus polarization basis set. The methylcarbene singlet-triplet energy difference is predicted to be 5 {plus_minus} 1 kcal/mol. Thus the CH{sub 3} substituent has the effect of reducing the methylene singlet-triplet splitting (9 kcal/mol) by about 4 kcal/mol. 23 refs., 2 figs., 2 tabs.

Gallo, M.M.; Schaefer, H.F. III [Univ. of Georgia, Athens, GA (United States)

1992-02-20

248

Triplet Exciton Formation as a Novel Photoprotection Mechanism in Chlorosomes of Chlorobium tepidum  

PubMed Central

Chlorosomes comprise thousands of bacteriochlorophylls (BChl c, d, or e) in a closely packed structure surrounded by a lipid-protein envelope and additionally contain considerable amounts of carotenoids, quinones, and BChl a. It has been suggested that carotenoids in chlorosomes provide photoprotection by rapidly quenching triplet excited states of BChl via a triplet-triplet energy transfer mechanism that prevents energy transfer to oxygen and the formation of harmful singlet oxygen. In this work we studied triplet energy transfer kinetics and photodegradation of chlorosomes isolated from wild-type Chlorobium tepidum and from genetically modified species with different types of carotenoids and from a carotenoid-free mutant. Supporting a photoprotective function of carotenoids, carotenoid-free chlorosomes photodegrade ?3 times faster than wild-type chlorosomes. However, a significant fraction of the BChls forms a long-lived, triplet-like state that does not interact with carotenoids or with oxygen. We propose that these states are triplet excitons that form due to triplet-triplet interaction between the closely packed BChls. Numerical exciton simulations predict that the energy of these triplet excitons may fall below that of singlet oxygen and triplet carotenoids; this would prevent energy transfer from triplet BChl. Thus, the formation of triplet excitons in chlorosomes serves as an alternative photoprotection mechanism.

Kim, Hanyoup; Li, Hui; Maresca, Julia A.; Bryant, Donald A.; Savikhin, Sergei

2007-01-01

249

Production Spectra of the ? NN Quasibound States in 3He( K -, ? ?) Reactions  

NASA Astrophysics Data System (ADS)

We theoretically demonstrate the inclusive and semiexclusive spectra in the 3He ( K -, ? ?) reactions at 600 MeV/c (4°) within a distorted-wave impulse approximation, using a coupled (2 N - ?) + (2 N - ?) model with a spreading potential. It is shown that a signal of a quasibound state is clearly observed near the ? threshold in the ? - spectrum, whereas a peak of a quasibound state is relatively reduced in the ? + spectrum. The mechanism of ? production for these spectra is discussed.

Harada, Toru; Hirabayashi, Yoshiharu

2013-08-01

250

A simple natural orbital mechanism of "pure" van der Waals interaction in the lowest excited triplet state of the hydrogen molecule.  

PubMed

A treatment of van der Waals (vdW) interaction by density-matrix functional theory requires a description of this interaction in terms of natural orbitals (NOs) and their occupation numbers. From an analysis of the configuration-interaction (CI) wave function of the 3Sigmau + state of H2 and the exact NO expansion of the two-electron triplet wave function, we demonstrate that the construction of such a functional is straightforward in this case. A quantitative description of the vdW interaction is already obtained with, in addition to the standard part arising from the Hartree-Fock determinant /1sigmag(r1)1sigmau(r2)/, only two additional terms in the two-electron density, one from the first "excited" determinant /2sigmag(r1)2sigmau(r2)/ and one from the state of 3Sigmau + symmetry belonging to the (1pig)1(1piu)1 configuration. The potential-energy curve of the 3Sigmau + state calculated around the vdW minimum with the exact density-matrix functional employing only these eight NOs and NO occupations is in excellent agreement with the full CI one and reproduces well the benchmark potential curve of Kolos and Wolniewicz [J. Chem. Phys. 43, 2429 (1965)]. The corresponding terms in the two-electron density rho2(r1,r2), containing specific products of NOs combined with prefactors that depend on the occupation numbers, can be shown to produce exchange-correlation holes that correspond precisely to the well-known intuitive picture of the dispersion interaction as an instantaneous dipole-induced dipole (higher multipole) effect. Indeed, (induced) higher multipoles account for almost 50% of the total vdW bond energy. These results serve as a basis for both a density-matrix functional theory of van der Waals bonding and for the construction of orbital-dependent functionals in density-functional theory that could be used for this type of bonding. PMID:16468859

Gritsenko, Oleg; Baerends, Evert Jan

2006-02-01

251

Equilibrium excited state and emission spectra of molecular aggregates from the hierarchical equations of motion approach.  

PubMed

The hierarchical equations of motion (HEOM) method was applied to calculate the emission spectra of molecular aggregates using the Frenkel exciton model. HEOM equations for the one-exciton excited state were first propagated until equilibration. The reduced density operator and auxiliary density operators (ADOs) were used to characterize the coupled system-bath equilibrium. The dipole-dipole correlation functions were then calculated to obtain the emission spectra of model dimers, and the B850 band of light-harvesting complex II (LH2) in purple bacteria. The effect of static disorder on equilibrium excited state and the emission spectra of LH2 was also explicitly considered. Several approximation schemes, including the high temperature approximation (HTA) of the HEOM, a modified version of the HTA, the stochastic Liouville equation approach, the perturbative time-local and time-nonlocal generalized quantum master equations, were assessed in the calculation of the equilibrium excited state and emission spectra. PMID:23387623

Jing, Yuanyuan; Chen, Liping; Bai, Shuming; Shi, Qiang

2013-01-28

252

Peptide charge state determination of tandem mass spectra from low-resolution collision induced dissociation  

PubMed Central

Abstract Background Charge states of tandem mass spectra from low-resolution collision induced dissociation can not be determined by mass spectrometry. As a result, such spectra with multiple charges are usually searched multiple times by assuming each possible charge state. Not only does this strategy increase the overall database search time, but also yields more false positives. Hence, it is advantageous to determine charge states of such spectra before database search. Results We propose a new approach capable of determining the charge states of low-resolution tandem mass spectra. Four novel and discriminant features are introduced to describe tandem mass spectra and used in Gaussian mixture model to distinguish doubly and triply charged peptides. By testing on three independent datasets with known validity, the results have shown that this method can assign charge states to low-resolution tandem mass spectra more accurately than existing methods. Conclusions The proposed method can be used to improve the speed and reliability of peptide identification.

2011-01-01

253

Rogue wave triplets  

NASA Astrophysics Data System (ADS)

We consider the family of 2nd order rogue wave rational solutions of the nonlinear Schrödinger equation (NLSE) with two free parameters. Surprisingly, these solutions describe a formation consisting of 3 separate first order rogue waves, rather than just two. We show that the 3 components of the triplet are located on an equilateral triangle, thus maintaining a certain symmetry in the solution, even in its decomposed form. The two free parameters of the family define the size and orientation of the triangle on the (x,t) plane.

Ankiewicz, Adrian; Kedziora, David J.; Akhmediev, Nail

2011-07-01

254

Intensities in Singlet-Triplet Bands of Diatomic Molecules  

Microsoft Academic Search

Intensity formulae are found for the rotational structure of bands arising from transitions between a singlet and a triplet state of a diatomic molecule. These intercombinations occur because the wave functions which diagonalize the orbit-spin interaction contain both singlet and triplet terms. In the transition 1Sigma-3Sigma two cases arise, according as the two states have the same or opposite symmetry

Robert Schlapp

1932-01-01

255

Supercooling and final-state effects on dilepton spectra  

SciTech Connect

We consider two problems associated with the production of dileptons during collisions between heavy nuclei at the Brookhaven Relativistic Heavy Ion Collider energy. One is the difference in dilepton yield between an idealized Maxwell construction of phase coexistence and a dynamical phase transition with finite nucleation and phase conversion rates. The other is the contribution from dilepton-producing reactions involving free-streaming hadrons in the final state. We find that the mass spectrum in the range 2[ital m][sub [pi

Srivastava, D.K. (Theoretical Physics Institute, University of Minnesota, Minneapolis, Minnesota 55455 (United States)); Kapusta, J.I. (School of Physics and Astronomy, University of Minnesota, Minneapolis, Minnesota 55455 (United States))

1993-07-01

256

Electronic States and Spectra of BiO  

Microsoft Academic Search

The electronic spectrum of the BiO radical has been studied by Fourier transform emission spectroscopy, laser-induced fluorescence, and excimer laser photolysis techniques. Six new electronic states,A1(? = 3\\/2) (Te= 11 528.8 cm?1, ?e= 530.4 cm?1, ?exe= 2.42 cm?1),G(? = 3\\/2) (Te= 20 273 cm?1, ?e= 499 cm?1, ?exe= 2.6 cm?1),H(? = 1\\/2) (Te= 20 469.76(6) cm?1, ?e= 471.63(18) cm?1, ?exe=

O. Shestakov; R. Breidohr; H. Demes; K. D. Setzer; E. H. Fink

1998-01-01

257

Triplet-triplet energy-transfer coupling: Theory and calculation  

NASA Astrophysics Data System (ADS)

Triplet-triplet (TT) energy transfer requires two molecular fragments to exchange electrons that carry different spin and energy. In this paper, we analyze and report values of the electronic coupling strengths for TT energy transfer. Two different methods were proposed and tested: (1) Directly calculating the off-diagonal Hamiltonian matrix element. This direct coupling scheme was generalized from the one used for electron transfer coupling, where two spin-localized unrestricted Hartree-Fock wave functions are used as the zero-order reactant and product states, and the off-diagonal Hamiltonian matrix elements are calculated directly. (2) From energy gaps derived from configuration-interaction-singles (CIS) scheme. Both methods yielded very similar results for the systems tested. For TT coupling between a pair of face-to-face ethylene molecules, the exponential attenuation factor is 2.59 A?-1(CIS/6-311+G**), which is about twice as large as typical values for electron transfer. With a series of fully stacked polyene pairs, we found that the TT coupling magnitudes and attenuation rates are very similar irrespective of their molecular size. If the polyenes were partially stacked, TT couplings were much reduced, and they decay more rapidly with distance than those of full-stacked systems. Our results showed that the TT coupling arises mainly from the region of close contact between the donor and acceptor frontier orbitals, and the exponential decay of the coupling with separation depends on the details of the molecular contacts. With our calculated results, nanosecond or picosecond time scales for TT energy-transfer rates are possible.

You, Zhi-Qiang; Hsu, Chao-Ping; Fleming, Graham R.

2006-01-01

258

Proximity effect in ferromagnet/triplet p-wave superconductor structures  

NASA Astrophysics Data System (ADS)

The superconducting proximity effect in normal metal/insulator/ferromagnet/triplet p-wave superconductor (N/I/FP) structures is studied based on an extended Blonder Tinkham Klapwijk (BTK) theory. Three kinds of pairings for the P side are chosen: p, p, p+ip waves. The transition from the “0” to “?” state is found in the conductance spectra with increasing the thickness of F or the ferromagnetic exchange energy. The large amplitude of the normalized conductance suggests the possible coexistence of the ferromagnetism and p-wave superconductivity in a small region near the F/P interface induced by the proximity effect.

Li, Hong; Yang, Wei; Yang, Xinjian; Qin, Minghui

2007-02-01

259

Chlorophyll triplet quenching and photoprotection in the higher plant monomeric antenna protein lhcb5.  

PubMed

In oxygenic photosynthetic organisms, chlorophyll triplets are harmful excited states readily reacting with molecular oxygen to yield the reactive oxygen species (ROS) singlet oxygen. Carotenoids have a photoprotective role in photosynthetic membranes by preventing photoxidative damage through quenching of chlorophyll singlets and triplets. In this work we used mutation analysis to investigate the architecture of chlorophyll triplet quenching sites within Lhcb5, a monomeric antenna protein of Photosystem II. The carotenoid and chlorophyll triplet formation as well as the production of ROS molecules were studied in a family of recombinant Lhcb5 proteins either with WT sequence, mutated into individual chlorophyll binding residues or refolded in vitro to bind different xanthophyll complements. We observed a site-specific effect in the efficiency of chlorophyll-carotenoid triplet-triplet energy transfer. Thus chlorophyll (Chl) 602 and 603 appear to be particularly important for triplet-triplet energy transfer to the xanthophyll bound into site L2. Surprisingly, mutation on Chl 612, the chlorophyll with the lower energy associated and in close contact with lutein in site L1, had no effect on quenching chlorophyll triplet excited states. Finally, we present evidence for an indirect role of neoxanthin in chlorophyll triplet quenching and show that quenching of both singlet and triplet states is necessary for minimizing singlet oxygen formation. PMID:23786371

Ballottari, Matteo; Mozzo, Milena; Girardon, Julien; Hienerwadel, Rainer; Bassi, Roberto

2013-07-08

260

Isotropic reorientations of fullerene C70 triplet molecules in solid glassy matrices revealed by light-induced electron paramagnetic resonance.  

PubMed

Continuous-wave X-band electron paramagnetic resonance (EPR) of fullerene C(70) molecules excited to a triplet state by continuous light illumination was studied in molecular glasses of o-terphenyl and cis/trans-decaline and in the glassy polymers polymethylmethacrylate (PMMA) and polystyrene (PS). Above ?100 K, a distinct narrowing of EPR lineshape of the triplet was observed, which was very similar for all systems studied. EPR lineshape was simulated reasonably well within a framework of a simple model of random jumps, which implies that the C(70) molecule performs isotropic orientational motion by sudden jumps of arbitrary angles. In simulations, a single correlation time ?(c) was used, varying in the range of 10(-7)-10(-8) s. Near and below 100 K electron spin echo (ESE) signals were also obtained which were found to decay exponentially. Correlation times ?(c) obtained from simulation of the EPR spectra in the slow-motion limit (?(c) close to 10(-7) s) turned out to be in good agreement with the phase memory times T(M) of the ESE decay, which additionally supports the employed simple model. The observed motional effects provide evidence that the nanostructure of the solid glassy media of different origins is soft enough to allow a large asymmetric C(70) molecule to reorient rapidly. Except for the EPR spectra of the triplet, in the center of the spectra, a small admixture of a narrow line was also observed; its possible nature is briefly discussed. PMID:21823712

Uvarov, Mikhail N; Kulik, Leonid V; Doktorov, Alexander B; Dzuba, Sergei A

2011-08-01

261

Evaluation of Triplet Aromaticity by the Isomerization Stabilization Energy.  

PubMed

The many manifestations of aromaticity have long fascinated both experimentalists and theoreticians. Due to their degenerate half-filled MOs, triplet [n]annulenes with 4n ?-electrons are also aromatic, but the degree of their stabilization has been difficult to quantify. The isomerization stabilization energy (ISE) method has been applied to evaluate the triplet aromaticity. The reliability of this approach is indicated by the strong correlation of the ISE results with NICS(1)zz, a magnetic indicator of triplet state aromaticity. PMID:23638944

Zhu, Jun; An, Ke; Schleyer, Paul von Ragué

2013-05-01

262

The electronic spectrum of Si3 I: Triplet D3h system  

NASA Astrophysics Data System (ADS)

We report the measurement of a jet-cooled electronic spectrum of the silicon trimer. Si3 was produced in a pulsed discharge of silane in argon, and the excitation spectrum examined in the 18 000-20 800 cm-1 region. A combination of resonant two-color two-photon ionization (R2C2PI) time-of-flight mass spectroscopy, laser-induced fluorescence/dispersed fluorescence, and equation-of-motion coupled-cluster calculations have been used to establish that the observed spectrum is dominated by the 13A1'' - a~ 3A2' transition of the D3h isomer. The spectrum has an origin transition at 18 600+/- 4 cm-1 and a short progression in the symmetric stretch with a frequency of ~445 cm-1, in good agreement with a predicted vertical transition energy of 2.34 eV for excitation to the 13A1'' state, which has a calculated symmetric stretching frequency of 480 cm-1. In addition, a ~505 cm-1 ground state vibrational frequency determined from sequence bands and dispersed fluorescence is in agreement with an earlier zero-electron kinetic energy study of the lowest D3h state and with theory. A weaker, overlapping band system with a ~360 cm-1 progression, observed in the same mass channel (m/z = 84) by R2C2PI but under different discharge conditions, is thought to be due to transitions from the (more complicated) singlet C2v ground state (1A1) state of Si3. Evidence of emission to this latter state in the triplet dispersed fluorescence spectra suggests extensive mixing in the excited triplet and singlet manifolds. Prospects for further spectroscopic characterization of the singlet system and direct measurement of the energy separation between the lowest singlet and triplet states are discussed.

Reilly, N. J.; Kokkin, D. L.; Zhuang, X.; Gupta, V.; Nagarajan, R.; Fortenberry, R. C.; Maier, J. P.; Steimle, T. C.; Stanton, J. F.; McCarthy, M. C.

2012-05-01

263

The gap equations for spin singlet and triplet ferromagnetic superconductors  

Microsoft Academic Search

We derive gap equations for superconductivity in coexistence with ferromagnetism. We treat singlet and triplet states with either equal spin pairing (ESP) or opposite spin pairing (OSP) states, and study the behaviour of these states as a function of exchange splitting. For the s-wave singlet state we find that our gap equations correctly reproduce the Clogston-Chandrasekhar limiting behaviour and the

B. J. Powell; James F. Annett; B. L. Györffy

2003-01-01

264

The gap equations for spin singlet and triplet ferromagnetic superconductors  

Microsoft Academic Search

We derive gap equations for superconductivity in coexistence with ferromagnetism. We treat singlet and triplet states with either equal spin pairing (ESP) or opposite spin pairing (OSP) states, and study the behaviour of these states as a function of exchange splitting. For the s-wave singlet state we find that our gap equations correctly reproduce the Clogston–Chandrasekhar limiting behaviour and the

B. J. Powell; James F. Annett; B. L. Gyorffy

2003-01-01

265

Proton hyperfine structure in the ESR. Delta. M sub s = +2 transitions of the triplet states of 1-naphthol and 1-naphtholate in glassy matrices. A parallel-polarized ESR study  

SciTech Connect

The effects of deprotonation on the spin distribution of 1-naphthol (1-ROH) in the lowest excited triplet (T{sub 1}) state have been studied by the parallel-polarized ESR technique. The proton hyperfine structures in {Delta}M{sub s} = {plus minus}2 transitions have been observed for the T{sub 1} states of 1-ROH and 1-naphtholate (1-RO{sup {minus}}) in random rigid solutions of ethanol at 77 K. The {alpha}-proton hyperfine splitting of 1-RO{sup {minus}} is smaller than that of 1-ROH. With the aid of the spin-density calculation within McLachlan's approximation, the effect of deprotonation on the spin densities at the {alpha}-carbon atoms of 1-ROH in the T{sub 1} state is discussed. This is the first report of the proton hyperfine structure of a T{sub 1} organic molecule in an ionic form.

Yagi, Mikio; Muramoto, Akira; Higuchi, Jiro (Yokohama National Univ. (Japan))

1990-02-22

266

Stark spectra of Rydberg states in atomic cesium in the vicinity of n = 18  

NASA Astrophysics Data System (ADS)

The Stark structures in a cesium atom around n = 18 are numerically calculated. The results show that the components of 20D states with a small azimuthal quantum number |m| shift upward a lot, and those with a large |m| shift downward a little within 1100 V/cm. All components of P states shift downward. Experimental work has been performed in ultracold atomic cesium. Atoms initially in 6P3/2 state are excited to high-n Rydberg states by a polarization light perpendicular to the field, and Stark spectra with |m| = 1/2, 3/2, 5/2 are simultaneously observed with a large linewidth for the first time. The observed spectra are analyzed in detail. The relative transition probability is calculated. The experimental results are in good agreement with our numerical computation.

Dong, Hui-Jie; Wang, Ting; Li, Chang-Yong; Zhao, Jian-Ming; Zhang, Lin-Jie

2013-07-01

267

Low temperature emission spectra of optically nonlinear N-benzyl-2-methyl-4-nitroaniline crystal  

NASA Astrophysics Data System (ADS)

The fluorescence and phosphorescence spectra of N-benzyl-2-methyl-4-nitroaniline (BNA) orthorhombic crystal were measured between 5 and 200 K. The fluorescence spectrum of BNA in a Shpol'skii matrix of n-heptane was also recorded at 5 K. The electronic absorption spectra parameters such as singlet and triplet state energies, dipole moments and oscillator strengths were calculated by semi-empirical and TD DFT methods. The calculated energies of singlet and triplet states and electronic transitions in the BNA molecule were compared with the experimental results. The phosphorescence decay time was estimated to be 270 ms at 5 K. It is presumed that the disappearance of vibronic structure above 30 K observed in the fluorescence spectra is caused by the nitro group vibrations while the structured phosphorescence originates from the trap states. The role of molecular shape towards emission processes in BNA crystal in terms of structure-property relationship is discussed.

Piela, Katarzyna; Kozankiewicz, Boles?aw; Lipi?ski, Józef; Magdalena Szostak, M.

2012-08-01

268

Electroweak corrections from triplet scalars  

NASA Astrophysics Data System (ADS)

We compute the electroweak S and T parameters induced by SU(2)L triplet scalars up to one-loop order. We consider the most general renormalizable potential for a triplet and the Standard Model Higgs doublet. Our calculation is performed by integrating out the triplet at the one-loop level and also includes the one-loop renormalization group running. Effective field theory framework allows us to work in the phase with unbroken SU(2)L×U(1)Y symmetry. Both S and T parameters exhibit decoupling when all dimensionful parameters are large while keeping dimensionless ratios fixed. We use bounds on S and T to constrain the triplet mass and couplings.

Khandker, Zuhair U.; Li, Daliang; Skiba, Witold

2012-07-01

269

LHC inner triplet powering strategy  

Microsoft Academic Search

In order to achieve a luminosity in excess of 1034 cm -2 s-1 at the Large Hadron Collider (LHC), special high gradient quadrupoles are required for the final focusing triplets. These low-P triplets, located in the four experimental insertions (ATLAS, CMS, ALICE, LHC-B), consist of four wide-aperture superconducting magnets: two outer quadrupoles, Q1 and Q3, with a maximum current of

Frederick Bordry; H. Thiesen

2001-01-01

270

Sensitized and heavy atom induced production of acenaphthylene triplet: A laser flash photolysis study  

SciTech Connect

The triplet state of acenaphthylene has been examined by nanosecond laser flash photolysis using sensitization and heavy atom perturbation techniques. Although acenaphthylene does not form any observable triplet upon direct flash excitation, a transient with microsecond lifetime ({lambda}{sub max} = 315 nm) is observable when a solution of the sample is excited by sensitizers (benzophenone, thioxanthone, benzil). This transient is ascribed to the triplet of acenaphthylene on the basis of its quenching behavior toward oxygen, ferrocene, azulene, and {beta}-carotene. Quantitative data concerning the triplet-triplet absorption and quenching constants are presented. The triplet energy is estimated to lie between 46 and 47 kcal/mol. The triplet can also be produced by direct excitation in solvents containing heavy atoms (ethyl bromide, ethyl iodide). The triplet yield is found to increase with an increase of the amount of the heavy atom containing solvent. No saturation limit is obtained. These facts together with the effect of heavy atoms on the T{sub 1} {yields} S{sub 0} process allow the differing behavior of ethyl bromide and ethyl iodide on the photodimerization process of acenaphthylene to be explained. Triplet-state parameters (extinction coefficient and triplet yield) have been estimated in these solvents by the energy-transfer technique and actinometry.

Samanta, A.; Fessenden, R.W. (Univ. of Notre Dame, IN (USA))

1989-07-27

271

NC-(CF2)4-CNSSN radical containing 1,2,3,5-dithiadiazolyl radical dimer exhibiting triplet excited states at low temperature and thermal hysteresis on melting-solidification: structural, spectroscopic, and magnetic characterization.  

PubMed

A high yield, one-pot synthesis of the 1,2,3,5-dithiadiazolyl radical NC-(CF2)4-CNSSN radical by reduction of the corresponding 1,3,2,4-dithiadiazolium salt is reported. In the solid state, the title compound is dimerized in trans-cofacial fashion with intra-dimeric Sdelta+...N(delta-) interactions of ca. 3.2 angstroms, and the dimeric units are linked by electrostatic -C triple bond N(delta-)...Sdelta+ interactions forming an infinite chain. Magnetic susceptibility measurements performed on the solid state sample indicate a magnetic moment of 1.8 microB per dimer (1.3 microB per monomer) at 300 K and a good fit to the Bleaney-Bowers model in the temperature range 2-300 K with 2J = -1500 +/- 50 cm(-1), g = 2.02(5), rho = 0.90(3)%, and TIP = 1.25(4) x 10(-3) emu mol(-1). The [NC-(CF2)4-CNSSN radical]2 dimer is the second example of a 1,2,3,5-dithiadiazolyl radical dimer with an experimentally detected triplet excited state as probed by solid-state EPR [2J = -1730 +/- 100 cm(-1), |D| = 0.0278(5) cm(-1), |E| = 0.0047(5) cm(-1)]. The value of the singlet-triplet gap has enabled us to estimate the "in situ" dimerization energy of the radical dimer as ca. -10 kJ mol(-1). The diradical character of the dimer was calculated [CASSCF(6,6)/6-31G*] as 35%. The title radical shows magnetic bistability in the temperature range of 305-335 K as probed by the solid-state EPR presumably arising from the presence of a metastable paramagnetic supercooled phase. Bistability is accompanied by thermochromic behavior with a color change from dark green (dimeric solid) to dark brown (paramagnetic liquid). PMID:18648707

Shuvaev, Konstantin V; Decken, Andreas; Grein, Friedrich; Abedin, Tareque S M; Thompson, Laurence K; Passmore, Jack

2008-06-26

272

Phosphorescence and zero-field optically detected magnetic resonance studies of the lowest excited triplet states of organometallic diimine complexes. 1. (Rh(bpy)/sub 3/)/sup 3 +/ and (Rh(phen)/sub 3/)/sup 3 +/  

SciTech Connect

The authors have made spectroscopic and optically detected magnetic resonance studies on /sup 3/..pi pi..* (Rh(bpy)/sub 3/)/sup 3 +/ and (Rh(phen)/sub 3/)/sup 3 +/ at liquid helium temperature. They have observed a well-resolved phosphorescence spectrum of (Rh(phen)/sub 3/)(BF/sub 4/)/sub 3/ that resembles that of 1,10-phenanthroline except for changes in some vibrational frequencies. The triplet lifetimes of the Rh complexes were compared with those of the Cd and Ir complexes in the light of the effect of d..pi..* states. Zero-field (zf) ODMR signals of the /sup 3/..pi pi..*Rh complexes were observed, and triplet sublevel properties, such as zf splittings (zfs) and radiative and nonradiative decay rate constants, were obtained. Very interestingly, small zfs (3-5 GHz) were observed, contrary to previous estimates. Rationalization of this observation is given. On the basis of the obtained data they discuss the structures, zf schemes, and radiative and nonradiative mechanisms in the /sup 3/..pi pi..* Rh complexes.

Komada, Y.; Yamauchi, S.; Hirota, N.

1986-11-20

273

Studies of low-lying triplet states in 1,3-C4F6, c-C4F6 and 2-C4F6 by electron energy-loss spectroscopy and ab initio calculations  

NASA Astrophysics Data System (ADS)

This Letter reports on the first measurements of the lowest lying triplet states as studied by electron energy loss spectroscopy for C4F6 isomers, hexafluoro-1,3-butadiene (1,3-C4F6), hexafluorocyclobutene (c-C4F6) and hexafluoro-2-butyne (2-C4F6). This study has been performed at an incident electron energy of 30 eV, 30°, whilst sweeping the energy loss over the range 2.0-15.0 eV. The electronic state spectroscopy has been investigated and the assignments supported by multi-reference quantum chemical calculations. The transition to the steepest electronic excited potential energy curve, is suggested to be dominant for 2-C4F6, due to the large broadening in its energy profile.

Limão-Vieira, P.; Duflot, D.; Anzai, K.; Kato, H.; Hoshino, M.; Silva, F. Ferreira da; Mogi, D.; Tanioka, T.; Tanaka, H.

2013-06-01

274

In-Gap Spin Excitations and Finite Triplet Lifetimes in the Dilute Singlet Ground State System SrCu{sub 2-x}Mg{sub x}(BO{sub 3}){sub 2}  

SciTech Connect

High resolution neutron scattering measurements on a single crystal of SrCu{sub 2-x}Mg{sub x}(BO{sub 3}){sub 2} with x{approx}0.05 reveal the presence of new spin excitations within the gap of this quasi-two-dimensional, singlet ground state system. The application of a magnetic field induces Zeeman-split states associated with S=1/2 unpaired spins which are antiferromagnetically correlated with the bulk singlet. Substantial broadening of both the one- and two-triplet excitations in the doped single crystal is observed, as compared with pure SrCu{sub 2}(BO{sub 3}){sub 2}. Theoretical calculations using a variational algorithm and a single quenched magnetic vacancy on an infinite lattice are shown to qualitatively account for these effects.

Haravifard, S.; Dunsiger, S. R.; Dabkowska, H. A. [Department of Physics and Astronomy, McMaster University, Hamilton, Ontario L8S 4M1 (Canada); El Shawish, S. [J. Stefan Institute, SI-1000 Ljubljana (Slovenia); Gaulin, B. D. [Department of Physics and Astronomy, McMaster University, Hamilton, Ontario L8S 4M1 (Canada); Canadian Institute for Advanced Research, 180 Dundas Street W, Toronto, Ontario M5G 1Z8 (Canada); Telling, M. T. F.; Perring, T. G. [Rutherford Appleton Laboratory, ISIS Pulsed Neutron Facility, Chilton, Didcot, Oxon OX110QX (United Kingdom); Bonca, J. [J. Stefan Institute, SI-1000 Ljubljana (Slovenia); Faculty of Mathematics and Physics, University of Ljubljana, SI-1000 Ljubljana (Slovenia)

2006-12-15

275

Determination of Relative Triplet Sublevel Populating Rates during Optical Pumping Using ODMR  

Microsoft Academic Search

A method is introduced, based on optical detection of triplet state magnetic resonance (ODMR), to determine the relative populating rates of photoexcited triplet state sublevels during optical pumping. Phosphorescence transients induced by microwave rapid passage during optical pumping are analyzed globally utilizing kinetic parameters obtained from separate microwave-induced delayed phosphorescence measurements to obtain relative sublevel populating rates. Results are unaffected

Andrzej Ozarowski; August H. Maki

2001-01-01

276

Alternative source of emissive CIDEP in the TREPR spectra of benzophenone in alcohols  

NASA Astrophysics Data System (ADS)

The flash photolysis EPR spectra of benzophenone (BP) in alcoholic solvents differ in terms of their chemically induced dynamic electron polarization (CIDEP) signatures when BP is photo-excited at different laser wavelengths. The difference is strongly dependent upon the concentration of BP and is attributed to the reaction of two BP triplet states to form a BP radical anion, BP radical cation pair which occurs on a timescale sufficiently rapid relative to relaxation in the BP triplet to transfer polarization into the resulting radicals. This polarized signal dominates the spectrum obtained by 266 nm photo-excitation due to the much larger extinction coefficient of BP at this wavelength.

Jones, Alex R.; Woodward, Jonathan R.

2006-05-01

277

Enhanced photovoltaic response of organic solar cell by singlet-to-triplet exciton conversion  

Microsoft Academic Search

Ir complex was doped to conjugated polymers, and the photoinduced absorption of triplet excitons in host materials was examined. A greatly enhanced intersystem crossing rate was observed, despite the decrease in triplet exciton lifetime. The authors find that the steady-state triplet exciton population in host polymer would increase by an order of magnitude. Conjugated polymer\\/colloidal CdSe nanocrystal hybrid solar cells

Chia-Ming Yang; Chi-Hui Wu; Hua-Hsin Liao; Kuei-Yuan Lai; Hong-Ping Cheng; Sheng-Fu Horng; Hsin-Fei Meng; Jow-Tsong Shy

2007-01-01

278

Symmetry breaking gives rise to energy spectra of three states of matter  

PubMed Central

A fundamental task of statistical physics is to start with a microscopic Hamiltonian, predict the system's statistical properties and compare them with observable data. A notable current fundamental challenge is to tell whether and how an interacting Hamiltonian predicts different energy spectra, including solid, liquid and gas phases. Here, we propose a new idea that enables a unified description of all three states of matter. We introduce a generic form of an interacting phonon Hamiltonian with ground state configurations minimising the potential. Symmetry breaking SO(3) to SO(2), from the group of rotations in reciprocal space to its subgroup, leads to emergence of energy gaps of shear excitations as a consequence of the Goldstone theorem, and readily results in the emergence of energy spectra of solid, liquid and gas phases.

Bolmatov, Dima; Musaev, Edvard T.; Trachenko, K.

2013-01-01

279

Surface states in the optical spectra of two-dimensional photonic crystals with various surface terminations  

NASA Astrophysics Data System (ADS)

Reflection and transmission spectra of two-dimensional photonic crystal slabs, fabricated by photoelectrochemical etching of deep macropores and trenches in Si, are investigated theoretically and experimentally. It is shown that the presence of an unstructured silicon interfacial layer between the air and the photonic crystal structure can give rise to surface (Tamm) states within the TE and TM photonic stop bands. In the presence of roughness of inner surfaces of air pores, the surface states show up as dips within the stop bands in the reflection spectrum. The calculated electromagnetic near-field distribution demonstrates the vortices between the upper pores at the frequency of the surface mode. The experimental reflection and transmission spectra are in a good agreement with theoretical calculations performed by the Fourier modal method in the scattering matrix form.

Dyakov, S. A.; Baldycheva, A.; Perova, T. S.; Li, G. V.; Astrova, E. V.; Gippius, N. A.; Tikhodeev, S. G.

2012-09-01

280

The state of absorbed hydrogen in the structure of reduced copper chromite from the vibration spectra.  

PubMed

The reduction of copper chromite, CuCr(2)O(4), is followed by means of thermogravimetric analysis. The reduced state is studied by means of FT IR spectroscopy, Raman spectroscopy and inelastic neutron scattering. The reduction of copper occurs in two stages: absorption of hydrogen at 250-400 degrees C and dehydration of the reduced state at above 450 degrees C. The measured vibrational spectra prove that a considerable amount of hydrogen is absorbed by the oxide structure with absorbed protons stabilized in OH and HOH-groups (geminal protons). Three groups of vibration bands are observed in the INS spectra, which can be assigned to stretching, bending and libration vibrations. An increase in the reduction temperature of copper chromite results in softening of the stretching and hardening of the bending vibrations, what can be related to the strengthening of hydrogen bonding. PMID:19606318

Khassin, Alexander A; Kustova, Galina N; Jobic, Hervé; Yurieva, Tamara M; Chesalov, Yury A; Filonenko, Georgii A; Plyasova, Lyudmila M; Parmon, Valentin N

2009-05-13

281

A comparison of solution and solid state electronic absorption spectra of pyridinium iodides  

Microsoft Academic Search

Summary Charge-transfer (CT) absorption spectra from CH2C12 solutions and Nujol mulls of a variety of pyridinium iodides have been compared. Factors such as hand grindings vs. mechanical milling, milling time, and support medium were examined with respect to effects on the position of the absorption bands in the solid state. Generally, the position of the low energy CT band appeared

Edward J. Poziomek; Raymond A. Mackay; Thaddeus J. Novak

1974-01-01

282

[C70] Fullerene-sensitized triplet-triplet annihilation upconversion.  

PubMed

We herein report the first instance of using pristine C70 as a heavy-atom free organic sensitizer for efficient triplet-triplet annihilation upconversion (UC) for both green-to-blue and red-to-green UC using 9,10-bis(phenylethynyl)anthracene and perylene as acceptors, respectively. C70 achieved quantum yields of 8% and 0.8% for green-to-blue and red-to-green UC, 25 to 35 times higher than C60, and showed improved stability under continuous laser irradiation compared to the benchmark platinum(ii)-octaethylporphyrin. PMID:24121743

Moor, Kyle; Kim, Jae-Hyuk; Snow, Samuel; Kim, Jae-Hong

2013-10-24

283

Sensitized phosphorescence excitation spectra of complexes of glyoxal, pyrazine, and phenol. Great enhancement of phosphorescence yield by complexation  

SciTech Connect

The sensitized phosphorescence excitation spectra of various complexes of glyoxal (small molecule limit), pyrazine (intermediate case), and phenol (statistical limit) prepared by supersonic expansion were observed simultaneously with the fluorescence excitation spectra. A great enhancement of the phosphorescence yield by the complexation was observed for the first time. The enhancement was found to be due to the vibrational predissociation of the complex within its triplet state.

Goto, A.; Fujii, M.; Mikami, N.; Ito, M.

1986-05-22

284

Triplet-relaxation microscopy with bunched pulsed excitation.  

PubMed

Obtaining high signal levels in fluorescence microscopy is usually spoiled by the concomitant population of the dark (triplet) state of the marker, which is often followed by photobleaching. Recently, we introduced the triplet relaxation (T-Rex) modality in fluorescence microscopy which led to a major increase in total signal and dye photostability. The idea behind T-Rex is to avoid the illumination of fluorophores in the triplet state, e.g. by using pulsed excitation with interpulse time distances that are long enough for the triplet state to relax between two pulses. While our previous implementation came at the expense of extended recording, here we investigate pulsed excitation patterns for T-Rex illumination implying shorter total recording times. In particular, we balance signal enhancement and imaging speed by exciting with bunches of quickly succeeding pulses that are separated by dark periods for triplet relaxation. Taking the green fluorescent protein and the organic dye Atto532 as examples, we observe the dependence of photobleaching and total fluorescence gain on the number of pulses within a bunch. Reaching almost T-Rex conditions this excitation scheme mimics fast scanning of the illumination beam and has the potential to improve a whole range of analytical tools that suffer from photobleaching and low signal levels. PMID:19337661

Donnert, Gerald; Eggeling, Christian; Hell, Stefan W

2009-03-09

285

Excited states and absorption spectra of ?-diketonate complexes of boron difluoride with aromatic substituents  

NASA Astrophysics Data System (ADS)

In the approximation of the time-dependent electron density functional theory, we have studied using the quantum-chemical method the nature of excited states of boron difluoride acetylacetonate F2BAA and its substituted derivatives that contain aromatic groups with one or two benzene cycles in the ?-position. Optimization of the geometry of complexes show coplanar positions of cycles for all compounds, except for that with the substituent C6H3(CH3)2. Based on the calculated transition energies and oscillator strengths, we have simulated the absorption spectra in the prevacuum range. The calculated absorption spectra have been compared with the experimental spectra in the gas phase or in solutions. We show that, in the absorption spectra of complexes that contain substituents with one benzene cycle, the first three bands are caused by the transition of ? electrons of the substituent to the LUMO of the chelate cycle. In complexes with two cycles in the substituent, the number of these transitions increases to five. As the ? system becomes more extended, a bathochromic shift of the first absorption band and an increase in the transition probability are observed.

Vovna, V. I.; Kazachek, M. V.; L'vov, I. B.

2012-04-01

286

Pairing Fluctuation Effects on the Single-Particle Spectra for the Superconducting State  

NASA Astrophysics Data System (ADS)

Single-particle spectra are calculated in the superconducting state for a fermionic system with an attractive interaction, as functions of temperature and coupling strength from weak to strong. The fermionic system is described by a single-particle self-energy that includes pairing-fluctuation effects in the superconducting state. The theory reduces to the ordinary BCS approximation in weak coupling and to the Bogoliubov approximation for the composite bosons in strong coupling. Several features of the single-particle spectral function are shown to compare favorably with experimental data for cuprate superconductors.

Pieri, P.; Pisani, L.; Strinati, G. C.

2004-03-01

287

The 2 1A 1 state of cis-hexatriene vapor: Resonance Raman spectra  

NASA Astrophysics Data System (ADS)

Raman spectra have been obtained on resonance with the 2 1A 1 state of room temperature cis-1,3,5-hexatriene vapor at 290.8 nm. Overtones and combination bands of totally symmetric stretching and bending modes, both alone and in combination with an interval probably assignable as the overtone of the lowest frequency skeletal bending mode of b 1 symmetry, are strongly enhanced. Vibrational intervals tentatively assigned to the a 2 and b 2 methylene torsions are also observed, consistent with a large change in the force constant for ?CH 2 twisting in the 2 1A 1 state.

Westerfield, Curtis; Myers, Anne B.

1993-01-01

288

Rotationally resolved photoelectron spectra in resonance enhanced multiphoton ionization of Rydberg states of NH  

SciTech Connect

Results of combined theoretical and experimental studies of photoelectron spectra resulting from (2+1) resonance enhanced multiphoton ionization (REMPI) via the {ital f} {sup 1}{Pi}(3{ital p}{sigma}), {ital g} {sup 1}{Delta}(3{ital p}{pi}), and {ital h} {sup 1}{Sigma}{sup +}(3{ital p}{pi}) Rydberg states of NH are reported. The overall agreement between these calculated and measured spectra is encouraging. Strong {Delta}{ital N}={ital N}{sup +}{minus}{ital N}{prime}=even peaks, particularly for {Delta}{ital N}=0, are observed in these spectra. Low-energy Cooper minima are predicted to occur in the l=2 wave of the {ital k}{pi}({sup 1}{Sigma}{sup +}), {ital k}{pi}({sup 1}{Sigma}{sup {minus}}), and {ital k}{pi}({sup 1}{Delta}) photoelectron channels for the {ital f} state, the {ital k}{pi}({sup 1}{Delta}), {ital k}{delta}({sup 1}{Pi}), and {ital k}{delta}({sup 1}{Phi}) channels for the {ital g} state, and the {ital k}{pi}({sup 1}{Sigma}{sup +}) and {ital k}{delta}({sup 1}{Pi}) channels for the {ital h} state of NH. Depletion of the {ital d} wave (l=2) contributions to the photoelectron matrix element in the vicinity of these Cooper minima subsequently enhances the relative importance of the odd l waves. The observed {Delta}{ital N} transitions are also affected by strong l mixing in the electronic continuum induced by the nonspherical molecular potential. Interference of continuum waves between degenerate ionization channels also determines the spectral pattern observed for photoionization of the {ital f} {sup 1}{Pi} state of NH. Photoelectron angular distributions and the angular momentum compositions of photoelectron matrix elements provide further insight into the origin of these Cooper minima.

Wang, K.; Stephens, J.A.; McKoy, V. (Arthur Amos Noyes Laboratory of Chemical Physics, California Institute of Technology, Pasadena, California 91125 (United States)); de Beer, E.; de Lange, C.A.; Westwood, N.P.C. (Laboratory for Physical Chemistry, University of Amsterdam, Nieuwe Achtergracht 127, 1018 WS Amsterdam (Netherlands))

1992-07-01

289

The dissociation mechanism of triplet formaldehyde  

NASA Astrophysics Data System (ADS)

Results are reported from theoretical calculations, using ab initio molecular electronic structure theory, of the height of the barrier against radical dissociation for the lowest triplet state of formaldehyde. The procedures and flexible basis sets employed are described, and the predictions are presented in extensive tables and discussed in detail. The barrier at temperature 0 K is found to be 7.8 kcal/mol when the zero-point vibrational-energy correction is applied, in relatively good agreement with the experimental values (2.9-6.0 kcal/mol) obtained by Chuang et al. (1987). The applicability of these studies to atmospheric chemistry is briefly indicated.

Yates, Brian F.; Yamaguchi, Yukio; Schaefer, Henry F., III

1990-12-01

290

Photophysics of the triple state of metal complexes of 9-anthracenecarboxylic acid  

Microsoft Academic Search

The triplet-triplet (T-T) absorption spectra and the T-T absorption decay kinetics are measured for solutions of 9-anthracenecarboxylic\\u000a acid (ACA) and its complexes with metal ions (Cd3+ and Ln3+=Y3+, La3+, Ce3+, Eu3+, Gd3+, and Tb3+) in dimethylsulfoxide (DMSO) by the methods of flashlamp and laser pulse photolysis. The rate constants k\\u000a T of intracomplex quenching of the triplet state are measured

T. A. Shakhverdov; R. Érgashev

2001-01-01

291

Low/Hard State Spectra of GRO J1655-40 Observed with Suzaku  

NASA Astrophysics Data System (ADS)

The Galactic black-hole binary GROJ1655-40, a source harboring superluminal jets, was observed with Suzaku on 2005 September 22-23. The source was detected over a broad and continuous energy range of 0.7-300keV, with an intensity of ˜50mCrab at 20keV. At a distance of 3.2kpc, the 0.7-300keV luminosity was ˜5.2 × 1036 ergs-1 (˜0.7% of the Eddington luminosity for a 6Modot black hole). The source was in a typical low/hard state, exhibiting a power-law shaped continuum with a photon index of ˜1.6. During the observation, the source intensity gradually decreased by 25% at energies above ˜3keV, and by 35% below 2keV. This, together with the soft X-ray spectra taken with the X-ray Imaging Spectrometer (XIS), suggests the presence of an independent soft component that can be represented by emission from a cool (˜0.2keV) disk. The hard X-ray spectra obtained with the Hard X-ray Detector reveal a high-energy spectral cutoff, with an e-folding energy of ˜200keV. The entire 0.7-300keV spectrum cannot be reproduced by a single thermal Comptonization model, even when considering reflection effects. Instead, the spectrum (except the soft excess) can be successfully explained by invoking two thermal-Comptonization components with different y-parameters. In contrast to the high/soft state spectra of this object, in which narrow iron absorption lines are detected with equivalent widths of 60-100eV, the present XIS spectra bear no such features beyond an upper-limit equivalent width of 23eV.

Takahashi, Hiromitsu; Fukazawa, Yasushi; Mizuno, Tsunefumi; Hirasawa, Ayumi; Kitamoto, Shunji; Sudoh, Keisuke; Ogita, Takayuki; Kubota, Aya; Makishima, Kazuo; Itoh, Takeshi; Parmar, Arvind N.; Ebisawa, Ken; Naik, Sachindra; Dotani, Tadayasu; Kokubun, Motohide; Ohnuki, Kousuke; Takahashi, Tadayuki; Yaqoob, Tahir; Angelini, Lorella; Ueda, Yoshihiro; Yamaoka, Kazutaka; Kotani, Taro; Kawai, Nobuyuki; Namiki, Masaaki; Kohmura, Takayoshi; Negoro, Hitoshi

2008-01-01

292

Direct Observation of Efficient Triplet--Triplet Energy Transfer in Phosphorescent Organic Light-Emitting Diode  

NASA Astrophysics Data System (ADS)

We report on the energy transfer mechanism between the host and the iridium dopant in phosphorescent organic light-emitting diodes (PHOLEDs). The excited-state energies of the host and the dopant are carefully defined to discuss the energy transfer. The PHOLED using bis(benzo[h]quinolin-10-olato-kN,kO)beryllium(II) (Bebq2) as the host and bis(4-pentafluorophenyl-2-phenylpyridine)(acetylacetonate)iridium(III) (m-PF-py) as the dopant shows a maximum external quantum efficiency (?ext) of about 15%, whereas the photoluminescence quantum yield of the emitting layer film is only 19%. The high ?ext of the PHOLED implies efficient triplet--triplet energy transfer from Bebq2 to m-PF-py.

Fukagawa, Hirohiko; Shimizu, Takahisa; Osada, Yoshichika; Kamada, Taisuke; Kiribayashi, Yukihiro; Yamamoto, Toshihiro; Shimidzu, Naoki

2013-05-01

293

Unified analysis of noncomparative methods for measuring the molar absorptivity of triplet-triplet transitions  

SciTech Connect

Noncomparative techniques for the measurement of the molar absorptivity of triplet-triplet absorption transitions, epsilon/sub T/*, are reviewed. The methods covered include singlet depletion, total depletion, intensity variation (and its pulsed analog), partial saturation, and the so-called kinetic method. A critical analysis of the conceptual foundations of these varied approaches is performed. The fundamental equations of each technique are derived from a general three-state kinetic model of excitation and decay. From this unified approach it becomes very clear where assumptions are made in the traditional derivations of the methods. Additionally, one comparative method, that termed relative actinometry, is discussed, since it may be treated in a unimolecular fashion consistent with the above approach. The only major epsilon/sub T/* method excluded from this review is that involving intermolecular energy transfer, a technique which has been thoroughly documented elsewhere.

Carmichael, I.; Hug, G.L.

1987-08-01

294

Chlorophyll triplet quenching by fucoxanthin in the fucoxanthin-chlorophyll protein from the diatom Cyclotella meneghiniana.  

PubMed

In this work we present an optically detected magnetic resonance (ODMR) study on the triplet states populated under illumination in the isolated fucoxanthin-chlorophyll light-harvesting complex from the diatom Cyclotella meneghiniana. Evidence for the quenching of chlorophyll triplet states by fucoxanthin is provided, showing that this carotenoid is able to perform the photoprotective role. For the first time, the magnetic parameters characterizing the fucoxanthin triplet state have been determined. The results reveal analogies but also differences with respect to the triplet-triplet energy transfer process, which involves chlorophylls a and carotenoids in the LHC complex from dinoflagellates and LHCII from higher plants. The degree of efficiency of the photoprotection mechanism, in these light harvesting complexes, is discussed in terms of pigment-protein structure. PMID:23026044

Di Valentin, Marilena; Büchel, Claudia; Giacometti, Giorgio Mario; Carbonera, Donatella

2012-09-28

295

Anorexia Nervosa in Identical Triplets  

Microsoft Academic Search

The cause of anorexia nervosa (AN) is unclear, but is likely multifactorial, including psychological, familial, environmental, societal, genetic, and other biological factors. This case report of identical 12- year-old female triplets simultaneously concordant for AN illustrates the importance of addressing all these components in evaluation and treatment, and the difficulty of determining the relative impor- tance of each factor in

Mae S. Sokol; Anna K. Carroll; Denise M. Heebink; Kristina M. Hoffman-Rieken; Christine S. Goudge; Douglas D. Ebers

296

Colour triplet-valued wavelets and splines  

Microsoft Academic Search

The concept of colour and and multispectral image recognition connects all the topics we are considering. Colour (multispectral) image processing is investigated using an algebraic approach based on triplet numbers. In the algebraic approach, each image element is considered not as a 3D vector, but as a triplet number. The main goal of the paper is to show that triplet

Valeri Labunets; Alexei Maidan; Ekaterina Labunets-Rundblad; Jaakko Astola

2001-01-01

297

Spin relaxation at the singlet-triplet crossing in a quantum dot  

NASA Astrophysics Data System (ADS)

We study spin relaxation in a two-electron quantum dot in the vicinity of the singlet-triplet crossing. The spin relaxation occurs due to a combined effect of the spin-orbit, Zeeman, and electron-phonon interactions. The singlet-triplet relaxation rates exhibit strong variations as a function of the singlet-triplet splitting. We show that the Coulomb interaction between the electrons has two competing effects on the singlet-triplet spin relaxation. One effect is to enhance the relative strength of spin-orbit coupling in the quantum dot, resulting in larger spin-orbit splittings and thus in a stronger coupling of spin to charge. The other effect is to make the charge density profiles of the singlet and triplet look similar to each other, thus diminishing the ability of charge environments to discriminate between singlet and triplet states. We thus find essentially different channels of singlet-triplet relaxation for the case of strong and weak Coulomb interactions. Finally, for the linear in momentum Dresselhaus and Rashba spin-orbit interactions, we calculate the singlet-triplet relaxation rates to leading order in the spin-orbit interaction and find that they are proportional to the second power of the Zeeman energy, in agreement with recent experiments on triplet-to-singlet relaxation in quantum dots.

Golovach, Vitaly N.; Khaetskii, Alexander; Loss, Daniel

2008-01-01

298

Equilibrium structure and anharmonic potential function of phosgene: Microwave spectra of vibrationally excited states  

NASA Astrophysics Data System (ADS)

The vibrational satellites in the microwave spectra of 35Cl2CO were measured and analyzed for the ?2, ?3, 2?3, ?4, ?5, ?6, and ?2 + ?3 states. The rotational constants for the ?5 state were first estimated by an analysis of anharmonic potential constants derived from the available rotational constants for the other excited states and other isotopic species and the electron diffraction intensity, and used for the assignment of its weak satellites. The Coriolis resonance between ?2 and ?4 was analyzed, and the difference in their wavenumbers, ?~4 - ?~2 = 9.553(3) cm-1, was obtained. The sign of the perturbation (positive) was determined using the infrared band envelope.

Yamamoto, Satoshi; Nakata, Munetaka; Sugie, Masaaki; Takeo, Harutoshi; Matsumura, Chi; Kuchitsu, Kozo

1984-06-01

299

Action Spectra of Photosystems I and II in State 1 and State 2 in Intact Sugar Maple Leaves.  

PubMed Central

Photochemical activity, measured as energy storage of photosystems I (PSI) and II (PSII) together and individually, is studied in sugar maple (Acer saccharum Marsh.) leaves in the spectral range between 400 and 700 nm in state 1 and state 2. Total photochemical activity remains the same in both state 1 and state 2 between 580 and 700 nm, but it is lower in state 2 between 400 and 580 nm. Both PSI and PSII activities change significantly during the state transition due to the migration of light-harvesting chlorophyll a/b protein complex of PSII (LHCII). In the action spectra of PSI and PSII, peak positions vary depending on the association or dissociation of LHCII, except for the peak at 470 nm in the PSII spectrum. PSII activity is about 3 times higher than or equal to PSI in state 1 or state 2, respectively, over most of the spectrum except in the blue and far-red regions. At 470 nm, PSII activity is 8 or 1.6 times higher than PSI in state 1 or state 2, respectively. The amplitude of LHCII coupling-induced change is the same in both PSI and PSII between 580 and 700 nm, but it is less in PSI than in PSII between 400 and 580 nm, which explains the lower photochemical activity of the leaf in state 2 than in state 1. This may be due to a decrease in energy transfer efficiency of carotenoids to chlorophylls in LHCII when it is associated with PSI.

Veeranjaneyulu, K.; Leblanc, R. M.

1994-01-01

300

Two-dimensional electronic spectra of symmetric dimers: Intermolecular coupling and conformational states  

NASA Astrophysics Data System (ADS)

We study the information content of two-dimensional (2D) electronic photon-echo (PE) spectra, with special emphasis on their potential to distinguish, for waiting times T=0, between different conformations of electronically coupled symmetric dimers. The analysis is performed on the basis of an analytical formula for the frequency-domain 2D PE signal. The symmetric dimers are modeled in terms of two identical, energy-degenerate, excitonically coupled pairs of electronic states in the site representation. The spectra of conformationally weighted ensembles, composed of either two or four dimers, are compared with their one-dimensional linear absorption counterparts. In order to provide a realistic coupling pattern for the ensemble consisting of four dimers, excitonic couplings are estimated on the basis of optimized geometries and site-transition dipole moments, calculated by standard semiempirical methods for the bridged bithiophene structure 1,2-bithiophene-2-yl-ethane-1,2-dion (T2[CO]2). In the framework of our model, the highly readable 2D PE spectra can unambiguously identify spectral doublets, by relating peak heights and positions with mutual orientations of site-localized transition dipoles.

Szöcs, V.; Pálszegi, T.; Lukeš, V.; Sperling, J.; Milota, F.; Jakubetz, W.; Kauffmann, H. F.

2006-03-01

301

The effect of bulk magnetic susceptibility on solid state NMR spectra of paramagnetic compounds  

PubMed

The effect of bulk magnetic susceptibility (BMS) on solid state NMR spectra of paramagnetic compounds was investigated theoretically and experimentally. The BMS shift was calculated for cylindrical and spherocylinderical containers with some ratios of the length L and the diameter D. The results show the best resolution can be obtained by using a long cylindrical sample container with L/D > 10 and by exciting only the region near the center of the container. The effect of the random orientations and distributions of crystallites in a powder sample was also calculated according to a model proposed by Schwerk et al. [J. Magn. Reson. A 119, 157 (1996)] with removing the Fermi contact term from their model. Static and the magic-angle spinning 13C NMR spectra were recorded on two paramagnetic compounds of Ln(C2D5SO4)3 . 8H2O where Ln = Pr, Yb. The modified theory predicts the BMS broadening of the experimental spectra very well. Copyright 1998 Academic Press. PMID:9716476

Kubo; Spaniol; Terao

1998-08-01

302

Ground-state configurations and unresolved transition arrays in extreme ultraviolet spectra of lanthanide ions  

SciTech Connect

Theoretical ground-state configurations of lanthanide ions calculated with the Cowan suite of codes are presented. Theoretical 4d-4f and 4p-4d spectra of Pd-like to Rb-like lanthanide ions calculated using the relativistic flexible atomic code are also shown. The effects of configuration interaction are investigated, and the results compare favorably with experiments in which, for increasing nuclear charge, strong emission peaks are observed to move toward shorter wavelength. The application of these strong emitters as extreme ultraviolet radiation sources, a topic of emerging interest, is discussed.

Kilbane, D.; O'Sullivan, G. [School of Physics, University College Dublin, Belfield, Dublin 4 (Ireland)

2010-12-15

303

Unifying darko-lepto-genesis with scalar triplet inflation  

NASA Astrophysics Data System (ADS)

We present a scalar triplet extension of the standard model to unify the origin of inflation with neutrino mass, asymmetric dark matter and leptogenesis. In presence of non-minimal couplings to gravity the scalar triplet, mixed with the standard model Higgs, plays the role of inflaton in the early Universe, while its decay to SM Higgs, lepton and dark matter simultaneously generate an asymmetry in the visible and dark matter sectors. On the other hand, in the low energy effective theory the induced vacuum expectation value of the triplet gives sub-eV Majorana masses to active neutrinos. We investigate the model parameter space leading to successful inflation as well as the observed dark matter to baryon abundance. Assuming the standard model like Higgs mass to be at 125-126 GeV, we found that the mass scale of the scalar triplet to be ?O(109) GeV and its trilinear coupling to doublet Higgs is ?0.09 so that it not only evades the possibility of having a metastable vacuum in the standard model, but also lead to a rich phenomenological consequences as stated above. Moreover, we found that the scalar triplet inflation strongly constrains the quartic couplings, while allowing for a wide range of Yukawa couplings which generate the CP asymmetries in the visible and dark matter sectors.

Arina, Chiara; Gong, Jinn-Ouk; Sahu, Narendra

2012-12-01

304

TRIPLET EXCITONS AND DELAYED FLUORESCENCE IN ANTHRACENE CRYSTALS  

Microsoft Academic Search

Delayed fluorescence was detected in laser-induced fluorescence in ; anthracene single crystals after the laser pulse ended. The rate of decay of ; this fluorescence and other experimental observations was explained by assuming ; that the singlet state giving rise to the fluorescence is produced by a ; bimolecular annihilation of triplet excitons generated directly by the laser ; light.

R. G. Kepler; J. C. Caris; P. Avakian; E. Abramson

1963-01-01

305

Autocorrelation of ARPES Spectra in the Pseudogap State of the Underdoped Curpates  

NASA Astrophysics Data System (ADS)

It has long been known that the normal state of the underdoped cuprate high Tc superconductors is characterized by a pseudogap in the anti-nodal region of the Brillouin zone and a set of disconnected set of excitations at the chemical potential, in the nodal region, known as Fermi arcs. Recently, quantum oscillation and angle resolved photoemission spectroscopy (ARPES) experiments have indicated that these Fermi arcs actually represent one side of a Fermi surface reconstructed into nodal hole pockets. These pockets, as well as a number of consequences of their formation, have been shown to be well described by the phenomenological model of Yang Rice and Zhang (YRZ) for the single particle Green's function. Here, we show how the autocorrelation of ARPES spectra - so-called AC-ARPES -- acquired in the normal pseudogap state of the cuprates may be used to examine this phenomenon.

Rameau, Jonathan; Yang, Hongbo; Burton, Cherise; Kidd, Tim; Rice, Maurice; Johnson, Peter

2013-03-01

306

Influence of ground-state scattering properties on photoassociation spectra near the intercombination line of bosonic ytterbium  

SciTech Connect

We study theoretically the properties of photoassociation spectra near the {sup 1}S{sub 0}-{sup 3}P{sub 1} inter-combination line of bosonic ytterbium. We construct a mass scaled model of the excited state interaction potential that well describes bound state energies obtained in a previous photoassociation experiment. We then use it to calculate theoretical photoassociation spectra in a range of ultracold temperatures using semianalytical theory developed by Bohn and Julienne.Photoassociation spectra not only give us the energies of excited bound states, but also provide information about the behavior of the ground state wavefunction. In fact, it can be shown that within the so-called reflection approximation the line intensity is proportional to the ground state wavefunction at the transition's Condon point. We show that in the case of ytterbium, the rotational structure of the photoassociation spectra depends heavily on the behavior of the ground-state wavefunction. The change of the scattering length from one isotope to another and the resulting occurence of shape resonances in higher partial waves determines the appearance and disapperance of rotational components, especially in the deeper lying states, whose respective Condon points lie near the ground state centrifugal barrier. Thus, photoassociation spectra differ qualitatively between isotopes.

Borkowski, M.; Ciurylo, R. [Instytut Fizyki, Uniwersytet Mikolaja Kopernika, ul. Grudziadzka 5/7, 87-100 Torun (Poland); Julienne, P. S. [Joint Quantum Institute, National Institute of Standards and Technology and University of Maryland, 100 Bureau Drive, Stop 8423, Gaithersburg, Maryland 20899-8423 (United States); Tojo, S. [Department of Physics, Faculty of Science, Gakushuin University, Tokyo 171-8588 (Japan); Enomoto, K. [Department of Physics, University of Toyama, 3190 Gofuku, Toyama 930-8555 (Japan); Takahashi, Y. [Department of Physics, Graduate School of Science, Kyoto University, Kyoto 606-8502 (Japan)

2010-10-29

307

Excited-state properties of nucleic acid components  

NASA Astrophysics Data System (ADS)

Measurements were made of the fluorescence and phosphorescence spectra and lifetimes, and also of the absorption spectra, lifetimes, extinction coefficients, and quantum yields of the T1 lower triplet states of thymine, uracil, their N, N'-dimethyl derivatives, thymidine, thymidine monophosphate, uridine, and uridine monophosphate in various solvents at 300 °K. The influence of the solvent on the quantum yield of the T1 state of nucleic acid components is discussed.

Salet, C.; Bensasson, R. V.; Becker, R. S.

1981-12-01

308

Triplet Transport to and Trapping by Acceptor End Groups on Conjugated Polyfluorene Chains  

SciTech Connect

Triplet excited states created in polyfluorene (pF) molecules having average lengths up to 170 repeat units were transported to and captured by trap groups at the ends in less {approx}40 ns. Almost all of the triplets attached to the chains reached the trap groups, ruling out the presence of substantial numbers of defects that prevent transport. The transport yields a diffusion coefficient D of at least 3 x 10{sup -4} cm{sup 2} s{sup -1}, which is 30 times typical molecular diffusion and close to a value for triplet transport reported by Keller (J. Am. Chem. Soc.2011, 133, 11289-11298). The triplet states were created in solution by pulse radiolysis; time resolution was limited by the rate of attachment of triplets to the pF chains. Naphthylimide (NI) or anthraquinone (AQ) groups attached to the ends of the chains acted as traps for the triplets, although AQ would not have been expected to serve as a trap on the basis of triplet energies of the separate molecules. The depths of the NI and AQ triplet traps were determined by intermolecular triplet transfer equilibria and temperature dependence. The trap depths are shallow, just a few times thermal energy for both, so a small fraction of the triplets reside in the pF chains in equilibrium with the end-trapped triplets. Trapping by AQ appears to arise from charge transfer interactions between the pF chains and the electron-accepting AQ groups. Absorption bands of the end-trapped triplet states are similar in peak wavelength (760 nm) and shape to the 760 nm bands of triplets in the pF chains but have reduced intensities. When an electron donor, N,N,N',N'-tetramethyl-p-phenylenediamine (TMPD), is added to the solution, it reacts with the end-trapped triplets to remove the 760 nm bands and to make the trapping irreversible. New bands created upon reaction with TMPD may be due to charge transfer states.

Sreearunothai, P.; Miller, J.; Estrada, A.; Asaoka, S.; Kowalczyk, M.; Jang, S.; Cook, A.R.; Preses, J.M.

2011-08-31

309

Chimpanzee triplets born in captivity  

Microsoft Academic Search

A female chimpanzee (Pan troglodytes) gave birth to triplets at the Lincoln Park Zoological Gardens, Chicago, Illinois. Of the three infants born, only one survived.\\u000a The other two, both sexed as males, were dead when they were discovered. When pathology was done on these infants, it was\\u000a found that aside from being underweight, chimpanzee No. 1 was 930 g and

Mark A. Rosenthal; Lhtcobt Park Zoological Gardens

1981-01-01

310

Observation of Singlet-Triplet Transitions in Capacitive Photocurrent Spectroscopy of Organic Solar Cells  

NASA Astrophysics Data System (ADS)

Fullerene derivatives such as [6,6]-phenyl-C61-butyric acid methyl ester (PC60BM) and [6,6]-phenyl-C71-butyric acid methyl ester (PC70BM) are promising electron acceptors for use in efficient organic solar cells. Capacitive photocurrent spectra of both PC60BM and PC70BM in conjunction with indium tin oxide (ITO) reveal peaks with wavelengths longer than the S_1 ?S_0 transitions. The energies of low-lying triplet states of both molecules calculated using the ZINDO/S method agree with the experimentally observed transition frequencies. An excitation mechanism that involves collisions between the photoinduced free electrons in ITO and the organic molecules on the interface is proposed to explain the experimental observation. Tests on other organic solar cells are in process. Possibilities of improving the conversion efficiency of organic solar cells utilizing this mechanism will be discussed. Hemant M. Shah and Bruce W. Alphenaar, unpublished result.

Liu, Hui; Liu, Jinjun; Shah, Hemant M.; Alphenaar, Bruce W.

2012-06-01

311

Laser flash photolysis study of paraquat reduction by photogenerated aromatic ketyl radicals and carbonyl triplets  

SciTech Connect

Results of a kinetic study based on 337.1-nm laser flash photolysis are presented for electron-transfer reactions with paraquat (PQ/sup 2 +/) as the oxidant for the triplets of a number of substituted benzophenones and acetophenones and the corresponding ketyl radicals. The ketyl radicals were generated from the ketone triplets by laser flash photolysis in the presence of excess of p-methoxyphenol. The electron-transfer rate constants (2 x 10/sup 8/-8 x 10/sup 9/ M/sup -1/ s/sup -1/) as well as the fractions (0.5-1.0) of the triplet quenching events that result in net reduction of PQ/sup 2 +/ correlate well with the electron-releasing nature of the substituents in the ketones. Quantitative data concerning the transient absorption spectra of substituted benzophenone triplets and diarylhydroxymenthyl radicals are also reported. 5 figures, 1 table.

Baral-Tosh, S.; Chattopadhyay, S.K.; Das, P.K.

1984-03-29

312

Theoretical study of the photochemical generation of triplet acetophenone.  

PubMed

Acetophenone has a rich photochemistry, which strongly depends on the absorbing state. For example, the excitation to the lowest singlet excited state (S1) leads to a triplet population with a phosphorescence quantum yield of one, while the excitation to S2 leads to photocleavage reactions. Here, we rationalize the photochemistry of acetophenone after being absorbed into the S1, S2 and S3 states by performing a systematic study of all the singlet and triplet minimum energy structures and state crossings between the relevant electronic states. We calculate these structures at the complete-active space self-consistent field (CASSCF) level of theory and at the correlated extended second-order quasi-degenerate multi-reference perturbation theory (XMCQDPT2), emphasizing the importance of correlation effects in the determination of structures. PMID:24113419

Huix-Rotllant, Miquel; Siri, Didier; Ferré, Nicolas

2013-10-23

313

Photosensitization of triplet carotenoid in photosynthetic light-harvesting complex of photosystem II  

SciTech Connect

A laser photolysis study, on the nanosecond time scale, has been carried out on the major light-harvesting chlorophyll-protein complex of photosystem II (LHC II..beta..). The transient triplet absorption of the isolated LHC II..beta.. has been compared to those of its constituent chromophores in dilute micellar aqueous solutions, namely, chlorophyll a, chlorophyll b, chlorophyll a + chlorophyll b, and chlorophyll a + ..beta..-carotene. The results indicate that the carotenoid in the LHC II..beta.. is photosensitized by triplet chlorophyll a and that the decay of the transient triplet absorption exhibits two transients, one in the approx. 50-ns range and the other in the approx. 10..mu..s time scales. The former transient is light-intensity dependent and is attributed to an annihilation process between two triplets of chlorophyll a, while the latter is due to the decay of the triplet carotenoid to its ground state.

Nechushtai, R.; Thornber, J.P.; Patterson, L.K.; Fessenden, R.W.; Levanon, H.

1988-03-10

314

Competition between Singlet and Triplet Superconductivity in the Extended Hubbard Model with Exchange Interaction on a Square Lattice  

NASA Astrophysics Data System (ADS)

Phase boundary between spin singlet and triplet superconductivity in the extended Hubbard model with exchange interaction on a square lattice is calculated within meanfield approximation. Basically, antiferromagnetic exchange interaction J is advantageous for the singlet pairing, while ferromagnetic J prefers the triplet pairing. When off-site interaction V is repulsive, the singlet phase and the triplet phase are separated by normal state in the phase diagram against V and J. If V is effectively attractive, however, the singlet and triplet states can compete against each other. We calculate the phase boundary between singlet and triplet phase for various band filling. It is shown that the triplet phase penetrates rather deeply into antiferromagnetic exchange regime for lower band filling, whereas the penetration of the singlet phase is confined in a narrow range of ferromagnetic exchange regime.

Hori, Yoshiki; Goto, Akira

2012-12-01

315

A study of the density of gap states in amorphous semiconductors from thermostimulated conductivity spectra  

NASA Astrophysics Data System (ADS)

A theoretical analysis of thermostimulated conductivity spectra ?TSC( T) has been applied to determine the density of gap states g( E) in a-Si: H and a-Si: H/a-SiN x : H multilayer structures. The results for g( E) are consistent with the results deduced from Fritzsche's analytical approach as well as other methods. A comparison has been made between the two different analytical approaches for ?TSC( T). We discuss the relationship between the energy of maximum thermostimulated current emission E m and quasi-Fermi level E q. We demonstrate that E q could be a better parameter than E m in the general theoretical treatment of thermostimulated conductivity.

Zhu, Meifang

1991-05-01

316

Gas-phase Electronic Spectra of Polyacetylene Cations: Relevance of Higher Excited States  

NASA Astrophysics Data System (ADS)

Transitions to higher electronic states of polyacetylene cations (HC2n H+, n = 4, 5, 6) have been measured in the gas phase at ~20 K. The absorption spectra were obtained using a resonant two-color, two-photon fragmentation technique in an ion trap, allowing a direct comparison between laboratory and astrophysical data. The purpose was to investigate the relevance of such transitions to astronomical observations because the general expectation is that the bands could be too broad due to fast intramolecular processes. It is shown that the origin bands are still narrow enough (1-10 cm-1) to be considered, especially as the higher-lying transitions often possess large oscillator strengths.

Rice, C. A.; Rudnev, V.; Dietsche, R.; Maier, J. P.

2010-07-01

317

First-principles calculation of ground and excited-state absorption spectra of ruby and alexandrite considering lattice relaxation  

NASA Astrophysics Data System (ADS)

We performed first-principles calculations of multiplet structures and the corresponding ground-state absorption and excited-state absorption spectra for ruby (Cr3+:?-Al2O3) and alexandrite (Cr3+:BeAl2O4) which included lattice relaxation. The lattice relaxation was estimated using the first-principles total energy and molecular-dynamics method of the CASTEP code. The multiplet structure and absorption spectra were calculated using the configuration-interaction method based on density-functional calculations. For both ruby and alexandrite, the theoretical absorption spectra, which were already in reasonable agreement with experimental spectra, were further improved by consideration of lattice relaxation. In the case of ruby, the peak positions and peak intensities were improved through the use of models with relaxations of 11 or more atoms. For alexandrite, the polarization dependence of the U band was significantly improved, even by a model with a relaxation of only seven atoms.

Watanabe, Shinta; Sasaki, Tomomi; Taniguchi, Rie; Ishii, Takugo; Ogasawara, Kazuyoshi

2009-02-01

318

Perturbations in the Spectra of High Rydberg States: Channel Interactions, Stark and Zeeman Effects  

NASA Astrophysics Data System (ADS)

Rydberg states of principal quantum number n?50 have been prepared by irradiation of an atomic beam of xenon with vacuum ultraviolet (VUV) radiation. Narrowband submillimeter-wave (THz) radiation was then used to record spectra of transitions from these Rydberg states to higher or lower-lying Rydberg states. The transitions were detected by selective field ionization and recording either the electrons or the ions, the latter offering the advantage of mass selection. Rydberg states of high principal quantum number are extremely sensitive to their environment, which can be exploited to characterize the experimental conditions under which the spectroscopic measurements are carried out. The high resolution achieved in the experiments (better than 100 kHz) enabled the study of the spectral lineshapes and line positions in dependence of weak electric (down to below 100?V/cm) and magnetic fields (down to a few ?T), and of the density of Rydberg atoms and ions generated in the experimental volume. The experiments rely on the use of a pulsed, broadly tunable, laser-based source of THz radiation for survey scans, and of a phase- and frequency-stabilized submillimeter-wave backward-wave oscillator-based radiation source for precision measurements. To illustrate the use of these sources, we present the results of the spectroscopic investigations of the hyperfine structure of 129Xe Rydberg states in spectral regions where s-d interactions are expected to play a role. F. Merkt and A. Osterwalder Int. Rev. Phys. Chem. 21, 385, (2002). J. Liu and F. Merkt Appl. Phys. Lett. 93, 131105, (2008). M. Schäfer, M. Andrist, H. Schmutz, F. Lewen, G. Winnewisser and F. Merkt J. Phys. B: At. Mol. Opt. Phys. 39, 831, (2006).

Haase, Christa; Schäfer, Martin; Hogan, Stephen D.; Merkt, Frédéric

2011-06-01

319

X-ray transient absorption structural characterization of the 3MLCT triplet excited state of cis-[Ru(bpy)2(py)2]2+.  

PubMed

The excited state dynamics and structure of the photochemically active complex cis-[Ru(bpy)2(py)2](2+) have been investigated using optical transient absorption (OTA) and X-ray transient absorption (XTA) spectroscopy, and density functional theory (DFT). Upon light-excitation in aqueous solution cis-[Ru(bpy)2(py)2](2+) undergoes ultrafast dissociation of one pyridine ligand to form cis-[Ru(bpy)2(py)(H2O)](2+). OTA measurements highlighted the presence of two major time components of 1700 ps and 130 ps through which the system decays to the ground-state and evolves towards the photoproduct. XTA data were acquired after 150 ps, 500 ps, and 3000 ps from laser excitation (?exc = 351 nm) and provided the transient structure of the (3)MLCT state corresponding to the longer time component in the OTA experiment. In excellent agreement with DFT, XTA shows that the (3)MLCT geometry is characterized by an elongation of the dissociating Ru-N(py) bond and a shortening of the trans Ru-N(bpy) bond with respect to the ground state. Conversely, calculations show that the (3)MC state has a highly distorted structure with Ru-N(py) bonds between 2.77-3.05 Å. PMID:23474490

Borfecchia, Elisa; Garino, Claudio; Salassa, Luca; Ruiu, Tiziana; Gianolio, Diego; Zhang, Xiaoyi; Attenkofer, Klaus; Chen, Lin X; Gobetto, Roberto; Sadler, Peter J; Lamberti, Carlo

2013-05-14

320

Triplets: experience in a tertiary centre  

Microsoft Academic Search

ObjectivesTo review triplet pregnancies managed within a single tertiary centre.MethodA retrospective review of triplet pregnancies from 2004 to 2010 at Leeds General Infirmary.ResultsThere were 17 sets of triplets: 9 trichorionic; 5 monochorionic diamniotic with a singleton and 3 monochorionic. 1 patient accepted reduction, 1 pregnancy spontaneously reduced and 1 abrupted at 22 weeks. 1 patient developed twin to twin transfusion

M Rathod; E Ferriman

2010-01-01

321

Vibrational Spectra and Structure of Tetramethyldiarsine in the Crystalline and Fluid States  

Microsoft Academic Search

The infrared spectra of solid and gaseous tetramethyldiarsine have been recorded from 4000 to 33 cm?1. The Raman spectra of the liquid and the solid have also been recorded. A comparison of the Raman spectra of the liquid and the solid indicates that there are two conformers present in the liquid phase. From a comparison of the infrared and Raman

J. R. Durig; J. M. Casper

1971-01-01

322

Electronic Structure and Singlet-Triplet Energy Splittings in Ethynyl Cyclobutadienes  

NASA Astrophysics Data System (ADS)

We investigated the effects of ethynyl substituents on singlet-triplet gaps in cyclobutadiene. These species are involved in Bergman Cyclization reactions and are possible intermediates in the formation of fullerenes and graphite sheets. Prediction of the singlet-triplet splitting in cyclobutadiene is challenging for single-reference ab initio methods such as HF, MP2 or DFT because of Jahn-Teller distortions and the diradical character of the singlet state. Ethynyl substituents in cyclobutadienes are thought to stabilize the triplet states and invert the order of the singlet and triplet in some of them. We determined the singlet-triplet energy splittings in substituted cyclobutadienes using the equations of motion spin flip coupled cluster with single and double excitations (EOM-SF-CCSD) method that accurately describes diradical states and singlet-triplet gaps in diradicals. O. L. Chapman, C. L. McIntosh, J. Pacansky, Cyclobutadiene. J. Am. Chem. Soc. 1973, 95, (2), 614-617. N. S. Goroff, Mechanism of Fullerene Formation. Acc. Chem. Res. 1996, 29, (2), 77-83. L.V. Slipchenko and A.I. Krylov, Singlet-Triplet Gaps in Diradicals by the Spin-Flip Approach: a Benchmark Study, J. Chem. Phys. 2002, 117, 4694-4708.

Thompson, Stephanie J.; Emmert, Frank Lee, III; Slipchenko, Lyudmila V.

2010-06-01

323

Reinvestigation of the triplet-minus-singlet spectrum of chloroplasts  

NASA Astrophysics Data System (ADS)

A comparison of the triplet-minus-singlet (TmS) absorption spectrum of spinach chloroplasts, recorded some thirty years ago, with the more recently published TmS spectrum of isolated Chl a/ b LHCII (light-harvesting complexes associated with photosystem II of higher plants) shows that the two spectra are very similar, which is to be expected, since only the carotenoid pigments contribute to each spectrum. Be that as it may, the comparison also reveals a dissimilarity: photoexcitation of the sample does, or does not, affect the absorbance in the Qy region (650-700 nm), depending on whether the sample is a suspension of chloroplasts or of isolated LHCII. The Qy-signal in the TmS spectrum of LHCII decays, it should be noted, at the same rate as the rest of the difference spectrum, and its most prominent feature is a negative peak. As the carotenoids do not absorb in the Qy region, the presence of a signal in this region calls for an explanation: van der Vos, Carbonera and Hoff, the first to find as well as fathom the phenomenon, attributed the Qy-signal to a change, in the absorption spectrum of a chlorophyll a (Chl a) molecule, brought about by the presence of triplet excitation on a neighbouring carotenoid (Car). The difference in the behaviours of chloroplasts and LHCII, if reproducible, would imply that the Car triplets which give rise to the TmS spectrum of chloroplasts do not influence the absorption spectra of their Chl a neighbours. With a view to reaching a firm conclusion about this vexed issue, spinach chloroplasts and thylakoids have been examined with the aid of the same kinetic spectrometer as that used for investigating LHCII; the TmS spectra of both chloroplasts and thylakoids contain prominent bleaching signals centred at 680 nm, and the triplet decay time in each case is comparable to that of the Chl a/ b LHCII triplets. Results pertaining to other closely related systems are recalled, and it is concluded that, so far as the overall appearance of the TmS spectrum is concerned, spinach chloroplasts are by no means abnormal.

Jávorfi, T.; Garab, G.; Razi Naqvi, K.

2000-01-01

324

Singlet-triplet superconducting quantum magnetometer  

NASA Astrophysics Data System (ADS)

Motivated by the recent experimental realization of a quantum interference transistor based on the superconducting proximity effect, we here demonstrate that the inclusion of a textured ferromagnet both strongly enhances the flux sensitivity of such a device and additionally allows for singlet-triplet switching by tuning a bias voltage. This functionality makes explicit use of the induced spin-triplet correlations due to the magnetic texture. Whereas the existence of such triplet correlations is well known, our finding demonstrates how spin-triplet superconductivity may be utilized for concrete technology, namely, to improve the functionality of ultrasensitive magnetometers.

Alidoust, Mohammad; Halterman, Klaus; Linder, Jacob

2013-08-01

325

Production of N2 Vegard-Kaplan and other triplet band emissions in the dayglow of Titan  

NASA Astrophysics Data System (ADS)

Recently the Cassini Ultraviolet Imaging Spectrograph (UVIS) has revealed the presence of N2 Vegard-Kaplan (VK) band A3?u+-X1?g+ emissions in Titan's dayglow limb observation. We present model calculations for the production of various N2 triplet states (viz., A3?u+,B3?g,C3?u,E3?u,W3?u, and B3?u ) in the upper atmosphere of Titan. The Analytical Yield Spectra technique is used to calculate steady state photoelectron fluxes in Titan's atmosphere, which are in agreement with those observed by the Cassini's CAPS instrument. Considering direct electron impact excitation, inter-state cascading, and quenching effects, the population of different levels of N2 triplet states are calculated under statistical equilibrium. Densities of all vibrational levels of each triplet state and volume production rates for various triplet states are calculated in the model. Vertically integrated overhead intensities for the same date and lighting conditions as reported by the UVIS observations for N2 Vegard-Kaplan A3?u+-X1?g+, First Positive B3?g-A3?u+, Second Positive (C3?u - B3?g), Wu-Benesch (W3?u - B3?g), and Reverse First Positive bands of N2 are found to be 132, 114, 19, 22, and 22 R, respectively. Overhead intensities are calculated for each vibrational transition of all the triplet band emissions of N2, which span a wider spectrum of wavelengths from ultraviolet to infrared. The calculated limb intensities of total and prominent transitions of VK band are presented. The model limb intensity of VK emission within the 150-190 nm wavelength region is in good agreement with the Cassini UVIS observed limb profile. An assessment of the impact of solar EUV flux on the N2 triplet band emission intensity has been made by using three different solar flux models, viz., Solar EUV Experiment (SEE), SOLAR2000 (S2K) model of Tobiska (Tobiska, W.K. [2004]. Adv. Space Res. 34, 1736-1746), and HEUVAC model of Richards et al. (Richards, P.G., Woods, T.N., Peterson, W.K. [2006]. Adv. Space Res. 37 (2), 315-322). The calculated N2 VK band intensity at the peak of limb intensity due to S2K and HEUVAC solar flux models is a factor of 1.2 and 0.9, respectively, of that obtained using SEE solar EUV flux. The effects of higher N2 density and solar zenith angle on the emission intensity are also studied. The model predicted N2 triplet band intensities during moderate (F10.7 = 150) and high (F10.7 = 240) solar activity conditions, using SEE solar EUV flux, are a factor of 2 and 2.8, respectively, higher than those during solar minimum (F10.7 = 68) condition.

Bhardwaj, Anil; Jain, Sonal Kumar

2012-04-01

326

Triplet energy transfer in photoexcited diketones  

SciTech Connect

The rate at which excitation energy transfers between chromophores of diketones was investigated. Energy transfer (ET) was induced by irradiation of the diketones with 313nm and 366nm ultraviolet light. The most significant aspect of this work is the assignment of rates for both exothermic and endothermic ET between the chromophores of a diketone molecule. By varying the most influential factors which determine ET rates, the difference in energy between the triplet excited states of each chromophore ([Delta]E) and the length of the alkyl tether linking the chromophores, two trends emerged. First, as the [Delta]E increased between two interacting chromophores within a given bichromophoric series of compounds, exothermic ET increased and endothermic ET decreased. Second,as the alkyl tether length connecting the two chromophores increased, both the exothermic and endothermic ET rates decreased. Intramolecular ET rates were derived by fitting the experimental photokinetic data with mathematical models.

Francesco, J.V.

1992-01-01

327

Spontaneous triplet, tubal ectopic gestation.  

PubMed Central

Only six cases of spontaneous, unilateral, triplet ectopic gestations have previously been reported. We now present a seventh case. The patient's prior obstetrical history was significant for a term stillbirth and a term cesarean section for breech. Quantitative betahCG was normal for gestational age; however, the increased trophoblastic mass of an inappropriately implanted multiple gestation may produce sufficient betahCG to mimic an intrauterine singleton gestation. Resolution was achieved via salpingostomy. This case is significant for being spontaneously conceived and not the result of assisted reproductive technologies. Furthermore, this case supports an association between prior cesarean section and ectopic gestation. Images Figure 1

Nwanodi, Oroma; Berry, Robert

2006-01-01

328

Excited-State Dynamics of Nitrated Push-Pull Molecules: The Importance of the Relative Energy of the Singlet and Triplet Manifolds  

Microsoft Academic Search

We present a study of the dynamics following photoexcitation in the first electronic band of NO2-para-substituted nitronaphthalenes. Our main goal was to determine the interplay between the nitro group, electron-donating substituents, and the solvent in defining the relative excited-state energies and their photoinduced pathways. We studied 4-nitro-1-naphthylamine and 1-methoxy-4-nitronaphthalene in solution samples through femtosecond fluorescence up-conversion and transient absorption techniques.

Elisa Collado-Fregoso; Jimena S. Zugazagoitia; Eddy F. Plaza-Medina; Jorge Peon

2009-01-01

329

Analysis of source spectra, attenuation, and site effects from central and eastern United States earthquakes  

SciTech Connect

This report describes the results from three studies of source spectra, attenuation, and site effects of central and eastern United States earthquakes. In the first study source parameter estimates taken from 27 previous studies were combined to test the assumption that the earthquake stress drop is roughly a constant, independent of earthquake size. 200 estimates of stress drop and seismic moment from eastern North American earthquakes were combined. It was found that the estimated stress drop from the 27 studies increases approximately as the square-root of the seismic moment, from about 3 bars at 10{sup 20} dyne-cm to 690 bars at 10{sup 25} dyne-cm. These results do not support the assumption of a constant stress drop when estimating ground motion parameters from eastern North American earthquakes. In the second study, broadband seismograms recorded by the United States National Seismograph Network and cooperating stations have been analysed to determine Q{sub Lg} as a function of frequency in five regions: the northeastern US, southeastern US, central US, northern Basin and Range, and California and western Nevada. In the third study, using spectral analysis, estimates have been made for the anelastic attenuation of four regional phases, and estimates have been made for the source parameters of 27 earthquakes, including the M{sub b} 5.6, 14 April, 1995, West Texas earthquake.

Lindley, G.

1998-02-01

330

Magnetic effects on the dynamics of organic triplets in the level anti-crossing region  

NASA Astrophysics Data System (ADS)

A fast magnetic field sweep (2.0 ×105Ts-1) is applied to probe the spin dynamics in the level anti-crossing (LAC) region of the photo-excited triplet states of pentacene- h14 in p-terphenyl (PHPT) and pentacene-d14 in p-terphenyl (PDPT) systems. From the pulsed zero-field FID (ZF FID) EPR measurements of the triplet signal at room temperature, the crossing is found to be a non-adiabatic passage at such a high jumping rate. Detailed examination of the initial population of the photo-excited triplet states of these two systems indicates that the nonadiabatic state mixing is the dominant mechanism for the polarization transfer (electron- nuclear spins) in the LAC region. The time dependent Schrödinger equation is applied to calculate the non-adiabatic transition probabilities, and to simulate the observed triplet population profiles with fast field sweeping.

Yang, Tran-Chin; Sloop, David J.; Weissman, S. I.; Lin, Tien-Sung

331

Competition between Final-State and Pairing-Gap Effects in the Radio-Frequency Spectra of Ultracold Fermi Atoms  

SciTech Connect

The radio-frequency spectra of ultracold Fermi atoms are calculated by including final-state interactions affecting the excited level of the transition and compared with the experimental data. A competition is revealed between pairing-gap effects which tend to push the oscillator strength toward high frequencies away from threshold and final-state effects which tend instead to pull the oscillator strength toward threshold. As a result of this competition, the position of the peak of the spectra cannot be simply related to the value of the pairing gap, whose extraction thus requires support from theoretical calculations.

Perali, A.; Pieri, P.; Strinati, G. C. [Dipartimento di Fisica, Universita di Camerino, I-62032 Camerino (Italy)

2008-01-11

332

Probing the quantum ground state of a spin-1 Bose-Einstein condensate with cavity transmission spectra  

SciTech Connect

We propose to probe the quantum ground state of a spin-1 Bose-Einstein condensate with the transmission spectra of an optical cavity. By choosing a circularly polarized cavity mode with an appropriate frequency, we can realize coupling between the cavity mode and the magnetization of the condensate. The cavity transmission spectra then contain information of the magnetization statistics of the condensate and thus can be used to distinguish the ferromagnetic and antiferromagnetic quantum ground states. This technique may also be useful for continuous observation of the spin dynamics of a spinor Bose-Einstein condensate.

Zhang, J. M. [Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100080 (China); Department of Physics, Henan Normal University, Xinxiang 453007 (China); Cui, S.; Jing, H. [Department of Physics, Henan Normal University, Xinxiang 453007 (China); Zhou, D. L.; Liu, W. M. [Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100080 (China)

2009-10-15

333

Resonance Raman Spectra of TNT and RDX Using Vibronic Theory, Excited-State Gradient, and Complex Polarizability Approximations.  

PubMed

Geometries, UV absorption bands, and resonance Raman (RR) cross sections of TNT and RDX are investigated using density functional theory (DFT) in conjunction with the Coulomb attenuated B3LYP exchange-correlation functional. The absorption and RR spectra are determined with use of vibronic (VB) theory, excited-state gradient, and complex polarizability (CPP) approximations. We examined low-energy isomers (two for TNT and four for RDX) whose energies differ by less than 1 kcal/mol, such that they would appreciably be populated at room temperature. The two TNT isomers differ by an internal rotation of the methyl group, while the four conformers of RDX differ by the arrangements of the nitro group relative to the ring. Our theoretical optical properties of the TNT and RDX isomers are in excellent agreement with experimental and recent CCSD-EOM results, respectively. For the two TNT isomers, the ultraviolet RR (UVRR) spectra are similar and in good agreement with recently measured experimental results. Additionally, the UVRR spectra computed using the excited-state and CPP approaches compare favorably with the VB theory results. On the other hand, the RR spectra of the RDX conformers differ from one another, reflecting the importance of the positioning of the NO(2) groups with respect to the ring. In the gas phase or in solution, RDX would give a spectrum associated with a conformationally averaged structure. It is encouraging that the computed spectra of the conformers show similarities to recent measured RDX spectra in acetonitrile solution, and reproduce the 10-fold decrease in the absolute Raman cross sections of RDX compared to TNT for the observed 229 nm excitation. We show that in TNT and RDX vibrational bands that couple to NO(2) or the ring are particularly resonance enhanced. Finally, the computed RDX spectra of the conformers present a benchmark for understanding the RR spectra of the solid-phase polymorphs of RDX. PMID:22770527

Al-Saidi, W A; Asher, Sanford A; Norman, Patrick

2012-07-23

334

Band Spectra which appear near Visible Triplet Lines of Mercury  

Microsoft Academic Search

RECENTLY, H. Kuhn1 has found a band which appears very near the principal series lines of alkali metals in absorption and has explained this band as being due to the diatomic molecules loosely combined by Van der Waals' cohesion forces. In the case of mercury, it seems that bands of the same nature are also emitted very close to the

E. Matuyama

1933-01-01

335

Experimental Observation of Singlet-Triplet Absorption in Pure Crystalline Benzene.  

National Technical Information Service (NTIS)

The triplet B(1u) from singlet A(1g) intrinsic absorption spectra of C6H6 and C6D6 at 4.2K have been obtained for the first time at high resolution using the phosphorescence-photoexcitation method. The spectrum exhibits very clear evidence of a pseudo-Jah...

D. M. Burland G. Castro G. W. Robinson

1969-01-01

336

Optical and dynamic nuclear polarization of 29Si nuclei via photoexcited triplet states of oxygen-vacancy complexes in isotopically controlled silicon  

NASA Astrophysics Data System (ADS)

Optical and dynamic nuclear polarization of 29Si nuclei under saturation of the electron paramagnetic resonance (EPR) transitions of the photoexcited spin S = 1 states (Si-SL1 centers) of the oxygen+vacancy complexes (A-centers) have been investigated using silicon single crystals with various 29Si nuclear abundances. The optical nuclear polarization alone led to the 29Si nuclear polarization enhancement by a factor of ˜500 in the magnetic fields below 50 mT, and such enhancement was found to decrease significantly in the stronger fields up to 300 mT. On the other hand, saturation of the EPR lines of Si-SL1 centers having the electron spin polarization of 70-80% was transferred successfully to surrounding 29Si nuclear spins to achieve the overall 29Si nuclear spin polarization of ˜6.4%, and a method to increase up to 13-15% is proposed. The optimum condition to achieve such a high degree of nuclear polarization was found by systematic investigations of the dynamic nuclear polarization mechanisms.

Itahashi, T.; Hayashi, H.; Rahman, M. R.; Itoh, K. M.; Vlasenko, L. S.; Vlasenko, M. P.; Poloskin, D. S.

2013-02-01

337

Acquiring impedance spectra from diode-coupled primary batteries to determine health and state of charge  

NASA Astrophysics Data System (ADS)

The U.S. Army uses BA5590 Lithium Sulfur Dioxide primary batteries for portable electronic systems. There remains a need, however, for technology that can rapidly assess these batteries and estimate their remaining state of health after being used without degrading them to determine if there is remaining useful life for additional missions. This allows the full range of charge to be consumed before the battery is recycled or disposed. Impedance spectroscopy measurements have been shown to be a useful diagnostic tool, but standard methods cannot be applied to the BA5590 batteries because of the up-front electronics. The BA5590 module is diode-coupled and a charge-neutral excitation signal would be half-wave rectified and completely corrupt the results. However, a rapid impedance spectrum measurement technique has been developed that can be used for the BA5590s based on the addition of a small discharge bias load super-imposed on the sinusoidal excitation signal. The feasibility of this approach was initially simulated and then successfully applied to cell strings on four fresh BA5590 modules. The results clearly showed consistent and repeatable impedance spectra with no significant impact on the SOC as a result of the measurement. Details of this measurement technique and discussion of the preliminary results are presented.

Christophersen, Jon P.; Morrison, John L.; Morrison, William H.

338

Multiconfigurational quadratic response functions for singlet and triplet perturbations - The phosphorescence lifetime of formaldehyde  

NASA Astrophysics Data System (ADS)

A formalism is presented for the calculation of quadratic response functions of multiconfigurational self-consistent field reference wave functions. The formalism is general in the sense that it applies equally well to singlet and triplet perturbations and it does not assume any permutational symmetry in the integrals of the perturbational operators. This formalism can be used to derive expressions for various properties related to singlet or triplet quadratic response functions and their residues. We focus on the spin-forbidden dipole transitions between singlet and triplet electronic states responsible for the long lifetime of phosphorescent states. The singlet-triplet transition moments are evaluated as the residues of quadratic response functions. Sample calculations are presented for the formaldehyde molecule.

Vahtras, Olav; Agren, Hans; Jorgensen, Poul; Jensen, Hans J. A.; Helgaker, Trygve; Olsen, Jeppe

1992-12-01

339

Photo-oxidation of methionine-containing peptides by the 4-carboxybenzophenone triplet state in aqueous solution. Competition between intramolecular two-centered three-electron bonded (S...S)+ and (S...N)+ formation.  

PubMed

Quantum yields for the formation of transients were measured following the quenching of triplet 4-carboxy-benzophenone (3CB*) by methionine-containing peptides in aqueous solutions. Ketyl radicals (CBH.), ketyl radical anions (CB.-) and various sulfur radical cations were identified following the triplet-quenching events. The presence of these intermediates indicated that the triplet-quenching mechanism can be characterized as mainly electron-transfer in nature. The quenching rate constants were of the order of 2 x 10(9) M-1 s-1. There were small, but significant, differences in the triplet-quenching rate constants, and these trends indicate the existence of multiple sulfur targets in the quenchers. The absorption of the transient products was followed in detail by using spectral-resolution analysis. From the absorption data, quantum yields were estimated for the formation of the various transients. There were differences found in the yields of the transient products between the experiments, where the quenchers were the "mixed" stereoisomers of methionylmethionine (L,D and D,L) and experiments where the quenchers were L,L and D,D stereoisomers. Triplet-quenching data from several other methionine-containing small oligopeptides were analyzed in an analogous manner. Systematic variations were observed, and these patterns were discussed in terms of competitive donation of protons to the CB.- within the charge-transfer complex. The competition was between protons on carbons adjacent to the sulfur-radical center and protons on the protonated amino groups of the radical cation. In addition, there was a competition between the two intramolecular two-centered, three-electron bonded species (S therefore S)+ and (S therefore N)+ that play roles in the secondary kinetics. PMID:10911722

Hug, G L; Bobrowski, K; Kozubek, H; Marciniak, B

2000-07-01

340

Heats of Formation of Triplet Ethylene, Ethylidene, and Acetylene  

SciTech Connect

Heats of formation of the lowest triplet state of ethylene and the ground triplet state of ethylidene have been predicted by high level electronic structure calculations. Total atomization energies obtained from coupled-cluster CCSD(T) energies extrapolated to the complete basis set limit using correlation consistent basis sets (CBS), plus additional corrections predict the following heats of formation in kcal/mol: Delta H0f(C2H4,3A1) = 80.1 at 0 K and 78.5 at 298 K, and Delta H0f(CH3CH,3A") = 86.8 at 0 K and 85.1 at 298 K, with an error of less than +-1.0 kcal/mol. The vertical and adiabatic singlet-triplet separation energies of ethylene were calculated as Delta ES-T,vert = 104.1 and Delta ES-T,adia = 65.8 kcal/mol. These results are in excellent agreement with recent quantum Monte Carlo (DMC) values of 103.5 +- 0.3 and 66.4 +- 0.3 kcal/mol. Both sets of computational values differ from the experimental estimate of 58 +- 3 kcal/mol for the adiabatic splitting. The computed singlet-triplet gap at 0 K for acetylene is Delta ES-T,adia(C2H2) = 90.5 kcal/mol, which is in notable disagreement with the experimental value of 82.6 kcal/mol. The heat of formation of the triplet is Delta H0f(C2H2,3B2) = 145.3 kcal/mol. There is a systematic underestimation of the singlet-triplet gaps in recent photodecomposition experiments by ~;;7 to 8 kcal/mol. For vinylidene, we predict Delta H0f(H2CC,1A1) = 98.8 kcal/mol at 298 K (exptl. 100.3 +- 4.0), Delta H0f(H2CC,3B2) = 146.2 at 298 K, and an energy gap Delta ES-T-adia(H2CC) = 47.7 kcal/mol.

Nguyen, M.T.; Matus, M.H.; Lester Jr, W.A.; Dixon, David A.

2007-06-28

341

Higgs triplets and limits from precision measurements  

SciTech Connect

In this letter, they present the results on a global fit to precision electroweak data in a Higgs triplet model. In models with a triplet Higgs boson, a consistent renormalization scheme differs from that of the Standard Model and the global fit shows that a light Higgs boson with mass of 100-200 GeV is preferred. Triplet Higgs bosons arise in many extensions of the Standard Model, including the left-right model and the Little Higgs models. The result demonstrates the importance of the scalar loops when there is a large mass splitting between the heavy scalars. It also indicates the significance of the global fit.

Chen, Mu-Chun; /Fermilab; Dawson, Sally; Krupovnickas, Tadas; /Brookhaven

2006-04-01

342

Determination of Peptide and Protein Ion Charge States by Fourier Transformation of Isotope-Resolved Mass Spectra  

SciTech Connect

We report an automated method for determining charge states from high-resolution mass spectra. Fourier transforms of isotope packets from high-resolution mass spectra are compared to Fourier transforms of modeled isotopic peak packets for a range of charge states. The charge state for the experimental ion packet is determined by the model isotope packet that yields the best match in the comparison of the Fourier transforms. This strategy is demonstrated for determining peptide ion charge states from 'zoom scan' data from a linear quadrupole ion trap mass spectrometer, enabling the subsequent automated identification of singly-through quadruply-charged peptide ions, while reducing the numbers of conflicting identifications from ambiguous charge state assignments. We also apply this technique to determine the charges of intact protein ions from LC-FTICR data, demonstrating that it is more sensitive under these experimental conditions than two existing algorithms. The strategy outlined in this paper should be generally applicable to mass spectra obtained from any instrument capable of isotopic resolution.

Tabb, Dave L [ORNL; Shah, Manesh B [ORNL; Strader, Michael B [ORNL; Connelly, Heather M [ORNL; Hettich, Robert {Bob} L [ORNL; Hurst, Gregory {Greg} B [ORNL

2006-01-01

343

Equations-of-motion method for triplet excitation operators in graphene.  

PubMed

The particle-hole continuum in the Dirac sea of graphene has a unique window underneath, which in principle leaves room for bound state formation in the triplet particle-hole channel (Baskaran and Jafari 2002 Phys. Rev. Lett. 89 016402). In this work, we construct appropriate triplet particle-hole operators and, using a repulsive Hubbard-type effective interaction, we employ equations of motion to derive approximate eigenvalue equations for such triplet operators. While the secular equation for the spin density fluctuations gives rise to an equation which is second order in the strength of the short range interaction, the explicit construction of the triplet operators obtained here shows that, in terms of these operators, the second-order equation can be factorized to two first-order equations, one of which gives rise to a solution below the particle-hole continuum of Dirac electrons in undoped graphene. PMID:22317782

Jafari, S A; Baskaran, G

2012-02-09

344

Polymer triplet energy levels need not limit photocurrent collection in organic solar cells.  

PubMed

We study charge recombination via triplet excited states in donor/acceptor organic solar cells and find that, contrary to intuition, high internal quantum efficiency (IQE) can be obtained in polymer/fullerene blend devices even when the polymer triplet state is significantly lower in energy than the intermolecular charge transfer (CT) state. Our model donor system comprises the copolymer PIDT-PhanQ: poly(indacenodithiophene-co-phenanthro[9,10-b]quinoxaline), which when blended with phenyl-C(71)-butyric acid methyl ester (PC(71)BM) is capable of achieving power conversion efficiencies of 6.0% and IQE ? 90%, despite the fact that the polymer triplet state lies 300 meV below the interfacial CT state. However, as we push the open circuit voltage (V(OC)) higher by tailoring the fullerene reduction potential, we observe signatures of a new recombination loss process near V(OC) = 1.0 V that we do not observe for PCBM-based devices. Using photoinduced absorption and photoluminescence spectroscopy, we show that a new recombination path opens via the fullerene triplet manifold as the energy of the lowest CT state approaches the energy of the fullerene triplet. This pathway appears active even in cases where direct recombination via the polymer triplet remains thermodynamically accessible. These results suggest that kinetics, as opposed to thermodynamics, can dominate recombination via triplet excitons in these blends and that optimization of charge separation and kinetic suppression of charge recombination may be fruitful paths for the next generation of panchromatic organic solar cell materials with high V(OC) and J(SC). PMID:23126491

Schlenker, Cody W; Chen, Kung-Shih; Yip, Hin-Lap; Li, Chang-Zhi; Bradshaw, Liam R; Ochsenbein, Stefan T; Ding, Feizhi; Li, Xiaosong S; Gamelin, Daniel R; Jen, Alex K-Y; Ginger, David S

2012-11-16

345

Highly efficient fluorescent-phosphorescent triplet-harvesting hybrid organic light-emitting diodes  

NASA Astrophysics Data System (ADS)

We demonstrate highly efficient white and nonwhite hybrid organic light-emitting diodes (OLEDs) in which singlet and triplet excited states, generated in the recombination zone, are utilized by fluorescence and phosphorescence, respectively. The excited states are formed at a blue fluorescent light-emitting layer (LEL), and the triplets diffuse through a spacer layer to one or more phosphorescent LEL(s). A key feature enabling the triplet diffusion in such OLEDs is the use of a blue fluorescent emitter with triplet energy above, or not much below, that of the fluorescent host. Additional material properties required for triplet harvesting are outlined. At 1000 cd/m2 a blue and yellow harvesting OLED shows 13.6% external quantum efficiency, 3.8 V, 30.1 lm/W, and color characteristics suitable for display application. High-efficiency harvesting R+G+B white, and B+G and B+R nonwhite OLEDs are also demonstrated. The triplet-harvesting mechanism was verified in all devices by physical methods including spectral analysis, time-resolved electroluminescence, magnetic field effect, and electron paramagnetic resonance.

Kondakova, Marina E.; Deaton, Joseph C.; Pawlik, Thomas D.; Giesen, David J.; Kondakov, Denis Y.; Young, Ralph H.; Royster, Tommie L.; Comfort, Dustin L.; Shore, Joel D.

2010-01-01

346

Paramagnetic effects on the NMR spectra of "diamagnetic" ruthenium(bis-phosphine)(bis-semiquinone) complexes.  

PubMed

Ligand substitution on cis-Ru(PPh(3))(2)(1,2-O(2)C(6)H(4))(2) gives cis-RuL(1)L(2)(1,2-O(2)C(6)H(4))(2) (L(1) = PPh(3), L(2) = P(OPh)(3), PBu(3); L(1) = L(2) = PBu(3), P(OMe)(3)). Syntheses of cis-Ru(PPh(3))(2)(3,4-O(2)C(6)H(2)(5-OH)CO(2)Me)(2) and cis-Ru(PPh(3))(2)(AGSQ)(2) (AGSQ = the semiquinone derived from 1,2,3-trihydroxyanthracene-9,10-dione) are also reported. The upfield chemical shifts and line broadening of the semiquinone 4,5-proton resonances in the NMR spectra indicate that these complexes, while having no detectable magnetic moments, have a weak, temperature-, ligand- and solvent-variable residual paramagnetism, not previously recognized in this series. Density functional theory (DFT) calculations predict a low-lying triplet state, about 14 kJ/mol (0.15 eV) above the singlet ground state. The paramagnetic effects on the NMR spectra are attributed to singlet-triplet equilibria. Temperature dependence of the proton resonances of the semiquinone rings of cis-Ru(PPh(3))(2)(1,2-O(2)C(6)H(4))(2) was used to calculate the singlet-triplet free energy difference as 17.5-18.0 kJ/mol in toluene. PMID:19400557

Le Guennic, Boris; Floyd, Tavon; Galan, Brandon R; Autschbach, Jochen; Keister, Jerome B

2009-06-15

347

Phenomenology of a lepton triplet  

SciTech Connect

The most general phenomenological model involving a lepton triplet with hypercharge {+-}1 is constructed. A distinctive feature of this model is the prediction of a doubly charged lepton and a new heavy Dirac neutrino. We study the phenomenology of these exotic leptons both in low-energy experiments and at the LHC. The model predicts flavor-changing neutral-current processes such as muon and tau rare decays, which are studied in detail in order to constrain the model parameters. All the decay channels of the exotic leptons are described for a wide range of parameters. It is found that, if the mixing parameters between the exotic and light leptons are not too small (>10{sup -6}), then they can be observable to a 3-5{sigma} statistical significance at the 7 TeV LHC with 10-50 fb{sup -1} luminosity for a 400 GeV mass and 14 TeV with 100-300 fb{sup -1} luminosity for a 800 GeV mass.

Delgado, Antonio [Department of Physics, University of Notre Dame, Notre Dame, Indiana 46556 (United States); Garcia Cely, Camilo; Han Tao [Department of Physics, University of Wisconsin, Madison, Wisconsin 53706 (United States); Wang Zhihui [Department of Physics, University of Wisconsin, Madison, Wisconsin 53706 (United States); Department of Physics, Harbin Institute of Technology, Harbin 150001 (China)

2011-10-01

348

An LDA+U study of the photoemission spectra of ground state phase of americium and curium  

NASA Astrophysics Data System (ADS)

We have investigated the photoemission spectra and other ground state properties such as equilibrium volume and bulk modulus of dhcp americium and the density of states and magnetic properties of dhcp curium using LDA+U method. Our calculations show that spin polarized americium is energetically favorable but spin degenerate configuration produces experimental quantities much better than that calculated using spin polarized configuration. The DOS calculated using LDA+U with both non-magnetic and spin polarized configurations is compared and the non-magnetic DOS is shown to be in good agreement with experimental photoemission spectra when U=4.5 eV. In spin polarized case, U is observed to increase the splitting between occupied and unoccupied bands by enhancing Stoner parameter. The results are shown to be in good agreement with that calculated using dynamical mean field theory for these two heavy actinides. For curium, exchange interaction appears to play the dominant role in its magnetic stability.

Islam, Md; Ray, Asok

2009-03-01

349

Automated charge state determination of complex isotope-resolved mass spectra by peak-target Fourier transform.  

PubMed

This study describes a new algorithm for charge state determination of complex isotope-resolved mass spectra. This algorithm is based on peak-target Fourier transform (PTFT) of isotope packets. It is modified from the widely used Fourier transform method because Fourier transform may give ambiguous charge state assignment for low signal-to-noise ratio (S/N) or overlapping isotopic clusters. The PTFT algorithm applies a novel "folding" strategy to enhance peaks that are symmetrically spaced about the targeted peak before applying the FT. The "folding" strategy multiplies each point to the high-m/z side of the targeted peak by its counterpart on the low-m/z side. A Fourier transform of this "folded" spectrum is thus simplified, emphasizing the charge state of the "chosen" ion, whereas ions of other charge states contribute less to the transformed data. An intensity-dependent technique is also proposed for charge state determination from frequency signals. The performance of PTFT is demonstrated using experimental electrospray ionization Fourier transform ion cyclotron resonance mass spectra. The results show that PTFT is robust for charge state determination of low S/N and overlapping isotopic clusters, and also useful for manual verification of potential hidden isotopic clusters that may be missed by the current analysis algorithms, i.e., AID-MS or THRASH. PMID:18293485

Chen, Li; Yap, Yee Leng

2008-01-01

350

Vibronic spectra, ab initio calculations, and structures of conformationally non-rigid molecules of oxalyl halides in the ground and lowest excited electronic states. Part IV: Analysis of the absorption spectra of oxalyl fluoride in the gas phase  

NASA Astrophysics Data System (ADS)

The gas phase absorption spectrum of oxalyl fluoride in the region of 37 000-29 300 cm-1 has been examined at high resolution. Singlet-singlet A˜Au?X˜Ag and singlet-triplet a˜Au?X˜Ag electronic transitions of the trans-conformer were found in the spectrum. The fundamental frequencies of trans-oxalyl fluoride in the A˜Au and a˜Au electronic states were determined. In the low resolution ultraviolet absorption spectrum of oxalyl fluoride in the gas phase the A˜B1?X˜A1 transition of the cis-conformer (?max) was found to be shifted to the blue by about 6000 cm-1 relative to the A˜Au?X˜Ag transition of the trans-conformer.

Godunov, I. A.; Yakovlev, N. N.; Maslov, D. V.; Bokarev, S. I.

2010-04-01

351

Effect of Molecular Symmetry on the Spectra and Dynamics of the Intramolecular Charge Transfer (ICT) State of Peridinin  

PubMed Central

The spectroscopic properties and dynamics of the excited states of two different synthetic analogues of peridinin were investigated as a function of solvent polarity using steady-state absorption, fluorescence, and ultrafast time-resolved optical spectroscopy. The analogues are denoted S-1- and S-2-peridinin and differ from naturally-occurring peridinin in the location of the lactone ring and its associated carbonyl group, known to be obligatory for the observation of a solvent dependence of the lifetime of the S1 state of carotenoids. Relative to peridinin, S-1- and S-2-peridinin have their lactone rings two and four carbons more toward the center of the ?-electron system of conjugated carbon-carbon double bonds, respectively. The present experimental results show that as the polarity of the solvent increases, the steady-state spectra of the molecules broaden, and the lowest excited state lifetime of S-1-peridinin changes from ~155 ps to ~17 ps which is similar to the magnitude of the effect reported for peridinin. The solvent-induced change in the lowest excited state lifetime of S-2-peridinin is much smaller and changes only from ~90 ps to ~67 ps as the solvent polarity is increased. These results are interpreted in terms of an intramolecular charge transfer (ICT) state that is formed readily in peridinin and S-1-peridinin, but not in S-2-peridinin. Quantum mechanical computations reveal the critical factors required for the formation of the ICT state and the associated solvent-modulated effects on the spectra and dynamics of these molecules and other carbonyl-containing carotenoids and polyenes. The factors are the magnitude and orientation of the ground and excited state dipole moments which must be suitable to generate sufficient mixing of the lowest two excited singlet states.

Enriquez, Miriam M.; Hananoki, Shohei; Hasegawa, Shinji; Kajikawa, Takayuki; Katsumura, Shigeo; Wagner, Nicole L.

2012-01-01

352

Magnetic-field cycling triplet-DNP/NMR system for true quantum computation with hyperpolarized nuclear spins  

NASA Astrophysics Data System (ADS)

Toward NMR quantum computing with hyperpolarization beyond the entanglement threshold, a system has been developed enabling dynamic nuclear polarization (DNP) using photo-excited triplet electron spins with X-band microwave apparatus, followed by solid-state NMR experiments using the polarized nuclear spin system. In order to perform the triplet-DNP and NMR experiments in different magnetic fields, the triplet-DNP system and the NMR system are made to be spatially separated, between which the sample can be shuttled. It is shown that the system developed in this work fulfils the requirements for solid-state NMR quantum computing with hyperpolarized nuclear spin systems.

Kagawa, A.; Negoro, M.; Takeda, K.; Kitagawa, M.

2009-04-01

353

Quantum and surface states of charge carriers in the optical spectra of nanoclusters in a low-permittivity matrix  

NASA Astrophysics Data System (ADS)

The optical spectra of quantum dots of CdS and ZnSe grown in borosilicate glass by the sol-gel method are obtained and analyzed. It is found that at concentrations of the two semiconductors x<0.06% the emission spectra are due to annihilation of free (internal) excitons in quantum states. The mean size of the quantum dots (QDs) for a given concentration of ZnSe and CdS is calculated and found to be in good agreement with the x-ray data, and the exciton binding energy is calculated with allowance for the dielectric mismatch between the semiconductor and matrix. It is proposed that this mismatch may be the cause giving rise to the exciton percolation level that is observed in QD arrays for both systems at x>0.06%. The emission from the surface level of CdS QDs in the region ~2.7 eV, formed by the outer atoms with dangling bonds, is observed for the first time, as is the emission band from surface localized states. The relation between the position of the maximum of this band and the energy of the 1S state of the free exciton is established. It is shown that the properties of surface localized states are largely similar to the analogous properties of localized states of 3D (amorphous semiconductors, substitutional solid solutions of substitution) and 2D (quantum wells and superlattices) structures.

Bondar, N. V.; Brodyn, M. S.

2008-01-01

354

Electronic structure and absorption spectra of yttrium quinaldinates with an island and polymer structure  

NASA Astrophysics Data System (ADS)

The electronic absorption spectra and electronic structure of yttrium quinaldinates with an island and polymer structure were studied. A comparative analysis of the energies of the singlet and triplet excited states, the total energies of complex compounds in the ground state, and Mulliken's bond overlap populations was performed by the TD-DFT method with the B3LYP density functional. For yttrium quinaldinate with a polymer structure, the distance between the highest occupied and lowest unoccupied orbitals was found to be longer than for the compound with an island structure. The transition energies were shifted to the blue region, which accounts for the higher stability of the polymer compound.

Kalinovskaya, I. V.; Emelina, T. B.; Mirochnik, A. G.; Karasev, V. E.

2011-08-01

355

Ozone spectroscopy in the electronic ground state: High-resolution spectra analyses and update of line parameters since 2003  

NASA Astrophysics Data System (ADS)

The state of the art analyses of high-resolution ozone spectra and a critical discussion of line parameters updated since the previous review by Rinsland et al. [J Quant Spectrosc Radiat Transfer 2003;82:207–18] are presented. We focus on recent works revisiting improved measurements and analyses of Fourier transform spectra below 5600 cm?1 and review Cavity Ring-Down Spectroscopy measurements and analyses in the 5850–7920 cm?1 spectral region which have been performed for 16O3 and all 18O enriched ozone isotopologues. Various issues related to resonance perturbations due to dark states are discussed as well as the issues concerning the accuracy of the experimental parameters, the data modelling and the data reduction. Comparisons of vibration levels determined from spectra analyses with predictions from the molecular potential functions are given. The procedures of empirical corrections for calculated line lists are described and the "intricate" question of absolute intensity determination is overviewed. Also, a review of deficiencies, challenge for improvements, and related works in progress are reported.

Barbe, A.; Mikhailenko, S.; Starikova, E.; De Backer, M.-R.; Tyuterev, Vl. G.; Mondelain, D.; Kassi, S.; Campargue, A.; Janssen, C.; Tashkun, S.; Kochanov, R.; Gamache, R.; Orphal, J.

2013-11-01

356

Action Spectra of Photosystems I and II in State 1 and State 2 in lntact Sugar Maple Leaves  

Microsoft Academic Search

~~ Photochemical activity, measured as energy storage of photo- systems I (PSI) and II (PSII) together and individually, is studied in sugar maple (Acer saccharum Marsh.) leaves in the spectral range between 400 and 700 nm in state 1 and state 2. Total photochemical activity remains the same in both state 1 and state 2 between 580 and 700 nm,

Konka Veeranjaneyulu; Roger M. Leblanc

1994-01-01

357

Time-resolved and temperature-dependent fluorescence spectra of anthracene and pyrene in crystalline and liquid states  

SciTech Connect

Excimer states of anthracene have been found not only in the cyrstalline phase at high temperatures but also in the liquid phase by observing stationary and time-resolved fluorescence spectra. Fluorescence decay times in the liquid phase are very short, 0.2-0.3 ns, without any emission wavelength dependence even at the excimer band. On the other hand, there seems to appear a separate component around the excimer band of pyrene liquid, of which the origin is tentatively assigned to a monomer emission band. The change of profiles in Raman spectra of anthracene at the transition from crystal to liquid has been observed and discussed in relation to the disordered and/or ordered structures.

Horiguchi, R.; Iwasaki, N.; Maruyama, Y.

1987-09-10

358

Improved Cell Typing by Charge-State Deconvolution of matrix-assisted laser desorption/ionization Mass Spectra  

SciTech Connect

Robust, specific, and rapid identification of toxic strains of bacteria and viruses, to guide the mitigation of their adverse health effects and optimum implementation of other response actions, remains a major analytical challenge. This need has driven the development of methods for classification of microorganisms using mass spectrometry, particularly matrix-assisted laser desorption ionization MS (MALDI) that allows high throughput analyses with minimum sample preparation. We describe a novel approach to cell typing based on pattern recognition of MALDI spectra, which involves charge-state deconvolution in conjunction with a new correlation analysis procedure. The method is applicable to both prokaryotic and eukaryotic cells. Charge-state deconvolution improves the quantitative reproducibility of spectra because multiply-charged ions resulting from the same biomarker attaching a different number of protons are recognized and their abundances are combined. This allows a clearer distinction of bacterial strains or of cancerous and normal liver cells. Improved class distinction provided by charge-state deconvolution was demonstrated by cluster spacing on canonical variate score charts and by correlation analyses. Deconvolution may enhance detection of early disease state or therapy progress markers in various tissues analyzed by MALDI.

Wilkes, Jon G.; Buzantu, Dan A.; Dare, Diane J.; Dragan, Yvonne P.; Chiarelli, M. Paul; Holland, Ricky D.; Beaudoin, Michael; Heinze, Thomas M.; Nayak, Rajesh; Shvartsburg, Alexandre A.

2006-05-30

359

Temperature dependence of the 1,6-diphenyl-1,3,5-hexatriene triplet lifetime in solution and theoretical evaluation of triplet conformer interconversion.  

PubMed

The 1,6-diphenyl-1,3,5-hexatriene (DPH) triplet decay rate constant in degassed benzene is strongly temperature-dependent. Photostationary states for the fluorenone-sensitized photoisomerization of DPH in degassed methylcyclohexane (MCH) favor the all-trans isomer and become richer in the cis isomers as the temperature is increased. The results are interpreted in terms of competing decays from equilibrated triplet conformers on the basis of the experimentally derived DPH triplet potential energy surface [Saltiel, J.; Crowder, J. M.; Wang, S. J. Am. Chem. Soc. 1999, 121, 895 902; 5352]. Calculated geometries and energy differences [B3LYP/6-311+G(d,p)] are consistent with the experimental model. PMID:20450222

Saltiel, Jack; Klima, Rodney; van de Burgt, L J; Wang, Shujun; Dmitrenko, Olga

2010-05-07

360

Laser Microwave Precision Measurements of 2 triplet S(1) and 2 triplet P Term Splittings in Helium-Like Li(+1).  

National Technical Information Service (NTIS)

The hyperfine structure (hfs) splittings of the metastable 1s2s triplet S(1) state of helium-like (6,7)Li(+1) have been measured with combined laser optical pumping and microwave resonance. A low energy Li(+1) ion beam, optically exicted by an intersectin...

U. Koetz J. Kowalski R. Neumann S. Noehte H. Suhr

1984-01-01

361

Higgs triplets, decoupling, and precision measurements  

SciTech Connect

Electroweak precision data has been extensively used to constrain models containing physics beyond that of the standard model. When the model contains Higgs scalars in representations other than SU(2) singlets or doublets, and hence {rho}{ne}1 at tree level, a correct renormalization scheme requires more inputs than the three needed for the standard model. We discuss the connection between the renormalization of models with Higgs triplets and the decoupling properties of the models as the mass scale for the scalar triplet field becomes much larger than the electroweak scale. The requirements of perturbativity of the couplings and agreement with electroweak data place strong restrictions on models with Higgs triplets. Our results have important implications for Little Higgs type models and other models with {rho}{ne}1 at tree level.

Chen, M.-C. [Department of Physics and Astronomy, University of California, Irvine, California 92697 (United States); Dawson, Sally [Department of Physics, Brookhaven National Laboratory, Upton, New York 11973 (United States); Jackson, C. B. [HEP Division, Argonne National Laboratory, 9700 Cass Avenue Argonne, Illinois 60439 (United States)

2008-11-01

362

Vibrational overtone spectra of N-H stretches and intramolecular dynamics on the ground and electronically excited states of methylamine  

SciTech Connect

The vibrational pattern and energy flow in the N-H stretch manifolds and the dissociation dynamics of methylamine (CH{sub 3}NH{sub 2}) were investigated via vibrationally mediated photodissociation. Action spectra and Doppler profiles, reflecting the yield of the ensuing H photofragments, versus near infrared/visible vibrational excitation and UV excitation, respectively, were measured. The jet-cooled action spectra and the simultaneously measured room temperature photoacoustic spectra of the first to third N-H stretching overtones exhibit broad features, somewhat narrower in the former, consisting of barely recognized multiple bands. Two phases of fitting of the spectroscopic data were performed. In the first phase, the raw data were analyzed to obtain band positions, types, intensities, and transition linewidths. In the second, the information derived from the first phase was then used as data in a fit to joint local mode/normal mode (LM/NM) and NM Hamiltonian parameters. The derived parameters predicted well band positions and allowed band assignment. The LM/NM Hamiltonian and the extracted Lorentzian linewidths enabled the determination of the initial pathways for energy redistribution and the overall temporal behavior of the N-H stretch and doorway states, as a result of Fermi couplings and interactions with bath states. The results indicate a nonstatistical energy flow in the V=2 manifold region, pointing to the dependence of the coupling on specific low order resonances rather than on the total density of bath states. The Doppler profiles suggest lower average translational energies for the released H photofragments, in particular, for V=3 and 4 as compared to V=1 and 2, implying a change in the mechanism for bond cleavage.

Marom, Ran; Zecharia, Uzi; Rosenwaks, Salman; Bar, Ilana [Department of Physics, Ben-Gurion University of the Negev, Beer-Sheva 84105 (Israel)

2008-04-21

363

Infrared and Microwave Spectra and Force Field of DBO: The Coriolis Interaction between the ?1and ?2+ ?3States  

NASA Astrophysics Data System (ADS)

The ?1and ?3bands of D11BO and the ?1band of D10BO were observed by using an infrared diode laser spectrometer. The DBO molecule was generated by an ac discharge in a mixture of BCl3, D2, O2, and He. As inferred previously, a strong Coriolis interaction was in fact found to take place between the ?1and ?2+ ?3states, and an analysis of the observed ?1spectra, which explicitly took into account this Coriolis interaction, predicted the pure rotational transition frequencies of DBO in the ?1state. Pure rotational lines were then detected by microwave spectroscopy, confirming the validity of the infrared assignment. In the microwave experiment DBO molecules were generated by a discharge in a mixture of B2D6and O2. The three fundamental bands and a hot band of D11BO, as well as the ?1and ?3bands of D10BO, were subsequently recorded in emission with a Fourier transform infrared spectrometer. DBO molecules were generated by the reaction of D2with HBO at temperatures above 800°C in a ceramic tube furnace. All of the observed spectra were simultaneously subjected to a least-squares analysis to obtain molecular parameters in the ground, ?1, ?2, ?3, and ?2+ ?3states. The results thus obtained improved the force field and molecular structure of the HBO/DBO molecules reported in a previous study (Y. Kawashima, Y. Endo, and E. Hirota, 1989,J. Mol. Spectrosc.133, 116-127).

Kawashima, Yoshiyuki; Colarusso, Pina; Zhang, K. Q.; Bernath, Peter; Hirota, Eizi

1998-11-01

364

AssignFit: A program for simultaneous assignment and structure refinement from solid-state NMR spectra  

NASA Astrophysics Data System (ADS)

AssignFit is a computer program developed within the XPLOR-NIH package for the assignment of dipolar coupling (DC) and chemical shift anisotropy (CSA) restraints derived from the solid-state NMR spectra of protein samples with uniaxial order. The method is based on minimizing the difference between experimentally observed solid-state NMR spectra and the frequencies back calculated from a structural model. Starting with a structural model and a set of DC and CSA restraints grouped only by amino acid type, as would be obtained by selective isotopic labeling, AssignFit generates all of the possible assignment permutations and calculates the corresponding atomic coordinates oriented in the alignment frame, together with the associated set of NMR frequencies, which are then compared with the experimental data for best fit. Incorporation of AssignFit in a simulated annealing refinement cycle provides an approach for simultaneous assignment and structure refinement (SASR) of proteins from solid-state NMR orientation restraints. The methods are demonstrated with data from two integral membrane proteins, one ?-helical and one ?-barrel, embedded in phospholipid bilayer membranes.

Tian, Ye; Schwieters, Charles D.; Opella, Stanley J.; Marassi, Francesca M.

2012-01-01

365

Ground state electronic structures and spectra of zinc complexes of porphyrin, tetraazaporphyrin, tetrabenzoporphyrin, and phthalocyanine: A density functional theory study  

NASA Astrophysics Data System (ADS)

Density functional theory (DFT) electronic structure calculations were carried out to predict the structures and ground-state spectra for zinc complexes of porphyrin (ZnP), tetraazaporphyrin (ZnTAP), tetrabenzoporphyrin (ZnTBP), and phthalocyanine (ZnPc). All four porphyrins are found to have stable D4h structures. Structurally, meso-tetraaza substitutions significantly reduce the central hole in ZnTAP and ZnPc compared to ZnP. The excitation energies and oscillator strengths, computed by time-dependent DFT, provide a good account of the observed spectra of all four compounds. The TDDFT spectrum of ZnPc has a number of bands in the Soret region, in agreement with the experimental spectra that have been determined through spectral deconvolution. The low energy n-->?* transition (Q') reported for ZnPc, however, was not found in the computed spectrum. The effects of meso-tetraaza substitutions and tetrabenzo annulations on the spectrum of ZnP are discussed.

Nguyen, Kiet A.; Pachter, Ruth

2001-06-01

366

Xanthophylls in light-harvesting complex II of higher plants: light harvesting and triplet quenching  

Microsoft Academic Search

A spectral and functional assignment of the xanthophylls in monomeric and trimeric light- harvesting complex II of green plants has been obtained using HPLC analysis of the pigment composition, laser-flash induced triplet-minus-singlet, fluorescence excitation, and absorption spectra. It is shown that violaxanthin is not present in monomeric preparations, that it has most likely a red-most absorption maximum at 510 nm

Erwin J. G. Peterman; Claudiu C. Gradinaru; Florentine Calkoen; Jeroen C. Borst; Rienk van Grondelle; Herbert van Amerongen

1997-01-01

367

Manganese-induced triplet blinking and photobleaching of single molecule cyanine dyes.  

PubMed

Irradiation of solutions of the cyanine dyes Cy3, Cy3B, and Cy5 in the presence of Mn(2+) causes an increase in the yield of formation of the triplet state of the dye. This results in increased photobleaching and triplet blinking. Experiments with other divalent ions and paramagnetic molecules suggest that the enhancement in the intersystem-crossing rate is related to the paramagnetic nature of the Mn(2+) cation. The results are consistent with a model in which the formation of a weak collisional complex between the dye and the ion results in mixing of the singlet and triplet states of the dye. These findings are particularly significant in single-molecule spectroscopy and super-resolution imaging methods, in which photobleaching and blinking play an important role. PMID:24039065

Ciuba, Monika A; Levitus, Marcia

2013-09-03

368

Modeling Excited States of Fluorescent Compounds with UV-Vis Spectra Calculations  

Microsoft Academic Search

Fluorescence is the property where molecules absorb electromagnetic radiation usually in the ultraviolet range and re-emit light in greater wavelengths, usually in the visible light range. We investigated the fluorescent molecules DMABN, ABN, MABN, MMD, caffeine, anthracene, salicylamide, and acetyl anthranilic acid through excited state computational chemistry calculations and observed the excited state quantum descriptors with a focus on peak

Eric Li; Amy Kim; Lisa Zhang

2007-01-01

369

Photochemistry of furyl- and thienyldiazomethanes: spectroscopic characterization of triplet 3-thienylcarbene.  

PubMed

Photolysis (? > 543 nm) of 3-thienyldiazomethane (1), matrix isolated in Ar or N(2) at 10 K, yields triplet 3-thienylcarbene (13) and ?-thial-methylenecyclopropene (9). Carbene 13 was characterized by IR, UV/vis, and EPR spectroscopy. The conformational isomers of 3-thienylcarbene (s-E and s-Z) exhibit an unusually large difference in zero-field splitting parameters in the triplet EPR spectrum (|D/hc| = 0.508 cm(-1), |E/hc| = 0.0554 cm(-1); |D/hc| = 0.579 cm(-1), |E/hc| = 0.0315 cm(-1)). Natural Bond Orbital (NBO) calculations reveal substantially differing spin densities in the 3-thienyl ring at the positions adjacent to the carbene center, which is one factor contributing to the large difference in D values. NBO calculations also reveal a stabilizing interaction between the sp orbital of the carbene carbon in the s-Z rotamer of 13 and the antibonding ? orbital between sulfur and the neighboring carbon-an interaction that is not observed in the s-E rotamer of 13. In contrast to the EPR spectra, the electronic absorption spectra of the rotamers of triplet 3-thienylcarbene (13) are indistinguishable under our experimental conditions. The carbene exhibits a weak electronic absorption in the visible spectrum (?(max) = 467 nm) that is characteristic of triplet arylcarbenes. Although studies of 2-thienyldiazomethane (2), 3-furyldiazomethane (3), or 2-furyldiazomethane (4) provided further insight into the photochemical interconversions among C(5)H(4)S or C(5)H(4)O isomers, these studies did not lead to the spectroscopic detection of the corresponding triplet carbenes (2-thienylcarbene (11), 3-furylcarbene (23), or 2-furylcarbene (22), respectively). PMID:22463599

Pharr, Caroline R; Kopff, Laura A; Bennett, Brian; Reid, Scott A; McMahon, Robert J

2012-03-30

370

Quenching excited triplet C{sub 60} fullerene by tetracyanoethylene in benzonitrile  

SciTech Connect

The main photophysical properties of C{sub 60} fullerene: The absorption spectra of excited singlet C{sub 60}, the inter-combinational conversion time, the quantum yield of triplet C{sub 60}, the triplet-triplet absorption spectra, and the channels and rate constants of the deactivation of triplet C{sub 60} have been established. The photochemical properties of C{sub 60} fullerene have been investigated to a lesser degree. C{sub 60} is known to be readily reduced (E{sub 1/2} = {minus}0.4 in relation to Ag/Ag{sup +}), in particular, photochemically. For example, photoexcitation of charge-transfer complexes of C{sub 60} with amines gives the radical anion C{sup {minus}}{sub 60} which is also formed in reactions of photoexcited C{sub 60} fullerene. The formation of the radical cation C{sup +}{sub 60} under the action of light has been detected in the reaction with colloidal TiO{sub 2}. The radical ion C{sup +}{sub 60} has been obtained in a homogeneous photochemical process: the reaction of unexcited C{sub 60} with excited singlet N-methylacridinium hexafluorophosphate or with the biphenyl radical cation generated in the reaction with excited singlet N-methylacridinium hexafluorophosphate. The formation of C{sup +}{sub 60} with an electron acceptor in a homogeneous process has not so far been observed. The purpose of this work has been to study the quenching of triplet {sup 3}C{sub 60} with an electron acceptor, tetracyanoethylene (TCNE), which is known to oxidize unsaturated or aromatic hydrocarbons in photochemical reactions.

Nadtochenko, V.A.; Denisov, N.N.; Rubtsov, I.V.; Lobach, A.S.; Moravsky, A.P. [Institute of Chemical Physics in Chernogolovka, Moscow (Russian Federation)

1994-01-01

371

Electronic spectra and excited-state dynamics of 4-fluoro-N,N-dimethylaniline  

NASA Astrophysics Data System (ADS)

Concerted ultrafast time-resolved spectroscopic experiments and ab initio computational (TDDFT) studies of the electronic transitions of 4-fluoro-N,N-dimethylaniline (FDMA) have been performed to investigate the mechanism of photo-induced intramolecular charge transfer (ICT). The compound FDMA shows dual fluorescence from a ??? state and a closely-lying twisted intramolecular charge transfer (TICT) state in both n-hexane and acetonitrile. The very similar lifetimes observed for the two emission bands indicate that the ??? and the TICT states are effectively in thermal equilibrium at room temperature.

Fujiwara, Takashige; Reichardt, Christian; Aaron Vogt, R.; Crespo-Hernández, Carlos E.; Zgierski, Marek Z.; Lim, Edward C.

2013-10-01

372

Nucleon, Delta and Omega excited state spectra at three pion mass values  

SciTech Connect

The energies of the excited states of the Nucleon, Delta and Omega are computed in lattice QCD, using two light quarks and one strange quark on anisotropic lattices. The calculations are performed at three values of the pion mass: 392(4), 438(3) and 521(3) MeV. We employ the variational method with a basis of about ten interpolating operators enabling six energies to be distinguished clearly in each irreducible representation of the octahedral group. We compare our calculations of nucleon excited states with the low-lying experimental spectrum. There is reasonable agreement for the pattern of states.

John Bulava, Robert G. Edwards, Balint Joo, David G. Richards, Eric Engelson, Huey-Wen Lin, Colin Morningstar, Stephen J. Wallace

2010-06-01

373

Ferromagnetic behavior of a triplet superconductor  

Microsoft Academic Search

Properties of a type II triplet superconductor with equal spin pairing are investigated using the phenomenological Ginzburg-Landau approach. It is shown that there exist two kinds of fluxons: vortices and magnetic skyrmions. Vector nature of the order parameter allows a direct coupling of the effective spin of the condensate to a magnetic field. This coupling, which is reminiscent to Zeeman

A. Knigavko; B. Rosenstein; Y. F. Chen; H. L. Huang; M. T. Lin

1999-01-01

374

Ferromagnetic behavior of a triplet superconductor  

Microsoft Academic Search

Properties of a type II triplet superconductor with equal spin pairing are investigated using the phenomenological Ginzburg–Landau approach. It is shown that there exist two kinds of fluxons: vortices and magnetic skyrmions. Vector nature of the order parameter allows a direct coupling of the effective spin of the condensate to a magnetic field. This coupling, which is reminiscent to Zeeman

A. Knigavko; B. Rosenstein; Y. F. Chen; H. L. Huang; M. T. Lin

1999-01-01

375

One Interesting Family of Diophantine Triplets  

ERIC Educational Resources Information Center

|In this note properties of two sequences generated by the recurrence relation G[subscript n] +2 = 4 G[subscript n] +1 - G[subscript n], are studied. It is shown that one of the sequences leads to a family of diophantine triplets. Some interesting properties of these sequences are also established.|

Deshpande, M. N.

2002-01-01

376

Perinatal care improves the outcome of triplets  

Microsoft Academic Search

Objective: To compare pregnancy complications and neonatal outcome of 85 triplet gestations cared for during the 15 years in a single perinatal unit. Methods: Pregnancies were divided in two groups according to the differences in the management plan and their outcomes were compared. Group I (N=44) consisted of pregnancies cared from 1986 to 1995, using standard model of care: preventive

Snjezana Skrablin; Ivan Kuvacic; Drzislav Kalafatic; Branimir Peter; Snjezana Gveric-Ahmetasevic; Nevena Letica-Protega; Jelena Polak-Babic

2002-01-01

377

Vibrational spectra of isomeric pyridinic carboxylic acids in solid state and in solution and their SERS studies in silver sol  

NASA Astrophysics Data System (ADS)

Raman spectroscopic studies of three isomeric pyridinic carboxylic acids, viz. picolinic, nicotinic and iso-nicotinic acid in solid state, in aqueous solution and in silver hydrosol, in the frequency range 900-1750 cm -1, have been made. Assignments of the observed bands have been proposed in relation to the molecular forms present in solid state and in solution. Different degrees of intensity enhancements of the Raman bands in surface-enhanced Raman scattering (SERS) have been observed in all the three isomeric molecules. In iso-nicotinic acid, the intensity enhancement has been found to be minimum. Comparisons of Raman spectra in aqueous solution with those due to SERS in silver sol indicate that picolinic and nicotinic acid adsorb perpendicularly to the sol surface whereas in iso-nicotinic acid it occurs via donation of a ?-electron of the aromatic ring, i.e. the plane of the ring lies parallel to the surface of the sol.

Chattopadhyay, S.; Brahma, S. K.

1993-04-01

378

Theory and application of triplet-valued wavelets  

Microsoft Academic Search

Color image processing is investigated in this paper using an algebraic approach based on triplet numbers. In the algebraic approach, each image element is considered not as a 3D vector, but as a triplet number. The main goal of the paper is to show that triplet algebra can be used to solve colour image processing problems in a natural and

Valeri Labounets; Alexei Maidan; Ekaterina V. Labunets-Rundblad; Jaakko T. Astola

2002-01-01

379

SuperTriplets: a triplet-based supertree approach to phylogenomics  

PubMed Central

Motivation: Phylogenetic tree-building methods use molecular data to represent the evolutionary history of genes and taxa. A recurrent problem is to reconcile the various phylogenies built from different genomic sequences into a single one. This task is generally conducted by a two-step approach whereby a binary representation of the initial trees is first inferred and then a maximum parsimony (MP) analysis is performed on it. This binary representation uses a decomposition of all source trees that is usually based on clades, but that can also be based on triplets or quartets. The relative performances of these representations have been discussed but are difficult to assess since both are limited to relatively small datasets. Results: This article focuses on the triplet-based representation of source trees. We first recall how, using this representation, the parsimony analysis is related to the median tree notion. We then introduce SuperTriplets, a new algorithm that is specially designed to optimize this alternative formulation of the MP criterion. The method avoids several practical limitations of the triplet-based binary matrix representation, making it useful to deal with large datasets. When the correct resolution of every triplet appears more often than the incorrect ones in source trees, SuperTriplets warrants to reconstruct the correct phylogeny. Both simulations and a case study on mammalian phylogenomics confirm the advantages of this approach. In both cases, SuperTriplets tends to propose less resolved but more reliable supertrees than those inferred using Matrix Representation with Parsimony. Availability: Online and JAVA standalone versions of SuperTriplets are available at http://www.supertriplets.univ-montp2.fr/ Contact: vincent.ranwez@univ-montp2.fr

Ranwez, Vincent; Criscuolo, Alexis; Douzery, Emmanuel J.P.

2010-01-01

380

Temperature dependence of the luminescence lifetime of hexanuclear molybdenum(II) chloride cluster. Identification of lower excited triplet sublevels  

Microsoft Academic Search

The temperature dependence of the luminescence lifetime has been investigated for the tetraethylammonium salt of the octakis(..mu..â-chloro)hexachlorohexamolybdate(2-) ion, (MoâClââ)\\/sup 2 -\\/, in the 1.4-300 K range. The lifetime tends to decrease as the temperature increases. The observed temperature dependence has been analyzed in terms of the emissions from several Boltzmann populated triplet sublevels. The lowest triplet state has been identified

Yuria Saito; Hideaki K. Tanaka; Yoichi Sasaki; Tohru Azumi

1985-01-01

381

Singlet and triplet Bardeen-Cooper-Schrieffer pairs in a gas of two-species fermionic polar molecules  

SciTech Connect

Taking into account the deformation of the Fermi surface, we investigate the spin-singlet and -triplet BCS pairings in a mixture of fermionic polar molecules with two different hyperfine states. In particular, we explore the relation between the critical temperatures and the Fock-exchange interaction. We also show that, by tuning short-range interaction between interspecies molecules, the singlet- and triplet-paired superfluids may coexist.

Shi, T.; Zhang, J.-N.; Sun, C.-P.; Yi, S. [Key Laboratory of Frontiers in Theoretical Physics, Institute of Theoretical Physics, Chinese Academy of Sciences, Beijing 100190 (China)

2010-09-15

382

Nucleon, ?, and ? excited state spectra in Nf=2+1 lattice QCD  

NASA Astrophysics Data System (ADS)

The energies of the excited states of the nucleon, ?, and ? are computed in lattice QCD, using two light quarks and one strange quark on anisotropic lattices. The calculation is performed at three values of the light quark mass, corresponding to pion masses m?=392(4), 438(3), and 521(3) MeV. We employ the variational method with a large basis of interpolating operators enabling six energies in each irreducible representation of the lattice to be distinguished clearly. We compare our calculation with the low-lying experimental spectrum, with which we find reasonable agreement in the pattern of states. The need to include operators that couple to the expected multihadron states in the spectrum is clearly identified.

Bulava, J.; Edwards, R. G.; Engelson, E.; Joó, B.; Lin, H.-W.; Morningstar, C.; Richards, D. G.; Wallace, S. J.

2010-07-01

383

Experimental and Theoretical Study of the Electronic States and Spectra of TeH and TeLi  

NASA Astrophysics Data System (ADS)

Gas-phase emission spectra of the hitherto unknown free radical TeLi have been measured in the NIR range with a Fourier-transform spectrometer. The emissions were observed from a fast flow system in which tellurium vapor in argon carrier gas was passed through a microwave discharge and mixed with lithium vapor in an observation tube. Two systems of blue-degraded bands were measured at high spectral resolution in the ranges 8000-9000 and 5700-6700 cm-1 and vibrational and rotational analyses were performed. In order to aid in the analysis of the experimental data, a series of relativistic configuration interaction calculations has been carried out to obtain potential curves for the low-lying states of TeLi and the isovalent TeH and also electric dipole transition moments connecting them. As in the TeH system, the ground state of TeLi is found to be X2?i, but with a remarkably smaller spin-orbit splitting. The TeLi calculations indicate a strongly bound A2?+ state, while in TeH the analogous state is computed to lie significantly higher at ~32 000 cm-1, and it is strongly predissociated. Based on the theoretical analysis, the observed TeLi band systems are assigned to the transitions A2?+(A1/2)-->X12?3/2(X13/2) and A2?+(A1/2)-->X22?1/2(X21/2). Analysis of the spectra has yielded the molecular constants (in cm-1) X12?3/2:?e=457.49(3), ?exe=2.482(9), B0=0.408908(8); X22?1/2: Te=2353.44(3), ?e=456.28(4), ?exe=2.635(8), B0=0.414954(8), p0=1.00637(4); A2?+: Te=8574.64(2), ?e=437.81(3), ?exe=2.581(8), B0=0.423903(8), p0=-0.19915(2), where the numbers in parentheses are the standard deviations of the parameters. Comparison of the isovalent TeLi and TeH systems emphasizes that the difference in bonding character (ionic in TeLi vs covalent in TeH) is responsible for qualitative differences in the electronic spectra of these two molecules.

Setzer, K. D.; Fink, E. H.; Alekseyev, A. B.; Liebermann, H.-P.; Buenker, R. J.

2001-04-01

384

Experimental and Theoretical Study of the Electronic States and Spectra of TeH and TeLi.  

PubMed

Gas-phase emission spectra of the hitherto unknown free radical TeLi have been measured in the NIR range with a Fourier-transform spectrometer. The emissions were observed from a fast flow system in which tellurium vapor in argon carrier gas was passed through a microwave discharge and mixed with lithium vapor in an observation tube. Two systems of blue-degraded bands were measured at high spectral resolution in the ranges 8000-9000 and 5700-6700 cm(-1) and vibrational and rotational analyses were performed. In order to aid in the analysis of the experimental data, a series of relativistic configuration interaction calculations has been carried out to obtain potential curves for the low-lying states of TeLi and the isovalent TeH and also electric dipole transition moments connecting them. As in the TeH system, the ground state of TeLi is found to be X(2)Pi(i), but with a remarkably smaller spin-orbit splitting. The TeLi calculations indicate a strongly bound A(2)Sigma(+) state, while in TeH the analogous state is computed to lie significantly higher at approximately 32 000 cm(-1), and it is strongly predissociated. Based on the theoretical analysis, the observed TeLi band systems are assigned to the transitions A(2)Sigma(+)(A1/2)-->X(1)(2)Pi(3/2)(X(1)3/2) and A(2)Sigma(+)(A1/2)-->X(2)(2)Pi(1/2)(X(2)1/2). Analysis of the spectra has yielded the molecular constants (in cm(-1)) X(1)(2)Pi(3/2):omega(e)=457.49(3), omega(e)x(e)=2.482(9), B(0)=0.408908(8); X(2)(2)Pi(1/2): T(e)=2353.44(3), omega(e)=456.28(4), omega(e)x(e)=2.635(8), B(0)=0.414954(8), p(0)=1.00637(4); A(2)Sigma(+): T(e)=8574.64(2), omega(e)=437.81(3), omega(e)x(e)=2.581(8), B(0)=0.423903(8), p(0)=-0.19915(2), where the numbers in parentheses are the standard deviations of the parameters. Comparison of the isovalent TeLi and TeH systems emphasizes that the difference in bonding character (ionic in TeLi vs covalent in TeH) is responsible for qualitative differences in the electronic spectra of these two molecules. Copyright 2001 Academic Press. PMID:11281700

Setzer, K. D.; Fink, E. H.; Alekseyev, A. B.; Liebermann, H.-P.; Buenker, R. J.

2001-04-01

385

EEG spectra, behavioral states and motor activity in rats exposed to acetylcholinesterase inhibitor chlorpyrifos  

Microsoft Academic Search

Exposure to organophosphates (OP) has been associated with sleep disorders such as insomnia and “excessive dreaming.” The central mechanisms of these effects are not well understood. OPs inhibit acetylcholinesterase (AChE) activity, leading to a hyperactivity of the brain cholinergic systems that are involved in sleep regulation. We studied alterations in the EEG, behavioral states, motor activity and core temperature in

Olga A. Timofeeva; Christopher J. Gordon

2002-01-01

386

Effect of paramagnetic cations on solid state C nuclear magnetic resonance spectra of natural organic materials  

Microsoft Academic Search

The effect of cation (Zn, Cu, Pr) amendment on the solid state C nuclear magnetic resonance (NMR) spectral properties of organic materials was investigated. The organic materials were chosen to represent structures found in natural organic matter (NOM) from soils, waters, sediments, sewage sludges and plant residues, and included cellulose, pectin, chitin, collagen, a commercial humic acid, and charcoal. Cation

Ronald J. Smernik; J. Malcolm Oades

2000-01-01

387

TDDFT calculations of electronic spectra of benzoxazoles undergoing excited state proton transfer.  

PubMed

Energies and oscillator strengths of vertical transitions for various rotameric and tautomeric species of 2-(2'-hydroxyphenyl)benzoxazole (HBO), 2,5-bis(2-benzoxazolyl)phenol (DBP) and 2,5-bis(2-benzoxazolyl)hydroquinone (BBHQ) have been calculated in the ground and first excited states with the use of TDDFT methods. The TDDFT results demonstrate good correspondence to the frequencies of absorption and fluorescence bands of the benzoxazoles reported for measurements in supersonic jets and solution, but fail to predict relative energies of the enol and keto tautomers of DBP and BBHQ in the excited state. Low intensity of the fluorescence bands attributed to the conformations of HBO and DBP that do not undergo excited state proton transfer is shown to be caused by low concentrations of the conformations in the ground state. For the three compounds large-amplitude twisting of the keto tautomer is found to be one of radiationless processes resulting in decrease of the fluorescence with a large Stokes shift. PMID:23475275

Syetov, Y

2013-03-09

388

Analysis of CH2a˜ 1A1 (1,0,0) and (0,0,1) Coriolis-coupled states, a˜ 1A1–X˜ 3B1 spin–orbit coupling, and the equilibrium structure of CH2a˜ 1A1 state  

Microsoft Academic Search

The symmetric and antisymmetric stretch spectra of a˜ 1A1 CH2 are measured with Doppler-limited resolution by infrared flash-kinetic spectroscopy between 2600 and 3050 cm?1. The spectra are significantly perturbed by spin–orbit interactions between near-resonant levels of X˜ 3B1 in both lower and upper levels of the transitions, and by Coriolis interaction between symmetric and antisymmetric stretch states. The triplet character

Hrvoje Petek; David J. Nesbitt; David C. Darwin; Peter R. Ogilby; C. Bradley Moore; D. A. Ramsay

1989-01-01

389

Styryl Bodipy-C(60) Dyads as Efficient Heavy-Atom-Free Organic Triplet Photosensitizers.  

PubMed

C(60)-styryl Bodipy dyads that show strong absorption of visible light (? = 64?600 M(-1) cm(-1) at 657 nm) and a long-lived triplet excited state (?(T) = 123.2 ?s) are prepared. The dyads were used as heavy-atom-free organic triplet photosensitizers for photooxidation of 1,5-dihydroxynaphthalene via the photosensitizing of singlet oxygen ((1)O(2)). The photooxidation efficiency of the dyads compared to the conventional Ir(III) complex (1)O(2) photosensitizer increased 19-fold. PMID:22571170

Huang, Ling; Yu, Xuerong; Wu, Wanhua; Zhao, Jianzhang

2012-05-01

390

Singlet-to-Triplet Excitations in the Unconventional Spin-Peierls System TiOBr  

SciTech Connect

We have performed time-of-flight neutron scattering measurements on powder samples of the unconventional spin-Peierls compound TiOBr using the fine-resolution Fermi chopper spectrometer (SEQUOIA) at the SNS. These measurements reveal two branches of magnetic excitations within the commensurate and incommensurate spin-Peierls phases, which we associate with n = 1 and n = 2 triplet excitations out of the singlet ground state. These measurements represent the first direct measure of the singlet-triplet energy gap in TiOBr, which is found to have a value of Eg 21 meV.

Clancy, James P [McMaster University; Gaulin, Bruce D. [McMaster University; Adams, Carl P [St. Francis Xavier University, Antigonish, Nova Scotia; Granroth, Garrett E [ORNL; Kolesnikov, Alexander I [ORNL; Sherline, Todd E [ORNL; Chou, F. C. [National Taiwan University

2011-01-01

391

Detuning-dependent Mollow triplet of a coherently-driven single quantum dot.  

PubMed

We present both experimental and theoretical investigations of a laser-driven quantum dot (QD) in the dressed-state regime of resonance fluorescence. We explore the role of phonon scattering and pure dephasing on the detuning-dependence of the Mollow triplet and show that the triplet sidebands may spectrally broaden or narrow with increasing detuning. Based on a polaron master equation approach, which includes electron-phonon interaction nonperturbatively, we derive a fully analytical expression for the spectrum. With respect to detuning dependence, we identify a crossover between the regimes of spectral sideband narrowing or broadening. We also predict regimes of phonon-induced squeezing and anti-squeezing of the spectral resonances. A comparison of the theoretical predictions to detailed experimental studies on the laser detuning-dependence of Mollow triplet resonance emission from single In(Ga)As QDs reveals excellent agreement. PMID:23481972

Ulhaq, Ata; Weiler, Stefanie; Roy, Chiranjeeb; Ulrich, Sven Marcus; Jetter, Michael; Hughes, Stephen; Michler, Peter

2013-02-25

392

Singlet and triplet reactivity of 7-methyl-3-carbethoxy-thioxanthen-9-one (ETX) towards electron donors  

NASA Astrophysics Data System (ADS)

The reactivities of singlet and triplet excited states with electron donors exhibiting various chemical structures were determined by using static fluorescence quenching and laser flash photolysis in acetonitrile. Multiple Rehm-Weller plots were clearly determined for both excited states. Accordingly, whatever the multiplicity of the excited states, the electronic delocalization of the donor was shown to be as relevant a parameter as ? Get for the determination of the quenching rates. In addition, for a given overall free energy change and chemical class, the triplet state reactivity is higher than that of the singlet state.

Jacques, P.; Burget, D.; Allonas, X.; Fouassier, J. P.

1994-09-01

393

How Aggregation and Conformational Scrambling of Unfolded States Govern Fluorescence Emission Spectra  

PubMed Central

In a case study on five homologous ?-amylases we analyzed the properties of unfolded states as obtained from treatments with GndHCl and with elevated temperatures. In particular the wavelength of the tryptophan fluorescence emission peak (?max) is a valuable parameter to characterize properties of the unfolded state. In all cases with a typical red shift of the emission spectrum occurring during structural unfolding we observed a larger magnitude of this shift for GndHCl-induced unfolding as compared to thermal unfolding. Although a quantitative relation between aggregation and reduction of the unfolding induced red shifts cannot be given, our data indicate that protein aggregation contributes significantly to smaller magnitudes of red shifts as observed during thermal unfolding. In addition, other properties of the unfolded states, most probable structural compactness or simply differences in the conformational scrambling, also affect the magnitude of red shifts. For the irreversible unfolding ?-amylases studied here, transition temperatures and magnitudes of red shifts are strongly depending on heating rates. Lower protein concentrations and smaller heating rates lead to larger red shifts upon thermal unfolding, indicating that under these conditions the protein aggregation is less pronounced.

Duy, C.; Fitter, J.

2006-01-01

394

Spin state and valence state of iron in Earth's lower mantle from synchrotron Mössbauer spectra of perovskite and post-perovskite up to 1.5 Mbar  

NASA Astrophysics Data System (ADS)

The electronic spin state and valence state of iron are fundamental parameters that govern the physical properties and chemical behavior of iron-bearing phases in the Earth's interior, including their densities, sound velocities, thermal conductivities, and chemical potentials. Of particular importance are pressure- induced changes in the spin state and valence state of iron in the predominant lower mantle phase perovskite and its high-pressure polymorph post-perovskite. These issues remain controversial due to limited experimental data on highly compressed samples, and due to the lack of theoretical guidance for interpreting experimental results. Here we present new synchrotron Mössbauer spectra of perovskite and post-perovskite samples under pressures up to 145 GPa. Samples were synthesized and characterized in the laser-heated diamond anvil cell at SPring-8, from gel starting material with the composition (Mg0.9Fe0.1)SiO3. Synchrotron Mössbauer measurements were carried out at beamlines 3-ID and 16-ID at the Advanced Photon Source. Our spectra of perovskite can be fitted with two or three iron sites with quadruple splitting of 2.97 and 0.5 mm/sec, respectively. For post-perovskite, the spectrum can be fitted with a single component that has a small quadruple splitting. We interpret these results on the basis of calculated hyperfine parameters of iron with various crystallographic sites and spin/valence states, and discuss implications for the physics and chemistry of the lowermost mantle. This work is supported by NSF through a collaborative project EAR 07-38973.

Li, J.; Chen, B.; Gao, L.; Alp, E. E.; Hirose, K.; Zhao, J.; Xiao, Y.; Bengston, A.; Morgan, D.

2008-12-01

395

New methods for the acquisition of ultra-wideline solid-state NMR spectra of spin-1/2 nuclides  

NASA Astrophysics Data System (ADS)

The Wideband Uniform Rate Smooth Truncation - Carr-Purcell Meiboom-Gill (WURST-CPMG) pulse sequence was recently introduced as a new method of acquiring ultra-wideline solid-state NMR (SSNMR) patterns of quadrupolar nuclei (Chem. Phys. Lett. 464 (2008) 97). Herein, we describe the application of the WURST-CPMG pulse sequence to stationary samples (i.e., non-spinning or "static" samples) of various spin-1/2 nuclides (119Sn, 207Pb, 199Hg and 195Pt) in order to examine its effectiveness for acquiring ultra-wideline SSNMR patterns. WURST-CPMG is compared to the CPMG and Cross Polarization (CP)-CPMG pulse sequences in select cases (119Sn and 207Pb, respectively), and its usefulness in obtaining ultra-wideline SSNMR spectra in a piecewise fashion is explored. In addition, a preliminary investigation of pulses generated using optimal control theory (OCT) for the purpose of wideline excitation is presented; spectra acquired using these pulses are compared with standard, rectangular pulses of similar pulse powers. Both methods show much promise for acquiring high quality wideline patterns dominated by chemical shift anisotropy, with minimal distortions and significantly reduced experimental times.

MacGregor, Alan W.; O'Dell, Luke A.; Schurko, Robert W.

2011-01-01

396

N 2 triplet band systems and atomic oxygen in the dayglow  

Microsoft Academic Search

New spectrographic observations of the Earth's dayglow have been acquired by the Arizona Airglow Experiment (GLO) flown on the space shuttle. GLO is an imaging spectrograph that records simultaneous vertical profiles of prominent Earth limb emissions occurring at wavelengths between 115 and 900 nm. This study addresses the measured emissions from the N2 triplet states (first positive, second positive, and

A. L. Broadfoot; D. B. Hatfield; E. R. Anderson; T. C. Stone; B. R. Sandel; J. A. Gardner; E. Murad; D. J. Knecht; C. P. Pike; R. A. Viereck

1997-01-01

397

N2 triplet band systems and atomic oxygen in the dayglow  

Microsoft Academic Search

New spectrographic observations of the Earth's dayglow have been acquired by the Arizona Airglow Experiment (GLO) flown on the space shuttle. GLO is an imaging spectrograph that records simultaneous vertical profiles of prominent Earth limb emissions occurring at wavelengths between 115 and 900 nm. This study addresses the measured emissions from the N2 triplet states (first positive, second positive, and

A. L. Broadfoot; D. B. Hatfield; E. R. Anderson; T. C. Stone; B. R. Sandel; J. A. Gardner; E. Murad; D. J. Knecht; C. P. Pike; R. A. Viereck

1997-01-01

398

Powering and Control Strategy for the Main Quadrupole Magnets of the LHC Inner Triplet System  

Microsoft Academic Search

The LHC particle accelerator uses a string of superconducting quadrupole magnets called the Inner Triplet to focus the beams before collision. This paper describes the powering of the magnets using nested circuits, and their control by decoupling of the currents using state feedback loops, and presents commissioning results.

F Bordry; D Nisbet; H Thiesen; J Thomsen

2010-01-01

399

Powering and control strategy for the main quadrupole magnets of the lhc Inner Triplet system  

Microsoft Academic Search

The LHC particle accelerator uses a string of superconducting quadrupole magnets called the Inner Triplet to focus the beams before collision. This paper describes the powering of the magnets using nested circuits, and their control by decoupling of the currents using state feedback loops, and presents commissioning results.

F. Bordry; D. Nisbet; H. Thiesen; J. Thomsen

2009-01-01

400

Quantum states for quantum processes: A toy model for ammonia inversion spectra  

SciTech Connect

Chemical transformations are viewed here as quantum processes modulated by external fields, that is, as shifts in reactant to product amplitudes within a quantum state represented by a linear (coherent) superposition of electronuclear basis functions; their electronic quantum numbers identify the ''chemical species.'' This basis set can be mapped from attractors built from a unique electronic configurational space that is invariant with respect to the nuclear geometry. In turn, the quantum numbers that label these basis functions and the semiclassical potentials for the electronic attractors may be used to derive reaction coordinates to monitor progress as a function of the applied field. A generalization of Feynman's three-state model for the ammonia inversion process illustrates the scheme; to enforce symmetry for the entire inversion process model and ensure invariance with respect to nuclear configurations, the three attractors and their basis functions are computed with a grid of fixed floating Gaussian functions. The external-field modulation of the effective inversion barrier is discussed within this conceptual approach. This analysis brings the descriptions of chemical processes near modern technologies that employ molecules to encode information by means of confinement and external fields.

Arteca, Gustavo A. [Departement de Chimie et Biochimie and Biomolecular Sciences Programme, Laurentian University, Ramsey Lake Road, Sudbury, Ontario, Canada P3E 2C6 (Canada); Department of Physical Chemistry, Uppsala University, A ring ngstroemlaboratoriet, Box 259, S-751 05 Uppsala (Sweden); Tapia, O. [Department of Physical Chemistry, Uppsala University, A ring ngstroemlaboratoriet, Box 259, S-751 05 Uppsala (Sweden)

2011-07-15

401

Vibrational Spectra and Structure of Coumaran and Its Ring-Puckering Potential Energy Functions in the S0 and S1(pi,pi*) Electronic States  

Microsoft Academic Search

The far-infrared (IR), jet-cooled fluorescence excitation (FES), single vibronic level fluorescence (SVLF), and ultraviolet (UV) absorption spectra of coumaran have been recorded and analyzed. The assignment of those spectra has allowed a detailed energy map of both the S0 and S1(pi,pi*) electronic states of the ring-puckering (nu45) vibration to be determined. A one-dimensional potential energy function for the ring-puckering vibration

Juan Yang; Martin Wagner; Katsuhiko Okuyama; Jaan Laane

2006-01-01

402

Hindered and modulated rotational states and spectra of adsorbed diatomic molecules  

SciTech Connect

Both vertical and horizontal adsorption configurations of a diatomic molecule were modeled as the rigid rotor with which the spatial motion was confined by a finite conical well. In addition to the polar hindering potential, a sinusoidal azimuthal modulation, which bears the local symmetry of the adsorption site, was incorporated. Eigenfunctions for different models were expressed analytically in terms of the hypergeometric functions, and eigenvalues were solved numerically. We found that the rotational energy levels exhibit oscillatory behavior when plotted as functions of the hindrance angle. This particular phenomenon was interpreted as the occurrence of resonance transmission of the rotor wave function at certain hindrance condition. We also found that the rotational levels were grouped into bands when the azimuthal modulation strength was increased. The solutions were used to calculate the rotational-state distribution of desorbed molecules, and agreement with the previous experiment was obtained. {copyright} {ital 1996 The American Physical Society.}

Shih, Y.T. [Institute of Electro-Optical Engineering, National Chiao Tung University, Hsinchu, Taiwan, Republic of (China); Chuu, D.S. [Department of Electrophysics, National Chiao Tung University, Hsinchu, Taiwan, Republic of (China); Mei, W.N. [Department of Physics, University of Nebraska at Omaha, Omaha, Nebraska 68182 (United States)

1996-10-01

403

Exchange-only optimized effective potential calculation of excited state spectra for He and Be atoms.  

SciTech Connect

The optimized effective potential (OEP) method allows orbital-dependent functionals to be used in density functional theory (DFT), which, in particular, allows exact exchange formulations of the exchange energy to be used in DFT calculations. Because the exact exchange is inherently self-interaction correcting, the resulting OEP calculations have been found to yield superior band-gaps for condensed-phase systems. Here we apply these methods to the isolated atoms He and Be, and compare to high quality experiments and calculations to demonstrate that the orbital energies accurately reproduce the excited state spectrum for these species. These results suggest that coupling the exchange-only OEP calculations with proper (orbital-dependent or other) correlation functions might allow quantitative accuracy from DFT calculations.

Desjarlais, Michael Paul; Muller, Richard Partain

2006-02-01

404

An unexpected spontaneous triplet heterotopic pregnancy.  

PubMed

A heterotopic pregnancy is the coexistence of one or more ectopic pregnancies and a single or multiple eutopic pregnancies. This potentially fatal condition rarely occurs in spontaneous conception cycles. We report a case of spontaneous triplet heterotopic pregnancy in a multigravida with no known risk factors. Ultrasound imaging was the diagnostic tool used and left salpingectomy via laparotomy was performed in this case report. PMID:15756372

Alsunaidi, Mohammed I

2005-01-01

405

Highlights of supersymmetric hypercharge ±1 triplets  

NASA Astrophysics Data System (ADS)

The discovery of a standard model (SM)-like Higgs boson with a relatively heavy mass m h and hints of di-photon excess has deep implication to supersymmetric standard models (SSMs). We consider the SSM extended with hypercharge ±1 triplets, and investigate two scenarios of it: (A) triplets significantly couple to the Higgs doublets, which can substantially raise m h and simultaneously enhance the Higgs to di-photon rate via light chargino loops; (B) oppositely, these couplings are quite weak and thus m h can not be raised. But the doubly-charged Higgs bosons, owing to the gauge group structure, naturally interprets why there is an excess rather than a deficient of Higgs to di-photon rate. Additionally, the pseudo Dirac triplet fermion is an inelastic non-thermal dark matter candidate. Light doubly-charged particles, especially the doubly-charged Higgs boson around 100 GeV in scenario B, are predicted. We give a preliminary discussion on their search at the LHC.

Kang, Zhaofeng; Liu, Yandong; Ning, Guo-Zhu

2013-09-01

406

Intra-valley Spin-triplet p+ip Superconducting Pairing in Lightly Doped Graphene  

NASA Astrophysics Data System (ADS)

We analyze various possible superconducting pairing states and their relative stabilities in lightly doped graphene. We show that, when inter-sublattice electron-electron attractive interaction dominates and Fermi level is close to Dirac points, the system will favor intra-valley spin-triplet p+ip pairing state. Based on the novel pairing state, we further propose a scheme for doing topological quantum computation in graphene by engineering local strain fields and external magnetic fields.

Zhou, Jianhui; Qin, Tao; Shi, Junren

2013-03-01

407

Intra-Valley Spin-Triplet p + ip Superconducting Pairing in Lightly Doped Graphene  

NASA Astrophysics Data System (ADS)

We analyze various possible superconducting pairing states and their relative stabilities in lightly doped graphene. It is shown that, when inter-sublattice electron-electron attractive interaction dominates and the Fermi level is close to the Dirac points, the system will favor intra-valley spin-triplet p + ip pairing state. Based on the novel pairing state, we further propose a scheme for doing topological quantum computation in graphene by engineering local strain fields and external magnetic fields.

Zhou, Jian-Hui; Qin, Tao; Shi, Jun-Ren

2013-01-01

408

Singlet-triplet separations measured by [sup 31]P[l brace][sup 1]H[r brace] NMR: Applications to quadruply bonded dimolybdenum and ditungsten complexes  

SciTech Connect

A series of quadruply bonded dimolybdenum and ditungsten compounds M[sub 2]X[sub 4](PP)[sub 2] (M = Mo, W; PP = bidentate phosphine ligands; X = Cl, Br, I) with internal rotational angles [chi] varying from 0.0 to 69.4[degrees] have been studied. Their [sup 31]P[l brace][sup 1]H[r brace] NMR spectra are characterized by their temperature-dependent shifts and line widths that broaden with increasing temperature. A nonlinear, least-squares fit of this temperature dependence of the paramagnetic shifts for their NMR signals allows the evaluation of the singlet-triplet energy separation ([minus]2J), the diamagnetic shift (H[sub dia]), and the electron-nucleus hyperfine coupling constant (A). The singlet-triplet energy separations for all the compounds investigated are found to be in the range 1200-3000 cm[sup [minus]1]. It is now clearly established that the ground state remains [sup 1]A[sub 1g] ([delta][sup 2]) even at [chi] = 45[degrees], where [sup 3]A[sub 2u] ([delta][delta]*) lies 1230 cm[sup [minus]1] above it. The [delta]-bond energy and electronic [delta]-barrier can also be experimentally estimated as 13.8[+-]0.5 kcal mol[sup [minus]1] and 10.3[+-]0.5 kcal mol[sup [minus]1], respectively. 32 refs., 3 figs., 1 tab.

Cotton, F.A.; Eglin, J.L.; Bo Hong; James, C.A. (Texas A M Univ., College Station (United States))

1993-05-12

409

Triplet correlation in sheared suspensions of Brownian particles  

NASA Astrophysics Data System (ADS)

Triplet microstructure of sheared concentrated suspensions of Brownian monodisperse spherical particles is studied by sampling realizations of a three-dimensional unit cell subject to periodic boundary conditions obtained in accelerated Stokesian dynamics simulations. Triplets are regarded as a bridge between particle pairs and many-particle clusters thought responsible for shear thickening. Triplet-correlation data for weakly sheared near-equilibrium systems display an excluded volume effect of accumulated correlation for equilateral contacting triplets. As the Péclet number increases, there is a change in the preferred contacting isosceles triplet configuration, away from the ``closed'' triplet where the particles lie at the vertices of an equilateral triangle and toward the fully extended rod-like linear arrangement termed the ``open'' triplet. This transition is most pronounced for triplets lying in the plane of shear, where the open triplets' angular orientation with respect to the flow is very similar to that of a contacting pair. The correlation of suspension rheology to observed structure signals onset of larger clusters. An investigation of the predictive ability of Kirkwood's superposition approximation (KSA) provides valuable insights into the relationship between the pair and triplet probability distributions and helps achieve a better and more detailed understanding of the interplay of the pair and triplet dynamics. The KSA is seen more successfully to predict the shape of isosceles contacting triplet nonequilibrium distributions in the plane of shear than for similar configurations in equilibrium hard-sphere systems; in the sheared case, the discrepancies in magnitudes of distribution peaks are attributable to two interaction effects when pair average trajectories and locations of particles change in response to real, or ``hard,'' and probabilistically favored (``soft'') neighboring excluded volumes and, in the case of open triplets, due to changes in the correlation of the farthest separated pair caused by the fixed presence of the particle in the middle.

Yurkovetsky, Yevgeny; Morris, Jeffrey F.

2006-05-01

410

The protein's role in triplet energy transfer in bacterial reaction centers.  

SciTech Connect

When photosynthetic organisms are subjected to high-light conditions in nature, electron transfer becomes blocked as the rate of conversion of light into charge-separated states in the reaction center (RC) exceeds the capacity of the soluble carriers involved in cyclic electron transfer. In that event, a well-characterized T{sub 0}-polarized triplet state {sup T}P, is formed on the primary donor, P, from the P{sup +}H{sub A}{sup {minus}} state (reviewed in [1]). In an aerobic or semi-aerobic environment, the major role of the carotenoid (C), also bound by the RC, is to quench {sup T}P prior to its sensitization of the {sup 1}{Delta}{sub g} singlet state of oxygen--a potentially damaging biological oxidant. The carotenoid performs this function efficiently in most bacterial RCs by rapidly accepting the triplet state from P and dissipating this excited-state energy into heat through internal conversion. The lowest-lying triplet states of P and the carotenoid are sufficiently different that {sup T}P can promote oxygen to its excited singlet state whereas {sup T}C can quench the {sup T}P state (reviewed in [2]).

Laible, P. D.

1998-08-14

411

Singlet and triplet emission from methylenediphenyl-diisocyanate-based poly(ester urethane): determination of the energy-level diagram  

NASA Astrophysics Data System (ADS)

Optical absorption and luminescence measurements have been made on 4,4'-methylenediphenyl 1,1'-diisocyanate (MDI)-based poly(ester urethane) (PESU) and model compounds diphenylmethane (DPM) and butanol-capped MDI. Phosphorescence spectra of the three samples are nearly identical with maxima at 527, 488, 451, and 422nm. However, onset of strong optical absorption near 300nm in PESU and MDI precludes observation of the corresponding fluorescence spectrum. In contrast, DPM exhibits weaker absorption with onset occurring near 270nm. Consequently, its fluorescence spectrum is revealed and characterized by maxima at 302, 294, 286, and 279nm. From these data we derive the energy-level diagram for PESU and show that phosphorescence is due to electronic transitions between the first excited triplet and singlet ground states (T1-->S0), whereas fluorescence transitions occur between both first and second excited singlet and ground states (S1-->S0, and S2-->S0). The experimentally derived values are in good agreement with previously published theoretical values for the electronic excited states of PESU.

Cooke, D. W.; Muenchausen, R. E.; Bennett, B. L.; Wrobleski, D. A.; Orler, E. B.

2003-02-01

412

Experimental Ca I oscillator strengths for the 4p-5s triplet  

NASA Astrophysics Data System (ADS)

Context: Transition lines of neutral calcium are observed in the spectra of stellar and substellar objects. In particular, the abundance of ?-elements in metal-poor stars can place important constraints on the galactic chemical evolution. Such stellar abundance analyses rely heavily on accurate values for the oscillator strength of the observable transitions. Theoretical oscillator strengths are available for most neutral calcium lines visible in stellar spectra, but there are a limited number of experimental values in the literature. Aims: We present new and improved experimental oscillator strengths for the optical Ca i 4p-5s triplet (6102.7, 6122.2, 6162.2 Å). In addition, we present experimental radiative lifetimes for seven energy levels in the triplet system of Ca i. Methods: The oscillator strengths were determined by combining radiative lifetimes with branching fractions. The radiative lifetimes were measured using laser-induced fluorescence, and the branching fractions were determined using intensity calibrated spectra measured with Fourier transform spectrometry. In addition, the spectra were used to determine accurate (d? = 0.001 Å, d? = 0.002 cm-1) laboratory wavelengths for the 4p-5s transitions. Results: Oscillator strengths for the Ca i 4p-5s lines were determined with an absolute uncertainty of 9%, an uncertainty of ± 0.04 dex in the log(gf) values. The branching fractions were determined with a higher accuracy, resulting in relative uncertainties of 2-3%.

Aldenius, M.; Lundberg, H.; Blackwell-Whitehead, R.

2009-08-01

413

Supercurrent through a multilevel quantum dot close to singlet-triplet degeneracy  

NASA Astrophysics Data System (ADS)

We investigate two serially aligned quantum dots in the molecular regime of large tunnel couplings t. A Zeeman field B is used to tune the energy difference of singlet and triplet spin configurations. Attaching this geometry to BCS source and drain leads with gap ? and phase difference ? gives rise to an equilibrium supercurrent J. To compute J in the presence of Coulomb interactions U between the dot electrons, we employ the functional renormalization group (FRG). For B?t, where the singlet and (one out of a) triplet spin states are equal in energy, the current exhibits characteristics of a 0-? transition similar to a single impurity. Its magnitude in the ? phase, however, jumps discontinuously at B=t, being smaller on the triplet side. By exploiting the flexibility of the FRG, we demonstrate that this effect is generic and calculate J for realistic experimental parameters ?, U, and gate voltages ?. To obtain a more thorough understanding of the discontinuity, we analytically treat the limit ?=?, where one can access the exact many-particle states. Finally, carrying out perturbation theory in the dot-lead couplings substantiates the intuitive picture that Cooper-pair tunneling is favored by a singlet spin configuration while inhibited by a triplet one.

Karrasch, C.; Andergassen, S.; Meden, V.

2011-10-01

414

Optical and time-resolved electron paramagnetic resonance studies of the excited states of para-methylcinnamic acid and para-methylcinnamate anion  

Microsoft Academic Search

Time-resolved electron paramagnetic resonance (EPR), fluorescence, and phosphorescence spectra have been observed for the\\u000a excited states oftrans-p-methylcinnamic acid (p-MeCA) andtrans-p-methylcinnamate anion (p-MeCA?) in rigid organic glasses at 77 K. With a stretched-polymer-film technique, we assigned the resonance fields in the time-resolved\\u000a EPR spectra of the lowest excited triplet (T1) states ofp-MeCA andp-MeCA?. From the analysis of these spectra we concluded

M. Yagi; I. Yamamoto; R. Sasase; K. Seki

2003-01-01

415

Bodipy derivatives as organic triplet photosensitizers for aerobic photoorganocatalytic oxidative coupling of amines and photooxidation of dihydroxylnaphthalenes.  

PubMed

We used iodo-Bodipy derivatives that show strong absorption of visible light and long-lived triplet excited states as organic catalysts for photoredox catalytic organic reactions. Conventionally most of the photocatalysts are based on the off-the-shelf compounds, usually showing weak absorption in the visible region and short triplet excited