Sample records for triplet state spectra

  1. Triplet state spectra and dynamics of geometric isomers of carotenoids.

    PubMed

    Pendon, Zeus D; der Hoef, Ineke; Lugtenburg, Johan; Frank, Harry A

    2006-04-01

    The observation of preferential binding of cis-carotenoids in purple bacterial photosynthetic reaction centers versus trans-isomers in antenna pigment protein complexes has led to the hypothesis that the natural selection of stereoisomers has physiological significance. In order to test this hypothesis, we have undertaken a systematic series of investigations comparing the optical spectroscopic properties and excited state dynamics of cis and trans isomers of carotenoids. The present work compares the triplet state spectra, lifetimes, and energy transfer rates of all-trans-spheroidene and 13,14-locked-cis-spheroidene, the latter of which is incapable of isomerizing to the all-trans configuration, and therefore provides a unique opportunity to examine the triplet state properties of a structurally stable cis molecule. The data reveal only small differences in spectra, decay dynamics, and transfer times and suggest there is little intrinsic advantage in either triplet energy transfer or triplet state decay arising from the inherently different isomeric forms of cis compared to trans carotenoids. PMID:16450049

  2. The Triplet State

    NASA Astrophysics Data System (ADS)

    Zahlan, A. B.

    2010-01-01

    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.

  3. Resonance Raman spectra of a perylene bis(dicarboximide) chromophore in ground and lowest triplet states.

    PubMed

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

    2013-09-26

    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

  4. Time-resolved ESR study of the triplet state of xanthone and the triplet-triplet energy transfer in cyclodextrins

    NASA Astrophysics Data System (ADS)

    Murai, Hisao; I'haya, Yasumasa J.

    1989-07-01

    The triplet state of xanthone embedded in a cyclodextrin cavity is studied using time-resolved ESR. ?-, ?- and ?-cyclodextrins provide different characteristic spectra of the xanthone triplet state, and these spectra clearly show the different inclusion conditions for xanthone in cyclodextrins. In ?-cyclodextrins, more than two molecules can be trapped in its cavity. The specific spin polarization induced through triplet-triplet energy transfer between aromatic molecules proves some fixed orientation of the energy donor and acceptor in ?-cyclodextrin. It is also shown that two xanthone molecules can be included in ?-cyclodextrin and the spin polarized triplet exciton is interchanged between them.

  5. Theory of optical spectra of photosystem II reaction centers: location of the triplet state and the identity of the primary electron donor.

    PubMed

    Raszewski, Grzegorz; Saenger, Wolfram; Renger, Thomas

    2005-02-01

    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. PMID:15556979

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

    PubMed Central

    Raszewski, Grzegorz; Saenger, Wolfram; Renger, Thomas

    2005-01-01

    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. PMID:15556979

  7. Electron paramagnetic resonance detection of carotenoid triplet states

    SciTech Connect

    Frank, H.A. (Univ. of Connecticut, Storrs); Bolt, J.D.; de B. Costa, S.M.; Sauer, K.

    1980-07-16

    Triplet states of carotenoids have been detected by X-band electron paramagnetic resonance (EPR) and are reported here for the first time. The systems in which carotenoid triplets are observed include cells of photosynthetic bacteria, isolated bacteriochlorophyll-protein complexes, and detergent micelles which contain ..beta..-carotene. It is well known that if electron transfer is blocked following the initial acceptor in the bacterial photochemical reaction center, back reaction of the primary radical pair produces a bacteriochlorophyll dimer triplet. Previous optical studies have shown that in reaction centers containing carotenoids the bacteriochlorophyll dimer triplet sensitizes the carotenoid triplet. We have observed this carotenoid triplet state by EPR in reaction centers of Rhodopseudomonas sphaeroides, strain 2.4.1 (wild type), which contain the carotenoid spheroidene. The zero-field splitting parameters of the triplet spectrum are /D/ = 0.0290 +- 0.0005 cm/sup -1/ and /E/ = 0.0044 +-0.0006 cm/sup -1/, in contrast with the parameters of the bacteriochlorophyll dimer triplet, which are /D/ = 0.0189 +- 0.0004 cm/sup -1/ and /E/ = 0.0032 +- 0.004 cm/sup -1/. Bacteriochlorophyll in a light harvesting protein complex from Rps. sphaeroides, wild type, also sensitizes carotenoid triplet formation. In whole cells the EPR spectra vary with temperature between 100 and 10 K. Carotenoid triplets also have been observed by EPR in whole cells of Rps. sphaeroides and cells of Rhodospirillum rubrum which contain the carotenoid spirilloxanthin. Attempts to observe the triplet state EPR spectrum of ..beta..-carotene in numerous organic solvents failed. However, in nonionic detergent micelles and in phospholipid bilayer vesicles ..beta..-carotene gives a triplet state spectrum with /D/ = 0.0333 +- 0.0010 cm/sup -1/ and /E/ = 0.0037 +- 0.0010 cm/sup -1/. 6 figures, 1 table.

  8. Fluorescence-detected chlorophyll triplet states in chlorophyll-proteins

    NASA Astrophysics Data System (ADS)

    Schaafsma, T. J.; Searle, G. F. W.; Koehorst, R. B. M.

    Chlorophyll (chl) occurs bound Co protein as discrete, well-defined complexes in photosynthetic membranes. Chlorophyll-proteins have been isolated from barley chloroplasts and chl triplet states observed at 4.2 K under continuous illumination using a fluorescence-detected zero field magnetic resonance technique. It will be shown chat chlorophyll proteins containing chl-? , give zero field splitting parameters characteristic of monomeric as wall as dimeric chi-?; proteins containing both chl-? and b, show chl-? and - b resonances. The spectra obtained are also characterised by their sign (increase or decrease in fluorescence intensity) and their linewidth. In some chlorophyll-proteins, two or more triplets could be observed by monitoring fluorescence at different wavelengths. The decay rates of the triplet state spin levels will also be discussed. We conclude that light-induced chl triplet states can be used to probe the magnetic environment and structure within chlorophyll-proteins.

  9. Properties of the Triplet State of Coumarin Substituted Compounds

    NASA Astrophysics Data System (ADS)

    Bryantseva, N. G.; Gadirov, R. M.; Nikonov, S. Yu.; Sokolova, I. V.

    2015-03-01

    The absorption spectra of the triplet excited state of coumarin sensitizers are investigated both theoretically and experimentally. The most intense triplet-triplet (TT) absorption bands are determined. The experimental spectra of the T-T absorption are compared with the theoretical T-T transitions. The phosphorescence spectra of five compounds are measured at a temperature of 77 K. The quantum phosphorescence yield is determined by the method of comparison with an etalon (8-methoxypsoralen). The phosphorescence lifetime is determined for the examined molecules at a temperature of 77 K. For 3,4-phenyl-4',5'-cyclohexylpsoralen, 4'-methyl-3,4-cycloheptylpsoralen, and 4'5'-dimethyl-3,4-cyclohexylpsoralen compounds, this time is equal to 1.1, 1.25, and 2.5 s, respectively. The main energy deactivation channel for all examined compounds is the phosphorescence. The positions of the lower excited triplet states, calculated by the quantum-chemical method of intermediate neglect of differential overlap with spectroscopic parameterization (INDO/S), are confirmed by the available experimental data.

  10. Electronic structure of the lowest triplet state of flavin mononucleotide.

    PubMed

    Kammler, Lydia; van Gastel, Maurice

    2012-10-18

    The electronic structure of flavin mononucleotide (FMN), an organic cofactor that plays a role in many important enzymatic reactions, has been investigated by electron paramagnetic resonance (EPR) spectroscopy, optical spectroscopy, and quantum chemistry. In particular, the triplet state of FMN, which is paramagnetic (total spin S = 1), allows an investigation of the zero field splitting parameters D and E, which are directly related to the two singly occupied molecular orbitals. Triplet EPR spectra and optical absorption spectra at different pH values in combination with time dependent density functional theory (TDDFT) reveal that the highest occupied orbital (HOMO) and lowest unoccupied orbital (LUMO) of FMN are largely unaffected by changes in the protonation state of FMN. Rather, the orbital structure of the lower lying doubly occupied orbitals changes dramatically. Additional EPR experiments have been carried out in the presence of AgNO(3), which allows the formation of an Ag-FMN triplet state with different zero field splitting parameters and population and depopulation rates. Addition of AgNO(3) only induces small changes in the optical spectrum, indicating that the Ag(+) ion only contributes to the zero field splitting by second order spin-orbit coupling and leaves the orbital structure unaffected. By a combination of the three employed methods, the observed bands in the UV/vis spectra of FMN at different pH values are assigned to electronic transitions. PMID:22998491

  11. Triplet-like correlation symmetry of continuous variable entangled states

    E-print Network

    Gerd Leuchs; Ruifang Dong; Denis Sych

    2009-06-05

    We report on a continuous variable analogue of the triplet two-qubit Bell states. We theoretically and experimentally demonstrate a remarkable similarity of two-mode continuous variable entangled states with triplet Bell states with respect to their correlation patterns. Borrowing from the two qubit language, we call these correlations triplet-like.

  12. Singlet and triplet excited states of a pyramidalized alkene: Electron-energy-loss spectra, photoelectron spectra, and calculations of the excited states of tricyclo[3.3.3.0 3,7]undec-3(7)-ene

    Microsoft Academic Search

    Christophe Bulliard; Michael Allan; Joseph M. Smith; David A. Hrovat; Weston Thatcher Borden; Stefan Grimme

    1997-01-01

    Spectroscopic consequences of alkene pyramidalization have been investigated by measuring the triplet and singlet excitation energies of the pyramidalized alkene, tricyclo[3.3.3.03,7]undec-3(7)-ene (1), and the unpyramidalized reference alkene, bicyclo[3.3.0]oct-1(5)-ene (2), using electron-energy-loss spectroscopy. The experimental excitation energies and intensities are compared with the results of density functional calculations that include configuration interaction and also with the results of CASPT2 calculations. The

  13. Time-resolved infrared spectroscopy of the lowest triplet state of thymine and thymidine

    NASA Astrophysics Data System (ADS)

    Hare, Patrick M.; Middleton, Chris T.; Mertel, Kristin I.; Herbert, John M.; Kohler, Bern

    2008-05-01

    Vibrational spectra of the lowest energy triplet states of thymine and its 2'-deoxyribonucleoside, thymidine, are reported for the first time. Time-resolved infrared (TRIR) difference spectra were recorded over seven decades of time from 300 fs to 3 ?s using femtosecond and nanosecond pump-probe techniques. The carbonyl stretch bands in the triplet state are seen at 1603 and ˜1700 cm -1 in room-temperature acetonitrile- d3 solution. These bands and additional ones observed between 1300 and 1450 cm -1 are quenched by dissolved oxygen on a nanosecond time scale. Density-functional calculations accurately predict the difference spectrum between triplet and singlet IR absorption cross sections, confirming the peak assignments and elucidating the nature of the vibrational modes. In the triplet state, the C4 dbnd O carbonyl exhibits substantial single-bond character, explaining the large (˜70 cm -1) red shift in this vibration, relative to the singlet ground state. Femtosecond TRIR measurements unambiguously demonstrate that the triplet state is fully formed within the first 10 ps after excitation, ruling out a relaxed 1n? ? state as the triplet precursor.

  14. Thiol-activated triplet-triplet annihilation upconversion: study of the different quenching effect of electron acceptor on the singlet and triplet excited States of bodipy.

    PubMed

    Zhang, Caishun; Zhao, Jianzhang; Cui, Xiaoneng; Wu, Xueyan

    2015-06-01

    Thiol-activated triplet-triplet annihilation (TTA) upconversion was studied with two different approaches, i.e., with 2,4-dinitrobenzenenesulfonyl (DNBS)-caged diiodoBodipy triplet photosensitizers (perylene as the triplet acceptor/emitter of the upconversion) and DNBS-caged Bodipy fluorophore as the triplet acceptor/emitter (PdTPTBP as the triplet photosensitizer, TPTBP = tetraphenyltetrabenzoporphyrin). The photophysical processes were studied with steady-state UV-vis absorption spectroscopy, fluorescence spectroscopy, electrochemical characterization, nanosecond transient absorption spectroscopy, and DFT/TDDFT computations. DNBS-caged triplet photosensitizer shows a shorter triplet state lifetime (24.7 ?s) than the uncaged triplet photosensitizer (86.0 ?s), and the quenching effect is due to photoinduced electron transfer (PET). TTA upconversion was enhanced upon cleavage of the DNBS moiety by thiols. On the other hand, the DNBS-caged Bodipy shows no fluorescence, but the uncaged fluorophore shows strong fluorescence; thus, TTA upconversion is able to be enhanced with the uncaged fluorophore as the triplet energy acceptor/emitter. The results indicate that the DNBS moiety exerts a significant quenching effect on the singlet excited state of Bodipy, but the quenching on the triplet excited state is much weaker. Calculation of the Gibbs free energy changes of the photoinduced electron transfer indicates that the singlet state gives a larger driving force for the PET process than the triplet state. PMID:25941747

  15. Triplet State Epr: AN Application to Three Iron - Flavoproteins.

    NASA Astrophysics Data System (ADS)

    Stevenson, Randy Claude

    This thesis is a comprehensive development of triplet spin Hamiltonians and the application of that formalism to the electron paramagnetic resonance (EPR) spectra of three iron-sulfur flavoproteins. These spectra developed only after the enzymes had been reduced with their substrates; the signals did not appear upon titration with other reducing agents such as dithionite. As a complement to that work, part of the thesis project included the further development of the multifrequency facilities at the University of Michigan. A new tunable 15 GHz EPR cavity for a P band spectrometer, a new 3 GHz cavity and a redesigned automatic frequency control unit (AFC) for an S band spectrometer contributed to the improvement and extension of the EPR capabilities. The data obtained from these spectrometers indicated that there was a spin-spin interaction due to two spin 1/2 systems, a singly reduced flavin and singly reduced {4Fe -4S} cluster, in a triplet state. Computer simulations confirmed that the interactions in trimethylamine dehydrogenase (TMAD), from a bacterium W3Al, and TMAD and dimethyamine dehydrogenase (DMAD) from a bacterium Hyphomicrobium X, are indeed spin-coupled triplet interactions. In addition, the computer simulations indicated that there was a distribution of zero field splittings among the various enzyme molecules constituting the samples, probably due to a variation in g anisotropy of the {4Fe-4S} center. However, these simulations represented only a phenomenological description. A plausible model for the spin-spin interaction, in terms of anisotropic exchange and magnetic dipole-dipole interactions, indicated that the structures of the paramagnetic sites among all three enzymes were very similar. The model limited the edge-edge interaction distance between reduced flavin and reduced {4Fe-4S} cluster to somewhere between 3 and 5 (ANGSTROM).

  16. Triplet excitons: Bringing dark states to light

    NASA Astrophysics Data System (ADS)

    Bardeen, Christopher J.

    2014-11-01

    Semiconducting quantum dots have been used to harvest triplet excitons produced through singlet fission in organic semiconductors. These hybrid organic-inorganic materials may boost the efficiency of solar cells.

  17. Spin density distribution of the excited triplet state of bacteriochlorophylls. Pulsed ENDOR and DFT studies.

    PubMed

    Marchanka, Aliaksandr; Lubitz, Wolfgang; van Gastel, Maurice

    2009-05-14

    The photoexcited triplet states of bacteriochlorophyll a and bacteriochlorophyll b have been investigated by ENDOR spectroscopy at 34 GHz in frozen solution and by DFT calculations. The spin density distributions in the triplet state were found to be similar for bacteriochlorophyll a and bacteriochlorophyll b except for the presence of spin density on carbon 8(1) in bacteriochlorophyll b. Judging from a comparison with ENDOR experiments for the radical cation and anion, the triplet state in bacteriochlorophylls cannot be explained as being a simple HOMO-->LUMO excitation of Gouterman orbitals. Rather, it must be described as a mixture of HOMO-->LUMO and HOMO-1-->LUMO excitations for a satisfactory explanation of the observed hyperfine interactions. The observed hyperfine couplings in the ENDOR spectra were assigned, and the field dependence of the signals was found to be fully compatible with the orientation of the zero-field splitting tensor determined from magnetophotoselection studies. PMID:19385592

  18. Selective quenching of triplet excited states of pteridines.

    PubMed

    Denofrio, M Paula; Ogilby, Peter R; Thomas, Andrés H; Lorente, Carolina

    2014-07-01

    Steady-state and time-resolved studies on quenching of excited states of pterin (Ptr) and lumazine (Lum) in the presence of iodide in aqueous solution have been performed. In contrast to the typical iodide enhancement in the triplet state population, iodide promotes a fast non-radiative T1? S0 transition for both Ptr and Lum. In this work, we present evidence for the effective iodide-induced deactivation of singlet and triplet excited states, with rate constants close to the diffusion-controlled limit (between 3 × 10(9) M(-1) s(-1) and 1 × 10(10) M(-1) s(-1)). The longer lifetimes of the triplet excited states over the singlet excited states increase the probability of deactivation (k(T)(q)?(0)(T)?k(S)(q)?(0)(S)). Therefore, at micromolar concentrations of iodide, where the deactivation of the singlet excited state is negligible, an efficient deactivation of the triplet excited states is observed. This selective deactivation of the excited triplet state is an analytical tool for the study of photosensitized reactions where pteridines are involved. PMID:24849022

  19. Vibrational mode interactions with the photoexcited triplet state of naphthalene

    NASA Astrophysics Data System (ADS)

    Nicholas, J. V.

    1981-09-01

    The temperature dependence of the triplet state splittings of naphthalene in either durene or diphenyl over 70-310 K shows that the D + E transition is coupled to a 265 cm -1 internal mode and D - E to both a 593 cm -1 internal mode and external modes with a Debye temperature of 133 K.

  20. Detection by two-photon ionization and magnetic trapping of cold Rb 2 triplet state molecules

    Microsoft Academic Search

    J. Lozeille; A. Fioretti; C. Gabbanini; Y. Huang; H. K. Pechkis; D. Wang; P. L. Gould; E. E. Eyler; W. C. Stwalley; M. Aymar; O. Dulieu

    2006-01-01

    .  We present detailed experimental spectra and accurate theoretical interpretation of resonance-enhanced \\u000a two-photon ionization of ultracold rubidium molecules in the\\u000a 14000–17000 cm-1 transition energy range. The dimers are formed in a\\u000a magneto-optical trap by photoassociation followed by radiative decay into the a?3?u+\\u000a lowest triplet state. The theoretical treatment of the process, which reproduces the main features \\u000a of the spectra, takes into account

  1. Transient EPR Reveals Triplet State Delocalization in a Series of Cyclic and Linear ?-Conjugated Porphyrin Oligomers.

    PubMed

    Tait, Claudia E; Neuhaus, Patrik; Peeks, Martin D; Anderson, Harry L; Timmel, Christiane R

    2015-07-01

    The photoexcited triplet states of a series of linear and cyclic butadiyne-linked porphyrin oligomers were investigated by transient Electron Paramagnetic Resonance (EPR) and Electron Nuclear DOuble Resonance (ENDOR). The spatial delocalization of the triplet state wave function in systems with different numbers of porphyrin units and different geometries was analyzed in terms of zero-field splitting parameters and proton hyperfine couplings. Even though no significant change in the zero-field splitting parameters (D and E) is observed for linear oligomers with two to six porphyrin units, the spin polarization of the transient EPR spectra is particularly sensitive to the number of porphyrin units, implying a change of the mechanism of intersystem crossing. Analysis of the proton hyperfine couplings in linear oligomers with more than two porphyrin units, in combination with density functional theory calculations, indicates that the spin density is localized mainly on two to three porphyrin units rather than being distributed evenly over the whole ?-system. The sensitivity of the zero-field splitting parameters to changes in geometry was investigated by comparing free linear oligomers with oligomers bound to a hexapyridyl template. Significant changes in the zero-field splitting parameter D were observed, while the proton hyperfine couplings show no change in the extent of triplet state delocalization. The triplet state of the cyclic porphyrin hexamer has a much decreased zero-field splitting parameter D and much smaller proton hyperfine couplings with respect to the monomeric unit, indicating complete delocalization over six porphyrin units in this symmetric system. This surprising result provides the first evidence for extensive triplet state delocalization in an artificial supramolecular assembly of porphyrins. PMID:26035477

  2. Short-lived excited triplet states studied by time-resolved EPR spectroscopy

    Microsoft Academic Search

    Noboru Hirota; Seigo Yamauchi

    2003-01-01

    In this review, we present an overview of the application of time-resolved electron paramagnetic resonance (TREPR) to the study of excited triplet states. After a brief discussion of background and experimental methods, triplet properties clarified by TREPR are reviewed to show how TREPR provides rich information about electronic and molecular structures and dynamic properties of the lowest excited triplet states.

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

    Microsoft Academic Search

    Arnold J. Hoff

    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

  4. Ultrafast photogeneration mechanisms of triplet states in para-hexaphenyl

    Microsoft Academic Search

    C. Zenz; G. Cerullo; G. Lanzani; W. Graupner; F. Meghdadi; G. Leising; S. de Silvestri

    1999-01-01

    We present femtosecond pump-probe measurements, both conventional and electric field-assisted, on organic light-emitting devices based on para-hexaphenyl. The dominant triplet exciton generation mechanism is assigned to nongeminate bimolecular recombination of photogenerated, spin-12 polarons. This process is active within a few hundred femtoseconds after photoexcitation and involves about 20% of the initially excited states. At higher photoexcitation densities, we observe an

  5. Electron binding capabilities of some silylenes having small singlet-triplet splittings or triplet ground states.

    PubMed

    Kalcher, Josef; Skurski, Piotr; Simons, Jack

    2007-01-18

    Several silyl and alkaline metal substituted silylenes have been investigated using the CAS-ACPF method in conjunction with the aug-cc-pVTZ basis sets. Silylsilylene and disilylsilylene are found to have singlet ground states with DeltaEST(-) values of 0.676 and 0.319 eV, respectively. The adiabatic ground state electron affinities are found to be 1.572 and 2.361 eV for HSiSiH(3) and Si(SiH(3))(2). respectively. Both silylenes possesses a stable 2A1 excited negative ion state, with respective adiabatic EA values of 0.037 and 1.000 eV. In contrast, all silylenes with at least one akaline metal substituent exhibit triplet neutral ground states. The metalated silylenes HSiLi, HSiNa, LiSiSiH(3), NaSiLi, SiLi(2), and SiNa(2) have adiabatic ground state EAs somewhat below 1 eV, but each of these negatively charged system possesses up to three bound excited negative ion states, some of which are dipole-bound states. PMID:17214478

  6. High-resolution spectroscopy of triplet states of Rb2 by femtosecond pump-probe photoionization of doped helium nanodroplets

    E-print Network

    Mudrich, M; Hippler, T; Giese, Ch; Dulieu, O; Stienkemeier, F

    2009-01-01

    The dynamics of vibrational wave packets in triplet states of rubidium dimers (Rb2) formed on helium nanodroplets are studied using femtosecond pump-probe photoionization spectroscopy. Due to fast desorption of the excited Rb2 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 >1.5ns. In the first excited triplet state (1)^3\\Sigma_g^+, 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.

  7. Triplet state of 4-methoxybenzyl alcohol chemisorbed on silica nanoparticles.

    PubMed

    Arce, Valeria B; Bertolotti, Sonia G; Oliveira, Fernando J V E; Airoldi, Claudio; Arques, Antonio; Santos-Juanes, Lucas; Gonzalez, Mónica C; Cobos, Carlos J; Allegretti, Patricia E; Mártire, Daniel O

    2012-06-01

    The knowledge of photochemical kinetics in colloidal systems is important in understanding environmental photochemistry on dispersed solid surfaces. As model materials for the chemically sorbed organic compounds present in natural environments, modified silica nanoparticles (NPs) were obtained here by condensation of the silanol groups of fumed silica nanoparticles with 4-methoxybenzyl alcohol. These particles were characterized by different techniques. To evaluate their toxicity, the inhibition of the natural luminescence emission of the marine bacterium Vibrio fischeri in suspensions of the particles was measured. Laser flash-photolysis experiments (?(exc) = 266 nm) performed with NP suspensions in acetonitrile-aqueous phosphate buffer mixtures showed the formation of the lowest triplet excited state of the chemisorbed organic groups (?(max) = 390 nm). DFT calculations of the absorption spectrum of this radical support the assignment. From the calculated triplet energy, a thermodynamically favorable energy transfer from these triplet states to oxygen to yield singlet molecular oxygen is predicted. A value of 0.09 was measured for the quantum yield of singlet molecular oxygen generation by air-saturated suspensions of the nanoparticles in the mixture of solvents acetonitrile-aqueous phosphate buffer. The quantum yield of singlet molecular oxygen generation by the free 4-methoxybenzyl alcohol in the same solvent is 0.31. PMID:22421904

  8. Step-Scan FTIR spectroscopy and quantum chemical calculations of xanthone in the triplet state

    NASA Astrophysics Data System (ADS)

    Buschhaus, L.; Kleinermanns, K.

    2014-10-01

    Step-Scan-FTIR spectroscopy has been used to measure the infrared spectrum of xanthone in the triplet state using chloroform as solvent. Xanthone is an important triplet sensitizer and therefore suitable as model system. Xanthone was excited at 266 nm and its IR triplet spectrum measured in the range 1000-1750 cm-1. The spectrum was analyzed by comparison with DFT/B3LYP/TZVP/COSMO calculations. Further on the results were compared to gas phase IR measurements of triplet xanthone and calculations of isolated xanthone. Mainly based on the calculations we tried to identify the geometry changes from the electronic ground state to the first triplet state.

  9. Automatic stellar spectra parameterisation in the IR CaII triplet region

    E-print Network

    Kordopatis, G; de Laverny, P; Bijaoui, A; Hill, V; Gilmore, G; Wyse, R F G; Ordenovic, C

    2011-01-01

    (Abridged) Galactic archaeology aims to determine the evolution of the Galaxy from the chemical and kinematical properties of its stars. The analysis of current large spectroscopic surveys (thousands of stars) and future ones (millions of stars) require automated analysis techniques to obtain robust estimates of the stellar parameters. Several on-going and planned spectroscopic surveys have selected their wavelength region to contain the IR CaII triplet and this paper focuses on the automatic analysis of such spectra. We investigated two algorithms, MATISSE and DEGAS, both of which compare the observed spectrum to a grid of synthetic spectra, but each uses a different mathematical approach for finding the optimum match and hence the best stellar parameters. We identified degeneracies in different regions of the HR diagram: hot dwarfs and giants share the same spectral signatures. Furthermore, the surface gravity of cooler dwarfs is difficult to determine accurately. These effects are intensified when the info...

  10. Triplet states of rubidium dimers on helium nanodroplets

    Microsoft Academic Search

    F. R. Brühl; R. A. Miron; W. E. Ernst

    2001-01-01

    Rubidium dimers in their 1 3Sigmau+ states are formed through collisions of Rb atoms that have been deposited on the surface of helium nanodroplets. Visible absorption spectra between 550 and 690 nm were probed by laser induced fluorescence and emission spectra measured for selected excitation wavelengths. A system absorbing around 595 nm with its emission to the ground state centered

  11. Triplet states of rubidium dimers on helium nanodroplets

    Microsoft Academic Search

    R. A. Miron; W. E. Ernst

    2001-01-01

    Rubidium dimers in their 1 3?u+ states are formed through collisions of Rb atoms that have been deposited on the surface of helium nanodroplets. Visible absorption spectra between 550 and 690 nm were probed by laser induced fluorescence and emission spectra measured for selected excitation wavelengths. A system absorbing around 595 nm with its emission to the ground state centered

  12. Triplet acetylenes as synthetic equivalents of 1,2-bicarbenes: phantom n,pi state controls reactivity in triplet photocycloaddition.

    PubMed

    Zeidan, Tarek A; Kovalenko, Serguei V; Manoharan, Mariappan; Clark, Ronald J; Ghiviriga, Ion; Alabugin, Igor V

    2005-03-30

    Diaryl acetylenes, in which one of the aryl groups is either a pyridine or a pyrazine, undergo efficient triplet state photocycloaddition to 1,4-cyclohexadiene with formation of 1,5-diaryl substituted tetracyclo[3.3.0.0(2,8).0(4,6)]octanes (homoquadricyclanes). In the case of pyrazinyl acetylenes, the primary homoquadricyclane products undergo a secondary photochemical rearangement leading to diaryl substituted tricyclo[3.2.1.0(4,6)]oct-2-enes. Mechanistic and photophysical studies suggest that photocycloaddition proceeds through an electrophilic triplet excited state whereas the subsequent rearrangement to the tricyclooctenes proceeds through a singlet excited state. Chemical and quantum yields for the cycloaddition, in general, correlate with the electron acceptor character of aryl substituents but are attenuated by photophysical factors, such as the competition between the conversion of acetylene singlet excited state into the reactive triplet excited states (intersystem crossing: ISC) and/or to the radical-anion (photoelectron transfer from the diene to the excited acetylene: PET). Dramatically enhanced ISC between pi-pi S(1) state and "phantom" n,pi triplet excited state is likely to be important in directing reactivity to the triplet pathway. The role of PET can be minimized by the judicious choice of reaction conditions (solvent, concentration, etc.). From a practical perspective, such reactions are interesting because "capping" of the triple bond with the polycyclic framework orients the terminal aryl (4-pyridyl, 4-tetrafluoropyridyl, phenyl, etc.) groups in an almost perfect 60 degrees angle and renders such molecules promising supramolecular building blocks, especially in the design of metal coordination polymers. PMID:15783209

  13. Model for Triplet State Engineering in Organic Light Emitting Diodes

    E-print Network

    Prodhan, Suryoday; Ramasesha, S

    2014-01-01

    Engineering the position of the lowest triplet state (T1) relative to the first excited singlet state (S1) is of great importance in improving the efficiencies of organic light emitting diodes and organic photovoltaic cells. We have carried out model exact calculations of substituted polyene chains to understand the factors that affect the energy gap between S1 and T1. The factors studied are backbone dimerisation, different donor-acceptor substitutions and twisted geometry. The largest system studied is an eighteen carbon polyene which spans a Hilbert space of about 991 million. We show that for reverse intersystem crossing (RISC) process, the best system involves substituting all carbon sites on one half of the polyene with donors and the other half with acceptors.

  14. Model for triplet state engineering in organic light emitting diodes.

    PubMed

    Prodhan, Suryoday; Soos, Zoltán G; Ramasesha, S

    2014-06-01

    Engineering the position of the lowest triplet state (T1) relative to the first excited singlet state (S1) is of great importance in improving the efficiencies of organic light emitting diodes and organic photovoltaic cells. We have carried out model exact calculations of substituted polyene chains to understand the factors that affect the energy gap between S1 and T1. The factors studied are backbone dimerisation, different donor-acceptor substitutions, and twisted geometry. The largest system studied is an 18 carbon polyene which spans a Hilbert space of about 991 × 10(6). We show that for reverse intersystem crossing process, the best system involves substituting all carbon sites on one half of the polyene with donors and the other half with acceptors. PMID:24908014

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

    NASA Astrophysics Data System (ADS)

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

    2009-03-01

    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.

  16. Triplet Acetylenes as Synthetic Equivalents of 1,2-Bicarbenes: Phantom n,* State Controls Reactivity in

    E-print Network

    Alabugin, Igor

    acetylene: PET). Dramatically enhanced ISC between -* S1 state and "phantom" n,* triplet excited state is likely to be important in directing reactivity to the triplet pathway. The role of PET can be minimized coordination polymers. Introduction The triple bond is among the most important functional groups in organic

  17. Excited triplet state photophysics of the sulphonated aluminium phthalocyanines bound to human serum albumin.

    PubMed

    Foley, M S; Beeby, A; Parker, A W; Bishop, S M; Phillips, D

    1997-03-01

    The binding of the sulphonated aluminum phthalocyanines to human serum albumin (HSA) in aqueous phosphate buffer solution at 25 degrees C has been studied by measuring the properties of the triplet excited states of these dyes. The triplet lifetimes were measured by triplet-triplet absorption flash photolysis. The triplet lifetime of the disulphonated AlS2Pc (2.5 microM) varies from 500 +/- 30 microseconds in the absence of protein to 1.100 microseconds and longer with HSA concentrations above 100 microM. Under identical conditions, the maximum triplet lifetimes of the mono-, tri- and tetrasulphonated compounds bound to HSA are shorter than those for the disulphonated species. The increase in the triplet state lifetimes is attributed to the ability of the bulk aqueous phase to interact with the sensitizer at the site of binding; the site of binding being dependent on the degree of sulphonation. For AlS2Pc and AlS3Pc at all HSA concentrations, and regardless of the degree of sulphonation, all the triplet state decay profiles follow simple pseudo-first-order kinetics. The exponential decay of the triplet phthalocyanine at all HSA concentrations is ascribed to the rapid association and dissociation of the phthalocyanine-HSA complex on the time-scales of the triplet state lifetimes. A simplified one-step binding model is utilized to describe the results. The association of AlS1Pc with HSA results in substantial quenching of the triplet state quantum yield, and a more complex model is required to analyze the results. The tetrasulphonated compound (AlS4Pc) binds to the protein at a site where it experiences some protection from the aqueous phase. PMID:9134751

  18. Stabilizing triplet excited states for ultralong organic phosphorescence

    NASA Astrophysics Data System (ADS)

    An, Zhongfu; Zheng, Chao; Tao, Ye; Chen, Runfeng; Shi, Huifang; Chen, Ting; Wang, Zhixiang; Li, Huanhuan; Deng, Renren; Liu, Xiaogang; Huang, Wei

    2015-07-01

    The control of the emission properties of synthetic organic molecules through molecular design has led to the development of high-performance optoelectronic devices with tunable emission colours, high quantum efficiencies and efficient energy/charge transfer processes. However, the task of generating excited states with long lifetimes has been met with limited success, owing to the ultrafast deactivation of the highly active excited states. Here, we present a design rule that can be used to tune the emission lifetime of a wide range of luminescent organic molecules, based on effective stabilization of triplet excited states through strong coupling in H-aggregated molecules. Our experimental data revealed that luminescence lifetimes up to 1.35 s, which are several orders of magnitude longer than those of conventional organic fluorophores, can be realized under ambient conditions. These results outline a fundamental principle to design organic molecules with extended lifetimes of excited states, providing a major step forward in expanding the scope of organic phosphorescence applications.

  19. Stabilizing triplet excited states for ultralong organic phosphorescence.

    PubMed

    An, Zhongfu; Zheng, Chao; Tao, Ye; Chen, Runfeng; Shi, Huifang; Chen, Ting; Wang, Zhixiang; Li, Huanhuan; Deng, Renren; Liu, Xiaogang; Huang, Wei

    2015-07-01

    The control of the emission properties of synthetic organic molecules through molecular design has led to the development of high-performance optoelectronic devices with tunable emission colours, high quantum efficiencies and efficient energy/charge transfer processes. However, the task of generating excited states with long lifetimes has been met with limited success, owing to the ultrafast deactivation of the highly active excited states. Here, we present a design rule that can be used to tune the emission lifetime of a wide range of luminescent organic molecules, based on effective stabilization of triplet excited states through strong coupling in H-aggregated molecules. Our experimental data revealed that luminescence lifetimes up to 1.35 s, which are several orders of magnitude longer than those of conventional organic fluorophores, can be realized under ambient conditions. These results outline a fundamental principle to design organic molecules with extended lifetimes of excited states, providing a major step forward in expanding the scope of organic phosphorescence applications. PMID:25849370

  20. Nonradiative relaxation of pyridine vapor: Transient absorption studies of triplet state formation, decay, quenching, and structure

    Microsoft Academic Search

    Jodye I. Selco; Patrick L. Holt; R. Bruce Weisman

    1983-01-01

    Relaxation processes in pyridine vapor have been studied using high-performance transient absorption spectrometry following excitation low in the S1 manifold. The ultraviolet spectrum of the lowest triplet state has been identified and measured, and its dependence on delay time and background pressure has been investigated for a variety of collision partners. It is concluded that formation of the triplet through

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

    E-print Network

    Jencova, Anna

    2010-01-01

    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.

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

    E-print Network

    Anna Jencova

    2010-08-05

    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.

  3. Switching of the triplet excited state of rhodamine/naphthaleneimide dyads: an experimental and theoretical study.

    PubMed

    Cui, Xiaoneng; Zhao, Jianzhang; Lou, Zhangrong; Li, Shujing; Wu, Huijian; Han, Ke-Li

    2015-01-01

    Rhodamine-bromonaphthaleneimide (RB-NI) and rhodamine-bromonaphthalenediimide (RB-NDI) dyads were prepared for switching of the triplet excited states. Bromo-NI or bromo-NDI parts in the dyads are the spin converters, i.e., the triplet state producing modules, whereas the RB unit is the acid-activatable electron donor/energy acceptor. NI and NDI absorb at 359 and 541 nm, and the T1 state energy levels are 2.25 and 1.64 eV, respectively. RB undertakes the reversible spirolactam (RB-c) ? opened amide (RB-o) transformation. RB-c shows no visible light absorption, and the triplet-state energy level is ET1 = 3.36 eV. Conversely RB-o shows strong absorption at 557 nm, and ET1 is 1.73 eV. Thus, the acid-activated fluorescence-resonance-energy-transfer (FRET) competes with the ISC of NI or NDI. No triplet state was observed for the dyads with nanosecond time-resolved transient absorption spectroscopy. Upon addition of acid, strong fluorescence and long-living triplet excited states were observed. Thus, the producing of triplet state is acid-activatable. The triplet state of RB-NI is localized on RB-o part, whereas in RB-NDI the triplet state is delocalized on both the NDI and RB-o units. The ISC of spin converter was not outcompeted by RET. These studies are useful for switching of triplet excited state. PMID:25436874

  4. Automatic stellar spectra parameterisation in the IR Ca ii triplet region

    NASA Astrophysics Data System (ADS)

    Kordopatis, G.; Recio-Blanco, A.; de Laverny, P.; Bijaoui, A.; Hill, V.; Gilmore, G.; Wyse, R. F. G.; Ordenovic, C.

    2011-11-01

    Context. Galactic archaeology aims to determine the evolution of the Galaxy from the chemical and kinematical properties of its individual stars. This requires the analysis of data from large spectroscopic surveys, with sample sizes in tens of thousands at present, with millions of stars being reached in the near future. Such large samples require automated analysis techniques and classification algorithms to obtain robust estimates of the stellar parameter values. Several on-going and planned spectroscopic surveys have selected their wavelength region to contain the IR Ca ii triplet (~?? 8500 Å) and the work presented in this paper focuses on the automatic analysis of such spectra. Aims: We aim to develop and test an automatic method by which one can obtain estimates of values of the stellar atmospheric parameters (effective temperature, surface gravity, overall metallicity) from a stellar spectrum. We also explore the degeneracies in parameter space, estimate the uncertainties in the derived parameter values and investigate the consequences of these limitations for achieving the goals of galactic archaeology. Methods: We investigated two algorithms, both of which compare the observed spectrum to a grid of synthetic spectra, but each uses a different mathematical approach for finding the optimum match and hence the best values of the stellar parameters. Our investigation of these algorithms' robustness can be widely applied because it amplifies the main problems that the other methods can encounter. The first algorithm, MATISSE, derives the values of each stellar parameter through a local fit to the spectrum such that each pixel in wavelength space is treated separately. The sensitivity of the flux at each wavelength to the value of a given stellar parameter is determined from the synthetic spectra. The observed spectrum is then projected using these sensitivity vectors to give an estimated value of the stellar parameters. This value depends on finding the true minimum in the fit and the algorithm must avoid being trapped in false local minima. The second algorithm, DEGAS, uses a pattern-recognition approach and consequently has a more global vision of the parameter space. The best-fit synthetic spectrum is derived through a series of comparisons between the observed and synthetic spectra, summed over wavelength pixels, with additional refinements in the set of synthetic spectra after each stage, i.e. a decision tree. Results: We identified physical degeneracies in different regions of the H - R diagram: hot dwarf and giant stars share the same spectral signatures. Furthermore, it is very difficult to determine an accurate value for the surface gravity of cooler dwarfs. These effects are intensified when the lack of information increases, which happens for low-metallicity stars or spectra with low signal-to-noise ratios (SNRs). Our results demonstrate that the local projection method is preferred for spectra with high SNR, whereas the decision-tree method is preferred for spectra of lower SNR. We therefore propose a hybrid approach, combining these methods, and demonstrate that sufficiently accurate results for the purposes of galactic archaeology studies are retrieved down to SNR ~ 20 for typical parameter values of stars belonging to the local thin or thick disc, and for SNR down to ~50 for the more metal-poor giant stars of the halo. Conclusions: If unappreciated, degeneracies in stellar parameters can introduce biases and systematic errors in derived quantities for target stars such as distances and full space motions. These can be minimised using the knowledge gained by thorough testing of the proposed stellar classification algorithm, which in turn lead to robust automated methods for the coming extensive spectroscopic surveys of stars in the Local Group.

  5. Theory of spin—lattice relaxation in the triplet state of naphthalene in durene

    NASA Astrophysics Data System (ADS)

    Vollmann, W.

    1981-05-01

    Spin—lattice relaxation in the photoexcited triplet state T 1 of naphthalene in durene can be induced by a two-phonon relaxation process. The intermediate states are the sublevels of another triplet state T 2 which has a spin hamiltonian different from that of T 1. In the present work the relaxation rates in T 1 are calculated within a stochastic and a quantum-mechanical approach. The stochastic treatment describes the thermally activated jump between T 1 and T 2 by a stochasticly time dependent hamiltonian which induces transition probabilities between the sublevels of an averaged triplet state which results from T 1 and T 2 by fast exchange. In the quantum-mechanical treatment Orbach's formulae for the two-phonon relaxation process are adapted to a system in which the intermediate states are represented by the sublevels of the triplet state T 2. The results of both theories are compared with each other and with experimental data.

  6. Decomposition of formyl fluoride on the lowest triplet state surface

    NASA Astrophysics Data System (ADS)

    Sumathi, R.; Chandra, A. K.

    1992-09-01

    Decomposition of formyl fluoride on the lowest triplet potential energy hypersurface is studied using ab initio quantum chemical methods. Dissociation energies and the barrier to dissociation from the lowest triplet HFCO into H( 2S) and FCO( 2A') are reported. Results reveal that the barrier to dissociation into F( 2P) + HCO( 2A') is very high. The triatomic radical, FCO( 2A') decomposes into F( 2P) + CO( 1?) from the high vibrational levels of the C-F stretch.

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

    SciTech Connect

    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

    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.

  8. Search for double charmonium decays of the P-wave spin-triplet bottomonium states

    E-print Network

    Shen, C P; Iijima, T

    2012-01-01

    Using a sample of 158 million $\\Upsilon(2S)$ events collected with the Belle detector, we search for the first time for double charmonium decays of the $P$-wave spin-triplet bottomonium states ($\\Upsilon(2S) \\to \\gamma \\chi_{bJ}$, $\\chi_{bJ} \\to \\jpsi \\jpsi$, $\\jpsi \\psp$, $\\psp \\psp$ for J=0, 1, and 2). No significant $\\chi_{bJ}$ signal is observed in the double charmonium mass spectra, and we obtain the following upper limits, $\\BR(\\chi_{bJ} \\to \\jpsi \\jpsi)psp)psp \\psp)<3.1\\times 10^{-5}$, $6.2\\times 10^{-5}$, $1.6\\times 10^{-5}$ for J=0, 1, and 2, respectively, at the 90% confidence level. These limits are significantly lower than the central values (with uncertainties of 50% to 70%) predicted using the light cone formalism but are consistent with calculations using the NRQCD factorization approach.

  9. Electron paramagnetic resonance lineshape analysis of the photoexcited triplet state of C60 in frozen solution. Exchange narrowing and dynamic Jahn-Teller effect

    NASA Astrophysics Data System (ADS)

    Bennati, Marina; Grupp, Arthur; Mehring, Michael

    1995-06-01

    The EPR lineshape of the photoinduced triplet state of C60 in frozen toluene solution was studied by pulsed EPR spectroscopy. Lineshape calculations of the triplet spectra were performed including dynamical exchange effects. The observed spectra in a glassy matrix are compatible with zero field splitting parameters ?D1? = 0.0114 cm-1 (12.2 mT) and ?E1? = 0.0005 cm-1 (0.5 mT). The temperature dependence of the powder lineshape was simulated using a dynamical exchange model, where the triplet principal axis jumps between all equivalent sites allowed by the D5d symmetry for the lowest excited triplet state. The determined exchange rate turned out to be only weakly temperature dependent and suggests that the dynamic process is due to tunneling between Jahn-Teller distorted states rather than to real molecular jumps. In addition we have observed a different triplet state with zero field splitting parameters ?D2? = 0.0100 cm-1 (10.6 mT), ?E2? = 0.0015 cm-1 (1.6 mT) after annealing of the matrix. We attribute this to a C60 dimer or, alternatively, to crystal field effects.

  10. Broadband Visible Light-Harvesting Naphthalenediimide (NDI) Triad: Study of the Intra-/Intermolecular Energy/Electron Transfer and the Triplet Excited State.

    PubMed

    Wu, Shuang; Zhong, Fangfang; Zhao, Jianzhang; Guo, Song; Yang, Wenbo; Fyles, Tom

    2015-05-21

    A triad based on naphthalenediimides (NDI) was prepared to study the intersystem crossing (ISC), the fluorescence-resonance-energy-transfer (FRET), as well as the photoinduced electron transfer (PET) processes. In the triad, the 2-bromo-6-alkylaminoNDI moiety was used as singlet energy donor and the spin converter, whereas 2,6-dialkylaminoNDI was used as the singlet/triplet energy acceptor. This unique structural protocol and thus alignment of the energy levels ensures the competing ISC and FRET in the triad. The photophysical properties of the triad and the reference compounds were studied with steady-state UV-vis absorption spectra, fluorescence spectra, nanosecond transient absorption spectra, cyclic voltammetry, and DFT/TDDFT calculations. FRET was confirmed with steady-state UV-vis absorption and fluorescence spectroscopy. Intramolecular electron transfer was observed in polar solvents, demonstrated by the quenching of both the fluorescence and triplet state of the energy acceptor. Nanosecond transient absorption spectroscopy shows that the T1 state of the triad is exclusively localized on the 2,6-dialkylaminoNDI moiety in the triad upon selective photoexcitation into the energy donor, which indicates the intramolecular triplet state energy transfer. The intermolecular triplet state energy transfer between the two reference compounds was investigated with nanosecond transient absorption spectroscopy. The photophysical properties were rationalized by TDDFT calculations. PMID:25919420

  11. Quantum chemistry-based interpretations on the lowest triplet state of luminescent lanthanides complexes. Part 1. Relation between the triplet state energy of hydroxamate complexes and their luminescence properties.

    PubMed

    Gutierrez, Fabien; Tedeschi, Christine; Maron, Laurent; Daudey, Jean-Pierre; Poteau, Romuald; Azema, Joëlle; Tisnès, Pierre; Picard, Claude

    2004-05-01

    In this paper, we evaluate the potential use of theoretical calculations to obtain an energy scale of the lowest ligand-centred triplet excited state in luminescent terbium(III) complexes. In these complexes, non-radiative deactivation of the terbium emitting state via a back-energy transfer process (T1<--Tb(5D4)) is a common quenching process. Consequently the prediction of the energy gap between these two excited states should be useful for programming highly luminescent Tb(III) systems. We report on a strategy based upon experimental and theoretical investigations of the excited state properties of a series of four simple aromatic hydroxamate ligands coordinated to Tb(III) and Gd(III) ions. By using previously reported crystallographic data, the structural and energies properties of these systems were investigated in the ground and first excited triplet states at the density functional theory (DFT) level of calculations. Our theoretical results are consistent with a triplet excited state T1 which is localised on one ligand only and whose the energy level is independent of the lanthanide ion nature (Tb(III), Gd(III)). A good agreement between the calculated adiabatic transition energies and experimental data derived from emission spectra is obtained when a corrective term is considered. These satisfactory results are an indication that this type of modelling can lead to discriminate in terms of the position of the lowest ligand triplet energy level the best antenna among a family of chromophoric compounds. In addition this theoretical approach has provided indications that the difference between the adiabatic transition energies of all the investigated complexes can be mainly explained by metal-ligand electrostatic interactions. The influence of the number of antennae on the quantum yield and the luminescence lifetime is discussed. PMID:15252626

  12. Valley spin-orbit interaction for the triplet and doublet 1sground states of lithium donor center in monoisotopic {sup 28}Si

    SciTech Connect

    Ezhevskii, Alexander A.; Popkov, Sergey A.; Soukhorukov, Andrey V.; Guseinov, Davud V.; Konakov, Anton A. [Lobachevsky State University of Nizhni Novgorod, Gagarin ave. 23, Nizhni Novgorod, 603950 (Russian Federation); Abrosimov, Nikolai V.; Riemann, Helge [Leibniz Institute for Crystal Growth, Max-Born-Str. 2 D-12489 Berlin (Germany)

    2013-12-04

    Valley spin-orbit interaction for the triplet and doublet 1s-ground states of lithium donor center in monoisotopic {sup 28}Si was studied in order to determine its contribution to the electron spin relaxation rate. We observed new electron paramagnetic resonance spectra of lithium in monoisotopic silicon with g<2.000 and found the spin Hamiltonian parameters for it. Using our experimental results and taking into account spin-orbit coupling between the triplet states and the triplet and doublet states we found that the lithium donor electron spectrum and g-factors for its states strongly depend on both the internal strains in the crystal and the intervalley spin-orbit interactions.

  13. Electronic structures and dynamics of the excited triplet states of ?,?-diphenylpolyynes

    NASA Astrophysics Data System (ADS)

    Nagano, Yasutomo; Ikoma, Tadaaki; Akiyama, Kimio; Tero-Kubota, Shozo

    2001-01-01

    The lowest excited triplet (T1) states of diphenylacetylene and several ?,?-diphenylpolyynes (DPY) having two, three, four and six triple bonds were studied using continuous wave time-resolved electron paramagnetic resonance (CW-TREPR), pulsed EPR, and phosphorescence spectroscopy. Linear and planar molecular structures in the T1 states of DPY were suggested from the magnetophotoselection experiments and observation of a strong 0-0 band in the well-resolved phosphorescence spectra. The spin density distributions, which were obtained by electron spin echo envelope modulation measurements and semi-empirical molecular orbital calculations, and the phosphorescence polarization normal to the long axis of molecule for the 0-0 bands suggested that the T1 states of DPY have a 3B1u(?x?x*) electronic configuration. DPY showed an abnormally large |D| value of the zero-field splitting parameters that increased with increasing molecular size. Such an unusual behavior of the D values is interpreted in terms of the spin-orbit interaction between the T1 and 3Au(?x?y*) states mainly due to their energy proximity which is probably characteristic of the excited states for the polyynes. The estimated energy gap between the 3?x?y* and 3?x?x* states for DPY ranges from 2900 cm-1 to 1400 cm-1. There existed a good correlation between the acceleration of the nonradiative decay rate constant from the T1 state and appearance of a ring twisting vibronic band with b1g symmetry in the phosphorescence spectra for DPY. Therefore, we concluded that the vibronic interaction between the 3?x?y* and 3?x?x* states promoted by the b1g vibration leads to a broadening of the potential surface of the T1 state which results in the fast radiationless decay to the ground state.

  14. A time-resolved electron nuclear double resonance (ENDOR) study of the photo-excited triplet state

    NASA Astrophysics Data System (ADS)

    Ohkoshi, Shin-ichi; Yamauchi, Seigo; Ohba, Yasunori; Iwaizumi, Masamoto

    1994-07-01

    A time-resolved ENDOR (TRENDOR) apparatus was constructed and applied to observe hyperfine couplings in the photo-excited triplet (T 1) state. The TRENDOR spectra of the T 1 states were observed both in mixed crystals and glass. The hyperfine coupling constants were obtained a 4-100 K for quinoxaline in single crystals of durene and p-dibromobenzene and for tetraphenyporphine (H 2TPP) in toluene glass. The time profile of the ENDOR signal was analyzed with population kinetics using a four-level system.

  15. Strongly emissive long-lived 3IL excited state of coumarins in cyclometalated Ir(III) complexes used as triplet photosensitizers and application in triplet-triplet annihilation upconversion.

    PubMed

    Yi, Xiuyu; Zhang, Caishun; Guo, Song; Ma, Jie; Zhao, Jianzhang

    2014-01-28

    Three different coumarin chromophores were used to prepare the Ir(III) complexes, i.e. coumarin 6 (Ir-1), 7-diethylamino coumarin (Ir-2) and x-phenyl-y-diethylamino coumarin (Ir-3). Ir(ppy)2(bpy)[PF6] was used as the reference complex (Ir-0). The coumarin units were connected to the coordination center of the complexes by using a C?C ?-conjugation bond. The photophysical properties of the complexes were studied with steady state and time-resolved absorption and luminescence spectroscopy, low-temperature luminescence (77 K), as well as DFT calculations. All the three new complexes show strong absorption of visible light (molar absorption coefficient ? is up to 42,000 M(-1) cm(-1) at 487 nm) and a long-lived triplet excited state (?T = 65.9 ?s), compared to the reference complex Ir(ppy)2(bpy)[PF6], which shows the typical weak visible light-absorption (? < 5000 M(-1) cm(-1) in the region beyond 400 nm) and a short triplet excited state (?T = 0.3 ?s). Interestingly the long-lived triplet excited states are strongly phosphorescent (quantum yield is up to 18.2%, with emission maxima at 607 nm), which is rare for phosphorescent transition metal complexes. With nanosecond time-resolved transient difference absorption spectroscopy we proved that a coumarin-localized triplet excited state ((3)IL) was produced upon photoexcitation. The complexes were used as triplet photosensitizers for triplet-triplet annihilation upconversion and upconversion quantum yields up to 22.8% were observed. Our results are useful for the preparation of visible light-harvesting transition metal complexes, the study of the triplet excited state of organic chromophores, as well as the application of these visible light-harvesting transition metal complexes as efficient triplet photosensitizers. PMID:24220517

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

    NASA Astrophysics Data System (ADS)

    Dyakonov, Vladimir

    2013-03-01

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

  17. Photodissociation and radiative association of HeH+ in the metastable triplet state.

    PubMed

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

    2013-10-01

    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

  18. Temperature-dependent Mollow triplet spectra from a single quantum dot: Rabi frequency renormalisation and sideband linewidth insensitivity

    E-print Network

    Yu-Jia Wei; Yu He; Yu-Ming He; Chao-Yang Lu; Jian-Wei Pan; Christian Schneider; Martin Kamp; Sven Höfling; Dara P. S. McCutcheon; Ahsan Nazir

    2014-09-17

    We investigate temperature-dependent resonance fluorescence spectra obtained from a single self-assembled quantum dot. A decrease of the Mollow triplet sideband splitting is observed with increasing temperature, an effect we attribute to a phonon-induced renormalisation of the driven dot Rabi frequency. We also present first evidence for a non-perturbative regime of phonon coupling, in which the expected linear increase in sideband linewidth as a function of temperature is cancelled by the corresponding reduction in Rabi frequency. These results indicate that dephasing in semiconductor quantum dots may be less sensitive to changes in temperature than expected from a standard weak-coupling analysis of phonon effects.

  19. Triplet State Formation in Photovoltaic Blends of DPP-Type Copolymers and PC71 BM.

    PubMed

    Ochsmann, Julian R; Chandran, Deepak; Gehrig, Dominik W; Anwar, Husna; Madathil, Pramod Kandoth; Lee, Kwang-Sup; Laquai, Frédéric

    2015-06-01

    The exciton dynamics in pristine films of two structurally related low-bandgap diketopyrrolopyrrole (DPP)-based donor-acceptor copolymers and the photophysical processes in bulk heterojunction solar cells using DPP copolymer:PC71 BM blends are investigated by broadband transient absorption (TA) pump-probe experiments covering the vis-near-infrared spectral and fs-?s dynamic range. The experiments reveal surprisingly short exciton lifetimes in the pristine poly-mer films in conjunction with fast triplet state formation. An in-depth analysis of the TA data by multivariate curve resolution analysis shows that in blends with fullerene as acceptor ultrafast exciton dissociation creates charge carriers, which then rapidly recombine on the sub-ns timescale. Furthermore, at the carrier densities created by pulsed laser excitation the charge carrier recombination leads to a substantial population of the polymer triplet state. In fact, virtually quantitative formation of triplet states is observed on the sub-ns timescale. However, the quantitative triplet formation on the sub-ns timescale is not in line with the power conversion efficiencies of devices indicating that triplet state formation is an intensity-dependent process in these blends and is reduced under solar illumination conditions, as free charge carriers can be extracted from the photoactive layer in devices. PMID:25923668

  20. EPR studies of the excited triplet states of C 60O and C 60C 2H 4N(CH 3) fullerene derivatives and C 70 in toluene and polymethylmethacrylate glasses and as films

    Microsoft Academic Search

    G. Agostini; C. Corvaja; L. Pasimeni

    1996-01-01

    The EPR spectra of excited triplet states of two fullerene derivatives, C60O and C60C2H4N(CH3), in the glassy matrices of toluene and of polymethylmethacrylate (PMMA) and as films were examined at low temperature and the magnetic parameters were measured. In films, species with zfs parameters smaller than those in toluene were found and they were assigned to triplet excitations visiting more

  1. Studies of the triplet state of the proton-transfer tautomer in salicylaldehydes

    NASA Astrophysics Data System (ADS)

    Chou, Pi-Tai; Chiou, Chau-Shuen; Yu, Wei-Shan; Wu, Guo-Ray; Wei, Tai-Huei

    2003-03-01

    The spectroscopy and dynamics of the low-lying triplet state of the proton-transfer tautomer in salicylaldehydes have been studied via internal heavy-atom effects coupled with a sensitive near-IR detecting system. For 3,5-diiodosalicylaldehyde a weak proton-transfer keto-tautomer phosphorescence was resolved with a maximum at 710 nm ( ? p˜1.8 ?s, ?obs˜5.23×10 -4) in a 77 K methylcyclohexane glass. The results, in combination with the time-resolved thermal lensing experiment, further deduced the triplet-state population yield and radiative decay rate to be 0.20 (298 K) and 3.12×10 2 s-1, respectively. Consequently, the energetics and dynamics of the triplet states during a proton transfer cycle are discussed in detail.

  2. Optical studies of triplet excitations in poly(p-phenylene vinylene)

    Microsoft Academic Search

    R. Österbacka; M. Wohlgenannt; D. Chinn; Z. V. Vardeny

    1999-01-01

    We have studied energy states in the triplet manifold in films of poly(p-phenylene vinylene) (PPV) using a multitude of optical spectroscopies including photoinduced absorption, photoluminescence, their optically detected magnetic resonances, as well as their photogeneration action spectra. We found that singlet fission into two triplets with opposite spins is an efficient route for triplet generation in PPV, similar in strength

  3. The role of triplet states in the emission mechanism of polymer light-emitting diodes

    E-print Network

    M. Arif; S. Mukhopadhyay; S. Ramasesha; S. Guha

    2009-03-01

    The blue emission of polyfluorene (PF) based light-emitting diodes (LEDs) is known to degrade due to a low energy green emission, which hitherto has been attributed to oxidative defects. By studying the electroluminescence from ethyl-hexyl substituted PF LEDs in the presence of oxygen and in an inert atmosphere, and by using trace quantities of paramagnetic impurities (PM) in the polymer, we show that the triplet states play a major role in the low energy emission mechanism. Our time-dependent many-body studies show that there is a large cross-section for the triplet formation in the electron-hole recombination process in presence of PM, and intersystem crossing from excited singlet to triplet states.

  4. Triplet state photochemistry and the three-state crossing of acetophenone within time-dependent density-functional theory

    SciTech Connect

    Huix-Rotllant, Miquel, E-mail: miquel.huix@gmail.com; Ferré, Nicolas, E-mail: nicolas.ferre@univ-amu.fr [Institut de Chimie Radicalaire (UMR-7273), Aix-Marseille Université, CNRS, 13397 Marseille Cedex 20 (France)] [Institut de Chimie Radicalaire (UMR-7273), Aix-Marseille Université, CNRS, 13397 Marseille Cedex 20 (France)

    2014-04-07

    Even though time-dependent density-functional theory (TDDFT) works generally well for describing excited states energies and properties in the Franck-Condon region, it can dramatically fail in predicting photochemistry, notably when electronic state crossings occur. Here, we assess the ability of TDDFT to describe the photochemistry of an important class of triplet sensitizers, namely, aromatic ketones. We take acetophenone as a test molecule, for which accurate ab initio results exist in the literature. Triplet acetophenone is generated thanks to an exotic three-state crossing involving one singlet and two triplets states (i.e., a simultaneous intersystem crossing and triplet conical intersection), thus being a stringent test for approximate TDDFT. We show that most exchange-correlation functionals can only give a semi-qualitative picture of the overall photochemistry, in which the three-state crossing is rather represented as a triplet conical intersection separated from the intersystem crossing. The best result overall is given by the double hybrid functional mPW2PLYP, which is even able to reproduce quantitatively the three-state crossing region. We rationalize this results by noting that double hybrid functionals include a larger portion of double excitation character to the excited states.

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

    SciTech Connect

    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

    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.

  6. Quenching of Triplet State Fluorophores for Studying Diffusion-Mediated Reactions in Lipid Membranes

    PubMed Central

    Strömqvist, Johan; Chmyrov, Andriy; Johansson, Sofia; Andersson, August; Mäler, Lena; Widengren, Jerker

    2010-01-01

    An approach to study bimolecular interactions in model lipid bilayers and biological membranes is introduced, exploiting the influence of membrane-associated electron spin resonance labels on the triplet state kinetics of membrane-bound fluorophores. Singlet-triplet state transitions within the dye Lissamine Rhodamine B (LRB) were studied, when free in aqueous solutions, with LRB bound to a lipid in a liposome, and in the presence of different local concentrations of the electron spin resonance label TEMPO. By monitoring the triplet state kinetics via variations in the fluorescence signal, in this study using fluorescence correlation spectroscopy, a strong fluorescence signal can be combined with the ability to monitor low-frequency molecular interactions, at timescales much longer than the fluorescence lifetimes. Both in solution and in membranes, the measured relative changes in the singlet-triplet transitions rates were found to well reflect the expected collisional frequencies between the LRB and TEMPO molecules. These collisional rates could also be monitored at local TEMPO concentrations where practically no quenching of the excited state of the fluorophores can be detected. The proposed strategy is broadly applicable, in terms of possible read-out means, types of molecular interactions that can be followed, and in what environments these interactions can be measured. PMID:21112307

  7. Photophysical and photochemical processes of excited singlet and triplet [3n]cyclophanes (N = 2-6) studied by emission measurements and steady-state and laser flash photolyses.

    PubMed

    Yamaji, Minoru; Okamoto, Hideki; Hakoshima, Yuhko; Shinmyozu, Teruo

    2015-03-12

    Photophysical and photochemical features of [3n]cyclophanes (3nCPs) (n = 2-6) in solution were investigated by emission and transient absorption measurements. The studied 3nCPs show excimer fluorescence without locally excited fluorescence whereas some of them emit excimer phosphorescence in rigid glass at 77 K. The probability of excimeric phosphorescence from transannular ?-electron systems was shown to strictly depend on the symmetric molecular structures. A feature of intersystem crossing from an excimeric fluorescence state to the excimeric triplet state was observed. Transient absorption spectra obtained upon laser flash photolysis of 3nCP revealed formation of the triplet excimer states. Triplet sensitization of 33CP using xanthone as the sensitizer demonstrated formation of triplet 33CP via triplet energy transfer whereas from the xanthone ketyl radical formation, it was inferred that triplet xanthone undergoes H atom abstraction from 32CP, providing a benzylic 32CP radical as the counter species. Based on kinetic and spectroscopic data obtained upon laser flash photolysis, differences in photochemical reactions of triplet xanthone between 32CP and 33CP were discussed. PMID:25685951

  8. Aqueous secondary organic aerosol (SOA) production from the oxidation of phenols by triplet excited state organics

    NASA Astrophysics Data System (ADS)

    Smith, J.; Yu, L.; Zhang, Q.; Anastasio, C.

    2011-12-01

    Recent literature has shown that atmospheric condensed-phase chemistry can play a significant role in the evolution of organic aerosols, including the formation of secondary organic aerosol (SOA). SOA formation from the oxidation of volatile organic compounds (VOCs) in the aqueous phase has largely focused on oxidations involving the hydroxyl radical and other oxidants, such as photochemically created triplet excited states, have not been fully investigated. Phenolic compounds are one of the primary carbon emission classes from biomass and wood combustion and have significant water solubility. Once in the aqueous phase, phenolic compounds can react with the triplet excited states of non-phenolic aromatic carbonyls (NPCs), particle-bound organics that are also emitted in large quantities from wood combustion. The oxidation of phenolic species in the condensed phase by triplet excited states can result in the production of SOA. A main goal of this study was to investigate bulk solution reaction kinetics under atmospherically relevant conditions in order to ascertain how these reactions can impact aqueous-phase SOA production. In our experiments, we studied the reactions of five phenols (phenol, guaiacol, syringol, catechol, and resorcinol) with the triplet state of 3,4-dimethoxybenzaldehyde (34-DMB) during simulated solar radiation. We have characterized the impacts of pH, ionic strength and reactant concentrations on the reaction behavior of this system. In addition, we analyzed the SOA formed using high-resolution aerosol mass spectrometry, ion chromatography, and liquid chromatography-mass spectrometry to infer the reaction mechanisms. Our evidence suggests that under atmospherically relevant conditions, triplet excited states can be the dominant oxidant of phenolics and contribute significantly to the total SOA budget.

  9. Position-dependent heavy atom effect in the subrates of the lowest triplet state of dichloronaphthalenes

    NASA Astrophysics Data System (ADS)

    Flatscher, G.; Friedrich, J.

    1980-07-01

    By means of the microwave-induced delayed phosphorescence (MIDP) technique, the dynamics of the lowest triplet state T 0 of several dichloronaphthalenes in naphthalene and durene are investigated. It is shown that the position dependence is very selective in the nonradiative decay of the spin-sublevels: The out-of-plane spin state is nearly not affected, while the in-plane states are strongly affected. The radiative rates, on the other hand, are not selectively influenced by the position of substitution. Besides, the results show that the dynamics of the lowest triplet state is determined by the type of substitution, rather than by the symmetry of the molecule. The spin—orbit coupling of the in-plane states seems to profit from some distortion the guest molecule experiences in the naphthalene host lattice.

  10. Singlet and Triplet State Transitions of Carotenoids in the Antenna Complexes of Higher-Plant Photosystem I

    E-print Network

    Romeo, Alessandro

    Singlet and Triplet State Transitions of Carotenoids in the Antenna Complexes of Higher characteristics of carotenoids associated with the antenna complexes of Photosystem I have been studied. Pigment a second carotenoid, peaking around 490 nm. Both these xanthophylls are involved in triplet quenching

  11. Aggregation-Induced Photon Upconversion through Control of the Triplet Energy Landscapes of the Solution and Solid States.

    PubMed

    Duan, Pengfei; Yanai, Nobuhiro; Kurashige, Yuki; Kimizuka, Nobuo

    2015-06-22

    Aggregation-induced photon upconversion (iPUC) based on control of the triplet energy landscape is demonstrated for the first time. When a triplet state of a cyano-substituted 1,4-distyrylbenzene derivative is sensitized in solution, no upconverted emission based on triplet-triplet annihilation (TTA) was observed. In stark contrast, crystalline solids obtained by drying the solution revealed clear upconverted emission. Theoretical studies unveiled an underlying switching mechanism: the excited triplets in solution immediately decay back to the ground state through conformational twisting around a C?C bond and photoisomerization, whereas this deactivation path is effectively inhibited in the solid state. The finding of iPUC phenomena highlights the importance of controlling excited energy landscapes in condensed molecular systems. PMID:25980805

  12. Triplet state quenching of phenosafranine dye by indolic compounds studied by transient absorption spectroscopy.

    PubMed

    Broglia, Martín F; Previtali, Carlos M; Bertolotti, Sonia G

    2015-02-01

    The interaction of the triplet state of the synthetic dye phenosafranine (3,7-diamino-5-phenylphenazinium chloride) with indolic compounds of biological relevance was investigated in water by means of laser flash photolysis. The rate constants for the triplet quenching were determined. The quenching process may be explained by an electron transfer from the indole to the dye in its triplet state. The rate constants present a typical dependence of an electron transfer process with the one-electron oxidation potential of the indole. Indole-3-acetic acid and its homologous indole propionic and indole butyric acids are the most effective quenchers with rate constants reaching the diffusion limit. Rate constants for indole itself, tryptophan and indole-3 carboxylic acid are one order of magnitude lower. The electron transfer nature of the quenching reaction is further confirmed by the detection of the semi-reduced form of the dye by its transient absorption. The absorption coefficients of the transient species were estimated, and the quantum yield of the charge separation process was determined. The efficiency of formation of radical species is between 60 and 90% of the triplets intercepted. PMID:25428794

  13. 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

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

    2005-01-01

    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.

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

    PubMed

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

    2012-08-01

    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

  15. Inter-and intraspecific variation in excited-state triplet energy transfer rates in reaction centers of photosynthetic bacteria.

    SciTech Connect

    Laible, P. D.; Morris, Z. S.; Thurnauer, M. C.; Schiffer, M.; Hanson, D. K.

    2003-08-01

    In protein-cofactor reaction center (RC) complexes of purple photosynthetic bacteria, the major role of the bound carotenoid (C) is to quench the triplet state formed on the primary electron donor (P) before its sensitization of the excited singlet state of molecular oxygen from its ground triplet state. This triplet energy is transferred from P to C via the bacteriochlorophyll monomer B{sub B}. Using time-resolved electron paramagnetic resonance (TREPR), we have examined the temperature dependence of the rates of this triplet energy transfer reaction in the RC of three wild-type species of purple nonsulfur bacteria. Species-specific differences in the rate of transfer were observed. Wild-type Rhodobacter capsulatus RCs were less efficient at the triplet transfer reaction than Rhodobacter sphaeroides RCs, but were more efficient than Rhodospirillum rubrum RCs. In addition, RCs from three mutant strains of R. capsulatus carrying substitutions of amino acids near P and B{sub B} were examined. Two of the mutant RCs showed decreased triplet transfer rates compared with wild-type RCs, whereas one of the mutant RCs demonstrated a slight increase in triplet transfer rate at low temperatures. The results show that site-specific changes within the RC of R. capsulatus can mimic interspecies differences in the rates of triplet energy transfer. This application of TREPR was instrumental in defining critical energetic and coupling factors that dictate the efficiency of this photoprotective process.

  16. Delayed fluorescence from the lowest 1B +3u state of anthracene, due to hetero-triplet—triplet annihilation of 3anthracene* and 3xanthone*

    NASA Astrophysics Data System (ADS)

    Nickel, Bernhard; Roden, Gabriele

    1982-04-01

    The P-type delayed fluorescence (DF) S i?S o of aromatic compounds results from the population of excited singlet states S i by triplet—triplet annihillation (TTA) of molecules in their lowest and metastable triplet state T 1 : T 1 + T 1? S i + S o; S i may be any excited singlet state whose excitation energy E(S i ? 2 E(T 1). TTA of unlike molecules A and B (hetero-TTA) may lead to excited singlet states either of A or of B. In particular, if E(T A1) < E(T 1B), hetero-TTA may lead to excited singlet states S kA which are not accessible by TTA of 2 T 1A. In the present paper we report the first example of the detection of the DF from a very short-lived upper excited singlet state S kA which has been populated by hetero-TTA. The systems investigated are liquid solutions of A = anthracene- h10 or anthracene- d10 or 9,10-dimethylanthracene and B = xanthone in 1,1,2-trichlorotrifluoroethane at 243 K. S kA is the lowest 1B 3U+ state (B b state) of anthracene.

  17. Room temperature triplet state spectroscopy of organic semiconductors

    E-print Network

    Reineke, Sebastian

    Organic light-emitting devices and solar cells are devices that create, manipulate, and convert excited states in organic semiconductors. It is crucial to characterize these excited states, or excitons, to optimize device ...

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

    NASA Astrophysics Data System (ADS)

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

    2012-03-01

    The lowest electronic state of distorted tetrahedral X4 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 D2d 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 K4 cluster) and 0.9 eV (for Cu4) above the absolute minimum of the corresponding systems, which is a spin singlet having a rhombus geometry.

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

    PubMed

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

    2012-03-01

    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

  20. Triplet state Stark spectroscopy above the phosphorescence origin of 2,4,5-trimethylbenzaldehyde

    NASA Astrophysics Data System (ADS)

    Winkler, I. C.; Hanson, D. M.

    1982-06-01

    The electric field effect on several of the bands in the phosphorescence excitation spectrum of 2,4,5-trimethylbenzaldehyde, isolated in a durene single crystal at 4.2 K, was measured. While the weak origin of the first triplet state at 4140 Å was sufficiently narrow (˜1 cm-1) to resolve the Stark splitting, the intense bands in the region previously assigned to the second triplet state near 4060 Å were broad (˜10 cm-1). A selective laser excitation technique was developed to determine the Stark splitting of these bands. It was found that the most intense peaks in the 4060 Å region have the same dipole moment difference vectors, within the measurement uncertainties, as the T1 origin. This result is unexpected since the first triplet state is known to be ??* in character, while the second is thought to be n?*. An explanation of these observations in terms of coupling of the T2 (n?*) state to a set of nearby T1(??*) vibronic states is proposed.

  1. Xanthone. I. optical detection of an extremely large sublevel splitting the lowest triplet state

    NASA Astrophysics Data System (ADS)

    Griesser, Hans J.; Bramley, Richard

    1982-06-01

    The phosphorescence spectrum of xanthone in n-hexane is resolved into three components, one of which is due to thermally activated emission from a n ?* origin. The other two emissions originate from extremely widely split sublevels of the lowest triplet state, which is of 3??* origin. higher energy of T L x, and T 1 y, and thus below 4K there is thermal depletion of T 1 z which has the largest radiative strength. Th consequence of spin-orbit coupling between the T x and T y sublevels of the-two very close-lying, lowest triplet states. There are signif mixing of orbital character, a mixing which is governed by spin-orbit coupling rather than vibronic coupling.

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

    SciTech Connect

    Clarke, R.H.

    1980-12-22

    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.

  3. A time-resolved EPR study of short-lived triplet states: Host and temperature dependences of triplet properties of phthalazine

    NASA Astrophysics Data System (ADS)

    Terazima, Masahide; Yamauchi, Seigo; Hirota, Noboru

    1985-10-01

    The triplet properties of phthalazine are investigated by means of the time-resolved EPR technique with laser excitation in various hosts over a wide range of temperature. The host and temperature dependences are interpreted satisfactorily in terms of the vibronic mixing between the 3n?* and 3??* states. From the host dependences of the EPR parameters the zfs of the pure 3n?* state of phthalazine is deduced to be Xn =0.027 cm-1, Yn =-0.058 cm-1, and Zn =0.031 cm-1. The fraction of the 3n?* character of the T1 state is estimated to be ˜0% in ethanol, benzoic acid (BAC), and 1, 4-dichlorobenzene (DCB), 14% in 1, 2, 4, 5-tetrachlorobenzene (TCB), 60% in biphenyl (BP), and 84% in durene. The temperature dependences of the zfs, linewidth, phosphorescence spectrum, and lifetime are investigated and the results are explained using a continuum model. From the simulation of the temperature dependence of the triplet lifetime in the DCB host the decay rate constant of the second excited triplet (3n?*) state is estimated to be 2.5×104 s-1. A drastic increase of the decay rate at higher temperatures suggests the presence of a higher 3n?* state with a decay rate constant of ˜106 s-1. Possible causes for the lack of phosphorescence and fast radiationless decay are also discussed.

  4. Rotational relaxation and triplet-state effects in the cw dye laser

    Microsoft Academic Search

    A. E. Siegman; D. W. Phillion; D. J. Kuizenga

    1972-01-01

    In a cw dye laser apparatus we measure first the fluorescence depolarization in the usual manner, and then the ratio of laser threshold pump powers for the laser polarization parallel and perpendicular to the linearly polarized pump source. From these two measurements we can obtain the important triplet-state parameter KT ? kST?T?T? ?e, as well as the rotational relaxation time

  5. Spectroscopy of triplet states of Rb by femtosecond pump-probe photoionization of doped helium nanodroplets

    Microsoft Academic Search

    M. Mudrich; Ph. Heister; T. Hippler; Ch. Giese; F. Stienkemeier; O. Dulieu

    2009-01-01

    The dynamics of vibrational wave packets in triplet states of rubidium dimers (Rb) formed on helium nanodroplets are studied using femtosecond pump-probe photoionization spectroscopy. Due to fast desorption of the excited Rb 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.

  6. Unveiling the triplet state of a 4-amino-7-nitrobenzofurazan derivative in cyclohexane.

    PubMed

    Sveen, Christopher; Macia, Nicolas; Zaremberg, Vanina; Heyne, Belinda

    2015-01-01

    The nitrobenzofurazan (NBD) moiety has gained tremendous popularity over the last decades due to its fluorogenic nature. Indeed, upon interaction with aliphatic amines, it generates a stable fluorescent adduct, which has been used for protein and lipid labeling. In fact the 4-amino substituted NBD belongs to the broad family of intramolecular charge transfer molecules, with the amino group acting as an electron donor upon photoexcitation, and the nitro group as an electron acceptor. Although the singlet excited state of 4-amino NBD derivatives has been abundantly studied, investigation of its triplet manifold is scarce and even the absence of intersystem crossing for this type of molecules has been suggested. However, intramolecular charge transfer molecules are known to undergo intersystem crossing and high phosphorescence quantum yields have been reported in a nonpolar solvent. In the present paper, we have investigated the photophysical and photochemical properties of N-hexyl-7-nitrobenzo[c][1,2,5]xadiazole-4-amine. We have shown the existence of a triplet state for this molecule in cyclohexane via nanosecond laser flash photolysis. Interestingly, deactivation of the triplet state leads to photoproducts formation, which are only present in the absence of oxygen. PMID:25515933

  7. Magnetic edge states and mixed-parity pairing in spin-triplet superconductors

    NASA Astrophysics Data System (ADS)

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

    2014-03-01

    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 and non-uniform spatial profile. To unveil the microscopic mechanism behind such 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 modulation of the electronic density near the edge of the system leads to a non-unitary superconducting state 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 non-unitary state and originates in the lifting of the spin-degeneracy of the Andreev bound-states. For chiral spin-triplet superconductors spin current flows along the interface and surface charge currents exhibit anomalous dependence on the magnetization. - A. Romano, P. Gentile, C. Noce, I. Vekhter, M. Cuoco, Phys. Rev. Lett. 110, 267002 (2013). This research has received funding from the EU -FP7/2007-2013 under grant agreement N. 264098 - MAMA, and was supported in part by US NSF via Grant No. DMR-1105339

  8. Transport signatures of superconducting hybrids with mixed singlet and chiral triplet states

    NASA Astrophysics Data System (ADS)

    Burset, Pablo; Keidel, Felix; Tanaka, Yukio; Nagaosa, Naoto; Trauzettel, Björn

    2014-08-01

    We propose a model for a superconductor where both spin-singlet and chiral triplet pairing amplitudes can coexist. By solving the Bogoliubov-de Gennes equations with a general pair potential that accounts for both spin states we study experimental signatures of normal metal and superconductor hybrids. The interplay between the spin-singlet and triplet correlations manifests in the appearance of two effective gaps. When the amplitude of the spin-triplet component is stronger than that of the spin singlet, a topological phase transition into a nontrivial regime occurs. As a result, the normal metal-superconductor conductance evolves from a conventional gap profile onto an unconventional zero-bias peak. Additionally, in the topologically nontrivial phase, Andreev bound states formed at Josephson junctions present zero-energy modes; the number of those modes depends on the relative chirality of the junction. Finally, we present results for the current-phase relation and the temperature dependence of the Josephson critical current within both topological phases for several system parameters.

  9. Phase control of the spin-triplet state in S/F/S Josephson junctions

    NASA Astrophysics Data System (ADS)

    Gingrich, Eric C.

    For decades, the proximity effect in superconductor/ferromagnetic (S/F) hybrid systems was thought to be very short-ranged, with coherence lengths on the order of a nanometer. That changed in 2003 when Bergeret et al. suggested systems involving s-wave superconductors and ferromagnets with non-collinear magnetizations could generate spin-triplet supercurrent. This was a significant prediction that radically changed the outlook for these systems, with the possibility of bringing the ferromagnetic coherence length up to ranges similar to the normal metal coherence length. With the experimental confirmation of the spin-triplet state in S/F/S Josephson junctions in 2010, the flood-gates opened into a range of interesting studies. We have performed measurements on the magnetic and superconducting properties of the multilayer Ni/[Co/Ni]n. This arrangement of ferromagnetic materials, when grown with thicknesses of 0.4 nm Ni and 0.2 nm Co, demonstrate a magnetization that lies perpendicular to the plane of the films. Because it will, in the virgin state, possess a non-collinear magnetization with ferromagnets which have magnetizations that lie within the plane, it is a convenient multilayer for the generation of spin-triplet supercurrent. Our measurements of S/F'/F/F'/S Josephson junctions, where F' is a hard ferromagnet and F is the Co/Ni multilayer, confirmed the presence of the spin-triplet state, and demonstrated the viability of the Co/Ni multilayer as a triplet generating ferromagnet. We have also performed studies on the characteristics of a number of soft ferromagnetic alloys. These alloys are important for their potential as a soft ferromagnetic switching layer for application in our triplet control devices. To that end, we have created sputtering targets for four different ferromagnetic alloys: Molybdenum-doped Permalloy, Niobium-doped Permalloy, Copper-doped Permalloy, and Palladium Iron. These studies have included: atomic concentration measurements using EDS, magnetic measurements using a commercial MPMS measurement system and GMR, and superconducting studies done by fabricating S/F'/F/F''/S Josephson junctions with F'' the soft ferromagnet of interest. Lastly, we have performed measurements to study the relative phase of two S/F'/F/F''/S Josephson junctions patterned into a Superconducting Quantum Interference Device (SQUID). The phase of the junctions is determined by the relative rotation of the magnetizations through the junction. By applying an external field to the junctions, and utilizing shape anisotropy to control the switching fields, the F'' layer can be switched in a single junction. The switch in the state can be observed by measuring the interference in the current driven through the SQUID, which responds to the relative phase of the two junctions in the loop. These measurements have yielded promising early results for the prospect of controlling the spin-triplet state.

  10. An ab initio investigation of the ground and low-lying singlet and triplet electronic states of XNO{sub 2} and XONO (X = Cl, Br, and I)

    SciTech Connect

    Peterson, Kirk A., E-mail: kipeters@wsu.edu [Department of Chemistry, Washington State University, Pullman, Washington 99164 (United States); Francisco, Joseph S. [Department of Chemistry, Purdue University, West Lafayette, Indiana 47907-2084 (United States)] [Department of Chemistry, Purdue University, West Lafayette, Indiana 47907-2084 (United States)

    2014-01-28

    A systematic ab initio treatment of the nitryl halides (XNO{sub 2}) and the cis- and trans- conformers of the halide nitrites (XONO), where X = Cl, Br, and I, have been carried out using highly correlated methods with sequences of correlation consistent basis sets. Equilibrium geometries and harmonic frequencies have been accurately calculated in all cases at the explicitly correlated CCSD(T)-F12b level of theory, including the effects of core-valence correlation for the former. Where experimental values are available for the equilibrium structures (ClNO{sub 2} and BrNO{sub 2}), the present calculations are in excellent agreement; however, the X-O distances are slightly too long by about 0.01 Å due to missing multireference effects. Accurate predictions for the iodine species are made for the first time. The vertical electronic excitation spectra have been calculated using equation-of-motion coupled cluster methods for the low-lying singlet states and multireference configuration interaction for both singlet and triplet states. The latter also included the effects of spin-orbit coupling to provide oscillator strengths for the ground state singlet to excited triplet transitions. While for ClNO{sub 2} the transitions to excited singlet states all occur at wavelengths shorter than 310 nm, there is one longer wavelength singlet transition in BrNO{sub 2} and two in the case of INO{sub 2}. The long wavelength tail in the XNO{sub 2} species is predicted to be dominated by transitions to triplet states. In addition to red-shifting from X = Cl to I, the triplet transitions also increase in oscillator strength, becoming comparable to many of the singlet transitions in the case of INO{sub 2}. Hence in particular, the latter species should be very photolabile. Similar trends are observed and reported for the halogen nitrites, many of which for the first time.

  11. Bunched laser cooling of a stored weak 7Li+ ion beam in a pure triplet state

    NASA Astrophysics Data System (ADS)

    Merz, P.; Grieser, R.; Huber, G.; Karpuk, S.; Sebastian, V.; Seelig, P.; Grieser, M.; Grimm, R.; Lauer, I.; Luger, V.; Schwalm, D.; Dax, A.; Engel, T.; Gerlach, M.; Kühl, T.; Winter, H.

    1998-11-01

    A preparation scheme for a 7Li+ ion beam in a storage ring is presented which provides ions in the metastable triplet states with well controlled longitudinal phase space properties. For both state selective preparation and beam cooling, laser- and electron-cooler forces are applied. The spatial- and momentum distributions of the ions are directly detected by a time resolved measurement of the fluorescence light. At low beam intensities, the remaining heating rate of such a beam is completely determined by residual gas scattering.

  12. Prediction of a neutral noble gas compound in the triplet state.

    PubMed

    Manna, Debashree; Ghosh, Ayan; Ghanty, Tapan K

    2015-05-26

    Discovery of the HArF molecule associated with H?Ar covalent bonding [Nature, 2000, 406, 874-876] has revolutionized the field of noble gas chemistry. In general, this class of noble gas compound involving conventional chemical bonds exists as closed-shell species in a singlet electronic state. For the first time, in a bid to predict neutral noble gas chemical compounds in their triplet electronic state, we have carried out a systematic investigation of xenon inserted FN and FP species by using quantum chemical calculations with density functional theory and various post-Hartree-Fock-based correlated methods, including the multireference configuration interaction technique. The FXeP and FXeN species are predicted to be stable by all the computational methods employed in the present work, such as density functional theory (DFT), second-order Møller-Plesset perturbation theory (MP2), coupled-cluster theory (CCSD(T)), and multireference configuration interaction (MRCI). For the purpose of comparison we have also included the Kr-inserted compounds of FN and FP species. Geometrical parameters, dissociation energies, transition-state barrier heights, atomic charge distributions, vibrational frequency data, and atoms-in-molecules properties clearly indicate that it is possible to experimentally realize the most stable state of FXeP and FXeN molecules, which is triplet in nature, through the matrix isolation technique under cryogenic conditions. PMID:25891838

  13. Tuning between singlet, triplet, and mixed pairing states in an extended Hubbard chain

    NASA Astrophysics Data System (ADS)

    Sun, Kuei; Chiu, Ching-Kai; Hung, Hsiang-Hsuan; Wu, Jiansheng

    2014-03-01

    We study spin-half fermions in a one-dimensional extended Hubbard chain at low filling. We identify three triplet and one singlet pairing channels in the system, which are independently tunable as a function of nearest-neighbor charge and spin interactions. In a large-size system with translational invariance, we derive gap equations for the corresponding pairing gaps and obtain a Bogoliubov-de Gennes Hamiltonian with its nontrivial topology determined by the interplay of these gaps. In an open-end system with a fixed number of particles, we compute the exact many-body ground state and identify the dominant pairing revealed by the pair density matrix. Both cases show competition between the four pairing states, resulting in broad regions for each of them and relatively narrow regions for mixed-pairing states in the parameter space. Our results enable the possibility of tuning a nanowire between singlet and triplet pairing states without breaking time-reversal or SU(2) symmetry, accompanied by a change in the system's topology.

  14. Variation of dipole moments with triplet state energy spacings in substituted benzaldehydes

    NASA Astrophysics Data System (ADS)

    Winkler, I. C.; Hanson, David M.

    1983-04-01

    Recent studies of the Stark effect on bands in the laser induced phosphorescence excitation spectrum of 2,4,5-trimethylbenzaldehyde, isolated in a durene single crystal, revealed that the dipole moment associated with the most intense feature in the spectrum, believed to arise from the T2(n?*) state, was the same within experimental uncertainty as that for the T1(??*) origin. This result may indicate that the T2(n?*) state is strongly coupled to a set of nearby T1(??*) vibronic levels. In order to evaluate the effect of the density of ??* vibronic levels on the dipole moment of the T2(n?*) state, we have made similar measurements on 2,4- and on 2,5-dimethylbenzaldehyde. We have found that as the T1-T2 energy spacing decreases, the dipole moment of the second triplet state becomes more characteristic of an n?* state.

  15. Electron spin lattice relaxation of the triplet state in disordered solids exhibits dispersion

    NASA Astrophysics Data System (ADS)

    Ozarowski, Andrzej; Qiang Wu, Jie; Maki, August H.

    1998-04-01

    Global analysis of microwave-induced delayed phosphorescence (MIDP) of photoexcited triplet states at 1.2 K is employed to obtain their spin-lattice relaxation (SLR) rate constants, and other relevant parameters. The phosphorescence decay kinetics of quinoxaline in crystalline durene and n-pentane are predicted accurately, but not in disordered solids nor of tryptophan in aqueous glass. For the latter, the decay fits a bimodal SLR distribution; a subset decays with slow SLR and as predicted, while the remainder displays the expected decay properties of fast SLR. Although not following this bimodal pattern, SLR of quinoxaline in disordered solids also exhibits dispersion.

  16. Studies of the triplet state of the proton-transfer tautomer in salicylaldehydes

    Microsoft Academic Search

    Pi-Tai Chou; Chau-Shuen Chiou; Wei-Shan Yu; Guo-Ray Wu; Tai-Huei Wei

    2003-01-01

    The spectroscopy and dynamics of the low-lying triplet state of the proton-transfer tautomer in salicylaldehydes have been studied via internal heavy-atom effects coupled with a sensitive near-IR detecting system. For 3,5-diiodosalicylaldehyde a weak proton-transfer keto-tautomer phosphorescence was resolved with a maximum at 710 nm (?p?1.8?s, ?obs?5.23×10?4) in a 77 K methylcyclohexane glass. The results, in combination with the time-resolved thermal

  17. Excited-state dynamics in nitro-naphthalene derivatives: intersystem crossing to the triplet manifold in hundreds of femtoseconds.

    PubMed

    Vogt, R Aaron; Reichardt, Christian; Crespo-Hernández, Carlos E

    2013-08-01

    Femtosecond transient absorption experiments and density functional calculations are presented for 2-methyl-1-nitronaphthalene, 2-nitronaphthalene, and 1-nitronaphthalene in cyclohexane and acetonitrile solutions. Excitation of 2-methyl-1-nitronaphthalene at 340 nm populates the Franck-Condon singlet state, which bifurcates into two barrierless decay channels with sub-200-fs lifetimes. The primary decay channel connects the Franck-Condon singlet excited state with a receiver triplet state, whereas the second, minor channel involves conformational relaxation to populate an intramolecular charge-transfer state, as previously reported for 1-nitronaphthalene (J. Chem. Phys. 2009, 113, 224518). Conversely, the experimental and computational data for 2-nitronaphthalene shows that almost the entire Franck-Condon singlet excited-state population intersystem crosses to the triplet state in less than 200 fs due to a sizable energy barrier of ca. 5 kcal/mol that must be surmounted to access the intramolecular charge-transfer state. Our results lend support to the idea that the probability of population transfer to the triplet manifold in these nitronaphthalene derivatives is controlled not only by the small energy gap between the Franck-Condon singlet excited state and the receiver triplet state but also by the region of configuration space sampled in the singlet excited-state potential energy surface at the time of excitation. It is proposed that the ultrafast intersystem crossing dynamics in these nitronaphthalene molecules most likely occurs between nonequilibrated excited states in the strongly nonadiabatic regime. PMID:23845162

  18. Theoretical radiative properties between states of the triplet manifold of NH radical

    SciTech Connect

    Owono Owono, L. C. [Department of Physics, Advanced Teachers' Training College, University of Yaounde I, P.O. Box 47, Yaounde (Cameroon); Centre for Atomic Molecular Physics and Quantum Optics (CEPAMOQ), Faculty of Science, University of Douala, P.O. Box 8580, Douala (Cameroon); Ben Abdallah, D.; Jaidane, N.; Ben Lakhdar, Z. [Laboratory of Atomic Molecular Spectroscopy and Applications (LSAMA), Faculty of Science, University Tunis El Manar, Campus Universitaire 1060 Tunis (Tunisia)

    2008-02-28

    Ab initio transition dipole moments between states of the triplet manifold of NH radical are determined at the complete active space self-consistent field, followed by the internally contracted multireference singles plus doubles configuration interaction level of theory with a modified aug-cc-pVTZ basis set that accounts for valence-Rydberg interactions. This enables the computation of various radiative characteristics such as Einstein coefficients, radiative lifetimes, and oscillator strengths. These properties concern as well valence and Rydberg states. For the valence states, only the (0, 0) band of the A {sup 3}{pi}-X {sup 3}{sigma}{sup -} transition has received some important amount of attention. Data for the other transitions are rather scarce and sometimes inexistent. The results obtained in this work show good agreement with the available experimental data in comparison to other theoretical numbers reported in the literature.

  19. R-matrix calculations of triplet gerade states of molecular hydrogen and their use for high-resolution spectroscopy

    NASA Astrophysics Data System (ADS)

    Oueslati, H.; Argoubi, F.; Bezzaouia, S.; Telmini, M.; Jungen, Ch.

    2014-03-01

    A variational R-matrix approach combined with multichannel quantum defect theory is used for a computational study of triplet gerade states of H2. Electron-ion reaction (quantum defect) matrices are calculated as functions of internuclear distance and energy for the bound and continuum ranges including singly and doubly excited configurations built on the 1?g (X+2?g+) and 1?u (A+2?u+) core states of the H2+ ion. It is shown how these matrices can be reduced to effective quantum defect functions adapted to the analysis of high-resolution spectra in the bound range. These R-matrix effective quantum defects are finally adjusted to the available experimental data [Sprecher et al., J. Phys. Chem. A 117, 9462 (2013), 10.1021/jp311793t], producing agreement with experiment to within 0.5 cm-1, nearly as good as obtained by Sprecher et al. In addition, the R-matrix calculations predict the evolution of the quantum defects for higher energies, in a range extending far into the electronic continuum.

  20. Phosphorescence and electron paramagnetic resonance study of a photoexcited triplet state: Advanced undergraduate experiment in molecular physics

    Microsoft Academic Search

    Raymond Chang; William R. Moomaw

    1976-01-01

    An experiment to investigate molecular multiplet structure is described. The phosphorescence spectrum and lifetime from the lowest triplet state of naphthalene is measured by optical spectroscopy, and the zero-field splitting parameters and the lifetime of paramagnetic resonances of this photoexcited state are determined by electron paramagnetic resonance.

  1. Efficient up-conversion of triplet excitons into a singlet state and its application for organic light emitting diodes

    Microsoft Academic Search

    Ayataka Endo; Keigo Sato; Kazuaki Yoshimura; Takahiro Kai; Atsushi Kawada; Hiroshi Miyazaki; Chihaya Adachi

    2011-01-01

    A material possessing a very small energy gap between its singlet and triplet excited states, DeltaE1-3, which allows efficient up-conversion of triplet excitons into a singlet state and leads to efficient thermally activated delayed fluorescence (TADF), is reported. The compound, 2-biphenyl-4,6-bis(12-phenylindolo[2,3-a] carbazole-11-yl)-1,3,5-triazine, breaks the restriction of a large energy gap, with a DeltaE1-3 of just 0.11 eV, while maintaining a

  2. Triplet excition emissions of octafluoronaphthalene crystalline complexes with naphthalene and durene

    NASA Astrophysics Data System (ADS)

    Chen, Freeman P.; Prasad, Paras N.

    1980-06-01

    The phosphorescence spectra of naphthalene-octafluoronaphthalene and durene-octafluoronaphthalene at 4.2 K reveal a localized exciton emission from octafluoronaphthalene, a weak intercomponent triplet-states quasi-resonance and a weak exciton-phonon coupling.

  3. Oxygen quenching of excited singlet and triplet states of polycyclic aromatic hydrocarbons in the vapor phase

    NASA Astrophysics Data System (ADS)

    Zalesskaya, G. A.; Kuchinsky, A. V.

    2010-01-01

    The quenching rate constants of excited singlet ( kSO2) and triplet ( kTO2) states by oxygen were investigated in the vapor phase for polycyclic aromatic hydrocarbons having distinguishing oxidation potentials Eox. The significant spread in the rate constants was found (4 × 10 5 s -1 Torr -1 < kSO2 < 1.2 × 10 7 s -1 Torr -1; 5 × 10 2 < kTO2 < 4 × 10 5 s -1 Torr -1). The values of both kSO2 and kTO2 change linearly in the logarithmic scale with free energy change for complete electron transfer ? GET, which points that the charge-transfer interactions are involved in the oxygen quenching of the S 1 and T 1 states.

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

    PubMed

    Mukhopadhyay, S; Ramasesha, S; Guha, S

    2010-01-28

    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. PMID:20113016

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

    NASA Astrophysics Data System (ADS)

    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

    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).

  6. Spectroscopic insights on imidazole substituted phthalocyanine photosensitizers: Fluorescence properties, triplet state and singlet oxygen generation

    NASA Astrophysics Data System (ADS)

    Zhang, Xian-Fu; Lin, Yong; Guo, Wenfeng; Zhu, Jingzhong

    2014-12-01

    Imidazole substituted metal phthalocyanine (Pc) complexes were synthesized. UV-vis absorption, steady state and time-resolved fluorescence, as well as laser flash photolysis were used to measure the photophysical and photosensitizing properties. All the imidazole-phthalocyanine conjugates show high ?T (quantum yield of excited triplet formation), high ?? (singlet oxygen formation yield, >0.50) and good fluorescence properties (quantum yield ?f > 0.20 and lifetime ?f > 3.0 ns). Compared to the unsubstituted Pc, both ?- and ?-imidazole substitutions result in the remarkable decrease in ?f and ?f, but the ?-substitution is stronger. The imidazole substitution, on the other hand, causes the increase of ?T, ?T, and ?? values. Magnesium phthalocyanine (MgPc) is more susceptible to the substitution than zinc phthalocyanine (ZnPc). The mechanism responsible for the result is suggested based on the involvement of intramolecular photoinduced electron transfer. The high ?? and appropriate fluorescence properties make the Pcs good candidate for PDT photosensitizers.

  7. Spin Triplet Superconducting State due to Broken Inversion Symmetry in Li(2)Pt(3)B.

    PubMed

    Nishiyama, M; Inada, Y; Zheng, Guo-qing

    2007-01-26

    We report (11)B and (195)Pt NMR measurements in noncentrosymmetric superconductor Li(2)Pt(3)B. We find that the spin susceptibility measured by the Knight shift remains unchanged across the superconducting transition temperature T(c). With decreasing temperature (T) below T(c), the spin-lattice relaxation rate 1/T(1) decreases with no coherence peak and is in proportion to T3. These results indicate that the Cooper pair is in the spin-triplet state and that there exist line nodes in the superconducting gap function. They are in sharp contrast to those in the isostructural Li(2)Pd(3)B which is a spin-singlet, s-wave superconductor, and are ascribed to the enhanced spin-orbit coupling due to the lack of spatial inversion symmetry. Our finding points to a new paradigm where exotic superconductivity arises in the absence of electron-electron correlations. PMID:17358799

  8. Intermolecular energy transfer of the spin-polarized triplet state in a ?-cyclodextrin cavity

    NASA Astrophysics Data System (ADS)

    Murai, Hisao; Mizunuma, Yasuhiro; Ashikawa, Kyoichi; Yamamoto, Yoshinori; I'Haya, Yasumasa J.

    1988-03-01

    The triplet-triplet energy-transfer process from xanthone to naphthalene was studied in a ?-cyclodextrin system at 77 K using a time-resolved ESR method. The efficient inclusion of these two molecules and the formation of a fixed configuration between them in a ?-cyclodextrin cavity were found with the aid of spin polarization transfer.

  9. Dynamics and transient absorption spectral signatures of the single-wall carbon nanotube electronically excited triplet state.

    PubMed

    Park, Jaehong; Deria, Pravas; Therien, Michael J

    2011-11-01

    We utilize femtosecond-to-microsecond time domain pump-probe transient absorption spectroscopy to interrogate for the first time the electronically excited triplet state of individualized single-wall carbon nanotubes (SWNTs). These studies exploit (6,5) chirality-enriched SWNT samples and poly[2,6-{1,5-bis(3-propoxysulfonic acid sodium salt)}naphthylene]ethynylene (PNES), which helically wraps the nanotube surface with periodic and constant morphology (pitch length = 10 ± 2 nm), providing a self-assembled superstructure that maintains structural homogeneity in multiple solvents. Spectroscopic interrogation of such PNES-SWNT samples in aqueous and DMSO solvents using E(22) excitation and a white-light continuum probe enables E(11) and E(22) spectral evolution to be monitored concomitantly. Such experiments not only reveal classic SWNT singlet exciton relaxation dynamics and transient absorption signatures but also demonstrate spectral evolution consistent with formation of a triplet exciton state. Transient dynamical studies evince that (6,5) SWNTs exhibit rapid S(1)?T(1) intersystem crossing (ISC) (?(ISC) ~20 ps), a sharp T(1)?T(n) transient absorption signal (?(max)(T(1)?T(n)) = 1150 nm; full width at half-maximum ? 350 cm(-1)), and a substantial T(1) excited-state lifetime (?(es) ? 15 ?s). Consistent with expectations for a triplet exciton state, T(1)-state spectral signatures and T(1)-state formation and decay dynamics for PNES-SWNTs in aqueous and DMSO solvents, as well as those determined for benchmark sodium cholate suspensions of (6,5) SWNTs, are similar; likewise, studies that probe the (3)[(6,5) SWNT]* state in air-saturated solutions demonstrate (3)O(2) quenching dynamics reminiscent of those determined for conjugated aromatic hydrocarbon excited triplet states. PMID:21970339

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

    Microsoft Academic Search

    Bediha Beser

    2010-01-01

    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

  11. Theoretical study of bending and symmetric stretching vibrational levels of the lowest five quintet and two triplet states of FeH 2

    Microsoft Academic Search

    Kiyoshi Tanaka; Katsuyuki Nobusada

    2004-01-01

    Adiabatic potential surfaces of the lowest two triplet states and the lowest five quintet states of FeH2 were calculated using ab initio multi-reference singly and doubly excited configuration interaction plus Davidson's type correction. Multi-reference coupled pair approximation was applied to obtain more accurate term energies of the triplet states. In contrast to the quintet states, which are known to be

  12. Vibrational levels of the transition state and rate of dissociation of triplet acetaldehyde

    NASA Astrophysics Data System (ADS)

    Leu, Gen-Hou; Huang, Cheng-Liang; Lee, Shih-Huang; Lee, Yu-Chang; Chen, I.-Chia

    1998-12-01

    Fluorescence decay of the S1 state of d4-acetaldehyde is measured. Below the dissociation threshold for formation of fragments of formyl and methyl radicals, single exponential decays of fluorescence are observed. Biexponential decay is observed when the excitation energies are near and above the dissociation threshold. Hence, in this region the mechanism for intramolecular relaxation of energy reaches the "intermediate case." Strong coupling between S1 and T1 states or reversible reaction for S1?T1 results in this biexponential behavior in the fluorescence decay of S1. Rates of appearance of DCO from dissociation of acetaldehyde are measured. The stepwise increases in plots of both rate of appearance of formyl radicals and rate of decay of excited acetaldehyde versus excitation energy for both isotopic variants of acetaldehyde are observed. According to fits to Rice-Ramsperger-Kassel-Marcus (RRKM) theory, these sharp increases correspond to vibrational levels of transition state in the triplet surface. Frequencies of torsional and C-C-O bending modes are determined to be (73±10) and (200±10) cm-1 for the transition state of CD3CDO and the torsional frequency (80±10) cm-1 for CH3CHO. That these fitted frequencies are less than values calculated with methods B3LYP and MP2 indicates a looser transition state than calculated for dissociation. From these fits the dissociation threshold for formation of radical fragments is determined to be 31 845 for CD3CDO and 31 650 cm-1 for CH3CHO.

  13. Spectroscopic investigations of intersystem crossing and triplet state structure in acetylene

    E-print Network

    Thom, Ryan L. (Ryan Louis), 1978-

    2006-01-01

    A multispectral study employing both Ultraviolet Laser Induced Fluorescence (UV-LIF) and Surface Electron Ejection by Laser Excited Metastables (SEELEM) spectroscopies has yielded a complete characterization of singlet-triplet ...

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

    SciTech Connect

    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)] [Arizona State Univ. Tempe, AZ (United States)

    1997-02-12

    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.

  15. The Photochemical Reaction Between Phenol and an Excited Triplet State is Enhanced in/on Ice Compared to in Solution

    NASA Astrophysics Data System (ADS)

    Chen, Z.; Anastasio, C.

    2014-12-01

    Photochemical reactions appear to play an important role in the processing of organic compounds in/on snow and ice. These reactions likely control the fate and lifetimes of organic compounds and influence the emissions of volatile organic compounds (VOC) from snow and ice. Triplet excited states of organic compounds (3C*) can be important aqueous oxidants in atmospheric drops and in surface waters, but little is known of this class of oxidants in frozen samples. When exposed to light, 3, 4-dimethoxybenzaldehyde (DMB), a product from biomass combustion, is excited to its triplet state (3DMB*), which can either return to the ground state, react with oxygen to form singlet oxygen, or oxidize organics, such as phenol. In this study, we examine the photochemical loss of phenol due to reaction with 3DMB* in laboratory ice samples as a function of pH, temperature, total solute, and oxygen concentration. Our results show that the rate of phenol loss due to 3DMB* is significantly enhanced in ice compared to the equivalent liquid sample at the same photon flux. This suggests that reactions of triplet excited states in ice can be significant sinks for organics, and perhaps reactive inorganic species, in snow and ice.

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

    NASA Astrophysics Data System (ADS)

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

    2013-02-01

    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 0^0_0 band of the T1(n, ?*) ? S0 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)], 10.1063/1.470569, 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)], 10.1002/qua.21803 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.

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

    PubMed

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

    2013-02-14

    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

  18. A Theoretical Study of the Photodissociation Mechanism of Cyanoacetylene in Its Lowest Singlet and Triplet Excited States

    Microsoft Academic Search

    Cheng Luo; Wei-Na Du; Xue-Mei Duan; Ze-Sheng Li

    2008-01-01

    Cyanoacetylene (H5C4C3C2N1) is a minor constituent of the atmosphere of Titan, and its photochemistry plays an important role in the formation of the haze surrounding the satellite. In this paper, the complete active space self-consistent field (CASSCF) and multiconfigurational second-order perturbation (CASPT2) approaches are employed to investigate the photochemical processes for cyanoacetylene in its first singlet and triplet excited states

  19. Toward enabling large-scale open-shell equation-of-motion coupled cluster calculations: triplet states of ?-carotene

    SciTech Connect

    Hu, Hanshi; Bhaskaran-Nair, Kiran; Apra, Edoardo; Govind, Niranjan; Kowalski, Karol

    2014-10-02

    In this paper we discuss the application of novel parallel implementation of the coupled cluster (CC) and equation-of-motion coupled cluster methods (EOMCC) in calculations of excitation energies of triplet states in beta-carotene. Calculated excitation energies are compared with experimental data, where available. We also provide a detailed description of the new parallel algorithms for iterative CC and EOMCC models involving single and doubles excitations.

  20. Spectroscopy of triplet states of Rb2 by femtosecond pump-probe photoionization of doped helium nanodroplets

    Microsoft Academic Search

    M. Mudrich; Ph. Heister; T. Hippler; Ch. Giese; O. Dulieu; F. Stienkemeier

    2009-01-01

    The dynamics of vibrational wave packets in triplet states of rubidium dimers (Rb2) formed on helium nanodroplets are studied using femtosecond pump-probe photoionization spectroscopy. Due to fast desorption of the excited Rb2 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 ≳1.5ns . In the first-excited

  1. Zero-field splitting of the lowest excited triplet states of C(60) and C(70) and benzene.

    PubMed

    van Gastel, Maurice

    2010-10-14

    The electronic structure of the lowest excited triplet states of C(60) and C(70) are characterized by a magnetic interaction between the unpaired electrons for which the zero-field-splitting parameter D is negative for the former and positive for the latter molecule. The sign of D has so far been qualitatively understood, and its magnitude has been found to critically depend on the degree of delocalization of the singly occupied molecular orbitals. In this contribution, the effect of spin polarization to the zero-field-splitting parameters of the fullerenes is evaluated, the inclusion of which results in quantitative agreement between the experimental and calculated D values. The direct spin-spin contribution is found to be dominant for both molecules. For C(60), a significant contribution of 20% of the total zero-field splitting has been found to derive from spin polarization. The physical reason for the sign difference of D for C(60) and C(70) is traced back to the relative phases of the local p(z) orbitals of adjacent carbon atoms near the equatorial plane in both singly occupied molecular orbitals. These relative phases differ for C(60) and C(70), because C(70) has an additional set of ten carbon atoms in its equatorial plane as compared to C(60). Additionally, the triplet wave function of C(70) is found to contain significant multireference character. In order to evaluate the effect of spin polarization in multireference systems, the zero-field-splitting parameters of the lowest triplet state of benzene have been evaluated in an illustrative and insightful calculation as well. Though this prototypical molecule is much smaller than C(60) and C(70), the electronic structure of its lowest excited triplet state is also of multireference character. For benzene, 18% of the total zero-field splitting arises from spin polarization. PMID:20845950

  2. Long-lived room temperature deep-red/near-IR emissive intraligand triplet excited state (3IL) of naphthalimide in cyclometalated platinum(II) complexes and its application in upconversion.

    PubMed

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

    2011-11-21

    [C(^)NPt(acac)] (C(^)N = cyclometalating ligand; acac = acetylacetonato) complexes in which the naphthalimide (NI) moiety is directly cyclometalated (NI as the C donor of the C-Pt bond) were synthesized. With 4-pyrazolylnaphthalimide, isomers with five-membered (Pt-2) and six-membered (Pt-3) chelate rings were obtained. With 4-pyridinylnaphthalimide, only the complex with a five-membered chelate ring (Pt-4) was isolated. A model complex with 1-phenylpyrazole as the C(^)N ligand was prepared (Pt-1). Strong absorption of visible light (? = 21,900 M(-1) cm(-1) at 443 nm for Pt-3) and room temperature (RT) phosphorescence at 630 nm (Pt-2 and Pt-3) or 674 nm (Pt-4) were observed. Long-lived phosphorescences were observed for Pt-2 (?(P) = 12.8 ?s) and Pt-3 (?(P) = 61.9 ?s). Pt-1 is nonphosphorescent at RT in solution because of the acac-localized T(1) excited state [based on density functional theory (DFT) calculations and spin density analysis], but a structured emission band centered at 415 nm was observed at 77 K. Time-resolved transient absorption spectra and spin density analysis indicated a NI-localized intraligand triplet excited state ((3)IL) for complexes Pt-2, Pt-3, and Pt-4. DFT calculations on the transient absorption spectra (T(1) ? T(n) transitions, n > 1) also support the (3)IL assignment of the T(1) excited states of Pt-2, Pt-3, and Pt-4. The complexes were used as triplet sensitizers for triplet-triplet-annihilation (TTA) based upconversion, and the results show that Pt-3 is an efficient sensitizer with an upconversion quantum yield of up to 14.1%, despite its low phosphorescence quantum yield of 5.2%. Thus, we propose that the sensitizer molecules at the triplet excited state that are otherwise nonphosphorescent were involved in the TTA upconversion process, indicating that weakly phosphorescent or nonphosphorescent transition-metal complexes can be used as triplet sensitizers for TTA upconversion. PMID:22029396

  3. Generation of Phosphorescent Triplet States via Photoinduced Electron Transfer: Energy and Electron Transfer Dynamics in Pt Porphyrin-Rhodamine B Dyads

    PubMed Central

    Mani, Tomoyasu; Niedzwiedzki, Dariusz M.; Vinogradov, Sergei A.

    2012-01-01

    Control over generation and dynamics of excited electronic states is fundamental to their utilization in all areas of technology. We present the first example of multichromophoric systems in which emissive triplet states are generated via a pathway involving photoinduced electron transfer (ET), as opposed to local intrachromophoric processes. In model dyads, PtP-Phn-pRhB+ (1-3, n=1-3), comprising platinum(II) meso-tetraarylporphyrin (PtP) and rhodamine B piperazine derivative (pRhB+), linked by oligo-p-phenylene bridges (Phn), upon selective excitation of pRhB+ at a frequency below that of the lowest allowed transition of PtP, room-temperature T1?S0 phosphorescence of PtP was observed. The pathway leading to the emissive PtP triplet state includes excitation of pRhB+, ET with formation of the singlet radical pair, intersystem crossing within that pair and subsequent radical recombination. Due to the close proximity of the triplet energy levels of PtP and pRhB+, reversible triplet-triplet (TT) energy transfer between these states was observed in dyads 1 and 2. As a result, the phosphorescence of PtP was extended in time by the long decay of the pRhB+ triplet. Observation of ET and TT in the same series of molecules enabled direct comparison of the distance attenuation factors ? between these two closely related processes. PMID:22400988

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

    NASA Astrophysics Data System (ADS)

    Sprecher, Daniel; Jungen, Christian; Merkt, Frédéric

    2013-10-01

    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.

  5. Influence of triplet states on the spectrum of collective spin-polaron excitations in a 2D kondo lattice

    NASA Astrophysics Data System (ADS)

    Val'Kov, V. V.; Shklyaev, A. A.; Korovushkin, M. M.; Barabanov, A. F.

    2011-10-01

    The normal and superconducting phases of the ensemble of spin polarons in a two-dimensional Kondo lattice have been considered under the conditions when the hopping integral is comparable to the s-d exchange interaction energy. The polaron excitation spectrum and the superconducting transition temperature have been found taking into account upper triplet states. The change in the concentration dependence of the critical temperature of the transition to the superconducting phase with the relation between the hopping integral and the integral of the s- d exchange coupling has been analyzed.

  6. Characteristics of the conductance in ferromagnet/spin-triplet superconductor junctions with helical p-wave states

    NASA Astrophysics Data System (ADS)

    Cheng, Qiang; Jin, Biao; Yu, Dongyang

    2015-06-01

    We study the charge conductance in ferromagnet/spin-triplet superconductor junctions with the helical superconducting states, kx x ˆ ±ky y ˆ or ky x ˆ ±kx y ˆ , which are consistent with the in-plane H c 2 , ab measurements of Sr2RuO4. The conductance shows strong anisotropic dependence on the orientation of the magnetization in ferromagnet and is simultaneously symmetric about some specific rotations. The effects of the magnetization magnitude and the height of the interfacial barrier are also investigated. The obtained results may provide helpful information about the pairing symmetries in Sr2RuO4.

  7. High-resolution spectroscopy of triplet states of Rb2 by femtosecond pump-probe photoionization of doped helium nanodroplets

    Microsoft Academic Search

    M. Mudrich; Ph. Heister; T. Hippler; Ch. Giese; O. Dulieu; F. Stienkemeier

    2009-01-01

    The dynamics of vibrational wave packets in triplet states of rubidium dimers\\u000a(Rb2) formed on helium nanodroplets are studied using femtosecond pump-probe\\u000aphotoionization spectroscopy. Due to fast desorption of the excited Rb2\\u000amolecules off the droplets and due to their low internal temperature, wave\\u000apacket oscillations can be followed up to very long pump-probe delay times\\u000a>1.5ns. In the first

  8. Direct observation of the solvent effects on the low-lying n?* and ??* excited triplet states of acetophenone derivatives in thermal equilibrium.

    PubMed

    Narra, Sudhakar; Shigeto, Shinsuke

    2015-03-01

    Low-lying excited triplet states of aromatic carbonyl compounds exhibit diverse photophysical and photochemical properties of fundamental importance. Despite tremendous effort in studying those triplet states, the effects of substituents and solvents on the energetics of the triplet manifold and on photoreactivity remain to be fully understood. We have recently studied the ordering of the low-lying n?* and ??* excited triplet states and its substituent dependence in acetophenone derivatives using nanosecond time-resolved near-IR (NIR) spectroscopy. Here we address the other important issue, the solvent effects, by directly observing the electronic bands in the NIR that originate from the lowest n?* and ??* states of acetophenone derivatives in four solvents of different polarity (n-heptane, benzene, acetonitrile, and methanol). The two transient NIR bands decay synchronously in all the solvents, indicating that the lowest n?* and ??* states are in thermal equilibrium irrespective of the solvent polarity studied here. We found that the ??* band increases in intensity relative to the n?* band as solvent polarity increases. These results are compared with the photoreduction rate constant for the acetophenone derivatives in the solvents to which 2-propanol was added as a hydrogen-atom donor. Based on the present findings, we present a comprehensive, solvent- and substituent-dependent energy level diagram of the low-lying n?* and ??* excited triplet states. PMID:25686256

  9. Geminate and Nongeminate Recombination of Triplet Excitons Formed by Singlet Fission

    NASA Astrophysics Data System (ADS)

    Bayliss, Sam L.; Chepelianskii, Alexei D.; Sepe, Alessandro; Walker, Brian J.; Ehrler, Bruno; Bruzek, Matthew J.; Anthony, John E.; Greenham, Neil C.

    2014-06-01

    We report the simultaneous observation of geminate and nongeminate triplet-triplet annihilation in a solution-processable small molecule TIPS-tetracene undergoing singlet exciton fission. Using optically detected magnetic resonance, we identify recombination of triplet pairs directly following singlet fission, as well as recombination of triplet excitons undergoing bimolecular triplet-triplet annihilation. We show that the two processes give rise to distinct magnetic resonance spectra, and estimate the interaction between geminate triplet excitons to be 60 neV.

  10. Rabi oscillation and electron-spin-echo envelope modulation of the photoexcited triplet spin system in silicon

    NASA Astrophysics Data System (ADS)

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

    2012-09-01

    We report on a pulsed electron paramagnetic resonance (EPR) study of the photoexcited triplet state (S=1) of oxygen-vacancy centers in silicon. Rabi oscillations between the triplet sublevels are observed using coherent manipulation with a resonant microwave pulse. The Hahn echo and stimulated echo decay profiles are superimposed with strong modulations known as electron-spin-echo envelope modulation (ESEEM). The ESEEM spectra reveal a weak but anisotropic hyperfine coupling between the triplet electron spin and a 29Si nuclear spin (I=1/2) residing at a nearby lattice site, that cannot be resolved in conventional field-swept EPR spectra.

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

    PubMed

    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

    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

  12. Coupled singlet-triplet analysis of two-color cold-atom photoassociation spectra J. M. Vogels,1

    E-print Network

    Heinzen, Daniel J.

    suited to analysis of the bound states of the alkali-metal dimers near their dissociation limit.70.Ca I. INTRODUCTION The techniques of laser cooling and evaporative cooling have opened the field of ultracold-atom physics for alkali- metal atoms, with spectacular research subjects such as Bose

  13. EPR studies of the excited triplet states of C 60O and C 60C 2H 4N(CH 3) fullerene derivatives and C 70 in toluene and polymethylmethacrylate glasses and as films

    NASA Astrophysics Data System (ADS)

    Agostini, G.; Corvaja, C.; Pasimeni, L.

    1996-01-01

    The EPR spectra of excited triplet states of two fullerene derivatives, C 60O and C 60C 2H 4N(CH 3), in the glassy matrices of toluene and of polymethylmethacrylate (PMMA) and as films were examined at low temperature and the magnetic parameters were measured. In films, species with zfs parameters smaller than those in toluene were found and they were assigned to triplet excitations visiting more than one molecule in the crystallites that form the film. When C 60C 2H 4N(CH 3) was excited in PMMA grown by in sity thermal polymerization a new triplet species was originated characterized by a dipolar splitting constant D about three times larger than that measured in toluene. Evidence was gained that such species participates to cross-linking in the polymer. The effect of PMMA matrix on the molecular dynamics of 3C 70 was also investigated. It was found that a dynamical model holds based on the pseudorotation of the molecule around the axis of larger dipolar splitting. Motion is activated with activation energy of 210 ± 50 cm -1 a value comparable with that obtained for pseudorotation of 3C 70 in cyclohexane.

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

    NASA Astrophysics Data System (ADS)

    Ghosh, Sanjib; Petrin, Michael; Maki, August H.

    1987-02-01

    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 durene host. In durene, the SLR rate constant between the two in-plane sublevels was found to be dominant, and was suggested to occur via an Orbach relaxation process involving a localized phonon state with rotated spin axes. It is proposed here that the dominant relaxation route between the short in-plane axis sublevel (Ty) and the out-of-plane axis sublevel (Tx) observed for quinoxaline in n-alkane hosts is the result of a spin-orbit-phonon coupling. In the temperature range of 2.5 to 4.2 K, the SLR rate constant Wyx exhibits Raman relaxation with a T7 temperature dependence in an n-pentane host. In n-hexane, where the relaxation is much faster than that in n-pentane, the mechanism observed appears to be a combination of a normal direct process and a Raman process in the temperature range of 1.2 to 3.2 K. Individual decay constants for the triplet sublevels in the temperature range investigated are also presented.

  15. Comparative ENDOR study at 34 GHz of the triplet state of the primary donor in bacterial reaction centers of Rb. sphaeroides and Bl. viridis.

    PubMed

    Marchanka, Aliaksandr; Lubitz, Wolfgang; Plato, Martin; van Gastel, Maurice

    2014-05-01

    The primary electron donor (P) in the photosynthetic bacterial reaction center of Rhodobacter sphaeroides and Blastochloris viridis consists of a dimer of bacteriochlorophyll a and b cofactors, respectively. Its photoexcited triplet state in frozen solution has been investigated by time resolved ENDOR spectroscopy at 34 GHz. The observed ENDOR spectra for (3)P865 and (3)P960 are essentially the same, indicating very similar spin density distributions. Exceptions are the ethylidene groups unique to the bacteriochlorophyll b dimer in (3)P960. Strikingly, the observed hyperfine coupling constants of the ethylidene groups are larger than in the monomer, which speaks for an asymmetrically delocalized wave function over both monomer halves in the dimer. The latter observation corroborates previous findings of the spin density in the radical cation states P 865 (•+) (Lendzian et al. in Biochim Biophys Acta 1183:139-160, 1993) and P 960 (•+) (Lendzian et al. in Chem Phys Lett 148:377-385, 1988). As compared to the bacteriochlorophyll monomer, the hyperfine coupling constants of the methyl groups 2(1) and 12(1) are reduced by at least a factor of two, and quantitative analysis of these couplings gives rise to a ratio of approximately 3:1 for the spin density on the halves PL:PM. Our findings are discussed in light of the large difference in photosynthetic activity of the two branches of cofactors present in the bacterial reaction center proteins. PMID:23184403

  16. Ab initio calculation of the NH(3?-)-NH(3?-) interaction potentials in the quintet, triplet, and singlet states

    NASA Astrophysics Data System (ADS)

    Dhont, Guillaume S. F.; van Lenthe, Joop H.; Groenenboom, Gerrit C.; van der Avoird, Ad

    2005-11-01

    We present the ab initio potential-energy surfaces of the NH-NH complex that correlate with two NH molecules in their ?-3 electronic ground state. Three distinct potential-energy surfaces, split by exchange interactions, correspond to the coupling of the SA=1 and SB=1 electronic spins of the monomers to dimer states with S =0, 1, and 2. Exploratory calculations on the quintet (S=2), triplet (S=1), and singlet (S=0) states and their exchange splittings were performed with the valence bond self-consistent-field method that explicitly accounts for the nonorthogonality of the orbitals on different monomers. The potential surface of the quintet state, which can be described by a single Slater determinant reference function, was calculated at the coupled cluster level with single and double excitations and noniterative treatment of the triples. The triplet and singlet states require multiconfiguration reference wave functions and the exchange splittings between the three potential surfaces were calculated with the complete active space self-consistent-field method supplemented with perturbative configuration interaction calculations of second and third orders. Full potential-energy surfaces were computed as a function of the four intermolecular Jacobi coordinates, with an aug-cc-pVTZ basis on the N and H atoms and bond functions at the midpoint of the intermolecular vector R. An analytical representation of these potentials was given by expanding their dependence on the molecular orientations in coupled spherical harmonics, and representing the dependence of the expansion coefficients on the intermolecular distance R by the reproducing kernel Hilbert space method. The quintet surface has a van der Waals minimum of depth De=675cm-1 at Re=6.6a0 for a linear geometry with the two NH electric dipoles aligned. The singlet and triplet surfaces show similar, slightly deeper, van der Waals wells, but when R is decreased the weakly bound NH dimer with S =0 and S =1 converts into the chemically bound N2H2 diimide (also called diazene) molecule with only a small energy barrier to overcome.

  17. Light Harvesting by Carotenoids Incorporated into the B850 Light-Harvesting Complex from Rhodobacter sphaeroides R-26.1: Excited-State Relaxation, Ultrafast Triplet

    E-print Network

    van Stokkum, Ivo

    picoseconds through the singlet fission mechanism [Gradinaru, C. C., et al. Proc. Natl. Acad. Sci. U.S.A. 2001 that binds the carotenoid and not on the carotenoid itself. More specifically, the singlet fission process S* carotenoid singlet excited state and the direct generation of carotenoid triplet states within

  18. Dynamic Quenching of Porphyrin Triplet States by Two-Photon Absorbing Dyes: Towards Two-Photon-Enhanced Oxygen Nanosensors

    PubMed Central

    Finikova, Olga S.; Chen, Ping; Ou, Zhongping; Kadish, Karl M.; Vinogradov, Sergei A.

    2008-01-01

    Two-photon-enhanced dendritic nanoprobes are being developed for two-photon (2P) laser scanning microscopy of oxygen [1]. In these molecular constructs, phosphorescence of metalloporphyrins is coupled to two-photon absorption (2PA) of electronically separate antenna dyes via intramolecular Förster-type resonance energy transfer (FRET). In the originally developed probes, competing electron transfer (ET) between the antennae and the long-lived triplet states of metalloporphyrins partially quenched the phosphorescence, reducing the probe's sensitivity and dynamic range. The rate of such ET can be reduced by tuning the redox potentials of the chromophores. In order to identify the optimal metalloporphyrin-2P antenna pairs, we performed screening of several phosphorescent Pt porphyrins (FRET acceptors) and 2P dyes (FRET donors) using dynamic quenching of phosphorescence. Phosphorescence lifetimes of Pt porphyrins were measured as a function of the dye concentration in organic solutions. The obtained Stern-Volmer quenching constants were correlated with the corresponding ET driving forces (?GET), calculated using the Rehm-Weller equation. FRET-pairs with minimal quenching rates were identified. The developed approach allows convenient screening of candidate-compounds for covalent assembly of 2P-enhanced triplet nanodevices. Systematic electrochemical measurements in a series of Pt porphyrins with varying peripheral substitution and conjugation pathways are presented. PMID:19030124

  19. Triplet states as non-radiative traps in multichromophoric entities: single molecule spectroscopy of an artificial and natural antenna system

    NASA Astrophysics Data System (ADS)

    Hofkens, Johan; Schroeyers, Wouter; Loos, Davey; Cotlet, Mircea; Köhn, Fabian; Vosch, Tom; Maus, Michael; Herrmann, A.; Müllen, K.; Gensch, Thomas; De Schryver, F. C.

    2001-09-01

    Energy transfer in antenna systems, ordered arrays of chromophores, is one of the key steps in the photosynthetic process. The photophysical processes taking place in such multichromophoric systems, even at the single molecule level, are complicated and not yet fully understood. Instead of directly studying individual antenna systems, we have chosen to focus first on systems for which the amount of chromophores and the interactions among the chromophores can be varied in a systematic way. Dendrimers with a controlled number of chromophores at the rim fulfill those requirements perfectly. A detailed photophysical study of a second-generation dendrimer, containing eight peryleneimide chromophores at the rim, was performed 'J. Am. Chem. Soc., 122 (2000) 9278'. One of the most intriguing findings was the presence of collective on/off jumps in the fluorescence intensity traces of the dendrimers. This phenomenon can be explained by assuming a simultaneous presence of both a radiative trap (energetically lowest chromophoric site) and a non-radiative trap (triplet state of one chromophore) within one individual dendrimer. It was shown that an analogue scheme could explain the collective on/off jumps in the fluorescence intensity traces of the photosynthetic pigment B-phycoerythrin (B-PE) ( Porphyridium cruentum). The different values of the triplet lifetime that could be recovered for a fluorescence intensity trace of B-PE were correlated with different intensity levels in the trace, suggesting different chromophores acting as a trap as function of time.

  20. Triplet states as non-radiative traps in multichromophoric entities: single molecule spectroscopy of an artificial and natural antenna system.

    PubMed

    Hofkens, J; Schroeyers, W; Loos, D; Cotlet, M; Köhn, F; Vosch, T; Maus, M; Herrmann, A; Müllen, K; Gensch, T; De Schryver, F C

    2001-09-14

    Energy transfer in antenna systems, ordered arrays of chromophores, is one of the key steps in the photosynthetic process. The photophysical processes taking place in such multichromophoric systems, even at the single molecule level, are complicated and not yet fully understood. Instead of directly studying individual antenna systems, we have chosen to focus first on systems for which the amount of chromophores and the interactions among the chromophores can be varied in a systematic way. Dendrimers with a controlled number of chromophores at the rim fulfill those requirements perfectly. A detailed photophysical study of a second-generation dendrimer, containing eight peryleneimide chromophores at the rim, was performed 'J. Am. Chem. Soc., 122 (2000) 9278'. One of the most intriguing findings was the presence of collective on/off jumps in the fluorescence intensity traces of the dendrimers. This phenomenon can be explained by assuming a simultaneous presence of both a radiative trap (energetically lowest chromophoric site) and a non-radiative trap (triplet state of one chromophore) within one individual dendrimer. It was shown that an analogue scheme could explain the collective on/off jumps in the fluorescence intensity traces of the photosynthetic pigment B-phycoerythrin (B-PE) (Porphyridium cruentum). The different values of the triplet lifetime that could be recovered for a fluorescence intensity trace of B-PE were correlated with different intensity levels in the trace, suggesting different chromophores acting as a trap as function of time. PMID:11603833

  1. Interfacial charge recombination via the triplet state? Mimicry of photoprotection in the photosynthetic process with a dye-sensitized TiO 2 solar cell reaction

    NASA Astrophysics Data System (ADS)

    Weng, Yu-Xiang; Li, Long; Liu, Yin; Wang, Li; Yang, Guo-Zhen; Sheng, Jian-Qun

    2002-04-01

    Evidence for the photoinduced charge recombination to the excited-triplet state has been observed in chemical solar cell reaction consisting of dye-sensitized TiO 2 colloidal ethanol solution, which mimicks the photoprotection function in the photosynthetic units. The dye is all -trans-retinoic acid, a structural analog of ?-carotenoid. Two channels of charge recombination, i.e., through triplet and ground states were observed by nano-second flash photolysis. The possibility of applying the function of photoprotection to the synthetic solar cell is discussed, which provides a potential entry of molecular engineering of the dye to improve the long term stability of the synthetic solar cell.

  2. Theory of triplet optical absorption in oligoacenes: From naphthalene to heptacene

    SciTech Connect

    Chakraborty, Himanshu, E-mail: chakraborty.himanshu@gmail.com; Shukla, Alok, E-mail: shukla@phy.iitb.ac.in [Department of Physics, Indian Institute of Technology Bombay, Powai, Mumbai 400076 (India)

    2014-10-28

    In this paper, we present a detailed theory of the triplet states of oligoacenes containing up to seven rings, i.e., starting from naphthalene all the way up to heptacene. In particular, we present results on the optical absorption from the first triplet excited state 1{sup 3}B{sub 2u}{sup +} of these oligomers, computed using the Pariser-Parr-Pople model Hamiltonian, and a correlated electron approach employing the configuration-interaction methodology at various levels. Excitation energies of various triplets states obtained by our calculations are in good agreement with the experimental results, where available. The computed triplet spectra of oligoacenes exhibits rich structure dominated by two absorption peaks of high intensities, which are well separated in energy, and are caused by photons polarized along the conjugation direction. This prediction of ours can be tested in future experiments performed on oriented samples of oligoacenes.

  3. Singlet oxygen and dye-triplet-state quenching in solid-state dye lasers consisting of pyrromethene 567-doped poly(methyl methacrylate).

    PubMed

    Ahmad, M; Rahn, M D; King, T A

    1999-10-20

    Solid-state dye lasers based on poly(methyl methacrylate) (PMMA) doped with Pyrromethene 567 dye (P567) have been investigated. The preparation techniques employed provided high photostability and laser damage threshold for P567 in pure PMMA with 270,000 pulses emitted before the conversion efficiency fell to half its initial value for a pump fluence of 0.16 J cm(-2). When PMMA was modified with 1, 4-diazobicyclo [2, 2, 2] octane singlet oxygen quencher, the longevity increased to 550,000 pulses, corresponding to a normalized photostability of 270 GJ mol(-1). Modification of PMMA with a triplet quencher (perylene) yielded no improvement, but in ethanol solutions both additives enhanced photostability. It is possible that in PMMA, stabilization by means of triplet quenching that depends on dye diffusion is prevented but that stabilization by means of singlet oxygen quenching that depends on the faster oxygen diffusion rate will succeed. PMID:18324161

  4. Matrix effects on the triplet state of the OLED emitter Ir(4,6-dFppy)2(pic) (FIrpic): investigations by high-resolution optical spectroscopy.

    PubMed

    Rausch, Andreas F; Thompson, Mark E; Yersin, Hartmut

    2009-03-01

    The sky-blue emitting compound Ir(4,6-dFppy)(2)(pic) (iridium(III)bis[2-(4',6'-difluorophenyl)pyridinato-N,C(2')]-picolinate), commonly referred to as FIrpic and representing a well-known emitter material for organic light emitting diodes (OLEDs), has been investigated in detail by optical spectroscopy. Studies at temperatures from T = 1.5 K to T = 300 K were carried out in CH(2)Cl(2) and tetrahydrofuran (THF). In CH(2)Cl(2), two discrete sites were observed at cryogenic temperatures and studied by site-selective, high-resolution spectroscopy. The investigations reveal that the molecules located at the two sites exhibit distinctly different photophysical properties. For example, the three substates I, II, and III of the emitting triplet state T(1) of the low-energy site A show a distinctly larger zero-field splitting (ZFS) and exhibit shorter individual decay times than observed for the high-energy site B. The vibrational satellite structures in the emission spectra of the substates I(A) and I(B) exhibit clear differences in the ranges of metal-ligand (M-L) vibrations. For the compound studied in a polycrystalline THF host, giving only strongly inhomogeneously broadened spectra, the ZFS parameters and substate decay times vary in a similar range as observed for the two discrete sites in the CH(2)Cl(2) matrix. Thus, the amount of ZFS, the emission decay times, and also the intensities of the M-L vibrational satellites are affected by the matrix cage, that is, the host environment of the emitting complex. These properties are discussed with respect to variations of spin-orbit coupling routes. In particular, changes of d-orbital admixtures, that is, differences of the metal-to-ligand charge transfer (MLCT) character in the emitting triplet, play an important role. The matrix effects are expected to be also of importance for FIrpic and other Ir(III) compounds when applied as emitters in amorphous OLED matrixes. PMID:19235957

  5. Effect of concentration on the formation of rose bengal triplet state on microcrystalline cellulose: a combined laser-induced optoacoustic spectroscopy, diffuse reflectance flash photolysis, and luminescence study.

    PubMed

    Litman, Yair; Voss, Matthew G; Rodríguez, Hernán B; San Román, Enrique

    2014-11-13

    Laser-induced optoacoustic spectroscopy (LIOAS), diffuse reflectance laser flash photolysis (DRLFP), and laser-induced luminescence (LIL) have been applied in conjunction to the determination of triplet state quantum yields of Rose Bengal (RB) supported on microcrystalline cellulose, a strongly light-scattering solid. Among the three used methods, the only one capable of providing absolute triplet quantum yields is LIOAS, but DRLFP and LIL aid in demonstrating that the LIOAS signal arises in fact from the triplet state and confirm the trend found with RB concentration. The coherence found for the three techniques demonstrates the usefulness of the approach. Observed triplet quantum yields are nearly constant within a limited concentration range, after which they decay strongly due to the generation of inactive dye aggregates or energy trapping centers. When quantum yields are divided by the fraction of absorbed light exciting the dye, the quotient falls off steadily with concentration, following the same trend as the observed fluorescence quantum yield. The conditions that maximize triplet formation are determined as a compromise between the rising light absorption and the decrease of quantum yield with RB concentration. PMID:25112797

  6. The photophysics of monomeric bacteriochlorophylls c and d and their derivatives: properties of the triplet state and singlet oxygen photogeneration and quenching

    NASA Technical Reports Server (NTRS)

    Krasnovsky, A. A. Jr; Cheng, P.; Blankenship, R. E.; Moore, T. A.; Gust, D.

    1993-01-01

    Measurements of pigment triplet-triplet absorption, pigment phosphorescence and photosensitized singlet oxygen luminescence were carried out on solutions containing monomeric bacteriochlorophylls (Bchl) c and d, isolated from green photosynthetic bacteria, and their magnesium-free and farnesyl-free analogs. The energies of the pigment triplet states fell in the range 1.29-1.34 eV. The triplet lifetimes in aerobic solutions were 200-250 ns; they increased to 280 +/- 70 microseconds after nitrogen purging in liquid solutions and to 0.7-2.1 ms in a solid matrix at ambient or liquid nitrogen temperatures. Rate constants for quenching of the pigment triplet state by oxygen were (2.0-2.5) x 10(9) M-1 s-1, which is close to 1/9 of the rate constant for diffusion-controlled reactions. This quenching was accompanied by singlet oxygen formation. The quantum yields for the triplet state formation and singlet oxygen production were 55-75% in air-saturated solutions. Singlet oxygen quenching by ground-state pigment molecules was observed. Quenching was the most efficient for magnesium-containing pigments, kq = (0.31-1.2) x 10(9) M-1 s-1. It is caused mainly by a physical process of singlet oxygen (1O2) deactivation. Thus, Bchl c and d and their derivatives, as well as chlorophyll and Bchl a, combine a high efficiency of singlet oxygen production with the ability to protect photochemical and photobiological systems against damage by singlet oxygen.

  7. Photophysical properties of some methylindoles and studies on quenching reactions in their excited singlet and triplet states in presence of the electron acceptor 2-nitrofluorene at 296 K as well as at 77 K

    NASA Astrophysics Data System (ADS)

    Sinha, S.; De, R.; Ganguly, T.

    1998-01-01

    Electronic absorption, steady state and time resolved, in the domain of nanosecond order, luminescence techniques were employed to study the photophysical properties of some electron donors methylindoles, e.g. 1-methylindole (1MI), 2-methylindole (2MI), 3-methylindole (3MI) and 5-methylindole (5MI) in nonpolar and polar environments at 296 K and in ethanol (EtOH) rigid glassy matrix at 77 K in the presence of electron acceptor 2-nitrofluorene (2NF). It has been proposed that at room temperature and in polar acetonitrile (ACN) solvent, MI (1, 2 or 3) emission originates mainly from the closely lying lowest excited states S 1 ( 1L b), S 2 ( 1L a) and the charge transfer (CT) exciplex state which is formed due to solute-highly polar solvent ACN interaction. This CT state has its origin in 1L a. The room temperature fluorescence quenchings of the MI donors in presence of acceptor 2NF are found to be mainly due to photoinduced electron transfer (ET), excitational energy transfer and transient quenching processes. Out of the three processes Förster's long range energy transfer seems to be the most dominant one. At 77 K singlet-singlet and triplet-triplet energy transfer processes seem to be responsible for the observed quenching in fluorescence and phosphorescence spectra of the donor molecules in presence of the acceptor 2NF.

  8. Organic luminescent molecule with energetically equivalent singlet and triplet excited states for organic light-emitting diodes.

    PubMed

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

    2013-06-14

    We demonstrate an organic molecule with an energy gap between its singlet and triplet excited states of almost zero (?E(ST) ? 0 eV). Such separation was realized through proper combination of an electron-donating indolocarbazole group and a diphenyltriazine electron-accepting moiety. Calculated and measured ?E(ST) 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%. PMID:25165959

  9. A terminal, fluxional ?4-benzene complex with a thermally accessible triplet state is the primary photoproduct in the intercyclobutadiene haptotropism of (CpCo)phenylenes.

    PubMed

    Albright, Thomas A; Drissi, Rima; Gandon, Vincent; Oldenhof, Sander; Oloba-Whenu, Oluwakemi A; Padilla, Robin; Shen, Hao; Vollhardt, K Peter C; Vreeken, Vincent

    2015-03-16

    Low-temperature irradiation of linear [3]- and [4]phenylene cyclopentadienylcobalt complexes generates labile, fluxional ?(4)-arene complexes, in which the metal resides on the terminal ring. Warming induces a haptotropic shift to the neighboring cyclobutadiene rings, followed by the previously reported intercyclobutadiene migration. NMR scrutiny of the primary photoproduct reveals a thermally accessible 16-electron cobalt ?(2)-triplet species, which, according to DFT computations, is responsible for the rapid symmetrization of the molecules along their long axes. Calculations indicate that the entire haptotropic manifold along the phenylene frame is governed by dual-state reactivity of alternating 18-electron singlets and 16-electron triplets. PMID:25644142

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

    PubMed Central

    2012-01-01

    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

  11. Hazard Analysis of Mortality Among Twins and Triplets in the United States: From 20 Weeks Gestation Through the First Year of Life 

    E-print Network

    DeSalvo, Bethany S.

    2011-08-08

    . This dissertation analyzes the hazard of fetal and infant death for twins and triplets in the United States between the years of 1995 and 2000. This dissertation had two main objectives: first, to examine the effects of the birthweight and gestational age...

  12. Accurate values for the nonrelativistic energies of the lowest singlet and triplet S-states of the 4 He-Isotop

    Microsoft Academic Search

    Heinz Kleindienst; Gerhard Pauli; Wolfgang Miiller

    1981-01-01

    Accurate lower and upper bounds for the nonrelativistic lowest energies1E0 and3E0 of the singlet and triplet-system of the4He-Isotop are calculated with the linearized method of variance minimization. The same was done for1E1 the energy of the first excitedS-state 21S.

  13. Photoinduced electron detachment and proton transfer: the proposal for alternative path of formation of triplet states of guanine (G) and cytosine (C) pair.

    PubMed

    Gu, Jiande; Wang, Jing; Leszczynski, Jerzy

    2015-02-12

    A viable pathway is proposed for the formation of the triplet state of the GC Watson-Crick base pair. It includes the following steps: (a) a low-energy electron is captured by cytosine in the GC pair, forming the cytosine base-centered radical anion GC(-•); and (b) photoradiation with energy around 5 eV initiates the electron detachment from either cytosine (in the gas phase) or guanine (in aqueous solutions). This triggers interbase proton transfer from G to C, creating the triplet state of the GC pair. Double proton transfer involving the triplet state of GC pair leads to the formation of less stable tautomer G(N2-H)(•)C(O2H)(•). Tautomerization is accomplished through a double proton transfer process in which one proton at the N3 of C(H)(•) migrates to the N1 of G(-H)(•); meanwhile, the proton at the N2 of G transfers to the O2 of C. This process is energetically viable; the corresponding activation energy is around 12-13 kcal/mol. The base-pairing energy of the triplet is found to be ?3-5 kcal/mol smaller than that of the singlet state. Thus, the formation of the triplet state GC pair in DNA double strand only slightly weakens its stability. The obtained highly reactive radicals are expected to cause serious damage in the DNA involved in biochemical processes, such as DNA replication where radicals are exposed in the single strands. PMID:25340559

  14. First and Second Triplets of Solid Benzene

    Microsoft Academic Search

    Steven D. Colson; Elliot R. Bernstein

    1965-01-01

    Absorption spectra have been taken of the O2-perturbed first (3B1u) and second (3E1u) triplets of solid benzene at 4.2°K. Spectra of both C6H6 and C6D6 were obtained. The (0–0) bands of the first triplet occur at 29 674±25 cm?1 for C6H6 and 29 851±25 cm?1 for C6D6. For the second triplet they lie at 36 560 cm?1±50 for C6H6 and

  15. Reversal of Hückel (anti)aromaticity in the lowest triplet states of hexaphyrins and spectroscopic evidence for Baird's rule

    NASA Astrophysics Data System (ADS)

    Sung, Young Mo; Yoon, Min-Chul; Lim, Jong Min; Rath, Harapriya; Naoda, Koji; Osuka, Atsuhiro; Kim, Dongho

    2015-05-01

    The reversal of (anti)aromaticity in a molecule's triplet excited state compared with its closed-shell singlet ground state is known as Baird's rule and has attracted the interest of synthetic, physical organic chemists and theorists because of the potential to modulate the fundamental properties of highly conjugated molecules. Here we show that two closely related bis-rhodium hexaphyrins (R26H and R28H) containing [26] and [28] ?-electron peripheries, respectively, exhibit properties consistent with Baird's rule. In the ground state, R26H exhibits a sharp Soret-like band and distinct Q-like bands characteristic of an aromatic porphyrinoid, whereas R28H exhibits a broad absorption spectrum without Q-like bands, which is typical of an antiaromatic porphyrinoid. In contrast, the T–T absorption of R26H is broad, weak and featureless, whereas that of R28H displays an intense and sharp Soret-like band. These spectral signatures, in combination with quantum chemical calculations, are in line with qualitative expectations based on Baird's rule.

  16. The lowest excited states of a chromate derivative. Resolved optical and odmr spectra of RbCrO 3Cl AND CsCrO 3Cl at 1.4 K

    NASA Astrophysics Data System (ADS)

    Miller, R. M.; Tinti, D. S.

    1986-10-01

    The phosphorescence, excitation and absorption spectra of the CrO 3Cl - anion in its neat rubidium and cesium salts at 1.4 K are reported. The spectra show sharp zero-phonon lines, which allow vibronic analyses of the phosphorescence spectra based on the respective Raman spectra. The zero-field splittings and lifetimes of the spin-triplet state of CrO 3Cl - anion in each of the salts have also been obtained. The results are compared with earlier results for the potassium salt.

  17. Low temperature pulsed EPR study at 34 GHz of the triplet states of the primary electron donor P865 and the carotenoid in native and mutant bacterial reaction centers of Rhodobacter sphaeroides†

    PubMed Central

    Marchanka, Aliaksandr; Paddock, Mark; Lubitz, Wolfgang; van Gastel, Maurice

    2008-01-01

    The photosynthetic charge separation in bacterial reaction centers occurs predominantly along one of two nearly symmetric branches of cofactors. Low temperature EPR spectra of the triplet states of the chlorophyll and carotenoid pigments in the reaction center of Rb. sphaeroides R-26.1, 2.4.1 and two double mutants GD(M203)/AW(M260) and LH(M214)/AW(M260) have been recorded at 34 GHz to investigate the relative activities of the ‘A’ and ‘B’ branches. The triplet states are found to derive from radical pair and intersystem crossing mechanisms and the rates of formation are anisotropic. The former mechanism is operative for Rb. sphaeroides R-26.1, 2.4.1 and mutant GD(M203)/AW(M260) and indicates that A-branch charge separation proceeds at temperatures down to 10 K. The latter mechanism, derived from the spin polarization and operative for mutant LH(M214)/AW(M260) indicates that no long-lived radical pairs are formed upon direct excitation of the primary donor and that virtually no charge separation at the B-branch occurs at low temperatures. When the temperature is raised above 30 K, B-branch charge separation is observed, which is at most 1% of A-branch charge separation. B-branch radical pair formation can be induced at 10 K with low yield by direct excitation of the bacteriopheophytin of the B-branch at 590 nm. The formation of a carotenoid triplet state is observed. The rate of formation depends on the orientation of the reaction center in the magnetic field and is caused by a magnetic field dependence of the oscillation frequency by which the singlet and triplet radical pair precursor states interchange. Combination of these findings with literature data provides strong evidence that the thermally activated transfer step on the B-branch occurs between the primary donor, P865, and the accessory bacteriochlorophyll, whereas this step is barrierless down to 10 K along the A-branch. PMID:18052205

  18. Highly efficient visible-light driven photochromism: developments towards a solid-state molecular switch operating through a triplet-sensitised pathway.

    PubMed

    Brayshaw, Simon K; Schiffers, Stephanie; Stevenson, Anna J; Teat, Simon J; Warren, Mark R; Bennett, Robert D; Sazanovich, Igor V; Buckley, Alastair R; Weinstein, Julia A; Raithby, Paul R

    2011-04-11

    We introduce a new highly efficient photochromic organometallic dithienylethene (DTE) complex, the first instance of a DTE core symmetrically modified by two Pt(II) chromophores [Pt(PEt(3))(2)(C?C)(DTE)(C?C)Pt(PEt(3))(2)Ph] (1), which undergoes ring-closure when activated by visible light in solvents of different polarity, in thin films and even in the solid state. Complex 1 has been synthesised and fully photophysically characterised by (resonance) Raman and transient absorption spectroscopy complemented by calculations. The ring-closing photoconversion in a single crystal of 1 has been followed by X-ray crystallography. This process occurs with the extremely high yield of 80%--considerably outperforming the other DTE derivatives. Remarkably, the photocyclisation of 1 occurs even under visible light (>400 nm), which is not absorbed by the non-metallated DTE core HC?C(DTE)C?CH (2) itself. This unusual behaviour and the high photocyclisation yields in solution are attributed to the presence of a heavy atom in 1 that enables a triplet-sensitised photocyclisation pathway, elucidated by transient absorption spectroscopy and DFT calculations. The results of resonance Raman investigation confirm the involvement of the alkynyl unit in the frontier orbitals of both closed and open forms of 1 in the photocyclisation process. The changes in the Raman spectra upon cyclisation have permitted the identification of Raman marker bands, which include the acetylide stretching vibration. Importantly, these bands occur in the spectral region unobstructed by other vibrations and can be used for non-destructive monitoring of photocyclisation/photoreversion processes and for optical readout in this type of efficiently photochromic thermally stable systems. This study indicates a strategy for generating efficient solid-state photoswitches in which modification of the Pt(II) units has the potential to tune absorption properties and hence operational wavelength across the visible range. PMID:21433129

  19. Quantum confinement-tunable intersystem crossing and the triplet state lifetime of cationic porphyrin-CdTe quantum dot nano-assemblies.

    PubMed

    Ahmed, Ghada H; Aly, Shawkat M; Usman, Anwar; Eita, Mohamed S; Melnikov, Vasily A; Mohammed, Omar F

    2015-05-11

    Here, we report a ground-state interaction between the positively charged cationic porphyrin and the negatively charged carboxylate groups of the thiol ligands on the surface of CdTe quantum dots (QDs), leading to the formation of a stable nanoassembly between the two components. Our time-resolved data clearly demonstrate that we can dramatically tune the intersystem crossing (ISC) and the triplet state lifetime of porphyrin by changing the size of the QDs in the nanoassembly. PMID:25846495

  20. 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)

    Kodet, John; Judge, Richard H.

    2007-05-01

    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 III r 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 D 2h, D 2 and C 2v can be accommodated in this version. Only constant

  1. Effect of deuterium substitution on the triplet state dipole moments of substituted benzaldehydes

    NASA Astrophysics Data System (ADS)

    Winkler, I. C.; Hanson, D. M.

    1984-11-01

    The laser induced phosphorescence excitation spectra of 2, 4, 5-trimethylbenzaldehyde -1h1 and-1d1, and 2, 5-dimethylbenzaldehyde -1h1 and -1d1 isolated in durene single crystals have been obtained, and the dipole moment difference vectors associated with the bands identified, from their intensities and positions in the spectra, as the T1 and T2 origins have been measured. Since the data indicate that the T2 origin is mixed with T1 vibronic levels, the symbol T2 is used only as a convenient label. The T2 band of TMB shifts 26 cm-1 to the red upon deuteration, and the corresponding band in DMB shifts 36 cm-1 to the blue. The magnitude of the dipole moment difference vector found for this band is +1.2 D in TMB and -2.0 D in DMB. The spectral shifts upon deuteration and these dipole moment difference values both are consistent with the T2 band in TMB being predominantly ??* in character and the T2 band in DMB being predominantly n?*. Upon deuteration, the dipole moment difference vector decreases for TMB and appears to increase for DMB. These variations may indicate that the coupling of the T2 origin with the T1 vibronic levels decreases in TMB and increases in DMB upon substitution of deuterium for the aldehydic hydrogen. No deuterium isotope effect on the dipole moment difference vectors for the T1 origin bands of these molecules was observed.

  2. Photochemistry of 3,4,9,10-perylenetetracarboxylic dianhydride dyes. 3. Singlet and triplet excited-state properties of the bis(2,5-di-tert-butylphenyl)imide derivative

    SciTech Connect

    Ford, W.E.; Kamat, P.V.

    1987-12-03

    Fluorescence lifetime and triplet-state spectral, kinetic, and energetic properties are reported for the first time for a perylenebis(dicarboximide) dye, N,N'-bis(2,5-di-tert-butylphenyl)-3,4,9,10-perylenebis(dicarboximide) (DBPI). The fluorescence lifetime (3.8 +/- 0.2 ns), quantum yield (greater than or equal to 0.95), and singlet-state energy (54 +/- 1 kcal mol/sup -1/) were determined for DBPI in a variety of organic solvents (24/sup 0/C). Triplet sensitization was used to characterize the triplet state of DBPI by laser flash photolysis and pulse radiolysis. The triplet-triplet absorption spectrum of DBPI had a maximum in the range 495-505 nm with an extinction coefficient of (6.3 +/- 0.7) x 10/sup 4/ M/sup -1/ cm/sup -1/, and the triplet-state energy and lifetime were 27.5 +/- 2 kcal mol /sup -1/ and approx. = 100 ..mu..s, respectively. Direct photoexcitation produced the DBPA triplet with very low quantum yields (<0.001). Excimerlike fluorescence spectral and lifetime data for DBPI in the solid state are also presented.

  3. Nonclassical properties of coherent states and excited coherent states for continuous spectra

    NASA Astrophysics Data System (ADS)

    Honarasa, G. R.; Tavassoly, M. K.; Hatami, M.; Roknizadeh, R.

    2011-02-01

    Based on the definition of coherent states for continuous spectra and analogous to photon-added coherent states for discrete spectra, we introduce the excited coherent states for continuous spectra. It is shown that the main axioms of Gazeau-Klauder coherent states will be satisfied, properly. Nonclassical properties and quantum statistics of coherent states, as well as the introduced excited coherent states, are discussed. In particular, through the study of quadrature squeezing and amplitude-squared squeezing, it will be observed that both classes of the above states can be classified in the intelligent states category.

  4. Time-resolved infrared spectroscopy of the lowest triplet state of thymine and thymidine

    E-print Network

    Herbert, John

    @chemistry.ohio-state.edu (B. Kohler). 1 Current address: University of Notre Dame, Radiation Laboratory, Notre Dame, IN 46556, explaining the large ($70 cmÀ1 ) red shift in this vibration, relative to the sin- glet ground state, USA. 2 Research Experiences for Undergraduates student. Current address: Chemical and Physical Biology

  5. Secondary organic aerosol from aqueous reactions of green leaf volatiles with organic triplet excited states and singlet molecular oxygen.

    PubMed

    Richards-Henderson, Nicole K; Pham, Andrew T; Kirk, Benjamin B; Anastasio, Cort

    2015-01-01

    Vegetation emits a class of oxygenated hydrocarbons--the green leaf volatiles (GLVs)--under stress or damage. Under foggy conditions GLVs might be a source of secondary organic aerosol (SOA) via aqueous reactions with hydroxyl radical (OH), singlet oxygen ((1)O2*), and excited triplet states ((3)C*). To examine this, we determined the aqueous kinetics and SOA mass yields for reactions of (3)C* and (1)O2* with five GLVs: methyl jasmonate (MeJa), methyl salicylate (MeSa), cis-3-hexenyl acetate (HxAc), cis-3-hexen-1-ol (HxO), and 2-methyl-3-butene-2-ol (MBO). Second-order rate constants with (3)C* and (1)O2* range from (0.13-22) × 10(8) M(-1) s(-1) and (8.2-60) × 10(5) M(-1) s(-1) at 298 K, respectively. Rate constants with (3)C* are independent of temperature, while values with (1)O2* show significant temperature dependence (Ea = 20-96 kJ mol(-1)). Aqueous SOA mass yields for oxidation by (3)C* are (84 ± 7)%, (80 ± 9)%, and (38 ± 18)%, for MeJa, MeSa, and HxAc, respectively; we did not measure yields for other conditions because of slow kinetics. The aqueous production of SOA from GLVs is dominated by (3)C* and OH reactions, which form low volatility products at a rate that is approximately half that from the parallel gas-phase reactions of GLVs. PMID:25426693

  6. Theory of Pairing Assisted Spin Polarization in Spin-Triplet Equal Spin Pairing: Origin of Extra Magnetization in Sr2RuO4 in Superconducting State

    NASA Astrophysics Data System (ADS)

    Miyake, Kazumasa

    2014-05-01

    It is shown that an extra magnetization is induced by an onset of the equal-spin-pairing of spin triplet superconductivity if the energy dependence of the density of states of quasiparticles exists in the normal state. It turns out that the effect is observable in Sr2RuO4 due to the existence of van Hove singularity in the density of states near the Fermi level, explaining the extra contribution in the Knight shift reported by Ishida et al. It is also quite non-trivial that this effect exists even without external magnetic field, which implies that the time reversal symmetry is spontaneously broken in the spin space.

  7. Narrow Energy Gap between Triplet and Singlet Excited States of Sn2+ in Borate Glass

    NASA Astrophysics Data System (ADS)

    Masai, Hirokazu; Yamada, Yasuhiro; Suzuki, Yuto; Teramura, Kentaro; Kanemitsu, Yoshihiko; Yoko, Toshinobu

    2013-12-01

    Transparent inorganic luminescent materials have attracted considerable scientific and industrial attention recently because of their high chemical durability and formability. However, photoluminescence dynamics of ns2-type ions in oxide glasses has not been well examined, even though they can exhibit high quantum efficiency. We report on the emission property of Sn2+-doped strontium borate glasses. Photoluminescence dynamics studies show that the peak energy of the emission spectrum changes with time because of site distribution of emission centre in glass. It is also found that the emission decay of the present glass consists of two processes: a faster S1-S0 transition and a slower T1-S0 relaxation, and also that the energy difference between T1 and S1 states was found to be much smaller than that of (Sn, Sr)B6O10 crystals. We emphasize that the narrow energy gap between the S1 and T1 states provides the glass phosphor a high quantum efficiency, comparable to commercial crystalline phosphors.

  8. A first detection of singlet to triplet conversion from the 1 1B u- to the 1 3A g state and triplet internal conversion from the 1 3A g to the 1 3B u state in carotenoids: dependence on the conjugation length

    NASA Astrophysics Data System (ADS)

    Rondonuwu, Ferdy S.; Watanabe, Yasutaka; Fujii, Ritsuko; Koyama, Yasushi

    2003-07-01

    Subpicosecond time-resolved absorption spectra were recorded in the visible region for a set of photosynthetic carotenoids having different numbers of conjugated double bonds ( n), which include neurosporene ( n=9), spheroidene ( n=10), lycopene ( n=11), anhydrorhodovibrin ( n=12) and spirilloxanthin ( n=13). Singular-value decomposition and global fitting of the spectral-data matrices lead us to a branched relaxation scheme including both (1) the singlet internal conversion in the sequence of 1 1B u+ ? 1 1B u- ? 2 1A g- ? 1 1A g-(ground), and (2) the singlet-to-triplet conversion of 1 1B u- ? 1 3A g followed by triplet internal conversion of 1 3A g ? 1 3B u.

  9. The singlet-triplet absorption and photodissociation of the HOCl, HOBr, and HOI molecules calculated by the MCSCF quadratic response method

    Microsoft Academic Search

    Boris F. Minaev

    1999-01-01

    The molecular absorption spectra of hypochlorous, hypobromous, and hypoiodous acids have been studied by multiconfiguration self-consistent field (MCSCF) calculations with linear and quadratic response techniques. The complete form of the spin-orbit coupling (SOC) operator is accounted. The singlet-triplet transition to the lowest triplet state ³A{double{underscore}prime} {l{underscore}arrow} X¹AⲠis shown to be responsible for the weak long-wavelength tail absorption and photodissociation

  10. Aqueous benzene-diols react with an organic triplet excited state and hydroxyl radical to form secondary organic aerosol.

    PubMed

    Smith, Jeremy D; Kinney, Haley; Anastasio, Cort

    2015-04-21

    Chemical processing in atmospheric aqueous phases, such as cloud and fog drops, can play a significant role in the production and evolution of secondary organic aerosol (SOA). In this work we examine aqueous SOA production via the oxidation of benzene-diols (dihydroxy-benzenes) by the triplet excited state of 3,4-dimethoxybenzaldehyde, (3)DMB*, and by hydroxyl radical, ?OH. Reactions of the three benzene-diols (catechol (CAT), resorcinol (RES) and hydroquinone (HQ)) with (3)DMB* or ?OH proceed rapidly, with rate constants near diffusion-controlled values. The two oxidants exhibit different behaviors with pH, with rate constants for (3)DMB* increasing as pH decreases from pH 5 to 2, while rate constants with ?OH decrease in more acidic solutions. Mass yields of SOA were near 100% for all three benzene-diols with both oxidants. We also examined the reactivity of atmospherically relevant mixtures of phenols and benzene-diols in the presence of (3)DMB*. We find that the kinetics of phenol and benzene-diol loss, and the production of SOA mass, in mixtures are generally consistent with rate constants determined in experiments containing a single phenol or benzene-diol. Combining our aqueous kinetic and SOA mass yield data with previously published gas-phase data, we estimate a total SOA production rate from benzene-diol oxidation in a foggy area with significant wood combustion to be nearly 0.6 ?g mair(-3) h(-1), with approximately half from the aqueous oxidation of resorcinol and hydroquinone, and half from the gas-phase oxidation of catechol. PMID:25797024

  11. Neutron interferometric measurement of the scattering length difference between the triplet and singlet states of n-$^3$He

    E-print Network

    M. G. Huber; M. Arif; W. C. Chen; T. R. Gentile; D. S. Hussey; T. C. Black; D. A. Pushin; C. B. Shahi; F. E. Wietfeldt; L. Yang

    2014-09-30

    We report a determination of the n-$^3$He scattering length difference $\\Delta b^{\\prime} = b_{1}^{\\prime}-b_{0}^{\\prime} = $ ($-5.411$ $\\pm$ $0.031$ (statistical) $\\pm$ $0.039$ (systematic)) fm between the triplet and singlet states using a neutron interferometer. This revises our previous result $\\Delta b^{\\prime} = $ (-5.610 $\\pm$ $0.027$ (statistical) $\\pm$ $0.032$ (systematic) fm obtained using the same technique in 2008. This revision is due to a re-analysis of the 2008 experiment that includes a more robust treatment of the phase shift caused by magnetic field gradients near the $^3$He cell. Furthermore, we more than doubled our original data set from 2008 by acquiring six months of additional data in 2013. Both the new data set and a re-analysis of the older data are in good agreement. Scattering lengths of low Z isotopes are valued for use in few-body nuclear effective field theories, provide important tests of modern nuclear potential models and in the case of $^3$He aid in the interpretation of neutron scattering from quantum liquids. The difference $\\Delta b^{\\prime}$ was determined by measuring the relative phase shift between two incident neutron polarizations caused by the spin-dependent interaction with a polarized $^3$He target. The target $^3$He gas was sealed inside a small, flat windowed glass cell that was placed in one beam path of the interferometer. The relaxation of $^3$He polarization was monitored continuously with neutron transmission measurements. The neutron polarization and spin flipper efficiency were determined separately using $^3$He analyzers and two different polarimetry analysis methods. A summary of the measured scattering lengths for n-$^3$He with a comparison to nucleon interaction models is given.

  12. Geminate and nongeminate recombination of triplet excitons formed by singlet fission.

    PubMed

    Bayliss, Sam L; Chepelianskii, Alexei D; Sepe, Alessandro; Walker, Brian J; Ehrler, Bruno; Bruzek, Matthew J; Anthony, John E; Greenham, Neil C

    2014-06-13

    We report the simultaneous observation of geminate and nongeminate triplet-triplet annihilation in a solution-processable small molecule TIPS-tetracene undergoing singlet exciton fission. Using optically detected magnetic resonance, we identify recombination of triplet pairs directly following singlet fission, as well as recombination of triplet excitons undergoing bimolecular triplet-triplet annihilation. We show that the two processes give rise to distinct magnetic resonance spectra, and estimate the interaction between geminate triplet excitons to be 60 neV. PMID:24972236

  13. Optically detected chlorine quadrupole resonance investigation of the symmetry of the excited triplet state of tetrachlorobenzene and tetrachloropyrazine in single crystals of durene

    NASA Astrophysics Data System (ADS)

    von Borczyskowski, C.; Fallmer, E.

    1983-12-01

    Optically detected nuclear quadrupole resonance (ODNQR) transitions are reported for tetrachloropyrazine (TCP) and tetrachlorobenzene (TCB) in single crystals of durene in zero and external magnetic fields. The analysis of the fine structure results in D = 4.192 GHz and E = 0.591 GHz (TCP) compared to D = 4.555 GHz and E = 0.872 GHz (TCB). For the ??* triplet state of TCP a rotation of in-plane spin axes by 12° relative to the ground-state symmetry axes is observed.

  14. Electron paramagnetic resonance of the excited triplet state of metal-free and metal-substituted cytochrome c.

    PubMed Central

    Angiolillo, P J; Vanderkooi, J M

    1995-01-01

    The photoactivated metastable triplate states of the porphyrin (free-base, i.e., metal-free) zinc and tin derivatives of horse cytochrome c were investigated using electron paramagnetic resonance. Zero-field splitting parameters, line shape, and Jahn-Teller distortion in the temperature range 3.8-150 K are discussed in terms of porphyrin-protein interactions. The zero-field splitting parameters D for the free-base, Zn and Sn derivatives are 465 x 10(-4), 342 x 10(-4) and 353 x 10(-4) cm-1, respectively, and are temperature invariant over the temperature ranges studied. AN E value at 4 K of 73 x 10(-4) cm-1 was obtained for Zn cytochrome c, larger than any previously found for Zn porphyrins derivatives of hemeproteins, showing that the heme site of cytochrome c imposes an asymmetric field. Though the E value for Zn cytochrome c is large, the geometry of the site appears quite constrained, as indicated by a spectral line shape showing a single species. Intersystem crossing occurred predominantly to the T2 > zero-field spin sublevel. EPR line shape changes with respect to temperature of Zn cyt c are interpreted in terms of vibronic coupling, and a maximum Jahn-Teller crystal-field splitting of approximately 180 cm-1 is obtained. Sn cytochrome c in comparison with the Zn protein exhibits a photoactivated triplet line shape that is less well resolved in the X-Y region. The magnitude of E value is approximately 60 x 10(-4) cm-1 at 4 K; its value rapidly tends toward zero with increasing temperature, from which a value for the Jahn-Teller crystal-field splitting of > or = 40 cm-1 is estimated. In contrast to those for the metal cytochromes, the magnitude of E value for the free-base derivative was essentially zero at all temperatures studied. This finding is discussed as a consequence of an excited-state tautomerization process that occurs even at 4 K. PMID:7647253

  15. Spectra

    NSDL National Science Digital Library

    The Exploratorium

    2012-06-26

    Learners construct a spectroscope out of a shoe box or mailing tube, diffraction grating, and other simple materials. They then use their spectroscope to observe spectra, the colors that make up light. Learners compare the spectra of various light sources. Use this activity to introduce learners to basic principles of light and color. Also, look at a related page about auroras to understand how distinguishing spectra of different atoms helps scientists understand the universe.

  16. Spectra

    NSDL National Science Digital Library

    Kaler, James B.

    Spectra is a website illustrating how astronomers use spectra to understand what stars are made of, their structures, and their evolution. The page begins with an introduction to the electromagnetic spectrum and then goes into detail about the properties of light. Then it discusses how matter both creates and destroys radiation. It goes on to interpret absorption and emission lines. The website ends with discussing how astronomers use spectra to understand stars, galaxies, and other objects in the universe.

  17. Zethrene biradicals: how pro-aromaticity is expressed in the ground electronic state and in the lowest energy singlet, triplet, and ionic states.

    PubMed

    Zafra, José Luis; González Cano, Rafael C; Ruiz Delgado, M Carmen; Sun, Zhe; Li, Yuan; López Navarrete, Juan T; Wu, Jishan; Casado, Juan

    2014-02-01

    A analysis of the electronic and molecular structures of new molecular materials based on zethrene is presented with particular attention to those systems having a central benzo-quinoidal core able to generate Kekulé biradicals whose stability is provided by the aromaticity recovery in this central unit. These Kekulé biradicals display singlet ground electronic states thanks to double spin polarization and have low-energy lying triplet excited states also featured by the aromaticity gain. Pro-aromatization is also the driving force for the stabilization of the ionized species. Moreover, the low energy lying singlet excited states also display a profound biradical fingerprint allowing to singlet exciton fission. These properties are discussed in the context of the size of the zethrene core and of its substitution. The work encompasses all known long zethrenes and makes use of a variety of experimental techniques, such as Raman, UV-Vis-NIR absorption, transient absorption, in situ spectroelectrochemistry and quantum chemical calculations. This study reveals how the insertion of suitable molecular modules (i.e., quinoidal) opens the door to new intriguing molecular properties exploitable in organic electronics. PMID:24511967

  18. Zethrene biradicals: How pro-aromaticity is expressed in the ground electronic state and in the lowest energy singlet, triplet, and ionic states

    NASA Astrophysics Data System (ADS)

    Zafra, José Luis; González Cano, Rafael C.; Ruiz Delgado, M. Carmen; Sun, Zhe; Li, Yuan; López Navarrete, Juan T.; Wu, Jishan; Casado, Juan

    2014-02-01

    A analysis of the electronic and molecular structures of new molecular materials based on zethrene is presented with particular attention to those systems having a central benzo-quinoidal core able to generate Kekulé biradicals whose stability is provided by the aromaticity recovery in this central unit. These Kekulé biradicals display singlet ground electronic states thanks to double spin polarization and have low-energy lying triplet excited states also featured by the aromaticity gain. Pro-aromatization is also the driving force for the stabilization of the ionized species. Moreover, the low energy lying singlet excited states also display a profound biradical fingerprint allowing to singlet exciton fission. These properties are discussed in the context of the size of the zethrene core and of its substitution. The work encompasses all known long zethrenes and makes use of a variety of experimental techniques, such as Raman, UV-Vis-NIR absorption, transient absorption, in situ spectroelectrochemistry and quantum chemical calculations. This study reveals how the insertion of suitable molecular modules (i.e., quinoidal) opens the door to new intriguing molecular properties exploitable in organic electronics.

  19. Real-time readout and lifetime measurements of single-triplet states in a Si/SiGe double quantum dot

    NASA Astrophysics Data System (ADS)

    Prance, Jonathan; Shi, Zhan; Simmons, Christie; Savage, Don; Lagally, Max; Schreiber, Lars; Vandersypen, Lieven; Friesen, Mark; Joynt, Robert; Coppersmith, Sue; Eriksson, Mark

    2012-02-01

    The singlet and triplet states of a two-electron double quantum dot can be used as the basis for a logical qubit that combines fast gating and robust readout via Pauli spin blockade. We present measurements of the lifetimes of these states in a Si/SiGe double dot at magnetic fields between 1T and 0T [1]. The lifetimes are found by analyzing the statistics of repeated single-shot measurements of the spin state of the system. This technique allows multiple relaxation processes to be observed simultaneously. At zero magnetic field we find that all four spin states have lifetimes of approximately 10ms. With increasing magnetic field the lifetimes of the S and T0 states show no noticeable change, while the lifetime of the T- state rises, reaching 3 seconds at 1T. [1] J. R. Prance, et al., e-print: arxiv.org/abs/1110.6431

  20. Unimolecular photodissociation dynamics of ketene (CH{sub 2}CO): The singlet/triplet branching ratio and experimental observation of the vibrational level thresholds of the transition-state

    SciTech Connect

    Kim, S.K.

    1993-05-01

    The rotational distributions of CO products from the dissociation of ketene at photolysis energies 10 cm{sup {minus}1} below, 56, 110, 200, 325, 425, 1,107, 1,435, 1,720, and 2,500 cm{sup {minus}1} above the singlet threshold, are measured in a supersonic free jet of ketene. The CO(v{double_prime} = 0) rotational distributions at 56, 110, 200, 325, and 425 cm{sup {minus}1} are bimodal. The peaks at low J`s, which are due to CO from the singlet channel, show that the product rotational distribution of CO product from ketene dissociation on the singlet surface is well described by phase space theory (PST). For CO(v{double_prime} = 0) rotational distributions at higher excess energies, the singlet and triplet contributions are not clearly resolved, and the singlet/triplet branching ratios are estimated by assuming that PST accurately predicts the CO rotational distribution from the singlet channel and that the distribution from the triplet channel changes little from that at 10 cm{sup {minus}1} below the singlet threshold. At 2,500 cm{sup {minus}1} excess energy, the CO(v{double_prime} = 1) rotational distribution is obtained, and the ratio of CO(v{double_prime} = 1) to CO(v{double_prime} = 0) products for the singlet channel is close to the variational RRKM calculation, 0.038, and the separate statistical ensembles (SSE) prediction, 0.041, but much greater than the PST prediction, 0.016. Rate constants for the dissociation of ketene (CH{sub 2}CO) and deuterated ketene (CD{sub 2}CO) have been measured at the threshold for the production of the CH(D){sub 2} and CO. Sharp peaks observed in photofragment excitation (PHOFEX) spectra probing CO (v = 0, J = 2) product are identified with the C-C-O bending mode of the transition state. RRKM calculations are carried out for two limiting cases for the dynamics of K-mixing in highly vibrationally excited reactant states.

  1. Magnetic Field Effects on Triplet-Triplet Annihilation in Solutions: Modulation of Visible/NIR Luminescence

    PubMed Central

    Mani, Tomoyasu; Vinogradov, Sergei A.

    2013-01-01

    Photon upconversion based on sensitized triplet-triplet annihilation (TTA) presents interest for such areas as photovoltaics and imaging. Usually energy upconversion is observed as p-type delayed fluorescence from molecules whose triplet states are populated via energy transfer from a suitable triplet donor, followed by TTA. Magnetic field effects (MFE) on delayed fluorescence in molecular crystals are well known; however, there exist only a few examples of MFE on TTA in solutions, and all of them are limited to UV-emitting materials. Here we present MFE on TTA-mediated visible and near infrared (NIR) emission, sensitized by far-red absorbing metalloporphyrins in solutions at room temperature. In addition to visible delayed fluorescence from annihilator, we also observed NIR emission from the sensitizer, occurring as a result of triplet-triplet energy transfer back from annihilator, termed “delayed phosphorescence”. This emission also exhibits MFE, but opposite in sign to the annihilator fluorescence. PMID:24143268

  2. The photoexcited triplet state of sapphyrin dication: Unusual spin alignment in monomers and spin delocalization in dimers

    SciTech Connect

    Levanon, H. [Hebrew Univ., Jerusalem (Israel)]|[Argonne National Lab., IL (United States); Michaeli, S.; Regev, A.; Galili, T. [Hebrew Univ., Jerusalem (Israel); Cyr, M.; Sessler, J.L. [Texas Univ., Austin, TX (United States). Dept. of Chemistry

    1990-01-31

    Sapphyrin (Sap) and its stable dicationic form, Sap{sup 2+}, originally prepared by Woodawrd and Johnson, are large porphyrin-like systems which exhibit unique photophysical and photochemical properties. We report on the triplet diode detection, by time-resolved CW EPR, of (Sap{sup 2+}){sup T} randomly oriented in toluene (as monomers), ethanol (as dimers), and partially oriented in a nematic liquid crystal (as monomers). The substantial reduction of both zero-field splitting (ZFS) parameters (D and E) in the dimer, is interpreted in terms of spin delocalization (charge transfer) among the monomers within the dimer, (Sap{sup 2+}){sub 2}. The EPR line shape of Sap{sup 2+} in the liquid crystal suggests that, unlike other known porphyrinoid systems, the ZFS term D is associated with the in-plane alignment of the triplet spins along the C{sub 2v} symmetry axis, Z.

  3. On the Photoelectron Spectra of Li4

    NASA Technical Reports Server (NTRS)

    Bauschlicher, Charles W., Jr.; Arnold, James O. (Technical Monitor)

    1996-01-01

    The most stable structure for Li4(-) is found to be the rhombus. Electron detachment from this structure does not seem able to fully explain the photoelectron spectra. The computed results are consistent with those Rao, Jena, and Ray who have proposed that the experimental spectra consists of a superposition of detachment from the Li4(-) rhombus and tetrahedron, forming the singlet and triplet states of Li4, respectively.

  4. Infrared absorption spectra of various doping states in cuprate superconductors

    SciTech Connect

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

    1992-02-01

    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.

  5. Infrared absorption spectra of various doping states in cuprate superconductors

    SciTech Connect

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

    1992-01-01

    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.

  6. Singlet and triplet potentials of the ground-state atom pair Rb + Cs studied by Fourier-transform spectroscopy

    SciTech Connect

    Docenko, O.; Tamanis, M.; Ferber, R.; Knoeckel, H.; Tiemann, E. [Laser Center, Department of Physics, University of Latvia, 19 Rainis boulevard, Riga LV-1586 (Latvia); Institute of Quantum Optics, Leibniz University Hannover, Welfengarten 1, D-30167 Hannover (Germany)

    2011-05-15

    A comprehensive study of the X {sup 1}{Sigma}{sup +} and a {sup 3}{Sigma}{sup +} electronic states of the Rb and Cs atom pair in RbCs is presented. Abundant spectroscopic data for the {sup 85}Rb{sup 133}Cs and {sup 87}Rb{sup 133}Cs isotopologues were obtained from Fourier-transform spectra of laser-induced fluorescence (LIF) from the B {sup 1}{Pi} and (4){sup 1}{Sigma}{sup +} states to the a {sup 3}{Sigma}{sup +} (4549 transitions) and X {sup 1}{Sigma}{sup +} (15 709 transitions) states. The X {sup 1}{Sigma}{sup +} state data were complemented by about 15 500 transitions obtained by Fellows et al.[J. Mol. Spectrosc. 197, 19 (1999)]. LIF progressions to the a {sup 3}{Sigma}{sup +} state range from v{sub a}=0 to 37, reaching an outer turning point at 15.97 A. For the X {sup 1}{Sigma}{sup +} state, by analyzing LIF from the shelflike (4){sup 1}{Sigma}{sup +}, the data are extended from v{sub x}=119 as observed in the above-cited paper to v{sub x}=129, extending the outer turning point from 10.7 to 17.55 A. From these data, potential energy curves were constructed simultaneously for both hyperfine coupled states X {sup 1}{Sigma}{sup +} and a {sup 3}{Sigma}{sup +} in a coupled-channels fitting routine. This allowed us to accurately model the potential close to the Rb(5s) + Cs(6s) atom-pair asymptote, which is required to simulate cold collision processes and to analyze the Feshbach resonances observed for {sup 87}Rb{sup 133}Cs by Pilch et al.[Phys. Rev. A 79, 042718 (2009)]. Dissociation energies were determined for the X {sup 1}{Sigma}{sup +} state as D{sub e}=3836.373(40) cm{sup -1} and for the a {sup 3}{Sigma}{sup +} state as D{sub e}=259.341(30) cm{sup -1}.

  7. Narrow chaotic compound autoionizing states in atomic spectra

    SciTech Connect

    Flambaum, V.V.; Gribakina, A.A.; Gribakin, G.F. [School of Physics, University of New South Wales, Sydney 2052 (Australia)] [School of Physics, University of New South Wales, Sydney 2052 (Australia)

    1996-09-01

    Simultaneous excitation of several valence electrons in atoms gives rise to a dense spectrum of compound autoionizing states (AIS). These states are almost chaotic superpositions of large numbers of many-electron basis states built of single-electron orbitals. The mean level spacing {ital D} between such states is very small (e.g., {ital D}{lt}0.01 eV for the numerical example of {ital J}{sup {pi}}=4{sup {minus}} states of Ce just above the ionization threshold). The autoionization widths of these states estimated by perturbations, {gamma}=2{pi}{vert_bar}{ital W}{vert_bar}{sup 2}, where {ital W} is the Coulomb matrix element coupling the AIS to the continuum, are also small, but comparable with {ital D} in magnitude: {gamma}{approximately}{ital D}. Hence the nonperturbative interaction of AIS with each other via the continuum is very essential. It suppresses greatly the widths of the autoionizing resonances ({Gamma}{approx_equal}{ital D}{sup 2}/3{gamma}{lt}{ital D}), and leads to the emergence of a {open_quote}{open_quote}collective{close_quote}{close_quote} doorway state which accumulates a large share of the total width. This state is in essence a modified single-particle continuum decoupled from the resonances due to its large width. Narrow compound AIS should be a common feature of atomic spectra at energies sufficient for excitation of several electrons above the ground-state configuration. The narrow resonances can be observed as peaks in the photoabsorption, or, in electron-ion scattering, as Fano-type profiles on the background provided by the wide doorway-state resonance. It is also shown that the statistics of electromagnetic and autoionization amplitudes involving compound states are close to Gaussian. {copyright} {ital 1996 The American Physical Society.}

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

    NASA Astrophysics Data System (ADS)

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

    2013-10-01

    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.

  9. Single-shot readout and relaxation of singlet/triplet states in exchange-coupled $^{31}$P electron spins in silicon

    E-print Network

    Juan P. Dehollain; Juha T. Muhonen; Kuan Y. Tan; André Saraiva; David N. Jamieson; Andrew S. Dzurak; Andrea Morello

    2014-06-11

    We present the experimental observation of a large exchange coupling $J \\approx 300$ $\\mu$eV between two $^{31}$P electron spin qubits in silicon. The singlet and triplet states of the coupled spins are monitored in real time by a Single-Electron Transistor, which detects ionization from tunnel-rate-dependent processes in the coupled spin system, yielding single-shot readout fidelities above 95%. The triplet to singlet relaxation time $T_1 \\approx 4$ ms at zero magnetic field agrees with the theoretical prediction for $J$-coupled $^{31}$P dimers in silicon. The time evolution of the 2-electron state populations gives further insight into the valley-orbit eigenstates of the donor dimer, valley selection rules and relaxation rates, and the role of hyperfine interactions. These results pave the way to the realization of 2-qubit quantum logic gates with spins in silicon, and highlight the necessity to adopt gating schemes compatible with weak $J$-coupling strengths.

  10. Single-shot readout and relaxation of singlet and triplet states in exchange-coupled 31P electron spins in silicon.

    PubMed

    Dehollain, Juan P; Muhonen, Juha T; Tan, Kuan Y; Saraiva, Andre; Jamieson, David N; Dzurak, Andrew S; Morello, Andrea

    2014-06-13

    We present the experimental observation of a large exchange coupling J ? 300 ?eV between two (31)P electron spin qubits in silicon. The singlet and triplet states of the coupled spins are monitored in real time by a single-electron transistor, which detects ionization from tunnel-rate-dependent processes in the coupled spin system, yielding single-shot readout fidelities above 95%. The triplet to singlet relaxation time T(1) ? 4 ms at zero magnetic field agrees with the theoretical prediction for J-coupled 31P dimers in silicon. The time evolution of the two-electron state populations gives further insight into the valley-orbit eigenstates of the donor dimer, valley selection rules and relaxation rates, and the role of hyperfine interactions. These results pave the way to the realization of two-qubit quantum logic gates with spins in silicon and highlight the necessity to adopt gating schemes compatible with weak J-coupling strengths. PMID:24972221

  11. Spin-lattice relaxation in the triplet state of the buried tryptophan residue of ribonuclease T1.

    PubMed Central

    Ghosh, S; Petrin, M; Maki, A

    1986-01-01

    The individual spin-lattice relaxation (SLR) rate constants (Wij) between the lowest triplet sublevels of the lone tryptophan residue buried in the interior of the globular protein ribonuclease T1 have been reported in the temperature range 1.2 to 3.0 K in zero applied magnetic field. The SLR rate constants between spin sublevels exhibit marked anisotropy in their magnitudes and also show appreciable sensitivity to the glycerol content of the aqueous cryogenic matrix. The temperature dependence of SLR suggests that in the temperature range investigated a direct process contributes dominantly to the SLR in this protein. PMID:3083881

  12. Anisotropic spin—lattice relaxation in the triplet state of naphtralene- h8 in n-pentane

    NASA Astrophysics Data System (ADS)

    Ghosh, Sanjib; Weers, Jeffry G.; Petrin, Michael; Maki, August H.

    1984-06-01

    The temperature dependence of the individual spin—lattice relaxation rate constants ( W ij) between the lowest triplet sublevels of naphthalene- h8 in a polycrystalline Shpol'skii matrix of n-pentane have been measured between 1.2 and 2.4 K in zero field. The total sublevel decay constants are evaluated and found to be independent of temperature. The W ij are found to be highly anisotropic, but the anisotropy pattern differs from that observed previously in a durene matrix.

  13. Ab initio calculation of the NH(3sigma-)-NH(3sigma-) interaction potentials in the quintet, triplet, and singlet states.

    PubMed

    Dhont, Guillaume S F; van Lenthe, Joop H; Groenenboom, Gerrit C; van der Avoird, Ad

    2005-11-01

    We present the ab initio potential-energy surfaces of the NH-NH complex that correlate with two NH molecules in their 3sigma- electronic ground state. Three distinct potential-energy surfaces, split by exchange interactions, correspond to the coupling of the S(A) = 1 and S(B) = 1 electronic spins of the monomers to dimer states with S = 0, 1, and 2. Exploratory calculations on the quintet (S = 2), triplet (S = 1), and singlet (S = 0) states and their exchange splittings were performed with the valence bond self-consistent-field method that explicitly accounts for the nonorthogonality of the orbitals on different monomers. The potential surface of the quintet state, which can be described by a single Slater determinant reference function, was calculated at the coupled cluster level with single and double excitations and noniterative treatment of the triples. The triplet and singlet states require multiconfiguration reference wave functions and the exchange splittings between the three potential surfaces were calculated with the complete active space self-consistent-field method supplemented with perturbative configuration interaction calculations of second and third orders. Full potential-energy surfaces were computed as a function of the four intermolecular Jacobi coordinates, with an aug-cc-pVTZ basis on the N and H atoms and bond functions at the midpoint of the intermolecular vector R. An analytical representation of these potentials was given by expanding their dependence on the molecular orientations in coupled spherical harmonics, and representing the dependence of the expansion coefficients on the intermolecular distance R by the reproducing kernel Hilbert space method. The quintet surface has a van der Waals minimum of depth D(e) = 675 cm(-1) at R(e) = 6.6a0 for a linear geometry with the two NH electric dipoles aligned. The singlet and triplet surfaces show similar, slightly deeper, van der Waals wells, but when R is decreased the weakly bound NH dimer with S = 0 and S = 1 converts into the chemically bound N2H2 diimide (also called diazene) molecule with only a small energy barrier to overcome. PMID:16292903

  14. Quasiclassical asymptotics and coherent states for bounded discrete spectra

    SciTech Connect

    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

    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.

  15. Energy harvesting of non-emissive triplet excitons in tetracene by emissive PbS nanocrystals.

    PubMed

    Thompson, Nicholas J; Wilson, Mark W B; Congreve, Daniel N; Brown, Patrick R; Scherer, Jennifer M; Bischof, Thomas S; Wu, Mengfei; Geva, Nadav; Welborn, Matthew; Voorhis, Troy Van; Bulovi?, Vladimir; Bawendi, Moungi G; Baldo, Marc A

    2014-11-01

    Triplet excitons are ubiquitous in organic optoelectronics, but they are often an undesirable energy sink because they are spin-forbidden from emitting light and their high binding energy hinders the generation of free electron-hole pairs. Harvesting their energy is consequently an important technological challenge. Here, we demonstrate direct excitonic energy transfer from 'dark' triplets in the organic semiconductor tetracene to colloidal PbS nanocrystals, thereby successfully harnessing molecular triplet excitons in the near infrared. Steady-state excitation spectra, supported by transient photoluminescence studies, demonstrate that the transfer efficiency is at least (90 ± 13)%. The mechanism is a Dexter hopping process consisting of the simultaneous exchange of two electrons. Triplet exciton transfer to nanocrystals is expected to be broadly applicable in solar and near-infrared light-emitting applications, where effective molecular phosphors are lacking at present. In particular, this route to 'brighten' low-energy molecular triplet excitons may permit singlet exciton fission sensitization of conventional silicon solar cells. PMID:25282507

  16. Negative Polaron and Triplet Exciton Diffusion inOrganometallic “Molecular Wires”

    SciTech Connect

    Schanze, K.S.; Miller, J.; Keller, J.M.; Sean McIlroy, S.; Sreearuothai, P.; Danilov, E.O.; Jiang, H.; Glusac, K.D.; Miller, J.R.

    2011-07-27

    The dynamics of negative polaron and triplet exciton transport within a series of monodisperse platinum (Pt) acetylide oligomers is reported. The oligomers consist of Pt-acetylide repeats, [PtL{sub 2}-C {triple_bond} C-Ph-C {triple_bond} C-]{sub n} (where L = PBu{sub 3} and Ph = 1,4-phenylene, n = 2, 3, 6, and 10), capped with naphthalene diimide (NDI) end groups. The Pt-acetylide segments are electro- and photoactive, and they serve as conduits for transport of electrons (negative polaron) and triplet excitons. The NDI end groups are relatively strong acceptors, serving as traps for the carriers. Negative polaron transport is studied by using pulse radiolysis/transient absorption at the Brookhaven National Laboratory Laser-Electron Accelerator Facility (LEAF). Electrons are rapidly attached to the oligomers, with some fraction initially residing upon the Pt-acetylide chains. The dynamics of transport are resolved by monitoring the spectral changes associated with transfer of electrons from the chain to the NDI end group. Triplet exciton transport is studied by femtosecond-picosecond transient absorption spectroscopy. Near-UV excitation leads to rapid production of triplet excitons localized on the Pt-acetylide chains. The excitons transport to the chain ends, where they are annihilated by charge separation with the NDI end group. The dynamics of triplet transport are resolved by transient absorption spectroscopy, taking advantage of the changes in spectra associated with decay of the triplet exciton and rise of the charge-separated state. The results indicate that negative polarons and excitons are transported rapidly, on average moving distances of 3 nm in less than 200 ps. Analysis of the dynamics suggests diffusive transport by a site-to-site hopping mechanism with hopping times of 27 ps for triplets and <10 ps for electrons.

  17. 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)

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

    2013-05-01

    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 rad 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.

  18. Photochemistry of 3,4,9,10-perylenetetracarboxylic dianhydride dyes. 3. Singlet and triplet excited-state properties of the bis(2,5-di-tert-butylphenyl)imide derivative

    Microsoft Academic Search

    William E. Ford; Prashant V. Kamat

    1987-01-01

    Fluorescence lifetime and triplet-state spectral, kinetic, and energetic properties are reported for the first time for a perylenebis(dicarboximide) dye, N,N'-bis(2,5-di-tert-butylphenyl)-3,4,9,10-perylenebis(dicarboximide) (DBPI). The fluorescence lifetime (3.8 +\\/- 0.2 ns), quantum yield (greater than or equal to 0.95), and singlet-state energy (54 +\\/- 1 kcal mol⁻¹) were determined for DBPI in a variety of organic solvents (24°C). Triplet sensitization was used to

  19. Poly(p-phenylene vinylene) in light-emitting diodes: Nature of the lowest singlet and triplet excited states and effects of derivatization

    SciTech Connect

    Cornil, J.; Beljonne, D.; Bredas, J.L. [Universite de Mons-Hainaut, Mons (Belgium)

    1995-12-01

    Poly(p-phenylene vinylene), PPV, has attracted a tremendous interest in the past few years, especially in the field of optic and electro-optic devices such as light-emitting diodes (LED`s). Here we focus our attention on three issues of prime importance when studying PPV (or its oligomers) as an emitting layer. The first topic deals with the modelling of the nature of the lowest singlet excited state (from which fluorescence originates) and of the lowest triplet excited states (also reached by the system following recombination of the charge carriers). In a second part, we analyze the way the optical transitions are affected by derivatization; we modulate the locations of the frontier levels by fixing {pi}-donor (methoxy) and {pi}-acceptor (cyano) substituents along the conjugated backbone. Finally, we investigate the metallization of the cyano-PPVs, by aluminum or alkali metals.

  20. Energy transfer from both triplet and singlet energy levels of PVK to DCM2 induced by heavy-ion

    NASA Astrophysics Data System (ADS)

    Luo, Jiaxiu; Xiao, Lixin; Chen, Zhijian; Qu, Bo; Gong, Qihuang

    2010-10-01

    The energy band of red light-emitting materials is usually very narrow, which easily results in non-radiative recombination of excited states. There also exists concentration quenching effect due to strong ?-? interaction. To avoid this, host-guest doping system is mostly used. On the other hand, the ratio of singlet and triplet excited state caused by recombination is 1:3. In comparison with the fluorescence (singlet to singlet), phosphorescence (triplet to singlet, but spin-forbidden) is much weaker, and the quantum yield is much lower. To enhance it and make full use of triplet excited state energy, heavy atom effect is commonly used to induce strong spin-orbital coupling leading to mix of singlet and triplet and release the forbidden triplet energy. Based on this, we fabricated polymer light-emitting diodes adopting polyvinylcarbazole (PVK) as the host and a red fluorescent dye, 2-{2-methyl-6-[2-(2,3,6,7-tetrahydro-1H,5H-pyrido[ 3,2,1-ij]quinolin-9-yl)-vinyl]-pyran-4-ylidene}-alononitrile (DCM2), as the dopant, and materials containing heavy-ion, kalium idode (KI) and bromo-carbazole, as energy transfer bridge to obtain complete energy transfer from excited states of both singlet and triplet energy level of PVK to ground state of singlet of DCM2. We found the current density of devices with heavy-ion materials were higher than device without it, and the weak blue emission from PVK host, existing in device of PVK:DCM2 device, can not be observed in electroluminescence spectra of device with heavy-ion materials, which indicates a complete energy transfer from both triplet and singlet energy levels.

  1. Photosensitization aspects of pinacyanol H-aggregates. Charge injection from singlet and triplet excited states into SnO{sub 2} nanocrystallites

    SciTech Connect

    Barazzouk, S.; Lee, H.; Hotchandani, S.; Kamat, P.V.

    2000-04-20

    The singlet and triplet excited-state behavior of a symmetric carbocyanine dye, 1,1{prime}-diethyl-2,2{prime}-carbocyanine (commonly referred as pinacyanol), adsorbed on SiO{sub 2} and SnO{sub 2} nanocrystallites has been investigated using transient absorption spectroscopy. The adsorption of the dye molecules on the negatively charged SiO{sub 2} or SnO{sub 2} colloids results in H-type aggregation. When excited with a 532 nm laser pulse they observe a short-lived ({tau} < 30 ps) singlet excited state of the H-aggregate on the SiO{sub 2} surface. In contrast to this observation, a long-lived cation radical formation is seen on the SnO{sub 2} surface. The dependence of the cation radical yield on the concentration of SnO{sub 2} colloids and the intensity of laser pulse excitation confirms direct electron transfer between the excited aggregate and SnO{sub 2} colloids. Both singlet and triplet excited states of the pinacyanol aggregate participate in the charge injection process on the SnO{sub 2} surface with heterogeneous electron-transfer rate constants of >5 x 10{sup 10} and 7 x 10{sup 9} s{sup {minus}1}, respectively. Such a charge injection process is also confirmed from the photocurrent generation at a dye-modified SnO{sub 2} electrode. The fast reverse electron transfer between the photoinjected electron and the cation radical of the dye aggregate is considered to be a major limiting factor in achieving high photoconversion efficiencies.

  2. Tuneable Singlet Exciton Fission and Triplet-Triplet Annihilation in an Orthogonal Pentacene Dimer

    E-print Network

    Lukman, Steven; Musser, Andrew J.; Chen, Kai; Athanasopoulos, Stavros; Yong, Chaw K.; Zeng, Zebing; Ye, Qun; Chi, Chunyan; Hodgkiss, Justin M.; Wu, Jishan; Friend, Richard H.; Greenham, Neil C.

    2015-01-01

    We report fast and highly efficient intramolecular singlet exciton fission in a pentacene dimer, consisting of two covalently attached, nearly orthogonal pentacene units. Fission to triplet excitons from this ground state geometry occurs within 1 ps...

  3. Accurate values for the nonrelativistic energies of the lowest singlet and triplet S-states of the 4 He-Isotop

    Microsoft Academic Search

    Heinz Kleindienst; Gerhard Pauli; Wolfgang Miiller

    1981-01-01

    Accurate lower and upper bounds for the nonrelativistic lowest energies1\\u000a E\\u000a 0 and3\\u000a E\\u000a 0 of the singlet and triplet-system of the4He-Isotop are calculated with the linearized method of variance minimization. The same was done for1\\u000a E\\u000a 1 the energy of the first excitedS-state 21\\u000a S.\\u000a \\u000a The results especially for1\\u000a E\\u000a 0 and3\\u000a E\\u000a 0 in a.u. are ?2.90330769975 ?1

  4. NO A{sup 2}{Sigma}{sup +}-X{sup 2}II chemiluminescence produced from the reaction of excited NO{sub 2} with acetylene and its derivatives in their triplet states

    SciTech Connect

    Sisk, Wade; Endo; Hiromu; Shibuya, Kazuhiko; Obi, Kinichi [Tokyo Institute of Technology, Meguro, Tokyo (Japan)

    1992-08-06

    This paper discusses how reacting excited NO{sub 2} with acetylene and its derivatives produced NO(A{sup 2}{Sigma}{sup +}) by a NO A{sup 2}{sigma}{sup +}-X{sup 2}II chemiluminescence produced by a triplet-state mechanism, with acetylene > methylacetylene > ethylacetylene > phenylacetylene > benzene in terms of efficiency. 22 refs., 8 figs., 2 tabs.

  5. Tuning the ion formation processes from triplet triplet annihilation to triplet-mediated photoionization

    NASA Astrophysics Data System (ADS)

    Jacques, P.; Allonas, X.; Sarbach, A.; Haselbach, E.; Vauthey, E.

    2003-08-01

    Free ion formation in acetonitrile is examined through transient photoconductivity for a set of ketones excited at different wavelengths. According to the photophysical parameters of the ketones and the incident photon energy, two mechanisms can be operative: triplet-triplet annihilation (bimolecular process) and/or photoionization (monomolecular biphotonic process). By using a tunable laser, excited state mediated photoionization was studied. From the threshold energy ( Ethr) required for this process to occur, ionization potentials in solution ( IS) were deduced and compared to the corresponding values in gas phase ( IG). A simple energetic model enables the determination of the oxidation potential ( Eox) of the ketones that are compared to the corresponding values obtained through electrochemical measurements.

  6. Triplet absorption in carbon nanotubes: a TD-DFT study

    E-print Network

    Sergei Tretiak

    2007-02-13

    We predict properties of triplet excited states in single-walled carbon nanotubes (CNTs) using a time-dependent density-functional theory (TD-DFT). We show that the lowest triplet state energy in CNTs to be about 0.2-0.3 eV lower than the lowest singlet states. Like in $\\pi$-conjugated polymers, the lowest CNT triplets are spatially localized. These states show strong optical absorption at about 0.5-0.6 eV to the higher lying delocalized triplet states. These results demonstrate striking similarity of the electronic features between CNTs and $\\pi$-conjugated polymers and provide explicit guidelines for spectroscopic detection of CNT triplet states.

  7. An electron spin polarization study of the interaction of photoexcited triplet molecules with mono- and polynitroxyl stable free radicals

    SciTech Connect

    Turro, N.J.; Khudyakov, I.V.; Bossmann, S.H. (Columbia Univ., New York, NY (United States)); Dwyer, D.W. (State Univ. of New York, Brockport (United States))

    1993-02-11

    Time-resolved electron spin resonance (TR ESR) has been used to investigate the chemically induced dynamic electron polarization (CIDEP) generated by the interaction of stable free radicals with the triplet states of benzophenone, benzil, and 2-acetylnaphthalene. The stable radicals were mono-, di-, tri-, and tetranitroxyl free radicals possessing the 2,2,6,6-tetramethylpiperidine-N-oxyl moiety. All of the stable radical systems investigated were found to be emissively polarized by interaction with the triplet states, and the phase of polarization was independent of the sign of zero-field splitting (D) of the interacting triple molecule. Possible and likely mechanisms of polarization transfer (creation) resulting from the interaction of photoexcited triplet molecules with nitroxyls in the strong electron exchange are discussed. The emissive CIDEP of nitroxyls observed in the interactions with triplet benzil, which has D > 0, provides strong support for the operation of the radical-triplet pair mechanism. Within the time scale of TR ESR experiments ([approximately]10[sup [minus]7]--10[sup [minus]6] s) no significant variation in the shape of the CIDEP spectra of the nitroxyls was observed, either in viscous media or in micelles. It is concluded that intramolecular spin exchange (or conformational change) of polynitroyls occurs much faster than the time resolution of the experiment. 24 refs., 6 figs., 1 tab.

  8. Mimicking the photosynthetic triplet energy-transfer relay

    SciTech Connect

    Gust, D.; Moore, T.A.; Moore, A.L.; Krasnovsky, A.A. Jr.; Liddell, P.A.; Nicodem, D.; DeGraziano, J.M.; Kerrigan, P.; Makings, L.R.; Pessiki, P.J. (Arizona State Univ., Tempe (United States))

    1993-06-30

    In the reaction centers of photosynthetic organisms, chlorophyll triplet states are sometimes formed by recombination of charge-separated intermediates. These triplets are excellent sensitizers for singlet oxygen formation. Carotenoid polyenes can provide photoprotection from singlet oxygen generation by rapidly quenching chlorophyll triplet states via triplet-triplet energy transfer. Because in bacteria the reaction center carotenoid is not located adjacent to the bacteriochlorophyll special pair, which is the origin of the charge separation, it has been postulated that quenching may occur via a triplet relay involving an intermediate chlorophyll monomer. We now report the synthesis and spectroscopic study of a covalently linked carotenoid (C)-porphyrin (P)-pyropheophorbide (Ppd) triad molecule which mimics this triplet relay. The pyropheophorbide singlet-state C-P-[sup 1]Ppd (generated by direct excitation or energy transfer from the attached porphyrin) undergoes intersystem crossing to the triplet C-P-[sup 3]Ppd. In oxygen-free solutions, this triplet decays to [sup 3]C-p-Ppd through a triplet-transfer relay involving an intermediate C-[sup 3]P-Ppd species. In aerated solutions, quenching of C-P-[sup 3]Ppd by the attached carotenoid competes with singlet oxygen sensitization and thus provides a degree of photoprotection. In a similar traid containing a zinc porphyrin moiety, triplet transfer is slow due to the higher energy of the C-[sup 3]P[sub Zn]-Ppd intermediate, and photoprotection via the relay is nonexistent. The triplet relay ceases to function at low temperatures in both the natural and biomimetic cases due to the endergonicity of the first step. 37 refs., 6 figs., 1 tab.

  9. Magnetic field effects on triplet exciton fission and fusion in a polydiacetylene

    Microsoft Academic Search

    R. H. Austin; G. L. Baker; S. Etemad; R. Thompson

    1989-01-01

    We have studied the origin and decay dynamics of triplet excitons in the conjugated polymer poly(4BCMU) in its sol(yellow) and gel(red) phases. Wavelength and intensity dependencies of the triplet yield show that the triplet exciton cannot be produced by excitation into the singlet exciton edge but only from higher lying states. The observed lifetime of the triplet state, coupled with

  10. Fractional-flux vortices and spin superfluidity in triplet superconductors.

    PubMed

    Babaev, Egor

    2005-04-01

    We discuss a novel type of fractional-flux vortices along with integer flux vortices in Kosterlitz-Thouless transitions in a triplet superconductor. We show that under certain conditions a spin-triplet superconductor should exhibit a novel state of spin superfluidity without superconductivity. PMID:15904018

  11. Overcoming low orbital overlap and triplet instability problems in TDDFT.

    PubMed

    Peach, Michael J G; Tozer, David J

    2012-10-01

    Low orbital overlap and triplet instability problems in time-dependent density functional theory (TDDFT) are investigated for a new benchmark set, encompassing challenging singlet and triplet excitation energies of local, charge-transfer, and Rydberg character. The low orbital overlap problem is largely overcome for both singlet and triplet states by the use of a Coulomb-attenuated functional. For all the categories of functional considered, however, errors associated with triplet instability problems plague high overlap excitations, as exemplified by the excited states of acenes and polyacetylene oligomers. Application of the Tamm-Dancoff approximation reduces these errors for both singlet and triplet states, while leaving low-overlap excitations unaffected. The study illustrates the synergy between overlap and stability and highlights the success of a combined, Coulomb-attenuated Tamm-Dancoff approach. PMID:22971224

  12. Solvent-induced configuration mixing and triplet excited-state inversion: insights from transient absorption and transient dc

    E-print Network

    solvents are a combination of signals from the 3 IL and 3 CT states, with the signal magnitude depending limiting, electroluminescence, singlet oxygen sensitization, cation sensing, vapochromism, and luminescent configuration mixing and state inversion for select molecules at room temperature,2b,5b no clear-cut examples

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

    NASA Astrophysics Data System (ADS)

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

    2010-03-01

    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.

  14. Highly Excited Rotational and Vibrational Levels of the Lowest Triplet States of He 2: Level Positions and Fine Structure

    NASA Astrophysics Data System (ADS)

    Hazell, I.; Norregaard, A.; Bjerre, N.

    1995-07-01

    We have used fast neutral beam laser spectroscopy to investigate transitions in the near-infrared, from the metastable a3? +u state to predissociating levels of the electronic state c3? +g of He 2. A number of transitions were not readily identified, while others were easily identified using the tables of M. L. Ginter ( J. Chem. Phys.42, 561-568, 1965). Predictions of the width and the position of lines were obtained using the potential for the c3? +g state, and led to identification of most lines as transitions between a3? +u and c3? +g in highly rotationally excited states. In a number of transitions the fine structure could be resolved. For these lines, the fine structure of the lower state was measured by laser-radiofrequency double-resonance spectroscopy. This gave the finestructure splittings for the N values: 7, 9, and 11 in ? = 2 of a3? +u and N = 25, 27, and 29 in ? = 0 of a3? +u, where the latter were identified by their fine-structure splittings. We discuss the possible upper state of the transitions from these highly excited rotational levels, and argue that the upper state must have predominantly c3? +g character, but must also include a significant admixture of the b3? g state due to rotational coupling. The measured fine structure is described by an effective fine-structure Hamiltonian including the spin-spin parameter, ?, and the spin-rotation parameter, ?. These parameters and their dependence on rotation, N, and internuclear distance, R, has been determined.

  15. Triplet state formation in photoexcited slip-stacked perylene-3,4:9,10-bis(dicarboximide) dimers on a xanthene scaffold.

    PubMed

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

    2013-10-10

    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

  16. Subpicosecond study of triplet exciton generation, transport and relaxation in isolated polydiacetylene chains

    Microsoft Academic Search

    Brett Kraabel; Duncan McBranch; Aslangul Claude; Lapersonne-Meyer Claudette; Michel Schott

    1998-01-01

    Triplet States of 3- and 4-BCMU isolated Polydiacetylene chains dispersed in their single crystal monomer matrix are studied by subpicosecond pump-probe experiments. The triplet population is monitored by an intense and narrow TT* photoinduced absorption band in the NIR. In our experimental conditions, we find that triplets are generated by two different processes: fission of singlets generated by the pump

  17. Electron-energy spectra of H- doubly excited states resulting from collisions of H- with He

    NASA Astrophysics Data System (ADS)

    Kimura, M.; Sato, H.; Hino, K.; Matsuzawa, M.

    1994-09-01

    Electron-energy spectra for H- doubly excited states resulting from collisions of H- with He are rigorously calculated within a semiclassical molecular representation by including couplings between doubly excited states and continuum states and their interference with direct-detachment processes. An energy sampling procedure, based on the Gauss quadratures, is used to discretize continuum states. The present theoretical result clarifies mechanisms of excitation to doubly excited states, quantitatively reproduces the experimental spectra first observed by Risley and Geballe in 1974, separates the contributions from each of three doubly excited states, and identifies the cause of the interference between channels arising from double-electron excitation and direct detachment with simultaneous excitation.

  18. He-like triplets observed by RESIK

    NASA Astrophysics Data System (ADS)

    Sylwester, B.; Sylwester, J.; Phillips, K. J. H.; Landi, E.

    The RESIK is a high sensitivity uncollimated bent crystal spectrometer which successfully operated aboard Russian CORONAS-F solar mission between 2001 and 2003 It measured systematically for the first time solar soft X-ray spectra in the four wavelength channels from 3 3 AA to 6 1 AA This range includes characteristic triplet lines of He-like ions of K Ar Cl and S in the respective spectral channels Interpretation of observed line ratios within each triplet provides diagnostics of plasma conditions in the emitting source We reduced the observed spectra for a number of flares using the absolute RESIK calibration software We analyzed the observed intensities of spectral line components comprising the triplets and investigated their time variability The evolution of important plasma parameters like temperature and emission measure have been studied for selected events Flaring plasma densities were measured from these parameters using X-ray brightness maps as determined from the RHESSI observations The CHIANTI v5 1 atomic data package was used as a consistent tool for spectral data analysis

  19. Quenching of chlorophyll a singlets and triplets by carotenoids in light-harvesting complex of photosystem II: comparison of aggregates with trimers

    NASA Astrophysics Data System (ADS)

    Naqvi, K. Razi; Melø, T. B.; Raju, B. Bangar; Jávorfi, Tamás; Simidjiev, Ilian; Garab, Gyözö

    1997-12-01

    Laser-induced changes in the absorption spectra of isolated light-harvesting chlorophyll a/ b complex (LHC II) associated with photosystem II of higher plants have been recorded under anaerobic conditions and at ambient temperature by using multichannel detection with sub-microsecond time resolution. Difference spectra (? A) of LHC II aggregates have been found to differ from the corresponding spectra of trimers on two counts: (i) in the aggregates, the carotenoid (Car) triplet-triplet absorption band (? A>0) is red-shifted and broader; and (ii) the features attributable to the perturbation of the Qy band of a chlorophyll a (Chl a) by a nearby Car triplet are more pronounced, than in trimers. Aggregation, which is known to be accompanied by a reduction in the fluorescence yield of Chl a, is shown to cause a parallel decline in the triplet formation yield of Chl a; on the other hand, the efficiency (100%) of Chl a-to-Car transfer of triplet energy and the lifetime (9.3 ?s) of Car triplets are not affected by aggregation. These findings are rationalized by postulating that the antenna Cars transact, besides light-harvesting and photoprotection, a third process: energy dissipation within the antenna. The suggestion is advanced that luteins, which are buried inside the LHC II monomers, as well as the other, peripheral, xanthophylls (neoxanthin and violaxanthin) quench the excited singlet state of Chl a by catalyzing internal conversion, a decay channel that competes with fluorescence and intersystem crossing; support for this explanation is presented by recalling reports of similar behaviour in bichromophoric model compounds in which one moiety is a Car and the other a porphyrin or a pyropheophorbide.

  20. Mass spectra of four quark states in hidden charm sector

    E-print Network

    Smruti Patel; Manan Shah; P C Vinodkumar

    2014-07-19

    Masses of the low lying four quark states in the hidden charm sector ($cq\\bar c \\bar q; q\\in u,d$) are calculated within the framework of a non-relativistic quark model. The four body system is considered as two two-body systems such as diquark-antidiquark ($Qq-\\bar Q \\bar q$) and quark antiquark-quark antiquark ($Q\\bar q -\\bar Qq$) molecular-like four quark states. Here, Cornell type potential has been used for describing the two body interactions among $Q-q$, $\\bar Q-\\bar q$, $Q-\\bar q$, $Qq-\\bar Q \\bar q$ and $Q\\bar q-\\bar Qq$, with appropriate string tensions. Our present analysis suggests the following exotic states, $X(3823)$, $Z_c(3900)$, $X(3915)$, $Z_c(4025)$, $\\psi(4040)$, $Z_1(4050)$ and $X(4160)$ as $Q\\bar q-\\bar Qq$ molecular-like four quark states while $Z_c(3885)$, $X(3940)$ and $Y(4140)$ as the diquark-antidiquark four quark states. We have been able to assign the $J^{PC}$ values for many of the recently observed exotic states according to their structure. Apart from this, we have identified the charged state $Z(4430)$ recently confirmed by LHCb as the first radial excitation of $Zc(3885)$ with G=+1 and $Y(4360)$ state as the first radial excitation of $Y(4008)$ with $G=-1$ and the state $\\psi(4415)$ as the first radial excitation of the $\\psi(4040)$ state.

  1. Singlet-triplet energy splitting between 1D and 3D (1s2 2s nd), n = 3, 4, 5, and 6, Rydberg states of the beryllium atom (9Be) calculated with all-electron explicitly correlated Gaussian functions

    NASA Astrophysics Data System (ADS)

    Sharkey, Keeper L.; Bubin, Sergiy; Adamowicz, Ludwik

    2014-11-01

    Accurate variational nonrelativistic quantum-mechanical calculations are performed for the five lowest 1D and four lowest 3D states of the 9Be isotope of the beryllium atom. All-electron explicitly correlated Gaussian (ECG) functions are used in the calculations and their nonlinear parameters are optimized with the aid of the analytical energy gradient determined with respect to these parameters. The effect of the finite nuclear mass is directly included in the Hamiltonian used in the calculations. The singlet-triplet energy gaps between the corresponding 1D and 3D states, are reported.

  2. Identification of Fe 3d empty states from the total current spectra of an ?(0001) surface

    NASA Astrophysics Data System (ADS)

    Møller, P. J.; Komolov, S. A.; Lazneva, E. F.

    1996-09-01

    An intensive triplet line is revealed in the total current spectrum (TCS) of a reconstructed 0953-8984/8/36/009/img7 surface. The nature of the observed structure in the TCS is discussed in comparison with previously reported data from photoemission, inverse photoemission and theoretical investigations. It is found to be a consequence of the electron transitions into an Fe 3d band of empty states. Energy locations of Fe 3d-band extrema (0953-8984/8/36/009/img8 and 0953-8984/8/36/009/img9 above the bottom of the conduction band) and its splitting 0953-8984/8/36/009/img10 are estimated from the proposed schemes of electron transitions.

  3. Paramagnetic Effects on Solid State Carbon-13 Nuclear Magnetic Resonance Spectra of Soil Organic Matter

    E-print Network

    Hemminga, Marcus A.

    Paramagnetic Effects on Solid State Carbon-13 Nuclear Magnetic Resonance Spectra of Soil Organic of doping experiments. The degree of signal loss caused by paramagnetic metals In this paper, we present with state 13 C NMR spectroscopy of soil organic matter the organic substrate and the type of NMR experiment

  4. Robustness of Spin-Triplet Pairing and Singlet–Triplet Pairing Crossover in Superconductor/Ferromagnet Hybrids

    NASA Astrophysics Data System (ADS)

    Kawabata, Shiro; Asano, Yasuhiro; Tanaka, Yukio; A. Golubov, Alexander

    2013-12-01

    We have investigated the proximity effect in superconductor/ferromagnet junctions in a systematic manner to discuss the relationship between the zero-energy peak (ZEP) of the local density of states (LDOS) and spin-triplet odd-frequency pairing. By exactly solving the nonlinear Usadel equations, we have found that the ZEP is realized in a wide range of geometrical and material parameters in the case of the noncollinear magnetization. This strongly suggests the robustness of the ZEP induced by spin-triplet odd-frequency pairing in such systems. We also found that the crossover from singlet pairing to triplet pairing can be detected by measuring the F layer thickness dependence of the ZEP height. Furthermore, we show how to observe signatures of spin-triplet odd-frequency pairing and the pairing crossover by LDOS measurement. Our results provide a direct way to experimentally detect signatures of the odd-frequency pairing state.

  5. CIFTER: automated charge-state determination for peptide tandem mass spectra.

    PubMed

    Na, Seungjin; Paek, Eunok; Lee, Cheolju

    2008-03-01

    Tandem mass spectrometry (MS/MS) has become a common and useful tool for analyzing complex protein mixtures. Database search programs are the most popular means for peptide identification from MS/MS spectra. However, estimations of charge states of peptide MS/MS spectra obtained from low-resolution mass spectrometers have not been reliable. They require repetitive database searches and additional analyses of the search results. We propose here an algorithm designed to reliably differentiate doubly charged spectra from triply charged ones. We conducted a rigorous analysis of various spectral features and their effects. We employed the distinguishing features found in our analysis and developed a classifier for multiply charged spectra using a machine learning approach. The test on various data sets showed that our method could be successfully applied independent of experimental setup and mass instrument. This algorithm can be used to prefilter spectra so that only reasonably good spectra are submitted to database search programs, thereby saving considerable time. The software for MS/MS charge-state determination, which we named "CIFTER", is available at a website http://prix.uos.ac.kr/sifter/cifter. PMID:18247484

  6. Even parity, orbital singlet, and spin triplet pairing for superconducting LaFeAsO1-xFx.

    PubMed

    Dai, Xi; Fang, Zhong; Zhou, Yi; Zhang, Fu-Chun

    2008-08-01

    We examine the spin-triplet superconducting state of even parity mediated by ferromagnetic Hund's coupling between electrons in two almost degenerate orbital bands. This state may be realized in the recently discovered LaFeAsO(1-x)F(x). It is robust against orbital-independent disorder. The splitting of the orbital degeneracy suppresses superconductivity and leads to an anisotropic spectrum in the Bogoliubov quasiparticle. The former predicts a strong pressure dependence of T(c) and the latter predicts Fermi pockets, which may be tested in angle resolved photoemission spectra. PMID:18764425

  7. Higher Energy States in the CO Dimer: Millimeter-Wave Spectra and Rovibrational Calculations

    E-print Network

    Higher Energy States in the CO Dimer: Millimeter-Wave Spectra and Rovibrational Calculations Leonid millimeter-wave data yielded the precise location of 33 new energy levels of A+ symmetry and 20 levels of A extensive millimeter-wave measurements of the 12C16O dimer have been made, and more than 300 new spectral

  8. Twins, Triplets, and Other Multiples

    MedlinePLUS

    ... what? Pregnancy This information in Spanish ( en español ) Twins, triplets, and other multiples How twins are formed ... can increase the likelihood of multiple births. How twins are formed Twins form in one of two ...

  9. TOURNAE DE PHYSIQUE Colloque Cl, supplment au n 12, Tome 37, Dcembre 1976, page C7-103 MCD OF THE MAIN TRIPLET-TRIPLET

    E-print Network

    Boyer, Edmond

    TOURNAE DE PHYSIQUE Colloque Cl, supplément au n° 12, Tome 37, Décembre 1976, page C7-103 MCD OF THE MAIN TRIPLET-TRIPLET TRANSITION OF THE F2-CENTRE IN KCL(*) J. M. ORTEGA Laboratoire de Physique des between the 3 2TU and 1 -fTu states. (*) Soumis au /. Physique. (**) Laboratoire associé au CNRS. Article

  10. Venus - Stein Triplet Crater

    NASA Technical Reports Server (NTRS)

    1990-01-01

    The Magellan synthetic aperture radar (SAR) imaged this unique 'triplet crater,' or 'crater field' during orbits 418-421 on 21 September 1990. These craters are 14 kilometers, 11 kilometers, and 9 kilometers in diameter, respectively, and are centered at latitude -30.1 degrees south and longitude 345.5 degrees east. The Magellan Science Team has proposed the name Stein for this crater field after the American author, Gertrude Stein. This name has not yet been approved by the International Astronomical Union. The crater field was formed on highly fractured plains. The impacts generated a considerable amount of low viscosity 'flows' thought to consist largely of shock-melted target material along with fragmented debris from the crater. The three craters appear to have relatively steep walls based on the distortion in the image of the near and far walls of the craters in the Magellan radar look direction (from the left). The flow deposits from the three craters extend dominantly to the northeast (upper right).

  11. Triplet exciton generation, transport and relaxation in isolated polydiacetylene chains: Subpicosecond pump-probe experiments

    Microsoft Academic Search

    B. Kraabel; D. Hulin; C. Aslangul; C. Lapersonne-Meyer; M. Schott

    1998-01-01

    Triplet states of 3- and 4-BCMU isolated polydiacetylene chains dispersed in their single-crystal monomer matrix are studied by subpicosecond pump-probe experiments. Triplet population is monitored by an intense and narrow TT? photoinduced absorption band near 1.35 eV at 20 K. In our experimental conditions, we find that triplets are generated by two different processes: fission of singlets generated by the

  12. Traces on ion yields and electron spectra of Ar inner-shell hollow states with Free-Electron Lasers

    E-print Network

    Wallis, A O G; Emmanouilidou, A

    2015-01-01

    We explore the formation by Free-Electron-Laser radiation of Ar hollow states with two or three inner-shell holes. We find that even charged Ar ion states can be more populated than odd charged Ar ion states. This depends on the pulse intensity and the number of energetically accessible inner- shell holes. Fully accounting for fine structure, we demonstrate that one electron spectra bare the imprints of Ar hollow states with two inner-shell holes. Moreover, we show how the Auger spectra of these hollow states can be extracted from two-electron coincidence spectra.

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

    NASA Astrophysics Data System (ADS)

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

    1984-06-01

    The vibrational satellites in the microwave spectra of 35Cl 2CO 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.

  14. Unraveling the electronic structure, spin States, optical and vibrational spectra of malaria pigment.

    PubMed

    Ali, Md Ehesan; Oppeneer, Peter M

    2015-06-01

    A detailed knowledge of the electronic structure and magnetic and optical properties of hemozoin, the malaria pigment, is essential for the design of effective antimalarial drugs and malarial diagnosis. By employing state-of-the-art electronic structure calculations, we have performed an in-depth investigation of the malaria pigment. Specifically, molecular bond lengths and spin states of the two Fe(III) heme centers and their exchange interaction, the UV/Vis absorption spectrum, and the IR vibrational spectra were calculated and compared with available experimental data. Our density functional theory (DFT)-based calculations predict a singlet ground spin state that stems from an S=5/2 spin state on each of the Fe heme centers with a very weak antiferromagnetic exchange interaction between them. Our theoretical UV/Vis and IR spectra provide explanations for various spectroscopic studies of hemozoin and ?-hematin (a synthetic analogue of hemozoin). A good comparison of calculated and measured properties demonstrates the convincing unveiling of the electronic structure of the malaria pigment. Based on the predicted vibrational spectra, we propose a unique spectral band from the nuclear resonance vibrational spectroscopy (NRVS) results that could be used as a key fingerprint for malarial detection. PMID:25933355

  15. Jet cooled spectra of pyrrolobenzene and of pyrrolobenzonitrile: the nature of the excited states

    NASA Astrophysics Data System (ADS)

    Belau, Leonid; Haas, Yehuda; Rettig, Wolfgang

    2002-09-01

    The jet cooled fluorescence and resonance enhanced multiphoton ionization (REMPI) excitation spectra of pyrrolobenzene (PB) and pyrrolobenzonitrile (PBN) were recorded in the UV range. Fluorescence lifetimes and emission spectra were obtained upon excitation up to 2200 cm-1 above the 0-0 band. The data indicate that the emission is from the forbidden L b-type state, while the absorption spectrum in solution is dominated by the L a-type state. The energy gap between S 1 and S 2, in these molecules is very small (around 500 cm-1); at room temperature, hot bands of the more allowed L a-type transition are expected to dominate the absorption spectrum.

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

    PubMed Central

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

    2013-01-01

    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. PMID:24077388

  17. Synchrotron and Compton Spectra from a Steady-state Electron Distribution

    NASA Astrophysics Data System (ADS)

    Rephaeli, Y.; Persic, M.

    2015-06-01

    Energy densities of relativistic electrons and protons in extended galactic and intracluster regions are commonly determined from spectral radio and (rarely) ?-ray measurements. The time-independent particle spectral density distributions are commonly assumed to have a power-law (PL) form over the relevant energy range. A theoretical relation between energy densities of electrons and protons is usually adopted, and energy equipartition is invoked to determine the mean magnetic field strength in the emitting region. We show that for typical conditions, in both star-forming and starburst (SB) galaxies, these estimates need to be scaled down substantially due to significant energy losses that (effectively) flatten the electron spectral density distribution, resulting in a much lower energy density than deduced when the distribution is assumed to have a PL form. The steady-state electron distribution in the nuclear regions of SB galaxies is calculated by accounting for Coulomb, bremsstrahlung, Compton, and synchrotron losses; the corresponding emission spectra of the latter two processes are calculated and compared to the respective PL spectra. We also determine the proton steady-state distribution by taking into account Coulomb and ? production losses, and briefly discuss implications of our steady-state particle spectra for estimates of proton energy densities and magnetic fields.

  18. Tuning the photophysical properties of anti-B18H22: efficient intersystem crossing between excited singlet and triplet states in new 4,4'-(HS)2-anti-B18H20.

    PubMed

    Saurí, Vicenta; Oliva, Josep M; Hnyk, Drahomír; Bould, Jonathan; Braborec, Jakub; Merchán, Manuela; Kubát, Pavel; Císa?ová, Ivana; Lang, Kamil; Londesborough, Michael G S

    2013-08-19

    The tuning of the photophysical properties of the highly fluorescent boron hydride cluster anti-B18H22 (1), by straightforward chemical substitution to produce 4,4'-(HS)2-anti-B18H20 (2), facilitates intersystem crossing from excited singlet states to a triplet manifold. This subsequently enhances O2((1)?g) singlet oxygen production from a quantum yield of ?? ? 0.008 in 1 to 0.59 in 2. This paper describes the synthesis and full structural characterization of the new compound 4,4'-(HS)2-anti-B18H20 (2) and uses UV-vis spectroscopy coupled with density functional theory (DFT) and ab initio computational studies to delineate and explain its photophysical properties. PMID:23889339

  19. Binding energies of the ground triplet state a^3? _u^+ of Rb2 and Cs2 in terms of the generalized Le Roy-Bernstein near-dissociation expansion

    NASA Astrophysics Data System (ADS)

    Sovkov, V. B.; Ivanov, V. S.

    2014-04-01

    Formulae of Le Roy-Bernstein near-dissociation theory are derived in a general isotope-invariant form, applicable to any term in the rotational expansion of a diatomic ro-vibrational term value. It is proposed to use the generalized Le Roy-Bernstein expansion to describe the binding energies (ro-vibrational term values) of the ground triplet state a^3? _u^+ of alkali metal dimers. The parameters of this description are determined for Rb2 and Cs2 molecules. This approach gives a recipe to calculate the whole variety of the binding energies with characteristic accuracies from ˜1 × 10-3 to 1 × 10-2 cm-1 using a relatively simple algebraic equation.

  20. Theoretical analysis of the structure of excited electronic states, Raman, and resonance Raman spectra of indole in the isolated state and aqueous solution

    NASA Astrophysics Data System (ADS)

    Ten, G. N.; Burova, T. G.; Berezin, K. V.; Yakovleva, A. A.; Nurlygayanova, M. N.; Baranov, V. I.

    2012-11-01

    The structure of the first excited electronic states of indole has been calculated for the isolated state and aqueous solution. The vibrational spectra of isolated indole have been calculated by the DFT method in the harmonic and anharmonic approximations. The resonance Raman spectra of indole have been calculated quantum mechanically in the Herzberg-Teller approximation. The effect of hydrogen bonds on the structure and vibrational (Raman and resonance Raman) spectra of indole has been analyzed.

  1. Magnetic correction of RHIC triplets

    SciTech Connect

    Wei, J.; Gupta, R.; Peggs, S.

    1993-06-01

    Triplets of large bore quadrupoles will be antisymmetrically placed on either side of all six intersection points of the Relativistic Heavy Ion collider (RHIC). In RHIC collision optics, the tiplets at the two experimental detectors are intended to enable the collision beta function to be reduced to the design goal of {beta}{sup *} = 1.0 meter in both planes, in order to minimize the spot size and maximize the luminosity. This requires running with {beta}{sub max} {approx} 1400 meters in the triplet, where the beams will have their largest size, both absolutely and as a fraction of the available aperture. Hence, the ultimate performance of RHIC rests on achieving the highest possible magnetic field quality in the triplets. This paper discusses the correction of magnetic errors expected in the quadrupole bodies and ends, using both these limped correctors and also quadrupole body tuning shims.

  2. Magnetic correction of RHIC triplets

    SciTech Connect

    Wei, J.; Gupta, R.; Peggs, S.

    1993-01-01

    Triplets of large bore quadrupoles will be antisymmetrically placed on either side of all six intersection points of the Relativistic Heavy Ion collider (RHIC). In RHIC collision optics, the tiplets at the two experimental detectors are intended to enable the collision beta function to be reduced to the design goal of [beta][sup *] = 1.0 meter in both planes, in order to minimize the spot size and maximize the luminosity. This requires running with [beta][sub max] [approx] 1400 meters in the triplet, where the beams will have their largest size, both absolutely and as a fraction of the available aperture. Hence, the ultimate performance of RHIC rests on achieving the highest possible magnetic field quality in the triplets. This paper discusses the correction of magnetic errors expected in the quadrupole bodies and ends, using both these limped correctors and also quadrupole body tuning shims.

  3. Xanthone. II. Vibronic coupling analysis from high resolution phosphorescence spectra

    NASA Astrophysics Data System (ADS)

    Griesser, Hans J.; Bramley, Richard

    1982-06-01

    High resolved phosphorescence spectra of xanthone have been recorded in four host matrices in order to study vibronic coupling between the lowest tripl origin in all hosts, and the energetically close-lying second triplet state T 2, which is of n?* orbital origin. In three hosts, there is thermall to phosphorescence from T 1. Vibrational analyses of the two emissions are reported. The vibrational structure of both emissions depends little on t vibronic mixing between the lowest two triplet states is weak, in spite of the small energy separation in some hosts. The importance of the different i 1 and its sublevels is discussed, and it is concluded that across energy separations smaller than about 200 cm -1 spin—orbit mixing is more orbital mixing between the 3??* and 3n?* configurations of xanthone.

  4. Excited-state Raman spectroscopy with and without actinic excitation: S1 Raman spectra of trans-azobenzene

    NASA Astrophysics Data System (ADS)

    Dobryakov, A. L.; Quick, M.; Ioffe, I. N.; Granovsky, A. A.; Ernsting, N. P.; Kovalenko, S. A.

    2014-05-01

    We show that femtosecond stimulated Raman spectroscopy can record excited-state spectra in the absence of actinic excitation, if the Raman pump is in resonance with an electronic transition. The approach is illustrated by recording S1 and S0 spectra of trans-azobenzene in n-hexane. The S1 spectra were also measured conventionally, upon n?* (S0 ? S1) actinic excitation. The results are discussed and compared to earlier reports.

  5. Stimulated emission depletion of triplet excitons in a phosphorescent organic laser

    Microsoft Academic Search

    M. Reufer; J. M. Lupton; U. Scherf

    2006-01-01

    Triplet formation is investigated in an optically pumped polymer laser by detecting the phosphorescence emission after excitation. A clear correlation is observed between the onset of lasing and a saturation of phosphorescence intensity due to stimulated emission depletion of the singlet state and the resulting reduction in intersystem crossing. The results are consistent with intersystem crossing constituting the dominant triplet

  6. Identification of a triplet pair intermediate in singlet exciton fission in solution.

    PubMed

    Stern, Hannah L; Musser, Andrew J; Gelinas, Simon; Parkinson, Patrick; Herz, Laura M; Bruzek, Matthew J; Anthony, John; Friend, Richard H; Walker, Brian J

    2015-06-23

    Singlet exciton fission is the spin-conserving transformation of one spin-singlet exciton into two spin-triplet excitons. This exciton multiplication mechanism offers an attractive route to solar cells that circumvent the single-junction Shockley-Queisser limit. Most theoretical descriptions of singlet fission invoke an intermediate state of a pair of spin-triplet excitons coupled into an overall spin-singlet configuration, but such a state has never been optically observed. In solution, we show that the dynamics of fission are diffusion limited and enable the isolation of an intermediate species. In concentrated solutions of bis(triisopropylsilylethynyl)[TIPS]-tetracene we find rapid (<100 ps) formation of excimers and a slower (?10 ns) break up of the excimer to two triplet exciton-bearing free molecules. These excimers are spectroscopically distinct from singlet and triplet excitons, yet possess both singlet and triplet characteristics, enabling identification as a triplet pair state. We find that this triplet pair state is significantly stabilized relative to free triplet excitons, and that it plays a critical role in the efficient endothermic singlet fission process. PMID:26060309

  7. When You Are a Twin or Triplet

    MedlinePLUS

    ... Body Works Main Page When You Are a Twin or Triplet KidsHealth > Kids > Feelings > My Home & Family > ... 7,000 triplet babies were born. Types of Twins There are two kinds of twins — fraternal and ...

  8. Electron energy spectra of H(-) autodetaching states resulting from collisions of H(-) with He at 1 KeV

    NASA Astrophysics Data System (ADS)

    Kimura, M.; Sato, H.; Hino, K.; Matsuzawa, M.

    Electron energy spectra for H(-) autodetaching states resulting from collisions H(-) with He at 1 keV are rigorously calculated by including couplings between doubly excited states and continuum states and their interference with direct detachment processes. An energy sampling procedure, based on the Gauss quadratures, is used to discretize continuum states. The present theoretical result, for the first time, clarifies mechanisms of excitation to doubly excited states, quantitatively reproduces the experimental spectra first observed by Risley and Geballe in 1974, separates the contributions from each of three autodetaching states, and identifies the cause of the interference between autodetaching and direct-detaching excitation channels.

  9. Non-Markovian Quantum State Diffusion for Temperature-Dependent Linear Spectra of Light Harvesting Aggregates

    E-print Network

    Ritschel, Gerhard; Möbius, Sebastian; Strunz, Walter T; Eisfeld, Alexander

    2014-01-01

    Non-Markovian Quantum State Diffusion (NMQSD) has turned out to be an effective method to calculate excitonic properties of aggregates composed of organic chromophores, taking into account the strong coupling of electronic transitions to vibrational modes of the chromophores. In this paper we show how to calculate linear optical spectra at finite temperatures in an efficient way. To this end we map a finite temperature environment to the zero temperature case using the so-called thermofield method. The zero temperature case equations can then be solved efficiently by standard integrators. As an example we calculate absorption and circular dichroism spectra of a linear aggregate. The formalism developed can be applied to calculate arbitrary correlation functions.

  10. Non-Markovian Quantum State Diffusion for Temperature-Dependent Linear Spectra of Light Harvesting Aggregates

    E-print Network

    Gerhard Ritschel; Daniel Suess; Sebastian Möbius; Walter T. Strunz; Alexander Eisfeld

    2014-12-18

    Non-Markovian Quantum State Diffusion (NMQSD) has turned out to be an efficient method to calculate excitonic properties of aggregates composed of organic chromophores, taking into account the coupling of electronic transitions to vibrational modes of the chromophores. NMQSD is an open quantum system approach that incorporates environmental degrees of freedom (the vibrations in our case) in a stochastic way. We show in this paper that for linear optical spectra (absorption, circular dichroism) no stochastics is needed, even for finite temperatures. Thus, the spectra can be obtained by propagating a single trajectory. To this end we map a finite temperature environment to the zero temperature case using the so-called thermofield method. The resulting equations can then be solved efficiently by standard integrators.

  11. Non-Markovian Quantum State Diffusion for temperature-dependent linear spectra of light harvesting aggregates.

    PubMed

    Ritschel, Gerhard; Suess, Daniel; Möbius, Sebastian; Strunz, Walter T; Eisfeld, Alexander

    2015-01-21

    Non-Markovian Quantum State Diffusion (NMQSD) has turned out to be an efficient method to calculate excitonic properties of aggregates composed of organic chromophores, taking into account the coupling of electronic transitions to vibrational modes of the chromophores. NMQSD is an open quantum system approach that incorporates environmental degrees of freedom (the vibrations in our case) in a stochastic way. We show in this paper that for linear optical spectra (absorption, circular dichroism), no stochastics is needed, even for finite temperatures. Thus, the spectra can be obtained by propagating a single trajectory. To this end, we map a finite temperature environment to the zero temperature case using the so-called thermofield method. The resulting equations can then be solved efficiently by standard integrators. PMID:25612697

  12. Triplet exciton caging in two dimensions

    Microsoft Academic Search

    S. Arnold; R. R. Alfano; M. Pope; W. Yu; P. Ho; R. Selsby; J. Tharrats; C. E. Swenberg

    1976-01-01

    It is proposed that the bimolecular process of triplet exciton fusion to form singlet excitons can be enhanced by reducing the size of the domain in which the triplet exciton pair is free to move. These small domains, or exciton cages, are much more effective when the host material is highly anisotropic, and the triplet excitons are constrained to move

  13. A unique case of conjoined triplets.

    PubMed

    Athanasiadis, Apostolos P; Tzannatos, Christinne; Mikos, Themistoklis; Zafrakas, Menelaos; Bontis, John N

    2005-06-01

    A unique case of conjoined triplets that was characterized as tricephalus, tetrabrachius, and tetrapus parapagothoracopagus is presented. Antenatal diagnosis of the conjoined triplet was made at 22 weeks of gestation with 2-dimensional ultrasonography and magnetic resonance imaging. Pregnancy was terminated by hysterotomy, and diagnosis of conjoined triplets was confirmed postnatally. PMID:15970906

  14. Experimental and theoretical study of the electronic states and spectra of PbLi

    NASA Astrophysics Data System (ADS)

    Setzer, K. D.; Borkowska-Burnecka, J.; Zyrnicki, W.; Pravilov, A. M.; Fink, E. H.; Das, K. K.; Liebermann, H.-P.; Alekseyev, A. B.; Buenker, R. J.

    2003-01-01

    Gas phase emission spectra of the hitherto unknown free radical PbLi have been measured in the NIR range with a Fourier-transform spectrometer. The emissions were observed from a fast flow system in which lead vapor in argon carrier gas was passed through a microwave discharge and mixed with lithium vapor in an observation tube. Five electronic transitions have been found in the wavenumber range 3800-10 000 cm -1. Bands from two excited states to the ground state were measured at high spectral resolution such that rotational analyses could be performed and accurate molecular parameters derived. 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 PbLi and also electric dipole transition moments connecting them. As in the lighter molecules of this group, CLi and SiLi, the ground state of PbLi is found to be X 4?-(X 1 1/2,X 2 3/2) with a spin splitting of about 2000 cm -1. The first excited state is A 2?1/2 ( A 1/2), and two observed band systems are assigned to the transitions A? X1 and A? X2. Two more excited states, B 2?3/2 ( B 3/2) and C 1/2, are identified from the observed spectra with the help of the computed data, and their spectroscopic constants are determined. In contrast to PbH and PbF, the ab initio results indicate a very complicated low-energy electronic structure for the PbLi radical, with 19 bound electronic states calculated to lie below 3 eV.

  15. The singlet-triplet absorption and photodissociation of the HOCl, HOBr, and HOI molecules calculated by the MCSCF quadratic response method

    SciTech Connect

    Minaev, B.F.

    1999-09-09

    The molecular absorption spectra of hypochlorous, hypobromous, and hypoiodous acids have been studied by multiconfiguration self-consistent field (MCSCF) calculations with linear and quadratic response techniques. The complete form of the spin-orbit coupling (SOC) operator is accounted. The singlet-triplet transition to the lowest triplet state {sup 3}A{double{underscore}prime} {l{underscore}arrow} X{sup 1}A{prime} is shown to be responsible for the weak long-wavelength tail absorption and photodissociation in these molecules. The transition is polarized along the O-X bond (X = Cl, Br, I) and has an oscillator strength equal 6 x 10{sup {minus}6}, 8 x 10{sup {minus}5}, and 2 x 10{sup {minus}4} for hypochlorous, hypobromous, and hypoiodous acids, respectively. The second singlet-triplet transition {sup 3}A{prime} {l{underscore}arrow} X{sup 1}A{prime} comes to the region of the first singlet-singlet {sup 1}A{double{underscore}prime} {l{underscore}arrow} X{sup 1}A{prime} absorption and contributes significantly to the total cross-section at wavelengths {lambda} {approx} 300--320 nm (X = Cl), {lambda} {approx} 340--360 nm (X = Br), and {lambda} {approx} 400 nm (X = I). In the last case the singlet-triplet transition {sup 3}A{prime} {l{underscore}arrow} X{sup 1}A{prime} produces predominant contribution to HOI absorption in the visible region. All states are dissociative, so the singlet-triplet absorption contributes to the yield of photolysis in the important near-UV and visible region close to the intense solar actinic flux. Contributions to the removal mechanisms for atmospheric HOCl, HOBr, and HOI species are shortly discussed. The minor loss process of ozone in troposphere because of the HOI reservoir sink is getting evident on the ground of this calculations. The importance of SOC accounting for atmospheric photochemistry problems is stressed.

  16. A dominant homolytic O-Cl bond cleavage with low-spin triplet-state Fe(IV)=O formed is revealed in the mechanism of heme-dependent chlorite dismutase.

    PubMed

    Sun, Shuo; Li, Ze-Sheng; Chen, Shi-Lu

    2014-01-21

    Chlorite dismutase (Cld) is a heme-dependent enzyme that catalyzes the decomposition of toxic chlorite (ClO2(-)) into innocuous chloride and O2. In this paper, using the hybrid B3LYP density functional theory (DFT) method including dispersion interactions, the Cld reaction mechanism has been studied with a chemical model constructed on the X-ray crystal structure. The calculations indicate that the reaction proceeds along a stepwise pathway in the doublet state, i.e. a homolytic O-Cl bond cleavage of the substrate leading to an O-Fe(heme) species and a ClO? radical, followed by a rebinding O-O bond formation between them. The O-Fe(heme) species is demonstrated to be a low-spin triplet-state Fe(IV)=O diradicaloid. A low-spin singlet-state Fe(IV)=O is much less stable than the former, with an energy difference of 9.2 kcal mol(-1). The O-Cl bond cleavage is rate-limiting with a barrier of 10.6 kcal mol(-1), in good agreement with the experimental reaction rate of 2.0 × 10(5) s(-1). Furthermore, a heterolytic O-Cl bond dissociation in the initial step is shown to be unreachable, which ensures the high efficiency of the Cld enzyme by avoiding the generation of chlorate byproduct observed in the reactions of synthetic Fe porphyrins. Also, the pathways in the quartet and sextet states are unfavorable for the Cld reaction. The present results reveal a detailed mechanism III (defined in the text) including an interesting di-radical intermediate composed of a low-spin triplet-state Fe(IV)=O and a ClO? radical. Compared to a competitive heterolytic Cl-O cleavage in synthetic Fe porphyrins, the revelation of the domination of homolysis in Cld indicates not only the high efficiency of enzyme, but also the sensitivity of a heme and the significance of the enzymatic active-site surroundings (the His170 and Arg183 residues in the present case), which gives more insights into heme chemistry. PMID:24162174

  17. Nonlinear optical spectra having characteristics of Fano interferences in coherently coupled lowest exciton biexciton states in semiconductor quantum dots

    SciTech Connect

    Gotoh, Hideki, E-mail: gotoh.hideki@lab.ntt.co.jp; Sanada, Haruki; Yamaguchi, Hiroshi; Sogawa, Tetsuomi [NTT Basic Research Laboratories, NTT Corporation, 3-1 Morinosato-Wakamiya, Atsugi-shi, Kanagawa 243-0198 (Japan)

    2014-10-15

    Optical nonlinear effects are examined using a two-color micro-photoluminescence (micro-PL) method in a coherently coupled exciton-biexciton system in a single quantum dot (QD). PL and photoluminescence excitation spectroscopy (PLE) are employed to measure the absorption spectra of the exciton and biexciton states. PLE for Stokes and anti-Stokes PL enables us to clarify the nonlinear optical absorption properties in the lowest exciton and biexciton states. The nonlinear absorption spectra for excitons exhibit asymmetric shapes with peak and dip structures, and provide a distinct contrast to the symmetric dip structures of conventional nonlinear spectra. Theoretical analyses with a density matrix method indicate that the nonlinear spectra are caused not by a simple coherent interaction between the exciton and biexciton states but by coupling effects among exciton, biexciton and continuum states. These results indicate that Fano quantum interference effects appear in exciton-biexciton systems at QDs and offer important insights into their physics.

  18. Diffusion and relaxation of triplet excitations in binary organicglasses

    NASA Astrophysics Data System (ADS)

    Lange, J.; Ries, B.; Bässler, H.

    1988-12-01

    The diffusion and relaxation of triplet excitations in benzophenone glasses, diluted by either methyltetrahydrofuran or durene, has been investigated by time-resolved phosphorescence spectroscopy at 77 and 10 K. Monitoring the spectral evolution of the inhomogeneously broadened 0-0 band as a function of time yields both the rate at which triplet excitations relax within the distribution of hopping states and the rate at which excitations are captured by deliberately added chemical traps. The experiments are in quantitative accord with the concept of random walk within a Gaussian distribution of uncorrelated benzophenone triplet levels, developed on the basis of Monte Carlo simulations. Transport is dispersive and the diffusivity scales approximately linearly with site concentration, at variance to what percolation theory would predict. Presence of traps has a feedback effect on the transport process.

  19. Influence of the projectile charge state on electron emission spectra from a Cu(111) surface

    NASA Astrophysics Data System (ADS)

    Archubi, C. D.; Silkin, V. M.; Gravielle, M. S.

    2015-09-01

    Double differential electron emission distributions produced by grazing impact of fast dressed ions on a Cu(111) surface are investigated focusing on the effects of the electronic band structure. The process is described within the Band-Structure-Based approximation, which is a perturbative method that includes an accurate representation of the electron-surface interaction, incorporating information of the electronic band structure of the solid. Differences in the behavior of the emission spectra for He+ q, Li+ q, Be+ q and C+ q projectiles with different charge states q are explained by the combined effect of the projectile trajectory and the projectile charge distribution.

  20. Triplet-triplet energy transfer and protection mechanisms against singlet oxygen in photosynthesis

    NASA Astrophysics Data System (ADS)

    Kihara, Shigeharu

    In photosynthesis, (bacterio)chlorophylls ((B)Chl) play a crucial role in light harvesting and electron transport. (B)Chls, however, are known to be potentially dangerous due to the formation of the triplet excited state which forms the singlet oxygen (1O2*) when exposed to the sunlight. Singlet oxygen is highly reactive and all modern organisms incorporate special protective mechanisms to minimize the oxidative damage. One of the conventional photoprotective mechanisms used by photosynthetic organisms is by the nearby carotenoids quenching the excess energy and releasing it by heat. In this dissertation, two major aspects of this process are studied. First, based on experimental data and model calculations, the oxygen content in a functioning oxygenic photosynthetic oxygen cell was determined. These organisms perform water splitting and as a result significant amount of oxygen can be formed within the organism itself. It was found, that contrary to some published estimates, the excess oxygen concentration generated within an individual cell is extremely low -- 0.025 ... 0.25 microM, i.e. about 103-104 times lower than the oxygen concentration in air saturated water. Such low concentrations imply that the first oxygenic photosynthetic cells that evolved in oxygen-free atmosphere of the Earth ~2.8 billion years ago might have invented the water splitting machinery (photosystem II) without the need for special oxygen-protective mechanisms, and the latter mechanisms could have evolved in the next 500 million years during slow rise of oxygen in the atmosphere. This result also suggests that proteins within photosynthetic membranes are not exposed to significant O2 levels and thus can be studied in vitro under the usual O2 levels. Second, the fate of triplet excited states in the Fenna Matthew Olson (FMO) pigment-protein complex is studied by means of time-resolved nanosecond spectroscopy and exciton model simulations. For the first time, the properties of several individual BChl pigments within that photosynthetic antenna complex are accessed via their triplet state dynamics. It is found that the currently used exciton model of FMO needs to be revised. It is also shown that triplet excited states can be readily transferred between the molecules. It is proposed that the triplet energy transfer between the BChl molecules can also serve as a protection mechanism. Finally, it is inferred that at least one of the BChl molecules within the FMO has a triplet state energy that is lower than that of singlet oxygen. This effectively prevents the formation of singlet oxygen and protects the complex from oxidative damage. The energy of BChl is apparently lowered by the specific protein environment, as in solution its energy is measured to be somewhat higher than the energy of singlet oxygen. Finally, the results of the triplet energy transfer within the cytochrome b6f complex are presented. This part of the work is not conclusive, and some of the problems encountered in experiments are described, as well as a new method of sample degassing developed for this type of study is presented.

  1. Solid-State Density Functional Theory Investigation of the Terahertz Spectra of the Structural Isomers 1,2-Dicyanobenzene and 1,3-Dicyanobenzene

    E-print Network

    Oklahoma State University

    Solid-State Density Functional Theory Investigation of the Terahertz Spectra of the Structural,3-DCB) have been modeled and assigned using solid-state density functional theory. The THz spectra, reinforcing the need for proper solid-state models in the analysis of the THz spectra of organic molecular

  2. Analysis of the energy spectra of ground states of deformed nuclei in the rare-earth region

    NASA Astrophysics Data System (ADS)

    A. Okhunov, A.; I. Turaeva, G.; A. Kassim, H.; U. Khandaker, M.; Noora, B. Rosli

    2015-04-01

    The 62Sm, 64Gd, 66Dy, 70Yb, 72Hf and 74W nuclei are classified as deformed nuclei. Low-lying bands are one of the most fundamental excitation modes in the energy spectra of deformed nuclei. In this paper a theoretical analysis of the experimental data within the phenomenological model is presented. The energy spectra of ground states are calculated. It is found that the low-lying spectra of ground band states are in good agreement with the experimental data. Supported by IIUM University Research Grant Type B (EDW B13-034-0919) and MOHE Fundamental Research Grant Scheme (FRGS13-074-0315)

  3. Volume 204, number $6 CHEMICAL PHYSICS LETTERS 26 March 1993 Triplet-triplet transition of Cs2studied

    E-print Network

    Kim, Bongsoo

    of alkali dimers attracted much attention as a possible candidate for contin- uously tunable lasers Although extensive studies have been done on the excited singlet states of the alkali dimers, much less of the alkali dimers, very few high-resolution studies are reported for the absorptions from the triplet ground

  4. Triplet xanthone in n-pentane: multiple emission from a single site

    NASA Astrophysics Data System (ADS)

    Griesser, Hans J.; Bramley, Richard

    1982-04-01

    The three phosphorescence components of xanthone in n-pentane originate from three states of one solvated species: From the z sublevel of the second triplet state, of 3n? * origin, and from two widely split sublevels of the lowest triplet state, of 3?? * origin. Its z sublevel is thermally depleted across the spin-orbit mixing induced zero-field sublevel splitting of 15.1 cm -1.

  5. Non-Thermal Signatures in Low State Spectra of Black Hole X-Ray Transients

    NASA Astrophysics Data System (ADS)

    Esin, A. A.; Tomsick, J. A.

    2001-05-01

    Many transient and persistent Black Hole X-ray Binaries (BHXBs) show characteristic state transitions between low/hard and high/soft spectral states. A typical low/hard state X-ray spectrum, as seen for example in Cyg X-1 and GRO J0422+32, is a power-law with a photon index of order 1.4-1.6 and an exponential cutoff with a characteristic e-folding energy ~ 100 keV. These spectra are generally interpreted as emission from hot thermal plasma modeled either as an accretion disk corona, or as a hot accretion flow inside a truncated thin disk. We show that low state spectra of three transient BHXBs, XTE J1118+480, XTE J1550-564, and 4U1630-47, do not show the characteristic hard X-ray turnover. The absence of the turnover is difficult to understand in the context of the thermal Comptonization models, and argues for the presence of non-thermal emission in these systems. We propose that a typical hard power-law spectrum can be produced both in the (thermal) accretion flow or in the (non-thermal) jet (as suggested by Fender et al. 2000). The strength of the jet emission relative to that from the accretion flow (and therefore whether we observe the thermal cutoff in the spectrum or not) can depend on several parameters, e.g. inclination of the jet with respect to the binary and the observer, mass accretion rate, accretion flow configuration. This work was supported by Chandra Postdoctoral Fellowship grant #PF8-10002 awarded by the Chandra X-Ray Center, which is operated by the SAO for NASA under contract NAS8-39073, and by a CASS Postdoctoral Fellowship.

  6. Understanding Singlet and Triplet Excitons in Acene Crystals from First Principles

    NASA Astrophysics Data System (ADS)

    Rangel Gordillo, Tonatiuh; Sharifzadeh, Sahar; Kronik, Leeor; Neaton, Jeffrey

    2014-03-01

    Singlet fission, a process in which two triplet excitons are formed from a singlet exciton, has the potential to increase the solar cell efficiencies above 100%. Efficient singlet fission has been reported in larger acene crystals, such as tetracene and pentacene, in part attributable to their low-lying triplet energies. In this work, we use many-body perturbation theory within the GW approximation and the Bethe-Salpeter equation approach to compute quasiparticle gaps, low-lying singlet and and triplet excitations, and optical absorption spectra across the entire acene family of crystals, from benzene to hexacene. We closely examine the degree of localization and charge-transfer character of the low-lying singlets and triplets, and their sensitivity to crystal environment, and discuss implications for the efficiency of singlet fission in this systems. This work supported by DOE and computational resources provided by NERSC.

  7. Electronic spectra and excited state dynamics of pentafluorophenol: Effects of low-lying ??? states

    NASA Astrophysics Data System (ADS)

    Karmakar, Shreetama; Mukhopadhyay, Deb Pratim; Chakraborty, Tapas

    2015-05-01

    Multiple fluorine atom substitution effect on photophysics of an aromatic chromophore has been investigated using phenol as the reference system. It has been noticed that the discrete vibronic structure of the S1?S0 absorption system of phenol vapor is completely washed out for pentafluorophenol (PFP), and the latter also shows very large Stokes shift in the fluorescence spectrum. For excitations beyond S1 origin, the emission yield of PFP is reduced sharply with increase in excess vibronic energy. However, in a collisional environment like liquid hydrocarbon, the underlying dynamical process that drives the non-radiative decay is hindered drastically. Electronic structure theory predicts a number of low-lying dark electronic states of ??? character in the vicinity of the lowest valence ??? state of this molecule. Tentatively, we have attributed the excitation energy dependent non-radiative decay of the molecule observed only in the gas phase to an interplay between the lowest ??? and a nearby dissociative ??? state. Measurements in different liquids reveal that some of the dark excited states light up with appreciable intensity only in protic liquids like methanol and water due to hydrogen bonding between solute and solvents. Electronic structure theory methods indeed predict that for PFP-(H2O)n clusters (n = 1-11), intensities of a number of ??? states are enhanced with increase in cluster size. In contrast with emitting behavior of the molecule in the gas phase and solutions of nonpolar and polar aprotic liquids, the fluorescence is completely switched off in polar protic liquids. This behavior is a chemically significant manifestation of perfluoro effect, because a very opposite effect occurs in the case of unsubstituted phenol for which fluorescence yield undergoes a very large enhancement in protic liquids. Several dynamical mechanisms have been suggested to interpret the observed photophysical behavior.

  8. Low-temperature laser photolysis of aromatic ketones. Transient absorption spectra in neat diethylaniline at 77 K

    NASA Astrophysics Data System (ADS)

    Hoshino, Mikio; Seki, Hiroshi; Shizuka, Haruo

    1989-02-01

    Optical absorption and luminescence studies have confirmed that benzophenone, xanthone, and fluorenone in neat diethylaniline form molecular complexes with diethylaniline at 77 K. The transient spectra of these aromatic ketones in neat diethylaniline were measured by nanosecond laser photolysis at 77 K. For benzophenone and xanthone, the transient spectra observed for the molecular complexes are in good agreement with a sum of the spectra of the anion radical of each ketone and the cation radical of diethylaniline, indicating that these transients are attributed to the triplet states of the molecular complexes with a strong charge-transfer interaction. On the other hand, the molecular complex of fluorenone in neat diethylaniline at 77 K gives the transient spectrum almost identical with the triplet-triplet absorption spectrum of fluorenone in toluene. The charge-transfer interaction between fluorenone and diethylaniline in the triplet molecular complex is concluded to be very weak. The laser photolysis of anthracene and pyrene in neat diethylaniline at 77 K were also studied for comparison with aromatic ketones.

  9. Ultrafast dissociation of triplets in pentacene induced by an electric field

    NASA Astrophysics Data System (ADS)

    Srimath Kandada, Ajay Ram; Petrozza, Annamaria; Lanzani, Guglielmo

    2014-08-01

    Singlet fission into a pair of triplet excitons in pentacene is envisaged to be a potential carrier multiplication route in organic photovoltaics. In order to shed light on the dissociation dynamics of the triplet states we performed electric field induced pump-probe experiments on polycrystalline films of pentacene. We find that the nascent triplet pair formed immediately after the fission process is susceptible to dissociation in the presence of the electric field. By measuring the temporal dynamics of the dissociation, we estimate its binding energy to be approximately 320 meV. After about 2 ps the triplets diffuse away from each other and the field assisted dissociation is substantially reduced. Our results suggest that if the nascent triplet pairs could be harvested at the interface in a device, the efficiency of the process would be higher.

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

    SciTech Connect

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

    1988-03-10

    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.

  11. Chimpanzee triplets born in captivity

    Microsoft Academic Search

    Mark A. Rosenthal; Lhtcobt Park Zoological Gardens

    1981-01-01

    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

  12. Picosecond 266-nm multiphoton laser photolysis studies on liquid alkane solution of aromatic hydrocarbons: Ultrafast solute triplet formation

    Microsoft Academic Search

    Hiroshi. Miyasaka; Hiroshi. Masuhara; Noboru. Mataga

    1990-01-01

    Triplet formation of aromatic hydrocarbon solute in aliphatic hydrocarbon solution in the picosecond to a few nanosecond time region induced by multiphoton excitation with 266-nm picosecond laser pulse is demonstrated. Mechanisms of the rapid triplet state formation, especially the contribution of the ionized state of solvent molecule to it, are discussed by comparing the results of picosecond laser photolysis studies

  13. Determination of the quantum yield of singlet-triplet conversion in complex organic compounds by the method of laser fluorimetry

    Microsoft Academic Search

    A. A. Banishev; D. V. Maslov; V. V. Fadeev

    2008-01-01

    The possibilities of the nonlinear laser fluorimetry method for determination of the quantum yield into the triplet state\\u000a are demonstrated. The values of the absorption cross section and the triplet-state quantum yield are determined from the fluorescent\\u000a saturation curves for 6-aminophenolenone and rhodamine 6G (used as a test material).

  14. Nitrogen pairs, triplets, and clusters in GaAs and GaP P. R. C. Kenta)

    E-print Network

    Kent, Paul

    Nitrogen pairs, triplets, and clusters in GaAs and GaP P. R. C. Kenta) and Alex Zunger National 2001 The electronic and atomic structure of substitutional nitrogen pairs, triplets, and clusters in Ga supercells. A single nitrogen impurity creates a localized a1(N) gap state in GaP, but in GaAs, the state

  15. Production of N2 Vegard-Kaplan and other triplet band emissions in the dayglow of Titan

    NASA Astrophysics Data System (ADS)

    Bhardwaj, Anil; Jain, Sonal Kumar

    2012-04-01

    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.

  16. The energies and kinetics of triplet carotenoids in the LH2 antenna complexes as determined by phosphorescence spectroscopy

    NASA Astrophysics Data System (ADS)

    Rondonuwu, Ferdy S.; Taguchi, Tokio; Fujii, Ritsuko; Yokoyama, Kyosuke; Koyama, Yasushi; Watanabe, Yasutaka

    2004-01-01

    The triplet (T 1) states of carotenoids (Cars) and bacteriochlorophyll a (BChl) in the LH2 antenna complexes from Rhodobacter sphaeroides G1C, Rba. sphaeroides 2.4.1 and Rhodospirillum molischianum, containing neurosporene, spheroidene and lycopene, respectively, were examined by stationary-state and time-resolved phosphorescence spectroscopy. The T 1 energies of Cars were determined, irrespective of the Car or BChl excitation, to be 7030 cm -1 (neurosporene), 6920 cm -1 (spheroidene) and 6870 cm -1 (lycopene), respectively, whereas that of BChl to be 7590 cm -1. In the Rba. sphaeroides G1C, the Car and BChl triplet states decayed in similar time constant as the BChl Q y state, a fact which indicates that the pair of triplet states decays through the triplet-triplet annihilation mechanism.

  17. Formation of ultracold 7Li85Rb molecules in the lowest triplet electronic state by photoassociation and their detection by ionization spectroscopy

    NASA Astrophysics Data System (ADS)

    Altaf, Adeel; Dutta, Sourav; Lorenz, John; Pérez-Ríos, Jesús; Chen, Yong P.; Elliott, D. S.

    2015-03-01

    We report the formation of ultracold 7Li85Rb molecules in the a3?+ electronic state by photoassociation (PA) and their detection via resonantly enhanced multiphoton ionization (REMPI). With our dual-species Li and Rb magneto-optical trap apparatus, we detect PA resonances with binding energies up to ˜62 cm-1 below the 7Li 2s 2S1/2 + 85Rb 5p 2P1/2 asymptote. In addition, we use REMPI spectroscopy to probe the a3?+ state and excited electronic 33? and 43?+ states and identify a3?+ (v? = 7-13), 33? (v?' = 0-10), and 43?+ (v?' = 0-5) vibrational levels. Our line assignments agree well with ab initio calculations. These preliminary spectroscopic studies on previously unobserved electronic states are crucial to discovering transition pathways for transferring ultracold LiRb molecules created via PA to deeply bound rovibrational levels of the electronic ground state.

  18. Highly efficient fluorescent-phosphorescent triplet-harvesting hybrid organic light-emitting diodes

    Microsoft Academic Search

    Marina E. Kondakova; Joseph C. Deaton; Thomas D. Pawlik; David J. Giesen; Denis Y. Kondakov; Ralph H. Young; Tommie L. Royster; Dustin L. Comfort; Joel D. Shore

    2010-01-01

    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

  19. Experimental and theoretical study of the electronic states and spectra of BiLi

    NASA Astrophysics Data System (ADS)

    Setzer, K. D.; Fink, E. H.; Liebermann, H.-P.; Buenker, R. J.; Alekseyev, A. B.

    2015-06-01

    Gas phase emission spectra of the hitherto unknown free radical BiLi were measured in the NIR range with a Fourier-transform spectrometer. The emissions were observed from a fast-flow system in which bismuth 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 observed in the range 6900-9800 cm-1 are assigned to the transitions A3?(A20+) ? X3?-(X10+, X21). The ?v = 0, +1, and -1 sequences of both systems were measured at high spectral resolution. Rotational and vibrational analyses of 12 bands have yielded the spectroscopic parameters of the X10+, X21, and A20+ states including a hfs splitting parameter of the X21 state. In order to aid in the analysis of the experimental data, a series of relativistic configuration interaction calculations has been carried out to obtain spectroscopic parameters and potential curves for the low-lying states of BiLi and also electric dipole transition moments connecting them.

  20. Triplet exciton dynamics in rubrene single crystals

    NASA Astrophysics Data System (ADS)

    Ryasnyanskiy, Aleksandr; Biaggio, Ivan

    2011-11-01

    The decay of the photoluminescence excited in rubrene single crystals by picosecond pulses is measured over 7 orders of magnitude and more than 4 time decades. We identify the typical decay dynamics due to triplet-triplet interaction. We show that singlet exciton fission and triplet fusion quantum yields in rubrene are both very large, and we directly determine a triplet exciton lifetime of 100±20 ?s, which explains the delayed buildup of a large photocurrent that has been reported earlier for low excitation densities.

  1. Singlet-triplet superconducting quantum magnetometer

    NASA Astrophysics Data System (ADS)

    Alidoust, Mohammad; Halterman, Klaus; Linder, Jacob

    2013-08-01

    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.

  2. Theoretical study of the radiative properties of the triplet states of the NH radical: Transition dipole moments, radiative lifetimes, photodissociation cross sections

    Microsoft Academic Search

    Kate P. Kirby; Evelyn M. Goldfield

    1991-01-01

    Abinitio transition dipole moments between the X 3?? and the A 3&Pgr; states of NH and the 2 3?? and 2 3&Pgr; dissociative states have been computed. These transition dipole moments have been used to compute photodissociation cross sections and interstellar photodissociation rates for NH. Photodissociation rates for NH in the interstellar radiation field range from 1.9 to 4.7×10?10 s?1

  3. A note on triplet-triplet fission of singlet excitons in molecular crystals

    Microsoft Academic Search

    K. Král

    1972-01-01

    The singlet exciton lifetime in the reaction of triplet-triplet fission due to purely electronic interaction is estimated in an ideal molecular crystal with favorable positions of singlet and triplet bands, for coherent plane wave form of exciton wave functions. An explicit form of the interaction of molecules in molecular crystal in second quantization reprezentation is presented, including exchange and charge-transfer

  4. Photo-physical properties and triplet-triplet absorption of platinum(II) acetylides in solid PMMA matrices

    Microsoft Academic Search

    Eirik Glimsdal; Robert Westlund; Mikael Lindgren

    2009-01-01

    Because of their strong nonlinear optical properties, Platinum(II) acetylides are investigated as potential chromophores for optical power limiting (OPL) applications. The strong excited state absorption and efficient intersystem crossing to the triplet states in these materials are desired properties for good OPL performance. We recently reported on OPL and photo-physical properties of Pt(II)-acetylide chromophores in solution, modified with thiophenyl or

  5. Formation of ultracold (7)Li(85)Rb molecules in the lowest triplet electronic state by photoassociation and their detection by ionization spectroscopy.

    PubMed

    Altaf, Adeel; Dutta, Sourav; Lorenz, John; Pérez-Ríos, Jesús; Chen, Yong P; Elliott, D S

    2015-03-21

    We report the formation of ultracold (7)Li(85)Rb molecules in the a(3)?(+) electronic state by photoassociation (PA) and their detection via resonantly enhanced multiphoton ionization (REMPI). With our dual-species Li and Rb magneto-optical trap apparatus, we detect PA resonances with binding energies up to ?62 cm(-1) below the (7)Li?2s?(2)S1/2?+?(85)Rb 5p?(2)P1/2 asymptote. In addition, we use REMPI spectroscopy to probe the a(3)?(+) state and excited electronic 3(3)? and 4(3)?(+) states and identify a(3)?(+) (v? = 7-13), 3(3)? (v?' = 0-10), and 4(3)?(+) (v?' = 0-5) vibrational levels. Our line assignments agree well with ab initio calculations. These preliminary spectroscopic studies on previously unobserved electronic states are crucial to discovering transition pathways for transferring ultracold LiRb molecules created via PA to deeply bound rovibrational levels of the electronic ground state. PMID:25796252

  6. DNA Photosensitization by an "Insider": Photophysics and Triplet Energy Transfer of 5-Methyl-2-pyrimidone Deoxyribonucleoside.

    PubMed

    Bignon, Emmanuelle; Gattuso, Hugo; Morell, Christophe; Dumont, Elise; Monari, Antonio

    2015-08-01

    The main chromophore of (6-4) photoproducts, namely, 5-methyl-2-pyrimidone (Pyo), is an artificial noncanonical nucleobase. This chromophore has recently been reported as a potential photosensitizer that induces triplet damage in thymine DNA. In this study, we investigate the spectroscopic properties of the Pyo unit embedded in DNA by means of explicit solvent molecular-dynamics simulations coupled to time-dependent DFT and quantum-mechanics/molecular-mechanics techniques. Triplet-state transfer from the Pyo to the thymine unit was monitored in B-DNA by probing the propensity of this photoactive pyrimidine analogue to induce a Dexter-type triplet photosensitization and subsequent DNA damage. PMID:26133111

  7. On the Nature of the Lowest Triplet Excited State of the [Rh2(1,3-diisocyanopropane)4]2+ Ion

    E-print Network

    Coppens, Philip

    by the density functional theory. Two locally stable geometrical conformations are found on the potential energy state originates from the dz2* (metal antibonding) to pz (ligand-metal bonding) electronic transition of the crystal matrix on geometry changes occurring during photoexcitation. We report here on a member

  8. Analysis of source spectra, attenuation, and site effects from central and eastern United States earthquakes

    SciTech Connect

    Lindley, G.

    1998-02-01

    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.

  9. Enhanced Triplet Formation in Polycrystalline Tetracene Films by Femtosecond Optical-Pulse Shaping

    Microsoft Academic Search

    Erik M. Grumstrup; Justin C. Johnson; Niels H. Damrauer

    2010-01-01

    Polycrystalline tetracene films have been explored using weak ˜30fs visible laser pulses that excite the lowest singlet exciton as well as coherent vibrational motion. Transient difference spectra show a triplet absorption which arises following singlet fission (SF) and persists for 1.6 ns without decay. Adaptive pulse shaping identifies multipulse optimal fields which maximize this absorption feature by ˜20%. These are

  10. [Singlet-triplet excitation fission in light-harvesting complexes of photosynthetic bacteria and in isolated carotenoids].

    PubMed

    Klenina, I B; Makhneva, Z K; Moskalenko, A A; Kuz'min, A N; Proskuriakov, I I

    2013-01-01

    Time-resolved electron paramagnetic resonance was used to study the properties of carotenoid triplet states populated in LH2 light-harvesting complexes of phototrophic bacteria Allochromatium minutissimum, Rhodopseudomonas palustris, and in carotenoid films free of bacteriochlorophyll. The study was performed on purified LH2 preparations not contaminated by reaction centers, and under selective pigment excitation. The obtained results enable a conclusion that the carotenoid triplet states, both in LH2 complexes and films, are populated in the process of homofission of singlet excitation into two triplets, which involves only carotenoid molecules. It is observed that the fission process in magnetic field leads to predominant population of the T0 spin sublevel of the triplet. One molecular spin sublevel of the triplet is demonstrated to possess an increased probability of intersystem crossing to the ground state, independent of the carotenoid configuration. Pigment composition of the LH2 protein heterodimers is discussed, and a conclusion of the possible PMID:23650855

  11. Isolated triplets of galaxies. I - List

    Microsoft Academic Search

    V. E. Karachentseva; I. D. Karachentsev; A. L. Shcherbanovsky

    1979-01-01

    A list of 84 northern isolated galaxy triplets with component apparent magnitudes no fainter than 15.7 is compiled on the basis of a complete examination of Palomar Sky Survey prints. Equatorial coordinates, photographic apparent magnitudes, angular diameters, angular separations, morphological types, radial velocities, and other characteristics of the triplet members are provided, along with finding charts. Three main types of

  12. Polaron pair mediated triplet generation in polymer/fullerene blends

    NASA Astrophysics Data System (ADS)

    Dimitrov, Stoichko D.; Wheeler, Scot; Niedzialek, Dorota; Schroeder, Bob C.; Utzat, Hendrik; Frost, Jarvist M.; Yao, Jizhong; Gillett, Alexander; Tuladhar, Pabitra S.; McCulloch, Iain; Nelson, Jenny; Durrant, James R.

    2015-03-01

    Electron spin is a key consideration for the function of organic semiconductors in light-emitting diodes and solar cells, as well as spintronic applications relying on organic magnetoresistance. A mechanism for triplet excited state generation in such systems is by recombination of electron-hole pairs. However, the exact charge recombination mechanism, whether geminate or nongeminate and whether it involves spin-state mixing is not well understood. In this work, the dynamics of free charge separation competing with recombination to polymer triplet states is studied in two closely related polymer-fullerene blends with differing polymer fluorination and photovoltaic performance. Using time-resolved laser spectroscopic techniques and quantum chemical calculations, we show that lower charge separation in the fluorinated system is associated with the formation of bound electron-hole pairs, which undergo spin-state mixing on the nanosecond timescale and subsequent geminate recombination to triplet excitons. We find that these bound electron-hole pairs can be dissociated by electric fields.

  13. Polaron pair mediated triplet generation in polymer/fullerene blends

    PubMed Central

    Dimitrov, Stoichko D.; Wheeler, Scot; Niedzialek, Dorota; Schroeder, Bob C.; Utzat, Hendrik; Frost, Jarvist M.; Yao, Jizhong; Gillett, Alexander; Tuladhar, Pabitra S.; McCulloch, Iain; Nelson, Jenny; Durrant, James R.

    2015-01-01

    Electron spin is a key consideration for the function of organic semiconductors in light-emitting diodes and solar cells, as well as spintronic applications relying on organic magnetoresistance. A mechanism for triplet excited state generation in such systems is by recombination of electron-hole pairs. However, the exact charge recombination mechanism, whether geminate or nongeminate and whether it involves spin-state mixing is not well understood. In this work, the dynamics of free charge separation competing with recombination to polymer triplet states is studied in two closely related polymer-fullerene blends with differing polymer fluorination and photovoltaic performance. Using time-resolved laser spectroscopic techniques and quantum chemical calculations, we show that lower charge separation in the fluorinated system is associated with the formation of bound electron-hole pairs, which undergo spin-state mixing on the nanosecond timescale and subsequent geminate recombination to triplet excitons. We find that these bound electron-hole pairs can be dissociated by electric fields. PMID:25735188

  14. Definition and determination of the triplet-triplet energy transfer reaction coordinate

    SciTech Connect

    Zapata, Felipe; Marazzi, Marco; Castaño, Obis; Frutos, Luis Manuel, E-mail: luisma.frutos@uah.es [Departamento de Química Física, Universidad de Alcalá, 28871 Alcalá de Henares, Madrid (Spain); Acuña, A. Ulises [Instituto de Química Física “Rocasolano”, C.S.I.C., Serrano 119, 28006 Madrid (Spain)] [Instituto de Química Física “Rocasolano”, C.S.I.C., Serrano 119, 28006 Madrid (Spain)

    2014-01-21

    A definition of the triplet-triplet energy transfer reaction coordinate within the very weak electronic coupling limit is proposed, and a novel theoretical formalism is developed for its quantitative determination in terms of internal coordinates The present formalism permits (i) the separation of donor and acceptor contributions to the reaction coordinate, (ii) the identification of the intrinsic role of donor and acceptor in the triplet energy transfer process, and (iii) the quantification of the effect of every internal coordinate on the transfer process. This formalism is general and can be applied to classical as well as to nonvertical triplet energy transfer processes. The utility of the novel formalism is demonstrated here by its application to the paradigm of nonvertical triplet-triplet energy transfer involving cis-stilbene as acceptor molecule. In this way the effect of each internal molecular coordinate in promoting the transfer rate, from triplet donors in the low and high-energy limit, could be analyzed in detail.

  15. The fate of the triplet excitations in the fenna-matthews-olson complex.

    PubMed

    Kihara, Shigeharu; Hartzler, Daniel A; Orf, Gregory S; Blankenship, Robert E; Savikhin, Sergei

    2015-05-01

    The fate of triplet excited states in the Fenna-Matthew-Olson (FMO) pigment-protein complex is studied by means of time-resolved nanosecond spectroscopy and exciton model simulations. Experiments reveal microsecond triplet excited-state energy transfer between the bacteriochlorophyll (BChl) pigments, but show no evidence of triplet energy transfer to molecular oxygen, which is known to produce highly reactive singlet oxygen and is the leading cause of photo damage in photosynthetic proteins. The FMO complex is exceptionally photo stable despite the fact it contains no carotenoids, which could effectively quench triplet excited states of (bacterio)chlorophylls and are usually found within pigment-protein complexes. It is inferred that the triplet excitation is transferred to the lowest energy pigment, BChl 3, within the FMO complex, whose triplet state energy is shifted by pigment-protein interactions below that of the singlet oxygen excitation. Thus, the energy transfer to molecular oxygen is blocked and the FMO does not need carotenoids for photo protection. PMID:25856694

  16. Spin-triplet superconductivity in the double-chain Hubbard model with ferromagnetic exchange interaction

    Microsoft Academic Search

    T. Shirakawa; Y. Ohta; S. Nishimoto

    2007-01-01

    We study possible occurrence of spin-triplet superconductivity in the model of two Hubbard chains coupled with ferromagnetic exchange interaction. We use the analytical bozonization method as well as the numerical exact-diagonalization and density-matrix renormalization group methods. We show that, in the low electron density region, the complete ferromagnetic state occurs and the triplet pairing correlation is most dominant, where we

  17. A systematic study of mirror and triplet energy differences

    NASA Astrophysics Data System (ADS)

    Lenzi, S. M.; Lau, R.

    2015-02-01

    Differences of excitation energy among analogue states in a broad mass range are calculated in the framework of the shell model by introducing isospin breaking interactions. Mirror and triplet energy differences along the N=Z line from mass A ~ 20 to A ~ 60 have been systematically studied using the same method. It is shown that in all cases an additional term not directly associated to the electromagnetic interaction is needed to reproduce the experimental data.

  18. Resonance Raman Spectra of TNT and RDX Using Vibronic Theory, Excited-State Gradient, and Complex Polarizability Approximations

    E-print Network

    Asher, Sanford A.

    Resonance Raman Spectra of TNT and RDX Using Vibronic Theory, Excited-State Gradient, and Complex bands, and resonance Raman (RR) cross sections of TNT and RDX are investigated using density functional, and complex polarizability (CPP) approximations. We examined low- energy isomers (two for TNT and four for RDX

  19. Jet cooled spectra of pyrrolobenzene and of pyrrolobenzonitrile: the nature of the excited states

    E-print Network

    Haas, Yehuda

    multiphoton ionization (REMPI) excitation spectra of pyr- rolobenzene (PB) and pyrrolobenzonitrile (PBN) were.V. All rights reserved. 1. Introduction PB [1,2] and PBN [3,4] were recently studied in liquid solution) action spectra. In addition, fluo- rescence decay times were obtained. The results on PBN are compared

  20. Vibrational ground-state population distributions of an N2 flowing afterglow deduced from electron energy-loss spectra

    Microsoft Academic Search

    M. D. White; K. J. Ross

    1976-01-01

    The vibrationally excited populations of ground-state N2 in a flowing afterglow have been determined from energy-loss spectra in the energy-loss region 7.0-10.5 eV. The data of White et al. (1976) for energy-loss spectra in the energy-loss region 10.5-12.5 eV have been re-analysed and confirm a non-Boltzmann population distribution of the vibrational levels. An electron energy-loss spectrum of the afterglow is

  1. Heats of Formation of Triplet Ethylene, Ethylidene, and Acetylene

    SciTech Connect

    Nguyen, M.T.; Matus, M.H.; Lester Jr, W.A.; Dixon, David A.

    2007-06-28

    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.

  2. The Calcium Triplet metallicity calibration for galactic bulge stars

    E-print Network

    Vasquez, S; Hill, V; Gonzalez, O A; Saviane, I; Rejkuba, M; Battaglia, G

    2015-01-01

    We present a new calibration of the Calcium II Triplet equivalent widths versus [Fe/H], constructed upon K giant stars in the Galactic bulge. This calibration will be used to derive iron abundances for the targets of the GIBS survey, and in general it is especially suited for solar and supersolar metallicity giants, typical of external massive galaxies. About 150 bulge K giants were observed with the GIRAFFE spectrograph at VLT, both at resolution R~20,000 and at R~6,000. In the first case, the spectra allowed us to perform direct determination of Fe abundances from several unblended Fe lines, deriving what we call here high resolution [Fe/H] measurements. The low resolution spectra allowed us to measure equivalent widths of the two strongest lines of the near infrared Calcium II triplet at 8542 and 8662 A. By comparing the two measurements we derived a relation between Calcium equivalent widths and [Fe/H] that is linear over the metallicity range probed here, -1<[Fe/H]<+0.7. By adding a small second or...

  3. The examination of berberine excited state by laser flash photolysis

    NASA Astrophysics Data System (ADS)

    Cheng, Lingli; Wang, Mei; Zhao, Ping; Zhu, Hui; Zhu, Rongrong; Sun, Xiaoyu; Yao, Side; Wang, Shilong

    2009-07-01

    The property of the excited triplet state of berberine (BBR) was investigated by using time-resolved laser flash photolysis of 355 nm in acetonitrile. The transient absorption spectra of the excited triplet BBR were obtained in acetonitrile, which have an absorption maximum at 420 nm. And the ratio of excitation to ionization of BBR in acetonitrile solvent was calculated. The self-decay and self-quenching rate constants, and the absorption coefficient of 3BBR* were investigated and the excited state quantum yield was determined. Furthermore utilizing the benzophenone (BEN) as a triplet sensitizer, and the ?-carotene (Car) as an excited energy transfer acceptor, the assignment of 3BBR* was further confirmed and the related energy transfer rate constants were also determined.

  4. Excited states and absorption spectra of 2-?-diketonato-1,3,2-benzodioxaborol with aromatic substituents: Quantum-chemistry modeling.

    PubMed

    Kazachek, M V; Svistunova, I V

    2015-09-01

    The nature of excited states of 2-?-diketonato-1,3,2-benzodioxaborol compounds with aromatic substituent have been studied by the quantum-chemical method in the approximation of the time-dependent electron density functional theory. We have measured the absorption spectra of these compounds in acetonitrile solution and compared them with the model spectra constructed on the basis of calculations. The calculations give two long-wavelength transitions with small oscillator strengths, caused by ?-? transitions with the charge transfer from the benzodioxo-group to the chelate fragment. Observed long-wavelength shoulders of the spectra bands correlate with the mentioned transitions. Typical high intensity bands for ?-? transitions in the ultra-violet range are caused by transitions of ?-electrons in the fragments. Increasing extension of ?-system gives the batochromic shift of these absorption bands and the growth of the probabilities of the transition. PMID:25863460

  5. Control of triplet supercurrent in superconductor/ferromagnet hybrid systems

    NASA Astrophysics Data System (ADS)

    Martinez, William; Pratt, W. P., Jr.; Birge, Norman O.

    2015-03-01

    A lot of excitement has been generated in superconductor/ferromagnet (S/F) systems since long-range spin-triplet correlations (LRTCs) were predicted. Despite the many breakthroughs so far in this field, the ability to control the triplet generation reliably still needs to be realized before these devices can be used in technological applications. One possible direction to control the state in such structures is to manipulate the magnetizations of the various F layers within, specifically to switch between colinear and non-colinear directions between the layers. In this work, we report on the progress made to control LRTC generation in such a way. Supported by the DOE-BES under grant DE-FG-02-06ER46341.

  6. Spectral diffusion of triplet excitation energy in molecular glasses and doped polymer solids

    NASA Astrophysics Data System (ADS)

    Kook, Seong-Keun; Hanson, David M.

    1990-10-01

    Steady state phosphorescence at 4.2 K is monitored for different concentrations of 4-methylbenzophenone (MBP) doped into polystyrene. At concentrations less than 20%, the spectra are characteristic of separated molecules embedded in a disordered matrix. As the concentration increases to 20%, the vibronic bands shift to longer wavelengths and become slightly sharper. At concentrations above 30%, the spectra have additional features due to aggregates, which appear to be characteristic of a segregated phase of MBP. Triplet excitation energy transport in glassy MBP and MBP doped into a polystyrene matrix is monitored for different excitation energies and temperatures using time-resolved spectroscopy. These experiments reveal that spectral diffusion at liquid helium temperatures is not thermally activated, and that the spectral diffusion efficiency increases abruptly at a critical mole fraction of acceptors, 0.054, which corresponds to a critical distance of 9.8 Å. Although low-dimensional energy transfer dynamics has been revealed in other studies of disordered systems, the results indicate that spectral diffusion in these systems is controlled by a three-dimensional exchange interaction and the emission of phonons and/or vibrons.

  7. Vibrational spectra, infrared radiative properties, and transition-state analysis of CFC substitutes

    NASA Astrophysics Data System (ADS)

    Tai, Stephanie

    This thesis examines the two main aspects of the global warming potential of chlorofluorocarbon (CFC) substitutes (hydrofluorocarbons (HFC) and hydrochlorofluorocarbons (HCFC)): their instantaneous infrared radiative forcing and their atmospheric lifetime. The former is examined for some HFCs and HCFCs through experimental absolute infrared intensity measurements; variations between our values and literature values can be attributed in part to differences in the method of pressure broadening. Instantaneous infrared radiative forcing (IIRF) terms for two fluoroethers are estimated employing a recently developed radiative forcing function, in conjunction with infrared cross sections and vibrational frequencies calculated with ab initio quantum-mechanical methods. A detailed IIRF error analysis is carried out to calibrate the utility of the ab initio method for this application. In the course of examining these properties, it has been useful to assign the vibrational modes of CHCl2CF3 (HCFC-123) and to reassign some of the vibrational modes of CHF2CH3 (HFC-152a), CF3CH3 (HFC-143a), and CF3CHF2 (HFC- 125). To accomplish this, experimental Raman spectra and ab initio computation of Raman intensities of these molecules are carried out. Structural trends in atomic charges and infrared intensities in the entire fluoroethane series are examined through the use of atomic polar tensor (APT) analysis. A specific sum rule for the total absolute infrared intensity and relationships to the degree of halogen substitution and structure are developed, that distinguish between absolute-infrared-intensity behavior among isomers. Dipole moments from APT components are found to be in essential agreement with experiment. The atmospheric lifetimes of the CFC substitutes are indirectly examined through the ab initio analysis of barrier heights of the primary degradation reaction, with the hydroxyl radical, in the atmosphere. Energies, geometries, and vibrational frequencies of the transition states and products of these reactions are also examined.

  8. Triplet-triplet exciton interactions and delayed fluorescence in single-wall carbon nanotubes

    NASA Astrophysics Data System (ADS)

    Hertel, Tobias; Spath, Florian; Stich, Dominik; Kraus, Hannes; Sperlich, Andreas; Dyakonov, Vladimir

    2013-03-01

    We present pump-probe-, time-correlated single photon counting and spin-sensitive photoluminescence studies of semiconducting single-wall carbon nanotubes (SWNTs) which unambiguously identify triplet-triplet annihilation as the mechanism underlying a long-lived delayed fluorescence (DF) signal. DF decays with a t - 0 . 9 power-law, characteristic of diffusion-limited annihilation reactions in 1-dimensional systems. The experiments allow to determine triplet diffusion constants in SWNTs to be on the order of 1cm2s-1 and the triplet lifetime which is found to be 60 +/- 30 ?s . The experiments indicate that the rate of diffusion-limited photo-reactions, here exemplified by triplet-triplet annihilation, can be reduced by one-dimensional confinement. A comparison of optical transients in aqueous and organic solvent environments also indicates how polaron pair dynamics can be influenced by the environment.

  9. Spin-triplet superconductivity in Sr2RuO4 probed by andreev reflection

    PubMed

    Laube; Goll; Lohneysen; Fogelstrom; Lichtenberg

    2000-02-14

    The superconducting gap function of Sr2RuO4 was investigated by means of quasiparticle reflection and transmission at the normal conductor-superconductor interface of Sr2RuO4-Pt point contacts. We found two distinctly different types of dV/dI vs V spectra either with a double-minimum structure or with a zero-bias conductance anomaly. Both types of spectra are expected in the limit of high and low transparency, respectively, of the interface barrier between a normal metal and a spin-triplet superconductor. Together with the temperature dependence of the spectra this result strongly supports a spin-triplet superconducting order parameter for Sr2RuO4. PMID:11017576

  10. Traces in ion yields and electron spectra of the formation of Ar inner-shell hollow states by free-electron lasers

    NASA Astrophysics Data System (ADS)

    Wallis, A. O. G.; Banks, H. I. B.; Emmanouilidou, A.

    2015-06-01

    We explore the formation of Ar hollow states with two or three inner-shell holes by free-electron-laser radiation. We find that even-charged Ar ion states can be more populated than odd-charged Ar ion states. This depends on the pulse intensity and the number of energetically accessible inner-shell holes. Fully accounting for fine structure, we demonstrate that one-electron spectra bear the imprints of Ar hollow states with two inner-shell holes. Moreover, we show how the Auger spectra of these hollow states can be extracted from two-electron coincidence spectra.

  11. Graphene as a tunable THz reservoir for shaping the Mollow triplet of an artificial atom via plasmonic effects

    E-print Network

    Ebrahim Forati; George W. Hanson; Stephen Hughes

    2014-07-26

    Using a realistic quantum master equation we show that the resonance fluorescence spectra of a two-level artificial atom (quantum dot) can be tuned by adjusting its photonic local density of states via biasing of one or more graphene monolayers. The structured photon reservoir is included using a photon Green function theory which fully accounts for the loss and dispersion. The field-driven Mollow triplet spectrum can be actively controlled by the graphene bias in the THz frequency regime. We also consider the effect of a dielectric support environment, and multiple graphene layers, on the emitted fluorescence. Finally, thermal bath effects are considered and shown to be important for low THz frequencies.

  12. Organic triplet emissions of arylacetylide moieties harnessed through coordination to [Au(PCy(3))]+. Effect of molecular structure upon photoluminescent properties.

    PubMed

    Chao, Hsiu-Yi; Lu, Wei; Li, Yanqin; Chan, Michael C W; Che, Chi-Ming; Cheung, Kung-Kai; Zhu, Nianyong

    2002-12-11

    A family of mono- and binuclear Cy(3)P-supported gold(I) complexes containing various pi-conjugated linear arylacetylide ligands, including the two homologous series (Cy(3)P)Au(Ctbd1;CC(6)H(4))(n)()(-)(1)(Ctbd1;CPh) and (Cy(3)P)Au(Ctbd1;CC(6)H(4))(n)()Ctbd1;CAu(PCy(3)) (n = 1-4), have been prepared. X-ray crystal analyses revealed no intermolecular aurophilic interactions in their crystal lattice. The lowest-energy singlet transitions are predominately intraligand in nature and exhibit both phenyl and acetylenic (1)(pipi) character. Strong photoluminescence is detected in solid and solution states under ambient conditions, with lifetimes in the microsecond regime. For complexes with a single arylacetylide group, only phosphorescence from the arylacetylide (3)(pipi) state is observed. Vibrational spacings in the solid-state emission spectra can be attributed to a combination of phenyl ring deformation and symmetric phenyl ring and Ctbd1;C stretches. Additional delayed-fluorescence emission is recorded for complexes with multiple p-arylacetylide units, and this is attributed to a triplet-triplet annihilation process. The phosphorescence energy of these complexes are readily modified by altering the length of the conjugated arylacetylide system, while the intensity of phosphorescence relative to fluorescence decreases when the p-arylacetylide chain is elongated. Information regarding the nature and relative energies of arylacetylide singlet and triplet excited states has been derived from the two homologous series and extrapolated to polymeric arylacetylide species. The (3)(pipi) excited-state reduction potentials E degrees [Au(+)/Au] (Au = 1a, 2, and 4) are estimated to be -1.80, -1.28, and -1.17 V versus SSCE, respectively. PMID:12465981

  13. DNA triplet repeat expansion and mismatch repair.

    PubMed

    Iyer, Ravi R; Pluciennik, Anna; Napierala, Marek; Wells, Robert D

    2015-06-01

    DNA mismatch repair is a conserved antimutagenic pathway that maintains genomic stability through rectification of DNA replication errors and attenuation of chromosomal rearrangements. Paradoxically, mutagenic action of mismatch repair has been implicated as a cause of triplet repeat expansions that cause neurological diseases such as Huntington disease and myotonic dystrophy. This mutagenic process requires the mismatch recognition factor MutS? and the MutL? (and/or possibly MutL?) endonuclease, and is thought to be triggered by the transient formation of unusual DNA structures within the expanded triplet repeat element. This review summarizes the current knowledge of DNA mismatch repair involvement in triplet repeat expansion, which encompasses in vitro biochemical findings, cellular studies, and various in vivo transgenic animal model experiments. We present current mechanistic hypotheses regarding mismatch repair protein function in mediating triplet repeat expansions and discuss potential therapeutic approaches targeting the mismatch repair pathway. PMID:25580529

  14. TRIO (Triplet Ionospheric Observatory) Mission

    NASA Astrophysics Data System (ADS)

    Lee, D.; Seon, J.; Jin, H.; Kim, K.; Lee, J.; Jang, M.; Pak, S.; Kim, K.; Lin, R. P.; Parks, G. K.; Halekas, J. S.; Larson, D. E.; Eastwood, J. P.; Roelof, E. C.; Horbury, T. S.

    2009-12-01

    Triplets of identical cubesats will be built to carry out the following scientific objectives: i) multi-observations of ionospheric ENA (Energetic Neutral Atom) imaging, ii) ionospheric signature of suprathermal electrons and ions associated with auroral acceleration as well as electron microbursts, and iii) complementary measurements of magnetic fields for particle data. Each satellite, a cubesat for ion, neutral, electron, and magnetic fields (CINEMA), is equipped with a suprathermal electron, ion, neutral (STEIN) instrument and a 3-axis magnetometer of magnetoresistive sensors. TRIO is developed by three institutes: i) two CINEMA by Kyung Hee University (KHU) under the WCU program, ii) one CINEMA by UC Berkeley under the NSF support, and iii) three magnetometers by Imperial College, respectively. Multi-spacecraft observations in the STEIN instruments will provide i) stereo ENA imaging with a wide angle in local times, which are sensitive to the evolution of ring current phase space distributions, ii) suprathermal electron measurements with narrow spacings, which reveal the differential signature of accelerated electrons driven by Alfven waves and/or double layer formation in the ionosphere between the acceleration region and the aurora, and iii) suprathermal ion precipitation when the storm-time ring current appears. In addition, multi-spacecraft magnetic field measurements in low earth orbits will allow the tracking of the phase fronts of ULF waves, FTEs, and quasi-periodic reconnection events between ground-based magnetometer data and upstream satellite data.

  15. Phenomenology of a lepton triplet

    SciTech Connect

    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

    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.

  16. Theoretical investigation of the relative stabilities of singlet and triplet disulfides

    NASA Astrophysics Data System (ADS)

    Ferris, Kim. F.; Franz, James A.; Sosa, Carlos P.; Bartlett, Rodney J.

    1991-10-01

    Ab initio molecular orbital calculations have been performed on the singlet ( 1A) and triplet ( 3A u) states of hydrogen persulfide (HSSH) at the SCF and post-SCF levels using a double zeta basis set augmented with polarization functions. The relative energies for this system were computed by many-body perturbation theory (MBPT) and coupled-cluster (CC) methods, indicating that the singlet and triplet states are both lower in energy than the isolated HS fragments. Structural information for 1[HSSH] determined at the SCF and post-SCF levels are in good agreement with experiment. The triplet state is very weakly bound (<5 kcal/mol) and lies approximately 50 kcal/mol above the singlet state.

  17. Final-state screening effect in the 3s photoemission spectra of Mn and Fe insulating compounds

    Microsoft Academic Search

    Gey-Hong Gweon; Je-Geun Park; S.-J. Oh

    1993-01-01

    The satellite structures of 3s core-level photoemission spectra of Mn and Fe dihalides and mono-oxides have been studied systematically. We found that exchange splitting between 3s holes and 3d electrons, intrashell electron correlation, and final-state screening (charge-transfer satellite) effects all contribute to their satellite structures. We extended the existing model of 2p core-hole satellite structures for transition-metal compounds [Park et

  18. Theoretical study of some bis-verdazyl diradicals: singlet triplet energy gap

    NASA Astrophysics Data System (ADS)

    Chung, Gyusung; Lee, Duckhwan

    2001-12-01

    The bis-verdazyl diradical (BVD) system is closely examined by using the multiconfiguration wavefunctions as well as the density functional theory (DFT). The totally symmetric singlet ground state turns out to have strong multiconfiguration character at all levels of theory. The singlet ground state takes on the planar structure while the most stable triplet state corresponds to the twisted form. The MCSCF+MCQDPT2 calculations are shown to be sufficient to predict the singlet-triplet energy gap which is insensitive to the electronic characters of the ring substituents.

  19. Nuclear Overhauser effect (NOE) enhancement of 11B NMR spectra of borane adducts in the solid state.

    PubMed

    Ashbrook, Sharon E; Dowell, Nicholas G; Prokes, Ivan; Wimperis, Stephen

    2006-05-31

    A strong 11B {1H} nuclear Overhauser effect (NOE) enhancement can be observed in solid-state 11B NMR spectra of borane adducts, yielding fractional enhancements, fI{S} = (I - I0)/I0, of the magic angle spinning (MAS) NMR signal of up to 155%. This is an interesting and unusual observation as 11B (spin I = 3/2) is a quadrupolar nucleus and the corresponding NOE is completely absent in solution. More generally, it shows that the NOE may have a wider role to play in solid-state NMR studies of dynamics than has been envisaged hitherto. PMID:16719446

  20. Restricted active space calculations of L-edge X-ray absorption spectra: From molecular orbitals to multiplet states

    NASA Astrophysics Data System (ADS)

    Pinjari, Rahul V.; Delcey, Mickaël G.; Guo, Meiyuan; Odelius, Michael; Lundberg, Marcus

    2014-09-01

    The metal L-edge (2p ? 3d) X-ray absorption spectra are affected by a number of different interactions: electron-electron repulsion, spin-orbit coupling, and charge transfer between metal and ligands, which makes the simulation of spectra challenging. The core restricted active space (RAS) method is an accurate and flexible approach that can be used to calculate X-ray spectra of a wide range of medium-sized systems without any symmetry constraints. Here, the applicability of the method is tested in detail by simulating three ferric (3d5) model systems with well-known electronic structure, viz., atomic Fe3+, high-spin [FeCl6]3- with ligand donor bonding, and low-spin [Fe(CN)6]3- that also has metal backbonding. For these systems, the performance of the core RAS method, which does not require any system-dependent parameters, is comparable to that of the commonly used semi-empirical charge-transfer multiplet model. It handles orbitally degenerate ground states, accurately describes metal-ligand interactions, and includes both single and multiple excitations. The results are sensitive to the choice of orbitals in the active space and this sensitivity can be used to assign spectral features. A method has also been developed to analyze the calculated X-ray spectra using a chemically intuitive molecular orbital picture.

  1. Restricted active space calculations of L-edge X-ray absorption spectra: From molecular orbitals to multiplet states

    SciTech Connect

    Pinjari, Rahul V.; Delcey, Mickaël G.; Guo, Meiyuan; Lundberg, Marcus, E-mail: marcus.lundberg@kemi.uu.se [Department of Chemistry - Ångström Laboratory, Uppsala University, SE-751 20 Uppsala (Sweden); Odelius, Michael [Department of Physics, Stockholm University, AlbaNova University Center, SE-106 91 Stockholm (Sweden)

    2014-09-28

    The metal L-edge (2p ? 3d) X-ray absorption spectra are affected by a number of different interactions: electron-electron repulsion, spin-orbit coupling, and charge transfer between metal and ligands, which makes the simulation of spectra challenging. The core restricted active space (RAS) method is an accurate and flexible approach that can be used to calculate X-ray spectra of a wide range of medium-sized systems without any symmetry constraints. Here, the applicability of the method is tested in detail by simulating three ferric (3d{sup 5}) model systems with well-known electronic structure, viz., atomic Fe{sup 3+}, high-spin [FeCl{sub 6}]{sup 3?} with ligand donor bonding, and low-spin [Fe(CN){sub 6}]{sup 3?} that also has metal backbonding. For these systems, the performance of the core RAS method, which does not require any system-dependent parameters, is comparable to that of the commonly used semi-empirical charge-transfer multiplet model. It handles orbitally degenerate ground states, accurately describes metal-ligand interactions, and includes both single and multiple excitations. The results are sensitive to the choice of orbitals in the active space and this sensitivity can be used to assign spectral features. A method has also been developed to analyze the calculated X-ray spectra using a chemically intuitive molecular orbital picture.

  2. Triplet-triplet exciton dynamics in single-walled carbon nanotubes

    NASA Astrophysics Data System (ADS)

    Stich, Dominik; Späth, Florian; Kraus, Hannes; Sperlich, Andreas; Dyakonov, Vladimir; Hertel, Tobias

    2014-02-01

    Semiconducting single-walled carbon nanotubes (SWNTs) are considered as building blocks for novel optoelectronic and photonic devices. Energy transport, dissipation and nonlinear optical properties of such devices depend critically on the dynamics of singlet and triplet excitons. However, little is known about triplet excitons in SWNTs despite their important role in photovoltaic, photoelectric and other applications. We present pump-probe and spin-sensitive photoluminescence studies of semiconducting SWNTs that allow the determination of the quantum yield of triplet formation (5 +/- 2%), the triplet lifetime (30 +/- 10 µs) and the triplet exciton size (0.65 nm). Triplet-triplet annihilation is also found to induce delayed fluorescence. The power-law decay of pump-probe and time-resolved photoluminescence signals is characteristic of diffusion-limited annihilation in one-dimensional systems and allows an estimation of the triplet diffusion constant of 0.1 cm2 s-1. This work suggests that exciton annihilation in SWNTs is reduced by one-dimensional confinement of diffusive exciton motion.

  3. Triplet energies and excimer formation in meta- and para-linked carbazolebiphenyl matrix materials.

    PubMed

    Bagnich, Sergey A; Rudnick, Alexander; Schroegel, Pamela; Strohriegl, Peter; Köhler, Anna

    2015-06-28

    We present a spectroscopic investigation on the effect of changing the position where carbazole is attached to biphenyl in carbazolebiphenyl (CBP) on the triplet state energies and the propensity to excimer formation. For this, two CBP derivatives have been prepared with the carbazole moieties attached at the (para) 4- and 4(')-positions (pCBP) and at the (meta) 3- and 3(')-positions (mCBP) of the biphenyls. These compounds are compared to analogous mCDBP and pCDBP, i.e. two highly twisted carbazoledimethylbiphenyls, which have a high triplet energy at about 3.0?eV and tend to form triplet excimers in a neat film. This torsion in the structure is associated with localization of the excited state onto the carbazole moieties. We find that in mCBP and pCBP, excimer formation is prevented by localization of the triplet excited state onto the central moiety. As conjugation can continue from the central biphenyls into the nitrogen of the carbazole in the para-connected pCBP, emission involves mainly the benzidine. By contrast, the meta-linkage in mCBP limits conjugation to the central biphenyl. The associated shorter conjugation length is the reason for the higher triplet energy of 2.8?eV in mCBP compared with the 2.65?eV in pCBP. PMID:25987578

  4. Electron energy spectra of H{sup {minus}} autodetaching states resulting from collisions of H{sup {minus}} with He at 1 keV

    SciTech Connect

    Kimura, M. [Argonne National Lab., IL (United States); Sato, H. [Argonne National Lab., IL (United States)]|[Rice Univ., Houston, TX (United States). Dept. of Physics; Hino, K.; Matsuzawa, M. [Univ. of Electro-Communications, Chofu, Tokyo (Japan). Dept. of Applied Physics and Chemistry

    1995-06-01

    Electron energy spectra for H{sup {minus}} autodetaching states resulting from collisions H{sup {minus}} with He at 1 keV are rigorously calculated by including couplings between doubly excited states and continuum states and their interference with direct detachment processes. An energy sampling procedure, based on the Gauss quadratures, is used to discretize continuum states. The present theoretical result, for the first time, clarifies mechanisms of excitation to doubly excited states, quantitatively reproduces the experimental spectra first observed by Risley and Geballe in 1974, separates the contributions from each of three autodetaching states, and identifies the cause of the interference between autodetaching and direct-detaching excitation channels.

  5. Spin orbit scattering effect on long-range odd frequency triplet pairing in ferromagnet/superconductor bilayers

    NASA Astrophysics Data System (ADS)

    Rachataruangsit, T.; Yoksan, S.

    2007-12-01

    A formulation of triplet proximity effect in a ferromagnet/superconductor bilayer based on the de Gennes correlation function method is presented by extending the Takahashi-Tachiki theory. The inhomogeneous in-plane spiral magnetic order is employed in this approach the superconducting order parameter is a conventional spin singlet s-wave pairing, and the induced triplet pair amplitude arises as a result of the broken time-reversal invariance due to the presence of the rotating exchange field. A new type of triplet condensate still possesses the s-wave state but the symmetry requires an odd frequency parity. We find that the inhomogeneous exchange interaction leads to the appearance of the long-range odd frequency triplet pair amplitude, and the inclusion of the spin orbit scattering affects both short-range and long-range triplet components. The superconducting critical temperature of the diffusive ferromagnet/superconductor sandwiches is determined from the secular equation of the linearized gap equation in order to investigate the behavior of the induced triplet pairing. It is found that the induced long-range triplet component exists which arises from the modulation of the in-plane pair amplitudes in the transverse direction. Moreover, the possibility of the cryptoferromagnetic state is demonstrated in favor of superconductivity and this may explain a possible origin of the magnetically dead layer.

  6. Triplet-Exciton Generation Mechanism in a New Soluble (Red-Phase) Polydiacetylene

    Microsoft Academic Search

    G. Lanzani; G. Cerullo; M. Zavelani-Rossi; S. de Silvestri; Davide Comoretto; Gianfranco Musso; Giovanna Dellepiane

    2001-01-01

    The time scale of covalent state relaxation and singlet fission into triplet pairs is determined in a solution of isolated polydiacetylene chains showing a remarkably sharp excitonic transition by applying the transient transmission difference spectroscopy technique with sub-10 fs optical pulses. Photoexcitation into the band of ionic states is followed by a branching within the first 100 fs which populates

  7. Excitation of {sup 1}S and {sup 3}S Metastable Helium Atoms to Doubly Excited States

    SciTech Connect

    Alagia, M. [CNR-ISMN Sezione Roma, Piazzale A. Moro 5, I-00185 Roma (Italy); Laboratorio Nazionale TASC, CNR-INFM, I-34012 Trieste (Italy); Coreno, M. [CNR-IMIP, Montelibretti, I-00016 Roma (Italy); Farrokhpour, H.; Omidyan, R.; Tabrizchi, M. [Department of Chemistry, Isfahan University of Technology, Isfahan 84156-83111 (Iran, Islamic Republic of); Franceschi, P. [Dipartimento di Fisica, Universita di Trento, I-38050 Povo (Tunisia) (Italy); Mihelic, A.; Zitnik, M. [Jozef Stefan Institute, P.O. Box 3000, SI-1001 Ljubljana (Slovenia); Moise, A.; Prince, K. C.; Richter, R. [Sincrotrone Trieste, in Area Science Park, I-34012 Basovizza, Trieste (Italy); Soederstroem, J. [Department of Physics, Uppsala University, Box 530, S-75121 Uppsala (Sweden); Synchrotron SOLEIL, l'Orme des Merisiers, Saint-Aubin, BP 48, F-91192 Gif-sur-Yvette Cedex (France); Stranges, S. [Dipartimento di Chimica, Universita'La Sapienza', I-00185 Roma (Italy); Laboratorio Nazionale TASC, CNR-INFM, I-34012 Trieste (Italy)

    2009-04-17

    We present spectra of triplet and singlet metastable helium atoms resonantly photoexcited to doubly excited states. The first members of three dipole-allowed {sup 1,3}P{sup o} series have been observed and their relative photoionization cross sections determined, both in the triplet (from 1s2s {sup 3}S{sup e}) and singlet (from 1s2s {sup 1}S{sup e}) manifolds. The intensity ratios are drastically different with respect to transitions from the ground state. When radiation damping is included the results for the singlets are in agreement with theory, while for triplets spin-orbit interaction must also be taken into account.

  8. Delayed fluorescence from upper excited singlet states of aromatic ketones

    NASA Astrophysics Data System (ADS)

    Nickel, Bernhard; Roden, Gabriele

    1980-09-01

    With liquid solutions of the aromatic ketones anthraquinone and xanthone, a P-type delayed fluorescence from upper excited singlet states, resulting from triplet-triplet annihilation, has been observed. Some peculiarities of the triplet-triplet annihilation of aromatic ketones are discussed.

  9. Nonunitary triplet pairing in the centrosymmetric superconductor LaNiGa2.

    PubMed

    Hillier, A D; Quintanilla, J; Mazidian, B; Annett, J F; Cywinski, R

    2012-08-31

    Muon spin rotation and relaxation experiments on the centrosymmetric intermetallic superconductor LaNiGa2 are reported. The appearance of spontaneous magnetic fields coincides with the onset of superconductivity, implying that the superconducting state breaks time reversal symmetry, similarly to noncentrosymmetric LaNiC2. Only four triplet states are compatible with this observation, all of which are nonunitary triplets. This suggests that LaNiGa2 is the centrosymmetric analogue of LaNiC2. We argue that these materials are representatives of a new family of paramagnetic nonunitary superconductors. PMID:23002872

  10. 3He-R : A topological s± superfluid with triplet pairing

    NASA Astrophysics Data System (ADS)

    Tzen Ong, T.; Coleman, Piers

    2014-11-01

    We show that when spin and orbital angular momenta are entangled by spin-orbit coupling, this transforms a topological spin-triplet superfluid/superconductor state, such as 3He-B , into a topological s± state, with nontrivial gapless edge states. Similar to 3He-B , the s± state also minimizes on-site Coulomb repulsion for weak to moderate interactions. A phase transition into a topological d -wave state occurs for sufficiently strong spin-orbit coupling.

  11. Outcomes of Triplets reduced to Twins versus non-reduced Triplet Pregnancies

    PubMed Central

    Raval, Donna B; Naglak, Mary; Iqbal, Sara N; Ramsey, Patrick S; Craparo, Frank

    2015-01-01

    Introduction This study examined the outcomes of triplet pregnancies selectively reduced to twin pregnancies, compared with non-reduced triplet pregnancies using a standardized approach. Material and Methods This study is an observational retrospective study of all women who presented to the Fetal Diagnostic Center between 1999–2009, had triplet pregnancies in the first trimester, received prenatal care and delivered at Abington Memorial Hospital. Data analysis was performed with SPPS version 15 for Windows using analysis of variance and Fisher’s Exact test. Results 132 triplet pregnancies were identified. In the reduced group (n = 30) compared to the non-reduced triplet group (n = 102) average gestational age of delivery was longer 34.6 weeks versus 31.2 weeks gestation (P = <0.0005) and days in hospital were less 9.0 versus 26.7 days (P = .001). There was a significantly lower incidence of gestational diabetes and preterm labor in reduced pregnancies. Rate of loss, defined as delivery less than 24 weeks, were similar [3.3% versus 4.9%]. Discussion Women electing to reduce a triplet pregnancy to twins have higher gestational ages at delivery, lower rates of gestational diabetes and preterm labor, and spent fewer days in hospital than non-reduced triplet pregnancies.

  12. Phenomenology of a SU(2) triplet Higgs.

    E-print Network

    Sabio Vera, Agustin

    ar X iv :h ep -p h/ 03 07 04 5v 1 3 Ju l 2 00 3 PHENOMENOLOGY OF A SU(2) TRIPLET HIGGS ? AGUST?´N SABIO VERA Cavendish Laboratory, University of Cambridge, Madingley Road, CB3 0HE, Cambridge, U.K. We study the Renormalization Group (RG) evolution... of the couplings in a model with a real SU(2) triplet in the Higgs sector. Insisting that the model remain valid up to 1 TeV we show that it is possible for there to be no light Higgs bosons without any otherwise dramatic deviation from the physics of the Standard...

  13. BVRI Surface Photometry of Isolated Galaxy Triplets

    NASA Astrophysics Data System (ADS)

    Hernández-Toledo, H. M.; Méndez-Hernández, H.; Aceves, H.; Olguín, L.

    2011-03-01

    Optical broadband BVRI observations of 54 galaxies selected from the Catalog of Isolated Triplets of Galaxies in the Northern Hemisphere have been carried out at San Pedro Mártir National Observatory to evaluate their photometric and morphological properties. We complement our analysis with Two-Micron All Sky Survey (2MASS) and Sloan Digital Sky Survey (SDSS) images and look for signatures likely related to interactions/mergers. We report apparent/absolute BVRI magnitudes and colors for the 54 galaxies. The membership of these galaxies is re-evaluated by imposing a reasonable condition of concordant redshifts upon the original selection criteria, rendering a final sample of 34 galaxies in 13 triplets, 12 galaxies in close pairs, and 8 galaxy outliers. The triplets are spiral-dominated systems in different dynamical stages from loosely interacting to almost merged objects. The incidence fraction of features likely associated with interactions is ~56%, similar to those found in northern and southern compact groups. The average fraction of bars is 35% with a mean value of maximum bar ellipticity epsilonmax ? 0.4. Bars are hosted in the late-type triplet spirals, almost twice more than in early-type spirals. The global fraction of rings is 20%, all in the late-type components. The overdensity of triplets with respect to the background and their current dynamical status, as devised from our estimate of their dynamical parameters, namely the harmonic radius RH , velocity dispersion ?, dimensionless crossing time H 0? c , and virial mass MV , appear to be sufficient to favor galaxy transformations similar to those seen in dense groups and clusters. By contrast, the lower fraction of bonafide ellipticals and the relatively higher fraction of late-type spirals make these triplets essentially different from the Hickson Compact Groups and more representative of the field. A modest 1.6 enhancement factor in the optical luminosity of the late-type triplet components relative to an isolated galaxy control sample is also interpreted as consistent with interactions in physically bounded aggregates. Our results lead us to suggest that non-negligible populations of physical triplets might be found in complete and well-observed samples. We provide individual mosaics for the 54 galaxies containing (1) logarithmic-scaled R-band images, (2) R-band sharp/filtered images, (3) (B - I) color index maps, (4) RGB images from the SDSS database, (5) co-added J + H + K images generated from the 2MASS archives that were also sharp/filtered, and (6) epsilon, position angle radial profiles from a surface photometry analysis of (a) the R band and (b) the co-added near-infrared images, all used for the present analysis.

  14. Conductance spectroscopy of spin-triplet superconductors.

    PubMed

    Asano, Yasuhiro; Tanaka, Yukio; Golubov, Alexander A; Kashiwaya, Satoshi

    2007-08-10

    We propose a novel experiment to identify the symmetry of superconductivity on the basis of theoretical results for differential conductance of a normal metal connected to a superconductor. The proximity effect from the superconductor modifies the conductance of the remote current depending remarkably on the pairing symmetry: spin singlet or spin triplet. The clear-cut difference in the conductance is explained by symmetry of Cooper pairs in a normal metal with respect to frequency. In the spin-triplet case, the anomalous transport is realized due to an odd-frequency symmetry of Cooper pairs. PMID:17930859

  15. Photochemistry of Furyl- and Thienyldiazomethanes: Spectroscopic Characterization of Triplet 3-Thienylcarbene

    PubMed Central

    Pharr, Caroline R.; Kopff, Laura A.; Bennett, Brian; Reid, Scott A.; McMahon, Robert J.

    2014-01-01

    Photolysis (? > 543 nm) of 3-thienyldiazomethane (1), matrix isolated in Ar or N2 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 C5H4S or C5H4O 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

  16. Triplet correlation functions in the Lennard-Jones fluid: Tests against molecular dynamics simulations

    NASA Astrophysics Data System (ADS)

    McNeil, William J.; Madden, William G.; Haymet, A. D. J.; Rice, Stuart A.

    1983-01-01

    A recent theory of Haymet, Rice, and Madden (HRM) for the pair and triplet correlation functions is tested at liquid state densities against new molecular dynamics results for the Lennard-Jones (12,6) fluid. The HRM integral equation, based on the Born-Green equation and a topological reduction of the diagrammatic expansion of the triplet correlation function, has been solved for a high temperature state (T*=2.74, ?*=0.80) and is found to give triplet correlation functions in good agreement with the molecular dynamics results. For a lower-temperature state (T*=0.73, ?*=0.85), where numerical difficulties have thus far frustrated attempts to obtain a self-consistent solution of the HRM integral equation, direct tests of the HRM closure are made using molecular dynamics pair correlation functions to evaluate the diagrams. Although some striking qualitative features of the triplet correlations are correctly described by the HRM closure for this low-temperature state, the HRM approach is not in quantitative agreement with the molecular dynamics results. Test calculations indicate that the principle source of these errors is the neglect of important higher-order diagrams for the triplet correlation function. A reorganization of the diagrammatic series is suggested which may identify the most important of these neglected diagrams. Additional computer simulation results are also reported for the purely repulsive Weeks-Chandler-Andersen (WCA) ``reference'' fluid and for the underlying hard sphere fluid. The similarity of the pair structures of these fluids, noted by WCA, is also found to hold with high accuracy for the triplet structures. It is suggested that these similarities may be exploited in applying the methods of HRM to the hard sphere fluid.

  17. EMITTING ELECTRONS SPECTRA AND ACCELERATION PROCESSES IN THE JET OF Mrk 421: FROM THE LOW STATE TO THE GIANT FLARE STATE

    SciTech Connect

    Yan Dahai; Zhang Li; Fan Zhonghui; Zeng Houdun [Department of Physics, Yunnan University, Kunming 650091, Yunnan (China); Yuan Qiang, E-mail: lizhang@ynu.edu.cn [Key Laboratory of Particle Astrophysics, Institute of High Energy Physics, Chinese Academy of Sciences, Beijing 100049 (China)

    2013-03-10

    We investigate the electron energy distributions (EEDs) and the acceleration processes in the jet of Mrk 421 through fitting the spectral energy distributions (SEDs) in different active states in the frame of a one-zone synchrotron self-Compton model. After assuming two possible EEDs formed in different acceleration models: the shock-accelerated power law with exponential cut-off (PLC) EED and the stochastic-turbulence-accelerated log-parabolic (LP) EED, we fit the observed SEDs of Mrk 421 in both low and giant flare states using the Markov Chain Monte Carlo method which constrains the model parameters in a more efficient way. The results from our calculations indicate that (1) the PLC and LP models give comparably good fits for the SED in the low state, but the variations of model parameters from low state to flaring can be reasonably explained only in the case of the PLC in the low state; and (2) the LP model gives better fits compared to the PLC model for the SED in the flare state, and the intra-day/night variability observed at GeV-TeV bands can be accommodated only in the LP model. The giant flare may be attributed to the stochastic turbulence re-acceleration of the shock-accelerated electrons in the low state. Therefore, we may conclude that shock acceleration is dominant in the low state, while stochastic turbulence acceleration is dominant in the flare state. Moreover, our result shows that the extrapolated TeV spectra from the best-fit SEDs from optical through GeV with the two EEDs are different. It should be considered with caution when such extrapolated TeV spectra are used to constrain extragalactic background light models.

  18. 1H NMR z-spectra of acetate methyl in stretched hydrogels: Quantum-mechanical description and Markov chain Monte Carlo relaxation-parameter estimation

    NASA Astrophysics Data System (ADS)

    Shishmarev, Dmitry; Chapman, Bogdan E.; Naumann, Christoph; Mamone, Salvatore; Kuchel, Philip W.

    2015-01-01

    The 1H NMR signal of the methyl group of sodium acetate is shown to be a triplet in the anisotropic environment of stretched gelatin gel. The multiplet structure of the signal is due to the intra-methyl residual dipolar couplings. The relaxation properties of the spin system were probed by recording steady-state irradiation envelopes ('z-spectra'). A quantum-mechanical model based on irreducible spherical tensors formed by the three magnetically equivalent spins of the methyl group was used to simulate and fit experimental z-spectra. The multiple parameter values of the relaxation model were estimated by using a Bayesian-based Markov chain Monte Carlo algorithm.

  19. Collisionally-Mediated Singlet-Triplet Crossing in ˜{a}1A1 CH_2 Revisited: (010) Coupling

    NASA Astrophysics Data System (ADS)

    Le, Anh T.; Hall, Gregory; Sears, Trevor

    2014-06-01

    Methylene, CH2, possesses a ground ˜{X}3B1 ground electronic state and an excited ˜{a}1A1 state only 3150cm-1 higher in energy. The collision-induced singlet-triplet crossing in the gaseous mixtures is important in determining overall reaction rates and chemical behavior. Accidental near-degeneracies between rotational levels of the singlet state and the vibrationally excited triplet state result in a few gateway rotational levels that mediate collision-induced intersystem crossing. The mixed states can be recognized and quantified by deperturbation, knowing the zero-order singlet and triplet energy levels. Hyperfine structure can be used as alternative indicator of singlet-triplet mixing. Non-zero mixing will induce hyperfine splittings intermediate between the unresolved hyperfine structure of pure singlet and the resolvable (?50MHz) splittings of pure triplet, arising from the (I\\cdotS) interaction in the ortho states, where nuclear spin I=1. Collision-induced intersystem crossing rates from the (010) state are comparable to those for (000), yet the identities and characters of the presumed gateway states are unknown. A new spectrometer is under construction to investigate triplet mixing rotational levels of ˜{a}1A1(010) by sub-Doppler measurements of perturbation-induced hyperfine splittings. Their observation will permit the identification of gateway states and quantification of the degree of triplet contamination of the singlet wavefunction. Progress in the measurements and the analysis of rotational energy transfer in (010) will be reported. Acknowledgments: Work at Brookhaven National Laboratory was carried out under Contract No. DE-AC02-98CH10886 with the U.S. Department of Energy and supported by its Office of Basic Energy Sciences, Division of Chemical Sciences, Geosciences and Biosciences. C.-H. Chang, G. E. Hall, T. J. Sears, J. Chem. Phys 133, 144310(2010) G. E. Hall, A. V. Komissarov, and T. J. Sears, J. Phys. Chem. A 108 7922-7927 (2004)

  20. Quantum Properties of Single-Domain Triplet Superconductors

    NASA Astrophysics Data System (ADS)

    Gulian, Armen M.; Wood, Kent S.

    2005-08-01

    In absence of external fields the ground state in triplet superconductors with broken time-reversal symmetry is degenerate, corresponding to two values of chirality N. Chirality corresponds to clockwise (N=1) and counter-clockwise (N=-1) spontaneous non-dissipative currents in single-domain superconductors. Interactions lift the degeneracy and yield a possibility of macroscopic quantum tunneling between the chiral states, observable in sufficiently small samples. For an appropriate initial state, coherent oscillations of the order parameter (and simultaneously, orbital and magnetic momentum) should take place with sign alternations of non-dissipative currents. Understanding the details of quantum properties of the ground state is the objective of this work. The method of investigation is in linking the phenomenological description of the superconductor with the spin-boson Hamiltonian approach.

  1. Triplet-excited dye molecules (eosine and methylene blue) quenching by H 2O 2 in aqueous solutions

    Microsoft Academic Search

    V. Yu. Gak; V. A. Nadtochenko; J. Kiwi

    1998-01-01

    The quenching of the triplet-excited dyes eosine and methylene blue (MB) by H2O2 has been studied by laser and steady-state photolysis. The quenching rate constant of the eosine triplet is kq = 2.4 ± 0.3 × 105 (M s)?1 and rate constant of MB quenching with H2O2 was found to be kq = 6.5 ± 0.5 × 105 (M s)?1.

  2. Synthesis of triplet-triplet annihilation upconversion nanocapsules under protective conditions.

    PubMed

    Katta, Kartheek; Busko, Dmitry; Avlasevich, Yuri; Muñoz-Espí, Rafael; Baluschev, Stanislav; Landfester, Katharina

    2015-06-01

    Triplet-triplet annihilation upconversion (TTA-UC) nanocapsules are synthesized under oxygen-protective conditions (i.e., complete darkness and argon atmosphere) by free-radical miniemulsion polymerization. These conditions help to exclude the oxidation of the emitter molecules caused by singlet oxygen, generated during the synthesis at daylight conditions and oxygen-rich environment. Subsequently, keeping all the other experimental conditions the same, samples synthesized at protective conditions demonstrate substantially increased UC efficiency. These experimental facts strongly support the hypothesis that posterior removing of oxygen from TTA-UC nanocapsules is not sufficient to obtain reproducible and sustainable UC results. The schematic representation shows the influence of sunlight on the formation of singlet oxygen and its effect on the triplet-triplet annihilation upconversion process. PMID:25630569

  3. Relative Pose Estimation Using Image Feature Triplets

    NASA Astrophysics Data System (ADS)

    Chuang, T. Y.; Rottensteiner, F.; Heipke, C.

    2015-03-01

    A fully automated reconstruction of the trajectory of image sequences using point correspondences is turning into a routine practice. However, there are cases in which point features are hardly detectable, cannot be localized in a stable distribution, and consequently lead to an insufficient pose estimation. This paper presents a triplet-wise scheme for calibrated relative pose estimation from image point and line triplets, and investigates the effectiveness of the feature integration upon the relative pose estimation. To this end, we employ an existing point matching technique and propose a method for line triplet matching in which the relative poses are resolved during the matching procedure. The line matching method aims at establishing hypotheses about potential minimal line matches that can be used for determining the parameters of relative orientation (pose estimation) of two images with respect to the reference one; then, quantifying the agreement using the estimated orientation parameters. Rather than randomly choosing the line candidates in the matching process, we generate an associated lookup table to guide the selection of potential line matches. In addition, we integrate the homologous point and line triplets into a common adjustment procedure. In order to be able to also work with image sequences the adjustment is formulated in an incremental manner. The proposed scheme is evaluated with both synthetic and real datasets, demonstrating its satisfactory performance and revealing the effectiveness of image feature integration.

  4. Singlet-triplet annihilation of singlet oxygen and triplet xanthene dye molecules in liquid solutions

    SciTech Connect

    Bryukhanov, V.V.; Ketsle, G.A.; Laurinas, V.C.; Levshin, L.V.; Muldakhmetov, Z.M.

    1987-10-01

    This paper presents experimental and theoretical data on the enhancement of delayed fluorescence of eosin and erythrocine molecules in liquid solutions under the action of dissolved oxygen which make it possible to postulate the existence of photophysical processes of singlet-triplet annihilation of singlet oxygen and triplet dye molecules. The study was carried out in a system consisting of a neodymium laser with an optical quantum multipler, a monochromator, and an oscillograph. The solvents used were propanol, acetone, and water.

  5. Nucleon, Delta and Omega excited state spectra at three pion mass values

    E-print Network

    John Bulava; Robert G. Edwards; Bálint Joó; David G. Richards; Eric Engelson; Huey-Wen Lin; Colin Morningstar; Stephen J. Wallace

    2010-11-05

    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.

  6. Nucleon, Delta and Omega excited state spectra at three pion mass values

    SciTech Connect

    John Bulava, Robert G. Edwards, Balint Joo, David G. Richards, Eric Engelson, Huey-Wen Lin, Colin Morningstar, Stephen J. Wallace

    2010-06-01

    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.

  7. Spin-triplet superconductivity in the double-chain Hubbard model with ferromagnetic exchange interaction

    NASA Astrophysics Data System (ADS)

    Shirakawa, T.; Ohta, Y.; Nishimoto, S.

    2007-03-01

    We study possible occurrence of spin-triplet superconductivity in the model of two Hubbard chains coupled with ferromagnetic exchange interaction. We use the analytical bozonization method as well as the numerical exact-diagonalization and density-matrix renormalization group methods. We show that, in the low electron density region, the complete ferromagnetic state occurs and the triplet pairing correlation is most dominant, where we find that the gap function behavior is py-wave like. We also show that, in the high electron density regions, the spin-singlet superconductivity anticipated by the weak coupling analysis is most dominant, where the gap function behavior is dxy-wave like.

  8. Molecular Structure-Intersystem Crossing Relationship of Heavy-Atom-Free BODIPY Triplet Photosensitizers.

    PubMed

    Ji, Shaomin; Ge, Jie; Escudero, Daniel; Wang, Zhijia; Zhao, Jianzhang; Jacquemin, Denis

    2015-06-01

    A thiophene-fused BODIPY chromophore displays a large triplet-state quantum yield (?T = 63.7%). In contrast, when the two thienyl moieties are not fused into the BODIPY core, intersystem crossing (ISC) becomes inefficient and ?T remains low (?T = 6.1%). First-principles calculations including spin-orbit coupling (SOC) were performed to quantify the ISC. We found larger SOC and smaller singlet-triplet energy gaps for the thiophene-fused BODIPY derivative. Our results are useful for studies of the photochemistry of organic chromophores. PMID:25942069

  9. Singlet-to-Triplet Excitations in the Unconventional Spin-Peierls System TiOBr

    SciTech Connect

    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

    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.

  10. Analysis of photon triplet generation in pulsed cascaded parametric down-conversion sources

    E-print Network

    Stephan Krapick; Christine Silberhorn

    2015-06-25

    We analyze the generation rates and preparation fidelities of photon triplet states in pulsed cascaded parametric down-conversion (PDC) under realistic experimental circumstances. As a model system, we assume a monolithically integrated device with negligible interface loss between the two consecutive PDC stages. We model the secondary down-conversion process in terms of a lossy channel and provide a detailed analysis of noise contributions. Taking variable pump powers into account, we estimate the impact of higher-order photon contributions and conversion processes on the achievable coincidence probabilities. At mean photon numbers of $\\langle m\\rangle\\sim0.25$ photons per pulse behind the first PDC stage, we expect around $4.0$ genuine photon triplets per hour. Additionally, we discuss fundamental limitations of our model system as well as feasible improvements to the detectable photon triplet rate.

  11. Analysis of photon triplet generation in pulsed cascaded parametric down-conversion sources

    E-print Network

    Krapick, Stephan

    2015-01-01

    We analyze the generation rates and preparation fidelities of photon triplet states in pulsed cascaded parametric down-conversion (PDC) under realistic experimental circumstances. As a model system, we assume a monolithically integrated device with negligible interface loss between the two consecutive PDC stages. We model the secondary down-conversion process in terms of a lossy channel and provide a detailed analysis of noise contributions. Taking variable pump powers into account, we estimate the impact of higher-order photon contributions and conversion processes on the achievable coincidence probabilities. At mean photon numbers of $\\langle m\\rangle\\sim0.25$ photons per pulse behind the first PDC stage, we expect around $4.0$ genuine photon triplets per hour. Additionally, we discuss fundamental limitations of our model system as well as feasible improvements to the detectable photon triplet rate.

  12. Experimental and Theoretical Study of the Electronic States and Spectra of TeH and TeLi

    NASA Astrophysics Data System (ADS)

    Setzer, K. D.; Fink, E. H.; Alekseyev, A. B.; Liebermann, H.-P.; Buenker, R. J.

    2001-04-01

    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.

  13. Composite spectra: XX. 45 Cancri. Two stars with very similar masses but quite different evolutionary states

    NASA Astrophysics Data System (ADS)

    Griffin, R. E. M.; Griffin, R. F.

    2015-02-01

    From accurate radial-velocity measurements covering 11 circuits of the orbit of the composite-spectrum binary 45 Cnc, together with high-resolution spectroscopy spanning nearly 3 circuits, we have (i) isolated cleanly the spectrum of the early-type secondary, (ii) classified the component spectra as G8 III and A3 III, (iii) derived the first double-lined orbit for the system and a mass ratio (M_1/M_2) of 1.035 ± 0.01, and (iv) extracted physical parameters for the component stars, deriving the masses and (log) luminosities of the G star and A star as 3.11 and 3.00 M?} R?, and 2.34 and 2.28 L?, respectively, with corresponding uncertainties of ±0.10 M? R? and ±0.09 L?. Since the mass ratio is close to unity, we argue that the more evolved component is unlikely to have been a red giant long enough to have made multiple ascents of the RGB, an argument that is supported somewhat by the rather high eccentricity of the orbit (e = 0.46) and the evolutionary time-scales of the two components, but chiefly by the presence of significant Li I in the spectrum of the cool giant.

  14. Superscars in billiards -- A model for doorway states in quantum spectra

    E-print Network

    S. Å berg; T. Guhr; M. Miski-Oglu; A. Richter

    2008-05-15

    In a unifying way, the doorway mechanism explains spectral properties in a rich variety of open mesoscopic quantum systems, ranging from atoms to nuclei. A distinct state and a background of other states couple to each other which sensitively affects the strength function. The recently measured superscars in the barrier billiard provide an ideal model for an in--depth investigation of this mechanism. We introduce two new statistical observables, the full distribution of the maximum coupling coefficient to the doorway and directed spatial correlators. Using Random Matrix Theory and random plane waves, we obtain a consistent understanding of the experimental data.

  15. Excitonic Excited States and Optical Spectra in Poly(p-Phenylenevinylene) Prepared by Carefully Controlled Thermal Elimination Reaction

    NASA Astrophysics Data System (ADS)

    Fukuda, Takashi; Kubo, Takaya; Takezoe, Hideo; Fukuda, Atsuo

    1992-01-01

    Optically excited excitonic states have been studied in poly(p-phenylenevinylene) films carefully prepared by the sulfonium salt method. The conspicuous vibronic structures in the reflection spectrum together with the steep absorption edge indicate that the conjugation length distribution has a smaller standard deviation than that reported by Rauscher et al. The small deviation also manifests itself in the more clearly resolved vibronic structures in the emission spectra. The photocurrent is excited only near the intrinsic absorption edge and its efficiency is very low. The resonance Raman spectrum does not show any multiphonon lines, and its relative intensity with respect to the emission intensity is considerably weak. Two strong Raman lines appear at 0.146 eV (1176 cm-1) and 0.197 eV (1586 cm-1), which are very close to the phonon energies in the vibronic spectra of emission and reflection, respectively; the transition process can be regarded as charge transfer between the phenylene and the vinylene groups.

  16. Electron paramagnetic resonance line shapes of photoexcited triplets with rotational diffusion

    NASA Astrophysics Data System (ADS)

    Gamliel, Dan; Levanon, Haim

    1992-11-01

    A new line shape formula is developed for magnetic resonance on systems which are initially far from thermal equilibrium. A formalism for treating electron paramagnetic resonance (EPR) of rotationally diffusing molecules is extended to include typical triplet states, in which intramolecular interactions are not very small compared with the Zeeman interaction. The two developments are combined to a new formalism for calculating line shapes of photoexcited triplet states undergoing rotational diffusion. Approximations are made for parts of the calculation, and their range of validity is examined. Simulations based on this theory for randomly oriented samples of chlorophyll a (Chl a) demonstrate the usefulness of the theory in calculating line shapes for both equilibrated and polarized photoexcited EPR triplets undergoing rotational diffusion. In particular we study the effect of anisotropy in the molecular diffusion tensor on the line shapes. A comparison is also made between simulated and experimental line shapes for two expanded porphyrinoids, cadmium-texaphyrin complex (TxP-Cd), and zincoctaethylporphycene (ZnOEPC). Finally, we present a series of dynamic line shapes for the photoexcited triplet state of C60 (buckminsterfullerene), discussing their correspondence with available experimental results.

  17. Quantum beats in crystalline tetracene delayed fluorescence due to triplet pair coherences produced by direct singlet fission.

    PubMed

    Burdett, Jonathan J; Bardeen, Christopher J

    2012-05-23

    A detailed analysis of the oscillations seen in the delayed fluorescence of crystalline tetracene is presented in order to study the mechanism of singlet fission. Three quantum beat frequencies of 1.06 ± 0.05, 1.82 ± 0.05, and 2.92 ± 0.06 GHz are resolved, which are damped on a time scale of 20 ns. The effects of sample morphology, excitation wavelength, and temperature are examined. A density matrix model for singlet fission is developed that quantitatively describes the frequencies, amplitudes, and damping of the oscillations. The model assumes a direct coupling of the initially excited singlet exciton to the triplet pair manifold. There is no electronic coherence between the singlet and triplet pair states, but the rapid singlet decay time of ?200 ps in solution-grown single crystals provides the impulsive population transfer necessary to create a coherent superposition of three zero-field triplet pair states |xx>, |yy>, and |zz> with overall singlet character. This superposition of the three states gives rise to the three quantum beat frequencies seen in the experiment. Damping of the quantum beats results from both population exchange between triplet and singlet manifolds and pure dephasing between the triplet pair states. By lowering the temperature and slowing the SF rate, the visibility of the oscillations decreases. There is no evidence of magnetic dipole-dipole coupling between the product triplets. Our model provides good overall agreement with the data, supporting the conclusion that singlet fission in tetracene proceeds through the "direct" mechanism without strong electronic coupling between the singlet and triplet pair states. PMID:22530591

  18. Satellite spectra for high-lying resonance states of heliumlike chromium and nickel

    SciTech Connect

    Karim, K.R. (Department of Physics, Illinois State University, Normal, IL (USA)); Bhalla, C.P. (Department of Physics, Cardwell Hall, Kansas State University, Manhattan, KS (USA))

    1990-09-15

    We report on the wavelengths and satellite intensity factors of heliumlike nickel and chromium ions undergoing dielectronic recombinations via several high-lying resonance states. We have considered the process 1{ital s}{sup 2}+{epsilon}{ital l}{r arrow}(1{ital s}2{ital lnl}{prime}){sup *}{r arrow}1{ital s}{sup 2}{ital ml}{prime}{prime}+{gamma} for {ital n}=5, 6, 7, and 8 with all possible values of {ital l} and {ital l}{prime}, where {ital n} is the principal quantum number of the outermost electron of the doubly excited intermediate resonance state. The calculations have been performed in the intermediate-coupling scheme using the multiconfiguration Hartree-Fock model.

  19. Fermiophobia in a Higgs triplet model

    SciTech Connect

    Akeroyd, A. G. [Department of Physics and Center for Mathematics and Theoretical Physics, National Central University, Chungli, Taiwan 320, Taiwan (China); NExT Institute and School of Physics and Astronomy, University of Southampton, Highfield, Southampton SO17 1BJ (United Kingdom); Diaz, Marco A.; Romero Maltrana, D. [Departamento de Fisica, Pontificia Universidad Catolica de Chile, Santiago 690441 (Chile); Rivera, Maximiliano A. [Departamento de Fisica, Universidad Tecnica Federico Santa Maria, Casilla 110-V, Valparaiso (Chile)

    2011-05-01

    A fermiophobic Higgs boson can arise in models with an extended Higgs sector, such as models with scalars in an isospin triplet representation. In a specific model with a scalar triplet and spontaneous violation of lepton number induced by a scalar singlet field, we show that fermiophobia is not a fine-tuned situation, unlike in two higgs doublet models. We study distinctive signals of fermiophobia which can be probed at the LHC. For the case of a small Higgs mass, a characteristic signal would be a moderate B(H{yields}{gamma}{gamma}) accompanied by a large B(H{yields}JJ) (where J is a Majoron), the latter being an invisible decay. For the case of a large Higgs mass there is the possibility of dominant H{yields}ZZ, WW and suppressed H{yields}JJ decay modes. In this situation, B(H{yields}ZZ) is larger than B(H{yields}WW), which differs from the SM prediction.

  20. Singlets and triplets in hybrid nanodevices

    NASA Astrophysics Data System (ADS)

    Agranovich, V. M.; Dubovskii, O. A.; La Rocca, G. C.

    2014-05-01

    An organic material thin layer can be used to resonantly absorb light and nonradiatively transfer excitation to an adjacent inorganic quantum well the optical nonlinearities of which can in this way be turned on more efficiently than by direct optical pumping. We theoretically consider this process in a hybrid structure based on crystalline tetracene in which the singlet exciton energy is close to twice the one of a triplet exciton and thermally activated singlet exciton fission into two triplets can be efficient. We investigate how the temperature dependence of the singlet exciton diffusion length affects the functional properties of such hybrid organic-inorganic nanostructures based on tetracene. We show how temperature activated fission opens a new possibility to turn on and off the indirect pumping due to energy transfer from the organic into the inorganic subsystem.

  1. Nonextensive triplet in geological faults system

    E-print Network

    de Freitas, D B; Scheerer, T M; Vilar, C S; Silva, R

    2013-01-01

    The San Andreas fault (SAF) in the USA is one of the most investigated self-organizing systems in nature. In this paper, we studied some geophysical properties of the SAF system in order to analyze the behavior of earthquakes in the context of Tsallis's $q$--Triplet. To that end, we considered 134,573 earthquake events in magnitude interval $2\\leq m<8$, taken from the Southern Earthquake Data Center (SCEDC, 1932 - 2012). The values obtained ("$q$--Triplet"$\\equiv$$\\{$$q$$_{stat}$,$q$$_{sen}$,$q$$_{rel}$$\\}$) reveal that the $q_{stat}$--Gaussian behavior of the aforementioned data exhibit long-range temporal correlations. Moreover, $q_{sen}$ exhibits quasi-monofractal behavior with a Hurst exponent of 0.87.

  2. The protein's role in triplet energy transfer in bacterial reaction centers.

    SciTech Connect

    Laible, P. D.

    1998-08-14

    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]).

  3. Quantum-dot Mollow triplet in a semiconductor cavity-QED system

    NASA Astrophysics Data System (ADS)

    Roy, C.; Hughes, S.

    2012-04-01

    We present a semiconductor quantum optics formalism to study the dynamics of a coherently-driven semiconductor quantum dot interacting with an acoustic phonon bath and a high Q microcavity. A quantum master equation is derived in the polaron frame, where multiphoton and multiphoton effects are included to all orders. As applications of the theory, we study the Mollow triplet of a driven quantum dot in the regime of semiconductor cavity-QED. Pronounced signatures of electron-phonon-photon scattering are observed through excitation-induced dephasing and off-resonant cavity coupling. We also present an effective phonon master in Lindblad form and show example quantum trajectory simulations that help one to understand the features in the Mollow triplet spectra.

  4. [Ca II triplet equivalent widths of spiral galaxy M31 and elliptical galaxy M32].

    PubMed

    Li, T; Deng, L; Zhao, G

    2000-08-01

    The Calcium II triplet (Ca II T) lines in the near infrared spectral region is very important feature for late type stars, which serves as an important metallicity indicator for such stars. This is also true for stellar systems composed mainly of late type stars, such as old stellar clusters and galaxies. In this work, we made observations of the very famous spiral galaxy M31 and its dwarf elliptical companion M32, using the OMR spectrograph attached to the 2.16-meter telescope in Beijing Astronomical Observatory. Near-infrared spectra of the nuclear and disk regions on M31, as well as two slices along the major and the minor axis of M32, are derived. Equivalent widths of the Ca II triplet lines are measured using normal astrophysical spectrum analyzing techniques. The results are fundamental data for these two galaxies, which can be applied to researches for stellar population analysis of these galaxies. PMID:12945350

  5. Satellite spectra from high-lying resonance states for heliumlike Si, Ca, and Ti

    SciTech Connect

    Karim, K.R. (Department of Physics, Illinois State University, Normal, Illinois 61761 (United States)); Bhalla, C.P. (Department of Physics, Kansas State University, Manhattan, Kansas 66506 (United States))

    1992-03-15

    We report on the wavelengths and satellite intensity factors for selected heliumlike ions undergoing dielectronic recombination via several higher-lying resonance states, viz., the 1{ital s}{sup 2}{epsilon}{ital l}{sub {ital c}}{r arrow}1{ital s}2{ital lnl}{prime}{r arrow}1{ital s}{sup 2}{ital ml}{prime}{prime} with {ital n}=5, 6, 7, and 8. The calculations have been performed in the intermediate-coupling scheme using the multiconfiguration Hartree-Fock atomic model.

  6. Twin and Triplet Drugs in Opioid Research

    NASA Astrophysics Data System (ADS)

    Fujii, Hideaki

    Twin and triplet drugs are defined as compounds that contain respectively two and three pharmacophore components exerting pharmacological effects in a molecule. The twin drug bearing the same pharmacophores is a "symmetrical twin drug", whereas that possessing different pharmacophores is a "nonsymmetrical twin drug." In general, the symmetrical twin drug is expected to produce more potent and/or selective pharmacological effects, whereas the nonsymmetrical twin drug is anticipated to show both pharmacological activities stemming from the individual pharmacophores (dual action). On the other hand, nonsymmetrical triplet drugs, which have two of the same pharmacophores and one different moiety, are expected to elicit both increased pharmacological action and dual action. The two identical portions could bind the same receptor sites simultaneously while the third portion could bind a different receptor site or enzyme. This review will mainly focus on the twin and triplet drugs with an evaluation of their in vivo pharmacological effects, and will also include a description of their pharmacology and synthesis.

  7. Quantum states for quantum processes: A toy model for ammonia inversion spectra

    SciTech Connect

    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

    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.

  8. Dressing effects in the attosecond transient absorption spectra of doubly excited states in helium

    NASA Astrophysics Data System (ADS)

    Argenti, L.; Jiménez-Galán, Á.; Marante, C.; Ott, C.; Pfeifer, T.; Martín, F.

    2015-06-01

    Strong-field manipulation of autoionizing states is a crucial aspect of electronic quantum control. Recent measurements of the attosecond transient absorption spectrum (ATAS) of helium dressed by a few-cycle visible pulse [C. Ott et al., Nature (London) 516, 374 (2014), 10.1038/nature14026] provide evidence of the inversion of Fano profiles. With the support of accurate ab initio calculations that reproduce the results of the latter experiment, here we investigate the new physics that arise from ATAS when the laser intensity is increased. In particular, we show that (i) previously unnoticed signatures of the dark 2 p21S doubly excited state are observed in the experimental spectrum, (ii) inversion of Fano profiles is predicted to be periodic in the laser intensity, and (iii) the ac Stark shift of the higher terms in the s p2,n + autoionizing series exceeds the ponderomotive energy, which is the result of a genuine two-electron contribution to the polarization of the excited atom.

  9. Pure Rotational Spectra of HNCO in the Far Infrared: Three Excited Bending States

    NASA Astrophysics Data System (ADS)

    Niedenhoff, M.; Yamada, K. M. T.; Winnewisser, G.

    1996-04-01

    Pure rotational transitions of the quasilinear molecule HNCO in the excited bending states, v4= 1, v5= 1, and v6= 1, were measured with high resolution in the far infrared employing the Giessen Fourier transform spectrometer. Besides a-type transitions with high rotational quantum numbers, b-type transitions from Ka= 1 ? 0 up to Ka= 5 ? 4 could be identified for ? 4and ? 6and from Ka= 2 ? 1 up to Ka= 7 ? 6 for ? 5. Effective molecular parameters were determined using the linear molecule Hamiltonian to reproduce the measured line positions for each subband. Several forbidden transitions between the in-planebending vibrations ? 4and ? 5and the out-of-planebending vibration ? 6could be identified, which enabled us to determine precisely the relative positions of the vibrational energy levels. The strong a-type Coriolis interaction, which causes the forbidden transitions, have been analyzed with the help of a Padé-formulation to describe the Karotational structure of the bending excited states. The considerably weaker b-type Coriolis interaction, which shifts the effective rotational parameters, has also been discussed.

  10. Time-resolved EPR and laser photolysis investigations of photoinduced ?-bond dissociation in an aromatic carbonyl compound having triplet ?,?* character

    NASA Astrophysics Data System (ADS)

    Yamaji, Minoru; Inomata, Susumu; Nakajima, Satoru; Akiyama, Kimio; Tero-Kubota, Shozo; Tobita, Seiji; Marciniak, Bronislaw

    2006-01-01

    Photochemical properties of photoinduced ?-bond dissociation in p-phenylbenzoylbenzyl phenyl sulfide (PPS) having the lowest triplet state (T 1) of ?,?* character in solution were investigated by time-resolved EPR and laser flash photolysis techniques. PPS was found to undergo photoinduced ?-bond cleavage in the excited lowest singlet state (S 1(n,?*)) with a quantum yield ( ?rad) of 0.15 for the radical formation, which was independent of excitation wavelengths. Based on the facts of the observation of the absorption spectrum of triplet PPS upon triplet sensitization of xanthone, and absence of CIDEP signal, ?-cleavage was shown to be absent in the T 1(?,?*) state of PPS. Considering the electronic character of the excited and dissociative states of PPS, a schematic energy diagram for the ?-bond dissociation of PPS was shown.

  11. Triplet correlation in sheared suspensions of Brownian particles

    NASA Astrophysics Data System (ADS)

    Yurkovetsky, Yevgeny; Morris, Jeffrey F.

    2006-05-01

    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.

  12. Broadband Emission Spectra from the Cygnus X-3 Jet in the Soft Spectral State

    NASA Astrophysics Data System (ADS)

    Zhang, Jian-Fu; Lu, Ju-Fu

    2015-02-01

    In order to understand the main observational characteristics of the Galactic X-ray binary Cygnus X-3, we propose a radiation model in which high-energy electrons accelerate in the dissipation zone of a jet and produce nonthermal broadband emissions. Broadband spectral energy distributions are computed to compare the AGILE and Fermi LAT data with the multi-band data during soft X-ray spectral states. By fitting observations at different locations of the jet, we find that the emission region is rather compact and should be located at a distance of about one orbital radius. Our results can explain the current multi-frequency observations and also predict the TeV band emission. The model could be tested by a polarization measurement at IR band, and/or by a correlation study between the GeV and TeV bands once very-high-energy observations are available.

  13. Photoemission spectra and thermal desorption characteristics of two states of oxygen on Pd

    NASA Astrophysics Data System (ADS)

    Weissman, D. L.; Shek, M. L.; Spicer, W. E.

    1980-02-01

    Two states of oxygen have been observed on Pd (111). The first is adsorbed on the surface and causes strong changes in the Pd d-band photoemission energy distribution curves (EDCs) at hv = 21.2 eV but no oxygen resonance below the d-bands. The second is identified with oxygen beneath the surface (in accord with the thermal desorption studies of Conrad et al.); it has little effect on the Pd d-band emission but produces a resonance at lower energy (˜5 eV below Ef). Evidence is presented indicating that the case with which oxygen can go beneath the Pd surface depends on the surface perfection of the crystal.

  14. Exchange-only optimized effective potential calculation of excited state spectra for He and Be atoms.

    SciTech Connect

    Desjarlais, Michael Paul; Muller, Richard Partain

    2006-02-01

    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.

  15. Exchange interaction between the triplet exciton and the localized spin in copper-phthalocyanine

    E-print Network

    Wei Wu

    2014-06-11

    Triplet excitonic state in the organic molecule may arise from a singlet excitation and the following inter-system crossing. Especially for a spin-bearing molecule, an exchange interaction between the triplet exciton and the original spin on the molecule can be expected. In this paper, such exchange interaction in copper-phthalocyanine (CuPc, spin-$\\frac{1}{2}$) was investigated from first-principles by using density-functional theory within a variety of approximations to the exchange correlation, ranging from local-density approximation to long-range corrected hybrid-exchange functional. The magnitude of the computed exchange interaction is in the order of meV with the minimum value (1.5 meV, ferromagnetic) given by the long-range corrected hybrid-exchange functional CAM-B3LYP. This exchange interaction can therefore give rise to a spin coherence with an oscillation period in the order of picoseconds, which is much shorter than the triplet lifetime in CuPc (typically tens of nanoseconds). This implies that it might be possible to manipulate the localised spin on Cu experimentally using optical excitation and inter-system crossing well before the triplet state disappears.

  16. Rotationally resolved photoelectron spectra in resonance enhanced multiphoton ionization of HCl via the F 1?2 Rydberg state

    NASA Astrophysics Data System (ADS)

    Wang, Kwanghsi; McKoy, V.

    1991-12-01

    Results of studies of rotational ion distributions in the X 2?3/2 and X 2?1/2 spin-orbit states of HCl+ resulting from (2+1') resonance enhanced multiphoton ionization (REMPI) via the S(0) branch of the F 1?2 Rydberg state are reported and compared with measured threshold-field-ionization zero-kinetic-energy spectra reported recently [K. S. Haber, Y. Jiang, G. Bryant, H. Lefebvre-Brion, and E. R. Grant, Phys. Rev. A (in press)]. These results show comparable intensities for J+=3/2 of the X 2?3/2 ion and J+=1/2 of the X 2?1/2 ion. Both transitions require an angular momentum change of ?N=-1 upon photoionization. To provide further insight into the near-threshold dynamics of this process, we also show rotationally resolved photoelectron angular distributions, alignment of the ion rotational levels, and rotational distributions for the parity components of the ion rotational levels. About 18% population is predicted to occur in the (+) parity component, which would arise from odd partial-wave contributions to the photoelectron matrix element. This behavior is similar to that in (2+1) REMPI via the S(2) branch of the F 1?2 state of HBr and was shown to arise from significant l mixing in the electronic continuum due to the nonspherical molecular ion potential. Rotational ion distributions resulting from (2+1) REMPI via the S(10) branch of the F 1?2 state are also shown.

  17. Pure Rotational Spectra of HNCO in the Far Infrared: Ground State Analysis

    NASA Astrophysics Data System (ADS)

    Niedenhoff, M.; Yamada, K. M. T.; Belov, S. P.; Winnewisser, G.

    1995-11-01

    The pure rotational spectrum of the quasilinear molecule HNCO and some of its isotopomers was measured with the Giessen high-resolution Fourier transform spectrometer in the far infrared. In addition to a-type transitions with high rotational quantum number, b-type transitions from Ka = 1 ? 0 to Ka = 8 ? 7 for HNCO and DNCO, and from Ka = 1 ? 0 to Ka = 5 ? 4 for HN 13CO were identified. Several rotational transitions near 600 GHz were also measured using the Cologne submillimeter-wave spectrometer with a high-frequency backward wave oscillator as source. Rotational parameters were determined using both Watson's S-reduced asymmetric rotor Hamiltonian and for comparison a linear molecule Hamiltonian. The centrifugal distortion resonance between the ground state and the lowest excited bending vibration was clearly observed and analyzed by a second-order perturbation treatment. The observed K dependence of the rotational parameter B( K) is caused by the combined effects of centrifugal distortion resonance and quasilinearity.

  18. Does interchain stacking morphology contribute to the singlet-triplet interconversion dynamics in polymer heterojunctions?

    NASA Astrophysics Data System (ADS)

    Bittner, Eric R.; Burghardt, Irene; Friend, Richard H.

    2009-02-01

    Time-dependent density functional theory (TD-DFT) is used to examine the effect of stacking in a model semiconducting polymer hetrojunction system consisting of two co-facially stacked oligomers. We find that the excited electronic states are highly sensitive to the alignment of the monomer units of the two chains. In the system we examined, the exchange energy is nearly identical to both the and band off-set at the heterojunction and to the exciton binding energy. Our results indicate that the triplet excitonic states are nearly degenerate with the singlet exciplex states opening the possibility for the interconversion of singlet and triplet electronic states at the heterojunction interface via spin-orbit coupling localized on the heteroatoms. Using Russell-Saunders theory, we estimate this interconversion rate to be approximately 700-800 ps, roughly a 5-10-fold increase compared to isolated organic polymer chains.

  19. Electron, Hole, Singlet, and Triplet Energy Transfer in Photoexcited Porphyrin-Naphthalenediimide Dyads.

    PubMed

    Yushchenko, Oleksandr; Hangarge, Rahul V; Mosquera-Vazquez, Sandra; Boshale, Sheshanath V; Vauthey, Eric

    2015-06-18

    The excited-state dynamics of two molecular dyads, consisting of zinc (1) and free-base (2) porphyrin connected via a peptide linker to a core-substituted naphthalenediimide (NDI) have been investigated using optical spectroscopy. These dyads exhibit rich photophysics because of the large number of electronic excited states below 3 eV. In the case of 1 in apolar solvents, excitation energy transfer from the vibrationally hot singlet excited porphyrin to the NDI takes place with a 500 fs time constant. Electronic energy ends up in the NDI-localized triplet state, which decays to the ground state on a microsecond timescale. In polar solvents, ground-state recovery is faster by 5 orders of magnitude because of the occurrence of charge separation followed by recombination. On the other hand, excitation energy transfer in 2 takes place in the opposite direction, namely from the NDI to the porphyrin, which then undergoes intersystem crossing to the triplet state, followed by triplet energy transfer back to the NDI. Therefore, four distinct local electronic excited states are consecutively populated after excitation of the NDI unit of 2, with the energy shuttling between the two ends of the dyad. PMID:25418961

  20. Triplet excitation migration for compound molecules in solid solutions

    NASA Astrophysics Data System (ADS)

    Bagnich, S. A.

    1994-07-01

    Migration of benzaldehyde triplet excitations in solid solution has been studied by the technique of capture by traps using steady-state excitation. The probabilities of excitation capture by a trap have been obtained as a function of the concentration of the indicated compound at various temperatures and trap concentrations. Analysis of the experimental dependencies for scaling in the system "benzaldehyde-1-bromonaphthalene in ethanol" results in values of the critical exponents ?=0.41 and ?=1.7 coinciding with the theoretical ones, obtained in the scope of percolation theory for three-dimensional space. The values of the critical exponents and the character of the dependencies are different when toluene or PMMA are used as matrices. We analyze the obtained experimental data within the cluster model of energy migration and the Blumen-Silby model.

  1. Skylab observations of the solar O I resonance triplet

    NASA Technical Reports Server (NTRS)

    Roussel-Dupre, D.

    1985-01-01

    Profile variations from center to limb, as well as at different heights above the quiet solar limb, are illustrated by profile observations of the solar O I resonant triplet at 1302, 1304, and 1306 A that were obtained with the Skylab S082-B spectrograph. Since these lines share a common upper energy level, source function equality should exist for them when the lower states are populated according to their statistical weights. Profile congruency and profile inversion calculations comparisons show, however, that this is not the case, suggesting either errors in the fine structure collision rates, or the H I Ly-beta flux preferentially depopulating the 1302 A lower level, or two-dimensional transfer effects.

  2. Quantum-Chemical Calculations of the Structure of the Triplet Reaction Complexes in Anionic Polymerization of Butadiene

    Microsoft Academic Search

    K. K. Kalninsh; A. F. Podolskii

    2001-01-01

    A new mechanism of anionic polymerization of butadiene, radically changing the existing concepts on the structure and properties of the reaction complex, is suggested. It is stated that an elementary chemical process involves excitation into the low-lying triplet state of the “living” polymer–monomer complex, characterized as a transfer of a charge (electron) and cation (Li+ or Na+) from the terminal

  3. Dual enhancement of electroluminescence efficiency and operational stability by rapid upconversion of triplet excitons in OLEDs

    PubMed Central

    Furukawa, Taro; Nakanotani, Hajime; Inoue, Munetomo; Adachi, Chihaya

    2015-01-01

    Recently, triplet harvesting via a thermally activated delayed fluorescence (TADF) process has been established as a realistic route for obtaining ultimate internal electroluminescence (EL) quantum efficiency in organic light-emitting diodes (OLEDs). However, the possibility that the rather long transient lifetime of the triplet excited states would reduce operational stability due to an increased chance for unwarranted chemical reactions has been a concern. Herein, we demonstrate dual enhancement of EL efficiency and operational stability in OLEDs by employing a TADF molecule as an assistant dopant and a fluorescent molecule as an end emitter. The proper combination of assistant dopant and emitter molecules realized a “one-way” rapid Förster energy transfer of singlet excitons from TADF molecules to fluorescent emitters, reducing the number of cycles of intersystem crossing (ISC) and reverse ISC in the TADF molecules and resulting in a significant enhancement of operational stability compared to OLEDs with a TADF molecule as the end emitter. In addition, we found that the presence of this rapid energy transfer significantly suppresses singlet-triplet annihilation. Using this finely-tuned rapid triplet-exciton upconversion scheme, OLED performance and lifetime was greatly improved. PMID:25673259

  4. Even-parity spin-triplet pairing by purely repulsive interactions for orbitally degenerate correlated fermions

    NASA Astrophysics Data System (ADS)

    Zegrodnik, M.; Bünemann, J.; Spa?ek, J.

    2014-03-01

    We demonstrate the stability of the spin-triplet paired s-wave (with an admixture of extended s-wave) state for the limit of purely repulsive interactions in a degenerate two-band Hubbard model of correlated fermions. The repulsive interactions limit represents an essential extension of our previous analysis (2013 New J. Phys. 15 073050), regarded here as I. We also show that near the half-filling the considered type of superconductivity can coexist with antiferromagnetism. The calculations have been carried out with the use of the so-called statistically consistent Gutzwiller approximation (SGA) for the case of a square lattice. We suggest that the electron correlations in conjunction with the Hund's rule exchange play the crucial role in stabilizing the real-space spin-triplet superconducting state. A sizable hybridization of the bands suppresses the homogeneous paired state.

  5. Infrared spectra and theoretical calculations for Fe, Ru, and Os metal hydrides and dihydrogen complexes.

    PubMed

    Wang, Xuefeng; Andrews, Lester

    2009-01-22

    Laser-ablated iron, ruthenium, and osmium atoms react with hydrogen in excess argon, neon and pure hydrogen to produce the FeH(2) molecule, and the FeH(2)(H(2))(3), RuH(H(2))(4), RuH(2)(H(2))(4), and (H(2))MH complexes (M = Fe, Ru, Os), as identified through infrared spectra with D(2) and HD substitution. DFT frequency calculations support the assignment of absorptions observed experimentally. The FeH(2) molecule has a quintet ground state with a quasi-linear structure, and is repulsive to the addition of one more H(2) ligand: however, with three more H(2) ligands, stable triplet and singlet state FeH(2)(H(2))(3) supercomplexes can be formed. The quintet FeH(2) molecule and FeH(2)(H(2))(3) supercomplex undergo reversible near-ultraviolet photochemical rearrangement in solid neon and hydrogen. The RuH(2) molecule has a bent triplet ground state and forms the stable singlet RuH(2)(H(2))(4) supercomplex, but only the latter is observed in these experiments. In like fashion RuH has a quartet ground state and the doublet RuH(H(2))(4) complex is trapped in solid hydrogen. All three (H(2))MH complexes with lower energy than MH(3) are trapped, and no absorptions are observed for MH(3) molecules. PMID:19099441

  6. X-ray absorption spectra for transition metal high-dielectrics: Final state differences for intra-and inter-atomic transitions

    E-print Network

    in transition metal TM and lanthanide series rare earth RE atom oxides, and their silicate and aluminate alloysX-ray absorption spectra for transition metal high- dielectrics: Final state differences for intra- and inter-atomic transitions G. Lucovskya) Departments of Physics, Materials Science and Engineering

  7. Ab initio calculations of optical spectra by solving the Bethe-Salpeter equation without empty states.Work

    NASA Astrophysics Data System (ADS)

    Rocca, Dario; Lu, Deyu; Galli, Giulia

    2009-03-01

    We present a novel first principle approach to solve the Bethe-Salpeter equation (BSE) that builds on recent progress in time-dependent density functional perturbation theory [1], and uses an eigenvalue decomposition representation of the dielectric matrix [2]. This approach does not require the explicit calculation of excited single particle electronic states, making it suitable for calculations involving large basis sets and/or a large number of transitions. The numerical solution of the BSE is obtained through a generalized, non-Hermitian Lanczos iterative algorithm and does not require the use of the Tamm-Dancoff approximation. Furthermore, since Lanczos coefficients are frequency independent, optical spectra may be obtained in a very broad energy range. The efficiency and accuracy of the new approach are demonstrated by calculating the optical properties of silicon nanoclusters with up to 1 nm diameter. [1] D. Rocca, R. Gebauer, Y Saad, and S. Baroni, J. Chem. Phys. 128, 154105 (2008). [2] H.Wilson, F.Gygi and G.Galli, Phys. Rev. B 78, 113303 (2008).

  8. Non-linear trans-Planckian corrections of spectra due to the non-trivial initial states

    NASA Astrophysics Data System (ADS)

    Yusofi, E.; Mohsenzadeh, M.

    2014-07-01

    Recent Planck results motivated us to use non-Bunch-Davies vacuum. In this paper, we use the excited-de Sitter mode as non-linear initial states during inflation to calculate the corrected spectra of the initial fluctuations of the scalar field. First, we consider the field in de Sitter space-time as background field and for the non-Bunch-Davies mode, we use the perturbation theory to the second order approximation. Also, unlike conventional renormalization method, we offer de Sitter space-time as the background instead Minkowski space-time. This approach preserve the symmetry of curved space-time and stimulate us to use excited mode. By taking into account this alternative mode and the effects of trans-Planckian physics, we calculate the power spectrum in standard approach and Danielsson argument. The calculated power spectrum with this method is finite, corrections of it is non-linear, and in de Sitter limit corrections reduce to linear form that obtained from several previous conventional methods.

  9. Pd(II) phthalocyanine-sensitized triplet-triplet annihilation from rubrene.

    PubMed

    Singh-Rachford, Tanya N; Castellano, Felix N

    2008-04-24

    Upconverted yellow singlet fluorescence from rubrene (5,6,11,12-tetraphenylnapthacene) was generated from selective excitation (lambdaex = 725 nm) of the red light absorbing triplet sensitizer palladium(II) octabutoxyphthalocyanine, PdPc(OBu)8, in vacuum degassed toluene solutions using a Nd:YAG/OPO laser system in concert with gated iCCD detection. The data are consistent with upconversion proceeding from triplet-triplet annihilation (TTA) of rubrene acceptor molecules. The TTA process was confirmed by the quadratic dependence of the upconverted delayed fluorescence intensity with respect to incident light, measured by integrating the corresponding kinetic traces as a function of the incident excitation power. In vacuum degassed toluene solutions, the red-to-yellow upconversion process is stable under continuous long wavelength irradiation and is readily visualized by the naked eye even at modest laser fluence (0.6 mJ/pulse). In aerated solutions, however, selective excitation of the phthalocyanine sensitizer leads to rapid decomposition of rubrene into its corresponding endoperoxide as evidenced by UV-vis (in toluene), 1H NMR (in d6-benzene), and MALDI-TOF mass spectrometry, consistent with the established reactivity of rubrene with singlet dioxygen. The upconversion process in this triplet sensitizer/acceptor-annihilator combination was preliminarily investigated in solid polymer films composed of a 50:50 mixture of an ethyleneoxide/epichlorohydrin copolymer, P(EO/EP). Films that were prepared under an argon atmosphere and maintained under this inert environment successfully achieve the anticipated quadratic incident power dependence, whereas air exposure causes the film to deviate somewhat from this dependence. To the best of our knowledge, the current study represents the first example of photon upconversion using a phthalocyanine triplet sensitizer, furthering the notion that anti-Stokes light-producing sensitized TTA appears to be a general phenomenon as long as proper energy criteria are met. PMID:18336014

  10. Ordering of PCDTBT Revealed by Time-Resolved Electron Paramagnetic Resonance Spectroscopy of Its Triplet Excitons.

    PubMed

    Biskup, Till; Sommer, Michael; Rein, Stephan; Meyer, Deborah L; Kohlstädt, Markus; Würfel, Uli; Weber, Stefan

    2015-06-22

    Time-resolved electron paramagnetic resonance (TREPR) spectroscopy is shown to be a powerful tool to characterize triplet excitons of conjugated polymers. The resulting spectra are highly sensitive to the orientation of the molecule. In thin films cast on PET film, the molecules' orientation with respect to the surface plane can be determined, providing access to sample morphology on a microscopic scale. Surprisingly, the conjugated polymer investigated here, a promising material for organic photovoltaics, exhibits ordering even in bulk samples. Orientation effects may significantly influence the efficiency of solar cells, thus rendering proper control of sample morphology highly important. PMID:25959127

  11. Enhanced Triplet Formation in Polycrystalline Tetracene Films by Femtosecond Optical-Pulse Shaping

    NASA Astrophysics Data System (ADS)

    Grumstrup, Erik M.; Johnson, Justin C.; Damrauer, Niels H.

    2010-12-01

    Polycrystalline tetracene films have been explored using weak ˜30fs visible laser pulses that excite the lowest singlet exciton as well as coherent vibrational motion. Transient difference spectra show a triplet absorption which arises following singlet fission (SF) and persists for 1.6 ns without decay. Adaptive pulse shaping identifies multipulse optimal fields which maximize this absorption feature by ˜20%. These are comprised of subpulses separated by time delays well correlated with the period of lattice vibrations suggesting such modes control the yield of SF photochemistry.

  12. Triplet exciton dissociation in singlet exciton fission photovoltaics.

    PubMed

    Jadhav, Priya J; Brown, Patrick R; Thompson, Nicholas; Wunsch, Benjamin; Mohanty, Aseema; Yost, Shane R; Hontz, Eric; Van Voorhis, Troy; Bawendi, Moungi G; Bulovi?, Vladimir; Baldo, Marc A

    2012-12-01

    Triplet exciton dissociation in singlet exciton fission devices with three classes of acceptors are characterized: fullerenes, perylene diimides, and PbS and PbSe colloidal nanocrystals. Using photocurrent spectroscopy and a magnetic field probe it is found that colloidal PbSe nanocrystals are the most promising acceptors, capable of efficient triplet exciton dissociation and long wavelength absorption. PMID:22968762

  13. Ultrafast Triplet Generation and its Sensitization Drives Efficient Photoisomerization of Tetra-cis-lycopene to All-trans-lycopene.

    PubMed

    Vijayalakshmi, Kanchustambham; Jha, Ajay; Dasgupta, Jyotishman

    2015-07-16

    Lycopene biosynthesis in photosynthetic organisms controls the metabolic flux of reaction center carotenoids like ?-carotene and lutein through the geometric four-step isomerization of 7,9,9',7'-tetra-cis-lycopene (prolycopene) to its all-trans form. In plants and cyanobacteria, a redox-controlled flavoenzyme carotenoid isomerase catalyzes the prolycopene isomerization although its functional loss inside the chloroplast can be rescued by light. In order to address the chloroplast-specificity and efficiency of the light-induced isomerization reaction, we need to critically understand the excited state dynamics of prolycopene and the nature of electronic states that lead to the isomerization. Using broadband femtosecond transient absorption spectroscopy, we observe ?610 fs rise of the long-lived triplet state from the photoexcited S2 with a quantum yield of ?0.19. The triplet state eventually triggers the first C?C bond isomerization at the symmetric 9 or 9' position on the tetra-cis backbone to yield the tri-cis product with 15% quantum efficiency. However, direct sensitization of the photoreactive triplet state via meso-tetraphenyl porphyrin sensitizer under steady state illumination leads to an efficient production of all-trans-lycopene with 58% quantum yield. Our work implies that chlorophyll-enriched chloroplasts should form an optimized photoreaction vessel for prolycopene isomerization, and synthetic utilization of such cis-carotenoids can lead to efficient triplet harvesting photon-conversion devices. PMID:26065440

  14. Singlet-triplet excitation spectrum of the CO-He complex. I. Potential surfaces and bound-bound CO(a 3?<--X 1?+) transitions

    NASA Astrophysics Data System (ADS)

    Zeimen, W. B.; Groenenboom, G. C.; van der Avoird, A.

    2003-07-01

    The interaction of He with metastable CO(a 3?) gives rise to two adiabatic potential surfaces of reflection symmetry A' and A? which were calculated with the partially spin-restricted open-shell single and double excitation coupled cluster method with perturbative triples, RCCSD(T). Two diabatic potentials were constructed and fitted analytically; the appropriate form of the angular expansion functions was derived from general invariance properties. From variational calculations on these diabatic potential surfaces we obtained the quasibound vibration-rotation-spin levels of the CO-He complex in its lowest triplet state. Only the lower spin-orbit levels of this complex with approximate quantum number ?=0 of the CO(a 3?) monomer were found to be stable with respect to dissociation into He and triplet CO. The potential and the bound van der Waals levels of the ground state CO(X 1?+)-He complex were recalculated and used in combination with the triplet excited state wave functions to compute the line strengths and the bound-bound part of the singlet-triplet excitation spectrum of the CO-He complex. The spin-forbidden singlet-triplet transitions access mainly the higher spin-orbit levels with |?|=1, but these were found to undergo rapid predissociation. The companion Paper II explicitly studies this process, predicts the excited state lifetimes, and generates the bound-continuum part of the CO-He singlet-triplet spectrum.

  15. Inverted Singlet-Triplet Qubit Coded on a Two-Electron Double Quantum Dot

    E-print Network

    Sebastian Mehl; David P. DiVincenzo

    2014-11-26

    The $s_z=0$ spin configuration of two electrons confined at a double quantum dot (DQD) encodes the singlet-triplet qubit (STQ). We introduce the inverted STQ (ISTQ) that emerges from the setup of two quantum dots (QDs) differing significantly in size and out-of-plane magnetic fields. The strongly confined QD has a two-electron singlet ground state, but the weakly confined QD has a two-electron triplet ground state in the $s_z=0$ subspace. Spin-orbit interactions act nontrivially on the $s_z=0$ subspace and provide universal control of the ISTQ together with electrostatic manipulations of the charge configuration. GaAs and InAs DQDs can be operated as ISTQs under realistic noise conditions.

  16. Singlet-Triplet Energy Gaps for Diradicals from Fractional-Spin Density-Functional Theory

    SciTech Connect

    Ess, Daniel H.; Johnson, E R; Hu, Xiangqian; Yang, W T

    2011-01-01

    Open-shell singlet diradicals are difficult to model accurately within conventional Kohn?Sham (KS) density-functional theory (DFT). These methods are hampered by spin contamination because the KS determinant wave function is neither a pure spin state nor an eigenfunction of the S2 operator. Here we present a theoretical foray for using single-reference closed-shell ground states to describe diradicals by fractional-spin DFT (FS-DFT). This approach allows direct, self-consistent calculation of electronic properties using the electron density corresponding to the proper spin eigenfunction. The resulting FS-DFT approach is benchmarked against diradical singlet?triplet gaps for atoms and small molecules. We have also applied FS-DFT to the singlet?triplet gaps of hydrocarbon polyacenes.

  17. Triplet behavior in weakly coupled chromophors in covalent pyridyl porphyrin-polymer systems

    NASA Astrophysics Data System (ADS)

    Siejak, Aleksandra; Wróbel, Danuta; Laskowska, Barbara; Avlasevich, Yuri S.

    2009-09-01

    The photophysical properties of the 5-(4-pyridyl)-10,15,20-tri(4-methyloxyphenyl)porphyrins covalently linked to polyethylene glycol - PEG of different molecular weights (35000, 20000 and 8000) dissolved in dimethylsulfoxide were studied. The singlet and triplet states of the porphyrin species behavior were discussed in terms of fluorescence and thermal relaxation processes. The absorption, fluorescence and photothermal experiments showed that in the porphyrins linked to the PEG systems in dimethylsulfoxide the dye moieties occur in weakly interacting dimers. The triplet state enhancement in the 5-(4-pyridyl)-10,15,20-tri(4-methyloxyphenyl)porphyrins covalently linked to PEG was discussed. It was shown that even that the weak interaction of the porphyrin species in the covalent systems with PEG is not detectable by the absorption and only slightly by fluorescence, it is possible to be performed by the complementary spectroscopic methods like photoacoustics and photothermal time resolved spectroscopy.

  18. Exciton mediated triplet superconductivity in Th system PrOs4Sb12

    NASA Astrophysics Data System (ADS)

    Koga, Mikito

    2005-03-01

    We investigate a possibility of triplet superconductivity mediated by crystal-field excitations in a skutterudite PrOs4Sb12. The dispersive excitation modes (excitons) are caused by an effective exchange interaction due to the conduction electrons coupled with the Pr f^2 states. The Cooper pairing interaction reflects the point group symmetry of the Pr site rather than the global symmetry of the Fermi surface. The Th symmetry (without fourfold symmetric axes) of the skutterudite crystals is a key to stability of the triplet Cooper pairing. We attempt to explain a possible superconducting state with broken time-reversal symmetry and a multiple superconducting phase in a magnetic field, recently reported by experiments.

  19. Correlation of photocurrent and electroabsorption spectra and their temperature dependence for conjugated light emitting polymers: The origin of the corresponding density of states

    NASA Astrophysics Data System (ADS)

    Tripathi, Awnish K.; Mohapatra, Y. N.

    2011-11-01

    Photocurrent (PC) and electroabsorption (EA) spectra of two different families of light emitting conjugated polymers viz. poly[2-methoxy-5-(2'-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV) and Arylenevinylene-co-pyrrolenevinylene (C8-AVPV) in standard sandwich diode configuration is measured. It is shown that EA spectra with a dominant positive peak at the onset has identical line shape as that of the first derivative of the PC spectra for both the materials. The temperature dependence of onset EA peak is studied in detail in the temperature range 10-300 K, and show redshift and narrowing with decrease in temperature. The temperature dependence of the signal height in the case of PC follows that of carrier mobility, while EA peak height follows occupancy within the density of states (DOS). At room temperature, the EA peak height shows very slow and nonexponential transients indicating relaxation in occupancy of states. The degree of nonexponentiality is seen to decrease with increase in reverse bias. The set of observations lead to the conclusion that the onset positive peak in both types of spectra is dominated by photoionization of localized states whose occupancy depends on the Fermi level, which in turn is controlled by variation in bias and temperature. A phenomenological model illustrating the origin of equivalence between EA and PC onset features is described. It is argued that the occurrence of a positive peak at the onset in such spectra, obtained for diode structures, is a signature of photoionization of defect states and the line shape corresponds to its polaronic DOS; hence correlation of PC and EA becomes a direct and powerful method of determination of near-gap joint DOS in molecular semiconductors.

  20. ATOMIC AND MOLECULAR PHYSICS: Theoretical analysis of ionic autoionization spectra of lanthanum via an intermediate state [Xe]5d6d 1P1

    NASA Astrophysics Data System (ADS)

    Zhong, Yin-Peng; Jia, Feng-Dong; Zhong, Zhi-Ping

    2009-10-01

    In the framework of multi-channel quantum defect theory, eigenquantum defects ?? and the transformation matrices Ui? of La+ are calculated from first principles by relativistic multi-channel theory, while the dipole matrix elements D? are obtained by fitting with experimental data. Then the ionic autoionization spectra of lanthanum via the intermediate state [Xe]5d6d 1P1 in the energy region of 90213-91905 cm-1 are obtained. Experimental peaks are classified and assigned by comparing with the corresponding calculated spectra. More specifically, four ionic autoionization Rydberg series converging to La2+ 5d5/2 2D5/2 and several states converging to higher lying states of La2+ are found and assigned.

  1. Identifying Inter-Residue Resonances in Crowded 2D 13C-13C Chemical Shift Correlation Spectra of Membrane Proteins by Solid-State MAS NMR Difference Spectroscopy

    PubMed Central

    Miao, Yimin; Cross, Timothy A.; Fu, Riqiang

    2013-01-01

    The feasibility of using difference spectroscopy, i.e. subtraction of two correlation spectra at different mixing times, for substantially enhanced resolution in crowded two-dimensional 13C-13C chemical shift correlation spectra is presented. With the analyses of 13C-13C spin diffusion in simple spin systems, difference spectroscopy is proposed to partially separate the spin diffusion resonances of relatively short intra-residue distances from the longer inter-residue distances, leading to a better identification of the inter-residue resonances. Here solid-state magic-angle-spinning (MAS) NMR spectra of the full length M2 protein embedded in synthetic lipid bilayers have been used to illustrate the resolution enhancement in the difference spectra. The integral membrane M2 protein of Influenza A virus assembles as a tetrameric bundle to form a protonconducting channel that is activated by low pH and is essential for the viral lifecycle. Based on known amino acid resonance assignments from amino acid specific labeled samples of truncated M2 sequences or from time-consuming 3D experiments of uniformly labeled samples, some inter-residue resonances of the full length M2 protein can be identified in the difference spectra of uniformly 13C labeled protein that are consistent with the high resolution structure of the M2 (22–62) protein (Sharma et al. 2010). PMID:23708936

  2. The superconducting spin valve and triplet superconductivity

    NASA Astrophysics Data System (ADS)

    Garifullin, I. A.; Leksin, P. V.; Garif'yanov, N. N.; Kamashev, A. A.; Fominov, Ya. V.; Schumann, J.; Krupskaya, Y.; Kataev, V.; Schmidt, O. G.; Büchner, B.

    2015-01-01

    A review of our recent results on the spin valve effect is presented. We have used a theoretically proposed spin switch design F1/F2/S comprising a ferromagnetic bilayer (F1/F2) as a ferromagnetic component, and an ordinary superconductor (S) as the second interface component. Based on it we have prepared and studied in detail a set of multilayers CoOx/Fe1/Cu/Fe2/S (S=In or Pb). In these heterostructures we have realized for the first time a full spin switch effect for the superconducting current, have observed its sign-changing oscillating behavior as a function of the Fe2-layer thickness and finally have obtained direct evidence for the long-range triplet superconductivity arising due to noncollinearity of the magnetizations of the Fe1 and Fe2 layers.

  3. Direct measurements of the current-phase relation in long-range spin-triplet SFS Josephson junctions

    NASA Astrophysics Data System (ADS)

    Hamilton, David; van Harlingen, Dale; Wang, Yixing; Birge, Norman

    2015-03-01

    We present direct measurements of the current-phase relation (CPR) of Josephson junctions which use multiple ferromagnetic layers to generate long-range spin-triplet pair correlations. Using a phase-sensitive Josephson interferometry technique, we obtain the phase and temperature dependence of this spin-triplet supercurrent. We also demonstrate the use of an inductive shunt to enhance this technique at higher critical currents. Our data suggest that the current-phase relation of these junctions is harmonic in character. Further measurements are planned in order to determine the ground state phase shift of these junctions.

  4. Magnetically tunable singlet-triplet spin qubit in a four-electron InGaAs coupled quantum dot

    NASA Astrophysics Data System (ADS)

    Weiss, K. M.; Miguel-Sanchez, J.; Elzerman, J. M.

    2013-11-01

    A pair of self-assembled InGaAs quantum dots filled with two electrons can act as a singlet-triplet spin qubit that is robust against nuclear spin fluctuations as well as charge noise. This results in a T2* coherence time two orders of magnitude longer than that of a single electron, provided the qubit is operated at a particular ``sweet spot'' in gate voltage. However, at this fixed operating point the ground-state splitting can no longer be tuned into resonance with e.g. another qubit, limiting the options for coupling multiple qubits. Here, we propose using a four-electron coupled quantum dot to implement a singlet-triplet qubit that features a magnetically tunable level splitting. As a first step towards full experimental realization of this qubit design, we use optical spectroscopy to demonstrate the tunability of the four-electron singlet-triplet splitting in a moderate magnetic field.

  5. Magnetically tunable singlet-triplet spin qubit in a four-electron InGaAs coupled quantum dot.

    PubMed

    Weiss, K M; Miguel-Sanchez, J; Elzerman, J M

    2013-01-01

    A pair of self-assembled InGaAs quantum dots filled with two electrons can act as a singlet-triplet spin qubit that is robust against nuclear spin fluctuations as well as charge noise. This results in a T2* coherence time two orders of magnitude longer than that of a single electron, provided the qubit is operated at a particular "sweet spot" in gate voltage. However, at this fixed operating point the ground-state splitting can no longer be tuned into resonance with e.g. another qubit, limiting the options for coupling multiple qubits. Here, we propose using a four-electron coupled quantum dot to implement a singlet-triplet qubit that features a magnetically tunable level splitting. As a first step towards full experimental realization of this qubit design, we use optical spectroscopy to demonstrate the tunability of the four-electron singlet-triplet splitting in a moderate magnetic field. PMID:24177037

  6. Third-order spontaneous parametric down-conversion in thin optical fibers as a photon-triplet source

    SciTech Connect

    Corona, Maria [Instituto de Ciencias Nucleares, Universidad Nacional Autonoma de Mexico, apdo. postal 70-543, DF 04510 Mexico City (Mexico); Departamento de Optica, Centro de Investigacion Cientifica y de Educacion Superior de Ensenada, Apartado Postal 2732, BC 22860 Ensenada (Mexico); Garay-Palmett, Karina; U'Ren, Alfred B. [Instituto de Ciencias Nucleares, Universidad Nacional Autonoma de Mexico, apdo. postal 70-543, DF 04510 Mexico City (Mexico)

    2011-09-15

    We study the third-order spontaneous parametric down-conversion (TOSPDC) process, as a means to generate entangled photon triplets. Specifically, we consider thin optical fibers as the nonlinear medium to be used as the basis for TOSPDC in configurations where phase matching is attained through the use of more than one fiber transverse modes. Our analysis in this paper, which follows from our earlier paper [Opt. Lett. 36, 190-192 (2011)], aims to supply experimentalists with the details required in order to design a TOSPDC photon-triplet source. Specifically, our analysis focuses on the photon triplet state, on the rate of emission, and on the TOSPDC phase-matching characteristics for the cases of frequency-degenerate and frequency nondegenerate TOSPDC.

  7. Signatures of triplet supercurrents in hybrid S/F structures

    NASA Astrophysics Data System (ADS)

    Richard, Caroline; Houzet, Manuel; Meyer, Julia; Spsms-Cea/Ujf Grenoble Team

    2014-03-01

    While ferromagnetism and conventional superconductivity appear as antagonist phases, the proximity effect in hybrid S/F structures offers a unique opportunity to study their interplay. In particular, spin-triplet odd-frequency superconducting correlations may be induced in a diffusive ferromagnet. We study the Josephson effect through a long ferromagnetic bilayer in the diffusive regime. For a non-collinear magnetization of the bilayer, we find that the current phase relation is dominated by its second harmonic, and corresponds to the long-range coherent propagation of two triplet pairs. Here, the superharmonicity is a signature of the Josephson coupling between a singlet superconductor and an effective triplet superconductor induced at the end of the ferromagnetic bilayer attached to the other lead. Then, we further study the critical current flowing between such two effective triplet reservoirs through a conventional superconducting layer. As a result of the competition between triplet/triplet and triplet/singlet couplings and under quite general conditions, we find that the critical current exhibits a maximum in the vicinity of the superconducting transition of the central layer.

  8. Pulsed-gate measurements of the singlet-triplet relaxation time in a two-electron double quantum dot

    E-print Network

    Petta, Jason

    Pulsed-gate measurements of the singlet-triplet relaxation time in a two-electron double quantum for the manipulation of electron spin because of the relative ease of confining and measuring single electrons.1 A spin for nearly degenerate two-electron spin states. This technique can be used to measure T1 in regimes for which

  9. Triplet correlations among similarly tuned cells impact population coding

    PubMed Central

    Cayco-Gajic, Natasha A.; Zylberberg, Joel; Shea-Brown, Eric

    2015-01-01

    Which statistical features of spiking activity matter for how stimuli are encoded in neural populations? A vast body of work has explored how firing rates in individual cells and correlations in the spikes of cell pairs impact coding. Recent experiments have shown evidence for the existence of higher-order spiking correlations, which describe simultaneous firing in triplets and larger ensembles of cells; however, little is known about their impact on encoded stimulus information. Here, we take a first step toward closing this gap. We vary triplet correlations in small (approximately 10 cell) neural populations while keeping single cell and pairwise statistics fixed at typically reported values. This connection with empirically observed lower-order statistics is important, as it places strong constraints on the level of triplet correlations that can occur. For each value of triplet correlations, we estimate the performance of the neural population on a two-stimulus discrimination task. We find that the allowed changes in the level of triplet correlations can significantly enhance coding, in particular if triplet correlations differ for the two stimuli. In this scenario, triplet correlations must be included in order to accurately quantify the functionality of neural populations. When both stimuli elicit similar triplet correlations, however, pairwise models provide relatively accurate descriptions of coding accuracy. We explain our findings geometrically via the skew that triplet correlations induce in population-wide distributions of neural responses. Finally, we calculate how many samples are necessary to accurately measure spiking correlations of this type, providing an estimate of the necessary recording times in future experiments. PMID:26042024

  10. Triplet diffusion in singlet exciton fission sensitized pentacene solar cells

    NASA Astrophysics Data System (ADS)

    Tabachnyk, Maxim; Ehrler, Bruno; Bayliss, Sam; Friend, Richard H.; Greenham, Neil C.

    2013-10-01

    Singlet fission sensitized photovoltaics have the potential to surpass the Shockley-Queisser limit for a single-junction structure. We investigate the dynamics of triplet excitons resulting from singlet fission in pentacene and their ionization at a C60 heterojunction. We model the generation and diffusion of excitons to predict the spectral response. We find the triplet diffusion length in polycrystalline pentacene to be 40 nm. Poly(3-hexylthiophene) between the electrode and pentacene works both to confine triplet excitons and also to transfer photogenerated singlet excitons into pentacene with 30% efficiency. The lower bound for the singlet fission quantum efficiency in pentacene is 180 ± 15%.

  11. Characterization of carotenoid aggregates by steady-state optical spectroscopy.

    PubMed

    Wang, Chen; Berg, Christopher J; Hsu, Cheng-Chih; Merrill, Brittany A; Tauber, Michael J

    2012-09-01

    The carotenoids have low-lying triplet excited states and can self-assemble in some solvents to form weakly or strongly coupled aggregates. These qualities make carotenoid aggregates useful for studies of singlet fission, where an outstanding goal is the correlation of interchromophoric coupling to the dynamics and yield of triplet excited states from a parent singlet excited state. Three aggregates of zeaxanthin, two weakly coupled and one strongly coupled, are characterized by steady-state spectroscopic methods including temperature-dependent absorption, fluorescence, and resonance Raman spectroscopy. The absorption spectra for each type of aggregate are distinct; however, an analysis of band positions reveals some important shared characteristics and suggests that the strongly coupled H-aggregate contains a subpopulation of weakly coupled constituents. Temperature-dependent absorption spectroscopy indicates that one of the weakly coupled aggregates can be converted to the other upon heating. The emission spectra of the three aggregates have similar profiles that are overall red-shifted by more than 1000 cm(-1) relative to the monomer. The emission quantum yields of the aggregates are 5 to 30 times less than that of the monomer, with the lowest yield for the strongly coupled aggregate. The vibrational spectra of the chromophores support only slight perturbations from the structure of solvated monomers. Our findings support the conclusion that all three aggregates are best characterized as H-aggregates, in agreement with a prior theoretical study of lutein aggregates. PMID:22873697

  12. Tunable singlet-triplet splitting in a few-electron Si/SiGe quantum dot

    NASA Astrophysics Data System (ADS)

    Shi, Zhan; Simmons, C. B.; Prance, J. R.; King Gamble, John; Friesen, Mark; Savage, D. E.; Lagally, M. G.; Coppersmith, S. N.; Eriksson, M. A.

    2011-12-01

    We measure the excited-state spectrum of a Si/SiGe quantum dot as a function of in-plane magnetic field and identify the spin of the lowest three eigenstates in an effective two-electron regime. We extract the singlet-triplet splitting, an essential parameter for spin qubits, from the data. We find it to be tunable by lateral displacement of the dot, which is realized by changing two gate voltages on opposite sides of the device. We present calculations showing the data are consistent with a spectrum in which the first excited state of the dot is a valley-orbit state.

  13. Spin-triplet s-wave local pairing induced by Hund's rule coupling

    NASA Astrophysics Data System (ADS)

    Han, Jong E.

    2004-03-01

    We show within the dynamical mean field theory that local symmetry-reducing interactions such as Hund's rule coupling produce local pairing superconductivity in the strongly correlated regime. Hund's rule driven spin-triplet superconductivity emerges from the pairing mediated by local spin fluctuations in the process of the pair exchange. The local orbital degrees of freedom are anti-symmetric on exchange, leaving the spins in the symmetric triplet state and the spatial part as fully gapped and symmetric s-wave. The general idea of local pairing can be applied to various strongly correlated multi-band systems including alkali-doped fullerenes with Jahn-Teller phonon coupling(J. E. Han, O. Gunnarsson, and Vincent H. Crespi, Phys. Rev. Lett. 90, 167006 (2003).).

  14. Giant triplet proximity effect in superconducting pseudo spin valves with engineered anisotropy

    NASA Astrophysics Data System (ADS)

    Wang, X. L.; Di Bernardo, A.; Banerjee, N.; Wells, A.; Bergeret, F. S.; Blamire, M. G.; Robinson, J. W. A.

    2014-04-01

    The proximity coupling of a thin superconducting layer and an inhomogeneous ferromagnet can lead to a significant reduction of the critical temperature due to the generation of spin-polarized triplet Cooper pairs. We report critical temperature measurements of Co/Cu/NiFe(Py)/Cu/Nb superconducting pseudo spin valves (PSVs) in which the magnetization of the soft layer (Py) can be independently rotated in-plane with a magnetic field to create an angle (?) between it and the magnetization of Co. Here we observe results consistent with spin-triplet theory and demonstrate large changes in ?TC up to -120 mK as the Py layer is rotated from 0° (Co and Py are parallel) to 90° (Co and Py are orthogonal), which offers the potential for active control of the superconducting state. The key to this achievement is engineered magnetic anisotropy in Py, which enables well-defined control over the magnetization configuration of the PSV.

  15. Possible triplet p +i p superconductivity in graphene at low filling

    NASA Astrophysics Data System (ADS)

    Ma, Tianxing; Yang, Fan; Yao, Hong; Lin, Hai-Qing

    2014-12-01

    We study the Hubbard model on the honeycomb lattice with nearest-neighbor hopping (t >0 ) and next-nearest-neighbor hopping (t'<0 ). When t'<-t /6 , the single-particle spectrum is featured by the continuously distributed Van Hove saddle points at the band bottom, where the density of states diverges in a power law. We investigate possible unconventional superconductivity in such systems with the Fermi level close to the band bottom by employing both random-phase-approximation and determinant quantum Monte Carlo approaches. Our study reveals a possible triplet p +i p superconductivity in this system with appropriate interactions. Our results might provide a possible route to look for triplet superconductivity with relatively high transition temperature in low-filled graphene and other similar systems.

  16. Triplet superconductivity in 3D Dirac semi-metal due to exchange interaction.

    PubMed

    Rosenstein, Baruch; Shapiro, B Ya; Li, Dingping; Shapiro, I

    2015-01-21

    Conventional phonon-electron interaction induces either triplet or one of two (degenerate) singlet pairing states in time reversal and inversion invariant 3D Dirac semi-metal. Investigation of the order parameters and energies of these states at zero temperature in a wide range of values of chemical potential ?, the effective electron-electron coupling constant ? and Debye energy TD demonstrates that when the exchange interaction is neglected the singlet always prevails, however, in significant portions of the (?, ?, TD) parameter space the energy difference is very small. This means that interactions that are small, but discriminate between the spin singlet and the spin triplet, are important in order to determine the nature of the superconducting order there. The best candidate for such an interaction in the materials under consideration is the exchange (the Stoner term) characterized by constant ?ex. We show that at values of ?ex, much smaller than ones creating Stoner instability to ferromagnetism ?ex ? 1, the triplet pairing becomes energetically favored over the singlet ones. The 3D quantum critical point at ? = 0 is considered in detail. This can be realized experimentally in optically trapped cold atom systems. PMID:25501668

  17. Quasiclassical Treatment and Odd-Parity/Triplet Correspondence in Topological Superconductors

    NASA Astrophysics Data System (ADS)

    Nagai, Yuki; Nakamura, Hiroki; Machida, Masahiko

    2014-05-01

    We construct a quasiclassical framework for topological superconductors with a strong spin–orbit coupling such as CuxBi2Se3. In a manner of the quasiclassical treatment, by decomposing the slowly varying component from a total quasiparticle wave function, the original massive Dirac Bogoliubov–de Gennes (BdG) Hamiltonian derived from a tight-binding model represented by an 8 × 8 matrix is reduced to a 4 × 4 matrix. The resultant equations are equivalent to Andreev-type equations of singlet or triplet superconductors, in which the apparent spin–orbit coupling vanishes. Using this formalism, we find that the odd-parity superconductivity in topological superconductors turns to the spin-triplet one. Moreover, in terms of quasiclassical treatment, we show that the topologically-protected zero-energy states in topological superconductors have correspond to the Andreev bound states established in a long history of studies of unconventional superconductors. This clearly indicates that low-energy nontrivial superconducting properties in the topological superconductors can be analyzed using established theoretical descriptions of the spin-triplet superconductors.

  18. Triplet dynamics in pentacene crystals: applications to fission-sensitized photovoltaics.

    PubMed

    Poletayev, Andrey D; Clark, Jenny; Wilson, Mark W B; Rao, Akshay; Makino, Yoshitaka; Hotta, Shu; Friend, Richard H

    2014-02-12

    The decay and transport of triplet excitons photogenerated via singlet exciton fission in polycrystalline and single-crystalline pentacene is reported. Using transient absorption spectroscopy, we find evidence for diffusion-mediated triplet-triplet annihilation. We estimate monomolecular lifetimes, bimolecular annihilation rate constants, and triplet exciton diffusion lengths. We discuss these results in the context of current solar cell device architectures. PMID:24375546

  19. Negative Ion Photoelectron Spectroscopy Confirms the Prediction that (CO)5 and (CO)6 Each Has a Singlet Ground State

    SciTech Connect

    Bao, Xiaoguang; Hrovat, David; Borden, Weston; Wang, Xue B.

    2013-03-20

    Cyclobutane-1,2,3,4-tetraone has been both predicted and found to have a triplet ground state, in which a b2g MO and an a2u MO is each singly occupied. In contrast, (CO)5 and (CO)6 have each been predicted to have a singlet ground state. This prediction has been tested by generating the (CO)5 - and (CO)6 - anions in the gas-phase by electrospray vaporization of solutions of, respectively, the croconate (CO)52- and rhodizonate (CO)62- dianions. The negative ion photoelectron (NIPE) spectra of the (CO)5•- radical anion give electron affinity (EA) = 3.830 eV and a singlet ground state for (CO)5, with the triplet higher in energy by 0.850 eV (19.6 kcal/mol). The NIPE spectra of the (CO)6•- radical anion give EA = 3.785 eV and a singlet ground state for (CO)6, with the triplet higher in energy by 0.915 eV (21.1 kcal/mol). (RO)CCSD(T)/aug-cc-pVTZ//(U)B3LYP/6-311+G(2df) calculations give EA values that are only ca. 1 kcal/mol lower than those measured and EST values that are only 2 - 3 kcal/mol higher than those obtained from the NIPE spectra. Thus, the calculations support the interpretations of the NIPE spectra and the finding, based on the spectra, that (CO)5 and (CO)6 both have a singlet ground state.

  20. Phonon density of states of Sn in textured SnO under high pressure: Comparison of nuclear inelastic x-ray scattering spectra to a shell model

    NASA Astrophysics Data System (ADS)

    Giefers, H.; Koval, S.; Wortmann, G.; Sturhahn, W.; Alp, E. E.; Hu, M. Y.

    2006-09-01

    The local phonon density of states (DOS) at the Sn site in tin monoxide (SnO) is studied at pressures up to 8GPa with Sn119 nuclear resonant inelastic x-ray scattering (NRIXS) of synchrotron radiation at 23.88keV . The preferred orientation (texture) of the SnO crystallites in the investigated samples is used to measure NRIXS spectra preferentially parallel and almost perpendicular to the c axis of tetragonal SnO . A subtraction method is applied to these NRIXS spectra to produce projected local Sn DOS spectra as seen parallel and perpendicular to the c axis of SnO . These experimentally obtained local Sn DOS spectra, both in the polycrystalline case as well as projected parallel and perpendicular to the c axis, are compared with corresponding theoretical phonon DOS spectra, derived from dispersion relations calculated with a recently developed shell model. Comparison between the experimental projected Sn DOS spectra and the corresponding theoretical DOS spectra enables us to follow the pressure-induced shifts of several acoustic and optic phonon modes. While the principal spectral features of the experimental and theoretical phonon DOS agree well at energies above 10meV , the pressure behavior of the low-energy part of the DOS is not well reproduced by the theoretical calculations. In fact, they exhibit, in contrast to the experimental data, a dramatic softening of two low-energy modes, their energies approaching zero around 2.5GPa , clearly indicating the limitations of the applied shell model. These difficulties are obviously connected with the complex Sn-O and Sn-Sn bindings within and between the Sn-O-Sn layers in the litharge structure of SnO . We derived from the experimental and theoretical DOS spectra a variety of elastic and thermodynamic parameters of the Sn sublattice, such as the Lamb-Mössbauer factor, the mean force constant, and Debye temperatures, as well as the vibrational contributions to the Helmholtz free energy, specific heat, entropy, and internal energy. We found, in part, good agreement between these values, for instance, for the Grüneisen parameters for some selected phonon modes, especially for some optical modes studied recently by Raman spectroscopy. We discuss in detail a possible anisotropy in the elastic parameters resulting from the litharge-type structure of SnO , for instance for the Lamb-Mössbauer factor, where we can compare with existing data from Sn119 -Mössbauer spectroscopy.

  1. Imaging the radical channel in acetaldehyde photodissociation: Competing mechanisms at energies close to the triplet exit barrier

    SciTech Connect

    Amaral, G. A.; Arregui, A.; Rodriguez, J. D.; Banares, L. [Departamento de Quimica Fisica I, Facultad de Ciencias Quimicas, Universidad Complutense de Madrid, Madrid 28040 (Spain); Rubio-Lago, L. [Departamento de Quimica Fisica I, Facultad de Ciencias Quimicas, Universidad Complutense de Madrid, Madrid 28040 (Spain); Instituto de Estructura de la Materia, CSIC, C/Serrano 123, Madrid 28006 (Spain)

    2010-08-14

    The photodissociation of acetaldehyde in the radical channel has been studied at wavelengths between 315 and 325 nm using the velocity-map imaging technique. Upon one-photon absorption at 315 nm, the molecule is excited to the first singlet excited state S{sub 1}, which, in turn, undergoes intersystem crossing to the first excited triplet state T{sub 1}. On the triplet surface, the molecule dissociates into CH{sub 3} and HCO radicals with large kinetic energy release (KER), in accordance with the well characterized exit barrier on T{sub 1}. However, at longer wavelengths (>320 nm), which correspond to excitation energies just below the triplet barrier, a sudden change in KER is observed. At these photolysis wavelengths, there is not enough energy to surpass the exit barrier on the triplet state, which leaves the possibility of unimolecular dissociation on S{sub 0} after internal conversion from S{sub 1}. We have characterized the fragments' KER at these wavelengths, as well as determined the energy partitioning for the radical fragments. A new accurate estimate of the barrier height on T{sub 1} is presented.

  2. Effects induced by gamma-irradiation and thermal treatment on the infrared spectra of ferrocene in its disordered state

    NASA Astrophysics Data System (ADS)

    Gaffar, M. A.; Abd-Elrahman, M. I.

    2004-10-01

    Lattice, rotation and intramolecular vibrations of ferrocene, Fe(C5H5)(2), crystallites of the C-2h(5) factor group in the disordered phase are calculated using the correlation theorem based on group theory. The correlation between the species of the C-1 site symmetry occupied by cyclopentadienyl molecules and those of the factor group C-2h, of the crystal are calculated. The number of lattice vibrations of the cyclopentadienyl molecules is found to be 12. with active modes in Raman and infrared (IR) spectra. The same number of rotations for the cyclopentadienyl molecules is expected to be allowed in both spectra. The active number of intramolecular vibrations for the cyclopentadienyl molecules having D-5 molecular symmetry is expected to be 80 vibrations in both the Raman and the IR spectra. The effect of gamma-irradiation with different doses and heat treatment at different temperatures on the IR spectra of ferrocene in the energy range 4000-200 cm(-1) is discussed. A number of bands continuously shifted their position, and a decrease in intensity with increasing gamma-dose is observed. New bands appeared in this spectral region for different annealing temperatures and different gamma-doses. These changes are discussed in terms of intermolecular interactions between molecules within the unit cell.

  3. Thermodynamic analysis of spectra

    NASA Astrophysics Data System (ADS)

    Mitchell, G. E.; Shriner, J. F.

    2008-04-01

    Although random matrix theory had its initial application to neutron resonances, there is a relative scarcity of suitable nuclear data. The primary reason for this is the sensitivity of the standard measures used to evaluate spectra—the spectra must be essential pure (no state with a different symmetry) and complete (no states missing). Additional measures that are less sensitive to these experimental limitations are of significant value. The standard measure for long range order is the ?3 statistic. In the original paper that introduced this statistic, Dyson and Mehta also attempted to evaluate spectra with thermodynamic variables obtained from the circular orthogonal ensemble. We consider the thermodynamic "internal energy" and evaluate its sensitivity to experimental limitations such as missing and spurious levels. Monte Carlo simulations suggest that the internal energy is less sensitive to mistakes than is ?3, and thus the internal energy can serve as a addition to the tool kit for evaluating experimental spectra.

  4. Nanostructured singlet fission photovoltaics subject to triplet-charge annihilation.

    PubMed

    Thompson, Nicholas J; Hontz, Eric; Congreve, Daniel N; Bahlke, Matthias E; Reineke, Sebastian; Van Voorhis, Troy; Baldo, Marc A

    2014-03-01

    Singlet exciton fission is an efficient multiple-exciton generation process that is vulnerable to a characteristic loss process: triplet-charge annihilation. This loss process is characterized in singlet-fission photovoltaics and losses as high as 40% are observed in poorly designed devices. Techniques are demonstrated to improve charge extraction and reduce triplet-charge annihilation to negligible levels at short-circuit conditions. PMID:24281738

  5. Production and installation of the LHC low-beta triplets

    SciTech Connect

    Feher, S.; Bossert, R.; DiMarco, J.; Karppinen, M.; Kerby, J.; Kimura, N.; Lamm, M.J.; Nakamoto, T.; Nicol, T.; Nobrega, A.; Ogitsu, T.; Ohuchi, N.; Ostojic, R.; Page,; Peterson, T.; Rabehl, R.; Schlabach, P.; Shintomi, T.; Strait, J.; Sylvester, C.; Tartaglia, M.; /Fermilab /CERN /KEK, Tsukuba

    2005-09-01

    The LHC performance depends critically on the low-{beta}, triplets, located on either side of the four interaction points. Each triplet consists of four superconducting quadrupole magnets, which must operate reliably at up to 215 T/m, sustain extremely high heat loads and have an excellent field quality. A collaboration of CERN, Fermilab and KEK was formed in 1996 to design and build the triplet systems, and after nine years of joint effort the production has been completed in 2005. We retrace the main events of the project and present the design features and performance of the low-{beta} quadrupoles, built by KEK and Fermilab, as well as of other vital elements of the triplet. The tunnel installation of the first triplet and plans for commissioning in the LHC are also presented. Apart from the excellent technical results, the construction of the LHC low-{beta} triplets has been a highly enriching experience combining harmoniously the different competences and approaches to engineering in a style reminiscent of high energy physics experiment collaborations, and rarely before achieved in construction of an accelerator.

  6. Stability and cooperativity of nucleic acid base triplets.

    PubMed

    Jiang, S P; Jernigan, R L; Ting, K L; Syi, J L; Raghunathan, G

    1994-10-01

    Geometries and stabilities of various base triplets have been studied using ab initio quantum chemical methods. Their optimized geometries are determined using the STO-3G basis set, and those of Hoogsteen and reverse Hoogsteen base pairs are evaluated with the 4-31G basis set. Moreover, the preferred hydrogen bond patterns of the bases in triple helices are discussed. A cooperative effect for base pairing in triplets is presented, and it can be either positive or negative. Almost all base triplets that contain Watson-Crick G:C base pairs show a positive cooperativity. Conversely, the base triplets with Watson-Crick A:T base pairs mostly display a negative cooperativity. The interaction energies of base triplets are reported and the relative stabilities of base triplets are found as follows: A+.GC > C+.GC(H) > C+.GC(rH) > G.GC(H) > G.GC(rH) > A.GC > T.AT(rH) > U.AU(H) > U.AT(H) > A.AT > G.AT > T.AT(m) > G.TA(2) > G.TA(1) H and rH denote the Hoogsteen and reverse Hoogsteen positions of the third base that would lead to parallel and antiparallel orientations respectively of the third chain with respect to the Watson-Crick paired purine chain. 'm' denotes the middle pairing scheme, in which the third base hydrogen bonds to both bases of Watson-Crick pair. PMID:7702776

  7. Impact of environmentally induced fluctuations on quantum mechanically mixed electronic and vibrational pigment states in photosynthetic energy transfer and 2D electronic spectra

    NASA Astrophysics Data System (ADS)

    Fujihashi, Yuta; Fleming, Graham R.; Ishizaki, Akihito

    2015-06-01

    Recently, nuclear vibrational contribution signatures in two-dimensional (2D) electronic spectroscopy have attracted considerable interest, in particular as regards interpretation of the oscillatory transients observed in light-harvesting complexes. These transients have dephasing times that persist for much longer than theoretically predicted electronic coherence lifetime. As a plausible explanation for this long-lived spectral beating in 2D electronic spectra, quantum-mechanically mixed electronic and vibrational states (vibronic excitons) were proposed by Christensson et al. [J. Phys. Chem. B 116, 7449 (2012)] and have since been explored. In this work, we address a dimer which produces little beating of electronic origin in the absence of vibronic contributions, and examine the impact of protein-induced fluctuations upon electronic-vibrational quantum mixtures by calculating the electronic energy transfer dynamics and 2D electronic spectra in a numerically accurate manner. It is found that, at cryogenic temperatures, the electronic-vibrational quantum mixtures are rather robust, even under the influence of the fluctuations and despite the small Huang-Rhys factors of the Franck-Condon active vibrational modes. This results in long-lasting beating behavior of vibrational origin in the 2D electronic spectra. At physiological temperatures, however, the fluctuations eradicate the mixing, and hence, the beating in the 2D spectra disappears. Further, it is demonstrated that such electronic-vibrational quantum mixtures do not necessarily play a significant role in electronic energy transfer dynamics, despite contributing to the enhancement of long-lived quantum beating in 2D electronic spectra, contrary to speculations in recent publications.

  8. Impact of environmentally induced fluctuations on quantum mechanically mixed electronic and vibrational pigment states in photosynthetic energy transfer and 2D electronic spectra.

    PubMed

    Fujihashi, Yuta; Fleming, Graham R; Ishizaki, Akihito

    2015-06-01

    Recently, nuclear vibrational contribution signatures in two-dimensional (2D) electronic spectroscopy have attracted considerable interest, in particular as regards interpretation of the oscillatory transients observed in light-harvesting complexes. These transients have dephasing times that persist for much longer than theoretically predicted electronic coherence lifetime. As a plausible explanation for this long-lived spectral beating in 2D electronic spectra, quantum-mechanically mixed electronic and vibrational states (vibronic excitons) were proposed by Christensson et al. [J. Phys. Chem. B 116, 7449 (2012)] and have since been explored. In this work, we address a dimer which produces little beating of electronic origin in the absence of vibronic contributions, and examine the impact of protein-induced fluctuations upon electronic-vibrational quantum mixtures by calculating the electronic energy transfer dynamics and 2D electronic spectra in a numerically accurate manner. It is found that, at cryogenic temperatures, the electronic-vibrational quantum mixtures are rather robust, even under the influence of the fluctuations and despite the small Huang-Rhys factors of the Franck-Condon active vibrational modes. This results in long-lasting beating behavior of vibrational origin in the 2D electronic spectra. At physiological temperatures, however, the fluctuations eradicate the mixing, and hence, the beating in the 2D spectra disappears. Further, it is demonstrated that such electronic-vibrational quantum mixtures do not necessarily play a significant role in electronic energy transfer dynamics, despite contributing to the enhancement of long-lived quantum beating in 2D electronic spectra, contrary to speculations in recent publications. PMID:26049423

  9. Singlet and triplet energy transfer in the peridinin-chlorophyll a-protein from Amphidinium carterae

    SciTech Connect

    Bautista, J.A.; Frank, H.A. [Univ. of Connecticut, Storrs, CT (United States). Dept. of Chemistry] [Univ. of Connecticut, Storrs, CT (United States). Dept. of Chemistry; Hiller, R.G.; Sharples, F.P. [Marquarie Univ., New South Wales (Australia). School of Biological Sciences] [Marquarie Univ., New South Wales (Australia). School of Biological Sciences; Gosztola, D. [Argonne National Lab., IL (United States). Chemistry Div.] [Argonne National Lab., IL (United States). Chemistry Div.; Wasielewski, M. [Argonne National Lab., IL (United States). Chemistry Div.] [Argonne National Lab., IL (United States). Chemistry Div.; [Northwestern Univ., Evanston, IL (United States). Dept. of Chemistry

    1999-04-08

    The spectroscopic properties of peridinin in solution, and the efficiency and dynamics of energy transfer from peridinin to chlorophyll a in the peridinin-chlorophyll-protein (PCP) from Amphidinium carterae, were studied by steady-state absorption, fluorescence, fluorescence excitation, and fast transient optical spectroscopy. Steady-state measurements of singlet energy transfer from peridinin to chlorophyll revealed an 88 {+-} 2% efficiency. Fast-transient absorption experiments showed that the excited S{sub 1} state of peridinin decayed in 13.4 {+-} 0.6 ps in methanol and 3.1 {+-} 0.4 ps in the PCP complex after direct excitation of the carotenoid. The onset of the bleaching of the chlorophyll absorption band at 672 nm, signifying the arrival of the excitation from the carotenoid, occurred in 3.2 {+-} 0.3 ps. These data show that the primary route of energy transfer from peridinin to chlorophyll in the PCP complex is through the S{sub 1} state of peridinin. Nanosecond time-resolved transient optical spectroscopy revealed that chlorophyll triplet states are efficiently quenched by peridinin whose triplet state subsequently decays with a lifetime of 10 {+-} 1 {micro}s in the PCP complex. Close association between the peridinins and chlorophyll, which is clearly evident in the 3-D structure of the PCP complex, along with proper alignment of pigments and energy state matching are responsible for the high efficiencies of the photochemical processes.

  10. Low-spin states of /sup 250/Cf populated in the electron capture decay of 2. 22-h /sup 250/Es. [ULTIPOLE TRANSITIONS; PARITY; ROTATIONAL STATES; SPIN; VIBRATIONAL STATES; GAMMA SPECTRA

    SciTech Connect

    Ahmad, I.; Sjoblom, R.K.

    1980-09-01

    Low-spin states of /sup 250/Cf have been investigated by measuring ..gamma.. rays and conversion electrons associated with the electron capture decay of 2.22-h /sup 250/Es. Mass-separated /sup 250/Es samples produced by the /sup 249/Cf(d,n) reaction were used for these measurements. The ..gamma..-ray spectra were measured with a 25-cm/sup 3/ coaxial Ge(Li) spectrometer and the electron spectra were measured with a cooled Si(Li) detector. Multipolarities of intense transitions in /sup 250/Cf were deduced and logft values of electron capture transitions were derived from measured electron capture intensities. On the basis of the results of the present investigation the following bandheads were identified in /sup 250/Cf: E (keV),K,I..pi..=871.6, 2,2-; 1031.9, 2,2+; 1154.2, 0,0+; 1175.5, 1,1-; 1210.0, 2,2-; 1244.4, 2,2+; 1266.5, 0,0+; and 1658.1, 2,2+. The 2.22-h state in /sup 250/Es has been given a spin-parity assignment of 1- with configuration )n(734)9/2-; p(633)7/2+)/sub 1//sub -/.

  11. Impact of environmentally induced fluctuations on quantum mechanically mixed electronic and vibrational pigment states in photosynthetic energy transfer and 2D electronic spectra

    E-print Network

    Fujihashi, Yuta; Ishizaki, Akihito

    2015-01-01

    Recently, nuclear vibrational contribution signatures in 2D electronic spectroscopy have attracted considerable interest, in particular as regards interpretation of the oscillatory transients observed in light-harvesting complexes. These transients have dephasing times that persist for much longer than theoretically predicted electronic coherence lifetime. As a plausible explanation for this long-lived spectral beating in 2D electronic spectra, quantum-mechanically mixed electronic and vibrational states (vibronic excitons) were proposed by Christensson et al. [J. Phys. Chem. B 116, 7449 (2012)] and have since been explored. In this work, we address a dimer which produces little beating of electronic origin in the absence of vibronic contributions, and examine the impact of protein-induced fluctuations upon electronic-vibrational quantum mixtures by calculating the electronic energy transfer dynamics and 2D electronic spectra in a numerically accurate manner. It is found that, at cryogenic temperatures, the e...

  12. Narrow chaotic compound autoionizing states in atomic spectra V. V. Flambaum, A. A. Gribakina, and G. F. Gribakin

    E-print Network

    Gribakin, Gleb

    state which accumulates a large share of the total width. This state is in essence a modified single compound states are close to Gaussian. S1050-2947 96 07208-3 PACS number s : 32.80.Dz, 31.50. w, 34.80. i I, the number of many-electron states that can be formed from them rapidly increases exponentially

  13. Particle and Energy Pair and Triplet Correlations in Liquids and Liquid Mixtures from Experiment and Simulation.

    PubMed

    Ploetz, Elizabeth A; Smith, Paul E

    2015-06-25

    Recent advances in fluctuation solution theory (FST) have provided access to information concerning triplet fluctuations and integrals, in addition to the established pair fluctuations and integrals, for liquids and liquid mixtures using both experimental and simulation data. Here, FST is used to investigate pair and triplet correlations for (i) pure water as provided by experiment and simulation using both polarizable and nonpolarizable water models, (ii) liquid mixtures of methanol and water as provided by experiment and simulation, and (iii) native and denatured states of proteins as provided by simulation. The last application is particularly powerful, as it provides exact equations for the volume, enthalpy, compressibility, thermal expansion, and heat capacity of a single protein form provided by a single simulation. In addition, a discussion of the quality of the integrals obtained from experiment and simulation is provided. The results clearly illustrate that FST can be a powerful tool for the analysis and interpretation of both experimental and simulation data in complex liquid mixtures, including biomolecular systems, and that current simulation protocols can provide reliable values for the pair and triplet correlations and integrals. PMID:25961333

  14. Trans-cis isomerization of vinylketones through triplet 1,2-biradicals.

    PubMed

    Ranaweera, R A A Upul; Scott, Tianeka; Li, Qian; Rajam, Sridhar; Duncan, Alexander; Li, Rui; Evans, Anthony; Bohne, Cornelia; Toscano, John P; Ault, Bruce S; Gudmundsdottir, Anna D

    2014-11-13

    The irradiation of trans-vinylketones 1a-c yields the corresponding cis isomers 2a-c. Laser flash photolysis of 1a and 1b with 308 and 355 nm lasers results in their triplet ketones (T1K of 1), which rearrange to form triplet 1,2-biradicals 3a and 3b, respectively, whereas irradiation with a 266 nm laser produces their cis-isomers through singlet reactivity. Time-resolved IR spectroscopy of 1a with 266 nm irradiation confirmed that 2a is formed within the laser pulse. In comparison, laser flash photolysis of 1c with a 308 nm laser showed only the formation of 2c through singlet reactivity. At cryogenic temperatures, the irradiation of 1 also resulted in 2. DFT calculations were used to aid in the characterization of the excited states and biradicals involved in the cis-trans isomerization and to support the mechanism for the cis-trans isomerization on the triplet surface. PMID:25046555

  15. Cascading Proximity Effect and Singlet-Triplet Mixing in Rotating Magnetization Junctions

    NASA Astrophysics Data System (ADS)

    Bill, Andreas; Baker, Thomas E.; Richie-Halford, Adam

    2015-03-01

    The proximity of a superconductor to an inhomogeneous magnetic material induces singlet and triplet pair correlations in the hybrid structure. The amount of each component and their presence deep in the magnetic material strongly depends on the magnetic inhomogeneity. We present a comparative study of pair correlations in a diffusive magnetic Josephson junction involving a multilayer with misaligned magnetization, a cosine-type helical structure and a more flexible and realistic domain wall of an exchange spring. Using the cascading effect we demonstrate that the three systems induce qualitatively different mixtures of correlations. In particular, we show that misaligned and continuously rotating magnetizations do not display the same physical state. Analyzing the Gor'kov functions we find that so-called short range singlet correlations can be found deep in the magnetic material and compete with triplet correlations giving rise to the so-called singlet-triplet 0 - ? transition. We gratefully acknowledge support from the National Science Foundation (DMR-1309341). TEB graciously thanks the support of the UC Irvine Achievement Rewards for College Scientists Fellowship.

  16. Tunable singlet-triplet splitting in a few-electron Si/SiGe quantum dot

    NASA Astrophysics Data System (ADS)

    Shi, Zhan; Simmons, Christie; Prance, Jonathan; Gamble, John; Friesen, Mark; Savage, Donald; Lagally, Max; Coppersmith, Susan; Eriksson, Mark

    2012-02-01

    The singlet-triplet energy splitting in a double quantum dot is an important parameter for singlet-triplet qubits, because it determines the energy gap for both initialization and readout. This splitting can also be used to perform gate operations in a newly proposed hybrid qubit [1]. We describe measurements in which we tune the singlet-triplet energy splitting by changing gate voltages on a Si/SiGe double quantum dot [2]. We argue that the energy is changed largely by lateral translation of the dot, which changes the local atomic structure that the electrons experience in the quantum dot, leading to variations in the valley-orbit coupling. We present calculations indicating the experimental results are consistent with the first excited state of the dot having non-zero valley-orbit coupling. [1] Z. Shi, et al., e-print: http://lanl.arxiv.org/abs/1110.6622. [2] Z. Shi, et al., e-print: http://lanl.arxiv.org/abs/1109.0511.

  17. A spin triplet supercurrent through the half-metallic ferromagnet CrO2.

    PubMed

    Keizer, R S; Goennenwein, S T B; Klapwijk, T M; Miao, G; Xiao, G; Gupta, A

    2006-02-16

    In general, conventional superconductivity should not occur in a ferromagnet, though it has been seen in iron under pressure. Moreover, theory predicts that the current is always carried by pairs of electrons in a spin singlet state, so conventional superconductivity decays very rapidly when in contact with a ferromagnet, which normally prohibits the existence of singlet pairs. It has been predicted that this rapid spatial decay would not occur if spin triplet superconductivity could be induced in the ferromagnet. Here we report a Josephson supercurrent through the strong ferromagnet CrO2, from which we infer that it is a spin triplet supercurrent. Our experimental set-up is different from those envisaged in the earlier predictions, but we conclude that the underlying physical explanation for our result is a conversion from spin singlet pairs to spin triplets at the interface. The supercurrent can be switched with the direction of the magnetization, analogous to spin valve transistors, and therefore could enable magnetization-controlled Josephson junctions. PMID:16482152

  18. Effect of an External Magnetic Field on the Up-Conversion Photoluminescence of Organic Films: The Role of Disorder in Triplet-Triplet Annihilation

    NASA Astrophysics Data System (ADS)

    Mezyk, J.; Tubino, R.; Monguzzi, A.; Mech, A.; Meinardi, F.

    2009-02-01

    We have investigated the influence of the magnetic field on the triplet-triplet annihilation process in organic films using a model multicomponent system for blue delayed up-conversion photoluminescence. In such a way, we have derived simple analytical expressions to estimate the overall annihilation probability, outlining the peculiar role played by the disorder and demonstrating that the triplet-triplet fusion in solid films is a diffusion limited process.

  19. High-triplet-energy dendrons: enhancing the luminescence of deep blue phosphorescent iridium(III) complexes.

    PubMed

    Lo, Shih-Chun; Harding, Ruth E; Shipley, Christopher P; Stevenson, Stuart G; Burn, Paul L; Samuel, Ifor D W

    2009-11-25

    Solution-processable blue phosphorescent emitters with high luminescence efficiency are highly desirable for large-area displays and lighting applications. This report shows that when a fac-tris[1-methyl-5-(4-fluorophenyl)-3-n-propyl-1H-[1,2,4]triazolyl]iridium(III) complex core is encapsulated by rigid high-triplet-energy dendrons, both the physical and photophysical properties can be optimized. The high-triplet-energy and rigid dendrons were composed of twisted biphenyl dendrons with the twisting arising from the use of tetrasubstituted branching phenyl rings. The blue phosphorescent dendrimer was synthesized using a convergent approach and was found to be solution-processable and to possess a high glass transition temperature of 148 degrees C. The dendrimer had an exceptionally high solution photoluminescence quantum yield (PLQY) of 94%, which was more than three times that of the simple parent core complex (27%). The rigid and high-triplet-energy dendrons were also found to control the intermolecular interactions that lead to the quenching of the luminescence in the solid state, and the film PLQY was found to be 60% with the emission having Commission Internationale de l'Eclairage coordinates of (0.16, 0.16). The results demonstrate that dendronization of simple chromophores can enhance their properties. Single layer neat dendrimer organic light-emitting diodes (OLEDs) had an external quantum efficiency (EQE) of 0.4% at 100 cd/m(2). Bilayer devices with an electron transport layer gave improved EQEs of up to 3.9%. Time-resolved luminescence measurements suggest that quenching of triplets by the electron transport layer used in the bilayer OLEDs limits performance. PMID:19919142

  20. Hybrid Spin and Valley Quantum Computing with Singlet-Triplet Qubits

    NASA Astrophysics Data System (ADS)

    Rohling, Niklas; Russ, Maximilian; Burkard, Guido

    2014-10-01

    The valley degree of freedom in the electronic band structure of silicon, graphene, and other materials is often considered to be an obstacle for quantum computing (QC) based on electron spins in quantum dots. Here we show that control over the valley state opens new possibilities for quantum information processing. Combining qubits encoded in the singlet-triplet subspace of spin and valley states allows for universal QC using a universal two-qubit gate directly provided by the exchange interaction. We show how spin and valley qubits can be separated in order to allow for single-qubit rotations.

  1. Hybrid Spin and Valley Quantum Computing with Singlet-Triplet Qubits

    NASA Astrophysics Data System (ADS)

    Rohling, Niklas; Russ, Maximilian; Burkard, Guido

    2015-03-01

    The valley degree of freedom in the electronic band structure of silicon, graphene, and other materials is often considered to be an obstacle for quantum computing (QC) based on electron spins in quantum dots. Here we show that control over the valley state opens new possibilities for quantum information processing. Combining qubits encoded in the singlet-triplet subspace of spin and valley states allows for universal QC using a universal two-qubit gate directly provided by the exchange interaction. We show how spin and valley qubits can be separated in order to allow for single-qubit rotations.

  2. Low-temperature (77 K) phosphorescence of triplet chlorophyll in isolated reaction centers of photosystem II.

    PubMed

    Neverov, Konstantin V; Krasnovsky, Alexander A; Zabelin, Alexey A; Shuvalov, Vladimir A; Shkuropatov, Anatoly Ya

    2015-08-01

    Phosphorescence characterized by the main emission band at 952 ± 1 nm (1.30 eV), the lifetime of 1.5 ± 0.1 ms and the quantum yield nearly equal to that for monomeric chlorophyll a in aqueous detergent dispersions, has been detected in isolated reaction centers (RCs) of spinach photosystem II at 77 K. The excitation spectrum shows maxima corresponding to absorption bands of chlorophyll a, pheophytin a, and ?-carotene. The phosphorescence intensity strongly depends upon the redox state of RCs. The data suggest that the phosphorescence signal originates from the chlorophyll triplet state populated via charge recombination in the radical pair [Formula: see text]. PMID:25712165

  3. Distance dependence of the tryptophan-disulfide interaction at the triplet level from pulsed phosphorescence studies on a model system.

    PubMed Central

    Li, Z; Lee, W E; Galley, W C

    1989-01-01

    In the present study the distance dependence of tryptophan-disulfide interaction is examined with a view to both utilizing the interaction as a more quantitative indicator of subtle conformational changes in proteins as well as elucidating the interaction mechanism. To examine perturbations specifically at the indole triplet level 2-(3-indolyl)-ethyl phenyl ketone (IEPK) in which excitation is transferred with high efficiency to the triplet state of the indole moiety was employed. Phosphorescence decays of IEPK excited by a laser pulse in 70/30 (vol/vol) ethanolether at 77 K were measured in the presence of various concentrations of simple disulfides. The nonexponential phosphorescence decays arising from a distribution of fixed chromophoreperturber separations and the steady-state quenching of IEPK were accounted for with an exponential dependence of the quenching rate constant with distance. The small effective Bohr radius (0.8 A) that appears in the exponent emphasizes the localized nature of the interaction. Comparison of the triplet quenching rate constant obtained at quencher contact with IEPK to that estimated in proteins suggests a dependence on the triplet energy of the indole moiety and an endothermic nature for the quenching process. The study predicts that in proteins tryptophan-disulfide interactions are very localized in nature and should give rise to detectable anomalous decays only out to 2 A beyond van der Waals contact between the interacting partners. PMID:2775831

  4. Transport of Triplet Excitons along Continuous 100 nm Polyfluorene Chains.

    PubMed

    Li, Xiang; Bird, Matthew; Mauro, Gina; Asaoka, Sadayuki; Cook, Andrew R; Chen, Hung-Cheng; Miller, John R

    2015-06-18

    Triplet excitons created in poly-2,7-(9,9-dihexyl)fluorene (pF) chains with end trap groups in solution are efficiently transported to and captured by the end groups. The triplets explore the entire lengths of the chains, even for ?100 nm long chains, enabling determination of the completeness of end-capping. The results show that the chains are continuous: they may contain transient barriers or traps, such as those from fluctuations of dihedral angles, but they are free of major defects that stop motion of the triplets. Quantitative determinations are aided by the addition of a strong electron donor, TMPD, which removes absorption bands of the end-trapped triplets. For chains having at least one end trap, triplet capture is quantitative on the 1 ?s time scale imposed by the use of the donor. Fractions of chains having no end traps were 0.15 for pF samples with anthraquinone (AQ) end traps and 0.063 with naphthylimide (NI) end traps. These determinations agreed with measurements by NMR for short (<40 polymer repeat units (PRU)) chains, where NMR determinations are accurate. The results find no evidence for traps or barriers to the transport of triplets, and places limits on the possible presence of defects as impenetrable barriers to less than one per 300 PRU. The present results present a paradigm different from the current consensus, derived from observations of singlet excitons, that conjugated chains are divided into "segments," perhaps by some kind of defects. For the present pF chains, the segmentation either does not apply to triplet excitons or is transient so that the defects are healed or surmounted in times much shorter than 1 ?s. Triplets on chains without end trap groups transfer to chains with end traps on a slower time scale. Rate constants for these bimolecular triplet transfer reactions were found to increase with the length of the accepting chain, as did rate constants for triplet transfer to the chains from small molecules like biphenyl. A second set of polyfluorenes with 2-butyloctyl side chains was found to have a much lower completeness of end-capping. PMID:25521161

  5. Spin-dependent charge transfer state design rules in organic photovoltaics.

    PubMed

    Chang, Wendi; Congreve, Daniel N; Hontz, Eric; Bahlke, Matthias E; McMahon, David P; Reineke, Sebastian; Wu, Tony C; Bulovi?, Vladimir; Van Voorhis, Troy; Baldo, Marc A

    2015-01-01

    Charge transfer states play a crucial role in organic photovoltaics, mediating both photocurrent generation and recombination losses. In this work, we examine recombination losses as a function of the electron-hole spacing in fluorescent charge transfer states, including direct monitoring of both singlet and triplet charge transfer state dynamics. Here we demonstrate that large donor-acceptor separations minimize back transfer from the charge transfer state to a low-lying triplet exciton 'drain' or the ground state by utilizing external pressure to modulate molecular spacing. The triplet drain quenches triplet charge transfer states that would otherwise be spin protected against recombination, and switches the most efficient origin of the photocurrent from triplet to singlet charge transfer states. Future organic solar cell designs should focus on raising the energy of triplet excitons to better utilize triplet charge transfer mediated photocurrent generation or increasing the donor-acceptor spacing to minimize recombination losses. PMID:25762410

  6. Spin-dependent charge transfer state design rules in organic photovoltaics

    NASA Astrophysics Data System (ADS)

    Chang, Wendi; Congreve, Daniel N.; Hontz, Eric; Bahlke, Matthias E.; McMahon, David P.; Reineke, Sebastian; Wu, Tony C.; Bulovi?, Vladimir; van Voorhis, Troy; Baldo, Marc A.

    2015-03-01

    Charge transfer states play a crucial role in organic photovoltaics, mediating both photocurrent generation and recombination losses. In this work, we examine recombination losses as a function of the electron-hole spacing in fluorescent charge transfer states, including direct monitoring of both singlet and triplet charge transfer state dynamics. Here we demonstrate that large donor–acceptor separations minimize back transfer from the charge transfer state to a low-lying triplet exciton ‘drain’ or the ground state by utilizing external pressure to modulate molecular spacing. The triplet drain quenches triplet charge transfer states that would otherwise be spin protected against recombination, and switches the most efficient origin of the photocurrent from triplet to singlet charge transfer states. Future organic solar cell designs should focus on raising the energy of triplet excitons to better utilize triplet charge transfer mediated photocurrent generation or increasing the donor–acceptor spacing to minimize recombination losses.

  7. Improving triplet-triplet-annihilation based upconversion systems by tuning their topological structure.

    PubMed

    Zimmermann, Jochen; Mulet, Roberto; Scholes, Gregory D; Wellens, Thomas; Buchleitner, Andreas

    2014-11-14

    Materials capable to perform upconversion of light transform the photon spectrum and can be used to increase the efficiency of solar cells by upconverting sub-bandgap photons, increasing the density of photons able to generate an electron-hole pair in the cell. Incoherent solar radiation suffices to activate upconverters based on sensitized triplet-triplet annihilation, which makes them particularly suited for this task. This process requires two molecular species, sensitizers absorbing low energy photons, and emitters generating higher frequency photons. Successful implementations exist in solutions and solids. However, solid upconverters exhibit lower efficiency than those in solution, which poses a serious problem for real applications. In the present work, we suggest a new strategy to increase the efficiency of sensitized upconverters that exploits the solid nature of the material. We show that an upconversion model system with molecules distributed as clusters outperforms a system with a random distribution of molecules, as used in current upconverters. Our simulations reveal a high potential for improvement of upconverter systems by exploring different structural configurations of the molecules. The implementation of advanced structures can push the performance of solid upconverters further towards the theoretical limit and a step closer to technological application of low power upconversion. PMID:25399129

  8. A general strategy for biocompatible, high-effective upconversion nanocapsules based on triplet-triplet annihilation.

    PubMed

    Liu, Qian; Yin, Baoru; Yang, Tianshe; Yang, Yongchao; Shen, Zhen; Yao, Ping; Li, Fuyou

    2013-04-01

    A general strategy for constructing high-effective upconversion nanocapsules based on triplet-triplet annihilation (TTA) was developed by loading both sensitizer and annihilator into BSA-dextran stabilized oil droplets. This strategy can maintain high translational mobility of the chromophores, avoid luminescence quenching of chromophore by aggregation, and decrease the O2-induced quenching of TTA-based upconversion emission. Pt(II)-tetraphenyl-tetrabenzoporphyrin (PtTPBP) and BODIPY dyes (BDP-G and BDP-Y with the maximal fluorescence emission at 528 and 546 nm, respectively) were chosen as sensitizer/annihilator couples to fabricate green and yellow upconversion luminescent emissive nanocapsules, named UCNC-G and UCNC-Y, respectively. In water under the atmospheric environment, interestingly, UCNC-G and UCNC-Y exhibit intense upconversion luminescence (UCL) emission (?ex = 635 nm) with the quantum efficiencies (?UCL) of 1.7% and 4.8%, respectively, whereas very weak UCL emission (?UCL < 0.1%) was observed for the corresponding previous reported SiO2-coating nanosystems because of aggregation-induced fluorescence quenching of annihilators. Furthermore, application of theses upconversion nanocapsules for high-contrast UCL bioimaging in vivo of living mice without removing the skin was demonstrated under 635-nm excitation with low power density of 12.5 mW cm(-2). PMID:23464990

  9. Electron spin dynamics of triplet and doublet molecules in room temperature ionic liquids studied by a time-resolved EPR method

    NASA Astrophysics Data System (ADS)

    Kawai, Akio; Hidemori, Takehiro; Shibuya, Kazuhiko

    2006-05-01

    A time-resolved (TR-) EPR method was applied to measure the triplet spectra of porphyrins such as ZnTPP (TPP, tetraphenylporphyrin) and H4TPP2+ in room temperature ionic liquids (RTIL). The spectra were successfully obtained at 298 K with clear canonical peaks of the triplet sublevels. Magneto-photo selection experiments were carried out for ZnTPP in NR4BF4 (NR4: N,N-diethyl-N-methyl-N-(2-methoxyethyl)ammonium) and H4TPP2+ in BmimPF6 (Bmim: 1-butyl-3-methylimidazolium). In these systems, the intensity ratio of the canonical peaks depends on the orientation between the laser polarization and the external magnetic field at the delay time on the order of submicro-seconds. This experimental finding suggests that there are very slow tumbling motions of ZnTPP and H4TPP2+ in RTILs. Electron spin polarization created in the triplet-doublet system is also successfully observed in RTILs by the TR-EPR method. Based on the analysis of the time evolution curves of both the triplet and doublet molecules, spin polarization mechanisms in the RTILs were discussed.

  10. Correcting human heart 31P NMR spectra for partial saturation. Evidence that saturation factors for PCr/ATP are homogeneous in normal and disease states

    NASA Astrophysics Data System (ADS)

    Bottomley, Paul A.; Hardy, Christopher J.; Weiss, Robert G.

    Heart PCr/ATP ratios measured from spatially localized 31P NMR spectra can be corrected for partial saturation effects using saturation factors derived from unlocalized chest surface-coil spectra acquired at the heart rate and approximate Ernst angle for phosphor creatine (PCr) and again under fully relaxed conditions during each 31P exam. To validate this approach in studies of normal and disease states where the possibility of heterogeneity in metabolite T1 values between both chest muscle and heart and normal and disease states exists, the properties of saturation factors for metabolite ratios were investigated theoretically under conditions applicable in typical cardiac spectroscopy exams and empirically using data from 82 cardiac 31P exams in six study groups comprising normal controls ( n = 19) and patients with dilated ( n = 20) and hypertrophic ( n = 5) cardiomyopathy, coronary artery disease ( n = 16), heart transplants ( n = 19), and valvular heart disease ( n = 3). When TR ? T1,(PCr), with T1(PCr) ? T1(ATP), the saturation factor for PCr/ATP lies in the range 1.5 ± 0.5, regardless of the T1 values. The precise value depends on the ratio of metabolite T1 values rather than their absolute values and is insensitive to modest changes in TR. Published data suggest that the metabolite T1 ratio is the same in heart and muscle. Our empirical data reveal that the saturation factors do not vary significantly with disease state, nor with the relative fractions of muscle and heart contributing to the chest surface-coil spectra. Also, the corrected myocardial PCr/ATP ratios in each normal or disease state bear no correlation with the corresponding saturation factors nor the fraction of muscle in the unlocalized chest spectra. However, application of the saturation correction (mean value, 1.36 ± 0.03 SE) significantly reduced scatter in myocardial PCr/ATP data by 14 ± 11% (SD) ( p ? 0.05). The findings suggest that the relative T1 values of PCr and ATP are substantially the same in chest and heart muscle and are unchanged in these disease states. The mean value for T1 (PCr)/ T1(ATP) is 2.16 ± 0.29 SE.

  11. Vibronic Coupling Investigation to Compute Phosphorescence Spectra of Pt(II) Complexes.

    PubMed

    Vazart, Fanny; Latouche, Camille; Bloino, Julien; Barone, Vincenzo

    2015-06-01

    The present paper reports a comprehensive quantum mechanical investigation on the luminescence properties of several mono- and dinuclear platinum(II) complexes. The electronic structures and geometric parameters are briefly analyzed together with the absorption bands of all complexes. In all cases agreement with experiment is remarkable. Next, emission (phosphorescence) spectra from the first triplet states have been investigated by comparing different computational approaches and taking into account also vibronic effects. Once again, agreement with experiment is good, especially using unrestricted electronic computations coupled to vibronic contributions. Together with the intrinsic interest of the results, the robustness and generality of the approach open the opportunity for computationally oriented chemists to provide accurate results for the screening of large targets which could be of interest in molecular materials design. PMID:25992912

  12. 78 FR 35658 - Spectra Energy Corp., Application for a New or Amended Presidential Permit

    Federal Register 2010, 2011, 2012, 2013, 2014

    2013-06-13

    ...DEPARTMENT OF STATE [Public Notice 8353] Spectra Energy Corp., Application for a New...State. ACTION: Notice of Receipt of Spectra Energy Corp., Application for a New...Department of State (DOS) has received from Spectra Energy Corp (``Spectra...

  13. Spontaneous internal field around the non-magnetic impurity in spin-triplet p-wave superconductivity

    NASA Astrophysics Data System (ADS)

    Takigawa, p.-wave superconductivity M.; Ichioka, M.; Kuroki, K.; Tanaka, Y.

    2005-11-01

    The electronic structure around an impurity in spin triplet p-wave superconductors is investigated by the Bogoliubov-de Gennes theory on a tight-binding model. We calculate the spontaneous current and the local density of states around the impurity and discuss the difference between sin px+i sin py-wave and sin(px+py)-i sin(-px+py)-wave superconducting states.

  14. Orphan spin operators enable the acquisition of multiple 2D and 3D magic angle spinning solid-state NMR spectra

    NASA Astrophysics Data System (ADS)

    Gopinath, T.; Veglia, Gianluigi

    2013-05-01

    We propose a general method that enables the acquisition of multiple 2D and 3D solid-state NMR spectra for U-13C, 15N-labeled proteins. This method, called MEIOSIS (Multiple ExperIments via Orphan SpIn operatorS), makes it possible to detect four coherence transfer pathways simultaneously, utilizing orphan (i.e., neglected) spin operators of nuclear spin polarization generated during 15N-13C cross polarization (CP). In the MEIOSIS experiments, two phase-encoded free-induction decays are decoded into independent nuclear polarization pathways using Hadamard transformations. As a proof of principle, we show the acquisition of multiple 2D and 3D spectra of U-13C, 15N-labeled microcrystalline ubiquitin. Hadamard decoding of CP coherences into multiple independent spin operators is a new concept in solid-state NMR and is extendable to many other multidimensional experiments. The MEIOSIS method will increase the throughput of solid-state NMR techniques for microcrystalline proteins, membrane proteins, and protein fibrils.

  15. Orphan spin operators enable the acquisition of multiple 2D and 3D magic angle spinning solid-state NMR spectra

    PubMed Central

    Gopinath, T.; Veglia, Gianluigi

    2013-01-01

    We propose a general method that enables the acquisition of multiple 2D and 3D solid-state NMR spectra for U-13C, 15N-labeled proteins. This method, called MEIOSIS (Multiple ExperIments via Orphan SpIn operatorS), makes it possible to detect four coherence transfer pathways simultaneously, utilizing orphan (i.e., neglected) spin operators of nuclear spin polarization generated during 15N-13C cross polarization (CP). In the MEIOSIS experiments, two phase-encoded free-induction decays are decoded into independent nuclear polarization pathways using Hadamard transformations. As a proof of principle, we show the acquisition of multiple 2D and 3D spectra of U-13C, 15N-labeled microcrystalline ubiquitin. Hadamard decoding of CP coherences into multiple independent spin operators is a new concept in solid-state NMR and is extendable to many other multidimensional experiments. The MEIOSIS method will increase the throughput of solid-state NMR techniques for microcrystalline proteins, membrane proteins, and protein fibrils. PMID:23676036

  16. Optical spectra and excited state relaxation dynamics of Sm3+ in Gd2SiO5 single crystal

    NASA Astrophysics Data System (ADS)

    Strz?p, A.; Lisiecki, R.; Solarz, P.; Dominiak-Dzik, G.; Ryba-Romanowski, W.; Berkowski, M.

    2012-01-01

    Single crystals of gadolinium orthosilicate Gd2SiO5 containing 0.5 at% and 5 at% of Sm3+ were grown by the Czochralski method. Optical absorption spectra, luminescence spectra and luminescence decay curves were recorded for these systems at 10 K and at room temperature. Comparison of optical spectra recorded in polarized light revealed that the anisotropy of this optically biaxial host affects the intensity distribution within absorption and emission bands related to transitions between multiplets rather than the overall band intensity. It has been found that among four bands of luminescence related to the 4G5/2?6HJ (J=5/2-11/2) transitions of Sm3+ in the visible and near infrared region the 4G5/2 ?6H7/2 one has the highest intensity with a peak emission cross section of 3.54×10-21 cm2 at 601 nm for light polarized parallel to the crystallographic axis c of the crystal. The luminescence decay curve recorded for Gd2SiO5:0.5 at% Sm3+ follows a single exponential time dependence with a lifetime 1.74 ms, in good agreement with the 4G5/2 radiative lifetime ? rad=1.78 ms calculated in the framework of Judd-Ofelt theory. Considerably faster and non-exponential luminescence decay recorded for Gd2SiO5:5 at% Sm3+ sample was fitted to that predicted by the Inokuti-Hirayama theory yielding the microparameter of Sm3+-Sm3+ energy transfer C da=1.264×10-52 cm6×s-1. It is concluded that the system under study may be of interest as a VUV-UV excited visible phosphor or laser material operating in the yellow region of the spectrum.

  17. [The molecular spectra and existence state of sulfonated phthalimidomethyl phthalocyanine hydroxyl aluminum as amphiphilic photosensitizer in aqueous alcoholic solutions and water].

    PubMed

    Huang, J; Liu, E; Dai, Z; Shen, C; Yang, S; Chen, N; Huang, J

    2000-10-01

    The sulfonated phthalimidomethyl phthalocyanine hydroxyl aluminum (Al(OH)PcSP) is an amphiphilic photosensitizer which was proved to have the photodynamic activities against cancer. The electronic absorption spectra and aggregation state of the Al(OH)PcSP in aqueous alcoholic solutions and water were investigated. The results showed that the Al(OH)PcSP existed in the form of monomer in aqueous alcoholic solutions. The increase in the carbon chain and hydroxy of alcohol in solutions had no significant effects on the absorption spectra behaviors of Al(OH)PcSP. But in water, the Al(OH)PcSP existed in the equilibrium between monomer and dimer. The dimerization constant was 5.7307 x 10(4) mol-1.L. The characteristic absorption peak of the Q band of the Al(OH)PcSP dimer was red shifted to 740.5 nm from that of the monomer (676.5 nm), which contrast with those of other metal phthalocyanines dimer. The study on the fluorescence spectra of Al(OH)PcSP in aqueous alcoholic solutions suggested that the fluorescence of the dimer was weak. PMID:12945414

  18. Neural-network analysis of the vibrational spectra of N-acetyl L-alanyl N'-methyl amide conformational states

    NASA Astrophysics Data System (ADS)

    Bohr, H. G.; Frimand, K.; Jalkanen, K. J.; Nieminen, R. M.; Suhai, S.

    2001-08-01

    Density-functional theory (DFT) calculations utilizing the Becke 3LYP hybrid functional have been carried out for N-acetyl L-alanine N'-methylamide and examined with respect to the effect of water on the structure, the vibrational frequencies, vibrational absorption (VA), vibrational circular dichroism (VCD), Raman spectra, and Raman optical activity (ROA) intensities. The large changes due to hydration in the structures, and the relative stability of the conformer, reflected in the VA, VCD, Raman spectra, and ROA spectra observed experimentally, are reproduced by the DFT calculations. A neural network has been constructed for reproducing the inverse scattering data (we infer the structural coordinates from spectroscopic data) that the DFT method could produce. The purpose of the network has also been to generate the large set of conformational states associated with each set of spectroscopic data for a given conformer of the molecule by interpolation. Finally the neural network performances are used to monitor a sensitivity analysis of the importance of secondary structures and the influence of the solvent. The neural network is shown to be good in distinguishing the different conformers of the small alanine peptide, especially in the gas phase.

  19. The covariance of the differences between experimental and theoretical chemical shifts as an aid for assigning two-dimensional heteronuclear correlation solid-state NMR spectra

    NASA Astrophysics Data System (ADS)

    Czernek, Ji?í; Brus, Ji?í

    2014-07-01

    A robust method for the assignment of two-dimensional heteronuclear correlations in the solid-state NMR spectra is described. It statistically evaluates the differences between measured and theoretical (obtained from first-principles calculations of the NMR chemical shielding property of periodic materials) chemical shifts. The values of the covariance of these differences, and of the standard deviations of the respective linear correlations, are elucidative for the spectral assignment process. The efficacy of the method is demonstrated for three crystalline systems: L-tyrosine hydrochloride, L-tyrosine ansolvate, and the polymorphic form I of o-acetylsalicylic acid.

  20. The unimolecular dissociation of H2CO on the lowest triplet potential-energy surface

    NASA Astrophysics Data System (ADS)

    Yamaguchi, Yukio; Wesolowski, Steven S.; Van Huis, Timothy J.; Schaefer, Henry F.

    1998-04-01

    The unimolecular dissociation reaction of H2CO on the triplet potential-energy surface has been studied via ab initio electronic structure theory. The stationary point geometries for the equilibrium and transition state are determined employing the configuration interaction with single and double excitations (CISD), coupled cluster with single and double excitations (CCSD), and CCSD with perturbative triple excitations [CCSD(T)] levels of theory with large basis sets up to the correlation consistent (cc)-pVQZ basis. With the best method, cc-pVQZ CCSD(T), the first excited triplet (ã 3A?) state lies 72.2 kcal/mol (25 260 cm-1) above the ground (X˜ 1A1) state of H2CO, which is in excellent agreement with the experimental observation of 72.03 kcal/mol (25 194 cm-1). The dissociation limit (H?+HCO?) is located at 86.3 kcal/mol (30 170 cm-1) above the ground state of H2CO, which is again in good agreement with the two experimentally determined values of 86.57 kcal/mol (30 280 cm-1) and 86.71 kcal/mol (30 328.5 cm-1). With the same method the triplet dissociation transition state lies 92.4 kcal/mol (32 300 cm-1) above the ground state. Consequently, the activation energy for the dissociation reaction of H2CO on the triplet surface is determined ab initio to be 18.9-20.1 kcal/mol (6620-7040 cm-1) (including an estimated error bar of 1.2 kcal/mol or 420 cm-1). The zero-point vibrationally corrected exit barrier height is predicted to be 4.9-6.1 kcal/mol (1710-2130 cm-1). These newly predicted energies are consistent with the recent experimental observations by the Moore group at University of California-Berkeley (1987) and by the Wittig group at University of Southern California (1997).

  1. Carrier-collision-induced formation of charged excitons and ultrafast dynamics fluorescence spectra.

    PubMed

    Chen, Ren-Ai; Wang, Cong; Li, Sheng; George, Thomas F

    2012-12-13

    After a hole injection layer is inserted into a polymer light-emitting material, the injection of positive charge not only easily causes distortion in the conjugated polymer chain but also produces positive polarons. The ultrafast dynamics shows that, when the positive polaron approaches and collides with the triplet exciton, that exciton will become charged, whereby the non-emissive triplet exciton becomes radiative and emits light. Furthermore, the lifetime of the charged triplet exciton is longer than the singlet exciton. This paper explicitly depicts the dynamic fluorescence spectra of the radiative transition of the charged triplet exciton occurring during the decay of the charged exciton, and also exhibits the difference between traditional adiabatic dynamics and non-adiabatic dynamics. PMID:23186537

  2. Rich Information on Quantum States and Ways to Calculate It in The Absorption Spectra of Au144 Gold Cluster Compound

    NASA Astrophysics Data System (ADS)

    Lopez-Lozano, Xochitl; Whetten, Robert L.; Weissker, Hans-Christian

    2015-03-01

    In recent decades, the prevalent view has been that noble-metal clusters of intermediate size necessarily have smooth optical absorption spectra of low information content in the near-IR, VIS and near-UV regions. At most, one expects a broad, smooth localized surface plasmon resonance feature. Recently, we demonstrate that, in contradistinction to the commonly held view, the optical absorption of the most widely applied gold cluster, the thiolate-protected Au144 cluster, exhibits a rich spectrum of bands that are individually visible over the entire near-IR, VIS and near-UV regions (1.0-4.0 eV), demonstrating high information content related to the quantum size effects which distinguish the nanoparticles from the bulk materials. In the calculation, the result is sensitive to the details of the structure. In the present work, we systematically compare the different structures actually used to date. We studied aspects like symmetry, geometry and type of ligands. In particular, we discuss the effect of their differences on the optical absorption spectra as well as how the theoretical methodology influences the final results.

  3. Methyl rotation in 1,2,4,5-tetramethylbenzene and tetramethylpyrazine in the solid state. Tunneling spectra by proton NMR

    NASA Astrophysics Data System (ADS)

    Takeda, Sadamu; Chihara, Hideaki

    The temperature dependence of proton spin-lattice relaxation behavior in 1,2,4,5-tetramethylbenzene (durene) and tetramethylpyrazine (TMP) was measured with particular attention to the dependence of magnetization recovery on the kind of pulse sequences. The tunneling spectra of the methyl groups of durene and TMP, which correspond to the tunneling-assisted maxima of the spin-lattice relaxation rate, were obtained by the NMR field-cycling method. The three tunneling splittings were observed for both materials in the low temperature limit: 29.3 ± 0.7 MHz, 25.3 ± 0.6 MHz, and 17.8 ± 0.5 MHz for durene and 26.8 ± 0.8 MHz, 20.2 ± 0.8 MHz, and 14.3 ± 0.6 MHz (or 6.4 ± 0.7 MHz) for TMP. Those tunneling spectra indicate collective rotational tunneling of the two neighboring methyl groups in the molecules. There is an indication that the apparent tunneling frequencies decrease as the temperature increases. The effects of correlated reorientation of two methyl groups on the spin-lattice relaxation rate are discussed.

  4. [Investigation of the microstructure of biological systems by triplet label].

    PubMed

    Kotel'niko, A I; Kuznetsov, S N; Fogel', V R; Likhtenshte?n, G I

    1979-01-01

    A method for investigating the microstruct and dynamics of biological systems by means of triplet-excited molecules is suggested. The method is based on the phenomenon of triplet excitation disactivation by exchange-resonance triplet-triplet energy transfer to the acceptor or by intercombination conversion induced by interaction of an excited molecule with a paramagnetic center. The disactivation efficiency was measured by registrating the phosphorescense decay kinetics. The interaction of the triplet label eosin isothiocyanate, covalently coupled with albumine, lysozyme, sarcoplasmic reticulum membrane and Ca-Mg-dependent sarcoplasmic reticulum ATPase, with O2, the stable nitroxide radicals and ions of Mn2+ was investigated to analyse the potentialities of this method. As a model system the eosin phosphorescence quenching by the same quenchers in glycerine-aguaous solutions was studied. The method permits to investigate the microviscosity and microstructure of biological objects in the label attached region on interaction of the label with a sound-quencher with constants being 10(4) divided by 10(9) M-1 sec-1 and to measure the lateral diffusion of molecules in highly viscosity media (10 divided by 10(5) santypuas). PMID:223037

  5. [Neonatal morbidity and hospital mortality of preterm triplets.

    PubMed

    Lamshing-Salinas, Priscilla; Rend Ón-Macías, Mario Enrique; Iglesias-Leboreiro, José; Bernárdez-Zapata, Isabel; Braverman-Bronstein, Ariela

    2013-01-01

    Background: multiple gestations have caused an increase in vulnerable preterm births. Our objective was to analyze neonatal morbidity and mortality in preterm triplets. Methods: we analyzed a cohort of 30 triplets in an obstetrics and gynecology hospital. Data were obtained during pregnancy, childbirth and neonatal period: birth order, sex, weight, height, malformations, advanced resuscitation, assisted ventilation, intraventricular hemorrhage, necrotizing enterocolitis, sepsis, pulmonary hypertension, bronchopulmonary dysplasia, days of hospitalization, and death. Results: 90 infants were analyzed. There was an omphalopagus con-joined twins case; 42 (70 %) had between 30-33 weeks and six between 24-29; 19 (21 %) had low weight for gestational age, and 18 (30 %) had a major malformation; 27 % required ventilatory support, 33 % sepsis, 32 % necrotizing enterocolitis, 21 % pulmonary hypertension, 14 % bronchopulmonary dysplasia and 2 % intraventricular hemorrhage, without statistically significant differences related to the order, presentation at birth, sex and number of placentas and amniotic sacs. Eight 24-week triplets died, four over 28 weeks, and a siamese (p = 38). There was no difference in hospital days between triplets. Conclusions: the triplets mortality is low and mainly associated with extreme prematurity, intrauterine growth restriction and sepsis. PMID:24290011

  6. Structural volume changes upon triplet formation of water-soluble porphyrins depend on the resonant effect of the substituents.

    PubMed

    Kruk, Mikalai M; Braslavsky, Silvia E

    2012-06-01

    Laser-induced optoacoustic spectroscopy was applied to evaluate the photoinduced structural volume changes upon triplet state formation, ?(T)V, of an aqueous solution of 5,10,15,20-tetrakis-(4-carboxyphenyl)-porphin. Two molecular forms differing in the ionization state of the carboxylic groups at the para-position of the phenyl ring were studied. The contractions, ?(T)V, for all water-soluble 5,10,15,20-tetra-aryl-porphyrin compounds studied to date show a linear correlation with the Hammett resonant ?(R) constant. This indicates that the resonance electronic communication spreading over the ?-orbitals between the meso-aryl rings and the porphyrin macrocycle determines the molecular contraction of the aqueous sphere around the macrocycle in the triplet state. PMID:22286746

  7. The Formation of IRIS Diagnostics. IV. The Mg II Triplet Lines as a New Diagnostic for Lower Chromospheric Heating

    NASA Astrophysics Data System (ADS)

    Pereira, Tiago M. D.; Carlsson, Mats; De Pontieu, Bart; Hansteen, Viggo

    2015-06-01

    A triplet of subordinate lines of Mg ii exists in the region around the h&k lines. In solar spectra these lines are seen mostly in absorption, but in some cases can become emission lines. The aim of this work is to study the formation of this triplet, and investigate any diagnostic value they can bring. Using 3D radiative magnetohydrodynamic simulations of quiet Sun and flaring flux emergence, we synthesize spectra and investigate how spectral features respond to the underlying atmosphere. We find that emission in the lines is rare and is typically caused by a steep temperature increase in the lower chromosphere (above 1500 K, with electron densities above 1017 m?3). In both simulations the lines are sensitive to temperature increases taking place at column masses ?5 · 10?4 g cm?2. Additional information can also be inferred from the peak-to-wing ratio and shape of the line profiles. Using observations from NASA's Interface Region Imaging Spectrograph we find both absorption and emission line profiles with similar shapes to the synthetic spectra, which suggests that these lines represent a useful diagnostic that complements the Mg ii h&k lines.

  8. Simulating one-photon absorption and resonance Raman scattering spectra using analytical excited state energy gradients within time-dependent density functional theory

    SciTech Connect

    Silverstein, Daniel W.; Govind, Niranjan; van Dam, Hubertus JJ; Jensen, Lasse

    2013-12-10

    A parallel implementation of analytical time-dependent density functional theory gra- dients is presented for the quantum chemistry program NWChem. The implementation is based on the Lagrangian approach developed by Furche and Ahlrichs. To validate our implementation, we first calculate the Stokes shifts for a range of organic dye molecules using a diverse set of exchange-correlation functionals (traditional density functionals, global hybrids and range-separated hybrids) followed by simulations of the one-photon absorption and resonance Raman scattering spectrum of the phenoxyl radical, the well-studied dye molecule rhodamine 6G and a molecular host-guest complex (TTF?CBPQT4+). The study of organic dye molecules illustrates that B3LYP and CAM-B3LYP generally give the best agreement with experimentally determined Stokes shifts unless the excited state is a charge transfer state. Absorption, resonance Raman, and fluorescence simulations for the phenoxyl radical indicate that explicit solvation may be required for accurate characterization. For the host-guest complex and rhodamine 6G, it is demonstrated that absorption spectra can be simulated in good agreement with experiment for most exchange-correlation functionals. However, because one-photon absorption spectra generally lack well-resolved vibrational features, resonance Raman simulations are necessary to evaluate the accuracy of the exchange-correlation functional for describing a potential energy surface.

  9. (1)H NMR z-spectra of acetate methyl in stretched hydrogels: quantum-mechanical description and Markov chain Monte Carlo relaxation-parameter estimation.

    PubMed

    Shishmarev, Dmitry; Chapman, Bogdan E; Naumann, Christoph; Mamone, Salvatore; Kuchel, Philip W

    2015-01-01

    The (1)H NMR signal of the methyl group of sodium acetate is shown to be a triplet in the anisotropic environment of stretched gelatin gel. The multiplet structure of the signal is due to the intra-methyl residual dipolar couplings. The relaxation properties of the spin system were probed by recording steady-state irradiation envelopes ('z-spectra'). A quantum-mechanical model based on irreducible spherical tensors formed by the three magnetically equivalent spins of the methyl group was used to simulate and fit experimental z-spectra. The multiple parameter values of the relaxation model were estimated by using a Bayesian-based Markov chain Monte Carlo algorithm. PMID:25486634

  10. Effect of Triplet Magnet Vibrations on RHIC Performance with High Energy Protons

    SciTech Connect

    Minty, M.

    2010-05-23

    In this report we present recent experimental data from the Relativistic Heavy Ion Collider (RHIC) illustrating effects resulting from {approx}10 Hz vibrations of the triplet quadrupole magnets in the interactions regions and evaluate the impact of these vibrations on RHIC collider performance. Measurements revealed modulation of the betatron tunes of appreciable magnitude relative to the total beam-beam parameter. Comparison of the discrete frequencies in the spectra of the measured beam positions and betatron tunes confirmed a common source. The tune modulations were shown to result from feed-down in the sextupole magnets in the interaction regions. In addition we show that the distortions to the closed orbit of the two counter-rotating beams produced a modulated crossing angle at the interaction point(s).

  11. VizieR Online Data Catalog: Empirical calibration of the near-IR Ca triplet (Cenarro+ 2001)

    NASA Astrophysics Data System (ADS)

    Cenarro; A. J.; Cardiel; N.; Gorgas; J.; Peletier; R. F.; Vazdekis; A.; Prada; F.

    2001-09-01

    File table contains details of the new near-IR stellar library observed to calibrate the Ca II triplet. It includes the indices CaT*, CaT and PaT measured over the final spectra as well as their corresponding errors. The Henry Draper Catalogue number, other names (mainly HR and BD numbers), coordinates, spectral type, luminosity class, apparent magnitude and atmospheric parameters (as derived in Paper II; Cenarro et al., 2001MNRAS.326..981C) are also given. (1 data file).

  12. Spectral triplets, statistical mechanics and emergent geometry in non-commutative quantum mechanics

    E-print Network

    F. G. Scholtz; B. Chakraborty

    2012-10-12

    We show that when non-commutative quantum mechanics is formulated on the Hilbert space of Hilbert-Schmidt operators (referred to as quantum Hilbert space) acting on a classical configuration space, spectral triplets as introduced by Connes in the context of non-commutative geometry arise naturally. A distance function as defined by Connes can therefore also be introduced. We proceed to give a simple and general algorithm to compute this function. Using this we compute the distance between pure and mixed states on quantum Hilbert space and demonstrate a tantalizing link between statistics and geometry.

  13. Triplet superconductivity in an organic superconductor probed by NMR Knight shift.

    PubMed

    Lee, I J; Brown, S E; Clark, W G; Strouse, M J; Naughton, M J; Kang, W; Chaikin, P M

    2002-01-01

    The nature of the superconducting state in quasi-one-dimensional organic conductors has remained controversial since its discovery. Here we present results of (77)Se NMR Knight shift (K(s)) experiments in (TMTSF)(2)PF(6) under 7 kbar of pressure with a magnetic field aligned along the most conducting a axis. We find no noticeable shift in K(s) upon cooling through the superconducting transition. Since K(s) directly probes the spin susceptibility chi(s), the fact that chi(s) remains unchanged through the superconducting transition strongly suggests spin-triplet superconductivity. PMID:11800982

  14. Atomic Spectra

    NSDL National Science Digital Library

    Nave, Carl R.

    This page from Hyperphysics contains images depicting the light emitted by several elements and their respective spectra. The page also provides a description of how the size of a holographic image scales with the wavelength of the light used to observe it.

  15. g State of Na2: Vibrational Numbering and Hyperfine Structure

    E-print Network

    Huennekens, John

    has proven to be a very powerful experimental tool in the spectroscopy of triplet states of alkali ground state. Since the ground state of all alkali dimers is of 1 g symmetry, transitions into triplet states at intermediate internuclear distances. With the development of narrowband lasers, it has become

  16. AN STIS ATLAS OF Ca II TRIPLET ABSORPTION LINE KINEMATICS IN GALACTIC NUCLEI

    SciTech Connect

    Batcheldor, D.; Mandalou, J. [Physics and Space Sciences Department, Florida Institute of Technology, 150 West University Boulevard, Melbourne, FL 32901 (United States); Axon, D. [School of Mathematical and Physical Sciences, University of Sussex, Sussex House, Brighton BN1 9RH (United Kingdom); Valluri, M. [Department of Astronomy, University of Michigan, Ann Arbor, MI 48109 (United States); Merritt, D., E-mail: dbatcheldor@fit.edu [Department of Physics, Rochester Institute of Technology, 84 Lomb Memorial Drive, Rochester, NY 14623-5603 (United States)

    2013-09-15

    The relations observed between supermassive black holes and their host galaxies suggest a fundamental link in the processes that cause these two objects to evolve. A more comprehensive understanding of these relations could be gained by increasing the number of supermassive black hole mass (M{sub .}) measurements. This can be achieved, in part, by continuing to model the stellar dynamics at the centers of galactic bulges using data of the highest possible spatial resolution. Consequently, we present here an atlas of galaxies in the Space Telescope Imaging Spectrograph (STIS) data archive that may have spectra suitable for new M{sub .} estimates. Archived STIS G750M data for all non-barred galactic bulges are co-aligned and combined, where appropriate, and the radial signal-to-noise ratios calculated. The line-of-sight velocity distributions from the Ca II triplet are then determined using a maximum penalized likelihood method. We find 19 out of 42 galaxies may provide useful new M{sub .} estimates since they are found to have data that is comparable in quality with data that has been used in the past to estimate M{sub .}. However, we find no relation between the signal-to-noise ratio in the previously analyzed spectra and the uncertainties of the black hole masses derived from the spectra. We also find that there is a very limited number of appropriately observed stellar templates in the archive from which to estimate the effects of template mismatching.

  17. UV-vis spectra of singlet state cationic polycyclic aromatic hydrocarbons: Time-dependent density functional theory study

    SciTech Connect

    Dominikowska, Justyna, E-mail: justyna@uni.lodz.pl; Domagala, Malgorzata; Palusiak, Marcin [Department of Theoretical and Structural Chemistry, University of ?ód?, Pomorska 163/165, 90-236 ?ód? (Poland)] [Department of Theoretical and Structural Chemistry, University of ?ód?, Pomorska 163/165, 90-236 ?ód? (Poland)

    2014-01-28

    A theoretical study of singlet state cations of polycyclic aromatic hydrocarbons is performed. Appropriate symmetry suitable for further calculations is chosen for each of the systems studied. The excitation states of such species are obtained by the time dependent density functional theory (TD-DFT) method. The computations are performed using both Pople and electronic response properties basis sets. The results obtained with the use of different basis sets are compared. The electronic transitions are described and the relationships for the lowest-lying transitions states of different species are found. The properties of in-plane and out-of-plane transitions are also delineated. The TD-DFT results are compared with the experimental data available.

  18. Nucleon, {Delta}, and {Omega} excited state spectra in N{sub f}=2+1 lattice QCD

    SciTech Connect

    Bulava, J. [NIC, DESY, Platanenallee 6, D-15738, Zeuthen (Germany); Edwards, R. G.; Joo, B.; Richards, D. G. [Thomas Jefferson National Accelerator Facility, Newport News, Virginia 23606 (United States); Engelson, E.; Wallace, S. J. [Department of Physics, University of Maryland, College Park, Maryland 20742 (United States); Lin, H-W. [Department of Physics, University of Washington, Seattle, Washington 98195-1560 (United States); Morningstar, C. [Department of Physics, Carnegie Mellon University, Pittsburgh, Pennsylvania 15213 (United States)

    2010-07-01

    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 calculation is performed at three values of the light quark mass, corresponding to pion masses m{sub {pi}=}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.

  19. Triplet superfluidity in quasi-one-dimensional conductors and ultra-cold Fermi gases

    Microsoft Academic Search

    Wei Zhang

    2006-01-01

    This thesis presents theoretical investigations of triplet superfluidity (triplet superconductivity) in quasi-one-dimensional organic conductors and ultra-cold Fermi gases. Triplet super.uidity is di.erent from its s-wave singlet counterpart since the order parameter is a complex vector and the interaction between fermions is in general anisotropic. Because of these distinctions, triplet superfluids have different physical properties in comparison to the s-wave case.

  20. Influences of quantum mechanically mixed electronic and vibrational pigment states in 2D electronic spectra of photosynthetic systems: Strong electronic coupling cases

    E-print Network

    Yuta Fujihashi; Graham R. Fleming; Akihito Ishizaki

    2015-06-03

    In 2D electronic spectroscopy studies, long-lived quantum beats have recently been observed in photosynthetic systems, and it has been suggested that the beats are produced by quantum mechanically mixed electronic and vibrational states. Concerning the electronic-vibrational quantum mixtures, the impact of protein-induced fluctuations was examined by calculating the 2D electronic spectra of a weakly coupled dimer with vibrational modes in the resonant condition [J. Chem. Phys. 142, 212403 (2015)]. This analysis demonstrated that quantum mixtures of the vibronic resonance are rather robust under the influence of the fluctuations at cryogenic temperatures, whereas the mixtures are eradicated by the fluctuations at physiological temperatures. However, this conclusion cannot be generalized because the magnitude of the coupling inducing the quantum mixtures is proportional to the inter-pigment coupling. In this study, we explore the impact of the fluctuations on electronic-vibrational quantum mixtures in a strongly coupled dimer. with an off-resonant vibrational mode. Toward this end, we calculate electronic energy transfer (EET) dynamics and 2D electronic spectra of a dimer that corresponds to the most strongly coupled bacteriochlorophyll molecules in the Fenna-Matthews-Olson complex in a numerically accurate manner. The quantum mixtures are found to be robust under the exposure of protein-induced fluctuations at cryogenic temperatures, irrespective of the resonance. At 300 K, however, the quantum mixing is disturbed more strongly by the fluctuations, and therefore, the beats in the 2D spectra become obscure even in a strongly coupled dimer with a resonant vibrational mode. Further, the overall behaviors of the EET dynamics are demonstrated to be dominated by the environment and coupling between the 0-0 vibronic transitions as long as the Huang-Rhys factor of the vibrational mode is small.

  1. First-principles study of phonons and related ground-state properties and spectra in Zn-IV-N2 compounds

    NASA Astrophysics Data System (ADS)

    Paudel, Tula R.; Lambrecht, Walter R. L.

    2008-09-01

    The Zn-IV-N2 compounds, with the group-IV element Si, Ge, and Sn, which have a common crystal structure closely related to the wurtzite-structure form a series analogous to the group-III nitrides GaN, AlN, and InN, respectively. Calculations of the phonons and related quantities in these materials are reported here using the density-functional perturbation-theory linear-response approach in the local-density approximation and using a plane-wave pseudopotential method. We focus on spectra, such as the imaginary part of the dielectric function and the energy-loss function as measurable by infrared absorption or reflectivity, and the Raman spectra. We also present phonon densities of states, band dispersions, and related integrated thermodynamic quantities such as the specific heat, and Helmholtz free energy and entropy as functions of temperature. Structural and elastic properties such as the lattice constants and bulk moduli are also reported. Finally, high-frequency and static dielectric tensors are presented. The trends in the series and the relation to the corresponding III-N nitrides are discussed. It is found that the bimodal bond-length distribution with IV-N bonds shorter than the Zn-N bonds (even for Sn) strongly modifies the spectra from those in III-N nitrides. While in ZnGeN2 and ZnSnN2 folded acoustic-like modes are clearly separated from the optic type modes, this is not the case in ZnSiN2 . The calculated Born effective charges indicate that ZnGeN2 has the lowest ionicity of the three materials.

  2. High-efficiency fluorescent organic light-emitting diodes enabled by triplet-triplet annihilation and horizontal emitter orientation

    NASA Astrophysics Data System (ADS)

    Mayr, Christian; Schmidt, Tobias D.; Brütting, Wolfgang

    2014-11-01

    A green organic light-emitting diode with the fluorescent emitter Coumarin 545T shows an external quantum efficiency ( ? EQE ) of 6.9%, clearly exceeding the classical limit of 5% for fluorescent emitters. The analysis of the angular dependent photoluminescence spectrum of the emission layer reveals that 86% of the transition dipole moments are horizontally oriented. Furthermore, transient electroluminescence measurements demonstrate the presence of a delayed emission originating from triplet-triplet annihilation. A simulation based efficiency analysis reveals quantitatively the origin for the high ? EQE : a radiative exciton fraction higher than 25% and a light-outcoupling efficiency of nearly 30%.

  3. Laser-induced fluorescence spectrum of the cyanocyclopentadienyl radical. A band system long attributed to triplet phenylnitrene

    Microsoft Academic Search

    David W. Cullin; N. Soundararajan; Matthew S. Platz; Terry A. Miller

    1990-01-01

    The UV electronic spectrum long attributed to the triplet phenylnitrene intermediate has been reexamined. A variety of evidence strongly indicates that the true carrier of this spectrum is not phenylnitrene, but the cyanocyclopentadienyl radical. This evidence is based upon the spin and rotational structure of the band, its ground-state vibrational frequency characteristic of a C{triple bond}N triple bond, and several

  4. Electronic structure and spontaneous internal field around nonmagnetic impurities in spin-triplet chiral p -wave superconductors

    NASA Astrophysics Data System (ADS)

    Takigawa, Mitsuaki; Ichioka, Masanori; Kuroki, Kazuhiko; Tanaka, Yukio

    2005-12-01

    The electronic structure around an impurity in spin-triplet p -wave superconductors is studied by the Bogoliubov-de Gennes theory on a tight-binding model, where we have chosen sinpx+isinpy -wave or sin(px+py)+isin(-px+py) -wave states, which are considered to be candidates for the pairing state in Sr2RuO4 . We calculate the spontaneous current and the local density of states around the impurity and discuss the difference between the two types of pairing. We propose that it is possible to discriminate the two pairing states by studying the spatial dependence of the magnetic field around a pair of impurities.

  5. Time-resolved electron paramagnetic resonance study of rhodium(III) corrole excited states.

    PubMed

    Wagnert, Linn; Berg, Alexander; Saltsman, Irena; Gross, Zeev; Rozenshtein, Vladimir

    2010-02-11

    Photoexcited states of three Rh(III) 5,10,15-tris(pentafluorophenyl)corroles coordinated by different axial ligands; namely, triphenylphosphine P(C(6)H(5))(3) group (1), pyridine C(6)H(5)N group (2), and two pyridine groups (3) were studied by X- and Q-band time-resolved electron paramagnetic resonance (TREPR) in frozen toluene and liquid crystal E-7. Transient mutations were utilized to identify multiplicity of the detected paramagnetic species. The spectra of 1 and 2 were assigned to triplet ((3)pipi*) states, while contributions of triplet ((3)dd and charge transfer (3)CT) and quintet ((5)dd) states were revealed in the spectrum of 3. The results are interpreted in terms of a peculiar nature of transition metal complexes with the unfilled d-shell, where close lying electronic states of different multiplicities may be mixed through configurational, spin-orbit, and vibronic coupling. From the EPR spectra, the spin-orbit coupling constant was estimated to be about 25 cm(-1). It is shown that different axial ligation of complexes shifts the relative energy of the excited states and, consequently, leads to population of different states. Plausible explanations of the effects governing unusual spectral and dynamic parameters of the photoexcited Rh corrole complexes are presented. PMID:20070101

  6. Novel triplet repeat containing genes in human brain: Cloning, expression, and length polymorphisms

    Microsoft Academic Search

    Shi Hua Li; R. L. Margolis; C. A. Ross; M. G. McInnis; S. E. Antonarakis

    1993-01-01

    Human genes containing triplet repeats may markedly expand in length and cause neuropsychiatric disease, explaining the phenomenon of anticipation (increasing severity or earlier age of onset in successive generations in a pedigree). To identify novel genes with triplet repeats, the authors screened a human brain cDNA library with oligonucleotide probes containing CTG or CCG triplet repeats. Fourteen of 40 clones

  7. Morphology Effectively Controls Singlet-Triplet Exciton Relaxation and Charge Transport in Organic Semiconductors

    E-print Network

    singlet- triplet exciton fission. In Pc films (as well as C60-doped films) this decay channel behavior in an organic semiconductor by effectively turning singlet- triplet exciton fission decay channelsMorphology Effectively Controls Singlet-Triplet Exciton Relaxation and Charge Transport in Organic

  8. Neonatal outcome of triplet versus twin and singleton pregnancies: a matched case control study

    Microsoft Academic Search

    Praveen Ballabh; Jaishree Kumari; Huda B AlKouatly; Melissa Yih; Ronald Arevalo; Zev Rosenwaks; Alfred N Krauss

    2003-01-01

    Objective: To determine the neonatal outcome of triplet gestations versus that of singletons and twins matched for gestational age. Study design: All live born triplet gestations delivered between 1 April 1993 and 31 March 2000 were compared to an age matched control group consisting of live born twins and singletons. The neonatal outcome of 116 sets of triplets was compared

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

    E-print Network

    Enhanced photovoltaic response of organic solar cell by singlet-to-triplet exciton conversion Chia-to-triplet conversion, greatly enhanced photovoltaic response of these hybrid organic solar cells was observed. The results suggest that triplet solar cells may be achieved by doping conventional photovoltaic materials

  10. Potassium spectra in the 700-7000 cm-1 domain: Transitions involving f-, g-, and h-states

    NASA Astrophysics Data System (ADS)

    Civiš, S.; Ferus, M.; Kubelík, P.; Jelinek, P.; Chernov, V. E.

    2012-05-01

    Context. The infrared (IR) range is becoming increasingly important to astronomical studies of cool or dust-obscured objects, such as dwarfs, disks, or planets, and in the extended atmospheres of evolved stars. A general drawback of the IR spectral region is the much lower number of atomic lines available (relative to the visible and ultraviolet ranges). Aims: We attempt to obtain new laboratory spectra to help us identify spectral lines in the IR. This may result in the discovery of new excited atomic levels that are difficult to compute theoretically with high accuracy, hence can be determined solely from IR lines. Methods: The K vapor was formed through the ablation of the KI (potassium iodide) target by a high-repetition-rate (1.0 kHz) pulsed nanosecond ArF laser (? = 193 nm, output energy of 15 mJ) in a vacuum (10-2 Torr). The time-resolved emission spectrum of the neutral atomic potassium (K i) was recorded in the 700-7000 cm-1 region using the Fourier transform infrared spectroscopy technique with a resolution of 0.02 cm-1. The f-values calculated in the quantum-defect theory approximation are presented for the transitions involving the reported K i levels. Results: Precision laboratory measurements are presented for 38 K i lines in the infrared (including 25 lines not measured previously in the laboratory) range using time-resolved Fourier transform infrared spectroscopy. The 6g, 6h, and 7h levels of K i are observed for the first time, in addition to updated energy values of the other 23 K i levels and the f-values for the transitions involving these levels. Conclusions: The recorded wave numbers are in good agreement with the data from the available solar spectrum atlases. Nevertheless, we correct their identification for three lines (1343.699, 1548.559, and 1556.986 cm-1).

  11. Odd triplet superconductivity in superconductor-ferromagnet structures.

    E-print Network

    Fominov, Yakov

    -Ferromagnet multilayers FSFSFSF No chance for Cooper pairs to penetrate the ferromagnet.(?) KT KT C K 101 1000 -= = 100A1 Odd triplet superconductivity in superconductor-ferromagnet structures. F.S. Bergeret, A.F. Volkov, K.B. Efetov S FF S-superconductor, F-ferromagnet #12;2 Common knowledge: Exchange field destroys

  12. Ultrafast singlet and triplet dynamics in microcrystalline pentacene films

    Microsoft Academic Search

    Henning Marciniak; Igor Pugliesi; Bert Nickel; Stefan Lochbrunner

    2009-01-01

    The exciton dynamics of microcrystalline pentacene films is investigated by femtosecond pump-probe experiments. Measurements are performed with ultrashort laser pulses applied at normal incidence and at an angle of incidence of 65° to disentangle singlet and triplet contributions by exploiting the different orientations of the molecular transition dipoles. The results indicate that the initial 70 fs fast relaxation step transforms

  13. Mother-daughter in vitro fertilization triplet surrogate pregnancy

    Microsoft Academic Search

    M. C. Michelow; J. Bernstein; M. J. Jacobson; J. L. McLoughlin; D. Rubenstein; A. I. Hacking; S. Preddy; I. J. Van der Wat

    1988-01-01

    A successful triplet pregnancy has been established in a surrogate gestational mother following the transfer of five embryos fertilized in vitro. The oocytes were donated by her biological daughter, and the sperm obtained from the daughter's husband. The daughter's infertility followed a total abdominal hysterectomy performed for a postpartum hemorrhage as a result of a placenta accreta. Synchronization of both

  14. Sulphur abundances in halo giants from the [S I] line at 1082 nm and the S I triplet around 1045 nm

    E-print Network

    Jönsson, H; Nissen, P E; Collet, R; Eriksson, K; Asplund, M; Gustafsson, B

    2011-01-01

    It is still debated whether or not the Galactic chemical evolution of sulphur in the halo followed the constant or flat trend with [Fe/H], ascribed to the result of explosive nucleosynthesis in type II SNe. The aim of this study is to try to clarify this situation by measuring the sulphur abundance in a sample of halo giants using two diagnostics; the S I triplet around 1045 nm and the [S I] line at 1082 nm. The latter of the two is not believed to be sensitive to non-LTE effects. We can thereby minimize the uncertainties in the diagnostic used and estimate the usefulness of the triplet in sulphur determination in halo K giants. We will also be able to compare our sulphur abundance differences from the two diagnostics with the expected non-LTE effects in the 1045 nm triplet previously calculated by others. High-resolution near-infrared spectra of ten K giants were recorded using the spectrometer CRIRES mounted on VLT. Two standard settings were used; one covering the S I triplet and one covering the [S I] lin...

  15. A Climatology of Tropospheric CO over the Central and Southeastern United States and the Southwestern Pacific Ocean Derived from Space, Air, and Ground-based Infrared Interferometer Spectra

    NASA Technical Reports Server (NTRS)

    McMillian, W. Wallace; Strow, L. Larrabee; Revercomb, H.; Knuteson, R.; Thompson, A.

    2003-01-01

    This final report summarizes all research activities and publications undertaken as part of NASA Atmospheric Chemistry and Modeling Analysis Program (ACMAP) Grant NAG-1-2022, 'A Climatology of Tropospheric CO over the Central and Southeastern United States and the Southwestern Pacific Ocean Derived from Space, Air, and Ground-based Infrared Interferometer Spectra'. Major project accomplishments include: (1) analysis of more than 300,000 AERI spectra from the ARM SGP site yielding a 5-year (1998-2002) timeseries of CO retrievals from the Lamont, OK AERI; (2) development of a prototype CO profile retrieval algorithm for AERI spectra; (3) validation and publication of the first CO retrievals from the Scanning High-resolution Interferometer Sounder (SHIS); and (4) development of a prototype AERI tropospheric O3 retrieval algorithm. Compilation and publication of the 5-year Lamont, OK timeseries is underway including a new collaboration with scientists at the Lawrence Berkeley National Laboratory. Public access to this data will be provided upon article submission. A comprehensive CO analysis of the archive of HIS spectra of remains as the only originally proposed activity with little progress. The greatest challenge faced in this project was motivating the University of Wisconsin Co-Investigators to deliver their archived HIS and AERIOO data along with the requisite temperature and water vapor profiles in a timely manner. Part of the supplied HIS dataset from ASHOE may be analyzed as part of a Master s Thesis under a separate project. Our success with the SAFARI 2000 SHIS CO analysis demonstrates the utility of such aircraft remote sensing data given the proper support from the instrument investigators. In addition to the PI and Co-I s, personnel involved in this CO climatology project include one Post Doctoral Fellow, one Research Scientist, two graduate students, and two undergraduate students. A total of fifteen presentations regarding research related to this project were delivered at eleven different scientific meetings. Thus far, three publications have resulted from this project with another five in preparation. No subject inventions resulted from this research project.

  16. Absence of singlet fission and carrier multiplication in a model conjugated polymer: tracking the triplet population through phosphorescence.

    PubMed

    Bange, Sebastian; Scherf, Ullrich; Lupton, John M

    2012-02-01

    Singlet fission, or multiple exciton generation, has been purported to occur in a variety of material systems. Given the current interest in exploiting this process in photovoltaics, we search for the direct signature of singlet fission, phosphorescence from the triplet state, in a model polymeric organic semiconductor for which photoinduced absorption experiments have implied a tripling of the intersystem crossing yield at the onset of fission. Fluorescence and phosphorescence are clearly discriminated using a picosecond gated photoluminescence excitation technique, at variable temperature. At low excitation densities, in a quasi-steady-state experiment, we detect no change of the relative triplet yield to within 4% for photon energies of almost three times the triplet energy of 2.1 eV. Identical results are obtained under nonlinear two-photon excitation. We conclude that assignments of singlet fission based on induced absorptions alone should be treated with caution and may substantially overestimate excited-state intersystem crossing yields, raising questions with regards to the applicability of the process in devices. PMID:22235946

  17. Evidence for spin-triplet odd-parity superconductivity close to type-II van Hove singularities

    NASA Astrophysics Data System (ADS)

    Meng, Zi Yang; Yang, Fan; Chen, Kuang-Shing; Yao, Hong; Kee, Hae-Young

    2015-05-01

    Searching for unconventional Cooper pairing states has been at the heart of superconductivity research since the discovery of BCS superconductors. In particular, spin-triplet odd-parity pairing states were recently revisited due to the possibility of tuning towards topological superconductors. In this context, it is interesting to note a recent proposal that such a spin-triplet pairing instability occurs when the band filling is near van Hove singularities (vHS) associated with momenta away from time-reversal invariant momenta named type-II vHS. However, this result was obtained within a weak coupling renormalization group with Fermi surface patch approximation. To explore superconducting instabilities beyond this weak coupling Fermi surface patch approximation, we perform systematic study on the Hubbard model in a two-dimensional square lattice using three different methods: random phase approximation, large-scale dynamical mean-field theory simulations with continuous time quantum Monte Carlo (CTQMC) impurity solver, and large-scale dynamical cluster simulations with the CTQMC cluster solver. We find, in a wide doping range centered around the type-II van Hove filling, a twofold degenerate, spin-triplet, odd-parity p -wave pairing state emerges due to repulsive interaction, when the Fermi surface is not sufficiently nested. Possible relevance of our findings to the recently discovered superconductors LaO1 -xFxBiS2 ,Ir1 -xPtxTe2 , and proposed doped BC3 are also discussed.

  18. Comparative analysis of the vibrational structure of the absorption spectra of acrolein in the excited ( S 1) electronic state

    NASA Astrophysics Data System (ADS)

    Koroleva, L. A.; Tyulin, V. I.; Matveev, V. K.; Pentin, Yu. A.

    2012-04-01

    The assignments of absorption bands of the vibrational structure of the UV spectrum are compared with the assignments of bands obtained by the CRDS method in a supersonic jet from the time of laser radiation damping for the trans isomer of acrolein in the excited ( S 1) electronic state. The ?00 trans = 25861 cm-1 values and fundamental frequencies, including torsional vibration frequency, obtained by the two methods were found to coincide in the excited electronic state ( S 1) for this isomer. The assignments of several absorption bands of the vibrational structure of the spectrum obtained by the CRDS method were changed. Changes in the assignment of (0-v') transition bands of the torsional vibration of the trans isomer in the Deslandres table from the ?00 trans trans origin allowed the table to be extended to high quantum numbers v'. The torsional vibration frequencies up to v' = 5 were found to be close to the frequencies found by analyzing the vibrational structure of the UV spectrum and calculated quantum-mechanically. The coincidence of the barrier to internal rotation (the cis-trans transition) in the one-dimensional model with that calculated quantum-mechanically using the two-dimensional model corresponds to a planar structure of the acrolein molecule in the excited ( S 1) electronic state.

  19. Influences of quantum mechanically mixed electronic and vibrational pigment states in 2D electronic spectra of photosynthetic systems: Strong electronic coupling cases

    E-print Network

    Fujihashi, Yuta; Ishizaki, Akihito

    2015-01-01

    In 2D electronic spectroscopy studies, long-lived quantum beats have recently been observed in photosynthetic systems, and it has been suggested that the beats are produced by quantum mechanically mixed electronic and vibrational states. Concerning the electronic-vibrational quantum mixtures, the impact of protein-induced fluctuations was examined by calculating the 2D electronic spectra of a weakly coupled dimer with vibrational modes in the resonant condition [J. Chem. Phys. 142, 212403 (2015)]. This analysis demonstrated that quantum mixtures of the vibronic resonance are rather robust under the influence of the fluctuations at cryogenic temperatures, whereas the mixtures are eradicated by the fluctuations at physiological temperatures. However, this conclusion cannot be generalized because the magnitude of the coupling inducing the quantum mixtures is proportional to the inter-pigment coupling. In this study, we explore the impact of the fluctuations on electronic-vibrational quantum mixtures in a strongl...

  20. Automatic stellar spectra parameterisation in the IR Ca ii triplet region

    Microsoft Academic Search

    G. Kordopatis; A. Recio-Blanco; P. de Laverny; A. Bijaoui; V. Hill; G. Gilmore; R. F. G. Wyse; C. Ordenovic

    2011-01-01

    Context. Galactic archaeology aims to determine the evolution of the Galaxy from the chemical and kinematical properties of its individual stars. This requires the analysis of data from large spectroscopic surveys, with sample sizes in tens of thousands at present, with millions of stars being reached in the near future. Such large samples require automated analysis techniques and classification algorithms