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1

Photodissociation of N2O: triplet states and triplet channel.  

PubMed

The role of triplet states in the UV photodissociation of N(2)O is investigated by means of quantum mechanical wave packet calculations. Global potential energy surfaces are calculated for the lowest two (3)A' and the lowest two (3)A'' states at the multi-reference configuration interaction level of electronic structure theory using the augmented valence quadruple zeta atomic basis set. Because of extremely small transition dipole moments with the ground electronic state, excitation of the triplet states has only a marginal effect on the far red tail of the absorption cross section. The calculations do not show any hint of an increased absorption around 280 nm as claimed by early experimental studies. The peak observed in several electron energy loss spectra at 5.4 eV is unambiguously attributed to the lowest triplet state 1(3)A'. Excitation of the 2(1)A' state and subsequent transition to the repulsive branch of the 2(3)A'' state at intermediate NN-O separations, promoted by spin-orbit coupling, is identified as the main pathway to the N(2)((1)?(g)(+))+O((3)P) triplet channel. The yield, determined in two-state wave packet calculations employing calculated spin-orbit matrix elements, is 0.002 as compared to 0.005 ± 0.002 measured by Nishida et al. [J. Phys. Chem. A 108, 2451 (2004)]. PMID:22112078

Schinke, R; Schmidt, J A; Johnson, M S

2011-11-21

2

Excited triplet state spectroscopy in the infrared  

NASA Astrophysics Data System (ADS)

A new method for the investigation of the infrared spectra of metastable excitedelectronic states is presented. With a Fourier Transform infrared spectrometer as the probe and a CW Xe lamp source as the pump, the infrared spectrum of the lowest triplet state of triphenylene isolated in a N 2 matrix at 15K has been examined. CH out-of-plane wagging modes are prominent and shifted from their ground state frequencies. It is expected that when fully developed this method will provide important information on excited state force constants and potential energy surfaces.

Baiardo, Joseph; Mukherjee, Ranajit; Vala, Martin

1982-03-01

3

Interpretation of resonance cars and shpolskii spectra with calculated molecular geometries, vibrational frequencies and relative intensities: Chrysene in it's lowest excited singlet and triplet state  

NASA Astrophysics Data System (ADS)

Coherent anti-Stokes Raman scattering (CARS) spectra of excited molecules as well as Shpolskii spectra provide information about geometry changes between ground and excited states. Vibrational frequencies and relative intensities from recently obtained CARS spectra of the chrysene S 1 and T 1 state and earlier observed Shpolskii spectra are interpreted in terms of molecular geometry and force-field changes by means of quantum-chemical consistent force field (QCFF) and Franck-Condon factor calculations. The comparison of observed and calculated relative intensities indicates a coupling between the S 1 and S 2 state enhancing some of the vibrational radiative singlet transitions both in absorption and fluorescence spectra whereas within the phosphorescence spectra proportionality to calculated Franck-Condon factors is obeyed. The T 1 state is the more loosely bound state and its geometry change is different from that of the S 1 state. The resonance CARS transitions in the S 1 state are assigned to totally symmetric vibrations getting their intensity by a coupling scheme analogous to the A term of the resonance Raman effect: the relative intensity of a transition is shown to be proportional to the Franck-Condon factor to the higher excited state and to the squared vibrational frequency. Using this relation this state can be identified by means of its finger-print-like intensity pattern.

Jung, Ch.; Lau, A.; Weigmann, H.-J.; Werncke, W.; Pfeiffer, M.

1982-11-01

4

Triplet state IR spectroscopy of aromatic homocycles and heterocycles  

NASA Astrophysics Data System (ADS)

The triplet (T 1) state IR spectra of 9 aromatic compounds, i.e. acenaphthene, biphenyl, chrysene, coronene, fluorene, 2-phenylpyridine, 5-monoazaphenanthrene (5-MAP) and triphenylene, embedded in rigid glass at 77 K are reported. The symmetry of the T 1 vibrations has been determined from IR linear dichroism measurements of T 1 excited molecules in stretched polymer films. The T 1 vibrational spectra were tentatively assigned on the basis of analogous experimental and theoretical results for the respective ground-state molecules.

Krumschmidt, Helga; Kryschi, Carola

1991-07-01

5

Triplet state dynamics in peridinin-chlorophyll-a-protein: a new pathway of photoprotection in LHCs?  

PubMed

This work investigates the interaction of carotenoid and chlorophyll triplet states in the peridinin-chlorophyll-a-protein (PCP) of Amphidinium carterae using step-scan Fourier transform infrared spectroscopy. We identify two carotenoid triplet state lifetimes of approximately 13 and approximately 42 mus in the spectral region between 1800 and 1100 cm(-1) after excitation of the 'blue' and 'red' peridinin (Per) conformers and the Q(y) of chlorophyll-a (Chl-a). The fast and slow decaying triplets exhibit different spectral signatures in the carbonyl region. The fast component generated at all excitation wavelengths is from a major conformer with a lactone stretching mode bleach at 1745 cm(-1). One (1720 cm(-1)) and two (1720 cm(-1) and 1741 cm(-1)) different Per conformers are observed for the slow component upon 670- and 530-480-nm excitation, respectively. The above result implies that (3)Per triplets are formed via two different pathways, corroborating and complementing visible triplet-singlet (T-S) spectra (Kleima et al., Biochemistry (2000), 39, 5184). Surprisingly, all difference spectra show that Per and Chl-a modes are simultaneously present during the (3)Per decay, implying significant involvement of (3)Chl-a in the (3)Per state. We suggest that this Per-Chl-a interaction via a delocalized triplet state lowers the (3)Per energy and thus provides a general, photoprotection mechanism for light-harvesting antenna complexes. PMID:17483182

Alexandre, Maxime T A; Lührs, Daniel C; van Stokkum, Ivo H M; Hiller, Roger; Groot, Marie-Louise; Kennis, John T M; van Grondelle, Rienk

2007-09-15

6

Triplet excitons: Bringing dark states to light  

NASA Astrophysics Data System (ADS)

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.

Bardeen, Christopher J.

2014-11-01

7

The triplet state of a platinum acetylide chromophore examined by time-resolved infrared spectroscopy and density functional theory  

NASA Astrophysics Data System (ADS)

To understand platinum acetylide molecular structure changes upon conversion to the triplet state, we measured time-resolved infrared (TRIR) spectra of the platinum acetylide complex trans-bis(tributylphosphine)bis(4-ethynyl-1-(2-phenylethynyl)benzene)platinum (abbreviated as PE2). We used density functional theory (DFT) methods to calculate the geometry, molecular orbitals and vibrational spectra of the ground and lowest energy triplet state of PE2. Solutions of PE2 were excited upon ns pulsed laser excitation at 355 nm and TRIR spectra were collected. The TRIR data show cumulenic vibrations in the triplet state as well as evidence for photoproduct formation. The DFT results support the experimental data, suggesting PE2's triplet state has quinone character.

Cooper, Thomas M.; Blaudeau, Jean-Philippe; Hall, Benjamin C.; Rogers, Joy E.; McLean, Daniel G.; Liu, Yonglin; Toscano, John P.

2004-12-01

8

Energy Transfer from the Upper Triplet States of Aromatic Molecules  

Microsoft Academic Search

The energy transfer from the upper triplet states of diphenylamine, naphthalene and triphenylene to toluene and hexene-1 is studed. Two mechanisms of dissipation transferred energy in solvents are discussed.

V. I. Gerko; L. S. Popov; M. V. Alfimov

1978-01-01

9

Photoelectrically detected magnetic resonance spectroscopy of the excited triplet states of point defects in silicon  

Microsoft Academic Search

Highly sensitive methods for the detection of the electron paramagnetic resonance (EPR) spectra based on the spin-dependent\\u000a microwave photoconductivity were applied to investigate the structural defects in irradiated silicon. The parameters of the\\u000a EPR spectra of the excited triplet states of radiation defects were determined and several models of the carbon related defects\\u000a were supposed.

L. S. Vlasenko

1999-01-01

10

Calculations of N 2 triplet states vibrational populations and band emissions in venusian dayglow  

NASA Astrophysics Data System (ADS)

A model for N 2 triplet states band emissions in the venusian dayglow has been developed for low and high solar activity conditions. Steady state photoelectron fluxes and volume excitation rates for N 2 triplet states have been calculated using the Analytical Yield Spectra (AYS) technique. Model calculated photoelectron flux is in good agreement with Pioneer Venus Orbiter-observed electron flux. Since inter-state cascading is important for the triplet states of N 2, populations of different levels of N 2 triplet states are calculated under statistical equilibrium considering direct electron impact excitation, and cascading and quenching effects. Densities of all vibrational levels of each triplet state are calculated in the model. Height-integrated overhead intensities of N 2 triplet band emissions are calculated, the values for Vegard-Kaplan (A3?u+-X1?g+), First Positive (B3?g-A3?u+), Second Positive ( C3? u - B3? g), and Wu-Benesch ( W3? u - B3? g) bands of N 2, are 1.9 (3.2), 3 (6), 0.4 (0.8), and 0.5 (1.1) kR, respectively, for solar minimum (maximum) conditions. The intensities of the three strong Vegard-Kaplan bands (0, 5), (0, 6), and (0, 7) are 94 (160), 120 (204), and 114 (194) R, respectively, for solar minimum (maximum) conditions. Limb profiles are calculated for VK (0, 4), (0, 5), (0, 6) and (0, 7) bands. The calculated intensities on Venus are about a factor 10 higher than those on Mars. The present study provides a motivation for a search of N 2 triplet band emissions in the dayglow of Venus.

Bhardwaj, Anil; Jain, Sonal Kumar

2012-02-01

11

MEASUREMENTS AND ANALYSIS OF HELIUM-LIKE TRIPLET RATIOS IN THE X-RAY SPECTRA OF O-TYPE STARS  

E-print Network

MEASUREMENTS AND ANALYSIS OF HELIUM-LIKE TRIPLET RATIOS IN THE X-RAY SPECTRA OF O-TYPE STARS of helium- like triplets in the X-ray spectra of O-type stars, including accounting for the spatial are made for four O stars using archival Chandra HETGS data. We assume an X-ray-emitting plasma spatially

Cohen, David

12

Theoretical study of triplet state properties of free-base porphin  

NASA Astrophysics Data System (ADS)

This paper presents results and analysis of various properties of the triplet state of free-base porphin (FBP) as calculated by density-functional theory. The radiative lifetime of phosphorescence lines and microwave signals in optical detection of magnetic resonance (ODMR) spectra are obtained using the B3LYP hybrid density-functional and the quadratic response method. The zero-field splitting (ZFS) in the lowest triplet state, a 3 B 2u, of FBP is calculated as an expectation value of spin-spin coupling operator using the self-consistent field wavefunction. The second-order contribution to ZFS from the spin-orbit coupling operator is found to be almost negligible. The interpretation of the ODMR spectrum is completed by computing the hyperfine tensors of the 14N, 13C and hydrogen atoms in the lowest triplet state. The most intense phosphorescence emission corresponds to the T z-spin-sublevel of the a 3 B 2u state, where the z-axis lies in the N-H direction of the FBP molecule in a qualitative agreement with ODMR data. The results indicate that the observed decay of the lowest triplet state of FBP molecule is determined by non-radiative deactivation. The calculated radiative rate constant for the T z-spin-sublevel kz = 2.65 × 10 -3 s -1 is in agreement with the value kz ? 2 × 10 -3 s -1, estimated by van Dorp et al. [W. van Dorp, W. Schoemaker, M. Soma, J. van der Waals, Mol. Phys. 30 (1975) 1701] from kinetic analysis of microwave-induced fluorescent signals. The correct prediction of the spin quantization axis of the most active spin sublevel and of its radiative lifetime in the lowest triplet state of the FBP molecule is taken as a proof of capability of the quadratic response time-dependent density-functional theory.

Loboda, Oleksandr; Tunell, Ingvar; Minaev, Boris; Ågren, Hans

2005-06-01

13

Visible light-harvesting trans bis(alkylphosphine) platinum(II)-alkynyl complexes showing long-lived triplet excited states as triplet photosensitizers for triplet-triplet annihilation upconversion.  

PubMed

Symmetric and asymmetric linear trans-bis(tributylphosphine) Pt(II) bis(acetylide) complexes with functionalized aryl alkynyl ligands (coumarin, naphthalimide and phenyl acetylides) were prepared, which show enhanced absorption in the visible region (molar absorption coefficients up to 76,800 M(-1) cm(-1) at 459 nm) and long-lived triplet excited states (up to 139.9 ?s). At room temperature, the naphthalimide acetylide-phenyl acetylide complex (Pt-4) shows dual emission (fluorescence-phosphorescence), whereas other complexes show only fluorescence emission. The triplet excited states of the complexes were studied with nanosecond time-resolved transient difference absorption spectroscopy and DFT calculations on the spin density surface. The complexes were used as triplet photosensitizers for ratiometric O2 sensing, as well as triplet-triplet annihilation (TTA) upconversion (upconversion quantum yield up to 27.2%). The TTA upconversion of the complexes requires triplet acceptors with different T1 state energy levels and was studied with nanosecond time-resolved emission spectroscopy. Our results are useful for designing new Pt(II) complexes that show strong absorption of visible light and long-lived triplet excited states, as well as for the application of these complexes as triplet photosensitizers for O2 sensing, photocatalysis and TTA upconversion. PMID:23629418

Liu, Lianlian; Huang, Dandan; Draper, Sylvia M; Yi, Xiuyu; Wu, Wanhua; Zhao, Jianzhang

2013-08-14

14

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

NASA Astrophysics Data System (ADS)

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.

Buschhaus, L.; Kleinermanns, K.

2014-10-01

15

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

NASA Astrophysics Data System (ADS)

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

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

2012-02-01

16

Room temperature triplet state spectroscopy of organic semiconductors  

NASA Astrophysics Data System (ADS)

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 performance in applications like displays and solar energy harvesting. This is complicated if the excited state is a triplet because the electronic transition is `dark' with a vanishing oscillator strength. As a consequence, triplet state spectroscopy must usually be performed at cryogenic temperatures to reduce competition from non-radiative rates. Here, we control non-radiative rates by engineering a solid-state host matrix containing the target molecule, allowing the observation of phosphorescence at room temperature and alleviating constraints of cryogenic experiments. We test these techniques on a wide range of materials with functionalities spanning multi-exciton generation (singlet exciton fission), organic light emitting device host materials, and thermally activated delayed fluorescence type emitters. Control of non-radiative modes in the matrix surrounding a target molecule may also have broader applications in light-emitting and photovoltaic devices.

Reineke, Sebastian; Baldo, Marc A.

2014-01-01

17

Protecting the triplet excited state in sterically congested platinum porphyrin.  

PubMed

Platinum tetrakis(2,4,6-triethylphenyl)porphyrin (Pt-1) was synthesized and its structural (X-ray), electrochemical and photophysical properties were fully characterized. Comparative studies of Pt-1 and its unsubstituted analog PtTPP show the effect of sterically congesting ortho-substituents on the dynamics of the triplet excited states. Lowered quenching rates by 3-4 times were observed for Pt-1vs. PtTPP in the presence of oxygen and perylene, and in concentration (self)-quenching experiments. PMID:24336738

Moiseev, A G; Margulies, E A; Schneider, J A; Bélanger-Gariépy, F; Perepichka, D F

2014-02-14

18

Excited states absorption spectra of porphyrins - Solvent effects  

NASA Astrophysics Data System (ADS)

We propose a combination of different techniques to obtain the absorption cross-section spectra of triplet- and singlet-states in porphyrin-like molecules. Two extensions of the Z-scan technique are employed (pulse train Z-scan and white-light Z-scan) together with absorbance spectroscopy and laser flash photolysis. This approach allowed us to investigate features of excited-states absorption of meso-tetrakis (methylpyridiniumyl) porphyrin (TMPyP) that revealed the influence of solvents on the vibronic structuration of the transitions assigned to triplet-states, probably caused by hydrogen bonds established between the porphyrin and solvent molecules.

Barbosa Neto, N. M.; Correa, D. S.; De Boni, L.; Parra, G. G.; Misoguti, L.; Mendonça, C. R.; Borissevitch, I. E.; Zílio, S. C.; Gonçalves, P. J.

2013-11-01

19

Excited triplet states as photooxidants in surface waters  

NASA Astrophysics Data System (ADS)

The chromophoric components of dissolved organic matter (DOM) are generally the main absorbers of sunlight in surface waters and therefore a source of transient reactants under irradiation. Such short-lived species can be relevant for the fate of various classes of chemical contaminants in the aquatic environment. The present contribution focuses on the role of excited triplet states of chromophoric DOM, 3CDOM*, as transient photooxidants initiating the transformation and degradation of organic chemical contaminants. An early study [1] indicated that 3CDOM* may play a dominant role in the photo-induced transformation of electron-rich phenols, a conclusion which was later fortified by the results of transient absorption investigations using aromatic ketones as model photosensitizers [2] and by a recent careful analysis of the effect of oxygen concentration on transformation rates [3]. The variety of aquatic contaminants shown to be affected by triplet-induced oxidation has kept increasing, phenylurea herbicides [4], sulfonamide antibiotics [5] and some phytoestrogens [6] being prominent examples. Recent research has shown that the triplet-induced transformation of specific contaminants, especially aromatic nitrogen compounds, could be inhibited by the presence of DOM, very probably due to its antioxidant moieties [7]. While such moieties are not relevant for the quenching of 3CDOM*, they are expected to react with it in a similar way as the studied contaminants. Analogous reactions can be postulated to occur in liquid or solid phases of the atmospheric environment, as demonstrated in the case of HONO formation [8]. References 1. Canonica, S.; Jans, U.; Stemmler, K.; Hoigné, J. Transformation kinetics of phenols in water: Photosensitization by dissolved natural organic material and aromatic ketones. Environ. Sci. Technol. 1995, 29 (7), 1822-1831. 2. Canonica, S.; Hellrung, B.; Wirz, J. Oxidation of phenols by triplet aromatic ketones in aqueous solution. J. Phys. Chem. A 2000, 104 (6), 1226-1232. 3. Golanoski, K. S.; Fang, S.; Del Vecchio, R.; Blough, N. V. Investigating the mechanism of phenol photooxidation by humic substances. Environ. Sci. Technol. 2012, 46 (7), 3912-3920. 4. Gerecke, A. C.; Canonica, S.; Müller, S. R.; Schärer, M.; Schwarzenbach, R. P. Quantification of dissolved natural organic matter (DOM) mediated phototransformation of phenylurea herbicides in lakes. Environ. Sci. Technol. 2001, 35 (19), 3915-3923. 5. Boreen, A. L.; Arnold, W. A.; McNeill, K. Triplet-sensitized photodegradation of sulfa drugs containing six-membered heterocyclic groups: Identification of an SO2 extrusion photoproduct. Environ. Sci. Technol. 2005, 39 (10), 3630-3638. 6. Felcyn, J. R.; Davis, J. C. C.; Tran, L. H.; Berude, J. C.; Latch, D. E. Aquatic photochemistry of isoflavone phytoestrogens: Degradation kinetics and pathways. Environ. Sci. Technol. 2012, 46 (12), 6698-6704. 7. Wenk, J.; Canonica, S. Phenolic antioxidants inhibit the triplet-induced transformation of anilines and sulfonamide antibiotics in aqueous solution. Environ. Sci. Technol. 2012, 46 (10), 5455-5462. 8. George, C.; Strekowski, R. S.; Kleffmann, J.; Stemmler, K.; Ammann, M. Photoenhanced uptake of gaseous NO2 on solid-organic compounds: a photochemical source of HONO? Faraday Discuss. 2005, 130, 195-210.

Canonica, S.

2012-12-01

20

Toward ferromagnetic materials: prediction of a triplet ground state for heterocyclic polyacenes  

NASA Astrophysics Data System (ADS)

Bis-1,2,4-triazines were explored as potential ground-state triplet molecules which might serve as components of ferromagnetic materials. Relationships between numbers of rings and singlet-triplet gaps were explored by hybrid density functional theory for a series of heterocyclic polyacenes. Available X-ray structures of bis-triazines are compared to computed model compounds and used to check the methodology. A hexacyclic bis-1,2,4-triazine is predicted to have a triplet ground state.

Strassner, Th.; Weitz, Amir; Rose, Jefferson; Wudl, Fred; Houk, K. N.

2000-05-01

21

Model for triplet state engineering in organic light emitting diodes.  

PubMed

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

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

2014-06-01

22

Model for Triplet State Engineering in Organic Light Emitting Diodes  

E-print Network

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.

Prodhan, Suryoday; Ramasesha, S

2014-01-01

23

Model for triplet state engineering in organic light emitting diodes  

NASA Astrophysics Data System (ADS)

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 × 106. 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.

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

2014-06-01

24

Resonance Raman characterization of the radical anion and triplet states of zinc tetraphenylporphine  

SciTech Connect

The photophysical properties of metalloporphyrins are important to a range of current research areas, ranging from solar energy conversion to photodynamic therapy. Resonance Raman (RR) spectra are reported for the anion radical and for the photoexcited triplet state of ZnTPP. RR spectra were obtained by excitation at 457.9 nm, at the anion absorption band maximum. Bands were assigned with the aid of pyrrole-d[sub 8] and phenyl-d[sub 20] isotopomers. The pattern of isotope shifts and polarizations was found to be quite similar to that of the neutral parent, ZnTPP. The frequency shift pattern is discussed in terms of the expectations for placing an electron in the e[sub g]* orbital, including the anticipated Jahn-Teller (J-T) effect. Although band overlaps make depolarization ratios difficult to quantitate, the [nu][sub 10] band is found to be essentially depolarized, indicating that the J-T effect is dynamic, rather than static in character, at least with respect to stretching of the C[sub a]C[sub m] bonds. The [nu][sub 2] and [nu][sub 10] downshifts are attributable to porphyrin core expansion upon reduction, but the [nu][sub 27] and [nu][sub 29] reductions are probably manifestations of the J-T effect. Triplet-state RR spectra were produced with 416-nm photolysis and 459-nm probe pulses (7 ns). The RR peaks were assigned via their polarizations and the d[sub 8] and d[sub 20] isotopomer shifts. The spectrum contains three strong bands of predominantly phenyl character. Their frequencies are unshifted relative to the ground state, implying negligible electronic involvement of the phenyl groups in the T[sub 1] state, but their enhancements indicate substantial involvement in the resonant T[sub n] state. This state is suggested to be produced by charge transfer from the porphyrin e[sub g]* to the phenyl [pi]* orbitals.

Reed, R.A.; Purrello, R.; Prendergast, K.; Spiro, T.G. (Princeton Univ., NJ (United States))

1991-11-28

25

Transient EPR of excited triplet states at 240 GHz  

NASA Astrophysics Data System (ADS)

High-frequency EPR not only increases the g-resolution, but also the attainable time-resolution in a transient/pulsed EPR experiment . For that reason we have built a multi-frequency super-heterodyne spectrometer with a sub-nanosecond detection time-resolution for transient EPR, which currently operates at 120 and 240 GHz. The design of this unique spectrometer is based largely on quasi-optical elements, resulting in very low losses in beam transport, while the mode and polarization of the (sub)millimeter waves remain well-defined. The use of a cylindrical configuration for the corrugated waveguide and sampleholder enables detection of the EPR transition in "induction mode", resulting in an appreciable gain in sensitivity. The room temperature sensitivity in the configuration without cavity is comparable to that at X-band frequencies for a sample of similar size, while the absolute sensitivity in a Fabry-Perot type cavity with a 0.1 cubic mm volume is twop orders of magnitude better. Though the multi-frequency spectrometer is a CW EPR spectrometer, the time-resolution is 600 ps, and enables the detection of very fast changes in absorption or reflection induced by laser excitation. One of the applications is the study of excited triplet states for which the g-anisotropy remains unresolved at X-band frequencies, as is the case in most porphyrin- and fullerene-based systems. Transient EPR at 240 GHz not only well resolves the g-anisotropy in these systems but can also indicate the directions of the g-tensor axes with respect to those of the Zero-Field Splitting tensor. Experimental results on model fullerene and porphyrin systems as well as the excited triplet state in the photosynthetic reaction center of Rhodobacter Sphaeroides R26 will be presented.

van Tol, Johan; Brunel, Louis-Claude; Budil, David; Zeng, Rhonghui; Maniero, Anna-Lisa; Pasimeni, Luigi; Angerhofer, Alex

2002-03-01

26

Switching of the triplet excited state of rhodamine-C60 dyads.  

PubMed

Acid-switching of the triplet excited state in rhodamine-C60 dyads was achieved. The rhodamine moiety acts as an acid-activated visible light-harvesting antenna and C60 as the singlet energy acceptor and the spin converter, and production of the triplet state was enhanced in the presence of acid. PMID:25360461

Wang, Fen; Cui, Xiaoneng; Lou, Zhangrong; Zhao, Jianzhang; Bao, Ming; Li, Xingwei

2014-12-21

27

Triplet-singlet conversion in ultracold Cs2 and production of ground-state molecules  

NASA Astrophysics Data System (ADS)

We propose a process to convert ultracold metastable Cs2 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 A1?u+-b3?u states. Using spectroscopic data and accurate quantum chemistry calculations for Cs2 potential curves and transition dipole moments, we show that this process competes favorably with the single-photon decay back to the lowest triplet state. In addition, we demonstrate that this conversion process represents a loss channel for vibrational cooling of metastable triplet molecules, preventing an efficient optical pumping cycle down to low vibrational levels.

Bouloufa, Nadia; Pichler, Marin; Aymar, Mireille; Dulieu, Olivier

2011-02-01

28

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

SciTech Connect

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

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

2010-06-15

29

Photoelectron imaging of NCCCN-: The triplet ground state and the  

E-print Network

; accepted 5 May 2010; published online 8 June 2010 The photoelectron spectra of NCCCN- have been measured, corresponding to the ground and first excited states of dycianocarbene. With support from theoretical calculations using the spin-flip coupled-cluster methods, the ground electronic state of HCCCN is assigned

Sanov, Andrei

30

Using photoexcited triplet states to probe small-molecule endohedral fullerenes by ESR  

NASA Astrophysics Data System (ADS)

Ortho to para conversion of molecular hydrogen H2 can be catalyzed by the use of a coupled paramagnet such as a fullerene in its triplet state. The recently synthesized endohedral fullerenes H2@C60 and H2@C70 were photoexcited to their long lived triplet state (S= 1) and probed by electron spin resonance (ESR) and electron nuclear double resonance (ENDOR) spectroscopic techniques. With these techniques we characterized both spin systems by extracting the hyperfine interaction the kinetic parameters of the triplet state and the spin relaxation times. The observed variations of the linewidths and the lineshape are discussed in the context of a dynamic Jahn-Teller effect. Irradiation of the H2@C70 at different temperatures reveals that the fullerene triplet state can serve as a spin catalyst for ortho to para interconversion while for the triplet H2@C60 no appreciable interconversion is observed

Filidou, Vasileia; Mamone, Salvatore; Bagno, Alessandro; Rastrelli, Federico; Murata, Yasujiro; Komatsu, Koichi; Lei, Xuegong; Li, Yongjun; Turro, Nicholas J.; Levitt, Malcolm H.; Morton, John J. L.

2013-03-01

31

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

E-print Network

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.

Anna Jencova

2010-08-05

32

Chlorophyll triplet states associated with Photosystem I and Photosystem II in thylakoids of the green alga Chlamydomonas reinhardtii.  

PubMed

The analysis of FDMR spectra, recorded at multiple emission wavelengths, by a global decomposition technique, has allowed us to characterise the triplet populations associated with Photosystem I and Photosystem II of thylakoids in the green alga Chlamydomonas reinhardtii. Three triplet populations are observed at fluorescence emissions characteristic of Photosystem II, and their zero field splitting parameters have been determined. These are similar to the zero field parameters for the three Photosystem II triplets previously reported for spinach thylakoids, suggesting that they have a widespread occurrence in nature. None of these triplets have the zero field splitting parameters characteristic of the Photosystem II recombination triplet observed only under reducing conditions. Because these triplets are generated under non-reducing redox conditions, when the recombination triplet is undetectable, it is suggested that they may be involved in the photoinhibition of Photosystem II. At emission wavelengths characteristic of Photosystem I, three triplet populations are observed, two of which are attributed to the P(700) recombination triplet frozen in two different conformations, based on the microwave-induced fluorescence emission spectra and the triplet minus singlet difference spectra. The third triplet population detected at Photosystem I emission wavelengths, which was previously unresolved, is proposed to originate from the antenna chlorophyll of the core or the unusually blue-shifted outer antenna complexes of this organism. PMID:17161376

Santabarbara, Stefano; Agostini, Giancarlo; Casazza, Anna Paola; Syme, Christopher D; Heathcote, P; Böhles, Felix; Evans, Michael C W; Jennings, Robert C; Carbonera, Donatella

2007-01-01

33

ADMR of carotenoid triplet states in bacterial photosynthetic antenna and reaction center complexes  

NASA Astrophysics Data System (ADS)

Using absorption detected magnetic resonance (ADMR) the triplet states of carotenoids have been detected in B880—RC complexes of the purple photosynthetic bacteria Rhodocyclus gelatinosus 149, Rhodopseudomonas acidophila 7050, Rhodopseudomonas palustris 8252, and Rhodospirillum rubrum S1, and in reaction center (RC) complexes of Rhodospirillum rubrum S1. The triplet states were identified as belonging to antenna carotenois in the all-trans conformation with conjugated chain lengths ranging from 10 to 13 double bonds, and to the RC carotenoid 15,15'-cis spirilloxanthin. Carotenoids with different numbers of conjugated double bonds have similar ability to quench the triplet states of the bacteriochlorophylls.

Aust, V.; Angerhofer, A.; Ullrich, J.; von Schütz, J. U.; Wolf, H. C.; Cogdell, R. J.

1991-06-01

34

Ab Initio Calculations of Singlet and Triplet Excited States of Chlorine Nitrate and Nitric Acid  

NASA Technical Reports Server (NTRS)

Ab initio calculations of vertical excitations to singlet and triplet excited states of chlorine nitrate and nitric acid are reported. The nature of the electronic transitions are examined by decomposing the difference density into the sum of detachment and attachment densities. Counterparts for the three lowest singlet excited states of nitric acid survive relatively unperturbed in chlorine nitrate, while other low-lying singlet states of chlorine nitrate appear to be directly dissociative in the ClO chromophore. These results suggest an assignment of the two main peaks in the experimental chlorine nitrate absorption spectrum. In addition, triplet vertical excitations and the lowest optimized triplet geometries of both molecules are studied.

Grana, Ana M.; Lee, Timothy J.; Head-Gordon, Martin; Langhoff, Stephen R. (Technical Monitor)

1994-01-01

35

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

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

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

2004-05-01

36

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

SciTech Connect

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.

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

37

Theoretical study of the absorption and nonradiative deactivation of 1-nitronaphthalene in the low-lying singlet and triplet excited states including methanol and ethanol solvent effects  

NASA Astrophysics Data System (ADS)

The photophysics of the 1-nitronaphthalene molecular system, after the absorption transition to the first singlet excited state, is theoretically studied for investigating the ultrafast multiplicity change to the triplet manifold. The consecutive transient absorption spectra experimentally observed in this molecular system are also studied. To identify the electronic states involved in the nonradiative decay, the minimum energy path of the first singlet excited state is obtained using the complete active space self-consistent field//configurational second-order perturbation approach. A near degeneracy region was found between the first singlet and the second triplet excited states with large spin-orbit coupling between them. The intersystem crossing rate was also evaluated. To support the proposed deactivation model the transient absorption spectra observed in the experiments were also considered. For this, computer simulations using sequential quantum mechanic-molecular mechanic methodology was used to consider the solvent effect in the ground and excited states for proper comparison with the experimental results. The absorption transitions from the second triplet excited state in the relaxed geometry permit to describe the transient absorption band experimentally observed around 200 fs after the absorption transition. This indicates that the T2 electronic state is populated through the intersystem crossing presented here. The two transient absorption bands experimentally observed between 2 and 45 ps after the absorption transition are described here as the T1-->T3 and T1-->T5 transitions, supporting that the intermediate triplet state (T2) decays by internal conversion to T1.

Orozco-Gonzalez, Yoelvis; Coutinho, Kaline; Peon, Jorge; Canuto, Sylvio

2012-08-01

38

Temperature-dependent mollow triplet spectra from a single quantum dot: rabi frequency renormalization and sideband linewidth insensitivity.  

PubMed

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 renormalization of the driven dot Rabi frequency. We also present first evidence for a nonperturbative regime of phonon coupling, in which the expected linear increase in sideband linewidth as a function of temperature is canceled 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. PMID:25216004

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

2014-08-29

39

Lifetimes and energies of the relaxed triplet states of cyclopentadiene and tetramethylbutadiene. A pulse radiolysis and pulsed laser study  

Microsoft Academic Search

The triplet states of cyclopentadiene and tetramethylbutadiene have been produced in benzene by pulse radiolysis. Energy-transfer experiments have established natural lifetimes of 1.7 ..mu..s and 73 ns, respectively. The observation of triplet energy transfer equilibria with pulse radiolysis and pulsed laser photolysis has established a relaxed triplet energy for cyclopentadiene of 58.0 +- 0.2 kcal mol⁻¹, which shows that relaxation

A. A. Gorman; I. R. Gould; I. Hamblett

1981-01-01

40

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

NASA Astrophysics Data System (ADS)

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

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

2011-11-01

41

Transition state vibrational level thresholds for the dissociation of triplet ketene  

E-print Network

September 1994; accepted 14 November 1994 Rate constants for the unimolecular dissociation of ketene CH2COTransition state vibrational level thresholds for the dissociation of triplet ketene Sang Kyu Kim B1) and CO (X~ 1 ) by photofragmentation in a cold jet. The rate constant increases in a stepwise

Kim, Sang Kyu

42

Study on the triplet state of triphenylene by microwave induced delayed phosphorescence and T<-- excitation spectroscopy  

Microsoft Academic Search

The lowest triplet state of triphenylene has been studied with the aid of microwave induced delayed phosphorescence (MIDP) and T> kyr > kzr for the 0,0 band and kxr ~= kyr >> kzr for the e' vibrational bands. Thus the spin sublevels acquire radiative activity through mechanisms similar to those for benzene. The T<--S excitation spectrum was found to be

Nobuyuki Nishi; Kazunori Matsui; Minoru Kinoshita; Jiro Higuchi

1979-01-01

43

Formation of Triplet Positron-helium Bound State by Stripping of Positronium Atoms in Collision with Ground State Helium  

NASA Technical Reports Server (NTRS)

Formation of triplet positron-helium bound state by stripping of positronium atoms in collision with ground state helium JOSEPH DI RlENZI, College of Notre Dame of Maryland, RICHARD J. DRACHMAN, NASA/Goddard Space Flight Center - The system consisting of a positron and a helium atom in the triplet state e(+)He(S-3)(sup e) was conjectured long ago to be stable [1]. Its stability has recently been established rigorously [2], and the values of the energies of dissociation into the ground states of Ps and He(+) have also been reported [3] and [4]. We have evaluated the cross-section for this system formed by radiative attachment of a positron in triplet He state and found it to be small [5]. The mechanism of production suggested here should result in a larger cross-section (of atomic size) which we are determining using the Born approximation with simplified initial and final wave functions.

Drachman, Richard J.

2006-01-01

44

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

NASA Astrophysics Data System (ADS)

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

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

2012-02-01

45

Highly efficient multifluorenyl host materials with unsymmetrical molecular configurations and localized triplet States for green and red phosphorescent devices.  

PubMed

Highly efficient green and red electro-phosphorescence is achieved in devices with the host material DPESPODEF3. The multiple fluorenyl moieties of the host material are arranged such that it has an unsymmetrical molecular configuration, and its triplet-state location is tuned such that it has independent energy (ET) and charge transfer (CT) channels. As a result, DPESPODEF3 can suppress triplet-triplet annihilation and triplet-polaron quenching. In the resulting green and red phosphorescent devices, impressive external quantum efficiencies of ca. 20% and 16% and power efficiencies of ca. 75 and 20 lm W(-1) , respectively, are observed. PMID:25212516

Han, Chunmiao; Zhu, Liping; Li, Jing; Zhao, Fangchao; Zhang, Zhen; Xu, Hui; Deng, Zhaopeng; Ma, Dongge; Yan, Pengfei

2014-11-01

46

The photoexcited triplet state as a probe of chromophore-protein interaction in myoglobin.  

PubMed Central

The photoexcited metastable triplet state of Mg(2+)-mesoporphyrin IX (MgMPIX) or Mg(2+)-protoporphyrin IX (MgPPIX) located in the heme pocket of horse myoglobin (Mb) was investigated by optical and electron paramagnetic resonance (EPR) spectroscopy, and its properties were compared with the model complexes, MgMPIX, MgPPIX, and Mg2+ etioporphyrin I (MgETIOI), in noncoordinating and coordinating organic glasses. Zero-field splitting parameters, line shape, and Jahn-Teller distortion in the temperature range of 3.8-110 K are discussed in terms of porphyrin-protein interactions. The triplet line shapes for MgMPIXMb and MGPPIXMb show no temperature-dependent spectral line shape changes suggestive of Jahn-Teller dynamics, and it is concluded that the energy splitting is >> 150 cm-1, suggesting symmetry breaking from the anisotropy of intermal electric fields of the protein, and consistent with previous predictions (Geissinger et al. 1995. J. Phys. Chem. 99:16527-16529). Both MgMPIXMb and MgPPIXMb demonstrate electron spin polarization at low temperature, and from the polarization pattern it can be concluded that intersystem crossing occurs predominantly into in-plane spin sublevels of the triplet state. The splitting in the Q0.0 absorption band and the temperature dependence and splitting of the photoexcited triplet state of myoglobin in which the iron was replaced by Mg2+ are interpreted in terms of effects produced by electric field asymmetry in the heme pocket. PMID:9726951

Angiolillo, P J; Vanderkooi, J M

1998-01-01

47

Room temperature triplet state spectroscopy of organic semiconductors  

E-print Network

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 ...

Reineke, Sebastian

48

Lifetimes and energies of the relaxed triplet states of cyclopentadiene and tetramethylbutadiene. A pulse radiolysis and pulsed laser study  

SciTech Connect

The triplet states of cyclopentadiene and tetramethylbutadiene have been produced in benzene by pulse radiolysis. Energy-transfer experiments have established natural lifetimes of 1.7 ..mu..s and 73 ns, respectively. The observation of triplet energy transfer equilibria with pulse radiolysis and pulsed laser photolysis has established a relaxed triplet energy for cyclopentadiene of 58.0 +- 0.2 kcal mol/sup -1/, which shows that relaxation from the Franck-Condon state is negligible. An approximate available triplet energy of 42 kcal mol/sup -1/ for the relaxed tetramethylbutadiene triplet has been determined. The rate constant data for energy transfer obtained by using both pulse radiolysis and pulsed laser photolysis appear totally consistent with vertical energy transfer processes only. 6 figures.

Gorman, A.A.; Gould, I.R.; Hamblett, I.

1981-07-29

49

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

SciTech Connect

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

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

2010-04-15

50

Conformational energetics of stable and metastable states formed by DNA triplet repeat oligonucleotides: Implications for triplet expansion diseases  

Microsoft Academic Search

We have embedded the hexameric triplet repeats (CAG)6 and (CTG)6 between two (GC)3 domains to produce two 30-mer hairpins with the sequences d[(GC)3(CAG)6(GC)3] and d[(GC)3(CTG)6(GC)3]. This construct reduces the conformational space available to these repetitive DNA sequences. We find that the (CAG)6 and (CTG)6 repeats form stable, ordered, single-stranded structures. These structures are stabilized at 62°C by an average enthalpy

J. Völker; N. Makube; G. E. Plum; H. H. Klump; K. J. Breslauer

2002-01-01

51

Time-resolved resonance Raman spectroscopy of excited singlet and triplet states of free-base meso-tetraphenylporphyrin  

SciTech Connect

Two-color time-resolved resonance Raman spectroscopy has been used to probe the lowest excited singlet (S[sub 1]) and triplet (T[sub 1]) states of free-base meso-tetraphenylporphyrin and meso-tetrakis(4-sulphonatophenyl)porphyrin in solution at room temperature. The spectra were recorded using 532-nm excitation pulses and time-delayed probe pulses ([Delta]T = 0-30 ns, 447 and 460 nm) near [lambda][sub max] of the S[sub 1] and T[sub 1] states. Significant shifts in frequency of the porphyrin core vibrations were observed upon excitation to either the S[sub 1] or T[sub 1] state. Several of the strongest polarized bands in the spectra of both excited states, including [nu][sub 1], [nu][sub 2], [nu][sub 4], [nu][sub 6], and [phi][sub 4], are assigned, and the information they give on the differences in electron distribution in the ground, S[sub 1], and T[sub 1] states is discussed. 16 refs., 3 figs., 1 tab.

Bell, S.E.J.; Hegarty, M.; McGarvey, J.J. (Queens Univ., Belfast (United Kingdom)); Al-Obaidi, A.H.R.; Hester, R.E. (Univ. of York (United Kingdom))

1993-11-11

52

Pigment-pigment interactions in thylakoids and LHCII of chlorophyll a/ c containing alga Pleurochloris meiringensis: analysis of fluorescence-excitation and triplet-minus-singlet spectra  

NASA Astrophysics Data System (ADS)

Time-resolved triplet-minus-singlet (TmS) difference spectra, ? A( ?; t), fluorescence excitation spectra, X( ?), and absorption spectra, A( ?), are used for probing pigment-pigment interactions in the thylakoids (Chl a/ c-Thyl) and isolated light-harvesting complexes associated with photosystem II (Chl a/ c-LHCII) of the alga Pleurochloris meiringensis, whose chromophores comprise chlorophyll a (Chl a), chlorophyll c (Chl c), and several carotenoids. The data provide information about interactions between Car*-and-Chl a0, Chl a†-and-Car 0, Car †-and-Chl a0 (where the abbreviation Car stands for carotenoid, an asterisk and a dagger denote singlet and triplet excitation, respectively, and the superscript 0 denotes a molecule in the ground state). In Chl a/c-Thyl, the efficiency of Car*?Chl a* transfer ( ?LH), determined by comparing A( ?) and X( ?), is slightly less than unity (ca. 0.85), whereas the efficiency of Chl a†?Car † transfer of triplet energy ( ?TT) must be much closer to unity, since no long-lived Chl a† could be detected; an interaction between Car † and Chl a0, already familiar from investigations concerning the TmS spectra of the trimers and aggregates of Chl a/ b-LHCII (the light-harvesting complex associated with the photosystem II of higher plants), which manifests itself through a depletion signal (in the Qy region of Chl a) decaying at the same rate as the Car TmS signal, is observed, and explained likewise. In Chl a/ c-LHCII, both efficiencies are found to be much lower; the drastic reduction in the two yields is attributed to the perturbation of the native molecular architecture of the complex by the detergent used in the isolation procedure. The overall TmS signal from Chl a/ c-LHCII can be decomposed into two contributions, ? A( ?; t)=? 1A( ?; t)+? 2A( ?; t), where ? 1A( ?; t) with a lifetime of about 8 ?s; ? 2A( ?; t), which persists for several hundred microseconds, is contributed by those Chl a† molecules which fail to transfer their excitation to a Car neighbour. A comparison of ? 1A( ?; t) with the TmS signal of thylakoids shows differences which parallel those previously reported for the TmS spectra of trimers and aggregates of Chl a/ b-LHCII: the carotenoid peak at 510 nm is broader, and the Qy depletion signal larger, in the difference spectrum of thylakoids. The absorption spectrum of Chl a/ c-LHCII show no signs of Chl a-Chl a excitonic interactions, since the Chl a-contribution to the spectrum can be reproduced well by simply red-shifting (by about 200 cm -1) the Q bands and the Soret band in the absorption spectrum of an ethanolic solution of Chl a, an observation consistent with the absence, reported in a recent study, of excitonic bands in the circular dichroism spectrum of Chl a/ c-LHCII.

Büchel, C.; Razi Naqvi, K.; Melø, T. B.

1998-05-01

53

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

NASA Astrophysics Data System (ADS)

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.

Gingrich, Eric C.

54

Phosphorescence properties and kinetics of the lowest triplet state T 1 of a series of pyrene derivatives as obtained by ODMR techniques  

NASA Astrophysics Data System (ADS)

The experimental results of an ODMR investigation of the radiative and nonradiative properties of the lowest electronically excited triplet state T 1 of a series of pyrene derivatives are presented. The paper gives the highly resolved phosphorescence spectra of 1,2-benzopyrene, naphtho-(2', 3' ; 1,2)-pyrene, anthraceno-(2', 3'; 1, 2)-pyrene, 1,2:6,7-dibenzo-pyrene, 1,2-benzonaphtho-(2', 3'; 6, 7)-pyrene and 1,2; 4,5-dibenzo-pyrene along with vibrational analyses and — in part — symmetry assignments. The correlation know from the literature between triplet energies and the ZFS-parameter D is discussed in terms of character orders. Three of the molecules exhibit an unusual deactivation behaviour similar to that of 3,4-benzo-pyrene where the out-of-plane level is not the slowest level. Several possibilities to explain this unexpected behaviour are discussed.

Bräuchle, Chr.; Kabza, H.; Voitländer, J.

1981-02-01

55

The dissociation dynamics of low lying triplet states in butane and butene molecules  

NASA Astrophysics Data System (ADS)

Butane, methylpropane, 1-,2-butene and isobutene are studied as a complete set of doubley methylated ethane and ethene molecules in order to probe the dissociation dynamics of their excited states. The butane and butene molecules are formed in electronically highly excited states by neutralization of their respective radical cations in collisions with alkali metal atoms. Processes that lead to dissociations into two fragments are measured with differential translational spectroscopy. it is found that the first triplet state is dominantly populated. Butanes exhibit direct dissociation of a carbon?carbon (C?C) bond via a repulsive state. Intramolecular vibrational energy redistribution (IVR) prior to dissociation is observed for the unsaturated butenes. For the butenes the C?C bond cleavage is even preceded by a hydrogen shift, resulting in molecular losses like methane and ethene. In this paper we stress the relations between the present results and optical excitation and electron scattering experiments. For butane the proposed dissociation via a repulsive triplet state is corroborated in ab initio calculations.

Beijersbergen, Jaap H. M.; de Koster, Chris. G.; van der Zande, Win J.; Kistemaker, Piet G.; Los, Joop

1992-02-01

56

Energy linkage between the singlet and triplet manifolds in LaH, and observation of new low-energy states  

NASA Astrophysics Data System (ADS)

Wavelength-resolved fluorescence spectra of jet-cooled LaH were obtained from D1, E1, and 0+(3?-) states by exciting isolated rotational levels. The observation of a3?1 and a3?2 states at 1259.5(5) and 1646(1) cm-1, respectively, established the missing energy link between the singlet and triplet manifolds. The low-energy b3?0,1 and B1?2 states predicted earlier from ab initio studies were also observed for the first time. Vibrational constants ?e = 1418(2) cm-1, ?exe = 15.6(7) cm-1 for the ground and ?G1/2 = 1326.1(7) and 1312(1) cm-1, respectively, for the a3?1 and b3?1 states were also determined. Vibrational frequencies were found to be in excellent agreement with earlier ab initio values. However, ab initio term energies and spin-orbit separation of 3?2-3?1 and 3?1-3?0 were found to be in poor agreement with the present observations. Also, the 3? state that was predicted to be inverted is observed to be regular.

Mukund, Sheo; Yarlagadda, Suresh; Bhattacharyya, Soumen; Nakhate, S. G.

2012-12-01

57

Spin-Triplet Pairing States in Ferromagnet/Ferromagnet/d-Wave Superconductor Heterojunctions with Noncollinear Magnetizations  

NASA Astrophysics Data System (ADS)

Tunneling conductance in clean ferromagnet/ ferromagnet/d-wave superconductor (F/F/d-wave S) double tunnel junctions is studied by use of four-component Bogoliubov de Gennes equations. The novel Andreev reflection appears due to noncollinear magnetizations, in which the incident electron and the Andreev-reflected hole come from the same spin subband, resulting in spin-triplet pairing states near the F/S interface. In the highly polarized Fs case, the conductance within the energy gap exhibits a conversion from a zero-bias dip in the parallel magnetizations to a spilt zero-bias peak in the perpendicular magnetizations.

Niu, Zhi Ping; Xing, D. Y.

2007-02-01

58

Ultrafast entangling gates between nuclear spins using photo-excited triplet states  

E-print Network

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

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

2012-01-23

59

Characterization of the triplet state of tanshinone IIA and its reactivity by laser flash photolysis.  

PubMed

Tanshinone IIA (Tan IIA) has the properties of cardiovascular protection, anti-inflammation, antioxidation and anticancer. Its light-induced instability has drawn our interests in its photochemistry. Therefore, laser flash photolysis herein was used to investigate the transient photochemistry of Tan IIA. Our results show that direct photoexcitation by 355 nm laser pulses or photosensitization by energy transfer can lead to the formation of the triplet state of Tan IIA ((3)Tan IIA*). The triplet absorption spectrum and molar absorption coefficient, and ISC quantum yield were determined. Self-quenching of (3)Tan IIA* by its ground state was identified as an autooxidation reaction. (3)Tan IIA* was proved to react quickly with N, N-dimethylaniline, tert-butylhydroquinone and propyl gallate via electron transfer with the diffusion-controlled rate constants. One of the products with maximum absorption around 390 nm was assigned to the radical anion of Tan IIA. Our results indicate that (3)Tan IIA* is a reactive transient species and can be generated by photosensitization or direct photoexcitation. According to our results, the possible role of Tan IIA as a photosensitizer to induce potential phototoxicity via Type-II pathway in the presence of O2 can be predicted. PMID:24325277

Li, Kun; Zhang, Qin; Wang, Mei; Zhu, Rongrong; Sun, Xiaoyu; Wu, Xianzheng; Wang, Shi-Long

2014-01-01

60

High-Field Transient Electron Paramagnetic Resonance of Excited Triplet States  

NASA Astrophysics Data System (ADS)

The zero-field splitting of the excited triplet states of organic molecules often is of the order of 1 GHz or less, and transient EPR at X-band is generally sufficient for the determination of the zero-field splitting and kinetic parameters in these type of molecules. However, information on the g-factor and g-anisotropy cannot be obtained at conventional EPR frequencies, and interpretations of the data in terms of electronic structure are mostly limited to symmetry considerations. On the other hand information of the g-anisotropy provides additional clues with respect to electronic structure, while a direct comparison with radical-ion forms of the molecules becomes possible. Experimental data of transient EPR at 240 GHz will be presented for a variety of methano-fullerenes and pyrrolidino-fullerenes, either embedded in a polymer of in partially oriented liquid crystals. It will be shown that transient EPR at these very high frequencies can accurately determine the g-anisotropy and in some cases the orientation of the g-tensor with respect to the ZFS tensor. The information gained will be discussed in relation to the electronic structure of the lowest excited triplet state of these molecules.

Bortolus, M.; van Tol, J.; Prato, M.; Maniero, A.-L.

2005-03-01

61

Infrared vibrational spectroscopy of [Ru(bpy)2(bpm)]2+ and [Ru(bpy)3]2+ in the excited triplet state.  

PubMed

This work involved a detailed investigation into the infrared vibrational spectra of ruthenium polypyridyl complexes, specifically heteroleptic [Ru(bpy)2(bpm)](2+) (bpy = 2,2'-bipyridine and bpm = 2,2'-bipyrimidine) and homoleptic [Ru(bpy)3](2+), in the excited triplet state. Transient spectra were acquired 500 ps after photoexcitation, corresponding to the vibrational ground state of the excited triplet state, using time-resolved infrared spectroscopy. We assigned the observed bands to specific ligands in [Ru(bpy)2(bpm)](2+) based on the results of deuterium substitution and identified the corresponding normal vibrational modes using quantum-chemical calculations. Through this process, the more complex vibrational bands of [Ru(bpy)3](2+) were assigned to normal vibrational modes. The results are in good agreement with the model in which excited electrons are localized on a single ligand. We also found that the vibrational bands of both complexes associated with the ligands on which electrons are little localized appear at approximately 1317 and 1608 cm(-1). These assignments should allow the study of the reaction dynamics of various photofunctional systems including ruthenium polypyridyl complexes. PMID:24528148

Mukuta, Tatsuhiko; Fukazawa, Naoto; Murata, Kei; Inagaki, Akiko; Akita, Munetaka; Tanaka, Sei'ichi; Koshihara, Shin-ya; Onda, Ken

2014-03-01

62

Study of photoreduction kinetics of xanthene dyes with intersystem crossing from upper triplet states  

NASA Astrophysics Data System (ADS)

Modeling of kinetics of photoprocesses in polyatomic molecules based on four-level energy scheme is carried out. The model includes the processes in dye under cw photoexcitation and takes into account a reverse intersystem crossing and photochemical reaction from the upper triplet states. The analytical time-dependent relation for dye concentration of the initial form was obtained taking into account the contrast of rates of various photoprocesses and using of quasistationary approximation. It was shown that rate constant of photolysis correlates with probability of intersystem crossing of the dyes. For the xanthene dyes in gelatin it was shown that simple experimental method of cw laser photolysis combined with the kinetic model could be effective technique of study of upper excited states participation.

Sizykh, A.; Slyusareva, E.; Tarbetskaya, K.

2007-06-01

63

Intramolecular interactions and deuteration effect in nonradiative deactivation of lowest triplet state of anthracene and naphthalene  

NASA Astrophysics Data System (ADS)

In the approximation of nonadiabatic interactions and considering all out-of-plane vibrational modes to be promoting ones, we calculate changes in the rate constants T s K {dg/ s } of the nonradiative degradation T {1/ s } ? S 0 of in-plane spin ( s) triplet states as a result of the complete deuteration of anthracene and naphthalene molecules. We examine how the deuteration, the frequency factor, and the shape of promoting vibrational modes affect the squared matrix elements of both nonadiabatic coupling and adiabatic vibronically induced spin-orbit (VISO) coupling of electronic states. The compensation effect of spin-orbit interactions in structural elements of the carbon backbone of the anthracene molecule is ascertained.

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

2011-07-01

64

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

PubMed

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

Mukhopadhyay, S; Ramasesha, S; Guha, S

2010-01-28

65

Singlet and triplet excited states and intersystem crossing in free-base porphyrin: TDDFT and DFT/MRCI study.  

PubMed

Extensive time-dependent DFT (TDDFT) and DFT/multireference configuration interaction (MRCI) calculations are performed on the singlet and triplet excited states of free-base porphyrin, with emphasis on intersystem crossing processes. The equilibrium geometries, as well as the vertical and adiabatic excitation energies of the lowest singlet and triplet excited states are determined. Single and double proton-transfer reactions in the first excited singlet state are explored. Harmonic vibrational frequencies are calculated at the equilibrium geometries of the ground state and of the lowest singlet and triplet excited states. Furthermore, spin-orbit coupling matrix elements of the lowest singlet and triplet states and their numerical derivatives with respect to nuclear displacements are computed. It is shown that opening of an unprotonated pyrrole ring as well as excited-state single and double proton transfer inside the porphyrin cavity lead to crossings of the potential energy curves of the lowest singlet and triplet excited states. It is also found that displacements along out-of-plane normal modes of the first excited singlet state cause a significant increase of the , , and spin-orbit coupling matrix elements. These phenomena lead to efficient radiationless deactivation of the lowest excited states of free-base porphyrin via intercombination conversion. In particular, the S1-->T1 population transfer is found to proceed at a rate of approximately 10(7) s(-1) in the isolated molecule. PMID:18189251

Perun, Serhiy; Tatchen, Jörg; Marian, Christel M

2008-02-01

66

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

NASA Astrophysics Data System (ADS)

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.

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

2014-12-01

67

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

PubMed

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. PMID:24997445

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

2014-12-10

68

Manifestation of the odd-frequency spin-triplet pairing state in diffusive ferromagnet/superconductor junctions  

NASA Astrophysics Data System (ADS)

Using the quasiclassical Green’s function formalism, we study the influence of the odd-frequency spin-triplet superconductivity on the local density of states (LDOS) in a diffusive ferromagnet (DF) attached to a superconductor. Various possible symmetry classes in a superconductor are considered which are consistent with the Pauli’s principle: even-frequency spin-singlet even-parity (ESE) state, even-frequency spin-triplet odd-parity (ETO) state, odd-frequency spin-triplet even-parity (OTE) state, and odd-frequency spin-singlet odd-parity (OSO) state. For each of these states, the pairing state in the DF is studied. Particular attention is paid to the study of spin-singlet s -wave and spin-triplet p -wave superconductors as the examples of ESE and ETO superconductors. For the spin-singlet case the magnitude of the OTE component of the pair amplitude is enhanced with the increase of the exchange field in the DF. When the OTE component is dominant at low energy, the resulting LDOS in the DF has a zero-energy peak (ZEP). On the other hand, in DF/spin-triplet p -wave superconductor junctions the LDOS has a ZEP in the absence of the exchange field, where only the OTE pairing state exists. With the increase of the exchange field, the ESE component of the pair amplitude induced in the DF is enhanced. Then, the resulting LDOS has a ZEP splitting. We demonstrate that the appearance of the dominant OTE component of the pair amplitude is the physical reason for the emergence of the ZEP of the LDOS.

Yokoyama, T.; Tanaka, Y.; Golubov, A. A.

2007-04-01

69

Piezospectroscopic studies of the triplet states of RbMnF3 J. Ferr (*), R. H. Petit (**)  

E-print Network

.70E 1. Introduction. - In previous papers [1-4], the experimental and theoretical study of Jahn-Teller effects in the four lowest orbital triplet excited states of Mn++ in RbMnF3 was reported. These studies a cubic perovskite structure and orders antiferromagnetically along the three fold axes below TN ~ 83 K

Paris-Sud XI, Université de

70

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

PubMed

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

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

2010-04-21

71

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

NASA Astrophysics Data System (ADS)

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

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

2003-11-01

72

Infrared spectra and density functional calculations of triplet pnictinidene N divided by ThF3, PvThF3 and As divided by ThF3 molecules.  

PubMed

Thorium atoms react with NF(3), PF(3), and AsF(3) to produce the first actinide triplet state pnictinidene molecules, N divided by ThF(3), P divided by ThF(3), and As divided by ThF(3), which are trapped in solid argon and identified from infrared spectra and comparison to computed vibrational frequencies. Density functional theory calculations for these lowest energy triplet state products converge essentially to C(3v) symmetry structures. Spin density calculations show that the two unpaired electrons are mostly localized in nitrogen 2p, phosphorus 3p, or arsenic 4p orbitals. Although thorium has a small spin density, the weak degenerate pi(alpha) molecular orbitals are populated entirely from the terminal N, P, or As based on DFT natural bond orbital analysis. This is in contrast with HC divided by ThF(3), which contains degenerate pi(alpha) molecular orbitals with 81% C and 19% Th character. PMID:20449204

Wang, Xuefeng; Andrews, Lester

2009-11-14

73

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

SciTech Connect

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

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

2013-01-01

74

Triplet excimers of fluoroquinolones in aqueous media.  

PubMed

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

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

2012-05-31

75

NPQ activation reduces chlorophyll triplet state formation in the moss Physcomitrella patens.  

PubMed

Plants live in variable environments in which light intensity can rapidly change, from limiting to excess conditions. Non-photochemical quenching (NPQ) is a regulatory mechanism which protects plants from oxidative stress by dissipating excess Chl singlet excitation. In this work, the physiological role of NPQ was assessed by monitoring its influence on the population of the direct source of light excess damage, i.e., Chl triplets ((3)Chl*). (3)Chl* formation was evaluated in vivo, with the moss Physcomitrella patens, by exploiting the high sensitivity of fluorescence-detected magnetic resonance (FDMR). A dark adapted sample was compared with a pre-illuminated sample in which NPQ was activated, the latter showing a strong reduction in (3)Chl* yield. In line with this result, mutants unable to activate NPQ showed only a minor effect in (3)Chl* yield upon pre-illumination.The decrease in (3)Chl* yield is equally experienced by all the Chl pools associated with PSII, suggesting that NPQ is effective in protecting both the core and the peripheral antenna complexes. Moreover, the FDMR results show that the structural reorganization in the photosynthetic apparatus, required by NPQ, does not lead to the formation of new (3)Chl* traps in the LHCs. This work demonstrates that NPQ activation leads to effective photoprotection, promoting a photosystem II state characterized by a reduced probability of (3)Chl* formation, due to a decreased singlet excited state population, while maintaining an efficient quenching of the (3)Chl* eventually formed by carotenoids. PMID:22634338

Carbonera, Donatella; Gerotto, Caterina; Posocco, Bianca; Giacometti, Giorgio Mario; Morosinotto, Tomas

2012-09-01

76

Transient Electron Paramagnetic Resonance of Excited Triplet States of Fullerene adducts  

NASA Astrophysics Data System (ADS)

The zero-field splitting (ZFS) of the excited triplet states of organic molecules often is of the order of 1 GHz or less, and transient EPR at X-band is generally sufficient for the determination of the zero-field splitting and kinetic parameters in these type of molecules. However, information on the g-factor and g-anisotropy cannot be obtained at conventional EPR frequencies, and interpretations of the data in terms of electronic structure are mostly limited to symmetry considerations. On the other hand information of the g-anisotropy provides additional clues with respect to electronic structure, while a direct comparison with radical-ion forms of the molecules becomes possible. This is especially important for those systems in which excited states play an important functional role, as is the case in photosynthesis. Experimental data of transient EPR at 240 GHz will be presented for a variety of systems, like fullerenes, porphyrins, thiophenes, and photosynthetic reaction centers, in non-oriented glasses and partially oriented in liquid crystals. It will be shown that transient EPR at these very high frequencies can accurately determine the g-anisotropy and in some cases the orientation of the g-tensor with respect to the ZFS tensor. The information gained will be discussed in relation to the electronic structure of these molecules.

Bortolus, Marco; van Tol, Johan; Maniero, Annalisa

2003-03-01

77

Singlet-Triplet Mixing in the 13d Rydberg state of ³He observed with stepwise laser excitation  

Microsoft Academic Search

The hyperfine structure of the singlet and triplet 13d Rydberg states in ³He have been studied by stepwise excitation with a single-mode uv laser (294.5 nm) and single-mode color-center laser (2.590 ..mu..m). The experimental results for the 13d state are in good agreement with semiempirical calculations. No difference in the electrostatic energy interval was found between the ³He and ⁴He

L. A. Bloomfield; H. Gerhardt; T. W. Haensch

1982-01-01

78

Singlet-triplet mixing in the 13d Rydberg state of 3He observed with stepwise laser excitation  

Microsoft Academic Search

The hyperfine structure of the singlet and triplet 13d Rydberg states in 3He have been studied by stepwise excitation with a single-mode uv laser (294.5 nm) and single-mode color-center laser (2.590 mum). The experimental results for the 13d state are in good agreement with semi-empirical calculations. No difference in the electrostatic energy interval was found between the 3He and 4He

L. A. Bloomfield; H. Gerhardt; T. W. Hänsch

1982-01-01

79

Spectroscopic investigations of intersystem crossing and triplet state structure in acetylene  

E-print Network

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 ...

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

2006-01-01

80

Light Absorption by Secondary Organic Aerosol Produced from Aqueous Reaction of Phenols with an Organic Excited Triplet State and Hydroxyl Radical  

NASA Astrophysics Data System (ADS)

Although reactions in atmospheric condensed phases can form and transform secondary organic aerosol (SOA), these reactions are not well represented in many air quality models. Previous experiments have focused on hydroxyl radical-mediated oxidation of low molecular weight precursors such as gyloxal and methylglyoxal. In our work we are examining aqueous SOA formed from phenols, which are emitted from biomass burning and formed from the oxidation of anthropogenic aromatics such as benzene and toluene. In this work we examine aqueous SOA production from oxidation of three phenols (phenol, guaiacol, syringol) and three benzene-diols (catechol, resorcinol, 1,4-hydroquinone) by hydroxyl radical (OH) and the triplet excited state of 3,4-dimethoxybenzaldehyde (DMB). Our focus is on light absorption by the reaction products, which we characterized by measuring UV-Vis spectra and calculating mass absorption coefficients. To understand the elemental and molecular composition of the SOA, we also analyzed the samples with high resolution mass spectrometry and infrared spectroscopy. Our results indicate that aqueous oxidation of phenols and benzene-diols via OH and triplet excited states efficiently produce SOA that is highly absorbing in the UV-A wavelengths, consists of both small and large molecular weight products, and is highly oxidized.

Smith, J.; Yu, L.; George, K.; Ruthenburg, T. C.; Dillner, A. M.; Zhang, Q.; Anastasio, C.

2012-12-01

81

Photoreduction and light-induced triplet-state formation in a single-site fluoroalkylated zinc phthalocyanine.  

PubMed

Electron-withdrawing perfluoroalkyl peripheral substituents enhance the photosensitizing properties of metal phthalocyanines while increasing their solubility, thus providing opportunities for advanced characterization of their catalytically-relevant excited states. Optical absorption and electron paramagnetic resonance (EPR) spectroscopy experiments reveal that red light induces the reduction of perfluoroisopropyl-substituted zinc(ii) phthalocyanine (F64PcZn) dissolved in ethanol. A similar photoreduction does not occur in toluene. Furthermore, intense UV irradiation causes the photodegradation of F64PcZn in ethanol, but low power UV illumination favours the formation of the triplet excited state, a prerequisite for new photocatalytic applications. The UV-induced triplet state of F64PcZn is characterized using a combination of transient EPR experiments and DFT computations. PMID:24842295

Moons, Hans; Loas, Andrei; Gorun, Sergiu M; Van Doorslaer, Sabine

2014-10-28

82

Toward Enabling Large-Scale Open-Shell Equation-of-Motion Coupled Cluster Calculations: Triplet States of ?-Carotene.  

PubMed

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 ?-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 singles and doubles excitations. PMID:24905471

Hu, Han-Shi; Bhaskaran-Nair, Kiran; Aprà, Edoardo; Govind, Niranjan; Kowalski, Karol

2014-10-01

83

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

NASA Astrophysics Data System (ADS)

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

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

2012-11-01

84

Nonradiative deactivation of the lowest triplet state of tetrachlorodibenzo- p-dioxin  

NASA Astrophysics Data System (ADS)

In the nonadiabatic approximation, we have studied how the shape of promoting out-of-plane vibrational modes and vibronically induced spin-orbit interactions in structural elements of the 2,3,7,8-tetrachlorodibenzo- p-dioxin molecule affect the energy degradation rate constants K {dg/ s } of triplet T {1/ s } sublevels.

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

2014-03-01

85

Triplet-EPR spectroscopy on the Diels-Alder adduct of C 60 and 4,5-dimethoxy- o-quinodimethane in frozen solution  

Microsoft Academic Search

Pulsed-EPR spectroscopy was used to study a modified C60 molecule (1) in its photoexcited triplet state. The analysis of the triplet EPR lineshape shows a break of the high symmetry of the lowest populated triplet state of C60 due to the modification of the C60 unity. The reported temperature dependence of the spectra is influenced by relaxation effects. Lineshape simulations

Marina Bennati; Arthur Grupp; Michael Mehring; Pavel Belik; Andreas Gügel; Klaus Müllen

1995-01-01

86

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

PubMed

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

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

2009-04-21

87

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

PubMed

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

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

2007-08-01

88

Two-photon absorption cross-section and triplet states of dendritic Pt-acetylides for OPL applications  

NASA Astrophysics Data System (ADS)

The photo-physical properties of bis((4-(phenylethynyl)phenyl)ethynyl)bis(tributylphosphine) platinum(II) with 2,2-bis(methylol)propionic acid (bis-MPA) dendritic substituents were studied. The introduction of dendrimer capping was found to give rise to protection from oxygen quenching of phosphorescent states with a considerably longer decay time of the phosphorescence (0.1 -0.4 ms range) for solvents with oxygen removed or dendrimers of larger size (G2-G4) or higher concentration. Presence of oxygen reduces the phosphorescence decay time to below 1 microsecond. Two-photon induced fluorescence and z-scan of fs pulses at low pulse repetition frequency at approximately 720 nm revealed that the two-photon absorption cross-section is in the order of 0.01 cm/GW, well below the 0.34cm/GW reported by Staromlynska et al [J. Staromlynska, T. McKay and P. Wilson, J. Appl. Phys. 88, 1726 (2000)] and similar for all dendrimer complexes as well as the non-capped Pt-acetylide. Z-scans performed at high pulse repetition frequency gives an apparent two-photon absorption cross-section that is higher due to the population of excited triplet states, and the contribution from incoherent multiphoton absorption involving the triplet states.

Glimsdal, Eirik; Eriksson, Anders; Vestberg, Robert; Malmstrom, Eva; Lindgren, Mikael

2005-08-01

89

Does the concept of Clar's aromatic sextet work for dicationic forms of polycyclic aromatic hydrocarbons?--testing the model against charged systems in singlet and triplet states.  

PubMed

The concept of Clar's ?-electron aromatic sextet was tested against a set of polycyclic aromatic hydrocarbons in neutral and doubly charged forms. Systems containing different types of rings (in the context of Clar's concept) were chosen, including benzene, naphthalene, anthracene, phenanthrene and triphenylene. In the case of dicationic structures both singlet and triplet states were considered. It was found that for singlet state dicationic structures the concept of aromatic sextet could be applied and the local aromaticity could be discussed in the context of that model, whereas in the case of triplet state dicationic structures Clar's model rather failed. Different aromaticity indices based on various properties of molecular systems were applied for the purpose of the studies. The discussion about the interdependence between the values of different aromaticity indices applied to neutral and charged systems in singlet and triplet states is also included. PMID:21614377

Dominikowska, Justyna; Palusiak, Marcin

2011-07-01

90

Nonradiative deactivation of the lowest triplet state of naphthalene and its hydroxy derivatives at 77 K  

NASA Astrophysics Data System (ADS)

The validity of an inductive resonance theory of energy transfer from the T 1? S 0 transition dipole to overtone vibrations of molecular groups containing H and D atoms is experimentally tested for a series of compounds whose conjugation systems are similar in size. To this end, by using kinetic, spectral, and luminescent methods (measurements of the phosphorescence decay times, phosphorescence spectra, ratios between the quantum yields of phosphorescence and fluorescence at 77 K, total quantum yields of fluorescence at 293 K, and ratios between the quantum yields of fluorescence at 293 and 77 K), the deactivation processes of the lowest excited T 1 and S 1 states of seven emitting centers (naphthalene, its hydroxy and dihydroxy derivatives, and their monoanions) in solutions in ethanol- h 6, ethanol- d 6, and their 2: 1 mixtures with diethyl ether are studied. For all the compounds studied, the rate constants k r of the radiative T 1? S 0 transition and the changes in the overlap integrals of the spectra of phosphorescence and absorption of overtones of CH stretching vibrations are determined. The rate constants of energy transfer k dd(CH) from the T 1? S 0 transition dipole to the stretching vibrations of the CH bonds are calculated without regard for the changes in the localization and orientation of this transition dipole in the compounds under study. The contribution of an individual CH group k nr(CH) to the total rate constant of nonradiative deactivation of the T 1 state averaged over the CH groups of the naphthalene ring system is ascertained. A good correlation between the changes in the constants k nr(CH) and k dd(CH) in the series of the hydroxy derivatives of naphthalene is found, which is indicative of the inductive resonance mechanism of the energy degradation of the T 1 state. The deviations from proportionality between the changes in these constants upon passing from naphthalene to its hydroxy derivatives, which correlate with a marked increase in the radiative constant k nr of the hydroxy derivatives in comparison with naphthalene, indicate changes in the strength and localization of the T 1? S 0 transition dipole moment and in its orientation with respect to the plane of the molecule that occur due to introduction of a heteroatom, oxygen, whose lone pair of electrons enters into conjugation with the ?electrons of the naphthalene ring system.

Goryaeva, E. M.; Shablya, A. V.; Ermolaev, V. L.

2003-08-01

91

Reactivity of aromatic amines with triplet 1,8-dihydroxyanthraquinone: A laser flash photolysis study  

Microsoft Academic Search

The property of the lowest excited triplet states of 1,8-dihydroxyanthraquinone (DHAQ) was investigated by using time-resolved laser flash photolysis at 355nm in organic solvents, i.e. acetonitrile and cyclohexane. The transient absorption spectra of the excited triplet DHAQ were obtained in acetonitrile, which have an absorption maximum at 480nm and two broad absorption bands around 350 and 650nm. 3DHAQ* is efficiently

Yang Pan; Yuhe Gao; Lei Yan; H. Pan; Jiafu Chen; Shuqin Yu

2007-01-01

92

Triplet-EPR spectroscopy on the Diels-Alder adduct of C 60 and 4,5-dimethoxy- o-quinodimethane in frozen solution  

NASA Astrophysics Data System (ADS)

Pulsed-EPR spectroscopy was used to study a modified C 60 molecule (1) in its photoexcited triplet state. The analysis of the triplet EPR lineshape shows a break of the high symmetry of the lowest populated triplet state of C 60 due to the modification of the C 60 unity. The reported temperature dependence of the spectra is influenced by relaxation effects. Lineshape simulations based on a triplet Hamiltonian including anisotropic T1/ T2 relaxation were performed. The results are discussed in relation to the behaviour of pure 3C 60.

Bennati, Marina; Grupp, Arthur; Mehring, Michael; Belik, Pavel; Gügel, Andreas; Müllen, Klaus

1995-07-01

93

Two-State Model of Antiaromaticity: The Triplet State. Is Hund's Rule Violated? Shmuel Zilberg and Yehuda Haas*  

E-print Network

always makes the triplet of lower energy, when more configurations are added, electron correlation may having an even number (2n) of electron bonds (antiaromatic compounds) is presented. In these systems for the reaction exchanging two bond-alternating structures. As a resonance hybrid of two equivalent valence bond

Haas, Yehuda

94

J. Phys. Chem. 1995, 99, 1199-1203 1199 Singlet and Triplet Excited State Behaviors of c60 in Nonreactive and Reactive Polymer  

E-print Network

of fullerenes, c60 and C70, in homogeneous and heterogeneous media (e.g., in organic cyclodex- trins,18 polymerJ. Phys. Chem. 1995, 99, 1199-1203 1199 Singlet and Triplet Excited State Behaviors of c60 to those observed in solutions. Encapsulation of c60 with PS results in the suppression of excited state

Sauvé, Geneviève

95

Reprinted from the Jozrr+~alof Scie?~tzfic6-Ivzdustvznl Research, 1973, Val 32, KO. 2, pp. 62-69 Is There a Triplet State in Photosynthesis?  

E-print Network

- tion, changlng the electron density configuration to one of higher energy. The excited singlet state is generally short-lived (10-8-10-9 sec) witn the valence electrons having opposite spi~s. [Lifetimes of Chl molecules can exist in the excited electronic state either in a singlet or triplet configu- C ration

Govindjee

96

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

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

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

2014-05-01

97

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

PubMed

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

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

2012-10-01

98

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

PubMed Central

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

2013-01-01

99

Triplet state of the semiquinone-Rieske cluster as an intermediate of electronic bifurcation catalyzed by cytochrome bc1.  

PubMed

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

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

2013-09-17

100

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

PubMed

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

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

2012-04-01

101

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

PubMed

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(3)B2u (+) 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. PMID:25362293

Chakraborty, Himanshu; Shukla, Alok

2014-10-28

102

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

. 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...

DeSalvo, Bethany S.

2011-08-08

103

Triplet Pair Correlations in s-Wave Superfluids as a Signature of the Fulde-Ferrell-Larkin-Ovchinnikov State  

E-print Network

triplet mixing which occurs when a balanced two-component system displays FFLO-type oscillations due as long as the condensation energy is larger than polarization energy gain in the normal phase [1]. A deep-wave) Feshbach resonance gives direct access to these triplet correlations. This method can be used

Demler, Eugene

104

Triplet and in-gap magnetic states in the ground state of the quantum frustrated fcc antiferromagnet Ba2YMoO6  

NASA Astrophysics Data System (ADS)

The geometrically frustrated double perovskite Ba2YMoO6 is characterized by quantum s=1/2 spins at the Mo5+ sites of an undistorted fcc lattice. Previous low-temperature characterization revealed an absence of static long-range magnetic order and suggested a nonmagnetic spin-singlet ground state. We report unique time-of-flight and triple-axis neutron spectroscopy of Ba2YMoO6 that shows a 28 meV spin excitation with a bandwidth of ˜4 meV, which vanishes above ˜125 K. We identify this as the singlet-triplet excitation that arises out of a singlet ground state, and further identify a weaker continuum of magnetic states within the gap, reminiscent of spin-polaron states arising due to weak disorder.

Carlo, J. P.; Clancy, J. P.; Aharen, T.; Yamani, Z.; Ruff, J. P. C.; Wagman, J. J.; van Gastel, G. J.; Noad, H. M. L.; Granroth, G. E.; Greedan, J. E.; Dabkowska, H. A.; Gaulin, B. D.

2011-09-01

105

Exploring the Triplet Excited State Potential Energy Surfaces of a Cyclometalated Pt(II) Complex: Is There Non-Kasha Emissive Behavior?  

PubMed

In this Article, we address the complexity of the emissive processes of a square-planar heteroleptic Pt(II) complex bearing 2-phenylpyridine (ppy) as cyclometalated ligand and an acetylacetonate derivative (dbm) as ancillary ligand. The origins of emission were identified with the help of density functional theory (DFT) and quadratic response (QR) time-dependent (TD)-DFT calculations including spin-orbit coupling (SOC). To unveil the photodeactivation mechanisms, we explored the triplet potential energy surfaces and computed the SOCs and the radiative decay rates (kr) from possible emissive states. We find that emission likely originates from a higher-lying (3)MLCT/(3)LLCT state and not from the Kasha-like (3)MLCT/(3)LCdbm state. The temperature-dependent nonradiative deactivation mechanisms were also elucidated. The active role of metal-centered ((3)MC) triplet excited states is confirmed for these deactivation pathways. PMID:25290077

Escudero, Daniel; Thiel, Walter

2014-10-20

106

Quantum interference effect on collisional energy transfer within singlet˜triplet mixed states of Na 2A 1?+u( v=8) ˜ b 3?0 u( v=14)  

NASA Astrophysics Data System (ADS)

In a previous study [G.-H. Sha, B. Jiang, J.-B. He, C.-H. Zhang, J. Chem. Phys. 102 (1995) 2772], the first evidence for collisional quantum interference (CQI) in intramolecular energy transfer within CO singlet˜triplet mixed states was obtained. We present here another evidence for CQI effect on energy transfer within the singlet˜triplet mixed states of Na 2( A 1?+u, v=8 ˜ b 3?0 u, v=14)+Na(3s) by optical-optical double resonance fluorescence spectroscopy. The measured state-to-state cross-sections show the unique feature of abnormal ? J-dependence of cross-sections due to constructive or destructive interference. Molecular rotation speed and interaction potential have important effect on the extent of interference.

Chen, X. L.; Chen, H. M.; Li, J.; Liu, Y. M.; Dai, X. C.; Sha, G. H.; Xie, J. C.; Zhang, C. H.; Li, Li

2000-02-01

107

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

E-print Network

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 neu...

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

2014-01-01

108

Structures of C 3H 6O species in the triplet state: methyloxirane, propanal, acetone, methyl vinyl ether and propenol  

NASA Astrophysics Data System (ADS)

The geometries of thirteen triplet C 3H 6O species, plus methyloxirane and propene in the ground state, have been completely optimized by analytic gradient (force) techniques at both the minimal STO-3G and split valence 3-21G basis set levels. Single calculations using the 6-31G? polarized basis set were performed for each 3-21G optimum structure. With the exception of bond angles at oxygen and the pyramidality at carbon radical centers, the geometries obtained with the two basis sets differ little. Except for the propene +O( 3P) atom, the addition of d, orbitals has little effect on the relative energies compared to the 3-21G energy differences (? E), but both were markedly different from the STO-3G results. Whereas the latter ? E values covered a range of almost 40 kcal mol -1, this range was reduced to 24.5 and 22.4 kcal mol -1 at the 3-21G and 6-31G -? levels, respectively.

Peterson, Michael R.; de Mare, George R.

109

On implementing nondestructive triplet Toffoli gate with entanglement swapping operations via the GHZ state analysis  

NASA Astrophysics Data System (ADS)

We investigate an novel implementation of a Toffoli gate using multiple independent auxiliary photons prepared beforehand in single-qubit states. This gate can be performed nondestructively with entanglement swapping via the Greenberger-Horne-Zeilinger state analysis. We evaluate the performance of the proposed Toffoli gate with the fidelity based on different computation bases. The multi-qubit-entanglement gate is no longer theoretical since it can be implemented in principle with single-qubit photons.

Guo, Ying; Zhao, Zhisheng; Wang, Yijun; Wang, Ping; Huang, Dazu; Lee, Moon Ho

2014-09-01

110

Aza-BODIPY derivatives: enhanced quantum yields of triplet excited states and the generation of singlet oxygen and their role as facile sustainable photooxygenation catalysts.  

PubMed

A new series of aza-BODIPY derivatives (4 a-4 c, 5 a,c, and 6 b,c) were synthesized and their excited-state properties, such as their triplet excited state and the yield of singlet-oxygen generation, were tuned by substituting with heavy atoms, such as bromine and iodine. The effect of substitution has been studied in detail by varying the position of halogenation. The core-substituted dyes showed high yields of the triplet excited state and high efficiencies of singlet-oxygen generation when compared to the peripheral-substituted systems. The dye 6 c, which was substituted with six iodine atoms on the core and peripheral phenyl ring, showed the highest quantum yields of the triplet excited state (?(T) =0.86) and of the efficiency of singlet-oxygen generation (?(?) =0.80). Interestingly, these dyes were highly efficient as photooxygenation catalysts under artificial light, as well as under normal sunlight conditions. The uniqueness of these aza-BODIPY systems is that they are stable under irradiation conditions, possess strong red-light absorption (620-680 nm), exhibit high yields of singlet-oxygen generation, and act as efficient and sustainable catalysts for photooxygenation reactions. PMID:22945021

Adarsh, Nagappanpillai; Shanmugasundaram, Madhesh; Avirah, Rekha R; Ramaiah, Danaboyina

2012-10-01

111

Singlet-triplet mixing in ns(n=12-14) Rydberg states of 3He  

Microsoft Academic Search

The hyperfine structure of the n3S (n=12-14) Rydberg levels in 3He have been studied by ultraviolet-infrared double-resonance laser spectroscopy. Using the frequency-doubled output of a CW ring dye laser the authors have populated the 1s5p 3P state of 3He by excitation from the metastable 1s2s 3S state at 294.5 nm. In a second step, an infrared single-mode colour-centre laser is

L. A. Bloomfield; H. Gerhardt; T. W. Hansch

1983-01-01

112

Application of equation-of-motion coupled-cluster methods to low-lying singlet and triplet electronic states of HBO and BOH  

E-print Network

Application of equation-of-motion coupled-cluster methods to low-lying singlet and triplet-consistent quadruple and quintuple zeta basis sets. The linear HBO X~ 1 + state is predicted to lie 48.3 kcal mol-1 2. The CCSDT BOH barrier to linearity is predicted to lie 3.7 kcal mol-1 0.16 eV . With a harmonic zero

Crawford, T. Daniel

113

The "excited state C-C bond cleavage-luminescence" phenomenon of a biphenyl-substituted methylenecyclopropane triggered by intermolecular energy transfer from triplet benzophenone.  

PubMed

Existence of the "excited state C-C bond cleavage-luminescence" phenomenon was demonstrated by utilizing intermolecular energy transfer from the excited-triplet benzophenone to 2,2-di(4-biphenylyl)-1-methylenecyclopropane (3). An excellent linear relationship between the intensity of the excitation laser light and that of luminescence clearly shows that formation of the corresponding excited trimethylenemethane biradical (3)4??* proceeds via a one-photon route. PMID:25267075

Matsui, Yasunori; Kido, Taiki; Ohta, Eisuke; Ikeda, Hiroshi

2014-11-21

114

Temperature study of indole, tryptophan and N-acetyl-L-tryptophanamide (NATA) triplet-state quenching by iodide in aqueous solution.  

PubMed

In this study, the temperature dependence of the measured phosphorescence lifetimes of aqueous indole, tryptophan and N-acetyl-L-tryptophanamide (NATA) between 6 and 55 °C in the absence and in the presence of iodide, a suitable intersystem crossing enhancer, has been determined. The obtained results suggest the existence of one process for the temperature-dependent, non-radiative deactivation of triplet states of the aqueous indoles in the absence of iodide. This process may be associated with the high sensitivity of indole triplet state lifetime to the subtle changes in the local viscosity of the surrounding aqueous environment or may be attributed to diffusional quenching by solvent molecules and/or by possible impurities present in water. However, the steep decrease in the measured phosphorescence lifetimes of indole and tryptophan with temperature suggests that diffusion-mediated quenching processes are not prevailing. Upon increasing concentration of iodide (up to 0.1 M), the obtained Arrhenius plots for the deactivation rate (1/?ph) of the triplet states of the studied indoles were linear, which provided strong support for the hypothesis of the existence of one temperature dependent non-radiative process for the de-excitation of indoles triplet state. Our results showed that this process is attributed to the diffusion-controlled solute-quenching by iodide and, most probably, proceeds via reversibly formed exciplex. At concentration of iodide higher than 0.1M highly curved Arrhenius plots were obtained, which may indicate a change in the rate determining step with a change in temperature. This change most probably is associated with a transition from diffusion-controlled exciplex formation followed by rate-determining exciplex deactivation at high temperature. PMID:23602958

Kowalska-Baron, Agnieszka; Ga??cki, Krystian; Wysocki, Stanis?aw

2013-07-01

115

Laser spectroscopy of HfO: Linkage of the triplet state manifolds  

SciTech Connect

The wavelength-resolved fluorescence excitation technique has been used to record the (0,0) band of the b{sup 3}{Pi}{sub 1} - X{sup 1}{Sigma}{sup +} electronic transition of HfO at a resolution of 0.03 cm{sup -1}. Previously, this transition has been assigned as a B{sup 1}{Pi}-X{sup 1}{Sigma}{sup +} electronic transition. The principal constants (in cm{sup -1}) obtained from recent and previous analyses are discussed. Ligand field theory (LFT) calculations were used to suggest electronic configurations for the excited states of HfO. New electronic assignments based on LFT predictions for the F and E states are indicated in parentheses.

Kaledin, L.A.; McCord, J.E.; Heaven, M.C. [Emory Univ. Atlanta, GA (United States)

1995-12-31

116

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

NASA Astrophysics Data System (ADS)

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 with the cc-pVTZ basis set. Fissions of the C4H5 and C2C3 bonds in S1 yield H(2S)+CCCN(A2?) and HCC(A2?)+CN(X2?+), respectively. In T1, the corresponding dissociation products are H(2S)+CCCN(X2?+) and HCC(X2?)+CN(X2?+). At the CASPT2(14,13)//CASSCF(14,13)+ZPE level, the barriers for the adiabatic dissociation of the C4H5 and C2C3 bonds are 6.11 and 6.94 eV in S1 and 5.71 and 6.39 eV in T1, respectively, taking the energy of S0 minimum as reference. Based on the calculated potential energy surfaces, the existence of a metastable excited molecule is anticipated upon 260-230 nm photoexcitation, which provides a probable approach for cyanoacetylene to polymerize. The internal conversion (IC) process through vibronic interaction followed by C4H5 fission in the ground state is found to account for the observed diffuse character in the UV absorption spectrum below 240 nm.

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

2008-11-01

117

a Quantum Chemical Study of Familiar and Exotic Low-Lying Singlet and Triplet States of CH2, CF2, and Chf  

NASA Astrophysics Data System (ADS)

High level MRCI and RCCSD(T) calculations using triple and quadruple zeta quality correlation consistent basis sets were used to study the low-lying singlet and triplet states of CH2, CF2, and CHF. The bonding in carbon was found to be very similar to that of sulfur, where there is also a competition between states that form through normal covalent bonding and recoupled pair bonding. The recoupled pair bonding model was used to investigate these states systematically to see how closely they resemble the behavior of SF2, which has a 1A1 ground state and 3B1 and 3A2 excited states. In addition to accounting for the separations and ordering of the lowest singlet and triplet states of each species, the less-studied 3A2 states of CH2 and CF2 and the 3A^" state of CHF were investigated and compared to gain insight into the underlying reasons for the energetic and bonding differences between these species. Interestingly, the 3A2 state of CH2 is a cyclic structure, the 3A2 state of CF2 is bent but not cyclic (resembling the same state of SF_2), and the analogous minimum structure on the 3A^" surface of CHF is a C---HF complex.

Xu, Lu; Woon, D. E.; Dunning, T. H., Jr.

2010-06-01

118

Proton polarization above 70% by DNP using photo-excited triplet states, a first step towards a broadband neutron spin filter  

NASA Astrophysics Data System (ADS)

The use of polarized protons as neutron spin filter is an attractive alternative to the well established neutron polarization techniques, as the large, spin-dependent neutron scattering cross-section for protons is useful up to the sub-MeV region. Employing optically excited triplet states for the dynamic nuclear polarization (DNP) of the protons relieves the stringent requirements of classical DNP schemes, i.e low temperatures and strong magnetic fields, making technically simpler systems with open geometries possible. Using triplet DNP a record polarization of 71% has been achieved in a pentacene doped naphthalene single crystal at a field of 0.36 T using a simple helium flow cryostat for cooling. Furthermore, by placing the polarized crystal in a neutron optics focus and de-focus scheme, the actual sample cross-section could be increased by a factor 35 corresponding to an effective spin filter cross-section of 18×18 mm2.

Eichhorn, T. R.; Niketic, N.; van den Brandt, B.; Filges, U.; Panzner, T.; Rantsiou, E.; Wenckebach, W. Th.; Hautle, P.

2014-08-01

119

Protonation-induced paramagnetism. Structures and stabilities of six- and seven-coordinate complexes of Os(II) in singlet and triplet states: a density functional study.  

PubMed

Li, Yeh, and Taube in 1993 (J. Am. Chem. Soc. 1993, 115, 10384) synthesized a number of complexes which can be formally regarded as protonated Os(II) species. Some of these were paramagnetic, in contrast to the diamagnetism of the closed shell 5d(6) Os(II) ions. This intriguing phenomenon is investigated theoretically using density functional theory. The geometries, stabilities, and electronic structures of a series of six- and seven-coordinate osmium complexes were studied in gas phase and aqueous solution using the B3P86 functional, in conjunction with the isodensity-polarized continuum model of solvation. The general formula for these complexes is [Os(NH(3))(4)H(L(1)(x)())(m)()(L(2)(y)())(n)()](()(x)()(+)(y)()(+3)+), where L(1) and L(2) = H(2)O, NH(3), CH(3)OH, CH(3)CN, Cl(-), and CN(-), which could be regarded as protonated Os(II) species or hydrides of Os(IV), although according to this work the osmium-hydrogen interaction is best described as a covalent Os(III)-H bond, in which the hydrogen is near-neutral. The ground states are generally found to be singlets, with low-lying triplet excited states. Solvation tends to favor the singlet states by as much as approximately 18 kcal mol(-)(1) in the 3+ ions, an effect which is proportional to the corresponding difference in molecular volumes. To have realistic estimates of the importance of spin-orbit coupling in these systems, the spin-orbit energy corrections were computed for triplet [Os(NH(3))(4)](2+), [Os(NH(3))(4)H](3+), and [Os(NH(3))(4)H(H(2)O)](3+), along with gas-phase Os and its ions as well as [Os(H(2)O)(6)](3+). The seven-coordinate triplet-state complex [Os(NH(3))(5)H(CH(3)OH)](3+), which had been successfully isolated by Li, Yeh, and Taube, is predicted to be a stable six-coordinate complex which strongly binds to a methanol molecule in the second coordination shell. The calculations further suggest that the singlet-triplet splitting would be very small, a few kilocalories per mole at most. The geometries and the electronic structures of the complexes are interpreted and rationalized in terms of Pauling's hybridization model in conjunction with conventional ligand field theory that effectively precludes the existence of true seven-coordinate triplet-state complexes of the above formula. PMID:11389632

Mylvaganam, K; Bacskay, G B; Hush, N S

2001-06-13

120

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

E-print Network

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.

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

121

Photoexcited triplet state properties of brominated and nonbrominated Ga(III)-corroles as studied by time-resolved electron paramagnetic resonance.  

PubMed

The effect of the corrole macrocycle bromination on its photoexcited triplet state parameters was examined in a comparison study of brominated and nonbrominated Ga(III) 5,10,15-tris(pentafluorophenyl)corroles, employing X-band (9.5 GHz) time-resolved electron paramagnetic resonance (TREPR) spectroscopy. It is demonstrated that the spectrum of the brominated Ga-corrole is characterized by an opposite polarization pattern and a larger zero-field splitting (ZFS) parameter |D|, compared to nonbrominated Ga-corrole. With the assignment of a negative sign for the ZFS parameter D, the dominant intersystem crossing (ISC) pathways are evaluated. Spectral line shape analysis reveals that in the brominated Ga-corrole,the out-of-plane triplet sublevel is overpopulated (A(Z) > A(X), A(Y)), while in nonbrominated Ga-corrole, the in-plane triplet sublevels are preferentially populated (A(X), A(Y) ? A(Z)). The differences in the photophysical properties of the corroles are attributed to the heavy atom effect upon corrole skeleton bromination, which enhances the spin-orbit coupling strength in the brominated complex, thus affecting its ISC and ZFS parameters. PMID:20112985

Wagnert, Linn; Rubin, Roy; Berg, Alexander; Mahammed, Atif; Gross, Zeev; Levanon, Haim

2010-11-18

122

Mass spectra of radially and orbitally excited states of mesons  

E-print Network

Meson mass spectra, evaluated in the framework of the relativistic model of quasi-independent quarks, are presented. Mass values are obtained with the help of numerical calculations based on the Dirac equation and by phenomenological mass formulae. The Dirac equation involves the potential, which is sum of the vector quasi-Coulombic potential and the scalar linear rising confinement potential. The phenomenological mass formulae are applied to excited meson states consisting of u-, d-quarks and antiquarks with isotopical spin I=1. A comparison of the evaluated mass spectra with existing data is performed. Problems of identification of some meson states in vector and scalar channels are discussed.

V. Khruschov; V. Savrin; S. Semenov

2005-12-28

123

One-radius triplets.  

PubMed

The one-radius triplet is an optical system that consists of three lenses. Either the radii of curvature of the lenses have the same absolute value or one radius of curvature has an infinitely large value. The advantage of such optical systems is that their production cost is less than that of systems with ordinary triplets. Here a theory of one-radius triplets is described and tables of parameters for their modification are provided. Residual aberrations are given for several selected triplets. One-radius triplets are suitable for use in laser technology and metrology. PMID:11900004

Miks, Antonin

2002-03-01

124

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

PubMed Central

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

Mani, Tomoyasu; Vinogradov, Sergei A.

2013-01-01

125

Spectra  

NSDL National Science Digital Library

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.

Exploratorium, The

2012-06-26

126

Spectra  

NSDL National Science Digital Library

Spectra is a very informative website about 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 great detail about the properties of light. Then it talks about how matter both creates and destroys radiation. Then it discusses how to interpret absorption and emission lines. The website ends with how astronomers use spectra to understand stars, galaxies, other objects in the universe.

Kaler, James

2004-07-16

127

Potential energy curves, spectroscopic constants and spin-orbit coupling: A theoretical study on twelve triplet ?-S states of Ge2 molecule  

NASA Astrophysics Data System (ADS)

The potential energy curves (PECs) of twelve triplet ?-S states and fourteen ? states generated from five triplet ?-S states of Ge2 molecule are calculated by an ab initio quantum chemical method. The PEC calculations are made for internuclear separations from 0.15 to 1.10 nm using the complete active space self-consistent field method, which is followed by the internally contracted multireference configuration interaction approach with the Davidson modification (MRCI + Q). The basis set used here is the aug-cc-pV5Z-pp. Convergent behavior is discussed and excellent convergence is observed with respect to the basis sets and level of theory. The PECs are extrapolated to the complete basis set limit by the total-energy extrapolation scheme. The spin-orbit coupling effect is accounted for by the Breit- Pauli Hamiltonian in combination with the aug-cc-pVTZ-pp basis set. With the PECs, the spectroscopic parameters are evaluated by fitting the first ten vibrational levels, which are obtained by solving the ro-vibrational Schrödinger equation using Numerov's method. The spectroscopic results are compared with those reported in the literature. Excellent agreement with available measurements is found. The vibrational levels and inertial rotation constants are calculated for each ?-S state and those of the first ten vibrational states are reported for the non-rotation Ge2 molecule. The spectroscopic parameters of the 13?{/u +}, 13? u , 23?{/u +}, 13? g , 23? g , 33? g , 13?{/u -}, 23?{/u -}, 23? u and 23?{/g -} ?-S states and the vibrational levels and inertial rotation constants of all the ?-S states determined by the MRCI + Q/Q5 calculations are expected to be reliable predicted ones.

Liu, Hui; Shi, Deheng; Sun, Jinfeng; Zhu, Zunlue

2013-02-01

128

Density functional theory calculations of the lowest energy quintet and triplet states of model hemes: role of functional, basis set, and zero-point energy corrections.  

PubMed

We investigated the effect of several computational variables, including the choice of the basis set, application of symmetry constraints, and zero-point energy (ZPE) corrections, on the structural parameters and predicted ground electronic state of model 5-coordinate hemes (iron(II) porphines axially coordinated by a single imidazole or 2-methylimidazole). We studied the performance of B3LYP and B3PW91 with eight Pople-style basis sets (up to 6-311+G*) and B97-1, OLYP, and TPSS functionals with 6-31G and 6-31G* basis sets. Only hybrid functionals B3LYP, B3PW91, and B97-1 reproduced the quintet ground state of the model hemes. With a given functional, the choice of the basis set caused up to 2.7 kcal/mol variation of the quintet-triplet electronic energy gap (DeltaEel), in several cases, resulting in the inversion of the sign of DeltaEel. Single-point energy calculations with triple-zeta basis sets of the Pople (up to 6-311G++(2d,2p)), Ahlrichs (TZVP and TZVPP), and Dunning (cc-pVTZ) families showed the same trend. The zero-point energy of the quintet state was approximately 1 kcal/mol lower than that of the triplet, and accounting for ZPE corrections was crucial for establishing the ground state if the electronic energy of the triplet state was approximately 1 kcal/mol less than that of the quintet. Within a given model chemistry, effects of symmetry constraints and of a "tense" structure of the iron porphine fragment coordinated to 2-methylimidazole on DeltaEel were limited to 0.3 kcal/mol. For both model hemes the best agreement with crystallographic structural data was achieved with small 6-31G and 6-31G* basis sets. Deviation of the computed frequency of the Fe-Im stretching mode from the experimental value with the basis set decreased in the order: nonaugmented basis sets, basis sets with polarization functions, and basis sets with polarization and diffuse functions. Contraction of Pople-style basis sets (double-zeta or triple-zeta) affected the results insignificantly for iron(II) porphyrin coordinated with imidazole. Poor performance of a "locally dense" basis set with a large number of basis functions on the Fe center was observed in calculation of quintet-triplet gaps. Our results lead to a series of suggestions for density functional theory calculations of quintet-triplet energy gaps in ferrohemes with a single axial imidazole; these suggestions are potentially applicable for other transition-metal complexes. PMID:18348545

Khvostichenko, Daria; Choi, Andrew; Boulatov, Roman

2008-04-24

129

First-principles Calculation of Excited State Spectra in QCD  

SciTech Connect

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

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

2011-05-24

130

First-principles Calculation of Excited State Spectra in QCD  

SciTech Connect

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

Jozef Dudek,Robert Edwards,Michael Peardon,David Richards,Christopher Thomas

2011-05-01

131

Costs of triplet pregnancy  

Microsoft Academic Search

OBJECTIVE: Our purpose was to describe the total costs involved in the delivery, prenatal, and neonatal care for triplet pregnancies.STUDY DESIGN: Twenty triplet pregnancies were born at our institution over the 1-year period between July 1, 1992, and June 30, 1993. Total charges for prenatal care, physician fees, antepartum admissions, delivery, postpartum inpatient and outpatient care, and neonatal inpatient and

David Chelmow; Alan S. Penzias; Gary Kaufman; Curtis Cetrulu

1995-01-01

132

The predicted spectrum and singlet-triplet interaction of the hypermetallic molecule SrOSr.  

PubMed

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 ã3?(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 ã3?(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 ã electronic states and find them to be very small. PMID:23506078

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

2013-10-01

133

Spectroscopic effects resulting from interacting singlet and triplet excited states: vibronic structure involving the O-H stretching mode in d-d absorption bands of Ni(H2O)6(2+).  

PubMed

The ligand-field absorption spectrum of the Ni(H2O)6(2+) cation has been thoroughly measured and analyzed over the past sixty years, often on crystals with low symmetry at the metal site, and its absorption band maxima have been used as a benchmark for increasingly sophisticated electronic structure calculations over the last decades. We present variable-temperature absorption spectra measured on crystals with cubic Th symmetry at the site of the nickel(ii) cation. This high site symmetry is confirmed for CsNi(H2O)6PO4 by X-ray diffraction and allows for a direct comparison with ligand-field calculations in Th symmetry, at the basis of an analysis of the vibronic structure in the energy range of the lowest-energy spin-forbidden transition, the "red" or middle band of the spectrum. This spectroscopic region displays effects of strong interactions between singlet and triplet excited states, influencing intensities and vibronic structure. A particular feature that has not been analyzed in detail is a clearly discernible vibronic progression involving the O-H stretching mode on the high-energy side of the absorption band. A quantitative model is presented and applied in order to rationalize this unusual effect, originating from coupling between normal coordinates, to the best of our knowledge the first analysis of this distinct spectroscopic feature arising from interacting excited states. PMID:25311941

Dobe, Christopher; González, Emmanuel; Tregenna-Piggott, Philip L W; Reber, Christian

2014-11-12

134

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

NASA Astrophysics Data System (ADS)

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.

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

135

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

PubMed

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

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

136

On the Photoelectron Spectra of Li4  

NASA Technical Reports Server (NTRS)

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.

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

1996-01-01

137

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

NASA Astrophysics Data System (ADS)

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

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

2006-07-01

138

Quasiclassical asymptotics and coherent states for bounded discrete spectra  

SciTech Connect

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

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

2010-12-15

139

Electronic States of Organic Molecules. 3. Photoelectron Spectra of Cycloalkenes and  

E-print Network

7179 Electronic States of Organic Molecules. 3. Photoelectron Spectra of Cycloalkenes Laboratories, Murray Hill, New Jersey 07974. Received February 24, 1976 Abstract: The photoelectron spectra (He of the optical spectra. We present the photoelectron spectra for a series of cy- cloalkenes (1

Ellison, Barney

140

Triplet state and in-gap scattering from the spin-^1/2 quantum antiferromagnet Ba2YMoO6  

NASA Astrophysics Data System (ADS)

The double perovskite material Ba2YMoO6 is known to exhibit an absence of long-range and short-range magnetic order down to at least 2K, indicating a high degree of geometric frustration of its tetrahedrally-coordinated spin-^1/2 Mo^5+ moments, and NMR results have implied the existence of a spin-singlet ground state. Though geometric frustration in both 3D and quasi-2D systems has been of intense interest in recent years, comparatively little attention has been given to FCC systems, which may exhibit geometric frustration as the FCC lattice can be viewed as a network of edge-sharing tetrahedra. We have conducted inelastic neutron scattering measurements using triple-axis and time-of-flight instruments, revealing a band of scattering at 28 meV which disappears above ˜125K; we identify this scattering band as the triplet excitation out of a singlet ground state. We also identify a weaker population of in-gap states which are reminiscent of spin-polaron states induced by weak disorder.

Carlo, J. P.; Clancy, J. P.; Aharen, T.; Yamani, Z.; Ruff, J. P. C.; Wagman, J. J.; van Gastel, G. J.; Noad, H. M. L.; Granroth, G. E.; Greedan, J. E.; Dabkowska, H. A.; Gaulin, B. D.

2012-02-01

141

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

Microsoft Academic Search

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

M. Buchheit; P. D. Loly

1972-01-01

142

Photolysis of chloride precursors as a method to prepare and characterize the triplet state of fluorenyl-substituted m-xylylene diradicals  

Microsoft Academic Search

Fluorenyl substituted m-xylylene triplet diradicals are conveniently generated from the corresponding dichloride precursors upon photolysis at <100 K in 2-MeTHF glass. Under similar conditions tert-butyl substituted Schlenk type m-xylylene could not be generated from the dichloride precursor 6. Compound 6, however could be dehalogenated with zinc dust in both toluene and 2-MeTHF to produce the triplet diradical.

Joseph J. Gajewski; Gitendra C. Paul

1998-01-01

143

Vector quarks in the Higgs triplet model  

NASA Astrophysics Data System (ADS)

We analyze the effects of introducing vector fermions in the Higgs triplet model. In this scenario, the model contains, in addition to the Standard Model particle content, one triplet Higgs representation and a variety of vectorlike fermion states, including singlet, doublet, and triplet states. We investigate the electroweak precision variables and impose restrictions on model parameters. We show that, for some representations, introducing vector quarks significantly alters the constraints on the mass of the doubly charged Higgs boson, bringing it in closer agreement with present experimental constraints. We also study the effects of introducing the vectorlike fermions on neutral Higgs phenomenology, in particular on the loop-dominated decays H??? and H?Z?, and the restrictions they impose on the parameter space.

Bahrami, Sahar; Frank, Mariana

2014-08-01

144

Low ionization lines in high luminosity quasars: The calcium triplet  

NASA Astrophysics Data System (ADS)

In order to investigate where and how low ionization lines are emitted in quasars we are studying a new collection of spectra of the CaII triplet at ?8498, ?8542, ?8662 observed with the Very Large Telescope (VLT) using the Infrared Spectrometer And Array Camera (ISAAC). Our sample involves luminous quasars at intermediate redshift for which CaII observations are almost nonexistent. We fit the CaII triplet and the OI ?8446 line using the H? profile as a model. We derive constraints on the line emitting region from the relative strength of the CaII triplet, OI ?8446 and H?.

Martínez-Aldama, Mary Loli; Dultzin, Deborah; Marziani, Paola; Sulentic, Jack W.; Chen, Yang; Bressan, Alessandro; Stirpe, Giovanna M.

2014-10-01

145

An attempt to enhance singlet-triplet transitions in vapors  

E-print Network

of the Apparatus- - 13 Y. Experiment- - 18 VI, Experimental Results 21 VII, Conclusions- - 26 LIST OF TABLES Table I. SO2-02 Absorption Spectra Data --- II NH3 02 Abeorption Spectra Data- III CH20-02 Abeorption Spectra Data- 27 - 27 vi LIST OF FIGUHKS...-triplet absorption transitions in NH and to enhance singlet-triplet transitions in CH20 and S02 by 3 subjecting the vapors of these substances to oxygen gas under high pressure, GHSPTER II PREVIOUS EXPERIMEHTSL EETHODS Kasha, X? To induce singlet...

Young, Bernard Theodore

2012-06-07

146

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

NASA Astrophysics Data System (ADS)

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

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

2002-09-01

147

Triplet-triplet energy transfer from a UV-A absorber butylmethoxydibenzoylmethane to UV-B absorbers.  

PubMed

The phosphorescence decay of a UV-A absorber, 4-tert-butyl-4'-methoxydibenzolymethane (BMDBM) has been observed following a 355 nm laser excitation in the absence and presence of UV-B absorbers, 2-ethylhexyl 4-methoxycinnamate (octyl methoxycinnamate, OMC) and octocrylene (OCR) in ethanol at 77 K. The lifetime of the lowest excited triplet (T1) state of BMDBM is significantly reduced in the presence of OMC and OCR. The observed quenching of BMDBM triplet by OMC and OCR suggests that the intermolecular triplet-triplet energy transfer occurs from BMDBM to OMC and OCR. The T1 state of OCR is nonphosphorescent or very weakly phosphorescent. However, we have shown that the energy level of the T1 state of OCR is lower than that of the enol form of BMDBM. Our methodology of energy-donor phosphorescence decay measurements can be applied to the study of the triplet-triplet energy transfer between UV absorbers even if the energy acceptor is nonphosphorescent. In addition, the delayed fluorescence of BMDBM due to triplet-triplet annihilation was observed in the BMDBM-OMC and BMDBM-OCR mixtures in ethanol at 77 K. Delayed fluorescence is one of the deactivation processes of the excited states of BMDBM under our experimental conditions. PMID:24329403

Kikuchi, Azusa; Oguchi-Fujiyama, Nozomi; Miyazawa, Kazuyuki; Yagi, Mikio

2014-01-01

148

Superachromatic air-spaced triplet.  

PubMed

A theoretical analysis of properties of superachromatic air-spaced triplets composed of thin lenses is described in this paper. An interesting result is shown in that the superachromatic air-spaced triplet cannot simultaneously correct field curvature and transverse and longitudinal chromatic aberration. The formulas for the calculation of parameters of an air-spaced triplet are derived and the procedure for the calculation of the shape of individual lenses of the triplet is described using the third-order aberration theory. The application of the described analysis is presented in an example of the design of a superachromatic triplet. PMID:25322401

Miks, Antonin; Novak, Jiri

2014-10-10

149

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

NASA Astrophysics Data System (ADS)

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

Jain, Sonal Kumar; Bhardwaj, Anil

2012-07-01

150

Lowest triplet (n,?*) state of 2-cyclohexen-1-one: characterization by cavity ringdown spectroscopy and quantum-chemical calculations.  

PubMed

The cavity ringdown (CRD) absorption spectrum of 2-cyclohexen-1-one (2CHO) was recorded over the range 401.5-410.5 nm in a room-temperature gas cell. The very weak band system (? ? 0.1 M(-1) cm(-1)) in this spectral region is due to the T1(n, ?*) ? S0 electronic transition. The 0(0)(0) origin band was assigned to the feature observed at 24,558.8 ± 0.3 cm(-1). We have assigned 46 vibronic transitions in a region extending from -200 to +350 cm(-1) relative to the origin band. For the majority of these transitions, we have made corresponding assignments in the spectrum of the deuterated derivative 2CHO-2,6,6-d3. From the assignments, we determined fundamental frequencies for several vibrational modes in the T1(n, ?*) excited state of 2CHO, including the lowest ring-twisting (99.6 cm(-1)) and ring-bending (262.2 cm(-1)) modes. These values compare to fundamentals of 122.2 cm(-1) and 251.9 cm(-1), respectively, determined previously for the isoconfigurational S1(n, ?*) excited state of 2CHO and 99 cm(-1) and 248 cm(-1), respectively, for the S0 ground state. With the aid of quantum-mechanical calculations, we have also ascertained descriptions for these two modes, thereby resolving ambiguities appearing in the previous literature. The ring-twisting mode (?39) contains a significant contribution from O=C-C=C torsion, whereas the ring-bending mode (?38 in the ground state) involves mainly the motion of C-5 with respect to the plane containing the other heavy atoms. The CRD spectroscopic data for the T1(n, ?*) state have allowed us to benchmark several computational methods for treating excited states, including time-dependent density functional theory and an equation-of-motion coupled cluster method. In turn, the computational results provide an explanation for observed differences in the T1(n, ?*) vs. S1(n, ?*) ring frequencies. PMID:24320384

McAnally, Michael O; Zabronsky, Katherine L; Stupca, Daniel J; Phillipson, Kaitlyn; Pillsbury, Nathan R; Drucker, Stephen

2013-12-01

151

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

Microsoft Academic Search

Chlorosomes comprise thousands of bacteriochlorophylls (BChl c, d, or e) in a closely packed structure surrounded by a lipid-protein envelope and additionally contain considerable amounts of carotenoids, quinones, and BChl a. It has been suggested that carotenoids in chlorosomes provide photoprotection by rapidly quenching triplet excited states of BChl via a triplet-triplet energy transfer mechanism that prevents energy transfer to

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

2007-01-01

152

He-like triplets observed by RESIK  

NASA Astrophysics Data System (ADS)

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

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

153

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

NASA Astrophysics Data System (ADS)

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

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

2001-11-01

154

Chemical characterization of SOA formed from aqueous-phase reactions of phenols with the triplet excited state of carbonyl and hydroxyl radical  

NASA Astrophysics Data System (ADS)

Phenolic compounds, which are emitted in significant amounts from biomass burning, can undergo fast reactions in atmospheric aqueous phases to form secondary organic aerosol (aqSOA). In this study, we investigate the reactions of phenol and two methoxy-phenols (syringol and guaiacol) with two major aqueous phase oxidants - the triplet excited states of an aromatic carbonyl (3C*) and hydroxyl radical (\\centerdot OH). We thoroughly characterize the low-volatility species produced from these reactions and interpret their formation mechanisms using aerosol mass spectrometry (AMS), nanospray desorption electrospray ionization mass spectrometry (nano-DESI MS), and ion chromatography (IC). A large number of oxygenated molecules are identified, including oligomers containing up to six monomer units, functionalized monomer and oligomers with carbonyl, carboxyl, and hydroxyl groups, and small organic acid anions (e.g., formate, acetate, oxalate, and malate). The average atomic oxygen-to-carbon (O / C) ratios of phenolic aqSOA are in the range of 0.85-1.23, similar to those of low-volatility oxygenated organic aerosol (LV-OOA) observed in ambient air. The aqSOA compositions are overall similar for the same precursor, but the reactions mediated by 3C* are faster than \\centerdot OH-mediated reactions and produce more oligomers and hydroxylated species at the point when 50% of the phenol had reacted. Profiles determined using a thermodenuder indicate that the volatility of phenolic aqSOA is influenced by both oligomer content and O / C ratio. In addition, the aqSOA shows enhanced light absorption in the UV-vis region, suggesting that aqueous-phase reactions of phenols are likely an important source of brown carbon in the atmosphere, especially in regions influenced by biomass burning.

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

2014-08-01

155

Mass Spectra of Radially and Orbitally Excited States of Mesons  

Microsoft Academic Search

Meson mass spectra, evaluated in the framework of the relativistic model of quasi-independent quarks, are presented. Mass values are obtained with the help of numerical calculations based on the Dirac equation and by phenomenological mass formulae. The Dirac equation involves the potential, which is sum of the vector quasi-Coulombic potential and the scalar linear rising confinement potential. The phenomenological mass

V. Khruschov; V. Savrin; S. Semenov

2006-01-01

156

Intramolecular triplet energy transfer in anthracene-based platinum acetylide oligomers.  

PubMed

Platinum acetylide oligomers that contain an anthracene moiety have been synthesized and subjected to photophysical characterization. Spectroscopic measurement and DFT calculations reveal that both the singlet and triplet energy levels of the anthracene segment are lower than those of the platinum acetylide segment. Thus, the platinum acetylide segment acts as a sensitizer to populate the triplet state of the anthrancene segment via intramolecular triplet-triplet energy transfer. The objective of this work is to understand the mechanisms of energy-transfer dynamics in these systems. Fluorescence quenching and the dominant triplet absorption that arises from the anthracene segment in the transient absorption spectrum of Pt4An give clear evidence that energy transfer adopts an indirect mechanism, which begins with singlet-triplet energy transfer from the anthracene segment to the platinum acetylide segment followed by triplet-triplet energy transfer to the anthracene segment. PMID:23819772

Li, Yongjun; Köse, Muhammet E; Schanze, Kirk S

2013-08-01

157

Mass spectra of radially and orbitally excited states of mesons  

Microsoft Academic Search

Meson mass spectra, evaluated in the framework of the relativistic model of\\u000aquasi-independent quarks, are presented. Mass values are obtained with the help\\u000aof numerical calculations based on the Dirac equation and by phenomenological\\u000amass formulae. The Dirac equation involves the potential, which is sum of the\\u000avector quasi-Coulombic potential and the scalar linear rising confinement\\u000apotential. The phenomenological mass

V. Khruschov; V. Savrin; S. Semenov

2005-01-01

158

Mapping Agricultural Crops with AVIRIS Spectra in Washington State  

NASA Technical Reports Server (NTRS)

Spectroscopy is used in the laboratory to measure the molecular components and concentrations of plant constituents to answer questions about the plant type, status, and health. Imaging spectrometers measure the upwelling spectral radiance above the Earth's surface as images. Ideally, imaging spectrometer data sets should be used to understand plant type, plant status, and health of plants in an agricultural setting. An Airborne Visible/Infrared Imaging Spectrometer (AVIRIS) data set was acquired over agricultural fields near Wallula, Washington on July 23rd, 1997. AVIRIS measures upwelling radiance spectra through 224 spectral channels with contiguous 10-nm sampling from 400 to 2500 nm in the solar-reflected spectrum. The spectra are measured as images of 11 by up to 800 km with 20-m spatial resolution. The spectral images measured by AVIRIS represent the integrated signal resulting from: the solar irradiance; two way transmittance and scattering of the atmosphere; the absorptions and scattering of surface materials; as well as the spectral, radiometric and spatial response functions of AVIRIS. This paper presents initial research to derive properties of the agricultural fields near Wallula from the calibrated spectral images measured by AVIRIS near the top of the atmosphere.

Green, Robert; Pavri, Betina; Roberts, Dar; Ustin, Susan

1998-01-01

159

Mapping Agricultural Crops with AVIRIS Spectra in Washington State  

NASA Technical Reports Server (NTRS)

Spectroscopy is used in the laboratory to measure the molecular components and concentrations of plant constituents to answer questions about the plant type, status, and health. Imaging spectrometers measure the upwelling spectral radiance above the Earth's surface as images. Ideally, imaging spectrometer data sets should be used to understand plant type, plant status, and health of plants in an agricultural setting. An Airborne Visible/Infrared Imaging Spectrometer (AVIRIS) data set was acquired over agricultural fields near Wallula, Washington on July 23rd, 1997. AVIRIS measures upwelling radiance spectra through 224 spectral channels with contiguous 10-nm sampling from 400 to 2500 run in the solar-reflected spectrum. The spectra are measured as images of 11 by up to 800 km with 20-m spatial resolution. The spectral images measured by AVIRIS represent the integrated signal resulting from: the solar irradiance; two way transmittance and scattering of the atmosphere; the absorptions and scattering of surface materials; as well as the spectral, radiometric and spatial response functions of AVIRIS. This paper presents initial research to derive properties of the agricultural fields near Wallula from the calibrated spectral images measured by AVIRIS near the top of the atmosphere.

Green, Robert O.; Pavri, Betina; Roberts, Dar; Ustin, Susan

2000-01-01

160

Spin-Orbit Perturbations Between the A(2)-SINGLET Sigma-Plus and TRIPLET-B(1)-PI(0) States of Sodium-Potassium  

NASA Astrophysics Data System (ADS)

In this dissertation, we present the study of spin-orbit perturbations between the A(2)^1 Sigma^+ and b(1)^3Pi _{o} states of the NaK molecule. A selected perturbed ro-vibrational level, A(2)^1 Sigma^+(v{s}{' },J^') - b(1)^3Pi_0(v {t}{'},J^ '), was excited from a specific level of the bound ground state, X(1)^1Sigma ^+(v^{''},J ^{''}), by a tunable, narrow-band, single-mode, cw dye-laser. Analyzing the spectrum of singlet transitions from the perturbed level, and using the narrow-band, stable and pricise frequency properties of the laser, the vibrational and rotational (v and J) quantum numbers for both the ground-state level and the perturbed level were correctly assigned. The energy of the unperturbed singlet level A(2)^1 Sigma^+(v{s}{' },J^'), corresponding to this A(2)^1Sigma^+(v{s }{'},J^') - b(1) ^3Pi_0(v{t}{ '},J^') perturbed level, was calculated from the accurate experimental constants of Ross and coworkers. We then accurately determined the energies of both mutually perturbing levels, and measured the ratios of A(2)^1Sigma^+ to X(1)^1Sigma^+ and b(1)^3Pi_0 to a(1)^3 Sigma^+ emission intensities for five perturbed pairs. The perturbation matrix element for each perturbed pair mid<1^3 Pi_0(v{t}{' },J^')mid{H} _ {so}mid2^1Sigma^+(v {s}{'},J^ ')>mid was determined by two partially independent methods based on shifts of levels and singlet/triplet amplitudes. The vibrational factor of the spin-orbit perturbation matrix element, < v{t}{' }(R)mid v{s}{' }(R)>, was computed from RKR potentials constructed from the well-known experimental constants of the NaK A(2)^1Sigma^+ and b(1)^3Pi_1 states. Then the electronic part of the perturbation matrix element, which is defined as H_{el}equiv mid<1^3Pi_0(v{t}{'},J^ ') mid{H}_{so}mid2 ^1Sigma^+(v{s}{ '},J^ ')>mid/ mid< v{t}{' }(R)mid v{s}{' }(R)>mid, was obtained. Our results for H_{el}, from both methods and for all five perturbed pairs studied, are consistent, and independent of vibrational and rotational quantum numbers, as expected. The determined best value for H_{el} is (15.64 +/- 0.39) cm^{ -1} for the NaK A(2)^1Sigma ^+(v{s}{'},J ^') - b(1)^3Pi_0(v {t}{'},J^ ') system. This value lies between analogous values for Na_2 and K_2 and is closer to the value for K_2. This is reasonable given that the A(2) ^1Sigma^+ and b(1)^3 Pi_{o} states of the NaK molecule both dissociate to the Na(3s) + K(4p) atomic limit.

Sun, Hongqiao

161

Spin-selective low temperature spectroscopy on single molecules with a triplet-triplet optical transition: Application to the NV defect center in diamond  

NASA Astrophysics Data System (ADS)

The spin-selective photokinetics of a single matrix-isolated impurity molecule with a triplet-triplet optical transition, T 0 T 1, is considered and the manifestations of the photokinetics in the fluorescence excitation spectra and intensity autocorrelation functions g (2)(?) of the molecule undergoing narrow-band optical excitation is studied to resolve the fine structure of the transition. The rates of intersystem crossings (ISCs) T 1? S? T 0 to and from a nonradiating singlet state S of the molecule and the rate of population relaxation among the ground ( T 0) state sublevels can be obtained from the spectra and g (2)(?) using the analytical expressions obtained. New experiments on an individual NV defect center in nanocrystals of diamond, where, for the first time, the fine structure of its triplet-triplet 3 A-3 E zero-phonon optical transition (~637 nm) at 1.4 K was resolved, are interpreted. It is concluded that the rate of the ISC transition from the m S =0 sublevel of the excited 3 E state to the singlet 1 A state (~1 kHz) is much slower than the rates from the m S =±1 substates, while the rates of ISC transitions to different m S substates of the ground 3 A state are close to each other (~1 Hz). As a result, only the optical transition between m S =0 sublevels in the 3 A-3 E manifold contributes strongly to the fluorescence. The experimentally observed double-exponential decay of the g (2)(?) function is explained by the two pathways available to the center for it to leave the S state: (i) the S? T 0( m S )=0) transition and (ii) the S? T 0( m S =±1) transitions followed by the slow spin-lattice relaxation T 0( m S =±1)? T 0( m S =0) (rate ~0.1 Hz). The work is important for studies where the NV center is used as a single photon source or for quantum information processing.

Nizovtsev, A. P.; Kilin, S. Ya.; Jelezko, F.; Popa, I.; Gruber, A.; Tietz, C.; Wrachtrup, J.

2003-06-01

162

Homomolecular non-coherent photon upconversion by triplet-triplet annihilation using a zinc porphyrin on wide bandgap semiconductors  

NASA Astrophysics Data System (ADS)

Non-coherent upconversion, realized by homomolecular triplet-triplet annihilation of a zinc metalloporphyrin absorber, has been measured for the metalloporphyrin adsorbed on metal oxide films (ZrO2, TiO2 and ZrO2/TiO2 mixed oxides) in which the semiconductor conduction band energy lies between the metalloporphyrin’s upconverted and prompt S1 excited states. Upconverted emission was observed for pure and mixed metal oxide films, regardless of the relative energies of the states, indicating electron transfer from upconverted states to the semiconductor was not competitive. Upconversion was attributed to aggregation of the absorber, likely in defects on the films, leading to efficient homomolecular triplet-triplet annihilation.

Giri, Neeraj Kumar; Ponce, Concepcion P.; Steer, Ronald P.; Paige, Matthew F.

2014-04-01

163

Analysis of the Energy Spectra of Ground States of Deformed Nuclei in rare-earth region  

E-print Network

The 62Sm, 64Gd, 64Dy, 70Y b, 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 the low-lying spectra of ground band states are in good agreement with the experimental data.

Okhunov, Abdurahim A; Khandaker, M U; Rosli, Noora B

2014-01-01

164

Analysis of the Energy Spectra of Ground States of Deformed Nuclei in rare-earth region  

E-print Network

The 62Sm, 64Gd, 64Dy, 70Y b, 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 the low-lying spectra of ground band states are in good agreement with the experimental data.

Abdurahim A. Okhunov; G. I. Turaeva; M. U. Khandaker; Noora B. Rosli

2014-05-28

165

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

NASA Astrophysics Data System (ADS)

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.

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

1996-09-01

166

PHYSICAL REVIEW A 87, 063405 (2013) Photoelectron spectra and high Rydberg states of lithium generated by intense lasers  

E-print Network

PHYSICAL REVIEW A 87, 063405 (2013) Photoelectron spectra and high Rydberg states of lithium photoelectron energy and momentum spectra and the population of high Rydberg states of lithium atoms by intense)]. It is shown that in the OBI regime, due to strong depletion of the ground state, the photoelectron spectra

Lin, Chii-Dong

167

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

PubMed Central

Abstract Background Charge states of tandem mass spectra from low-resolution collision induced dissociation can not be determined by mass spectrometry. As a result, such spectra with multiple charges are usually searched multiple times by assuming each possible charge state. Not only does this strategy increase the overall database search time, but also yields more false positives. Hence, it is advantageous to determine charge states of such spectra before database search. Results We propose a new approach capable of determining the charge states of low-resolution tandem mass spectra. Four novel and discriminant features are introduced to describe tandem mass spectra and used in Gaussian mixture model to distinguish doubly and triply charged peptides. By testing on three independent datasets with known validity, the results have shown that this method can assign charge states to low-resolution tandem mass spectra more accurately than existing methods. Conclusions The proposed method can be used to improve the speed and reliability of peptide identification. PMID:22166140

2011-01-01

168

Hydrogen triplet laser as a high average-power laser  

NASA Astrophysics Data System (ADS)

In 1967, Herzberg predicted the existence of the hydrogen triplet series lasers and noted that the far infrared laser ((Delta) V equals 0) transitions should produce very strong laser action. A laser in the hydrogen triplet spectrum was discovered and reported by Barr and McKnight in 1982. Dabrowski and Herzberg confirmed the spectroscopic assignments of the laser lines, and restated that there should be a strong laser on the triplet transitions. The experimental work was strictly oriented to discovering the existence of these lasers. Thus the deductions we make concerning power capability are limited by the type of data available. The experiments show that: (1) the laser is on the triplet series lines as stated above, (2) the three lines start emission within a fraction of a microsecond of one another and terminate at approximately the same time, and (3) the lines seem to be self terminating.

Barr, Thomas A., Jr.; McKnight, William B.

1993-05-01

169

Triplet quenching by diacyl peroxides  

NASA Astrophysics Data System (ADS)

Benzoyl and decanoyl peroxides are efficient quenchers of various triplet sensitizers: kinetic studies using laser photolysis techniques indicate that electronic energy transfer and charge transfer to the peroxide are important factors contributing to the quenching process.

Ingold, K. U.; Johnston, L. J.; Lusztyk, J.; Scaiano, J. C.

1984-10-01

170

Lepton flavor violation in the triplet Higgs model  

NASA Astrophysics Data System (ADS)

The triplet Higgs model, which is an extension of the standard model with a weak-scale triplet Higgs boson, is capable of generating small neutrino masses naturally. We investigate lepton flavor violation mediated by the triplet Higgs boson. We stress that various neutrino mass patterns could be distinguished by measuring the lepton flavor violating processes. ?? eee decay is significantly enhanced in the case of the degenerate masses or the inverted-hierarchical masses compared with that in the case of the hierarchical masses. On the other hand, the ?? e? rate and the ?- e conversion ratio in nuclei is almost insensitive to the mass spectra. We also emphasize that these decay rates tend to increase as the magnitude of Ue3 increases. Lepton flavor nonconserving ? decay modes are expected to be unobservable at planned experiments in the light of the current upper bounds of flavor violating muonic decay.

Kakizaki, Mitsuru; Ogura, Yoshiteru; Shima, Fumitaka

2003-07-01

171

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

PubMed

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

Na, Seungjin; Paek, Eunok; Lee, Cheolju

2008-03-01

172

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

PubMed

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

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

2013-11-28

173

Interpreting the charge state assignment in electrospray mass spectra of bioparticles.  

PubMed

In electrospray ionization mass spectra of heterogeneous protein complexes and other bioparticles, accurate mass determination is often hampered by the inaccuracy in determination of the charge states for individual signals. Here, we describe an algorithm that automatically minimizes the standard deviation in a series of related ion peaks with varying numbers of charges. The algorithm assumes that the mass is invariant and allows the determination of the correct charge state in a peak series. The analysis results in a periodic pattern, which can be interpreted as a harmonic oscillator, when the minimum standard deviation of a charge state series is found. We observed that a mass resolution of much less than 1000 in the acquired mass spectra is sufficient to achieve a correct charge state assignment. Moreover, the boundaries of mixed species can be identified by examining the loss of periodicity in the pattern of the analysis. We tested our algorithm successfully on novel spectra and on spectra reported in the literature with sample masses up to several million Dalton, e.g., viral particles, polyethylene glycol polymers, and polystyrene nanoparticles. PMID:21361376

Tseng, Yao-Hsin; Uetrecht, Charlotte; Heck, Albert J R; Peng, Wen-Ping

2011-03-15

174

Magnetic correction of RHIC triplets  

SciTech Connect

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.

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

1993-01-01

175

Magnetic correction of RHIC triplets  

SciTech Connect

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.

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

1993-06-01

176

Ground-state and excitation spectra of the negative- U Hubbard model  

Microsoft Academic Search

We study the negative-{ital U} Hubbard model by exact diagonalization of a 4Ã4 cluster with different numbers of particles. We calculate the ground-state energy and wave function as well as the one-particle, charge- and spin-excitation spectra. We show that the BCS approximation gives results in good agreement with the exact ones for the ground-state energy and wave function in the

H. E. Castillo; C. A. Balseiro

1992-01-01

177

Ground-state and excitation spectra of the negative-U Hubbard model  

Microsoft Academic Search

We study the negative-U Hubbard model by exact diagonalization of a 4×4 cluster with different numbers of particles. We calculate the ground-state energy and wave function as well as the one-particle, charge- and spin-excitation spectra. We show that the BCS approximation gives results in good agreement with the exact ones for the ground-state energy and wave function in the whole

H. E. Castillo; C. A. Balseiro

1992-01-01

178

Electronic states, bonding, and x-ray absorption spectra of Pd2Si  

Microsoft Academic Search

The electronic properties of Pd2 Si are analyzed in light of a self-consistent calculation of the electronic states. By using the linear muffin-tin orbitals method in the atomic-sphere approximation, energy bands, densities of states, x-ray photoabsorption spectra, and the total energy have been determined. The basic bonding interaction between Pd and Si is found to be a bonding-antibonding coupling between

O. Bisi; O. Jepsen; O. K. Andersen

1987-01-01

179

Ground-state and excitation spectra of a strongly correlated lattice by the coupled cluster method.  

PubMed

The coupled cluster method is applied to a strongly correlated lattice Hamiltonian, and the coupled cluster linear response method is extended to the calculation of electronic spectra by finding an approximation to a resolvent operator which describes the spectral response of the coupled cluster solution to excitation operators. In this spectral coupled cluster method, the ground and excited states appear as resonances in the spectra, and the resolvent can be iteratively improved in selected spectral regions. The method is applied to a MnO(2) plane model which corresponds to previous experimental works. PMID:22736514

Mirone, Alessandro

2012-09-17

180

Sn(iv) Schiff base complexes: triplet photosensitizers for photoredox reactions.  

PubMed

We present the synthesis and characterization of a series of four fluorescent Sn(iv) Schiff base complexes, which also possess long-lived triplet excited states. The complexes absorb visible light (?max = 420 to 462 nm) and the optical properties are easily tunable without laborious synthetic elaboration. The triplet excited states are not luminescent, but can be observed and followed using nanosecond transient absorption spectroscopy. The lifetimes of the triplet excited states are on the order of 500 ?s-10 ms in PMMA matrices. The triplet state energies were estimated via energy transfer reactions with a series of organic triplet acceptors. In addition, the photoexcited complexes react with electron donors and acceptors in solution. These results demonstrate the potential for the development of photosensitizers based on main group elements with high spin orbit coupling constants. PMID:25043697

Grusenmeyer, Tod A; King, Albert W; Mague, Joel T; Rack, Jeffrey J; Schmehl, Russell H

2014-11-12

181

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

PubMed

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

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

2014-07-21

182

Reinvestigation of the triplet-minus-singlet spectrum of chloroplasts  

Microsoft Academic Search

A comparison of the triplet-minus-singlet (TmS) absorption spectrum of spinach chloroplasts, recorded some thirty years ago, with the more recently published TmS spectrum of isolated Chla\\/b LHCII (light-harvesting complexes associated with photosystem II of higher plants) shows that the two spectra are very similar, which is to be expected, since only the carotenoid pigments contribute to each spectrum. Be that

T. Jávorfi; G Garab; K Razi Naqvi

2000-01-01

183

Triplet Repeats Replication by 2D-GE 17 ANALYSIS OF TRIPLET REPEAT DNAS AND RNAS  

E-print Network

, disease. The mechanisms of triplet repeat expansions are not yet under- stood. The role of several geneticTriplet Repeats Replication by 2D-GE 17 II ANALYSIS OF TRIPLET REPEAT DNAS AND RNAS #12;18 Krasilnikova and Mirkin #12;Triplet Repeats Replication by 2D-GE 19 19 From: Methods in Molecular Biology, vol

Mirkin, Sergei

184

Triplet repeats and human disease  

Microsoft Academic Search

In recent years a new mechanism of genetic disease has been discovered in which triplet DNA sequences (trinucleotides) expand either to interrupt or to compromise a gene. So far, ten genetic loci have been identified in which this event takes place. The presence of these expansions, sometimes containing thousands of repeated trinucleotides, provides a clue as to how processing of

Robert H. Singer

1996-01-01

185

Linearized coherent states for Hamiltonian systems with two equidistant ladder spectra  

NASA Astrophysics Data System (ADS)

A simple way to construct exactly solvable Hamiltonians whose spectra contain two equidistant ladders, one finite and another infinite, appears when applying supersymmetric quantum mechanics to the harmonic oscillator. Some of those supersymmetric partners have third order differential ladder operators, although the order of the transformation is higher than one. In this work the linearized coherent states for these specific Hamiltonians are studied. To each SUSY partner Hamiltonian corresponds two families of linearized coherent states: one inside the subspace associated with the isospectral part of the spectrum and another one in the finite subspace generated by the states inserted through the SUSY technique.

Bermudez, D.; Contreras-Astorga, A.; Fernández C, D. J.

2014-05-01

186

Metallicities for old stellar systems from Ca II triplet strengths in member giants  

Microsoft Academic Search

The spectra of giants in six well-studied Galactic globulars spanning a wide range of abundance are used to investigate the utility of the Ca II triplet as an abundance indicator. The calibration resulting from these clusters is used to derive metal abundances from the spectra of giants in Eridanus, Pal 12, and the Carina dwarf spheroidal galaxy. The results obtained

T. E. Armandroff; G. S. Da costa

1991-01-01

187

Spectral and kinetic parameters of phosphorescence of triplet chlorophyll a in the photosynthetic apparatus of plants.  

PubMed

Spectral and kinetic parameters and quantum yield of IR phosphorescence accompanying radiative deactivation of the chlorophyll a (Chl a) triplet state were compared in pigment solutions, greening and mature plant leaves, isolated chloroplasts, and thalluses of macrophytic marine algae. On the early stages of greening just after the Shibata shift, phosphorescence is determined by the bulk Chl a molecules. According to phosphorescence measurement, the quantum yield of triplet state formation is not less than 25%. Further greening leads to a strong decrease in the phosphorescence yield. In mature leaves developing under normal irradiation conditions, the phosphorescence yield declined 1000-fold. This parameter is stable in leaves of different plant species. Three spectral forms of phosphorescence-emitting chlorophyll were revealed in the mature photosynthetic apparatus with the main emission maxima at 955, 975, and 995 nm and lifetimes ~1.9, ~1.5, and 1.1-1.3 ms. In the excitation spectra of chlorophyll phosphorescence measured in thalluses of macrophytic green and red algae, the absorption bands of Chl a and accessory pigments - carotenoids, Chl b, and phycobilins - were observed. These data suggest that phosphorescence is emitted by triplet chlorophyll molecules that are not quenched by carotenoids and correspond to short wavelength forms of Chl a coupled to the normal light harvesting pigment complex. The concentration of the phosphorescence-emitting chlorophyll molecules in chloroplasts and the contribution of these molecules to chlorophyll fluorescence were estimated. Spectral and kinetic parameters of the phosphorescence corresponding to the long wavelength fluorescence band at 737 nm were evaluated. The data indicate that phosphorescence provides unique information on the photophysics of pigment molecules, molecular organization of the photosynthetic apparatus, and mechanisms and efficiency of photodynamic stress in plants. PMID:24910208

Krasnovsky, A A; Kovalev, Yu V

2014-04-01

188

Ground-state and excitation spectra of the negative- U Hubbard model  

SciTech Connect

We study the negative-{ital U} Hubbard model by exact diagonalization of a 4{times}4 cluster with different numbers of particles. We calculate the ground-state energy and wave function as well as the one-particle, charge- and spin-excitation spectra. We show that the BCS approximation gives results in good agreement with the exact ones for the ground-state energy and wave function in the whole range of {ital U}. In the one-particle excitation spectrum the BCS dispersion relation gives the position of the most intense peaks of the exact calculation. Lower-energy (quasiparticle) excitations, which are interpreted as strongly dressed Bogoliubov quasiparticles, also appear. The occurrence of pair-breaking and collective excitations in the charge- and spin-excitation spectra and the interplay between one-particle and collective modes are discussed.

Castillo, H.E.; Balseiro, C.A. (Centro Atomico Bariloche and Instituto Balseiro, 8400 San Carlos de Bariloche (Argentina))

1992-05-01

189

Ground-state and excitation spectra of the negative-U Hubbard model  

NASA Astrophysics Data System (ADS)

We study the negative-U Hubbard model by exact diagonalization of a 4×4 cluster with different numbers of particles. We calculate the ground-state energy and wave function as well as the one-particle, charge- and spin-excitation spectra. We show that the BCS approximation gives results in good agreement with the exact ones for the ground-state energy and wave function in the whole range of U. In the one-particle excitation spectrum the BCS dispersion relation gives the position of the most intense peaks of the exact calculation. Lower-energy (quasiparticle) excitations, which are interpreted as strongly dressed Bogoliubov quasiparticles, also appear. The occurrence of pair-breaking and collective excitations in the charge- and spin-excitation spectra and the interplay between one-particle and collective modes are discussed.

Castillo, H. E.; Balseiro, C. A.

1992-05-01

190

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

PubMed Central

A fundamental task of statistical physics is to start with a microscopic Hamiltonian, predict the system's statistical properties and compare them with observable data. A notable current fundamental challenge is to tell whether and how an interacting Hamiltonian predicts different energy spectra, including solid, liquid and gas phases. Here, we propose a new idea that enables a unified description of all three states of matter. We introduce a generic form of an interacting phonon Hamiltonian with ground state configurations minimising the potential. Symmetry breaking SO(3) to SO(2), from the group of rotations in reciprocal space to its subgroup, leads to emergence of energy gaps of shear excitations as a consequence of the Goldstone theorem, and readily results in the emergence of energy spectra of solid, liquid and gas phases. PMID:24077388

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

2013-01-01

191

Double core vacancy states in x-ray photoabsorption spectra of gas phase sulfur molecules  

Microsoft Academic Search

Double-core-vacancy excited states are observed in the photoabsorption spectra of gas-phase sulfur compounds such as SF6 and SF5Cl, near the sulfur K edge, i.e. in the 2400-2800 eV photon energy range, where one observes EXAFS oscillations. We interpret the structure as originating from the 1s2p electron excitation into unoccupied valence orbitals. In SF6, one observes a doublet with an energy

S. Bodeur; C. Reynaud; K. Bisson; P. Millié; I. Nenner; U. Rockland; H. Baumgärtel

1992-01-01

192

Solid-state NMR spectra of lipid-anchored proteins under magic angle spinning.  

PubMed

Solid-state NMR is a promising tool for elucidating membrane-related biological phenomena. We achieved the measurement of high-resolution solid-state NMR spectra for a lipid-anchored protein embedded in lipid bilayers under magic angle spinning (MAS). To date, solid-state NMR measurements of lipid-anchored proteins have not been accomplished due to the difficulty in supplying sufficient amount of stable isotope labeled samples in the overexpression of lipid-anchored proteins requiring complex posttranslational modification. We designed a pseudo lipid-anchored protein in which the protein component was expressed in E. coli and attached to a chemically synthesized lipid-anchor mimic. Using two types of membranes, liposomes and bicelles, we demonstrated different types of insertion procedures for lipid-anchored protein into membranes. In the liposome sample, we were able to observe the cross-polarization and the (13)C-(13)C chemical shift correlation spectra under MAS, indicating that the liposome sample can be used to analyze molecular interactions using dipolar-based NMR experiments. In contrast, the bicelle sample showed sufficient quality of spectra through scalar-based experiments. The relaxation times and protein-membrane interaction were capable of being analyzed in the bicelle sample. These results demonstrated the applicability of two types of sample system to elucidate the roles of lipid-anchors in regulating diverse biological phenomena. PMID:24517164

Nomura, Kaoru; Harada, Erisa; Sugase, Kenji; Shimamoto, Keiko

2014-03-01

193

Chimpanzee triplets born in captivity  

Microsoft Academic Search

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

Mark A. Rosenthal; Lhtcobt Park Zoological Gardens

1981-01-01

194

The evidence of quasi-free positronium state in GiPS-AMOC spectra of glycerol  

E-print Network

We present the results of processing of Age-Momentum Correlation (AMOC) spectra that were measured for glycerol by the Gamma-induced positron spectroscopy (GiPS) facility. Our research has shown that the shape of experimental s(t) curve cannot be explained without introduction of the intermediate state of positronium (Ps), called quasi-free Ps. This state yields the wide Doppler line near zero lifetimes. We discuss the possible properties of this intermediate Ps state from the viewpoint of developed model. The amount of annihilation events produced by quasi-free Ps is estimated to be less than 5% of total annihilations. In the proposed model, quasi-free Ps serves as a precursor for trapped Ps of para- and ortho-states.

Zvezhinskiy, D; Wagner, A; Krause-Rehberg, R; Stepanov, S V

2013-01-01

195

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

E-print Network

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.

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

2014-01-01

196

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

E-print Network

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.

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

2014-08-30

197

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

NASA Astrophysics Data System (ADS)

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.

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

2014-05-01

198

Ultrafast dissociation of triplets in pentacene induced by an electric field  

NASA Astrophysics Data System (ADS)

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.

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

2014-08-01

199

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

SciTech Connect

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

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

1988-03-10

200

Spinon excitation spectra of the resonating valence bond states in the high temperature superconducting cuprates  

NASA Astrophysics Data System (ADS)

Magnetic excitations of the resonating valence bond (RVB) states were searched in high temperature superconducting cuprates by Raman scattering. Ho et al. [C.-M. Ho et al., Phys. Rev. Lett. 86 (2001) 1626] disclosed that the spin excitation in the two-dimensional resonating valence bond state has a magnon-like dispersion and a spinon continuum above it. The density of states of the spin excitation has a peak at 1.5 J which is lower than the 2.36 J of the spin wave. We found that the A spectra have a broad peak at 1.5 J in common at the underdoped region of p?0.15 in LSCO, Bi2201, and Bi2212 and p?0.1 in YBCO. The B peak and the B peak in the two-magnon region have a fine structure of the spin wave. The carrier density dependence is discussed.

Sugai, S.; Takayanagi, Y.; Hosokawa, T.; Suzuki, H.; Hayamizu, N.; Muroi, T.; Sone, Y.; Mabuchi, H.

2010-12-01

201

Experimental and Theoretical Study of the Electronic States and Spectra of BiNa.  

PubMed

Gas-phase emission spectra of the hitherto unknown free radical BiNa have been 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 sodium vapor in an observation tube. Two systems of blue-degraded bands observed in the ranges 8900-9800 and 7200-7800 cm(-1) were measured at high spectral resolution and vibrational and rotational analyses were performed. 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 BiNa and also electric dipole transition moments connecting them. As in the isovalent BiH system, the ground state of BiNa is found to be X(3)Sigma(-) with a spin splitting of about 1769 cm(-1). The first excited state is A(3)Pi, and the observed band systems are assigned to the transitions A(3)Pi(A(2)0(+)) --> X(3)Sigma(-)(X(1)0(+), X(2)1). Comparison with earlier work on the isovalent BiH system emphasizes that the relative weakness of the varsigma MO in BiNa is responsible for qualitative differences in the electronic spectra of these two systems. Copyright 2000 Academic Press. PMID:11148086

Setzer; Uibel; Zyrnicki; Pravilov; Fink; Liebermann; Alekseyev; Buenker

2000-12-01

202

Photophysics of platinum tetrayne oligomers: delocalization of triplet exciton.  

PubMed

A series of platinum tetrayne oligomers, all-trans-Cl-Pt(P2)-[(C?C)4-Pt(P2)]n-Cl, where P = tri(p-tolyl)phosphine and n = 1-3, was subjected to a detailed photophysical investigation. The photoluminescence of each oligomer at low temperature (T < 140 K) in a 2-methyltetrahydrofuran (Me-THF) glass features an intense and narrow 0-0 phosphorescence band accompanied by a vibronic progression of sub-bands separated by ca. 2100 cm(-1). The emission arises from a (3)?,?* triplet state concentrated on the (C?C)4 carbon chain and the vibronic progression originates from coupling of the excitation to the ?(C?C) stretch. All of the experimental data including ambient temperature absorption, low-temperature photoluminescence, and ambient temperature transient absorption spectroscopy provide clear evidence that the triplet state is localized on a chromophore consisting of approximately two -[(C?C)4-Pt(P2)]- repeat units. Density functional theory calculations support the hypothesis that the triplet-triplet absorption arises from transitions that are delocalized over two repeat units. PMID:24814902

Li, Yongjun; Winkel, Russell W; Weisbach, Nancy; Gladysz, John A; Schanze, Kirk S

2014-11-13

203

Observation of a novel emission from an exciplex of triplet 4-phenylbenzophenone with triethylamine  

NASA Astrophysics Data System (ADS)

Exciplex formation of excited 4-phenylbenzophenone (PBP) triplet with triethylamine (TEA) in organic solution has been studied by steady state and pulse-laser photo-luminescence measurements. Direct evidence for triplet exciplex formation was provided by the observation of emission at longer wavelengths than that of the phosphorescence of PBP. The quenching mechanism is proposed to involve a ?, ? ? triplet of PBP to form an exciplex with the ground state of TEA. The difference in the photophysics between 3(?, ? ?) PBP and 3(n, ? ?) benzophenone (BP) probably plays an important role in the electron-transfer process.

Chen, Shun-Chi; Fang, Tai-Shan

2007-12-01

204

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

NASA Astrophysics Data System (ADS)

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.

Gotoh, Hideki; Sanada, Haruki; Yamaguchi, Hiroshi; Sogawa, Tetsuomi

2014-10-01

205

Equilibrium geometry of the HCCP triplet ground state: phospho-carbene, phospho-allene or phosphorene? A combined density functional and ab initio study  

Microsoft Academic Search

The equilibrium geometry of the ground-state HCCP radical was determined by ab initio SCF, CASSCF, MP2, CI and density functional B3LYP calculations using different basis sets. The HCCP radical is predicted to be linear at all levels of calculation considered, in agreement with the experimental conclusion. The calculated molecular orbitals show that the HCCP ground state is of phosphorene form

Guo-Quan Shao; Wei-Hai Fang

1998-01-01

206

Radical ion pair mediated triplet formation in polymer-fullerene blend films.  

PubMed

Efficient triplet formation is observed for films of high ionisation potential polythiophenes blended with a fullerene derivative, and assigned to formation via geminate charge recombination of bound radical ion pair states. PMID:17268677

Ohkita, Hideo; Cook, Steffan; Astuti, Yeni; Duffy, Warren; Heeney, Martin; Tierney, Steve; McCulloch, Iain; Bradley, Donal D C; Durrant, James R

2006-10-01

207

Reinvestigation of the triplet-minus-singlet spectrum of chloroplasts  

NASA Astrophysics Data System (ADS)

A comparison of the triplet-minus-singlet (TmS) absorption spectrum of spinach chloroplasts, recorded some thirty years ago, with the more recently published TmS spectrum of isolated Chl a/ b LHCII (light-harvesting complexes associated with photosystem II of higher plants) shows that the two spectra are very similar, which is to be expected, since only the carotenoid pigments contribute to each spectrum. Be that as it may, the comparison also reveals a dissimilarity: photoexcitation of the sample does, or does not, affect the absorbance in the Qy region (650-700 nm), depending on whether the sample is a suspension of chloroplasts or of isolated LHCII. The Qy-signal in the TmS spectrum of LHCII decays, it should be noted, at the same rate as the rest of the difference spectrum, and its most prominent feature is a negative peak. As the carotenoids do not absorb in the Qy region, the presence of a signal in this region calls for an explanation: van der Vos, Carbonera and Hoff, the first to find as well as fathom the phenomenon, attributed the Qy-signal to a change, in the absorption spectrum of a chlorophyll a (Chl a) molecule, brought about by the presence of triplet excitation on a neighbouring carotenoid (Car). The difference in the behaviours of chloroplasts and LHCII, if reproducible, would imply that the Car triplets which give rise to the TmS spectrum of chloroplasts do not influence the absorption spectra of their Chl a neighbours. With a view to reaching a firm conclusion about this vexed issue, spinach chloroplasts and thylakoids have been examined with the aid of the same kinetic spectrometer as that used for investigating LHCII; the TmS spectra of both chloroplasts and thylakoids contain prominent bleaching signals centred at 680 nm, and the triplet decay time in each case is comparable to that of the Chl a/ b LHCII triplets. Results pertaining to other closely related systems are recalled, and it is concluded that, so far as the overall appearance of the TmS spectrum is concerned, spinach chloroplasts are by no means abnormal.

Jávorfi, T.; Garab, G.; Razi Naqvi, K.

2000-01-01

208

Reinvestigation of the triplet-minus-singlet spectrum of chloroplasts.  

PubMed

A comparison of the triplet-minus-singlet (TmS) absorption spectrum of spinach chloroplasts, recorded some thirty years ago, with the more recently published TmS spectrum of isolated Chla/b LHCII (light-harvesting complexes associated with photosystem II of higher plants) shows that the two spectra are very similar, which is to be expected, since only the carotenoid pigments contribute to each spectrum. Be that as it may, the comparison also reveals a dissimilarity: photoexcitation of the sample does, or does not, affect the absorbance in the Qy region (650-700 nm), depending on whether the sample is a suspension of chloroplasts or of isolated LHCII. The Qy-signal in the TmS spectrum of LHCII decays, it should be noted, at the same rate as the rest of the difference spectrum, and its most prominent feature is a negative peak. As the carotenoids do not absorb in the Qy region, the presence of a signal in this region calls for an explanation: van der Vos, Carbonera and Hoff, the first to find as well as fathom the phenomenon, attributed the Qy-signal to a change, in the absorption spectrum of a chlorophyll a (Chla) molecule, brought about by the presence of triplet excitation on a neighbouring carotenoid (Car). The difference in the behaviours of chloroplasts and LHCII, if reproducible, would imply that the Car triplets which give rise to the TmS spectrum of chloroplasts do not influence the absorption spectra of their Chla neighbours. With a view to reaching a firm conclusion about this vexed issue, spinach chloroplasts and thylakoids have been examined with the aid of the same kinetic spectrometer as that used for investigating LHCII; the TmS spectra of both chloroplasts and thylakoids contain prominent bleaching signals centred at 680 nm, and the triplet decay time in each case is comparable to that of the Chla/b LHCII triplets. Results pertaining to other closely related systems are recalled, and it is concluded that, so far as the overall appearance of the TmS spectrum is concerned, spinach chloroplasts are by no means abnormal. PMID:10728872

Jávorfi, T; Garab, G; Naqvi, K R

2000-01-01

209

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

NASA Astrophysics Data System (ADS)

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.

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

2004-01-01

210

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

E-print Network

The Galactic black-hole binary GRO J1655$-$40 was observed with Suzaku on 2005 September 22--23, for a net exposure of 35 ks with the X-ray Imaging Spectrometer (XIS) and 20 ks with the Hard X-ray Detector (HXD). The source was detected over a broad and continuous energy range of 0.7--300 keV, with an intensity of $\\sim$50 mCrab at 20 keV. At a distance of 3.2 kpc, the 0.7--300 keV luminosity is $ \\sim 5.1 \\times 10^{36}$ erg s$^{-1}$ ($\\sim 0.7$ % of the Eddington luminosity for a 6 $M_{\\odot}$ black hole). The source was in a typical low/hard state, exhibiting a power-law shaped continuum with a photon index of $\\sim 1.6$. During the observation, the source intensity gradually decreased by 25% at energies above $\\sim 3$ keV, and by 35% below 2 keV. This, together with the soft X-ray spectra taken with the XIS, suggests the presence of an independent soft component that can be represented by emission from a cool ($\\sim 0.2$ keV) disk. The hard X-ray spectra obtained with the HXD reveal a high-energy spectral cutoff, with an e-folding energy of $\\sim 200$ keV. Since the spectral photon index above 10 keV is harder by $\\sim 0.4$ than that observed in the softer energy band, and the e-folding energy is higher than those of typical reflection humps, the entire 0.7--300 keV spectrum cannot be reproduced by a single thermal Comptonization model, even considering reflection effects. Instead, the spectrum (except the soft excess) can be successfully explained by invoking two thermal-Comptonization components with different $y$-parameters. In contrast to the high/soft state spectra of this object in which narrow iron absorption lines are detected with equivalent widths of 60--100 eV, the present XIS spectra bear no such features beyond an upper-limit equivalent width of 25 eV.

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

2007-07-26

211

Infrared Spectroscopy of the Mass 31 Cation: Protonated Formaldehyde VS. The Triplet Methoxy Cation  

NASA Astrophysics Data System (ADS)

The m/z=31 cation is produced by ionization and fragmentation of methanol, ethanol, dimethyl ether, etc. Two structures have been proposed, protonated formaldehyde (^1CH_2OH^+) and the triplet methoxy cation (^3CH_3O^+). The infrared spectrum of the mass 31 cation is obtained using infrared photodissociation spectroscopy with Ar tagging. The spectrum reveals the presence of two stable isomers, protonated formaldehyde (^1CH_2OH^+) and the triplet methoxy cation (^3CH_3O^+). The triplet methoxy cation has been studied extensively and is predicted to interconvert to protonated formaldehyde through an essentially barrierless process on a timescale much faster than our experiment (>100 ?s). The presence of two structural isomers is verified by comparison of spectra from different precursors and spectra of different temperature ions from the same precursor.

Mosley, J. D.; Cheng, T. C.; Duncan, M. A.

2012-06-01

212

Capacitative coupling of singlet-triplet qubits in different interqubit geometries  

NASA Astrophysics Data System (ADS)

In the singlet-triplet qubit architecture, the two-qubit interactions required in universal quantum computing can be implemented by capacitative coupling, by exploiting the charge distribution differences of the singlet and triplet states. The efficiency of this scheme is limited by decoherence, that can be mitigated by stronger coupling between the qubits. In this paper, we study the capacitative coupling of singlet-triplet qubits in different geometries of the two-qubit system. The effects of the qubit-qubit distance and the relative orientation of the qubits on the capacitative coupling strength are discussed using an accurate microscopic model and exact diagonalization of it. We find that trapezoidal quantum dot formations allow strong coupling with low charge distribution differences between the singlet and triplet states. The analysis of geometry on the capacitative coupling is also extended to the many-qubit case and the creation of cluster states.

Hiltunen, Tuukka; Harju, Ari

2014-09-01

213

Doublet-triplet fermionic dark matter  

NASA Astrophysics Data System (ADS)

We extend the Standard Model (SM) by adding a pair of fermionic SU(2) doublets with opposite hypercharge and a fermionic SU(2) triplet with zero hypercharge. We impose a discrete Z2 symmetry that distinguishes the SM fermions from the new ones. Then, gauge invariance allows for two renormalizable Yukawa couplings between the new fermions and the SM Higgs field, as well as for direct masses for the doublet (MD) and the triplet (MT). After electroweak symmetry breaking, this model contains, in addition to SM particles, two charged Dirac fermions and a set of three neutral Majorana fermions, the lightest of which contributes to dark matter (DM). We consider a case where the lightest neutral fermion is an equal admixture of the two doublets with mass MD close to the Z-boson mass. This state remains stable under radiative corrections thanks to a custodial SU(2) symmetry and is consistent with the experimental data from oblique electroweak corrections. Moreover, the amplitudes relevant to spin-dependent or spin-independent nucleus-DM particle scattering cross sections both vanish at tree level. They arise at one loop at a level that may be observed in near future DM direct detection experiments. For Yukawa couplings comparable to the top quark, the DM particle relic abundance is consistent with observation, not relying on coannihilation or resonant effects, and has a mass at the electroweak scale. Furthermore, the heavier fermions decay to the DM particle and to electroweak gauge bosons making this model easily testable at the LHC. In the regime of interest, the charged fermions suppress the Higgs decays to diphotons by 45%-75% relative to SM prediction.

Dedes, Athanasios; Karamitros, Dimitrios

2014-06-01

214

[Intermediate states formed during discharge separation in the reaction centers of Rhodospirillum rubrum in the presence of a low-redox potential].  

PubMed

The intermediate short-lived states arising in reaction centre preparations (RC) of purple bacterium Rhodospirillum rubrum are investigated under the conditions of low redox potential. Excitation by 353 and 530 nm laser pulses produced two states characterized by optical absorption changes in the range of 350--650 nm and lifetimes: 10--30 ns for the first state and 2.5 +/- 0.5 microseconds for the second one. The first state is similar to the state PF, described previously by Parson et al. for RC from Rps. sphaeroides. Carotenoid extraction with isooctane resulted in changing the spectrum with tau = 2.5 microseconds and in the appearance of new absorption changes similar to those for the R state observed before in carotenoidless bacterial strains within microsecond time range. The comparison of the microsecond spectra with difference spectra (continuous light minus dark) of RC from R. rubrum in the range of 350--650 nm made it possible to identify the states with tau = 2.5 microseconds as carotenoid triplet states. The ratio of quantum yields of PR and carotenoid triplet states production was determined as being 1 : 1. The conclusion was made that triplet-triplet energy transfer from state PR to carotenoid is responsible for the production of carotenoid triplet states. PMID:418326

Godik, V I; Samuilov, V D; Borisov, A Iu

1978-01-01

215

Estimation of ground and excited state dipole moments of 6-methoxyquinoline from solvatochromic effect on absorption and fluorescence spectra  

NASA Astrophysics Data System (ADS)

The electronic absorption and fluorescence spectra of 6-methoxyquinoline (6MQ) have been recorded at room temperature in solvents of different polarities. The spectral data have been used to evaluate the ground and first excited singlet state dipole moments using the solvatochromic shift method. Higher dipole moment is obtained for the excited state as compared to ground state. The results indicate a more polar excited state, which may be due to charge transfer character of 6MQ.

Varma, Y. Tej; Joshi, Sunita; Pant, Debi D.

2013-06-01

216

Hydrophobic clustering in nonnative states of a protein: Interpretation of chemical shifts in NMR spectra of denatured states of lysozyme  

SciTech Connect

Chemical shifts of resonances of specific protons in the 1H NMR spectrum of thermally denatured hen lysozyme have been determined by exchange correlation with assigned native state resonances in 2D NOESY spectra obtained under conditions where the two states are interconverting. There are subtle but widespread deviations of the measured shifts from the values which would be anticipated for a random coil; in the case of side chain protons these are virtually all net upfield shifts and it is shown that this may be the averaged effect of interactions with aromatic rings in a partially collapsed denatured state. In a very few cases, notably that of two sequential tryptophan residues, it is possible to interpret these effects in terms of specific, local interresidue interactions. Generally, however, there is no correlation with either native state shift perturbations or with sequence proximity to aromatic groups. Diminution of most of the residual shift perturbations on reduction of the disulfide cross-links confirms that they are not simply effects of residues adjacent in the sequence. Similar effects of chemical denaturants, with the disulfides intact, demonstrate that the shift perturbations reflect an enhanced tendency to side chain clustering in the thermally denatured state. The temperature dependences of the shift perturbations suggest that this clustering is noncooperative and is driven by small, favorable enthalpy changes. While the extent of conformational averaging is clearly much greater than that observed for a homologous protein, alpha-lactalbumin, in its partially folded molten globule state, the results clearly show that thermally denatured lysozyme differs substantially from a random coil, principally in that it is partially hydrophobically collapsed.

Evans, P.A.; Topping, K.D.; Woolfson, D.N.; Dobson, C.M. (Cambridge University (England))

1991-01-01

217

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

PubMed

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

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

2013-01-01

218

Singlet-triplet interaction in Group 2 M2O hypermetallic oxides  

NASA Astrophysics Data System (ADS)

This ab initio study of Group 2 M2O hypermetallic oxides focuses mainly on the two heaviest members, Ba2O and Ra2O. In accordance with previous studies in our group on the Be, Mg, Ca and Sr hypermetallic oxides, we find that the BaOBa and RaORa molecules have a linear X?g+ ground electronic state and a very low lying first excited a?u+ triplet electronic state. Special attention is placed on calculating and understanding how the singlet-triplet splitting and singlet-triplet interaction strength vary down the series. The calculations reveal that MgOMg shows the largest singlet-triplet splitting and does not fit into the overall trend down the Group 2 series of elements. However, in all cases the extent of the singlet-triplet interaction between vibronic levels of the X? and ã states is very small. On the experimental side, there is literature evidence for the formation of electronically excited Ba2O in oxidation reactions of barium dimers, and our calculations of excited singlet and triplet state energies support that assignment.

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

2014-07-01

219

Higgs triplets and limits from precision measurements  

SciTech Connect

In this letter, they present the results on a global fit to precision electroweak data in a Higgs triplet model. In models with a triplet Higgs boson, a consistent renormalization scheme differs from that of the Standard Model and the global fit shows that a light Higgs boson with mass of 100-200 GeV is preferred. Triplet Higgs bosons arise in many extensions of the Standard Model, including the left-right model and the Little Higgs models. The result demonstrates the importance of the scalar loops when there is a large mass splitting between the heavy scalars. It also indicates the significance of the global fit.

Chen, Mu-Chun; /Fermilab; Dawson, Sally; Krupovnickas, Tadas; /Brookhaven

2006-04-01

220

Protonated triplet-excited flavin resolved by step-scan FTIR spectroscopy: implications for photosensory LOV domains.  

PubMed

Among many other functions, flavin serves as a chromophore in LOV (light-, oxygen-, or voltage-sensitive) domains of blue light sensors. These sensors regulate central responses in many organisms such as the growth of plants towards light. The triplet-excited state of flavin ((3)Fl) has been identified as a key intermediate in the photocycle of LOV domains, either in its neutral or protonated state. Even time-resolved infrared spectroscopy could not resolve unambiguously whether (3)Fl becomes protonated during the photoreaction, because the protonated triplet-excited state (3)FlH(+) has not been characterized before. Here, the step-scan Fourier transform infrared (FTIR) technique was applied to the flavin mononucleotide (FMN) in aqueous solution at different pH values to resolve laser-induced changes in the time range from 1.5 ?s to 860 ?s. A high-pressure-resistant flow cell system was established to account for the irreversibility of the photoreaction and the small path length. Several marker bands were identified in the spectrum of (3)Fl in water and assigned by quantum chemical calculations. These bands exhibit a solvent-induced shift as compared with previous spectra of (3)Fl in organic solvents. The marker bands undergo a further distinct shift upon formation of (3)FlH(+). Band patterns can be clearly separated from those of the anion radical or the fully reduced state resolved in the presence of an electron donor. A comparison to spectra of (3)Fl in LOV domains leads to the conclusion that (3)FlH(+) is not formed in the photoreaction of these blue light sensors. PMID:23493824

Thöing, Christian; Pfeifer, Anna; Kakorin, Sergej; Kottke, Tilman

2013-04-28

221

Orientational effect on intramolecular triplet excimer formation in 1,n-dinaphthylalkanes  

SciTech Connect

The time-resolved emission spectra of a series of di-{beta}-substituted 1,n-dinaphthylalkanes have been investigated in isooctane at room temperature. Phosphorescence from the triplet excimer has been observed for the longer alkyl chain derivatives (n = 3,4) but not from the short-chain species (n = 1,2). Under identical experimental conditions, the excimer phosphorescence from the {beta}derivatives is blue shifted and is much weaker than that of the corresponding {alpha} isomers. Furthermore, the decay rates are much greater for the di-{beta} molecules. These results confirm the previously proposed L-shaped structure of the triplet excimers of naphthalene.

Locke, R.J.; Lim, E.C. (Wayne State Univ., Detroit, MI (USA))

1989-08-10

222

(??1) ? (??1), (??1) emission spectra of chlorofluorobenzene cations in the gaseous phase and their lifetimes in the (0o) states  

USGS Publications Warehouse

The radiative decay of seventeen electronically excited chlorofluorobenzene cations in the gaseous phase has been detected. The reported emission spectra, which have been obtained using low energy electron beam excitation, are assigned to the B(??-1 ??? X(??-1 electronic transitions of these cations on the basis of their Ne(I) photoelectron spectra. In another sixteen chloroflourobenzene cations, the B ??? X radiative decay could not be detected, from which is inferred that the B states are now associated with Cl 3p(??-1 ionisation processes. The lifetimes of the studied cations in the lowest vibrational levels of the B(??-1 state have been measured. ?? 1980.

Maier, J. P.; Marthaler, O.; Mohraz, M.; Shiley, R. H.

1980-01-01

223

Size-dependent density of states and optical spectra of CdSe quantum rods and tubes  

NASA Astrophysics Data System (ADS)

In this Letter we study electronic structure of CdmSem quantum rods (QRs) and quantum tubes (QTs) of different sizes. We demonstrate that HOMO-LUMO and optical gaps are higher for quantum tubes than for quantum rods with approximately the same diameters and lengths. In addition we calculate the density of states (DOS) and optical absorption spectra using TDDFT and CIS methods as well as DFT for the DOS calculations. We determine that the DOS and optical spectra are rather different for all samples. The TDDFT and CIS calculations exhibit similar but slightly shifted spectra. The DFT calculations are essentially different from the TDDFT and CIS ones. Thus, we conclude that the DFT method has to be used with care for DOS and optical spectra calculations.

Proshchenko, Vitaly; Dahnovsky, Yuri

2014-03-01

224

Repeated multiple maternities in triplet families.  

PubMed

In earlier studies, scientists have attempted to identify genetic and environmental factors affecting the rate of multiple maternities among humans. We contribute to these studies by analysing the frequencies of multiple maternities in sibships containing triplets. Use of the Hellin transformation is included in evaluation of the triplet rate. Our results indicate greater frequencies of repeated multiple maternities in the sibships than expected, based on population frequencies. The excesses obtained are more marked in triplet maternities than in twin maternities. The transformed triplet rate shows results similar to the twinning rate. The findings also indicate that in families, the influence of maternal factors on the frequencies of multiple maternities is stronger than the influence of paternal factors. PMID:24717303

Fellman, Johan; Eriksson, Aldur W

2014-06-01

225

Electronic Spectra and Excited States of Neptunyl and Its [NpO2Cl4]2? Complex  

SciTech Connect

Electronic states and spectra of NpO2 2+ and NpO2Cl4 2? with a Np 5f1 ground-state configuration, related to low-lying 5f?5f and ligand-to-metal chargetransfer (CT) transitions, are investigated, using restricted-active-space perturbation theory (RASPT2) with spin?orbit coupling. Restrictions on the antibonding orbital occupations have little influence on the 5f?5f transition energies, but an important impact on the CT states with an open bonding orbital shell. The present calculations provide significant improvement over previous literature results. The assignment of the experimental electronic spectra of Cs2NpO2Cl4 is refined, based on our calculations of NpO2Cl4 2?. Assignments on the basis of bare NpO2 2+ are less reliable, since the equatorial Cl ligands perturb the excited-state energies considerably. Calculated changes of the Np?O bond lengths are in agreement with the observed short symmetric-stretching progressions in the f?f spectra and longer progressions in the CT spectra of neptunyl. A possible luminescence spectrum of the lowest quartet CT state is predicted.

Su, Jing; Schwarz, W H E.; Li, Jun

2012-03-05

226

Polymer triplet energy levels need not limit photocurrent collection in organic solar cells.  

PubMed

We study charge recombination via triplet excited states in donor/acceptor organic solar cells and find that, contrary to intuition, high internal quantum efficiency (IQE) can be obtained in polymer/fullerene blend devices even when the polymer triplet state is significantly lower in energy than the intermolecular charge transfer (CT) state. Our model donor system comprises the copolymer PIDT-PhanQ: poly(indacenodithiophene-co-phenanthro[9,10-b]quinoxaline), which when blended with phenyl-C(71)-butyric acid methyl ester (PC(71)BM) is capable of achieving power conversion efficiencies of 6.0% and IQE ? 90%, despite the fact that the polymer triplet state lies 300 meV below the interfacial CT state. However, as we push the open circuit voltage (V(OC)) higher by tailoring the fullerene reduction potential, we observe signatures of a new recombination loss process near V(OC) = 1.0 V that we do not observe for PCBM-based devices. Using photoinduced absorption and photoluminescence spectroscopy, we show that a new recombination path opens via the fullerene triplet manifold as the energy of the lowest CT state approaches the energy of the fullerene triplet. This pathway appears active even in cases where direct recombination via the polymer triplet remains thermodynamically accessible. These results suggest that kinetics, as opposed to thermodynamics, can dominate recombination via triplet excitons in these blends and that optimization of charge separation and kinetic suppression of charge recombination may be fruitful paths for the next generation of panchromatic organic solar cell materials with high V(OC) and J(SC). PMID:23126491

Schlenker, Cody W; Chen, Kung-Shih; Yip, Hin-Lap; Li, Chang-Zhi; Bradshaw, Liam R; Ochsenbein, Stefan T; Ding, Feizhi; Li, Xiaosong S; Gamelin, Daniel R; Jen, Alex K-Y; Ginger, David S

2012-12-01

227

Singlet-triplet separation in BN and C 2: Simple yet exceptional systems for advanced correlated methods  

NASA Astrophysics Data System (ADS)

The singlet-triplet separation in the BN molecule, as well as in the isoelectronic C 2, are examined via the recently developed reduced multi-reference coupled-cluster method with singles and doubles that is perturbatively corrected for triples, RMR CCSD(T), using the correlation consistent basis sets (cc-pV nZ, n = 2, 3, 4, and 5). Unlike the often used CCSD(T) method, which fails to predict the correct ground state for BN, the RMR CCSD(T) method yields a triplet ground state for BN and a singlet ground state for C 2, as well as a realistic singlet-triplet separation energy.

Li, Xiangzhu; Paldus, Josef

2006-11-01

228

Acquiring impedance spectra from diode-coupled primary batteries to determine health and state of charge  

NASA Astrophysics Data System (ADS)

The U.S. Army uses BA5590 Lithium Sulfur Dioxide primary batteries for portable electronic systems. There remains a need, however, for technology that can rapidly assess these batteries and estimate their remaining state of health after being used without degrading them to determine if there is remaining useful life for additional missions. This allows the full range of charge to be consumed before the battery is recycled or disposed. Impedance spectroscopy measurements have been shown to be a useful diagnostic tool, but standard methods cannot be applied to the BA5590 batteries because of the up-front electronics. The BA5590 module is diode-coupled and a charge-neutral excitation signal would be half-wave rectified and completely corrupt the results. However, a rapid impedance spectrum measurement technique has been developed that can be used for the BA5590s based on the addition of a small discharge bias load super-imposed on the sinusoidal excitation signal. The feasibility of this approach was initially simulated and then successfully applied to cell strings on four fresh BA5590 modules. The results clearly showed consistent and repeatable impedance spectra with no significant impact on the SOC as a result of the measurement. Details of this measurement technique and discussion of the preliminary results are presented.

Christophersen, Jon P.; Morrison, John L.; Morrison, William H.

229

Charge state determination of peptide tandem mass spectra using support vector machine (SVM)  

Microsoft Academic Search

A single mass spectrometry experiment could produce hundreds of thousands of tandem mass spectra. Several search engines have been developed to interpret tandem mass spectra. All search engines need to determine the masses of peptide ions from mass\\/charge ratios of ions. Unfortunately, mass spectrometers do not detect the charges of ions. A current strategy is to search candidate peptides multiply

An-min Zou; Jiarui Ding; Jin-hong Shi; Fang-xiang Wu

2008-01-01

230

Charge state determination of peptide tandem mass spectra using support vector machine (SVM)  

Microsoft Academic Search

A single mass spectrometry experiment could produce hundreds of thousands of tandem mass spectra. Several search engines have been developed to interpret tandem mass spectra. All search engines need to determine the masses of peptide ions from their mass\\/charge ratios. Unfortunately, mass spectrometers do not detect the charges of ions. A current strategy is to search candidate peptides multiple times,

An-Min Zou; Jin-Hong Shi; Jiarui Ding; Fang-Xiang Wu

2010-01-01

231

Optical and photodynamic properties of higher-lying states of rose bengal.  

E-print Network

??We have studied the photophysics and photochemistry of the higher-lying triplet states of rose bengal (tetraiodo-tetrachlorofluorescein) in water. Triplet-triplet absorption spectroscopy is used to identify… (more)

Larkin, John Michael (1970 - )

2007-01-01

232

Triplet-triplet energy transfer in fucoxanthin-chlorophyll protein from diatom Cyclotella meneghiniana: insights into the structure of the complex.  

PubMed

Although the major light harvesting complexes of diatoms, called FCPs (fucoxanthin chlorophyll a/c binding proteins), are related to the cab proteins of higher plants, the structures of these light harvesting protein complexes are much less characterized. Here, a structural/functional model for the "core" of FCP, based on the sequence homology with LHCII, in which two fucoxanthins replace the central luteins and act as quenchers of the Chl a triplet states, is proposed. Combining the information obtained by time-resolved EPR spectroscopy on the triplet states populated under illumination, with quantum mechanical calculations, we discuss the chlorophyll triplet quenching in terms of the geometry of the chlorophyll-carotenoid pairs participating to the process. The results show that local structural rearrangements occur in FCP, with respect to LHCII, in the photoprotective site. PMID:23856166

Di Valentin, Marilena; Meneghin, Elena; Orian, Laura; Polimeno, Antonino; Büchel, Claudia; Salvadori, Enrico; Kay, Christopher W M; Carbonera, Donatella

2013-10-01

233

Improving the quality of 2D solid-state NMR spectra of microcrystalline proteins by covariance analysisw  

E-print Network

Improving the quality of 2D solid-state NMR spectra of microcrystalline proteins by covariance transformation (2D FT). Since a high spectral resolution is mandatory in both dimensions of 13 C­13 C correlation is obtained from the prescription C = (FT ÁF)1/2 , where F is the matrix of the 2D FT spectrum, FT

234

NMR crystallography: The effect of deuteration on high resolution 13 state NMR spectra of a 7-TM protein  

E-print Network

on the 13 C linewidths of U-13 C, 15 N 2D crystalline bacteriorhodopsin (bR) from Halobacterium salinariumNMR crystallography: The effect of deuteration on high resolution 13 C solid state NMR spectra, and indirect, 9­17 ppm, dimensions). The measured 13 C NMR line-widths observed for both protonated

Watts, Anthony

235

Automated charge state determination of complex isotope-resolved mass spectra by peak-target Fourier transform  

Microsoft Academic Search

This study describes a new algorithm for charge state determination of complex isotope-resolved mass spectra. This algorithm\\u000a is based on peak-target Fourier transform (PTFT) of isotope packets. It is modified from the widely used Fourier transform\\u000a method because Fourier transform may give ambiguous charge state assignment for low signal-to-noise ratio (S\\/N) or overlapping\\u000a isotopic clusters. The PTFT algorithm applies a

Li Chen; Yee Leng Yap

2008-01-01

236

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

E-print Network

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.

Ebrahim Forati; George W. Hanson; Stephen Hughes

2014-07-26

237

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

E-print Network

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.

Forati, Ebrahim; Hughes, Stephen

2014-01-01

238

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

NASA Astrophysics Data System (ADS)

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 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 are shown to be important for low THz frequencies.

Forati, Ebrahim; Hanson, George W.; Hughes, Stephen

2014-08-01

239

Sensitivity of electromagnetic spectra to equation of state and initial energy density in the Pb+Pb collisions at SPS  

E-print Network

We study Pb+Pb collisions at 158 A GeV/c using a hydrodynamical approach. We test different equations of state (EoSs) and different initial conditions and show that there are more than one initial state for each EoS which reproduce the observed hadronic spectra. We also find that different equations of state favour different freeze-out temperature. Simultaneously we calculate the thermal dilepton and photon spectra for each EoS and initial state. We compare the dilepton mass spectrum to data measured by the CERES collaboration and find that the differences in spectra obtained using different EoSs and initial states are not resolvable within the current experimental resolution. However, at invariant masses over 2 GeV the difference in the yield due to various initial states is close to an order of magnitude. We also study the rapidity distribution of lepton pairs and find that for masses around 800 MeV the shape of the distribution depends strongly on the EoS.

Pasi Huovinen; P. V. Ruuskanen; Josef Sollfrank

1998-07-29

240

Triplet-triplet exciton dynamics in single-walled carbon nanotubes  

NASA Astrophysics Data System (ADS)

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.

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

2014-02-01

241

Efficient delayed fluorescence via triplet-triplet annihilation for deep-blue electroluminescence.  

PubMed

Four 2-(styryl)triphenylene derivatives (TSs) were synthesized for deep-blue dopant materials. By using a pyrene-containing compound, DMPPP, as the host, the TS-doped devices exhibited significant delayed fluorescence via triplet-triplet annihilation, providing the highest quantum efficiency of 10.2% and a current efficiency of 12.3 cd A(-1). PMID:24835343

Chou, P-Y; Chou, H-H; Chen, Y-H; Su, T-H; Liao, C-Y; Lin, H-W; Lin, W-C; Yen, H-Y; Chen, I-C; Cheng, C-H

2014-07-01

242

PCA and FA analysis of steady-state fluorescence spectra of camptothecin  

NASA Astrophysics Data System (ADS)

Fluorescence spectroscopy methods are widely used in biomedical research. The fluorescence spectra of camptothecin (CPT) -- anticancer agent are analyzed in this paper. CPT can exist in two forms: lactone and carboxylate. Only the lactone form is biologically active. Under physiological conditions (pH 7.4) the lactone form hydrolyses and converts into inactive carboxylate form. There are some differences in fluorescence spectra of lactone and carboxylate form of CPT -- the emission spectra of carboxylate form is slightly red-shifted and is characterized by lower intensity. Principal components analysis (PCA) fallowed by factor analysis (FA) enable to detect presence of both forms on the basis of series of time dependent set of spectra, to follow changes in their contributions and to determine these contributions.

Kruszewski, Stefan; Siuda, Ryszard; Ziomkowska, Blanka; Cyrankiewicz, Michal

2003-04-01

243

Electronic density of states and the x-ray photoelectron spectra of the valence band of Cu-Pd alloys  

SciTech Connect

We present self-consistent-field Korringa-Kohn-Rostoker coherent-potential-approximation calculations of the electronic density of states of random Cu/sub c/Pd/sub 1-c/ alloys. We find strong hybridization of the palladium d bands with the copper d bands over the entire concentration range. We do not obtain a palladium virtual bound state for the copper-rich alloys and therefore contradict the interpretation generally placed on valence-band x-ray photoelectron spectroscopy (XPS) spectra for Cu-Pd. Nevertheless, our first-principles calculations of the XPS spectra are in excellent agreement with recent measurements, and we discuss why this is so. Furthermore, we compare our density of states at the Fermi energy with specific-heat measurements.

Winter, H.; Durham, P.J.; Temmerman, W.M.; Stocks, G.M.

1986-02-15

244

Imaging the radical channel in acetaldehyde photodissociation: Competing mechanisms at energies close to the triplet exit barrier  

Microsoft Academic Search

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 S1, which, in turn, undergoes intersystem crossing to the first excited triplet state T1. On the triplet surface, the molecule dissociates

G. A. Amaral; A. Arregui; L. Rubio-Lago; J. D. Rodríguez; L. Bañares

2010-01-01

245

Triplet correlation functions in liquid water.  

PubMed

Triplet correlations have been shown to play a crucial role in the transformation of simple liquids to anomalous tetrahedral fluids [M. Singh, D. Dhabal, A. H. Nguyen, V. Molinero, and C. Chakravarty, Phys. Rev. Lett. 112, 147801 (2014)]. Here we examine triplet correlation functions for water, arguably the most important tetrahedral liquid, under ambient conditions, using configurational ensembles derived from molecular dynamics (MD) simulations and reverse Monte Carlo (RMC) datasets fitted to experimental scattering data. Four different RMC data sets with widely varying hydrogen-bond topologies fitted to neutron and x-ray scattering data are considered [K. T. Wikfeldt, M. Leetmaa, M. P. Ljungberg, A. Nilsson, and L. G. M. Pettersson, J. Phys. Chem. B 113, 6246 (2009)]. Molecular dynamics simulations are performed for two rigid-body effective pair potentials (SPC/E and TIP4P/2005) and the monatomic water (mW) model. Triplet correlation functions are compared with other structural measures for tetrahedrality, such as the O-O-O angular distribution function and the local tetrahedral order distributions. In contrast to the pair correlation functions, which are identical for all the RMC ensembles, the O-O-O triplet correlation function can discriminate between ensembles with different degrees of tetrahedral network formation with the maximally symmetric, tetrahedral SYM dataset displaying distinct signatures of tetrahedrality similar to those obtained from atomistic simulations of the SPC/E model. Triplet correlations from the RMC datasets conform closely to the Kirkwood superposition approximation, while those from MD simulations show deviations within the first two neighbour shells. The possibilities for experimental estimation of triplet correlations of water and other tetrahedral liquids are discussed. PMID:25381528

Dhabal, Debdas; Singh, Murari; Wikfeldt, Kjartan Thor; Chakravarty, Charusita

2014-11-01

246

Helium Spectra in Atonic Mechanics  

NASA Astrophysics Data System (ADS)

In our model of the helium atom, we postulate that the angular momentum of each electron divided by equals an integer, n, plus a fraction,?n. By minimizing the energy the energy of the helium atom, we find that the ?n values are a function of the total angular momenta, J, irrespective of the integer, n. We thus obtain a set of ?n values for the singlet and triplet states of helium. The ?n values are related to fractals. In our model, we made adjustments to the electron mass so that the calculated energy values agree with the seventeen values for the singlet 1s-ns configurations listed in NIST Atomic Spectra Database Levels Data. The adjustments to the electron mass were usually very close to unity except for the ground state for which the adjustment was ˜5%. (Adjustments like these suggest that we may be able to study three-body effects with spectral accuracy.) By doing this, we had good agreement with all of the NIST spectral values for helium (191 lines of He I, and 243 lines of He II). This conceptually and mathematically simple procedure can be used for other atoms.

Phillips, Alfred, Jr.

2008-03-01

247

Triplet energy transfer in conjugated polymers. III. An experimental assessment regarding the influence of disorder on polaronic transport  

NASA Astrophysics Data System (ADS)

It is a general notion that, in organic semiconductors, the transport of electronic excitations, such as neutral excitons of singlet or triplet type and charge carriers, is controlled by both, polaron and disorder effects. For compounds with low energetic disorder triplet exciton diffusion can be described in the framework of Marcus-theory [see Sudha Devi ,Phys. Rev. B 78, 045210 (2008)], and a theoretical model for diffusion in more disordered compounds has been developed [see Fishchuk , Phys. Rev. B 78, 045211 (2008)]. Here we experimentally demonstrate that such a modified Marcus-type model is suitable to describe triplet exciton transport in commonly used poly( p -phenylene)-type polymers and oligomers. In particular, we provide a quantitative spectroscopic assessment of the polaronic and the disorder contribution to triplet exciton transport as a function of conjugation length. Franck-Condon analyses of the phosphorescence spectra and temperature-dependent triplet diffusion combined with analytic transport theory demonstrate that, in contrast to charge carriers, Marcus-type jump rates with dominantly polaronic activation energies control the motion of triplet excitons above a transition temperature.

Hoffmann, Sebastian T.; Scheler, Esther; Koenen, Jan-Moritz; Forster, Michael; Scherf, Ullrich; Strohriegl, Peter; Bässler, Heinz; Köhler, Anna

2010-04-01

248

Xanthophylls in light-harvesting complex II of higher plants: light harvesting and triplet quenching  

Microsoft Academic Search

A spectral and functional assignment of the xanthophylls in monomeric and trimeric light- harvesting complex II of green plants has been obtained using HPLC analysis of the pigment composition, laser-flash induced triplet-minus-singlet, fluorescence excitation, and absorption spectra. It is shown that violaxanthin is not present in monomeric preparations, that it has most likely a red-most absorption maximum at 510 nm

Erwin J. G. Peterman; Claudiu C. Gradinaru; Florentine Calkoen; Jeroen C. Borst; Rienk van Grondelle; Herbert van Amerongen

1997-01-01

249

Oxygen from the lambda7774 High-Excitation Triplet in Open Cluster Dwarfs: Hyades  

Microsoft Academic Search

Oxygen abundances have been derived from the near-IR, high-excitation O I lambda7774 triplet in high-resolution, high signal-to-noise ratio spectra of 45 Hyades dwarfs using standard one-dimensional, plane-parallel LTE models. Effective temperatures of the stellar sample range from 4319 to 6301 K, and the derived relative O abundances as a function of Teff evince a trichotomous morphology. At Teff>6100 K, there

Simon C. Schuler; Jeremy R. King; Donald M. Terndrup; Marc H. Pinsonneault; Norman Murray; L. M. Hobbs

2006-01-01

250

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

NASA Astrophysics Data System (ADS)

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.

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

2014-09-01

251

Synthetic CA II Triplet Lines  

NASA Astrophysics Data System (ADS)

RESUMEN. Se hicieron calculos de sintesis del espectro en el ititervalo de longitud de onda - 8700 A, ara ? oder verificar el comporta- mien to de diferentes lineas moleculares y at5micas como funci5n de los parametros esteldres de temperatura, gravedad y metalicidad. El espec- tro sintetico ha sido generado para:(a) todas las , (b) solamente de CN, (c) solamente de TiO, y (d) solamente lineas at6micas. Abstract. Spectrum synthesis calculations are carried out in the wavelength interval X 8300 - 8700 A, in order to verify the behaviour of different molecular and atomic lines as a function of the stellar para meters temperature, gravity and metallicity. Synthetic spectra were ge nerated for: (a) all lines, (b) only CN lines, (c) only TiO lines, and (d) only atomic lines Key `td6: LINE-PROFILE - ST S-AThOSPHERES

Erdelyi, M. M.; Barbuy, B.

1990-11-01

252

One Interesting Family of Diophantine Triplets  

ERIC Educational Resources Information Center

In this note properties of two sequences generated by the recurrence relation G[subscript n] +2 = 4 G[subscript n] +1 - G[subscript n], are studied. It is shown that one of the sequences leads to a family of diophantine triplets. Some interesting properties of these sequences are also established.

Deshpande, M. N.

2002-01-01

253

Chemotherapeutically induced deletion of expanded triplet repeats  

Microsoft Academic Search

The number of neurodegenerative disorders associated with the expansion of DNA repeats, currently about 18, continues to increase as additional diseases caused by this novel type of mutation are identified. Typically, expanded repeats are biased toward further expansion upon intergenerational transmission, and disease symptoms show an earlier age of onset and greater severity as the length of the triplet repeat

Vera I. Hashem; Richard R. Sinden

2002-01-01

254

Triplet Repeat Mutations in Human Disease  

Microsoft Academic Search

Triplet repeats are the sites of mutation in three human heritable disorders, spinal and bulbar muscular atrophy (SBMA), fragile X syndrome, and myotonic dystrophy (DM). These repeats are GC-rich and highly polymorphic in the normal population. Fragile X syndrome and DM are examples of diseases in which premutation alleles cause little or no disease in the individual, but give rise

C. Thomas Caskey; Antonio Pizzuti; Ying-Hui Fu; Raymond G. Fenwick Jr.; David L. Nelson

1992-01-01

255

Photochemistry of Furyl- and Thienyldiazomethanes: Spectroscopic Characterization of Triplet 3-Thienylcarbene  

PubMed Central

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

Pharr, Caroline R.; Kopff, Laura A.; Bennett, Brian; Reid, Scott A.; McMahon, Robert J.

2014-01-01

256

Triplet correlation functions in the Lennard-Jones fluid: Tests against molecular dynamics simulations  

NASA Astrophysics Data System (ADS)

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.

McNeil, William J.; Madden, William G.; Haymet, A. D. J.; Rice, Stuart A.

1983-01-01

257

Triplet-Triplet Absorption Studies on Aromatic and Heterocyclic Molecules at 77 °K  

Microsoft Academic Search

Triplet-triplet absorption spectroscopy has been extended both to numerous new molecules of current spectroscopic interest and to lower energy spectral regions (to 10 000 cm?1) of previously investigated molecules. Measurements have been carried out by the method of steady cross illumination using a modified Cary 14 spectrophotometer.Eight new T-T transitions have been found in the present research. New lower energy

Bryan R. Henry; Michael Kasha

1967-01-01

258

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

Microsoft Academic Search

We study the information content of two-dimensional (2D) electronic photon-echo (PE) spectra, with special emphasis on their potential to distinguish, for waiting times T=0, between different conformations of electronically coupled symmetric dimers. The analysis is performed on the basis of an analytical formula for the frequency-domain 2D PE signal. The symmetric dimers are modeled in terms of two identical, energy-degenerate,

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

2006-01-01

259

Raman Spectra of Hydrogen and Deuterium Sulfides in the Gas, Liquid and Solid States  

Microsoft Academic Search

Raman spectra have been obtained for H2S and D2S as gas, liquid and solid. Only one frequency has been obtained in the gas and liquid although three are permitted by the selection principles. In the solids, a single line and a close doublet have been obtained. With the available infra-red and Raman data, it is not possible to make quantitative

George M. Murphy; John E. Vance

1938-01-01

260

Calculation of absorption spectra involving multiple excited states: approximate methods based on the mixed quantum classical Liouville equation.  

PubMed

We investigate the calculation of absorption spectra based on the mixed quantum classical Liouville equation (MQCL) methods. It has been shown previously that, for a single excited state, the averaged classical dynamics approach to calculate the linear and nonlinear spectroscopy can be derived using the MQCL formalism. This work focuses on problems involving multiple coupled excited state surfaces, such as in molecular aggregates and in the cases of coupled electronic states. A new equation of motion to calculate the dipole-dipole correlation functions within the MQCL formalism is first presented. Two approximate methods are then proposed to solve the resulted equations of motion. The first approximation results in a mean field approach, where the nuclear dynamics is governed by averaged forces depending on the instantaneous electronic states. A modification to the mean field approach based on first order moment expansion is also proposed. Numerical examples including calculation of the absorption spectra of Frenkel exciton models of molecular aggregates, and the pyrazine molecule are presented. PMID:24588146

Bai, Shuming; Xie, Weiwei; Zhu, Lili; Shi, Qiang

2014-02-28

261

Vibrational spectra of Li{sub 3} first-excited electronic doublet state: Geometric-phase effects and statistical analysis  

SciTech Connect

The authors present J = 0 calculations of all bound and pseudobound vibrational states of Li{sub 3} in its first-excited electronic doublet state by using a realistic double many-body expansion potential-energy surface and a minimum-residual filter diagonalization technique. The action of the system Hamiltonian on the wave function was evaluated by the spectral transform method in hyperspherical coordinates. Calculations of the vibrational spectra were carried out both without consideration and with consideration of geometric-phase effects. Dynamic Jahn-Teller and geometric-phase effects are found to play a significant role, while the calculated fundamental symmetric stretching frequency is larger by 8.3% than its reported experimental value of 326 cm{sup {minus}1}. From the neighbor-spacing distributions of the levels, it is observed that the title vibrational spectrum is quasi-regular in the short range and quasi-irregular in the long range. By the {Delta}{sub 2} standard defined in this article, it is found that the spectra are more nonuniform than those of the trough states for the ground electronic state.

Varandas, A.J.C.; Xu, Z.R.

1999-07-01

262

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

SciTech Connect

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.

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

263

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

NASA Astrophysics Data System (ADS)

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

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

1991-08-01

264

Demonstration of entanglement of electrostatically coupled singlet-triplet qubits.  

PubMed

Quantum computers have the potential to solve certain problems faster than classical computers. To exploit their power, it is necessary to perform interqubit operations and generate entangled states. Spin qubits are a promising candidate for implementing a quantum processor because of their potential for scalability and miniaturization. However, their weak interactions with the environment, which lead to their long coherence times, make interqubit operations challenging. We performed a controlled two-qubit operation between singlet-triplet qubits using a dynamically decoupled sequence that maintains the two-qubit coupling while decoupling each qubit from its fluctuating environment. Using state tomography, we measured the full density matrix of the system and determined the concurrence and the fidelity of the generated state, providing proof of entanglement. PMID:22499942

Shulman, M D; Dial, O E; Harvey, S P; Bluhm, H; Umansky, V; Yacoby, A

2012-04-13

265

Electronic structure of some adenosine receptor antagonists. III. Quantitative investigation of the electronic absorption spectra of alkyl xanthines  

NASA Astrophysics Data System (ADS)

Quantitative and comparative investigation of the electronic absorption spectra of theophylline, caffeine and their derivatives is reported. The spectra of theophylline, caffeine and theobromine were compared to establish the predominant tautomeric species in solution. This comparison, analysis of solvent effects and assignments of the observed transitions via MO computations indicate the exits of only one tautomeric species in solution that is the N7 form. A low-lying triplet state was identified which corresponds to a HOMO-LUMO transition. This relatively long-lived T 1 state is always less polar than the ground state and may very well underlie the photochemical reactivity of alkyl xanthines. Substituents of different electron donating or withdrawing strengths and solvent effects are investigated and analyzed. The present analysis is facilitated via computer deconvolution of the observed spectra and MO computation.

Moustafa, H.; Shalaby, Samia H.; El-sawy, K. M.; Hilal, Rifaat

2002-07-01

266

EMITTING ELECTRONS SPECTRA AND ACCELERATION PROCESSES IN THE JET OF Mrk 421: FROM THE LOW STATE TO THE GIANT FLARE STATE  

SciTech Connect

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.

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

267

Mouse models of triplet repeat diseases  

Microsoft Academic Search

Triplet repeat expansions were first discovered in 1991 and since then have been found to be the mutation underlying a range\\u000a of neurodegenerative, neuromuscular, and cognitive disorders including fragile X syndrome, myotonic dystrophy, Friedreich's\\u000a ataxia, and the polyglutamine disorders that include Huntington's disease. The repeats exert their detrimental effects through\\u000a different molecular mechanisms dependent on whether they are located in

Gillian P. Bates; Roman Gonitel

2006-01-01

268

Highlights of supersymmetric hypercharge ±1 triplets  

NASA Astrophysics Data System (ADS)

The discovery of a standard model (SM)-like Higgs boson with a relatively heavy mass m h and hints of di-photon excess has deep implication to supersymmetric standard models (SSMs). We consider the SSM extended with hypercharge ±1 triplets, and investigate two scenarios of it: (A) triplets significantly couple to the Higgs doublets, which can substantially raise m h and simultaneously enhance the Higgs to di-photon rate via light chargino loops; (B) oppositely, these couplings are quite weak and thus m h can not be raised. But the doubly-charged Higgs bosons, owing to the gauge group structure, naturally interprets why there is an excess rather than a deficient of Higgs to di-photon rate. Additionally, the pseudo Dirac triplet fermion is an inelastic non-thermal dark matter candidate. Light doubly-charged particles, especially the doubly-charged Higgs boson around 100 GeV in scenario B, are predicted. We give a preliminary discussion on their search at the LHC.

Kang, Zhaofeng; Liu, Yandong; Ning, Guo-Zhu

2013-09-01

269

Nucleon, Delta and Omega excited state spectra at three pion mass values  

E-print Network

The energies of the excited states of the Nucleon, Delta and Omega are computed in lattice QCD, using two light quarks and one strange quark on anisotropic lattices. The calculations are performed at three values of the pion mass: 392(4), 438(3) and 521(3) MeV. We employ the variational method with a basis of about ten interpolating operators enabling six energies to be distinguished clearly in each irreducible representation of the octahedral group. We compare our calculations of nucleon excited states with the low-lying experimental spectrum. There is reasonable agreement for the pattern of states.

John Bulava; Robert G. Edwards; Bálint Joó; David G. Richards; Eric Engelson; Huey-Wen Lin; Colin Morningstar; Stephen J. Wallace

2010-11-05

270

Nucleon, Delta and Omega excited state spectra at three pion mass values  

SciTech Connect

The energies of the excited states of the Nucleon, Delta and Omega are computed in lattice QCD, using two light quarks and one strange quark on anisotropic lattices. The calculations are performed at three values of the pion mass: 392(4), 438(3) and 521(3) MeV. We employ the variational method with a basis of about ten interpolating operators enabling six energies to be distinguished clearly in each irreducible representation of the octahedral group. We compare our calculations of nucleon excited states with the low-lying experimental spectrum. There is reasonable agreement for the pattern of states.

John Bulava, Robert G. Edwards, Balint Joo, David G. Richards, Eric Engelson, Huey-Wen Lin, Colin Morningstar, Stephen J. Wallace

2010-06-01

271

Intra-Valley Spin-Triplet p + ip Superconducting Pairing in Lightly Doped Graphene  

NASA Astrophysics Data System (ADS)

We analyze various possible superconducting pairing states and their relative stabilities in lightly doped graphene. It is shown that, when inter-sublattice electron-electron attractive interaction dominates and the Fermi level is close to the Dirac points, the system will favor intra-valley spin-triplet p + ip pairing state. Based on the novel pairing state, we further propose a scheme for doing topological quantum computation in graphene by engineering local strain fields and external magnetic fields.

Zhou, Jian-Hui; Qin, Tao; Shi, Jun-Ren

2013-01-01

272

Intra-valley Spin-triplet p+ip Superconducting Pairing in Lightly Doped Graphene  

NASA Astrophysics Data System (ADS)

We analyze various possible superconducting pairing states and their relative stabilities in lightly doped graphene. We show that, when inter-sublattice electron-electron attractive interaction dominates and Fermi level is close to Dirac points, the system will favor intra-valley spin-triplet p+ip pairing state. Based on the novel pairing state, we further propose a scheme for doing topological quantum computation in graphene by engineering local strain fields and external magnetic fields.

Zhou, Jianhui; Qin, Tao; Shi, Junren

2013-03-01

273

Low temperature absorption spectra and ground state electronic structure of tetrakis(2,6-di-tert-butylphenoxide)uranium(IV)  

SciTech Connect

The optical spectroscopy of the homoleptic U(IV) aryloxide compound U(O-2,6-t-Bu{sub 2}C{sub 6}H{sub 3}){sub 4} could give unique insight into actinide electronic structure because the complex has unusually high symmetry. Its synthesis and characterization were described in a recent paper. The characterization included presentation of several optical spectra in solution accompanied by a brief, qualitative discussion of the molecular properties that give rise to the observed features. This paper presents optical absorption data on microcrystalline solid samples at low temperature. Discussion of the data focuses generally on effect of the ligands on 5f{sup 2} electronic configuration of central U(IV) ion and specifically on properties of the ground state and the lowest lying electronic state.

Berg, J.M.

1993-10-01

274

The protein's role in triplet energy transfer in bacterial reaction centers.  

SciTech Connect

When photosynthetic organisms are subjected to high-light conditions in nature, electron transfer becomes blocked as the rate of conversion of light into charge-separated states in the reaction center (RC) exceeds the capacity of the soluble carriers involved in cyclic electron transfer. In that event, a well-characterized T{sub 0}-polarized triplet state {sup T}P, is formed on the primary donor, P, from the P{sup +}H{sub A}{sup {minus}} state (reviewed in [1]). In an aerobic or semi-aerobic environment, the major role of the carotenoid (C), also bound by the RC, is to quench {sup T}P prior to its sensitization of the {sup 1}{Delta}{sub g} singlet state of oxygen--a potentially damaging biological oxidant. The carotenoid performs this function efficiently in most bacterial RCs by rapidly accepting the triplet state from P and dissipating this excited-state energy into heat through internal conversion. The lowest-lying triplet states of P and the carotenoid are sufficiently different that {sup T}P can promote oxygen to its excited singlet state whereas {sup T}C can quench the {sup T}P state (reviewed in [2]).

Laible, P. D.

1998-08-14

275

The spectra of qq states and glueballs  

NASA Astrophysics Data System (ADS)

Data from LEAR on overlinepp ? final states with I = 0, C = +1 reveal s-channel resonances corresponding to all q overlineq states ( J = 0 to 5) expected in the mass range 1920-2400 MeV/c 2. They lie on parallel straight-line trajectories of s = M2 v. radial excitation number. In addition there are four extra states which fail to fit on to these trajectories: f0(1500), f0(2105), f2(1980) and ?(2190). All have exotic properties and appear in J/? radiative decays: this suggests glueball character. Their mass ratios agree within errors (typically ±4%) with recent Lattice Gauge calculations of Morningstar and Peardon for the lowest four glueballs.

Bugg, D. V.

2001-04-01

276

EEG spectra, behavioral states and motor activity in rats exposed to acetylcholinesterase inhibitor chlorpyrifos  

Microsoft Academic Search

Exposure to organophosphates (OP) has been associated with sleep disorders such as insomnia and “excessive dreaming.” The central mechanisms of these effects are not well understood. OPs inhibit acetylcholinesterase (AChE) activity, leading to a hyperactivity of the brain cholinergic systems that are involved in sleep regulation. We studied alterations in the EEG, behavioral states, motor activity and core temperature in

Olga A. Timofeeva; Christopher J. Gordon

2002-01-01

277

Formation and calculations of the simple terminal triplet pnictinidene molecules N/MF(3), P/MF(3), and As/MF(3) (M = Ti, Zr, Hf).  

PubMed

Laser-ablated Ti, Zr, and Hf atoms react with NF(3), PF(3), or AsF(3) to produce triplet state terminal pnictinidene N/MF(3), P/MF(3), or As/MF(3) molecules, which are trapped in an argon matrix. Products are identified from infrared spectra and comparison to theoretically predicted vibrations. Density functional theory calculations converge to C(3v) symmetry structures for these lowest energy products. The two unpaired electrons in nitrogen 2p, phosphorus 3p, or arsenic 4p orbitals are shared in different small amounts with empty metal nd orbitals leading to very weak degenerate pialpha molecular orbitals based on bonding orbital analysis and spin density calculations. This weak pi bonding interaction with early transition metal group 4 nd orbitals is optimum for Zr with phosphorus 3p orbitals. PMID:19402628

Wang, Xuefeng; Lyon, Jonathan T; Andrews, Lester

2009-07-01

278

Formation of secondary triplet species after excitation of fluoroquinolones in the presence of relatively strong bases.  

PubMed

Laser flash photolysis of 7-(piperazin-1-yl) fluoroquinolones leads to the formation of a triplet excited state (3A*) at the end of the pulse (lambdamax 520, 610, and 620 nm for enoxacin, ciprofloxacin, and norfloxacin, respectively). Phosphate and bicarbonate buffers react with 3A* to form a secondary triplet (3B*, reaction rates (0.8-9.9) x 108 M-1 s-1), whose T-T absorption is red-shifted (lambdamax 670 nm for enoxacin, 700 nm for ciprofloxacin and norfloxacin). The formation of a secondary triplet is not a common process and disagrees with previous work suggesting that electron transfer occurs between phosphate buffer and the primary triplet excited state with the formation of the anion radical of the fluoroquinolone (FQ.-). We have shown that the FQ.- transient absorption spectrum is quite distinct from that of 3B*. The photophysical characteristics of 3B* have been determined by energy transfer to naproxen, and it has been found that its energy is lower than that of 3A*. PMID:18717558

Lorenzo, Fernando; Navaratnam, Suppiah; Allen, Norman S

2008-09-17

279

Exchange interaction between the triplet exciton and the localized spin in copper-phthalocyanine  

NASA Astrophysics Data System (ADS)

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-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 localized spin on Cu experimentally using optical excitation and inter-system crossing well before the triplet state disappears.

Wu, Wei

2014-06-01

280

Supercurrent through a multilevel quantum dot close to singlet-triplet degeneracy  

NASA Astrophysics Data System (ADS)

We investigate two serially aligned quantum dots in the molecular regime of large tunnel couplings t. A Zeeman field B is used to tune the energy difference of singlet and triplet spin configurations. Attaching this geometry to BCS source and drain leads with gap ? and phase difference ? gives rise to an equilibrium supercurrent J. To compute J in the presence of Coulomb interactions U between the dot electrons, we employ the functional renormalization group (FRG). For B?t, where the singlet and (one out of a) triplet spin states are equal in energy, the current exhibits characteristics of a 0-? transition similar to a single impurity. Its magnitude in the ? phase, however, jumps discontinuously at B=t, being smaller on the triplet side. By exploiting the flexibility of the FRG, we demonstrate that this effect is generic and calculate J for realistic experimental parameters ?, U, and gate voltages ?. To obtain a more thorough understanding of the discontinuity, we analytically treat the limit ?=?, where one can access the exact many-particle states. Finally, carrying out perturbation theory in the dot-lead couplings substantiates the intuitive picture that Cooper-pair tunneling is favored by a singlet spin configuration while inhibited by a triplet one.

Karrasch, C.; Andergassen, S.; Meden, V.

2011-10-01

281

Photosensitized cis-trans isomerization in aqueous solution. pH effect on the efficiency of triplet-triplet energy transfer to maleic acid  

Microsoft Academic Search

Aromatic ketones, made water soluble by the introduction of ionic substituents, photosensitize cis reversible transfer isomerization in the maleic-fumaric acid system. The photostationary-state cis\\/trans ratio depends on the triplet energy of the sensitizer and the pH of the medium. All sensitizers studied show a pH effect on the cis\\/trans ratio which varies from 2.8 to 1.2 and is independent of

Atma Gupta; Rehana Mukhtar; Stanley Seltzer

1980-01-01

282

Pump-probe photoionization detection of singlet and triplet decay in anisole and p-cresol in a supersonic free jet  

SciTech Connect

The singlet and triplet decay of anisole and p-cresol in a supersonic free jet were determined by delayed photoionization mass spectrometry. A biexponential decay was observed in p-cresol yielding a triplet lifetime of 400 +/- 10 ns and a singlet life less than or equal to 5 ns. Very different behavior was observed for anisole. Evidence suggests the triplet state is decaying at a rate approximately 10 times greater than in p-cresol while the anisole S/sub 1/ state decays at least 5 times more slowly than the p-cresol S/sub 1/.

Lipert, R.J.; Colson, S.D.; Sur, A.

1988-01-14

283

Enhancement of Vibronic and Ground-State Vibrational Coherences in 2D Spectra of Photosynthetic Complexes  

PubMed Central

A vibronic-exciton model is applied to investigate the recently proposed mechanism of enhancement of coherent oscillations due to mixing of electronic and nuclear degrees of freedom. We study a dimer system to elucidate the role of resonance coupling, site energies, vibrational frequency and energy disorder in the enhancement of vibronic-exciton and ground-state vibrational coherences, and to identify regimes where this enhancement is significant. For a heterodimer representing two coupled bachteriochloropylls of the FMO complex, long-lived vibronic coherences are found to be generated only when the frequency of the mode is in the vicinity of the electronic energy difference. Although the vibronic-exciton coherences exhibit a larger initial amplitude compared to the ground-state vibrational coherences, we conclude that, due to the dephasing of the former, both type of coherences have a similar magnitude at longer population time. PMID:23778355

Chenu, Aurélia; Christensson, Niklas; Kauffmann, Harald F.; Man?al, Tomáš

2013-01-01

284

Photophysical properties and thermochromic shifts of electronic spectra of Nile Red in selected solvents. Excited states dipole moments  

NASA Astrophysics Data System (ADS)

Photophysical parameters, the rate constants for radiative ( kF) and nonradiative ( kIC) for Nile Red (NR) in aprotic polar solvents incapable of hydrogen bonding with NR have been determined. No regular polarity dependence on kIC were observed in contrast to other authors. The effect of temperature on absorption and fluorescence spectra of NR in two selected solvents: ethyl acetate and 1,2-dichloroethane was studied and the electric dipole moment in the excited state S 1 was determined using the Bilot and Kawski theory [L. Bilot, A. Kawski, Z. Naturforsch. 17a (1962) 621, L. Bilot, A. Kawski, Z. Naturforsch. 18a (1963) 10, 256]. For the previously obtained dipole moment in the ground state ?g = 8.2 D [A. Kawski, P. Bojarski, B. Kukli?ski, Chem. Phys. Lett. 463 (2008) 410] the change from thermochromic measurements upon excitation of NR is equal to ? ? = ?e - ?g = 1.75 ± 0.5 D and is in good agreement with the value ? ? = 1.8 ± 1 D from solvatochromic method. A comparison of the obtained ? ? value with those of other authors is given and discussed. It has been concluded that the difference between the excited ?e and ground ?g state dipole moments for NR is too small to create a TICT state.

Kawski, A.; Kukli?ski, B.; Bojarski, P.

2009-05-01

285

Singlet and triplet emission from methylenediphenyl-diisocyanate-based poly(ester urethane): determination of the energy-level diagram  

NASA Astrophysics Data System (ADS)

Optical absorption and luminescence measurements have been made on 4,4'-methylenediphenyl 1,1'-diisocyanate (MDI)-based poly(ester urethane) (PESU) and model compounds diphenylmethane (DPM) and butanol-capped MDI. Phosphorescence spectra of the three samples are nearly identical with maxima at 527, 488, 451, and 422 nm. However, onset of strong optical absorption near 300 nm in PESU and MDI precludes observation of the corresponding fluorescence spectrum. In contrast, DPM exhibits weaker absorption with onset occurring near 270 nm. Consequently, its fluorescence spectrum is revealed and characterized by maxima at 302, 294, 286, and 279 nm. From these data we derive the energy-level diagram for PESU and show that phosphorescence is due to electronic transitions between the first excited triplet and singlet ground states (T 1?S 0), whereas fluorescence transitions occur between both first and second excited singlet and ground states (S 1?S 0, and S 2?S 0). The experimentally derived values are in good agreement with previously published theoretical values for the electronic excited states of PESU.

Cooke, D. W.; Muenchausen, R. E.; Bennett, B. L.; Wrobleski, D. A.; Orler, E. B.

2003-02-01

286

Calculated photoelectron pitch angle and energy spectra. [steady state angular and altitude anisotropies  

NASA Technical Reports Server (NTRS)

Calculations of the steady-state photoelectron energy and angular distribution in the altitude region between 120 and 1000 km are presented. The distribution is found to be isotropic at all altitudes below 250 km, while above this altitude anisotropies in both pitch angle and energy are found. The isotropy found in the angular distribution below 250 km implies that photoelectron transport below 250 km is insignificant, while the angular anisotropy found above this altitude implies a net photoelectron current in the upward direction.

Mantas, G. P.; Bowhill, S. A.

1975-01-01

287

Jahn-Teller enhanced fundamental bands in the infrared spectra of degenerate electronic states  

NASA Astrophysics Data System (ADS)

Scharf and Miller have shown recently that the symmetry selection rule of Child and Longuet-Higgins for infrared vibrational transitions in degenerate electronic states is incomplete, and that vibrational transitions that do not satisfy their selection rule can be exceptionally strong because the intensity is enhanced by the Jahn-Teller effect. The present paper provides a compact set of symmetry rules for the Jahn-Teller-enhanced vibrations, and considers the general rotational structure for the three types of Jahn-Teller-enhanced fundamentals, namely symmetric-top perpendicular bands, symmetric-top parallel bands, and spherical-top bands. The detailed equations of Child and Longuet-Higgins for the symmetric-top perpendicular case are valid, including the Jahn-Teller enhancement, but their generalization to other cases does not take account of the distinctive symmetry properties of the Jahn-Teller enhanced contribution. In the present calculations the use of an effective dipole moment operator to allow for the mixing of states by the Jahn-Teller interaction shows that the symmetry of the enhanced transitions is associated with the antisymmetric square of the electronic symmetry species, whereas the normal contributions considered by Child and Longuet-Higgins are associated with the symmetric square.

Watson, James K. G.

288

X-ray photoelectron spectra, theoretical band structures, and densities of states for BaTiO3 and KNbO3  

Microsoft Academic Search

X-ray photoelectron spectra of the valence bands and core levels for electron binding energies ranging from 0 to 45 eV, are presented for the two perovskite-type compounds BaTiO3 and KNbO3. Theoretical band structures and densities of states are calculated using a parametrized tight-binding method. The validity of the comparison between theoretical results and experimental valence-band spectra is discussed. The effects

P. Pertosa; F. M. Michel-Calendini

1978-01-01

289

Triplet Supercurrents in Half Metals and Unconventional Proximity Effects  

E-print Network

-wave') Spin-unpolarized Spin-polarized (for constant singlet order parameter) #12;Effect of disorder constant All induced triplet components at surface stay unaffected by disorder! All what changes proximity effect in S/Half-Metal Junctions Effect of disorder, s-wave and p-wave triplets Josephson effect

Fominov, Yakov

290

A new proposal for the ground state of the FeO- cluster in the gas phase and for the assignment of its photoelectron spectra.  

PubMed

High-level multireference CASPT2 calculations are performed to determine the electronic structures of the FeO and FeO(-) clusters. Geometry optimizations of all possible low-lying states of the two unsaturated complexes are carried out at the mentioned theoretical level by calculating their potential energy curves. FeO(-) is proposed to possess a (6)Sigma(+) ground state as opposed to the (4)Delta state, which has been put forward as the ground state by previous computational studies. On this basis an alternative assignment of the photoelectron spectra of this anion is postulated. All features of these spectra are tentatively attributed to either septet or quintet states of the neutral FeO cluster. The lowest energy band in the spectra is then the result of electron detachments to the (5)Delta ground state and the (5)Sigma(+) lowest excited state. The second lowest band might be due to the (7)Sigma(+). Two higher energy bands are thought to originate from two (5)Pi states and a (5)Phi. Vibrational progressions that are observed for some bands could be explained in terms of the calculated potential energy profiles of the relevant states. Credibility for the proposed assignment is rendered by the good correspondence between experiment and our computational method concerning the bond distance and dipole moment for the ground state of FeO. PMID:19719319

Hendrickx, Marc F A; Anam, Koteswara R

2009-07-30

291

FT-IR and FT-Raman spectra of 5-fluoroorotic acid with solid state simulation by DFT methods  

NASA Astrophysics Data System (ADS)

FT-Raman and FT-IR studies of the biomolecule 5-fluoroorotic acid in the solid state were carried out. The unit cell found in the crystal was simulated as a tetramer form by density functional calculations. They were performed to clarify wavenumber assignments of the experimental observed bands in the spectra. Correlations with the molecule of uracil were made, and specific scale equations were employed to scale the wavenumbers of 5-fluoroorotic acid. Good reproduction of the experimental wavenumbers is obtained and the % error is very small in the majority of the bands. This fact confirms our simplified solid state model. The molecular structure was fully optimized using DFT and MP2 methods. The relative stability of both the syn and anti conformations was investigated, and the anti-form was found to be slightly more stable, by 7.49 kJ/mol at the MP2 level. The structures of all possible tautomeric forms were determined. The keto-form appeared as the most stable one. The NBO atomic charges and several thermodynamic parameters were also calculated.

Cuellar, A.; Alcolea Palafox, M.; Rastogi, V. K.; Kiefer, W.; Schlücker, S.; Rathor, S. K.

2014-11-01

292

Determination of the Charge State Distributions from X-ray Spectra in Au Plasmas at the OMEGA Laser  

NASA Astrophysics Data System (ADS)

The determination of the charge state distributions (CSD) of highly ionized Au in Non-LTE high-density plasmas (˜ 10^21 cm-3) is critical for benchmarking radiation-hydrodynamic physics codes. Predictive calculations of the CSD have produced widely varying results. We present Au CSD’s inferred from spectroscopic measurements of reduced-scale hohlraum target experiments at the OMEGA Laser having high electron temperatures (5 - 10 keV). Time integrated spectra were recorded with the Henway crystal spectrometer. Time and spatially resolved spectral measurements were done with a new spectrometer, the MSPEC. The MSPEC can accommodate a variety of crystal configurations, connects to a standard X-ray framing camera, and has a better spectral range and resolution than previous instruments. Measurements of the 5f->3d transitions in Ni- to Na-like Au and the 3d->2p transitions in Co- to Ne-like Au were compared to atomic modeling from the Hebrew University Lawrence Livermore Atomic Code and the Flexible Atomic Code to infer the CSD and average ionization state (Z=58.5±1.3). The experimentally inferred CSDs will be compared with predictions from several available codes. This work was performed by the University of California LLNL under the auspices of the DOE under contract W-7405-ENG-48.

May, M.; Chung, H. K.; Hansen, S. B.; Brown, G.; Hinkel, D. E.; Schneider, M. B.; Widmann, K.; Austrheim-Smith, C.; Cone, K.

2006-10-01

293

Triplet extinction coefficients of some laser dyes. II  

SciTech Connect

We measured the triplet extinction coefficients over the laser action spectral region of DODC, DMC, Sulforhodamine B, Rhodamine 575, Coumarin 523, Coumarin 521, Coumarin 504, Coumarin 498, Coumarin 490, LD466, bis-MSB, and BBO. We employed the different lines from an argon and a krypton ion cw laser for excitation. McClure's method was again employed to measure the triplet extinction coefficients. We provide a simplified derivation of McClure's equation. The triplet extinction coefficient of Rhodamine 575 was also measured by using the depletion method and improving it by reconstructing for true triplet-triplet (T-T) absorption. The ET value obtained is in good agreement with the one obtained by McClure's method.

Pavlopoulos, T.G.; Golich, D.J.

1990-01-01

294

Zeaxanthin Protects Plant Photosynthesis by Modulating Chlorophyll Triplet Yield in Specific Light-harvesting Antenna Subunits*  

PubMed Central

Plants are particularly prone to photo-oxidative damage caused by excess light. Photoprotection is essential for photosynthesis to proceed in oxygenic environments either by scavenging harmful reactive intermediates or preventing their accumulation to avoid photoinhibition. Carotenoids play a key role in protecting photosynthesis from the toxic effect of over-excitation; under excess light conditions, plants accumulate a specific carotenoid, zeaxanthin, that was shown to increase photoprotection. In this work we genetically dissected different components of zeaxanthin-dependent photoprotection. By using time-resolved differential spectroscopy in vivo, we identified a zeaxanthin-dependent optical signal characterized by a red shift in the carotenoid peak of the triplet-minus-singlet spectrum of leaves and pigment-binding proteins. By fractionating thylakoids into their component pigment binding complexes, the signal was found to originate from the monomeric Lhcb4–6 antenna components of Photosystem II and the Lhca1–4 subunits of Photosystem I. By analyzing mutants based on their sensitivity to excess light, the red-shifted triplet-minus-singlet signal was tightly correlated with photoprotection in the chloroplasts, suggesting the signal implies an increased efficiency of zeaxanthin in controlling chlorophyll triplet formation. Fluorescence-detected magnetic resonance analysis showed a decrease in the amplitude of signals assigned to chlorophyll triplets belonging to the monomeric antenna complexes of Photosystem II upon zeaxanthin binding; however, the amplitude of carotenoid triplet signal does not increase correspondingly. Results show that the high light-induced binding of zeaxanthin to specific proteins plays a major role in enhancing photoprotection by modulating the yield of potentially dangerous chlorophyll-excited states in vivo and preventing the production of singlet oxygen. PMID:23066020

Dall'Osto, Luca; Holt, Nancy E.; Kaligotla, Shanti; Fuciman, Marcel; Cazzaniga, Stefano; Carbonera, Donatella; Frank, Harry A.; Alric, Jean; Bassi, Roberto

2012-01-01

295

How to calculate linear absorption spectra with lifetime broadening using fewest switches surface hopping trajectories: A simple generalization of ground-state Kubo theory  

NASA Astrophysics Data System (ADS)

In this paper, we develop a surface hopping approach for calculating linear absorption spectra using ensembles of classical trajectories propagated on both the ground and excited potential energy surfaces. We demonstrate that our method allows the dipole-dipole correlation function to be determined exactly for the model problem of two shifted, uncoupled harmonic potentials with the same harmonic frequency. For systems where nonadiabatic dynamics and electronic relaxation are present, preliminary results show that our method produces spectra in better agreement with the results of exact quantum dynamics calculations than spectra obtained using the standard ground-state Kubo formalism. As such, our proposed surface hopping approach should find immediate use for modeling condensed phase spectra, especially for expensive calculations using ab initio potential energy surfaces.

Petit, Andrew S.; Subotnik, Joseph E.

2014-07-01

296

Triplet sensitized photolysis of a vinyl azide: direct detection of a triplet vinyl azide and nitrene.  

PubMed

Photolysis of vinylazide 1, which has a built-in acetophenone triplet sensitizer, in argon-saturated toluene results in azirine 2, whereas irradiation in oxygen-saturated toluene yields cyanide derivatives 3 and 4. Laser flash photolysis of azide 1 in argon-saturated acetonitrile shows formation of vinylnitrene 1c, which has a ?max at ?300 nm and a lifetime of ?1 ms. Vinylnitrene 1c is formed with a rate constant of 4.25 × 10(5) s(-1) from triplet 1,2-biradical 1b. Laser flash photolysis of 1 in oxygen-saturated acetonitrile results in 1c-O (?max = 430 nm, ? ? 420 ?s acetonitrile). Density functional theory (DFT) calculations were used to aid in the characterization of the intermediates formed upon irradiation of azide 1 and to validate the proposed mechanism for its photoreactivity. PMID:25163813

Rajam, Sridhar; Jadhav, Abhijit V; Li, Qian; Sarkar, Sujan K; Singh, Pradeep N D; Rohr, Ahleah; Pace, Tamara C S; Li, Rui; Krause, Jeanette A; Bohne, Cornelia; Ault, Bruce S; Gudmundsdottir, Anna D

2014-10-01

297

Singlet-triplet annihilation limits exciton yield in poly(3-hexylthiophene)  

E-print Network

Control of chain length and morphology in combination with single-molecule spectroscopy techniques provide a comprehensive photophysical picture of excited-state losses in the prototypical conjugated polymer poly(3-hexylthiophene) (P3HT). A universal self-quenching mechanism is revealed, based on singlet-triplet exciton annihilation, which accounts for the dramatic loss in fluorescence quantum yield of a single P3HT chain between its solution (unfolded) and bulk-like (folded) state. Triplet excitons fundamentally limit the fluorescence of organic photovoltaic materials, which impacts on the conversion of singlet excitons to separated charge carriers, decreasing the efficiency of energy harvesting at high excitation densities. Interexcitonic interactions are so effective that a single P3HT chain of >100 kDa weight behaves like a two-level system, exhibiting perfect photon-antibunching.

Steiner, Florian; Lupton, John M

2014-01-01

298

Non-linear trans-Planckian corrections of spectra due to the non-trivial initial states  

NASA Astrophysics Data System (ADS)

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.

Yusofi, E.; Mohsenzadeh, M.

2014-07-01

299

Fast acquisition of multi-dimensional spectra in solid-state NMR enabled by ultra-fast MAS  

NASA Astrophysics Data System (ADS)

The advantages offered by ultra-fast (>60 kHz) magic angle spinning (MAS) rotation for the study of biological samples, notably containing paramagnetic centers are explored. It is shown that optimal conditions for performing solid-state 13C NMR under 60 kHz MAS are obtained with low-power CW 1H decoupling, as well as after a low-power 1H, 13C cross-polarization step at a double-quantum matching condition. Acquisition with low-power decoupling highlights the existence of rotational decoupling sidebands. The sideband intensities and the existence of first and second rotary conditions are explained in the framework of the Floquet-van Vleck theory. As a result, optimal 13C spectra of the oxidized, paramagnetic form of human copper zinc superoxide dismutase (SOD) can be obtained employing rf-fields which do not exceed 40 kHz during the whole experiment. This enables the removal of unwanted heating which can lead to deterioration of the sample. Furthermore, combined with the short 1H T 1s, this allows the repetition rate of the experiments to be shortened from 3 s to 500 ms, thus compensating for the sensitivity loss due to the smaller sample volume in a 1.3 mm rotor. The result is that 2D 13C- 13C correlation could be acquired in about 24 h on less than 1 mg of SOD sample.

Laage, Ségolène; Sachleben, Joseph R.; Steuernagel, Stefan; Pierattelli, Roberta; Pintacuda, Guido; Emsley, Lyndon

2009-02-01

300

Fast acquisition of multi-dimensional spectra in solid-state NMR enabled by ultra-fast MAS.  

PubMed

The advantages offered by ultra-fast (>60 kHz) magic angle spinning (MAS) rotation for the study of biological samples, notably containing paramagnetic centers are explored. It is shown that optimal conditions for performing solid-state (13)C NMR under 60 kHz MAS are obtained with low-power CW (1)H decoupling, as well as after a low-power (1)H,(13)C cross-polarization step at a double-quantum matching condition. Acquisition with low-power decoupling highlights the existence of rotational decoupling sidebands. The sideband intensities and the existence of first and second rotary conditions are explained in the framework of the Floquet-van Vleck theory. As a result, optimal (13)C spectra of the oxidized, paramagnetic form of human copper zinc superoxide dismutase (SOD) can be obtained employing rf-fields which do not exceed 40 kHz during the whole experiment. This enables the removal of unwanted heating which can lead to deterioration of the sample. Furthermore, combined with the short (1)H T(1)s, this allows the repetition rate of the experiments to be shortened from 3 s to 500 ms, thus compensating for the sensitivity loss due to the smaller sample volume in a 1.3 mm rotor. The result is that 2D (13)C-(13)C correlation could be acquired in about 24 h on less than 1 mg of SOD sample. PMID:19028122

Laage, Ségolène; Sachleben, Joseph R; Steuernagel, Stefan; Pierattelli, Roberta; Pintacuda, Guido; Emsley, Lyndon

2009-02-01

301

Photoinduced absorption studies of triplet-enhanced conjugated polymer-based diodes  

NASA Astrophysics Data System (ADS)

Trace concentration of metallic impurities present at the ppm level in conjugated polymers allow transition between the singlet and triplet manifolds, thus permitting photophysical studies of the triplet states at room temperature. We present photoinduced absorption (PIA) studies of diphenyl-substituted ladder-type poly paraphenylene (PhLPPP) containing a trace concentration of covalently bound Pd atoms. In the bulk polymer sample, the T1-TN peak is observed at ˜ 1.3 eV, which is also known to blue shift with increasing temperatures. In this work we present PIA studies as a function of an applied electric field from PhLPPP-based diodes. In addition to the T1-TN peak at 1.3 eV, we also observe a strong signal at 1.35 eV, which is traced to the interface between the polymer and the hole transport layer. Field-induced PIA from polymer devices is thus a promising tool for probing weak electronic states, such as the triplet and charge transfer states, and further provides a mechanism for disentangling bulk and interface properties.

Moghe, Dhanashree; Guha, Suchi; Samiullah, Mohammad

2010-03-01

302

Photoinduced interfacial electron injection in RuN3-TiO 2 thin films: Resolving picosecond timescale injection from the triplet state of the protonated and deprotonated dyes  

NASA Astrophysics Data System (ADS)

Using femtosecond transient absorption spectroscopy we have studied light-induced electron injection from the sensitizer RuN3 and its partly deprotonated tetrabutylamonium salt to nano-structured TiO 2 film. Previous studies have suggested significant differences in electron injection dynamics for these dyes and some results have indicated that aggregation of the sensitizer may lead to slow injection. By measuring transient absorption spectra and kinetics of RuN3 and RuN3-TBA in solution and attached to TiO 2 film we show that the electron injection dynamics are very similar for the two forms of the dye and that aggregation has only moderate effects on the electron transfer dynamics.

Pellnor, M.; Myllyperkiö, P.; Korppi-Tommola, J.; Yartsev, A.; Sundström, V.

2008-09-01

303

Infrared spectra and theoretical calculations for Fe, Ru, and Os metal hydrides and dihydrogen complexes.  

PubMed

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

Wang, Xuefeng; Andrews, Lester

2009-01-22

304

Electronic spectra and intersystem spin-orbit coupling in 1,2- and 1,3-squaraines.  

PubMed

The main photophysical properties of a series of recently synthetized 1,2- and 1,3-squaraines, including absorption electronic spectra, singlet-triplet energy gaps, and spin-orbit matrix elements, have been investigated by means of density functional theory (DFT) and time-dependent DFT approaches. A benchmark of three exchange-correlation functionals has been performed in six different solvent environments. The investigated 1,2 squaraines have been found to possess two excited triplet states (T1 and T2 ) that lie below the energy of the excited singlet one (S1 ). The radiationless intersystem spin crossing efficiency is thus enhanced in both the studied systems and both the transitions could contribute to the excited singlet oxygen production. Moreover, they have a singlet-triplet energy gap higher than that required to generate the cytotoxic singlet oxygen species. According to our data, these compounds could be used in photodynamic therapy applications that do not require high tissue penetration. © 2014 Wiley Periodicals, Inc. PMID:25178476

Alberto, Marta E; Mazzone, Gloria; Quartarolo, Angelo D; Sousa, Flavio Fortes Ramos; Sicilia, Emilia; Russo, Nino

2014-11-01

305

Time-dependent density functional study of the electronic spectra of oligoacenes in the charge states ?1, 0, +1, and +2  

Microsoft Academic Search

We present a systematic theoretical study of the five smallest oligoacenes (naphthalene, anthracene, tetracene, pentacene, and hexacene) in their anionic, neutral, cationic, and dicationic charge states. We used density functional theory (DFT) to obtain the ground-state optimised geometries, and time-dependent DFT (TD-DFT) to evaluate the electronic absorption spectra. Total-energy differences enabled us to evaluate the electron affinities and first and

G. Malloci; G. Mulas; G. Cappellini; C. Joblin

2007-01-01

306

Excitation dynamics in Phycoerythrin 545: modeling of steady-state spectra and transient absorption with modified Redfield theory.  

PubMed

We model the spectra and excitation dynamics in the phycobiliprotein antenna complex PE545 isolated from the unicellular photosynthetic cryptophyte algae Rhodomonas CS24. The excitonic couplings between the eight bilins are calculated using the CIS/6-31G method. The site energies are extracted from a simultaneous fit of the absorption, circular dichroism, fluorescence, and excitation anisotropy spectra together with the transient absorption kinetics using the modified Redfield approach. Quantitative fit of the data enables us to assign the eight exciton components of the spectra and build up the energy transfer picture including pathways and timescales of energy relaxation, thus allowing a visualization of excitation dynamics within the complex. PMID:20643051

Novoderezhkin, Vladimir I; Doust, Alexander B; Curutchet, Carles; Scholes, Gregory D; van Grondelle, Rienk

2010-07-21

307

Triplet Excitation Energy Transfer with Constrained Density Functional Theory  

E-print Network

We study the electronic coupling matrix element for triplet excitation energy-transfer processes with a number of different computational methods. For the first time, constrained density functional theory (CDFT) is applied ...

Yeganeh, Sina

308

The ground state infrared spectra of several isotopic forms of the CdH and ZnH radicals  

SciTech Connect

The infrared spectra of six isotopic forms of cadmium monohydride, ({sup 116}CdH (7.6%), {sup 114}CdH (28.9%), {sup 113}CdH (12.3%), {sup 112}CdH (24.1%), {sup 111}CdH (12.7%), and {sup 110}CdH (12.4%)) and four isotopic forms of zinc hydride ({sup 68}ZnH (18.6%), {sup 67}ZnH (4.1%), {sup 66}ZnH (27.8%), and {sup 64}ZnH (48.9%)) have been observed in natural abundance in their ground electronic state ({sup 2}{Sigma}{sup +}) in the gas phase using a diode laser spectrometer. A number of transitions of {sup 108}CdH (0.9%) and {sup 106}CdH (1.2%) and {sup 70}ZnH (0.6%) were also observed, but too little data was accumulated to allow a good analysis. The hydrides were produced by reaction of hydrogen with metal vapor at elevated temperature in an electric discharge. The analysis of the experimental data was carried out in two ways. (a) A complete set of Dunham parameters and spin--rotation parameters ({gamma} parameters) was determined for each isotopic species of the two radicals and (b) a set of mass-independent parameters were calculated for both ZnH and CdH. Since only information over the isotopic species of the heavy atom was produced in each case, effects arising from a breakdown of the Born--Oppenheimer approximation were negligible. The effects of the strong anharmonicity present in these two molecules on the values of the parameters are discussed.

Urban, R.; Magg, U.; Birk, H.; Jones, H. (Abteilung Physikalische Chemie, Universitaet Ulm D-7900 Ulm, Federal Republic of Germany (DE))

1990-01-01

309

Protein induced singlet-triplet quasidegeneracy in the active site of [NiFe]-hydrogenase  

NASA Astrophysics Data System (ADS)

Molecular hydrogen oxidation and reduction on [NiFe]-hydrogenase is an inspiring example of using abundant first row transition metals to catalyze biologically and industrially important chemical reactions. We demonstrate that by rotating terminal thiolate ligands in the active site of [NiFe]-hydrogenase, either the singlet or triplet electronic state can be made a ground state. The two states become degenerate when the ligand orientations are similar to those observed in [NiFe]-hydrogenase, where this orientation is enforced by the protein backbone. The unusual distorted coordination geometry of Ni can explain the inability of the structural models of [NiFe]-hydrogenase to bind molecular hydrogen.

Yson, Renante L.; Gilgor, Jessica L.; Guberman, Benjamin A.; Varganov, Sergey A.

2013-07-01

310

Nanostructured singlet fission photovoltaics subject to triplet-charge annihilation.  

PubMed

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

Thompson, Nicholas J; Hontz, Eric; Congreve, Daniel N; Bahlke, Matthias E; Reineke, Sebastian; Van Voorhis, Troy; Baldo, Marc A

2014-03-01

311

Connecting Dark Energy to Neutrinos with an Observable Higgs Triplet  

E-print Network

To connect the scalar field (acceleron) responsible for dark energy to neutrinos, the usual strategy is to add unnaturally light neutral singlet fermions (right-handed neutrinos) to the Standard Model. A better choice is actually a Higgs triplet, through the coupling of the acceleron to the trilinear Higgs triplet-double-doublet interaction. This hypothesis predicts an easily observable doubly-charged Higgs boson at the forthcoming Large Hadron Collider (LHC).

Ernest Ma; Utpal Sarkar

2006-02-14

312

Structural basis for triplet repeat disorders: a computational analysis  

Microsoft Academic Search

Motivation: Over a dozen major degenerative disorders, including myotonic distrophy, Huntington's disease and fragile X syndrome, result from unstable expansions of particular trinucleotides. Remarkably, only some of all the possible triplets, namely CAG\\/CTG, CGG\\/CCG and GAA\\/TTC, have been associated with the known pathological expansions. This raises some basic questions at the DNA level. Why do particular triplets seem to be

Pierre Baldi; Søren Brunak; Yves Chauvin; Anders Gorm Pedersen

1999-01-01

313

Rotationally resolved S1<--S0 electronic spectra of fluorene, carbazole, and dibenzofuran: Evidence for Herzberg-Teller coupling with the S2 state  

NASA Astrophysics Data System (ADS)

Rotationally resolved fluorescence excitation spectra of the S1?S0 origin bands and higher vibronic bands of fluorene (FLU), carbazole (CAR), and dibenzofuran (DBF) have been observed and assigned. Analyses of these data show that replacement of the CH2 group in FLU with a NH group in CAR and an O atom in DBF produces only localized changes in structure, in the ground state. But the three molecules exhibit different changes in geometry when they are excited by light. The S1 states of the three molecules also are electronically very different. The S1?S0 transition moments of CAR and DBF are parallel to the C2 symmetry axis whereas the corresponding transition moment in FLU is perpendicular to this axis. Herzberg-Teller coupling involving the S2 state also has been observed in the spectra of higher vibronic bands of CAR and DBF. Possible reasons for these behaviors are discussed.

Yi, John T.; Alvarez-Valtierra, Leonardo; Pratt, David W.

2006-06-01

314

Steady-state analysis of three-photon absorption spectra via density-matrix method in a three-coupled-quantum-well nanostructure  

NASA Astrophysics Data System (ADS)

We numerically simulate three-photon absorption spectra in a three-coupled-quantum-well nanostructure interacting with a pump field, a coherent coupling field, and a probe field. We find that the three-photon absorption spectra can be dramatically influenced due to the intensities of the coupling field and pump field changing under the three-photon resonance condition. The effect of the frequency detuning of the pump field on the three-photon absorption spectra is also discussed. The study in our case is much more practical than the study in the case of its atomic counterpart in the sense of flexible design and the wide adjustable parameters. Thus it may open up some new possibilities for technological applications in optoelectronics and solid-state quantum information science.

Deng, Li

2010-05-01

315

Production and installation of the LHC low-beta triplets  

SciTech Connect

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.

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

316

Direct observation of the intermolecular triplet-triplet energy transfer from UV-A absorber 4- tert -butyl-4?-methoxydibenzoylmethane to UV-B absorber octyl methoxycinnamate  

NASA Astrophysics Data System (ADS)

Triplet energy transfer (TET) is an important photostabilization process for organic UV absorbers, such as 4- tert-butyl-4'-methoxydibenzoylmethane (BM-DBM) and octyl methoxycinnamate (OMC). To characterize interactions between UV absorbers as TET the interactions between BM-DBM and OMC have been studied through measurements of EPR and time-resolved phosphorescence spectra. The EPR Bmin signals and the phosphorescence of OMC were observed through the selective excitation of BM-DBM at 365 nm in EtOH at 77 K. These results indicate that the intermolecular TET occurs from BM-DBM to OMC. This is the first report of the experimental evidence of the TET between the organic UV absorbers.

Kikuchi, Azusa; Yagi, Mikio

2011-09-01

317

Emission spectra of InGaN/AlGaN/GaN quantum well heterostructures: Model of the two-dimensional joint density of states  

SciTech Connect

The luminescence spectra of light emitting diodes based on InGaN/AlGaN/GaN heterostructures with multiple quantum wells are analyzed in the context of a model of the two-dimensional density of states in the active region. The model accounts for the potential fluctuations, the statistics of occupation of the wells with charge carriers, and specific features of the extraction of radiation from the structure. The model describes the position of the maxima of the spectra and the exponential decline of the emission intensity in the short-and long-wavelength regions as well as the modification of the spectra under variations in the current. The problems of limitations of the model and the physical meaning of the parameters are discussed. The examples of approximation of the spectra of blue light emitting diodes based on InGaN/AlGaN/GaN heterostructures show the necessity of determining the temperature in the active region independently and taking into account the interference in the planar structure. The differences of the shape of the spectra from that obtained in the simple model depend not only on the properties of the quantum wells but also on the nonuniformities in the distribution of In in InGaN.

Badgutdinov, M. L.; Yunovich, A. E. [Moscow State University, Department of Physics (Russian Federation)], E-mail: yunovich@phys.msu.ru

2008-04-15

318

B3LYP calculations of the potential energy surfaces of the thermal dissociations and the triplet ground state of pyrolysis products XN( x˜ 3?-) for halogen azides XN 3 (X: F, Cl, Br, I)  

NASA Astrophysics Data System (ADS)

Mechanisms of XN 3 (X: F, Cl, Br, I) dissociations are proposed based on B3LYP calculated potential energy surfaces. The energy gaps between the ground-state reactants XN3( x˜ 1A') and the intersystem crossing (ISC) points are only a little lower than respective potential energy barriers of the spin-allowed reactions, XN3( x˜ 1A')? XN(a 1?)+ N2( x˜ 1?g+) . The ISC point, therefore, is considered as a 'transition state' of the spin-forbidden reactions, XN3( x˜ 1A')? XN( x˜ 3?-)+ N2( x˜ 1?g+) . The methods of IRC and topological analysis of electron density are used to predict the thermal dissociation pathway of the reactions studied.

Zeng, Yanli; Meng, Lingpeng; Zheng, Shijun; Wang, Dianxun

2003-08-01

319

Imaging the radical channel in acetaldehyde photodissociation: Competing mechanisms at energies close to the triplet exit barrier  

SciTech Connect

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.

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

320

Diffusion of barium atoms in the 6s5d triplet-D(J) levels and the 6s(2) singlet-S(0) ground state through noble gas perturbers  

Microsoft Academic Search

We describe a set of experiments that investigate diffusion of barium 6s5d3D J metastable level and 6s2\\/ 1S0 ground state atoms through the noble gases: He, Ne, Ar, Kr, and Xe. The barium metastable levels were populated through optical pumping of the 6s2\\/ 1S0 \\/to 6s6p 3P1o intercombination transition with a pulsed laser, followed by spontaneous or stimulated emission into

Raychel Kristine Namiotka

1998-01-01

321

Improving triplet-triplet-annihilation based upconversion systems by tuning their topological structure.  

PubMed

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

Zimmermann, Jochen; Mulet, Roberto; Scholes, Gregory D; Wellens, Thomas; Buchleitner, Andreas

2014-11-14

322

Broadband up-conversion at subsolar irradiance: triplet-triplet annihilation boosted by fluorescent semiconductor nanocrystals.  

PubMed

Conventional solar cells exhibit limited efficiencies in part due to their inability to absorb the entire solar spectrum. Sub-band-gap photons are typically lost but could be captured if a material that performs up-conversion, which shifts photon energies higher, is coupled to the device. Recently, molecular chromophores that undergo triplet-triplet annihilation (TTA) have shown promise for efficient up-conversion at low irradiance, suitable for some types of solar cells. However, the molecular systems that have shown the highest up-conversion efficiency to date are ill suited to broadband light harvesting, reducing their applicability. Here we overcome this limitation by combining an organic TTA system with highly fluorescent CdSe semiconductor nanocrystals. Because of their broadband absorption and spectrally narrow, size-tunable fluorescence, the nanocrystals absorb the radiation lost by the TTA chromophores, returning this energy to the up-converter. The resulting nanocrystal-boosted system shows a doubled light-harvesting ability, which allows a green-to-blue conversion efficiency of ?12.5% under 0.5 suns of incoherent excitation. This record efficiency at subsolar irradiance demonstrates that boosting the TTA by light-emitting nanocrystals can potentially provide a general route for up-conversion for different photovoltaic and photocatalytic applications. PMID:25322197

Monguzzi, A; Braga, D; Gandini, M; Holmberg, V C; Kim, D K; Sahu, A; Norris, D J; Meinardi, F

2014-11-12

323

Spin state selective coherence transfer: A method for discrimination and complete analyses of the overlapped and unresolved 1H NMR spectra of enantiomers  

NASA Astrophysics Data System (ADS)

In general, the proton NMR spectra of chiral molecules aligned in the chiral liquid crystalline media are broad and featureless. The analyses of such intricate NMR spectra and their routine use for spectral discrimination of R and S optical enantiomers are hindered. A method is developed in the present study which involves spin state selective two dimensional correlation of higher quantum coherence to its single quantum coherence of a chemically isolated group of coupled protons. This enables the spin state selective detection of proton single quantum transitions based on the spin states of the passive nuclei. The technique provides the relative signs and magnitudes of the couplings by overcoming the problems of enantiomer discrimination, spectral complexity and poor resolution, permitting the complete analyses of the otherwise broad and featureless spectra. A non-selective 180° pulse in the middle of MQ dimension retains all the remote passive couplings. This accompanied by spin selective MQ-SQ conversion leads to spin state selective coherence transfer. The removal of field inhomogeneity contributes to dramatically enhanced resolution. The difference in the cumulative additive values of chemical shift anisotropies and the passive couplings, between the enantiomers, achieved by detecting Nth quantum coherence of N magnetically equivalent spins provides enhanced separation of enantiomer peaks. The developed methodology has been demonstrated on four different chiral molecules with varied number of interacting spins, each having a chiral centre.

Baishya, Bikash; Prabhu, Uday Ramesh; Suryaprakash, N.

2008-05-01

324

Quantitative treatment of the effect of solvent on the electronic absorption and fluorescence spectra of substituted coumarins: Evaluation of the first excited singlet-state dipole moments.  

PubMed

The electronic absorption and fluorescence spectra of coumarin and 11 substituted coumarins were measured in several solvents (dioxane, ethyl ether, ethyl acetate, ethanol, dimethylformamide, acetonitrile, and dimethyl sulfoxide). Ground-state dipole moments were determined in dioxane at 298 K. The results were used to obtain the first excited singlet-state dipole moments of the coumarins under study by the solvatochromic shift method (Bakhshiev, Kawski-Chamma-Viallet, McRae, and Suppan correlations). Also, the ground- and the first excited singlet-state dipole moments were calculated using a combination of the PPP method (?-contribution) and the vector sum of the ?-bond and group moments (?-contribution). In general, the first excited singlet-state dipole moments of the coumarins are noticeably higher than the corresponding ground-state values, indicating a substantial redistribution of the?-electron densities resulting in a more polar excited state. There is a reasonably good agreement between the calculated and the experimental dipole moments. PMID:24226910

Aaron, J J; Buna, M; Parkanyi, C; Antonious, M S; Tine, A; Cisse, L

1995-12-01

325

Triplet excited fluoroquinolones as mediators for thymine cyclobutane dimer formation in DNA.  

PubMed

A series of fluoroquinolones (FQs), including enoxacin (ENX), pefloxacin (PFX), norfloxacin (NFX), its N(4')-acetyl derivative (ANFX), ofloxacin (OFX), and rufloxacin (RFX) have been investigated to determine their potential as DNA photosensitizers via thymine cyclobutane dimer (T<>T) formation in DNA. At fluoroquinolone concentrations and light doses insufficient to produce direct single strand breaks, ENX, PFX, and NFX were able to produce T<>T dimers in DNA, revealed by enzymatic treatment with T4 endonuclease V. By contrast, ANFX, OFX, and RFX were inefficient in this assay. The absolute values of the triplet energies of ENX, PFX, NFX, ANFX, OFX, and RFX were estimated by means of laser flash photolysis, using flurbiprofen, 4-biphenylcarboxylic acid, and naproxen as energy acceptors. They were found to be 273, 269, 269, 265, 262, and 253 kJ/mol, respectively. Other triplet excited state properties of the FQs, including quantum yields and lifetimes, were also studied. All the results indicate that the threshold ET value required for a given compound to become a potential DNA photosensitizer via T<>T formation is in the range defined by the triplet energies of NFX and ANFX (265-269 kJ/mol). This provides the basis for an alert rule: any chemical (drugs, cosmetics, pesticides, etc.) with higher ET has to be considered with regard to its potential photogenotoxicity. PMID:17523621

Lhiaubet-Vallet, Virginie; Cuquerella, M Consuelo; Castell, Jose V; Bosca, Francisco; Miranda, Miguel A

2007-06-28

326

Trans-Cis Isomerization of Vinylketones through Triplet 1,2-Biradicals.  

PubMed

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

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

327

Singlet and triplet energy transfer in the peridinin-chlorophyll a-protein from Amphidinium carterae  

SciTech Connect

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.

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

328

Hybrid spin and valley quantum computing with singlet-triplet qubits.  

PubMed

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. PMID:25379928

Rohling, Niklas; Russ, Maximilian; Burkard, Guido

2014-10-24

329

Hybrid Spin and Valley Quantum Computing with Singlet-Triplet Qubits  

NASA Astrophysics Data System (ADS)

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.

Rohling, Niklas; Russ, Maximilian; Burkard, Guido

2014-10-01

330

Competition between concerted and stepwise dynamics in the triplet di-?-methane rearrangement.  

PubMed

The molecular dynamics of the triplet-state Zimmerman di-?-methane rearrangement of dibenzobarrelene were computed with B3LYP and M06-2X density functionals. All productive quasiclassical trajectories involve sequential formation and cleavage of C-C bonds and an intermediate with lifetimes ranging from 13 to 1160?fs. Both dynamically concerted and stepwise trajectories are found. The average lifetime of this intermediate is significantly shorter than predicted by either transition-state theory or the Rice-Ramsperger-Kassel-Marcus model, thus indicating the non-statistical nature of the reaction mechanism. PMID:24616069

Jiménez-Osés, Gonzalo; Liu, Peng; Matute, Ricardo A; Houk, Kendall N

2014-08-11

331

Oxygen Intermediates and Mixed Valence States of Cytochrome Oxidase: Infrared Absorption Difference Spectra of Compounds A, B, and C of Cytochrome Oxidase and Oxygen  

Microsoft Academic Search

A study of the near-infrared absorption spectra of three oxygen compounds of membrane-bound cytochrome oxidase (ferrocytochrome c:oxygen oxidoreductase; EC 1.9.3.1) shows that the formation of compound A (oxycytochrome oxidase) causes no significant infrared absorbance changes at -103 degrees. At -64 degrees, the formation of compound C from the mixed-valence state of the oxidase leads to increased absorption at 740-750 nm.

Britton Chance; J. S. Leigh

1977-01-01

332

Calculation and analysis of vibrational spectra of adenine–thymine, guanine–cytosine, and adenine–uracil complementary pairs in the condensed state  

Microsoft Academic Search

We have calculated the frequencies of the normal vibrations of the complementary nucleic acid base pairs adenine–thymine,\\u000a guanine–cytosine, adenine–uracil, corresponding to the Watson–Crick structure, and the adenine–uracil pair, corresponding\\u000a to the Hoogsteen structure, in condensed states and we interpret the spectra. We determine the contributions of hydrogen bonds\\u000a to the vibrational modes of the complementary pairs. We have analyzed the

G. N. Ten; T. G. Burova; V. I. Baranov

2009-01-01

333

Effects induced by gamma-irradiation and thermal treatment on the infrared spectra of ferrocene in its disordered state  

NASA Astrophysics Data System (ADS)

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.

Gaffar, M. A.; Abd-Elrahman, M. I.

2004-10-01

334

Excited states and electronic spectra of annulated dinuclear free-base phthalocyanines: A theoretical study on near-infrared-absorbing dyes  

NASA Astrophysics Data System (ADS)

The electronic excited states and electronic absorption spectra of annulated dinuclear free-base phthalocyanine (C58H30N16) are studied through quantum chemical calculations using the symmetry-adapted cluster-configuration interaction (SAC-CI) method. Three tautomers are possible with respect to the position of the pyrrole protons; therefore, the SAC-CI calculations for these tautomers were performed. The structures of the Q-band states are discussed based on the character of their molecular orbitals. The lower energy shift of the Q-bands because of dimerization is explained by the decrease in the HOMO-LUMO gaps resulting from the bonding and antibonding interactions between the monomer units. The electronic dipole moments of the nonsymmetric tautomer were calculated, and the possibility of charge-separated excited states is discussed. The relative energies of these tautomers are examined using density functional theory (DFT) calculations for several peripheral substituents. The relative energies of these tautomers significantly depend on the substituents, and therefore, the abundance ratios of the three tautomers were affected by the substituents. The absorption spectra were simulated from the SAC-CI results weighted by the Boltzmann factors obtained from the DFT calculations. The SAC-CI spectra reproduce the experimental findings well. The thermal-averaged SAC-CI spectra could explain the observed substituent effect on the structure of the Q-bands in terms of the relative stabilities and the abundance ratios of the tautomers. The SAC-CI and time-dependent density functional theory calculations are also compared. The CAM-B3LYP results agreed with the trends of the SAC-CI results; however, the CAM-B3LYP calculation overestimated the excitation energies in comparison with the SAC-CI and experimental results.

Fukuda, Ryoichi; Ehara, Masahiro

2012-03-01

335

DNA CTG triplet repeats involved in dynamic mutations of neurologically related gene sequences form stable duplexes.  

PubMed Central

DNA triplet repeats, 5'-d(CTG)n and 5'-d(CAG)n, are present in genes which have been implicated in several neurodegenerative disorders. To investigate possible stable structures formed by these repeating sequences, we have examined d(CTG)n, d(CAG)n and d(CTG).d(CAG)n (n = 2 and 3) using NMR and UV optical spectroscopy. These studies reveal that single stranded (CTG)n (n > 2) forms stable, antiparallel helical duplexes, while the single stranded (CAG)n requires at least three repeating units to form a duplex. NMR and UV melting experiments show that the Tm increases in the order of [(CAG)3]2 < [(CTG)3]2 << (CAG)3.(CTG)3. The (CTG)3 duplex is stable and exhibits similar NMR spectra in solutions containing 0.1-4 M NaCl and at a pH range from 4.6 to 8.8. The (CTG)3 duplex, which contains multiple-T.T mismatches, displays many NMR spectral characteristics similar to those of B-form DNA. However, unique NOE and 1H-31P coupling patterns associated with the repetitive T.T mismatches in the CTG repeats are discerned. These results, in conjunction with recent in vitro studies suggest that longer CTG repeats may form hairpin structures, which can potentially cause interruption in replication, leading to dynamic expansion or deletion of triplet repeats. PMID:7501450

Smith, G K; Jie, J; Fox, G E; Gao, X

1995-01-01

336

Negative Ion Photoelectron Spectroscopy Confirms the Prediction that (CO)5 and (CO)6 Each Has a Singlet Ground State  

SciTech Connect

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.

Bao, Xiaoguang; Hrovat, David; Borden, Weston; Wang, Xue B.

2013-03-20

337

Solvent effects on the absorption and fluorescence spectra of quinine sulphate: Estimation of ground and excited-state dipole moments  

NASA Astrophysics Data System (ADS)

Ground and excited state dipole moments of probe quinine sulphate (QS) was obtained using Solvatochromic shift method. Higher dipole moment is observed for excited state as compared to the ground state which is attributed to the higher polarity of excited state.

Joshi, Sunita; Pant, Debi D.

2012-06-01

338

Odd triplet pairing in clean superconductor/ferromagnet heterostructures.  

PubMed

We study triplet pairing correlations in clean ferromagnet (F)/superconductor (S) nanojunctions, via fully self-consistent solution of the Bogoliubov-de Gennes equations. We consider FSF trilayers, with S being an s-wave superconductor, and an arbitrary angle alpha between the magnetizations of the two F layers. We find that contrary to some previous expectations, triplet correlations, odd in time, are induced in both the S and F layers in the clean limit. We investigate their behavior as a function of time, position, and alpha. The triplet amplitudes are largest at times on the order of the inverse Debye frequency, and at that time scale they are long-ranged in both S and F. The zero temperature condensation energy is found to be lowest when the magnetizations are antiparallel. PMID:17930543

Halterman, Klaus; Barsic, Paul H; Valls, Oriol T

2007-09-21

339

Electronic excited states of chromium and vanadium bisarene complexes revisited: interpretation of the absorption spectra on the basis of TD DFT calculations.  

PubMed

The nature and energies of the (arene)2Cr, (arene)2V and (arene)2Cr(+) (arene = ?(6)-C6H6, ?(6)-C6H5Me, ?(6)-1,3-C6H4Me2, and ?(6)-1,3,5-C6H3Me3) electronic excited states have been determined on the basis of the time-dependent density functional theory (TD DFT) approach and comparison with the gas-phase and condensed-phase absorption spectra. Both valence-shell and Rydberg electronic excitations were taken into account. The TD DFT results appear to describe correctly the influence of the metal atom and the ligand on the band positions and intensities in the UV-visible absorption spectra as well as the mixing of Rydberg and intravalency states. The TD DFT calculations suggest new assignments for long-wavelength valence-shell absorption bands in the spectra of (arene)2V and (arene)2Cr(+). PMID:25005427

Ketkov, Sergey; Isachenkov, Nikolai; Rychagova, Elena; Tzeng, Wen-Bih

2014-11-12

340

Oxygen from the ?7774 High-Excitation Triplet in Open Cluster Dwarfs: Hyades  

NASA Astrophysics Data System (ADS)

Oxygen abundances have been derived from the near-IR, high-excitation O I ?7774 triplet in high-resolution, high signal-to-noise ratio spectra of 45 Hyades dwarfs using standard one-dimensional, plane-parallel LTE models. Effective temperatures of the stellar sample range from 4319 to 6301 K, and the derived relative O abundances as a function of Teff evince a trichotomous morphology. At Teff>6100 K, there is evidence of an increase in the O abundances with increasing Teff, consistent with non-LTE (NLTE) predictions. At intermediate Teff (5450 K<=Teff<=6100 K), the O abundances are flat, and star-to-star values are in good agreement, having a mean value of [O/H]=+0.25+/-0.02 however, systematic errors at the <~0.10 dex level might exist. The O abundances for stars with Teff<=5450 K show a striking increase with decreasing Teff, in stark contrast to expectations and canonical NLTE calculations. The cool Hyades triplet results are compared to those recently reported for dwarfs in the Pleiades cluster and the UMa moving group; qualitative differences between the trends observed in these stellar aggregates point to a possible age-related diminution of triplet abundance trends in cool open cluster dwarfs. Correlations with age-related phenomena, i.e., chromospheric activity and photospheric spots, faculae, and/or plages, are investigated. No correlation with Ca II H+K chromospheric activity indicators is observed. Multicomponent LTE ``toy'' models have been constructed in order to simulate photospheric temperature inhomogeneities that could arise from the presence of starspots, and we demonstrate that photospheric spots are a plausible source of the triplet trends among the cool dwarfs. Based on observations obtained with the Mayall 4 m telescope at Kitt Peak National Observatory, a division of the National Optical Astronomy Observatory, which is operated by the Association of Universities for Research in Astronomy, Inc., under cooperative agreement with the National Science Foundation. This paper includes data taken with the Harlan J. Smith 2.7 m telescope at the McDonald Observatory of the University of Texas at Austin.

Schuler, Simon C.; King, Jeremy R.; Terndrup, Donald M.; Pinsonneault, Marc H.; Murray, Norman; Hobbs, L. M.

2006-01-01

341

??e? and ??l? decays in the fermion triplet seesaw model  

NASA Astrophysics Data System (ADS)

In the framework of the seesaw models with triplets of fermions, we evaluate the decay rates of ??e? and ??l? transitions. We show that although, due to neutrino mass constraints, those rates are in general expected to be well under the present experimental limits, this is not necessarily always the case. Interestingly enough, the observation of one of those decays in planned experiments would nevertheless contradict bounds stemming from present experimental limits on the ??eee and ??3l decay rates, as well as from ? to e conversion in atomic nuclei. Such detection of radiative decays would therefore imply that there exist sources of lepton flavor violation not associated to triplet fermions.

Abada, A.; Biggio, C.; Bonnet, F.; Gavela, M. B.; Hambye, T.

2008-08-01

342

The Triplet State: Emerging Applications of Room Temperature Phosphorescence Spectroscopy  

Microsoft Academic Search

Room?temperature phosphorescence (RTP) has been exploited for analytical research for over 30 years now due to the widespread recognition of its unique properties as a selective and sensitive technique, complementary to fluorescence. Recent years have seen the awakening of medical, geological, industrial, and technological interest in its application. The trend continues, driven by the achievements that have already been made

2007-01-01

343

Spectral triplets, statistical mechanics and emergent geometry in non-commutative quantum mechanics  

E-print Network

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.

F. G. Scholtz; B. Chakraborty

2012-06-22

344

Crystal Field Triplets: A New Route to Non-Fermi-Liquid Physics  

SciTech Connect

A model for crystal field triplet ground states of rare earth or actinide ions with dipolar and quadrupolar couplings to conduction electrons is studied for the first time with renormalization group methods. The quadrupolar coupling leads to a new nontrivial, non-Fermi-liquid fixed point, which survives in an intermediate valence Anderson model. The calculated magnetic susceptibility displays one parameter scaling, going as T{sup {minus}{alpha}} ({alpha}{approx}0.4 ) at intermediate temperatures, reminiscent of the non-Fermi-liquid alloy UCu{sub 5{minus}x} Pd{sub x} . {copyright} {ital 1999} {ital The American Physical Society}

Koga, M.; Zarand, G.; Cox, D.L. [Department of Physics, University of California, Davis, California 95616 (United States)] [Department of Physics, University of California, Davis, California 95616 (United States); Zarand, G. [Research Group of the Hungarian Academy of Sciences, Institute of Physics, TU Budapest, H-1521 (Hungary)] [Research Group of the Hungarian Academy of Sciences, Institute of Physics, TU Budapest, H-1521 (Hungary)

1999-09-01

345

Long range triplet Josephson current and 0?? transitions in tunable domain walls  

NASA Astrophysics Data System (ADS)

The order parameter of superconducting pairs penetrating an inhomogeneous magnetic material can acquire a long range triplet component (LRTC) with non-zero spin projection. This state has been predicted and generated in proximity systems and Josephson junctions. We show, using a realistic domain wall of an exchange spring bilayer, how the LRTC emerges and can be tuned with the twisting of the magnetization. We also introduce a new kind of Josephson current reversal, the singlet-LRTC 0–? transition, that can be observed in one and the same system either by tuning the domain wall or by varying temperature.

Baker, Thomas E.; Richie-Halford, Adam; Bill, Andreas

2014-09-01

346

Solvent effect on the absorption and fluorescence spectra of 7-acetoxy-6-(2,3-dibromopropyl)-4,8-dimethylcoumarin: Determination of ground and excited state dipole moments  

NASA Astrophysics Data System (ADS)

The ground state (?g) and excited state (?e) dipole moments of 7-acetoxy-6-(2,3-dibromopropyl)-4,8-dimethylcoumarin (abbreviated as 7ADDC) are estimated from solvatochromic shifts of absorption and fluorescence spectra as a function of the dielectric constant (?) and refractive index (n). While the ground state dipole moment is determined by using Bilot-Kawski method, the excited state dipole moment is calculated by using Bilot-Kawski, Lippert-Mataga, Bakhshiev, Kawski-Chamma-Viallet and Reichardt correlation methods. Excited state dipole moment is observed as larger than the ground state dipole moment due to substantial ?-electron density redistribution. The ground state and excited state dipole moments are observed as parallel to each other with angle of 0°. Solute-solvent interactions are analyzed by means of linear solvation free energy relationships (LSER) using dielectric constant function (f(?)), refractive index function (f(n)) and Kamlet-Taft parameters (? and ?). Atomic charges, electron densities and molecular orbitals are calculated in vacuum and with solvent effect by using both DFT and TDDFT methods. Solvent accessible surface, molecular electrostatic potential (MEP) and electrostatic potential (ESP) are visualized as a result of DFT calculations.

Gülseven S?d?r, Yadigar; S?d?r, ?sa

2013-02-01

347

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)

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.

Bottomley, Paul A.; Hardy, Christopher J.; Weiss, Robert G.

348

Application of Infrared Spectroscopy to the Analysis of Inorganic Nitrates. Phase II: Spectra of Inorganic Nitrates in the Solid State; Quantitative Determination of Inorganic Nitrates by the Pellet Technique.  

National Technical Information Service (NTIS)

A comprehensive survey was made of the spectra of inorganic nitrates in the solid state (pellet or mull technique). The spectra of 77 inorganic nitrates are listed in tabular form and are divided into the following four groups: anhydrous ionic nitrates, a...

D. E. Chasan, G. Norwitz

1969-01-01

349

Intensity of the oxygen 130nm triplet through the atmosphere of Mars and Venus; Comparison with Spicam data.  

NASA Astrophysics Data System (ADS)

The problem of the oxygen emission in the planetary atmospheres is crucial to constraint the atmospheric models and had never been directly measured. The oxygen 130nm triplet is optically thick in those atmospheres and is resonant with sun radiations. The instruments SPICAV and SPICAM are able to measure the intensity of this triplet without any spectral resolution. The Hubble space telescope with the STIS instrument is able to get enough spectral resolution to see the lines profile. In previous simulations, the overlapping between this triplet and lines of the CO fourth positive band has never been taken into account. We present new simulations calculating the oxygen 130nm triplet intensity and line profile taking into account the overlapping problem with a partial redistribution. Due to the structure of the triplet, we had to develop a new expression of the RII redistribution function. The effects of the CO lines modified strongly the O 130nm line parameters, intensity and line profile. These effects depend strongly of the geometry of the line of sight. We show that it is essential to take this problem into account in both the martian and venusian cases and that this could be a very useful way to get strong information on both the CO and the O states in these atmosphere for various geometrical conditions. After fitting these simulations with 2 Spicam data sets with two different Ls angles, we find that it is coherent with strong seasonal variations of the O and CO concentrations. EPSC Abstracts, Vol. 3, EPSC2008-A-00417, 2008 European Planetary Science Congress, Author(s) 2008

Mathieu, Barthelemy; Guillaume, Gronoff; Jean, Lilensten; Jean-Yves, Chaufray; Cyril, Simon

2008-09-01

350

[Analysis of the allele polymorphism of (CTG)n and (GAG)n triplet repeats in DM, DRPLA, and SCA1 genes in various populations of Russia].  

PubMed

Polymorphism of highly polymorphic triplet repeats CTG of the 3'-untranslated region of the myotonin protein kinase gene and CAG of the genes associated with dentatorobral-pallidoluysian atrophy (DRPLA, or Hew River syndrome) and spinocerebellar ataxia type 1 (SCA1) was analyzed in several ethnic populations of Russia. A difference in allele spectra of the three genes was demonstrated for populations differing in ethnic origin. PMID:12500681

Popova, S N; Slominski?, P A; Galushkin, S N; Tarskaia, L A; Spitsyn, V A; Guseva, I A; Limborskaia, S A

2002-11-01

351

Time-dependent density functional study of the electronic spectra of oligoacenes in the charge states -1, 0, +1, and +2  

E-print Network

We present a systematic theoretical study of the five smallest oligoacenes (naphthalene, anthracene, tetracene, pentacene, and hexacene) in their anionic,neutral, cationic, and dicationic charge states. We used density functional theory (DFT) to obtain the ground-state optimised geometries, and time-dependent DFT (TD-DFT) to evaluate the electronic absorption spectra. Total-energy differences enabled us to evaluate the electron affinities and first and second ionisation energies, the quasiparticle correction to the HOMO-LUMO energy gap and an estimate of the excitonic effects in the neutral molecules. Electronic absorption spectra have been computed by combining two different implementations of TD-DFT: the frequency-space method to study general trends as a function of charge-state and molecular size for the lowest-lying in-plane long-polarised and short-polarised $\\pi\\to\\pi^\\star$ electronic transitions, and the real-time propagation scheme to obtain the whole photo-absorption cross-section up to the far-UV....

Malloci, G; Cappellini, G; Joblin, C

2007-01-01

352

Augmenting Ridge Curves with Minutiae Triplets for Fingerprint Indexing  

E-print Network

Augmenting Ridge Curves with Minutiae Triplets for Fingerprint Indexing Arun Ross and Rajiv, Morgantown, WV 26506 ABSTRACT Given a query fingerprint, the goal of indexing is to identify and retrieve a set of candidate fingerprints from a large database in order to determine a possible match

Ross, Arun Abraham

353

Triplets where monozygotic siblings are concordant for arson.  

PubMed

Triplets are described where the two genetically identical brothers are arsonists and both have sociopathic personality disorder rated using the Personality Assessment Schedule. The third, non-identical brother has not committed arson and does not have a personality disorder. PMID:8264371

Jenaway, A; Swinton, M

1993-10-01

354

Singlet and triplet polaron relaxation in doubly charged self-assembled quantum dots  

NASA Astrophysics Data System (ADS)

Polaron relaxation in self-assembled InAs/GaAs quantum dot samples containing 2 electrons per dot is studied using far-infrared, time-resolved pump probe measurements for transitions between the s-like ground and p-like first excited conduction band states. Spin flip transitions between singlet and triplet states are observed experimentally in the decay of the absorption bleaching, which shows a clear biexponential dependence. The initial fast decay (~30 ps) is associated with the singlet polaron decay, while the decay component with the longer time constant (~5 ns) corresponds to the excited state triplet lifetime. The results are explained by considering the intrinsic Dresselhaus spin orbit interaction, which induces spin flip transitions by acoustic phonon emission or phonon anharmonicity. We have calculated the spin flip decay times, and good agreement is obtained between the experiment and the simulation of the pump probe signal. Our results demonstrate the importance of spin-mixing effects for intraband energy relaxation in InAs/GaAs quantum dots.

Grange, T.; Zibik, E. A.; Ferreira, R.; Bastard, G.; Carpenter, B. A.; Phillips, P. J.; Stehr, D.; Winnerl, S.; Helm, M.; Steer, M. J.; Hopkinson, M.; Cockburn, J. W.; Skolnick, M. S.; Wilson, L. R.

2007-08-01

355

Novel triplet repeat containing genes in human brain: Cloning, expression, and length polymorphisms  

Microsoft Academic Search

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

Shi Hua Li; R. L. Margolis; C. A. Ross; M. G. McInnis; S. E. Antonarakis

1993-01-01

356

Unstable expansion of triplet repeats as a new disease mechanism for neurodegenerative diseases  

Microsoft Academic Search

Conclusion As discussed in the present review, many challenging issues regarding the molecular mechanisms of neurodegeneration are associated with investigation of triplet repeat diseases. Since the molecular structures of the causative genes for triplet repeat diseases have been fully elucidated, triplet repeat diseases no doubt offer the best model systems to investigate the pathophysiology of neurodegenerative diseases, and it is

Shoji Tsuji

1996-01-01

357

Examining the potential role of DNA polymerases ? and ? in triplet repeat instability in yeast  

Microsoft Academic Search

Triplet repeats undergo frequent mutations in human families afflicted with certain neurodegenerative diseases and also in model organisms. Although the molecular mechanisms of triplet repeat instability are still being identified, it is likely that aberrant DNA synthesis plays an important role. Many DNA polymerases stall at triplet repeat sequences, probably due to the adoption of unusual DNA secondary structures. One

Michael J Dixon; Robert S Lahue

2002-01-01

358

AN STIS ATLAS OF Ca II TRIPLET ABSORPTION LINE KINEMATICS IN GALACTIC NUCLEI  

SciTech Connect

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.

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

359

Ground and excited state properties of carbazole-based dyads: correlation with their respective absorption and fluorescence spectra  

Microsoft Academic Search

The ground and excited states of covalently linked carbazole-based dimers were investigated theoretically and experimentally. Geometry optimizations of the ground state of N,N?-diethyl-2,2?-bicarbazole (CC), 2-(N-ethylcarbazol-2-yl)thiophene (CT), and 2-(N-ethylcarbazol-2-yl)furan (CF) were carried out at the restricted Hartree–Fock level (RHF\\/6-31G*). It is found that CC and CT are nonplanar in their ground electronic states (S0), whereas CF is completely planar in the

Michel Belletête; Mélanie Bédard; Mario Leclerc; Gilles Durocher

2004-01-01

360

Polarized x-ray absorption spectra of La{sub 1-x}Sr{sub 1+x}MnO{sub 4}: Electronic state of Mn atoms  

SciTech Connect

We have measured polarized x-ray-absorption near-edge structure and extended x-ray-absorption fine structure spectra at the Mn K edge on La{sub 1-x}Sr{sub 1+x}MnO{sub 4} samples with x=0, 0.3, and 0.5 at different temperatures from 50 K up to 300 K. Both fluorescence and total electron yield modes were used for polarized measurements, whereas nonpolarized absorption spectra have also been recorded in transmission mode on powder samples for x=0, 0.3, 0.45, 0.5, and 0.55. The experiment discards the presence of distinct Mn{sup 3+}/Mn{sup 4+} integer valence states for any of the mixed-valence samples (x=0.3,0.5) in the whole temperature range. The local structure (geometrical and electronic) around the Mn atom is anisotropic in all samples. Moreover, there is no significant change in the Mn local geometric and electronic structure of compounds with 0.45{<=}x{<=}0.55 crossing the charge-ordering transition (T{sub CO}=230 K). The anisotropy in the absorption spectra is then explained in terms of the tetragonal distortion of the MnO{sub 6} octahedron. It decreases as x increases, the oxygen environment being nearly isotropic for La{sub 0.5}Sr{sub 1.5}MnO{sub 4}. Anisotropy is also observed at the prepeaks. The intensity of the in-plane structures strongly increases with the Sr content, indicating that the doped holes mainly go into the ab plane. We conclude that the electronic state of Mn atoms can be only described in terms of an intermediate valence, even for anisotropic samples such as two-dimensional La-Sr manganites.

Herrero-Martin, Javier; Garcia, Joaquin; Subias, Gloria; Blasco, Javier; Sanchez, Maria Concepcion [Instituto de Ciencia de Materiales de Aragon, Departamento de Fisica de la Materia Condensada, CSIC-Universidad de Zaragoza, Pedro Cerbuna 12, 50009 Zaragoza (Spain)

2005-08-15

361

Optical and time-resolved electron paramagnetic resonance studies of the excited states of a UV-B absorber (4-methylbenzylidene)camphor.  

PubMed

The excited states of UV-B absorber (4-methylbenzylidene)camphor (MBC) have been studied through measurements of UV absorption, phosphorescence, triplet-triplet (T-T) absorption, and steady-state and time-resolved electron paramagnetic resonance spectra in ethanol. The energy level and lifetime of the lowest excited triplet (T(1)) state of MBC were determined. The energy level of the T(1) state of MBC is much lower than that of photolabile 4-tert-butyl-4'-methoxydibenzoylmethane. The weak phosphorescence and strong time-resolved EPR signals, and T-T absorption band of MBC were observed. These facts suggest that the significant proportion of the lowest excited singlet (S(1)) molecules undergoes intersystem crossing to the T(1) state and the deactivation process from the T(1) state is predominantly radiationless. The quantum yields of singlet oxygen production by MBC determined by time-resolved near-IR luminescence measurements are 0.05 ± 0.01 and 0.06 ± 0.01 in ethanol and in acetonitrile, respectively. The photostability of MBC arises from the (3)??* character in the T(1) state. The zero-field splitting parameters in the T(1) state are D = 0.0901 cm(-1) and E = -0.0498 cm(-1). The sublevel preferentially populated by intersystem crossing is T(y) (y close to in-plane short axis and to the C?O direction). PMID:23320917

Kikuchi, Azusa; Shibata, Kenji; Kumasaka, Ryo; Yagi, Mikio

2013-02-21

362

High-resolution solid-state 13C CP MAS NMR spectra of some ?-cyclodextrin inclusion complexes with nitriles  

NASA Astrophysics Data System (ADS)

?-cyclodextrin inclusion complexes of 3-aminobenzonitrile, 4-aminobenzonitrile, and adamantane-1-carbonitrile were studied by means of high-resolution solid-state CP MAS 13C NMR spectroscopy. The interactions between the host and guest molecules are discussed.

Okazaki, M.; McDowell, C. A.

1983-11-01

363

Narrow chaotic compound autoionizing states in atomic spectra V. V. Flambaum, A. A. Gribakina, and G. F. Gribakin  

E-print Network

. This behavior follows from simple combinatorial consideration, and is realized in excited states of rare- mentalists see, e.g., 2 and 3 , where the first observation of Rydberg series in any actinide was made for U

Gribakin, Gleb

364

Electronic density of states and the x-ray photoelectron spectra of the valence band of Cu-Pd alloys  

Microsoft Academic Search

We present self-consistent-field Korringa-Kohn-Rostoker coherent-potential-approximation calculations of the electronic density of states of random Cu\\/sub c\\/Pd\\/sub 1-c\\/ alloys. We find strong hybridization of the palladium d bands with the copper d bands over the entire concentration range. We do not obtain a palladium virtual bound state for the copper-rich alloys and therefore contradict the interpretation generally placed on valence-band x-ray

H. Winter; P. J. Durham; W. M. Temmerman; G. M. Stocks

1986-01-01

365

Simulating one-photon absorption and resonance Raman scattering spectra using analytical excited state energy gradients within time-dependent density functional theory  

SciTech Connect

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.

Silverstein, Daniel W.; Govind, Niranjan; van Dam, Hubertus JJ; Jensen, Lasse

2013-12-10

366

Utilizing Afterglow Magnetization from Cross-Polarization Magic-Angle-Spinning Solid-State NMR Spectroscopy to Obtain Simultaneous Heteronuclear Multidimensional Spectra  

PubMed Central

The time required for data acquisition and subsequent spectral assignment are limiting factors for determining biomolecular structure and dynamics using solid state NMR spectroscopy. While strong magnetic dipolar couplings give rise to relatively broad spectra lines, the couplings also mediate the coherent magnetization transfer via the Hartmann Hahn cross polarization (HH-CP) experiment. This mechanism is used in nearly all backbone assignment experiments for carrying out polarization transfer between 1H, 15N, and 13C. In this Article, we describe a general spectroscopic approach to use the residual or afterglow magnetization from the 15N to 13C selective HH-CP experiment to collect a second multidimensional heteronuclear dataset. This approach allowed for the collection of two multidimensional (2D NCA and NCO or 3D NCACX and NCOCX) datasets at the same time. These experiments were performed using instrumentation available on all standard solid state NMR spectrometers configured for magic angle spinning and were demonstrated on uniformly [13C,15N] and [1,3-13C] glycerol labeled ubiquitin. This method is compatible with several other sensitivity enhancement experiments and can be used as an isotopic filtering tool to reduce the spectral complexity and decrease the time needed for assigning spectra. PMID:22582831

Banigan, James R.; Traaseth, Nathaniel J.

2012-01-01

367

Automatic stellar spectra parameterisation in the IR Ca ii triplet region  

Microsoft Academic Search

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

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

2011-01-01

368

Einstein Observatory SSS and MPC observations of the complex X-ray spectra of Seyfert galaxies. [Solid State Spectrometer and Monitor Proportional Counter  

NASA Technical Reports Server (NTRS)

The X-ray spectra of 25 Seyfert galaxies measured with the Solid State Spectrometer on the Einstein Observatory have been investigated. This new investigation utilizes simultaneous data from the Monitor Proportional Counter, and automatic correction for systematic effects in the Solid State Spectrometer which were previously handled subjectively. It is found that the best-fit single-power-law indices generally agree with those previously reported, but that soft excesses of some form are inferred for about 48 percent of the sources. One possible explanation of the soft excess emission is a blend of soft X-ray lines, centered around 0.8 keV. The implications of these results for accretion disk models are discussed.

Turner, T. J.; Weaver, K. A.; Mushotzky, R. F.; Holt, S. S.; Madejski, G. M.

1991-01-01

369

Atomic Spectra  

NSDL National Science Digital Library

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.

Nave, Carl R.

2010-03-12

370

Atomic Spectra  

NSDL National Science Digital Library

This well-illustrated page from Hyperphysics contains the light emitted by several elements and their respective spectra as well. 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.

Nave, Carl R.

2007-12-20

371

Atomic Spectra  

NSDL National Science Digital Library

In this Flash animation the user can view the atomic emission spectra (400-700nm) of eight different elements. A dragable marker allows the user to approximate the wavelength of the various spectral lines. The effect of resolution can be examined in the sodium spectrum in the region 550-600nm.

372

Nucleon, {Delta}, and {Omega} excited state spectra in N{sub f}=2+1 lattice QCD  

SciTech Connect

The energies of the excited states of the nucleon, {Delta}, and {Omega} are computed in lattice QCD, using two light quarks and one strange quark on anisotropic lattices. The 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.

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

373

Entanglement spectra of the q-deformed Affleck-Kennedy-Lieb-Tasaki model and matrix product states  

E-print Network

We exactly calculate the reduced density matrix of matrix product states (MPS). Our compact result enables one to perform analytic studies of entanglement in MPS. In particular, we consider the MPS ground states of two anisotropic spin chains. One is a q-deformed Affleck-Kennedy-Lieb-Tasaki (AKLT) model and the other is a general spin-1 quantum antiferromagnet with nearest-neighbor interactions. Our analysis shows how anisotropy affects entanglement on different continuous parameter manifolds. We also construct an effective boundary spin model that describes a block of spins in the ground state of the q-deformed AKLT Hamiltonian. The temperature of this effective model is given in terms of the deformation parameter q.

Raul A. Santos; Francis N. C. Paraan; Vladimir E. Korepin; Andreas Klümper

2011-12-02

374

Detection of distinct power spectra in soft and hard X-ray bands in the hard state of GRS 1915+105  

NASA Astrophysics Data System (ADS)

The well-known black hole X-ray binary GRS 1915+105 is a unique source in the sense that it cannot be classified within the standard picture of black hole binary states. In this work, we study archival XMM-Newton observations taken between 2003 and 2004 of the ? variability class of GRS 1915+105, which corresponds to the hard state in the standard black hole X-ray binary state classification. The crucial point of our study is that by using XMM-Newton data, we can access the variability below 3 keV, an energy range that is not covered with RXTE. We focus on the study of the power spectral shape in the soft and hard X-ray band, in light of our work done with Swift on MAXI J1659-152. In the hard band (above 2.5 keV), power density spectra consist of band-limited noise and quasi-periodic oscillations, corresponding to the power spectral shape seen in the hard or intermediate state, while in the soft band the averaged power density spectrum is consistent with a power-law noise, corresponding to the power spectral shape usually seen in the soft state. The coexisting of two different power spectral shapes in the soft and hard band, where the soft-band power spectrum is dominated by a power-law noise, is consistent with MAXI J1659-152, and confirms the energy dependence of power spectral states. Our additional spectral analysis shows that the disc component does contribute to the soft-band flux. These findings support that the observed black hole power spectral state depends on which spectral component we are looking at, which implies that power spectral analysis is probably a more sensitive method than spectral modelling to trace the emergence of the disc component in the hard or intermediate state.

Stiele, H.; Yu, W.

2014-06-01

375

Resonant energy transfer of triplet excitons from pentacene to PbSe nanocrystals  

NASA Astrophysics Data System (ADS)

The efficient transfer of energy between organic and inorganic semiconductors is a widely sought after property, but has so far been limited to the transfer of spin-singlet excitons. Here we report efficient resonant-energy transfer of molecular spin-triplet excitons from organic semiconductors to inorganic semiconductors. We use ultrafast optical absorption spectroscopy to track the dynamics of triplets, generated in pentacene through singlet exciton fission, at the interface with lead selenide (PbSe) nanocrystals. We show that triplets transfer to PbSe rapidly (<1 ps) and efficiently, with 1.9 triplets transferred for every photon absorbed in pentacene, but only when the bandgap of the nanocrystals is close to resonance (±0.2 eV) with the triplet energy. Following triplet transfer, the excitation can undergo either charge separation, allowing photovoltaic operation, or radiative recombination in the nanocrystal, enabling luminescent harvesting of triplet exciton energy in light-emitting structures.

Tabachnyk, Maxim; Ehrler, Bruno; Gélinas, Simon; Böhm, Marcus L.; Walker, Brian J.; Musselman, Kevin P.; Greenham, Neil C.; Friend, Richard H.; Rao, Akshay

2014-11-01

376

Resonant energy transfer of triplet excitons from pentacene to PbSe nanocrystals.  

PubMed

The efficient transfer of energy between organic and inorganic semiconductors is a widely sought after property, but has so far been limited to the transfer of spin-singlet excitons. Here we report efficient resonant-energy transfer of molecular spin-triplet excitons from organic semiconductors to inorganic semiconductors. We use ultrafast optical absorption spectroscopy to track the dynamics of triplets, generated in pentacene through singlet exciton fission, at the interface with lead selenide (PbSe) nanocrystals. We show that triplets transfer to PbSe rapidly (<1 ps) and efficiently, with 1.9 triplets transferred for every photon absorbed in pentacene, but only when the bandgap of the nanocrystals is close to resonance (±0.2 eV) with the triplet energy. Following triplet transfer, the excitation can undergo either charge separation, allowing photovoltaic operation, or radiative recombination in the nanocrystal, enabling luminescent harvesting of triplet exciton energy in light-emitting structures. PMID:25282509

Tabachnyk, Maxim; Ehrler, Bruno; Gélinas, Simon; Böhm, Marcus L; Walker, Brian J; Musselman, Kevin P; Greenham, Neil C; Friend, Richard H; Rao, Akshay

2014-11-01

377

Two-axis control of a singlet-triplet qubit with an integrated micromagnet  

PubMed Central

The qubit is the fundamental building block of a quantum computer. We fabricate a qubit in a silicon double-quantum dot with an integrated micromagnet in which the qubit basis states are the singlet state and the spin-zero triplet state of two electrons. Because of the micromagnet, the magnetic field difference ?B between the two sides of the double dot is large enough to enable the achievement of coherent rotation of the qubit’s Bloch vector around two different axes of the Bloch sphere. By measuring the decay of the quantum oscillations, the inhomogeneous spin coherence time T2* is determined. By measuring T2* at many different values of the exchange coupling J and at two different values of ?B, we provide evidence that the micromagnet does not limit decoherence, with the dominant limits on T2* arising from charge noise and from coupling to nuclear spins. PMID:25092298

Wu, Xian; Ward, D. R.; Prance, J. R.; Kim, Dohun; Gamble, John King; Mohr, R. T.; Shi, Zhan; Savage, D. E.; Lagally, M. G.; Friesen, Mark; Coppersmith, S. N.; Eriksson, M. A.

2014-01-01

378

Accurate calculations of geometries and singlet-triplet energy differences for active-site models of [NiFe] hydrogenase.  

PubMed

We have studied the geometry and singlet-triplet energy difference of two mono-nuclear Ni(2+) models related to the active site in [NiFe] hydrogenase. Multiconfigurational second-order perturbation theory based on a complete active-space wavefunction with an active space of 12 electrons in 12 orbitals, CASPT2(12,12), reproduces experimental bond lengths to within 1 pm. Calculated singlet-triplet energy differences agree with those obtained from coupled-cluster calculations with single, double and (perturbatively treated) triple excitations (CCSD(T)) to within 12 kJ mol(-1). For a bimetallic model of the active site of [NiFe] hydrogenase, the CASPT2(12,12) results were compared with the results obtained with an extended active space of 22 electrons in 22 orbitals. This is so large that we need to use restricted active-space theory (RASPT2). The calculations predict that the singlet state is 48-57 kJ mol(-1) more stable than the triplet state for this model of the Ni-SIa state. However, in the [NiFe] hydrogenase protein, the structure around the Ni ion is far from the square-planar structure preferred by the singlet state. This destabilises the singlet state so that it is only ?24 kJ mol(-1) more stable than the triplet state. Finally, we have studied how various density functional theory methods compare to the experimental, CCSD(T), CASPT2, and RASPT2 results. Semi-local functionals predict the best singlet-triplet energy differences, with BP86, TPSS, and PBE giving mean unsigned errors of 12-13 kJ mol(-1) (maximum errors of 25-31 kJ mol(-1)) compared to CCSD(T). For bond lengths, several methods give good results, e.g. TPSS, BP86, and M06, with mean unsigned errors of 2 pm for the bond lengths if relativistic effects are considered. PMID:24647807

Delcey, Mickaël G; Pierloot, Kristine; Phung, Quan M; Vancoillie, Steven; Lindh, Roland; Ryde, Ulf

2014-05-01

379

Changes in EEG power spectra and behavioral states in rats exposed to the acetylcholinesterase inhibitor chlorpyrifos and muscarinic agonist oxotremorine  

Microsoft Academic Search

Organophosphates (OPs) inhibit acetylcholinesterase (AChE) activity causing cholinergic stimulation in the central nervous system (CNS). Cholinergic systems are crucial in electroencephalogram (EEG) generation and regulation of behavior; however, little is known about how OP exposure affects the EEG and behavioral states. We recorded EEG, core temperature and motor activity before and after exposure to the OP pesticide chlorpyrifos (CHP) in

Olga A Timofeeva; Christopher J Gordon

2001-01-01

380

Steady-state spectra, current, and stability diagram of a quantum dot: A nonequilibrium variational cluster approach  

NASA Astrophysics Data System (ADS)

We calculate steady-state properties of a strongly correlated quantum dot under voltage bias by means of nonequilibrium cluster perturbation theory and the nonequilibrium variational cluster approach, respectively. Results for the steady-state current are benchmarked against data from accurate matrix product state based time evolution. We show that for low to medium interaction strength, nonequilibrium cluster perturbation theory already yields good results, while for higher interaction strength the self-consistent feedback of the nonequilibrium variational cluster approach significantly enhances the accuracy. We report the current-voltage characteristics for different interaction strengths. Furthermore we investigate the nonequilibrium local density of states of the quantum dot and illustrate that within the variational approach a linear splitting and broadening of the Kondo resonance is predicted which depends on interaction strength. Calculations with applied gate voltage, away from particle-hole symmetry, reveal that the maximum current is reached at the crossover from the Kondo regime to the doubly occupied or empty quantum dot. Obtained stability diagrams compare very well to recent experimental data [A. V. Kretinin , Phys. Rev. BPRBMDO1098-012110.1103/PhysRevB.84.245316 84, 245316 (2011)].

Nuss, Martin; Heil, Christoph; Ganahl, Martin; Knap, Michael; Evertz, Hans Gerd; Arrigoni, Enrico; von der Linden, Wolfgang

2012-12-01

381

The X-ray spectra of the flaring and quiescent states of YZ CMi observed by XMM-Newton  

NASA Astrophysics Data System (ADS)

We analyse the X-ray spectrum of the active late-type star YZ CMi (M4.5V); for quiescent as well as active stages, we derive emission measure (EM) distributions, elemental abundances, and electron temperatures and densities, which are in turn used to estimate flare loop lengths as well as coronal magnetic field strengths. YZ CMi was observed in the wavelength range 1-40 Å by the X-ray detectors RGS, EPIC-MOS and EPIC-pn onboard XMM-Newton. Some flares occurred during the observation. We perform a multi-temperature fit and model the differential EM of both the flaring and the quiescent parts of the spectrum and derive the coronal temperature distribution, EMs, and elemental abundances of the flaring and quiescent states. The observed temperature covers a range from about 1.3 to 42 MK. The total volume EM in this temperature interval is 13.7+/-.8×1050cm-3 for the quiescent state and 21.7+/-1.4×1050cm-3 for the active state. The abundance pattern in the quiescent state shows some depletion of low first ionization potential (FIP) elements relative to high-FIP elements, indicating the presence of an I(nverse)FIP effect in this active star. No abundance differences between the quiescent and the active states are established. Based on the X-ray light curves in combination with the temperature, density and EM, the coronal magnetic field strength at flare-site is found to be between 50 and 100 G and the flaring loop lengths are estimated to be in the range of 5 -13 × 109 cm.

Raassen, A. J. J.; Mitra-Kraev, U.; Güdel, M.

2007-08-01

382

78 FR 35658 - Spectra Energy Corp., Application for a New or Amended Presidential Permit  

Federal Register 2010, 2011, 2012, 2013

...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...

2013-06-13

383

Triplet Nodeless Superconductivity Scenario in the Quasi-One-Dimensional Layered Conductor Li0.9Mo6O17  

NASA Astrophysics Data System (ADS)

We solve a theoretical problem about the upper critical magnetic field, parallel to a conducting axis of a layered quasi-one-dimensional superconductor. In particular, we consider the case, where triplet superconducting order parameter is not sensitive to the Pauli destructive effects against superconductivity and has no zeros on two quasi-one-dimensional pieces of the Fermi surface. We demonstrate [1] that in this case the orbital destructive effects against superconductivity can destroy superconducting state at magnetic fields much higher than the so-called Clogston-Chandrasekhar paramagnetic limit. Comparison of our theoretical results with the very recent experimental data [2] is in favor of a triplet superconducting pairing in the layered quasi-one-dimensional superconductor Li0.9Mo6O17.[4pt] [1] A.G. Lebed and O. Sepper, Phys. Rev. Lett., submitted.[0pt] [2] J.-F. Mercure et al., Phys. Rev. Lett. 108, 187003 (2012).

Lebed, Andrei; Sepper, Otar

2013-03-01

384

atomic spectra 1 Atomic Spectra  

E-print Network

. Eisberg and Resnick: Quantum Physics of Atoms, Molecules, Solids, Nuclei and Particles, pp. 95-119, p286 Physics, pp. 88-93 (Rutherford nuclear model), 93-106 (atomic structure and electron spectra) 2. D. W. Preston and E. R. Dietz: The Art of Experimental Physics, pp. 397- 399, resolution of optical instruments

Glashausser, Charles

385

HEAT EXCHANGER DESIGN STUDIES FOR AN LHC INNER TRIPLET UPGRADE  

SciTech Connect

A luminosity upgrade of the CERN Large Hadron Collider (LHC) is planned to coincide with the expected end of life of the existing inner triplet quadrupole magnets. The upgraded inner triplet will have much larger heat loads to be removed from the magnets by the cryogenics system. A number of cryogenics design studies have been completed under the LHC Accelerator Research Program (LARP), including investigations of required heat exchanger characteristics to transfer this heat from the pressurized He II bath to the saturated He II system. This paper discusses heat exchangers both external to the magnet cold mass and internal to the magnet cold mass. A possible design for a heat exchanger external to the magnet cold mass is also presented.

Rabehl, R. J.; Huang, Y. [Fermi National Accelerator Laboratory Batavia, Illinois, 60510 (United States)

2008-03-16

386

Recognition of hypermethylated triplet repeats in vitro by cationic nanoparticles  

NASA Astrophysics Data System (ADS)

Genomic DNA contains many higher-order structural deviations from the Watson-Crick global average. The massive expansion and hypermethylation of the duplex triplet repeat (CCG)n(CGG)n has characteristic higher-order structures that are associated with the fragile X syndrome. We have used luminescent mineral nanoparticles of protein-sized cadmium sulfide in optical assays to detect anomalous DNA structures. The photoluminescence of these particles is sensitive to the presence and nature of adsorbates. We previously found that our nanoparticles bind the fragile X repeat well but do not bind to normal double-helical DNA. In this study, we have determined that these particles are also able to detect the hypermethylated forms of these triplet repeats. Therefore, these nanoparticles may form the basis for future optical assays of higher-order DNA structures, especially those associated with human disease.

Gearheart, Latha A.; Caswell, Kimberlyn; Murphy, Catherine J.

2001-04-01

387

Recognition of hypermethylated triplet repeats in vitro by cationic nanoparticles  

Microsoft Academic Search

Genomic DNA contains many higher-order structural deviations from the Watson-Crick global average. The massive expansion and hypermethylation of the duplex triplet repeat (CCG)n(CGG)n has characteristic higher-order structures that are associated with the fragile X syndrome. We have used luminescent mineral nanoparticles of protein-sized cadmium sulfide in optical assays to detect anomalous DNA structures. The photoluminescence of these particles is sensitive

Latha A. Gearheart; Kimberlyn Caswell; Catherine J. Murphy

2001-01-01

388

Conservative management of triplet pregnancy after delivery of one foetus.  

PubMed

This paper intends to demonstrate that the conservative management of triplet pregnancy after delivery of one foetus is a feasible and reasonable approach. Three cases of triplet pregnancy with successful conservative management after miscarriage of one foetus, are presented and compared with cases in the literature. The route of delivery, as well as the role of tocolysis, cerclage, prophylactic antibiotic therapy and corticosteroids are discussed. Guidelines for conservative treatment are proposed. The deliveries of our three pregnancies were delayed by 63, 44 and 22 days respectively. Foetal and neonatal evolution are normal in five of the remaining foetuses. Only one intrauterine death is observed. No maternal complications with sequelae are reported. After abortion of the first triplet, contractions often persist and the birth of the two remaining foetuses may be unavoidable. Nevertheless, in our experience, confirmed by some reports in the literature, prolongation of the pregnancy after expulsion of the first foetus is possible. It can be achieved by cervical cerclage associated with tocolytic and antibiotic therapy. This management is not associated with significantly increased foetal-maternal morbidity. PMID:10918617

Biard, J M; Bernard, P; Thomas, K; Hubinont, C

2000-06-01

389

Detection change points of triplet periodicity of gene.  

PubMed

The triplet periodicity (TP) is a distinguished property of protein coding sequences. There are complex genes with more than one TP type along their sequence. We say that these genes contain a triplet periodicity change point. The aim of the work is to find all genes that contain TP change point and attempt to compare the positions of change point in genes with known biological data. We have developed a mathematical method to identify triplet periodicity changes along a sequence. We have found 311,221 genes with the TP change point in the KEGG/Genes database (version 48). It is about 8% from the total database volume (4013150). We showed that the repetitive sequences are not the only cause of such events. We suppose that the TP change point may indicate a fusion of genes or domains. We performed BLAST analysis to find potential ancestral genes for the parts of genes with TP change point. As a result we found that in 131323 cases sequences with TP change point have proper similarities for one or both parts. The relationship between TP change point and the fusion events in genes is discussed. The program realization of the method is available by request to authors. PMID:21982972

Suvorova, Yulia M; Rudenko, Valentina M; Korotkov, Eugene V

2012-01-01

390

Supersymmetric Custodial Higgs Triplets and the Breaking of Universality  

E-print Network

Higgs triplet models are known to have difficulties obtaining agreement with electroweak precision data and in particular constraints on the $\\rho$ parameter. Either a global $SU(2)_L \\otimes SU(2)_R$ symmetry has to be imposed on the scalar potential at the electroweak scale, as done in the well-known Georgi-Machacek (GM) model, or the triplet vacuum expectation values must be very small. We construct a supersymmetric model that can satisfy constraints on the $\\rho$ parameter, even if these two conditions are not fulfilled. We supersymmetrize the GM model by imposing the $SU(2)_L \\otimes SU(2)_R$ symmetry at a scale $\\mathcal M$, which we argue should be at or above the messenger scale, where supersymmetry breaking is transmitted to the observable sector. We show that scales $\\mathcal M$ well above 100 TeV and sizable contributions from the triplets to electroweak symmetry breaking can be comfortably accommodated. We discuss the main phenomenological properties of the model and demonstrate that the departure from custodial symmetry at the electroweak scale, due to radiative breaking, can show up at the LHC as a deviation in the `universal' relation for the Higgs couplings to $WW$ and $ZZ$. As a by-product of supersymmetry, we also show that one can easily obtain both large tree-level \\emph{and} one loop corrections to the Higgs mass. This allows for stops that can be significantly lighter and with smaller mixing than those needed in the MSSM.

Mateo Garcia-Pepin; Stefania Gori; Mariano Quiros; Roberto Vega; Roberto Vega-Morales; Tien-Tien Yu

2014-09-19

391

Supersymmetric Custodial Higgs Triplets and the Breaking of Universality  

E-print Network

Higgs triplet models are known to have difficulties obtaining agreement with electroweak precision data and in particular constraints on the $\\rho$ parameter. Either a global $SU(2)_L \\otimes SU(2)_R$ symmetry has to be imposed on the scalar potential at the electroweak scale, as done in the well-known Georgi-Machacek (GM) model, or the triplet vacuum expectation values must be very small. We construct a supersymmetric model that can satisfy constraints on the $\\rho$ parameter, even if these two conditions are not fulfilled. We supersymmetrize the GM model by imposing the $SU(2)_L \\otimes SU(2)_R$ symmetry at a scale $\\mathcal M$, which we argue should be at or above the messenger scale, where supersymmetry breaking is transmitted to the observable sector. We show that scales $\\mathcal M$ well above 100 TeV and sizable contributions from the triplets to electroweak symmetry breaking can be comfortably accommodated. We discuss the main phenomenological properties of the model and demonstrate that the departure...

Garcia-Pepin, Mateo; Quiros, Mariano; Vega, Roberto; Vega-Morales, Roberto; Yu, Tien-Tien

2014-01-01

392

Triplet repeats in transcripts: structural insights into RNA toxicity.  

PubMed

Tandem repeats of various trinucleotide motifs are frequent entities in transcripts, and RNA structures formed by these sequences depend on the motif type and number of reiterations. The functions performed by normal triplet repeats in transcripts are poorly understood, but abnormally expanded repeats of certain types trigger pathogenesis in several human genetic disorders known as the triplet repeat expansion diseases (TREDs). The diseases caused by expanded non-coding CUG and CGG repeats in transcripts include myotonic dystrophy type 1 and fragile X-associated tremor ataxia syndrome. Another group of disorders in which transcripts containing translated CAG repeats play an auxiliary role in pathogenesis include Huntington's disease and several spinocerebellar ataxias. In this review, we gathered existing knowledge regarding the structural features of triplet repeats in transcripts and discussed this in the context of various pathogenic mechanisms assigned to toxic RNA repeats. These mechanisms include aberrant alternative splicing, the inhibition of nuclear transport and export, induction of the innate immune response, alteration of a microRNA biogenesis pathway and abnormal activation of an RNA interference pathway. We also provide ideas for future investigations to reveal further mechanisms of pathogenesis directly triggered by mutant RNA repeats in TREDs. PMID:23052488

Galka-Marciniak, Paulina; Urbanek, Martyna O; Krzyzosiak, Wlodzimierz J

2012-11-01

393

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)

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.

McMillian, W. Wallace; Strow, L. Larrabee; Revercomb, H.; Knuteson, R.; Thompson, A.

2003-01-01

394

THERMAL NEUTRON SPECTRA IN GRAPHITE  

Microsoft Academic Search

A pulsed, high-current, electron linear accelerator is used to excite ; thermal-neutron spectra in a graphite asemmbly. The steady-state energy spectra ; of neutrons are measured at several temperatures by pulsed-beam time-of-flight ; techniques. The measured spectra are compared with theoretical predictions which ; use free- and bound-carbon scattering kernels. The scattering kernel for carbon ; bound in graphite is

D. E. Parks; J. R. Beyster; N. F. Wikner

1962-01-01

395

Abundance gradients in cooling flow clusters: Ginga Large Area Counters and Einstein Solid State Spectrometer spectra of A496, A1795, A2142, and A2199  

NASA Technical Reports Server (NTRS)

We analyze the Ginga Large Area Counters (LAC) and Einstein Solid State Spectrometer (SSS) spectra of four cooling flow clusters, A496, A1795, A2142, and A2199, each of which shows firm evidence of a relatively cool component. The inclusion of such cool spectral components in joint fits of SSS and LAC data leads to somewhat higher global temperatures than are derived from the high-energy LAC data alone. We find little evidence of cool emission outside the SSS field of view. Metal abundances appear to be centrally enhanced in all four clusters, with varying degrees of model dependence and statistical significance: the evidence is statistically strongest for A496 and A2142, somewhat weaker for A2199 and weakest for A1795. We also explore the model dependence in the amount of cold, X-ray-absorbing matter discovered in these clusters by White et al.

White, Raymond E., III; Day, C. S. R.; Hatsukade, Isamu; Hughes, John P.

1994-01-01

396

Fine structure of the spectra of giant pulses from actively Q-switched solid-state lasers with injection of external radiation  

NASA Astrophysics Data System (ADS)

A theoretical and experimental investigation was made of the problem of controlling the mode structure of the spectra of giant pulses from actively Q-switched solid-state lasers by injection of external radiation at a frequency independent of the natural frequencies of the resonator. A marked difference was observed between the spectral kinetic characteristics of giant pulses from neodymium-glass and ruby lasers. On the basis of a comparison with previously established differences in the free-lasing dynamics, an explanation of this observation by nonlinear mode interaction is proposed and confirmed theoretically and experimentally. A method of improving the mode selection efficiency under giant pulse conditions using passive negative feedback is proposed and implemented experimentally using a neodymium-glass laser. Giant pulse generation with a spectral width of <= 5 × 10-4cm-1 and a power of 20 MW was obtained using an actively Q-switched neodymium-glass laser.

Ga?ner, A. V.; Gulev, V. S.; Pivtsov, V. S.; Folin, Kim G.

1980-08-01

397

Two-Dimensional (2+n) Rempi Spectroscopy: State Interactions, Photofragmentations and Energetics of the Hydrogen Halides  

NASA Astrophysics Data System (ADS)

Mass spectra are recorded for one-colour (2 + n) resonance enhanced multiphoton ionization (REMPI) of HX (X = Cl, Br) as a function of resonance excitation energy to obtain two-dimensional REMPI data. Perturbations due to Rydberg to ion-pair state interactions show as line shifts, ion signal intensity variations as well as band width broadenings depending on rotational quantum numbers, J ' . The data allow determination of parameters relevant to the nature and strength of state interactions as well as dissociation and ionization processes. Alterations in X+ and HX+ signal intensities prove to be very useful for spectra assignments. Agust Kvaran, Kristjan Matthiasson and Huasheng Wang, " Two-Dimensional (2+n) Resonance Enhanced Multiphoton Ionization of HCl: State Interactions and Photorupture Channels via Low-Energy Triplet Rydberg States ", J. Chem. Phys., 131(4), 044324, (2009).

Long, Jingming; Wang, Huasheng; Kvaran, Agust

2011-06-01

398

Absorption and Fluorescent Properties of Pyrylium Compounds: II. Spectra and Cross Sections for Absorption from the Ground and Excited States of the Structurally Rearranged Form  

NASA Astrophysics Data System (ADS)

The nonstationary absorption of solutions of 2,4,6-substituted pyrylium salt is studied by the pump-probe method. The solutions in methylene chloride are studied upon picosecond pumping and probing with different time delays. The solutions in methyl ethyl ketone are studied upon pumping and synchronous probing by nanosecond pulses. It is shown that excitation of the initially nonplanar molecule causes its structural rearrangement. As a result, substituent 2 enters into the pyrylium ring plane and two nonstationary conformers are formed that differ in the position of substituent 6. The motion upon structural rearrangement has a small amplitude, and localization of molecular orbitals changes only slightly. The temperature dependence of the nonstationary absorption is studied in the range from 293 to 223 K. The spectra and cross sections are measured for transitions from the S0 and S1 states. In addition, the activation energies and kinetic parameters of the rearrangement in the ground and excited states are determined. Experimental data are compared with theoretical calculations of the transitions from the S1 state. It is shown that a partial flattening of conformer molecules results in the long-wavelength shift of the bands and an increase in the cross sections for transitions localized on a flat part of the molecule and does not change parameters of the band localized on the molecular part that did not change upon the rearrangement but remained nonplanar.

Bonch-Bruevich, A. M.; Gadonas, R.; Kaliteevskaya, E. N.; Krasauskas, V.; Pyalakauskas, A.; Razumova, T. K.; Roshal', A. D.; Tarnovski?, A. N.

2000-11-01

399

Stellar Absorption Lines in the Spectra of Seyfert Galaxies  

E-print Network

We have measured the strengths of Ca II Triplet and Mgb stellar absorption lines in the nuclear and off-nuclear spectra of Seyfert galaxies. These features are diluted to varying degrees by continuum emission from the active nucleus and from young stars. Ca II Triplet strengths can be enhanced if late-type supergiant stars dominate the near-IR light. Thus, objects with strong Ca II Triplet and weak Mgb lines may be objects with strong bursts of star formation. We find that for most of our sample the line strengths are at least consistent with dilution of a normal galaxy spectrum by a power law continuum, in accord with the standard model for AGN. However, for several Seyferts in our sample, it appears that dilution by a power law continuum cannot simultaneously explain strong Ca II Triplet and relatively weak Mgb. Also, these objects occupy the region of the IRAS color-color diagram characteristic of starburst galaxies. In these objects it appears that the optical to near-IR emission is dominated by late-type supergiants produced in a circumnuclear burst of star formation.

Charles Nelson; Mark Whittle

1998-11-03

400

Reaction of HOD+ with NO2: effects of OD and OH stretching, bending, and collision energy on reactions on the singlet and triplet potential surfaces.  

PubMed

Integral cross sections and product recoil velocity distributions were measured for the reaction of HOD(+) with NO(2), in which the HOD(+) reactant was prepared in its ground state and with mode-selective excitation in the 001 (OH stretch), 100 (OD stretch), and 010 (bend) modes. In addition, we measured the 300 K thermal kinetics in a selected ion flow tube reactor and report product branching ratios different from previous measurements. Reaction is found to occur on both the singlet and triplet surfaces with near-unit efficiency. At 300 K, the product branching indicates that triplet ? singlet transitions occur in about 60% of triplet-coupled collisions, which we attribute to long interaction times mediated by complexes on the triplet surface. Because the collision times are much shorter in the beam experiments, the product distributions show no signs of such transitions. The dominant product on the singlet surface is charge transfer. Reactions on the triplet surface lead to NO(+), NO(2)H(+), and NO(2)D(+). There is also charge transfer, producing NO(2)(+) (a(3)B(2)); however, this triplet NO(2)(+) mostly predissociates. The NO(2)H(+)/NO(2)D(+) cross sections peak at low collision energies and are insignificant above ~1 eV due to OH/OD loss from the nascent product ions. The effects of HOD(+) vibration are mode-specific. Vibration inhibits charge transfer, with the largest effect from the bend. The NO(2)H(+)/NO(2)D(+) channels are also vibrationally inhibited, and the mode dependence reveals how energy in different reactant modes couples to the internal energy of the product ions. PMID:21291191

Boyle, Jason M; Bell, David M; Anderson, Scott L; Viggiano, A A

2011-02-24

401

Computational determination of the dominant triplet population mechanism in photoexcited benzophenone.  

PubMed

In benzophenone, intersystem crossing occurs efficiently between the S1(n?*) state and the T1 state of dominant n?* character, leading to excited triplet states after photoexcitation. The transition mechanism between S1(n?*) and T1 is still a matter of debate, despite several experimental studies. Quantum mechanical calculations have been performed in order to assess the relative efficiencies of previously proposed mechanisms, in particular, the direct S1? T1 and indirect S1? T2(??*) ? T1 ones. Multiconfigurational wave function based methods are used to discuss the nature of the relevant states and also to determine minimum energy paths and conical intersections. It is found that the T1 state has a mixed n?*/??* character and that the T2(??*) state acts as an intermediate state between the S1 and T1 states. This result is in line with recent experiments, which suggested a two-step kinetic model to populate the phosphorescent state after photoexcitation [Aloïse et al., J. Phys. Chem. A, 2008, 112, 224-231]. PMID:25340634

Sergentu, Dumitru-Claudiu; Maurice, Rémi; Havenith, Remco W A; Broer, Ria; Roca-Sanjuán, Daniel

2014-12-14

402

Infrared spectra and electronic structures of agostic uranium methylidene molecules.  

PubMed

Through reactions of laser-ablated uranium atoms with methylene halides CH2XY (XY = F2, FCl, and Cl2), a series of new actinide methylidene molecules CH2UF2, CH2UFCl, and CH2UCl2 are formed as the major products. The identification of these complexes has been accomplished via matrix infrared spectra, isotopic substitution, and relativistic density functional calculations of the vibrational frequencies and infrared intensities. Density functional calculations using the generalized gradient approach (PW91) show that these CH2UXY methylidene complexes prefer highly distorted agostic structures rather than the ethylene-like symmetric structures. The calculated agostic angles ([angle]H-C-U) are around 89 degrees for all the three uranium complexes, and the predicted vibrational modes and isotopic shifts agree well with experimental values. Electronic structure calculations reveal that these U(IV) molecules all have strong C=U double bonds in the triplet ground states with 5f (2) configurations. The calculated bond lengths and bond energies indicate that the C=U double bonds are slightly weaker in the fluoride species than in the chloride species because of the radial contraction of the U (6d) orbitals by the inductive effect of the fluorine substituent. The agostic uranium methylidene complexes are compared with analogous transition metal and thorium complexes, which reveal interesting differences in their chemistries. PMID:18237123

Lyon, Jonathan T; Andrews, Lester; Hu, Han-Shi; Li, Jun

2008-03-01

403

Rotational spectra of isotopic species of methyl cyanide, CH3CN, in their ground vibrational states up to terahertz frequencies  

E-print Network

Methyl cyanide is an important trace molecule in star-forming regions. It is one of the more common molecules used to derive kinetic temperatures in such sources. As preparatory work for Herschel, SOFIA, and in particular ALMA we want to improve the rest frequencies of the main as well as minor isotopologs of methyl cyanide. The laboratory rotational spectrum of methyl cyanide in natural isotopic composition has been recorded up to 1.63 THz. Transitions with good signal-to-noise ratio could be identified for CH3CN, (13)CH3CN, CH3(13)CN, CH3C(15)N, CH2DCN, and (13)CH3(13)CN in their ground vibrational states up to about 1.2 THz. The main isotopic species could be identified even in the highest frequency spectral recordings around 1.6 THz. The highest J' quantum numbers included in the fit are 64 for (13)CH3(13)CN and 89 for the main isotopic species. Greatly improved spectroscopic parameters have been obtained by fitting the present data together with previously reported transition frequencies. The present dat...

Müller, Holger S P; Pearson, John C; 10.1051/0004-6361/200912932

2009-01-01

404

Metastable Dark States Enable Ground State Depletion Microscopy of Nitrogen Vacancy  

E-print Network

(triplet or redox) state. In the variant called SSIM (saturable structured illumination microscopy),14Metastable Dark States Enable Ground State Depletion Microscopy of Nitrogen Vacancy Centers with a resolution >10 times beyond the diffraction barrier (Microscopy, color center, diamond

Hell, Stefan W.

405

Sensitive triplet exciton detection in polyfluorene using Pd-coordinated porphyrin.  

PubMed

We developed a sensitive spectroscopic method to probe triplet concentration in thin films of polyfluorene (PF) at room temperature. The energy of photoexcited triplet excitons is transferred to the guest metal-organic complex, meso-tetratolylporphyrin-Pd (PdTPP), and detected as phosphorescent emission. The phosphorescence intensity of PdTPP-PF blends is proportional to the independently measured triplet concentration using photoinduced absorption experiments. The high sensitivity of this method allows room temperature detection of triplet excitons in spin-coated polymer films as thin as 10 nm. We found that the triplet lifetime is independent of PdTPP concentration and therefore this method is nearly non-perturbing for the triplet population. PMID:21731962

Mikhnenko, Oleksandr V; Blom, Paul W M; Loi, Maria Antonietta

2011-08-28

406

Phosphorescence versus Thermally Activated Delayed Fluorescence. Controlling Singlet-Triplet Splitting in Brightly Emitting and Sublimable Cu(I) Compounds.  

PubMed

Photophysical properties of two highly emissive three-coordinate Cu(I) complexes, (IPr)Cu(py2-BMe2) (1) and (Bzl-3,5Me)Cu(py2-BMe2) (2), with two different N-heterocyclic (NHC) ligands were investigated in detail (IPr = 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene; Bzl-3,5Me = 1,3-bis(3,5-dimethylphenyl)-1H-benzo[d]imidazol-2-ylidene; py2-BMe2 = di(2-pyridyl)dimethylborate). The compounds exhibit remarkably high emission quantum yields of more than 70% in the powder phase. Despite similar chemical structures of both complexes, only compound 1 exhibits thermally activated delayed blue fluorescence (TADF), whereas compound 2 shows a pure, yellow phosphorescence. This behavior is related to the torsion angles between the two ligands. Changing this angle has a huge impact on the energy splitting between the first excited singlet state S1 and triplet state T1 and therefore on the TADF properties. In addition, it was found that, in both compounds, spin-orbit coupling (SOC) is particularly effective compared to other Cu(I) complexes. This is reflected in short emission decay times of the triplet states of only 34 ?s (1) and 21 ?s (2), respectively, as well as in the zero-field splittings of the triplet states amounting to 4 cm(-1) (0.5 meV) for 1 and 5 cm(-1) (0.6 meV) for 2. Accordingly, at ambient temperature, compound 1 exhibits two radiative decay paths which are thermally equilibrated: one via the S1 state as TADF path (62%) and one via the T1 state as phosphorescence path (38%). Thus, if this material is applied in an organic light-emitting diode, the generated excitons are harvested mainly in the singlet state, but to a significant portion also in the triplet state. This novel mechanism based on two separate radiative decay paths reduces the overall emission decay time distinctly. PMID:25260042

Leitl, Markus J; Krylova, Valentina A; Djurovich, Peter I; Thompson, Mark E; Yersin, Hartmut

2014-11-12

407

High Intrachain Order Promotes Triplet Formation from Recombination of Long-Lived Polarons in Poly(3-hexylthiophene) J-Aggregate Nanofibers.  

PubMed

Photoluminescence (PL) of single poly(3-hexylthiophene) (P3HT) J-aggregate nanofibers (NFs) exhibits strong quenching under intensity-modulated pulsed excitation. Initial PL intensities (I0) decay to steady-state levels (ISS) typically within ?1-10 ?s, and large quenching depths (I0/ISS >2) are observed for ?70% of these NFs. Similar studies of polymorphic, H-aggregate type P3HT NFs show much smaller PL quenching depths (I0/ISS ?1.2). P3HT chains in J-type NF ?-stacks possess high intrachain order, which has been shown previously to promote the formation of long-lived, delocalized polarons. We propose that these species recombine nongeminately to triplets on time scales of >1 ns. The identity of triplets as the dominant PL quenchers was confirmed by subjecting NFs to oxygen, resulting in an instantaneous loss of triplet PL quenching (I0/ISS ?1). The lower intrachain order in H-type NFs, similar to P3HT thin-film aggregates, localizes excitons and polarons, leading to efficient geminate recombination that suppresses triplet formation at longer time scales. Our results demonstrate the promise of self-assembly strategies to control intrachain ordering within multichromophoric polymeric aggregate assemblies to tune exciton coupling and interconversion processes between different spin states. PMID:25285851

Thomas, Alan K; Garcia, José A; Ulibarri-Sanchez, Jordan; Gao, Jian; Grey, John K

2014-10-28

408

ON THE CONSTANCY OF THE PHOTON INDEX OF X-RAY SPECTRA OF 4U 1728-34 THROUGH ALL SPECTRAL STATES  

SciTech Connect

We present an analysis of the spectral properties observed in X-rays from neutron star X-ray binary 4U 1728-34 during transitions between the low- and high-luminosity states when the electron temperature kT{sub e} of the Compton cloud monotonically decreases from 15 to 2.5 keV. We analyze the transition episodes from this source observed with Beppo SAX and RXTE satellites. We find that the X-ray broadband energy spectra of 4U 1728-34 during all spectral states can be modeled by a combination of a thermal (blackbody-like) component, a Comptonized component (which we herein denote as COMPTB), and a Gaussian component. Spectral analysis using this model provides evidence that the photon power-law index {Gamma} is almost constant ({Gamma} = 1.99 {+-} 0.02) when kT{sub e} changes from 15 to 2.5 keV during these spectral transitions. We explain this quasi-stability of the index {Gamma} by the model in which the spectrum is dominated by the strong thermal Comptonized component formed in the transition layer (TL) between the accretion disk and neutron star surface. The index quasi-stability takes place when the energy release in the TL is much higher than the flux coming to the TL from the accretion disk. Moreover, this index stability effect now established for 4U 1728-34 during spectral evolution of the source was previously suggested for a number of other neutron binaries. This intrinsic property of the neutron star is fundamentally different from that in black hole binary sources for which the index monotonically increases during spectral transition from the low state to the high state and saturates at high values of the mass accretion rate.

Seifina, Elena [Sternberg Astronomical Institute, Moscow State University, Universitetsky Prospect 13, Moscow 119992 (Russian Federation); Titarchuk, Lev, E-mail: seif@sai.msu.ru, E-mail: titarchuk@fe.infn.it, E-mail: lev@milkyway.gsfc.nasa.gov [Dipartimento di Fisica, Universita di Ferrara, Via Saragat 1, I-44100 Ferrara (Italy)

2011-09-10

409

Applications of an Energy Transfer Model to Three Problems in Planetary Regoliths: The Solid-State Greenhouse, Thermal Beaming, and Emittance Spectra  

NASA Technical Reports Server (NTRS)

Several problems of interest in planetary infrared remote sensing are investigated using a new radiative-conductive model of energy transfer in regoliths: the solid-state greenhouse effect, thermal beaming, and reststrahlen spectra. The results of the analysis are as follows: (1) The solid-state greenhouse effect is self-limiting to a rise of a few tens of degrees in bodies of the outer solar system. (2) Non-Lambertian directional emissivity can account for only about 20% of the observed thermal beaming factor. The remainder must have another cause, presumably surface roughness effects. (3) The maximum in a reststrahlen emissivity spectrum does not occur exactly at the Christiansen wavelength where, by definition, the real part of the refractive index equals one, but rather at the first transition minimum in reflectance associated with the transition from particle scattering being dominated by volume scattering to that dominated by strong surface scattering. The transparency feature is at the second transition minimum and does not require the presence of a second band at longer wavelength for its occurance. Subsurface temperature gradients have only a small effect on emissivity bands.

Hapke, Bruce

1996-01-01

410

Triplet repeat length bias and variation in the human transcriptome  

PubMed Central

Length variation in short tandem repeats (STRs) is an important family of DNA polymorphisms with numerous applications in genetics, medicine, forensics, and evolutionary analysis. Several major diseases have been associated with length variation of trinucleotide (triplet) repeats including Huntington's disease, hereditary ataxias and spinobulbar muscular atrophy. Using the reference human genome, we have catalogued all triplet repeats in genic regions. This data revealed a bias in noncoding DNA repeat lengths. It also enabled a survey of repeat-length polymorphisms (RLPs) in human genomes and a comparison of the rate of polymorphism in humans versus divergence from chimpanzee. For short repeats, this analysis of three human genomes reveals a relatively low RLP rate in exons and, somewhat surprisingly, in introns. All short RLPs observed in multiple genomes are biallelic (at least in this small sample). In contrast, long repeats are highly polymorphic and some long RLPs are multiallelic. For long repeats, the chimpanzee sequence frequently differs from all observed human alleles. This suggests a high expansion/contraction rate in all long repeats. Expansions and contractions are not, however, affected by natural selection discernable from our comparison of human-chimpanzee divergence with human RLPs. Our catalog of human triplet repeats and their surrounding flanking regions can be used to produce a cost-effective whole-genome assay to test individuals. This repeat assay could someday complement SNP arrays for producing tests that assess the risk of an individual to develop a disease, or become part of personalized genomic strategy that provides therapeutic guidance with respect to drug response. PMID:19805156

Molla, Michael; Delcher, Arthur; Sunyaev, Shamil; Cantor, Charles; Kasif, Simon

2009-01-01

411

Constraints from LFV processes in the Higgs triplet model  

NASA Astrophysics Data System (ADS)

Constraints from lepton flavor violating processes are translated into lower bounds on {v_? }{m_{{H^{ ± ± }}}} in the Higgs Triplet Model by considering correlations through the neutrino mass matrix. It is shown that ? ? e?, rare ? decays (especially, tau to bar ? ee ), and the muonium conversion can give a more stringent bound on {v_? }{m_{{H^{ ± ± }}}} in some parameter regions than the bound from ? to bar eee which is expected naively to give the most stringent one. We consider the cases of suppressed ? to bar eee not only for CP-conserving sets of phases but also for arbitrary values.

Fukuyama, Takeshi; Sugiyama, Hiroaki; Tsumura, Koji

2010-03-01

412

Triplet exciton abstracts hydrogen from diphenylmethane doped in benzophenone crystal  

NASA Astrophysics Data System (ADS)

When a benzophenone single crystal doped with diphenylmethane in 10(exp -2) mol/mol is irradiated with UV light from a xenon lamp for a few minutes, the emission drastically changes from blue to green. This change has been found to be due to the formation of diphenylmethyl radical through hydrogen abstraction by triplet benzophenone. This provides a means of doping a crystal with an energy acceptor whose concentration can be continuously varied by UV irradiation (photochemical doping). The rate constant for energy transfer is estimated.

Saitow, Ken-Ichi; Endo, Kazuyuki; Katoh, Ryuzi; Kotani, Masahiro

1994-10-01

413

Optical control of the singlet-triplet transition in Rb2  

NASA Astrophysics Data System (ADS)

By controlling nonresonant dynamic Stark shifts it is possible to effectively decouple the intramolecular couplings of simple molecules. We have illustrated this effect in the 1?u1?1?u3 transition in Rb2. The laser scheme implies two important control knobs: the laser frequency, which must be chosen to avoid both single and multiphoton resonances and to select different electronic environments for the singlet and triplet states, and the pulse intensity, which must amplify the asymmetry in the dynamic polarizabilities that allows the decoupling, avoiding undesired strong-pulse effects. The mechanism of the scheme implies not only brute-force energy shifts but also light-induced reshaping of the potentials to avoid the undesired crossings. Quantitative aspects of the method are analyzed by using molecular models of increasing complexity for Rb2.

González-Vázquez, Jesús; Sola, Ignacio R.; Santamaria, Jesus; Malinovsky, Vladimir S.

2006-09-01

414

Optical control of the singlet-triplet transition in Rb2.  

PubMed

By controlling nonresonant dynamic Stark shifts it is possible to effectively decouple the intramolecular couplings of simple molecules. We have illustrated this effect in the 1 (1)Sigma(u)-->1 (3)Pi(u) transition in Rb(2). The laser scheme implies two important control knobs: the laser frequency, which must be chosen to avoid both single and multiphoton resonances and to select different electronic environments for the singlet and triplet states, and the pulse intensity, which must amplify the asymmetry in the dynamic polarizabilities that allows the decoupling, avoiding undesired strong-pulse effects. The mechanism of the scheme implies not only brute-force energy shifts but also light-induced reshaping of the potentials to avoid the undesired crossings. Quantitative aspects of the method are analyzed by using molecular models of increasing complexity for Rb(2). PMID:17014182

González-Vázquez, Jesús; Sola, Ignacio R; Santamaria, Jesus; Malinovsky, Vladimir S

2006-09-28

415

Dynamics of the excited states of [Ir(ppy)2bpy]+ with triple phosphorescence.  

PubMed

We investigated the relaxation dynamics of bis(2-phenylpyridinato-)(2,2'-bipyridine)iridium(III), [Ir(ppy)(2)bpy](+) using the technique of time-resolved spectroscopy. In the visible emission spectra this molecule exhibits triple phosphorescence: displaying blue, green, and orange bands. From the dependence of spectral shifts with polarity of solvent, decay lifetimes, and the results of calculations using time-dependent density functional theory, we assigned these three emitting states to be triplet interligand charge-transfer ((3)LLCT), metal-to-ligand ppy charge transfer ((3)MLCT(ppy)), and metal-to-ligand bpy charge transfer ((3)MLCT(bpy)) states. The blue states were formed promptly after excitation at wavelength 355 nm; the one lying at higher energy decaying with a time coefficient 0.79-2.56 ns is assigned to be a triplet MLCT, and the other at lower energy decaying in 1.5-2.8 ?s is assigned to (3)LLCT(A), A symmetry. This decay time coefficient of (3)LLCT(A) decreases with increasing dielectric constant of the solvent indicating this state mixing of some MLCT character. The green state (3)MLCT(ppy) decays in 0.13-4.8 ns to a nearby intermediate state either (3)MLCT(ppy) or (3)MLCT(bpy). The orange state (3)MLCT(bpy) is coupled to the intermediate state to have a rise time about 0.36-0.84 ns and decays in 425-617 ns. Although many triplet states exist in a small energy range, they couple weakly to display triple emission. All (3)LLCT and (3)MCLT states are coupled to the singlet (1)LLCT manifold directly and/or indirectly and contribute to the emission in the visible range. PMID:20809643

Wu, Shih-Hsiang; Ling, Jung-Wei; Lai, Szu-Hsueh; Huang, Min-Jie; Cheng, Chien Hong; Chen, I-Chia

2010-09-30

416

Self-generation of phase coherence in multiply-coupled triplet system  

NASA Astrophysics Data System (ADS)

We have demonstrated in previous presentations that large amplitude MHD waves observed in the solar wind are not completely phase random (as assumed in quasi-linear theories), but are almost always phase correlated to a certain degree. This presumably is a consequence of nonlinear interaction among the MHD waves. Recently we have developed a method to quantitatively evaluate the phase coherence among waves from a given turbulence time series, via comparison of structure functions of the original data as well as its phase shuffled and phase coherent surrogates (Hada et al., 2003; Koga and Hada, 2003). From a statistical study using Geotail magnetic field data, it is concluded that the phase correlation is almost always non-zero, is enhanced when the turbulence energy is high (nonlinear interaction is strong), and that the waves only within a finite frequency range are responsible for the generation of the phase coherence. In order to understand the physical mechanism of the phase coherence generation, we have constructed a simple model of weak turbulence by coupling multiple triplets, which are the minimum units of nonlinear interaction among the modes (nonlinear interaction of three waves in resonance). According to our numerical simulations, long time statistical behavior of the coupled system critically depends on how the triplets are connected: if the connection is given in such a 'physical' way that the frequency of each mode can be uniquely determined, the system approaches the SOC state as time elapses; otherwise, the system does not evolve to any statistically interesting state. Furthermore, adjacent modes often tend to phase synchronize, as the modes exchange energy (quanta) between them. Implications of the results to the phase coherence detected in the solar wind data will be discussed.

Hada, T.; Nariyuki, Y.

2004-12-01

417

Empirical calibration of the near-IR Ca II triplet - I. The stellar library and index definition  

E-print Network

A new stellar library at the near-IR spectral region developed for the empirical calibration of the Ca II triplet and stellar population synthesis modeling is presented. The library covers the range 8348-9020 Angstrom at 1.5 Angstrom (FWHM) spectral resolution, and consists of 706 stars spanning a wide range in atmospheric parameters. We have defined a new set of near-IR indices, CaT*, CaT and PaT, which mostly overcome the limitations of previous definitions, the former being specially suited for the measurement of the Ca II triplet strength corrected for the contamination from Paschen lines. We also present a comparative study of the new and the previous calcium indices, as well as the corresponding transformations between the different systems. A thorough analysis of the sources of index errors and the procedure to calculate them is given. Finally, index and error measurements for the whole stellar library are provided together with the final spectra.

A. J. Cenarro; N. Cardiel; J. Gorgas; R. F. Peletier; A. Vazdekis; F. Prada

2001-09-10

418

Yet another plasma diagnostic with He-like triplet: Probing energetic electrons behind SNR shocks with ASTRO-H SXS  

NASA Astrophysics Data System (ADS)

We present a new X-ray line diagnostic to probe energetic electrons behind SNR shocks. SNR shocks are believed to be acceleration sites of the Galactic cosmic rays up to knee energy. In the early stage of acceleration, particles must have sufficient energies to cross the shock to enter diffusive shock acceleration. This requires supra-thermal energies for electrons, however, we currently do not know how electrons depart from the thermal pool to attain such energies. Hence observational constraints on the amount and energy distribution of supra-thermal electrons are awaited. Here we propose a new X-ray line diagnostic using the He-like triplet to detect and characterise the energy distribution of supra-thermal electrons. We simulate X-ray spectra of SNR plasma interacting with energetic electrons and find that the forbidden line of the He-like triplet is enhanced via inner-shell ionisation process of Li-like ions. Such an effect can be precisely measured by high-resolution spectroscopy with the coming ASTRO-H SXS instrument.

Sawada, Makoto; Kaastra, Jelle

419

Galaxy triplets in Sloan Digital Sky Survey Data Release 7 - II. A connection with compact groups?  

NASA Astrophysics Data System (ADS)

We analyse a sample of 71 triplets of luminous galaxies derived from the work of O'Mill et al. We compare the properties of triplets and their members with those of control samples of compact groups, the 10 brightest members of rich clusters and galaxies in pairs. The triplets are restricted to have members with spectroscopic redshifts in the range 0.01 ? z ? 0.14 and absolute r-band luminosities brighter than Mr = -20.5. For these member galaxies, we analyse the stellar mass content, the star formation rates, the Dn(4000) parameter and (Mg - Mr) colour index. Since galaxies in triplets may finally merge in a single system, we analyse different global properties of these systems. We calculate the probability that the properties of galaxies in triplets are strongly correlated. We also study total star formation activity and global colours, and define the triplet compactness as a measure of the percentage of the system total area that is filled by the light of member galaxies. We concentrate in the comparison of our results with those of compact groups to assess how the triplets are a natural extension of these compact systems. Our analysis suggests that triplet galaxy members behave similarly to compact group members and galaxies in rich clusters. We also find that systems comprising three blue, star-forming, young stellar population galaxies (blue triplets) are most probably real systems and not a chance configuration of interloping galaxies. The same holds for triplets composed of three red, non-star-forming galaxies, showing the correlation of galaxy properties in these systems. From the analysis of the triplet as a whole, we conclude that, at a given total stellar mass content, triplets show a total star formation activity and global colours similar to compact groups. However, blue triplets show a high total star formation activity with a lower stellar mass content. From an analysis of the compactness parameter of the systems we find that light is even more concentrated in triplets than in compact groups. We propose that triplets composed of three luminous galaxies, should not be considered as an analogous of galaxy pairs with a third extra member, but rather they are a natural extension of compact groups.

Duplancic, Fernanda; O'Mill, Ana Laura; Lambas, Diego G.; Sodré, Laerte; Alonso, Sol

2013-08-01

420

Ultrafast dynamics of singlet-singlet and singlet-triplet exciton annihilation in poly(3- 2' -methoxy- 5' octylphenyl)thiophene films  

NASA Astrophysics Data System (ADS)

Singlet-singlet (S-S) and singlet-triplet (S-T) exciton annihilation was studied in poly(3- 2' -methoxy- 5' octylphenyl)thiophene films. For the S-S exciton annihilation studies, transient absorption spectroscopy at excitation laser pulse fluences of 1.2×1013-4.4×1014photons/cm2 and 2.5kHz pulse repetition rate was applied. The obtained kinetics demonstrate a typical nonexponential character with intensity-dependent amplitudes and lifetimes. In time-resolved fluorescence experiments, low excitation pulse fluences of 1.6×109-2.2×1012photons/cm2 at high repetition rates of 0.4, 0.8, 4, and 81MHz lead to S-T exciton annihilation as a result of triplet exciton accumulation. S-T annihilation kinetics results in monoexponential decay of the fluorescence kinetics and manifests itself as a decrease of the singlet exciton lifetime. The calculated time-independent S-S and S-T exciton annihilation rates strongly support the conclusion that the processes are controlled by the interchain diffusion of singlet excitons. Despite the low efficiency of S-T annihilation compared to that of S-S annihilation, it has a substantial effect on the singlet exciton lifetime due to a relatively long triplet lifetime (60?s) . Thus, even optical excitation with low fluence at high pulse repetition rate creates a significant concentration of triplet states that efficiently quenches singlet excitons.

Zaushitsyn, Yuri; Jespersen, Kim G.; Valkunas, Leonas; Sundström, Villy; Yartsev, Arkady

2007-05-01