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1

The Triplet State  

NASA Astrophysics Data System (ADS)

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

Zahlan, A. B.

2010-01-01

2

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

PubMed

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

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

2013-09-26

3

Triplet excited state spectra and dynamics of carotenoids from the thermophilic purple photosynthetic bacterium Thermochromatium tepidum  

SciTech Connect

Light-harvesting complex 2 from the anoxygenic phototrophic purple bacterium Thermochromatium tepidum was purified and studied by steady-state absorption, fluorescence and flash photolysis spectroscopy. Steady-state absorption and fluorescence measurements show that carotenoids play a negligible role as supportive energy donors and transfer excitation to bacteriochlorophyll-a with low energy transfer efficiency of ~30%. HPLC analysis determined that the dominant carotenoids in the complex are rhodopin and spirilloxanthin. Carotenoid excited triplet state formation upon direct (carotenoid) or indirect (bacteriochlorophyll-a Q{sub x} band) excitation shows that carotenoid triplets are mostly localized on spirilloxanthin. In addition, no triplet excitation transfer between carotenoids was observed. Such specific carotenoid composition and spectroscopic results strongly suggest that this organism optimized carotenoid composition in the light-harvesting complex 2 in order to maximize photoprotective capabilities of carotenoids but subsequently drastically suppressed their supporting role in light-harvesting process.

Niedzwiedzki, Dariusz; Kobayashi, Masayuki; Blankenship, R. E.

2011-01-01

4

Photodissociation of N2O: Triplet states and triplet channel  

NASA Astrophysics Data System (ADS)

The role of triplet states in the UV photodissociation of N_2O is investigated by means of quantum mechanical wave packet calculations. Global potential energy surfaces are calculated for the lowest two 3A' and the lowest two 3A'' 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 13A'. Excitation of the 21A' state and subsequent transition to the repulsive branch of the 23A'' state at intermediate NN-O separations, promoted by spin-orbit coupling, is identified as the main pathway to the N_2(^1? _g^+)+O(^3P) 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)], 10.1021/jp037034o.

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

2011-11-01

5

Phosphorescence and triplet state energies of oligothiophenes.  

PubMed

The phosphorescence spectra of a series of small oligothiophenes (nT, n = 1-3) incorporating a variety of substituents, end cappers, and functional groups have been recorded for the first time using gated detection in combination with nanosecond excitation in frozen solution at 80 K. The vibrationally resolved emission spectra provide accurate estimates of the T(1) and S(1) levels, and the singlet-triplet energy gap. Theoretical quantum chemical calculations performed at the DFT (B3LYP/6-31G*) level reproduce all experimental trends accurately and provide quantitative description of the S(0)-T(1) energy difference. The geometry relaxation in the excited state shows that the "natural" size of the triplet exciton is about 3-4 thiophene units. PMID:16851510

Wasserberg, Dorothee; Marsal, Philippe; Meskers, Stefan C J; Janssen, René A J; Beljonne, David

2005-03-17

6

Chlorophyll triplet states associated with photosystem II of thylakoids.  

PubMed

The analysis of FDMR thylakoid spectra, determined at multiple emission wavelengths, by a global decomposition technique, has revealed the presence of three previously undescribed triplet populations at emission wavelengths characteristic of Photosystem II chlorophyll/protein complexes. Their zero-field splitting parameters have been determined in order to compare them with the well-studied PSII recombination triplet state. None of these triplets have the zero-field splitting parameters characteristic of the recombination triplet and are therefore probably not generated directly in the reaction center. On the basis of their microwave-induced emission spectra, it is suggested that two are probably generated in the core complex(es) while the third may be generated in the external antenna. These triplets are formed under nonreducing redox conditions, when the recombination triplet is undetectable. It is suggested that they may be involved in the photoinhibitory damage of Photosystem II. The triplet-minus-singlet spectrum associated with the recombination triplet state has been determined for thylakoids after reduction of the secondary acceptors. Its main peak is at 685 nm, slightly red shifted with respect to earlier reports, with a weak signal, of opposite sign at approximately 675 nm. The 685 nm peak indicates that at cryogenic temperatures, the triplet is located on the long-wavelength chlorophyll state present in the reaction center complex of Photosystem II (D1.D2.Cytb(559) complex). From the absence of a clear structure in the 680 nm absorption region, this long-wavelength absorbing state does not appear to be strongly coupled to P(680), though it must be associated with one of the "inner core" pigments recently identified in the photosystem II crystallographic structure [Zouni et al. (2001) Nature 408, 739-743]. PMID:12069611

Santabarbara, Stefano; Bordignon, Enrica; Jennings, Robert C; Carbonera, Donatella

2002-06-25

7

Triplet-state energies and substituent effects of excited aroyl compounds in the gas phase.  

PubMed

Triplet-state energy values obtained from the gas phase are still scarce. In this study, the triplet-state energies of 58 aroyl compounds, introduced as gas chromatographic peaks at atmospheric pressure and typically 473 K, have been determined from the 0-0 bands of their n --> pi* type phosphorescence spectra in excited nitrogen. Correlations of those gas-phase triplet-state energies with Hammett constants could be observed for substituted acetophenones, benzaldehydes and benzophenones. PMID:10728860

Lin, Z P; Aue, W A

2000-01-01

8

Triplet states of cyclopropenylidene and its isomers  

NASA Astrophysics Data System (ADS)

The unique importance of the cyclopropenylidene molecule conveys significance to its low-lying isomers. Eleven low-lying electronic triplet stationary points as well as the two lowest singlet structures of C3H2 have been systematically investigated. This research used coupled cluster (CC) methods with single and double excitations and perturbative triple excitations [CCSD(T)] and Dunning's correlation-consistent polarized valence cc-pVXZ (where X=D, T, and Q) basis sets. Geometries, dipole moments, vibrational frequencies, and associated infrared intensities of the targeted molecules have been predicted. The electronic ground state of cyclopropenylidene (3S, the global minimum) is the X˜ A11 state with C2v point group symmetry. Among the 11 triplet stationary points, 7 structures are found to be minima, 2 structures to be transition states, and 2 structures to be higher-order saddle points. For the six lowest-lying triplet structures and singlet propadienylidene (2S), relative energies (zero-point vibrational energy corrected values in parentheses) with respect to the global minimum [ X˜ A11 (3S)] at the cc-pVQZ-UCCSD(T) level of theory are predicted to be propynylidene B31(3cT)]71.2(69.9)triplet equilibrium structures are all energetically well below the dissociation limit to [C(P3)+C2H2(X˜ ?1g+)].

Wu, Qunyan; Cheng, Qianyi; Yamaguchi, Yukio; Li, Qianshu; Schaefer, Henry F.

2010-01-01

9

Chlorophyll a and carotenoid triplet states in light-harvesting complex II of higher plants.  

PubMed Central

Laser-flash-induced transient absorption measurements were performed on trimeric light-harvesting complex II to study carotenoid (Car) and chlorophyll (Chl) triplet states as a function of temperature. In these complexes efficient transfer of triplets from Chl to Car occurs as a protection mechanism against singlet oxygen formation. It appears that at room temperature all triplets are being transferred from Chl to Car; at lower temperatures (77 K and below) the transfer is less efficient and chlorophyll triplets can be observed. In the presence of oxygen at room temperature the Car triplets are partly quenched by oxygen and two different Car triplet spectral species can be distinguished because of a difference in quenching rate. One of these spectral species is replaced by another one upon cooling to 4 Ki demonstrating that at least three carotenoids are in close contact with chlorophylls. The triplet minus singlet absorption (T-S) spectra show maxima at 504-506 nm and 517-523 nm, respectively. In the Chl Qy region absorption changes can be observed that are caused by Car triplets. The T-S spectra in the Chl region show an interesting temperature dependence which indicates that various Car's are in contact with different Chl a molecules. The results are discussed in terms of the crystal structure of light-harvesting complex II. PMID:8599673

Peterman, E J; Dukker, F M; van Grondelle, R; van Amerongen, H

1995-01-01

10

Triplet State Dynamics in Peridinin-Chlorophyll-a-Protein: A New Pathway of Photoprotection in LHCs?  

PubMed Central

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 ?13 and ?42 ?s in the spectral region between 1800 and 1100 cm?1 after excitation of the ‘blue’ and ‘red’ peridinin (Per) conformers and the Qy 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 3Per 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 3Per decay, implying significant involvement of 3Chl-a in the 3Per state. We suggest that this Per-Chl-a interaction via a delocalized triplet state lowers the 3Per 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

2007-01-01

11

Reactions of excited triplet states of metal substituted myoglobin with dioxygen and quinone.  

PubMed

The triplet state absorption and phosphorescence of Zn and Pd derivatives of myoglobin were compared. Both metal derivatives exhibit long triplet state lifetimes at room temperature, but whereas the Pd derivative showed exponential decay and an isosbestic point in the transient absorption spectra, the decay of the Zn derivative was nonsingle exponential and the transient absorption spectra showed evidence of more than one excited state species. No difference was seen in triplet quenching by oxygen for either derivative, indicating that differences in the polypeptide chain between the two derivatives are not large enough to affect oxygen penetrability. Quenching was also observed by anthraquinone sulfonate. In this case, the possibility of long-range transfer by an exchange mechanism is considered. PMID:2383630

Papp, S; Vanderkooi, J M; Owen, C S; Holtom, G R; Phillips, C M

1990-07-01

12

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

13

Optically Detected Magnetic Resonance (ODMR) of photoexcited triplet states.  

PubMed

Optically Detected Magnetic Resonance (ODMR) is a double resonance technique which combines optical measurements (fluorescence, phosphorescence, absorption) with electron spin resonance spectroscopy. After the first triplet-state ODMR experiments in zero magnetic field reported in 1968 by Schmidt and van der Waals, the number of double resonance studies on excited triplet states grew rapidly. Photosynthesis has proven to be a fruitful field of application due to the intrinsic possibility of forming photo-induced pigment triplet states in many sites of the photosynthetic apparatus. The basic principles of this technique are described and examples of application in Photosynthesis are reported. PMID:19238576

Carbonera, Donatella

2009-01-01

14

Formylmethylene: the triplet ground state and the lowest singlet state.  

PubMed

The ground triplet state and lowest singlet state of formylmethylene have been proposed as important intermediates in the Wolff rearrangement of ?-diazo ketones into ketenes. The ground triplet state of formylmethylene has been examined experimentally, but the lowest singlet state has yet to be observed. We predict equilibrium geometries, energies, bonding, dipole moments, and harmonic vibrational frequencies for these two lowest states of formylmethylene at the cc-pVQZ CCSD(T) level of theory. The singlet-triplet energy difference [?E(S-T)] is quite sensitive to the level of theory. The highly accurate cc-pVQZ CCSD(T) level of theory yields the most reliable result of only 2.0 kcal mol(-1). An estimate based on the experimentally characterized CH2 molecule yields ?E(S-T) = 1.27 kcal mol(-1). In addition, accurate quartic force fields have been determined at the cc-pVTZ CCSD(T) level of theory. Fundamental vibrational frequencies, anharmonic constants, and vibration-rotation coupling constants were determined using vibrational second-order perturbation theory (VPT2). Our results should aid in experimental detection and characterization of the lowest singlet state of formylmethylene, which is highly desirable for better understanding the mechanism of the Wolff rearrangement. PMID:23406310

Guan, Jun; Randall, Katherine R; Schaefer, Henry F; Li, Huidong

2013-03-14

15

Spectroscopic characterization of triplet forming states in photosystem II.  

PubMed

Fluorescence and electron paramagnetic resonance (EPR) measurements have been applied to characterize chlorophyll triplet formation in the reaction center of photosystem II (PSII). A highly triplet forming state was generated in PSII membranes by chemical double reduction of the primary electron acceptor QA. In triplet forming PSII centers, the steady-state yield of chlorophyll fluorescence decreased to about 70% of the maximal fluorescence yield observed in closed PSII centers in which QA is singly reduced. The results are well interpreted in the framework of a model where the charge state of QA electrostatically controls the yield of primary charge separation [Schatz, G. H., Brock, H., & Holzwarth, A. R. (1988) Biophys. J. 54, 397-405]. Thus, high triplet yield and decreased, although still quite high, fluorescence indicate a charge-neutralized state of PSII in which QA is singly or doubly reduced and protonated or absent. The EPR signal of the triplet primary chlorophyll donor, 3P680, is suppressed by illumination at 77 K concomitant with the formation of a cationic radical (g = 2.0025-2.0027, and 0.92 mT wide) that is stable in the dark. This is attributed to the oxidation of an accessory chlorophyll (Chl) in the vicinity of P680. Electrostatic repulsion between Chl+ and P680+ is likely to prevent primary charge separation, and in turn triplet formation, providing a further example of electrostatic control of primary charge separation. The triplet P680 EPR signal is also suppressed in the presence of oxygen. This effect, which is almost completely reversible by removing the oxygen, is attributed to the interaction of triplet P680 with triplet O2. PMID:1320926

Vass, I; Styring, S

1992-07-01

16

Triplet state in photosystem II reaction centers as studied by 130 GHz EPR  

NASA Astrophysics Data System (ADS)

The triplet state in the reaction centers of photosystem II was studied by high-field/high-frequency (130 GHz) EPR in the temperature range 50-90 K. At 50 K, the zero-field splitting parameters of the EPR spectrum correspond well to those of a chlorophyll monomer, in agreement with earlier studies. In the high magnetic field of 4.6 T employed in this study, the g-anisotropy of the triplet state becomes apparent and leads to a shift of the canonical positions of the triplet EPR spectrum. Assuming that triplet g- and zero-field tensors are coaxial, the principal values of the triplet g-tensor are determined to be 2.00324, 2.00306 and 2.00231 with an error of ±0.00004. Lifting this assumption results in higher g-anisotropy. At higher temperatures, the shape of the spectra changes significantly. Triplet excitation hopping involving the accessory chlorophyll B A and P A or P B (equivalents of the special pair bacteriochlorophylls of the bacterial reaction centers) can partially explain those changes, but the most prominent features indicate that also the electron acceptor I A (a pheophytin molecule) must be involved.

Pashenko, S. V.; Proskuryakov, I. I.; Germano, M.; van Gorkom, H. J.; Gast, P.

2003-11-01

17

“Unusual” lines observed in low-frequency cw ENDOR of photoexcited triplet state molecules: the primary donor triplet in photosynthetic reaction centers as an example  

Microsoft Academic Search

The origin of frequently observed “negative” (opposite phase) ENDOR lines in the low-frequency region of triplet state ENDOR\\u000a spectra is explained in terms of microwave hole burning and RF modulation phenomena. From this, a new method of detecting\\u000a burnt side holes in EPR spectra is derived which is based on cw ENDOR instrumentation. The method uses the modulation satellites\\u000a that

A. A. Dubinskii; M. Huber; Yu. Grishin; K. Möbius

1995-01-01

18

The triplet state of indigo: Electronic structure calculations  

NASA Astrophysics Data System (ADS)

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

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

2007-11-01

19

Room temperature triplet state spectroscopy of organic semiconductors  

E-print Network

Organic light emitting devices and solar cells are machines that create, manipulate and destroy 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 fluorescen...

Reineke, Sebastian

2013-01-01

20

Determination of the probability of excited singlet state generation for molecules during triplet-triplet heteroannihilation  

SciTech Connect

An increased intensity of delayed fluorescence (DF) of dyes in alcohols as a result of addition of aromatic hydrocarbons has been observed. The authors understanding of this process is incomplete and mainly based on information extracted from the rate constant of the excited singlet state formation as a result of triplet pair annihilation. It is therefore important to develop new methods for determining the probability of occurrence of the luminescence process, i.e., the fraction of annihilation acts which lead to the excited singlet state formation. In the present work this parameter is determined from analysis of some peculiarities in the DF kinetics for the studied system. Binary mixtures of anthracene with dyes in propyl alcohol were used as model systems.

Ketsle, G.A.; Kucherenko, M.G.; Levshin, L.V.; Muldakhmetov, Z.M.

1987-09-01

21

Ultrafast photogeneration mechanisms of triplet states in para-hexaphenyl  

Microsoft Academic Search

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

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

1999-01-01

22

p-Benzyne derivatives that have exceptionally small singlet-triplet gaps and even a triplet ground state.  

PubMed

In an effort to find a p-benzyne (1,4-didehydrobenzene) derivative with a triplet ground state, we have investigated tetrasubstitution by -F, -NH(2), -CH(3), and -NO(2) groups. These were predicted to reduce the singlet-triplet gap, but none led to a triplet ground state because of unexpected destabilization of one of the radical orbitals. This effect is likely the result of rehybridization of the substituted C atom, which has been observed for substituted benzene and perturbs the side sigma and sigma* orbital energies of the phenyl ring. The role of substituent rotation on the energy difference between the two nominally singly occupied orbitals (S and A) was then investigated. The energy of the A radical orbital was found to be much more sensitive to perturbations within the sigma C[bond]C framework than the S MO. Consequently, we believe that rehybridization of the ring carbons destabilizes the A radical orbital and can lead to large singlet-triplet splittings. To test this hypothesis, calculations on a p-benzyne with 2,6 substitution by oxygen were performed. Interestingly, a triplet ground state was predicted. Yet, examination of the geometry and wave function showed that 2,6-quinone p-benzyne is a very twisted molecule with a C3-C4-C5 allene linkage and a C1 triplet carbene center. PMID:12713336

Clark, Aurora E; Davidson, Ernest R

2003-05-01

23

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

PubMed Central

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 per base of 1.38 kcal·mol?1 for the CAG triplet and 2.87 kcal·mol?1 for the CTG triplet, while being entropically destabilized by 3.50 cal·K?1·mol?1 for the CAG triplet and 7.6 cal·K?1·mol?1 for the CTG triplet. Remarkably, these values correspond, respectively, to 1/3 (for CAG) and 2/3 (for CTG) of the enthalpy and entropy per base values associated with Watson–Crick base pairs. We show that the presence of the loop structure kinetically inhibits duplex formation from the two complementary 30-mer hairpins, even though the duplex is the thermodynamically more stable state. Duplex formation, however, does occur at elevated temperatures. We propose that this thermally induced formation of a more stable duplex results from thermal disruption of the single-stranded order, thereby allowing the complementary domains to associate (perhaps via “kissing hairpins”). Our melting profiles show that, once duplex formation has occurred, the hairpin intermediate state cannot be reformed, consistent with our interpretation of kinetically trapped hairpin structures. The duplex formed by the two complementary oligonucleotides does not have any unusual optical or thermodynamic properties. By contrast, the very stable structures formed by the individual single-stranded triplet repeat sequences are thermally and thermodynamically unusual. We discuss this stable, triplet repeat, single-stranded structure and its interconversion with duplex in terms of triplet expansion diseases. PMID:12417759

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

2002-01-01

24

Singlet-triplet energy splitting and excited states of phenylnitrene.  

PubMed

The vertical and adiabatic singlet-triplet energy splittings (Delta E ST) of phenylnitrene were computed by a variety of multireference configuration interaction and perturbation theory methods employing basis sets of up to quadruple-xi quality and extrapolation to the complete basis set limit. The vertical and adiabatic energy gaps are 18.9 and 15.9 kcal mol (-1), respectively, the latter in reasonable agreement with the revised experimental value of 15.1 +/- 0.2 kcal mol (-1). The energy difference between both states at the geometry of the a (1)A 2 singlet state was also considered and amounts to 13.8 kcal mol (-1). In obtaining accurate state energy splittings, basis set completeness turns out to be a more important issue than the level of dynamical electron correlation treatment. Density functional theory that is frequently employed to investigate phenylnitrenes and their rearrangements yields varying results and, depending on the functional, gives adiabatic energy differences between 9 and 16 kcal mol (-1). The b (1)A 1 state has a similar geometry as the ground state of 1 and is 31 kcal mol (-1) higher in energy. According to best estimates, the next higher singlet states, c (1)A 1 and d (1)B 1, are 57 and 72 kcal mol (-1) above the ground state. In the triplet manifold, vertical excitation energies to the A (3)B 1 and B (3)A 2 states are 71 and 77 kcal mol (-1), respectively. PMID:18714972

Winkler, Michael

2008-09-18

25

Measurement of Dipole Moments and Lifetimes of Triplet States of Fluorenone and Its Derivatives by Time Resolved Microwave Dielectric Absorption  

NASA Astrophysics Data System (ADS)

The technique of time resolved microwave dielectric absorption has been used to study the excited triplet states formed by the laser flash photolysis. The details of the experimental method and apparatus are discussed. The triplet state lifetimes and triplet state dipole moments of fluorenone and its derivatives are reported. The triplet state lifetime of fluorenone agrees with that obtained by optical absorption. The lifetime measurements with argon purging and with air equilibrated solution confirm the formation of triplet states. A marked increase in the triplet state dipole moment of fluorenone and its derivatives is observed and implies that their lowest triplet state is of (?, ?*) in nature.

Santhamurthy, Arathi; Rao, Tetali; Sobhanadri, Jandhyala; Murthy, Vemori

1998-04-01

26

Excited-state dynamics of naphthoylnaphthvalene: valence isomerization of the lowest excited singlet state and intermolecular hydrogen-atom abstraction of the lowest excited triplet state  

Microsoft Academic Search

By measurements of phosphorescence and transient absorption spectra as well as steady-state photolysis of the title compound (NNV), it is concluded as follows: (1) In benzene and ethanol, intersystem crossing from the lowest excited singlet (1NNV?) to triplet (3NNV?) states competes withvalence isomerization of 1NNV? yielding ground-state naphthoylnaphthalene (NN). (2) In ethanol, the NNV ketyl radical (generated by hydrogen-atom abstraction

Toshihiro Nakayama; Tetsuhiko Nagahara; Sadao Miki; Kumao Hamanoue

1997-01-01

27

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

28

Room temperature triplet state spectroscopy of organic semiconductors  

PubMed Central

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. PMID:24445870

Reineke, Sebastian; Baldo, Marc A.

2014-01-01

29

Room temperature triplet state spectroscopy of organic semiconductors.  

PubMed

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. PMID:24445870

Reineke, Sebastian; Baldo, Marc A

2014-01-01

30

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

31

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

32

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

PubMed Central

Fluorescence emission and triplet-minus-singlet (T-S) absorption difference spectra of the CP47 core antenna complex of photosystem II were measured as a function of temperature and compared to those of chlorophyll a in Triton X-100. Two spectral species were found in the chlorophyll T-S spectra of CP47, which may arise from a difference in ligation of the pigments or from an additional hydrogen bond, similar to what has been found for Chl molecules in a variety of solvents. The T-S spectra show that the lowest lying state in CP47 is at approximately 685 nm and gives rise to fluorescence at 690 nm at 4 K. The fluorescence quantum yield is 0.11 +/- 0.03 at 4 K, the chlorophyll triplet yield is 0.16 +/- 0.03. Carotenoid triplets are formed efficiently at 4 K through triplet transfer from chlorophyll with a yield of 0.15 +/- 0.02. The major decay channel of the lowest excited state in CP47 is internal conversion, with a quantum yield of about 0.58. Increase of the temperature results in a broadening and blue shift of the spectra due to the equilibration of the excitation over the antenna pigments. Upon increasing the temperature, a decrease of the fluorescence and triplet yields is observed to, at 270 K, a value of about 55% of the low temperature value. This decrease is significantly larger than of chlorophyll a in Triton X-100. Although the coupling to low-frequency phonon or vibration modes of the pigments is probably intermediate in CP47, the temperature dependence of the triplet and fluorescence quantum yield can be modeled using the energy gap law in the strong coupling limit of Englman and Jortner (1970. J. Mol. Phys. 18:145-164) for non-radiative decays. This yields for CP47 an average frequency of the promoting/accepting modes of 350 cm-1 with an activation energy of 650 cm-1 for internal conversion and activationless intersystem crossing to the triplet state through a promoting mode with a frequency of 180 cm-1. For chlorophyll a in Triton X-100 the average frequency of the promoting modes for non-radiative decay is very similar, but the activation energy (300 cm-1) is significantly smaller. Images FIGURE 3 FIGURE 5 FIGURE 6 PMID:7711252

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

1995-01-01

33

Two-step unsymmetrical quantum key distribution protocol using GHZ triplet states  

Microsoft Academic Search

The security, efficiency, transmission distance and error rate are important parameters of a quantum key distribution scheme. In this article, the former two parameters are focused on. To reach high efficiency, an unsymmetrical quantum key distribution scheme that employs Greenberger-Horne-Zeilinger (GHZ) triplet states and dense coding mechanism is proposed, in which a GHZ triplet state can be used to share

HUANG Peng; LIU Ye; ZHOU Nan-run; ZENG Gui-hua

2009-01-01

34

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

35

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

36

Dynamics of excited-state intramolecular proton transfer reactions in piroxicam. Role of triplet states  

NASA Astrophysics Data System (ADS)

The picosecond time-resolved fluorescence and transient absorption behavior of piroxicam at room temperature are reported. The keto tautomer in the excited singlet state ( 1K*) formed via the fast intramolecular proton transfer (? 20 ps) is observed. The short-lived (7.5 ns) triplet state of keto tauomer ( 3K*) is generated from 1K * in toluene whereas it is hardly observed in ethanol. Consequently, rapid reverse proton transfer takes place from 3K * to the enol triplet state ( 3E *.

Cho, Dae Won; Kim, Yong Hee; Yoon, Minjoong; Jeoung, Sae Chae; Kim, Dongho

1994-08-01

37

A fluorescence detected magnetic resonance investigation of the carotenoid triplet states associated with photosystem II of isolated spinach thylakoid membranes.  

PubMed

The carotenoid triplet populations associated with the fluorescence emission chlorophyll forms of Photosystem II have been investigated in isolated spinach thylakoid membranes by means of fluorescence detected magnetic resonance in zero field (FDMR). The spectra collected in the 680-690 nm emission range, have been fitted by a global analysis procedure. At least five different carotenoid triplet states coupled to the terminal emitting chlorophyll forms of PS II, peaking at 682 nm, 687 nm and 692 nm, have been characterised. The triplets associated with the outer antenna emission forms, at 682 nm, have zero field splitting parameters |D| = 0.0385 cm-1, |E| = 0.00367 cm-1; |D| = 0.0404 cm-1, |E| = 0.00379 cm-1 and |D| = 0.0386 cm-1, |E| = 0.00406 cm-1 which are very similar to those previously reported for the xanthophylls of the isolated LHC II complex. Therefore the FDMR spectra recorded in this work provide insights into the organisation of the LHC II complex in the unperturbed environment represented by thylakoid membranes. The additional carotenoid triplet populations, detected by monitoring the chlorophyll emission at 687 and 692 nm, are assigned to carotenoids bound to inner antenna complexes and hence attributed to beta-carotene molecules. PMID:16172946

Santabarbara, Stefano; Agostini, Giancarlo; Heathcote, Peter; Carbonera, Donatella

2005-11-01

38

Remarkable observations on triplet-sensitized reactions. the di-pi-methane rearrangement of acyclic 1,4-dienes in the triplet excited state.  

PubMed

Previous studies have led to the conclusion that a large majority of acyclic 1,4-dienes do not undergo photochemical di-pi-methane (DPM) rearrangement under triplet-sensitized irradiation. The results of a detailed analysis of these processes demonstrate that a series of these compounds do indeed undergo highly efficient DPM rearrangement from their triplet excited states when suitable triplet sensitizers are used. PMID:19685921

Armesto, Diego; Ortiz, Maria J; Agarrabeitia, Antonia R; Martin-Fontecha, Mar; El-Boulifi, Noureddin; Duran-Sampedro, Gonzalo; Enma, Danielle

2009-09-17

39

The electronic structure of the lutein triplet state in plant light-harvesting complex II.  

PubMed

Carotenoid molecules are essential for the life of photosynthetic organisms in that they protect the cell from the photo-oxidative damage induced by light-stress conditions. One of the photo-protective mechanisms involves triplet-triplet energy transfer from the chlorophyll molecules to the carotenoids: a process that is strongly dependent on the electronic properties of the triplet states involved. Here, we obtain a clear description of the triplet state of lutein in LHCII from higher plants for the first time by density functional theory (DFT) calculations. DFT predictions have been validated by comparison with hyperfine couplings obtained with pulsed-ENDOR spectroscopy. Knowledge of the spin density distribution, the frontier orbitals and orbital excitations forms a basis for discussing the requirements for an efficient triplet-triplet energy transfer. The results obtained for the lutein in LHCII are compared with those of the highly-substituted carotenoid peridinin in PCP from Amphidinium carterae [Di Valentin et al., Biochim. Biophys. Acta, 2008, 1777, 295-307]. The presence of substituents in the peridinin molecule does not alter significantly the triplet state electronic structure compared to lutein. Despite the unusual spectroscopic behaviour of the peridinin excited singlet state, lutein and peridinin have similar triplet state properties. In both molecules the unpaired spins are delocalized uniformly over the whole ?-conjugated system in an alternating even-odd pattern. PMID:22864767

Salvadori, Enrico; Di Valentin, Marilena; Kay, Christopher W M; Pedone, Alfonso; Barone, Vincenzo; Carbonera, Donatella

2012-09-21

40

The high-frequency two-electron photo-ionization cross section of triplet states  

Microsoft Academic Search

Numerical values are obtained for several different characteristics of the two-electron photoionization at high, but non-relativistic frequencies for triplet excited states. The new high precision wave functions describing several lowest excited states of the type \\

Rajmund Krivec; Miron Ya. Amusia; Victor Mandelzweig

2002-01-01

41

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

42

Carotenoid triplet states in photosystem II: coupling with low-energy states of the core complex.  

PubMed

The photo-excited triplet states of carotenoids, sensitised by triplet-triplet energy transfer from the chlorophyll triplet states, have been investigated in the isolated Photosystem II (PSII) core complex and PSII-LHCII (Light Harvesting Complex II) supercomplex by Optically Detected Magnetic Resonance techniques, using both fluorescence (FDMR) and absorption (ADMR) detection. The absence of Photosystem I allows us to reach the full assignment of the carotenoid triplet states populated in PSII under steady state illumination at low temperature. Five carotenoid triplet ((3)Car) populations were identified in PSII-LHCII, and four in the PSII core complex. Thus, four (3)Car populations are attributed to ?-carotene molecules bound to the core complex. All of them show associated fluorescence emission maxima which are relatively red-shifted with respect to the bulk emission of both the PSII-LHCII and the isolated core complexes. In particular the two populations characterised by Zero Field Splitting parameters |D|=0.0370-0.0373 cm(-1)/|E|=0.00373-0.00375 cm(-1) and |D|=0.0381-0.0385 cm(-1)/|E|=0.00393-0.00389 cm(-1), are coupled by singlet energy transfer with chlorophylls which have a red-shifted emission peaking at 705 nm. This observation supports previous suggestions that pointed towards the presence of long-wavelength chlorophyll spectral forms in the PSII core complex. The fifth (3)Car component is observed only in the PSII-LHCII supercomplex and is then assigned to the peripheral light harvesting system. PMID:25481107

Santabarbara, Stefano; Agostini, Alessandro; Casazza, Anna Paola; Zucchelli, Giuseppe; Carbonera, Donatella

2015-02-01

43

Quenching of chlorophyll triplet states by carotenoids in reconstituted Lhca4 subunit of peripheral light-harvesting complex of photosystem I.  

PubMed

In this study, triplet quenching, the major photoprotection mechanism in antenna proteins, has been studied in the light-harvesting complex of photosystem I (LHC-I). The ability of carotenoids bound to LHC-I subunit Lhca4, which is characterized by the presence of the red-most absorption components at wavelength >700 nm, to protect the system through quenching of the chlorophyll triplet states, has been probed, by analyzing the induction of carotenoid triplet formation. We have investigated this process at low temperature, when the funneling of the excitation toward the low-lying excited states of the Chls is stronger, by means of optically detected magnetic resonance (ODMR), which is well-suited for investigation of triplet states in photosynthetic systems. The high selectivity and sensitivity of the technique has made it possible to point out the presence of specific interactions between carotenoids forming the triplet states and specific chlorophylls characterized by red-shifted absorption, by detection of the microwave-induced Triplet minus Singlet (T-S) spectra. The effect of the red forms on the efficiency of triplet quenching was specifically probed by using the Asn47His mutant, in which the red forms have been selectively abolished (Morosinotto, T., Breton, J., Bassi, R., and Croce, R. (2003) J. Biol. Chem. 278, 49223-49229). Lack of the red forms yields into a reduced efficiency of the triplet quenching in LHC-I thus suggesting that the "red Chls" play a role in enhancing triplet quenching in LHC-I and, possibly, in the whole photosystem I. PMID:15938623

Carbonera, Donatella; Agostini, Giancarlo; Morosinotto, Tomas; Bassi, Roberto

2005-06-14

44

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

SciTech Connect

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

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

1986-10-23

45

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

46

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

47

Excited-state dynamics of naphthoylnaphthvalene: valence isomerization of the lowest excited singlet state and intermolecular hydrogen-atom abstraction of the lowest excited triplet state  

NASA Astrophysics Data System (ADS)

By measurements of phosphorescence and transient absorption spectra as well as steady-state photolysis of the title compound (NNV), it is concluded as follows: (1) In benzene and ethanol, intersystem crossing from the lowest excited singlet ( 1NNV ?) to triplet ( 3NNV ?) states competes withvalence isomerization of 1NNV ? yielding ground-state naphthoylnaphthalene (NN). (2) In ethanol, the NNV ketyl radical (generated by hydrogen-atom abstraction of 3NNV ? from the solvent molecule) also undergoes rapid valence isomerization and recombination of two NN ketyl radicals thus formed yields 1,1,2,2-tetranaphthyl-1,2-ethanediol (naphthopinacol).

Nakayama, Toshihiro; Nagahara, Tetsuhiko; Miki, Sadao; Hamanoue, Kumao

1997-03-01

48

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

SciTech Connect

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

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

2009-10-15

49

The lowest triplet state of tetramethyl-1,3-cyclobutanedithione. I. Single-crystal polarized absorption spectrum  

NASA Astrophysics Data System (ADS)

The single-crystal polarized absorption spectrum of tetramethyl-1,3-cyclobutanedithione (TMCBDT) has been measured in the region of the lowest triplet state. All bands are polarized exclusively perpendicular to the tetragonal unit cell c axis. The 0-0 band which lies at 594.3 nm is the most intense feature with active vibrations at 309, 329, 600, 913, and 969 cm -1 of lower intensity. The electronic transition is assigned to 3A u ? 1A g (n˜ =) in the D 2h molecular point group. Weak, low-frequency vibrations (< 100 cm -1) observed near the origin band (and several other vibronic bands) have been analyzed using a model in which the excited triplet and ground electronic states are described by double-minimum potentials (DMPs). The parameters for these states were found by fitting the low-temperature (1.6 K) absorption and emission crystal spectra using the Coon, Naugle, and McKenzie method. A 23 cm -1 potential barrier is found for the ground state and a 95 cm -1 one for the triplet state. Using these results the temperature dependence of the absorption spectrum was simulated and it is shown that the essential features of the observed temperature behavior are accounted for. Finally, it is suggested that the DMP in both states results from either an intramolecular torsional motion and/or a particular lattice mode.

Baiardo, Joseph; Vala, Martin; Trabjerg, Ib

1983-09-01

50

Singlet and triplet excited state properties of natural chlorophylls and bacteriochlorophylls  

SciTech Connect

Ten naturally occurring chlorophylls (a, b, c{sub 2}, d) and bacteriochlorophylls (a, b, c, d, e, g) were purified and studied using the optical spectroscopic techniques of both steady state and time-resolved absorption and fluorescence. The studies were carried out at room temperature in nucleophilic solvents in which the central Mg is hexacoordinated. The comprehensive studies of singlet excited state lifetimes show a clear dependency on the structural features of the macrocycle and terminal substituents. The wide-ranging studies of triplet state lifetime demonstrate the existence of an energy gap law for these molecules. The knowledge of the dynamics and the energies of the triplet state that were obtained in other studies allowed us to construct an energy gap law expression that can be used to estimate the triplet state energies of any (B)chlorophyll molecule from its triplet lifetime obtained in a liquid environment.

Niedzwiedzki, Dariusz; Blankenship, R. E.

2010-01-01

51

Decay dynamics of the triplet state of 2,6-dimethyl-4H-1-benzothiopyran-4-thione in solution  

Microsoft Academic Search

The phosphorescence decay kinetics and transient triplet-triplet absorption of 2,6-dimethyl-4H-1-benzothiopyran-4-thione (DMBTPT) were recorded in deoxygenated n-hexane, n-hexadecane and 3-methylpentane solutions. The measurements of DMBTPT in the triplet state were performed using a flash photolysis system with an excimer laser as excitation source. The triplet state decay constant at infinite dilution (k0) and teh self-quenching rate constant (ksq) for DMBTPT at

Marek Sikorski; W?odzimierz Augustyniak; Igor V. Khmelinskii

1996-01-01

52

Carotenoid triplet states associated with the long-wavelength-emitting chlorophyll forms of photosystem I in isolated thylakoid membranes.  

PubMed

The carotenoid triplet populations associated with the long-wavelength-emitting chlorophyll forms of photosystem I (PS I)(dagger) have been investigated in isolated spinach thylakoids by means of fluorescence-detected magnetic resonance in zero field. The spectra collected in the 730-800 nm emission range can be globally fitted assuming the presence of four different carotenoid triplet states coupled to long-wavelength-emitting forms of PS I, having zero-field-splitting parameters /D/ = 0.0359 cm(-1) and /E/ = 0.00371 cm(-1), /D/ = 0.0382 cm(-1) and /E/ = 0.00388 cm(-1), /D/ = 0.0395 cm(-1) and /E/ = 0.00397 cm(-1), and /D/ = 0.0405 cm(-1) and /E/ = 0.00411 cm(-1). On the basis of the triplet-associated fluorescence emission profile, it is suggested that those triplets are associated with light-harvesting complex I, the peripheral antenna complex of PS I. PMID:16866470

Santabarbara, Stefano; Carbonera, Donatella

2005-01-20

53

Triplet states via intermediate neglect of differential overlap: Benzene, pyridine and the diazines  

Microsoft Academic Search

The intermediate neglect of differential overlap technique is modified and applied to the calculation of excited triplet states. The resulting method generally reproduces the transition energies of the better-classified observations within a rms error of 1000 cm-1. Trends are well reproduced, and the calculated orders ofn-p* and p-p* triplet states are in good accord with the experimental information to date.

Joan E. Ridley; Michael C. Zerner

1976-01-01

54

Intersystem Crossings of the Triplet and Singlet States in Cobalt and Copper Mononitrosyls  

NASA Astrophysics Data System (ADS)

Local minima on the singlet, triplet, and quintet potential energy surfaces (PES) of cobalt and copper mononitrosyls are studied by DFT with the B3LYP functional. While quintet states are separated from the triplet and singlet states by a high energy gap, the linear singlet local minimum and the triplet transition state of CoNO lie close together. The ordering of local minima by relative stability of low-lying excited states with respect to the ground state was assessed by B3LYP, the coupled-cluster method CCSD(T), and complete active space calculations (CAS MP2). The ground state of CoNO is 3A'; two local minima were found in singlet states: linear, 1?+, and side-on configuration, 1A1. The occurrence of bound states on the triplet and singlet PES of CoNO and CuNO was examined by CASSCF. The crossing of the singlet and triplet PES of CoNO is a conical intersection; the geometry of the bound state is linear, with elongated N-O bond. The activation energy for the spin-forbidden transition 3A' ? 1?+ is estimated to be 154.7 kJ mol-1. For CuNO, the triplet and singlet PES do not cross but are separated by a small energy gap. Copper nitrosyl is of lower thermodynamic stability than cobalt nitrosyl. A triplet ground state 3A'' with bent configuration is predicted by B3LYP, confirmed by CAS MP2, and a very close-lying singlet state 1A' is found with nearly identical geometry. Unlike CoNO, the linear triplet CuNO in 3?- state is not a transition state, but a local minimum, lying close to the dissociation limit Cu + NO. Vibrational frequencies are calculated for the gas-phase molecules and for the metal nitrosyl entrapped in solid Ar matrix. Under the influence of the noble gas matrix, the energy gap between the singlet and the triplet CuNO is reduced, and the singlet and triplet states of bent CuNO become nearly isoenergetic in agreement with experimental data. The linear CoNO in 1?+ state is the most stable configuration in the Ar matrix, with one Ar atom coordinated to the metal center.

Uzunova, Ellie L.

2009-09-01

55

IR spectrum and localization of excitation of reaction center of photosystem II in triplet state  

NASA Astrophysics Data System (ADS)

Using the density functional theory, vibrations of different model forms of the chlorophyll a molecule in the ground and triplet states have been calculated. The assignment of the experimental difference IR spectrum corresponding to the formation of the triplet state of the photosynthetic reaction center of photosystem II has been proposed on this basis. It has been shown that molecules of accessory chlorophyll B A and B B located between the special pair and H A and H B pheophytin molecules can be involved in the intermolecular hydrogen bond with the water molecule. The energy of this interaction in the triplet state of molecules for B A is larger on 6 kcal/mol. This allows us to relate this pigment to the location of the triplet excitation at the reaction center of photosystem II.

Ivashin, N. V.

2010-04-01

56

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

PubMed

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

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

2011-05-01

57

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

58

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

E-print Network

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

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

2014-09-17

59

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

PubMed

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

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

2012-07-20

60

Intramolecular RET enhanced visible light-absorbing bodipy organic triplet photosensitizers and application in photooxidation and triplet-triplet annihilation upconversion.  

PubMed

Resonance energy transfer (RET) was used for the first time to enhance the visible light absorption of triplet photosensitizers. The intramolecular energy donor (boron-dipyrromethene, Bodipy) and acceptor (iodo-Bodipy) show different absorption bands in visible region, thus the visible absorption was enhanced as compared to the monochromophore triplet photosensitizers (e.g., iodo-Bodipy). Fluorescence quenching and excitation spectra indicate that the singlet energy transfer is efficient for the dyad triplet photosensitizers. Nanosecond time-resolved transient absorption spectroscopy has confirmed that the triplet excited states of the dyads are distributed on both the energy donor and acceptor, which is the result of forward singlet energy transfer from the energy donor to the energy acceptor and in turn the backward triplet energy transfer. This 'ping-pong' energy transfer was never reported for organic molecular arrays, and so it is useful to study the energy level of organic chromophores. The triplet photosensitizers were used for singlet oxygen ((1)O2) mediated photooxidation of 1,5-dihydroxylnaphthalene to produce juglone. The visible light absorption of the new visible light-absorbing triplet photosensitizers are higher than the conventional monochromophore based triplet photosensitizers, as a result, the (1)O2 photosensitizing ability is improved with the new triplet photosensitizers. Triplet-triplet annihilation upconversion with these triplet photosensitizers was also studied. Our results are useful to design the triplet photosensitizers showing strong visible light absorbance and for their applications in photocatalysis and photodynamic therapy. PMID:23790008

Zhang, Caishun; Zhao, Jianzhang; Wu, Shuo; Wang, Zilong; Wu, Wanhua; Ma, Jie; Guo, Song; Huang, Ling

2013-07-17

61

Triplet excited States as a source of relevant (bio)chemical information.  

PubMed

The properties of triplet excited states are markedly medium-dependent, which turns this species into valuable tools for investigating the microenvironments existing in protein binding pockets. Monitoring of the triplet excited state behavior of drugs within transport proteins (serum albumins and ?1-acid glycoproteins) by laser flash photolysis constitutes a valuable source of information on the strength of interaction, conformational freedom and protection from oxygen or other external quenchers. With proteins, formation of spatially confined triplet excited states is favored over competitive processes affording ionic species. Remarkably, under aerobic atmosphere, the triplet decay of drug@protein complexes is dramatically longer than in bulk solution. This offers a convenient dynamic range for assignment of different triplet populations or for stereochemical discrimination. In this review, selected examples of the application of the laser flash photolysis technique are described, including drug distribution between the bulk solution and the protein cavities, or between two types of proteins, detection of drug-drug interactions inside proteins, and enzyme-like activity processes mediated by proteins. Finally, protein encapsulation can also modify the photoreactivity of the guest. This is illustrated by presenting an example of retarded photooxidation. PMID:25515745

Jiménez, M Consuelo; Miranda, Miguel A

2014-01-01

62

The Paternò-Büchi reaction: importance of triplet states in the excited-state reaction pathway.  

PubMed

The Paternò-Büchi (PB) reaction between an excited carbonyl compound and an alkene has been widely studied, but so far little is known about the excited-state dynamics of the reaction. In this investigation, we used a compound in which a formyl and a vinyl group are attached to a [2.2]paracyclophane in order to obtain a model system in pre-reactive conformation for the PB reaction. We studied the excited-state dynamics of the isolated molecule in a molecular beam using femtosecond time-resolved photoelectron spectroscopy and ab initio calculations. The results show that inter-system crossing within two picoseconds competes efficiently with the reaction in the singlet manifold. Thus, the PB reaction in this model system takes place in the triplet state on a time scale of nanoseconds. This result stresses the importance of triplet states in the excited-state pathway of the PB reaction involving aromatic carbonyl compounds, even in situations in which the reacting moieties are in immediate vicinity. PMID:22614254

Brogaard, Rasmus Y; Schalk, Oliver; Boguslavskiy, Andrey E; Enright, Gary D; Hopf, Henning; Raev, Vitaly; Tarcoveanu, Eliza; Sølling, Theis I; Stolow, Albert

2012-05-21

63

Photochemistry of Squaraine Dyes: Excited Triplet State and Redox Properties of Crown Ether Squaraines  

E-print Network

Photochemistry of Squaraine Dyes: Excited Triplet State and Redox Properties of Crown Ether: October 17, 1995X The excited state and redox properties of three crown-ether derivatives of squaraines reported on the synthesis, photophysics, and metal ion binding properties of several crown ether

Sauvé, Geneviève

64

Porphyrin triplet state as a potential spin label for nanometer distance measurements by PELDOR spectroscopy.  

PubMed

This work demonstrates, for the first time, the feasibility of applying pulsed electron-electron double resonance (PELDOR/DEER) to determine the interspin distance between a photoexcited porphyrin triplet state (S = 1) and a nitroxide spin label chemically incorporated into a small helical peptide. The PELDOR trace shows deep envelope modulation induced by electron-electron dipole interaction between the partners in the pair, providing an accurate distance measurement. This new labeling approach has a high potential for measuring nanometer distances in more complex biological systems due to the sensitivity acquired from the spin polarization of the photoexcited triplet state spectrum. PMID:24735449

Di Valentin, Marilena; Albertini, Marco; Zurlo, Enrico; Gobbo, Marina; Carbonera, Donatella

2014-05-01

65

A DFT Study on Deactivation of Triplet Excited State Riboflavin by Polyphenols  

PubMed Central

The deactivation of triplet excited state riboflavin by polyphenols, e.g. rutin and catechin, was studied on the basis of density functional theory calculations. The results show that the H-atom transfer pathway is more feasible on thermodynamic grounds in comparison with the direct energy transfer or direct electron transfer pathways involved in the triplet excited state riboflavin deactivation by rutin/catechin. The findings are helpful to understand the protective effect of polyphenols against the riboflavin induced photosensitizing damage. PMID:19325725

Ji, Hong-Fang; Shen, Liang

2008-01-01

66

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

Microsoft Academic Search

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

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

1999-01-01

67

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

NASA Astrophysics Data System (ADS)

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

Dyakonov, Vladimir

2013-03-01

68

Exploring two-state reactivity pathways in the cycloaddition reactions of triplet methylene.  

PubMed

Spin forbidden 1,2-cycloadditions of triplet methylene to alkenes have been theoretically studied as an example of the two-state reactivity paradigm in organic chemistry. The cycloadditions of triplet methylene to ethylene and the (E)- and (Z)-2-butene isomers show spin inversion after the transition state and therefore with no effect on the reaction rate. A local analysis shows that while triplet methylene addition to alkenes leading to the formation of a biradical intermediate is driven by spin polarization, the ring closure step to yield cyclopropane is a pericyclic process. We have found that at the regions in the potential energy surface where the spin crossover is likely to occur, the spin potential in the direction of increasing spin multiplicity, mu(+)(s), tends to equalize the one in the direction of decreasing spin multiplicity, mu(-)(s). This equalization facilitates the spin transfer process driven by changes in the spin density of the system. PMID:16833743

Pérez, Patricia; Andrés, J; Safont, V S; Contreras, Renato; Tapia, O

2005-05-12

69

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

NASA Astrophysics Data System (ADS)

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

Huix-Rotllant, Miquel; Ferré, Nicolas

2014-04-01

70

A theoretical and observational analysis of He I triplet lines in class 1 Seyfert galaxy spectra  

NASA Technical Reports Server (NTRS)

The equations of statistical equilibrium are solved for 11 levels of the helium atom that are most relevant to the production and radiative transfer of He I triplet lines. Solutions are obtained for several densities and temperatures over a run of optical depth in the 10,830-A line, and the results for emission-line strengths are plotted. Spectrophotometric scans and pertinent line strengths are presented for the class 1 Seyfert galaxies 3C 120, NGC 7469, and Mrk 618, as well as for Mrk 335, which exhibits a 'more normal' He I 5876/H-beta ratio. A comparison of the theoretically determined line intensities with the observational results verifies that the He I triplet line intensities are significantly enhanced by electron collisional excitation from 2(3)P and 2(3)S. It is suggested that the gas which gives rise to the broad He I lines in 3C 120, Mrk 618, and NGC 7469 is characterized by a number density of about 5 billion per cu cm, a temperature of approximately 15,000 K, and an optical depth of 100 to 120 in the 10,830-A line.

Feldman, F. R.; Macalpine, G. M.

1978-01-01

71

Production and reactions of triplet CS: Matrix infrared and ultraviolet spectra of C{sub 2}S{sub 2}  

SciTech Connect

Matrix infrared and visible-ultraviolet absorption spectroscopy and ab initio electronic structure calculations have been used to characterize the reaction products from a Tesla coil Ar/CS{sub 2} discharge. The discharge is an excellent source of CS, which reacts with other molecules to form the major C{sub 3}S{sub 2} product and the transient C{sub 2}S{sub 2} species. The spectra of discharged mixed isotopic samples Ar/{sup 12}CS{sub 2}/{sub 13}CS{sub 2} and Ar/C{sup 32}S{sub 2} exhibit triplet patterns in the CS antisymmetric stretching region, which unambiguously identifies the new C{sub 2}S{sub 2} molecule with two equivalent CS subgroups. The magnitudes of the {sup 12,13}C and {sup 32,34}S isotopic shifts further characterize the diatomic CS subgroup nature of C{sub 2}S{sub 2}. Another product contains two equivalent CS subgroups interacting with inequivalent S atom(s). The formation of C{sub 2}S{sub 2}({sup 3}{Sigma}) from the simple CS{sub 2} discharge requires triplet CS. Evidence was also obtained for other transient cumulene species. 32 refs., 8 figs., 7 tabs.

Bohn, R.B.; Hannachi, Y.; Andrews, L. [Univ. of Virginia, Charlottesville, VA (United States)

1992-07-29

72

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

73

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

SciTech Connect

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

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

2011-02-15

74

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

75

State-resolved thermalization of singlet and mixed singlet-triplet states of CH2.  

PubMed

The role of mixed states in the collision-induced thermalization, intersystem crossing, and reactive loss of CH(2) (~a (1)A1) has been monitored using Doppler-resolved transient frequency modulation absorption spectroscopy. Singlet CH(2) is produced in a hot initial distribution of translation and rotational energy states in the 308 nm photodissociation of ketene in a large excess of argon. Collisions with Ar and ketene cool the translational and rotational degrees of freedom, while depleting the total singlet CH(2) population through reaction and intersystem crossing. Direct monitoring of the time-dependent populations of rotational levels containing mixed singlet and triplet character reveals a rapid interconversion between the two components, but no discernable difference between the kinetics of the pure singlet and mixed states at longer times. PMID:16965013

Komissarov, Anatoly V; Lin, Ao; Sears, Trevor J; Hall, Gregory E

2006-08-28

76

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

PubMed Central

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

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

2010-01-01

77

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

78

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

NASA Astrophysics Data System (ADS)

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

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

2011-12-01

79

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

PubMed

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

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

2015-03-12

80

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

NASA Astrophysics Data System (ADS)

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

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

2007-05-01

81

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

PubMed

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

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

2015-02-01

82

Pulse ENDOR and density functional theory on the peridinin triplet state involved in the photo-protective mechanism in the peridinin-chlorophyll a-protein from Amphidinium carterae.  

PubMed

The photoexcited triplet state of the carotenoid peridinin in the Peridinin-chlorophyll a-protein of the dinoflagellate Amphidinium carterae has been investigated by pulse EPR and pulse ENDOR spectroscopies at variable temperatures. This is the first time that the ENDOR spectra of a carotenoid triplet in a naturally occurring light-harvesting complex, populated by energy transfer from the chlorophyll a triplet state, have been reported. From the electron spin echo experiments we have obtained the information on the electron spin polarization dynamics and from Mims ENDOR experiments we have derived the triplet state hyperfine couplings of the alpha- and beta-protons of the peridinin conjugated chain. Assignments of beta-protons belonging to two different methyl groups, with aiso=7.0 MHz and aiso=10.6 MHz respectively, have been made by comparison with the values predicted from density functional theory. Calculations provide a complete picture of the triplet spin density on the peridinin molecule, showing that the triplet spins are delocalized over the whole pi-conjugated system with an alternate pattern, which is lost in the central region of the polyene chain. The ENDOR investigation strongly supports the hypothesis of localization of the triplet state on one peridinin in each subcluster of the PCP complex, as proposed in [Di Valentin et al. Biochim. Biophys. Acta 1777 (2008) 186-195]. High spin density has been found specifically at the carbon atom at position 12 (see Fig. 1B), which for the peridinin involved in the photo-protective mechanism is in close contact with the water ligand to the chlorophyll a pigment. We suggest that this ligated water molecule, placed at the interface between the chlorophyll-peridinin pair, is functioning as a bridge in the triplet-triplet energy transfer between the two pigments. PMID:18243124

Di Valentin, Marilena; Ceola, Stefano; Agostini, Giancarlo; Giacometti, Giorgio Mario; Angerhofer, Alexander; Crescenzi, Orlando; Barone, Vincenzo; Carbonera, Donatella

2008-03-01

83

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

84

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

NASA Astrophysics Data System (ADS)

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

Nickel, Bernhard; Roden, Gabriele

1982-04-01

85

Kinetic Parameters of Photo-Excited Triplet State of Pentacene Determined by Dynamic Nuclear Polarization  

NASA Astrophysics Data System (ADS)

The lifetimes and spin-lattice relaxation time of photo-excited triplet electron of pentacene doped in p-terphenyl at room temperature have been investigated. Values of spin-lattice relaxation time previously reported in ESR studies are inconsistent with each other. In this paper, we determined these time constants based on proton signals enhanced by dynamic nuclear polarization using the electrons (Triplet-DNP). The combined analysis of dependences of proton signal intensities on the delay time of polarization transfer and laser pulse structure allows us to disentangle contributions of the lifetimes and spin-lattice relaxation time. The lifetimes of triplet sublevels with ms = 0 and ±1 were determined to be 22.3 and 88 µs, respectively. The spin-lattice relaxation time was found to be longer than 300 µs, hence the time evolution of the electron population in the triplet state is governed by the lifetimes. It was also found that the proton signal enhancement is limited at a high repetition rate by the partial cancellation of the electron spin polarization by the remaining population produced by the preceding laser pulses.

Kawahara, Tomomi; Sakaguchi, Satoshi; Tateishi, Kenichiro; Tang, Tsz Leung; Uesaka, Tomohiro

2015-04-01

86

Spectra of Herbig Ae/Be stars in the region of the Ca II infrared triplet.  

NASA Astrophysics Data System (ADS)

Near-infrared spectra of 9 Herbig Ae/Be stars and 3 Be stars of ? Cas-type were obtained on an infrared image tube. Strong Ca II, P11-P20 and O I 8446 emission lines were identified, similar to the emission spectrum of T Tauri-type stars.

Kotyshev, V. V.

87

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

PubMed

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

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

2002-04-01

88

Theoretical Study on Reactions of Triplet Excited State Thioxanthone with Indole  

PubMed Central

In the present work, a theoretical study on the deactivation of triplet excited (T1) state thioxanthone (TX) by indole (INH) was performed, based on density functional theory calculations. Three feasible pathways, namely direct electron transfer from INH to T1 state TX, electron transfer followed by proton transfer from INH.+ to TX.?, and H-atom transfer from nitrogen of INH to keto oxygen of T1 state TX, were proposed theoretically to be involved in T1 state TX deactivation by INH. PMID:20057945

Shen, Liang; Ji, Hong-Fang

2009-01-01

89

Wave packet dynamics in triplet states of Na2 attached to helium nanodroplets.  

PubMed

The dynamics of vibrational wave packets excited in Na2 dimers in the triplet ground and excited states is investigated by means of helium nanodroplet isolation (HENDI) combined with femtosecond pump-probe spectroscopy. Different pathways in the employed resonant multiphoton ionization scheme are identified. Within the precision of the method, the wave packet dynamics appears to be unperturbed by the helium droplet environment. PMID:17461563

Claas, Patrick; Droppelmann, Georg; Schulz, Claus Peter; Mudrich, Marcel; Stienkemeier, Frank

2007-08-01

90

A theoretical study of selected singlet and triplet states of CO molecule  

NASA Technical Reports Server (NTRS)

The results of the configuration calculations of six singlet electronic states and one triplet electronic state of CO are presented. The potential energy curves, spectroscopic constants, and electron transition moments are calculated, along with electronic dipole moment functions for three states. The self consistent field and configuration calculations used to obtain the electronic wave functions are described. The theoretical results are found to be in good agreement with the experimental measurements, and in the case of the dipole moment function calculations, preferable to them.

Cooper, D. M.; Langhoff, S. R.

1981-01-01

91

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

NASA Astrophysics Data System (ADS)

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

Sapunov, V. V.

1992-10-01

92

Anthralin-derived transients--I. The triplet state and the products of its reaction with oxygen in benzene.  

PubMed

Direct laser excitation in benzene of 1,8-dihydroxy-9-anthrone (anthralin) does not lead to transient species with lifetimes in the nanosecond time regime or longer. The triplet state has been produced in benzene by pulse radiolysis and characterised in terms of its absorption spectrum (lambda max 560 nm), natural lifetime (11 microseconds), self-quenching properties (kmicrosecond = 2.6 x 10(7) l mol-1 s-1) and triplet energy (234 kJ mol-1). There is no tendency in the non-polar medium for production of either the triplet or ground state in a tautomeric form. The observed triplet state reacts with oxygen with a typical rate constant, 2.2 x 10(9) l mol-1 s-1. The products of this reaction are singlet oxygen (approximately 64%) and the anthralin radical (approximately 14%). PMID:2727083

Bruce, J M; Gorman, A A; Hamblett, I; Kerr, C W; Lambert, C; McNeeney, S P

1989-04-01

93

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.

94

Total Cross Sections for the Excitation of the Triplet States in Molecular Nitrogen  

Microsoft Academic Search

A consistent set of total cross sections for electron impact excitation of the A3Sigma+u, B3Pig, W3Deltau, B'3Sigma-u, C3Piu, E3Sigma+g, and D3Sigma+u triplet states of molecular nitrogen from the X1Sigma+g state has been calculated quantum mechanically for incident electron energies from threshold to 80 eV. The Ochkur-Rudge exchange scattering and Franck-Condon approximations were employed to obtain these cross sections. Minimum and

D. C. Cartwright

1970-01-01

95

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

SciTech Connect

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

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

2014-01-28

96

Rydberg and autoionizing triplet states in Helium up to the N = 5 threshold  

SciTech Connect

Energy levels of highly excited bound Rydberg states, the position and widths of autoionizing states, and oscillator strengths are calculated for He {sup 3}S, {sup 3}P{sup e}, {sup 3}P{sup o}, {sup 3}D{sup e} and {sup 3}D{sup o} symmetries up to the N = 5 He{sup +} excitation threshold. The calculations are performed with the K-matrix B-spline method with maximum orbital angular momentum l{sub max} = 8. Reliable doubly excited-state parameters up to the n = 20 multiplet below each ionization threshold are presented. One thousand and six hundred newly identified bound and metastable states, seven times those available in literature, fill many gaps, reveal a dozen intruder states, and allow new speculations on propensity rules and radiative decays of triplet Rydberg states.

Argenti, L. [DICASM, Universita di Bologna, via Saragozza 8, I-40136 Bologna (Italy)], E-mail: luca.argenti@gmail.com

2008-11-15

97

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

SciTech Connect

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

Burkhart, R.D.

1998-01-01

98

Singlet and triplet states of trions in ZuSe-based quantum wells probed by magnetic fields to 50 Tesla  

SciTech Connect

Singlet and triplet states of positively (X{sup +}) and negatively (X{sup -}) charged excitons in ZnSe-based quantum wells have been studied by means of photoluminescence in pulsed magnetic fields up to 50 T. The binding energy of the X{sup -} singlet state shows a monotonic increase with magnetic field with a tendency to saturation, while that of the X{sup +} slightly decreases. The triplet X{sup +} and X{sup -} states, being unbound at zero magnetic field, noticeably increase their binding energy in high magnetic fields. The experimental evidence for the interaction between the triplet and singlet states of lTions leading to their anticrossing in magnetic fields has been found.

Astakhov, G. V.; Yakovlev, D. R.; Crooker, S. A. (Scott A.); Barrick, T. (Todd); Dzyubenko, A. B.; Sander, Thomas; Kochereshko, V. P.; Ossau, W.; Faschinger, W.; Waag, A.

2002-01-01

99

Laser-induced reduction of a dye characterised by a high triplet-state yield and dissolved in a polymer  

SciTech Connect

An investigation was made of the photoreduction kinetics of a dye in a solid polymer solution under the influence of laser radiation corresponding to the band of the first singlet - singlet transition. Participation of higher triplet states was considered in a model of the photoreduction of a dye characterised by a high intersystem crossing yield. An analytic solution was obtained for a system of kinetic equations. This solution takes into account the difference between the photoprocess rates. It is shown that a linear dependence of the effective dye-photoreduction rate on the laser radiation intensity can serve as a test of the participation of higher triplet states in the reaction. A comparison of the theoretical and experimental results obtained in the present study is used to determine the ratio of the photoreduction and deactivation rate constants of the higher triplet state of eosin K. (interaction of laser radiation with matter. laser plasma)

Sizykh, A G; Tarakanova, E A; Tatarinova, L L [Quantum Electronics Division, Krasnoyarsk State University, Krasnoyarsk (Russian Federation)

2000-01-31

100

Valence isomerization of quadricyclane-norbornadiene derivatives via triplet state. Correlation of the mechanism with triplet conformation of the olefinic moiety  

NASA Astrophysics Data System (ADS)

The mechanism of the valence isomerization between methyl 5-aryl-tetracyclo[3.2.0.0 2,70 4,6]-heptane-1-carboxylate ( 1) and methyl 3-aryl-bicyclo[2.2.1]hepta-2,5-diene-2-carboxylate ( 2) under the triplet sensitization in benzene has been studied by pulse radiolysis and stationary experiments. The valence isomerization proceeds via a 1,3-biradical intermediate favorably to 1 for the phenyl derivatives where the most stable conformation of the corresponding olefinic analogue is a twisted form. In the case of 1-naphthyl derivatives where the conformation of the olefinic analogue is a planar form, an adiabatic cycloreversion of 1 to 2 takes place. An equilibrium state between a 1,3-biradical intermediate and a triplet state with a structure of norbornadiene is estimated for 2-naphthyl derivatives. Correlation of the mechanism for the valence isomerization with the conformation of corresponding olefinic analogue has been discussed on the basis of the potential energy surfaces for the isomerization.

Nakabayashi, Kenichi; Nishino, Hideo; Toki, Susumu; Takamuku, Setsuo

101

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

102

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

103

Two-Qubit Couplings of Singlet-Triplet Qubits Mediated by One Quantum State  

E-print Network

We describe high-fidelity entangling gates between singlet-triplet qubits (STQs) which are coupled via one quantum state (QS). The QS can be provided by a quantum dot itself or by another confined system. The orbital energies of the QS are tunable using an electric gate close to the QS, which changes the interactions between the STQs independent of their single-qubit parameters. Short gating sequences exist for the controlled NOT (CNOT) operations. We show that realistic quantum dot setups permit excellent entangling operations with gate infidelities below $10^{-3}$, which is lower than the quantum error correction threshold of the surface code. We consider limitations from fabrication errors, hyperfine interactions, spin-orbit interactions, and charge noise in GaAs and Si heterostructures.

Sebastian Mehl; Hendrik Bluhm; David P. DiVincenzo

2014-08-05

104

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

E-print Network

, suggesting a specific role for each of them. The recently published structure of LHCII (4), the major antennaSinglet and Triplet State Transitions of Carotenoids in the Antenna Complexes of Higher characteristics of carotenoids associated with the antenna complexes of Photosystem I have been studied. Pigment

Romeo, Alessandro

105

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

106

Reaction of the m-THPC triplet state with the antioxidant Trolox and the anesthetic Propofol: modulation of photosensitization mechanisms relevant to photodynamic therapy?  

PubMed

Antioxidants may affect the outcome of photodynamic therapy (PDT) through the inactivation of reactive oxygen species. Their direct interaction with photosensitizers excited at the triplet state is also worthy of interest. This process is investigated by laser flash photolysis of m-THPC (meso-tetra(3-hydroxyphenyl)chlorin, Foscan) hydroalcoholic solutions added with Trolox (TrOH), a standard antioxidant or Propofol (PfOH, Diprivan(®)), a common anesthetic agent also characterized for its antioxidant properties. Transient UV-visible absorption spectra, kinetics at selected wavelengths and final spectra after extensive laser irradiation show that both compounds react with the m-THPC triplet state, (3)m-THPC, to ultimately restore the photosensitizer in its ground state. For PfOH, this process mainly appears as a single step obeying pseudo-first order kinetics. The bimolecular rate constant for the quenching of (3)m-THPC by PfOH is around 2 × 10(6) M(-1) s(-1), a value increased to some extent by the water content of the solution. A bimolecular reaction between (3)m-THPC and TrOH is observed with a rate constant of similar magnitude and dependence upon water. However, the reaction leads, at least partly, to intermediate species assigned to the TrO? radical and the m-THPC anion radical. Within a few ms, these species back react to yield m-THPC in its ground state. A general mechanism involving an intermediate activated complex with some charge transfer character is proposed. Depending on the redox potentials for the oxidation of the antioxidant, this complex evolves predominantly either toward the formation of radicals (TrOH) or back to the photosensitizer ground state (PfOH). Notably, the kinetics data suggest that Propofol may quench (3)m-THPC at concentrations relevant of clinical situation in PDT involving anesthesia. PMID:22307091

Friaa, O; Maillard, P; Brault, D

2012-04-01

107

Enhanced Access to the Dark Triplet States of 7Li 2 through New Singlet-Triplet A1? +u ˜ b3? u Perturbation Window Levels: Perturbation-Facilitated Optical-Optical Double Resonance Study of the 2 3? +g State  

NASA Astrophysics Data System (ADS)

Two new pairs of singlet-triplet A1?+u ? b3?u mixed levels of 7Li2 have been observed and used here as 'window' levels in cw perturbation-facilitated optical-optical double-resonance (PFOODR) experiments. Previously, only one b3?u vibrational level, v = 19, was known to mix with the singlet A1?+uv = 13 level, resulting in three perturbed A ? b pairs [L. Li, T. An, T.-J. Whang, A. M. Lyyra, W. C. Stwalley, R. W. Field, and R. A. Bernheim, J. Chem. Phys. 96, 3342 (1992)]. The scarcity of window levels and the resulting difficulty in accessing the dark triplet states of Li2 is caused by the weak spin-orbit interaction of Li2. The two new mixed b3?uv = 15 and 22 levels reported here enhance access to the dark triplet state manifold through expansion of the Franck-Condon overlap factor range. Furthermore, the earlier range of accessible rotational levels, N = 5, 7, and 10, is now expanded to include N = 8 and N = 16, thereby allowing for more reliable determination of the excited triplet states rotational structure. To demonstrate the importance of the new A1?+u ? b3?u mixed levels, we have studied the 23?+g state by cw PFOODR fluorescence excitation spectroscopy. New molecular constants and RKR potential curve have been determined. As previously reported [L. Li, G. Lazarov, and A. M. Lyyra, J. Mol. Spectrosc. 191, 387 (1998)], the 23?+g state interacts with the repulsive 13?g state by L-uncoupling and predissociates. We show that some 23?g levels predissociate accidentally by the 13?g state via the 23?+g state through L-uncoupling.

Lazarov, Guenadiy; Lyyra, A. Marjatta; Li, Li

2001-01-01

108

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

109

Triplet-triplet energy transfer in Peridinin-Chlorophyll a-protein reconstituted with Chl a and Chl d as revealed by optically detected magnetic resonance and pulse EPR: comparison with the native PCP complex from Amphidinium carterae.  

PubMed

The triplet state of the carotenoid peridinin, populated by triplet-triplet energy transfer from photoexcited chlorophyll triplet state, in the reconstituted Peridinin-Chlorophyll a-protein, has been investigated by ODMR (Optically detected magnetic resonance), and pulse EPR spectroscopies. The properties of peridinins associated with the triplet state formation in complexes reconstituted with Chl a and Chl d have been compared to those of the main-form peridinin-chlorophyll protein (MFPCP) isolated from Amphidinium carterae. In the reconstituted samples no signals due to the presence of chlorophyll triplet states have been detected, during either steady state illumination or laser-pulse excitation. This demonstrates that reconstituted complexes conserve total quenching of chlorophyll triplet states, despite the biochemical treatment and reconstitution with the non-native Chl d pigment. Zero field splitting parameters of the peridinin triplet states are the same in the two reconstituted samples and slightly smaller than in native MFPCP. Analysis of the initial polarization of the photoinduced Electron-Spin-Echo detected spectra and their time evolution, shows that, in the reconstituted complexes, the triplet state is probably localized on the same peridinin as in native MFPCP although, when Chl d replaces Chl a, a local rearrangement of the pigments is likely to occur. Substitution of Chl d for Chl a identifies previously unassigned bands at approximately 620 and approximately 640 nm in the Triplet-minus-Singlet (T-S) spectrum of PCP detected at cryogenic temperature, as belonging to peridinin. PMID:19150328

Di Valentin, Marilena; Agostini, Giancarlo; Salvadori, Enrico; Ceola, Stefano; Giacometti, Giorgio Mario; Hiller, Roger G; Carbonera, Donatella

2009-03-01

110

Laser-induced phosphorescence spectroscopy in supersonic jets. The lowest triplet states of glyoxal, methylglyoxal, and biacetyl  

Microsoft Academic Search

We report the first structural study of the lowest triplet states of three ?-dicarbonyls (glyoxal, methylglyoxal, and biacetyl) using the technique of laser-induced phosphorescence (LIP) spectroscopy in supersonic jets. At the level of vibrational resolution, 3Au glyoxal appears to have a geometry very similar to that of the ground state. But the T1?S0 transitions of methylglyoxal and biacetyl each exhibit

Lee H. Spangler; David W. Pratt

1986-01-01

111

Vibrational frequencies of the ground and lowest excited triplet state of thioformaldehyde h2, d2, and hd  

NASA Astrophysics Data System (ADS)

Harmonic vibrational frequencies calculated by ab initio methods with double zeta plus polarization basis sets are reported for the ? and ? states of H2CS, D2CS, and HDCS. These frequencies are scaled to predict as yet unknown experimental values. For the triplet state, vibrational energy levels are given for a double minimum potential in the out-of-plane bending coordinate within a rigid bender approximation.

Goddard, J. D.; Clouthier, D. J.

1982-05-01

112

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

NASA Astrophysics Data System (ADS)

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

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

2013-03-01

113

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

114

Triplet photosensitizers: from molecular design to applications.  

PubMed

Triplet photosensitizers (PSs) are compounds that can be efficiently excited to the triplet excited state which subsequently act as catalysts in photochemical reactions. The name is originally derived from compounds that were used to transfer the triplet energy to other compounds that have only a small intrinsic triplet state yield. Triplet PSs are not only used for triplet energy transfer, but also for photocatalytic organic reactions, photodynamic therapy (PDT), photoinduced hydrogen production from water and triplet-triplet annihilation (TTA) upconversion. A good PS should exhibit strong absorption of the excitation light, a high yield of intersystem crossing (ISC) for efficient production of the triplet state, and a long triplet lifetime to allow for the reaction with a reactant molecule. Most transition metal complexes show efficient ISC, but small molar absorption coefficients in the visible spectral region and short-lived triplet excited states, which make them unsuitable as triplet PSs. One obstacle to the development of new triplet PSs is the difficulty in predicting the ISC of chromophores, especially of organic compounds without any heavy atoms. This review article summarizes some molecular design rationales for triplet PSs, based on the molecular structural factors that facilitate ISC. The design of transition metal complexes with large molar absorption coefficients in the visible spectral region and long-lived triplet excited states is presented. A new method of using a spin converter to construct heavy atom-free organic triplet PSs is discussed, with which ISC becomes predictable, C60 being an example. To enhance the performance of triplet PSs, energy funneling based triplet PSs are proposed, which show broadband absorption in the visible region. Applications of triplet PSs in photocatalytic organic reactions, hydrogen production, triplet-triplet annihilation upconversion and luminescent oxygen sensing are briefly introduced. PMID:23450221

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

2013-06-21

115

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

SciTech Connect

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

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

2014-10-02

116

Formation of the Triplet State of Naphthalene in the Pulse Radiolysis of Gaseous Mixtures of Benzene and Naphthalene  

Microsoft Academic Search

A significant yield of the lowest triplet state of naphthalene is observed when 1.9 atm benzene containing small amounts of naphthalene is pulse irradiated in the gas phase at 120°C. The yield is independent of naphthalene concentration from 0.3 mole % to at least 3 mole %. Electron scavengers (SF6 and CCl4) decrease the yield by 70%, as does a

Masaru Nishikawa; Myran C. Sauer Jr.

1969-01-01

117

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

Microsoft Academic Search

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

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

2008-01-01

118

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

119

Kinetics of electron transfer in quenching of triplet state of xanthene dyes by cyanide complexes of transition metals  

SciTech Connect

The authors investigated the kinetics of electron transfer between molecules of dyes in the TS (eosin, Bengal rose) and cyanide complexes of Fe(II), Fe(III), Mo(IV), W(IV), Ru(II), and Co(III) in aqueous solutions. The authors found that electron transfer is the principal mechanism for quenching of the triplet state of eosin and Bengal rose by cyanide complexes of W(IV), Mo(IV), Fe(II), and Fe(III). The systems consisting of eosin or Bengal rose and cyanide complexes are not characterized by a single value of the internal barrier to electron transfer. Values have been calculated for the internal barriers to the electron transfer reaction in quenching of the triplet state of eosin and Bengal rose by cyanide complexes of W(IV), Mo(IV), Fe(II), Fe(III), Co(III), and Ru(II), and values have been estimated for the internal barriers to self-exchange reactions of eosin and Bengal rose in the triplet state.

Zakharova, G.V.; Knoll, H.; Hennig, H.; Chibisov, A.K.

1987-09-10

120

Computational Modeling of the Triplet Metal-to-Ligand Charge-Transfer Excited-State Structures of Mono-Bipyridine-Ruthenium(II)  

E-print Network

of Mono-Bipyridine-Ruthenium(II) Complexes and Comparisons to their 77 K Emission Band Shapes Richard L in the lowest energy triplet metal to ligand charge-transfer (3 MLCT = T0) excited states of ruthenium

Schlegel, H. Bernhard

121

Solvent-induced changes on the polarity of the triplet excited state of 2-chlorothioxanthone: From time-resolved absorption and resonance Raman spectroscopies  

NASA Astrophysics Data System (ADS)

Solvent polarity has been known to influence the triplet state structure and reactivity. Here, we present our experimental and theoretical study on the effect of solvent on the lowest triplet excited state structure of 2-chlorothioxanthone (CTX). Time-resolved absorption (TA) spectroscopy has been employed to understand the triplet state electronic structure; whereas solvent-induced structural changes have been studied using time-resolved resonance Raman (TR3) spectroscopy. Both the DFT and TD-DFT calculations have been performed in the solution phase employing self-consistent reaction field implicit solvation model to support the experimental data. It has been observed that CO stretching frequencies of the excited triplet state are sensitive to the solvent polarity and increase with the increase in the solvent polarity. Both TA and TR3 studies reveal that specific solvent effect (H-bonding) is more pronounced in comparison to the nonspecific solvent effect.

Pandey, Rishikesh; Umapathy, Siva

2014-01-01

122

ENDOR on the triplet state of the primary electron donor in the photosynthetic bacterium Rhodobacter sphaeroides — One step forward in a still unfinished story  

Microsoft Academic Search

The electronic structure of the primary electron donor (D) of the photosynthetic bacteriumRhodobacter sphaeroides is investigated by ENDOR in the photoinduced triplet state of D. Hyperfine (hf) splittings of the triplet state measured\\u000a on frozen solutions are given and compared to the results obtained earlier (Lendzian F., van Willigen H., Sastry S., Möbius\\u000a K., Scheer H., Feick R.: Chem. Phys.

M. Huber; A. A. Doubinskii; C. W. M. Kay; K. Möbius

1997-01-01

123

Triplet state magnetic resonance and fluorescence spectroscopy of metal-substituted hemoglobins.  

PubMed

Fluorescence detected magnetic resonance (FDMR) spectra detected at 596 nm of zinc-substituted hemoglobins at 4.2 K show a split D-E transition, which is not observed for zinc protoporphyrins ligated by methylimidazole in glasses. Incorporation of the zinc heme into the globin pocket is also accompanied by a blue shift of the fluorescence of 20 nm at 4.2 K. FDMR spectra recorded at 576 nm do not show the D-E splitting. The D-E splitting and the huge blue shift are not observed for the magnesium-substituted hemoglobins. Fluorescence measurements at 4.2 K and 77 K, and EPR measurements at 110 K, were carried out to obtain information about the ligation states of the zinc and magnesium protoporphyrins in glasses and in hemoglobin. The results are explained by considering ligation effects and distortion of the porphyrin plane. PMID:8994622

Polm, M W; Schaafsma, T J

1997-01-01

124

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

125

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

PubMed Central

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

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

2012-01-01

126

The metastable triplet state of CrO2 - 4 in a calcium sulphate host: Electron-spin-echo experiments  

NASA Astrophysics Data System (ADS)

An electron paramagnetic resonance (EPR) study with laser flash excitation and electron-spin-echo detection is reported on the very weakly luminescent state of the CrO2-4 ion in an anhydrite (CaSO4) host. On excitation a lowering of symmetry of the chromate ion occurs, and four sets of congruent excited species are observed, interrelated by the orthorhombic symmetry of the crystal. The results can be fitted to a spin Hamiltonian for an orbitally nondegenerate triplet state with parameters D=-20.337 GHz, E=-0.211 GHz, g11=1.961, g22= 1.989, and g33=1.9817. The relaxation behavior of the triplet state has been studied by varying (1) the delay between the laser flash and the first microwave pulse and (2) the interval ? between the microwave pulses. The lifetimes of the zero-field spin states are ?x=2.2, ?y=0.73, and ?z=0.023 ?s. Because of the very fast decay of the Tz level and attendant very short relaxation time T2 for most orientations of the magnetic field, the four ``allowed'' stationary EPR transitions in our X-band experiment could only be observed by using a stripline cavity and reducing ? to less than 100 ns.

Coremans, C. J. M.; Groenen, E. J. J.; van der Waals, J. H.

1990-09-01

127

Triplet excitations in carbon nanostructures  

NASA Astrophysics Data System (ADS)

We show that the energy differences between the lowest optical singlet exciton and the lowest triplet exciton in semiconducting single-walled carbon nanotubes with diameter ˜1 nm and graphene nanoribbons with widths ˜2 nm are an order of magnitude smaller than in the ?-conjugated polymer poly(para-phenylenevinylene). Our calculated energy gaps between the singlet and triplet excitons are in excellent agreement with the measured values in three different nanotubes with diameters close to 1 nm. The spatial extent of the triplet exciton is nearly the same as that of the singlet exciton in wide nanotubes and nanoribbons, in contrast to that in ?-conjugated polymers in which the triplet exciton exhibits strong spatial confinement. Weakly confined behavior of the triplet state begins in nanoribbons with widths as narrow as 2.5 times the graphene unit lattice vector. We discuss possible consequences of the small singlet-triplet energy difference in the carbon nanostructures on device applications.

Aryanpour, K.; Mazumdar, S.; Zhao, H.

2012-02-01

128

Switching of the triplet excited state of styryl 2,6-diiodo-bodipy and its application in acid-activatable singlet oxygen photosensitizing.  

PubMed

IodoBodipy-styrylBodipy dyads triplet photosensitizers were prepared (B-1 and B-2) which contain acid-responsive moiety. Both compounds show broadband visible light absorption, due to the resonance energy transfer (RET) between the two different visible light-harvesting Bodipy units. The photophysical properties of the dyads were studied with steady-state and nanosecond time-resolved transient absorption spectroscopy. The production of triplet excited state is switched ON or OFF by protonation/deprotonation of the amino group in the dyads. In the neutral form, the excited state is short-lived (<10 ns) and no singlet oxygen ((1)O2) photosensitizing was observed. Upon protonation, a long-lived triplet excited state was observed (?T = 3.1 ?s) and the (1)O2 quantum yield (??) is up to 73.8%. The energy levels of the components of the dyads were changed upon protonation and this energy level tuning exerts significant influence on the triplet state property of the dyad. Acid-activated shuffling of the localization of the triplet excited state between two components of a dyad was observed. Furthermore, we observed a rare example that a chromophore giving shorter absorption wavelength is acting as the singlet energy acceptor in RET. The experimental results were rationalized by density functional theory (DFT) and time-dependent DFT (TDDFT) calculations. PMID:25279767

Huang, Ling; Yang, Wenbo; Zhao, Jianzhang

2014-11-01

129

Observation of the long-lived triplet excited state of perylenebisimide (PBI) in C^N cyclometalated Ir(III) complexes and application in photocatalytic oxidation.  

PubMed

Perylenebisimide (PBI) was used to prepare C^N cyclometalated Ir(III) complexes that show strong absorption of visible light and it is the first time the long-lived triplet excited state of PBI chromophore was observed in a transition metal complex (?T = 22.3 ?s). Previously, the lifetime of the triplet state of PBI in transition metal complexes was usually shorter than 1.0 ?s. Long-lived triplet excited states are useful for applications in photocatalysis or other photophysical processes concerning triplet-triplet-energy-transfer. PBI and amino-PBI were used for preparation of cyclometalated Ir(III) complexes (Ir-2 and Ir-3), in which the PBI chromophore was connected to the coordination center via C?C ?-conjugation bond. The new complexes show strong absorption in visible region (? = 34,200 M(-1) cm(-1) at 541 nm for Ir-2, and ? = 19,000 at 669 nm for Ir-3), compared to the model complex Ir(ppy)(bpy)[PF6] Ir-1 (? < 5000 M(-1) cm(-1) in the region beyond 400 nm). The nanosecond time-resolved transient absorption and DFT calculations indicated that PBI-localized long-lived (3)IL states were populated for Ir-2 and Ir-3 upon photoexcitation. The complexes were used as triplet photosensitizers for (1)O2-mediated photooxidation of 1,5-dihydronaphthalene to produce juglone, an important intermediate for preparation of anti-cancer compounds. (1)O2 quantum yields (?(?)) up to 91% were observed for the new Ir(III) complexes and the overall photosensitizing ability is much higher than the conventional Ir(III) complex Ir-1, which shows the typical weak visible light absorption in visible region. Our results are useful for preparation of transition metal complexes that show strong absorption of visible light and long-lived triplet excited state and for the application of these complexes in photocatalysis. PMID:23677279

Sun, Jifu; Zhong, Fangfang; Zhao, Jianzhang

2013-07-14

130

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

NASA Astrophysics Data System (ADS)

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

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

2003-03-01

131

Geminate and Nongeminate Recombination of Triplet Excitons Formed by Singlet Fission  

NASA Astrophysics Data System (ADS)

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

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

2014-06-01

132

Triplet electron paramagnetic resonance detection of porphyrinoids in fluid liquid crystals at elevated temperatures  

NASA Astrophysics Data System (ADS)

The photoexcited triplet state of two porphyrinoids, H2TTP and a Cd complex of Texaphyrin (Cd-TxP), oriented in liquid crystals were examined by time-resolved electron paramagnetic resonance (EPR) spectroscopy as a function of temperature. The low probability of molecular tumbling in the liquid crystalline phase allows the detection of triplets by fast EPR, at temperatures (300 K) which are above the hosts' melting points, and where the fluid properties of the matrices are maintained. Line shape and kinetic analyses of the triplet spectra provide data on spin relaxation rates, interchromophore interactions, and on the dynamic behavior of the liquid crystalline hosts, driven by the external magnetic field.

Regev, Ayelet; Levanon, Haim; Murai, Toshiaki; Sessler, Jonathan L.

1990-04-01

133

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

134

Triplet-triplet energy transfer in the major intrinsic light-harvesting complex of Amphidinium carterae as revealed by ODMR and EPR spectroscopies.  

PubMed

We present an optically detected magnetic resonance (ODMR) and electron paramagnetic resonance (EPR) spectroscopic study on the quenching of photo-induced chlorophyll triplet states by carotenoids, in the intrinsic light-harvesting complex (LHC) from the dinoflagellate Amphidinium carterae. Two carotenoid triplet states, differing in terms of optical and magnetic spectroscopic properties, have been identified and assigned to peridinins located in different protein environment. The results reveal a parallelism with the triplet-triplet energy transfer (TTET) process involving chlorophyll a and luteins observed in the LHC-II complex of higher plants. Starting from the hypothesis of a conserved alignment of the amino acid sequences at the cores of the LHC and LHC-II proteins, the spin-polarized time-resolved EPR spectra of the carotenoid triplet states of LHC have been calculated by a method which exploits the conservation of the spin momentum during the TTET process. The analysis of the spectra shows that the data are compatible with a structural model of the core of LHC which assigns the photo-protective function to two central carotenoids surrounded by the majority of Chl a molecules present in the protein, as found in LHC-II. However, the lack of structural data, and the uncertainty in the pigment composition of LHC, leaves open the possibility that this complex posses a different arrangement of the pigments with specific centers of Chl triplet quenching. PMID:20599677

Di Valentin, Marilena; Salvadori, Enrico; Agostini, Giancarlo; Biasibetti, Federico; Ceola, Stefano; Hiller, Roger; Giacometti, Giorgio Mario; Carbonera, Donatella

2010-10-01

135

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

E-print Network

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

van Stokkum, Ivo

136

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

PubMed Central

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

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

2008-01-01

137

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

SciTech Connect

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

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

2014-10-28

138

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

NASA Astrophysics Data System (ADS)

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 13B_{2u}+ 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.

Chakraborty, Himanshu; Shukla, Alok

2014-10-01

139

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)B(2u)(+) 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

140

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

NASA Technical Reports Server (NTRS)

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

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

1993-01-01

141

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

142

Identification by time-resolved EPR of the peridinins directly involved in chlorophyll triplet quenching in the peridinin-chlorophyll a-protein from Amphidinium carterae.  

PubMed

The mechanism of triplet-triplet energy transfer in the peridinin-chlorophyll-protein (PCP) from Amphidinium carterae was investigated by time-resolved EPR (TR-EPR). The approach exploits the concept of spin conservation during triplet-triplet energy transfer, which leads to spin polarization conservation in the observed TR-EPR spectra. The acceptor (peridinin) inherits the polarization of the donor (chlorophyll) in a way which depends on the relative geometrical arrangement of the donor-acceptor couple. Starting from the initially populated chlorophyll triplet state and taking the relative positions among Chls and peridinins from the X-ray structure of PCP, we calculated the expected triplet state polarization of any peridinin in the complex. Comparison with the experimental data allowed us to propose a path for triplet quenching in the protein. The peridinin-chlorophyll pair directly involved in the triplet-triplet energy transfer coincides with the one having the shortest center to center distance. A water molecule, which is coordinated to the central Mg atom of the Chl, is also placed in close contact with the peridinin. The results support the concept of localization of the triplet state mainly in one specific peridinin in each of the two pigment subclusters related by a pseudo C2 symmetry. PMID:17991454

Di Valentin, Marilena; Ceola, Stefano; Salvadori, Enrico; Agostini, Giancarlo; Carbonera, Donatella

2008-02-01

143

atomic spectra 1 Atomic Spectra  

E-print Network

Physics, pp. 88-93 (Rutherford nuclear model), 93-106 (atomic structure and electron spectra) 2. D. Watomic spectra 1 Atomic Spectra '96, THK-MRM Object To become familiar with the construction and interpret spin-orbit doublets and triplets in alkali spectra. References 1. Serway, Moses and Moyer: Modern

Glashausser, Charles

144

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

145

A Terminal, Fluxional ?(4) -Benzene Complex with a Thermally Accessible Triplet State is the Primary Photoproduct in the Intercyclobutadiene Haptotropism of (CpCo)phenylenes.  

PubMed

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

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

2015-03-16

146

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

147

Effect of H2 Binding on the Nonadiabatic Transition Probability between Singlet and Triplet States of the [NiFe]-Hydrogenase Active Site.  

PubMed

We investigate the effect of H2 binding on the spin-forbidden nonadiabatic transition probability between the lowest energy singlet and triplet electronic states of [NiFe]-hydrogenase active site model, using a velocity averaged Landau-Zener theory. Density functional and multireference perturbation theories were used to provide parameters for the Landau-Zener calculations. It was found that variation of the torsion angle between the terminal thiolate ligands around the Ni center induces an intersystem crossing between the lowest energy singlet and triplet electronic states in the bare active site and in the active site with bound H2. Potential energy curves between the singlet and triplet minima along the torsion angle and H2 binding energies to the two spin states were calculated. Upon H2 binding to the active site, there is a decrease in the torsion angle at the minimum energy crossing point between the singlet and triplet states. The probability of nonadiabatic transitions at temperatures between 270 and 370 K ranges from 35% to 32% for the active site with bound H2 and from 42% to 38% for the bare active site, thus indicating the importance of spin-forbidden nonadiabatic pathways for H2 binding on the [NiFe]-hydrogenase active site. PMID:25603170

Kaliakin, Danil S; Zaari, Ryan R; Varganov, Sergey A

2015-02-12

148

Conservation of spin polarization during triplet-triplet energy transfer in reconstituted peridinin-chlorophyll-protein complexes.  

PubMed

Peridinin-chlorophyll-protein (PCP) complexes, where the N-terminal domain of native PCP from Amphidinium carterae has been reconstituted with different chlorophyll (Chl) species, have been investigated by time-resolved EPR in order to elucidate the details of the triplet-triplet energy transfer (TTET) mechanism. This spectroscopic approach exploits the concept of spin conservation during TTET, which leads to recognizable spin-polarization effects in the observed time-resolved EPR spectra. The spin polarization produced at the acceptor site (peridinin) depends on the initial polarization of the donor (chlorophyll) and on the relative geometric arrangement of the donor-acceptor spin axes. A variation of the donor triplet state properties in terms of population probabilities or triplet spin axis directions, as produced by replacement of chlorophyll a (Chl a) with non-native chlorophyll species (ZnChl a and BacterioChl a) in the reconstituted complexes, is unambiguously reflected in the polarization pattern of the carotenoid triplet state. For the first time, in the present investigation spin-polarization conservation has been shown to occur among natural cofactors in protein complexes during the TTET process. Proving the validity of the assumption of spin conservation adopted in the EPR spectral analysis, the results reinforce the hypothesis that in PCP proteins peridinin 614, according to X-ray nomenclature (Hofmann, E.; et al. Science 1996, 272, 1788-1791), is the carotenoid of election in the photoprotection mechanism based on TTET. PMID:21942385

Di Valentin, Marilena; Tait, Claudia; Salvadori, Enrico; Ceola, Stefano; Scheer, Hugo; Hiller, Roger G; Carbonera, Donatella

2011-11-17

149

Singly and doubly excited states in ejected electron spectra of neon at high incident electron energies  

NASA Astrophysics Data System (ADS)

Ejected electron spectroscopy has been used to study singly and doubly excited states of neon at constant incident electron energies between 505 and 2018 eV and ejection angles from 10° to 130° with high resolution in ejected energy range from 12 to 46 eV. The full ejected electron energy range has been studied at two extreme incidence energies and three ejected angles, namely 40°, 90° and 130°. The low energy region (12 to 21.5 eV) has been investigated at 505 eV over the full angular range and at 90° at six incident energies from 505 to 2018 eV. The features in the ejected electron spectra have been attributed to the autoionisation of Ne+ (2s2p6nl) excited states and Ne (2s2p5nln'l' and 2s22p4nln'l') double excited autionising states. Lower energy ejected electrons arise from simultaneous excitation of s and p electrons above the second ionisation potential (62.53 eV) while higher energy ejected electrons are coming from singly and doubly excited states. The high resolution and high sensitivity allowed us to see separated singlet from triplet states at high incident energies. Comparison with previous works gives a good agreement in energy positions of measured features. At the highest ejected electron energies only the features coming from double excitation are present, but with very low intensities in the spectra due to the small cross sections and high background. New resonances are found whose classification needs new experimental and theoretical investigations. Contribution to the Topical Issue "Elementary Processes with Atoms and Molecules in Isolated and Aggregated States", edited by Friedrich Aumayr, Bratislav Marinkovic, Stefan Matejcik, John Tanis and Kurt H. Becker.

Jureta, Jozo J.; Marinkovi?, Bratislav P.; Milosavljevi?, Aleksandar R.; Avaldi, Lorenzo

2015-03-01

150

Photoinduced electron detachment and proton transfer: the proposal for alternative path of formation of triplet States of Guanine (g) and Cytosine (C) pair.  

PubMed

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

Gu, Jiande; Wang, Jing; Leszczynski, Jerzy

2015-02-12

151

Preparation of ketocoumarins as heavy atom-free triplet photosensitizers for triplet-triplet annihilation upconversion.  

PubMed

A series of ketocoumarin compounds were prepared as heavy atom-free triplet photosensitizers. The photophysical properties of the compounds were studied with steady state and time-resolved spectroscopy. The compounds show absorption in the visible spectral region (molar absorption coefficients are up to ? = 136,000 M(-1) cm(-1) at 448 nm) and long-lived triplet excited states (?T = 199.7 ?s) upon visible light photoexcitation. The compounds were used as triplet photosensitizers for singlet oxygen ((1)O2)-mediated photooxidation of 1,5-dihydroxylnaphthalene (DHN) to produce juglone. (1)O2 quantum yields of these compounds were determined in the range of 0.28-0.48. The ketocoumarins were also used as triplet photosensitizers for triplet-triplet annihilation (TTA) upconversion, and upconversion quantum yields up to 11.3% were observed. The results are useful for preparation of heavy atom-free triplet photosensitizers and for their application in photocatalysis and TTA upconversion. PMID:23467514

Huang, Dandan; Sun, Jifu; Ma, Lihua; Zhang, Caishun; Zhao, Jianzhang

2013-05-01

152

Two-Color Photoassociation Spectroscopy of the Triplet Ground State of Na2  

NASA Astrophysics Data System (ADS)

We use a two-color cw photoassociation scheme to measure the position of vibrational levels of textNa2 with binding energies of 811 GHz with up to 30 MHz resolution. These levels are identified as belonging to the ``a'' sideset^3?_u^+ ground state: an improvement of three orders of magnitude over previous results. These vibrational levels are found by inducing an Autler-Townes splitting between an intermediate excited state and a particular ground state. For this purpose, we have identified a vibrational level in the sideset^3?_g^+ state (about 570 textcm-1 below the textS_1/2 + textP_1/2 limit) with a relatively large overlap with the ground states. By choosing states of different angular momentum characters within the excited vibrational level, we observed rotational and hyperfine features on the ground vibrational states. Totaling about 40 states identified this way. We also observed splitting of many of the ground-state lines. These splittings are compatible to what is expected from spin-spin dipolar interaction.

de Araujo, L.; Gensemer, S.; Weinstein, J.; Fatemi, F.; Jones, K.; Lett, P.; Tiesinga, E.

2002-05-01

153

The role of C-H and C-C stretching modes in the intrinsic non-radiative decay of triplet states in a Pt-containing conjugated phenylene ethynylene.  

PubMed

The intrinsic non-radiative decay (internal conversion) from the triplet excited state in phosphorescent dyes can be described by a multi-phonon emission process. Since non-radiative decay of triplet excitons can be a significant process in organic light-emitting diodes, a detailed understanding of this decay mechanism is important if the overall device efficiency is to be controlled. We compare a deuterated Pt(II)-containing phenylene ethynylene with its non-deuterated counterpart in order to investigate which phonon modes control to the non-radiative decay path. We observe that deuteration does not decrease the non-radiative decay rate. A Franck-Condon analysis of the phosphorescence spectra shows that the electronic excitation is coupled strongly to the breathing mode of the phenyl ring and the C?C carbon stretching modes, while high-energy C-H or C-D stretching modes play an insignificant role. We, therefore, associate the internal conversion process with the carbon-carbon stretching vibrations. PMID:22401471

Köhler, Anna; Khan, Amena L T; Wilson, Joanne S; Dosche, Carsten; Al-Suti, Mohammed K; Shah, Hakikulla H; Khan, Muhammad S

2012-03-01

154

The role of C-H and C-C stretching modes in the intrinsic non-radiative decay of triplet states in a Pt-containing conjugated phenylene ethynylene  

NASA Astrophysics Data System (ADS)

The intrinsic non-radiative decay (internal conversion) from the triplet excited state in phosphorescent dyes can be described by a multi-phonon emission process. Since non-radiative decay of triplet excitons can be a significant process in organic light-emitting diodes, a detailed understanding of this decay mechanism is important if the overall device efficiency is to be controlled. We compare a deuterated Pt(II)-containing phenylene ethynylene with its non-deuterated counterpart in order to investigate which phonon modes control to the non-radiative decay path. We observe that deuteration does not decrease the non-radiative decay rate. A Franck-Condon analysis of the phosphorescence spectra shows that the electronic excitation is coupled strongly to the breathing mode of the phenyl ring and the C?C carbon stretching modes, while high-energy C-H or C-D stretching modes play an insignificant role. We, therefore, associate the internal conversion process with the carbon-carbon stretching vibrations.

Köhler, Anna; Khan, Amena L. T.; Wilson, Joanne S.; Dosche, Carsten; Al-Suti, Mohammed K.; Shah, Hakikulla H.; Khan, Muhammad S.

2012-03-01

155

Communication: DMRG-SCF study of the singlet, triplet, and quintet states of oxo-Mn(Salen)  

SciTech Connect

We use CHEMPS2, our free open-source spin-adapted implementation of the density matrix renormalization group (DMRG) [S. Wouters, W. Poelmans, P. W. Ayers, and D. Van Neck, Comput. Phys. Commun. 185, 1501 (2014)], to study the lowest singlet, triplet, and quintet states of the oxo-Mn(Salen) complex. We describe how an initial approximate DMRG calculation in a large active space around the Fermi level can be used to obtain a good set of starting orbitals for subsequent complete-active-space or DMRG self-consistent field calculations. This procedure mitigates the need for a localization procedure, followed by a manual selection of the active space. Per multiplicity, the same active space of 28 electrons in 22 orbitals (28e, 22o) is obtained with the 6-31G{sup *}, cc-pVDZ, and ANO-RCC-VDZP basis sets (the latter with DKH2 scalar relativistic corrections). Our calculations provide new insight into the electronic structure of the quintet.

Wouters, Sebastian, E-mail: sebastianwouters@gmail.com; Van Speybroeck, Veronique; Van Neck, Dimitri [Center for Molecular Modelling, Ghent University, Technologiepark 903, 9052 Zwijnaarde (Belgium); Bogaerts, Thomas [Center for Molecular Modelling, Ghent University, Technologiepark 903, 9052 Zwijnaarde (Belgium); Center for Ordered Materials, Organometallics and Catalysis, Ghent University, Krijgslaan 281 (S3), 9000 Gent (Belgium); Van Der Voort, Pascal [Center for Ordered Materials, Organometallics and Catalysis, Ghent University, Krijgslaan 281 (S3), 9000 Gent (Belgium)

2014-06-28

156

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

157

Triplet State Absorption in Carbon Nanotubes: A TD-DFT Study  

E-print Network

Society Published on Web 05/11/2007 #12;known how relaxation of photoexcitations occurs in CNTs.6,18 Recent studies attribute this property to the "dark" singlet excitons below the optically allowed states

Tretiak, Sergei

158

Some calculations on the ground and lowest-triplet state of helium in the fixed-nucleus approximation  

SciTech Connect

The series solution method developed by Pekeris [Phys. Rev. 112, 1649 (1958); 115, 1216 (1959)] for the Schroedinger equation for two-electron atoms, as generalized by Frost [ital et] [ital al]. [J. Chem. Phys. 41, 482 (1964)] to handle any three particles with a Coulomb interaction, has been used. The wave function is expanded in triple orthogonal set in three [ital perimetric] coordinates. From the Schroedinger equation an explicit recursion relation for the coefficients in the expansion is obtained, and the vanishing of the determinant of these coefficients provides the condition for the energy eigenvalues and for the eigenvectors. The Schroedinger equation is solved and the matrix elements are produced algebraically by using the computer algebra system MAPLE. The substitutions for a particular atom and diagonalization were performed by a program written in the C language. Since the determinant is sparse, it is possible to go to the order of 1078 as Pekeris did without using excessive memory or computer CPU time. By using a nonlinear variational parameter in the expression used to remove the energy, nonrelativistic energies, within the fixed-nucleus approximation, have been obtained. For the ground-state singlet 1 [sup 1][ital S] state, this is of the accuracy claimed by Frankowski and Pekeris [Phys. Rev. 146, 46 (1966); 150, 366(E) (1966)] using logarithmic terms for [ital Z] from 1 to 10, and for the triplet 2 [sup 3][ital S] state, energies have been obtained to 12 decimal places of accuracy, which, with the exception of [ital Z]=2, are lower than any previously published, for all [ital Z] from 3 to 10.

Cox, H. (Department of Mathematics, University of York, Heslington, York, YO15DD (United Kingdom)); Smith, S.J.; Sutcliffe, B.T. (Department of Chemistry, University of York, Heslington, York, YO15DD (United Kingdom))

1994-06-01

159

The effect of the oxidative properties of [Mg(H 2 O) 6 ] in the triplet and singlet states on the energetics of adenosine triphosphate cleavage  

Microsoft Academic Search

The interaction of the adenosine triphosphate (ATP) molecule (the ATP subsystem) with the magnesium complex [Mg(H2O)6]2+ (the Mg subsystem) in the singlet (S) and triplet (T) states in an aqueous medium mimicked by 78 water molecules was studied\\u000a by the molecular dynamics (density functional theory) method MD DFT:B3LYP with the 6–31G** basis set at T = 310 K. Potential energy

A. A. Tulub; V. E. Stefanov

2009-01-01

160

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

161

Intramolecular switching between dipolar resonance structures in singlet and triplet excited states detected by TRMC  

NASA Astrophysics Data System (ADS)

Transient changes in the real and imaginary component of the complex permittivity of a flash-photolyzed solution can be monitored with nanosecond time resolution using the time-resolved microwave conductivity (TRMC) technique. Effects caused by rapid (picosecond), flip—flop switching between dipolar resonance structures in the S 1 and T 1 states of molecules with mirror symmetry have been observed.

Warman, John M.; Schuddeboom, Wouter; Jonker, Stephan A.; de Haas, Matthijs P.; Paddon-Row, Michael N.; Zachariasse, Klaas A.; Launay, Jean-Pierre

1993-07-01

162

Triplet supercurrents in ferromagnets  

NASA Astrophysics Data System (ADS)

In almost all superconductors the pairs of electrons which carry the charge are in the so-called singlet state in which the quantum spin of the two electrons is antiparallel. During the past five years there has been increasing evidence that proximity coupling between singlet superconductors and ferromagnets can sometimes generate triplet pairs within the ferromagnet in which the spins of the electrons are parallel rather than antiparallel -- the evidence being that supercurrents can be passed through thicknesses of ferromagnetic material which are simply too large for singlet pairs to survive. The superconductor-ferromagnet proximity effect describes the fast decay of a spin-singlet supercurrent originating from the superconductor upon entering the neighboring ferromagnet. For strong ferromagnets such as Co, a thickness of only a few nanometres is sufficient to almost completely suppress the critical current of a Nb/Co/Nb Josephson junction. Here we report experiments in which a conical magnet (holmium) is placed at the interface between the superconductor and ferromagnet. The results showed that a long-ranged supercurrent can occur through the ferromagnetic Co layer but only for certain critical thicknesses of the Ho [1]. These thicknesses correspond to maximum magnetic inhomogeneity on the Ho and are therefore consistent with models which predict that a spin-mixing interface between the superconductor and ferromagnet can generate triplet pairs which are long-ranged in the ferromagnet. This paper reports recent experiments which aim to understand further the behaviour of triplet pairs in superconductor / ferromagnet heterostructures. [4pt] [1] J. W. A. Robinson, J. D. S. Witt, and M. G. Blamire, "Controlled Injection of Spin-Triplet Supercurrents into a Strong Ferromagnet" Science 329, 59-61 (2010).

Blamire, Mark

2011-03-01

163

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

164

The effect of the structure and conformational dynamics on quenching of triplet states of porphyrins and their chemical dimers by molecular oxygen and on singlet oxygen generation  

NASA Astrophysics Data System (ADS)

Quantum-chemical calculations are performed to analyze the factors affecting rate constant k T of quenching of the lowest triplet state by molecular oxygen and quantum yield ?? of singlet oxygen generation in chemical dimers of porphyrins bound by phenyl spacers at one of the meso positions (OEP)2-Ph, (TPP)2, and their Zn complexes. It is established that, for both types of dimers, the triplet excitation is localized on one of the macrocycles. The steric hindrance of macrocycles at the site of the phenyl ring of (OEP)2-Ph, (ZnOEP)2-Ph, and their monomeric analogues OEP-Ph and ZnOEP-Ph facilitates its rotation by 90° in the triplet state. The lowest triplet state energy in this ( U) conformation is lower than 7800 cm-1, which makes impossible electronic excitation energy transfer to molecular oxygen. The potential barrier of transformation to the U conformation is considerably lower for dimers than for monomers. Because of this, the rate of conformational transformations for dimers is higher and some of the (OEP)2-Ph and (ZnOEP)2-Ph molecules have time to transform into the new U conformation before diffusion collision with O2 molecules in solution. This leads to a noticeable decrease in ?? in accordance with experimental data. It is shown that the behavior of k T in the series of the studied dimers, their monomeric analogues, and relative compounds corresponds to the model of dipole-dipole electronic excitation energy transfer 1(3M⋯3?{g/-}) ? 1(1M0⋯1?g) in collisional complexes.

Ivashin, N. V.; Shchupak, E. E.; Sagun, E. I.

2015-01-01

165

Properties of the triplet metastable states of the alkaline-earth-metal atoms  

SciTech Connect

The static and dynamic properties of the alkaline-earth-metal atoms in their metastable state are computed in a configuration interaction approach with a semiempirical model potential for the core. Among the properties determined are the scalar and tensor polarizabilities, the quadrupole moment, some of the oscillator strengths, and the dispersion coefficients of the van der Waals interaction. A simple method for including the effect of the core on the dispersion parameters is described.

Mitroy, J.; Bromley, M.W.J. [Faculty of TIE, Charles Darwin University, Darwin NT 0909 (Australia)

2004-11-01

166

A perimidine-derived non-Kekulé triplet diradical.  

PubMed

6,9-Di(tert-butyl)-1-methyltetrazolo[1,5-a]perimidine (1) has been synthesized from naphthalene in seven steps. The EPR spectra, recorded after irradiation of 1 in a butyronitrile matrix at 77 K (lambda = 351 nm) and in Ar and Xe matrixes at 4.6 K (lambda > or = 345 nm), showed a six-line, high-field signal (Delta m(S) = +/- 1), centered at 3350 G in butyronitrile, along with a half-field signal (Delta m(S) = +/- 2), which is characteristic for triplets. Simulation of the observed EPR spectra gave values for the zero-field splitting parameters of |D/hc|/cm(-1) = 0.0105, |E/hc|/cm(-1) = 0.0014 in butyronitrile and |D/hc|/cm(-1) = 0.0107, |E/hc|/cm(-1) = 0.0016 in Ar. These EPR parameters are consistent with the diradical 5,8-di(tert-butyl)-2-(N-methylimino)perimidine-1,3-diyl ((3)2) as source of the EPR spectra. Linearity of the Curie-Weiss plot and UB3LYP and (14/14)CASPT2 calculations of the singlet-triplet energy difference (DeltaE(ST) approximately 8-10 kcal/mol) indicate that the triplet is the ground state of 2, as predicted for such a nondisjoint diradical. PMID:18547111

Quast, Helmut; Nüdling, Wolfgang; Klemm, Gerhard; Kirschfeld, Andreas; Neuhaus, Patrik; Sander, Wolfram; Hrovat, David A; Borden, Weston Thatcher

2008-07-01

167

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

168

Photodegradation mechanism of sulfonamides with excited triplet state dissolved organic matter: A case of sulfadiazine with 4-carboxybenzophenone as a proxy.  

PubMed

Excited triplet states of dissolved organic matter ((3)DOM*) are important players for photodegradation sulfonamide antibiotics (SAs) in sunlit natural waters. However, the triplet-mediated reaction mechanism was poorly understood. In this study, we investigated the reaction adopting sulfadiazine as a representative SA and 4-carboxybenzophenone (CBBP)as a proxy of DOM. Results showed that the excited triplet state of CBBP ((3)CBBP*) is responsible for the photodegradation of sulfadiazine. The reaction of (3)CBBP* with substructure model compounds verified there are two reaction sites (amino-or sulfonyl-N atoms) of sulfadiazine. Density functional theory calculations were performed, which unveiled that electrons transfer from the N reaction sites to the carbonyl oxygen atom of (3)CBBP* moiety, followed by proton transfers, leading to the formation of sulfadiazine radicals. Laser flash photolysis experiments were performed to confirm the mechanism. Thus, this study identified that the photodegradation mechanism of SAs initiated by (3)DOM*, which is important for understanding the photochemical fate, predicting the photoproducts, and assessing the ecological risks of SAs in the aquatic environment. PMID:25731147

Li, Yingjie; Wei, Xiaoxuan; Chen, Jingwen; Xie, Hongbin; Zhang, Ya-Nan

2015-06-15

169

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

170

Ground and Excited State Spectra of a Quantum Dot  

NASA Astrophysics Data System (ADS)

We present linear and nonlinear magnetoconductance measurements of the ground and excited state spectra for successive electron occupancy in a gate defined lateral quantum dot. Previous measurementsfootnote D.R. Stewart, D. Sprinzak, C.M. Marcus, C.I. Duruoz and J.S. Harris Jr., Science 278, (1997). showed a direct correlation between the mth excited state of the N-electron system and the ground state of the (N+m)-electron system for m up to 4, consistent to a large degree with a single-particle picture. Here we report quantitative deviations of the excited state spectra from the spectrum of ground state magnetoconductances, attributed to many-body interactions in the finite system of N ~200 electrons. We also describe the behaviour of anticrossings in the ground state magnetoconductances. We acknowledge the support of JSEP (DAAH04-94-G-0058), ARO (DAAH04-95-1-0331), ONR-YIP (N00014-94-1-0622) and the NSF-PECASE program. D.S. acknowledges the support of MINERVA grant.

Stewart, D. R.; Sprinzak, D.; Patel, S. R.; Marcus, C. M.; Duruoz, C. I.; Harris, J. S.

1998-03-01

171

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.

The Exploratorium

2012-06-26

172

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

PubMed

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

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

2015-04-01

173

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

174

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

NASA Astrophysics Data System (ADS)

We report a determination of the n -3He scattering length difference ? b'=b1'-b0'=[-5.411 ±0.031 (statistical)±0.039 (systematic)] fm between the triplet and singlet states using a neutron interferometer. This revises our previous result ? b'=[-5.610 ±0.027 (statistical)±0.032 (systematic)] fm obtained using the same technique in 2008 [Huber et al., Phys. Rev. Lett. 102, 200401 (2009), 10.1103/PhysRevLett.102.200401; Huber et al., Phys. Rev. Lett. 103, 179903(E) (2009), 10.1103/PhysRevLett.103.179903]. This revision is attributable to a reanalysis of the 2008 experiment that now includes a systematic correction caused by magnetic-field gradients near the 3He cell which had been previously underestimated. Furthermore, we more than doubled our original data set from 2008 by acquiring 6 months of additional data in 2013. Both the new data set and a reanalysis 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 3He, aid in the interpretation of neutron scattering from quantum liquids. The difference ? b' was determined by measuring the relative phase shift between two incident neutron polarizations caused by the spin-dependent interaction with a polarized 3He target. The target 3He gas was sealed inside a small, flat-windowed glass cell that was placed in one beam path of the interferometer. The relaxation of 3He polarization was monitored continuously with neutron transmission measurements. The neutron polarization and spin-flipper efficiency were determined separately using 3He analyzers and two different polarimetry analysis methods. A summary of the measured scattering lengths for n -3He with a comparison to nucleon interaction models is given.

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

2014-12-01

175

In Gap Excitations and Triplet Lifetime Broadening in the Dilute Singlet Ground State System SrCu2-xMgx(BO3)2  

NASA Astrophysics Data System (ADS)

We have carried out high resolution time-of-flight neutron scattering measurements on a new high quality single crystal of SrCu2-xMgx(BO3)2 with x = 0.1. These studies revealed the presence of new excitations within the singlet-triplet gap of this quasi-two dimensional, dilute, singlet ground state system. These new excitations showed little or no shift in energy with increasing applied magnetic field. In addition, we observe substantial broadening of the three triplet excitations in the dilute single crystal, as compared with pure SrCu2(BO3)2.^1 The triplet excitations in doped SrCu2-xMgx(BO3)2 therefore possess finite lifetimes at low temperatures in the range that can be measured with cold neutron spectroscopy. We have also calculated the dynamical spin structure factor using the zero temperature Lanczos method, and solving a Shastry-Sutherland model at zero and finite doping for different strengths of external magnetic field. This theory reproduces all the qualitative features observed in the experiments on SrCu2-xMgx(BO3)2. ^1 B.D. Gaulin et al., Phys. Rev. Lett., 93, 267202, 2004.

Haravifard, S.; Dunsiger, S. R.; Gaulin, B. D.; Dabkowska, H. A.; Telling, M. T. F.; El Shawish, S.; Bonca, J.

2006-03-01

176

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

PubMed

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

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

2014-06-13

177

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

E-print Network

Far infrared spectra of solid state aliphatic amino acids in different protonation states Aurélien of zwitterionic, cationic, and anionic forms of aliphatic amino acids in solid state have been studied for all aliphatic amino acids due to the lack of structural data. This work is intended to provide

Paris-Sud XI, Université de

178

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

SciTech Connect

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

Zafra, José Luis; González Cano, Rafael C.; Ruiz Delgado, M. Carmen; López Navarrete, Juan T.; Casado, Juan, E-mail: casado@uma.es [Department of Physical Chemistry, University of Málaga, Campus de Teatinos s/n, Málaga 29071 (Spain)] [Department of Physical Chemistry, University of Málaga, Campus de Teatinos s/n, Málaga 29071 (Spain); Sun, Zhe; Li, Yuan; Wu, Jishan [Department of Chemistry, National University of Singapore, 3 Science Drive 3, Singapore 117543 (Singapore)] [Department of Chemistry, National University of Singapore, 3 Science Drive 3, Singapore 117543 (Singapore)

2014-02-07

179

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

PubMed

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

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

2014-02-01

180

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

NASA Astrophysics Data System (ADS)

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

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

2014-02-01

181

Reversible photoswitching of triplet-triplet annihilation upconversion using dithienylethene photochromic switches.  

PubMed

Reversible photoswitched triplet-triplet annihilation upconversion (TTA UC) was demonstrated with dithienylethene (DTE) derivatives as the photochromic units, 2,6-diiodoBodipy as the triplet photosensitizer, and perylene as the triplet acceptor/emitter. The TTA UC is undisturbed by the open-form DTE but can be switched OFF upon photoirradiation of the mixture of the three components at 254 nm, i.e., by the closed-form DTE. Subsequent visible light irradiation restores the TTA UC. By studying the competitive triplet-state energy-transfer processes with nanosecond time-resolved transient difference absorption and fluorescence spectroscopy, we confirmed that the quenching of the perylene triplet excited state by closed-form DTE is dominant among the four possible quenching processes. PMID:24936705

Cui, Xiaoneng; Zhao, Jianzhang; Zhou, Yuhan; Ma, Jie; Zhao, Yilong

2014-07-01

182

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

Microsoft Academic Search

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

Kazuyuki Takeda; K. Takegoshi; Takehiko Terao

2002-01-01

183

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

SciTech Connect

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

Kim, S.K.

1993-05-01

184

Excited states and electronic spectra of extended tetraazaporphyrins  

NASA Astrophysics Data System (ADS)

Electronic excited states, electronic absorption, and magnetic circular dichroism (MCD) spectra of free-base tetraazaporphyrin (TAP), phthalocyanine (Pc), naphthalocyanine (Nc), and anthracocyanine (Ac) were studied by quantum chemical calculations using the symmetry-adapted cluster-configuration interaction (SAC-CI) method. Not only optically allowed states including the Q- and B-bands but also optically forbidden states were calculated for transitions whose excitation energies were lower than 4.5 eV. The present SAC-CI calculations consistently assigned the absorption and MCD peaks as optically allowed ? ??? excitations, although these calculations using double-zeta basis limit quantitative agreement and discussion. For Nc and Ac, excited states beyond the four-orbital model appeared in the low-energy region. The low-energy shifts of the Q-bands with the extension of molecular size were explained by the orbital energies. The splitting of the Q-bands decreases with extension of the molecular size. This feature was reproduced by the SAC-CI calculations but the configuration interaction with single excitations and time-dependent density functional theory calculations failed to reproduce this trend. Electron correlation in the excited states is important in reproducing this splitting of the Q-bands and in describing the energy difference between the B2u and B3u states of free-base porphyrins.

Fukuda, Ryoichi; Ehara, Masahiro; Nakatsuji, Hiroshi

2010-10-01

185

Harvesting highly electronically excited energy to triplet manifolds: state-dependent intersystem crossing rate in Os(II) and Ag(I) complexes.  

PubMed

A series of newly synthesized Os(II) and Ag(I) complexes exhibit remarkable ratiometric changes of intensity for phosphorescence versus fluorescence that are excitation wavelength dependent. This phenomenon is in stark contrast to what is commonly observed in condensed phase photophysics. While the singlet to triplet intersystem crossing (ISC) for the titled complexes is anomalously slow, approaching several hundred picoseconds in the lowest electronic excited state (S(1) ? T(1)), higher electronic excitation leads to a much accelerated rate of ISC (10(11)-10(12) s(-1)), which is competitive with internal conversion and/or vibrational relaxation, as commonly observed in heavy transition metal complexes. The mechanism is rationalized by negligible metal d orbital contribution in the S(1) state for the titled complexes. Conversely, significant ligand-to-metal charge transfer character in higher-lying excited states greatly enhances spin-orbit coupling and hence the ISC rate. The net result is to harvest high electronically excited energy toward triplet states, enhancing the phosphorescence. PMID:22515479

Hsu, Cheng-Chih; Lin, Chao-Chen; Chou, Pi-Tai; Lai, Chin-Hung; Hsu, Chien-Wei; Lin, Chen-Huey; Chi, Yun

2012-05-01

186

Kinetic Monte Carlo study of triplet-triplet annihilation in organic phosphorescent emitters  

NASA Astrophysics Data System (ADS)

The triplet-triplet annihilation (TTA) rate in organic phosphorescent materials such as used in organic light-emitting diodes is determined predominantly either by the rate of single-step Förster-type triplet-triplet interactions, or by multi-step triplet diffusion. We show how kinetic Monte Carlo simulations may be used to analyze the role of both processes. Under steady state conditions, the effective triplet-triplet interaction rate coefficient, kTT, which is often regarded as a constant, is found to depend actually on the number of excitons lost upon a triplet-triplet interaction process and to show a significant higher-order dependence on the triplet volume density. Under the conditions encountered in transient photoluminescence (PL) studies, kTT is found to be effectively constant in the case of diffusion-dominated TTA. However, for the case of single-step TTA, a strongly different decay of the emission intensity is found, which also deviates from an analytic expression proposed in the literature. We discuss how the transient PL response may be used to make a distinction between both mechanisms. The simulations are applied to recently published work on the dye concentration dependence of the TTA rate in materials based on the archetypal green emitter tris[2-phenylpyridine]iridium (Ir(ppy)3).

van Eersel, H.; Bobbert, P. A.; Coehoorn, R.

2015-03-01

187

The g -tensor anisotropy of the triplet state of the primary electron donor in the photosynthetic bacterium Rhodobacter sphaeroides by high-field (95 GHz) EPR  

Microsoft Academic Search

The anisotropy of theg-tensor of the light-induced triplet state of the primary electron donor (D) of the photosynthetic bacteriumRhodobacter sphaeroides is determined by electron-spin-echo-detected electron paramagnetic resonance at 95 GHz. Measurements on frozen solutions\\u000a of quinone-depleted reaction centers yield g-values along the principal directions of the zero-field splitting tensor (Norris\\u000a J.R., Budil D.E., Gast P., Chang C.H., ElKabbani O., Schiffer

A. Labahnt; M. Huber

2001-01-01

188

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

189

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

190

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

SciTech Connect

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

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

2000-01-27

191

Triplet state properties of [Os(phen) 2(dppene)] 2+ in different host materials and host to guest energy transfer in PVK  

NASA Astrophysics Data System (ADS)

Emission properties of [Os(phen) 2(dppene)] 2+ were investigated from 1.4 to 300 K in ethanol, PMMA, and PVK, a matrix which is frequently applied in OLEDs. These data provide the zero-field splitting values of the emitting T 1 state and the individual decay times of its substates. The T 1 state is assigned to be largely of MLCT character. The splittings change only moderately due to variation of the matrix, whereas the individual decay times are substantially affected. Further, energy transfer from the triplet state of PVK to [Os(phen) 2(dppene)] 2+ was studied by applying time-resolved emission spectroscopy and is assigned to be dominantly of Dexter type.

Pentlehner, Dominik; Grau, Ilias; Yersin, Hartmut

2008-03-01

192

Final state-selected spectra in unimolecular reactions: A transition-state-based random matrix model for overlapping resonances  

E-print Network

Final state-selected spectra in unimolecular reactions: A transition-state- based random matrix-0482 Received 26 September 1994; accepted 13 February 1995 Final state-selected spectra in unimolecular decomposition are obtained by a random matrix version of Feshbach's optical model. The number of final states

Reisler, Hanna

193

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

NASA Astrophysics Data System (ADS)

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

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

2013-05-01

194

Engineering the ground- and excited-state absorption spectra of broadband reverse saturable absorbers  

NASA Astrophysics Data System (ADS)

We exploit the strong spin-orbit coupling in iridium to modify the linear absorption spectrum of a novel iridium(III) complex so as to broaden the spectral region over which it exhibits reverse saturable absorption. We discuss the design of the new chromophore, present its ground-state absorption spectrum, and report values of its singlet excited-state lifetime and singlet and triplet excited-state absorption cross sections, determined from femtosecond transient difference absorption measurements and nanosecond and picosecond open-aperture Z scans.

Pritchett, Timothy M.; Ferry, Michael J.; Shensky, William M.; Mott, Andrew G.; Pei, Chengkui; Sun, Wenfang

2014-10-01

195

Photoexcitation of the triplet exciton in single wall carbon nanotubes  

E-print Network

The carbon nanotube photoexcitation spectrum is dominated by excitonic transitions, rather than interband transitions between continuum states. There are eight distinct excitonic transitions (four singlet and four triplet), ...

Santos, Tiffany S.

196

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

197

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

198

Photolysis of alpha-azidoacetophenones: direct detection of triplet alkyl nitrenes in solution.  

PubMed

We report the first detection of triplet alkyl nitrenes in fluid solution by laser flash photolysis of alpha-azido acetophenone derivatives, 1. Alphazides 1 contain an intramolecular triplet sensitizer, which ensures formation of the triplet alkyl nitrene by bypassing the singlet nitrene intermediate. At room temperature, azides 1 cleave to form benzoyl and methyl azide radicals in competition with triplet energy transfer to form triplet alkyl nitrene. The major photoproduct 3 arises from interception of the triplet alkyl nitrene with benzoyl radicals. The triplet alkyl nitrene intermediates are also trapped with molecular oxygen to yield the corresponding 2-nitrophenylethanone. Laser flash photolysis of 1 reveals that the triplet alkyl nitrenes have absorption around 300 nm. The triplet alkyl nitrenes were further characterized by obtaining their UV and IR spectra in argon matrices. (13)C and (15)N isotope labeling studies allowed us to characterize the C-N stretch of the nitrene intermediate at 1201 cm(-)(1). PMID:14535770

Singh, Pradeep N D; Mandel, Sarah M; Robinson, Rachel M; Zhu, Zhendong; Franz, Roberto; Ault, Bruce S; Gudmundsdóttir, Anna D

2003-10-17

199

Raman Spectra of Compounds in the Gaseous and Liquid States  

Microsoft Academic Search

An apparatus for exciting the Raman spectra of gases and liquids at temperatures up to 300°C is described. For phosphorus trichloride, methyl chloride, methyl bromide, methyl alcohol, methylene chloride, methylene bromide, chloroform, and carbon tetrachloride, the Raman spectra of the gas and the liquid at the same temperature have been photographed in juxtaposition with a liquid-prism spectrograph of speed f:

J. Rud Nielsen; Newton E. Ward

1942-01-01

200

Mixing of Exciton and Charge-Transfer States in Photosystem II Reaction Centers: Modeling of Stark Spectra with Modified Redfield Theory  

PubMed Central

We propose an exciton model for the Photosystem II reaction center (RC) based on a quantitative simultaneous fit of the absorption, linear dichroism, circular dichroism, steady-state fluorescence, triplet-minus-singlet, and Stark spectra together with the spectra of pheophytin-modified RCs, and so-called RC5 complexes that lack one of the peripheral chlorophylls. In this model, the excited state manifold includes a primary charge-transfer (CT) state that is supposed to be strongly mixed with the pure exciton states. We generalize the exciton theory of Stark spectra by 1), taking into account the coupling to a CT state (whose static dipole cannot be treated as a small parameter in contrast to usual excited states); and 2), expressing the line shape functions in terms of the modified Redfield approach (the same as used for modeling of the linear responses). This allows a consistent modeling of the whole set of experimental data using a unified physical picture. We show that the fluorescence and Stark spectra are extremely sensitive to the assignment of the primary CT state, its energy, and coupling to the excited states. The best fit of the data is obtained supposing that the initial charge separation occurs within the special-pair PD1PD2. Additionally, the scheme with primary electron transfer from the accessory chlorophyll to pheophytin gave a reasonable quantitative fit. We show that the effectiveness of these two pathways is strongly dependent on the realization of the energetic disorder. Supposing a mixed scheme of primary charge separation with a disorder-controlled competition of the two channels, we can explain the coexistence of fast sub-ps and slow ps components of the Phe-anion formation as revealed by different ultrafast spectroscopic techniques. PMID:17526589

Novoderezhkin, Vladimir I.; Dekker, Jan P.; van Grondelle, Rienk

2007-01-01

201

Magnetic-field dependent optically detected ESR in the photoexcited triplet states of bridged Zr(IV) metallocenes  

Microsoft Academic Search

We report on the magnetic-field-dependent optically detected magnetic resonance (ODMR) spectra for polycrystalline samples\\u000a of the bridged Zr(IV) metallocenes, Me2Si2)ZrCl2 ( (dimethylsilylbis(cyclopentadienyl)zirconium-dichloride) and Me2C2)ZrCl2 (iso-propylidenebis(cyclopentadienyl)zirconium-dichloride). ODMR spectra at zero magnetic field were recorded by frequency\\u000a sweeping a microwave source from 0.1 to 10 GHz with the sample contained in a microwave helix. ODMR spectra at finite magnetic\\u000a fields were recorded

S. K. Misra; B. Endeward; M. Bernardo; P. Brant; H. Thomann

2003-01-01

202

Interplay between Coulomb and Jahn-Teller effects in icosahedral systems with triplet electronic states coupled to h-type vibrations  

NASA Astrophysics Data System (ADS)

We will consider the role played by electron-vibration and electron-electron interactions, through Jahn-Teller (JT) and Coulomb interactions, respectively, in icosahedral systems in which triplet electronic states are coupled to hg-type vibrations. Starting from the electronic terms that arise from consideration of Coulomb interactions, we introduce JT couplings both within the terms and between nondegenerate terms. We show how the symmetry of the JT distortion can change when extra electrons are added, and give the conditions under which JT distortions can be suppressed entirely when the Coulomb interactions are sufficiently large. The relevance of our results to anions of the fullerene molecule C60 are briefly discussed, and existing experimental measurements are used to estimate values for the quadratic JT coupling constants for these anions.

Alqannas, Haifa S.; Lakin, Andrew J.; Farrow, Joseph A.; Dunn, Janette L.

2013-10-01

203

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

SciTech Connect

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

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

1992-08-06

204

Statistical equilibrium in cometary C2. III - Triplet-singlet, Phillips, Ballik-Ramsay, and Mulliken bands  

NASA Technical Reports Server (NTRS)

A new series of vibrational bands is predicted which arises from transitions between the lowest electron states of the triplet and singlet states of homonuclear C2. The predictions are useful for C2 identifications and for disentangling congested low resolution spectra that characterize new observations. Predictions are also made for Mulliken, Phillips, and Ballik-Ramsay band sequences, and all calculations are made with the assumed molecular constants and computational methods of KSO-II.

Swamy, K. S. K.; Odell, C. R.

1981-01-01

205

Triplet absorption in carbon nanotubes: a TD-DFT study  

E-print Network

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

Sergei Tretiak

2007-02-13

206

The efficiency of the generation of photochemically active triplet states in oils containing various amounts of natural pigments  

Microsoft Academic Search

Absorption, fluorescence emission and excitation spectra as well as time resolved photothermal signals of oils, obtained by pressing the following types of seeds: evening primrose seeds, rapeseeds, borage seeds and viper's bugloss seeds, were measured. It was found that the oils differed in the compositions of fatty acids, acid values, peroxide values and contents of pigments. The oils contained not

Halina Pie?kowska; Alina Dudkowiak; Dariusz Muszy?ski; Danuta Fr?ckowiak

2005-01-01

207

Simultaneous analysis of the Ballik-Ramsay and Phillips systems of C2 and observation of forbidden transitions between singlet and triplet states  

NASA Astrophysics Data System (ADS)

6229 lines of the Ballik-Ramsay system (b3?g--a3?u) and the Phillips system (A1?u-X1?g+) of C2 up to v = 8 and J = 76, which were taken from the literature or assigned in the present work, were analyzed simultaneously by least-squares fitting with 82 Dunham-like molecular parameters and spin-orbit interaction constants between the b3?g- and X1?g+ states with a standard deviation of 0.0037 cm-1 for the whole data set. As a result of the deperturbation analysis, the spin-orbit interaction constant AbX was determined as 6.333(7) cm-1 and the energy difference between the X1?g+ and a3?u states was determined as 720.008(2) cm-1 for the potential minima or 613.650(3) cm-1 for the v = 0 levels with Merer and Brown's N2 Hamiltonian for 3? states, which is about 3.3 cm-1 larger than the previously determined value. Due to this sizable change, a new energy-level crossing was found at J = 2 for v = 3 (F1) of b3?g- state and v = 6 of X1?g+ state, where the strong interaction causes a nearly complete mixing of the wave functions of the b3?g- and X1?g+ states and the forbidden transitions become observable. Using the predictions of our deperturbation analysis, we were able to identify 16 forbidden transitions between the singlet and triplet states at the predicted frequencies with the expected intensities, which verifies our value for the energy difference between the X1?g+ and a3?u states.

Chen, Wang; Kawaguchi, Kentarou; Bernath, Peter F.; Tang, Jian

2015-02-01

208

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

NASA Astrophysics Data System (ADS)

A benchmark theoretical study of the electronic ground state and of the vertical and adiabatic singlet-triplet (ST) excitation energies of benzene (n =1) and n-acenes (C4n+2H2n+4) ranging from naphthalene (n =2) to heptacene (n =7) is presented, on the ground of single- and multireference calculations based on restricted or unrestricted zero-order wave functions. High-level and large scale treatments of electronic correlation in the ground state are found to be necessary for compensating giant but unphysical symmetry-breaking effects in unrestricted single-reference treatments. The composition of multiconfigurational wave functions, the topologies of natural orbitals in symmetry-unrestricted CASSCF calculations, the T1 diagnostics of coupled cluster theory, and further energy-based criteria demonstrate that all investigated systems exhibit a A1g singlet closed-shell electronic ground state. Singlet-triplet (S0-T1) energy gaps can therefore be very accurately determined by applying the principles of a focal point analysis onto the results of a series of single-point and symmetry-restricted calculations employing correlation consistent cc-pVXZ basis sets (X=D, T, Q, 5) and single-reference methods [HF, MP2, MP3, MP4SDQ, CCSD, CCSD(T)] of improving quality. According to our best estimates, which amount to a dual extrapolation of energy differences to the level of coupled cluster theory including single, double, and perturbative estimates of connected triple excitations [CCSD(T)] in the limit of an asymptotically complete basis set (cc-pV?Z), the S0-T1 vertical excitation energies of benzene (n =1) and n-acenes (n =2-7) amount to 100.79, 76.28, 56.97, 40.69, 31.51, 22.96, and 18.16 kcal/mol, respectively. Values of 87.02, 62.87, 46.22, 32.23, 24.19, 16.79, and 12.56 kcal/mol are correspondingly obtained at the CCSD(T)/cc-pV?Z level for the S0-T1 adiabatic excitation energies, upon including B3LYP/cc-PVTZ corrections for zero-point vibrational energies. In line with the absence of Peierls distortions, extrapolations of results indicate a vanishingly small S0-T1 energy gap of 0 to ˜4 kcal/mol (˜0.17 eV) in the limit of an infinitely large polyacene.

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

2009-12-01

209

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

Microsoft Academic Search

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

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

1989-01-01

210

Electronic absorption spectra of binuclear rhodium (I) isocyanide complexes. Comparison of ground-state and d. sigma. * yields p. sigma. excited-state bond energies  

SciTech Connect

The polarized single-crystal absorption spectra of (Rh{sub 2}b{sub 4})(BPh{sub 4}){sub 2}{center dot}CH{sub 3}CN and (Rh{sub 2}(TMB){sub 4})(BPh{sub 4}){sub 2} have been measured and analyzed (b = 1,3-diisocyanopropane; TMB = 2,5-diisocyano-2,5-dimethylhexane). The results indicate that the fully allowed transitions near 550 and 310 nm in these d{sup 8}-d{sup 8} complexes are {sup 1}A{sub 1} {yields} {sup 1}A{sub 2} (d{sigma} {yields} p{sigma}) and {sup 1}A{sub 1} {yields} {sup 1}E (d{sub xz}, d{sub yz} {yields} p{sigma}), respectively (D{sub 4} point group designations). The weak singlet {yields} triplet systems associated with both excitations also have been identified. The vibronic structure of the {sup 1}A{sub 1g} {yields} {sup 3}A{sub 2u} system of Rh{sub 2}b{sub 4}{sup 2+} has been analysis in detail. The Rh-Rh bond length in the {sup 3}A{sub 2u} state of Rh{sub 2}b{sub 4}{sup 2+} is estimated from a Franck-Condon analysis to be 2.93 {angstrom} (the ground-state value is 3.24 {angstrom}). The ground-state and excited-state Rh-Rh bond energies are estimated to be 12 {plus minus} 6 and 36 {plus minus} 6 kcal/mol, respectively.

Rice, S.F.; Miskowski, V.M.; Gray, H.B. (California Institute of Technology, Pasadena (USA))

1988-12-28

211

Dependence of the Efficiency of Triplet-Triplet Energy Transfer on the Distance Between the Donor and Acceptor  

NASA Astrophysics Data System (ADS)

The triplet-triplet and singlet-singlet energy transfer is investigated both experimentally and theoretically in the anthracene - Nile red system. Quantum-chemical investigations of the special features in the formation of electronically excited states and photoprocesses in the donor-acceptor pair are performed. It is demonstrated that atypical distance dependence of the efficiency of triplet-triplet energy transfer in the Langmuir-Blodgett multilayered thin films is caused by additional quenching of donor particles due to the process of energy transfer to acceptor centers by the inductive-resonant mechanism.

Ibraev, N. Kh.; Seliverstova, E. V.; Artyukhov, V. Ya.

2015-01-01

212

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

213

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

214

Ground-state transitions beyond the singlet-triplet transition for a two-electron quantum dot  

NASA Astrophysics Data System (ADS)

We studied electrostatic confinement effects on correlated electronic states in vertical quantum dots in high magnetic fields. We prepared vertical quantum dots with different lateral confinement strengths and investigated the magnetic field evolution of the electronic states. We observed that the formation of the maximum density droplet state corresponding to filling factor ?=1 shifts to lower magnetic field as the lateral confinement energy becomes weaker. In addition, we found a ground-state transition in the ?<1 regime for the most weakly laterally confined two-electron quantum dot that is predicted to appear beyond an easily accessible magnetic field in standard vertical quantum dots more typically investigated.

Nishi, Yoshifumi; Tokura, Yasuhiro; Gupta, James; Austing, Guy; Tarucha, Seigo

2007-03-01

215

Degradation of organic pollutants in/on snow and ice by singlet molecular oxygen (¹O?*) and an organic triplet excited state.  

PubMed

Singlet molecular oxygen (¹O?*) can be a significant sink for a variety of electron-rich pollutants in surface waters and atmospheric drops. We recently found that ¹O?* concentrations are enhanced by up to a factor of 10(4) on illuminated ice compared to in the equivalent liquid solution, suggesting that ¹O?* could be an important oxidant for pollutants in snow. To examine this, here we study the degradation of three model organic pollutants: furfuryl alcohol (to represent furans), tryptophan (for aromatic amino acids), and bisphenol A (for phenols). Each compound was studied in illuminated aqueous solution and ice containing Rose Bengal (RB, a sensitizer for ¹O?*) and sodium chloride (to adjust the concentration of total solutes). The RB-mediated loss of each organic compound is enhanced on illuminated ice compared to in solution, by factors of 6400 for furfuryl alcohol, 8300 for tryptophan, and 50 for bisphenol A for ice containing 0.065 mM total solutes. Rates of loss of furfuryl alcohol and tryptophan decrease at a higher total solute concentration, in qualitative agreement with predictions from freezing-point depression. In contrast, the loss of bisphenol A on ice is independent of total solute concentration. Relative to liquid tests, the enhanced loss of tryptophan on ice during control experiments made with deoxygenated solutions and solutions in D?O show that the triplet excited state of Rose Bengal may also contribute to loss of pollutants on ice. PMID:24487942

Bower, Jonathan P; Anastasio, Cort

2014-04-01

216

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

217

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

NASA Astrophysics Data System (ADS)

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

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

1995-07-01

218

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

PubMed

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

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

2013-10-10

219

Spectroscopic properties of the peridinins involved in chlorophyll triplet quenching in high-salt peridinin-chlorophyll a-protein from Amphidinium carterae as revealed by optically detected magnetic resonance, pulse EPR and pulse ENDOR spectroscopies.  

PubMed

The photoexcited triplet state of the carotenoid peridinin in the high-salt peridinin-chlorophyll a-protein (HSPCP) of the dinoflagellate Amphidinium carterae was investigated by ODMR (optically detected magnetic resonance), pulse EPR and pulse ENDOR spectroscopies. The properties of peridinins associated to the triplet state formation in HSPCP were compared to those of peridinins involved in triplet state population in the main-form peridinin-chlorophyll protein (MFPCP), previously reported. In HSPCP no signals due to the presence of chlorophyll triplet state have been detected, during either steady-state illumination or laser-pulse excitation, meaning that peridinins play the photo-protective role with 100% efficiency as in MFPCP. The general spectroscopic features of the peridinin triplet state are very similar in the two complexes and allow drawing the conclusion that the triplet formation pathway and the triplet localization in one specific peridinin in each subcluster are the same in HSPCP and MFPCP. However some significant differences also emerged from the analysis of the spectra. Zero field splitting parameters of the peridinin triplet states are slightly smaller in HSPCP and small changes are also observed for the hyperfine splittings measured by pulse ENDOR and assigned to the beta-protons belonging to one of the two methyl groups present in the conjugated chain, (a(iso)=10.3 MHz in HSPCP vs a(iso)=10.6 MHz in MFPCP). The differences are explained in terms of local distortion of the tails of the conjugated chains of the peridinin molecules, in agreement with the conformational data resulting from the X-ray structures of the two complexes. PMID:18602887

Di Valentin, Marilena; Ceola, Stefano; Salvadori, Enrico; Agostini, Giancarlo; Giacometti, Giorgio Mario; Carbonera, Donatella

2008-10-01

220

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

221

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

222

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

Microsoft Academic Search

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

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

1998-01-01

223

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

NASA Astrophysics Data System (ADS)

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.

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

2013-12-01

224

Dynamics of ground state absorption spectra in donor-acceptor pairs with ultrafast charge recombination.  

PubMed

A theoretical approach to simulation of the transient spectra in molecular systems with ultrafast photoinduced nonradiative electronic transitions is developed. The evolution of the excited and ground state populations as well as the nonradiative transitions between them are calculated in the framework of the stochastic multichannel point-transition model involving the reorganization of the medium and the intramolecular high frequency vibrational modes. Simulations of transient spectra of donor-acceptor pairs excited in the charge-transfer band that are accompanied by ultrafast charge recombination into the ground state demonstrate a possibility of positive band appearance in the transient absorption spectrum caused by those systems in the ground state, which returned there from the excited state. The region of the parameters of the donor-acceptor systems where a positive ground state absorption signal can be observed is discussed. A qualitative comparison of the simulated transient spectra with the experimental data on betaine-30 is presented. PMID:25686470

Fedunov, Roman G; Plotnikova, Anastasiia V; Ionkin, Vladimir N; Ivanov, Anatoly I

2015-03-12

225

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

226

Electronic States and Spectra of BiO  

NASA Astrophysics Data System (ADS)

The electronic spectrum of the BiO radical has been studied by Fourier transform emission spectroscopy, laser-induced fluorescence, and excimer laser photolysis techniques. Six new electronic states, A1(? = 3/2) ( Te= 11 528.8 cm -1, ? e= 530.4 cm -1, ? exe= 2.42 cm -1), G(? = 3/2) ( Te= 20 273 cm -1, ? e= 499 cm -1, ? exe= 2.6 cm -1), H(? = 1/2) ( Te= 20 469.76(6) cm -1, ? e= 471.63(18) cm -1, ? exe= 2.153(35) cm -1), I(? = 1/2) ( Te= 21 982.50(2) cm -1, ? e= 506.50(11) cm -1, ? exe= 3.263(34) cm -1), J(? = 3/2) ( Te= 25 598.95(42) cm -1, ? e= 489.95(16) cm -1, ? exe= 2.309(45) cm -1), and K(? = 1/2) ( Te= 26 744.7(2) cm -1, ? e= 420.6(4) cm -1, ? exe= 5.25(5) cm -1), and 14 new electronic transitions ( A1? X1, G ? X2, H ? X1, H ? A2( A), I ? X1, I ? A2, J ? X1, J ? X2, K ? X1, K ? X2, K ? A2, B ? X2, B ? A2, C ? X2) have been detected. Time-resolved measurements of the fluorescence decays have yielded the radiative lifetimes of the v= 0 levels of most states up to <30 500 cm -1energy (? X2= 480 ± 100 ?s, ? A2= 9.3 ± 1.5 ?s, ? H= 15 ± 3 ?s, ? I= 16 ± 3 ?s, ? J= 4.9 ± 0.9 ?s, ? K= 2.6 ± 0.3 ?s, ? B= 0.55 ± 0.08 ?s, ? C= 0.84 ± 0.15 ?s) and rate constants for quenching of the states by some rare gas atoms and simple molecules. The new electronic states A1, G, H, I, J, and Kand the previously known levels X1, X2, A2( A), B, C, and Dare assigned to spin-orbit states arising from low-energy valence configurations of BiO with the help of detailed theoretical data calculated by Alekseyev et al.( J. Chem. Phys.100,8956-8968 (1994)).

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

1998-07-01

227

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

228

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 (compound with formula C6H5OH)), guaiacol (2-methoxyphenol), and syringol (2,6-dimethoxyphenol) with two major aqueous-phase oxidants - the triplet excited states of an aromatic carbonyl (3C*) and hydroxyl radical (· 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 · OH-mediated reactions and produce more oligomers and hydroxylated species at the point when 50% of the phenolic compound has 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-visible region, suggesting that aqueous-phase reactions of phenols may contribute to formation of secondary brown carbon in the atmosphere, especially in regions influenced by biomass burning.

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

2014-12-01

229

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

SciTech Connect

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 (•OH). We thoroughly characterize the low-volatility species produced from these reactions and interpret their formation mechanisms using aerosol mass spectrometry (AMS), desorption electrospray ionization mass spectrometry (DESIMS), 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 •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, Lu; Smith, Jeremy; Laskin, Alexander; Anastasio, Cort N.; Laskin, Julia; Zhang, Qi

2014-12-23

230

The auxochromic group in the triplet manifold  

NASA Astrophysics Data System (ADS)

The spectral locations of the low energy triplet-triplet ( T-T) and singlet-singlet ( S-S) maxima of coumarin, 6-methyl, 7-methoxy, 7-hydroxy, 7-hydroxy-4-methyl, 7-amino-4-methyl, 7-ethylamino-4,6-dimethyl, 7-dimethylamino-4-methyl, 7-diethylamino-4-methyl coumarin, coumarin 339 and LD 490 were measured. The spectral location of the fluorescence maxima of all the auxochromic group substituted coumarin derivatives were also determined. In addition, the low energy S-S absorption and T-T absorption and polarization spectra of coumarin and 7-diethylamino-4-methyl coumarin were recorded. The importance of polarization of S-S and T-T absorption bands as related to substitution effects is briefly reviewed. T-T laser photoselection spectroscopy is employed to furnish experimental data on the arrangement of singlet and triplet dipoles relative to each other within the molecular frame of a molecule. It was found that the order of effectiveness of the auxochromic group in causing spectral red shifts in the singlet manifold is the same as in the triplet manifold. Using wavelength units the spectral red shifts (bathochromic effect) in the triplet manifold are much larger when compared to the red shift as a result of the auxochromic group substitution in the singlet manifold. When expressed in wavenumbers (energy), however, the red shifts appear to be about the same. The importance of these red shifts, as related to the laser action properties of laser dyes, are discussed. It is concluded that laser dyes superior to the coumarin laser dyes could be synthesized.

Pavlopoulos, Theodore G.

231

Rotational spectra of the X 2Sigma(+) states of CaH and CaD  

NASA Technical Reports Server (NTRS)

The rotational spectra of the 2Sigma(2+) ground states of calcium monohydride and monodeuteride have been recorded in absorption between 250 and 700 GHz. The gas phase free radicals have been produced in a ceramic furnace by the reaction of elemental calcium with molecular hydrogen or deuterium in the presence of an electrical discharge. The molecular constants including the rotational constant, centrifugal distortion constants, spin-rotation constants, and magnetic hyperfine interaction constants have been extracted from the spectra.

Frum, C. I.; Oh, J. J.; Cohen, E. A.; Pickett, H. M.

1993-01-01

232

Triplet dark matter from leptogenesis  

NASA Astrophysics Data System (ADS)

A triplet dark matter candidate from thermal leptogenesis is considered with building a model. The model is based on the standard two-Higgs-doublet model and seesaw mechanism with Higgs triplets. The parameters (couplings and masses) are adjusted for the observed small neutrino mass and the leptogenesis. Dark matter particles can annihilate and decay in this model. The time evolution of the dark matter number is governed by (co)annihilations in the expanding universe, and its mass is constrained by the observed relic density. The dark matter can decay into final states with three leptons (two charged leptons and one neutrino). We investigate whether the decay in a galaxy can account for cosmic ray anomalies in the positron and electron spectrum. A noticeable point is that if the dark matter decays into each lepton with different branching ratios, cosmic ray anomalies in AMS-02 measurements of the positron fraction and the Fermi LAT measurements of the electrons-plus-positrons flux could be simultaneously accounted for from its decay products.

Heo, Jae Ho; Kim, C. S.

2014-04-01

233

Dynamics and configurations of galaxy triplets  

NASA Technical Reports Server (NTRS)

The purpose is to infer the probable dynamical states of galaxy triplets by the observed data on their configurations. Two methods are proposed for describing the distributions of the triplet configuration parameters characterizing a tendency to alignment and hierarchy: (1) obtaining a representative sample of configurations and determining its statistical parameters (moments and percentages); and (2) dividing the region of possible configurations of triple systems (Agekian and Anosova, 1967) into a set of segments and finding the probabilities for the configurations to find themselves in each of them. Both these methods allow representation of the data by numerical simulations as well as observations. The effect of projection was studied. It rather overestimates the alignment and hierarchy of the triple systems. Among the parameters of interest there are found some parameters that are least sensitive to projection effects. The samples consist of simulated galaxy triplets (with hidden mass) as well as of 46 probably physical triple galaxies (Karachentseva et al., 1979). The observed triples as well as numerical models show a tendency to alignment. The triple galaxies do not show any tendency to hierarchy (formation of the temporary binaries), but this tendency may be present for simulated triplets without significant dark matter. The significant hidden mass (of order ten times the total mass of a triplet) decreases the probability of forming a binary and so weakens the hierarchy. Small galaxy groups consisting of 3 to 7 members are probably the most prevalent types of galaxy aggregate (Gorbatsky, 1987). Galaxy triplets are the simplest groups, but dynamically nontrivial ones.

Anosova, Joanna P.; Orlov, Victor V.; Chernin, Arthur D.; Ivanov, Alexei V.; Kiseleva, Ljudmila G.

1990-01-01

234

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

NASA Astrophysics Data System (ADS)

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

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

2014-11-01

235

Geometry and bonding in the ground and lowest triplet state of D 6 h symmetric crenellated edged C 6[3 m ( m ?1)+1]H 6(2 m ?1) ( m = 2, … , 6) graphene hydrocarbon molecules  

Microsoft Academic Search

Ab initio plane wave all valence electron based DFT calculations were used to explore the dichotomy of perimeter vs. interior in the electronic and geometric structure of the D6h singlet ground state and D2h lowest triplet state of planar graphene hydrocarbon molecules with crenellated (arm chair) edges and the general formula C6[3m(m?1)+1] H6(2m?1) where m=2,…,6. The largest molecule C546H66 was

Michael R. Philpott; Yoshiyuki Kawazoe

2009-01-01

236

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

Microsoft Academic Search

Many transient and persistent Black Hole X-ray Binaries (BHXBs) show characteristic state transitions between low\\/hard and high\\/soft spectral states. A typical low\\/hard state X-ray spectrum, as seen for example in Cyg X-1 and GRO J0422+32, is a power-law with a photon index of order 1.4-1.6 and an exponential cutoff with a characteristic e-folding energy ~ 100 keV. These spectra are

A. A. Esin; J. A. Tomsick

2001-01-01

237

Influence of an electric field on photostimulated states in NH4BPh4 films  

NASA Astrophysics Data System (ADS)

The influence of an electric field on stable photostimulated triplet states of NH4BPh4 at a temperature of 77 K have been studied by EPR spectroscopy. It has been established that, on exposure to UV radiation, electron capture by traps in the band gaps takes place with formation of triplet state. After application of an electric field, triplet states are destructed because, with an increase in the applied voltage, a gradual inclination of energy bands takes place and electrons found in traps on different energy levels are released. The assumption that captured electrons are found in traps on different energy levels is confirmed by earlier studies of thermoluminescence spectra.

Antonova, O. V.; Nadolinny, V. A.; Il'inchik, E. A.; Trubin, S. V.

2012-10-01

238

Singlet-triplet quenching in high intensity fluorescent organic light emitting diodes  

NASA Astrophysics Data System (ADS)

Electroluminescence (EL) transient turn-on peaks with more than twice the brightness of the steady-state EL are observed in fluorescent organic light emitting diodes with a doped emission layer. By modeling both the singlet and triplet population dynamics, we identify the EL drop after the peak as due to singlet-triplet (ST) quenching. The peak recovery following a double voltage pulse sequence is explained in terms of triplet population relaxation through triplet-triplet quenching. A mechanism of using phosphors in the emission region is proposed for reducing ST quenching.

Zhang, Yifan; Whited, Matthew; Thompson, Mark E.; Forrest, Stephen R.

2010-08-01

239

X-ray spectra and valence states of cations in nanostructured half-doped manganite  

NASA Astrophysics Data System (ADS)

Soft X-ray absorption (XAS) and emission (XES) spectroscopies were applied to determine valence states of manganese ions in nanostructured powder of half-doped manganite obtained by milling in a ball mill. XAS spectra were measured both in surface-sensitivity total electron-yield and in bulk-sensitivity total fluorescence-yield modes. O K XES and O 1 s XAS spectra characterized the occupied and unoccupied partial O 2 p densities of states are compared with band-structure calculations made using the TB-LMTO-ASA codes. Experimental Mn 2 p, Ca 2 p, and La 3 XAS spectra are compared with results of crystal field atomic multiplet calculations. For the nanostructured system of , concentrations of Mn ions are found to be increased with increasing the time of milling.

Galakhov, V. R.; Mesilov, V. V.; Shamin, S. N.; Gizhevskii, B. A.; Skorikov, N. A.; Naumov, S. V.; Vilkov, O. Yu.

2015-02-01

240

Restoring symmetry in two-dimensional solid-state NMR correlation spectra  

NASA Astrophysics Data System (ADS)

The intrinsic asymmetry of 2D solid-state homonuclear NMR correlation spectra that arises from a non-uniform preparation of the magnetization can be removed by equilibrating the magnetization in the initial stage of the experiments through dipolar recoupling induced by PARIS or PARISxy schemes. Both methods ensure magnetization exchange with modest radio-frequency amplitudes and permit one to create an initial state that restores the symmetry about the main diagonal of 2D spectra of uniformly labeled biomolecules. This improves the determination of structural and kinetic information. Both recoupling schemes may also be used to record nearly quantitative peak amplitudes in 1D cross-polarization magic-angle-spinning spectra.

Herbert-Pucheta, Jose-Enrique; Pelupessy, Philippe; Bodenhausen, Geoffrey; Tekely, Piotr

2012-06-01

241

Triplet diffusion leads to triplet-triplet annihilation in organic phosphorescent emitters  

NASA Astrophysics Data System (ADS)

In organic materials, triplet-triplet annihilation (TTA) can be dominated by triplet diffusion or triplet-to-triplet energy transfer. Here, we discuss the diffusion and transfer dominated mechanisms in the context of photoluminescence (PL) transient measurements from thin films of archetype phosphorescent organic light emitters based on Ir and Pt complexes. We find that TTA in these emitters is controlled by diffusion due to a Dexter-type exchange interaction, suggesting triplet radiative decay and TTA are independent processes. Minimizing the PL and absorption spectral overlap in phosphorescent emitters can lead to a significantly decreased TTA rate, and thus suppressed efficiency roll-off in phosphorescent organic light emitting diodes at high brightness.

Zhang, Yifan; Forrest, Stephen R.

2013-12-01

242

Carotenoid triplet yields in normal and deuterated Rhodospirillum rubrum.  

PubMed

Quantum yields of carotenoid triplet formation in Rhodospirillum rubrum wild type and fully deuterated cells and chromatophores were determined in weak laser flashes for excitation wavelength lambda i = 530 nm (mainly absorbed by the carotenoid spirilloxanthin) and for lambda i = 608 nm (mainly absorbed by bacteriochlorophyll) in the presence and absence of magnetic fields. All experiments were performed at room temperature and in the absence of oxygen. The quantum yield of reaction center bacteriochlorophyll oxidation in wild type preparations, in which all reaction centers are in state PIX, at lambda i = 608 nm is close to unity, whereas the quantum yield of antenna carotenoid triplet formation is low (about 5%); P is the primary electron donor, a bacteriochlorophyll dimer, I the primary acceptor, a bacteriopheophytin, and X the secondary acceptor, an iron-ubiquinone complex. In cells in which the reaction centers are in the state P+IX(-), the antenna carotenoid triplet yield is about 0.2. In contrast, at lambda i = 530 nm, the quantum yield of P+ formation is relatively low (0.3) and the yield of the antenna carotenoid triplet state in state PIX unusually high (0.3). At increasing light intensities of 530 nm only about 3 carotenoids per reaction center of the 15 carotenoids present are efficiently photoconverted into the triplet state, which indicates that there are two different pools of carotenoids, one with a low efficiency for transfer of electronic excitation to bacteriochlorophyll and a high yield for triplet formation, the other with a high transfer efficiency and a low triplet yield. The absorption difference spectrum of the antenna carotenoid triplet, excited by 608 or 530 nm light in the state P+IX(-) does not show the peak at 430 nm, that is present in the difference spectrum of the reaction center carotenoid triplet, mainly observed at lambda i = 608 nm with weak flashes. The yield of the reaction center carotenoid triplet, generated in chromatophores in the state PIX(-), is decreased by about 10% by a magnetic field of 0.6 T. In a magnetic field of 0.6 T the yield of the carotenoid triplet, formed by 530 nm excitation in chromatophores at ambient redox potential, is decreased by about 45%. The high quantum yield of formation and the pronounced magnetic field effect for the carotenoid triplet generated by direct excitation at 530 nm can be explained by assuming that this triplet is not formed by intersystem crossing, but by fission of the singlet excitation into two triplet excitations and subsequent annihilation (triplet pair mechanism), or by charge separation and subsequent recombination (radical pair mechanism). Fully deuterated bacteria give essentially the same triplet yields, both in the reaction center and in the antenna carotenoids and show the same magnetic field effects as non-deuterated samples. This indicates that hyperfine interactions do not play a major role in the dephasing of the spins in the radical pair P+I- nor in the formation of the antenna carotenoid triplet. PMID:6773564

Rademaker, H; Hoff, A J; van Grondelle, R; Duysens, L N

1980-09-01

243

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

244

Spectra of random operators with absolutely continuous integrated density of states  

SciTech Connect

The structure of the spectrum of random operators is studied. It is shown that if the density of states measure of some subsets of the spectrum is zero, then these subsets are empty. In particular follows that absolute continuity of the integrated density of states implies singular spectra of ergodic operators is either empty or of positive measure. Our results apply to Anderson and alloy type models, perturbed Landau Hamiltonians, almost periodic potentials, and models which are not ergodic.

Rio, Rafael del, E-mail: delrio@iimas.unam.mx, E-mail: delriomagia@gmail.com [Departamento de Fisica Matematica, Instituto de Investigaciones en Matemáticas Aplicadas y en Sistemas, Universidad Nacional Autónoma de México, C.P. 04510, México D.F. (Mexico)

2014-04-15

245

Identification of the sites of chlorophyll triplet quenching in relation to the structure of LHC-II from higher plants. Evidence from EPR spectroscopy.  

PubMed

The Chlorophyll a (Chl a) molecules involved in the triplet-triplet energy transfer to the central luteins in trimeric LHC-II are identified by time-resolved and pulse EPR techniques. The concept of spin angular momentum conservation during triplet-triplet energy transfer is exploited for the calculation of the spin polarization of the carotenoid triplet states. The sites with the highest probability of forming triplet states, which are quenched by the central luteins, result to be Chl603 and Chl612. "Unquenched" Chl triplet states are produced by photoexcitation in the LHC-II complex. Putative sites of these triplet states are Chl614, Chl611, Chl604, and Chl613 since they do not contribute to the formation of the observed carotenoid triplet states. PMID:19725570

Di Valentin, Marilena; Biasibetti, Federico; Ceola, Stefano; Carbonera, Donatella

2009-10-01

246

Dimethyl ether: laboratory spectra up to 2.1 THz. Torsion-rotational spectra within the vibrational ground state  

NASA Astrophysics Data System (ADS)

Dimethyl ether (CH_3OCH_3) is one of the largest organic molecules detected in the interstellar medium. As an asymmetric top molecule with two methyl groups which undergo large amplitude motions and a dipole moment of ?=1.3 D, it conveys a dense spectrum throughout the terahertz region and contributes to the spectral line confusion in astronomical observations at these frequencies. In this paper, we present rotational spectra of dimethyl ether in its ground vibrational states, which have been measured in the laboratory and analyzed covering frequencies up to 2.1 THz. The analysis is based on an effective Hamiltonian for a symmetric two-top rotor and includes experimental data published so far. Frequency predictions are presented up to 2.5 THz for astronomical applications with accuracies better than 1 MHz. Table A.1 is only available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/504/635

Endres, C. P.; Drouin, B. J.; Pearson, J. C.; Müller, H. S. P.; Lewen, F.; Schlemmer, S.; Giesen, T. F.

2009-09-01

247

An unusual pathway of excitation energy deactivation in carotenoids: Singlet-to-triplet conversion on an  

E-print Network

and argue that fission of the singlet state into a pair of triplet states on individual carotenoid moleculesAn unusual pathway of excitation energy deactivation in carotenoids: Singlet-to-triplet conversion singlet state to nearby (bacterio)chlorophyll molecules. In photo- synthetic bacteria, the efficiency

van Stokkum, Ivo

248

Triplet-extinction coefficients of some laser dyes. 1  

SciTech Connect

For flashlamp-pumped dye lasers, the negative effect of triplet-state losses on laser action efficiency is well known. Oscilloscope traces of laser pulses showed that laser action diminishes much sooner than the flashlamp excitation pulse. This effect was attributed to the buildup of triplet-state dye molecules during the excitation from the flashlamp pulse. Triplet-extinction coefficients epsilon(T) were measured over the laser-action spectral region of Rhodamine 6G; Rhodamine B; Rhodamine 110; Fluorol-7GA; Coumarin 540A; Coumarin 522; Coumarin 1; Coumarin 120; 4,4'-diphenyl stilbene; and 2,7-bis(4-methoxy-phenyl)-9,9-dipropylfluorene. The different lines from an argon-ion cw laser were employed for excitation. McClure's method was used to obtain the triplet extinction coefficients Epsilon(T). The method requires the measurement of triplet optical densities OD(T) as a function of different cw laser-excitation intensities (powers) I(ex). The importance of triplet-state losses on dye-laser efficiency is reviewed. The laser action properties of the laser dyes studied are briefly discussed as they relate to the measured epsilon=(T) values.

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

1989-03-01

249

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

E-print Network

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

Wallis, A O G; Emmanouilidou, A

2015-01-01

250

Triplet extinction coefficients of some laser dyes I  

SciTech Connect

We measured the triplet extinction coefficients epsilon/sub T/ over the laser action spectral region of Rhodamine 6G; Rhodamine B; Rhodamine 110; Fluorol-7GA; Coumarin 540A; Coumarin 522; Coumarin 1; Coumarin 120; 4,4'-diphenyl stilbene; and 2,7-bis-(4-methoxy-phenyl)-9,9-dipropylfluorene. We employed the different lines from an argon ion cw laser for excitation. McClure's method was used to obtain the triplet extinction coefficients epsilon/sub T/. The method requires the measurement of triplet optical densities OD/sub T/ as a function of different cw laser excitation intensities (powers) I/sub ex/ . The importance of triplet-state losses on dye laser efficiency is reviewed. The laser action properties of the laser dyes we studied are briefly discussed as they relate to the measured epsilon/sub T/ values.

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

1988-07-15

251

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

252

ELECTRONIC SOLUTION SPECTRA FOR URANIUM AND NEPTUNIUM IN OXIDATION STATES (III) TO (VI) IN ANHYDROUS HYDROGEN FLUORIDE  

SciTech Connect

Spectra have been recorded for solutions in anhydrous hydrogen fluoride (AHF) of uranium and neptunium in oxidation states (III) to (VI). The spectra for U(III), Np(III) and Np(IV) in AHF are very similar to those in acidified aqueous solution, but that for U(IV) suggests that the cationic species is UF{sub 2}{sup 2+}. The AHF spectra for the elements in oxidation states (V) and (VI) are not comparable with those of the formally analogous aqueous solutions, where the elements exist as well-defined dioxo-cations. However, the AHF spectra can be related to spectra in the gas phase, in the solid state or in non-aqueous solvents for each element in its appropriate oxidation state.

Baluka, M.; Edelstein, N.; O'Donnell, T. A.

1980-10-01

253

Singlet-Triplet Mixing Due to g-Factor Mismatch in Double Quantum Dot  

NASA Astrophysics Data System (ADS)

Two electron spins form the spin singlet or triplet state if these spins have the same g-factor value, or a mix state consisting of both the singlet and triplet states if these spins have different g-factor values. It is considered that two energy levels of electrons are formed in a double quantum dot device for use in quantum information processing; however, the g-factors of the electrons have not been treated as an important factor because they cannot be changed easily in experiments. We introduce a numerical calculation method for the singlet-triplet mix state due to the g-factor mismatch in double quantum dots. It is found that this mismatch changes the energy levels of the original singlet and triplet states; thus, it affects the intersecting points of the energy levels of the singlet and triplet states where a dynamic nuclear polarization appears via hyperfine interaction.

Takahashi, Ryo; Kono, Kimitoshi; Tarucha, Seigo; Ono, Keiji

2011-04-01

254

Twins, Triplets, and Other Multiples  

MedlinePLUS

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

255

Multiples: Twins, Triplets and Beyond  

MedlinePLUS

... page It's been added to your dashboard . Multiples: twins, triplets and beyond When a woman is carrying ... What is the difference between identical and fraternal twins? Identical twins (also called monozygotic twins) occur when ...

256

Correlations between ground and excited state spectra of a quantum Dot  

PubMed

The ground and excited state spectra of a semiconductor quantum dot with successive electron occupancy were studied with linear and nonlinear magnetoconductance measurements. A direct correlation was observed between the mth excited state of the N-electron system and the ground state of the (N + m)-electron system for m up to 4. The results are consistent with a single-particle picture in which a fixed spectrum of energy levels is successively filled, except for a notable absence of spin degeneracy. Further departures from the single-particle picture due to electron-electron interaction were also observed. Magnetoconductance fluctuations of ground states show anticrossings where wave function characteristics are exchanged between adjacent levels. PMID:9388178

Stewart; Sprinzak; Marcus; Duruoz; Harris

1997-12-01

257

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

Microsoft Academic Search

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

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

1998-01-01

258

Venus - Stein Triplet Crater  

NASA Technical Reports Server (NTRS)

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

1990-01-01

259

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

260

Photoassociation and photoinduced charge transfer in bridged diaryl compounds. 6. Intramolecular triplet excimers of dicarbazolylalkanes and their comparison to an intermolecular triplet excimer of carbazole  

SciTech Connect

A time-resolved emission study of intramolecular triplet excimer formation has been carried out for dicarbazolylmethane (DCM) and dicarbazolylpropane (DCP) in fluid solution at room temperature. The triplet excimer formation was deduced from the comparison of the phosphorescence with the corresponding emission from the intermolecular triplet excimer of carbazole. It has been found that whereas the triplet excimer formation in DCP is evident in both polar and nonpolar solvents, the excimer formation in DCM is observed only in polar solvents at longer delay times. The result indicates that the conformation favored by the triplet excimer is more readily attainable in DCP than in DCM. The enhancement of the triplet excimer formation by polar solvent, which is also observed for carbazole, suggests that the triplet excimers are stabilized (at least in part) by charge resonance interactions. Comparison of the temporal characteristics of the normal delayed fluorescence of DCP with those of the corresponding excimer phosphorescence suggests that the delayed fluorescence at long delay times is produced by bimolecular annihilation of the intramolecular triplet excimers. This in turn implies that the excited singlet-state species produced by bimolecular annihilation of the triplet excimers is unstable and rearranges into monomeric (i.e., non-interacting) conformation prior to its decay by emission of radiation. 16 refs., 7 figs.

Cai, J.; Lim, E.C. (Univ. of Akron, OH (United States))

1994-03-10

261

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

PubMed

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

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

2015-01-21

262

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

NASA Astrophysics Data System (ADS)

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

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

2015-01-01

263

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

264

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

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

2014-12-18

265

Unimolecular decomposition of chemically activated triplet C4HD3 complexes: A combined crossed-beam and ab initio study  

NASA Astrophysics Data System (ADS)

The crossed molecular beam technique was utilized to investigate the reaction of ground state carbon atoms, C(3Pj), with d3-methylacetylene, CD3CCH(X1A1), at an average collision energy of 21.1 kJ mol-1. Product angular distributions and time-of-flight spectra were recorded. Only the deuterium loss was observed; no atomic hydrogen emission was detected experimentally. Forward-convolution fitting of the data combined with electronic structure calculations show that the reaction is indirect and initiated by a barrierless interaction of the carbon atom to the ?-system of the methylacetylene molecule. Reactions with large impact parameters yield a triplet trans-methylpropene-1-diylidene complex whereas—to a minor amount—the formation of a triplet methylcyclopropenylidene intermediate is governed by smaller impact parameters. Both collision complexes rearrange via hydrogen migration and ring opening, respectively, to two distinct triplet methylpropargylene intermediates. A deuterium atom loss via a tight transition state located about 30 kJ mol-1 above the n-C4H3 product is a likely reaction pathway. The formation of the thermodynamically less stable cyclic isomer remains to be investigated closer. The D atom loss pathway represents an entrance barrierless and exothermic route to synthesize an extremely reactive C4H3 hydrocarbon radical in combustion processes and extraterrestrial environments.

Kaiser, R. I.; Mebel, A. M.; Lee, Y. T.; Chang, A. H. H.

2001-09-01

266

TRANSCRIPTION DESTABILIZES TRIPLET REPEATS  

PubMed Central

Triplet repeat expansion is the molecular basis for several human diseases. Intensive studies using systems in bacteria, yeast, flies, mammalian cells, and mice have provided important insights into the molecular processes that are responsible for mediating repeat instability. The age-dependent, ongoing repeat instability in somatic tissues, especially in terminally differentiated neurons, strongly suggests a robust role for pathways that are independent of DNA replication. Several genetic studies have indicated that transcription can play a critical role in repeat instability, potentially providing a basis for the instability observed in neurons. Transcription-induced repeat instability can be modulated by several DNA repair proteins, including those involved in mismatch repair (MMR) and transcription-coupled nucleotide excision repair (TC-NER). Though the mechanism is unclear, it is likely that transcription facilitates the formation of repeat-specific secondary structures, which act as intermediates to trigger DNA repair, eventually leading to changes in the length of the repeat tract. In addition, other processes associated with transcription can also modulate repeat instability, as shown in a variety of different systems. Overall, the mechanisms underlying repeat instability in humans are unexpectedly complicated. Because repeat-disease genes are widely expressed, transcription undoubtedly contributes to the repeat instability observed in many diseases, but it may be especially important in nondividing cells. Transcription-induced instability is likely to involve an extensive interplay not only of the core transcription machinery and DNA repair proteins, but also of proteins involved in chromatin remodeling, regulation of supercoiling, and removal of stalled RNA polymerases, as well as local DNA sequence effects. PMID:18973172

Lin, Yunfu; Hubert, Leroy; Wilson, John H.

2013-01-01

267

Binding energies of the ground triplet state a{sup 3}?{sub u}{sup +} of Rb{sub 2} and Cs{sub 2} in terms of the generalized Le Roy–Bernstein near-dissociation expansion  

SciTech Connect

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

Sovkov, V. B.; Ivanov, V. S. [V.A. Fock Institute of Physics and Department of Physics of St. Petersburg State University, Ulyanovskaya Street 1, Petrodvoretz, St. Petersburg 198504 (Russian Federation)] [V.A. Fock Institute of Physics and Department of Physics of St. Petersburg State University, Ulyanovskaya Street 1, Petrodvoretz, St. Petersburg 198504 (Russian Federation)

2014-04-07

268

Stimulated emission depletion of triplet excitons in a phosphorescent organic laser  

NASA Astrophysics Data System (ADS)

Triplet formation is investigated in an optically pumped polymer laser by detecting the phosphorescence emission after excitation. A clear correlation is observed between the onset of lasing and a saturation of phosphorescence intensity due to stimulated emission depletion of the singlet state and the resulting reduction in intersystem crossing. The results are consistent with intersystem crossing constituting the dominant triplet formation pathway in conjugated polymers. Excitation at different wavelengths has no effect on the triplet saturation behavior, which allows the authors to exclude singlet fission or breaking as the origin of triplet formation. The method constitutes an implementation of a highly nondegenerate excitonic switch.

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

2006-10-01

269

X-ray and gamma-ray spectra of Cyg X-1 in the soft state  

E-print Network

We present X-ray/gamma-ray observations of Cyg X-1 in the soft state during 1996 May-June. We analyze ASCA, RXTE and OSSE data. The spectrum consists of soft X-ray blackbody emission of an optically thick accretion disk in the vicinity of a black hole and a power law with an energy index alpha around 1.2-1.5 extending to at least several hundred keV. In the spectra, we find the presence of strong Compton reflection, which probably comes from the disk.

Marek Gierlinski; Andrzej A. Zdziarski; Tadayasu Dotani; Ken Ebisawa; Keith Jahoda; W. Neil Johnson

1997-07-19

270

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

SciTech Connect

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

2014-10-15

271

Optically detected magnetic resonance spectra of the lowest triplet state of 1-iodonaphthalene in durene at zero and high magnetic fields  

Microsoft Academic Search

This paper describes the results of optically detected magnetic resonance (ODMR) experiments on photoexcited 1-iodonaphthalene (1IN) in a durene host crystal at liquid helium temperatures. The structure observed in both the zero-field (zf) and high-field ODMR transitions is interpreted in terms of a spin Hamiltonian which includes the complete iodine (I=5\\/2) nuclear quadrupole and hyperfine interactions. Principal values of D

G. Kothandaraman; D. W. Pratt; D. S. Tintit

1975-01-01

272

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

E-print Network

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

Oklahoma State University

273

A Theory of Electron Transfer and Steady-State Optical Spectra of Chromophores with Varying Electronic Polarizability  

E-print Network

A Theory of Electron Transfer and Steady-State Optical Spectra of Chromophores with Varying in the state with hider solute polarizability. The dependence of the ET rate on the equilibrium energy gap from the side of exothermic reactions and broader for the state with a higher polarizability

Matyushov, Dmitry

274

Conduction band states of transition metal (TM) high-k gate dielectrics as determined from X-ray absorption spectra  

E-print Network

V for ZrO2. Finally, the experimental spin­orbit splittings are 5.6 eV ± 0.3 eV for the Ti 2p states, 13 strengths for the d* and s* features in the p state spectra for TiO2, ZrO2 and HfO2 are markedly different for the ZrO2 M3 and M2 spectra, and are stronger for the HfO2 N2,3 spectra. 0026-2714/$ - see front matter Ó

275

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

276

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

PubMed

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

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

2012-10-26

277

Stimulated emission depletion of triplet excitons in a phosphorescent organic laser  

Microsoft Academic Search

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

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

2006-01-01

278

High triplet yield from singlet fission in a thin film of 1,3-diphenylisobenzofuran.  

PubMed

Direct observation of triplet absorption and ground-state depletion upon pulsed excitation of a polycrystalline thin solid film of 1,3-diphenylisobenzofuran at 77 K revealed a 200 ± 30% triplet yield, which was attributed to singlet fission. PMID:21043452

Johnson, Justin C; Nozik, Arthur J; Michl, Josef

2010-11-24

279

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

NASA Astrophysics Data System (ADS)

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

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

2001-05-01

280

'Blueberry' Triplets Born in Rock  

NASA Technical Reports Server (NTRS)

This microscopic image, taken at the outcrop region dubbed 'Berry Bowl' near the Mars Exploration Rover Opportunity's landing site, shows the sphere-like grains or 'blueberries' that fill Berry Bowl. Of particular interest is the blueberry triplet, which indicates that these geologic features grew in pre-existing wet sediments. Other sphere-like grains that form in the air, such as impact spherules or ejected volcanic material called lapilli, are unlikely to fuse along a line and form triplets. This image was taken by the rover's microscopic imager on the 46th martian day, or sol, of its mission.

2004-01-01

281

When You Are a Twin or Triplet  

MedlinePLUS

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

282

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

NASA Astrophysics Data System (ADS)

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

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

2008-01-01

283

Triplet exciton caging in two dimensions  

Microsoft Academic Search

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

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

1976-01-01

284

OptaDOS: A tool for obtaining density of states, core-level and optical spectra from electronic structure codes  

NASA Astrophysics Data System (ADS)

We present OptaDOS, a program for calculating core-electron and low-loss electron energy loss spectra (EELS) and optical spectra along with total-, projected- and joint-density of electronic states (DOS) from single-particle eigenenergies and dipole transition coefficients. Energy-loss spectroscopy is an important tool for probing bonding within a material. Interpreting these spectra can be aided by first principles calculations. The spectra are generated from the eigenenergies through integration over the Brillouin zone. An important feature of this code is that this integration is performed using a choice of adaptive or linear extrapolation broadening methods which we show produces higher accuracy spectra than standard fixed-width Gaussian broadening. OptaDOS may be straightforwardly interfaced to any electronic structure code. OptaDOS is freely available under the GNU General Public licence from http://www.optados.org.

Morris, Andrew J.; Nicholls, Rebecca J.; Pickard, Chris J.; Yates, Jonathan R.

2014-05-01

285

Particle diffusion and localized acceleration in inhomogeneous AGN jets - I. Steady-state spectra  

NASA Astrophysics Data System (ADS)

We study the acceleration, transport, and emission of particles in relativistic jets. Localized stochastic particle acceleration, spatial diffusion, and synchrotron as well as synchrotron self-Compton (SSC) emission are considered in a leptonic model. To account for inhomogeneity, we use a 2D axisymmetric cylindrical geometry for both relativistic electrons and magnetic field. In this first phase of our work, we focus on steady-state spectra that develop from a time-dependent model. We demonstrate that small isolated acceleration region in a much larger emission volume are sufficient to accelerate particles to high energy. Diffusive escape from these small regions provides a natural explanation for the spectral form of the jet emission. The location of the acceleration regions within the jet is found to affect the cooling break of the spectrum in this diffusive model. Diffusion-caused energy-dependent inhomogeneity in the jets predicts that the SSC spectrum is harder than the synchrotron spectrum. There can also be a spectral hardening towards the high-energy section of the synchrotron spectrum, if particle escape is relatively slow. These two spectral hardening effects indicate that the jet inhomogeneity might be a natural explanation for the unexpected hard ?-ray spectra observed in some blazars.

Chen, Xuhui; Pohl, Martin; Böttcher, Markus

2015-02-01

286

Diffusion length and langevin recombination of singlet and triplet excitons in organic heterojunction solar cells.  

PubMed

We derived new expressions for the diffusion length of singlet and triplet excitons by using the Föster and Dexter transfer mechanisms, respectively, and have found that the diffusion lengths of singlet and triplet excitons are comparable. By using the Langevin recombination theory, we derived the rate of recombination of dissociated free charges into their excitonic states. We found that in some organic polymers the probabilities of recombination of free charge carriers back into the singlet and triplet states are approximately 65.6 and 34.4?%, respectively, indicating that Langevin-type recombination into triplet excitons in organic semiconductors is less likely. This implies that the creation of triplet excitons may be advantageous in organic solar cells, because this may lead to dissociated free charge carriers that can be collected at their respective electrodes, which should result in better conversion efficiency. PMID:25735545

Ompong, David; Singh, Jai

2015-04-27

287

Electron number dependence of spin triplet-singlet relaxation time  

NASA Astrophysics Data System (ADS)

In a GaAs single quantum dot, the relaxation time T1 between spin triplet and singlet states has been measured for the last few even electron numbers. The singlet-triplet energy separation EST is tuned as a control parameter for the comparison of T1 between different electron numbers. T1 steadily decreases with increasing electron numbers from 2-electrons to 6-electrons. This implies an enhancement of the spin-orbit coupling strength due to multi-electron interaction in a quantum dot.

Li, H. O.; Xiao, M.; Cao, G.; You, J.; Guo, G. P.

2014-02-01

288

Spontaneous Spin Accumulation in Singlet-Triplet Josephson Junctions  

NASA Astrophysics Data System (ADS)

We study the Andreev bound states in a Josephson junction between a singlet and a triplet superconductors. Because of the mismatch in the spin symmetries of pairing, the energies of the spin-up and -down quasiparticles are generally different. This results in imbalance of spin populations and net spin accumulation at the junction in equilibrium. This effect can be detected using probes of local magnetic field, such as the scanning SQUID, Hall, and Kerr probes. It may help to identify potential triplet pairing in (TMTSF)2X, Sr2RuO4, and oxypnictides.

Sengupta, K.; Yakovenko, Victor M.

2008-10-01

289

First-principles calculation of ground and excited-state absorption spectra of ruby and alexandrite considering lattice relaxation  

NASA Astrophysics Data System (ADS)

We performed first-principles calculations of multiplet structures and the corresponding ground-state absorption and excited-state absorption spectra for ruby (Cr3+:?-Al2O3) and alexandrite (Cr3+:BeAl2O4) which included lattice relaxation. The lattice relaxation was estimated using the first-principles total energy and molecular-dynamics method of the CASTEP code. The multiplet structure and absorption spectra were calculated using the configuration-interaction method based on density-functional calculations. For both ruby and alexandrite, the theoretical absorption spectra, which were already in reasonable agreement with experimental spectra, were further improved by consideration of lattice relaxation. In the case of ruby, the peak positions and peak intensities were improved through the use of models with relaxations of 11 or more atoms. For alexandrite, the polarization dependence of the U band was significantly improved, even by a model with a relaxation of only seven atoms.

Watanabe, Shinta; Sasaki, Tomomi; Taniguchi, Rie; Ishii, Takugo; Ogasawara, Kazuyoshi

2009-02-01

290

Spectral editing of two-dimensional magic-angle-spinning solid-state NMR spectra for protein resonance assignment  

E-print Network

ARTICLE Spectral editing of two-dimensional magic-angle-spinning solid-state NMR spectra % for the CH selection experiment, and are demon- strated on well-characterized model proteins GB1 Recent progress in magic-angle-spinning (MAS) solid-state NMR (SSNMR) spectroscopy has made it possible

Hong, Mei

291

GAS-PHASE ELECTRONIC SPECTRA OF POLYACETYLENE CATIONS: RELEVANCE OF HIGHER EXCITED STATES  

SciTech Connect

Transitions to higher electronic states of polyacetylene cations (HC{sub 2n}H{sup +}, n = 4, 5, 6) have been measured in the gas phase at {approx}20 K. The absorption spectra were obtained using a resonant two-color, two-photon fragmentation technique in an ion trap, allowing a direct comparison between laboratory and astrophysical data. The purpose was to investigate the relevance of such transitions to astronomical observations because the general expectation is that the bands could be too broad due to fast intramolecular processes. It is shown that the origin bands are still narrow enough (1-10 cm{sup -1}) to be considered, especially as the higher-lying transitions often possess large oscillator strengths.

Rice, C. A.; Rudnev, V.; Dietsche, R.; Maier, J. P., E-mail: j.p.maier@unibas.c [Department of Chemistry, University of Basel, Klingelbergstr. 80, CH-4056 Basel (Switzerland)

2010-07-15

292

Excited-state Raman spectroscopy with and without actinic excitation: S{sub 1} Raman spectra of trans-azobenzene  

SciTech Connect

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 S{sub 1} and S{sub 0} spectra of trans-azobenzene in n-hexane. The S{sub 1} spectra were also measured conventionally, upon n?* (S{sub 0} ? S{sub 1}) 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. [Department of Chemistry, Humboldt-Universität zu Berlin, Brook-Taylor-Str. 2, D-12489 Berlin (Germany)] [Department of Chemistry, Humboldt-Universität zu Berlin, Brook-Taylor-Str. 2, D-12489 Berlin (Germany)

2014-05-14

293

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

NASA Astrophysics Data System (ADS)

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

Kihara, Shigeharu

294

Aromaticity effects on the profiles of the lowest triplet-state potential-energy surfaces for rotation about the C=C bonds of olefins with five-membered ring substituents: an example of the impact of Baird's rule.  

PubMed

A density functional theory study on olefins with five-membered monocyclic 4n and 4n+2 ?-electron substituents (C4H3X; X=CH(+), SiH(+), BH, AlH, CH2, SiH2, O, S, NH, and CH(-)) was performed to assess the connection between the degree of substituent (anti)aromaticity and the profile of the lowest triplet-state (T1) potential-energy surface (PES) for twisting about olefinic C=C bonds. It exploited both Hückel's rule on aromaticity in the closed-shell singlet ground state (S0) and Baird's rule on aromaticity in the lowest ??* excited triplet state. The compounds CH2=CH(C4H3X) were categorized as set A and set B olefins depending on which carbon atom (C2 or C3) of the C4H3X ring is bonded to the olefin. The degree of substituent (anti)aromaticity goes from strongly S0 -antiaromatic/T1 -aromatic (C5H4 (+)) to strongly S0 -aromatic/T1- antiaromatic (C5H4(-)). Our hypothesis is that the shapes of the T1 PESs, as given by the energy differences between planar and perpendicularly twisted olefin structures in T1 [?E(T1)], smoothly follow the changes in substituent (anti)aromaticity. Indeed, correlations between ?E(T1) and the (anti)aromaticity changes of the C4 H3 X groups, as measured by the zz-tensor component of the nucleus-independent chemical shift ?NICS(T1;1)zz , are found both for sets A and B separately (linear fits; r(2) =0.949 and 0.851, respectively) and for the two sets combined (linear fit; r(2) =0.851). For sets A and B combined, strong correlations are also found between ?E(T1) and the degree of S0 (anti)aromaticity as determined by NICS(S0,1)zz (sigmoidal fit; r(2) =0.963), as well as between the T1 energies of the planar olefins and NICS(S0,1)zz (linear fit; r(2) =0.939). Thus, careful tuning of substituent (anti)aromaticity allows for design of small olefins with T1 PESs suitable for adiabatic Z/E photoisomerization. PMID:23794153

Zhu, Jun; Fogarty, Heather A; Möllerstedt, Helene; Brink, Maria; Ottosson, Henrik

2013-08-01

295

Infrared laser spectroscopy of jet-cooled carbon clusters: structure of triplet C6  

NASA Technical Reports Server (NTRS)

We report the first structural characterization of the triplet isomer of C6. Forty-one rovibrational/fine structure transitions in the nu 4(sigma u) antisymmetric stretch fundamental of the C6 cluster have been measured by diode laser absorption spectroscopy of a supersonic carbon cluster beam. The observed spectrum is characteristic of a centrosymmetric linear triplet state with cumulene-type bonding. The measured ground state rotational constant B0 = 0.048 479 (10)cm-1 and the effective bond length r(eff) = 1.2868 (1) angstroms are in good agreement with ab initio predictions for the linear triplet (3 sigma g-) state of C6.

Hwang, H. J.; Van Orden, A.; Tanaka, K.; Kuo, E. W.; Heath, J. R.; Saykally, R. J.

1993-01-01

296

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

SciTech Connect

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

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

2011-08-31

297

DFT study of substituted and benzannelated aryl cations: substituent dependency of singlet/triplet ratio.  

PubMed

By using density functional theory (DFT) method at the B3LYP/6-311+G level, it has been shown that the preference for the singlet-state phenyl cation can be dramatically increased relative to the triplet state by introducing onium cationic substituents in the para position. At this level of theory, the singlet ground state for the parent phenyl cation was found to be lower than the triplet by 19.6 kcal/mol. Introduction of electron-donating substituent groups, namely -NMe(2), -NH(2), and -SMe in the para position, strongly favors the triplet state. The -OMe and -SH groups cause a similar but smaller effect, whereas -OH substitution results in an energetically identical system. Protonation of these substituent groups form onium-phenyl dications for which a complete reversal of the relative stabilities in favor of the singlet ground state are indicated with -SH(2)(+), -SMeH(+), and -NH(3)(+) showing the largest singlet/triplet energy difference. The -N(2)(+) group in the para position has a similar effect. Benzannelation also increases the relative stability of triplet aryl cation. Whereas the 1-naphththyl and 2-naphthyl cations are energetically identical, in the 9-anthracenyl cation the triplet minimum lies 13.4 kcal/mol below the singlet minimum. Introduction of activating groups, i.e., OH and NMe(2) at the 4-position of the 1-naphthyl cation, greatly increases the relative stability of the triplet state. Upon heteroatom protonation, the singlet/triplet energy gap is substantially narrowed but the triplet state still remains lower in energy. Structural features in the resulting dications are discussed and compared with the corresponding monocations. The NBO charges at the cationic centers were also compared. We have also calculated the dediazoniation and decarbonylation energetics for mono- and bis-o-trimethylsilyl-substituted benzenediazonium and benzoyl cation to aryl cations in order to probe the effect of beta-silyl stabilization of the positive charge. PMID:11975546

Laali, Kenneth K; Rasul, Golam; Prakash, G K Surya; Olah, George A

2002-05-01

298

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

NASA Astrophysics Data System (ADS)

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

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

2012-06-01

299

Nearly Perfect Triplet-Triplet Energy Transfer from Wannier Excitons to Naphthalene in Organic-Inorganic Hybrid Quantum-Well Materials  

NASA Astrophysics Data System (ADS)

We report the observation of extremely efficient energy transfer (greater than 99%) in an organic-inorganic hybrid quantum-well structure consisting of perovskite-type lead bromide well layers and naphthalene-linked ammonium barrier layers. Time-resolved photoluminescence measurements confirm that the transfer is triplet-triplet Dexter-type energy transfer from Wannier excitons in the inorganic well to the triplet state of naphthalene molecules in the organic barrier. Using measurements in the 10 300 K temperature range, we also investigated the temperature dependence of the energy transfer.

Ema, K.; Inomata, M.; Kato, Y.; Kunugita, H.; Era, M.

2008-06-01

300

Spectroscopic and dynamical studies of acetylene and hydrogen cyanide: S/sub 0/ surfaces, unstable isomers, and triplet states: Final technical report  

SciTech Connect

Progress is reported in the following areas of research: statistical properties of C/sub 2/H/sub 2/ spectra in the 28,000 cm/sup -1/ region; properties of C/sub 2/H/sub 2/ X-bar ..sigma../sub g//sup +/ levels in the 11,400-15,600 cm/sup -1/ region; a spectroscopic study of the acetylene-vinylidene isomerization; an unsuspected Fermi perturbation in the acetylene A-bar 'Au 3..nu../sub 3/ level; acetylene quantum beats and anticrossing spectroscopy; and unimolecular decomposition of acetylene; determination of the heat of formation of the CCH radical. (PLG)

Kinsey, J.L.; Field, R.W.

1987-01-01

301

Heavy vector triplets: bridging theory and data  

NASA Astrophysics Data System (ADS)

We introduce a model-independent strategy to study narrow resonances which we apply to a heavy vector triplet of the Standard Model (SM) group for illustration. The method is based on a simplified phenomenological Lagrangian which reproduces a large class of explicit models. Firstly, this allows us to derive robust model-independent phenomenological features and, conversely, to identify the peculiarities of different explicit realizations. Secondly, limits on ? × BR can be converted into bounds on a few relevant parameters in a fully analytic way, allowing for an interpretation in any given explicit model. Based on the available 8 TeV LHC analyses, we derive current limits and interpret them for vector triplets arising in weakly coupled (gauge) and strongly coupled (composite) extensions of the SM. We point out that a model-independent limit setting procedure must be based on purely on-shell quantities, like ? × BR. Finite width effects altering the limits can be considerably reduced by focusing on the on-shell signal region. We illustrate this aspect with a study of the invariant mass distribution in di-lepton searches and the transverse mass distribution in lepton-neutrino final states. In addition to this paper we provide a set of online tools available at a dedicated webpage [1].

Pappadopulo, Duccio; Thamm, Andrea; Torre, Riccardo; Wulzer, Andrea

2014-09-01

302

Assignment of bacteriochlorophyll a ligation state from absorption and resonance raman spectra  

SciTech Connect

Absorption and Soret excitation resonance Raman (RR) spectra have been obtained for a series of coordination forms on monomeric bacteriochlorophyll a (BChl a). Strong and moderate intensity bands are observed in the RR spectrum at 1609 and 1530 cm/sup -1/ for five-coordinate species, which shift to 1595 and 1512 cm/sup -1/, respectively, in the six-coordinate form. These coordination-sensitive vibrations are independent of the nature of the axial ligand and are suggested to have significant C/sub a/ C/sub m/ character, while several other less intense coordination-sensitive bands at 1463, 1444, and 1375 cm/sup -1/ are considered to arise from C/sub b/C/sub b/ and C/sub a/N stretching vibrations. These coordination-sensitive RR bands were used to determine BChl a ligation state in the solvents used, and structure correlations based on absorption maxima have been developed. The Q/sub x/ absorption band position is sensitive not only to BChl a Mg/sup 2 +/ coordination number but also to the nature of the axial ligand, i.e., oxygen, sulfur, or nitrogen. Q/sub x/ maxima are observed at 570, 575-580, and 582 nm for five-coordinate oxygen, sulfur, and nitrogen ligands, respectively, and at 590-595 and 605-612 nm, for six-coordinate oxygen and nitrogen species, respectively. The Q/sub y/ absorption maximum is insensitive to coordination number changes but is dependent on the nature of the axial ligand: 770 nm for oxygen ligand(s) and 775 nm for nitrogen ligand(s). A similar series of absorption and Soret excitation RR spectra were obtained for the demetalated form of BChl a, BPheo a.

Callahan, P.M.; Cotton, T.M.

1987-11-11

303

A singlet - triplet T+ based qubit  

NASA Astrophysics Data System (ADS)

We theoretically show that the electronic two-spin states singlet and triplet T+ are promising candidates for the implementation of a qubit in GaAs double quantum dots (DQD). A coherent superposition of the two-spin states is obtained by finite time Landau-Zener-St"uckelberg interferometry [1] and the single qubit rotations are performed by means of an external magnetic field with a typical amplitude of about 100 mT. In such a system, the coherent manipulation of the qubit takes place in a time scale of about 1 ns. We also study the nuclear induced decoherence, mainly due to hyperfine contact coupling between the electronic and nuclear spins, and compute the decoherence time T2^* ˜10 ns. [4pt] [1] H. Ribeiro and G. Burkard, Phys. Rev. Lett. 102, 216802 (2009)

Ribeiro, Hugo; Petta, Jason; Burkard, Guido

2010-03-01

304

Triplet excitations in graphene-based systems  

NASA Astrophysics Data System (ADS)

In this paper we investigate the excitations in a single graphene layer and in a single-walled carbon nanotube, i.e. the spectrum of magnetic excitations is calculated. In the absence of interactions in these systems there is a unique gap in the electron-hole continuum. We show that in the presence of Coulomb correlations bound states, magnons, appear in this forbidden region. The Coulomb interaction is examined in the context of the Pariser-Parr-Pople (PPP) model which takes into account the long-range nature of the interaction. The energy of the new bound states depends on the strength of the Coulomb forces. The calculations are performed for arbitrary electron-hole (e\\text-h) momentum q . In the end, this work finally settles the discussion sabout the existence of triplet excitations in graphene which has been lasting for a decade in the literature.

Posvyanskiy, V.; Arnarson, L.; Hedegård, P.

2015-02-01

305

(??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

306

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

307

Electron paramagnetic resonance studies of the lowest triplet states of 1,2-benzanthracene- d12, chrysene- d12, and 1,2;5,6-dibenzanthracene- d14 in single-crystal p-terphenyl in the range from 4 to 240 K, and their implications concerning phase transitions in p-terphenyl below 240 K  

NASA Astrophysics Data System (ADS)

Low-field electron paramagnetic resonance studies from 65 to 240 K of the zero-field splittings of triplet 1,2-benzanthracene- d12 dilutely substituted in single-crystal p-terphenyl have yielded 193.0 ± 0.3 K as the best value of the temperature at which a phase transition sets in upon cooling, and at which it is completed upon warming, these crystals. Similar studies of triplet chrysene- d12 (from 7.7 to 80 K) and of 1,2;5,6-dibenzanthracene- d14 (from 7.4 to 100.7 K) dilutely substituted in single-crystal p-terphenyl give evidence of a previously unreported second phase transition intrinsic to p-terphenyl, but influenced measurably by the presence of dilute guests. In chrysene substituted p-terphenyl, the system for which our present data most clearly indicate a second phase transition, the transition temperature lies in the range from 7.9 to 8.2 K. Our results for these phase transitions are discussed in the context of recent experimental and theoretical results for crystalline p-terphenyl below room temperature. Multiple orientation of these triplet guests and their interactions with p-terphenyl host are discussed for all three systems, and several notable features of the spectra are described.

Chen, M.-C.; Cullick, A. S.; Gerkin, Roger E.; Lundstedt, Alan P.

1980-03-01

308

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

E-print Network

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

Kent, Paul

309

Intensity formulas for triplet bands  

NASA Technical Reports Server (NTRS)

Previous work in this area is surveyed and the mathematics involved in determining the quantitative intensity measurements in triplet bands is presented. Explicit expressions for the intensity distribution in the branches of the 3 Sigma-3 Pi and 1 Sigma-3Pi bands valid for all values of the coupling constant Y of the 3 Pi terms are given. The intensity distribution calculated according to the formulas given is compared with measurements of PH, 3 Pi-3 Sigma. Good quantitative agreement is obtained.

Budo, A.

1982-01-01

310

Anorexia nervosa in identical triplets.  

PubMed

The cause of anorexia nervosa (AN) is unclear, but is likely multifactorial, including psychological, familial, environmental, societal, genetic, and other biological factors. This case report of identical 12-year-old female triplets simultaneously concordant for AN illustrates the importance of addressing all these components in evaluation and treatment, and the difficulty of determining the relative importance of each factor in the cause of an individual's eating disorder. An overly close relationship and competitiveness between the girls, treated at times as a triplet group rather than as individuals, as well as stressful family dynamics, were probably important antecedents to the girls' AN. The girls encouraged each other and competed to lose weight. Brief individual and family psychotherapy, parent counseling, nutritional counseling, and psychoeducation led to successful treatment. The triplets were encouraged in treatment to compete with and encourage each other to obtain treatment goals, including eating more healthily and achieving healthy weights. A literature review of AN twins studies is also presented, as these studies add to our understanding of the relative importance of shared genes and shared environment in the development of AN. These studies also add insight into treating individuals from families with multiple affected relatives. PMID:19407712

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

2009-03-01

311

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

NASA Astrophysics Data System (ADS)

Recently the Cassini Ultraviolet Imaging Spectrograph (UVIS) has revealed the presence of N2 Vegard-Kaplan (VK) band A3?u+-X1?g+ emissions in Titan's dayglow limb observation. We present model calculations for the production of various N2 triplet states (viz., A3?u+,B3?g,C3?u,E3?u,W3?u, and B3?u ) in the upper atmosphere of Titan. The Analytical Yield Spectra technique is used to calculate steady state photoelectron fluxes in Titan's atmosphere, which are in agreement with those observed by the Cassini's CAPS instrument. Considering direct electron impact excitation, inter-state cascading, and quenching effects, the population of different levels of N2 triplet states are calculated under statistical equilibrium. Densities of all vibrational levels of each triplet state and volume production rates for various triplet states are calculated in the model. Vertically integrated overhead intensities for the same date and lighting conditions as reported by the UVIS observations for N2 Vegard-Kaplan A3?u+-X1?g+, First Positive B3?g-A3?u+, Second Positive (C3?u - B3?g), Wu-Benesch (W3?u - B3?g), and Reverse First Positive bands of N2 are found to be 132, 114, 19, 22, and 22 R, respectively. Overhead intensities are calculated for each vibrational transition of all the triplet band emissions of N2, which span a wider spectrum of wavelengths from ultraviolet to infrared. The calculated limb intensities of total and prominent transitions of VK band are presented. The model limb intensity of VK emission within the 150-190 nm wavelength region is in good agreement with the Cassini UVIS observed limb profile. An assessment of the impact of solar EUV flux on the N2 triplet band emission intensity has been made by using three different solar flux models, viz., Solar EUV Experiment (SEE), SOLAR2000 (S2K) model of Tobiska (Tobiska, W.K. [2004]. Adv. Space Res. 34, 1736-1746), and HEUVAC model of Richards et al. (Richards, P.G., Woods, T.N., Peterson, W.K. [2006]. Adv. Space Res. 37 (2), 315-322). The calculated N2 VK band intensity at the peak of limb intensity due to S2K and HEUVAC solar flux models is a factor of 1.2 and 0.9, respectively, of that obtained using SEE solar EUV flux. The effects of higher N2 density and solar zenith angle on the emission intensity are also studied. The model predicted N2 triplet band intensities during moderate (F10.7 = 150) and high (F10.7 = 240) solar activity conditions, using SEE solar EUV flux, are a factor of 2 and 2.8, respectively, higher than those during solar minimum (F10.7 = 68) condition.

Bhardwaj, Anil; Jain, Sonal Kumar

2012-04-01

312

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

313

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

314

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.

315

Spectra of black-hole binaries in the low/hard state: from radio to X-rays  

E-print Network

We propose a jet model for the low/hard state of Galactic black-hole X-ray sources that can explain the energy spectra from radio to X-rays. The model assumes that i) there is a magnetic field along the axis of the jet; ii) the electron density in the jet drops inversely proportional to distance; and iii) the electrons in the jet follow a power law distribution function. We have performed Monte Carlo simulations of Compton upscattering of soft photons from the accretion disk and have found power-law high-energy spectra with photon-number index in the range 1.5 - 2 and cutoff at a few hundred keV. The spectrum at long wavelengths (radio, infrared, optical) is modeled to come from synchrotron radiation of the energetic electrons in the jet. We find flat to inverted radio spectra that extend from the radio up to about the optical band. For magnetic field strengths of the order of 10^5-10^6G at the base of the jet, the calculated spectra agree well in slope and flux with the observations. Our model has the advantage over other existing models that it also explains many of the existing timing data such as the time lag spectra, the hardening of the power density spectra and the narrowing of the autocorrelation function with increasing photon energy.

Dimitrios Giannios

2005-04-07

316

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

PubMed

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

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

2015-03-21

317

Competition between singlet and triplet superconductivity  

E-print Network

The competition between singlet and triplet superconductivity is examined in consideration of correlations on an extended Hubbard model. It is shown that the triplet superconductivity may not be included in the common Hubbard model since the strong correlation favors the singlet superconductivity, and thus the triplet superconductivity should be induced by the electron-phonon interaction and the ferromagnetic exchange interaction. We also present a superconducting qualification with which magnetism is unbeneficial to superconductivity.

Tian De Cao; Tie Bang Wang

2009-10-04

318

Microwave spectra of methyl chloride, methyl bromide, and methyl iodide in the nu6 = 1 excited vibrational state  

Microsoft Academic Search

The rotational spectra of CH335Cl, CH337Cl, CH379Br, CH381Br, and CH3I in the nu6 state were observed between 8 and 240 GHz. For CH3Br and CH3I, the present data were combined with the pure quadrupole resonances of Oka et al. to determine the molecular constants. Our measurements have enabled us to notably improve the molecular constants for the nu6 excited states.

A. Dubrulle; J. Burie; D. Boucher; F. Herlemont; J. Demaison

1981-01-01

319

Triplet exciton dynamics in rubrene single crystals  

NASA Astrophysics Data System (ADS)

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

Ryasnyanskiy, Aleksandr; Biaggio, Ivan

2011-11-01

320

A triplet mechanism for the formation of thymine-thymine (6-4) dimers in UV-irradiated DNA.  

PubMed

The reaction pathway for the photochemical formation of thymine-thymine (6-4) dimers in DNA is explored using hybrid density functional theory techniques in gas and in bulk solvent. It is concluded that the photo-induced cycloaddition displays favorable energy barriers in the triplet excited state. The stepwise cycloaddition in the triplet excited state involves the initial formation of a diradical followed by ring closure via singlet-triplet interaction. The key geometric features and electron spin densities are also discussed. The difference in barriers of H3' transfer for the lowest-lying triplet and singlet states shows that the singlet oxetane intermediate could catch the second photon to accelerate the rate of proton transfer, leading to formation of the Dewar structure. The present results provide a rationale for the formation of thymine-thymine (6-4) dimers in the triplet excited states. PMID:21455506

Yang, Zhao bo; Zhang, Ru bo; Eriksson, Leif A

2011-05-21

321

Generating Spectra from Ground State Wave Functions: Unraveling Anharmonic Effects in the OH^-\\cdot H_2O and H_5O_2^+ Vibrational Predissociation Spectra  

NASA Astrophysics Data System (ADS)

An approach is described for calculating anharmonicspectra for polyatomic molecules using only the ground state probability amplitude. The underlying theory is based on properties of harmonic oscillator wave functions and is tested for Morse Oscillators with a range of anharmonicities. More extensive tests are performed with H_3O_2^-, using the potential and dipole surfaces of Bowman and co-workers. The resulting energies are compared to earlier studies that employed the same potential surface and the agreement is shown to be very good. The vibrational spectra are calculated for H_3O_2^-, D_3O_2^- and H_5O_2^+ and its deuterated analogues. When possible, comparisons are made experimental spectra from 600 - 4500 cm^{-1}. The frequencies and intensities of the fundamentals are found to be in excellent agreement and many combination bands involving one quantum of excitation in each of two modes are also well-reproduced. A. B. McCoy, E. G. Diken and Mark A. Johnson, J. Phys. Chem. A in press J. Am. Chem. Soc. 2004, 126, 5042

McCoy, Anne B.

2009-06-01

322

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

Microsoft Academic Search

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

K. Král

1972-01-01

323

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

SciTech Connect

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{sup ?1} cm{sup ?1}) in this spectral region is due to the T{sub 1}(n, ?*) ? S{sub 0} electronic transition. The 0{sub 0}{sup 0} origin band was assigned to the feature observed at 24?558.8?±?0.3 cm{sup ?1}. We have assigned 46 vibronic transitions in a region extending from ?200 to +350 cm{sup ?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-d{sub 3}. From the assignments, we determined fundamental frequencies for several vibrational modes in the T{sub 1}(n, ?{sup *}) excited state of 2CHO, including the lowest ring-twisting (99.6 cm{sup ?1}) and ring-bending (262.2 cm{sup ?1}) modes. These values compare to fundamentals of 122.2 cm{sup ?1} and 251.9 cm{sup ?1}, respectively, determined previously for the isoconfigurational S{sub 1}(n, ?{sup *}) excited state of 2CHO and 99 cm{sup ?1} and 248 cm{sup ?1}, respectively, for the S{sub 0} 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 (?{sub 39}) contains a significant contribution from O=C–C=C torsion, whereas the ring-bending mode (?{sub 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 T{sub 1}(n, ?{sup *}) 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 T{sub 1}(n, ?{sup *}) vs. S{sub 1}(n, ?{sup *}) ring frequencies.

McAnally, Michael O.; Zabronsky, Katherine L.; Stupca, Daniel J.; Phillipson, Kaitlyn; Pillsbury, Nathan R.; Drucker, Stephen, E-mail: druckers@uwec.edu [Department of Chemistry, University of Wisconsin-Eau Claire, Eau Claire, Wisconsin 54702-4004 (United States)] [Department of Chemistry, University of Wisconsin-Eau Claire, Eau Claire, Wisconsin 54702-4004 (United States)

2013-12-07

324

Generation of long-lived methylviologen radical cation in the triplet-state mediated electron transfer in a ?-cyclodextrin based supramolecular triad  

NASA Astrophysics Data System (ADS)

A novel tris(bipyridyl)ruthenium-pyrene-methylviologen supramolecular triad was assembled through inclusion complexation of adamantane-linked Ru(II)-Py dyad in MV2+-linked ?-cyclodextrin. Excitation of the Ru(II) chromophore populated its 3MLCT which upon energy transfer gave 3Py, which donates an electron to MV2+ to give Ru(II)-Pyrad +-MVrad +. A second electron transfer then occurs from Ru(II) to Pyrad + to give the supramolecular Ru(III)-Py-MVrad + charge separated state. Laser flash photolysis experiments confirmed formation of MVrad + which exhibited 100 ?s lifetime. Steady state irradiation of the self-assembled system in the presence of sacrificial donor also led to formation of long-lived MVrad +.

Rakhi, Arikkottira M.; Gopidas, Karical R.

2015-01-01

325

Acylgermanes: Excited state processes and reactivity  

NASA Astrophysics Data System (ADS)

The excited state processes of an acetyltriphenylgermane as well as the generation and the reactivity of the germyl radical are studied by laser flash photolysis, ESR spin trapping experiments and MO calculations. The transient spectra, the dissociation quantum yield, the singlet excited state S 1 lifetime, the S 1 quenching by an iodonium salt, the triplet state energy level ET, the Ge-C bond dissociation energy BDE, the interaction of the germyl radical with oxygen, double bonds and an iodonium salt, and the ESR spectra are determined. A triplet cleavage process is clearly evidenced; a singlet cleavage should likely contribute. The overall reactivity is discussed and compared to that of parent compounds. The acetyltriphenylgermane behaves as a high performance photoinitiator in the free radical polymerization and free radical promoted cationic polymerizations.

Lalevée, J.; Allonas, X.; Fouassier, J. P.

2009-02-01

326

A new algorithm for predicting triplet-triplet energy-transfer activated complex coordinate in terms of accurate potential-energy surfaces.  

PubMed

The new algorithm presented here allows, for the first time, the determination of the optimal geometrical distortions that an acceptor molecule in the triplet-triplet energy-transfer process undergoes, as well as the dependence of the activation energy of the process on the triplet energy difference of donor and acceptor molecules. This algorithm makes use of the complete potential-energy surfaces (singlet and triplet states), and contrasts with the first-order approximation already published [L. M. Frutos, O. Castano, J. L. Andres, M. Merchan, and A. U. Acuna, J. Chem. Phys. 120, 1208 (2004)] in which an expansion of the potential-energy surfaces was used. This algorithm is gradient based and finds the best trajectory for the acceptor molecule, starting from S(0) ground-state equilibrium geometry, to achieve the maximum variation of the singlet-triplet energy gap with the minimum energy of activation on S(0). Therefore, the algorithm allows the determination of a "reaction path" for the triplet-triplet energy-transfer processes. Also, the algorithm could also serve eventually to find minimum-energy crossing (singlet-triplet) points on the potential-energy surface, which can play an important role in the intersystem crossing process for the acceptor molecules to recover their initial capacity as acceptors. Also addressed is the misleading use of minimum-energy paths in T(1) to describe the energy-transfer process by comparing these results with those obtained using the new algorithm. The implementation of the algorithm is illustrated with different potential-energy surface models and it is discussed in the frame of nonvertical behavior. PMID:16178590

Frutos, Luis Manuel; Castaño, Obis

2005-09-01

327

A new algorithm for predicting triplet-triplet energy-transfer activated complex coordinate in terms of accurate potential-energy surfaces  

NASA Astrophysics Data System (ADS)

The new algorithm presented here allows, for the first time, the determination of the optimal geometrical distortions that an acceptor molecule in the triplet-triplet energy-transfer process undergoes, as well as the dependence of the activation energy of the process on the triplet energy difference of donor and acceptor molecules. This algorithm makes use of the complete potential-energy surfaces (singlet and triplet states), and contrasts with the first-order approximation already published [L. M. Frutos, O. Castaño, J. L. Andrés, M. Merchán, and A. U. Acuña, J. Chem. Phys. 120, 1208 (2004)] in which an expansion of the potential-energy surfaces was used. This algorithm is gradient based and finds the best trajectory for the acceptor molecule, starting from S0 ground-state equilibrium geometry, to achieve the maximum variation of the singlet-triplet energy gap with the minimum energy of activation on S0. Therefore, the algorithm allows the determination of a "reaction path" for the triplet-triplet energy-transfer processes. Also, the algorithm could also serve eventually to find minimum-energy crossing (singlet-triplet) points on the potential-energy surface, which can play an important role in the intersystem crossing process for the acceptor molecules to recover their initial capacity as acceptors. Also addressed is the misleading use of minimum-energy paths in T1 to describe the energy-transfer process by comparing these results with those obtained using the new algorithm. The implementation of the algorithm is illustrated with different potential-energy surface models and it is discussed in the frame of nonvertical behavior.

Frutos, Luis Manuel; Castaño, Obis

2005-09-01

328

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

Microsoft Academic Search

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

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

2010-01-01

329

Abundances, charge states, and energy spectra of helium and heavy ions during solar particle events  

NASA Technical Reports Server (NTRS)

Carbon and oxygen energy spectra observed during several solar events indicate a systematic deviation of these spectra from a simple power law: the spectra bend down below about 100 keV/nuc and the amount of this bending is highly correlated with the size of the flare, as measured by the 'event averaged' flux of 130-220 keV protons. The energy spectra of helium computed for the same time periods do not show a similar feature. A large variability of the alpha/CNO ratio is found from event to event (from 2 to about 20 at 40 keV/nuc), and in all cases examined the carbon and oxygen nuclei are nearly fully stripped. These results are interpreted as evidence for storage of energetic ions in hot coronal regions, followed by strong adiabatic deceleration.

Gloeckler, G.; Sciambi, R.; Fan, C. Y.; Hovestadt, D.

1975-01-01

330

[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

331

Study of the interaction between triplet riboflavin and the alpha-, betaH- and betaL-crystallins of the eye lens.  

PubMed

Time-resolved photolysis studies of riboflavin (RF) were carried out in the presence and absence of alpha-, betaH- and betaL-crystallins of bovine eye lens. The transient absorption spectra, recorded 5 micros after the laser pulse, reveal the presence of the absorption band (625-675 nm) of the RF neutral triplet state (tau = 42 micros) accompanied by the appearance of a long-lived absorption (tau = 320 micros) in the 500-600 nm region due to the formation of the semireduced RF radical. The RF excited state is quenched by the crystallin proteins through a mechanism that involves electron transfer from the proteins to the flavin, as shown by the decrease of the triplet RF band with the concomitant increase of the band of its semireduced form. Tryptophan loss on RF-sensitized photooxidation of the crystallins when irradiated with monochromatic visible light (450 nm) in a 5% oxygen atmosphere was studied. A direct correlation was found between the triplet RF quenching rate constants by the different crystallin fractions and the decomposition rate constants for the exposed and partially buried tryptophans in the proteins. The RF-sensitized photooxidation of the crystallins is accompanied by the decrease of the low molecular weight constituents giving rise to its multimeric forms. A direct correlation was observed between the initial rate of decrease of the low molecular weight bands corresponding to the irradiated alpha-, betaH- and betaL-crystallins and the quenching constant values of triplet RF by the different crystallins. The correlations found in this study confirm the importance of the Type-I photosensitizing mechanism of the crystallins, when RF acts as a sensitizer at low oxygen concentration, as can occur in the eye lens. PMID:12812297

Viteri, Gabriela; Edwards, Ana Maria; De la Fuente, Julio; Silva, Eduardo

2003-05-01

332

Polaron pair mediated triplet generation in polymer/fullerene blends  

NASA Astrophysics Data System (ADS)

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

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

2015-03-01

333

Polaron pair mediated triplet generation in polymer/fullerene blends.  

PubMed

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

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

2015-01-01

334

Polaron pair mediated triplet generation in polymer/fullerene blends  

PubMed Central

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

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

2015-01-01

335

Exchange Interaction Makes Superconductivity in 3D Dirac Semi-metal Triplet  

NASA Astrophysics Data System (ADS)

Conventional electron-phonon coupling induces either odd (triplet) or even (singlet) pairing states in a time reversal and inversion invariant Dirac semi-metal. In a certain range of the chemical potential and parameters characterizing the pairing attraction (effective electron-electron coupling constant and the Debye energy ) the energy of the singlet although always lower, prevails by a very slim margin over the triplet. This means that interactions that are small but discriminate between the spin singlet and the spin triplet determine the nature of the superconducting order there. It is shown that in materials close enough to the Dirac point ( ) a moderate exchange constant (below Stoner instability to ferromagnetism) stabilizes the odd pairing superconducting state. The 3D quantum critical point at of transition to the triplet superconductivity governs the physics of the superconductor.

Rosenstein, B.; Shapiro, B. Ya.; Li, Dingping; Shapiro, I.

2015-04-01

336

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

337

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

SciTech Connect

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

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

2014-01-21

338

Low-energy effective theory, unitarity, and nondecoupling behavior in a model with heavy Higgs-triplet fields  

SciTech Connect

We discuss the properties of a model incorporating both a scalar electroweak Higgs doublet and an electroweak Higgs triplet. We construct the low-energy effective theory for the light Higgs doublet in the limit of small (but nonzero) deviations in the {rho} parameter from one, a limit in which the triplet states become heavy. For {delta}{rho}>0, perturbative unitarity of WW scattering breaks down at a scale inversely proportional to the renormalized vacuum expectation value of the triplet field (or, equivalently, inversely proportional to the square root of {delta}{rho}). This result imposes an upper limit on the mass scale of the heavy triplet bosons in a perturbative theory; we show that this upper bound is consistent with dimensional analysis in the low-energy effective theory. Recent articles have shown that the triplet bosons do not decouple, in the sense that deviations in the {rho} parameter from one do not necessarily vanish at one-loop in the limit of large triplet mass. We clarify that, despite the nondecoupling behavior of the Higgs triplet, this model does not violate the decoupling theorem since it incorporates a large dimensionful coupling. Nonetheless, we show that if the triplet-Higgs boson masses are of order the grand unified theory scale, perturbative consistency of the theory requires the (properly renormalized) Higgs-triplet vacuum expectation value to be so small as to be irrelevant for electroweak phenomenology.

Chivukula, R. Sekhar; Christensen, Neil D.; Simmons, Elizabeth H. [Department of Physics and Astronomy, Michigan State University, East Lansing, Michigan 48824 (United States)

2008-02-01

339

Paramagnetic effects on the NMR spectra of "diamagnetic" ruthenium(bis-phosphine)(bis-semiquinone) complexes.  

PubMed

Ligand substitution on cis-Ru(PPh(3))(2)(1,2-O(2)C(6)H(4))(2) gives cis-RuL(1)L(2)(1,2-O(2)C(6)H(4))(2) (L(1) = PPh(3), L(2) = P(OPh)(3), PBu(3); L(1) = L(2) = PBu(3), P(OMe)(3)). Syntheses of cis-Ru(PPh(3))(2)(3,4-O(2)C(6)H(2)(5-OH)CO(2)Me)(2) and cis-Ru(PPh(3))(2)(AGSQ)(2) (AGSQ = the semiquinone derived from 1,2,3-trihydroxyanthracene-9,10-dione) are also reported. The upfield chemical shifts and line broadening of the semiquinone 4,5-proton resonances in the NMR spectra indicate that these complexes, while having no detectable magnetic moments, have a weak, temperature-, ligand- and solvent-variable residual paramagnetism, not previously recognized in this series. Density functional theory (DFT) calculations predict a low-lying triplet state, about 14 kJ/mol (0.15 eV) above the singlet ground state. The paramagnetic effects on the NMR spectra are attributed to singlet-triplet equilibria. Temperature dependence of the proton resonances of the semiquinone rings of cis-Ru(PPh(3))(2)(1,2-O(2)C(6)H(4))(2) was used to calculate the singlet-triplet free energy difference as 17.5-18.0 kJ/mol in toluene. PMID:19400557

Le Guennic, Boris; Floyd, Tavon; Galan, Brandon R; Autschbach, Jochen; Keister, Jerome B

2009-06-15

340

A systematic study of mirror and triplet energy differences  

NASA Astrophysics Data System (ADS)

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

Lenzi, S. M.; Lau, R.

2015-02-01

341

An LDA+U study of the photoemission spectra of ground state phase of americium and curium  

NASA Astrophysics Data System (ADS)

We have investigated the photoemission spectra and other ground state properties such as equilibrium volume and bulk modulus of dhcp americium and the density of states and magnetic properties of dhcp curium using LDA+U method. Our calculations show that spin polarized americium is energetically favorable but spin degenerate configuration produces experimental quantities much better than that calculated using spin polarized configuration. The DOS calculated using LDA+U with both non-magnetic and spin polarized configurations is compared and the non-magnetic DOS is shown to be in good agreement with experimental photoemission spectra when U=4.5 eV. In spin polarized case, U is observed to increase the splitting between occupied and unoccupied bands by enhancing Stoner parameter. The results are shown to be in good agreement with that calculated using dynamical mean field theory for these two heavy actinides. For curium, exchange interaction appears to play the dominant role in its magnetic stability.

Islam, Md; Ray, Asok

2009-03-01

342

The solid state 13C-NMR and 19F-NMR spectra of some graphite fluorides  

Microsoft Academic Search

The solid state 13C nuclear magnetic resonance spectra of fluorinated graphites show two resonances, one of which is assigned to aromatic carbon and the other to aliphatic carbon. The resonances are very broad with the high-field resonance centered at about 35 ppm below tetramethylsilane (TMS) and a low-field resonance centered at about 160 ppm below tetramethylsilane. The high-field resonance is

Charles A. Wilkie; Gong-Yu Lin; Daniel T. Haworth

1979-01-01

343

Infrared and Raman spectra and theoretical calculations for benzocyclobutane in its electronic ground state.  

PubMed

The infrared and Raman spectra of vapor-phase and liquid-phase benzocyclobutane (BCB) have been recorded and assigned. The structure of the molecule was calculated using the MP2/cc-pVTZ basis set and the vibrational frequencies and spectral intensities were calculated using the B3LYP/cc-pVTZ level of theory. The agreement between experimental and calculated spectra is excellent. In order to allow comparisons with related molecules, ab initio and DFT calculations were also carried out for indan (IND), tetralin (TET), 1,4-benzodioxan (14BZD), 1,3-benzodioxan (13BZD) and 1,4-dihydronaphthalene (14DHN). The ring-puckering, ring-twisting, and ring-flapping vibrations were of particular interest as these reflect the rigidity of the bicyclic ring system. The infrared spectra of BCB show very nice examples of vapor-phase band types and combination bands. PMID:24507997

Ocola, Esther J; Shin, Hee Won; Laane, Jaan

2015-02-01

344

Infrared and Raman spectra and theoretical calculations for benzocyclobutane in its electronic ground state  

NASA Astrophysics Data System (ADS)

The infrared and Raman spectra of vapor-phase and liquid-phase benzocyclobutane (BCB) have been recorded and assigned. The structure of the molecule was calculated using the MP2/cc-pVTZ basis set and the vibrational frequencies and spectral intensities were calculated using the B3LYP/cc-pVTZ level of theory. The agreement between experimental and calculated spectra is excellent. In order to allow comparisons with related molecules, ab initio and DFT calculations were also carried out for indan (IND), tetralin (TET), 1,4-benzodioxan (14BZD), 1,3-benzodioxan (13BZD) and 1,4-dihydronaphthalene (14DHN). The ring-puckering, ring-twisting, and ring-flapping vibrations were of particular interest as these reflect the rigidity of the bicyclic ring system. The infrared spectra of BCB show very nice examples of vapor-phase band types and combination bands.

Ocola, Esther J.; Shin, Hee Won; Laane, Jaan

2015-02-01

345

Transition structures and barriers for the 1,2-H shifts in diphosphene (HP?PH), phosphazene (HP?NH), and diimide (HN?NH). A theoretical study of the singlet and triplet states  

NASA Astrophysics Data System (ADS)

The lowest singlet and triplet potential energy surfaces for reactions HP?PH ? H 2PP, HP?NH? H 2PN, HP?NH ? H 2NP, and HN?NH?H 2NN are investigated and compared by means of ab initio calculations. The protonation of the title compounds is also investigated.

Ito, Keiji; Nagase, Shigeru

1986-05-01

346

A theoretical study of the absorption spectra of indole and its analogs: indene, benzimidazole, and 7-azaindole  

NASA Astrophysics Data System (ADS)

The complete active space (CAS) SCF method and multiconfigurational second-order perturbation theory (CASPT2) have been used to study the electronic spectra of indole, indene, benzimidazole, and 7-azaindole. Singlet and triplet excited states and transition properties in the absorption spectra, such as oscillator strengths and transition moment directions, have been computed and the experimental data interpreted in order to gain insight into the rich spectroscopy of these compounds, which are alternative candidates to indole as biochemical probes in the characterization of protein properties.

Borin, Antonio Carlos; Serrano-Andrés, Luis

2000-12-01

347

Equations-of-motion method for triplet excitation operators in graphene  

NASA Astrophysics Data System (ADS)

The particle-hole continuum in the Dirac sea of graphene has a unique window underneath, which in principle leaves room for bound state formation in the triplet particle-hole channel (Baskaran and Jafari 2002 Phys. Rev. Lett. 89 016402). In this work, we construct appropriate triplet particle-hole operators and, using a repulsive Hubbard-type effective interaction, we employ equations of motion to derive approximate eigenvalue equations for such triplet operators. While the secular equation for the spin density fluctuations gives rise to an equation which is second order in the strength of the short range interaction, the explicit construction of the triplet operators obtained here shows that, in terms of these operators, the second-order equation can be factorized to two first-order equations, one of which gives rise to a solution below the particle-hole continuum of Dirac electrons in undoped graphene.

Jafari, S. A.; Baskaran, G.

2012-03-01

348

Quantum gates for the singlet-triplet T+ qubit  

NASA Astrophysics Data System (ADS)

We theoretically show that hyperfine interactions can be harnessed for quantum gate operations in GaAs semiconductor quantum dots [1]. In the presence of an external magnetic field B, which splits the triplet states, the hyperfine interaction results in an avoided crossing between the spin singlet S and spin triplet T+, which form the basis of a new type of spin qubit. Coherent quantum control for this qubit is achieved through Landau-Zener-St"uckelberg transitions at the S-T+ avoided crossing [2]. A set of suitable transitions allows to build any single qubit gates on timescales shorter than the decoherence time T2^* ˜16ns [1]. We also show how to build a conditional two-qubit gate by capacitively coupling two S-T+ qubits. [4pt] [1] H. Ribeiro, J. R. Petta, and G. Burkard, Phys. Rev. B 82, 115445 (2010). [2] H. Ribeiro and G. Burkard, Phys. Rev. Lett. 102, 216802 (2009).

Ribeiro, Hugo; Petta, J. R.; Burkard, Guido

2011-03-01

349

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

350

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

NASA Astrophysics Data System (ADS)

We demonstrate highly efficient white and nonwhite hybrid organic light-emitting diodes (OLEDs) in which singlet and triplet excited states, generated in the recombination zone, are utilized by fluorescence and phosphorescence, respectively. The excited states are formed at a blue fluorescent light-emitting layer (LEL), and the triplets diffuse through a spacer layer to one or more phosphorescent LEL(s). A key feature enabling the triplet diffusion in such OLEDs is the use of a blue fluorescent emitter with triplet energy above, or not much below, that of the fluorescent host. Additional material properties required for triplet harvesting are outlined. At 1000 cd/m2 a blue and yellow harvesting OLED shows 13.6% external quantum efficiency, 3.8 V, 30.1 lm/W, and color characteristics suitable for display application. High-efficiency harvesting R+G+B white, and B+G and B+R nonwhite OLEDs are also demonstrated. The triplet-harvesting mechanism was verified in all devices by physical methods including spectral analysis, time-resolved electroluminescence, magnetic field effect, and electron paramagnetic resonance.

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

2010-01-01

351

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

SciTech Connect

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.

Bai, Shuming; Xie, Weiwei; Zhu, Lili; Shi, Qiang, E-mail: qshi@iccas.ac.cn [Beijing National Laboratory for Molecular Sciences, State Key Laboratory for Structural Chemistry of Unstable and Stable Species, Institute of Chemistry, Chinese Academy of Sciences, Zhongguancun, Beijing 100190 (China)] [Beijing National Laboratory for Molecular Sciences, State Key Laboratory for Structural Chemistry of Unstable and Stable Species, Institute of Chemistry, Chinese Academy of Sciences, Zhongguancun, Beijing 100190 (China)

2014-02-28

352

Photochemical studies of alkylammonium molybdates. Part 12. O?Mo charge-transfer triplet-states-initiated self-assembly to {Mo154} ring- and tube-molybdenum-blues  

NASA Astrophysics Data System (ADS)

The chemically induced dynamic electron-spin-polarization technique is employed in order to investigate the primary steps of the photoredox reaction between polyoxomolybdates and alkylammonium cations as both proton and electron-donors in solutions. An observation of emissive electron-spin-polarization signals of alkylamino radical cations for the photoredox reaction between polyoxomolybdates and alkylammonium cations in solutions reveals that the O?Mo ligand-to-metal charge-transfer triplet states are involved in the transfers of both proton and electron from alkylammonium cation to polyoxomolybdate anions. Prolonged photolysis of aqueous solutions containing [Mo36O112(H2O)16]8-, [iPrNH3]+, and LaCl3 at pH 1.0 leads to formation of two kinds of {Mo154} molybdenum-blues, [Mo28VMo126VIO462H28(H2O)70]·156.5H2O (1) and [iPrNH3]8 [Mo28VMo126VIO458H12(H2O)66]·127H2O (2), which were X-ray crystallographically characterized. The former exhibits the intact car-tire-shaped {Mo154} ring structure (with thickness of about 1.1 nm and with outer- and inner-rings of approximately 3.5- and 2.3-nm diameters, respectively) derived formally from the dehydrated cyclic heptamerization of four-electron reduced building blocks of {Mo22} (?[Mo4VMo18VIO70H12(H2O)10]) with overall symmetry of D7d. The anion for the latter, [Mo28VMo126VIO458H12(H2O)66]8- (2a), exhibits a nanotube structure of {Mo154} rings, each inner ring of which contains a bis(?-oxo)-linkaged [MoO2(?-O)(?-H2O)MoO2]2+ unit replacing one of seven [Mo(H2O)O2(?-O)Mo(H2O)O2]2+linker units. The neighboring {Mo154} rings are connected by six Mo-O-Mo bridge between inner-rings consisting of 7 head- and 14 linkers-MoO6 octahedra for each.

Yamase, T.; Prokop, P.; Arai, Y.

2003-08-01

353

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

354

Dirac Triplet Extension of the MSSM  

E-print Network

In this paper we explore extensions of the Minimal Supersymmetric Standard Model involving two $SU(2)_L$ triplet chiral superfields that share a superpotential Dirac mass yet only one of which couples to the Higgs fields. This choice is motivated by recent work using two singlet superfields with the same superpotential requirements. We find that, as in the singlet case, the Higgs mass in the triplet extension can easily be raised to $125\\,\\text{GeV}$ without introducing large fine-tuning. For triplets that carry hypercharge, the regions of least fine tuning are characterized by small contributions to the $\\mathcal T$ parameter, and light stop squarks, $m_{\\tilde t_1} \\sim 300-450\\,\\text{GeV}$; the latter is a result of the $\\tan\\beta$ dependence of the triplet contribution to the Higgs mass. Despite such light stop masses, these models are viable provided the stop-electroweakino spectrum is sufficiently compressed.

Alvarado, C; Martin, A; Ostdiek, B

2015-01-01

355

Dark matter in inert triplet models  

SciTech Connect

We study the inert triplet models, in which the standard model is extended to have a new SU(2){sub L} triplet scalar (Y=0 or 2) with an Z{sub 2} symmetry. We show that the neutral component of the triplet can be a good dark matter candidate. In particular, for the hypercharge Y=0 triplet model, the WMAP data favors the region where the dark matter mass is around 5.5 TeV, which is also consistent with the direct detection experiments. In contrast, for the Y=2 model, although dark matter with its mass around 2.8 TeV is allowed by WMAP, it is excluded by the direct detection experiments because the spin-independent cross section is enhanced by the Z-mediated tree-level scattering process.

Araki, Takeshi [Institute of High Energy Physics, Chinese Academy of Sciences, Beijing 100049 (China); Geng, C. Q. [Department of Physics, National Tsing Hua University, Hsinchu, Taiwan 300 (China); National Center for Theoretical Sciences, Hsinchu, Taiwan 300 (China); Nagao, Keiko I. [Department of Physics, National Tsing Hua University, Hsinchu, Taiwan 300 (China)

2011-04-01

356

About electrons in Triplet Production  

E-print Network

It is usually assumed that the difficulties arising from the indistinguishability of the two electrons in the triplet produced by photons of high energy in the field of an electron may be avoided simply by ruling out the contributions of all the Feynmann diagrams as well as the Borsellino. In this way, the question of indistinguishability becomes meaningless, there is a clear distinction between the recoil electron and the pair electron; and it is well-known that the entire mechanism works well if the photon energy is high enough. In this work we have analyzed the eight Feynmann diagrams and we have shown that for energies lower to $\\sim 1000mc^2$, the assumption just described is not a good approximation. We propose a different way to work: we classify the electrons into the less energetic and the most energetic ones without taking into account their origin, and to define, only to keep the experimental treatment that the less energetic ones will be called the recoil electrons, while the most energetic ones will be called the pair or created electron. Under these conditions (lower or higher energy value), we have calculated the contribution of the different diagrams to the distribution, and how these distributions are modified by introducing a threshold for the momentum detection for electrons.

M. L. Iparraguirre; G. O. Depaola

2014-06-11

357

Vibrational overtone spectra of N-H stretches and intramolecular dynamics on the ground and electronically excited states of methylamine  

SciTech Connect

The vibrational pattern and energy flow in the N-H stretch manifolds and the dissociation dynamics of methylamine (CH{sub 3}NH{sub 2}) were investigated via vibrationally mediated photodissociation. Action spectra and Doppler profiles, reflecting the yield of the ensuing H photofragments, versus near infrared/visible vibrational excitation and UV excitation, respectively, were measured. The jet-cooled action spectra and the simultaneously measured room temperature photoacoustic spectra of the first to third N-H stretching overtones exhibit broad features, somewhat narrower in the former, consisting of barely recognized multiple bands. Two phases of fitting of the spectroscopic data were performed. In the first phase, the raw data were analyzed to obtain band positions, types, intensities, and transition linewidths. In the second, the information derived from the first phase was then used as data in a fit to joint local mode/normal mode (LM/NM) and NM Hamiltonian parameters. The derived parameters predicted well band positions and allowed band assignment. The LM/NM Hamiltonian and the extracted Lorentzian linewidths enabled the determination of the initial pathways for energy redistribution and the overall temporal behavior of the N-H stretch and doorway states, as a result of Fermi couplings and interactions with bath states. The results indicate a nonstatistical energy flow in the V=2 manifold region, pointing to the dependence of the coupling on specific low order resonances rather than on the total density of bath states. The Doppler profiles suggest lower average translational energies for the released H photofragments, in particular, for V=3 and 4 as compared to V=1 and 2, implying a change in the mechanism for bond cleavage.

Marom, Ran; Zecharia, Uzi; Rosenwaks, Salman; Bar, Ilana [Department of Physics, Ben-Gurion University of the Negev, Beer-Sheva 84105 (Israel)

2008-04-21

358

Electronic spectra of GdF reanalyzed by decomposing state functions according to f-shell angular momentum  

NASA Astrophysics Data System (ADS)

The electronic structure of the GdF molecule was studied by means of four-component relativistic configuration interaction (CI) calculations [S. Yamamoto, H. Tatewaki, and T. Saue, J. Chem. Phys. 129, 244505 (2008), 10.1063/1.3039794]. To analyze the electronic spectra more accurately, the CI wave function is decomposed according to the angular momentum (?f) generated from the (4f)7 electrons. The weight of a specified ?f is referred to as the "f-shell Omega component weight." This ?f plays a crucial role in classifying the strong electronic transitions from the upper states (0.7 eV-3.0 eV) to the lower states (˜0.55 eV). For these transitions, the upper and lower states have almost identical ?f weights. This appears to be a necessary condition for a transition to be strong. The same condition is expected to hold for other lanthanide linear molecules. A point charge model is also studied, acting as a simplified model of GdF; it successfully reproduces the spectra of GdF, justifying studies based on ligand field theory.

Yamamoto, Shigeyoshi; Tatewaki, Hiroshi

2011-04-01

359

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

NASA Astrophysics Data System (ADS)

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

Chung, Gyusung; Lee, Duckhwan

2001-12-01

360

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

361

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

362

Spectra of the lowest excited singlet states of rhodamine 6G and rhodamine B  

Microsoft Academic Search

Excited states of laser dyes were generated in solution by an intense 6 ns laser pump pulse tuned to the absorption maximum of the longest wavelength, ground state absorption band. They were interrogated by a shorter, simultaneous, monochromatic pulse of smaller diameter, concentric and collinear with the pump, having a crossed polarization. Plots of transmission curves against intensity for the

P. Hammond

1979-01-01

363

Pregnancy outcome of early multifetal pregnancy reduction: triplets to twins versus triplets to singletons.  

PubMed

Multifetal pregnancy reduction (MPR) of triplets to twins results in improved pregnancy outcomes compared with triplet gestations managed expectantly. Perinatal outcomes of early transvaginal MPR from triplets to twins were compared with reduction from triplets to singletons. Seventy-four trichorionic triplet pregnancies that underwent early transvaginal MPR at 6-8 weeks gestation were included. Cases were divided into two groups according to the initial procedure: reduction to twin (n = 55) or to singleton (n = 19) gestations. Infants from triplet pregnancies reduced to twins were delivered earlier (36.6 versus 37.9 weeks; P = 0.04) and had lower mean birth weights (2364?g versus 2748?g; P = 0.02) compared with those from triplets reduced to singleton gestations. The rates of pregnancy loss before 24 weeks (3.6% versus 5.3%), as well as of preterm delivery before 32 and 34 weeks of gestation (0% versus 5.3% and 7.3% versus 5.3%, respectively) were similar between the twin and singleton pregnancies. No significant difference was found in the prevalence of gestational diabetes (15.1% versus 5.6%) or gestational hypertension (24.5% versus 16.7%) between the groups. Selective reduction of triplet pregnancies to singleton rather than twin gestations is associated with improved outcomes. PMID:25444505

Haas, Jigal; Hourvitz, Ariel; Dor, Jehoshua; Yinon, Yoav; Elizur, Shai; Mazaki-Tovi, Shali; Barzilay, Eran; Shulman, Adrian

2014-12-01

364

Scalar triplet flavored leptogenesis: a systematic approach  

E-print Network

Type-II seesaw is a simple scenario in which Majorana neutrino masses are generated by the exchange of a heavy scalar electroweak triplet. When endowed with additional heavy fields, such as right-handed neutrinos or extra triplets, it also provides a compelling framework for baryogenesis via leptogenesis. We derive in this context the full network of Boltzmann equations for studying leptogenesis in the flavored regime. To this end we determine the relations which hold among the chemical potentials of the various particle species in the thermal bath. This takes into account the SM Yukawa interactions of both leptons and quarks as well as sphaleron processes which, depending on the temperature, may be classified as faster or slower than the Hubble rate. We find that when leptogenesis is enabled by the presence of an extra triplet, lepton flavor effects allow the production of the $B-L$ asymmetry through lepton number conserving CP asymmetries. This scenario becomes dominant as soon as the triplets couple more to leptons than to SM scalar doublets. In this case, the way the $B-L$ asymmetry is created through flavor effects is novel: instead of invoking the effect of $L$-violating inverse decays faster than the Hubble rate, it involves the effect of $L$-violating inverse decays slower than the Hubble rate. We also analyze the more general situation where lepton number violating CP asymmetries are present and actively participate in the generation of the $B-L$ asymmetry, pointing out that as long as $L$-violating triplet decays are still in thermal equilibrium when the triplet gauge scattering processes decouple, flavor effects can be striking, allowing to avoid all washout suppression effects from seesaw interactions. In this case the amount of $B-L$ asymmetry produced is limited only by a universal gauge suppression effect, which nevertheless goes away for large triplet decay rates.

D. Aristizabal Sierra; Mikael Dhen; Thomas Hambye

2014-07-30

365

Scalar triplet flavored leptogenesis: a systematic approach  

NASA Astrophysics Data System (ADS)

Type-II seesaw is a simple scenario in which Majorana neutrino masses are generated by the exchange of a heavy scalar electroweak triplet. When endowed with additional heavy fields, such as right-handed neutrinos or extra triplets, it also provides a compelling framework for baryogenesis via leptogenesis. We derive in this context the full network of Boltzmann equations for studying leptogenesis in the flavored regime. To this end we determine the relations which hold among the chemical potentials of the various particle species in the thermal bath. This takes into account the standard model Yukawa interactions of both leptons and quarks as well as sphaleron processes which, depending on the temperature, may be classified as faster or slower than the Universe Hubble expansion. We find that when leptogenesis is enabled by the presence of an extra triplet, lepton flavor effects allow the production of the B-L asymmetry through lepton number conserving CP asymmetries. This scenario becomes dominant as soon as the triplets couple more to leptons than to standard model scalar doublets. In this case, the way the B-L asymmetry is created through flavor effects is novel: instead of invoking the effect of L-violating inverse decays faster than the Hubble rate, it involves the effect of L-violating decays slower than the Hubble rate. We also analyze the more general situation where lepton number violating CP asymmetries are present and actively participate in the generation of the B-L asymmetry, pointing out that as long as L-violating triplet decays are still in thermal equilibrium when the triplet gauge scattering processes decouple, flavor effects can be striking, allowing to avoid all washout suppression effects from seesaw interactions. In this case the amount of B-L asymmetry produced is limited only by a universal gauge suppression effect, which nevertheless goes away for large triplet decay rates.

Aristizabal Sierra, D.; Dhen, Mikaël; Hambye, Thomas

2014-08-01

366

Buried Well-Screened State in Photoemission Spectra of La1-xSrxMnO3  

NASA Astrophysics Data System (ADS)

We performed x-ray photoemission spectroscopy (XPS) and hard x-ray photoemission spectroscopy (HX-PES) study on a magnetoresistive manganite La1-xSrxMnO3. We observed the Mn3+ well-screened final state in the Mn 2p3/2 XPS spectra in a wide range of x, particularly for the x = 0.8 sample, although this spectral weight was considered to be observable only by HX-PES. An elaborate multiple-peak fitting of the Mn 2p3/2 spectra revealed that (1) the Mn3+ well-screened final state alone did not represent the metallic conductivity, (2) there was a Mn4+ well-screened peak "buried" in the location of the Mn3+ main peak, and (3) the sum of the both Mn3+ and Mn4+ well-screened spectral weights as a function of x qualitatively followed the room temperature electrical conductivity in the whole range of x.

Hishida, Tomoko; Ohbayashi, Kazusige; Kobata, Masaaki; Ikenaga, Eiji; Sugiyama, Takeharu; Kobayashi, Keisuke; Okawa, Mario; Saitoh, Tomohiko

367

Photoluminescence spectra of ZnS:X- (X = F and I) nanoparticles synthesized via a solid-state reaction  

NASA Astrophysics Data System (ADS)

ZnS:X- (X = F and I) nanoparticles have been prepared successfully via a solid-state method at low temperature, and the effects of doping with X- on the photoluminescence (PL) properties of ZnS nanoparticles have been investigated. X-ray powder diffraction (XRD), energy-dispersive X-ray spectrum (EDS), transmission electron microscope (TEM), ultraviolet-visible diffusion reflection spectra, and emission and excitation spectra were used to characterize the crystal structure, chemical compositions, diameter, surface states, and optical properties of ZnS:X- (X = F and I) nanoparticles. XRD studies showed the phase singularity of ZnS:X- particles having zinc-blende (cubic) structure with an average crystallite size 4.7-11.0 nm. The results indicated that the PL of doping halogen ZnS nanoparticles can be enhanced remarkably by controlling suitable halogen doping, and the most intense emission was obtained when X/Zn = 0.3 and 0.45 under 387 nm excitation corresponding to X = F and I, respectively. The emission intensity of ZnS:F- (F/Zn = 0.3) nanoparticles was higher than that of ZnS:I- (I/Zn = 0.45), and exhibited strong emission with an intensity about 9 times higher than the undoped nanoparticles. It was found that the PL of ZnS nanoparticles doped with various halogens was decreased with the increase of the halogen ion radius.

Chen, Zhong; Li, Xiao Xia; Du, Guoping; Yu, Quanmao

2014-04-01

368

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

369

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

370

The Ca II Triplet as an Abundance Indicator  

E-print Network

How can we accurately determine the metallicity of faint red giant stars in nearby galaxies? The equivalent widths of the broad absorption lines from Ca II at 8498, 8542, and 8662 Angstrom (the calcium triplet) have shown a smooth relationship to metallicity, [Fe/H], in Galactic globular clusters, i.e., old, metal-poor stars. The exact relationship depends on the [Fe/H] scale assumed. The sensitivity of the sum of the equivalent widths, sum{W_{Ca II}}, to [Fe/H] has been well studied for metal-poor stars, but theory and observations show that sum{W_{Ca II}} will become less sensitive to [Fe/H] for young or metal-rich stars, but this needs to be calibrated. Built into the present calibration of sum{W_{Ca II}} to [Fe/H] is also a dependence on the Galactic [Ca/Fe] to [Fe/H] relationship, which is a function of the Galaxy's star formation history and chemical evolution. Our goal is to remove uncertainties in the [Fe/H] scale used in previous calibrations and remove the dependence on galactic evolution. We are obtaining high dispersion spectra to self-consistently calibrate the calcium triplet to give [Ca/H] abundances, and extend the current calibration to near-solar metallicities and to ages as young as 2 Gyr.

T. Bosler; T. Smecker-Hane; A. McWilliam

2001-10-30

371

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

Microsoft Academic Search

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

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

2001-01-01

372

Composite spectra: XX. 45 Cancri. Two stars with very similar masses but quite different evolutionary states  

NASA Astrophysics Data System (ADS)

From accurate radial-velocity measurements covering 11 circuits of the orbit of the composite-spectrum binary 45 Cnc, together with high-resolution spectroscopy spanning nearly 3 circuits, we have (i) isolated cleanly the spectrum of the early-type secondary, (ii) classified the component spectra as G8 III and A3 III, (iii) derived the first double-lined orbit for the system and a mass ratio (M_1/M_2) of 1.035 ± 0.01, and (iv) extracted physical parameters for the component stars, deriving the masses and (log) luminosities of the G star and A star as 3.11 and 3.00 M?} R?, and 2.34 and 2.28 L?, respectively, with corresponding uncertainties of ±0.10 M? R? and ±0.09 L?. Since the mass ratio is close to unity, we argue that the more evolved component is unlikely to have been a red giant long enough to have made multiple ascents of the RGB, an argument that is supported somewhat by the rather high eccentricity of the orbit (e = 0.46) and the evolutionary time-scales of the two components, but chiefly by the presence of significant Li I in the spectrum of the cool giant.

Griffin, R. E. M.; Griffin, R. F.

2015-02-01

373

1H NMR z-spectra of acetate methyl in stretched hydrogels: Quantum-mechanical description and Markov chain Monte Carlo relaxation-parameter estimation  

NASA Astrophysics Data System (ADS)

The 1H NMR signal of the methyl group of sodium acetate is shown to be a triplet in the anisotropic environment of stretched gelatin gel. The multiplet structure of the signal is due to the intra-methyl residual dipolar couplings. The relaxation properties of the spin system were probed by recording steady-state irradiation envelopes ('z-spectra'). A quantum-mechanical model based on irreducible spherical tensors formed by the three magnetically equivalent spins of the methyl group was used to simulate and fit experimental z-spectra. The multiple parameter values of the relaxation model were estimated by using a Bayesian-based Markov chain Monte Carlo algorithm.

Shishmarev, Dmitry; Chapman, Bogdan E.; Naumann, Christoph; Mamone, Salvatore; Kuchel, Philip W.

2015-01-01

374

Renormalizing Chiral Nuclear Forces: Triplet Channels  

SciTech Connect

We discuss the subleading contact interactions, or counterterms, of the triplet channels of nucleon-nucleon scattering in the framework of chiral effective field theory, with S and P waves as the examples. The triplet channels are special in that it allows the singular attraction of one-pion exchange to modify Weinberg's original power counting (WPC) scheme. With renormalization group invariance as the constraint, our power counting for the triplet channels can be summarized as a modified version of naive dimensional analysis that, when compared with WPC, the subleading counterterms are enhanced as much as the leading one. More specifically, this means that WPC needs no modification in {sup 3}S{sub 1}-{sup 3}D{sub 1} and {sup 3}P{sub 1} whereas a two-order enhancement is necessary in both {sup 3}P{sub 0} and {sup 3}P{sub 2} - {sup 3}F{sub 2}.

Bingwei Long, Chieh-Jen Yang

2012-03-01

375

Renormalizing Chiral Nuclear Forces: Triplet Channels  

E-print Network

We discuss the subleading contact interactions, or counterterms, of the triplet channels of nucleon-nucleon scattering in the framework of chiral effective field theory, with S and P waves as the examples. The triplet channels are special in that they allow the singular attraction of one-pion exchange to modify Weinberg's original power counting (WPC) scheme. With renormalization group invariance as the constraint, our power counting for the triplet channels can be summarized as a modified version of naive dimensional analysis in which, when compared with WPC, all of the counterterms in a given partial wave (leading or subleading) are enhanced by the same amount. More specifically, this means that WPC needs no modification in 3S1-3D1 and 3P1, whereas a two-order enhancement is necessary in both 3P0 and 3P2 - 3F2.

Bingwei Long; Chieh-Jen Yang

2012-03-14

376

Renormalizing Chiral Nuclear Forces: Triplet Channels  

E-print Network

We discuss the subleading contact interactions, or counterterms, of the triplet channels of nucleon-nucleon scattering in the framework of chiral effective field theory, with S and P waves as the examples. The triplet channels are special in that it allows the singular attraction of one-pion exchange to modify Weinberg's original power counting (WPC) scheme. With renormalization group invariance as the constraint, our power counting for the triplet channels can be summarized as a modified version of naive dimensional analysis that, when compared with WPC, the subleading counterterms are enhanced as much as the leading one. More specifically, this means that WPC needs no modification in 3S1-3D1 and 3P1 whereas a two-order enhancement is necessary in both 3P0 and 3P2 - 3F2.

Long, Bingwei

2011-01-01

377

Renormalizing chiral nuclear forces: Triplet channels  

NASA Astrophysics Data System (ADS)

We discuss the subleading contact interactions, or counterterms, of the triplet channels of nucleon-nucleon scattering in the framework of chiral effective field theory, with S and P waves as the examples. The triplet channels are special in that they allow the singular attraction of one-pion exchange to modify Weinberg's original power-counting (WPC) scheme. With renormalization group invariance as the constraint, our power counting for the triplet channels can be summarized as a modified version of naive dimensional analysis in which, when compared with WPC, all of the counterterms in a given partial wave (leading or subleading) are enhanced by the same amount. More specifically, this means that WPC needs no modification in 3S1-3D1 and 3P1, whereas a two-order enhancement is necessary in both 3P0 and 3P2-3F2.

Long, Bingwei; Yang, C.-J.

2012-03-01

378

Radical-triplet pair interactions as probes of long-range polymer motion in solution.  

PubMed

Radical-triplet pair interactions are used to investigate the dynamics of acrylic polymers in dilute solution. Methyl methacrylate was randomly copolymerized with a small amount of an amine-containing monomer to create the polymers. The amine subunits were then oxidized to nitroxide moieties (stable free radicals). Using time-resolved electron paramagnetic resonance (TREPR) spectroscopy on the sub-microsecond time scale, competition is observed between two deactivation processes of the ester side chain photoexcited triplet state: (1) Norrish I ?-cleavage, leading to a 21-line main chain polymeric free radical TREPR spectrum with emissive triplet mechanism spin polarization, and (2) spin polarization transfer or quenching by a nearby stable nitroxide radical, which gives a 3-line spectrum exhibiting emissive radical-triplet pair spin polarization. The main chain polymer radical signal dominates the TREPR spectrum if the probability of radical-triplet pair encounters is low. These competing reactions show a strong dependence on nitroxide incorporation (mol %), temperature, solvent, and acrylic polymer ester side chain structure. A comparison of steady state EPR and TREPR signals from inter- vs intramolecular processes clearly demonstrates the influence of polymer chain dynamics on the observed phenomena. PMID:25061948

Sim, Sooyeon; Forbes, Malcolm D E

2014-08-21

379

Triplet correlation functions in liquid water  

NASA Astrophysics Data System (ADS)

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.

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

2014-11-01

380

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

381

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

382

Assessing the quantitative reliability of solid-state 13C NMR spectra of kerogens across a gradient of thermal maturity.  

PubMed

Five type II kerogens, shown by elemental analysis and Rock-Eval pyrolysis to represent a gradient of thermal maturity, were further characterized using a range of solid-state 13C NMR spectroscopic techniques. 13C cross polarization (CP) NMR spectra of the kerogens confirmed the well-established pattern of increasing aromaticity with increasing thermal maturity. Spin counting showed that CP observability was around 50% for the immature kerogens, and only 14-25% for the mature kerogens. Spin counting also showed that the direct polarization (DP) observabilities were >80% for all but one of the kerogens. Despite the large differences in observability between the two techniques, aromaticities derived from corresponding CP and DP spectra differed by only 1-15%. The RESTORE technique showed that the low CP observability of the immature kerogens was due mostly to rapid T(1rho)H relaxation, whereas both rapid T(1rho)H relaxation and slow polarization transfer contributed to the low CP observability of the mature kerogens. PMID:16310345

Smernik, Ronald J; Schwark, Lorenz; Schmidt, Michael W I

2006-06-01

383

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

384

Ultrabright fluorescent OLEDS using triplet sinks  

DOEpatents

A first device is provided. The first device further comprises an organic light emitting device. The organic light emitting device further comprises an anode, a cathode, and an emissive layer disposed between the anode and the cathode. The emissive layer further comprises an organic host compound, an organic emitting compound capable of fluorescent emission at room temperature, and an organic dopant compound. The triplet energy of the dopant compound is lower than the triplet energy of the host compound. The dopant compound does not strongly absorb the fluorescent emission of the emitting compound.

Zhang, Yifan; Forrest, Stephen R; Thompson, Mark

2013-06-04

385

How disorder controls the kinetics of triplet charge recombination in semiconducting organic polymer photovoltaics.  

PubMed

Recent experiments by Rao et al. (Nature, 2013, 500, 435-439) indicate that recombination of triplet charge-separated states is suppressed in organic polymer-fullerene based bulk-heterojunction (BHJ) photovoltaic cells exhibiting a high degree of crystallinity in the fullerene phase relative to systems with more disorder. In this paper, we use a series of Frenkel-exciton lattice models to rationalize these results in terms of wave-function localization, interface geometry, and density of states. In one-dimensional co-linear and co-facial models of the interface, increasing local energetic disorder in one phase localizes the interfacial triplet charge-transfer ((3)CT) states and increases the rate at which these states relax to form lower-energy triplet excitons. In two dimensional BHJ models, energetic disorder within the fullerene phase plays little role in further localizing states pinned to the interface. However, inhomogeneous broadening introduces strong coupling between the interfacial (3)CT and nearby fullerene triplet excitons and can enhance the decay of these states in systems with higher degrees of energetic disorder. PMID:24922118

Bittner, Eric R; Lankevich, Vladimir; Gélinas, Simon; Rao, Akshay; Ginger, David A; Friend, Richard H

2014-10-14

386

Achieving the photon up-conversion thermodynamic yield upper limit by sensitized triplet-triplet annihilation.  

PubMed

Triplet-triplet annihilation (TTA) based up-conversion is a promising strategy for light harvesting the low-energy tail of the solar spectrum with photovoltaic technologies. Here, we present a bi-component system for photon managing via TTA that allows bypassing the classical statistic limit of 2/5 in the singlet generation, achieving a near unitary conversion efficiency. This result is obtained because of the peculiar relative position of the triplet and singlet energy levels of perylene, used as up-converter and emitter. The system shows a record red-to-blue external up-conversion yield of ?10% under an irradiance of 1 sun. PMID:25574759

Hoseinkhani, S; Tubino, R; Meinardi, F; Monguzzi, A

2015-01-28

387

Vibrational spectra of halobenzene cations in the ground and B~ 2 electronic states obtained by one-photon mass-analyzed threshold  

E-print Network

by referring to the assignments for the ionic ground states and those for the neutral molecules. From the MATI spectra, the ionization energies of fluoro-, chloro-, bromo-, and iodobenzene to the ionic ground states Spectroscopy of polyatomic cations is important for the study of composition of flame, stratosphere, etc

Kim, Myung Soo

388

Collisionally-Mediated Singlet-Triplet Crossing in ˜{a}1A1 CH_2 Revisited: (010) Coupling  

NASA Astrophysics Data System (ADS)

Methylene, CH2, possesses a ground ˜{X}3B1 ground electronic state and an excited ˜{a}1A1 state only 3150cm-1 higher in energy. The collision-induced singlet-triplet crossing in the gaseous mixtures is important in determining overall reaction rates and chemical behavior. Accidental near-degeneracies between rotational levels of the singlet state and the vibrationally excited triplet state result in a few gateway rotational levels that mediate collision-induced intersystem crossing. The mixed states can be recognized and quantified by deperturbation, knowing the zero-order singlet and triplet energy levels. Hyperfine structure can be used as alternative indicator of singlet-triplet mixing. Non-zero mixing will induce hyperfine splittings intermediate between the unresolved hyperfine structure of pure singlet and the resolvable (?50MHz) splittings of pure triplet, arising from the (I\\cdotS) interaction in the ortho states, where nuclear spin I=1. Collision-induced intersystem crossing rates from the (010) state are comparable to those for (000), yet the identities and characters of the presumed gateway states are unknown. A new spectrometer is under construction to investigate triplet mixing rotational levels of ˜{a}1A1(010) by sub-Doppler measurements of perturbation-induced hyperfine splittings. Their observation will permit the identification of gateway states and quantification of the degree of triplet contamination of the singlet wavefunction. Progress in the measurements and the analysis of rotational energy transfer in (010) will be reported. Acknowledgments: Work at Brookhaven National Laboratory was carried out under Contract No. DE-AC02-98CH10886 with the U.S. Department of Energy and supported by its Office of Basic Energy Sciences, Division of Chemical Sciences, Geosciences and Biosciences. C.-H. Chang, G. E. Hall, T. J. Sears, J. Chem. Phys 133, 144310(2010) G. E. Hall, A. V. Komissarov, and T. J. Sears, J. Phys. Chem. A 108 7922-7927 (2004)

Le, Anh T.; Hall, Gregory; Sears, Trevor

2014-06-01

389

Bartl et al. SUPPLEMENTAL DATA FIG. 1S. Comparison of the FTIR difference spectra of the Meta states of rhodopsin reconstituted  

E-print Network

1 Bartl et al. SUPPLEMENTAL DATA FIG. 1S. Comparison of the FTIR difference spectra of the Meta spectrum of 9-cis rhodopsin recorded at pH 5.5, 20 °C (brown). B, FTIR difference spectra of 9-cis ac isomerization state does not influence the pKa significantly. #12;3 FIG. 2S. UV/Vis and FTIR spectroscopy of ac

Palczewski, Krzysztof

390

Single vibronic level fluorescence spectra from the S 1( 1B 2u) state of p-difluorobenzene vapor  

NASA Astrophysics Data System (ADS)

1B 2u ? 1A 1g fluorescence spectra have been obtained after pumping each of 19 bands in the S1 ? S0 absorption of p-difluorobenzene under collision-free conditions. The fluorescence analyses provide new assignments of some absorption bands and confirmations of others so that the assignment of the principal structure in absorption is essentially secure. Only the identity of some sequence forming modes remains unconfirmed. The assignments confirm a number of excited-state fundamentals and provide new values for others (Table I). Analysis of the weaker structure in zero-point S1 fluorescence gives a full picture of vibrational activity in the S1 ? S0 transition. In so far as can be determined, the vibrational activities in fluorescence and absorption are in complete correspondence. The vibrational activity in the allowed p-difluorobenzene transition replicates to a good degree that found in the forbidden transition of benzene. Evidence suggesting a nonplanar S1 state is found. A Franck-Condon analysis is given for progressions in three modes, and several strong Fermi resonances are identified in the S1 state.

Coveleskie, R. A.; Parmenter, C. S.

1981-03-01

391

Assigning States in the Jahn-Teller Coupled Infrared Spectra of CH_3O and CD_3O  

NASA Astrophysics Data System (ADS)

The ground tilde{X}^2E vibrations of the methoxy radical have intrigued both experimentalists and theorists alike due to the presence of a conical intersection at the C3v molecular geometry. This conical intersection causes methoxy's vibrational spectrum to be strongly influenced by Jahn-Teller coupling, this leading to large amplitude vibrations and extensive mixing of the two lowest electronic states. This coupling combined with spin-orbit and Fermi couplings greatly complicates the assignments of states. In this talk we describe our efforts to assign the states of both CH_3O and CD_3O. Using the potential energy force field and calculated spectra of Nagesh and Sibert^1 as a starting point, vibrational mixing is considered using various zero-order representations. When the zero-order states are the diabatic normal mode states, there is sufficient mode mixing that the normal mode quantum numbers are no longer good labels. The mixing of the zero-order states can be reduced by including additional terms in the zero-order Hamiltonian, H^o. We consider the choice of including the first order Jahn-Teller coupling between one of the three degenerate normal modes. As the rocking motion has the largest Jahn-Teller coupling, this is the coupling that is included in H^o. Although the normal mode quantum numbers of the rocking basis functions are no longer good quantum numbers, due to the Jahn-Teller induced vibronic mixing, the zero-order states can be labeled with the linear Jahn-Teller quantum numbers.^2 This work extends these ideas by considering an H^o that includes linear Jahn-Teller coupling between two sets of degenerate vibrations. Plots of the resulting zero-order states are presented, and the spectral transitions recently observed3 for both CH_3O and CD_3O in a p-H_2 matrix are assigned using these basis functions. The extent of state-mixing found for the full Hamiltonian H for various choices of H^o is illustrated via the use of correlation diagrams obtained by plotting the eigenvalues of H^o + ? (H-H^o) as a function of ? where ? varies from zero to one. [^1] Nagesh, J.; Sibert, E. L. J. Phys. Chem. A, 2012, 116, 3846-3855. [^2] Barckholtz, T. A.; Miller, T. A. Int. Revs. in Phys. Chem., 1998, 17, 435-524. [^3] Yu-Fang Lee, Wei-Te Chou, and Yuan-Pern Lee (private communication).

Johnson, Britta; Sibert, Edwin

2014-06-01

392

Use of Bound-Free Structured Spectra in Determining RKR Potentials: The 4 3? g State of Na 2  

NASA Astrophysics Data System (ADS)

The RKR potential function of the Na2 43?g state determined by Y. Liu, H. Chen, J. Li, D. Chen, Li Li, and R. W. Field (J. Mol. Spectrosc.192, 32 (1998)) is checked for its ability to reproduce the experimental continuum of the Na2 43?g(v=12, N=23)?a3?+u bound-free transition observed by G. Lazarov, A. M. Lyyra, Li Li, and J. Huennekens (J. Mol. Spectrosc.196, 259 (1999)). A significant difference between the experimental and simulated bound-free spectra is found even though about 300 rovibrational term values spanning the range of v=2-25 vibrational quantum numbers and N=6-15 rotational quantum numbers were used for the construction of this RKR potential. The new potential curve of the Na2 43?g state was determined by applying the two-step global fit procedure of V. S. Ivanov, V. B. Sovkov, Li Li, A. M. Lyyra, G. Lazarov, and J. Huennekens (J. Mol. Spectrosc.194, 147 (1999)) to a set of all the available spectroscopic data on the Na2 43?g state. This 43?g state is perturbed by the 63?g+ state through L-uncoupling. The 'nonperturbed' RKR potential is constructed from a subset of the nonperturbed rovibrational term values solely. The potential curve constructed from the nonperturbed levels only is very close to the potential curve obtained by the two-step global fit and reproduces the term values and the bound-free continuum with the same accuracy.

Ivanov, V. S.; Sovkov, V. B.; Gallice, N.; Li, Li; Liu, Y.; Lyyra, A. M.; Magnier, S.

2001-09-01

393

Photoemission spectra and thermal desorption characteristics of two states of oxygen on Pd  

NASA Astrophysics Data System (ADS)

Two states of oxygen have been observed on Pd (111). The first is adsorbed on the surface and causes strong changes in the Pd d-band photoemission energy distribution curves (EDCs) at hv = 21.2 eV but no oxygen resonance below the d-bands. The second is identified with oxygen beneath the surface (in accord with the thermal desorption studies of Conrad et al.); it has little effect on the Pd d-band emission but produces a resonance at lower energy (˜5 eV below Ef). Evidence is presented indicating that the case with which oxygen can go beneath the Pd surface depends on the surface perfection of the crystal.

Weissman, D. L.; Shek, M. L.; Spicer, W. E.

1980-02-01

394

Synchrotron and Compton Spectra from a Steady-State Electron Distribution  

E-print Network

Energy densities of relativistic electrons and protons in extended galactic and intracluster regions are commonly determined from spectral radio and (rarely) $\\gamma$-ray measurements. The time-independent particle spectral density distributions are commonly assumed to have a power-law (PL) form over the relevant energy range. A theoretical relation between energy densities of electrons and protons is usually adopted, and energy equipartition is invoked to determine the mean magnetic field strength in the emitting region. We show that for typical conditions, in both star-forming and starburst galaxies, these estimates need to be scaled down substantially due to significant energy losses that (effectively) flatten the electron spectral density distribution, resulting in a much lower energy density than deduced when the distribution is assumed to have a PL form. The steady-state electron distribution in the nuclear regions of starburst galaxies is calculated by accounting for Coulomb, bremsstrahlung, Compton, a...

Rephaeli, Yoel

2015-01-01

395

Hindered and modulated rotational states and spectra of adsorbed diatomic molecules  

SciTech Connect

Both vertical and horizontal adsorption configurations of a diatomic molecule were modeled as the rigid rotor with which the spatial motion was confined by a finite conical well. In addition to the polar hindering potential, a sinusoidal azimuthal modulation, which bears the local symmetry of the adsorption site, was incorporated. Eigenfunctions for different models were expressed analytically in terms of the hypergeometric functions, and eigenvalues were solved numerically. We found that the rotational energy levels exhibit oscillatory behavior when plotted as functions of the hindrance angle. This particular phenomenon was interpreted as the occurrence of resonance transmission of the rotor wave function at certain hindrance condition. We also found that the rotational levels were grouped into bands when the azimuthal modulation strength was increased. The solutions were used to calculate the rotational-state distribution of desorbed molecules, and agreement with the previous experiment was obtained. {copyright} {ital 1996 The American Physical Society.}

Shih, Y.T. [Institute of Electro-Optical Engineering, National Chiao Tung University, Hsinchu, Taiwan, Republic of (China)] [Institute of Electro-Optical Engineering, National Chiao Tung University, Hsinchu, Taiwan, Republic of (China); Chuu, D.S. [Department of Electrophysics, National Chiao Tung University, Hsinchu, Taiwan, Republic of (China)] [Department of Electrophysics, National Chiao Tung University, Hsinchu, Taiwan, Republic of (China); Mei, W.N. [Department of Physics, University of Nebraska at Omaha, Omaha, Nebraska 68182 (United States)] [Department of Physics, University of Nebraska at Omaha, Omaha, Nebraska 68182 (United States)

1996-10-01

396

Broadband Emission Spectra from the Cygnus X-3 Jet in the Soft Spectral State  

NASA Astrophysics Data System (ADS)

In order to understand the main observational characteristics of the Galactic X-ray binary Cygnus X-3, we propose a radiation model in which high-energy electrons accelerate in the dissipation zone of a jet and produce nonthermal broadband emissions. Broadband spectral energy distributions are computed to compare the AGILE and Fermi LAT data with the multi-band data during soft X-ray spectral states. By fitting observations at different locations of the jet, we find that the emission region is rather compact and should be located at a distance of about one orbital radius. Our results can explain the current multi-frequency observations and also predict the TeV band emission. The model could be tested by a polarization measurement at IR band, and/or by a correlation study between the GeV and TeV bands once very-high-energy observations are available.

Zhang, Jian-Fu; Lu, Ju-Fu

2015-02-01

397

BVRI Surface Photometry of Isolated Galaxy Triplets  

Microsoft Academic Search

Optical broadband BVRI observations of 54 galaxies selected from the Catalog of Isolated Triplets of Galaxies in the Northern Hemisphere have been carried out at San Pedro Mártir National Observatory to evaluate their photometric and morphological properties. We complement our analysis with Two-Micron All Sky Survey (2MASS) and Sloan Digital Sky Survey (SDSS) images and look for signatures likely related

H. M. Hernández-Toledo; H. Méndez-Hernández; H. Aceves; L. Olguín

2011-01-01

398

Relative Pose Estimation Using Image Feature Triplets  

NASA Astrophysics Data System (ADS)

A fully automated reconstruction of the trajectory of image sequences using point correspondences is turning into a routine practice. However, there are cases in which point features are hardly detectable, cannot be localized in a stable distribution, and consequently lead to an insufficient pose estimation. This paper presents a triplet-wise scheme for calibrated relative pose estimation from image point and line triplets, and investigates the effectiveness of the feature integration upon the relative pose estimation. To this end, we employ an existing point matching technique and propose a method for line triplet matching in which the relative poses are resolved during the matching procedure. The line matching method aims at establishing hypotheses about potential minimal line matches that can be used for determining the parameters of relative orientation (pose estimation) of two images with respect to the reference one; then, quantifying the agreement using the estimated orientation parameters. Rather than randomly choosing the line candidates in the matching process, we generate an associated lookup table to guide the selection of potential line matches. In addition, we integrate the homologous point and line triplets into a common adjustment procedure. In order to be able to also work with image sequences the adjustment is formulated in an incremental manner. The proposed scheme is evaluated with both synthetic and real datasets, demonstrating its satisfactory performance and revealing the effectiveness of image feature integration.

Chuang, T. Y.; Rottensteiner, F.; Heipke, C.

2015-03-01

399

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

400

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

401

Photophysics of Soret-Excited Tetrapyrroles in Solution. IV. Radiationless Decay and Triplet-Triplet Annihilation Investigated Using Tetraphenylporphinato Sn(IV)  

NASA Astrophysics Data System (ADS)

The S2 population decay rates and triplet-triplet annihilation efficiencies of Sn(IV)Cl2TPP have been measured in fluid solutions using its weak S2-S0 fluorescence as a metric. A detailed description of the excited-state photophysics of Sn(IV)Cl2TPP has allowed comparisons to be made between this rigid, D4h axially coordinated molecule and axially uncoordinated tetrapyrroles of greater flexibility and lower symmetry. S2-S1 internal conversion is the major S2 population decay path for Sn(IV)Cl2TPP as it is for the S2 states of all other d0 and d10 metalated tetrapyrroles. The S2 state of Sn(IV)Cl2TPP exhibits S2-S1 relaxation rates that follow the energy gap law of radiationless transition theory and are only slightly faster than those exhibited by MgTPP and the weak coupling limit. Differences in S2-S1 radiationless decay rates among the series MTPP (M = Mg, Zn, Cd, SnCl2) cannot be traced to differences in the displacements of the S2 and S1 potential surfaces. Instead, the most likely source of the large differences in S2-S1 radiationless decay rates between CdTPP and Sn(IV)Cl2TPP is the lower symmetry of the former (near C4v), which permits a much larger number of vibrations to participate in S2-S1 vibronic coupling. Triplet-triplet annihilation of the type 2T1 ? S2 + S0 has been observed in Sn(IV)Cl2TPP for the first time, but is of substantially lower efficiency than seen in ZnTPP in noncoordinating solvents because of its shorter triplet lifetime and the shielding effects of its axial Cl ligands, which tend to block the short-range interaction needed for Dexter energy transfer.

Maiti, Manisankar; Danger, Brook R.; Steer, Ronald P.

2009-09-01

402

A comparative study of triplet and radical-anion photoionization of propiophenone  

NASA Astrophysics Data System (ADS)

The photoionization of propiophenone via two different routes was investigated by single-pulse and two-pulse laser-flash photolysis with observation of the hydrated electron and the respective photoionizable intermediate, the triplet or the radical anion. From the dependences of the absolute concentrations on the excitation intensity, kinetic constants and quantum yields were obtained. In the presence of a large surplus of a sacrificial electron donor (triethylamine or DABCO), the reaction is cyclic, with the radical anion of the ketone first formed by photoinduced electron transfer, and then ionized by another photon to regenerate the starting material, all within the same laser flash. The quantum yield of photoionization of the radical anion is 0.25 at 308 nm. In the absence of a donor, the ketone triplet is ionized. The intensity dependences indicate a more complex mechanism than a consecutive reaction and provide evidence for an additional photoreaction of the triplet, presumably regeneration of the starting material by reverse intersystem crossing via a chemical pathway. The quantum yield of photoionization of the triplet is 0.05 at 308 nm and 0.02 at 355 nm. As the electronic configurations of the autoionizing upper excited states are very similar, it is proposed that the lower quantum yield in the case of the triplet might be due to competing deactivation channels, which are not open to the upper excited radical anion.

Goez, Martin; Zubarev, Valentin

2004-12-01

403

Singlet-triplet annihilation of singlet oxygen and triplet xanthene dye molecules in liquid solutions  

SciTech Connect

This paper presents experimental and theoretical data on the enhancement of delayed fluorescence of eosin and erythrocine molecules in liquid solutions under the action of dissolved oxygen which make it possible to postulate the existence of photophysical processes of singlet-triplet annihilation of singlet oxygen and triplet dye molecules. The study was carried out in a system consisting of a neodymium laser with an optical quantum multipler, a monochromator, and an oscillograph. The solvents used were propanol, acetone, and water.

Bryukhanov, V.V.; Ketsle, G.A.; Laurinas, V.C.; Levshin, L.V.; Muldakhmetov, Z.M.

1987-10-01

404

Raman and infrared spectra of cellobiose in the solid state: What can be learned from single-molecule calculations?  

NASA Astrophysics Data System (ADS)

Fourier-transform infrared and Raman scattering spectra of solid cellobiose are measured. The monitored spectra are compared to vibrational spectra of isolated cellobiose, computed by the vibrational self-consistent field (VSCF) method and from classical molecular dynamics (MD) simulations. Partial agreement is found between the measured and calculated features, allowing interpretation of parts of the spectra in terms of single-molecule calculations. Deviations between the measured spectra and the calculated ones could be due to environment effects on the molecule, not included in the model, or due to errors in the vibrational methods used. Future investigations of this issue seem desirable.

Xie, Hong-bin; Pincu, Madeleine; Brauer, Brina; Gerber, R. Benny; Bar, Ilana

2011-10-01

405

A computational investigation on singlet and triplet exciton couplings in acene molecular crystals.  

PubMed

Quantum chemical calculations (DFT, TDDFT and ZINDO/S) of singlet and triplet exciton couplings are presented and discussed for some acene derivatives (such as anthracene, tetracene, 9,10-di(phenyl)anthracene and 9,10-bis(phenylethynyl)anthracene). An accurate excited state single molecule characterization has been carried out followed by an analysis of the inter-molecular excitonic interactions, taking place in the crystalline phase. These have been correlated to exciton coupling terms obtaining guidelines for the choice of molecular materials with large exciton couplings. Such organic systems are likely to show multiexciton processes such as singlet fission (SF) and triplet-triplet annihilation (TTA) which are useful in energy conversion phenomena to be exploited in photonic and optoelectronic devices. PMID:21947306

Quarti, Claudio; Fazzi, Daniele; Del Zoppo, Mirella

2011-11-01

406

Sensitized non-coherent photon upconversion by intramolecular triplet-triplet annihilation in a diphenylanthracene pendant polymer  

NASA Astrophysics Data System (ADS)

Non-coherent photon upconversion by rapid intramolecular triplet-triplet annihilation has been observed following nanosecond laser excitation of Ru(dmb)3 and sequential two-fold triplet energy sensitization of a polymer containing 30 pendant diphenylanthracene groups. A global kinetic analysis of the system has been performed; the intramolecular annihilation step occurs on a sub-nanosecond time scale.

Tilley, Andrew J.; Robotham, Benjamin E.; Steer, Ronald P.; Ghiggino, Kenneth P.

2015-01-01

407

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

408

The fluoroformyloxyl radical geometry and ground-state rotational spectra of the free FC18O2. radical  

NASA Astrophysics Data System (ADS)

The rotational spectra of the isotopically substituted free fluoroformyloxyl radical FC18O2. were measured using the Prague millimeter-wave high-resolution spectrometer. More than 110 rotational-fine-hyperfine transition lines were observed and assigned to appropriate quantum numbers in the frequency range of 235-270 GHz. The obtained transition frequencies were analyzed with standard effective Hamiltonians to acquire a set of precise rotational, centrifugal-distortion, fine, and hyperfine structure molecular constants. Merging the new FC18O2. isotopologue molecular parameters with those previously obtained for the ordinary FC16O2. radical, the substitution molecular geometry in the ground vibronic state was evaluated. The molecular parameters for both radical isotopologues were also calculated by several quantum chemistry methods and their calculated mutual ratios are in remarkable agreement with the experimental FC16O2./FC18O2. parameter ratios. The measurements, assignments of the 18-oxygen isotopologue FC18O2. radical millimeter-wave transitions, as well as the derivation of the fluoroformyloxyl radical ground-state geometry have been carried out for the first time.

Koucký, Jan; Kolesniková, Lucie; Uhlíková, Tereza; Varga, Juraj; Kania, Patrik; Beckers, Helmut; Willner, Helge; Urban, Št?pán

2012-03-01

409

STELLAR ABSORPTION LINES IN THE SPECTRA OF SEYFERT Charles Nelson, 1 Mark Whittle 2  

E-print Network

the strengths of Ca II triplet and Mgb stellar absorption lines in the nuclear and off­nuclear spectra in a circumnuclear burst of star formation. INTRODUCTION The nuclear spectra of Seyfert galaxies can be thought & PREVIOUS RESULTS Nelson & Whittle (1995, NW95) obtained nuclear optical and near­IR spectra for a large

Nelson III, Charles H.

410

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

SciTech Connect

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. [Department of Chemistry, University of Pennsylvania, 231 S. 34th Street, Philadelphia, Pennsylvania 19104 (United States)

2014-07-07

411

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

412

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

413

Quantum beats in crystalline tetracene delayed fluorescence due to triplet pair coherences produced by direct singlet fission.  

PubMed

A detailed analysis of the oscillations seen in the delayed fluorescence of crystalline tetracene is presented in order to study the mechanism of singlet fission. Three quantum beat frequencies of 1.06 ± 0.05, 1.82 ± 0.05, and 2.92 ± 0.06 GHz are resolved, which are damped on a time scale of 20 ns. The effects of sample morphology, excitation wavelength, and temperature are examined. A density matrix model for singlet fission is developed that quantitatively describes the frequencies, amplitudes, and damping of the oscillations. The model assumes a direct coupling of the initially excited singlet exciton to the triplet pair manifold. There is no electronic coherence between the singlet and triplet pair states, but the rapid singlet decay time of ?200 ps in solution-grown single crystals provides the impulsive population transfer necessary to create a coherent superposition of three zero-field triplet pair states |xx>, |yy>, and |zz> with overall singlet character. This superposition of the three states gives rise to the three quantum beat frequencies seen in the experiment. Damping of the quantum beats results from both population exchange between triplet and singlet manifolds and pure dephasing between the triplet pair states. By lowering the temperature and slowing the SF rate, the visibility of the oscillations decreases. There is no evidence of magnetic dipole-dipole coupling between the product triplets. Our model provides good overall agreement with the data, supporting the conclusion that singlet fission in tetracene proceeds through the "direct" mechanism without strong electronic coupling between the singlet and triplet pair states. PMID:22530591

Burdett, Jonathan J; Bardeen, Christopher J

2012-05-23

414

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

415

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

416

Boson-boson mixtures and triplet correlations  

NASA Astrophysics Data System (ADS)

The hypernetted-chain formalism for boson-boson mixtures described by an extended Jastrow correlated wave function is derived, taking into account elementary diagrams and triplet correlations. The energy of an ideal boson 3He-4He mixture is computed for low values of the 3He concentration. The zero-3He-concentration limit provides a 3He chemical potential in good agreement with the experimental value, when a McMillan two-body correlation factor and the Lennard-Jones potential are adopted. If the Euler equations for the two-body correlation factors are solved in presence of triplet correlations, the agreement is again improved. At the experimental 4He equilibrium density, the 3He chemical potential turns out to be -2.58 K, to be compared with the experimental value, -2.79 K.

Fabrocini, A.; Polls, A.

1984-08-01

417

Singlets and triplets in hybrid nanodevices  

NASA Astrophysics Data System (ADS)

An organic material thin layer can be used to resonantly absorb light and nonradiatively transfer excitation to an adjacent inorganic quantum well the optical nonlinearities of which can in this way be turned on more efficiently than by direct optical pumping. We theoretically consider this process in a hybrid structure based on crystalline tetracene in which the singlet exciton energy is close to twice the one of a triplet exciton and thermally activated singlet exciton fission into two triplets can be efficient. We investigate how the temperature dependence of the singlet exciton diffusion length affects the functional properties of such hybrid organic-inorganic nanostructures based on tetracene. We show how temperature activated fission opens a new possibility to turn on and off the indirect pumping due to energy transfer from the organic into the inorganic subsystem.

Agranovich, V. M.; Dubovskii, O. A.; La Rocca, G. C.

2014-05-01

418

Delayed interval delivery in a triplet gestation.  

PubMed

A 27-year-old Ghanaian primigravida with a known triamniotic trichorionic triplet pregnancy presented at 17 weeks gestation following a miscarriage of one triplet at home. Examination and investigation revealed no signs of imminent delivery or infection. After careful counselling with regard to prognosis and options available for management, the couple opted for intervention including rescue cerclage. The patient received antibiotic prophylaxis for five days and daily progesterone suppositories until delivery. An ultrasound scan was performed every three weeks to monitor fetal growth and cervical length. At 24 weeks corticosteroids for fetal lung maturity were given. At 31 weeks gestation she experienced spontaneous rupture of membranes followed by active labour and forceps delivery. There were no maternal complications. Both babies were born in a good condition, but required ventilatory support for 72 h. PMID:23188854

Wooldridge, Rachel J; Oliver, Emily A; Singh, Tulika

2012-01-01

419

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