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1

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

2

Time-resolved electron paramagnetic resonance spectra of photoexcited triplet states of electron-donor-acceptor complexes in frozen solution: Methylated benzenes and chlorinated phthalic anhydrides  

NASA Astrophysics Data System (ADS)

Phthalic anhydride (PA) and chlorinated PAs in frozen methyl substituted benzenes provided the time-resolved electron paramagnetic resonance (TREPR) spectra of the electron-donor-acceptor (EDA) complexes. The chlorine substitution of PA reduced the zero-field splitting parameters, D, due to the contribution of the spin-orbit interaction caused by heavy atoms such as chlorine. The increase of the number of methyl group on benzene, which apparently reduced the ionization potential, worked to decrease the D value of the EDA complex. The charge-transfer (CT) ratios were measured more exactly by the absolute value of (Delta m(sub s)) = 1 transition of the triplet states. The major axes of these systems were also safely presumed. The sign of the 100% charge transferred EDA complex was found negative because of the CT ratio plots and the spin-polarization pattern of the TREPR spectra.

Murai, Hisao; Minami, Masashi; I'Haya, Yasumasa J.

1994-09-01

3

Naphthalene in the higher triplet excited state.  

PubMed

Naphthalene in the higher triplet excited state Np(Tn) was generated from the two-step excitation method using two-colour two-laser flash photolysis technique and the lifetime of Np(Tn) was estimated to be 4.5 ps from the triplet energy quenching by quenchers such as p-dichlorobenzene, o-dicyanobenzene and carbon tetrachloride. PMID:12585401

Cai, Xichen; Hara, Michihiro; Kawai, Kiyohiko; Tojo, Sachiko; Majima, Tetsuro

2003-01-21

4

Triplet state dipole moments of aminobenzonitriles.  

PubMed

The triplet state dipole moments mu(T) of a series of 4-amino- and 3-aminobenzonitriles in cyclohexane, benzene, and 1,4-dioxane are recalculated from previously published [J. Phys. Chem. 1992, 96, 10809] time-resolved microwave conductivity data, on the basis of newly measured intersystem crossing yields. For 4-(dimethylamino)benzonitrile (DMABN), the following values are now determined for mu(T): 8.3 D (cyclohexane), 8.9 D (benzene), and 9.7 D (1,4-dioxane), as compared with the previously reported dipole moment of 12 D for the first and the last solvent. With the other aminobenzonitriles, similar mu(T) data are obtained, between 6.9 D for 4-aminobenzonitrile (ABN) in n-hexane and 10.0 D for 4-(di-n-decylamino)benzonitrile (DDABN) in 1,4-dioxane. The increase of mu(T) observed for all aminobenzonitriles when going from cyclohexane via benzene to 1,4-dioxane may indicate that their triplet dipole moments become larger with increasing solvent polarity. The present mu(T) of DMABN, between 8.3 and 9.7 D, although larger than the ground state dipole moment mu(0) of 6.6 D, is somewhat smaller than that of the locally excited (LE) state (9.9 D) but considerably smaller than the dipole moment of the intramolecular charge transfer (ICT) state (17 D). By comparing these mu(X) data with the frequency (CN) of the cyano vibration in each state, it appears that at least for DMABN in the triplet state (CN) is not a reliable indication of the extent of charge transfer as compared with the other states S0, LE, and ICT. PMID:18217728

Demeter, Attila; Zachariasse, Klaas A

2008-02-21

5

The triplet state in bacterial photosynthesis: Possible mechanisms of the primary photo-act  

PubMed Central

In vitro and in vivo triplet state electron paramagnetic resonance (epr) spectra of bacteriochlorophylls (Bchls) show important differences in (a) electron spin polarization (esp), and (b) zero field splitting (ZFS) parameters. The unusual esp and ZFS properties of the observed in vivo triplet state are best interpreted as arising from a short-lived radical pair precursor (not directly observable by epr) formed in or with the special pair of bacteriochlorophyll molecules involved in the primary photo-act. PMID:16592270

Thurnauer, Marion C.; Katz, Joseph J.; Norris, James R.

1975-01-01

6

An atlas of Calcium triplet spectra of active galaxies  

E-print Network

We present a spectroscopic atlas of active galactic nuclei covering the region around the 8498, 8542, 8662 Calcium triplet (CaT) lines. The sample comprises 78 objects, divided into 43 Seyfert 2s, 26 Seyfert 1s, 3 Starburst and 6 normal galaxies. The spectra pertain to the inner ~300 pc in radius, and thus sample the central kinematics and stellar populations of active galaxies. The data are used to measure stellar velocity dispersions (sigma_star) both with cross-correlation and direct fitting methods. These measurements are found to be in good agreement with each-other and with those in previous studies for objects in common. The CaT equivalent width is also measured. We find average values and sample dispersions of W_CaT of 4.6+/-2.0, 7.0 and 7.7+/-1.0 angstrons for Seyfert 1s, Seyfert 2s and normal galaxies, respectively. We further present an atlas of [SIII]\\lambda 9069 emission line profiles for a subset of 40 galaxies. These data are analyzed in a companion paper which addresses the connection between stellar and Narrow Line Region kinematics, the behaviour of the CaT equivalent width as a function of sigma_star, activity type and stellar population properties.

A. Garcia-Rissmann; L. R. Vega; N. V. Asari; R. Cid Fernandes; H. Schmitt; R. M. Gonzalez Delgado; T. Storchi-Bergmann

2005-02-23

7

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

E-print Network

Coupled singlet-triplet analysis of two-color cold-atom photoassociation spectra J. M. Vogels,1 R phase method to treat the short-range part of the molecular potentials. We apply this method to analyze information on the interactions between cold atoms, making use of measured energies of bound diatomic states

Heinzen, Daniel J.

8

The triplet state of fac-Ir(ppy)3.  

PubMed

The emitting triplet state of fac-Ir(ppy)(3) (fac-tris(2-phenylpyridine)iridium) is studied for the first time on the basis of highly resolved optical spectra in the range of the electronic 0-0 transitions. For the compound dissolved in CH(2)Cl(2) and cooled to cryogenic temperatures, three 0-0 transitions corresponding to the triplet substates I, II, and III are identified. They lie at 19,693 cm(-1) (507.79 nm, I ? 0), 19,712 cm(-1) (507.31 nm, II ? 0), and 19,863 cm(-1) (503.45 nm, III ? 0). From the large total zero-field splitting (ZFS) of 170 cm(-1), the assignment of the emitting triplet term as a (3)MLCT state (metal-to-ligand charge transfer state) is substantiated, and it is seen that spin-orbit couplings to higher lying (1,3)MLCT states are very effective. Moreover, the studies provide emission decay times for the three individual substates of ?(I) = 116 ?s, ?(II) = 6.4 ?s, and ?(III) = 200 ns. Further, group-theoretical considerations and investigations under application of high magnetic fields up to B = 12 T allow us to conclude that all three substates are nondegenerate and that the symmetry of the complex in the CH(2)Cl(2) matrix cage is lower than C(3). It follows that the triplet parent term is of (3)A character. Studies of the emission decay time and photoluminescence quantum yield, ?(PL), of Ir(ppy)(3) in poly(methylmethacrylate) (PMMA) in the temperature range of 1.5 ? T ? 370 K reveal average and individual radiative and nonradiative decay rates and quantum yields of the substates. In the range 80 ? T ? 370 K, ?(PL) is as high as almost 100%. The quantum yield ?(PL) drops to ?88% when cooled to T = 1.5 K. The investigations show further that the emission properties of Ir(ppy)(3) depend distinctly on the complex's environment or the matrix cage according to distinct changes of spin-orbit coupling effectiveness. These issues also have consequences for optimizations of the material's properties if applied as an organic light-emitting diode (OLED) emitter. PMID:20853860

Hofbeck, Thomas; Yersin, Hartmut

2010-10-18

9

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

10

Ground state of naphthyl cation: Singlet or triplet?  

SciTech Connect

We present a benchmark theoretical investigation on the electronic structure and singlet-triplet(S-T) gap of 1- and 2-naphthyl cations using the CCSD(T) method. Our calculations reveal that the ground states of both the naphthyl cations are singlet, contrary to the results obtained by DFT/B3LYP calculations reported in previous theoretical studies. However, the triplet states obtained in the two structural isomers of naphthyl cation are completely different. The triplet state in 1-naphthyl cation is (?,?) type, whereas in 2-naphthyl cation it is (?,?{sup ?}) type. The S-T gaps in naphthyl cations and the relative stability ordering of the singlet and the triplet states are highly sensitive to the basis-set quality as well as level of correlation, and demand for inclusion of perturbative triples in the coupled-cluster ansatz.

Dutta, Achintya Kumar; Vaval, Nayana, E-mail: np.vaval@ncl.res.in; Pal, Sourav, E-mail: s.pal@ncl.res.in [Physical Chemistry Division, CSIR-National Chemical Laboratory, Pune 411008 (India)] [Physical Chemistry Division, CSIR-National Chemical Laboratory, Pune 411008 (India); Manohar, Prashant U. [Department of Chemistry, BITS Pilani, Pilani Campus (India)] [Department of Chemistry, BITS Pilani, Pilani Campus (India)

2014-03-21

11

Ground state of naphthyl cation: singlet or triplet?  

PubMed

We present a benchmark theoretical investigation on the electronic structure and singlet-triplet(S-T) gap of 1- and 2-naphthyl cations using the CCSD(T) method. Our calculations reveal that the ground states of both the naphthyl cations are singlet, contrary to the results obtained by DFT/B3LYP calculations reported in previous theoretical studies. However, the triplet states obtained in the two structural isomers of naphthyl cation are completely different. The triplet state in 1-naphthyl cation is (?,?) type, whereas in 2-naphthyl cation it is (?,?') type. The S-T gaps in naphthyl cations and the relative stability ordering of the singlet and the triplet states are highly sensitive to the basis-set quality as well as level of correlation, and demand for inclusion of perturbative triples in the coupled-cluster ansatz. PMID:24655185

Dutta, Achintya Kumar; Manohar, Prashant U; Vaval, Nayana; Pal, Sourav

2014-03-21

12

Ab initio study of low-lying triplet states of the lithium dimer.  

PubMed

Observation of Bose-Einstein condensation in Li27 initiated the interest in the scattering length of two ground state lithium atoms when they approach each other as a radical pair triplet aSigmau+3 state. But some properties of this state are still unknown. In present work, a number of low-lying triplet states of lithium molecule are calculated by multi-configuration self-consistent field (MCSCF) and response techniques with account of spin-orbit coupling, spin-spin coupling and some other magnetic perturbations. The singlet-triplet transition probabilities to the ground state are also presented. Most results are connected with the weakly bound lowest triplet a3Sigmau+ state, whose radiative lifetime and spin-splitting are unknown so far in spite of its great importance in Bose-Einstein condensation. Calculations indicate that this state has a very small spin-splitting, lambdass=-0.01 cm-1, which is negligible in comparison with the line-width in experimental Fourier transform spectra published so far. Similar splitting is obtained for the upper state of the 1(3)Sigmag+--a3Sigmau+ transition. This is in agreement with experimental rovibronic analysis of the 1(3)Sigmag+--a3Sigmau+ band system in which the triplet structure was not resolved. The radiative lifetime of the a3Sigmau+ state is predicted to exceed 10 h. PMID:16099708

Minaev, Boris

2005-12-01

13

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

14

Low-lying triplet states of diphosphene and diphosphinylidene.  

PubMed

In this research, six low-lying triplet states of diphosphene (HPPH) and disphosphinylidene (PPH(2)) are systematically investigated starting from self-consistent field theory and proceeding to multireference coupled cluster methods using a wide range of basis sets. For each structure, the geometry, energy, dipole moment, harmonic vibrational frequencies, and infrared intensities are predicted. The triplet potential energy surface (PES) of P(2)H(2) is presented, based on systematically extrapolated coupled cluster energies and accounting for core-valence correlation, zero-point vibrational energy, and diagonal Born-Oppenheimer effects. Both (3)A'' pyramidal PPH(2) and (3)B skewed HPPH are minima on the triplet PES and lie 27.4 ± 0.3 and 32.4 ± 0.3 kcal mol(-1) above the global minimum structure closed-shell (1)A(g) trans-HPPH, respectively. The energy barrier for the isomerization reaction [(3)B skewed HPPH ? (3)A'' pyramidal PPH(2)] is predicted to be 16.4 ± 0.3 kcal mol(-1). On this triplet PES, two equivalent (3)B skewed HPPH are converted via the (3)B(u) trans-HPPH transition state with a barrier of 9.1 ± 0.3 kcal mol(-1) or via the (3)B(2) cis-HPPH transition state with a barrier of 11.1 ± 0.3 kcal mol(-1). Moreover, the two equivalent (3)A'' pyramidal PPH(2) structures are connected through the (3)A(2) planar PPH(2) transition state with a barrier of 18.6 ± 0.3 kcal mol(-1). The energy crossing of the singlet and triplet adiabatic PES is studied using Mukherjee multireference coupled cluster method with the cc-pVQZ basis set, which predicts that the (3)B skewed HPPH is 1.4 kcal mol(-1) lower in energy than the corresponding (1)A skewed HPPH at the (3)B skewed HPPH optimized geometry. PMID:20836526

Lu, Tongxiang; Hao, Qiang; Simmonett, Andrew C; Evangelista, Francesco A; Yamaguchi, Yukio; Fang, De-Cai; Schaefer, Henry F

2010-10-14

15

Quantum chemical study on the population of the lowest triplet state of psoralen  

NASA Astrophysics Data System (ADS)

The efficient population of the low-lying triplet ?? * state of psoralen is studied with the quantum chemical CASPT2 method. Minima, singlet-triplet crossings, conical intersections, and reaction paths on the low-lying singlet and triplet states hypersurfaces of the system have been computed together with electronic energy gaps and spin-orbit coupling terms. A mechanism is proposed, favorable in the gas phase, for efficient deactivation of the initially populated singlet excited ?? * state, starting with an intersystem crossing with an n? * triplet state and evolving via a conical intersection toward the final lowest-lying ?? * triplet state, protagonist of the reactivity of psoralen.

Serrano-Pérez, Juan José; Merchán, Manuela; Serrano-Andrés, Luis

2007-01-01

16

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

17

Long-distance electron transfer from a triplet excited state  

NASA Astrophysics Data System (ADS)

Electron transfer from the triplet excited state of N,N,N',N'-tetramethylphenylene diamine to phthalic anhydride has been monitored by phosphorescence emission decay. The kinetics of the transfer process were observed directly and the rate constant depends exponentially on the reacting distance, k(r) = 1 × 10 4 exp(-0.58 r) s -1. The electron transfer rate has been found to be invariant over the temperature interval 77-143 K.

Murtagh, James; Thomas, J. Kerry

18

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

PubMed

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

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

2012-06-01

19

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

20

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

21

A triplet ground state for cationic polyaromatic hydrocarbons after hydrogen loss  

NASA Astrophysics Data System (ADS)

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

Galue, H. A.; Oomens, J.

2011-05-01

22

Model for triplet state engineering in organic light emitting diodes  

NASA Astrophysics Data System (ADS)

Engineering the position of the lowest triplet state (T1) relative to the first excited singlet state (S1) is of great importance in improving the efficiencies of organic light emitting diodes and organic photovoltaic cells. We have carried out model exact calculations of substituted polyene chains to understand the factors that affect the energy gap between S1 and T1. The factors studied are backbone dimerisation, different donor-acceptor substitutions, and twisted geometry. The largest system studied is an 18 carbon polyene which spans a Hilbert space of about 991 × 106. We show that for reverse intersystem crossing process, the best system involves substituting all carbon sites on one half of the polyene with donors and the other half with acceptors.

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

2014-06-01

23

The effects of triplet perturbers on photophysical processes in the Ã1Au state of acetylene  

NASA Astrophysics Data System (ADS)

Rotationally resolved excitation spectra of the acetylene à 1Au?X˜ 1?g+ transition were recorded by measuring separately the total emission in two spectral regions: UV (200-400 nm) and NIR (0.9-1.5 ?m). UV emission is due to Ã?X˜ transitions. The source of the NIR signal is suggested by the observation that the NIR:UV intensity ratio is approximately constant throughout the V02K01 subband. (V denotes the trans-bending mode.) This is consistent with C2H à 2??X˜2?+ NIR transitions occurring as a result of resonance-enhanced two-photon excitation of predissociated Rydberg states. The V03K01 subband shows significant fluctuations in the NIR:UV intensity ratio. The increase in trans-bending excitation from 2?3' to 3?3' enables accidental resonances with background states (both triplet and S1) to alter the NIR emission intensity. Triplet perturbers can facilitate Tn (n>1)?T1 NIR transitions or modify the resonance enhancement of C2H Ø-state production. Extra lines in the V03K01 subband, due to an S1 anharmonic perturber, show dramatically diminished NIR but enhanced UV emission intensity. This indicates that the perturbing state is anomalously resistant to photodissociation.

Drucker, Stephen; O'Brien, Jonathan P.; Patel, Paresh; Field, Robert W.

1997-02-01

24

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

25

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

NASA Astrophysics Data System (ADS)

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

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

2010-06-01

26

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

NASA Astrophysics Data System (ADS)

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

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

2013-03-01

27

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|=0.0370-0.0373cm(-1)/|E|=0.00373-0.00375cm(-1) and |D|=0.0381-0.0385cm(-1)/|E|=0.00393-0.00389cm(-1), are coupled by singlet energy transfer with chlorophylls which have a red-shifted emission peaking at 705nm. 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

28

Energy splitting between triplet and singlet exciplex states determined with E-type delayed fluorescence  

NASA Astrophysics Data System (ADS)

In the redox system with N, N-diethylaniline as electron donor and 1,4-dicyanobenzene as electron acceptor the singlet and triplet exciplex states in the nonpolar solvent methylcyclohexane are almost degenerate. The lowest excited state is the triplet exciplex state from which the singlet exciplex state is populated in a fast endothermic reaction. The energy splitting has been determined experimentally as ? E ? 0.1 eV via E-type delayed fluorescence.

Frederichs, Bernd; Staerk, Hubert

2008-07-01

29

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

30

Singlet-Triplet Mixing in the n=3 States of Helium  

Microsoft Academic Search

We have measured the energy-independent ratio of the proton apparent-excitation cross sections between corresponding triplet and singlet states of helium for the n=3 level. In the Russell-Saunders description of the states of helium, proton excitation of triplet states is forbidden; i. e., DeltaS=1 transitions are not allowed (Wigner spin rule). However, the spin-orbit interaction for the two electrons in helium

Daniel Krause; Edward A. Soltysik

1972-01-01

31

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

32

(?*,?*), (?*,?*) and Rydberg triplet excited states of hydrogen peroxide and other molecules bearing two adjacent heteroatoms.  

PubMed

The properties of the lowest triplet excited states of a series of small molecules containing two or more adjacent heteroatoms have been investigated. High-level coupled cluster and MRCI+Q calculations were employed to probe the properties of the triplet excited states of hydrogen peroxide, hydrazine, hydroxylamine, fluoroamines, oxygen difluoride, hypofluorous acid, chlorine, fluorine, and disulfane. All of the molecules investigated except hydroxylamine are predicted to have bound lowest triplet excited states that are either (?*,?*) or (?*,?*) as in H2O2, HOF, OF2, H2S2, Cl2, NH2F, NHF2, or NF3, or are Rydberg states (hydrazine, also H2O2 and H2S2). The heteroatom-heteroatom bond dissociation enthalpies of the triplet states range from very small values as predicted for hydrogen peroxide or fluorine, to BDEs around 8-9 kcal mol(-1) that should allow for an experimental observation of the triplet state, such as in disulfane or monofluoroamine. For all triplet minima investigated except NF3 and F2, CCSD(T) gave results in agreement with the multireference method MRCI+Q, and in excellent agreement with available experimental data (BDEs, ground-state geometries). Due to multireference problems, CCSD(T) does not provide a good description for longer heteroatom-heteroatom distances, and in some cases (e.g., Cl2) it wrongly predicts the presence of a transition state for bond formation on the triplet spin manifold, where the reaction is known experimentally and, as predicted by MRCI+Q, is known to be barrierless. Finally, the (3)?(u) state of F2 is poorly described by CCSD(T) theory, the equilibrium bond distance is significantly underestimated relative to MRCI+Q, and CCSD(T) places the triplet state above the energy of two fluorine atoms. The T1 diagnostic, frequently used to assess the quality of CCSD(T) calculations, does not appear to provide a valid criterion for the systems studied. The formation of H2O2 on the triplet potential energy hypersurface might possibly open up an additional channel for formation of hydrogen peroxide from two hydroxyl radicals. Due to a low density of states in triplet H2O2, and due to competing formation of water + O((3)P) from a hydrogen-bridged HO···HO triplet radical pair, such a reaction channel probably only can play a role at low temperatures. PMID:24592897

Hill, J Grant; Bucher, Götz

2014-03-27

33

Radical cations and triplet states of 1,2-disubstituted cyclopropanes: comparison of potential surfaces.  

PubMed

Radical ion pairs generated by photo-induced electron transfer from 1,2-disubstituted cyclopropanes to various acceptors undergo return electron transfer in pairs of singlet and triplet multiplicity. The pair energies relative to the reactant ground states and to accessible triplet states, respectively, determine the competition between the recombination pathways. The potential surfaces of the radical cations and triplet states of 1,2-diphenyl-, 1, and 1,2-dimethylcyclopropane, 2, have been examined by density functional theory calculations. The radical cation surfaces have minima at geometries that retain significant bonding between C-1 and C-2, preventing geometric isomerization of the radical cations. The triplet potential surfaces are dissociative with minimal rotational differentiation at long distances between C-1 and C-2. PMID:22223030

Roth, Heinz D; Sauers, Ronald R

2012-06-01

34

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

SciTech Connect

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

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

2013-12-04

35

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

NASA Astrophysics Data System (ADS)

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

Ezhevskii, Alexander A.; Popkov, Sergey A.; Soukhorukov, Andrey V.; Guseinov, Davud V.; Abrosimov, Nikolai V.; Riemann, Helge; Konakov, Anton A.

2013-12-01

36

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

PubMed

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

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

2013-10-01

37

Determination of the triplet state energies of a series of conjugated porphyrin oligomers.  

PubMed

We report a systematic study of the photophysical parameters relevant to photodynamic therapy (PDT) by a new type of sensitizers, conjugated porphyrin oligomers. Due to the strong nonlinear properties of oligomers containing 2, 4 and 8 porphyrin units, these molecules are attractive candidates for PDT via multiphoton excitation. The triplet state energy levels for all molecules have been determined by the triplet quenching method, phosphorescence measurements and DFT calculations. We find that the triplet energies of all the oligomers are sufficient to generate singlet oxygen, >94 kJ mol(-1). However, low singlet oxygen quantum yields are observed for the tetramer and the octamer, as compared to the conjugated dimer and monomeric porphyrin, reflecting the decrease in triplet yield. Thus the conjugated porphyrin dimer is the most promising core structure for PDT applications via multiphoton excitation. PMID:17549270

Kuimova, Marina K; Hoffmann, Markus; Winters, Mikael U; Eng, Mattias; Balaz, Milan; Clark, Ian P; Collins, Hazel A; Tavender, Susan M; Wilson, Craig J; Albinsson, Bo; Anderson, Harry L; Parker, Anthony W; Phillips, David

2007-06-01

38

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

PubMed

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

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

2011-10-01

39

Non-adiabatic charge state transitions in singlet-triplet qubits  

NASA Astrophysics Data System (ADS)

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

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

2013-10-01

40

Vibrational states of the triplet electronic state of H3+. The role of non-adiabatic coupling and geometrical phase  

E-print Network

Vibrational energies and wave functions of the triplet state of the H3+ ion have been determined. In the calculations, the ground and first excited triplet electronic states are included as well as the non-Born-Oppenheimer coupling between them. A diabatization procedure transforming the two adiabatic ab initio potential energy surfaces of the triplet-H3+ state into a 2x2 matrix is employed. The diabatization takes into account the non-Born-Oppenheimer coupling and the effect of the geometrical phase due to the conical intersection between the two adiabatic potential surfaces. The results are compared to the calculation involving only the lowest adiabatic potential energy surface of the triplet-H3+ ion and neglecting the geometrical phase. The energy difference between results with and without the non-adiabatic coupling and the geometrical phase is about a wave number for the lowest vibrational levels.

Alijah, Alexander

2015-01-01

41

Photophysics of protoporphyrin ions in vacuo: Triplet-state lifetimes and quantum yields  

NASA Astrophysics Data System (ADS)

Lifetimes of triplet-state molecules and triplet quantum yields are important parameters in photobiology as they determine the generation of singlet-oxygen upon irradiation with visible light. Here we report lifetimes of protoporphyrin IX (pp) in vacuo measured in an ion storage ring. We find that after 532 nm photon absorption, pp- (free base and negatively charged carboxylate) and pp+ (single protonation of ring nitrogen) have triplet-state lifetimes of 12 and 6 ms, respectively. After 415 or 390 nm absorption the lifetime of the anion is shorter (1.5 and 0.6 ms) as expected from the increase in temperature. Triplet quantum yields of pp- and pp+ are similar, 0.6-0.7, close to values reported for the free base and monocation in solution. The other channel, direct decay to the electronic ground state and subsequent dissociation of vibrationally excited ions, is much faster than triplet-singlet intersystem crossing. We measured lifetimes of 63 ?s, 96 ?s, and 0.3 ms after 390, 415, and 532 nm excitation, respectively. A fit of a statistical model to the pp- decay results in an Arrhenius activation energy of 0.5±0.2 eV for CO2 loss and a low preexponential factor (106-1010 s-1), indicative of an entropic barrier.

Calvo, M. Reyes; Andersen, Jens Ulrik; Hvelplund, Preben; Nielsen, Steen Brøndsted; Pedersen, Ulrik V.; Rangama, Jimmy; Tomita, Shigeo; Forster, James S.

2004-03-01

42

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

43

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

SciTech Connect

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

2014-04-07

44

Statistical mechanics for unstable states in Gel'fand triplets and investigations of parabolic potential barriers  

Microsoft Academic Search

Free energies and other thermodynamical quantities are investigated in canonical and grand canonical ensembles of statistical mechanics involving unstable states which are described by the generalized eigenstates with complex energy eigenvalues in the conjugate space of Gel'fand triplet. The theory is applied to the systems containing parabolic potential barriers (PPB's). The entropy and energy productions from PPB systems are studied.

Tsunehiro Kobayashi; Toshiki Shimbori

2001-01-01

45

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

46

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

47

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

48

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

SciTech Connect

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

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

2006-06-19

49

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

50

Singlet and Triplet Excited States of Emissive, Conjugated Bis(porphyrin) Compounds Probed by Optical and EPR Spectroscopic  

E-print Network

by Optical and EPR Spectroscopic Methods Rene´e Shediac, Mike H. B. Gray, H. Tetsuo Uyeda, Robert C. Johnson), electroabsorption (Stark), and transient triplet-triplet absorption spectroscopic methods. Pump-probe fluorescence emitting states polarized exclusively along the axis defined by the ethyne moiety. Stark spectroscopic

51

Forbidden nuclear magnetic resonance transitions between singlet and triplet states in spin- 1/2 pair systems in rotating solids  

NASA Astrophysics Data System (ADS)

Forbidden transitions between singlet and triplet nuclear spin states in chemically equivalent spin- 1/2 pair systems were observed in the 31P cross-polarization magic-angle spinning (CPMAS) nuclear magnetic resonance (NMR) spectrum of 1,2-bis (2,4,6-tri-tert-butylphenyl) diphosphene (TBPDP). The fine structure of the resonance lines changed dramatically with rotor spinning frequency. Using the average Hamiltonian theory, the origin of these singular phenomena was revealed to be due to high-order anisotropic interactions in the solid state. From analysis of the spectra, the value of the J coupling between the chemically equivalent 31P nuclei in TBPDP was estimated to be 577 ± 15 Hz.

Nakai, Toshihito; Challoner, Robin; McDowell, Charles A.

1991-05-01

52

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

SciTech Connect

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

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

2003-08-01

53

The triplet-state lifetime of indole derivatives in aqueous solution.  

PubMed

An important feature of tryptophan phosphorescence, crucial for probing protein structure and dynamics, is the drastic reduction of the lifetime (tau) in fluid solutions. Initial reports of indole and derivatives showed that tau decreases from 6 s in rigid glasses to about 1 ms in aqueous solutions at ambient temperature. Recently a report by Fischer et al. questioned the validity of the millisecond lifetime, claiming that in millimolar electrolyte solutions tau is about 40 micros, similar to the 12-30 micros of earlier determinations based on flash photolysis. Longer lived phosphorescence was detected in pure water but because it exhibited an initial growing phase and an anomalously large triplet yield, the emission was attributed to an artifact arising from the slow, first-order, geminate recombination of the radical cation and electron generated by photochemistry. In this study, we reexamine both the phosphorescence lifetime and the triplet quantum yield of indole, N-acetyl tryptophanamide (NATA), N-methyl tryptophan and the tryptophan-glycine-glycine tripeptide under the same conditions adopted by Fischer et al. as well as over a wider range of electrolyte and buffering salts concentrations, pH, solvent and temperature. Throughout, the results show that the phosphorescence decay is slow and uniform down to the 12 micros resolution of the instrument, with no evidence of short-lived, 40 micros-like components. Most compelling was the similarity between the fluorescence-normalized triplet yield of indole derivatives in water and that of W59 in the protein ribonuclease T1 or of NATA in rigid glasses. Its invariance over experimental conditions that varied the production of photoproducts several fold and the characteristic susceptibility of the triplet lifetime to O2, proton and ground state quenching demonstrated that the triplet state was formed predominantly through normal intersystem crossing and that its unquenched lifetime was at least 9 ms. PMID:15623331

Strambini, Giovanni B; Kerwin, Bruce A; Mason, Bruce D; Gonnelli, Margherita

2004-01-01

54

Reactivity of the NO dimer: on the role of the triplet electronic states.  

PubMed

We performed ab initio calculations to investigate the lowest triplet and singlet electronic states of the NO dimer and their mutual spin-orbit couplings. The electronic structure calculations are done using multiconfigurational approaches and a large diffuse basis set. A high density of electronic states is found favoring their mutual interactions by vibronic and spin-orbit couplings. We used our potential curves and spin-orbit couplings to discuss the mechanisms for the IR dissociation and the UV photodissociation of the NO dimer and the electronic de-excitation of NO (A(2)Sigma(+)) after collision with NO (X(2)Pi). For these reactions, multistep pathways, which involve the long-range and the molecular regions of the potential energy surfaces of the triplet and singlet electronic states of N(2)O(2), are suggested. A qualitative agreement between our findings and previous experimental assumptions is found. PMID:19743862

Marouani, S; Bahri, M; Batis, H; Hochlaf, M

2010-03-11

55

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

SciTech Connect

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

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

2010-04-15

56

Repopulation of nitrogen excited triplet state following laser-induced filamentation.  

PubMed

Laser-induced filamentation was used to study the dynamics of excited molecular nitrogen decay processes. It is well-known that upper excited nitrogen triplet states can be repopulated at time delays far longer than their fluorescence lifetimes. Examination of the time-resolved emission from several different species indicates that there are two major mechanisms acting to repopulate the N2(C(3)?u) excited state. The results implicate dissociative electron recombination with the nitrogen cation dimer, N4(+), and energy pooling between two N2(A(3)?u(+)) triplet states as the main pathways to repopulate the emissive upper triplet state. The densities of N2(A(3)?u(+)) and free electrons produced during filamentation were measured under atmospheric pressures in nitrogen and estimated to be [N2(A(3)?u(+))]0 = 3 × 10(15) cm(–3) and [e(–)]0 = 3 × 10(13) cm(–3). The methods outlined in this report could find significant utility in measuring the concentration profiles of these important reactive intermediates within laser-induced filaments produced under different conditions. PMID:24991979

Arnold, Bradley R; Roberson, Stephen D; Pellegrino, Paul M

2014-11-13

57

Statistical mechanics for unstable states in Gel'fand triplets and investigations of parabolic potential barriers.  

PubMed

Free energies and other thermodynamical quantities are investigated in canonical and grand canonical ensembles of statistical mechanics involving unstable states which are described by the generalized eigenstates with complex energy eigenvalues in the conjugate space of Gel'fand triplet. The theory is applied to the systems containing parabolic potential barriers (PPB's). The entropy and energy productions from PPB systems are studied. An equilibrium for a chemical process described by reactions A+CB <==>AC+B is also discussed. PMID:11414955

Kobayashi, T; Shimbori, T

2001-05-01

58

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

NASA Astrophysics Data System (ADS)

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

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

1998-05-01

59

Spectrum and polarization of helium doubly excited triplet states  

NASA Astrophysics Data System (ADS)

The beam-foil spectrum of helium from 2050 to 3600 Å has been acquired at 160-keV incident ion energy using a multiple-scan, computerized system. Eleven doubly-excited-state transitions, including two not previously observed, have been assigned, and the agreement between experimental and theoretical energy levels is excellent. The Stokes parameters as a function of foil-tilt angle have been measured for the two strongest transitions (2578 and 3013 Å) from 0° to 80° in 10° increments and for two weaker transitions (2562 and 2818 Å) at 0°, 20°, 40°, and 60°. The polarization patterns are quite different from those of the helium singlets and include the first measurement of negative MI (a Stokes parameter) at 0° foil tilt for helium at this energy. The lifetime of the 2578-Å transition has been investigated in detail. The present result, 0.109+/-0.004 ns, agrees with previous measurements and yields an upper limit to the autoionization width of the 2p3p 3D levels of 6×10-6 eV.

Brooks, Robert L.; Pinnington, Eric H.

1980-08-01

60

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

NASA Astrophysics Data System (ADS)

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

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

2014-08-01

61

Collective Modes and Spin Fluctuations for Spin-Triplet Superconducting State in Sr 2 RuO 4  

Microsoft Academic Search

First we calculate the collective order parameter modes for the most promising candidates of spin-triplet p-wave pairing states in the layered perovskite structure of Sr2RuO4. The pairing interaction and accordingly the equations for the order parameter fluctuations are decomposed in terms of spin-triplet pairing states corresponding to the irreducible representations of the point group D4h. Asymmetric pairing interaction and spin-orbit

L. Tewordt

1999-01-01

62

A spectroscopic and computational study of the singlet and triplet excited states of synthetic ?-functionalized chlorins  

NASA Astrophysics Data System (ADS)

This paper presents a comparative investigation of the absorption, fluorescence, electron paramagnetic resonance (EPR), and transient triplet-triplet absorption spectroscopic properties and triplet state dynamics of two functionalized, synthetic, meso-phenylchlorins. The chromophores investigated are the novel 2-hydroxy-3-oxa-5,10,15,20-tetrakisphenylchlorin ( 3) and the known 2,3-dioxo-5,10,15,20-tetrakisphenylchlorin ( 4). In these chromophores, one peripheral ?CH?CH? bond of the parent porphyrin meso-tetrakisphenylporphyrin (TPP, 1) was formally replaced by a ?CH(OH)O? (lactol) or a ?-diketone moiety. The spectroscopic data are compared with results from investigations on the parent porphyrin TPP studied here and the parent chlorin 5,10,15,20-tetrakisphenylchlorin (TPC, 2) from the literature. The spectroscopic observables are examined both qualitatively within the framework of the four orbital model and quantitatively using MNDO-PSDCI methods. The results delineate the role of ?-lactol and ?-dicarbonyl moieties in controlling the electronic and spectroscopic properties of these chromophores. This investigation serves as the foundation from which to derive a general understanding of the effects of ?-functionalization on the electronic properties of chlorin-type chromophores. This knowledge is required for the design and understanding of long-wavelength absorbing and fluorescing chromophores to be used in light harvesting systems and photomedicine.

Brückner, Christian; McCarthy, Jason R.; Daniell, Heather W.; Pendon, Zeus D.; Ilagan, Robielyn P.; Francis, Tasha M.; Ren, Lei; Birge, Robert R.; Frank, Harry A.

2003-11-01

63

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

Microsoft Academic Search

In this work, the spectroscopic characteristics of carotenoids associated with the antenna complexes of Photosystem I have been studied. Pigment composition, absorption spectra, and laser-induced triplet-minus-singlet (T-S) spectra were determined for native LHCI from the wild type (WT) and lut2 mutant from Arabidopsis thaliana as well as for reconstituted individual Lhca WT and mutated complexes. All WT complexes bind lutein

Roberta Croce; Milena Mozzo; Tomas Morosinotto; Alessandro Romeo; Rainer Hienerwadel; Roberto Bassi

2007-01-01

64

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

NASA Astrophysics Data System (ADS)

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

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

1992-02-01

65

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

66

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

NASA Astrophysics Data System (ADS)

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

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

2012-12-01

67

Optimal values of rovibronic energy levels for triplet electronic states of molecular deuterium  

NASA Astrophysics Data System (ADS)

An optimal set of 1050 rovibronic energy levels for 35 triplet electronic states of D2 has been obtained by means of a statistical analysis of all available wavenumbers of triplet-triplet rovibronic transitions studied in emission, absorption, laser and anticrossing spectroscopic experiments of various authors. We used a new method of analysis (Lavrov and Ryazanov 2005 JETP Lett. 81 371-4), which does not need any a priori assumptions concerning the molecular structure, being based on only two fundamental principles: Rydberg-Ritz and maximum likelihood. The method provides the opportunity to obtain the root-mean-square estimates for uncertainties of the experimental wavenumbers independent from those presented in the original papers. A total of 234 from 3822 published wavenumber values were found to be spurious, while the remaining set of the data may be divided into 20 subsets (samples) of uniformly precise data having close to normal distributions of random errors within the samples. New experimental wavenumber values of 125 questionable lines were obtained in the present work. Optimal values of the rovibronic levels were obtained from the experimental data set consisting of 3713 wavenumber values (3588 old and 125 new). The unknown shift between levels of ortho- and para-deuterium was found by least-squares analysis of the a3?+g, v = 0, N = 0 ÷ 18 rovibronic levels with odd and even values of N. All the energy levels were obtained relative to the lowest vibro-rotational level (v = 0, N = 0) of the a3?+g electronic state, and presented in tabular form together with the standard deviations of the empirical determination. New energy-level values differ significantly from those available in the literature.

Lavrov, B. P.; Umrikhin, I. S.

2008-05-01

68

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

69

Identification and reactivity of the triplet excited state of 5-hydroxytryptophan.  

PubMed

Both the neurotransmitter serotonin and the unnatural amino acid 5-hydroxytryptophan (5HT), contain the 5-hydroxyindole chromophore. The photochemistry of 5HT is being investigated in relation to the multiphoton excitation of this chromophore to produce a characteristic photoproduct with green fluorescence ('hyperluminescence'). Laser flash photolysis (308 nm) of 5HT in aqueous solution at neutral pH produces both the neutral 5-indoloxyl radical (lambda(max) 400-420 nm) and another transient absorption with lambda(max) 480 nm and lifetime of 2 micros in deaerated solutions. Based on quenching by oxygen and beta-carotene, the species at 480 nm is identified as the triplet excited state of 5HT. In acidic solution a new oxygen-insensitive intermediate with lambda(max) 460 is assigned to the radical cation of 5HT. Time-resolved measurements of luminescence at 1270 nm have shown that the triplet state of 5HT is able to react with oxygen to form singlet excited oxygen (1O2*) with a quantum yield of approximately 0.1. However, 5HT has also been found to be an effective quencher of singlet oxygen with a second order rate constant of 1.3 x 10(8) dm3 mol(-1) s(-1). The results are discussed in the light of recent observations on the multiphoton-excited photochemistry of serotonin. PMID:15708522

Dad, S; Bisby, R H; Clark, I P; Parker, A W

2005-03-01

70

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

NASA Astrophysics Data System (ADS)

Sapphyrin (Sap) and its stable dicationic form, Sap2+, originally prepared by Woodward and Johnson, are large porphyrin-like systems which exhibit unique chemical and photochemical properties which are directly related to the primary donor ("special pair") in primary photosynthesis. We report on the photoexcited triplet detection by time-resolved cw-EPR, of the dication dissolved in toluene, a nematic liquid crystal, and ethanol. In the former two solvents of low dielectric constants, the Sap2+ exists as a monomer, whereas in ethanol the stable form is the dimer, (Sap2+)2. The triplet state of the dimer exhibits a substantial reduction of both zero-field splitting (ZFS) parameters (D and E) as compared to the monomer. This observation is interpreted in terms of triplet spin delocalization (charge-transfer character) within the dimer, which may be considered as a supermolecule. Moreover, the triplet-EPR line shape of (Sap2+)T oriented in the liquid crystal indicates that, unlike other known porphyrinoid systems, the ZFS term, D, is associated with the in-plane, head-to-tail, alignment of the triplet electron spins. These unusual triplet properties suggest a negative value of the ZFS parameter D for the monomer and dimer.

Levanon, Haim; Regev, Ayelet; Michaeli, Shalom; Galili, Tamar; Cyr, Mike; Sessler, Jonathan L.

1990-11-01

71

J-state interference signatures in the Second Solar Spectrum: Modeling the Cr I triplet at 5204-5208 A  

E-print Network

The scattering polarization in the solar spectrum is traditionally modeled with each spectral line treated separately, but this is generally inadequate for multiplets where J-state interference plays a significant role. Through simultaneous observations of all the 3 lines of a Cr I triplet, combined with realistic radiative transfer modeling of the data, we show that it is necessary to include J-state interference consistently when modeling lines with partially interacting fine structure components. Polarized line formation theory that includes J-state interference effects together with partial frequency redistribution for a two-term atom is used to model the observations. Collisional frequency redistribution is also accounted for. We show that the resonance polarization in the Cr I triplet is strongly affected by the partial frequency redistribution effects in the line core and near wing peaks. The Cr I triplet is quite sensitive to the temperature structure of the photospheric layers. Our complete frequency...

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

2012-01-01

72

Laser Spectroscopy of ZrO: Accurate Term Energies for the Triplet States  

NASA Astrophysics Data System (ADS)

The wavelength-resolved fluorescence excitation technique has been used to record the (0, 0) bands of the satellite e3? 1- a3? 1 and e3? 2- a3? 2 transitions of ZrO at a resolution of 0.03 cm -1. These data were combined with previous high-resolution analyses of the ZrO B system (B. Simard et al., Faraday Discuss. Chem. Sec.86, 163-180, 1988) and with the analysis of the intercombination e3? 1- X1? + transition (P. D. Hammer and S. P. Davis, Astrophys. J. Lett.237, 51-53, 1980) to obtain accurate term energies for the triplet states of 90Zr 16O. Ligand field theory calculations were used to suggest electronic configurations for the excited states of ZrO.

Kaledin, L. A.; Mccord, J. E.; Heaven, M. C.

1995-11-01

73

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

74

Two-qubit couplings of singlet-triplet qubits mediated by one quantum state  

NASA Astrophysics Data System (ADS)

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 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.

Mehl, Sebastian; Bluhm, Hendrik; DiVincenzo, David P.

2014-07-01

75

Triplet-state photophysics of naphthalene and. alpha. ,. omega. -diphenylpolyenes included in heavy-cation-exchanged zeolites  

SciTech Connect

Heavy-cation-exchanged zeolites offer a powerful new medium for observing external heavy-atom perturbation of organic triplet states. In this Letter the authors report the use of optically detected magnetic resonance measurements to determine the geometric mode of interaction between the perturbing heavy atom and naphthalene within the X- and Y-type faujasites exchanged with K{sup +}, Rb{sup +}, and Cs{sup +}. Building upon these results, the authors demonstrate the use of the heavy-cation-exchanged zeolites as spectroscopic matrices enabling the detection of triplet phosphorescence from a series of all-trans-{alpha},{omega}-diphenylpolyenes for which phosphorescence has not been previously observed.

Ramamurthy, V.; Caspar, J.V.; Corbin, D.R. (E.I. du Pont de Nemours and Co., Wilmington, DE (USA)); Schlyer, B.D.; Maki, A.H. (Univ. of California, Davis (USA))

1990-05-03

76

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

SciTech Connect

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

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

2013-01-01

77

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

78

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

NASA Astrophysics Data System (ADS)

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

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

1998-12-01

79

Influence of substitution on the T-T absorption spectra in furocoumarins  

NASA Astrophysics Data System (ADS)

The present paper deals with compounds called photosensitizers, namely, psoralen, 3,4-phenyl-4',5'- cyclohexylpsoralen, 4'-methyl-3,4-cycloheptyl psoralen, 4',5'-dimethyl-3,4-cyclohexyl psoralen (fig. 1). The absorption spectra from excited triplets states were investigated. The computed triplet-triplet absorption spectra of research compounds have been determined using INDO method. The experimental triplet-triplet absorption spectra have been obtained using the technique of laser flash photolysis in ethanol. The compare of computed and experimental data is shows that the computed second band wavelenght throughout agree very well (0,5-6 nm) with experimental data.

Bryantseva, N. G.

2006-11-01

80

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

81

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

82

Thermodynamic changes in the photoinduced proton-transfer reaction of the triplet state of safranine-T.  

PubMed

The enthalpy and volume changes occurring in the triplet excited state proton-transfer reactions of safranine-T (SH+) in aqueous solutions at pH 4.8, 8.3, and 10.4 were investigated using time-resolved photoacoustics (TRP). The transient triplet state species were also studied using laser-flash photolysis (LFP). The LFP experiments showed the prompt formation of 3SH+ with a triplet quantum yield phiT = 0.28 between pH 4.8 and 10.4. At pH 8.3 3SH+ decays directly to the ground state. However, at pH 4.8 and 10.4, 3SH+ reacts with protons or hydroxy ions to form the dication 3SH2(2+) or the neutral 3S species, with diffusion-controlled rate constants of kH+ = 1.6 x 10(10) M(-1) s(-1), and kHO- = 2.6 x 10(10) M(-1) s(-1), respectively. Under the same experimental conditions, the TRP measurements allowed the accurate determination of the energy content of the rapidly formed triplet state 3SH+ i.e. E(T) = 175 kJ mol(-1). The slow component (0.1-3 micros) of the TRP signal at pH 4.8 and 10.4 was attributed to the formation of the species 3SH2(2+) and 3S, respectively. The enthalpy changes associated with the proton-transfer reactions of 3SH+, calculated from the values of the heat released as obtained by TRP, were in remarkable agreement with the values estimated from the thermodynamic data of the acid-base equilibria of the triplet states of the dye. The formation of 3SH+ was accompanied by a volume expansion of 1.8 cm3 mol(-1), which was explained by changes in the hydrogen-bonding interaction of the dye with its solvation sphere. Instead, the volume changes observed upon the formation of 3SH2(2-) and 3S accounted for the electrostrictive effect produced by the change in the charge distribution on the dye after the proton-transfer reaction. PMID:12659500

Borsarelli, Claudio D; Bertolotti, Sonia G; Previtali, Carlos M

2002-08-01

83

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

84

Laboratory Detection of HC6N, a Carbon Chain with a Triplet Electronic Ground State  

NASA Astrophysics Data System (ADS)

A linear triplet isomer of HC6N has been detected by Fourier transform microwave spectroscopy in a supersonic molecular beam. A total of 85 hyperfine components from six rotational transitions between 8 and 18 GHz were measured to an uncertainty of 5 kHz; a similar set of transitions were detected for the 15N isotopic species, produced using an isotopically enriched precursor gas sample. The spectroscopic constants for both species, including the fine and hyperfine coupling constants, were determined to very high accuracy, and these allow calculation of the radio spectrum to a fraction of 1 km s-1 in equivalent radial velocity. Triplet HC6N is a highly polar, low-lying isomer; measurements show it to be about 10 times more abundant than a ring-chain isomer recently detected with the same spectrometer.

Gordon, V. D.; McCarthy, M. C.; Apponi, A. J.; Thaddeus, P.

2000-09-01

85

The long-lived triplet excited state of an elongated ketoprofen derivative and its interactions with amino acids and nucleosides.  

PubMed

The aim of the present work was to find a ketoprofen (KP) equivalent suitable for time-resolved studies on the interactions of its KP-like triplet state with biomolecules or their simple building blocks, under physiologically relevant conditions. Such a compound should fulfill the following requirements: (i) it should be soluble in aqueous media; (ii) its triplet lifetime should be longer than that of KP, ideally in the microsecond range; and (iii) its photodecarboxylation should be slow enough to avoid interference in the time-resolved studies associated with formation of photoproducts. Here, the glycine derivative of ketoprofen (KPGly) has been found to fulfill all the above requirements. In a first stage, the attention has been focused on the photophysical and photochemical properties of KPGly, and then on its excited-state interactions with key amino acids and nucleosides. In acetonitrile, the typical benzophenone-like triplet-triplet absorption (3KPGly) with lambda(max) at 520 nm and a lifetime of 5.3 micros was observed. This value is very close to that of 3KP (5.6 micros) obtained under the same conditions. In methanol, the 3KPGly features were also close to those of 3KP with detection of a short-lived triplet state that evolves to give a ketyl radical. By contrast with the behavior of KP, in deaerated aqueous solutions at pH = 7.4, the transient detected in the case of KPGly displayed two bands at lambda(max) at 330 and 520 nm, very similar to those observed in acetonitrile solution but with a lifetime of 7.5 micros at 520 nm. Hence, it was assigned to the KPGly triplet. In the case of KP, efficient decarboxylation occurs in the subnanosecond time scale, via intramolecular electron transfer. This process gives rise to a detectable carbanion intermediate (lifetime approximately 250 ns) and prevents detection of the shorter-lived 3KP signal. In a second stage, the attention has been focused on the excited-state interactions between 3KPGly and amino acids or nucleosides; for this purpose, 2'-deoxyguanosine (dGuo), thymidine (Thd), tryptophan (Trp), and tyrosine (Tyr) have been chosen as photosensitization targets. In general, efficient quenching (rate constant kq > 109 M(-1) x s(-1)) was observed; it was attributed for dGuo, Tyr, and Trp to a photochemical reaction involving initial electron transfer from the biological target to 3KPGly, followed by proton transfer from the amino acid or the nucleoside radical cation to KPGly-*. As a matter of fact, ketyl radical together with guanosinyl, tyrosinyl, or tryptophanyl radicals were detected; this supports the proposed mechanism. The results with Thd were somewhat different, as the efficient 3KPGly quenching was ascribed to oxetane formation by a Paterno Büchi photocycloaddition. PMID:17590040

Lhiaubet-Vallet, Virginie; Belmadoui, Noureddine; Climent, Maria J; Miranda, Miguel A

2007-07-19

86

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

87

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

PubMed

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

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

2013-09-01

88

Singlet and triplet state transitions of carotenoids in the antenna complexes of higher-plant photosystem I.  

PubMed

In this work, the spectroscopic characteristics of carotenoids associated with the antenna complexes of Photosystem I have been studied. Pigment composition, absorption spectra, and laser-induced triplet-minus-singlet (T-S) spectra were determined for native LHCI from the wild type (WT) and lut2 mutant from Arabidopsis thaliana as well as for reconstituted individual Lhca WT and mutated complexes. All WT complexes bind lutein and violaxanthin, while beta-carotene was found to be associated only with the native LHCI preparation and recombinant Lhca3. In the native complexes, the main lutein absorption bands are located at 492 and 510 nm. It is shown that violaxanthin is able to occupy all lutein binding sites, but its absorption is blue-shifted to 487 and 501 nm. The "red" lutein absorbing at 510 nm was found to be associated with Lhca3 and Lhca4 which also show a second carotenoid, peaking around 490 nm. Both these xanthophylls are involved in triplet quenching and show two T-S maxima: one at 507 nm (corresponding to the 490 nm singlet absorption) and the second at 525 nm (with absorption at 510 nm). The "blue"-absorbing xanthophyll is located in site L1 and can receive triplets from chlorophylls (Chl) 1012, 1011, and possibly 1013. The red-shifted spectral component is assigned to a lutein molecule located in the L2 site. A 510 nm lutein was also observed in the trimers of LHCII but was absent in the monomers. In the case of Lhca, the 510 nm band is present in both the monomeric and dimeric complexes. We suggest that the large red shift observed for this xanthophyll is due to interaction with the neighbor Chl 1015. In the native T-S spectrum, the contribution of carotenoids associated with Lhca2 is visible while the one of Lhca1 is not. This suggests that in the Lhca2-Lhca3 heterodimeric complex energy equilibration is not complete at least on a fast time scale. PMID:17326666

Croce, Roberta; Mozzo, Milena; Morosinotto, Tomas; Romeo, Alessandro; Hienerwadel, Rainer; Bassi, Roberto

2007-03-27

89

DFT spin-orbit coupling between singlet and triplet excited states: A case of psoralen compounds  

NASA Astrophysics Data System (ADS)

We present a computational protocol in which our method is used to compute spin-orbit (SO) matrix elements on time-dependent-density functional theory (TD-DFT). These SO contributions, computed employing our SO program package, MolSOC, have been expressed, in turn, in terms of weighted coefficients and SO matrix elements between singlet and triplet wave functions arising from a given one-electron transition. The protocol has been applied to study psoralen compound and its derivatives obtained from the replacement of one oxygen with sulfur or selenium. The obtained results have been compared with those reported in literature.

Chiodo, Sandro G.; Russo, Nino

2010-04-01

90

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

91

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

92

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

93

Heteroatom effects in XC5H5C Arduengo-type carbenes (X = CH, N, P, and As) in singlet and triplet states  

NASA Astrophysics Data System (ADS)

Internal energy difference, ? E s-t; enthalpy difference, ? H s-t; Gibbs free energy difference, ? G s-t, between the singlet (s) and triplet states (t) of XC5H5C, 1X (X = CH, N, P, and As) were computed at B3LYP/6-311++G** and MP2/6-311++G**//B3LYP/6-311++G** levels of theory. The ? G s-t between the singlet and triplet states of 1 X were changed in the order: 1 P > 1 As > 1 N .

Vessally, Esmail; Poorheravi, Mohammad Reza; Edjlali, Ladan; Motallebzadeh, Maryam

2014-07-01

94

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

PubMed

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

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

2014-11-13

95

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

PubMed

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

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

2013-09-17

96

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

97

Time-dependent density-functional theory calculations of triplet-triplet absorption  

Microsoft Academic Search

We present density-functional theory calculations of triplet-triplet absorption by three different approaches based on time-dependent density-functional theory (DFT): unrestricted DFT linear response, open-shell restricted DFT linear response applied to the triplet state, and quadratic response with triplet excitations applied to the ground state. Comparison is also made with corresponding results obtained by Hartree-Fock and multiconfiguration self-consistent-field response theory. Two main

Peter Cronstrand; Zilvinas Rinkevicius; Yi Luo; Hans Gren

2005-01-01

98

Benchmark calculations on the lowest-energy singlet, triplet, and quintet states of the four-electron harmonium atom.  

PubMed

For a wide range of confinement strengths ?, explicitly-correlated calculations afford approximate energies E(?) of the ground and low-lying excited states of the four-electron harmonium atom that are within few ?hartree of the exact values, the errors in the respective energy components being only slightly higher. This level of accuracy constitutes an improvement of several orders of magnitude over the previously published data, establishing a set of benchmarks for stringent calibration and testing of approximate electronic structure methods. Its usefulness is further enhanced by the construction of differentiable approximants that allow for accurate computation of E(?) and its components for arbitrary values of ?. The diversity of the electronic states in question, which involve both single- and multideterminantal first-order wavefunctions, and the availability of the relevant natural spinorbitals and their occupation numbers make the present results particularly useful in research on approximate density-matrix functionals. The four-electron harmonium atom is found to possess the (3)P+ triplet ground state at strong confinements and the (5)S- quintet ground state at the weak ones, the energy crossing occurring at ??? 0.0240919. PMID:25084902

Cioslowski, Jerzy; Strasburger, Krzysztof; Matito, Eduard

2014-07-28

99

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

100

Exploring the triplet excited state potential energy surfaces of a cyclometalated Pt(II) complex: is there non-Kasha emissive behavior?  

PubMed

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

Escudero, Daniel; Thiel, Walter

2014-10-20

101

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

PubMed Central

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

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

2008-01-01

102

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

NASA Astrophysics Data System (ADS)

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

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

2014-09-01

103

Twofold spin-triplet pairing states and tunneling conductance in ferromagnet/ferromagnet/iron pnictide superconductor heterojunctions  

SciTech Connect

By applying an extended eight-component Bogoliubov–de Gennes equation, we study theoretically the tunneling conductance in clean ferromagnet/ferromagnet/iron pnictide superconductor (FM/FM/iron-based SC) heterojunctions. Under the condition of noncollinear magnetizations, twofold novel Andreev reflections exist due to the existence of two bands in the SC, in which the incident electron and the two Andreev-reflected holes, belonging to the same spin subband, form twofold spin-triplet pairing states near the FM/iron-based SC interface. It is shown that the conversions of the conductance not only between the zero-bias peak and valley at zero energy but also between the peaks and dips at two gap energies are strongly dependent on both the interband coupling strength in the SC and the spin polarization in the FM. The qualitative differences from tunneling into a conventional s-wave SC are also presented, which may help with experimentally probing and identifying the antiphase s-wave pairing symmetry in the iron-based SC. -- Highlights: •An eight-component Bogoliubov–de Gennes (BDG) equation. •Twofold novel ARs and twofold usual ARs. •Conversions of conductance between the zero-bias peak and valley at zero energy. •Conversions of conductance between peaks and dips at two gap energies. •The importance of the interband coupling strength in the SC.

Yang, X. [Department of Physics and Institute of Theoretical Physics, Nanjing Normal University, Nanjing 210023 (China)] [Department of Physics and Institute of Theoretical Physics, Nanjing Normal University, Nanjing 210023 (China); Tao, Y.C., E-mail: yctao88@163.com [Department of Physics and Institute of Theoretical Physics, Nanjing Normal University, Nanjing 210023 (China); Dong, Z.C. [Department of Physics, Nantong University, Nantong 226001 (China)] [Department of Physics, Nantong University, Nantong 226001 (China); Hu, J.G. [Department of Physics, Yangzhou University, Yangzhou 225002 (China)] [Department of Physics, Yangzhou University, Yangzhou 225002 (China)

2013-06-15

104

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

PubMed

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

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

2015-01-01

105

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

NASA Astrophysics Data System (ADS)

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

Kodet, John; Judge, Richard H.

2007-05-01

106

Wavelength-dependent photochemistry of W(CO){sub 4}(en) (en = ethylenediamine): Evidence for distinct chemical reactivities from singlet and triplet ligand field excited states  

SciTech Connect

Studies of the photophysical and photochemical properties of organometallic compounds have now been extensively performed for over 25 years. In considering the photoreactivity of such complexes, it has usually been assumed that their singlet excited states are extremely short-lived and unreactive as a consequence of effective intersystem crossing mechanisms facilitated by the heavy metal and rapid internal conversions to the ground state. In this paper the authors report quantitative photochemical measurements obtained for W(CO){sub 4}(en) (en = ethylenediamine) following excitation into the lowest energy LF absorption manifold at several wavelengths. This system is of particular significance because, unlike most other substituted metal carbonyl complexes, its lowest lying LF absorption band is well removed from other electronic transitions and the lowest energy LF triplet absorption is a distinctive feature of the spectrum. Following excitation at various wavelengths, therefore, it is possible to populate the LF single and triplet energy levels exclusively and determine their quantitative photochemical reactivities directly. The results for W(CO){sub 4}(en) demonstrate conclusively that the LF excited states undergo separate photosubstitutional pathways and that reaction from the lowest lying LF triplet state takes place with a substantially reduced photoefficiency.

Panesar, R.S.; Dunwoody, N.; Lees, A.J. [State Univ. of New York, Binghamton, NY (United States). Dept. of Chemistry] [State Univ. of New York, Binghamton, NY (United States). Dept. of Chemistry

1998-04-06

107

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

108

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

109

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

110

An R-matrix study of singlet and triplet continuum states of N2  

NASA Astrophysics Data System (ADS)

A systematic calculation of the positions and widths of the resonances converging on the first two excited states of N_2^+ (A ^2\\Pi _u and B ^2\\Sigma _u^+) is presented. A closely-spaced grid of geometries is used to give continuous resonance curves without the need for curve fitting. Three methods, fitting the eigenphase sum, the time-delay method and the R-matrix specific QB method, are tested. Fits to the longest three time-delays are found to give the most reliable and complete determination of the resonance parameters. The low excitation energies of the A and B ion states results in complex resonance features with many avoided crossings leading to pronounced structures in both the resonance curves and the associated widths. The resonance curves likely to be important for dissociative recombination are identified. Their positions generally agree well with the calculations of Guberman, although in some cases their widths are narrower. Full data on all curves is provided.

Little, Duncan A.; Tennyson, Jonathan

2014-05-01

111

Narrow energy gap between triplet and singlet excited states of Sn2+ in borate glass.  

PubMed

Transparent inorganic luminescent materials have attracted considerable scientific and industrial attention recently because of their high chemical durability and formability. However, photoluminescence dynamics of ns(2)-type ions in oxide glasses has not been well examined, even though they can exhibit high quantum efficiency. We report on the emission property of Sn(2+)-doped strontium borate glasses. Photoluminescence dynamics studies show that the peak energy of the emission spectrum changes with time because of site distribution of emission centre in glass. It is also found that the emission decay of the present glass consists of two processes: a faster S1-S0 transition and a slower T1-S0 relaxation, and also that the energy difference between T1 and S1 states was found to be much smaller than that of (Sn, Sr)B6O10 crystals. We emphasize that the narrow energy gap between the S1 and T1 states provides the glass phosphor a high quantum efficiency, comparable to commercial crystalline phosphors. PMID:24345869

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

2013-01-01

112

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

E-print Network

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

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

2011-03-08

113

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

114

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

115

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

116

Stereodifferentiating drug-biomolecule interactions in the triplet excited state: studies on supramolecular carprofen/protein systems and on carprofen-tryptophan model dyads.  

PubMed

Stereoselective interaction between a chiral nonsteroidal antiinflammatory drug, namely carprofen (CP), and human serum albumin (HSA) was studied, and the results were compared with those obtained with model dyads. In the presence of albumin the same triplet-triplet transition was detected for both CP stereoisomers; however, time-resolved measurements revealed a remarkable stereodifferentiation in the CP/HSA interaction. For each stereoisomer, the decay dynamics evidenced the presence of two components with different lifetimes that can be correlated with complexation of CP to the two possible albumin binding sites (site I and site II). This assignment was confirmed by using ibuprofen, a site II displacer. Thus, the shorter lived components, for which stereodifferentiation was more important (tauR/tauS ca. 4), were ascribed to the CP triplet state in site I; the lifetime shortening can be attributed to electron-transfer quenching by the only tryptophan (Trp) of the protein. Laser flash photolysis of model dyads containing covalently linked CP and Trp revealed formation of the expected Trp radical cation, providing support for such a mechanism. Moreover, significant stereodifferentiation was observed between the (R)- and (S)-CP-Trp dyads. In the case of CP/HSA complexes, as well as in the model compounds, the stereodifferentiation detected in the decays is in good agreement with that observed in the formation of the only CP photoproduct, resulting from a photodehalogenation process. Moreover, stereodifferentiation was also found to occur for the photobinding of CP to the protein. PMID:17214494

Lhiaubet-Vallet, Virginie; Boscá, Francisco; Miranda, Miguel A

2007-01-18

117

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

PubMed Central

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

Angiolillo, P J; Vanderkooi, J M

1995-01-01

118

Fractional quantum numbers deduced from experimental ground state meson spectra  

E-print Network

Based on the Caputo definition of the fractional derivative the ground state spectra of mesons are classified as multiplets of the fractional rotation group. The comparison with the experimental values leads to the conclusion, that quarks carry an up to now unrevealed fractional multiplicative quantum number, which we call fractional hyper charge.

Richard Herrmann

2010-03-26

119

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

120

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

121

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

122

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

123

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

SciTech Connect

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

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

1990-01-31

124

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

125

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

126

Spectra  

NSDL National Science Digital Library

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

Exploratorium, The

2012-06-26

127

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

PubMed Central

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

Ghosh, S; Petrin, M; Maki, A

1986-01-01

128

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

NASA Astrophysics Data System (ADS)

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

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

2013-02-01

129

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

E-print Network

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

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

2014-06-11

130

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

PubMed

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

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

2014-06-13

131

Single-Shot Readout and Relaxation of Singlet and Triplet States in Exchange-Coupled P31 Electron Spins in Silicon  

NASA Astrophysics Data System (ADS)

We present the experimental observation of a large exchange coupling J ?300 ?eV between two P31 electron spin qubits in silicon. The singlet and triplet states of the coupled spins are monitored in real time by a single-electron transistor, which detects ionization from tunnel-rate-dependent processes in the coupled spin system, yielding single-shot readout fidelities above 95%. The triplet to singlet relaxation time T1?4 ms at zero magnetic field agrees with the theoretical prediction for J-coupled P31 dimers in silicon. The time evolution of the two-electron state populations gives further insight into the valley-orbit eigenstates of the donor dimer, valley selection rules and relaxation rates, and the role of hyperfine interactions. These results pave the way to the realization of two-qubit quantum logic gates with spins in silicon and highlight the necessity to adopt gating schemes compatible with weak J-coupling strengths.

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

2014-06-01

132

Magnetic Field Effects: Triplet-Charge Annihilation versus Triplet-Triplet Annihilation in Organic Semiconductors  

NASA Astrophysics Data System (ADS)

Triplet-charge reaction and triplet-triplet annihilation are two important processes in generating magnetic field effects in organic semiconductors. This presentation reports experimental studies on triplet-charge annihilation (TCA) versus triplet-triplet annihilation (TTA) in organic semiconductors. Specifically, we separately adjust the triplet-charge and triplet-triplet interactions towards the generation of TCA and TTA by changing triplet density, charge confinement, and charge/exciton ratio based on organic light-emitting diodes. We then use magnetic field effects of electroluminescence (MFEEL) to study the TCA and TTA through spin interactions. We observe that the electroluminescence can clearly show negative response to applied magnetic field when triplets and charges are simultaneously confined within close proximity. On contrast, the electroluminescence only exhibits positive MFEEL when triplets are confined within close proximity. Therefore, it can be concluded that the TCA is a major process to annihilate triplets through Coulomb interaction in organic semiconductors.

Hu, Bin; Shao, Ming; Yan, Liang; Li, Mingxing

2012-02-01

133

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

134

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

PubMed

In accordance with previous studies in our group on Be, Mg, and Ca hypermetallic oxides, we find that SrOSr has a linear X?1?(g)+ ground electronic state and a very low lying first excited ã3?(u)+ triplet electronic state. No gas-phase spectrum of this molecule has been assigned yet, and to encourage and assist in its discovery we present a complete ab initio simulation, with absolute intensities, of the infrared absorption spectrum for both electronic states. The three-dimensional potential energy surfaces and the electric dipole moment surfaces of the X?1?(g)+ and ã3?(u)+ electronic states are calculated using a multireference configuration interaction (MRCISD) approach in combination with internally contracted multireference perturbation theory (RS2C) based on complete active space self-consistent field (CASSCF) wave functions applying a Sadlej pVTZ basis set for both O and Sr and the Stuttgart relativistic small-core effective core potential for Sr. The infrared spectra are simulated using the MORBID program system. We also calculate vertical excitation energies and transition moments for several excited singlet and triplet electronic states in order to predict the positions and intensities of the most prominent singlet and triplet electronic absorption bands. Finally, for this heavy molecule, we calculate the singlet–triplet interaction matrix elements between close-lying vibronic levels of the X? and ã electronic states and find them to be very small. PMID:23506078

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

2013-10-01

135

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.

136

Negative Polaron and Triplet Exciton Diffusion inOrganometallic “Molecular Wires”  

SciTech Connect

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

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

2011-07-27

137

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

138

Quasiclassical asymptotics and coherent states for bounded discrete spectra  

SciTech Connect

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

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

2010-12-15

139

An optical-optical double resonance probe of the lowest triplet state of jet-cooled thiophosgene: rovibronic structures and electronic relaxation.  

PubMed

The vibrational structure, rotational structure, and electronic relaxation of the "dark" T1 3A2(n,pi*) state of jet-cooled thiophosgene have been investigated by two-color S2<--T1<--S0 optical-optical double resonance (OODR) spectroscopy, which monitors the S2-->S0 fluorescence generated by S2<--T1 excitation. This method is capable of isolating the T1 vibrational structure into a1, b1, and b2 symmetry blocks. The fluorescence-detected vibrational structure of the Tz spin state of T1 shows that the CS stretching frequency as well as the barrier height for pyramidal deformation are significantly greater in the 3A2(n,pi*) state than in the corresponding 1A2(n,pi*) state. The differing vibrational parameters of the T1 thiophosgene relative to the S1 thiophosgene can be attributed to the motions of unpaired electrons that are better correlated when they are in the excited singlet state than when they are in the triplet state of same electron configuration. A set of T1 structural parameters and the information concerning the T1 spin states have been obtained from least-square fittings of the rotationally resolved T1<--S0 excitation spectrum. The nearly degenerate mid R:x and mid R:y spin states are well removed from mid R:z spin component, indicating that T1 thiophosgene is a good example of case (ab) coupling. The decay of the mid R:z spin state of T1 thiophosgene, obtained from time-resolved S2<--T1<--S0 OODR experiment, is characteristic of strong-coupling intermediate-case decay in which an initial rapid decay is followed by recurrences and/or a long-lived quasiexponential decay. PMID:16599668

Fujiwara, Takashige; Lim, Edward C; Judge, Richard H; Moule, David C

2006-03-28

140

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

Microsoft Academic Search

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

M. Buchheit; P. D. Loly

1972-01-01

141

Incompatible quartets, triplets, and characters  

PubMed Central

We study a long standing conjecture on the necessary and sufficient conditions for the compatibility of multi-state characters: There exists a function f(r) such that, for any set C of r-state characters, C is compatible if and only if every subset of f(r) characters of C is compatible. We show that for every r?2, there exists an incompatible set C of ?(r2)r-state characters such that every proper subset of C is compatible. This improves the previous lower bound of f(r)?r given by Meacham (1983), and f(4)?5 given by Habib and To (2011). For the case when r=3, Lam, Gusfield and Sridhar (2011) recently showed that f(3)=3. We give an independent proof of this result and completely characterize the sets of pairwise compatible 3-state characters by a single forbidden intersection pattern. Our lower bound on f(r) is proven via a result on quartet compatibility that may be of independent interest: For every n?4, there exists an incompatible set Q of ?(n2) quartets over n labels such that every proper subset of Q is compatible. We show that such a set of quartets can have size at most 3 when n=5, and at most O(n3) for arbitrary n. We contrast our results on quartets with the case of rooted triplets: For every n?3, if R is an incompatible set of more than n?1 triplets over n labels, then some proper subset of R is incompatible. We show this bound is tight by exhibiting, for every n?3, a set of n?1 triplets over n taxa such that R is incompatible, but every proper subset of R is compatible. PMID:23547777

2013-01-01

142

Measurement of magnetic field effects on radical recombination reactions using triplet triplet energy transfer  

NASA Astrophysics Data System (ADS)

Previously, the effect of applied magnetic fields on the yield of the reaction of the radical ions of pyrene and 1,3-dicyanobenzene (DCB) has been measured by monitoring the emission of the pyrene/1,3-DCB exciplex formed from the singlet state of the spin-correlated radical pair (SCRP). This Letter describes an alternative approach that relies on energy transfer from the excited triplet state of pyrene to the tris(2,2'-bipyridyl)ruthenium(II) ion, Ru(bpy)32+, allowing the recombination of the triplet SCRP to be monitored by emission spectroscopy. Measurements of magnetic field effects in combination with time-resolved flash photolysis and luminescence experiments confirm triplet-triplet energy transfer as the reaction mechanism.

Henbest, K. B.; Maeda, K.; Athanassiades, E.; Hore, P. J.; Timmel, C. R.

2006-04-01

143

Mixing of exciton and charge-transfer states in Photosystem II reaction centers: modeling of Stark spectra with modified Redfield theory.  

PubMed

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

2007-08-15

144

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

E-print Network

population imbalance enforces anisotropic Fulde-Ferrell (FF) or inhomogeneous Larkin-Ovchinikov (LO) states the unpo- larized BCS and the polarized normal Fermi gas phases. Those states are characterized in electron systems. Hence, experiments with ultracold atoms can provide unique signatures of exotic many

Demler, Eugene

145

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

146

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

147

An attempt to enhance singlet-triplet transitions in vapors  

E-print Network

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

Young, Bernard Theodore

2012-06-07

148

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

PubMed

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

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

2013-04-25

149

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

150

Biradicals by triplet recombination of radical ion pairs.  

PubMed

Radical ion pairs generated by photoinduced electron transfer may undergo return electron transfer (RET) in pairs of singlet or triplet multiplicity. RET efficiencies are determined by the free energy of RET and the topologies of the potential surfaces of parent molecule, radical ion and triplet state. If radical ion geometries are different from the corresponding triplet states, RET occurs either with cleavage ("dissociative" RET; 1,2-diphenylcyclopropane radical cations) or formation of C-C bonds ("associative" RET; norbornadiene radical cation). Radical ions of some strained ring compounds spontaneously undergo ring-opening; RET to such species form ring-opened triplets without major geometry changes. CIDNP spectroscopy offers unique insights into triplet RET. PMID:18465009

Roth, Heinz D

2008-05-01

151

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

PubMed

Far infrared spectra of zwitterionic, cationic, and anionic forms of aliphatic amino acids in solid state have been studied experimentally. Measurements were done on glycine, L-alanine, L-valine, L-leucine, and L-isoleucine powder samples and film samples obtained from dried solutions prepared at pH ranging from 1 to 13. Solid state density functional theory calculations were also performed, and detailed potential energy distributions were obtained from normal mode results. A good correspondence between experimental and simulated spectra was achieved and this allowed us to propose an almost complete band assignment for the far infrared spectra of zwitterionic forms. In the 700-50 cm(-1) range, three regions were identified, each corresponding to a characteristic set of normal modes. A first region between 700 and 450 cm(-1) mainly contained the carboxylate bending, rocking, and wagging modes as well as the ammonium torsional mode. The 450-250 cm(-1) region was representative of backbone and sidechain skeletal bending modes. At last, the low wavenumber zone, below 250 cm(-1), was characteristic of carboxylate and skeletal torsional modes and of lattice modes. Assignments are also proposed for glycine cationic and anionic forms, but could not be obtained for all aliphatic amino acids due to the lack of structural data. This work is intended to provide fundamental information for the understanding of peptides vibrational properties. PMID:20331320

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

2010-03-21

152

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

153

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

154

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

155

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

156

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

157

Time-resolved CIDEP study of the photogenerated camphorquinone radical anion: a case of dual singlet and triplet precursors  

SciTech Connect

Photoreduction of camphorquinone in 2-propanol produced electron spin polarized camphorquinone radical anions. The time-resolved electron spin resonance spectra of the spin-polarized radical anions provided the first evidence of dual singlet and triplet precursors in the CIDEP phenomenon. With the results from fluorescence quenching experiments, the time dependence of the CIDEP spectra can be accounted for qualitatively by the changes of the relative contributions to the polarization among the singlet pair, F and triplet pairs, and the triplet mechanisms.

Depew, M.C.; Wan, J.K.S.

1986-12-04

158

Mapping Agricultural Crops with AVIRIS Spectra in Washington State  

NASA Technical Reports Server (NTRS)

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

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

2000-01-01

159

Structure-dependent photophysical properties of singlet and triplet metal-to-ligand charge transfer states in copper(I) bis(diimine) compounds.  

PubMed

The photophysical properties of singlet and triplet metal-to-ligand charge transfer (MLCT) states of [Cu(I)(diimine)(2)](+), where diimine is 2,9-dimethyl-1,10-phenanthroline (dmphen), 2,9-dibutyl-1,10-phenanthroline (dbphen), or 6,6'-dimethyl-2,2'-bipyridine (dmbpy), were studied. On 400 nm laser excitation of [Cu(dmphen)(2)](+) in CH(2)Cl(2) solution, prompt (1)MLCT fluorescence with a quantum yield of (2.8 +/- 0.8) x 10(-5) was observed using a picosecond time-correlated single photon counting technique. The quantum yield was dependent on the excitation wavelength, suggesting that relaxation of the Franck-Condon state to the lowest (1)MLCT competes with rapid intersystem crossing (ISC). The fluorescence lifetime of the copper(I) compound was 13-16 ps, unexpectedly long despite a large spin-orbit coupling constant of 3d electrons in copper (829 cm(-1) ). Quantum chemical calculations using a density functional theory revealed that the structure of the lowest (1)MLCT in [Cu(dmphen)(2)](+) (1(1)B(1)) was flattened due to the Jahn-Teller effect in 3d(9) electronic configuration, and the dihedral angle between the two phenanthroline planes (dha) was about 75 degrees with the dha around 90 degrees in the ground state. Intramolecular reorganization energy for the radiative transition of 1(1)B(1) was calculated as 2.1 x 10(3) cm(-1), which is responsible for the large Stokes shift of the fluorescence observed (5.4 x 10(3) cm(-1)). To understand the sluggishness of the intersystem crossing (ISC) of (1)MLCT of the copper(I) compounds, the strength of the spin-orbit interaction between the lowest (1)MLCT (1(1)B(1)) and all (3)MLCT states was calculated. The ISC channels induced by strong spin-orbit interactions (ca. 300 cm(-1)) between the metal-centered HOMO and HOMO - 1 were shown to be energetically unfavorable in the copper(I) compounds because the flattening distortion caused large splitting (6.9 x 10(3) cm(-1)) between these orbitals. The possible ISC is therefore induced by weak spin-orbit interactions (ca. 30 cm(-1)) between ligand-centered molecular orbitals. Further quantum mechanical study on the spin-orbit interaction between the lowest (3)MLCT (1(3)A) and all (1)MLCT states indicated that the phosphorescence borrows intensity from 2(1)B(1). The radiative rate of the phosphorescence was also structure-sensitive. The flattening distortion reduced the transition dipole moment of 2(1)B(1) --> the ground state, and decreased the extent of mixing between 1(3)A and 2(1)B(1), thereby considerably reducing the phosphorescence radiative rate at the MLCT geometry compared to that at the ground state geometry. The theoretical calculation satisfactorily reproduced the radiative rate of ca. 10(3) s(-1) and accounted for the structure-sensitive phosphorescence intensities of copper(I) bis(diimine) compounds recently demonstrated by Felder et al. (Felder, D.; Nierengarten, J. F.; Barigelletti, F.; Ventura, B.; Armaroli, N. J. Am. Chem. Soc. 2001, 123, 6291). PMID:14514312

Siddique, Zainul Abedin; Yamamoto, Yuichi; Ohno, Takeshi; Nozaki, Koichi

2003-10-01

160

Microwave spectra of alkali metal tetrahydroborates in excited vibrational states  

NASA Astrophysics Data System (ADS)

We have observed two sets of vibrational satellites for each of LiBH 4, NaBH 4, NaBD 4, and KBH 4 and have assigned them to the non-degenerate alkali metal-boron stretching state and the degenerate BH 4 bending (or internal rotation) state. The observed spectral patterns were found to be quite different for different molecular species. The most conspicuous anomaly was the DJK constant of NaBH 4, which was opposite in sign for the two vibrational states and was accounted for by accidental degeneracy of the two states strongly coupled by a Coriolis interaction.

Kawashima, Yoshiyuki; Hirota, Eizi

1992-05-01

161

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

NASA Astrophysics Data System (ADS)

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

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

1997-12-01

162

Triplet-triplet energy-transfer coupling: Theory and calculation  

NASA Astrophysics Data System (ADS)

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

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

2006-01-01

163

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

E-print Network

The 62Sm, 64Gd, 64Dy, 70Y b, 72Hf and 74W nuclei are classified as deformed nuclei. Low-lying bands are one of the most fundamental excitation modes in the energy spectra of deformed nuclei. In this paper a theoretical analysis of the experimental data within the phenomenological model is presented. The energy spectra of ground states are calculated. It is found the low-lying spectra of ground band states are in good agreement with the experimental data.

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

2014-05-28

164

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

165

Dominance of the triplet mechanism in the electron spin polarisation of slowly reacting triplets.  

PubMed

For the triplet mechanism (TM) of electron spin polarisation in photochemically generated free radicals to dominate, the chemical reaction has to be very fast and capable of competing with the electron spin-lattice relaxation process of the triplet. This is a well-established condition. Here we report a counter example of electron spin polarisation, where this condition appears to be violated, and a dominant spin polarisation characteristic of the TM is observed, even when the triplet reacts very slowly. The system studied is the photoreduction of 4,4'-dihydroxy-benzophenone (DHBP) in 2-propanol producing the DHBP ketyl radical and the (CH3)2C?OH radical. At room temperature, electron spin polarisation of the time-resolved EPR (TREPR) spectra of this system is dominated by the radical pair mechanism involving ST0 mixing, as the rate of the hydrogen abstraction reaction cannot compete with the spin-lattice relaxation of triplet DHBP. However, with the lowering of temperature, TREPR spectra dominated by a net emissive polarisation are seen, even though the rate of the reaction remains slow. Existence of this single-phase, hyperfine-line independent emissive polarisation due to the TM is established by the simulation of their TREPR spectra at -48 °C. To explain the increased contribution of the TM with the lowering of temperature, we proposed that the presence of two hydroxyl groups of DHBP could form hydrogen bonds with the solvent and steadily increase the micro-viscosity experienced by DHBP appreciably as the temperature was lowered. This would progressively increase the rotational correlation time of triplet DHBP, enabling the TM route to contribute increasingly to the radical generation. TREPR experiments with 4,4'-dimethoxy-benzophenone in 2-propanol, where similar hydrogen bonding is not possible, showed the spectra to be dominated by the ST0-RPM with little contribution of a net emissive signal. This observation qualitatively confirmed our proposal of enhanced micro-viscosity experienced by DHBP in 2-propanol at low temperatures, resulting in the enhanced emissive spin polarisation due to the TM, even though the chemical reaction remains slow. PMID:24522151

Rane, Vinayak; Das, Ranjan

2014-03-28

166

Enhanced efficiency in high-brightness fluorescent organic light emitting diodes through triplet management  

NASA Astrophysics Data System (ADS)

We demonstrate suppressed singlet-triplet (S-T) quenching, and hence increased quantum efficiency, in high-brightness fluorescent organic light emitting diodes (OLEDs) by reducing the guest triplet population through the introduction of a triplet manager molecule into the emission layer (EML). As an example, an OLED whose EML consists of the red fluorophore, 4-(dicyanomethylene)-2-methyl-6-julolidyl-9-enyl-4H-pyran doped into the host, tris(8-hydroxyquinoline) Al (Alq3) is blended with the triplet manager, 9,10-di(naphtha-2-yl)anthracene. The manager triplet energy is less than that of the host or dopant, leading to efficient triplet removal from the dopant without affecting the radiative singlet population. Measurements suggest the complete suppression of S-T quenching using the triplet management strategy, leading to >100% increase in the steady-state OLED external quantum efficiency.

Zhang, Yifan; Slootsky, Michael; Forrest, Stephen R.

2011-11-01

167

Infrared spectrum and molecular structure of lowest electronically excited triplet state of 1,4-dicyano-2,3,5,6-tetrafluorobenzene in low-temperature matrices  

NASA Astrophysics Data System (ADS)

An infrared spectrum of the T 1 state for 1,4-dicyano-2,3,5,6-tetrafluorobenzene in a low-temperature argon matrix was measured with a Fourier transform infrared spectrophotometer. The density-functional-theory calculation was performed to assign the observed bands. The optimized geometrical structure in the T 1 state is found to have two stable forms, planar ( D2 h) and non-planar ( C2 v), the former being more stable than the latter by 35.1 kJ mol -1. The T 1 state is identified as the planar form by a comparison of the observed matrix spectrum with the calculated spectral patterns. This assignment is confirmed by an analysis of the matrix-isolation phosphorescence spectra, where the observed vibronic bands are assigned to the fundamental and/or combination bands of the a g vibrational modes in analogy with those of 1,4-dicyanobenzene, where the T 1 structure belongs to D2 h symmetry.

Akai, Nobuyuki; Negishi, Daisuke; Kudoh, Satoshi; Takayanagi, Masao; Nakata, Munetaka

2004-01-01

168

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

169

EPR study of the luminescent triplet state of VO/sup 3-//sub 4/ in YVO/sub 4/ and YP/sub 0. 96/V/sub 0. 04/O/sub 4/ single crystals at 1. 2 K  

SciTech Connect

An EPR study with optical detection is reported of the luminescent triplet state of the VO/sup 3-//sub 4/ ion in single crystals of YVO/sub 4/ and YPO/sub 4/ doped with VO/sup 3-//sub 4/ . The experiments in an external magnetic field and in zero field can be fitted by a spin Hamiltonian for an orbitally nondegenerate triplet state. Signals originate from four symmetry-related species; the directions of the principal axes of the four ZFS tensors indicate a lowering of symmetry of the VO/sup 3-//sub 4/ ion in accordance with a static Jahn--Teller effect by which the tetrahedron tends to a trigonal pyramid on excitation. For YVO/sub 4/ the ZFS parameters are: chemically bondDchemically bond = 0.58 +- 0.04, chemically bondEchemically bond = 13.72 +- 0.04 GHz, and for YPO/sub 4/: chemically bondDchemically bond = 1.12 +- 0.04, chemically bondEchemically bond = 12.98 +- 0.04 GHz (z axisparallelV--O bond and yperpendicularac or bc crystallographic plane). For the mixed crystal the lifetimes of the individual spin levels were determined: tau/sub x/ = 0.35, tau/sub y/ = 3.3, tau/sub z/ = 1.4 ms.

Barendswaard, W.; Weber, R.T.; van der Waals, J.H.

1987-10-01

170

Low ionization lines in high luminosity quasars: The calcium triplet  

E-print Network

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 $\\lambda$8498, $\\lambda$8542, $\\lambda$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 $\\lambda$8446 line using the H$\\beta$ profile as a model. We derive constraints on the line emitting region from the relative strength of the CaII triplet, OI $\\lambda$8446 and H$\\beta$.

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

2013-01-01

171

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

172

The use of dendrimers as high-performance shells for round-trip energy transfer: efficient trans-cis photoisomerization from an excited triplet state produced within a dendrimer shell.  

PubMed

A series of stilbene-cored poly(benzyl ether) dendrimers with benzophenone peripheries were synthesized and their photophysical and photochemical properties were studied. Fluorescence studies revealed that singlet-singlet energy transfer (SSET) from the stilbene core to the benzophenone units took place efficiently in dendrimers of all generations. Similarly, phosphorescence and time-resolved spectroscopic measurements indicated efficient triplet-triplet energy transfer (TTET) from the benzophenone periphery to the stilbene core. Upon excitation at 310 nm, the stilbene core isomerizes via an energy round trip within the dendrimer shell. The quantum yields for the energy round trip (?(ERT)), defined as the product of the quantum yields of SSET, intersystem crossing, and TTET (?(ERT) = ?(SS)?(isc)?(TT)), were extremely high for all generations--99%, 95% and 94% for G1, G2, and G3, respectively--which means that the excitation energy of the dendrimer core was transferred to the dendrimer periphery and back to the core almost quantitatively. The quantum yield for photoisomerization of G1-G3 via an energy round trip was higher than for other stilbene-cored dendrimers, which mainly isomerize from the excited singlet state. Photostability in the dendrimers was also demonstrated and discussed. PMID:21063588

Miura, Yousuke; Momotake, Atsuya; Takeuchi, Keiichirou; Arai, Tatsuo

2011-01-01

173

Ultrafast dynamics and excited state spectra of open-chain carotenoids at room and low temperatures.  

PubMed

Many of the spectroscopic features and photophysical properties of carotenoids are explained using a three-state model in which the strong visible absorption of the molecules is associated with an S0 (1(1)Ag-) --> S2 (1(1)Bu+) transition, and the lowest lying singlet state, S1 (2(1)Ag-), is a state into which absorption from the ground state is forbidden by symmetry. However, semiempirical and ab initio quantum calculations have suggested additional excited singlet states may lie either between or in the vicinity of S1 (2(1)Ag-) and S2 (1(1)Bu+), and some ultrafast spectroscopic studies have reported evidence for these states. One such state, denoted S*, has been implicated as an intermediate in the depopulation of S2 (1(1)Bu+) and as a pathway for the formation of carotenoid triplet states in light-harvesting complexes. In this work, we present the results of an ultrafast, time-resolved spectroscopic investigation of a series of open-chain carotenoids derived from photosynthetic bacteria and systematically increasing in their number of pi-electron carbon-carbon double bonds (n). The molecules are neurosporene (n = 9), spheroidene (n = 10), rhodopin glucoside (n = 11), rhodovibrin (n = 12), and spirilloxanthin (n = 13). The molecules were studied in acetone and CS2 solvents at room temperature. These experiments explore the effect of solvent polarity and polarizability on the spectroscopic and kinetic behavior of the molecules. The molecules were also studied in ether/isopentane/ethanol (EPA) glasses at 77 K, in which the spectral resolution is greatly enhanced. Analysis of the data using global fitting techniques has revealed the ultrafast dynamics of the excited states and spectral changes associated with their decay, including spectroscopic features not previously reported. The data are consistent with S* being identified with a twisted conformational structure, the yield of which is increased in molecules having longer pi-electron conjugations. In particular, for the longest molecule in the series, spirilloxanthin, the experiments and a detailed quantum computational analysis reveal the presence of two S* states associated with relaxed S1 (2(1)Ag-) conformations involving nearly planar 6-s-cis and 6-s-trans geometries. We propose that in polar solvents, the ground state of spirilloxanthin takes on a corkscrew conformation that generates a net solute dipole moment while decreasing the cavity formation energy. Upon excitation and relaxation into the S1 (2(1)Ag-) state, the polyene unravels and flattens into a more planar geometry with comparable populations of 6-s-trans and 6-s-cis conformations. PMID:17441762

Niedzwiedzki, Dariusz; Koscielecki, Jeremy F; Cong, Hong; Sullivan, James O; Gibson, George N; Birge, Robert R; Frank, Harry A

2007-05-31

174

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

E-print Network

Jet cooled spectra of pyrrolobenzene and of pyrrolobenzonitrile: the nature of the excited states Berlin, Germany Received 24 May 2002 Abstract The jet cooled fluorescence and resonance enhanced obtained for these mol- ecules in a supersonic jet. The goal of the mea- surements was to establish a data

Haas, Yehuda

175

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

176

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

177

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

PubMed

Formulae of Le Roy-Bernstein near-dissociation theory are derived in a general isotope-invariant form, applicable to any term in the rotational expansion of a diatomic ro-vibrational term value. It is proposed to use the generalized Le Roy-Bernstein expansion to describe the binding energies (ro-vibrational term values) of the ground triplet state a(3) ?(u)(+) of alkali metal dimers. The parameters of this description are determined for Rb2 and Cs2 molecules. This approach gives a recipe to calculate the whole variety of the binding energies with characteristic accuracies from ?1 × 10(-3) to 1 × 10(-2) cm(-1) using a relatively simple algebraic equation. PMID:24712793

Sovkov, V B; Ivanov, V S

2014-04-01

178

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

NASA Astrophysics Data System (ADS)

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

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

2014-04-01

179

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

180

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

181

'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

182

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

183

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

184

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

185

Concentration quenching of fluorescence and triplet formation of chlorophyll a and pheophytin in solutions  

Microsoft Academic Search

The first measurements of the concentration dependence of the quantum yield of formation of chlorophyll triplet states were made by the authors of [3, 4]. They showed that the quantum yield of triplet formation was greatly reduced at concentrations 5 ?9 10-3-10 -2 mole ?9 liter -1. Because of the special nature of the system selected for investigation (chlorophyll in

A. P. Losev; É. I. Zen'kevich; E. I. Sagun

1977-01-01

186

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

187

Global analysis of steady-state polarized fluorescence spectra using trilinear curve resolution.  

PubMed Central

Global analysis using trilinear curve resolution is described and shown to be a powerful method for the resolution of polarized fluorescence data arrays, in which the measured fluorescence intensity is a separable function of polarization orientation, excitation wavelength, and emission wavelength. This methodology is applicable to mixtures the components of which have linearly independent excitation and emission spectra and distinct anisotropies. Normalized excitation and emission spectra of individual components can be uniquely determined without prior assumptions concerning spectral shapes (e.g., sum of Gaussians) and without the uncertainties inherent in bilinear techniques such as principal component analysis or factor analysis. The normalized excitation and emission vectors are combined with the total absorption spectrum of the multicomponent mixture to compute absolute absorption and emission spectra. The precision of this methodology is evaluated as a function of noise, overlap, relative intensity, and anisotropy difference between components using simulated mixtures of the DNA bases. The ability of this method to extract individual spectra from steady-state fluorescence data arrays is illustrated for mixtures containing two and three components. PMID:8218915

Phillips, G R; Georghiou, S

1993-01-01

188

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

189

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

190

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

191

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

SciTech Connect

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

Minaev, B.F.

1999-09-09

192

Near-infrared photopolymerization: Initiation process assisted by self-quenching and triplet-triplet annihilation of excited cyanine dyes  

NASA Astrophysics Data System (ADS)

The mechanism of radical polymerization photoinitiated by a near-infrared absorbing indotricarbocyanine (HITC) was investigated using an indirect kinetics method based on the photobleaching dynamics of the dye. Despite similar photophysical features in glycerol and in pentaerythritol triacrylate monomer, HITC undergoes a very fast photobleaching in the acrylate resin which leads to photopolymerization at high power regime. The addition of an amine induces the decrease of photopolymerization threshold by a factor 5 with unexpected dye regeneration. These effects were correlated to the reactivity of the reduced and oxidized forms of HITC produced via triplet-triplet annihilation and ground state quenching processes.

Dika, Ihab; Malval, Jean-Pierre; Soppera, Olivier; Bardinal, Véronique; Barat, David; Turck, Colette; Spangenberg, Arnaud; Bruyant, Aurélien

2011-10-01

193

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

E-print Network

Improving the quality of 2D solid-state NMR spectra of microcrystalline proteins by covariance: covariance processing of two-dimensional NMR spectra of microcrystalline proteins improves spectral quality of microcrystalline proteins improves spectral resolution and sensitivity over conventional Fourier transformation

194

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

195

Chimpanzee triplets born in captivity  

Microsoft Academic Search

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

Mark A. Rosenthal; Lhtcobt Park Zoological Gardens

1981-01-01

196

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

197

Heavy Vector Triplets: Bridging Theory and Data  

E-print Network

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 cross-section times 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 a cross-section times 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.

Duccio Pappadopulo; Andrea Thamm; Riccardo Torre; Andrea Wulzer

2014-02-18

198

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

PubMed

Gas-phase emission spectra of the hitherto unknown free radical BiNa have been measured in the NIR range with a Fourier transform spectrometer. The emissions were observed from a fast-flow system in which bismuth vapor in argon carrier gas was passed through a microwave discharge and mixed with sodium vapor in an observation tube. Two systems of blue-degraded bands observed in the ranges 8900-9800 and 7200-7800 cm(-1) were measured at high spectral resolution and vibrational and rotational analyses were performed. To aid in the analysis of the experimental data, a series of relativistic configuration interaction calculations has been carried out to obtain potential curves for the low-lying states of BiNa and also electric dipole transition moments connecting them. As in the isovalent BiH system, the ground state of BiNa is found to be X(3)Sigma(-) with a spin splitting of about 1769 cm(-1). The first excited state is A(3)Pi, and the observed band systems are assigned to the transitions A(3)Pi(A(2)0(+)) --> X(3)Sigma(-)(X(1)0(+), X(2)1). Comparison with earlier work on the isovalent BiH system emphasizes that the relative weakness of the varsigma MO in BiNa is responsible for qualitative differences in the electronic spectra of these two systems. Copyright 2000 Academic Press. PMID:11148086

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

2000-12-01

199

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

200

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

NASA Astrophysics Data System (ADS)

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

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

2014-10-01

201

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

NASA Astrophysics Data System (ADS)

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 the band of covalent states. The latter start to dissociate into triplet excitations, completing the process in about 300 fs.

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

2001-10-01

202

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

203

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

204

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

SciTech Connect

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

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

1984-03-29

205

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

206

Photophysics of platinum tetrayne oligomers: delocalization of triplet exciton.  

PubMed

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

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

2014-11-13

207

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

E-print Network

using excited electronic state ab initio equation-of-motion coupled-cluster EOM-CC methods. A new implementation of open-shell EOM-CC including iterative partial triple excitations EOM-CC3 was tested. Coupled

Crawford, T. Daniel

208

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

209

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

2009-05-15

210

Product state distributions for the C + (4P)+H2(D2) reaction from chemiluminescence spectra  

NASA Astrophysics Data System (ADS)

Optical emission resulting from low-energy (1-3 eVc.m.) impact of metastable C+(4P) ions on H2 and D2 molecules has been studied spectroscopically in the 2700-3900 Å range. The b 3?--a 3? transition of CH+ (CD+) was resolved into numerous bands. From a spectrum simulation by computer, rotational-vibrational population distributions of the excited triplet state were obtained. In contrast to previous related studies, the vibrational excitation decreases with increasing collision energy. One-parameter surprisal fits of the vibrational (and, to a lesser extent, the rotational) population distributions are found to be unsatisfactory. The reaction is discussed in terms of changes of molecular orbital occupancy, which suggest a direct interaction mechanism. This is consistent with the observed population distributions.

Kusunoki, I.; Ottinger, Ch.

1982-02-01

211

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

212

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

NASA Astrophysics Data System (ADS)

The equilibrium geometry of the ground-state HCCP radical was determined by ab initio SCF, CASSCF, MP2, CI and density functional B3LYP calculations using different basis sets. The HCCP radical is predicted to be linear at all levels of calculation considered, in agreement with the experimental conclusion. The calculated molecular orbitals show that the HCCP ground state is of phosphorene form that has been modified by a phospho-allene, which is to some extent different from the experimental result. The calculated rotational constant is close to the experimental value, a larger discrepancy exists in the harmonic vibrational frequencies predicted at the different computational levels.

Shao, Guo-Quan; Fang, Wei-Hai

1998-06-01

213

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

214

Rapid acquisition of 14N solid-state NMR spectra with broadband cross polarization.  

PubMed

Nitrogen is an element of utmost importance in chemistry, biology and materials science. Of its two NMR-active isotopes, (14)N and (15)N, solid-state NMR (SSNMR) experiments are rarely conducted upon the former, due to its low gyromagnetic ratio (?) and broad powder patterns arising from first-order quadrupolar interactions. In this work, we propose a methodology for the rapid acquisition of high quality (14)N SSNMR spectra that is easy to implement, and can be used for a variety of nitrogen-containing systems. We demonstrate that it is possible to dramatically enhance (14)N NMR signals in spectra of stationary, polycrystalline samples (i.e., amino acids and active pharmaceutical ingredients) by means of broadband cross polarization (CP) from abundant nuclei (e.g., (1)H). The BRoadband Adiabatic INversion Cross-Polarization (BRAIN-CP) pulse sequence is combined with other elements for efficient acquisition of ultra-wideline SSNMR spectra, including Wideband Uniform-Rate Smooth-Truncation (WURST) pulses for broadband refocusing, Carr-Purcell Meiboom-Gill (CPMG) echo trains for T2-driven S/N enhancement, and frequency-stepped acquisitions. The feasibility of utilizing the BRAIN-CP/WURST-CPMG sequence is tested for (14)N, with special consideration given to (i) spin-locking integer spin nuclei and maintaining adiabatic polarization transfer, and (ii) the effects of broadband polarization transfer on the overlapping satellite transition patterns. The BRAIN-CP experiments are shown to provide increases in signal-to-noise ranging from four to ten times and reductions of experimental times from one to two orders of magnitude compared to analogous experiments where (14)N nuclei are directly excited. Furthermore, patterns acquired with this method are generally more uniform than those acquired with direct excitation methods. We also discuss the proposed method and its potential for probing a variety of chemically distinct nitrogen environments. PMID:24123255

Harris, Kristopher J; Veinberg, Stanislav L; Mireault, Christopher R; Lupulescu, Adonis; Frydman, Lucio; Schurko, Robert W

2013-11-25

215

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

216

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

217

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

218

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

219

[Absorption and magnetic circular dichroism spectra of nonequilibrium states of hemoproteins. III. Complexes of peroxidase].  

PubMed

Absorption and magnetic curcular dichroism spectra of nonequilibrium states of peroxidase and its complexes with F-, N3-, CN- produced by reduction of oxidased forms of proteins by thermalysed electrons at 77 degrees K were studied. Mixtures of high spin and low spin ferroforms were found in nonequilibrium states of peroxidase and complexes with F- and N3-, the content of the high spin ferroform increasing as follows: N3- complex less than peroxidase less than fluorine complex. Only low spin ferroforms was found after low temperature reduction of the cyanide complex. The existence of the low spin ferroform in equilibrium states of peroxidase and its complex with F- was explained by location of iron near the porphyrine plane. In the case of azide and cyanide complexes the existence of the low spin form is due to the presence of these ligands in heme iron's coordination sphere. The temperature relaxation of all nonequilibrium forms was investigated and a possible mechanism of the process is proposed. PMID:740001

Magonov, S N; Davydov, R M; Bliumenfel'd, L A; Arutiunian, A M; Sharonov, Iu A

1978-01-01

220

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

221

Enhancement of intersystem crossing by substitution: assignment of a long-lived triplet state by magnetic field effects in a non-viscous medium  

NASA Astrophysics Data System (ADS)

The photoinduced electron transfer reactions in four similar donor-acceptor systems, N-ethyl carbazole (ECZ)-1,4-dicyanobenzene (DCB), 1,4,5,8,9-pentamethyl carbazole (PMC)-DCB, ECZ-1,2,4,5-tetracyanobenzene (TCNB) and PMC-TCNB have been studied to establish the effect of substitutions on the mechanistic pathways of electron transfer (ET) reactions. The initial spin states of the transients have been characterized by laser flash photolysis and magnetic field effect studies. The presence of more -CN groups in TCNB compared to DCB alters the ET pathways, by enhancing intersystem crossing. The temperature and free energy dependencies of these systems have been utilized to evaluate the process from the theoretical viewpoint.

Aich, S.; Basu, S.

1997-12-01

222

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

223

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

SciTech Connect

This report describes the results from three studies of source spectra, attenuation, and site effects of central and eastern United States earthquakes. In the first study source parameter estimates taken from 27 previous studies were combined to test the assumption that the earthquake stress drop is roughly a constant, independent of earthquake size. 200 estimates of stress drop and seismic moment from eastern North American earthquakes were combined. It was found that the estimated stress drop from the 27 studies increases approximately as the square-root of the seismic moment, from about 3 bars at 10{sup 20} dyne-cm to 690 bars at 10{sup 25} dyne-cm. These results do not support the assumption of a constant stress drop when estimating ground motion parameters from eastern North American earthquakes. In the second study, broadband seismograms recorded by the United States National Seismograph Network and cooperating stations have been analysed to determine Q{sub Lg} as a function of frequency in five regions: the northeastern US, southeastern US, central US, northern Basin and Range, and California and western Nevada. In the third study, using spectral analysis, estimates have been made for the anelastic attenuation of four regional phases, and estimates have been made for the source parameters of 27 earthquakes, including the M{sub b} 5.6, 14 April, 1995, West Texas earthquake.

Lindley, G.

1998-02-01

224

[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

225

Singlet and triplet energies of ?-oligothiophenes: A spectroscopic, theoretical, and photoacoustic study: Extrapolation to polythiophene  

Microsoft Academic Search

The triplet state energies, ET(0–0), for the ?-oligothiophenes (?n’s) with n=1–7, were determined and vary from 18 000 cm?1 (?2) to 13 000 cm?1 (?7). The data were obtained from spectroscopic and calorimetric measurements. It was found that the triplet energies decrease with the increase ring number (n), leveling off beginning with the ?-oligothiophene with n=5. A linear relation was

J. Seixas de Melo; Lu?´s M. Silva; Lu?´s G. Arnaut; R. S. Becker

1999-01-01

226

Resonance Raman spectra of TNT and RDX using vibronic theory, excited-state gradient, and complex polarizability approximations.  

PubMed

Geometries, UV absorption bands, and resonance Raman (RR) cross sections of TNT and RDX are investigated using density functional theory (DFT) in conjunction with the Coulomb attenuated B3LYP exchange-correlation functional. The absorption and RR spectra are determined with use of vibronic (VB) theory, excited-state gradient, and complex polarizability (CPP) approximations. We examined low-energy isomers (two for TNT and four for RDX) whose energies differ by less than 1 kcal/mol, such that they would appreciably be populated at room temperature. The two TNT isomers differ by an internal rotation of the methyl group, while the four conformers of RDX differ by the arrangements of the nitro group relative to the ring. Our theoretical optical properties of the TNT and RDX isomers are in excellent agreement with experimental and recent CCSD-EOM results, respectively. For the two TNT isomers, the ultraviolet RR (UVRR) spectra are similar and in good agreement with recently measured experimental results. Additionally, the UVRR spectra computed using the excited-state and CPP approaches compare favorably with the VB theory results. On the other hand, the RR spectra of the RDX conformers differ from one another, reflecting the importance of the positioning of the NO2 groups with respect to the ring. In the gas phase or in solution, RDX would give a spectrum associated with a conformationally averaged structure. It is encouraging that the computed spectra of the conformers show similarities to recent measured RDX spectra in acetonitrile solution, and reproduce the 10-fold decrease in the absolute Raman cross sections of RDX compared to TNT for the observed 229 nm excitation. We show that in TNT and RDX vibrational bands that couple to NO2 or the ring are particularly resonance enhanced. Finally, the computed RDX spectra of the conformers present a benchmark for understanding the RR spectra of the solid-phase polymorphs of RDX. PMID:22770527

Al-Saidi, W A; Asher, Sanford A; Norman, Patrick

2012-08-01

227

Photoprotection in the antenna complexes of photosystem II: role of individual xanthophylls in chlorophyll triplet quenching.  

PubMed

In this work the photoprotective role of all xanthophylls in LHCII, Lhcb4, and Lhcb5 is investigated by laser-induced Triplet-minus-Singlet (TmS) spectroscopy. The comparison of native LHCII trimeric complexes with different carotenoid composition shows that the xanthophylls in sites V1 and N1 do not directly contribute to the chlorophyll triplet quenching. The largest part of the triplets is quenched by the lutein bound in site L1, which is located in close proximity to the chlorophylls responsible for the low energy state of the complex. The lutein in the L2 site is also active in triplet quenching, and it shows a longer triplet lifetime than the lutein in the L1 site. This lifetime difference depends on the occupancy of the N1 binding site, where neoxanthin acts as an oxygen barrier, limiting the access of O(2) to the inner domain of the Lhc complex, thereby strongly contributing to the photostability. The carotenoid triplet decay of monomeric Lhcb1, Lhcb4, and Lhcb5 is mono-exponential, with shorter lifetimes than observed for trimeric LHCII, suggesting that their inner domains are more accessible for O(2). As for trimeric LHCII, only the xanthophylls in sites L1 and L2 are active in triplet quenching. Although the chlorophyll to carotenoid triplet transfer is efficient (95%) in all complexes, it is not perfect, leaving 5% of the chlorophyll triplets unquenched. This effect appears to be intrinsically related to the molecular organization of the Lhcb proteins. PMID:18079125

Mozzo, Milena; Dall'Osto, Luca; Hienerwadel, Rainer; Bassi, Roberto; Croce, Roberta

2008-03-01

228

Heats of Formation of Triplet Ethylene, Ethylidene, and Acetylene  

SciTech Connect

Heats of formation of the lowest triplet state of ethylene and the ground triplet state of ethylidene have been predicted by high level electronic structure calculations. Total atomization energies obtained from coupled-cluster CCSD(T) energies extrapolated to the complete basis set limit using correlation consistent basis sets (CBS), plus additional corrections predict the following heats of formation in kcal/mol: Delta H0f(C2H4,3A1) = 80.1 at 0 K and 78.5 at 298 K, and Delta H0f(CH3CH,3A") = 86.8 at 0 K and 85.1 at 298 K, with an error of less than +-1.0 kcal/mol. The vertical and adiabatic singlet-triplet separation energies of ethylene were calculated as Delta ES-T,vert = 104.1 and Delta ES-T,adia = 65.8 kcal/mol. These results are in excellent agreement with recent quantum Monte Carlo (DMC) values of 103.5 +- 0.3 and 66.4 +- 0.3 kcal/mol. Both sets of computational values differ from the experimental estimate of 58 +- 3 kcal/mol for the adiabatic splitting. The computed singlet-triplet gap at 0 K for acetylene is Delta ES-T,adia(C2H2) = 90.5 kcal/mol, which is in notable disagreement with the experimental value of 82.6 kcal/mol. The heat of formation of the triplet is Delta H0f(C2H2,3B2) = 145.3 kcal/mol. There is a systematic underestimation of the singlet-triplet gaps in recent photodecomposition experiments by ~;;7 to 8 kcal/mol. For vinylidene, we predict Delta H0f(H2CC,1A1) = 98.8 kcal/mol at 298 K (exptl. 100.3 +- 4.0), Delta H0f(H2CC,3B2) = 146.2 at 298 K, and an energy gap Delta ES-T-adia(H2CC) = 47.7 kcal/mol.

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

2007-06-28

229

ANALYZING THE LOW STATE OF EF ERIDANI WITH HUBBLE SPACE TELESCOPE ULTRAVIOLET SPECTRA  

SciTech Connect

Time-resolved spectra throughout the orbit of EF Eri during its low accretion state were obtained with the solar blind channel on the Advanced Camera for Surveys on board the Hubble Space Telescope. The overall spectral distribution exhibits peaks at 1500 and 1700 A, while the UV light curves display a quasi-sinusoidal modulation over the binary orbit. Models of white dwarfs (WDs) with a hot spot and cyclotron emission were attempted to fit the spectral variations throughout the orbit. A non-magnetic WD with a temperature of {approx}10,000 K and a hot spot with a central temperature of 15,000 K generally match the broad absorptions at 1400 and 1600 A with those expected for the quasi-molecular H features H{sub 2} and H{sup +}{sub 2}. However, the flux in the core of the Ly{alpha} absorption does not go to zero, implying an additional component, and the flux variations throughout the orbit are not well matched at long wavelengths. Alternatively, a 9500 K WD with a 100 MG cyclotron component can fit the lowest (phase 0.0) fluxes, but the highest fluxes (phase 0.5) require an additional source of magnetic field or temperature. The 100 MG field required for the UV fit is much higher than that which fits the optical/IR wavelengths, which would support previous suggestions of a complex field structure in polars.

Szkody, Paula; Mukadam, Anjum [Department of Astronomy, University of Washington, Box 351580, Seattle, WA 98195 (United States); Gaensicke, Boris T. [Department of Physics, University of Warwick, Coventry CV4 7AL (United Kingdom); Campbell, Ryan K. [CTIO, Casilla 603, La Serena (Chile); Harrison, Thomas E.; Holtzman, Jon; Boberg, Owen [Department of Astronomy, New Mexico State University, Box 30001, Las Cruces, NM 88003 (United States); Howell, Steve B. [National Optical Astronomy Observatory, 950 North Cherry Avenue, Tucson, AZ 85726 (United States); Walter, Frederick M. [Department of Physics and Astronomy, Stony Brook University, Stony Brook, NY 11794 (United States); Henden, Arne; Dillon, William [AAVSO, 49 Bay State Road, Cambridge, MA 02138 (United States); Dealaman, Shannon [Rutgers University, Piscataway, NJ 08854 (United States); Perone, Christian S., E-mail: szkody@astro.washington.ed, E-mail: anjum@astro.washington.ed [Rua Victor Adalberto Kessler 114, Porto Alegra/Rio Grande do Sul (Brazil)

2010-06-20

230

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.

231

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

E-print Network

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

Asher, Sanford A.

232

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

E-print Network

-transmembrane; NMR, nuclear magnetic resonance; MAS, magic angle spinning; DGK, diaglycerol kinase; CP, crossNMR crystallography: The effect of deuteration on high resolution 13 C solid state NMR spectra, and indirect, 9­17 ppm, dimensions). The measured 13 C NMR line-widths observed for both protonated

Watts, Anthony

233

Solid state effects in the NEXAFS spectra of alkane-based van der Waals crystals: Breakdown of molecular model  

E-print Network

Solid state effects in the NEXAFS spectra of alkane-based van der Waals crystals: Breakdown der Waals interactions between alkane molecules, of covalent C­H orbitals and van der Waals forces in alkane crystals is $98.5% covalent. It is thus

234

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

PubMed

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

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

2012-12-01

235

Analysis of (030),(110), and (011) interacting states of D II 16O from hot temperature emission spectra  

NASA Astrophysics Data System (ADS)

This study is the continuation of our analysis of emission spectra of pure D II0. The spectra have been recorded in the 320 - 860 and 1750 - 4300 cm -1 spectral regions at different pressures and temperatures. The measurements were performed in an alumina cell with an effective length of hot gas of about 50 cm. All spectra have been recorded by using the Bruker IFS 120 spectrometer at the Physikalisch-Chemisches-Institut, Justus-Liebig-Universitat Giessen, Germany). More than 5600 lines have been assigned to the second triad {(030), (110), (011)} of interacting states of the D II 160 molecule. These transitions were assigned to 24 vibration-rotation and rotational bands. An extended set of more than 1500 experimental rovibrational levels for the (030), (110), and (011) interacting states has been obtained. The maximum values of rotational quantum numbers are J max = 30 and K a max = 21 with E max = 10568 cm -1 for the (011) state; J max = 29 and K a max = 21 with E max= 10540 cm -1 for the (030) state, and Jm 26 and Ka max 22 with Eniax 10488 cm1 for the (110) state. A comparison of the observed energy levels with the best available values from literature and with the global prediction is discussed.

Starikova, Eugeniya N.; Mikhailenko, Semen N.; Mellau, Georg Ch.; Tyuterev, Vladimir G.

2006-12-01

236

Quantum chemical simulations of excited-state absorption spectra of photosynthetic bacterial reaction center and antenna complexes.  

PubMed

The semiempirical ZINDO/S CIS configuration interaction method has been used to study the ground- and excited-state absorption spectra of wild type and heterodimer M202HL reaction centers from purple bacterium Rhodobacter sphaeroides as well as of peripheral LH2 and LH3 light harvesting complexes from purple bacterium Rhodopseudomonas acidophila. The calculations well reproduce the experimentally observed excited-state absorption spectra between 1000 and 17,000 cm(-1), despite the necessarily limited number of chromophores and protein subunits involved in the calculations. The electron density analysis reveals that the charge transfer between adjacent chromophores dominates the excited-state absorption spectra. Clear spectroscopic differences observed between the wild type and heterodimer reaction centers as well as between the LH2 and LH3 antenna complexes arise from differences in the energy level manifolds of the complexes, particularly those of the charge transfer states. The calculations also imply that the lowest excited state of the bacterial reaction centers has charge transfer character that is related to charge transfer within the special pair and between the special pair and the accessory bacteriochlorophyll of the photosynthetically active electron transfer branch. PMID:21466178

Linnanto, J; Freiberg, A; Korppi-Tommola, J

2011-05-12

237

Analyzing the Low State of EF Eridani with Hubble Space Telescope Ultraviolet Spectra  

NASA Astrophysics Data System (ADS)

Time-resolved spectra throughout the orbit of EF Eri during its low accretion state were obtained with the solar blind channel on the Advanced Camera for Surveys on board the Hubble Space Telescope. The overall spectral distribution exhibits peaks at 1500 and 1700 Å, while the UV light curves display a quasi-sinusoidal modulation over the binary orbit. Models of white dwarfs (WDs) with a hot spot and cyclotron emission were attempted to fit the spectral variations throughout the orbit. A non-magnetic WD with a temperature of ~10,000 K and a hot spot with a central temperature of 15,000 K generally match the broad absorptions at 1400 and 1600 Å with those expected for the quasi-molecular H features H2 and H+ 2. However, the flux in the core of the Ly? absorption does not go to zero, implying an additional component, and the flux variations throughout the orbit are not well matched at long wavelengths. Alternatively, a 9500 K WD with a 100 MG cyclotron component can fit the lowest (phase 0.0) fluxes, but the highest fluxes (phase 0.5) require an additional source of magnetic field or temperature. The 100 MG field required for the UV fit is much higher than that which fits the optical/IR wavelengths, which would support previous suggestions of a complex field structure in polars. Based on observations made with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555, and with the Apache Point Observatory 3.5 m telescope which is owned and operated by the Astrophysical Research Consortium.

Szkody, Paula; Mukadam, Anjum; Gänsicke, Boris T.; Campbell, Ryan K.; Harrison, Thomas E.; Howell, Steve B.; Holtzman, Jon; Walter, Frederick M.; Henden, Arne; Dillon, William; Boberg, Owen; Dealaman, Shannon; Perone, Christian S.

2010-06-01

238

Quadrupole effects in high-resolution phosphorus-31 solid-state NMR spectra of triphenylphosphine copper(I) complexes  

NASA Astrophysics Data System (ADS)

High-resolution 31P solid-state NMR spectra of triphenylphosphine copper(I) complexes, obtained by combining proton dipolar decoupling, proton-phosphorus cross polarization, and magic-angle sample spinning, often reveal asymmetric quartets rather than single resonance lines. These splittings arise from coupling with the nuclear spin {3}/{2} of the quadrupolar copper nucleus. Theoretical NMR spectra of spins I = {1}/{2} coupled to spins S > {1}/{2} are presented for powders spinning at the magic angle. Scalar as well as dipolar interactions are considered for the S = 1 and S = {3}/{2} cases. The magnetic field dependence of the observed asymmetric quartets in bis(triphenylphosphine)copper(I)nitrate can be accounted for by assuming a combination of scalar and dipolar coupling between phosphorus and copper. The spectra allow the determination of the scalar coupling constant, the dipolar coupling constant, and the copper quadrupole constant. Also, their signs can be established.

Menger, E. M.; Veeman, W. S.

239

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

E-print Network

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

Ebrahim Forati; George W. Hanson; Stephen Hughes

2014-07-26

240

The examination of berberine excited state by laser flash photolysis  

NASA Astrophysics Data System (ADS)

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

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

2009-07-01

241

Atomistic modeling of two-dimensional electronic spectra and excited-state dynamics for a light harvesting 2 complex.  

PubMed

The Light Harvesting 2 (LH2) complex is a vital part of the photosystem of purple bacteria. It is responsible for the absorption of light and transport of the resulting excitations to the reaction center in a highly efficient manner. A general description of the chromophores and the interaction with their local environment is crucial to understand this highly efficient energy transport. Here we include this interaction in an atomistic way using mixed quantum-classical (molecular dynamics) simulations of spectra. In particular, we present the first atomistic simulation of nonlinear optical spectra for LH2 and use it to study the energy transport within the complex. We show that the frequency distributions of the pigments strongly depend on their positions with respect to the protein scaffold and dynamics of their local environment. Furthermore, we show that although the pigments are closely packed the transition frequencies of neighboring pigments are essentially uncorrelated. We present the simulated linear absorption spectra for the LH2 complex and provide a detailed explanation of the states responsible for the observed two-band structure. Finally, we discuss the energy transfer within the complex by analyzing population transfer calculations and 2D spectra for different waiting times. We conclude that the energy transfer from the B800 ring to the B850 ring is mediated by intermediate states that are delocalized over both rings, allowing for a stepwise downhill energy transport. PMID:25554919

van der Vegte, C P; Prajapati, J D; Kleinekathöfer, U; Knoester, J; Jansen, T L C

2015-01-29

242

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

243

Hiking on the potential energy surface of a functional tyrosinase model--implications of singlet, broken-symmetry and triplet description.  

PubMed

The singlet, open-shell singlet and triplet potential energy surfaces (PES) for the peroxo state of a catalytic functional tyrosinase model have been investigated by density functional theory calculations. The broken-symmetry solution exhibits considerable stabilisation over the whole PES but the importance of the triplet state is unravelled as well. PMID:24212127

Hoffmann, Alexander; Herres-Pawlis, Sonja

2014-01-14

244

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

245

Effect of nearest-neighbor ions on excited ionic states, emission spectra, and line profiles in hot and dense plasmas  

NASA Technical Reports Server (NTRS)

The effect of the cylindrical symmetry imposed by the nearest-neighbor ions on the ionic levels and the emission spectra of a Li-like Kr ion immersed in hot and dense plasmas is investigated using the Stein et al. (1989) two-centered model extended to include computations of the line profiles, shifts, and widths, as well as the energy-level mixing and the forbidden transition probabilities. It is shown that the cylindrical symmetry mixes states with different orbital quantum numbers l, particularly for highly excited states, and, thereby, gives rise to forbidden transitions in the emission spectrum. Results are obtained for the variation of the ionic level shifts and mixing coefficients with the distance to the nearest neighbor. Also obtained are representative computed spectra that show the density effects on the spectral line profiles, shifts, and widths, and the forbidden components in the spectrum.

Salzmann, D.; Stein, J.; Goldberg, I. B.; Pratt, R. H.

1991-01-01

246

A simple method for analyzing 51V solid-state NMR spectra of complex systems.  

PubMed

Five vanadium complexes as models for biological systems were investigated using (51)V-MAS-NMR spectroscopy. All spectra show an uncommon line shape, which can be attributed to a shorter relaxation time of the satellite transition in contrast to the central one. A method for the reliable analysis of such kind of spectra is presented for the first time and the most important NMR parameters of the investigated complexes (quadrupolar coupling constant C(Q), asymmetry of the EFG tensor ?(Q), isotropic chemical shift ?(iso), chemical shift anisotropy ?(?) and asymmetry of the CSA tensor ?(?)) are presented. These results are of particular importance with respect to the analysis of the (51)V-MAS-NMR spectra of vanadium moieties in biological matrices such as vanadium chloroperoxidase, which show hitherto unexplained low intensity of the satellite sideband pattern. PMID:21601435

Fenn, Annika; Wächtler, Maria; Breitzke, Hergen; Buchholz, Axel; Lippold, Ines; Plass, Winfried; Buntkowsky, Gerd

2011-09-01

247

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

248

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

249

Use of an artificial immune system derived method for the charge state assignment of small-molecule mass spectra.  

PubMed

Knowing the charge state of an ion in a mass spectrum is crucial to being able to assign a formula to it. For many small-molecule peaks in complex mass spectra, the intensities of the isotopic peaks are too low to allow the charge state to be calculated from isotopic spacings, which is the basis of the conventional method of determining the charge state of an ion. A novel artificial intelligence derived method for identifying the charge state of ions, in the absence of any isotopic information or a series of charge states, has been developed using an artificial immune system approach. This technique has been tested against synthetic and real data sets and has proven successful in identifying the majority of multiply charged ions, thereby significantly improving the peak assignment rate and confidence. PMID:22881189

Kilgour, David P A; Mackay, C Logan; Langridge-Smith, Patrick R R; O'Connor, Peter B

2012-09-01

250

Effect of Molecular Symmetry on the Spectra and Dynamics of the Intramolecular Charge Transfer (ICT) State of Peridinin  

PubMed Central

The spectroscopic properties and dynamics of the excited states of two different synthetic analogues of peridinin were investigated as a function of solvent polarity using steady-state absorption, fluorescence, and ultrafast time-resolved optical spectroscopy. The analogues are denoted S-1- and S-2-peridinin and differ from naturally-occurring peridinin in the location of the lactone ring and its associated carbonyl group, known to be obligatory for the observation of a solvent dependence of the lifetime of the S1 state of carotenoids. Relative to peridinin, S-1- and S-2-peridinin have their lactone rings two and four carbons more toward the center of the ?-electron system of conjugated carbon-carbon double bonds, respectively. The present experimental results show that as the polarity of the solvent increases, the steady-state spectra of the molecules broaden, and the lowest excited state lifetime of S-1-peridinin changes from ~155 ps to ~17 ps which is similar to the magnitude of the effect reported for peridinin. The solvent-induced change in the lowest excited state lifetime of S-2-peridinin is much smaller and changes only from ~90 ps to ~67 ps as the solvent polarity is increased. These results are interpreted in terms of an intramolecular charge transfer (ICT) state that is formed readily in peridinin and S-1-peridinin, but not in S-2-peridinin. Quantum mechanical computations reveal the critical factors required for the formation of the ICT state and the associated solvent-modulated effects on the spectra and dynamics of these molecules and other carbonyl-containing carotenoids and polyenes. The factors are the magnitude and orientation of the ground and excited state dipole moments which must be suitable to generate sufficient mixing of the lowest two excited singlet states. PMID:22889055

Enriquez, Miriam M.; Hananoki, Shohei; Hasegawa, Shinji; Kajikawa, Takayuki; Katsumura, Shigeo; Wagner, Nicole L.

2012-01-01

251

Effect of Molecular Symmetry on the Spectra and Dynamics of the Intramolecular Charge Transfer (ICT) state of peridinin.  

PubMed

The spectroscopic properties and dynamics of the excited states of two different synthetic analogues of peridinin were investigated as a function of solvent polarity using steady-state absorption, fluorescence, and ultrafast time-resolved optical spectroscopy. The analogues are denoted S-1- and S-2-peridinin and differ from naturally occurring peridinin in the location of the lactone ring and its associated carbonyl group, known to be obligatory for the observation of a solvent dependence of the lifetime of the S(1) state of carotenoids. Relative to peridinin, S-1- and S-2-peridinin have their lactone rings two and four carbons more toward the center of the ?-electron system of conjugated carbon-carbon double bonds, respectively. The present experimental results show that as the polarity of the solvent increases, the steady-state spectra of the molecules broaden, and the lowest excited state lifetime of S-1-peridinin changes from ?155 to ?17 ps which is similar to the magnitude of the effect reported for peridinin. The solvent-induced change in the lowest excited state lifetime of S-2-peridinin is much smaller and changes only from ?90 to ?67 ps as the solvent polarity is increased. These results are interpreted in terms of an intramolecular charge transfer (ICT) state that is formed readily in peridinin and S-1-peridinin, but not in S-2-peridinin. Quantum mechanical computations reveal the critical factors required for the formation of the ICT state and the associated solvent-modulated effects on the spectra and dynamics of these molecules and other carbonyl-containing carotenoids and polyenes. The factors are the magnitude and orientation of the ground- and excited-state dipole moments which must be suitable to generate sufficient mixing of the lowest two excited singlet states. PMID:22889055

Enriquez, Miriam M; Hananoki, Shohei; Hasegawa, Shinji; Kajikawa, Takayuki; Katsumura, Shigeo; Wagner, Nicole L; Birge, Robert R; Frank, Harry A

2012-09-01

252

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

PubMed

The metal L-edge (2p ? 3d) X-ray absorption spectra are affected by a number of different interactions: electron-electron repulsion, spin-orbit coupling, and charge transfer between metal and ligands, which makes the simulation of spectra challenging. The core restricted active space (RAS) method is an accurate and flexible approach that can be used to calculate X-ray spectra of a wide range of medium-sized systems without any symmetry constraints. Here, the applicability of the method is tested in detail by simulating three ferric (3d(5)) model systems with well-known electronic structure, viz., atomic Fe(3+), high-spin [FeCl6](3-) with ligand donor bonding, and low-spin [Fe(CN)6](3-) that also has metal backbonding. For these systems, the performance of the core RAS method, which does not require any system-dependent parameters, is comparable to that of the commonly used semi-empirical charge-transfer multiplet model. It handles orbitally degenerate ground states, accurately describes metal-ligand interactions, and includes both single and multiple excitations. The results are sensitive to the choice of orbitals in the active space and this sensitivity can be used to assign spectral features. A method has also been developed to analyze the calculated X-ray spectra using a chemically intuitive molecular orbital picture. PMID:25273421

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

2014-09-28

253

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

254

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

255

Ultrafast studies of the excited-state dynamics of copper and nickel phthalocyanine tetrasulfonates: potential sensitizers for the two-photon photodynamic therapy of tumors.  

PubMed

In order to evaluate the potential of copper and nickel phthalocyanine tetrasulfonates as sensitizers for two-photon photodynamic therapy, we conducted kinetic femtosecond measurements of transient absorption and bleaching of their excited state dynamics in aqueous solution. Samples were pumped with 620 nm and 310 nm laser light, which allowed us to study relaxation processes from both the first and second singlet (or doublet for the copper phthalocyanine) excited states. A second excitation from the first excited triplet state, approximately 685 and 105 ps after the first excitation for copper and nickel phthalocyanine tetrasulfonate respectively, was the most efficient way to bring the molecules to an upper triplet state. Presumably this highest triplet state can inflict molecular damage on adjacent biomolecules int eh absence of oxygen, resulting in the desired cytotoxic cellular response. Transient absorption spectra at different fixed delays indicate that optimum efficiency would require that the second photon has a wavelength of approximately 750 nm. PMID:14768627

Fournier, Michel; Pépin, Claude; Houde, Daniel; Ouellet, René; van Lier, Johan E

2004-01-01

256

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

257

Phenomenology of a SU(2) triplet Higgs.  

E-print Network

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

Sabio Vera, Agustin

258

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

259

States of Excitons and Linear Optical Spectra in Metallic Single-Walled Carbon Nanotubes  

NASA Astrophysics Data System (ADS)

Considering the exciton effect, the excitation energy and its binding energy of the metallic single-walled carbon nanotubes (SWNTs) are theoretically studied by using the simple tight-binding model, based on which the linear absorption spectra are also calculated. It is found that due to the trigonal warping effect, the excitation energies of the linear optical spectra all are split into two corresponding ones. Additionally, the splitting depends on both the chirality and the transition energy: (1) the splitting is maximal for the zigzag tubes, the splitting decreases with the increasing chiral angle; (2) the higher the transition energy is, the larger the splitting is. It is very interesting to find that the obtained results are in good agreement with the experimental results.

Yu, Gui-Li; Li, Gui-Chen; Jia, Yong-Lei; Tang, Gang

2014-09-01

260

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

261

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

262

Electronic structure, excited states, and photoelectron spectra of uranium, thorium, and zirconium bis(Ketimido) complexes (C5R5)2M[-NCPh2]2 (M = Th, U, Zr; R = H, CH3).  

PubMed

Organometallic actinide bis(ketimide) complexes (C5Me5)2An[-N=C(Ph)(R)]2 (where R = Ph, Me, and CH2Ph) of thorium(IV) and uranium(IV) have recently been synthesized that exhibit chemical, structural, and spectroscopic (UV-Visible, resonance-enhanced Raman) evidence for unusual actinide-ligand bonding. [Da Re et al., J. Am. Chem. Soc., 2005, 127, 682; Jantunen et al., Organometallics, 2004, 23, 4682; Morris et al., Organometallics, 2004, 23, 5142.] Similar evidence has been observed for the group 4 analogue (C5H5)2Zr[-N=CPh2]2. [Da Re et al., J. Am. Chem. Soc., 2005, 127, 682.] These compounds have important implications for the development of new heavy-element systems that possess novel electronic and magnetic properties. Here, we have investigated M-ketimido bonding (M = Th, U, Zr), as well as the spectroscopic properties of the highly colored bis-ketimido complexes, using density functional theory (DFT). Photoelectron spectroscopy (PES) has been used to experimentally elucidate the ground-state electronic structure of the thorium and uranium systems. Careful examination of the ground-state electronic structure, as well as a detailed modeling of the photoelectron spectra, reveals similar bonding interactions between the thorium and uranium compounds. Using time-dependent DFT (TDDFT), we have assigned the bands in the previously reported UV-Visible spectra for (C5Me5)2Th[-N=CPh2]2, (C5Me5)2U[-N=CPh2]2, and (C5H5)2Zr[-N=CPh2]2. The low-energy transitions are attributed to ligand-localized N p --> C=N pi excitations. These excited states may be either localized on a single ketimido unit or may be of the ligand-ligand charge-transfer type. Higher-energy transitions are cyclopentadienyl pi --> CN pi or cyclopentadienyl pi --> phenyl pi in character. The lowest-energy excitation in the (C5Me5)2U[-N=Ph2]2 compound is attributed to f-f and metal-ligand charge-transfer transitions that are not available in the thorium and zirconium analogues. Geometry optimization and vibrational analysis of the lowest-energy triplet state of the zirconium and thorium compounds also aids in the assignment and understanding of the resonance-enhanced Raman data that has recently been reported. [Da Re et al., J. Am. Chem. Soc., 2005, 127, 682.]. PMID:16839076

Clark, Aurora E; Martin, Richard L; Hay, P Jeffrey; Green, Jennifer C; Jantunen, Kimberly C; Kiplinger, Jaqueline L

2005-06-23

263

J. Phys. Chem. 1990, 94, 6963-6969 6963 Singlet-Triplet Energy Gaps in Chlorine-Substituted Methylenes and Silylenest  

E-print Network

J. Phys. Chem. 1990, 94, 6963-6969 6963 Singlet-Triplet Energy Gaps in Chlorine: August 11. 1989; In Final Form: March 12, 1990) The singlet-triplet splittingsof chlorine-consistentconfiguration interaction (DCCI) method. All chlorine-substituted methylenes and silylenes have singlet ground states

Goddard III, William A.

264

Edge-mode combinations in the entanglement spectra of non-Abelian fractional quantum Hall states on the torus  

NASA Astrophysics Data System (ADS)

We present a detailed analysis of bipartite entanglement in the non-Abelian Moore-Read fractional quantum Hall state of bosons and fermions on the torus. In particular, we show that the entanglement spectra can be decomposed into intricate combinations of different sectors of the conformal field theory describing the edge physics, and that the edge level counting and tower structure can be microscopically understood by considering the vicinity of the thin-torus limit. We also find that the boundary entropy density of the Moore-Read state is markedly higher than in the Laughlin states investigated so far. Despite the torus geometry being somewhat more involved than in the sphere geometry, our analysis and insights may prove useful when adopting entanglement probes to other systems that are more easily studied with periodic boundary conditions, such as fractional Chern insulators and lattice problems in general.

Liu, Zhao; Bergholtz, Emil J.; Fan, Heng; Läuchli, Andreas M.

2012-01-01

265

Metal-enhanced up-conversion fluorescence: effective triplet-triplet annihilation near silver surface.  

PubMed

Up-conversion phenomena are traditionally related to two- or multiphoton processes occurring under relatively high excitation intensities. Here we present the first results of ultralow excitation intensity (in order of Wcm(-2)) continuous-wave (CW) excited up-conversion fluorescence in Kretschmann surface plasmon geometry. The active system is a blue-emitting polymer matrix blended with metalated porphyrine macrocycles. The up-conversion fluorescence is a consequence of a two-particle triplet-triplet annihilation process (TTA). PMID:16351199

Baluschev, Stanislav; Yu, Fang; Miteva, Tzenka; Ahl, Stefanie; Yasuda, Akio; Nelles, Gabriele; Knoll, Wolfgang; Wegner, Gerhard

2005-12-01

266

SuperTriplets: a triplet-based supertree approach to phylogenomics  

PubMed Central

Motivation: Phylogenetic tree-building methods use molecular data to represent the evolutionary history of genes and taxa. A recurrent problem is to reconcile the various phylogenies built from different genomic sequences into a single one. This task is generally conducted by a two-step approach whereby a binary representation of the initial trees is first inferred and then a maximum parsimony (MP) analysis is performed on it. This binary representation uses a decomposition of all source trees that is usually based on clades, but that can also be based on triplets or quartets. The relative performances of these representations have been discussed but are difficult to assess since both are limited to relatively small datasets. Results: This article focuses on the triplet-based representation of source trees. We first recall how, using this representation, the parsimony analysis is related to the median tree notion. We then introduce SuperTriplets, a new algorithm that is specially designed to optimize this alternative formulation of the MP criterion. The method avoids several practical limitations of the triplet-based binary matrix representation, making it useful to deal with large datasets. When the correct resolution of every triplet appears more often than the incorrect ones in source trees, SuperTriplets warrants to reconstruct the correct phylogeny. Both simulations and a case study on mammalian phylogenomics confirm the advantages of this approach. In both cases, SuperTriplets tends to propose less resolved but more reliable supertrees than those inferred using Matrix Representation with Parsimony. Availability: Online and JAVA standalone versions of SuperTriplets are available at http://www.supertriplets.univ-montp2.fr/ Contact: vincent.ranwez@univ-montp2.fr PMID:20529895

Ranwez, Vincent; Criscuolo, Alexis; Douzery, Emmanuel J.P.

2010-01-01

267

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

NASA Astrophysics Data System (ADS)

The vibrational pattern and energy flow in the N-H stretch manifolds and the dissociation dynamics of methylamine (CH3NH2) 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

2008-04-01

268

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

269

Emitting Electrons Spectra and Acceleration Processes in the Jet of Mrk 421: From the Low State to the Giant Flare State  

NASA Astrophysics Data System (ADS)

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; Yuan, Qiang; Fan, Zhonghui; Zeng, Houdun

2013-03-01

270

Singlet and triplet energies of alpha-oligothiophenes: A spectroscopic, theoretical, and photoacoustic study: Extrapolation to polythiophene  

Microsoft Academic Search

The triplet state energies, ET(0-0), for the alpha-oligothiophenes (alphan's) with n=1-7, were determined and vary from 18 000 cm-1 (alpha2) to 13 000 cm-1 (alpha7). The data were obtained from spectroscopic and calorimetric measurements. It was found that the triplet energies decrease with the increase ring number (n), leveling off beginning with the alpha-oligothiophene with n=5. A linear relation was

J. Seixas de Melo; Luís M. Silva; Luís G. Arnaut; R. S. Becker

1999-01-01

271

Sensitive marker bands for the detection of spin states of heme in surface-enhanced resonance Raman scattering spectra of metmyoglobin.  

PubMed

Surface-enhanced resonance Raman scattering (SERRS) spectra of myoglobin (Mb) with various ligands were measured. In the resonance Raman scattering (RRS) spectra, peaks at around 1610 and 1640 cm(-1) have so far been used to discriminate between the heme iron in a high or low spin state. In the SERRS spectra, however, the spin state cannot be distinguished by the corresponding peaks. Alternatively, the intensity ratio of the SERRS peak at 1560 cm(-1) to that at 1620 cm(-1) was applied to detect the spin states sensitively (1.5 × 10(5) times compared with the RRS); namely, a high ratio was obtained from met-Mb in the high spin state at pH ? 7 except for in a strong acid solution. The different marker bands between the SERRS and RRS spectra may be due to the enhancement order from the surface selection rule. PMID:25335784

Kitahama, Yasutaka; Egashira, Masatoshi; Suzuki, Toshiaki; Tanabe, Ichiro; Ozaki, Yukihiro

2014-12-21

272

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

273

Photophysics of soret-excited tetrapyrroles in solution. IV. Radiationless decay and triplet-triplet annihilation investigated using tetraphenylporphinato Sn(IV).  

PubMed

The S(2) population decay rates and triplet-triplet annihilation efficiencies of Sn(IV)Cl(2)TPP have been measured in fluid solutions using its weak S(2)-S(0) fluorescence as a metric. A detailed description of the excited-state photophysics of Sn(IV)Cl(2)TPP has allowed comparisons to be made between this rigid, D(4h) axially coordinated molecule and axially uncoordinated tetrapyrroles of greater flexibility and lower symmetry. S(2)-S(1) internal conversion is the major S(2) population decay path for Sn(IV)Cl(2)TPP as it is for the S(2) states of all other d(0) and d(10) metalated tetrapyrroles. The S(2) state of Sn(IV)Cl(2)TPP exhibits S(2)-S(1) 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 S(2)-S(1) radiationless decay rates among the series MTPP (M = Mg, Zn, Cd, SnCl(2)) cannot be traced to differences in the displacements of the S(2) and S(1) potential surfaces. Instead, the most likely source of the large differences in S(2)-S(1) radiationless decay rates between CdTPP and Sn(IV)Cl(2)TPP is the lower symmetry of the former (near C(4v)), which permits a much larger number of vibrations to participate in S(2)-S(1) vibronic coupling. Triplet-triplet annihilation of the type 2T(1) --> S(2) + S(0) has been observed in Sn(IV)Cl(2)TPP 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. PMID:19778026

Maiti, Manisankar; Danger, Brook R; Steer, Ronald P

2009-10-22

274

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

275

Supersonic jet fluorescence spectra of 4-methylstyrene: Ground state vibration wavenumbers and improved torsional potential functions  

NASA Astrophysics Data System (ADS)

Single vibronic level (dispersed) fluorescence spectra of 4-methylstyrene, with excitation in various excited vibrational levels of S1, have provided wavenumbers of some a' and a? vibrations in S0 and energy levels for the C(1)-C(?) vinyl torsional and the methyl torsional vibrations. The estimated values of the parameters for the torsional potentials are V ?2= 943±58 cm -1, V ?4= -208±31 cm -1, for vinyl torsion in S0; V ?3= 28±4 cm -1, V ?6= -7±1 cm -1, for methyl torsion in S0; and V ?3= -8±4 cm -1, V ?6= -19±4 cm -1, for methyl torsion in S1. The vinyl group is coplanar with the benzene ring in S0. The methyl group is eclipsed, relative to the benzene ring, in S0, but almost staggered in S1.

Hollas, J. Michael; Taday, Philip F.; Gordon, Robert D.

1992-05-01

276

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

277

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

278

Electronic spectra and excited-state dynamics of 4-fluoro-N,N-dimethylaniline  

NASA Astrophysics Data System (ADS)

Concerted ultrafast time-resolved spectroscopic experiments and ab initio computational (TDDFT) studies of the electronic transitions of 4-fluoro-N,N-dimethylaniline (FDMA) have been performed to investigate the mechanism of photo-induced intramolecular charge transfer (ICT). The compound FDMA shows dual fluorescence from a ??? state and a closely-lying twisted intramolecular charge transfer (TICT) state in both n-hexane and acetonitrile. The very similar lifetimes observed for the two emission bands indicate that the ??? and the TICT states are effectively in thermal equilibrium at room temperature.

Fujiwara, Takashige; Reichardt, Christian; Aaron Vogt, R.; Crespo-Hernández, Carlos E.; Zgierski, Marek Z.; Lim, Edward C.

2013-10-01

279

Photolysis of 4-chlororesorcinol in water: competitive formation of a singlet ketene and a triplet carbene.  

PubMed

Research on photoinduced reactions of halogenated phenols is of interest for environmental photochemistry and for synthetic organic chemistry. Previous studies have uncovered interesting mechanistic features, including ring contraction from benzene to cyclopentadiene from ortho derivatives and two-electron processes forming carbocations and carbenes from para derivatives. In the present work, we studied the aqueous photochemistry of 4-chlororesorcinol (1), which combines the conformational properties of both types of derivatives, using nanosecond transient absorption spectroscopy and photoproduct analysis. The absorption spectra obtained upon pulsed laser excitation of 1 showed the occurrence of both o-Cl and p-Cl elimination, the first observed transients being the ketene 3-hydroxy-6-fulvenone (2, ?(max) = 255 nm) and the carbene 2-hydroxy-4-oxo-2,5-cyclohexadienylidene (3, ?(max) = 405 and 395 nm). The reactivities of 2 and 3, the spectra of the secondary transients and the analysis of the final products showed that the two HCl elimination pathways take place concurrently. Most probably, the bifurcation step is the competition between intersystem crossing on the molecular level and o-Cl elimination on the singlet surface; p-Cl elimination proceeds on the triplet surface. Remarkably, the quantum yield of p-Cl elimination from 1 is lower by one order of magnitude compared to that found in para-halogenated phenols, while that of o-Cl elimination from 1 is comparable to ortho-halogenated phenol. To explain this result, we propose that o-Cl elimination is the major deactivation step, forming an intermediate singlet cation which is able to recombine to ground state 1, thereby limiting the observed photochemical quantum yields. PMID:20859579

Richard, Claire; Krajnik, Paul; Grabner, Gottfried

2010-11-14

280

Fermiophobia in a Higgs triplet model  

SciTech Connect

A fermiophobic Higgs boson can arise in models with an extended Higgs sector, such as models with scalars in an isospin triplet representation. In a specific model with a scalar triplet and spontaneous violation of lepton number induced by a scalar singlet field, we show that fermiophobia is not a fine-tuned situation, unlike in two higgs doublet models. We study distinctive signals of fermiophobia which can be probed at the LHC. For the case of a small Higgs mass, a characteristic signal would be a moderate B(H{yields}{gamma}{gamma}) accompanied by a large B(H{yields}JJ) (where J is a Majoron), the latter being an invisible decay. For the case of a large Higgs mass there is the possibility of dominant H{yields}ZZ, WW and suppressed H{yields}JJ decay modes. In this situation, B(H{yields}ZZ) is larger than B(H{yields}WW), which differs from the SM prediction.

Akeroyd, A. G. [Department of Physics and Center for Mathematics and Theoretical Physics, National Central University, Chungli, Taiwan 320, Taiwan (China); NExT Institute and School of Physics and Astronomy, University of Southampton, Highfield, Southampton SO17 1BJ (United Kingdom); Diaz, Marco A.; Romero Maltrana, D. [Departamento de Fisica, Pontificia Universidad Catolica de Chile, Santiago 690441 (Chile); Rivera, Maximiliano A. [Departamento de Fisica, Universidad Tecnica Federico Santa Maria, Casilla 110-V, Valparaiso (Chile)

2011-05-01

281

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

282

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

283

Experimental and Theoretical Study of the Electronic States and Spectra of TeH and TeLi.  

PubMed

Gas-phase emission spectra of the hitherto unknown free radical TeLi have been measured in the NIR range with a Fourier-transform spectrometer. The emissions were observed from a fast flow system in which tellurium vapor in argon carrier gas was passed through a microwave discharge and mixed with lithium vapor in an observation tube. Two systems of blue-degraded bands were measured at high spectral resolution in the ranges 8000-9000 and 5700-6700 cm(-1) and vibrational and rotational analyses were performed. In order to aid in the analysis of the experimental data, a series of relativistic configuration interaction calculations has been carried out to obtain potential curves for the low-lying states of TeLi and the isovalent TeH and also electric dipole transition moments connecting them. As in the TeH system, the ground state of TeLi is found to be X(2)Pi(i), but with a remarkably smaller spin-orbit splitting. The TeLi calculations indicate a strongly bound A(2)Sigma(+) state, while in TeH the analogous state is computed to lie significantly higher at approximately 32 000 cm(-1), and it is strongly predissociated. Based on the theoretical analysis, the observed TeLi band systems are assigned to the transitions A(2)Sigma(+)(A1/2)-->X(1)(2)Pi(3/2)(X(1)3/2) and A(2)Sigma(+)(A1/2)-->X(2)(2)Pi(1/2)(X(2)1/2). Analysis of the spectra has yielded the molecular constants (in cm(-1)) X(1)(2)Pi(3/2):omega(e)=457.49(3), omega(e)x(e)=2.482(9), B(0)=0.408908(8); X(2)(2)Pi(1/2): T(e)=2353.44(3), omega(e)=456.28(4), omega(e)x(e)=2.635(8), B(0)=0.414954(8), p(0)=1.00637(4); A(2)Sigma(+): T(e)=8574.64(2), omega(e)=437.81(3), omega(e)x(e)=2.581(8), B(0)=0.423903(8), p(0)=-0.19915(2), where the numbers in parentheses are the standard deviations of the parameters. Comparison of the isovalent TeLi and TeH systems emphasizes that the difference in bonding character (ionic in TeLi vs covalent in TeH) is responsible for qualitative differences in the electronic spectra of these two molecules. Copyright 2001 Academic Press. PMID:11281700

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

2001-04-01

284

Twin and Triplet Drugs in Opioid Research  

NASA Astrophysics Data System (ADS)

Twin and triplet drugs are defined as compounds that contain respectively two and three pharmacophore components exerting pharmacological effects in a molecule. The twin drug bearing the same pharmacophores is a "symmetrical twin drug", whereas that possessing different pharmacophores is a "nonsymmetrical twin drug." In general, the symmetrical twin drug is expected to produce more potent and/or selective pharmacological effects, whereas the nonsymmetrical twin drug is anticipated to show both pharmacological activities stemming from the individual pharmacophores (dual action). On the other hand, nonsymmetrical triplet drugs, which have two of the same pharmacophores and one different moiety, are expected to elicit both increased pharmacological action and dual action. The two identical portions could bind the same receptor sites simultaneously while the third portion could bind a different receptor site or enzyme. This review will mainly focus on the twin and triplet drugs with an evaluation of their in vivo pharmacological effects, and will also include a description of their pharmacology and synthesis.

Fujii, Hideaki

285

Superscars in billiards -- A model for doorway states in quantum spectra  

E-print Network

In a unifying way, the doorway mechanism explains spectral properties in a rich variety of open mesoscopic quantum systems, ranging from atoms to nuclei. A distinct state and a background of other states couple to each other which sensitively affects the strength function. The recently measured superscars in the barrier billiard provide an ideal model for an in--depth investigation of this mechanism. We introduce two new statistical observables, the full distribution of the maximum coupling coefficient to the doorway and directed spatial correlators. Using Random Matrix Theory and random plane waves, we obtain a consistent understanding of the experimental data.

S. Å berg; T. Guhr; M. Miski-Oglu; A. Richter

2008-05-15

286

Proton and electron transfer in the excited state quenching of phenosafranine by aliphatic amines.  

PubMed

The quenching of the excited singlet and triplet states of phenosafranine by aliphatic amines was investigated in acetonitrile and methanol. The rate constants for the quenching of the excited singlet state depend on the one-electron redox potential of the amine suggesting a charge transfer process. However, for the triplet state, quenching dependence on the redox potential either is opposite to the expectation or there is not dependence at all. Moreover, in MeOH the first-order rate constant for the decay of the triplet state, k(obs) presents a downward curvature as a function of the amine concentration. This behavior was interpreted in terms of the reversible formation of an intermediate excited complex, and from a kinetic analysis the equilibrium constant K(exc) could be extracted. The log K(exc) shows a linear relationship with the pKb of the amine. On the other hand, for the triplet state quenching in acetonitrile k(obs) varies linearly with the amine concentration. Nevertheless, the quenching rate constants correlate satisfactorily with pKb and not with the redox potential. The results were interpreted in terms of a proton transfer quenching, reversible in the case of MeOH and irreversible in MeCN. This was further confirmed by the transient absorption spectra obtained by laser flash photolysis. The transient absorption immediately after the triplet state quenching could be assigned to the unprotonated form of the dye. At later times the spectrum matches the semireduced form of the dye. The overall process corresponds to a one-electron reduction of the dye mediated by the deprotonated triplet state. PMID:17576369

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

2007-01-01

287

Measurement of triplet extinction coefficients of organic compounds by McClure's method  

NASA Astrophysics Data System (ADS)

We tested M CC LURE'S method for measuring the triplet extinction coefficients ? T of organic compounds on anthracene and pyrene, using the u.v. lines from a krypton ion cw laser as a steady-state excitation source. Our values for anthracene ? T = 82 × 10 31/mole cm at 426 nm and pyrene ? T = 37 × 10 3l/mole cm at 413 nm agree well with values obtained by other methods. M CC LURE derived his linear relationship from kinetic considerations. One simply measures triplet optical densities (OD T) at a fixed wavelength (e.g. at a triplet absorption maximum) as functions of different cw laser excitation intensities (powers) I ex. A plot of 1/OD T against 1/ I ex yields a straight line. Extrapolating to the intersection of the ordinate (1/ I ex = 0, or I ex = ?) yields 1/OD ?T. Since, at infinite excitation intensity I ex, the concentration of the triplet state molecules N T is equal to the original concentration N S of the ground state concentration, ? T can be easily calculated from ? T = OD ?T/ N Sd where OD ?T is the triplet optical density at infinite excitation intensity, NS is the original concentration of molecules (at ground state), and d is the thickness of the sample. The success of this method requires the production of high concentrations of triplet state molecules N T, as well as steady-state excitation. CW lasers fulfill all these requirements. We discuss the spectroscopic equipment employed for measuring triplet optical densities in some detail. Methods for reducing heat gradients (noise) in liquid nitrogen, laser excitation spot sizes, reduction of spherical aberrations, etc., are reviewed. We varied the cw laser illumination density (laser power/area) by setting the focusing lens at different distances from the sample, and measured 1/OD T as a function of 1/ I ex. As long as the size of the excitation area was not below a critical size, all the straight lines obtained at different lens settings converged well into only one value of 1/OD ?T. Measurements were also performed at different concentrations of the solutes.

Pavlopoulos, Theodore G.

288

Mollow triplet for cavity-mediated laser cooling  

NASA Astrophysics Data System (ADS)

Here we analyze cavity-mediated laser cooling for an experimental setup with an external trap which strongly confines the motion of a particle in the direction of the cavity axis. It is shown that the stationary-state phonon number exhibits three sharp minima as a function of the atom-cavity detuning due to a direct atom-phonon-photon coupling term in the system Hamiltonian. These resonances have the same origin as the Mollow triplet in the resonance fluorescence of a laser-driven atomic system. It is shown that a laser-Rabi-frequency-dependent atom-cavity detuning yields the lowest stationary-state phonon number for a wide range of experimental parameters.

Kim, Oleg; Beige, Almut

2013-11-01

289

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

290

The charge-trapping and triplet-triplet annihilation processes in organic light-emitting diodes: A duty cycle dependence study on magneto-electroluminescence  

NASA Astrophysics Data System (ADS)

We studied the magneto-electroluminescence (MEL) in tri-(8-hydroxyquinoline)-aluminum (Alq3)-based organic light-emitting devices through both steady-state and transient methods. As the magnetic field increases, the MEL exhibits a rapid rise, followed by the saturation tendency at all voltages in the steady-state measurement, but in the transient measurement it first increases to a maximum and then decreases to negative values when the driving voltages are higher than 8V. Furthermore, we found that the MEL strongly depends on the duty cycle of the pulse voltage. Finally, by employing the triplet-triplet annihilation model combined with the charge trapping effects, we explained the duty cycle dependence of MELs.

Peng, Qiming; Chen, Ping; Li, Feng

2013-01-01

291

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

NASA Astrophysics Data System (ADS)

Triplet excitonic state in the organic molecule may arise from a singlet excitation and the following inter-system crossing. Especially for a spin-bearing molecule, an exchange interaction between the triplet exciton and the original spin on the molecule can be expected. In this paper, such exchange interaction in copper-phthalocyanine (CuPc, spin-1/2) was investigated from first-principles by using density-functional theory within a variety of approximations to the exchange correlation, ranging from local-density approximation to long-range corrected hybrid-exchange functional. The magnitude of the computed exchange interaction is in the order of meV with the minimum value (1.5 meV, ferromagnetic) given by the long-range corrected hybrid-exchange functional CAM-B3LYP. This exchange interaction can therefore give rise to a spin coherence with an oscillation period in the order of picoseconds, which is much shorter than the triplet lifetime in CuPc (typically tens of nanoseconds). This implies that it might be possible to manipulate the localized spin on Cu experimentally using optical excitation and inter-system crossing well before the triplet state disappears.

Wu, Wei

2014-06-01

292

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

NASA Astrophysics Data System (ADS)

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

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

2011-10-01

293

Theoretical studies on aurophilicity and excited-state properties in binuclear gold (I) trithiocarbonate and related complexes  

Microsoft Academic Search

The MP2 and unrestricted MP2 methods were performed to fully optimize the structures of [Au2(S2CS)2]2? (1) in the ground and lowest-energy triplet excited states, respectively. It was shown that upon excitation the Au–Au distance shortens about 0.156Å with respect to the 2.814Å one in the ground state. In the calculations, vibrational frequencies at the MP2 level and solution absorption spectra

Yuan-Ru Guo; Qing-Jiang Pan; Gui-Zhen Fang; Zhi-Ming Liu

2005-01-01

294

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

295

Exchange-only optimized effective potential calculation of excited state spectra for He and Be atoms.  

SciTech Connect

The optimized effective potential (OEP) method allows orbital-dependent functionals to be used in density functional theory (DFT), which, in particular, allows exact exchange formulations of the exchange energy to be used in DFT calculations. Because the exact exchange is inherently self-interaction correcting, the resulting OEP calculations have been found to yield superior band-gaps for condensed-phase systems. Here we apply these methods to the isolated atoms He and Be, and compare to high quality experiments and calculations to demonstrate that the orbital energies accurately reproduce the excited state spectrum for these species. These results suggest that coupling the exchange-only OEP calculations with proper (orbital-dependent or other) correlation functions might allow quantitative accuracy from DFT calculations.

Desjarlais, Michael Paul; Muller, Richard Partain

2006-02-01

296

Determination of the Effective Ground State Potential Energy Function of Ozone from High-Resolution Infrared Spectra.  

PubMed

The effective ground state potential energy function of the ozone molecule near the C(2v) equilibrium configuration was obtained in a least-squares fit to the largest sample of experimental, high-resolution vibration-rotation data used for this purpose so far. The fitting is based on variational calculations carried out with the extended Morse Oscillator Rigid Bender Internal Dynamics model. The potential function is expanded in Morse-type functions of the stretching variables and in cosine of the bending angle. The present calculation produces results in significantly better agreement with experiment than previous determinations of the potential energy surface, and the energies predicted with the new surface are sufficiently accurate to be useful for the assignment of new high-resolution spectra. The rms (root-mean-square) deviation of the fit of rovibrational data up to J = 5 is 0.02 cm(-1). For the set of all 60 band centers of the (16)O(3) molecule included in the Atlas of Ozone Line Parameters, the rms deviation is 0.025 cm(-1), and for all band centers determined so far from high-resolution spectra, including those recently observed and assigned in Reims corresponding to highly excited stretching and bending vibrations (v(1) + v(2) + v(3) = 6), the rms deviation is 0.1 cm(-1). The "dark states" that produce resonance perturbations in the observed bands are described with experimental accuracy up to the (v(1)v(2)v(3)) = (080) state. Extrapolation tests demonstrate the predictive power of the potential function obtained: rotational extrapolation up to J = 10 for the 11 lowest vibrational states results in an rms deviation of 0.06cm(-1). Also, vibrational energies measured by low-resolution Raman spectroscopy (which were not included in the input data for the fit) are calculated within the experimental accuracy (rms = 1.6 cm(-1)) of the experimental values up to the dissociation limit. The statistical analysis suggests that the accuracy of the equilibrium geometry and force constants of the molecule is considerably improved relative to previous determinations. The long-range behavior of the fitted potential at the dissociation limit O(3) --> O(2) + O shows very good agreement with experimental data. The new potential energy surface was used to predict the band centers of the isotopomers (17)O(3) and (18)O(3). Copyright 1999 Academic Press. PMID:10527781

Tyuterev; Tashkun; Jensen; Barbe; Cours

1999-11-01

297

Understanding the terahertz spectra of crystalline pharmaceuticals: terahertz spectroscopy and solid-state density functional theory study of (S)-(+)-ibuprofen and (RS)-ibuprofen.  

PubMed

The potential applications of terahertz (THz) spectroscopy in the analysis of pharmaceutical products in their crystalline state have prompted the need for a more thorough understanding of the fundamental vibrational motions contributing to the THz spectra. The detection of variations in crystal structure and the reliable assignment of observed THz absorption features can be aided by the use of solid-state density functional theory (DFT). In this study, solid-state DFT with periodic boundary conditions was used to simulate the crystalline structure and assign the experimental THz spectra (10-90 cm(-1)) of the enantiomerically pure and racemic forms of the common pharmaceutical compound ibuprofen. The results clearly demonstrate the capabilities of DFT methodologies to accurately reproduce the THz spectra of large complicated molecular systems and provide insight into the internal and external vibrational motions that form the basis of THz spectroscopy. PMID:20815081

King, Matthew D; Buchanan, William D; Korter, Timothy M

2011-03-01

298

Mechanism for singlet fission in pentacene and tetracene: from single exciton to two triplets.  

PubMed

Singlet fission (SF) could dramatically increase the efficiency of organic solar cells by producing two triplet excitons from each absorbed photon. While this process has been known for decades, most descriptions have assumed the necessity of a charge-transfer intermediate. This ab initio study characterizes the low-lying excited states in acene molecular crystals in order to describe how SF occurs in a realistic crystal environment. Intermolecular interactions are shown to localize the initially delocalized bright state onto a pair of monomers. From this localized state, nonadiabatic coupling mediated by intermolecular motion between the optically allowed exciton and a dark multi-exciton state facilitates SF without the need for a nearby low-lying charge-transfer intermediate. An estimate of the crossing rate shows that this direct quantum mechanical process occurs in well under 1 ps in pentacene. In tetracene, the dark multi-exciton state is uphill from the lowest singlet excited state, resulting in a dynamic interplay between SF and triplet-triplet annihilation. PMID:22084927

Zimmerman, Paul M; Bell, Franziska; Casanova, David; Head-Gordon, Martin

2011-12-14

299

Dual enhancement of electroluminescence efficiency and operational stability by rapid upconversion of triplet excitons in OLEDs  

PubMed Central

Recently, triplet harvesting via a thermally activated delayed fluorescence (TADF) process has been established as a realistic route for obtaining ultimate internal electroluminescence (EL) quantum efficiency in organic light-emitting diodes (OLEDs). However, the possibility that the rather long transient lifetime of the triplet excited states would reduce operational stability due to an increased chance for unwarranted chemical reactions has been a concern. Herein, we demonstrate dual enhancement of EL efficiency and operational stability in OLEDs by employing a TADF molecule as an assistant dopant and a fluorescent molecule as an end emitter. The proper combination of assistant dopant and emitter molecules realized a “one-way” rapid Förster energy transfer of singlet excitons from TADF molecules to fluorescent emitters, reducing the number of cycles of intersystem crossing (ISC) and reverse ISC in the TADF molecules and resulting in a significant enhancement of operational stability compared to OLEDs with a TADF molecule as the end emitter. In addition, we found that the presence of this rapid energy transfer significantly suppresses singlet-triplet annihilation. Using this finely-tuned rapid triplet-exciton upconversion scheme, OLED performance and lifetime was greatly improved. PMID:25673259

Furukawa, Taro; Nakanotani, Hajime; Inoue, Munetomo; Adachi, Chihaya

2015-01-01

300

Electron energy-loss spectra of coupled electronic states: Effects of Rydberg-valence interactions in O2  

NASA Astrophysics Data System (ADS)

The concept of the ``generalized transition moment'' is extended beyond the region of applicability of the first Born approximation and is used in the analysis of electron energy-loss spectra for O2, presented here, which have been measured at intermediate impact energies. A coupled-channel theoretical treatment of the strongly mixed Rydberg and valence states that dominate the optically allowed spectrum is used to explain the relative intensities of many unusual features occurring in the 7-11.2-eV energy-loss region. For these electronically excited states of 3?-u and 3?u symmetry, the evolution of the shape of the corresponding electron energy-loss spectrum as the scattering conditions are changed is controlled essentially by one parameter: the ratio of the diabatic generalized transition moments into the Rydberg and valence components of the mixed electronic states. The generalized Rydberg transition moment is found to decrease much faster than the valence moment as the momentum transferred in the collision increases. The results of the coupled-channel analysis also indicate that the more diffuse spectral features are generally asymmetric, those in the 7-9.8-eV region changing slightly in position as the scattering conditions are altered. Thus, the Gaussian-line-shape-based models that have been employed previously in attempts to decompose the diffuse part of the electron energy-loss spectrum for O2, into contributions from different electronic states, are unlikely to have given meaningful results. As a consequence of the Rydberg-valence interactions, it is found that some vibrational levels of the mixed states give rise to features in the electron energy-loss spectrum which are anomalously strong at the low impact energies and large scattering angles for which normal optically allowed transitions are expected to decline in relative strength. These ``persistent lines'' are easily confused with those from the optically forbidden transitions which increase in relative intensity under such conditions. Thus, the coupled-channel technique is found to be a valuable aid to the assignment of features in the electron energy-loss spectrum.

Lewis, B. R.; England, J. P.; Gibson, S. T.; Brunger, M. J.; Allan, M.

2001-02-01

301

Triplet exciton dissociation in singlet exciton fission photovoltaics.  

PubMed

Triplet exciton dissociation in singlet exciton fission devices with three classes of acceptors are characterized: fullerenes, perylene diimides, and PbS and PbSe colloidal nanocrystals. Using photocurrent spectroscopy and a magnetic field probe it is found that colloidal PbSe nanocrystals are the most promising acceptors, capable of efficient triplet exciton dissociation and long wavelength absorption. PMID:22968762

Jadhav, Priya J; Brown, Patrick R; Thompson, Nicholas; Wunsch, Benjamin; Mohanty, Aseema; Yost, Shane R; Hontz, Eric; Van Voorhis, Troy; Bawendi, Moungi G; Bulovi?, Vladimir; Baldo, Marc A

2012-12-01

302

Variational Analysis of Mass Spectra and Decay Constants for Ground State Pseudoscalar and Vector Mesons in Light-Front Quark Model  

E-print Network

Using the variational principle, we compute mass spectra and decay constants of ground state pseudoscalar and vector mesons in the light-front quark model with the QCD-motivated effective Hamiltonian including the hyperfine interaction. By smearing out the Dirac delta function in the hyperfine interaction, we avoid the issue of negative infinity in applying the variational principle to the computation of meson mass spectra. In comparison with the previous computation handling the hyperfine interaction as perturbation, our variational analysis provides an overall improvement on the agreement with the experimental data of mass spectra for the ground state pseudoscalar and vector mesons from $\\pi$ to $\\Upsilon$. By taking a larger harmonic oscillator basis in our trial wave function, we also obtain the better agreement between the experimental data of decay constants and the results from our model calculation for these mesons.

Choi, Ho-Meoyng; Li, Ziyue

2015-01-01

303

Distribución Espacial de Ancho Equivalente del Triplete del CaII a partir de Imágenes GMOS  

NASA Astrophysics Data System (ADS)

Using Gemini+GMOS imagery obtained through the filters i, z and CaT, we developed a technique for estimating the value of the Ca II triplet (CaT) equivalent width (EW). The map generated through arithmetic operations with the near infrared images was calibrated with long slit spectra obtained with REOSC spectrograph at CASLEO. We apply this technique to the study of M 83 central region and present the preliminary results on the spatial distribution of the EW(CaT) within an area of 40 per 40 square arcsec around the double nucleus of M 83, with a spatial resolution of 0.8 arcsec. FULL TEXT IN SPANISH.

Díaz, R. J.; Mast, D.

304

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

NASA Astrophysics Data System (ADS)

Polycrystalline tetracene films have been explored using weak ˜30fs visible laser pulses that excite the lowest singlet exciton as well as coherent vibrational motion. Transient difference spectra show a triplet absorption which arises following singlet fission (SF) and persists for 1.6 ns without decay. Adaptive pulse shaping identifies multipulse optimal fields which maximize this absorption feature by ˜20%. These are comprised of subpulses separated by time delays well correlated with the period of lattice vibrations suggesting such modes control the yield of SF photochemistry.

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

2010-12-01

305

Enhanced triplet formation in polycrystalline tetracene films by femtosecond optical-pulse shaping.  

PubMed

Polycrystalline tetracene films have been explored using weak ? 30 fs visible laser pulses that excite the lowest singlet exciton as well as coherent vibrational motion. Transient difference spectra show a triplet absorption which arises following singlet fission (SF) and persists for 1.6 ns without decay. Adaptive pulse shaping identifies multipulse optimal fields which maximize this absorption feature by ? 20%. These are comprised of subpulses separated by time delays well correlated with the period of lattice vibrations suggesting such modes control the yield of SF photochemistry. PMID:21231627

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

2010-12-17

306

Non-Linear Trans-Planckian Corrections of Spectra due to the Non-trivial Initial States  

E-print Network

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.

E. Yusofi; M. Mohsenzadeh

2014-10-06

307

Non-Linear Trans-Planckian Corrections of Spectra due to the Non-trivial Initial States  

E-print Network

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

2014-01-01

308

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

PubMed Central

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

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

2012-01-01

309

Investigating the Singlet-Triplet Gap in Tetramethyleneethane using Quantum Monte Carlo Techniques  

NASA Astrophysics Data System (ADS)

Tetramethyleneethane (TME) is an organic molecule composed of two allyl subunits that is the simplest disjoint diradical. The ground state according to experimental and theoretical evidence is a singlet state with ^1A symmetry. footnotetextClifford, E. P.; Wenthold, P. G.; Lineberger, W. C.; Ellison, G. B.; Wang, C. X.; Grabowski, J. J.; Vila, F.; Jordan, K. D. J. Chem. Soc., Perkin Trans. 2 1998, 1015. Due to the near degeneracy of the frontier orbitals, however, this state is inherently two-configurational. As the molecule is twisted through torsional angles about the central C-C bond, we compute the singlet-triplet gap using quantum Monte Carlo (QMC). In its diffusion Monte Carlo (DMC) variant, QMC is an exact method for solving the Schr"odinger equation within the bounds of the fixed-node approximation. footnotetext J.B. Anderson, J. Chem. Phys. 63, 1499 (1975). DMC calculations using a multi-configurational trial wave function produce the correct ordering of the singlet and triplet states. We also investigate an alternate approach, full configuration interaction quantum Monte Carlo (FCIQMC). We compare the FCIQMC singlet-triplet energy gap as a function of torsional angle with the different theoretical methods.

Pozun, Zachary; Hermann, Jan; Jordan, Kenneth

2013-03-01

310

Superfluid phases of triplet pairing and rapid cooling of the neutron star in Cassiopeia A  

E-print Network

In a simple model it is demonstrated that the neutron star surface temperature evolution is sensitive to the phase state of the triplet superfluid condensate. A multicomponent triplet pairing of superfluid neutrons in the core of a neutron star with participation of several magnetic quantum numbers leads to neutrino energy losses exceeding the losses from the unicomponent pairing. A phase transition of the neutron condensate into the multicomponent state triggers more rapid cooling of superfluid core in neutron stars. This makes it possible to simulate an anomalously rapid cooling of neutron stars within the minimal cooling paradigm without employing any exotic scenarios suggested earlier for rapid cooling of isolated neutron star in Cassiopeia A.

Lev B. Leinson

2014-11-25

311

Singlet-Triplet Annihilation Limits Exciton Yield in Poly(3-Hexylthiophene)  

NASA Astrophysics Data System (ADS)

Control of chain length and morphology in combination with single-molecule spectroscopy techniques provides a comprehensive photophysical picture of excited-state losses in the prototypical conjugated polymer poly(3-hexylthiophene) (P3HT). Our examination reveals a universal self-quenching mechanism, based on singlet-triplet exciton annihilation, which accounts for the dramatic loss in fluorescence quantum yield of a single P3HT chain between its solution (unfolded) and bulklike (folded) state. Triplet excitons fundamentally limit the fluorescence of organic photovoltaic materials, which impacts the conversion of singlet excitons to separated charge carriers, decreasing the efficiency of energy harvested at high excitation densities. Interexcitonic interactions are so effective that a single P3HT chain of order 100 kDa weight behaves like a 2-level system, exhibiting perfect photon antibunching.

Steiner, Florian; Vogelsang, Jan; Lupton, John M.

2014-04-01

312

The speed limit for protein folding measured by triplet–triplet energy transfer  

PubMed Central

A direct measure of intramolecular chain diffusion is obtained by the determination of triplet–triplet energy-transfer rates between a donor and an acceptor chromophore attached at defined points on a polypeptide chain. Single exponential kinetics of contact formation are observed on the nanosecond time scale for polypeptides in which donor and acceptor are linked by repeating units of glycine and serine residues. The rates depend on the number of peptide bonds (N) separating donor and acceptor and show a maximum for the shortest peptides (N = 3) with a time constant (? = 1/k) of 20 ns. This sets an upper limit for the speed of formation of the first side-chain contacts during protein folding. PMID:10449738

Bieri, Oliver; Wirz, Jakob; Hellrung, Bruno; Schutkowski, Mike; Drewello, Mario; Kiefhaber, Thomas

1999-01-01

313

Dark Matter in the Higgs Triplet Model  

E-print Network

The inability to predict neutrino masses and the existence of the dark matter are two essential shortcomings of the Standard Model. The Higgs Triplet Model provides an elegant resolution of neutrino masses via the seesaw mechanism. We show here that introducing vectorlike leptons in the model also provides a resolution to the problem of dark matter. We investigate constraints, including the invisible decay width of the Higgs boson and the electroweak precision variables, and impose restrictions on model parameters. We analyze the effect of the relic density constraint on the mass and Yukawa coupling of dark matter. We also calculate the cross sections for indirect and direct dark matter detection and show our model predictions for the neutrino and muon fluxes from the Sun, and the restrictions they impose on the parameter space. With the addition of vectorlike leptons, the model is completely consistent with dark matter constraints, in addition to improving electroweak precision and doubly charged mass restri...

Bahrami, Sahar

2015-01-01

314

The superconducting spin valve and triplet superconductivity  

NASA Astrophysics Data System (ADS)

A review of our recent results on the spin valve effect is presented. We have used a theoretically proposed spin switch design F1/F2/S comprising a ferromagnetic bilayer (F1/F2) as a ferromagnetic component, and an ordinary superconductor (S) as the second interface component. Based on it we have prepared and studied in detail a set of multilayers CoOx/Fe1/Cu/Fe2/S (S=In or Pb). In these heterostructures we have realized for the first time a full spin switch effect for the superconducting current, have observed its sign-changing oscillating behavior as a function of the Fe2-layer thickness and finally have obtained direct evidence for the long-range triplet superconductivity arising due to noncollinearity of the magnetizations of the Fe1 and Fe2 layers.

Garifullin, I. A.; Leksin, P. V.; Garif'yanov, N. N.; Kamashev, A. A.; Fominov, Ya. V.; Schumann, J.; Krupskaya, Y.; Kataev, V.; Schmidt, O. G.; Büchner, B.

2015-01-01

315

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

Microsoft Academic Search

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

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

2007-01-01

316

Experimental aspects in acquisition of wide bandwidth solid-state MAS NMR spectra of low-? nuclei with different opportunities on two commercial NMR spectrometers.  

PubMed

The acquisition and different appearances observed for wide bandwidth solid-state MAS NMR spectra of low-? nuclei, using (14)N as an illustrative nucleus and employing two different commercial spectrometers (Varian, 14.1T and Bruker, 19.6T), have been compared/evaluated and optimized from an experimental NMR and an electronic engineering point of view, to account for the huge differences in these spectra. The large differences in their spectral appearances, employing the recommended/standard experimental set-up for the two different spectrometers, are shown to be associated with quite large differences in the electronic design of the two types of preamplifiers, which are connected to their respective probes through a 50? cable, and are here completely accounted for. This has led to different opportunities for optimum performances in the acquisition of nearly ideal wide bandwidth spectra for low-? nuclei on the two spectrometers by careful evaluation of the length for the 50? probe-to-preamp cable for the Varian system and appropriate changes to the bandwidth (Q) of the NMR probe used on the Bruker spectrometer. Earlier, we reported quite distorted spectra obtained with Varian Unity INOVA spectrometers (at 11.4 and 14.1T) in several exploratory wide bandwidth (14)N MAS NMR studies of inorganic nitrates and amino acids. These spectra have now been compared/evaluated with fully analyzed (14)N MAS spectra correspondingly acquired at 19.6T on a Bruker spectrometer. It is shown that our upgraded version of the STARS simulation/iterative-fitting software is capable of providing identical sets for the molecular spectral parameters and corresponding fits to the experimental spectra, which fully agree with the electronic measurements, despite the highly different appearances for the MAS NMR spectra acquired on the Varian and Bruker spectrometers. PMID:21704544

Jakobsen, Hans J; Bildsøe, Henrik; Gan, Zhehong; Brey, William W

2011-08-01

317

Triplet pi-diradical dication of directly meso-beta-linked porphyrin dimer.  

PubMed

Directly linked bisporphyrin, Zn(II)2 5,10,15,20-tetrakis(2,4,6-trimethylphenyl)-2-(10,15,20-tris(3,5-di-tert-butylphenyl)porphyrin-5-yl)porphyrin, was investigated on the basis of the magnetic property of its bis(pi-radical cation). A stable triplet state of the bis(pi-radical cation) of the bisporphyrin, which obeys the Curie law, was successfully observed. PMID:14759189

Segawa, Hiroshi; Senshu, Yutaka; Nakazaki, Jotaro; Susumu, Kimihiro

2004-02-11

318

Vibration Wavenumbers of 2-Aminobenzotrifluoride in the Ground and S1 Electronic States from Its Infrared, Raman, and Supersonic Jet S1-S0 Fluorescence Spectra  

NASA Astrophysics Data System (ADS)

Raman and infrared spectra of 2-aminobenzotrifluoride, in the liquid phase, and single vibronic level fluorescence (SVLF) spectra, in a supersonic jet, have been recorded and assigned to give an almost complete set of fundamental vibration wavenumbers in S0. In the SVLF spectrum, the assignment of the I 02 band, where ? I is the NH 2-inversion vibration, is not so straightforward as for 3- and 4-aminobenzotrifluoride, and the most likely assignment is discussed. The fluorescence excitation spectrum gives some lower vibrational wavenumbers in the S1 electronic state and shows a long progression in the CF 3 torsional mode.

Ribeiroclaro, P. J. A.; Teixeiradias, J. J. C.; Gordon, R. D.; Hollas, J. M.

1993-12-01

319

Singlet-triplet oscillations with pairs of neutral atoms in an optical superlattice  

NASA Astrophysics Data System (ADS)

We show the creation, detection and manipulation of effective-spin triplet and singlet pairs with ultracold ^87 Rb atoms in an optical superlattice. Starting from two atoms on a lattice site being in different Zeeman states labeled by | > and | >, we split the sites into symmetric double-wells to form delocalized spin triplets | >+ | >. We use a magnetic field gradient to achieve a coherent coupling between the triplet and the corresponding singlet state. The detection of the emerging oscillations relies on measuring the parity of the spatial two-body wavefunction after merging the double-wells. A superexchange coupling between adjacent double-wells realizes a SWAP operation that stretches the entangled pairs over more than one lattice spacing. Our method provides a tool to detect short-range spin correlations e.g. emerging in Fermi-Hubbard type systems close to the Neel temperature. The SWAP operation realizes an important step towards the creation of robust multiparticle entangled states suitable for one-way quantum computing.

Trotzky, Stefan; Chen, Yu-Ao; Schnorrberger, Ute; Cheinet, Patrick; Fölling, Simon; Bloch, Immanuel

2010-03-01

320

Signatures of spin-triplet excitations in optical conductivity of valence bond solids  

NASA Astrophysics Data System (ADS)

We show that the optical responses below the Mott gap can be used to probe the spin-triplet excitations in valence bond solid (VBS) phases in Mott insulators. The optical conductivity in this regime arises due to the electronic polarization mechanism via virtual electron-hopping processes. We apply this mechanism to the Hubbard model with spin–orbit couplings and/or the corresponding spin model with significant Dzyaloshinskii–Moriya (DM) interactions, and compute the optical conductivity of VBS states on both ideal and deformed Kagome lattices. In the case of the deformed Kagome lattice, we study the antiferromagnet Rb2Cu3SnF12 with the pinwheel VBS state. In case of the ideal Kagome lattice, we explore the optical conductivity signatures of the spin-triplet excitations for three VBS states with (1) a 12-site unit cell, (2) a 36-site unit cell with six-fold rotation symmetry, and (3) a 36-site unit cell with three-fold rotation symmetry, respectively. We find that increasing the DM interactions generally leads to broad and smooth features in the optical conductivity with interesting experimental consequences. The optical conductivity reflects the features of the spin-triplet excitations that can be measured in future experiments.

Hwang, Kyusung; Bhattacharjee, Subhro; Kim, Yong Baek

2014-12-01

321

Fluorescence excitation and ultraviolet absorption spectra and theoretical calculations for benzocyclobutane: Vibrations and structure of its excited S{sub 1}(?,?{sup *}) electronic state  

SciTech Connect

The fluorescence excitation spectra of jet-cooled benzocyclobutane have been recorded and together with its ultraviolet absorption spectra have been used to assign the vibrational frequencies for this molecule in its S{sub 1}(?,?{sup *}) electronic excited state. Theoretical calculations at the CASSCF(6,6)/aug-cc-pVTZ level of theory were carried out to compute the structure of the molecule in its excited state. The calculated structure was compared to that of the molecule in its electronic ground state as well as to the structures of related molecules in their S{sub 0} and S{sub 1}(?,?{sup *}) electronic states. In each case the decreased ? bonding in the electronic excited states results in longer carbon-carbon bonds in the benzene ring. The skeletal vibrational frequencies in the electronic excited state were readily assigned and these were compared to the ground state and to the frequencies of five similar molecules. The vibrational levels in both S{sub 0} and S{sub 1}(?,?{sup *}) states were remarkably harmonic in contrast to the other bicyclic molecules. The decreases in the frequencies of the out-of-plane skeletal modes reflect the increased floppiness of these bicyclic molecules in their S{sub 1}(?,?{sup *}) excited state.

Shin, Hee Won; Ocola, Esther J.; Laane, Jaan, E-mail: laane@mail.chem.tamu.edu [Department of Chemistry, Texas A and M University, College Station, Texas 77843-3255 (United States)] [Department of Chemistry, Texas A and M University, College Station, Texas 77843-3255 (United States); Kim, Sunghwan [National Center for Biotechnology Information, National Library of Medicine, National Institutes of Health, Department of Health and Human Services, 8600 Rockville Pike, Bethesda, Maryland 20894 (United States)] [National Center for Biotechnology Information, National Library of Medicine, National Institutes of Health, Department of Health and Human Services, 8600 Rockville Pike, Bethesda, Maryland 20894 (United States)

2014-01-21

322

Fluorescence excitation and ultraviolet absorption spectra and theoretical calculations for benzocyclobutane: Vibrations and structure of its excited S1(?,?*) electronic state  

PubMed Central

The fluorescence excitation spectra of jet-cooled benzocyclobutane have been recorded and together with its ultraviolet absorption spectra have been used to assign the vibrational frequencies for this molecule in its S1(?,?*) electronic excited state. Theoretical calculations at the CASSCF(6,6)/aug-cc-pVTZ level of theory were carried out to compute the structure of the molecule in its excited state. The calculated structure was compared to that of the molecule in its electronic ground state as well as to the structures of related molecules in their S0 and S1(?,?*) electronic states. In each case the decreased ? bonding in the electronic excited states results in longer carbon-carbon bonds in the benzene ring. The skeletal vibrational frequencies in the electronic excited state were readily assigned and these were compared to the ground state and to the frequencies of five similar molecules. The vibrational levels in both S0 and S1(?,?*) states were remarkably harmonic in contrast to the other bicyclic molecules. The decreases in the frequencies of the out-of-plane skeletal modes reflect the increased floppiness of these bicyclic molecules in their S1(?,?*) excited state. PMID:25669377

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

2014-01-01

323

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

PubMed

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

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

2014-11-01

324

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

NASA Astrophysics Data System (ADS)

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

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

2006-06-01

325

Triplet diffusion in singlet exciton fission sensitized pentacene solar cells  

NASA Astrophysics Data System (ADS)

Singlet fission sensitized photovoltaics have the potential to surpass the Shockley-Queisser limit for a single-junction structure. We investigate the dynamics of triplet excitons resulting from singlet fission in pentacene and their ionization at a C60 heterojunction. We model the generation and diffusion of excitons to predict the spectral response. We find the triplet diffusion length in polycrystalline pentacene to be 40 nm. Poly(3-hexylthiophene) between the electrode and pentacene works both to confine triplet excitons and also to transfer photogenerated singlet excitons into pentacene with 30% efficiency. The lower bound for the singlet fission quantum efficiency in pentacene is 180 ± 15%.

Tabachnyk, Maxim; Ehrler, Bruno; Bayliss, Sam; Friend, Richard H.; Greenham, Neil C.

2013-10-01

326

Effects of state-selective charge-exchange processes on the He-like spectra from the Alcator C tokamak  

SciTech Connect

The effects of a low-energy charge-exchange process between hydrogenlike ions and neutral hydrogen on x-ray spectra of He-like argon ions from the Alcator C tokamak are investigated. Dependences of charge-exchange cross sections on both the principal and angular momentum quantum numbers {ital n} and {ital l} are estimated from the observed spectra, taking cascade effects into account with the use of a collisional radiative model.

Kato, T.; Masai, K. (National Institute for Fusion Science, Nagoya 464-01 (Japan)); Fujimoto, T. (Department of Engineering Science, Kyoto University, Kyoto 606 (Japan)); Koike, F. (School of Medicine, Kitasato University, Kanagawa 228 (Japan)); Kaellne, E. (Department of Physics I, The Royal Institute of Technology, S-10044 Stockholm (Sweden)); Marmar, E.S.; Rice, J.E. (Plasma Fusion Center, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139 (United States))

1991-11-15

327

Identifying Inter-Residue Resonances in Crowded 2D 13C-13C Chemical Shift Correlation Spectra of Membrane Proteins by Solid-State MAS NMR Difference Spectroscopy  

PubMed Central

The feasibility of using difference spectroscopy, i.e. subtraction of two correlation spectra at different mixing times, for substantially enhanced resolution in crowded two-dimensional 13C-13C chemical shift correlation spectra is presented. With the analyses of 13C-13C spin diffusion in simple spin systems, difference spectroscopy is proposed to partially separate the spin diffusion resonances of relatively short intra-residue distances from the longer inter-residue distances, leading to a better identification of the inter-residue resonances. Here solid-state magic-angle-spinning (MAS) NMR spectra of the full length M2 protein embedded in synthetic lipid bilayers have been used to illustrate the resolution enhancement in the difference spectra. The integral membrane M2 protein of Influenza A virus assembles as a tetrameric bundle to form a protonconducting channel that is activated by low pH and is essential for the viral lifecycle. Based on known amino acid resonance assignments from amino acid specific labeled samples of truncated M2 sequences or from time-consuming 3D experiments of uniformly labeled samples, some inter-residue resonances of the full length M2 protein can be identified in the difference spectra of uniformly 13C labeled protein that are consistent with the high resolution structure of the M2 (22–62) protein (Sharma et al. 2010). PMID:23708936

Miao, Yimin; Cross, Timothy A.; Fu, Riqiang

2013-01-01

328

Communication: Manipulating the singlet-triplet equilibrium in organic biradical materials  

SciTech Connect

We investigated the tunability of the singlet-triplet equilibrium population in the organic biradical 1,4-phenylenedinitrene via magneto-optical spectroscopy. A rich magnetochromic response occurs because applied field increases the concentration of the triplet state species, which has a unique optical signature by comparison with the singlet biradical and the precursor molecule. A Curie-like analysis of the magneto-optical properties allows us to extract the spin gap, which is smaller than previously supposed. These measurements establish the value of local-probe photophysical techniques for magnetic property determination in open-shell systems such as biradicals where a traditional electron paramagnetic resonance Curie law analysis has intrinsic limitations.

Guenaydin-Sen, Oe.; Fosso-Tande, J.; Chen, P.; White, J. L.; Musfeldt, J. L. [Department of Chemistry, University of Tennessee, Knoxville, Tennessee 37996 (United States); Allen, T. L.; Lahti, P. M. [Department of Chemistry, University of Massachusetts, Amherst, Massachusetts 01003 (United States); Cherian, J.; Tokumoto, T.; McGill, S. [National High Magnetic Field Laboratory, Tallahassee, Florida 32310 (United States); Harrison, R. J. [Department of Chemistry, University of Tennessee, Knoxville, Tennessee 37996 (United States); Computer Science and Mathematics Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831 (United States)

2011-12-28

329

Possible triplet p +i p superconductivity in graphene at low filling  

NASA Astrophysics Data System (ADS)

We study the Hubbard model on the honeycomb lattice with nearest-neighbor hopping (t >0 ) and next-nearest-neighbor hopping (t'<0 ). When t'<-t /6 , the single-particle spectrum is featured by the continuously distributed Van Hove saddle points at the band bottom, where the density of states diverges in a power law. We investigate possible unconventional superconductivity in such systems with the Fermi level close to the band bottom by employing both random-phase-approximation and determinant quantum Monte Carlo approaches. Our study reveals a possible triplet p +i p superconductivity in this system with appropriate interactions. Our results might provide a possible route to look for triplet superconductivity with relatively high transition temperature in low-filled graphene and other similar systems.

Ma, Tianxing; Yang, Fan; Yao, Hong; Lin, Hai-Qing

2014-12-01

330

Theoretical Analysis of the Triplet Excited State of the [Pt2(H2P2O5)4]4-Ion and Comparison with Time-Resolved X-ray  

E-print Network

Coppens* Contribution from the Department of Chemistry, State UniVersity of New York at Buffalo, Buffalo, New York 14260-3000 Received July 25, 2002 ; E-mail: coppens@acsu.buffalo.edu Abstract: A full a lifetime of 9-10 µs in water and acetonitrile solutions, and a high quantum yield (r ) 0

Coppens, Philip

331

Quasiclassical Treatment and Odd-Parity/Triplet Correspondence in Topological Superconductors  

NASA Astrophysics Data System (ADS)

We construct a quasiclassical framework for topological superconductors with a strong spin–orbit coupling such as CuxBi2Se3. In a manner of the quasiclassical treatment, by decomposing the slowly varying component from a total quasiparticle wave function, the original massive Dirac Bogoliubov–de Gennes (BdG) Hamiltonian derived from a tight-binding model represented by an 8 × 8 matrix is reduced to a 4 × 4 matrix. The resultant equations are equivalent to Andreev-type equations of singlet or triplet superconductors, in which the apparent spin–orbit coupling vanishes. Using this formalism, we find that the odd-parity superconductivity in topological superconductors turns to the spin-triplet one. Moreover, in terms of quasiclassical treatment, we show that the topologically-protected zero-energy states in topological superconductors have correspond to the Andreev bound states established in a long history of studies of unconventional superconductors. This clearly indicates that low-energy nontrivial superconducting properties in the topological superconductors can be analyzed using established theoretical descriptions of the spin-triplet superconductors.

Nagai, Yuki; Nakamura, Hiroki; Machida, Masahiko

2014-05-01

332

Triplet superconductivity in 3D Dirac semi-metal due to exchange interaction  

NASA Astrophysics Data System (ADS)

Conventional phonon–electron interaction induces either triplet or one of two (degenerate) singlet pairing states in time reversal and inversion invariant 3D Dirac semi-metal. Investigation of the order parameters and energies of these states at zero temperature in a wide range of values of chemical potential ?, the effective electron–electron coupling constant ? and Debye energy TD demonstrates that when the exchange interaction is neglected the singlet always prevails, however, in significant portions of the (?, ?, TD) parameter space the energy difference is very small. This means that interactions that are small, but discriminate between the spin singlet and the spin triplet, are important in order to determine the nature of the superconducting order there. The best candidate for such an interaction in the materials under consideration is the exchange (the Stoner term) characterized by constant ?ex. We show that at values of ?ex, much smaller than ones creating Stoner instability to ferromagnetism ?ex ? 1, the triplet pairing becomes energetically favored over the singlet ones. The 3D quantum critical point at ? = 0 is considered in detail. This can be realized experimentally in optically trapped cold atom systems.

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

2015-01-01

333

Triplet superconductivity in 3D Dirac semi-metal due to exchange interaction.  

PubMed

Conventional phonon-electron interaction induces either triplet or one of two (degenerate) singlet pairing states in time reversal and inversion invariant 3D Dirac semi-metal. Investigation of the order parameters and energies of these states at zero temperature in a wide range of values of chemical potential ?, the effective electron-electron coupling constant ? and Debye energy TD demonstrates that when the exchange interaction is neglected the singlet always prevails, however, in significant portions of the (?, ?, TD) parameter space the energy difference is very small. This means that interactions that are small, but discriminate between the spin singlet and the spin triplet, are important in order to determine the nature of the superconducting order there. The best candidate for such an interaction in the materials under consideration is the exchange (the Stoner term) characterized by constant ?ex. We show that at values of ?ex, much smaller than ones creating Stoner instability to ferromagnetism ?ex ? 1, the triplet pairing becomes energetically favored over the singlet ones. The 3D quantum critical point at ? = 0 is considered in detail. This can be realized experimentally in optically trapped cold atom systems. PMID:25501668

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

2015-01-21

334

Solid-state density functional theory investigation of the terahertz spectra of the structural isomers 1,2-dicyanobenzene and 1,3-dicyanobenzene.  

PubMed

The high-resolution waveguide terahertz (THz) time-domain spectra (20-100 cm(-1)) of the two structural isomers 1,2-dicyanobenzene (1,2-DCB) and 1,3-dicyanobenzene (1,3-DCB) have been modeled and assigned using solid-state density functional theory. The THz spectra of these similar molecules are distinctly different in the low-frequency region with the differences being driven by modifications of the crystal packing arrangement between the isomers. Simulations utilizing the hybrid density functionals B3LYP and PBE0 were performed to determine the origins of the observed vibrational features. External lattice vibrations (hindered translations and rotations) are found to dominate these spectra, reinforcing the need for proper solid-state models in the analysis of the THz spectra of organic molecular solids. These calculations were able to account for all of the observed spectral features exhibited by both isomers, even in the case of 1,2-DCB, where the spectrum was found to be the result of two coexisting crystalline polymorphs. PMID:21049898

Oppenheim, Keith C; Korter, Timothy M; Melinger, Joseph S; Grischkowsky, Daniel

2010-12-01

335

Triplet dynamics in pentacene crystals: applications to fission-sensitized photovoltaics.  

PubMed

The decay and transport of triplet excitons photogenerated via singlet exciton fission in polycrystalline and single-crystalline pentacene is reported. Using transient absorption spectroscopy, we find evidence for diffusion-mediated triplet-triplet annihilation. We estimate monomolecular lifetimes, bimolecular annihilation rate constants, and triplet exciton diffusion lengths. We discuss these results in the context of current solar cell device architectures. PMID:24375546

Poletayev, Andrey D; Clark, Jenny; Wilson, Mark W B; Rao, Akshay; Makino, Yoshitaka; Hotta, Shu; Friend, Richard H

2014-02-12

336

Triplets with Extremely Low Birth Weight Face High Risks  

MedlinePLUS

... Miller 301-496-5133 Triplets with extremely low birth weight face high risks NIH study shows higher death, ... research was published online in Pediatrics. Extremely low birth weight (ELBW) infants are the smallest category of preterm ...

337

Ultrafast singlet and triplet dynamics in microcrystalline pentacene films  

NASA Astrophysics Data System (ADS)

The exciton dynamics of microcrystalline pentacene films is investigated by femtosecond pump-probe experiments. Measurements are performed with ultrashort laser pulses applied at normal incidence and at an angle of incidence of 65° to disentangle singlet and triplet contributions by exploiting the different orientations of the molecular transition dipoles. The results indicate that the initial 70 fs fast relaxation step transforms the optically excited excitons in a reasonable mobile species with strongly reduced radiative transition strength. Fission into triplet excitons takes place on the picosecond time scale as a secondary, thermally activated process and with a small total yield of approximately 2%. Evidence is provided that the dominant species are singlet excitons with excimer character. To the subsequent dynamics contribute diffusion driven exciton-exciton annihilation and trapping of singlet and triplet excitons. Values for diffusion constants and trap densities are extracted by modeling the measurements with rate equations which include singlet and triplet dynamics.

Marciniak, Henning; Pugliesi, Igor; Nickel, Bert; Lochbrunner, Stefan

2009-06-01

338

Stability constraints in triplet extension of MSSM  

E-print Network

We study the stability constraints on the parameter space of a triplet extension of MSSM. Existence of unbounded from below directions in the potential can spoil successful Electroweak (EW) symmetry breaking by making the corresponding minimum unstable, and hence the model should be free from those directions. Avoiding those directions restricts the parameter space of the model. We derive four stability constraints, of which only three independent from each other. After scanning the model's parameter space for phenomenologically viable data points, we impose the stability constraints and find that only about a quarter of the data points features a stable EW minimum. At those data points featuring stability, $\\mu$ and the up Higgs soft mass turn out to be smaller than about a TeV in absolute value, which make the mass of the lightest chargino and neutralino smaller than about 700 GeV. Two relevant phenomenological consequences of lifting the unbounded from below directions are that the lightest Higgs boson dec...

Das, Moumita; Roy, Sourov

2015-01-01

339

New Aspects in Physics on Gel'fand Triplets  

Microsoft Academic Search

New observations in Gel'fand triplets are studied. An interesting one is vortex phenomena that stem from zero energy solutions of two-dimensional Schrödinger equations with central potentials V(?) ? ?r(?2 = x2 + y2 and r ? -2), which are eigenstates of conjugate spaces of Gel'fand triplets. The zero energy solutions for all the potentials V(?) are shown to have the

Tsunehiro Kobayashi

2003-01-01

340

Nanostructured singlet fission photovoltaics subject to triplet-charge annihilation.  

PubMed

Singlet exciton fission is an efficient multiple-exciton generation process that is vulnerable to a characteristic loss process: triplet-charge annihilation. This loss process is characterized in singlet-fission photovoltaics and losses as high as 40% are observed in poorly designed devices. Techniques are demonstrated to improve charge extraction and reduce triplet-charge annihilation to negligible levels at short-circuit conditions. PMID:24281738

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

2014-03-01

341

Vibration wavenumbers of 4-aminobenzotrifluoride in the ground and S1 electronic states from its supersonic jet S1- S0 fluorescence, infrared, and Raman spectra  

NASA Astrophysics Data System (ADS)

Single vibronic level fluorescence (SVLF) spectra, in a supersonic jet, and infrared and Raman spectra of 4-aminobenzotrifluoride have been recorded and assigned to give, apart from some a2 vibrations, a complete set of fundamental vibration wavenumbers in the S0 electronic state. A supersonic jet fluorescence excitation spectrum has given some of the lower vibration wavenumbers in the S1 electronic state. Observation of the I20, NH 2-inversion band in the SVLF spectrum agrees with the interpretation of the far infrared spectrum. Several CF 3 torsional levels in S0 are populated, even in the supersonic jet, and one result of this is to allow the observation of vibrations which are of b1 symmetry in the C2 v point group and which would be forbidden in the rigid molecule.

Ribeiro-Claro, Paulo J. A.; Teixeira-Dias, JoséJ. C.; Gordon, Robert D.; Hollas, J. Michael

1991-09-01

342

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

SciTech Connect

The photodissociation of acetaldehyde in the radical channel has been studied at wavelengths between 315 and 325 nm using the velocity-map imaging technique. Upon one-photon absorption at 315 nm, the molecule is excited to the first singlet excited state S{sub 1}, which, in turn, undergoes intersystem crossing to the first excited triplet state T{sub 1}. On the triplet surface, the molecule dissociates into CH{sub 3} and HCO radicals with large kinetic energy release (KER), in accordance with the well characterized exit barrier on T{sub 1}. However, at longer wavelengths (>320 nm), which correspond to excitation energies just below the triplet barrier, a sudden change in KER is observed. At these photolysis wavelengths, there is not enough energy to surpass the exit barrier on the triplet state, which leaves the possibility of unimolecular dissociation on S{sub 0} after internal conversion from S{sub 1}. We have characterized the fragments' KER at these wavelengths, as well as determined the energy partitioning for the radical fragments. A new accurate estimate of the barrier height on T{sub 1} is presented.

Amaral, G. A.; Arregui, A.; Rodriguez, J. D.; Banares, L. [Departamento de Quimica Fisica I, Facultad de Ciencias Quimicas, Universidad Complutense de Madrid, Madrid 28040 (Spain); Rubio-Lago, L. [Departamento de Quimica Fisica I, Facultad de Ciencias Quimicas, Universidad Complutense de Madrid, Madrid 28040 (Spain); Instituto de Estructura de la Materia, CSIC, C/Serrano 123, Madrid 28006 (Spain)

2010-08-14

343

Production and installation of the LHC low-beta triplets  

SciTech Connect

The LHC performance depends critically on the low-{beta}, triplets, located on either side of the four interaction points. Each triplet consists of four superconducting quadrupole magnets, which must operate reliably at up to 215 T/m, sustain extremely high heat loads and have an excellent field quality. A collaboration of CERN, Fermilab and KEK was formed in 1996 to design and build the triplet systems, and after nine years of joint effort the production has been completed in 2005. We retrace the main events of the project and present the design features and performance of the low-{beta} quadrupoles, built by KEK and Fermilab, as well as of other vital elements of the triplet. The tunnel installation of the first triplet and plans for commissioning in the LHC are also presented. Apart from the excellent technical results, the construction of the LHC low-{beta} triplets has been a highly enriching experience combining harmoniously the different competences and approaches to engineering in a style reminiscent of high energy physics experiment collaborations, and rarely before achieved in construction of an accelerator.

Feher, S.; Bossert, R.; DiMarco, J.; Karppinen, M.; Kerby, J.; Kimura, N.; Lamm, M.J.; Nakamoto, T.; Nicol, T.; Nobrega, A.; Ogitsu, T.; Ohuchi, N.; Ostojic, R.; Page,; Peterson, T.; Rabehl, R.; Schlabach, P.; Shintomi, T.; Strait, J.; Sylvester, C.; Tartaglia, M.; /Fermilab /CERN /KEK, Tsukuba

2005-09-01

344

The prediction of metastable impact electronic spectra (MIES): perfect and defective MgO(001) surfaces by state-of-the-art methods  

NASA Astrophysics Data System (ADS)

We re-examine the theory of metastable impact electron spectroscopy (MIES) in its application to insulating surfaces. This suggests a quantitative approach which takes advantage of recent developments in highly efficient many-electron computational techniques. It gives a basis to the interpretation of experimental MIES spectra for perfect and defective surfaces. Our method is based on a static approach to predicting Auger de-excitation (AD) rates of He?(1s2s) projectiles. A key quantity is the surface density of states (DOS) projected on the 1s orbital of the He? atom, which is calculated along its trajectory. We use density functional theory within both supercell geometry and embedded cluster models to calculate MIES spectra for the perfect MgO surface and for an MgO surface with different concentrations of adsorbed oxygen atoms. First we calculate the Auger de-excitation rates at various positions of the projectile above the surface. To predict MIES spectra, we integrate over projectile trajectories, with a subsequent weighted averaging with respect to various lateral positions of He? above the MgO surface unit cell. It is important to examine final-state effects for a correct comparison between theory and experiment, especially when there are localised defect states.

Kantorovich, L. N.; Shluger, A. L.; Sushko, P. V.; Stoneham, A. M.

2000-01-01

345

Photophysics of the Triple State of Metal Complexes of 9-anthracenecarboxylic Acid  

NASA Astrophysics Data System (ADS)

The triplet-triplet (T-T) absorption spectra and the T-T absorption decay kinetics are measured for solutions of 9-anthracenecarboxylic acid (ACA) and its complexes with metal ions (Cd3+ and Ln3+=Y3+, La3+, Ce3+, Eu3+, Gd3+, and Tb3+) in dimethylsulfoxide (DMSO) by the methods of flashlamp and laser pulse photolysis. The rate constants k T of intracomplex quenching of the triplet state are measured for ACA complexes with ions Gd3+, Ce3+, Tb3+, and Eu3+. Larger values of k T in complexes of ACA with paramagnetic ions Ce3+, Tb3+, and Eu3+, which have low-lying energy levels, compared to the values of k T for complexes with other ligands (pyrene-3-sulfonate, pyrene-1,3,6,8-tetrasulfonate, and benzo[ghi]perylene-1,2-dicarboxylate) were explained by the lower energy of the triplet state of ACA (14400 cm-1). For a complex with a paramagnetic ion Gd3+, which has no low-lying energy levels, the value of k T is close to that measured by us earlier for the inner-sphere complex of pyrene-1,3,6,8-tetrasulfonate with the same ion. These results confirm our earlier assumption about the inner-sphere complexing of ACA with Ln3+ ions in DMSO.

Shakhverdov, T. A.; Érgashev, R.

2001-02-01

346

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

NASA Astrophysics Data System (ADS)

Materials capable to perform upconversion of light transform the photon spectrum and can be used to increase the efficiency of solar cells by upconverting sub-bandgap photons, increasing the density of photons able to generate an electron-hole pair in the cell. Incoherent solar radiation suffices to activate upconverters based on sensitized triplet-triplet annihilation, which makes them particularly suited for this task. This process requires two molecular species, sensitizers absorbing low energy photons, and emitters generating higher frequency photons. Successful implementations exist in solutions and solids. However, solid upconverters exhibit lower efficiency than those in solution, which poses a serious problem for real applications. In the present work, we suggest a new strategy to increase the efficiency of sensitized upconverters that exploits the solid nature of the material. We show that an upconversion model system with molecules distributed as clusters outperforms a system with a random distribution of molecules, as used in current upconverters. Our simulations reveal a high potential for improvement of upconverter systems by exploring different structural configurations of the molecules. The implementation of advanced structures can push the performance of solid upconverters further towards the theoretical limit and a step closer to technological application of low power upconversion.

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

2014-11-01

347

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

PubMed

Materials capable to perform upconversion of light transform the photon spectrum and can be used to increase the efficiency of solar cells by upconverting sub-bandgap photons, increasing the density of photons able to generate an electron-hole pair in the cell. Incoherent solar radiation suffices to activate upconverters based on sensitized triplet-triplet annihilation, which makes them particularly suited for this task. This process requires two molecular species, sensitizers absorbing low energy photons, and emitters generating higher frequency photons. Successful implementations exist in solutions and solids. However, solid upconverters exhibit lower efficiency than those in solution, which poses a serious problem for real applications. In the present work, we suggest a new strategy to increase the efficiency of sensitized upconverters that exploits the solid nature of the material. We show that an upconversion model system with molecules distributed as clusters outperforms a system with a random distribution of molecules, as used in current upconverters. Our simulations reveal a high potential for improvement of upconverter systems by exploring different structural configurations of the molecules. The implementation of advanced structures can push the performance of solid upconverters further towards the theoretical limit and a step closer to technological application of low power upconversion. PMID:25399129

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

2014-11-14

348

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

PubMed

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

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

2014-11-12

349

Characterization of carotenoid aggregates by steady-state optical spectroscopy.  

PubMed

The carotenoids have low-lying triplet excited states and can self-assemble in some solvents to form weakly or strongly coupled aggregates. These qualities make carotenoid aggregates useful for studies of singlet fission, where an outstanding goal is the correlation of interchromophoric coupling to the dynamics and yield of triplet excited states from a parent singlet excited state. Three aggregates of zeaxanthin, two weakly coupled and one strongly coupled, are characterized by steady-state spectroscopic methods including temperature-dependent absorption, fluorescence, and resonance Raman spectroscopy. The absorption spectra for each type of aggregate are distinct; however, an analysis of band positions reveals some important shared characteristics and suggests that the strongly coupled H-aggregate contains a subpopulation of weakly coupled constituents. Temperature-dependent absorption spectroscopy indicates that one of the weakly coupled aggregates can be converted to the other upon heating. The emission spectra of the three aggregates have similar profiles that are overall red-shifted by more than 1000 cm(-1) relative to the monomer. The emission quantum yields of the aggregates are 5 to 30 times less than that of the monomer, with the lowest yield for the strongly coupled aggregate. The vibrational spectra of the chromophores support only slight perturbations from the structure of solvated monomers. Our findings support the conclusion that all three aggregates are best characterized as H-aggregates, in agreement with a prior theoretical study of lutein aggregates. PMID:22873697

Wang, Chen; Berg, Christopher J; Hsu, Cheng-Chih; Merrill, Brittany A; Tauber, Michael J

2012-09-01

350

Experimental observation of the triplet spin-valve effect in a superconductor-ferromagnet heterostructure  

NASA Astrophysics Data System (ADS)

The theory of superconductor-ferromagnet heterostructures with two ferromagnetic layers predicts the generation of a long-range, odd-in-frequency triplet pairing at noncollinear alignment (NCA) of the magnetizations of the F layers. This triplet pairing has been detected in a Nb/Cu41Ni59/normal conducting- (nc-) Nb/Co/CoOx spin-valve-type proximity effect heterostructure, in which a very thin Nb film between the F layers serves as a spacer of nc metal. The resistance of the sample as a function of an external magnetic field shows that for not too high fields, the system is superconducting at a collinear alignment of the Cu41Ni59 and Co layer magnetic moments but switches to the normal conducting state at a NCA configuration. This indicates that the superconducting transition temperature Tc for NCA is lower than the fixed measuring temperature. The existence of a minimum Tc, at the NCA regime below that one for parallel or antiparallel alignments of the F-layer magnetic moments, is consistent with the theoretical prediction of a singlet superconductivity suppression by the long-range triplet pairing generation.

Zdravkov, V. I.; Kehrle, J.; Obermeier, G.; Lenk, D.; Krug von Nidda, H.-A.; Müller, C.; Kupriyanov, M. Yu.; Sidorenko, A. S.; Horn, S.; Tidecks, R.; Tagirov, L. R.

2013-04-01

351

Phonon density of states of Sn in textured SnO under high pressure: Comparison of nuclear inelastic x-ray scattering spectra to a shell model  

NASA Astrophysics Data System (ADS)

The local phonon density of states (DOS) at the Sn site in tin monoxide (SnO) is studied at pressures up to 8GPa with Sn119 nuclear resonant inelastic x-ray scattering (NRIXS) of synchrotron radiation at 23.88keV . The preferred orientation (texture) of the SnO crystallites in the investigated samples is used to measure NRIXS spectra preferentially parallel and almost perpendicular to the c axis of tetragonal SnO . A subtraction method is applied to these NRIXS spectra to produce projected local Sn DOS spectra as seen parallel and perpendicular to the c axis of SnO . These experimentally obtained local Sn DOS spectra, both in the polycrystalline case as well as projected parallel and perpendicular to the c axis, are compared with corresponding theoretical phonon DOS spectra, derived from dispersion relations calculated with a recently developed shell model. Comparison between the experimental projected Sn DOS spectra and the corresponding theoretical DOS spectra enables us to follow the pressure-induced shifts of several acoustic and optic phonon modes. While the principal spectral features of the experimental and theoretical phonon DOS agree well at energies above 10meV , the pressure behavior of the low-energy part of the DOS is not well reproduced by the theoretical calculations. In fact, they exhibit, in contrast to the experimental data, a dramatic softening of two low-energy modes, their energies approaching zero around 2.5GPa , clearly indicating the limitations of the applied shell model. These difficulties are obviously connected with the complex Sn-O and Sn-Sn bindings within and between the Sn-O-Sn layers in the litharge structure of SnO . We derived from the experimental and theoretical DOS spectra a variety of elastic and thermodynamic parameters of the Sn sublattice, such as the Lamb-Mössbauer factor, the mean force constant, and Debye temperatures, as well as the vibrational contributions to the Helmholtz free energy, specific heat, entropy, and internal energy. We found, in part, good agreement between these values, for instance, for the Grüneisen parameters for some selected phonon modes, especially for some optical modes studied recently by Raman spectroscopy. We discuss in detail a possible anisotropy in the elastic parameters resulting from the litharge-type structure of SnO , for instance for the Lamb-Mössbauer factor, where we can compare with existing data from Sn119 -Mössbauer spectroscopy.

Giefers, H.; Koval, S.; Wortmann, G.; Sturhahn, W.; Alp, E. E.; Hu, M. Y.

2006-09-01

352

The cavity ringdown spectrum of the visible electronic system of thiophosgene: An estimation of the lifetime of the T[sub 1]([tilde a]; [sup 3]A[sub 2]) triplet state  

SciTech Connect

To obtain insights into the photophysical properties of collision-free T[sub 1]([tilde a] hthinsp;[sup 3]A[sub 2]) thiophosgene, Cl[sub 2]CS, the cavity ringdown (CRD) spectrum of the T[sub 1][l arrow]S[sub 0] absorption system was recorded under supersonic jet conditions and compared with the corresponding excitation spectrum of the total emission. It was found that none of the T[sub 1][l arrow]S[sub 0] bands in the CRD spectrum appears in the excitation spectrum, indicating that the T[sub 1] thiophosgene decays almost exclusively by the nonradiative T[sub 1][r arrow]S[sub 0] intersystem crossing (ISC). An estimation of the T[sub 1] nonradiative lifetime was made using the T[sub 1][endash]S[sub 0] spin-orbit coupling and the Franck[endash]Condon factors for the T[sub 1][r arrow]S[sub 0] ISC based on the [ital ab initio] equilibrium structures and vibrational frequencies for the T[sub 1] and S[sub 0] states, computed at the MP2/6-31G(d,p) and MP4/6-31G(d,p) level of theory. The nonradiative life, calculated as the 1/e of the survival probability, is approximately 20 ps for barrier heights of 770[endash]845 cm[sup [minus]1] and out-of-plane angles of 32.07[degree][endash]32.69[degree]. (The thiophosgene adopts a pyramidal conformation with the C[double bond]S bond bent from the ClCCl plane by about 32[degree].) The computed lifetime is comparable to the lower-limit lifetime of [approximately]50 ps obtained from the quantum yields [Phi][sub P][le]10[sup [minus]3][Phi][sub F] with [Phi][sub F][approx]1.0 and the measured S[sub 1] fluorescence lifetime of 4 [mu]s. The short T[sub 1] nonradiative lifetime of thiophosgene can be attributed to the large matrix elements of the T[sub 1][endash]S[sub 0] spin-orbit coupling (V=150 hthinsp;cm[sup [minus]1]) and the strong out-of-plane deformation of the T[sub 1] state relative to the planar S[sub 0] state, that provides the large Franck[endash]Condon factors for the T[sub 1][r arrow]S[sub 0] ISC. It is proposed that a similar pyramidal deformation is also responsible for the absence of phosphorescence from T[sub 1] thiocyclobutanone. Consistent with this supposition, T[sub 1] cyclopentanone, which is nearly planar at the thiocarbonyl carbon center, exhibits strong phosphorescence under similar experimental conditions. [copyright] [ital 1999 American Institute of Physics.

Moule, D.C.; Burling, I.R. (Department of Chemistry, Brock University, St. Catharines, Ontario, L2S3A1 (Canada)); Liu, H.; Lim, E.C. (Knight Chemical Laboratory, University of Akron, Akron, Ohio 44325-3601 (United States))

1999-09-01

353

The cavity ringdown spectrum of the visible electronic system of thiophosgene: An estimation of the lifetime of the T{sub 1}({tilde a};{sup 3}A{sub 2}) triplet state  

SciTech Connect

To obtain insights into the photophysical properties of collision-free T{sub 1}({tilde a}&hthinsp;{sup 3}A{sub 2}) thiophosgene, Cl{sub 2}CS, the cavity ringdown (CRD) spectrum of the T{sub 1}{l_arrow}S{sub 0} absorption system was recorded under supersonic jet conditions and compared with the corresponding excitation spectrum of the total emission. It was found that none of the T{sub 1}{l_arrow}S{sub 0} bands in the CRD spectrum appears in the excitation spectrum, indicating that the T{sub 1} thiophosgene decays almost exclusively by the nonradiative T{sub 1}{r_arrow}S{sub 0} intersystem crossing (ISC). An estimation of the T{sub 1} nonradiative lifetime was made using the T{sub 1}{endash}S{sub 0} spin-orbit coupling and the Franck{endash}Condon factors for the T{sub 1}{r_arrow}S{sub 0} ISC based on the {ital ab initio} equilibrium structures and vibrational frequencies for the T{sub 1} and S{sub 0} states, computed at the MP2/6-31G(d,p) and MP4/6-31G(d,p) level of theory. The nonradiative life, calculated as the 1/e of the survival probability, is approximately 20 ps for barrier heights of 770{endash}845 cm{sup {minus}1} and out-of-plane angles of 32.07{degree}{endash}32.69{degree}. (The thiophosgene adopts a pyramidal conformation with the C{double_bond}S bond bent from the ClCCl plane by about 32{degree}.) The computed lifetime is comparable to the lower-limit lifetime of {approximately}50 ps obtained from the quantum yields {Phi}{sub P}{le}10{sup {minus}3}{Phi}{sub F} with {Phi}{sub F}{approx}1.0 and the measured S{sub 1} fluorescence lifetime of 4 {mu}s. The short T{sub 1} nonradiative lifetime of thiophosgene can be attributed to the large matrix elements of the T{sub 1}{endash}S{sub 0} spin-orbit coupling (V=150&hthinsp;cm{sup {minus}1}) and the strong out-of-plane deformation of the T{sub 1} state relative to the planar S{sub 0} state, that provides the large Franck{endash}Condon factors for the T{sub 1}{r_arrow}S{sub 0} ISC. It is proposed that a similar pyramidal deformation is also responsible for the absence of phosphorescence from T{sub 1} thiocyclobutanone. Consistent with this supposition, T{sub 1} cyclopentanone, which is nearly planar at the thiocarbonyl carbon center, exhibits strong phosphorescence under similar experimental conditions. {copyright} {ital 1999 American Institute of Physics.}

Moule, D.C.; Burling, I.R. [Department of Chemistry, Brock University, St. Catharines, Ontario, L2S3A1 (Canada)] [Department of Chemistry, Brock University, St. Catharines, Ontario, L2S3A1 (Canada); Liu, H.; Lim, E.C. [Knight Chemical Laboratory, University of Akron, Akron, Ohio 44325-3601 (United States)] [Knight Chemical Laboratory, University of Akron, Akron, Ohio 44325-3601 (United States)

1999-09-01

354

Hybrid spin and valley quantum computing with singlet-triplet qubits  

E-print Network

The valley degree of freedom in the electronic band structure of silicon, graphene, and other materials is often considered to be an obstacle for quantum computing (QC) based on electron spins in quantum dots. Here we show that control over the valley state opens new possibilities for quantum information processing. Combining qubits encoded in the singlet-triplet subspace of spin and valley states allows for universal QC using a universal two-qubit gate directly provided by the exchange interaction. We show how spin and valley qubits can be separated in order to allow for single-qubit rotations.

Niklas Rohling; Maximilian Russ; Guido Burkard

2014-03-27

355

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

PubMed

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

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

2014-08-11

356

Direct recovery of fluctuation spectra from tomographic shear spectra  

SciTech Connect

Forthcoming experiments will enable us to determine high precision tomographic shear spectra. Matter density fluctuation spectra, at various z, should then be recovered from them, in order to constrain the model and determine the DE state equation. Available analytical expressions, however, do the opposite, enabling us to derive shear spectra from fluctuation spectra. Here we find the inverse expression, yielding density fluctuation spectra from observational tomographic shear spectra. The procedure involves SVD techniques for matrix inversion. We show in detail how the approach works and provide a few examples.

Mezzetti, Marino; Bonometto, Silvio A.; Murante, Giuseppe [Department of Physics, Astronomy Unit, Trieste University, Via Tiepolo 11, I 34143 Trieste (Italy); Casarini, Luciano, E-mail: mezzetti@oats.inaf.it, E-mail: bonometto@oats.inaf.it, E-mail: casarini@mib.infn.it, E-mail: murante@oats.inaf.it [Departamento de Fisica, UFES, Avenida Fernando Ferrari 514, Vitória, Espírito Santo (Brazil)

2012-06-01

357

Anharmonic Franck-Condon simulation of the absorption and fluorescence spectra for the low-lying S1 and S2 excited states of pyrimidine  

NASA Astrophysics Data System (ADS)

Intensities and profiles of vibronic spectra of the low-lying singlet excited states were investigated with anharmonic and harmonic Franck-Condon simulations for pyrimidine. The first-order anharmonic correction shows dynamic shift of spectra that is exactly same as difference of reorganization energy between ground and excited states. The first-order correction show intensity enhancement of absorption and intensity weakening of fluorescence for S1 state, and dynamic shift is also significant. On the other hand, the first-order correction is negligible for S2 state. The main spectral progressions are well described by totally symmetry modes ?6a, ?1 and ?12. One mode from non-total symmetry ?16a contributes to the weak band at 16a2 transition for S1 state. Four ab initio methods were employed in simulation; CASSCF, CASPT2, DFT and TD-DFT, and coupled-cluster singles-doubles (CCSD) and the equation-of-motion (EOM-CCSD) methods. They all work well, but CASSCF method show the best agreement with experiment for the weak-band intensities.

Yang, Ling; Zhu, Chaoyuan; Yu, Jianguo; Lin, Sheng Hsien

2012-05-01

358

The {ital T}{sub 1}({ital n}{pi}{asterisk}){l_arrow}{ital S}{sub 0} laser induced phosphorescence excitation spectrum of acetaldehyde in a supersonic free jet: Torsion and wagging potentials in the lowest triplet state  

SciTech Connect

The laser induced {ital T}{sub 1}({ital n}{pi}{asterisk}){l_arrow}{ital S}{sub 0} phosphorescence excitation spectrum of jet-cooled acetaldehyde has been observed for the first time with a rotating slit nozzle excitation system. The vibronic origins were fitted to a set of levels that were obtained from a Hamiltonian that employed flexible torsion-wagging large amplitude coordinates. The potential surface extracted from the fitting procedure yielded barriers to torsion and inversion of 609.68 and 869.02 cm{sup {minus}1}, respectively. Minima in the potential hypersurface at {theta}=61.7{degree} and {alpha}=42.2{degree} defined the equilibrium positions for the torsion and wagging coordinates. A comparison to the corresponding {ital S}{sub 1}-state parameters showed that the torsion barrier (in cm{sup {minus}1}) does not greatly change, {ital S}{sub 1}/{ital T}{sub 1}=710.8/609.7, whereas the barrier height for the wagging-inversion barrier increases dramatically, 574.4/869.0. {copyright} {ital 1996 American Institute of Physics.}

Liu, H.; Lim, E.C. [Knight Chemical Laboratory, The University of Akron, Akron, Ohio 44325-3601 (United States)] [Knight Chemical Laboratory, The University of Akron, Akron, Ohio 44325-3601 (United States); Munoz-Caro, C.; Nino, A. [E. U. Informatica, Universidad de Castilla---La Mancha, Ronda de Calatrava 5, 13071 Ciudad Real (Spain)] [E. U. Informatica, Universidad de Castilla---La Mancha, Ronda de Calatrava 5, 13071 Ciudad Real (Spain); Judge, R.H. [Department of Chemistry, University of Wisconsin---Parkside, Kenosha, Wisconsin 53141-2000 (United States)] [Department of Chemistry, University of Wisconsin---Parkside, Kenosha, Wisconsin 53141-2000 (United States); Moule, D.C. [Department of Chemistry, Brock University, St. Catharine`s, Ontario L2S 3A1 (Canada)] [Department of Chemistry, Brock University, St. Catharine`s, Ontario L2S 3A1 (Canada)

1996-08-01

359

Jet-cooled fluorescence spectra and carbonyl wagging potential energy functions of tetrahydrofuran-3-one and tetrahydrothiophen-3-one in their S 1(n,??) excited states  

NASA Astrophysics Data System (ADS)

The jet-cooled fluorescence excitation spectra of states of tetrahydrofuran-3-one and tetrahydrothiophen-3-one have been recorded and analyzed. The carbonyl inversion bands, which arise from double-minimum potential energy functions in the excited states, were fit with functions of the form V = ax4 - bx2 or V = cx2 + dexp(- fx2). The furanone was found to have an inversion barrier in the S 1(n,??) state of 1152 cm -1 (13.8 kJ mol -1) while the thiophenone has a barrier of 659 cm -1 (7.9 kJ mol -1). The two molecules have their potential energy minima for the S 1(n,??) state at carbonyl wagging angles of 26 and 20°, respectively. The results here, together with previous data for several other cyclic ketones, demonstrate that the inversion barrier increases with the ring angle strain at the ketone carbon atom.

Laane, Jaan; Sagear, Paul A.; Lee, S. N.

1997-06-01

360

Theoretical study on vibrational circular dichroism spectra of tris(acetylacetonato)metal(III) complexes: anharmonic effects and low-lying excited states.  

PubMed

The open-shell density functional theory calculations with M06 exchange-correlation functional and all-electron Douglas-Kroll second order scalar relativistic correction were performed to interpret the vibrational circular dichroism (VCD) spectra of four kinds of tris(acetylacetonato)metal(III), [M(III)(acac)(3)] (acac = acetylacetonato, M = Ru, Cr, Co, and Rh). It was deduced that the experimental spectra were well reproduced by the calculation with harmonic approximation in case of [Co(III)(acac)(3)] (d(6); S = 0), [Rh(III)(acac)(3)] (d(6); S = 0), and [Ru(III)(acac)(3)] (d(5); S = 1/2). In case of [Cr(III)(acac)(3)] (d(3); S = 3/2), anharmonic effects should be taken into account to predict the accurate vibrational frequencies of closely located modes. Time-dependent density functional theory calculations were performed to estimate the contribution of excited states in the VCD spectra. As a consequence, the presence of the low-lying excited states was predicted for [Ru(III)(acac)(3)] alone, which agreed with the experimental observation. PMID:21895198

Mori, Hirotoshi; Yamagishi, Akihiko; Sato, Hisako

2011-08-28

361

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

PubMed

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

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

2014-12-21

362

The origin of the absorption spectra of porphyrin N- and dithiaporphyrin S-oxides in their neutral and protonated states.  

PubMed

meso-Tetraphenylporphyrin N-oxide (1) and meso-tetraphenyl-21,23-dithiaporphyrin S-oxide (3) possess optical spectra that are distinctly different from their parent porphyrins, meso-tetraphenylporphyrin (2) and meso-tetraphenyl-21,23-dithiaporphyrin (4), respectively. The hyperporphyrin spectra were reproduced and classified using TD CAM-B3LYP and SCS-CC2 computational methods. Calculations revealed the electronic and conformational influences of the N- and S-oxide functionalities. While the N-oxide under acidic conditions forms a dication with a UV-vis spectrum that is nearly indistinguishable from that of the diprotonated parent porphyrin, the diprotonated S-oxide possesses a much different UV-vis spectrum from diprotonated parent dithiaporphyrin. A computational study of the protonation events revealed the site and degree of protonation and rationalized the regular and hyperporphyrin UV-vis spectra of the neutral and protonated species, respectively. The study illuminates the electronic effects of the relatively rare modification of the inner porphyrin heteroatoms. It also illustrates a case in which TD CAM-B3LYP reaches its limits to make reliable predictions about the optical properties of a porphyrinoid, making the use of higher methods essential. PMID:25537692

Bruhn, Torsten; Brückner, Christian

2015-02-01

363

Aberrant EEG functional connectivity and EEG power spectra in resting state post-traumatic stress disorder: a sLORETA study.  

PubMed

The aim of the present study was to explore the modifications of EEG power spectra and EEG connectivity of resting state (RS) condition in patients with post-traumatic stress disorder (PTSD). Seventeen patients and seventeen healthy subjects matched for age and gender were enrolled. EEG was recorded during 5min of RS. EEG analysis was conducted by means of the standardized Low Resolution Electric Tomography software (sLORETA). In power spectra analysis PTSD patients showed a widespread increase of theta activity (4.5-7.5Hz) in parietal lobes (Brodmann Area, BA 7, 4, 5, 40) and in frontal lobes (BA 6). In the connectivity analysis PTSD patients also showed increase of alpha connectivity (8-12.5Hz) between the cortical areas explored by Pz-P4 electrode. Our results could reflect the alteration of memory systems and emotional processing consistently altered in PTSD patients. PMID:25046862

Imperatori, Claudio; Farina, Benedetto; Quintiliani, Maria Isabella; Onofri, Antonio; Castelli Gattinara, Paola; Lepore, Marta; Gnoni, Valentina; Mazzucchi, Edoardo; Contardi, Anna; Della Marca, Giacomo

2014-10-01

364

Evidence for water-mediated triplet-triplet energy transfer in the photoprotective site of the peridinin-chlorophyll a-protein.  

PubMed

Experimental and theoretical studies indicate that water molecules between redox partners can significantly affect their electron-transfer and possibly also the triplet-triplet energy transfer (TTET) properties when in the vicinity of chromophores. In the present work, the interaction of an intervening water molecule with the peridinin triplet state in the peridinin-chlorophyll a-protein (PCP) from Amphidinium carterae is studied by using orientation selective (2)H electron spin echo envelope modulation (ESEEM) spectroscopy, in conjunction with quantum mechanical calculations. This water molecule is located at the interface between the chlorophyll and peridinin pigments involved in the photoprotection mechanism (Chl601(602)-Per614(624), for nomenclature see reference [1]), based on TTET. The characteristic deuterium modulation pattern is observed in the electron spin-echo envelopes for the PCP complex exchanged against (2)H2O. Simulations of the time- and frequency-domain two-pulse and three-pulse ESEEM require two types of coupled (2)H. The more strongly coupled (2)H has an isotropic coupling constant (aiso) of -0.4MHz. This Fermi contact contribution for one of the two water protons and the precise geometry of the water molecule at the interface between the chlorophyll and peridinin pigments, resulting from the analysis, provide experimental evidence for direct involvement of this structured water molecule in the mechanism of TTET. The PCP antenna, characterised by a unity efficiency of the process, represents a model for future investigations on protein- and solvent-mediated TTET in the field of natural/artificial photosynthesis. PMID:23871938

Di Valentin, Marilena; Tait, Claudia E; Salvadori, Enrico; Orian, Laura; Polimeno, Antonino; Carbonera, Donatella

2014-01-01

365

Theory of X-ray absorption spectra of strongly correlated copper oxides  

NASA Astrophysics Data System (ADS)

It has been shown that theoretical X-ray absorption spectra of highly correlated systems can be presented as a product of a single-electron part obtained by the self-consistent field X ?-scattered wave (SCFX ?-SW) method, and of a multi-electron part obtained by exact diagonalization of the Hamiltonian of the multi-band multi-electron p-d model. Using that model, the influence of strong correlation effects on the Cu K- and CuL 2,3-spectra of La 2- xSr xCuO 4 ( x = 0, 0.2, 1) has been studied. In terms of that model, the main peak of the Cu K-spectrum for x = 0 was assigned to the Cud 10L- configuration and only one satellite was assigned to the Cu d9-configuration. Comparison of the theoretical with the experimental data shows that the ground state of the two-holes in the CuO 4 cell is triplet. In that case additional satellites of Cud 9L- and Cu d8-configurations are observed. The same conclusions have been made concerning polarized CuL 2,3-spectra for the fully doped LaSrCuO 4 excluding the peak with the energy 2.8 eV above the threshold, which was assigned to the transitions into quasi-stationary states due to existence of a high barrier in the Cu d-state Hartree-Fock potential.

Avramov, Pavel V.; Ovchinnikov, Sergei G.; Gavrichkov, Vladimir A.; Ruzankin, Sergei Ph.

1997-02-01

366

[Neonatal morbidity and hospital mortality of preterm triplets.  

PubMed

Background: multiple gestations have caused an increase in vulnerable preterm births. Our objective was to analyze neonatal morbidity and mortality in preterm triplets. Methods: we analyzed a cohort of 30 triplets in an obstetrics and gynecology hospital. Data were obtained during pregnancy, childbirth and neonatal period: birth order, sex, weight, height, malformations, advanced resuscitation, assisted ventilation, intraventricular hemorrhage, necrotizing enterocolitis, sepsis, pulmonary hypertension, bronchopulmonary dysplasia, days of hospitalization, and death. Results: 90 infants were analyzed. There was an omphalopagus con-joined twins case; 42 (70 %) had between 30-33 weeks and six between 24-29; 19 (21 %) had low weight for gestational age, and 18 (30 %) had a major malformation; 27 % required ventilatory support, 33 % sepsis, 32 % necrotizing enterocolitis, 21 % pulmonary hypertension, 14 % bronchopulmonary dysplasia and 2 % intraventricular hemorrhage, without statistically significant differences related to the order, presentation at birth, sex and number of placentas and amniotic sacs. Eight 24-week triplets died, four over 28 weeks, and a siamese (p = 38). There was no difference in hospital days between triplets. Conclusions: the triplets mortality is low and mainly associated with extreme prematurity, intrauterine growth restriction and sepsis. PMID:24290011

Lamshing-Salinas, Priscilla; Rend Ón-Macías, Mario Enrique; Iglesias-Leboreiro, José; Bernárdez-Zapata, Isabel; Braverman-Bronstein, Ariela

2013-01-01

367

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

NASA Technical Reports Server (NTRS)

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

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

1995-01-01

368

atomic spectra 1 Atomic Spectra  

E-print Network

Physics, pp. 88-93 (Rutherford nuclear model), 93-106 (atomic structure and electron spectra) 2. D. W 3. Beiser: Concepts of Modern Physics, pp. 131-161 (atomic structure and electron spectra) 4. E. Lamb, Jr. and R. C. Retherford: The Structure of the Hydrogen Atom by a Microwave Method, Phys

Glashausser, Charles

369

Correcting human heart 31P NMR spectra for partial saturation. Evidence that saturation factors for PCr/ATP are homogeneous in normal and disease states  

NASA Astrophysics Data System (ADS)

Heart PCr/ATP ratios measured from spatially localized 31P NMR spectra can be corrected for partial saturation effects using saturation factors derived from unlocalized chest surface-coil spectra acquired at the heart rate and approximate Ernst angle for phosphor creatine (PCr) and again under fully relaxed conditions during each 31P exam. To validate this approach in studies of normal and disease states where the possibility of heterogeneity in metabolite T1 values between both chest muscle and heart and normal and disease states exists, the properties of saturation factors for metabolite ratios were investigated theoretically under conditions applicable in typical cardiac spectroscopy exams and empirically using data from 82 cardiac 31P exams in six study groups comprising normal controls ( n = 19) and patients with dilated ( n = 20) and hypertrophic ( n = 5) cardiomyopathy, coronary artery disease ( n = 16), heart transplants ( n = 19), and valvular heart disease ( n = 3). When TR ? T1,(PCr), with T1(PCr) ? T1(ATP), the saturation factor for PCr/ATP lies in the range 1.5 ± 0.5, regardless of the T1 values. The precise value depends on the ratio of metabolite T1 values rather than their absolute values and is insensitive to modest changes in TR. Published data suggest that the metabolite T1 ratio is the same in heart and muscle. Our empirical data reveal that the saturation factors do not vary significantly with disease state, nor with the relative fractions of muscle and heart contributing to the chest surface-coil spectra. Also, the corrected myocardial PCr/ATP ratios in each normal or disease state bear no correlation with the corresponding saturation factors nor the fraction of muscle in the unlocalized chest spectra. However, application of the saturation correction (mean value, 1.36 ± 0.03 SE) significantly reduced scatter in myocardial PCr/ATP data by 14 ± 11% (SD) ( p ? 0.05). The findings suggest that the relative T1 values of PCr and ATP are substantially the same in chest and heart muscle and are unchanged in these disease states. The mean value for T1 (PCr)/ T1(ATP) is 2.16 ± 0.29 SE.

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

370

Ultraviolet Absorption Spectra and the Quasi-planarity of Pyridine and its d5 Isotopomer in its S1(?,?*) Excited State  

NASA Astrophysics Data System (ADS)

The ultraviolet absorption spectra of pyridine-d0 and --d5 vapor have been recorded and analyzed in the 32,000 to 38,000 cm-1 region. The electronic band origins are at 34,767 (d0) and 34,945 cm-1 (d5) for the two isotopomers. For both molecules series of transitions for ?18, the out-of-plane ring-bending vibration, in the excited electronic state can be observed, and a one-dimensional potential energy function of the form V = ax^4 -- bx^2 can be determined, where x is the out-of-plane vibrational coordinate. In the S0 electronic ground state pyridine is rigid and planar with ?18 at 403 cm-1. In the S1(?,?*) excited state ?18 drops to 59.5 cm-1 and the molecule becomes floppy with a tiny barrier to planarity of 3 cm-1 resulting in a quasi-planar structure.

Boopalachandran, Praveen; McCann, Kathleen; Laane, Jaan

2007-10-01

371

Orphan spin operators enable the acquisition of multiple 2D and 3D magic angle spinning solid-state NMR spectra  

NASA Astrophysics Data System (ADS)

We propose a general method that enables the acquisition of multiple 2D and 3D solid-state NMR spectra for U-13C, 15N-labeled proteins. This method, called MEIOSIS (Multiple ExperIments via Orphan SpIn operatorS), makes it possible to detect four coherence transfer pathways simultaneously, utilizing orphan (i.e., neglected) spin operators of nuclear spin polarization generated during 15N-13C cross polarization (CP). In the MEIOSIS experiments, two phase-encoded free-induction decays are decoded into independent nuclear polarization pathways using Hadamard transformations. As a proof of principle, we show the acquisition of multiple 2D and 3D spectra of U-13C, 15N-labeled microcrystalline ubiquitin. Hadamard decoding of CP coherences into multiple independent spin operators is a new concept in solid-state NMR and is extendable to many other multidimensional experiments. The MEIOSIS method will increase the throughput of solid-state NMR techniques for microcrystalline proteins, membrane proteins, and protein fibrils.

Gopinath, T.; Veglia, Gianluigi

2013-05-01

372

Triplet supertree heuristics for the tree of life  

PubMed Central

Background There is much interest in developing fast and accurate supertree methods to infer the tree of life. Supertree methods combine smaller input trees with overlapping sets of taxa to make a comprehensive phylogenetic tree that contains all of the taxa in the input trees. The intrinsically hard triplet supertree problem takes a collection of input species trees and seeks a species tree (supertree) that maximizes the number of triplet subtrees that it shares with the input trees. However, the utility of this supertree problem has been limited by a lack of efficient and effective heuristics. Results We introduce fast hill-climbing heuristics for the triplet supertree problem that perform a step-wise search of the tree space, where each step is guided by an exact solution to an instance of a local search problem. To realize time efficient heuristics we designed the first nontrivial algorithms for two standard search problems, which greatly improve on the time complexity to the best known (naïve) solutions by a factor of n and n2 (the number of taxa in the supertree). These algorithms enable large-scale supertree analyses based on the triplet supertree problem that were previously not possible. We implemented hill-climbing heuristics that are based on our new algorithms, and in analyses of two published supertree data sets, we demonstrate that our new heuristics outperform other standard supertree methods in maximizing the number of triplets shared with the input trees. Conclusion With our new heuristics, the triplet supertree problem is now computationally more tractable for large-scale supertree analyses, and it provides a potentially more accurate alternative to existing supertree methods. PMID:19208181

Lin, Harris T; Burleigh, J Gordon; Eulenstein, Oliver

2009-01-01

373

Excited state solvatochromic and prototropic behaviour of 4-aminodiphenylamine and 4,4'-diaminodiphenylamine—A comparative study by electronic spectra  

NASA Astrophysics Data System (ADS)

Solvatochromic and prototropic behaviour of 4-aminodiphenylamine (4ADA) and 4,4'-diaminodiphenylamine (DADA) have been investigated in the solvents of different polarity and at various acid-base concentrations in the ground and excited states using absorption and fluorescence spectra. Solvatochromic shifts have been analysed and observed shifts are explained by the hydrogen bonding interactions. The prototropic study reveals that (i) absorption maximum of monocation of DADA is red shifted to its neutral form, and (ii) the fluorescence of 4ADA is red shifted on protonation. The abnormal fluorescence of 4ADA + is found to be due to large solvent relaxation in polar medium.

Nayaki, S. Kothai; Swaminathan, M.

2006-06-01

374

CF 3-torsional potentials of 2-aminobenzotrifluoride in the S 0 and S 1 electronic states from fluorescence spectra in a supersonic jet  

NASA Astrophysics Data System (ADS)

Both fluorescence excitation and dispersed fluorescence spectra of 2-aminobenzotrifluoride in a supersonic jet show quite extensive vibrational structure due to the CF 3-torsional motion in the S 1 and S 0 electronic states, respectively. This structure has been assigned and results in CF 3-torsional potentials with parameters V3=450 cm -1, V6=83 cm -1 in S 0 and V3=240 cm -1, V6=-67 cm -1 in S 1. There is some evidence which points to interaction between an amino-hydrogen atom and the fluorine atoms: this may be due to hydrogen bonding or steric effects, or both.

Gordon, Robert D.; Michael Hollas, J.; Ribeiro-Claro, Paulo J. A.; Teixeira-Dias, José J. C.

1993-08-01

375

The kinetics of in vivo state transitions in mesophyll and guard cell chloroplasts monitored by 77 k fluorescence emission spectra.  

PubMed

Fluorescence emission spectral peaks at 685, 695 and 730 nanometers (F685, F695, and F730) were recorded 77 K from diluted leaf tissue and epidermal powders prepared from Saxifraga cernua. The time course for state 1 to state 2 transitions was monitored as changes in the ratios of the three emission peaks. During illumination with light 2 (580 nm) the F730/F695 and F730/F685 ratios increased within minutes to establish a condition characteristic of state 2. A major difference between the two chloroplast types was the more rapid establishment of state 2 by mesophyll chloroplasts. An increase in light 2 intensity caused an increase in the magnitude of the F730/F695 ratio for both chloroplast types and, for guard cell chloroplasts, a decrease in the time required to establish the new ratio. The role of reversible phosphorylation of the light-harvesting chlorophyll a/b protein complex in regulating state transitions for both mesophyll and guard cell chloroplasts was assessed using DCMU and sodium fluoride, a specific phosphatase inhibitor. DCMU-treated mesophyll and epidermal tissues failed to show a state 1-state 2 transition. NaF-treated tissues attained state 2 but lacked the ability to revert back to state 1. PMID:16665160

Mawson, B T; Cummins, W R

1986-12-01

376

Spectroscopy of the low-lying states of the group III-V diatomics, AlP, GaP, InP, and GaAs via anion photodetachment spectroscopy  

NASA Astrophysics Data System (ADS)

The low-lying electronic states of AlP, GaP, InP, and GaAs have been probed using anion photoelectron spectroscopy and zero electronic kinetic energy spectroscopy. We observe transitions from the anion 2Sigma+ and low-lying 2Pi states to the triplet (3Sigma- and 3Pi states) and singlet (1Pi, 1Sigma+, and 1Delta states) manifolds of the neutral species. The spectra of the triplet manifolds are particularly complex, with overlapping spin-orbit and vibrational progressions. Spin-orbit splittings, term energies, and vibrational frequencies are reported and compared to previous electronic structure calculations on the anions and neutrals, as well as to those parameters determined previously for the isovalent homonuclear diatomics Si2, Ge2, and Sn2.

Gomez, Harry; Taylor, Travis R.; Zhao, Yuexing; Neumark, Daniel M.

2002-11-01

377

Simulating one-photon absorption and resonance Raman scattering spectra using analytical excited state energy gradients within time-dependent density functional theory  

SciTech Connect

A parallel implementation of analytical time-dependent density functional theory gra- dients is presented for the quantum chemistry program NWChem. The implementation is based on the Lagrangian approach developed by Furche and Ahlrichs. To validate our implementation, we first calculate the Stokes shifts for a range of organic dye molecules using a diverse set of exchange-correlation functionals (traditional density functionals, global hybrids and range-separated hybrids) followed by simulations of the one-photon absorption and resonance Raman scattering spectrum of the phenoxyl radical, the well-studied dye molecule rhodamine 6G and a molecular host-guest complex (TTF?CBPQT4+). The study of organic dye molecules illustrates that B3LYP and CAM-B3LYP generally give the best agreement with experimentally determined Stokes shifts unless the excited state is a charge transfer state. Absorption, resonance Raman, and fluorescence simulations for the phenoxyl radical indicate that explicit solvation may be required for accurate characterization. For the host-guest complex and rhodamine 6G, it is demonstrated that absorption spectra can be simulated in good agreement with experiment for most exchange-correlation functionals. However, because one-photon absorption spectra generally lack well-resolved vibrational features, resonance Raman simulations are necessary to evaluate the accuracy of the exchange-correlation functional for describing a potential energy surface.

Silverstein, Daniel W.; Govind, Niranjan; van Dam, Hubertus JJ; Jensen, Lasse

2013-12-10

378

Einstein Observatory SSS and MPC observations of the complex X-ray spectra of Seyfert galaxies. [Solid State Spectrometer and Monitor Proportional Counter  

NASA Technical Reports Server (NTRS)

The X-ray spectra of 25 Seyfert galaxies measured with the Solid State Spectrometer on the Einstein Observatory have been investigated. This new investigation utilizes simultaneous data from the Monitor Proportional Counter, and automatic correction for systematic effects in the Solid State Spectrometer which were previously handled subjectively. It is found that the best-fit single-power-law indices generally agree with those previously reported, but that soft excesses of some form are inferred for about 48 percent of the sources. One possible explanation of the soft excess emission is a blend of soft X-ray lines, centered around 0.8 keV. The implications of these results for accretion disk models are discussed.

Turner, T. J.; Weaver, K. A.; Mushotzky, R. F.; Holt, S. S.; Madejski, G. M.

1991-01-01

379

Initial- and final-state excitations in KL{sub 23}L{sub 23} Auger spectra of Cu and Ni metals, induced near threshold  

SciTech Connect

High-energy resolution KL{sub 23}L{sub 23} Auger spectra of polycrystalline Cu and Ni metals were measured while tuning the energy of the exciting x-rays in the near threshold region up to 50 eV above the K absorption edge. The intensity evolution of the pronounced satellite lines as a function of photon energy reveals different behavior for particular satellites as a consequence of initial state and final state shake excitations. The satellite intensity development near threshold is compared to predictions of different simple models based on the free atom approximation. The observed energy separations between the satellites and the {sup 1}D{sub 2} main diagram line is in accord with results from a cluster molecular orbital model and confirms the assignment based on the satellite intensity evolution curves concerning the origin of the satellites.

Koever, L.; Berenyi, Z.; Cserny, I. [Institute of Nuclear Research of the Hungarian Academy of Sciences, P.O. Box 51, H-4032 Debrecen (Hungary); Lugosi, L. [Institute of Nuclear Research of the Hungarian Academy of Sciences, P.O. Box 51, H-4032 Debrecen (Hungary); Graduate School of Materials Science, Nara Institute of Science and Technology, Surface and Materials Science Laboratory, 8916-5, Takayama, Ikoma 630-0192 (Japan); Drube, W.; Medicherla, V. R. R. [Hamburger Synchrotronstrahlungslabor HASYLAB at Deutsches Elektronen-Synchrotron DESY, Notkestrasse 85, D-22603 Hamburg (Germany); Mukoyama, T. [Kansai Gaidai University, Hirakata, Osaka 573-1001 (Japan)

2006-05-15

380

Infrared spectra and molecular structure of excited electronic metastable states of the nitroprusside anion, [Fe(CN) 5NO] 2-  

NASA Astrophysics Data System (ADS)

Na 2[Fe(CN) 5NO].2H 2O (SNP) and Ba[Fe(CN) 5NO].3H 2O (BNP) irradiated at low temperature with light in the green—blue region exhibit two new sets of infrared (IR) bands. These can be assigned to two, long-lived, electronically excited metastable states of the [Fe(CN) 5NO] 2- (NP) ion. Upon heating, these states depopulate following decay processes with different onset temperatures. We considerably extend here previous polarized IR data on irradiated SNP (100) plates to include the other basal planes. All IR-active CN, NO and FeN stretching modes and FENO bending modes of NP in both metastable states exhibit frequency down shifts This points to a softening of the corresponding bonds upon excitation. Relative frequency shift values observed for modes associated with the FeNO group are about one order of magnitude larger than the corresponding values for CN stretching modes. This supports the conclusion that the metastable states are reached through an electronic transition involving mainly the metal( nd)-NO bonding. We employ dichroic measurements in SNP to estimate the orientation in the lattice of the transition dipole moment vector corresponding to the NO mode of NP in both metastable states. Results show that the FeNO group is not appreciably bent upon excitation of NP to either of these states.

Güida, J. A.; Aymonino, P. J.; Piro, O. E.; Castellano, E. E.

1993-04-01

381

Augmenting Ridge Curves with Minutiae Triplets for Fingerprint Indexing  

E-print Network

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

Ross, Arun Abraham

382

Ultrafast singlet and triplet dynamics in microcrystalline pentacene films  

Microsoft Academic Search

The exciton dynamics of microcrystalline pentacene films is investigated by femtosecond pump-probe experiments. Measurements are performed with ultrashort laser pulses applied at normal incidence and at an angle of incidence of 65° to disentangle singlet and triplet contributions by exploiting the different orientations of the molecular transition dipoles. The results indicate that the initial 70 fs fast relaxation step transforms

Henning Marciniak; Igor Pugliesi; Bert Nickel; Stefan Lochbrunner

2009-01-01

383

Basic moments of phonon density of states spectra and characteristic phonon temperatures of group IV, III-V, and II-VI materials  

NASA Astrophysics Data System (ADS)

We have redigitized a large variety of phonon density of states (PDOS) spectra, that have been published by diferent researchers for group IV (diamond, 3C-SiC, Si, and Ge), III-V (BN, BP, BAs, BSb, AlN, AlP, AlAs, AlSb, GaN, GaP, GaAs, GaSb, InN, InP, InAs, and InSb), and II-VI materials (ZnO, ZnS, ZnSe, ZnTe, CdS, and CdTe), including calculations of their moments, ??n?, of orders n =-1, 1, 2, and 4. Notwithstanding the obvious differences in concrete shapes of spectra presented for one and the same material by different authors, the respective magnitudes of estimated moments have been found in most cases to be nearly the same (to within uncertainties of some few percent). For most materials under study, the average phonon temperatures of the lower and upper sections of PDOS spectra, ?L and ?U, are found to be by factors of order 0.6 lower or 1.4 higher, respectively, than the average phonon temperature, ?P, of the total PDOS spectra. The estimated high-temperature limits of Debye temperatures, ?D(?), are found to be significantly higher (by factors of order 1.4) than ?P, implying an order-of-magnitude equality, ?D(?)??U (within differences not exceeding an order of ±10%, for all materials under study). The phonon temperatures, ?g, that are effective in controlling the observable temperature dependences of fundamental energy gaps, Eg(T), are found to be usually of the same order as the respective average phonon temperatures, ?g??P. The existing differences between these two qualitatively different types of characteristic phonon temperatures are seen to be limited, for diamond, 3C-SiC, Si, Ge, AlN, GaN, GaP, GaAs, GaSb, InP, InSb, ZnS, ZnSe, ZnTe, and CdTe, to an order of ±12%. We design an exemplary way for precalculating harmonic parts of isochoric heat capacities on the basis of the estimated quadruplets of PDOS spectra moments. This novel calculation scheme is exemplified for silicon and germanium.

Pässler, Roland

2007-05-01

384

Computational study of the spin-state energies and UV-Vis spectra of bis(1,4,7-triazacyclononane) complexes of some first-row transition metal cations.  

PubMed

We report here computed spin-state energies and UV-Vis spectra for several transition metal complexes with a triazacyclononane ligand. Our results show that the spin ground-state is correctly obtained with either OPBE or SSB-D, except for the high-spin ground-state of the Co(ii) complex that was properly described only by SSB-D. The UV-Vis spectra from TD-DFT reproduce in general rather well the experimental spectra, but in cases of the Cr(III) and Co(II) complexes it clearly failed. Better results for the UV-Vis spectra have been obtained by using Ligand Field DFT. PMID:23235435

Zlatar, Matija; Gruden-Pavlovi?, Maja; Güell, Mireia; Swart, Marcel

2013-05-14

385

Morphology Effectively Controls Singlet-Triplet Exciton Relaxation and Charge Transport in Organic Semiconductors  

E-print Network

singlet- triplet exciton fission. In Pc films (as well as C60-doped films) this decay channel behavior in an organic semiconductor by effectively turning singlet- triplet exciton fission decay channelsMorphology Effectively Controls Singlet-Triplet Exciton Relaxation and Charge Transport in Organic

386

Anomalous Behavior of Dark States in Quantum Gases of Li6  

NASA Astrophysics Data System (ADS)

We create atom-molecule dark states in a degenerate Fermi gas of Li6 in both weakly and strongly interacting regimes using two-photon Raman scattering to couple fermion pairs to bound molecular states in the ground singlet and triplet potential. Near the unitarity point in the BEC-BCS crossover regime, the atom number revival height associated with the dark state abruptly and unexpectedly decreases and remains low for magnetic fields below the Feshbach resonance center at 832.2 G. With a weakly interacting Fermi gas at 0 G, we perform precision dark-state spectroscopy of the least-bound vibrational levels of the lowest singlet and triplet potentials. From these spectra, we obtain binding energies of the v''=9, N''=0 level of the a(13?u+) potential and the v''=38, N''=0 level of the X(11?g+) potential with absolute uncertainty as low as 20 kHz. For the triplet potential, we resolve the molecular hyperfine structure.

Semczuk, Mariusz; Gunton, Will; Bowden, William; Madison, Kirk W.

2014-08-01

387

UV-vis spectra of singlet state cationic polycyclic aromatic hydrocarbons: Time-dependent density functional theory study  

SciTech Connect

A theoretical study of singlet state cations of polycyclic aromatic hydrocarbons is performed. Appropriate symmetry suitable for further calculations is chosen for each of the systems studied. The excitation states of such species are obtained by the time dependent density functional theory (TD-DFT) method. The computations are performed using both Pople and electronic response properties basis sets. The results obtained with the use of different basis sets are compared. The electronic transitions are described and the relationships for the lowest-lying transitions states of different species are found. The properties of in-plane and out-of-plane transitions are also delineated. The TD-DFT results are compared with the experimental data available.

Dominikowska, Justyna, E-mail: justyna@uni.lodz.pl; Domagala, Malgorzata; Palusiak, Marcin [Department of Theoretical and Structural Chemistry, University of ?ód?, Pomorska 163/165, 90-236 ?ód? (Poland)] [Department of Theoretical and Structural Chemistry, University of ?ód?, Pomorska 163/165, 90-236 ?ód? (Poland)

2014-01-28

388

UV-vis spectra of singlet state cationic polycyclic aromatic hydrocarbons: Time-dependent density functional theory study  

NASA Astrophysics Data System (ADS)

A theoretical study of singlet state cations of polycyclic aromatic hydrocarbons is performed. Appropriate symmetry suitable for further calculations is chosen for each of the systems studied. The excitation states of such species are obtained by the time dependent density functional theory (TD-DFT) method. The computations are performed using both Pople and electronic response properties basis sets. The results obtained with the use of different basis sets are compared. The electronic transitions are described and the relationships for the lowest-lying transitions states of different species are found. The properties of in-plane and out-of-plane transitions are also delineated. The TD-DFT results are compared with the experimental data available.

Dominikowska, Justyna; Domagala, Malgorzata; Palusiak, Marcin

2014-01-01

389

Steady-state and laser flash photolysis studies of bridgehead-substituted dibenzobarrelenes  

SciTech Connect

The photochemistry of bridgehead-substituted dibenzobarrelenes has been investigated by steady-state photolysis, product analysis, and time-resolved laser flash photolysis. 4b-Substituted dibenzosemibullvalenes are formed as major photoproducts from dibenzobarrelenes, bearing acetoxy, formyl, ethyl, and methoxy 9-bridgehead substitutents, whereas 8b-substituted dibenzosemibullvalenes (or products derived from them) are formed from 9-hydroxy- and 9-cyano-substituted dibenzobarrelenes. Laser flash photolysis gives rise to transient phenomena attributable to the triplets of dibenzobarrelenes (phi/sub T/ = 0.2-0.7 in benzene). These are characterized by broad and diffuse absorption spectra, short lifetimes (0.07-11 /sup +/s), and varying degrees of quenchability by azulene, ferrocene, ..beta..-cartene, and p-methoxyphenol. The rate constants for triplet quenching by the latter quenchers as well as oxygen and di-tert-butylnitroxy radicals are presented.

Murty, B.A.R.C.; Pratapan, S.; Kumar, C.V.; Das, P.K.; George, M.V.

1985-01-01

390

Atomic Spectra  

NSDL National Science Digital Library

In this Flash animation the user can view the atomic emission spectra (400-700nm) of eight different elements. A dragable marker allows the user to approximate the wavelength of the various spectral lines. The effect of resolution can be examined in the sodium spectrum in the region 550-600nm.

391

Atomic Spectra  

NSDL National Science Digital Library

This page from Hyperphysics contains images depicting the light emitted by several elements and their respective spectra. The page also provides a description of how the size of a holographic image scales with the wavelength of the light used to observe it.

Nave, Carl R.

2010-03-12

392

Absence of singlet fission and carrier multiplication in a model conjugated polymer: tracking the triplet population through phosphorescence.  

PubMed

Singlet fission, or multiple exciton generation, has been purported to occur in a variety of material systems. Given the current interest in exploiting this process in photovoltaics, we search for the direct signature of singlet fission, phosphorescence from the triplet state, in a model polymeric organic semiconductor for which photoinduced absorption experiments have implied a tripling of the intersystem crossing yield at the onset of fission. Fluorescence and phosphorescence are clearly discriminated using a picosecond gated photoluminescence excitation technique, at variable temperature. At low excitation densities, in a quasi-steady-state experiment, we detect no change of the relative triplet yield to within 4% for photon energies of almost three times the triplet energy of 2.1 eV. Identical results are obtained under nonlinear two-photon excitation. We conclude that assignments of singlet fission based on induced absorptions alone should be treated with caution and may substantially overestimate excited-state intersystem crossing yields, raising questions with regards to the applicability of the process in devices. PMID:22235946

Bange, Sebastian; Scherf, Ullrich; Lupton, John M

2012-02-01

393

Search for narrow states in the inclusive ?-ray spectra resulting from antiproton annihilations at rest in liquid hydrogen and deuterium  

NASA Astrophysics Data System (ADS)

The energy spectrum of ? rays produced in proton-antiproton annihilation at rest in hydrogen and deuterium has been measured with good energy resolution and high statistics. The data were taken using the PS183 magnetic pair spectrometer at CERN's Low Energy Antiproton Ring. A detailed search of the ? spectrum yielded no evidence of ? transitions to narrow states with widths consistent with the spectrometer resolution. In hydrogen, upper limits (95% C.L.) are obtained for the yield of narrow states of (2-5)×10-4 for states below 1700 MeV/c2, and (5-10)×10-4 for states between 1700 and 1800 MeV/c2. In deuterium, the corresponding upper limits are (1-7)×10-3 for masses between 700 and 1730 MeV/c2, and (1-2)×10-3 for masses between 1750 and 1835 MeV/c2. These results contradict reports of the observation of narrow lines made by previous experiments.

Graf, N. A.; Fero, M.; Gee, M.; Mandelkern, M.; Ray, R.; Schultz, D.; Schultz, J.; Usher, T.; Armstrong, T. A.; Biard, J.; Lewis, R. A.; Playfer, S. M.; Smith, G. A.; Soulliere, M. J.; Bassalleck, B.; Wolfe, D. M.; Denes, P.; Büche, G.; Bürcker, L.; Koch, H.; Schwertel, J.; Angelopoulos, A.; Apostolakis, A.; Rozaki, H.; Sakelliou, L.

1991-10-01

394

Neutral Higgs Bosons in the Higgs Triplet Model with nontrivial mixing  

E-print Network

We revisit the neutral Higgs sector of the Higgs Triplet Model, with non-negligible mixing in the CP-even Higgs sector. We examine the possibility that one of the Higgs boson state is the particle observed at the LHC at 125 GeV, and the other is either the small LEP excess at 98 GeV; or the CMS excess at 136 GeV; or that the neutral Higgs bosons are (almost) degenerate and have both mass 125 GeV. We show that, under general considerations, an (unmixed) neutral Higgs boson cannot have an enhanced decay branching ratio into gamma gamma with respect to the Standard Model one. An enhancement is however possible for the mixed case, but only for the heavier of the two neutral Higgs bosons, and not for mass-degenerate Higgs bosons. At the same time the branching ratios into WW^*,ZZ^*, bb and tau tau are similar to the Standard Model, or reduced. We correlate the branching ratios of both Higgs states into Z gamma to those into gamma gamma for the three scenarios. The mixed neutral sector of the Higgs triplet model exhibits some features which could distinguish it from other scenarios at the LHC.

Fatemeh Arbabifar; Sahar Bahrami; Mariana Frank

2012-11-29

395

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

PubMed

The (1)H NMR signal of the methyl group of sodium acetate is shown to be a triplet in the anisotropic environment of stretched gelatin gel. The multiplet structure of the signal is due to the intra-methyl residual dipolar couplings. The relaxation properties of the spin system were probed by recording steady-state irradiation envelopes ('z-spectra'). A quantum-mechanical model based on irreducible spherical tensors formed by the three magnetically equivalent spins of the methyl group was used to simulate and fit experimental z-spectra. The multiple parameter values of the relaxation model were estimated by using a Bayesian-based Markov chain Monte Carlo algorithm. PMID:25486634

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

2015-01-01

396

First-principles study of phonons and related ground-state properties and spectra in Zn-IV-N2 compounds  

NASA Astrophysics Data System (ADS)

The Zn-IV-N2 compounds, with the group-IV element Si, Ge, and Sn, which have a common crystal structure closely related to the wurtzite-structure form a series analogous to the group-III nitrides GaN, AlN, and InN, respectively. Calculations of the phonons and related quantities in these materials are reported here using the density-functional perturbation-theory linear-response approach in the local-density approximation and using a plane-wave pseudopotential method. We focus on spectra, such as the imaginary part of the dielectric function and the energy-loss function as measurable by infrared absorption or reflectivity, and the Raman spectra. We also present phonon densities of states, band dispersions, and related integrated thermodynamic quantities such as the specific heat, and Helmholtz free energy and entropy as functions of temperature. Structural and elastic properties such as the lattice constants and bulk moduli are also reported. Finally, high-frequency and static dielectric tensors are presented. The trends in the series and the relation to the corresponding III-N nitrides are discussed. It is found that the bimodal bond-length distribution with IV-N bonds shorter than the Zn-N bonds (even for Sn) strongly modifies the spectra from those in III-N nitrides. While in ZnGeN2 and ZnSnN2 folded acoustic-like modes are clearly separated from the optic type modes, this is not the case in ZnSiN2 . The calculated Born effective charges indicate that ZnGeN2 has the lowest ionicity of the three materials.

Paudel, Tula R.; Lambrecht, Walter R. L.

2008-09-01

397

Two-axis control of a singlet-triplet qubit with an integrated micromagnet.  

PubMed

The qubit is the fundamental building block of a quantum computer. We fabricate a qubit in a silicon double-quantum dot with an integrated micromagnet in which the qubit basis states are the singlet state and the spin-zero triplet state of two electrons. Because of the micromagnet, the magnetic field difference ?B between the two sides of the double dot is large enough to enable the achievement of coherent rotation of the qubit's Bloch vector around two different axes of the Bloch sphere. By measuring the decay of the quantum oscillations, the inhomogeneous spin coherence time T2* is determined. By measuring T2* at many different values of the exchange coupling J and at two different values of ?B, we provide evidence that the micromagnet does not limit decoherence, with the dominant limits on T2* arising from charge noise and from coupling to nuclear spins. PMID:25092298

Wu, Xian; Ward, D R; Prance, J R; Kim, Dohun; Gamble, John King; Mohr, R T; Shi, Zhan; Savage, D E; Lagally, M G; Friesen, Mark; Coppersmith, S N; Eriksson, M A

2014-08-19

398

Solvent induced shifts of electronic spectra IV. Computational study on PRODAN fluorescence and implications to the excited state structure.  

PubMed

Vertical S(1)-S(0) electronic transitions of the highly solvent-sensitive fluorescence label 2-propionyl-6-dimethylamino naphthalene (PRODAN) are modeled by semiempirical CISD AM1 and TD DFT calculations in a large number of solvents of different polarity and hydrogen donating ability. Calculations correctly reproduce the observed solvent induced shifts of the emission maxima. The fluorescence Frank-Condon transition energies in solvent can be predicted quantitatively at the AM1 SM5.42 OPEN(2,2) C.I.=5 CISD level. For the planar PRODAN emitting state at the latter level we obtain a regression with practically unit slope and zero intercept for aprotic solvents. The respective relationship for the O-twisted S(1) state has a slope of 0.59 and intercept of 9100 cm(-1). These results support the concept that no geometry twist in the S(1) state of PRODAN is necessary to explain the observed solvent effects on fluorescence. PMID:19010722

Bakalova, Snezhana M; Kaneti, Jose

2009-02-01

399

Physical State And Composition Of Mars Polar Caps And Seasonal Condensations By Radiative Transfer Modelling Of Visible-IR Spectra From OMEGA/MEX Observations.  

NASA Astrophysics Data System (ADS)

The determination of the physical state of the ices composing the surface layer of the Mars polar caps and seasonal condensations is of prime importance for the understanding of the microphysics of the sublimation/condensation/deposition processes of volatiles. It is also a prerequisite for an accurate mapping of the abundance of the ices and of their physical characteristics by spectral inversion of the OMEGA observations. Four observations covering about the whole bright south polar cap have been recorded by the OMEGA imaging spectrometer before the southern autumn equinox and a whole series of observations of the north polar cap and the retreating seasonal condensations have been acquired during the full northern spring. We first extracted several end-member and representative spectra of the different types of icy terrains determined from statistical analyses (ACP) of selected observations of the south and north polar regions. Then, using our radiative transfer code in layered media (Douté and Schmitt 1998) together with laboratory spectra on ices we study the coexistence modes at the centimetre scale (granular mixtures, layered deposits, Å) and at the pixel scale (geographical mixture) of CO2 ice, H2O ice and dust on the polar caps and seasonal condensations. Finally we derive their corresponding relative abundances (mass fraction, layer thickness, surface fractions) and compare the values obtained from different north and south polar area. From these results the sublimation/condensation/deposition processes of volatiles and dust in both hemispheres are discussed. We acknowledge support from CNES.

Schmitt, B.; Douté, S.; Altieri, F.; Bellucci, G.; OMEGA

2004-11-01

400

Accurate calculations of geometries and singlet-triplet energy differences for active-site models of [NiFe] hydrogenase.  

PubMed

We have studied the geometry and singlet-triplet energy difference of two mono-nuclear Ni(2+) models related to the active site in [NiFe] hydrogenase. Multiconfigurational second-order perturbation theory based on a complete active-space wavefunction with an active space of 12 electrons in 12 orbitals, CASPT2(12,12), reproduces experimental bond lengths to within 1 pm. Calculated singlet-triplet energy differences agree with those obtained from coupled-cluster calculations with single, double and (perturbatively treated) triple excitations (CCSD(T)) to within 12 kJ mol(-1). For a bimetallic model of the active site of [NiFe] hydrogenase, the CASPT2(12,12) results were compared with the results obtained with an extended active space of 22 electrons in 22 orbitals. This is so large that we need to use restricted active-space theory (RASPT2). The calculations predict that the singlet state is 48-57 kJ mol(-1) more stable than the triplet state for this model of the Ni-SIa state. However, in the [NiFe] hydrogenase protein, the structure around the Ni ion is far from the square-planar structure preferred by the singlet state. This destabilises the singlet state so that it is only ?24 kJ mol(-1) more stable than the triplet state. Finally, we have studied how various density functional theory methods compare to the experimental, CCSD(T), CASPT2, and RASPT2 results. Semi-local functionals predict the best singlet-triplet energy differences, with BP86, TPSS, and PBE giving mean unsigned errors of 12-13 kJ mol(-1) (maximum errors of 25-31 kJ mol(-1)) compared to CCSD(T). For bond lengths, several methods give good results, e.g. TPSS, BP86, and M06, with mean unsigned errors of 2 pm for the bond lengths if relativistic effects are considered. PMID:24647807

Delcey, Mickaël G; Pierloot, Kristine; Phung, Quan M; Vancoillie, Steven; Lindh, Roland; Ryde, Ulf

2014-05-01

401

Resonant energy transfer of triplet excitons from pentacene to PbSe nanocrystals.  

PubMed

The efficient transfer of energy between organic and inorganic semiconductors is a widely sought after property, but has so far been limited to the transfer of spin-singlet excitons. Here we report efficient resonant-energy transfer of molecular spin-triplet excitons from organic semiconductors to inorganic semiconductors. We use ultrafast optical absorption spectroscopy to track the dynamics of triplets, generated in pentacene through singlet exciton fission, at the interface with lead selenide (PbSe) nanocrystals. We show that triplets transfer to PbSe rapidly (<1 ps) and efficiently, with 1.9 triplets transferred for every photon absorbed in pentacene, but only when the bandgap of the nanocrystals is close to resonance (±0.2 eV) with the triplet energy. Following triplet transfer, the excitation can undergo either charge separation, allowing photovoltaic operation, or radiative recombination in the nanocrystal, enabling luminescent harvesting of triplet exciton energy in light-emitting structures. PMID:25282509

Tabachnyk, Maxim; Ehrler, Bruno; Gélinas, Simon; Böhm, Marcus L; Walker, Brian J; Musselman, Kevin P; Greenham, Neil C; Friend, Richard H; Rao, Akshay

2014-11-01

402

Resonant energy transfer of triplet excitons from pentacene to PbSe nanocrystals  

NASA Astrophysics Data System (ADS)

The efficient transfer of energy between organic and inorganic semiconductors is a widely sought after property, but has so far been limited to the transfer of spin-singlet excitons. Here we report efficient resonant-energy transfer of molecular spin-triplet excitons from organic semiconductors to inorganic semiconductors. We use ultrafast optical absorption spectroscopy to track the dynamics of triplets, generated in pentacene through singlet exciton fission, at the interface with lead selenide (PbSe) nanocrystals. We show that triplets transfer to PbSe rapidly (<1 ps) and efficiently, with 1.9 triplets transferred for every photon absorbed in pentacene, but only when the bandgap of the nanocrystals is close to resonance (±0.2 eV) with the triplet energy. Following triplet transfer, the excitation can undergo either charge separation, allowing photovoltaic operation, or radiative recombination in the nanocrystal, enabling luminescent harvesting of triplet exciton energy in light-emitting structures.

Tabachnyk, Maxim; Ehrler, Bruno; Gélinas, Simon; Böhm, Marcus L.; Walker, Brian J.; Musselman, Kevin P.; Greenham, Neil C.; Friend, Richard H.; Rao, Akshay

2014-11-01

403

Microscopic theory of the Raman and infrared spectra of transition-metal dichalcogenides in the charge-density-wave state  

Microsoft Academic Search

Microscopic description of the Raman scattering and infrared absorption of transition-metal dichalcogenides in the charge-density-wave (CDW) state is developed in terms of the hybridization and multiphonon processes in which the condensed phonons participate. They are classified according to the strength of the CDW-(i) strong, 1T-TaS2 and 1T-TaSe2; (ii) intermediate, 1T-VSe2, 1T-TiSe2, 2H-TaSe2, and 2H-TaS2; and (iii) weak, 2H-NbSe2-and detailed analysis

Naoto Nagaoso; Eiichi Hanamura

1984-01-01

404

Abundance gradients in cooling flow clusters: Ginga Large Area Counters and Einstein Solid State Spectrometer spectra of A496, A1795, A2142, and A2199  

NASA Technical Reports Server (NTRS)

We analyze the Ginga Large Area Counters (LAC) and Einstein Solid State Spectrometer (SSS) spectra of four cooling flow clusters, A496, A1795, A2142, and A2199, each of which shows firm evidence of a relatively cool component. The inclusion of such cool spectral components in joint fits of SSS and LAC data leads to somewhat higher global temperatures than are derived from the high-energy LAC data alone. We find little evidence of cool emission outside the SSS field of view. Metal abundances appear to be centrally enhanced in all four clusters, with varying degrees of model dependence and statistical significance: the evidence is statistically strongest for A496 and A2142, somewhat weaker for A2199 and weakest for A1795. We also explore the model dependence in the amount of cold, X-ray-absorbing matter discovered in these clusters by White et al.

White, Raymond E., III; Day, C. S. R.; Hatsukade, Isamu; Hughes, John P.

1994-01-01

405

Atomic versus ionized states in many-particle systems and the spectra of reduced density matrices: A model study  

NASA Astrophysics Data System (ADS)

We study the spectrum of appropriate reduced density matrices for a model consisting of one quantum particle ("electron") in a classical fluid (of "protons") at thermal equilibrium. The quantum and classical particles interact by a shortrange, attractive potential such that the quantum particle can form "atomic" bound states with a single classical particle. We consider two models for the classical component: an ideal gas and the "cell model of a fluid." We find that when the system is at low density the spectrum of the "electron-proton" pair density matrix has, in addition to a continuous part, a discrete part that is associated with "atomic" bound states. In the high-density limit the discrete eigenvalues disappear in the case of the cell model, indicating the existence of pressure ionization or a Mott effect according to a general criterion for characterizing bound and ionized electron-proton pairs in a plasma proposed recently by M. Girardeau. For the ideal gas model, on the other hand, eigenvalues remain even at high density.

Lebowitz, Joel L.; Macris, Nicolas; Martin, Philippe A.

1992-06-01

406

Millimeter wave and terahertz spectra and global fit of torsion-rotation transitions in the ground, first and second excited torsional states of 13CH3OH methanol  

NASA Astrophysics Data System (ADS)

Methanol is observed in a wide range of astrophysical sources throughout the universe, and comprehensive databases of the millimeter and THz spectra of CH3OH and its principal isotopologues represent important tools for the astronomical community. A previous combined analysis of microwave and millimeter wave spectra of 13CH3OH together with Fourier transform far-infrared spectra was limited to the first two torsional states, ?t = 0 and 1, for J values up to 20. The limits on frequency and quantum number coverage have recently been extended by new millimeter and THz measurements on several different spectrometers in the Cologne laboratory in the frequency windows 34-70 GHz, 75-120 GHz, 240-340 GHz, 360-450 GHz and 1.12-1.50 THz. With the new data, the global treatment has now been expanded to include the first three torsional states for J values up to 30. The current 13CH3OH data set contains about 2300 microwave, millimeter-wave, sub-millimeter and THz lines and about 17,100 Fourier-transform far-infrared lines, representing the most recent available information in the quantum number ranges J ? 30, K ? 13 and ?t ? 2. The transitions have been successfully fitted to within the assigned measurement uncertainties of ±50 kHz for most of the frequency-measured (i.e. MW, MMW, Sub-MMW, THz) lines and ±6 MHz for the FIR lines. A convergent global fit was achieved using 103 adjustable parameters to reach an overall weighted standard deviation of 1.37. Our new C-13 methanol database is improved substantially compared to the existing one (Li-Hong et al., 1997), and will be available in the Cologne Database for Molecular Spectroscopy, CDMS (http://www.astro.uni-koeln.de/cdms/), in support of astronomical studies associated with results from HIFI (Heterodyne Instrument for the Far-Infrared) on the Herschel Space Observatory and new observations from SOFIA (Stratospheric Observatory For Infrared Astronomy) and ALMA (Atacama Large Millimeter/Submillimeter Array).

Xu, Li-Hong; Lees, R. M.; Hao, Yun; Müller, H. S. P.; Endres, C. P.; Lewen, F.; Schlemmer, S.; Menten, K. M.

2014-09-01

407

Correlating lipid bilayer fluidity with sensitivity and resolution of polytopic membrane protein spectra by solid-state NMR spectroscopy.  

PubMed

Solid-state NMR spectroscopy has emerged as an excellent tool to study the structure and dynamics of membrane proteins under native-like conditions in lipid bilayers. One of the key considerations in experimental design is the uniaxial rotational diffusion of the protein that can affect the NMR spectral observables. In this regard, temperature plays a fundamental role in modulating the phase properties of the lipids, which directly influences the rotational diffusion rate of the protein in the bilayer. In fact, it is well established that below the main phase transition temperature of the lipid bilayer the protein's motion is significantly slowed while above this critical temperature the rate is increased. In this article, we carried out a systematic comparison of the signal intensity and spectral resolution as a function of temperature using magic-angle-spinning (MAS) solid-state NMR spectroscopy. These observables were directly correlated with the relative fluidity of the lipid bilayer as inferred from differential scanning calorimetry (DSC). We applied our hybrid biophysical approach to two polytopic membrane proteins from the small multidrug resistance family (EmrE and SugE) reconstituted into model membrane lipid bilayers (DMPC-14:0 and DPPC-16:0). From these experiments, we conclude that the rotational diffusion giving optimal spectral resolution occurs at a bilayer fluidity of ~5%, which corresponds to the percentage of lipids in the fluid or liquid-crystalline fraction. At the temperature corresponding to this critical value of fluidity, there is sufficient mobility to reduce inhomogeneous line broadening that occurs at lower temperatures. A greater extent of fluidity leads to faster uniaxial rotational diffusion and a sigmoidal-type reduction in the NMR signal intensity, which stems from intermediate-exchange dynamics where the motion has a similar frequency as the NMR observables (i.e., dipolar couplings and chemical shift anisotropy). These experiments provide insight into the optimal temperature range and corresponding bilayer fluidity to study membrane proteins by solid-state NMR spectroscopy. This article is part of a Special Issue entitled, NMR Spectroscopy for Atomistic Views of Biomembranes and Cell Surfaces. Guest Editors: Lynette Cegelski and David P. Weliky. PMID:24835018

Banigan, James R; Gayen, Anindita; Traaseth, Nathaniel J

2015-01-01

408

Spin-triplet supercurrent in planar geometry ferromagnetic Josephson junctions  

NASA Astrophysics Data System (ADS)

The spin-triplet supercurrent in ferromagnetic Josephson junctions is obtained by surrounding the central ferromagnet with noncollinear ferromagnetic layers, F' [1]. In metallic ferromagnets, the long-range nature of the spin-triplet supercurrent has only been tested to lengths of a few tens of nm [2]. In this work, we are fabricating and measuring S/F'/F/F'/S junctions where the central F layer has a lateral geometry with lengths up to a few hundred nm. We will report on our recent progress. [4pt] [1] A.F. Volkov, F.S. Bergeret and K.B. Efetov, Phys. Rev. Lett., 90, 117006 (2003).[0pt] [2] M.A. Khasawneh, T.S. Khaire, C. Klose, W.P. Pratt, Jr., and N.O. Birge, Supercond. Sci. Technol., 24, 024005 (2011).

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

2013-03-01

409

Organic Photodetectors Using Triplet Materials Doped in Polyalkylfluorene  

NASA Astrophysics Data System (ADS)

The characteristics of violet-sensitive organic photodetectors (OPDs) utilizing polyalkylfluorene and triplet materials have been studied as a host and a dopant material, respectively. For the photo absorption layer, poly(9, 9-dioctylfluorene) [PFO] and a phosphorescent iridium complex (Iridium (III) bis(2-(4, 6-difluorophenyl)pyridinato-N, C2) [FIrpic] or Iridium (III) bis(2-(2'-benzothienyl)pyridinato-N, C3')(acetyl-acetonate) [(btp)2Ir(acac)]) were used as a host and a dopant material, respectively. PFO: (btp)2Ir(acac) device showed less photocurrent than PFO device because (btp)2Ir(acac) enhances recombination of the photo generated carriers in the photo absorption layer. On the other hand, PFO : FIrpic device showed larger photocurrent than PFO device due to triplet energy transfer from FIrpic to PFO. A cutoff frequency of 20MHz was observed using a sinusoidal modulated violet laser light illumination under the reverse bias of 8V.