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1

The Triplet State  

NASA Astrophysics Data System (ADS)

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

Zahlan, A. B.

2010-01-01

2

Triplet state spectra and dynamics of peridinin analogs having different extents of ?-electron conjugation  

Microsoft Academic Search

The Peridinin-Chlorophyll a-Protein (PCP) complex has both an exceptionally efficient light-harvesting ability and a highly effective protective capacity\\u000a against photodynamic reactions involving singlet oxygen. These functions can be attributed to presence of a substantial amount\\u000a of the highly-substituted and complex carotenoid, peridinin, in the protein and the facts that the low-lying singlet states\\u000a of peridinin are higher in energy than

Shanti Kaligotla; Sara Doyle; Dariusz M. Niedzwiedzki; Shinji Hasegawa; Takayuki Kajikawa; Shigeo Katsumura; Harry A. Frank

2010-01-01

3

Laser-induced temperature dependent triplet state lifetime of rubreneperoxide.  

PubMed

A number of photophysical properties of three different types of rubreneperoxides have been measured experimentally by flash spectroscopy technique, including the two-photon absorption, fluorescence, delayed fluorescence and temperature dependent triplet-triplet absorption spectra. Excited singlet and triplet state lifetimes are temperature dependent. Lowest triplet state lifetimes were measured from 77 K to 50 degrees C. Experimental observations showed that as we decreased the temperature of rubreneperoxides, most of the molecules migrate to the lowest vibrational and rotational energy levels of the ground electronic state. Similar migration is also observed for the lowest triplet state. Therefore at 77 K, we can get the clean absorption an emission spectra and decay curves for the lowest triplet state. At 50 degrees C, due to the P- and/or E-type of delayed fluorescences, decay of T(1) state, in other words disappearance of the T(1) state is becoming faster than at low temperature (below room temperature). PMID:17561439

Bayrakçeken, Fuat; Sevinç, Papatya C

2007-12-31

4

Singlet And Triplet Trion States In QW Structures  

NASA Astrophysics Data System (ADS)

Photoluminescence (PL) spectra of modulation-doped CdTe/CdMgTe quantum well structures containing two dimensional electron gases different electron concentrations have been studied in magnetic fields up to 45T. Recombination line of triplet trion state was found in the spectra. A model calculation of PL spectra in magnetic fields, which takes into account singlet and triplet trion states, was carried out. It was shown that the dark triplet becomes observable in PL spectra because it becomes the only recombination channel when the formation of the singlet trion state is suppressed by magnetic fields.

Andronikov, D.; Kochereshko, V.; Platonov, A.; Crooker, S. A.; Barrick, T.; Karczewski, G.

2005-06-01

5

Triplet-Triplet Absorption and Polarization Spectra of some Syn-Dioxabimanes.  

National Technical Information Service (NTIS)

The triplet-triplet (T-T) absorption and polarization, singlet-singlet (S-S) absorption, and fluorescence spectra of syn-(methyl, hydrogen), syn-(tetramethylene), syn-(methyl, chloro)bimane, as well as those of syn-(phenyl, chloro), syn-(methyl, phenyl), ...

T. G. Pavlopoulos J. H. Boyer C. M. Lau I. R. Politzer

1989-01-01

6

Electron paramagnetic resonance detection of carotenoid triplet states  

SciTech Connect

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

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

1980-07-16

7

Research on Triplet States and Photochromism.  

National Technical Information Service (NTIS)

The report describes research studies on the photochromic properties of the triplet states of aromatic compounds for application to the problem of flash blindness protection. Effort was concentrated on the measurement of optical densities attained as a fu...

D. Weber M. W. Windsor

1964-01-01

8

Green light-excitable naphthalenediimide acetylide-containing cyclometalated Ir(III) complex with long-lived triplet excited states as triplet photosensitizers for triplet-triplet annihilation upconversion.  

PubMed

Naphthalenediimide (NDI) was connected to the ligand of a cyclometalated Ir(III) complex (Ir-1) via a C?C triple bond to enhance the absorption in the visible region and to access long-lived triplet excited states. Ir(ppy)2(bpy)[PF6] (Ir-2, ppy = 2-phenylpyridine and bpy = 2,2'-bipyridine) was used as a model complex. The photophysical properties of the complexes were studied with steady state and time-resolved spectroscopy. Ir-1 shows strong absorption in the visible region (? = 11,000 M(-1) cm(-1) at 542 nm) and in comparison Ir-2 shows typically weak absorption in the visible region (? < 3000 M(-1) cm(-1) above 400 nm). Room temperature near IR emission at 732 nm (?(P) = 0.1%) was observed for Ir-1, which is attributed to the NDI localized emissive triplet excited state, by transient absorption spectra and DFT calculations on the spin density surface. The lifetime of the NDI-localized triplet excited state is up to 130.0 ?s, which is rarely reported for Ir(III) complexes. In comparison, Ir-2 shows phosphorescence at 578 nm and the triplet state lifetime is a typical value of 0.3 ?s. The complexes were used as triplet photosensitizers for triplet-triplet annihilation (TTA) upconversion and an upconversion quantum yield of 6.7% was observed with Ir-1. No upconversion was observed with Ir-2 as the triplet photosensitizer at the same experimental conditions. PMID:23471114

Ma, Lihua; Guo, Song; Sun, Jifu; Zhang, Caishun; Zhao, Jianzhang; Guo, Huimin

2013-05-14

9

Benzophenones in the higher triplet excited states.  

PubMed

Transient phenomena of benzophenone (BP) in the higher triplet excited state (Tn) have been investigated by the two-colour two-laser excitation method. Triplet energy transfer from BP(Tn) to quenchers (Q) occurred within the duration of a laser pulse (5 ns) to give Q(T1) with higher triplet energy than that of BP(T1). The quantum yield of the triplet energy-transfer quenching of BP(Tn) by CCl4 was found to be 0.0023 +/- 0.0002 from the bleaching of the transient absorption of BP(T1) and the absorbed photon number. It appears that internal conversion from BP(Tn) to BP(T1) is the predominant process. The lifetimes (tauTn) of BP(Tn) and several substituted benzophenones (BPs) in the higher triplet excited state [BPs(Tn)] were estimated from the dependence of the Q concentration on the efficiency of the triplet energy-transfer quenching of BP(Tn) by Q, and found to be 110-450 ps, depending on the nature of the substituents on the BPs. The effect of the substituents on tauTn may be explained by the energy gap between the Tn and T1 states, because the main deactivation pathway for BPs(Tn) is the internal conversion process. In contrast, the substituent effect on the lifetimes of BPs(T1) cannot be explained by the energy gap law. The transient behaviour of Q(T1) depends on the properties of the quencher. Sequential triplet energy transfer from Q(T1) to BP occurred for p-dichlorobenzene and tert-butylbenzene as quenchers, while Q(T1) reacted partly with Q to form triplet excimers (3Q2*) for benzene, chlorobenzene, and o-dichlorobenzene as quenchers. When CCl4 was used as the quencher, the homolytic cleavage of a C-Cl bond of CCl4(T1) occurred to give Cl* and Cl3C* radicals. PMID:14690236

Cai, Xichen; Sakamoto, Masanori; Hara, Michihiro; Sugimoto, Akira; Tojo, Sachiko; Kawai, Kiyohiko; Endo, Masayuki; Fujitsuka, Mamoru; Majima, Tetsuro

2003-11-01

10

Theoretical studies of highly excited triplet states of sodium-potassium  

Microsoft Academic Search

Calculations have been performed to investigate the fine and hyperfine structure of highly excited triplet states of the NaK molecule. Prof. Huennekens' AMO group observed high-resolution spectra of numerous ro-vibrational levels (v, N) of various triplet states of the NaK molecule. The experimental measurements of the fine and hyperfine structure of the 1 3Delta and 33pi states were analyzed to

Angela D. Wilkins

2007-01-01

11

Size effects in photoexcitation of triplet states of ammonium tetraphenylborate  

NASA Astrophysics Data System (ADS)

This paper reports on the results of complex investigations of photoexcited states of ammonium tetraphenylborate, which are characterized by self-sensitized luminescence. It has been established that the excitation by UV light at 77 K leads to the formation of stable triplet states due to the capture of electrons on electron traps. The EPR and luminescence excitation spectra exhibit the formation of a set of triplet states with different distances between electrons and holes. The performed investigations give grounds to affirm that, in bulk samples, cations in the structure of ammonium tetraphenylborate are electron traps. When the size of the ammonium tetraphenylborate sample is changed to 6 and 3 nm, the capture of excited electrons on sorbed oxygen molecules becomes dominant. In this case, the appearance of the spectrum of O{2/-} anion radicals has been detected by the EPR method. The proposed interpretation of the observed effects has been confirmed by the thermoluminescence data on the recombination of electron-hole pairs, which correlate with a change in the intensity of the EPR spectra during annealing.

Nadolinny, V. A.; Antonova, O. V.; Il'inchik, E. A.; Kovalev, M. K.; Mel'gunov, M. S.; Yelisseev, A. P.; Ryadun, A. A.

2011-02-01

12

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

Microsoft Academic Search

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

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

1997-01-01

13

Quenching of excited triplet states by dissolved natural organic matter.  

PubMed

Excited triplet states of aromatic ketones and quinones are used as proxies to assess the reactivity of excited triplet states of the dissolved organic matter ((3)DOM*) in natural waters. (3)DOM* are crucial transients in environmental photochemistry responsible for contaminant transformation, production of reactive oxygen species, and potentially photobleaching of DOM. In recent photochemical studies aimed at clarifying the role of DOM as an inhibitor of triplet-induced oxidations of organic contaminants, aromatic ketones have been used in the presence of DOM, and the question of a possible interaction between their excited triplet states and DOM has emerged. To clarify this issue, time-resolved laser spectroscopy was applied to measure the excited triplet state quenching of four different model triplet photosensitizers induced by a suite of DOM from various aquatic and terrestrial sources. While no quenching for the anionic triplet sensitizers 4-carboxybenzophenone (CBBP) and 9,10-anthraquinone-2,6-disulfonic acid (2,6-AQDS) was detected, second-order quenching rate constants with DOM for the triplets of 2-acetonaphthone (2AN) and 3-methoxyacetophenone (3MAP) in the range of 1.30-3.85 × 10(7) L mol(C)(-1) s(-1) were determined. On the basis of the average molecular weight of DOM molecules, the quenching for these uncharged excited triplet molecules is nearly diffusion-controlled, but significant quenching (>10%) in aerated water is not expected to occur below DOM concentrations of 22-72 mg(C) L(-1). PMID:24083647

Wenk, Jannis; Eustis, Soren N; McNeill, Kristopher; Canonica, Silvio

2013-11-19

14

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

NASA Astrophysics Data System (ADS)

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

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

2008-05-01

15

Two-photon chemistry from upper triplet states of thymine.  

PubMed

Photolysis of the benzophenone chromophore by means of high energy laser pulses has been used as a tool to populate upper thymine-like triplet states via intramolecular sensitization. These species undergo characteristic n?* triplet photoreactivity, as revealed by the Norrish-Yang photocyclization of 5-tert-butyluracil. PMID:24099523

Vendrell-Criado, Victoria; Rodríguez-Muñiz, Gemma M; Yamaji, Minoru; Lhiaubet-Vallet, Virginie; Cuquerella, M Consuelo; Miranda, Miguel A

2013-11-01

16

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

PubMed Central

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

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

1990-01-01

17

Computational and experimental studies on the triplet states of various N-substituted 4,5,6,7-tetrachlorophthalimides.  

PubMed

The triplet-triplet absorption spectra of three newly synthesized N-substituted 4,5,6,7-tetrachlorophthalimides (TCP) were measured experimentally and calculated with density functional theory. The heavy atom effect increases the intersystem crossing rate, and the transient triplet absorbance could be measured. Fluorescence emission was not observed. The transient absorption spectra show two peaks in the region of 385-410 nm and 770-830 nm having a red shift with increasing size of N substituent. The singlet and triplet states and their vertical transitions were investigated theoretically by NEVPT2/CASSCF(12,9) and CAM-B3LYP methods for a benchmark molecule N-Phenyl-maleimide, and by CAM-B3LYP for N-Phenyl-TCP. It is shown that the singlet excited S1 state and the pi-pi* triplet state have similar geometries, thus intersystem crossing is most likely for N-Phenyl-TCP. No crossing between the singlet ground state and the singlet excited states could be found on the linear synchronous transit paths of S0-S1-T1-S0 states using CAM-B3LYP method. The computed singlet ground state absorption and triple-triplet absorption spectra agree well with the experimental ones, in both spectra the first state is a pi-pi* state while the second state is the n-pi* state with an energetic difference of 0.1 eV. PMID:24992990

Kelterer, Anne-Marie; Mansha, Asim; Iftikhar, Faiza Jan; Zhang, Yan; Wang, Wei; Xu, Jian-Hua; Grampp, Günter

2014-07-01

18

Selective quenching of triplet excited states of pteridines.  

PubMed

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

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

2014-07-18

19

Bacteriochlorophyll protein structure - studies with polarized light and triplet state electron paramagnetic resonance  

SciTech Connect

Light harverting bacteriochlorophyll-protein complexes from Rhodopseudomonas sphaeroides 2.4.1 (B800 + 850) and R-26 (LH-R26) mutant are solubiliized in SDS and imbedded in polyvinyl alcohol. Stretching induces orientation, and the linear dichroism of visible and near infrared absorption is analyzed. Based on a simple model, angles between the particle axis system and the transition dipole moments are found. Reaction centers of the photosynthetic bacterium Rhodopseudomonas sphaeroides R-26, give rise to large triplet state EPR signals upon illumination at low temperature (11 K). Utilizing monochromatic polarized light to generate the EPR spectra (magnetophotoselection), it is shown that the intensities of the observed triplet signals are strongly dependent upon the wavelength and polarization direction of the excitation. Triplet states of carotenoids have been detected by EPR and are reported here for the first time. The systems in which carotenoid triplets are observed include cells of photosynthetic bacteria, isolated bacteriochlorophyll-protein complexes, and detergent micelles which contain ..beta..-carotene. The carotenoid triplet state is detected in reaction centers of Rhodopseudomonas sphaeroides 2.4.1 (wild type), which contain the carotenoid spheroidene.

Bolt, J.D.

1980-02-01

20

Bound state spectrum of the triplet states in the Be atom  

NASA Astrophysics Data System (ADS)

The bound state spectrum of the low-lying triplet states in the Be atom is investigated. In particular, we perform accurate computations of the bound triplet S,P,D,F,G, H and I states in the Be atom. The results of these calculations are employed to draw the spectral diagram which contains the energy levels of the triplet states. Based on our computational results we can observe transitions from the low-lying bound states to the weakly-bound Rydberg states. For the 23S,33S and 43S states in the Be atom we also determine a number of bound states properties.

Frolov, Alexei M.; Ruiz, María Belén

2014-03-01

21

Theoretical study of triplet state properties of free-base porphin  

NASA Astrophysics Data System (ADS)

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

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

2005-06-01

22

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

SciTech Connect

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

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

1987-09-01

23

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

PubMed

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

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

2013-08-14

24

Impact of triplet absorption and triplet-singlet annihilation on the dynamics of optically pumped organic solid-state lasers  

Microsoft Academic Search

We study the dynamics of a diode pumped organic semiconductor laser based on the polymer-polymer guest-host system F8BT and MEH-PPV. Regardless of the duration of the pump pulse, lasing persists for only a few nanoseconds. In two separate experiments we study in detail the contribution of triplet-singlet annihilation and triplet state absorption. On this basis we were able to model

M. Lehnhardt; T. Riedl; T. Weimann; W. Kowalsky

2010-01-01

25

Rhenium(I) tricarbonyl polypyridine complexes showing strong absorption of visible light and long-lived triplet excited states as a triplet photosensitizer for triplet-triplet annihilation upconversion.  

PubMed

The preparation of rhenium(I) tricarbonyl polypyridine complexes that show a strong absorption of visible light and long-lived triplet excited state and the application of these complexes as triplet photosensitizers for triplet-triplet annihilation (TTA) based upconversion are reported. Imidazole-fused phenanthroline was used as the N^N coordination ligand, on which different aryl groups were attached (Phenyl, Re-0; Coumarin, Re-1 and naphthyl, Re-2). Re-1 shows strong absorption of visible light (? = 60,800 M(-1) cm(-1) at 473 nm). Both Re-1 and Re-2 show long-lived T(1) states (lifetime, ?(T), is up to 86.0 ?s and 64.0 ?s, respectively). These properties are in contrast to the weak absorption of visible light and short-lived triplet excited states of the normal rhenium(I) tricarbonyl polypyridine complexes, such as Re-0 (? = 5100 M(-1) cm(-1) at 439 nm, ?(T) = 2.2 ?s). The photophysical properties of the complexes were fully studied with steady state and time-resolved absorption and emission spectroscopes, as well as DFT calculations. The intra-ligand triplet excited state is proposed to be responsible for the exceptionally long-lived T(1) states of Re-1 and Re-2. The Re(I) complexes were used as triplet photosensitizers for TTA based upconversion and an upconversion quantum yield up to 17.0% was observed. PMID:22714817

Yi, Xiuyu; Zhao, Jianzhang; Wu, Wanhua; Huang, Dandan; Ji, Shaomin; Sun, Jifu

2012-08-01

26

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

PubMed Central

We have embedded the hexameric triplet repeats (CAG)6 and (CTG)6 between two (GC)3 domains to produce two 30-mer hairpins with the sequences d[(GC)3(CAG)6(GC)3] and d[(GC)3(CTG)6(GC)3]. This construct reduces the conformational space available to these repetitive DNA sequences. We find that the (CAG)6 and (CTG)6 repeats form stable, ordered, single-stranded structures. These structures are stabilized at 62°C by an average enthalpy per base of 1.38 kcal·mol?1 for the CAG triplet and 2.87 kcal·mol?1 for the CTG triplet, while being entropically destabilized by 3.50 cal·K?1·mol?1 for the CAG triplet and 7.6 cal·K?1·mol?1 for the CTG triplet. Remarkably, these values correspond, respectively, to 1/3 (for CAG) and 2/3 (for CTG) of the enthalpy and entropy per base values associated with Watson–Crick base pairs. We show that the presence of the loop structure kinetically inhibits duplex formation from the two complementary 30-mer hairpins, even though the duplex is the thermodynamically more stable state. Duplex formation, however, does occur at elevated temperatures. We propose that this thermally induced formation of a more stable duplex results from thermal disruption of the single-stranded order, thereby allowing the complementary domains to associate (perhaps via “kissing hairpins”). Our melting profiles show that, once duplex formation has occurred, the hairpin intermediate state cannot be reformed, consistent with our interpretation of kinetically trapped hairpin structures. The duplex formed by the two complementary oligonucleotides does not have any unusual optical or thermodynamic properties. By contrast, the very stable structures formed by the individual single-stranded triplet repeat sequences are thermally and thermodynamically unusual. We discuss this stable, triplet repeat, single-stranded structure and its interconversion with duplex in terms of triplet expansion diseases.

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

2002-01-01

27

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

Microsoft Academic Search

We predict properties of triplet excited states in single-walled carbon nanotubes (CNTs) using a time-dependent density-functional theory (TD-DFT). We show that the lowest triplet state energy in CNTs to be about 0.2-0.3 eV lower than the lowest singlet states. Like in $\\\\pi$-conjugated polymers, the lowest CNT triplets are spatially localized. These states show strong optical absorption at about 0.5-0.6 eV

Sergei Tretiak

2007-01-01

28

Atomic Sulfur in Cometary Comae Based on UV Spectra of the S I Triplet near 1814 A  

Microsoft Academic Search

We present a detailed study of the S I triplet emissions near 1814 A in a variety of comets. Even in a moderately dense cometary coma the ground-state component (1807 A) of the triplet turns out to be more or less optically deep. Therefore, any straightforward interpretation of the measured S I flux in terms of a g factor and

Ronald Meier; Michael F. A'Hearn

1997-01-01

29

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

NASA Astrophysics Data System (ADS)

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

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

2013-08-01

30

Triplet excited states of cyclic disulfides and related compounds: electronic structures, geometries, energies, and decay.  

PubMed

We have performed a computational study on the properties of a series of heterocycles bearing two adjacent heteroatoms, focusing on the structures and electronic properties of their first excited triplet states. If the heteroatoms are both heavy chalcogens (S, Se, or Te) or isoelectronic species, then the lowest excited triplet state usually has (?*, ?*) character. The triplet energies are fairly low (30-50 kcal mol(-1)). The (?*, ?*) triplet states are characterized by a significantly lengthened bond between the two heteroatoms. Thus, in 1,2-dithiolane (1b), the S-S bond length is calculated to be 2.088 Å in the singlet ground state and 2.568 Å in the first triplet excited state. The spin density is predicted to be localized almost exclusively on the sulfur atoms. Replacing one heavy chalcogen atom by an oxygen atom or an NR group results in a significant destabilization of the (?*, ?*) triplet excited state, which then no longer is lower in energy than an open-chain biradical. The size of the heterocyclic ring also contributes to the stability of the (?*, ?*) triplet state, with five-membered rings being more favorable than six-membered rings. Benzoannulation, finally, usually lowers the energy of the (?*, ?*) triplet excited states. If one of the heteroatoms is an oxygen or nitrogen atom, however, the corresponding lowest triplet states are better described as ?,?-biradicals. PMID:21268665

Ginagunta, Saroja; Bucher, Götz

2011-02-01

31

Excited triplet states as photooxidants in surface waters  

NASA Astrophysics Data System (ADS)

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

Canonica, S.

2012-12-01

32

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

NASA Astrophysics Data System (ADS)

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

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

2009-10-01

33

Intersystem crossing to excited triplet state of aza analogues of nucleic acid bases in acetonitrile.  

PubMed

Excited state characteristics of aza analogues of nucleic acid bases, 8-azaadenine (8AA), 5-azacytosine (5AC), 8-azaguanine (8AG), and 6-azauracil (6AU), in acetonitrile solution were comprehensively investigated with steady state absorption and emission spectra, transient absorption measurements, emission measurements for the singlet oxygen molecule, and time-dependent density functional theory (TD-DFT) calculations. The triplet-triplet absorption spectrum of 8AA whose peak was 455 nm was observed for the first time. Sensitized singlet oxygen formation of 8AA was also observed in O(2)-saturated acetonitrile with quantum yields of 0.15 +/- 0.02. It was concluded that there were two kinds of aza analogues of nucleic acid bases: type A had substantial quantum yield for the intersystem crossing and potential of O2 (1Delta(g)) formation (8AA and 6AU), and type B did not (5AC and 8AG). TD-DFT calculations indicated that type A molecules had a dark 1npi* state below the first allowed 1pipi* state, while both S1 and S2 states for type B molecules had a pipi* character. It strongly suggested that the dark 1npi* state below the 1pipi* state would play an important role in the ISC process of aza analogues of nucleic acid bases. PMID:19795828

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

2009-11-01

34

Model for triplet state engineering in organic light emitting diodes.  

PubMed

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

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

2014-06-01

35

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

36

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

SciTech Connect

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

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

1991-11-28

37

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

PubMed

We predict properties of triplet excited states in single-walled carbon nanotubes (CNTs) using a time-dependent density-functional theory (TD-DFT). We show that the lowest triplet state energy in CNTs to be about 0.2-0.3 eV lower than the lowest singlet state energies. Like in pi-conjugated polymers, the lowest CNT triplets are spatially localized. These states show strong optical absorption at about 0.5-0.6 eV to the higher lying delocalized triplet states. These results demonstrate striking similarity of the electronic features between CNTs and pi-conjugated polymers and provide explicit guidelines for spectroscopic detection of CNT triplet states. PMID:17497817

Tretiak, Sergei

2007-08-01

38

Suppressing triplet state extension for highly efficient ambipolar phosphine oxide host materials in blue PHOLEDs.  

PubMed

A series of phosphine oxide hosts were constructed to investigate the influence of the triplet state extension in hosts on electrophosphorescence, in which DPESPOPhCz with the carbazolyl-localized triplet state endowed its blue-emitting PHOLEDs with favourable performance, including an external quantum efficiency more than 13%. PMID:24473273

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

2014-03-11

39

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

NASA Astrophysics Data System (ADS)

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

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

1994-08-01

40

Autoionization of H2 Induced by a Doubly Excited Triplet State.  

National Technical Information Service (NTIS)

The photoionization of molecular hydrogen has been extensively studied in recent years. For the singlet states, a variety of schemes for multiphoton excitation from the ground state has been developed. The spectroscopy of the triplet states usually starts...

N. Bjerre S. R. Keiding L. J. Lembo H. Helm

1988-01-01

41

Influence of nature of central metal atom in tetrapyrrole pigments on triplet state deactivation processes  

SciTech Connect

A pulse photolysis method has been used to study the absorption spectra and kinetics of deactivation of triplet molecules of tetra-4-tert-butylphthalocyanine, meso-tetraphenylporphine, and their metal derivatives in degassed liquid toluene solutions. The position of the triplet-triplet absorption maximum is only very slightly dependent on the nature of the central atom. The lifetime tau of the triplet molecules of the phthalocyanines, in contrast to the porphyrins, decreases with increasing atomic number of the central atom. The lifetime tau of triplet molecules of the phthalocyanines, in contrast to the porphines, becomes shorter as the atomic number of the central atom increases. The inner heavy atom influence the magnitude of tau for the diphthalocyanines less than for the monophthalocyanines; this is related to the smaller degree of overlapping of the electron shells of the metal atom and the ligand in the case of the diphthalocyanines.

Kapinus, E.I.; Staryi, V.P.; Dilung, I.I.

1985-07-01

42

A time-resolved EPR study of the triplet states of 4-phenylpyridine and its protonated cation and of biphenyl  

NASA Astrophysics Data System (ADS)

Time-resolved EPR spectra have been observed for the lowest triplet states of biphenyl 4-phenylpyridine (PPY) and 4-phenylpyridinium (PPYH +) in ethanol at 77 K. The sublevel preferentially populated by intersystem crossing is T z (top sublevel) in biphenyl. Following the protonation of PPY, ( Py - Px) / ( Pz - Px) changes from 9 in PPY to 1 in PPYH + ( Pi are relative populating rates; the y and z axes are parallel to the in-plane short and long axes, respectively).

Yagi, Mikio; Itoh, Isami; Komura, Akinori; Hayashi, Kazuyoshi; Higuchi, Jiro

1993-08-01

43

Bright and dark triplet states of the negatively charged magnetoexcitons revealed in photoluminescence and time-resolved measurements  

SciTech Connect

Continuous and time-resolved magnetophotoluminescence measurements of three GaAs/Al{sub x}Ga{sub 1-x}As heterostructures have been made in high magnetic fields. The spectra revealed the presence of a singlet and two triplet states (the so-called ''bright'' and ''dark'' states) of the negatively charged magnetoexciton, in addition to the neutral exciton. For an asymmetrically doped single quantum well sample, the singlet and the dark triplet states converge (and possibly cross) at a field of about 40 T. The two single heterojunction samples on the other hand show no such convergence, and the singlet remains the fundamental state at least in fields to 60 T. The lifetimes of the charged magnetoexcitons increased linearly with field, whereas the neutral exciton was essentially field independent. The results clarify earlier experimental studies, and provide a confirmation of a recent theory of the behavior of charged magnetoexcitons in magnetic fields by Wojs [Phys Rev. B 62, 4630 (2000)].

Munteanu, F. M.; Rickel, D. G.; Perry, C. H.; Kim, Yongmin; Simmons, J. A.; Reno, J. L.

2000-12-15

44

Coherent Storage of Photoexcited Triplet States Using Si29 Nuclear Spins in Silicon  

NASA Astrophysics Data System (ADS)

Pulsed electron paramagnetic resonance spectroscopy of the photoexcited, metastable triplet state of the oxygen-vacancy center in silicon reveals that the lifetime of the ms=±1 sublevels differs significantly from that of the ms=0 state. We exploit this significant difference in decay rates to the ground singlet state to achieve nearly ˜100% electron-spin polarization within the triplet. We further demonstrate the transfer of a coherent state of the triplet electron spin to, and from, a hyperfine-coupled, nearest-neighbor Si29 nuclear spin. We measure the coherence time of the Si29 nuclear spin employed in this operation and find it to be unaffected by the presence of the triplet electron spin and equal to the bulk value measured by nuclear magnetic resonance.

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

2012-03-01

45

Electron-Impact Excitation Cross Section for the Two Lowest Triplet States of Molecular Hydrogen  

Microsoft Academic Search

Calculations for the electron-impact excitation cross sections of molecular hydrogen from its ground (X1Sigmag+) to its first (b3Sigmau+) and second (a3Sigmag+) triplet states were performed using the Ochkur (O) and Ochkur-Rudge (OR) approximations. All nuclear motions were taken into account. It was found that the first triplet cross section is sensitive to the choice of the ground-state wave function whereas

David C. Cartwright; Aron Kuppermann

1967-01-01

46

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

Microsoft Academic Search

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

Joan E. Ridley; Michael C. Zerner

1976-01-01

47

Electron-transfer mechanism of the triplet state quenching of aluminium tetrasulfonated phthalocyanine by cytochrome c  

Microsoft Academic Search

The mechanism of electron-transfer from aluminium tetrasulfonated phthalocyanine triplet state to cytochrome c was investigated in this work. This reaction successfully quenches the dye triplet state due to the formation of complexes between the solute and the protein at the active site. The electron-transfer rate constant is around 3×107 s?1, and is in accordance with previous results for the singlet

César A. T. Lai; L. F. Vieira Ferreira

2006-01-01

48

Photoexcited singlet and triplet states of a UV absorber ethylhexyl methoxycrylene.  

PubMed

The excited states of UV absorber, ethylhexyl methoxycrylene (EHMCR) have been studied through measurements of UV absorption, fluorescence, phosphorescence and electron paramagnetic resonance (EPR) spectra in ethanol. The energy levels of the lowest excited singlet (S1) and triplet (T1) states of EHMCR were determined. The energy levels of the S1 and T1 states of EHMCR are much lower than those of photolabile 4-tert-butyl-4'-methoxydibenzoylmethane. The energy levels of the S1 and T1 states of EHMCR are lower than those of octyl methoxycinnamate. The weak phosphorescence and EPR B(min) signals were observed and the lifetime was estimated to be 93 ms. These facts suggest that the significant proportion of the S1 molecules undergoes intersystem crossing to the T1 state, and the deactivation process from the T1 state is predominantly radiationless. The photostability of EHMCR arises from the (3)??* character in the T1 state. The zero-field splitting (ZFS) parameter in the T1 state is D** = 0.113 cm(-1). PMID:23136952

Kikuchi, Azusa; Hata, Yuki; Kumasaka, Ryo; Nanbu, Yuichi; Yagi, Mikio

2013-01-01

49

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

PubMed

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

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

2004-05-01

50

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

PubMed

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

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

2014-01-28

51

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

PubMed

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

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

2012-10-01

52

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

53

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

PubMed

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

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

2012-07-20

54

Cycloreversion of quadricyclane derivative via triplet state. Adiabatic vs. biradicaloidal mechanism  

SciTech Connect

Photochemically induced interconversion between norbornadiene and quadricyclane has been the focus of considerable attention in connection with the storage of solar energy. A variety of sensitization methods have been applied to the valence isomerization of norbornadiene and its derivatives, including direct photolysis, triplet sensitization, complexation with metal ions, and donor-acceptor interaction. For triplet excitation, it has been reported that norbornadiene in a triplet state isomerizes efficiently to a ground state of quadricyclane through a biradicaloidal intermediate on the basis of photochemical investigation of the corresponding cyclic azoalkanes. In the present paper, on the other hand, the authors have found that a naphthalene derivative of quadricyclane isomerizes inversely to the corresponding norbornadiene derivative via the triplet in a very high yield, and the cycloreversion has been substantiated to be an adiabatic process by convincing experimental supports. Furthermore, it might be pointed out that the conformation of the olefinic moiety of the norbornadiene in the relaxed triplet state, i.e., planar or twisted, is one of the important factors which control the reaction mechanism, i.e., adiabatic or biradicaloidal.

Nishino, H.; Toki, S.; Takamuku, S.

1986-08-06

55

Optically detected magnetic resonance of the triplet state of copper-center-donor pairs in CdS  

NASA Astrophysics Data System (ADS)

Eight distinct types of triplet-state optically detected magnetic resonance (ODMR) spectra have been obtained at 2 K by monitoring the intensity of a broad emission band (peak wavelength 720 nm) observed for undoped, vapor-phase CdS crystals. Several of the ODMR spectra show hyperfine structure due to copper. The signals are attributed to exchange-coupled pairs consisting of a shallowly bound electron and a hole that is localized in the 3d shell of a copper ion. The copper ion is part of an associate center CuX, which can be oriented either parallel to or at 109° to the crystal c axis. The eight different spectra correspond to different geometrical arrangements of this center and of a nearby donor impurity. Recombination of the electron bound to this complex defect with the copper-center hole gives rise to the optical emission. It is shown how the hyperfine and g tensors for the triplet centers can be related to the corresponding quantities for the individual S=12 electron and hole centers from which they are constructed.

Davies, J. J.; Cox, R. T.; Nicholls, J. E.

1984-10-01

56

Porphyrin Triplet State as a Potential Spin Label for Nanometer Distance Measurements by PELDOR Spectroscopy.  

PubMed

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

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

2014-05-01

57

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

58

State equations for nonrational spectra  

NASA Astrophysics Data System (ADS)

This paper develops an infinite dimensional theory for filtering and control in the presence of non-rational spectra. It begins with a review of the original work of A.V. Balakrishnan for the continues time case. This work formulates an auxiliary state space signal model for the case of non-rational spectra. The result is the recovery of Kalman like signal generation models with the resulting separation principle for control. New results, based on unpublished notes of Balakrishnan, on discretization of the model are developed. Although the results can and will be generalized, this paper only covers the 1D theory.

Washburn, Donald C.

1999-08-01

59

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

PubMed

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. PMID:24712791

Huix-Rotllant, Miquel; Ferré, Nicolas

2014-04-01

60

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

NASA Astrophysics Data System (ADS)

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

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

2011-11-01

61

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

62

Peculiarities of the triplet relaxed excited state structure in thallium-doped cesium halide crystals  

Microsoft Academic Search

Four bands, all belonging to the main thallium centre, are detected in the triplet luminescence spectrum of thallium-doped cesium halides under excitation in impurity absorption bands. Their spectral, polarization and kinetics characteristics are studied at 0.35 to 360 K. The parameters of the corresponding relaxed excited states (RES) minima are calculated. Two ultraviolet emission bands are ascribed to electronic transitions

V. Nagirnyi; A. Stolovich; S. Zazubovich; V. Zepelin; M. Nikl; E. Mihokova; G. P. Pazzi

1995-01-01

63

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

National Technical Information Service (NTIS)

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

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

1972-01-01

64

All-optical control of quantum state singlet-triplet character by Autler-Townes splitting.  

NASA Astrophysics Data System (ADS)

Using a four level extended Lambda excitation scheme [1] in ^7Li2, we have demonstrated that Autler --Townes splitting can be used to modify the mixing coefficients and thus the amount of singlet or triplet character of a pair of rovibrational A^1?u^+ and b^3?u states perturbed by the spin-orbit interaction. The singlet triplet pair of levels is naturally separated by an energy gap of 600 MHz. As indicated earlier [2] such control of molecular valence electron spin polarization can be used to create new gateway levels to the dark manifold of triplet states in molecular systems with a singlet ground state in which the spin orbit interaction is very weak and only a few gateway levels to triplet states exist naturally. In addition, a direct measurement of the spin-orbit interaction strength is possible from the observed AT splitting lineshape [2]. *E. Ahmed et al., J. Chem. Phys. 124, 084308 --1 to 13 (2006). *T. Kirova and F. C. Spano, Phys. Rev. A, 71, 063816 (2005).

Salihoglu, Omer; Qi, Peng; Ingram, Sonja; Ahmed, Ergin; Lyyra, Marjatta

2008-05-01

65

The Temperature Dependence of Triplet State Reaction Rate and Quantum Yield for an Intramolecular Enone Photocycloaddition.  

National Technical Information Service (NTIS)

Valence photoisomerization (320-380 nm) of endo-tricyclo-deca-4, 8-diene-3-one has been studied as a function of temperature. At 4 - 51 the isomerization quantum yield is independent of temperature. In the same range the lifetime for the triplet state res...

G. Jones B. R. Ramachandran

1976-01-01

66

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

NASA Astrophysics Data System (ADS)

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

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

2011-12-01

67

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

PubMed Central

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

Angiolillo, P J; Vanderkooi, J M

1998-01-01

68

Monitoring triplet state dynamics with fluorescence correlation spectroscopy: Bias and correction.  

PubMed

A marker's dark triplet state is of great importance in fluorescence microscopy: It serves as a means to switch off fluorescent markers and is thus the enabling element for several super-resolution methods. On the other hand, intersystem-crossing to the electronic dark triplet state strongly reduces the fluorescence yield in conventional fluorescence microscopy. The ability to determine the kinetic parameters of transitions into the triplet state is thus of great importance and because fluorescence correlation spectroscopy (FCS) can be applied without disturbing the system under study, it is one of the preferred methods to do so. However, conventional FCS observations of triplet dynamics suffer from bias due to the spatially inhomogeneous irradiance profile of the excitation laser. Herein, we present a novel method to correct this bias and verify it by analyzing both Monte Carlo simulated and experimental data of the organic dye Rhodamine 110 in aqueous solution for both continuous-wave and pulsed excitation. Importantly, our approach can be readily generalized to most other FCS experiments that determine intensity dependent kinetic parameters. Microsc. Res. Tech. 77:528-536, 2014. © 2014 Wiley Periodicals, Inc. PMID:24729575

Schönle, Andreas; Von Middendorff, Claas; Ringemann, Christian; Hell, Stefan W; Eggeling, Christian

2014-07-01

69

Near-IR absorption of chloranil-alkylbenzene triplet exciplexes: estimation of the transfer integral between the triplet excited state (DA *) and the ion-pair state (D +A -)  

NASA Astrophysics Data System (ADS)

Triplet exciplexes between chloranil and alkylbenzenes (benzene, toluene, m-xylene and mesitylene) have been studied by near-IR transient absorption spectroscopy. In the near-IR wavelength range (600-1600 nm), the charge transfer transition from a triplet excited state to an ion-pair state of these exciplexes can be observed. From the peak positions, the transfer integral V between the triplet excited state and the ion-pair state can be estimated as about V=0.5 eV.

Katoh, Ryuzi; Murata, Shigeo; Tachiya, M.

2002-01-01

70

High-resolution spectroscopy and quantum-defect model for the gerade triplet np and nf Rydberg states of He2  

NASA Astrophysics Data System (ADS)

Photoionization spectra and Rydberg-state-resolved threshold-ionization spectra of the gerade triplet np Rydberg states of 4He2 located in the vicinity of the X^+ ^2? _u^+ (v^+=0) ionization threshold were recorded from the 2s? a ^3? _u^+ metastable state. An accuracy of 0.01 cm-1 was achieved for the experimental term values of the observed Rydberg states. The data were combined with spectroscopic data on low-lying triplet np and nf Rydberg states from the literature to derive energy- and internuclear-distance-dependent eigenquantum-defect parameters of multichannel quantum-defect theory (MQDT). The MQDT calculations reproduce the experimental data within their experimental uncertainties and enabled the derivation of potential-energy curves for the lowest triplet p Rydberg states (n = 2-5) of He2. The eigenquantum-defect parameters describing the p -f interaction were found to be larger than 0.002 at the energies corresponding to the high-n Rydberg states, so that the p -f interaction plays an important role in the autoionization dynamics of np Rydberg states with v+ = 0. By extrapolating the experimental term values of triplet np Rydberg states of 4He2 in the range of principal quantum number n between 87 and 110, the positions of the (v+ = 0, N+ = 3) and (v+ = 0, N+ = 5) levels of the ground state of 4He_2^+ were determined to lie 70.937(3) cm-1 and 198.369(6) cm-1, respectively, above the (v+ = 0, N+ = 1) ground rotational level.

Sprecher, D.; Liu, J.; Krähenmann, T.; Schäfer, M.; Merkt, F.

2014-02-01

71

High-resolution spectroscopy and quantum-defect model for the gerade triplet np and nf Rydberg states of He2.  

PubMed

Photoionization spectra and Rydberg-state-resolved threshold-ionization spectra of the gerade triplet np Rydberg states of (4)He2 located in the vicinity of the X(+) (2)?(u)(+) (?(+) = 0) ionization threshold were recorded from the 2s? a (3)?(u)(+) metastable state. An accuracy of 0.01?cm(-1) was achieved for the experimental term values of the observed Rydberg states. The data were combined with spectroscopic data on low-lying triplet np and nf Rydberg states from the literature to derive energy- and internuclear-distance-dependent eigenquantum-defect parameters of multichannel quantum-defect theory (MQDT). The MQDT calculations reproduce the experimental data within their experimental uncertainties and enabled the derivation of potential-energy curves for the lowest triplet p Rydberg states (n = 2-5) of He2. The eigenquantum-defect parameters describing the p?-f interaction were found to be larger than 0.002 at the energies corresponding to the high-n Rydberg states, so that the p?-f interaction plays an important role in the autoionization dynamics of np Rydberg states with v(+) = 0. By extrapolating the experimental term values of triplet np Rydberg states of (4)He2 in the range of principal quantum number n between 87 and 110, the positions of the (v(+) = 0, N(+) = 3) and (v(+) = 0, N(+) = 5) levels of the ground state of (4)He(+)(2) were determined to lie 70.937(3)?cm(-1) and 198.369(6)?cm(-1), respectively, above the (v(+) = 0, N(+) = 1) ground rotational level. PMID:24527912

Sprecher, D; Liu, J; Krähenmann, T; Schäfer, M; Merkt, F

2014-02-14

72

Off-Centre Effects in the Triplet Relaxed Excited State of Ga+ Centres in CsBr:Ga Crystal  

Microsoft Academic Search

Spectra, polarization and decay kinetics of the triplet and singlet emission of Ga+ centres in CsBr:Ga crystals have been studied in the temperature range of 0.1 to 400 K. It has been found that the triplet AX and AT emission bands coincide. Two slow components have been observed in the decay kinetics of each emission at T < 1.5 K

K. Kalder; V. Korrovits; V. Nagirnyi; A. Stolovits; S. Zazubovich; V. Babin

1997-01-01

73

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

PubMed

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

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

2012-08-01

74

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

75

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

76

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

SciTech Connect

Supramolecular systems synthesized to model the photosynthetic reaction center (RC) are designed to mimic several key properties of the RC protein. Thus far, most RC models fulfill only a subset of these criteria, with very few reports employing time-resolved electron paramagnetic resonance spectroscopy (TREPR). We now report TREPR results on a photosynthetic model system (1) in a nematic liquid crystal (LC) that does not contain the natural pigments, yet closely mimics the spin dynamics of triplet state formation found only in photosynthetic RCs. The design of supermolecule 1 follows criteria established for promoting high quantum yield charge separation in glassy media. The observation of this triplet state in 1 by TREPR demonstrates that most of the electronic states found in the primary photochemistry of photosynthetic RCs can be mimicked successfully in synthetic models interacting with LCs. 12 refs., 3 figs.

Hasharoni, K.; Levanon, H. [Hebrew Univ., Jerusalem (Israel); Greenfield, S.R.; Gosztola, D.J.; Svec, W.A. [Argonne National Lab., IL (United States); Wasiclewski, M.R. [Argonne National Lab., IL (United States)]|[Northwestern Univ., Evanston, IL (United States)

1995-08-02

77

Does bimolecular charge recombination in highly exergonic electron transfer afford the triplet excited state or the ground state of a photosensitizer?  

PubMed

The investigations were made on photoinduced electron transfer (ET) from the singlet excited state of rubrene (1RU*) to p-benzoquinone derivatives (duroquinone, 2,5-dimethyl-p-benzoquinone, p-benzoquinone, 2,5-dichloro-p-benzoquinone, and p-chloranil) in benzonitrile (PhCN) by using the steady state and time-resolved spectroscopies. The photoinduced ET produces solvent-separated type charge-separated (CS) species and the charge-recombination (CR) process between RU radical cation and semiquinone radical anions obeys second-order kinetics. Not only the CS species but also the triplet excited state of RU (3RU*) is seen in the transient absorption spectra upon laser excitation of a PhCN solution of RU and p-benzoquinone derivatives. The comparison of their time profiles clearly suggests that the CR process between RU radical cation and semiquinone radical anions to the ground state is independent from the deactivation of 3RU*. This indicates that the CR in a highly exergonic ET occurs at a longer distance with a large solvent reorganization energy, which results in faster ET to the ground state than to the triplet excited state that is lower in energy than the CS state. Photoinduced ET from 3RU* in addition from 1RU* also occurs when p-benzoquinone derivatives with electron-withdrawing substituents were employed as electron acceptors. PMID:18173251

Murakami, Motonobu; Ohkubo, Kei; Mandal, Paulami; Ganguly, Tapan; Fukuzumi, Shunichi

2008-01-31

78

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

SciTech Connect

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

Clarke, R.H.

1980-12-22

79

Quantum oscillations and polarization of nuclear spins in photoexcited triplet states.  

PubMed

The unique physical properties of photoexcited triplet states have been explored in numerous spectroscopic studies employing electron paramagnetic resonance (EPR). So far, however, no quantum interference effects were found in these systems in the presence of a magnetic field. In this study, we report the successful EPR detection of nuclear quantum oscillations in an organic triplet state subject to an external magnetic field. The observed quantum coherences can be rationalized using an analytical theory. Analysis suggests that the nuclear spins are actively involved in the intersystem crossing process. The novel mechanism also acts as a source of oscillatory nuclear spin polarization that gives rise to large signal enhancement in nuclear magnetic resonance (NMR). This opens new perspectives for the analysis of chemically induced dynamic nuclear polarization in mechanistic studies of photoactive proteins. PMID:20666450

Kothe, Gerd; Yago, Tomoaki; Weidner, Jörg-Ulrich; Link, Gerhard; Lukaschek, Michail; Lin, Tien-Sung

2010-11-18

80

Triplet States of HOCl and HClO.  

National Technical Information Service (NTIS)

In view of the current interest in the relative importance of HOC and/or its isomer HClO in the problem of the ozone depletion in the stratosphere, we report the results of some recent calculations on the 3A' states of HOCl and HClO. To our knowledge, the...

A. G. Turner

1986-01-01

81

Electron-Impact Excitation Cross Sections of the Lowest-Lying Triplet States of Benzene  

Microsoft Academic Search

Calculations of electron-impact excitation cross sections of the lowest-lying triplet states 3B1u, 3E1u, 3B2u of benzene are carried out, using the Ochkur and Ochkur–Rudge approximations. Electronic wavefunctions are constructed from the LCAO molecular orbitals for ? electrons in benzene, and nuclear motions are disregarded. It is found that the differential cross section has a peak at a large scattering angle

Michio Matsuzawa

1969-01-01

82

High resolution probe of spin-orbit coupling and the singlet-triplet gap in chlorocarbene  

NASA Astrophysics Data System (ADS)

Among the most important of chemical intermediates are the carbenes, characterized by a divalent carbon that generates low-lying biradical (triplet) and spin-paired (singlet) configurations with unique chemical reactivities. The ``holy grail'' of carbene chemistry has been determining the singlet-triplet gap and intersystem crossing rates. We report here the first high resolution spectra of singlet-triplet transitions in a prototypical singlet carbene, CHCl, which probe in detail the triplet state structure and spin-orbit coupling with the ground singlet state. Our spectra reveal a pronounced vibrational state dependence of the triplet state spin-spin splitting parameter, which we show is a sensitive probe of spin-orbit coupling with nearby singlet states. The parameters derived from our spectra, including a precise determination of the singlet-triplet energy gap, are in excellent agreement with recent ab initio calculations.

Tao, Chong; Mukarakate, Calvin; Judge, Richard H.; Reid, Scott A.

2008-05-01

83

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

84

Optical Absorption Line Shapes Due to Transition from Orbital Singlet to Triplet States of Defect Centers with Cubic Symmetry  

Microsoft Academic Search

Structures in the optical absorption line shapes have been investigated for the transitions from orbital singlet to triplet states of defect centers with cubic environment. In the triplet excited states both the spin-orbit and the linear electron-lattice interactions have been taken into account. Under the classical Franck-Condon approximation, line shapes are specified by the combination of the four coupling constants

Kikuo Cho

1968-01-01

85

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

PubMed

Long-range corrected hybrids represent an increasingly popular class of functionals for density functional theory (DFT) that have proven to be very successful for a wide range of chemical applications. In this Communication, we examine the performance of these functionals for time-dependent (TD)DFT descriptions of triplet excited states. Our results reveal that the triplet energies are particularly sensitive to the range-separation parameter; this sensitivity can be traced back to triplet instabilities in the ground state coming from the large effective amounts of Hartree-Fock exchange included in these functionals. As such, the use of standard long-range corrected functionals for the description of triplet states at the TDDFT level is not recommended. PMID:22029290

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

2011-10-21

86

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

87

Long-lived room-temperature deep-red-emissive intraligand triplet excited state of naphthalimide in cyclometalated Ir(III) complexes and its application in triplet-triplet annihilation-based upconversion.  

PubMed

Cyclometalated Ir(III) complexes with acetylide ppy and bpy ligands were prepared (ppy = 2-phenylpyridine, bpy = 2,2'-bipyridine) in which naphthal (Ir-2) and naphthalimide (NI) were attached onto the ppy (Ir-3) and bpy ligands (Ir-4) through acetylide bonds. [Ir(ppy)(3)] (Ir-1) was also prepared as a model complex. Room-temperature phosphorescence was observed for the complexes; both neutral and cationic complexes Ir-3 and Ir-4 showed strong absorption in the visible range (?=39,600? M(-1) ?cm(-1) at 402?nm and ?=25,100? M(-1) ?cm(-1) at 404?nm, respectively), long-lived triplet excited states (?(T)=9.30??s and 16.45??s) and room-temperature red emission (?(em)=640?nm, ?(p)=1.4?% and ?(em)=627?nm, ?(p)=0.3?%; cf. Ir-1: ?=16,600? M(-1) ?cm(-1) at 382?nm, ?(em)=1.16 ?s, ?(p)=72.6?%). Ir-3 was strongly phosphorescent in non-polar solvent (i.e., toluene), but the emission was completely quenched in polar solvents (MeCN). Ir-4 gave an opposite response to the solvent polarity, that is, stronger phosphorescence in polar solvents than in non-polar solvents. Emission of Ir-1 and Ir-2 was not solvent-polarity-dependent. The T(1) excited states of Ir-2, Ir-3, and Ir-4 were identified as mainly intraligand triplet excited states ((3)IL) by their small thermally induced Stokes shifts (?E(s)), nanosecond time-resolved transient difference absorption spectroscopy, and spin-density analysis. The complexes were used as triplet photosensitizers for triplet-triplet annihilation (TTA) upconversion and quantum yields of 7.1?% and 14.4?% were observed for Ir-2 and Ir-3, respectively, whereas the upconversion was negligible for Ir-1 and Ir-4. These results will be useful for designing visible-light-harvesting transition-metal complexes and for their applications as triplet photosensitizers for photocatalysis, photovoltaics, TTA upconversion, etc. PMID:22615134

Sun, Jifu; Wu, Wanhua; Zhao, Jianzhang

2012-06-25

88

Density of states spectra in ferromagnet/superconductor/ferromagnet heterostructures  

NASA Astrophysics Data System (ADS)

We investigate density of states (DOS) spectra of a ferromagnet/superconductor/ferromagnet structure by including the interface spin-flip scattering potential into the existing mean-field Hamiltonian. We show that the spin-flip scattering can lead to electron spin mixing in the vicinity of an FS interface, enabling s-wave singlet and odd-frequency triplet pairs conversion and the existence of Andreev bound states with subgap energy (±?b) via the intra- and interband Andreev reflections. This adds spin-resolved subgap peaks to the DOS spectrum. The relevant elastic co-tunneling at ±?b enhances the local conductance, while its competition with the crossed Andreev reflection will lead to a sign change in the nonlocal differential conductance with the bias energy.

Meng, Hao; Wen, Lin; Zha, Guo-Qiao; Zhou, Shi-Ping

2011-06-01

89

Triplet formation involving a polar transition state in a well-defined intramolecular perylenediimide dimeric aggregate.  

PubMed

A cofacially stacked perylenediimide (PDI) dimer with a xanthene linker was studied under a variety of conditions (solvent, temperature) and serves as a model for the molecular interactions occurring in solid films. Intrinsically, the PDI units have a fluorescence quantum yield (Phi F) close to unity, but Phi F is lowered by a factor of 6-50 at room temperature when two PDI moieties are held in a cofacial arrangement, while the decay time of the most emissive state is increased significantly (tau F = 27 ns in toluene) compared to a monomeric PDI molecule (tau F = 4 ns). Fluorescence measurements show a strong solvent and temperature dependence of the characteristics of the emissive excited state. In a glassy matrix of toluene (TOL) or 2-methyltetrahydrofuran (2-MeTHF), Phi F is high, and the decay time is long (tau F = approximately 50 ns). At higher temperature, both Phi F and tau F are reduced. Interestingly, at room temperature, Phi F and tau F are also reduced with increasing solvent polarity, revealing the presence of a polar transition state. Photoinduced absorption of the stacked molecules from the picosecond to the microsecond time scale shows that after photoexcitation reorganization occurs in the first nanoseconds, followed by intersystem crossing (ISC), producing the triplet excited state. Using singlet oxygen ( (1)Delta g) luminescence as a probe, a triplet quantum yield (Phi T) greater than 50% was obtained in air-saturated 2-Me-THF. Triplet formation is exceptional for PDI chromophores, and the enhanced ISC is explained by a decay involving a highly polar transition state. PMID:18543890

Veldman, Dirk; Chopin, Stéphanie M A; Meskers, Stefan C J; Groeneveld, Michiel M; Williams, René M; Janssen, René A J

2008-07-01

90

Triplet states in isotopically mixed anthracene crystals: High resolution optical spectroscopy  

NASA Astrophysics Data System (ADS)

The triplet O,O transitions of guest and host in isotopically mixed anthracene crystals of various compositions (A- h10, 13C-monosubstituted A- h10, A- d1h9, A- d2hg in A- d10 and A- d10 in A- h10) have been investigated using high resolution laser excitation spectroscopy. The guest aggregate spectra have been studied in polarized light as a function of guest concentration up to 15%. The analyses allow us to identify the monomer, dimer and trimer lines. From the dimer splittings the dominant resonance pair interactions are dedu The comparison of different mixed crystal systems with guest levels below and above the host exciton band reveals that quasiresonance and superexchange corrections are of minor importance. The experimental resonance pair interactions are used to calculate the triplet exciton band structure of anthracen and the observed guest polarization behaviour is interpreted quantitatively by the Rashba effect. Finally, the lower Davydov component of the host is s and broadened with increasing guest concentration. The shift is discussed using a theoretical model of Lifshitz.

Port, H.; Rund, D.; Wolf, H. C.

1981-08-01

91

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

PubMed Central

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

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

1993-01-01

92

An ab initio investigation of the ground and low-lying singlet and triplet electronic states of XNO2 and XONO (X = Cl, Br, and I)  

NASA Astrophysics Data System (ADS)

A systematic ab initio treatment of the nitryl halides (XNO2) 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 (ClNO2 and BrNO2), 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 ClNO2 the transitions to excited singlet states all occur at wavelengths shorter than 310 nm, there is one longer wavelength singlet transition in BrNO2 and two in the case of INO2. The long wavelength tail in the XNO2 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 INO2. 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.; Francisco, Joseph S.

2014-01-01

93

Products of the triplet excited state produced in the radiolysis of liquid benzene.  

PubMed

The radiation chemical yields of the products derived from the triplet excited state produced in the radiolysis of liquid benzene with gamma-rays, 10 MeV 4He ions, and 10 MeV 12C ions have been determined. Iodine scavenging techniques have been used to examine the formation and role of radicals, especially the H atom and phenyl radical. For all irradiation types examined here, the increase in hydrogen iodide yields with increasing iodine concentration matches the increase in iodobenzene yields. This agreement suggests that the benzene triplet excited state is the common precursor for the H atom and the phenyl radical. Pulse radiolysis studies in liquid benzene have determined the rate coefficients for the reactions of phenyl radicals with iodine and with the solvent benzene to be 9.3 x 10(9) M(-1) s(-1) and 3.1 x 10(5) M(-1) s(-1), respectively. Direct measurements of polymer formation, which refers to trimers (C18) and higher order compounds (>C18), in liquid benzene radiolysis using gamma-rays, 4He ions, and 12C ions at relatively high doses have been performed using gel permeation chromatography. The yields of trimers increase from gamma-rays to 12C ions due to the increased importance of intratrack radical-radical reactions that can be scavenged by the radical scavenging reactions of iodine. On the other hand, the >C18 product yields decrease from gamma-rays to 12C ions. The structure of the polymer consists of a partly saturated ring as determined by infrared and gas chromatography/mass spectrometry studies. A schematic representation for the radiolytic decomposition of the benzene triplet excited state is presented. PMID:16539438

Enomoto, Kazuyuki; Laverne, Jay A; Pimblott, Simon M

2006-03-23

94

Selective triplet-state formation during charge recombination in a fullerene/Bodipy molecular dyad (Bodipy=borondipyrromethene).  

PubMed

A conformationally restricted molecular dyad has been synthesized and subjected to detailed photophysical examination. The dyad comprises a borondipyrromethene (Bodipy) dye covalently linked to a buckminsterfullerene C60 residue, and is equipped with hexadecyne units at the boron centre in order to assist solubility. The linkage consists of a diphenyltolane, attached at the meso position of the Bodipy core and through an N-methylpyrrolidine ring at the C60 surface. Triplet states localised on the two terminals are essentially isoenergetic. Cyclic voltammetry indicates that light-induced electron transfer from Bodipy to C60 is thermodynamically favourable and could compete with intramolecular energy transfer in the same direction. The driving force for light-induced electron abstraction from Bodipy by the singlet excited state of C60 depends critically on the solvent polarity. Thus, in non-polar solvents, light-induced electron transfer is thermodynamically uphill, but fast excitation energy transfer occurs from Bodipy to C60 and is followed by intersystem crossing and subsequent equilibration of the two triplet excited states. Moving to a polar solvent switches on light-induced electron transfer. Now, in benzonitrile, the charge-transfer state (CTS) is positioned slightly below the triplet levels, such that charge recombination restores the ground state. However, in CH2Cl2 or methyltetrahydrofuran, the CTS is slightly higher in energy than the triplet levels, and decays, in part, to form the triplet state localized on the C60 residue. This step is highly specific and does not result in direct formation of the triplet excited state localized on the Bodipy unit. Subsequent equilibration of the two triplets takes place on a relatively slow timescale. PMID:19551782

Ziessel, Raymond; Allen, Ben D; Rewinska, Dorota B; Harriman, Anthony

2009-07-27

95

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

NASA Astrophysics Data System (ADS)

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

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

2012-06-01

96

A time-resolved electron spin resonance study of the triplet states of 2,2?-bipyridine and its singly protonated cation  

NASA Astrophysics Data System (ADS)

Time-resolved ESR spectra have been observed for the lowest triplet states of 2,2'-bipyridine (bpy) and singly protonated bpy (bpyH +) in ethanol at 77 K. With the aid of computer simulation, it is concluded that the T z sublevel is most active in S 1?T 1 intersystem crossing in both molecules studied and ( Pz- Px)/( Py- Px) changes from 9 in s-trans-bpy to 1.5 in bpyH + ( Pi are relative populating rates; y and z, close to in-plane long and short axes, respectively).

Yagi, Mikio; Deguchi, Yasuaki; Shioya, Yasushi; Higuchi, Jiro

1988-03-01

97

The role of environment in the nonradiative relaxation of the triplet state of naphthalene derivatives in solid solutions at 77 K  

Microsoft Academic Search

The nonradiative relaxation of the triplet states of oxy-and amino-derivatives of naphthalene and conjugated ions is studied\\u000a by luminescent and kinetic methods (measurements of the phosphorescence decay and of phosphorescence excitation and phosphorescence\\u000a spectra) in solid solutions of ethanol-h\\u000a 6, ethanol-d\\u000a 6, and mixtures of toluene-h\\u000a 8 with piperidine-h\\u000a 11 at 77 K. It is found that, along with intramolecular

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

2001-01-01

98

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

SciTech Connect

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

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

2002-01-01

99

Characterization of the Triplet State of Tanshinone IIA and its Reactivity by Laser Flash Photolysis.  

PubMed

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

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

2014-05-01

100

High-Field Transient Electron Paramagnetic Resonance of Excited Triplet States  

NASA Astrophysics Data System (ADS)

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

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

2005-03-01

101

Secondary organic aerosol production from aqueous reactions of atmospheric phenols with an organic triplet excited state.  

PubMed

Condensed-phase chemistry plays a significant role in the formation and evolution of atmospheric organic aerosols. Past studies of the aqueous photoformation of secondary organic aerosol (SOA) have largely focused on hydroxyl radical oxidation, but here we show that triplet excited states of organic compounds ((3)C*) can also be important aqueous oxidants. We studied the aqueous photoreactions of three phenols (phenol, guaiacol, and syringol) with the aromatic carbonyl 3,4-dimethoxybenzaldehyde (DMB); all of these species are emitted by biomass burning. Under simulated sunlight, DMB forms a triplet excited state that rapidly oxidizes phenols to form low-volatility SOA. Rate constants for these reactions are fast and increase with decreasing pH and increasing methoxy substitution of the phenols. Mass yields of aqueous SOA are near 100% for all three phenols. For typical ambient conditions in areas with biomass combustion, the aqueous oxidation of phenols by (3)C* is faster than by hydroxyl radical, although rates depend strongly on pH, oxidant concentrations, and the identity of the phenol. Our results suggest that (3)C* can be the dominant aqueous oxidant of phenols in areas impacted by biomass combustion and that this is a significant pathway for forming SOA. PMID:24364694

Smith, Jeremy D; Sio, Vicky; Yu, Lu; Zhang, Qi; Anastasio, Cort

2014-01-21

102

Triplet-state-mediated super-resolution imaging of fluorophore-labeled gold nanorods.  

PubMed

Triplet-state-mediated super-resolution imaging was used to map the positions of fluorescently labeled double-stranded DNA bound to the surface of gold nanorods. In order to isolate individual fluorophores bound to the nanorod surface, imaging conditions were optimized such that the majority of the fluorophores were forced into a triplet dark state, and fluorescence from approximately one molecule at a time was detected. The fluorescence from the emitting single molecule was then fit to a two-dimensional (2D) Gaussian to localize its position relative to the nanorod substrate. The reconstructed super-resolution images showed excellent agreement with the shape and orientation of the nanorods, although, based on correlated atomic force microscopy, they consistently under-estimated nanorod size. The apparent DNA ligand binding on the gold nanorod surface showed significant heterogeneity, with examples of preferential binding to nanorod ends, uniform binding across the nanorod surface, and site-specific binding to a single end of the nanorod. This heterogeneity would be hidden in a typical ensemble or diffraction-limited measurement, highlighting the need for single nanoparticle super-resolution imaging studies. PMID:24254973

Blythe, Karole L; Titus, Eric J; Willets, Katherine A

2014-03-17

103

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

SciTech Connect

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

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

2008-02-28

104

The discrimination between triplet state and radical cation in the pulse radiolysis of bithiophene in CCl 4  

NASA Astrophysics Data System (ADS)

The triplet state ( 32T) and the radical cation (2T +rad ) of 2,2'-bithiophene (2T) are characterized by pulse radiolysis in CCl 4. Two main absorption bands at 360 and 420 nm are respectively attributed to 32T* and to 2T +rad . The triplet, induced in an excited state through a Förster mechanism, undergoes a conformational rearrangement ( k6=(6.8±0.9)×10 6 s -1). The radical cation is produced both through a resonance charge transfer and a second diffusional process; the two oxidizing species are respectively CCl 4+rad and (CCl +3?Cl -) solv through the mediation of a singlet excited state, 12T*.

Emmi, Salvatore S.; D'Angelantonio, Mila; Beggiato, Giancarlo; Camaioni, Nadia

1999-08-01

105

Theoretical study of the reaction of carbon monoxide with oxygen molecules in the ground triplet and singlet delta states.  

PubMed

Quantum chemical calculations were carried out to study the reaction of carbon monoxide with molecular oxygen in the ground triplet and singlet delta states. Transition states and intermediates that connect the reactants with products of the reaction on the triplet and singlet potential energy surfaces were identified on the base of coupled-cluster method. The values of energy barriers were refined by using compound techniques such as CBS-Q, CBS-QB3, and G3. The calculations showed that there exists an intersection of triplet and singlet potential energy surfaces. This fact leads to the appearance of two channels for the triplet CO+O(2)(X(3)?(g)(-)) reaction, which produces atomic oxygen in the ground O((3)P) and excited O((1)D) states. The appropriate rate constants of all reaction paths were estimated on the base of nonvariational transition-state theory. It was found that the singlet reaction rate constant is much greater than the triplet one and that the reaction channel CO+O(2)(a(1)?(g)) should be taken into consideration to interpret the experimental data on the oxidation of CO by molecular oxygen. PMID:21338155

Sharipov, Alexander; Starik, Alexander

2011-03-17

106

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

NASA Astrophysics Data System (ADS)

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

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

2014-03-01

107

Triplet to Triplet Absorption in Organic Molecules for Use in Photochromic Devices.  

National Technical Information Service (NTIS)

The photochromic properties of several substituted aromatics and heterocyclics have been investigated. The absorption spectra, phosphorescence lifetime T-T absorption spectra and the product of triplet extinction coefficient and triplet formation efficien...

J. L. Kropp M. W. Windsor

1968-01-01

108

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

109

Investigation of the triplet state of chlorophylls: Final report, May 1, 1975 through April 30, 1987  

SciTech Connect

Our research program over the past twelve year period has utilized the triplet state of chlorophyll as a (nondestructive) probe into the structural and dynamical nature of the photosynthetic unit. Using primarily zero-field optically detected magnetic resonance spectroscopy, supplemented by resonance raman spectroscopy, we have examined the chlorophyll molecule for a range of environments in both in vivo systems and in model chlorophyll units in vitro. Our research effort has focused on chlorophyll in the presence of simple organic ligands, in lipid bilayer vesicles, in synthetically reconstituted protein, and on the surface of metal and non-metal substrates. Aim of the research was to detail the physical features and interactions of the photosynthetic pigment systems through examination of pigment subunits of the photosynthetic apparatus and model systems which represent them.

Clarke, R.H.

1987-06-01

110

Photochemical production of organic matter triplet states in water samples from mountain lakes, located below or above the tree line.  

PubMed

The production of triplet states (T(*)) of chromophoric dissolved organic matter (CDOM), reacting with the probe molecule 2,4,6-trimethylphenol (TMP) was measured upon irradiation of water samples, taken from lakes located in a mountain area (NW Italy) between 1450 and 2750 m above sea level. The lakes are located below or above the tree line and surrounded by different vegetation types (trees, alpine meadows or exposed rocks). The most photoactive samples belonged to lakes below the tree line and their fluorescence spectra and CDOM optical features suggested the presence of a relatively elevated amount of humic (allochthonous) material. The lowest (negligible) photoactivity was found for a lake surrounded by exposed rocks. Its CDOM showed an important autochthonous contribution (due to in-lake productivity) and considerably higher spectral slope compared to the other samples, suggesting low CDOM molecular weight and/or aromaticity. Among the samples, CDOM photoactivity (measured as the rate of TMP-reactive T(*) photoproduction) decreased with changing vegetation type in the order: trees, meadows, rocks. It could be connected with decreasing contribution from catchment runoff and increasing contribution from autochthonous processes and possibly precipitation. PMID:22575209

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

2012-08-01

111

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

NASA Astrophysics Data System (ADS)

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

Snyder, James W.; Mazziotti, David A.

2010-04-01

112

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

PubMed

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

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

2010-04-21

113

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

PubMed

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

Friaa, O; Maillard, P; Brault, D

2012-04-01

114

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

PubMed

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

Wang, Xuefeng; Andrews, Lester

2009-11-14

115

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

NASA Astrophysics Data System (ADS)

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

Fursa, Dmitry V.; Bray, Igor

1999-02-01

116

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

117

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

118

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

NASA Astrophysics Data System (ADS)

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

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

2012-12-01

119

Photoreduction of Pt(IV) Chloro Complexes: Substrate Chlorination by a Triplet Excited State.  

PubMed

The Pt(IV) complexes trans-Pt(PEt3)2(Cl)3(R) 2 (R = Cl, Ph, 9-phenanthryl, 2-trifluoromethylphenyl, 4-trifluoromethylphenyl, 3-perylenyl) were prepared by chlorination of the Pt(II) complexes trans-Pt(PEt3)2(R)(Cl) 1 with Cl2(g) or PhICl2. Mixed bromo-chloro complexes trans,trans-Pt(PEt3)2(Cl)2(Br)(R) (R = 9-phenanthryl, 4-trifluoromethylphenyl), trans,cis-Pt(PEt3)2(Cl)2(Br)(4-trifluoromethylphenyl), trans,trans-Pt(PEt3)2(Br)2(Cl)(R) (R = 9-phenanthryl), and trans,cis-Pt(PEt3)2(Br)2(Cl)(4-trifluoromethylphenyl) were obtained by halide exchange or by oxidative addition of Br2 to 1 or Cl2 to trans-Pt(PEt3)2(R)(Br). Except for 2 (R = Ph, 4-trifluoromethylphenyl), all of the Pt(IV) complexes are photosensitive to UV light and undergo net halogen reductive elimination to give Pt(II) products, trans-Pt(PEt3)2(R)(X) (X = Cl, Br). Chlorine trapping experiments with alkenes indicate a reductive-elimination mechanism that does not involve molecular chlorine and is sensitive to steric effects at the Pt center. DFT calculations suggest a radical pathway involving (3)LMCT excited states. Emission from a triplet is observed in glassy 2-methyltetrahydrofuran at 77 K where photoreductive elimination is markedly slowed. PMID:24971643

Perera, Tharushi A; Masjedi, Mehdi; Sharp, Paul R

2014-07-21

120

Triplet photosensitizers: from molecular design to applications.  

PubMed

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

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

2013-06-21

121

Visible light-harvesting cyclometalated Ir(III) complexes as triplet photosensitizers for triplet-triplet annihilation based upconversion.  

PubMed

Visible light-harvesting cyclometalated Ir(III) complexes with 3-(2-benzothiazoly)-7-diethylaminocoumarin as the C^N cyclometalation ligands were prepared. The ancillary N^N ligand is either 6-piperidine naphthalimide-phenanthroline (Ir-1) or 9-aminophenanthroline (Ir-3). Ir(ppy)(2)(Phen) was prepared as model complex (Ir-2). Ir-1 and Ir-3 show strong absorption of visible light (? = 109,000 M(-1) cm(-1) or 112,000 M(-1) cm(-1) at 486 or 484 nm, respectively). All the complexes show room temperature phosphorescence with drastically different phosphorescence quantum yields (?(P) = 4.3%, 44.3% and 46.0% for Ir-1, Ir-2 and Ir-3, respectively). With steady state and time-resolved spectra, as well as DFT calculations, the T(1) excited states of Ir-1 and Ir-3 were proposed to be the (3)IL state, whereas the (3)MLCT state was proposed for Ir-2. Long-lived emissive triplet excited states (7.6 ?s and 54.5 ?s) were observed for Ir-1 and Ir-3, compared to the short T(1) excited state lifetime of Ir-2 (1.2 ?s). The complexes were used as triplet photosensitizers for triplet-triplet annihilation upconversion and upconversion quantum yields (?(UC)) of 19.3% and 12.7% were observed for Ir-1 and Ir-3, respectively. No upconversion was observed for Ir-2 under the same experimental conditions. PMID:22842479

Ma, Lihua; Guo, Huimin; Li, Qiuting; Guo, Song; Zhao, Jianzhang

2012-09-21

122

New absorption band in the near IR assigned to a bound triplet state of the f? in NaI  

Microsoft Academic Search

Summary  TheF ? F? optical conversion in NaI is reduced by an external magnetic field, but not completely suppressed. In order to explain such\\u000a unexpected result both a spin mixing in the optical cycle of theF-centre and the existence of a bound triplet state of the F?-centre have been considered. Absorption measurements have disclosed\\u000a a new band at 1.4 eV whose

G. Baldacchini; G. P. Gallerano; U. M. Grassano; F. Lüty

1983-01-01

123

Angular Dependence of Low-Energy Electron-Impact Excitation Cross Section of the Lowest Triplet States of H2  

Microsoft Academic Search

The differential cross sections for the electron-impact excitation of the lowest triplet states of molecular hydrogen (b 3?u+, a 3?g+) have been calculated from threshold to 85 eV impact energy using the Ochkur–Rudge theory. For the X 1?g+ ? b 3?u+ transition, the relative differential cross sections were measured with a low-energy, high-resolution electron-impact spectrometer from 10° to 80° scattering

S. Trajmar; D. C. Cartwright; J. K. Rice; R. T. Brinkmann; A. Kuppermann

1968-01-01

124

Solvent effects on rates of photochemical reactions of rose bengal triplet state studied by nanosecond laser photolysis  

Microsoft Academic Search

Bimolecular rate constants of energy transfer, electron-transfer, and H-atom abstraction reaction have been determined by following the transient absorption bands of the triplet states of rose bengal [3(RB2?)?] at about 1020nm with various substrates using nanosecond laser flash photolysis. For electron acceptor (1,4-benzoquinone), electron-transfer takes place via an exciplex. Exciplex formation was found to be predominant in high viscosity solvents

Shafiqul D.-M. Islam; Osamu Ito

1999-01-01

125

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

NASA Astrophysics Data System (ADS)

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

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

2013-02-01

126

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

SciTech Connect

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

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

1987-09-10

127

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

NASA Astrophysics Data System (ADS)

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

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

2012-11-01

128

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

NASA Astrophysics Data System (ADS)

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

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

2014-03-01

129

A discrete/continuum QM/MM MD study of the triplet state of acetone in aqueous solution  

NASA Astrophysics Data System (ADS)

The structural and electronic properties of the relatively long-lived (20 ?s) triplet state of acetone in aqueous solution have been studied using an effective QM/MM molecular dynamics approach (GLOB model) based on non-periodic boundary conditions and localized basis functions. In particular, the striking consequences of the n ? ? ? electron promotion on the acetone structure and on its microsolvation have been analyzed in some detail and compared to the behaviour of the acetone ground-state. Moreover, the phosphorescence emission spectrum calculated on sampled molecular configurations, shows a Stokes shift in good agreement with available experimental data.

Brancato, Giuseppe; Rega, Nadia; Barone, Vincenzo

2008-03-01

130

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.

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

2012-01-01

131

Spectrum of the autoionizing triplet gerade Rydberg states of H2 and its analysis using multichannel quantum-defect theory.  

PubMed

A new spectrum of the autoionizing triplet states of gerade symmetry of H2 has been recorded from the ?? = 1–4, N? = 1–3 rovibrational levels of the metastable c 3?(u)– state in a supersonic beam. The spectrum consists of overlapping ns and nd Rydberg series with n in the range between 4 and 45 converging to the ?+ = 1–4, N+ = 0–5 levels of the X+ 2?(g)+ ground state of H2+. Numerous perturbations caused by s–d and rovibrational channel interactions are revealed in the spectrum and were fully assigned by combining double-resonance experiments and ab initio multichannel quantum-defect theory (MQDT). The energy- and internuclear-distance-dependent eigenquantum-defect parameters of MQDT were derived from available ab initio calculations of the low-lying electronic states of H2 and the ground state of H2(+) and were subsequently refined in a global fit to experimental data. The positions of 552 triplet ns and nd Rydberg levels of H2 (361 of which were measured in the present study) could be reproduced with a root-mean-square deviation of 0.2 cm(–1). PMID:23428200

Sprecher, Daniel; Jungen, Christian; Merkt, Frédéric

2013-10-01

132

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

133

Electron spin polarization transfer to the charge-separated state from locally excited triplet configuration: theory and its application to characterization of geometry and electronic coupling in the electron donor-acceptor system.  

PubMed

We present a theoretical model of analysis of the time-resolved electron paramagnetic resonance (TREPR) spectrum of the charge-separated (CS) state generated by the photoinduced electron transfer (ET) reaction via the locally excited triplet state in an electron donor-acceptor (D-A) system with a fixed molecular orientation. We show, by the stochastic-Liouville equation, that chemically induced dynamic electron polarization (CIDEP) of the triplet mechanism is explained by lack of transfer of quantum coherence terms in the primary triplet spin state, resulting in net emissive or absorptive electron spin polarization (ESP) which is dependent on anisotropy of the singlet-triplet intersystem crossing in the precursor excited state. This disappearance of the coherence is clearly shown to occur when the photoinduced ET rate is smaller than the angular frequency of the Zeeman splitting: the transferred coherence terms are averaged to be zero due to effective quantum oscillations during the time that the chemical reaction proceeds. The above theory has been applied to elucidate the molecular geometries and spin-spin exchange interactions (2J) of the CS states for both folded and extended conformers by computer simulations of TREPR spectra of the zinc porphyrin-fullerene dyad (ZnP-C(60)) bridged by diphenyldisilane. On the extended conformation, the electronic coupling is estimated from the 2J value. It has been revealed that the coupling term is smaller than the reported electronic interactions of the porphyrin-C(60) systems bridged by diphenylamide spacers. The difference in the electronic couplings has been explained by the difference in the LUMO levels of the bridge moieties that mediate the superexchange coupling for the long-range ET reaction. PMID:20509645

Kobori, Yasuhiro; Fuki, Masaaki; Murai, Hisao

2010-11-18

134

Turning on the triplet state channel in the excess electron scavenging by nitroxyl radicals in liquid alkanes  

NASA Astrophysics Data System (ADS)

It has been found that the effective radius of the reaction of excess electrons capture by 4-phenyl-2,2,3,5,5-pentamethyl-imidazolidin-1-oxyl in n-dodecane, n-decane, and n-hexane increases steeply by a factor of about four, reaching values typical for molecular acceptors, when the temperature is reduced below 290, 280, and 250, respectively. A kinetic model of the capture that is based on the assumption of equilibrium between electron detachment and intersystem crossing in the triplet state of the diradical anion is suggested and briefly discussed.

Borovkov, Vsevolod I.; Ivanishko, Irina S.; Beregovaya, Irina V.; Reznikov, Vladimir A.

2012-04-01

135

Triplet excitations in carbon nanostructures  

NASA Astrophysics Data System (ADS)

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

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

2012-02-01

136

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

PubMed

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

Sun, Jifu; Zhong, Fangfang; Zhao, Jianzhang

2013-07-14

137

Inversion of 4-methoxybenzophenone triplet in aqueous solutions.  

PubMed

The triplet state of 4-methoxybenzophenone (4-MBP) has been investigated by laser flash photolysis and emission techniques in several solvents. In non-polar cyclohexane, 4-MBP triplet has an (n,pi*) configuration with the typical triplet-triplet absorption spectrum of benzophenone (lambda(max) ca. 525 nm). However, due to the proximity of the two lowest triplet states of different configuration, some unusual features are observed in polar solvents. Thus, 4-MBP shows in aqueous solutions a transient absorption spectrum with lambda(max) at 450 and 680 nm, which can be attributed to a T1 (pi,pi*) state. Further, transient absorption spectra due to T1 (n,pi*) and T2 (pi,pi*) being simultaneously populated are observed upon laser excitation of 4-MBP in polar solvents such as acetonitrile or methanol. The triplet state inversion (n,pi* to pi,pi*) is also detected by the measurement of triplet quenching rate constants by 1,4-cyclohexadiene (a good hydrogen donor) in acetonitrile and water (kH ca. 2 x 10(8) and 5 x 10(5) M(-1) s(-1), respectively) and by the determination of room-temperature phosphorescence (the emission quantum yield at room-temperature decreases from 0.004 in acetonitrile to less than 1 x 10(-6) in water). Further, the energy of the 4-MBP triplet state is ca. 288 kJ mol(-1) both in polar and non-polar organic solvents, while in water it drops to 275 kJ mol(-1). The photophysical properties of 4-MBP are compared with those of 4-aminobenzophenone (4-ABP), which also possesses an electron-donating group. In polar organic solvents such as acetonitrile, the transient absorption spectrum and the quenching rate constant of hydrogen abstraction for triplet 4-ABP are practically the same as those obtained for 4-MBP in aqueous solutions. On the other hand, a small T2 (pi,pi*) contribution is observed in the triplet-triplet absorption spectrum of 4-ABP in cyclohexane. PMID:12665309

Boscá, Francisco; Cosa, Gonzalo; Miranda, Miguel A; Scaiano, J C

2002-09-01

138

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

139

Laser photolysis studies on the electron-transfer reaction from the photoexcited triplet state of chloroindium(III) tetraphenylporphyrin to methylviologen in methanol solutions  

SciTech Connect

Laser photolysis studies were carried out for chloroindium (III) tetraphenylporphyrin, C1In/sup III/TPP, in methanol solutions. The triplet states of (In/sup III/)/sup +/TPP and methylviologen, MV/sup 2 +/, were found to form a triplet exciplex with an association constant of 6.5 x 10/sup 2/M/sup -1/. The triplet exciplex partly dissociates to the cation radical of (In/sup III/)/sup +/TPP, (In/sup III/)/sup +/TPP/sup +/), and methylviologen cation radical, MV/sup +/, followed by the back electron transfer from MV/sup +/ to ((In/sup III/)/sup +/TPP/sup +/) to regenerate MV/sup 2 +/ and (In/sup III/)/sup +/TPP. The triplet exciplex reacts with triethanolamine, TEA, presumably to produce a new triplet exciplex, /sup 3/((In/sup III/)/sup +/TPP(TEA)(MV/sup 2 +/)), in which a TEA molecule is considered to occupy the axial position. No ionic dissociation from this triplet exciplex was observed. Photolysis of the methanol solution of C1In/sup III/TPP containing 0.5 M TEA and 10-/sup 3/ M MV/sup 2 +/ gives rise to the formation of MV/sup +/ as a final product. The absorption spectroscopy study revealed that C1In/sup III/TPP in a methanol solution at 0.5 M TEA is transformed to (In/sup III/TPP(TEA)/sub 2/)/sup +/(C1/sup -/), in which two TEA molecules are located in the axial positions. On the basis of the laser photolysis study the triplet state of (In/sup III/TPP(TEA)/sub 2/)/sup +/ is confirmed to undergo efficient electron transfer toward MV/sup 2 +/, resulting in the formation of MV/sup 2 +/. 29 refs., 6 figs.

Hoshino, M.; Seki, H.; Shizuka, H.

1985-01-31

140

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

PubMed

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

Spa?ek, J; Zegrodnik, M

2013-10-30

141

Theoretical study of the reaction of ethane with oxygen molecules in the ground triplet and singlet delta states.  

PubMed

Quantum chemical calculations are carried out to study the reaction of ethane with molecular oxygen in the ground triplet and singlet delta states. Transition states, intermediates, and possible products of the reaction on the triplet and singlet potential energy surfaces are identified on the basis of the coupled-cluster method. The basis set dependence of coupled-cluster energy values is estimated by the second-order perturbation theory. The values of energy barriers are also refined by using the compound CBS-Q and G3 techniques. It was found that the C(2)H(6) + O(2)(X(3)?(g)(-)) reaction leads to the formation of C(2)H(5) and HO(2) products, whereas the C(2)H(6) + O(2)(a(1)?(g)) process produces C(2)H(4) and H(2)O(2) molecules. The appropriate rate constants of these reaction paths are estimated on the basis of variational and nonvariational transition-state theories assuming tunneling and possible nonadiabatic transitions in the temperature range 500-4000 K. The calculations showed that the rate constant of the C(2)H(6) + O(2)(a(1)?(g)) reaction path is much greater than that of the C(2)H(6) + O(2)(X(3)?(g)(-)) one. At the same time, the singlet and triplet potential surface intersection is detected that leads to the appearance of the nonadiabatic quenching channel O(2)(a(1)?(g)) + C(2)H(6) ? O(2)(X (3)?(g)(-)) + C(2)H(6). The rate constant of this process is estimated with the use of the Landau-Zener model. It is demonstrated that, in the case of the existence of thermal equilibrium in the distribution of molecules over the electronic states, at low temperatures (T < 1200 K) the main products of the reaction of C(2)H(6) with O(2) are C(2)H(4) and H(2)O(2), rather than C(2)H(5) and HO(2). At higher temperature (T > 1200 K) the situation is inverted. PMID:22823469

Sharipov, Alexander S; Starik, Alexander M

2012-08-23

142

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

Microsoft Academic Search

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

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

2007-01-01

143

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

NASA Astrophysics Data System (ADS)

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

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

2012-09-01

144

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

PubMed Central

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

2013-01-01

145

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

146

Non-adiabatic and intersystem crossing dynamics in SO2. II. The role of triplet states in the bound state dynamics studied by surface-hopping simulations.  

PubMed

The importance of triplet states in the photorelaxation dynamics of SO2 is studied by mixed quantum-classical dynamics simulations. Using the SHARC method, standing for Surface Hopping including ARbitrary Couplings, intersystem crossing (ISC) processes caused by spin-orbit coupling are found occurring on an ultrafast time scale (few 100 fs) and thus competing with internal conversion. While in the singlet-only dynamics only oscillatory population transfer between the (1)B1 and (1)A2 states is observed, in the dynamics including singlet and triplet states we find additionally continuous ISC to the (3)B2 state and to a smaller extent to the (3)B1/(3)A2 coupled states. The populations obtained from the dynamics are discussed with respect to the overall nuclear motion and in the light of recent TRPEPICO studies [I. Wilkinson, A. E. Boguslavskiy, J. Mikosch, D. M. Villeneuve, H.-J. Wörner, M. Spanner, S. Patchkovskii, and A. Stolow, "Excited state dynamics in SO2. I. Bound state relaxation studied by time-resolved photoelectron-photoion coincidence spectroscopy," J. Chem. Phys. 140, 204301 (2014)]. PMID:24880275

Mai, Sebastian; Marquetand, Philipp; González, Leticia

2014-05-28

147

Non-adiabatic and intersystem crossing dynamics in SO2. II. The role of triplet states in the bound state dynamics studied by surface-hopping simulations  

NASA Astrophysics Data System (ADS)

The importance of triplet states in the photorelaxation dynamics of SO2 is studied by mixed quantum-classical dynamics simulations. Using the SHARC method, standing for Surface Hopping including ARbitrary Couplings, intersystem crossing (ISC) processes caused by spin-orbit coupling are found occurring on an ultrafast time scale (few 100 fs) and thus competing with internal conversion. While in the singlet-only dynamics only oscillatory population transfer between the 1B1 and 1A2 states is observed, in the dynamics including singlet and triplet states we find additionally continuous ISC to the 3B2 state and to a smaller extent to the 3B1/3A2 coupled states. The populations obtained from the dynamics are discussed with respect to the overall nuclear motion and in the light of recent TRPEPICO studies [I. Wilkinson, A. E. Boguslavskiy, J. Mikosch, D. M. Villeneuve, H.-J. Wörner, M. Spanner, S. Patchkovskii, and A. Stolow, "Excited state dynamics in SO2. I. Bound state relaxation studied by time-resolved photoelectron-photoion coincidence spectroscopy," J. Chem. Phys. 140, 204301 (2014)].

Mai, Sebastian; Marquetand, Philipp; González, Leticia

2014-05-01

148

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

NASA Astrophysics Data System (ADS)

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

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

1998-12-01

149

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

PubMed Central

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

2012-01-01

150

Thermal and solvent effects on the triplet formation in cinnoline.  

PubMed

Cinnoline (1,2-diazanaphthalene) is of particular interest among the diazanaphthalenes. Its triplet quantum yield upon photoexcitation depends strongly on the temperature and the solvent environment. At the beginning of this study, the properties of the lowest triplet electronic state were not understood either. To elucidate the photophysics of cinnoline, we implemented algorithms based on the time-dependent approach for calculating intersystem crossing rates and one-photon spectra of thermally equilibrated vibronic levels. Our quantum chemical investigations reveal that the triplet formation in hydrocarbon solutions at low temperatures is an El-Sayed forbidden process. At higher temperatures and in hydroxylic solutions an additional El-Sayed allowed channel opens up, increasing the intersystem crossing rate substantially. Furthermore, we have solved the old puzzle concerning the character of the lowest triplet state of cinnoline. In the gas phase the electronic structure has mainly n?* character with additional contributions from ??* configurations since the nuclear arrangement in the pyridazine ring is not planar. In hydroxylic solvents, the electronic structure of the T1 state is altered. The simulation of the triplet emission shows that the experimentally observed phosphorescence of cinnoline in ethanol most certainly stems from the (3)(??*) emission. PMID:24469462

Etinski, Mihajlo; Tatchen, Jörg; Marian, Christel M

2014-03-14

151

Influence of ionic strength on triplet-state natural organic matter loss by energy transfer and electron transfer pathways.  

PubMed

Triplet state excited natural organic matter chromophores ((3)NOM*) are important reactive intermediates in indirect photochemical processes, yet the impact of salt concentrations relevant to estuarine and marine environments on (3)NOM* is poorly understood. The formation rates, pseudo-first-order loss rate constants, and steady-state concentration of (3)NOM* were monitored using the sorbate probe method in synthetic matrices with increasing ionic strength (IS) to seawater values using seawater halides or other salts. The steady-state concentration of (3)NOM* approximately doubled at seawater IS, regardless of the salt used, due to a decrease in the (3)NOM* decay rate constant. The electron transfer-mediated degradation of 2,4,6-trimethylphenol (TMP) by (3)NOM* was significantly slowed at higher IS. A model is proposed wherein high IS slows intra-organic matter electron transfer pathways, an important (3)NOM* loss pathway, leading to longer (3)NOM* lifetimes. Although IS did not appear to impact energy transfer pathways directly, the higher (3)NOM* steady-state concentrations promote energy transfer interactions. The observed decrease in decay rate constant, increase in steady-state concentration of (3)NOM* at high IS, and the inhibition of electron transfer pathways should be considered when determining the fate of organic pollutants in estuarine and marine environments. PMID:23952218

Parker, Kimberly M; Pignatello, Joseph J; Mitch, William A

2013-10-01

152

Chlorophyll Photochemistry in Condensed Media: Triplet State Quenching and Electron Transfer to Quinone in Cellulose Acetate Films.  

National Technical Information Service (NTIS)

Chlorophyll a was incorporated into cellulose acetate films and the triplet decay and electron transfer to p-benzoquinone in aqueous solution was studied using laser flash photolysis and ESR. The triplet was found to decay by first order kinetics with the...

G. Cheddar F. Castelli G. Tollin

1979-01-01

153

Rate of carotenoid triplet formation in solubilized light-harvesting complex II (LHCII) from spinach.  

PubMed Central

In the present study the rate of triplet transfer from chlorophyll to carotenoids in solubilized LHCII was investigated by flash spectroscopy using laser pulses of approximately 2 ns for both pump and probe. Special attention has been paid to calibration of the experimental setup and to avoid saturation effects. Carotenoid triplets were identified by the pronounced positive peak at approximately 507 nm in the triplet-singlet difference spectra. DeltaOD (507 nm) exhibits a monoexponential relaxation kinetics with characteristic lifetimes of 2-9 micros (depending on the oxygen content) that was found to be independent of the pump pulse intensity. The rise of DeltaOD (507 nm) was resolved via a pump probe technique where an optical delay of up to 20 ns was used. A thorough analysis of these experimental data leads to the conclusion that the kinetics of carotenoid triplet formation in solubilized LHCII is almost entirely limited by the lifetime of the excited singlet state of chlorophyll but neither by the pulse width nor by the rate constant of triplet-triplet transfer. Within the experimental error the rate constant of triplet-triplet transfer from chlorophyll to carotenoids was estimated to be kTT > (0.5 ns)-1. This value exceeds all data reported so far by at least one order of magnitude. The implications of this finding are briefly discussed.

Schodel, R; Irrgang, K D; Voigt, J; Renger, G

1998-01-01

154

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

PubMed

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

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

2013-05-01

155

Influence of intermediate states on photoelectron spectra  

NASA Astrophysics Data System (ADS)

We investigate the information contained in the photoelectron spectra (PES) of electrons emitted from an atom, molecule, or cluster under the influence of a laser pulse. Basic patterns are evaluated in a simple potential well model. The results are corroborated by realistic applications to the cluster Na9+ calculated within a time-dependent density functional formalism. The final PES are composed from an interplay between features of the laser pulse and spectral properties of the emitting system. We discuss the mutual influences and the possibilities for disentangling the various effects.

Pohl, A.; Reinhard, P.-G.; Suraud, E.

2001-12-01

156

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.

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

2008-01-01

157

New aspects of the photodissociation of water in the first absorption band: How strong is excitation of the first triplet state?  

NASA Astrophysics Data System (ADS)

We consider the possibility of the X~ 1A1-->3B1 excitation of water at wavelengths near 193 nm, i.e., in the red tail of the first absorption band. The corresponding excited-state potential-energy surface is calculated by quantum mechanical methods and the dynamics calculations are performed in the time-dependent representation. It is shown that an absorption cross section for exciting the triplet state 3B1, that at its maximum is about five hundred times (or more) smaller than the corresponding cross section for excitation of the 1B1 state, might explain the surprisingly small H+OD/D+OH branching ratio in the photodissociation of HOD at 193 nm measured by Plusquellic et al. (the foregoing paper). The singlet-triplet transition dipole moment estimated in this way also explains the unexpectedly small cross section ratio for H2O and D2O measured at 193 nm.

Schröder, Thomas; Schinke, Reinhard; Ehara, Masahiro; Yamashita, Koichi

1998-10-01

158

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

PubMed

We use CheMPS2, our free open-source spin-adapted implementation of the density matrix renormalization group (DMRG) [S. Wouters, W. Poelmans, P. W. Ayers, and D. Van Neck, Comput. Phys. Commun. 185, 1501 (2014)], to study the lowest singlet, triplet, and quintet states of the oxo-Mn(Salen) complex. We describe how an initial approximate DMRG calculation in a large active space around the Fermi level can be used to obtain a good set of starting orbitals for subsequent complete-active-space or DMRG self-consistent field calculations. This procedure mitigates the need for a localization procedure, followed by a manual selection of the active space. Per multiplicity, the same active space of 28 electrons in 22 orbitals (28e, 22o) is obtained with the 6-31G(*), cc-pVDZ, and ANO-RCC-VDZP basis sets (the latter with DKH2 scalar relativistic corrections). Our calculations provide new insight into the electronic structure of the quintet. PMID:24985611

Wouters, Sebastian; Bogaerts, Thomas; Van Der Voort, Pascal; Van Speybroeck, Veronique; Van Neck, Dimitri

2014-06-28

159

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

160

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

SciTech Connect

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

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

1987-12-03

161

Modification of Zeeman states in a magnetic field and the alignment-orientation transition in triplet exciton emission in gallium selenide  

NASA Astrophysics Data System (ADS)

The magnetic-field-induced optical alignment-orientation transition in a system of triplet bound excitons in a resonantly excited GaSe crystal has been studied using optical spectroscopy. It has been demonstrated that this effect can be assigned to a variation of the properties of Zeeman (spin) states of triplet excitons in a magnetic field, which initiates a change in the optical activity of these states in circularly and linearly polarized light. For the transition to become possible, the model requires that the electronic system of the crystal supports spin-orbit coupling. The approach employed permits the adequate description of experimental data, as well as calculation of the evolution of the effect during the bound-exciton lifetime.

Starukhin, A. N.; Nelson, D. K.; Razbirin, B. S.

2012-02-01

162

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

NASA Astrophysics Data System (ADS)

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

Gien, T. T.

2012-11-01

163

Thermal conductivity near Hc2 for spin-triplet superconducting states with line nodes in Sr2RuO4  

Microsoft Academic Search

We calculate the thermal conductivity kappa in magnetic fields near Hc2 for spin-triplet superconducting states with line nodes vertical and horizontal relative to the RuO2 planes. The method for calculating the Green's functions takes into account the spatial variation of the order parameter and superconducting flow for the Abrikosov vortex lattice. For in-plane magnetic field we obtain variations of the

L. Tewordt; D. Fay

2001-01-01

164

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

165

Triplet-state photoexcitation dipole-jump relaxation method to observe adsorption/desorption kinetics at a reversed-phase silica/solution interface.  

PubMed

Electronic excitation of a probe chromophore can lead to a change in dipole moment that influences its activity or solubility in solution and changes its relative affinity for partitioning between two phases. Photoexcitation of a probe molecule can, therefore, perturb a sorption equilibrium, and the relaxation kinetics of the probe to the new equilibrium conditions can be monitored in a time-resolved luminescence experiment. The adsorption/desorption kinetics of rose bengal, distributed between a C-18 derivatized porous-silica surface and a liquid mobile-phase solution, were investigated. These kinetics were determined by observing their effect on the phosphorescence decay of the triplet state of rose bengal and its quenching by ferricyanide. The methanol/water solvent compositions were varied to alter the fraction of adsorbed rose bengal. The adsorption rate constant for the triplet state was determined from the dependence of the phosphorescence relaxation rate on dye concentration in solution. The results indicate that the adsorption kinetics are diffusion controlled and that the relaxation is influenced by efficient triplet-energy transfer between excited- and ground-state rose bengal at the C-18 silica/solution interface. PMID:12038748

Shield, Stephanie R; Harris, Joel M

2002-05-15

166

Addition of ketene silyl acetals to the triplet excited state of C{sub 60} via photoinduced electron transfer leading to the fullereneacetates  

SciTech Connect

The photochemical carbon-carbon bond formation of C{sub 60} with ketene silyl acetals is described to give a new way for fullerene functionalization chemistry. The photoaddition of ketene silyl acetals to C{sub 60} occurs efficiently under irradiation of the visible light in benzene as well as benzonitrile to yield the fullereneacetates. The comparison of the observed rate constants determined from the dependence of the quantum yields on the concentrations of ketene silyl acetals as well as the quenching of triplet excited state of C{sub 60} by ketene silyl acetals with those predicted for the electron transfer processes indicates that the photoaddition proceeds via photoinduced electron transfer from ketene silyl acetals to the triplet excited state of C{sub 60}. The negative shift in the one-electron reduction potentials by the adduct formation of C{sub 60} is examined by the cyclic voltammetry measurements. The factors to control the formation of mono- and bisadducts of C{sub 60} are clarified based on the rates of photoinduced electron transfer from ketene silyl acetals to the triplet excited states of C{sub 60} and the adducts. 40 refs., 7 figs., 2 tabs.

Mikami, Koichi; Matsumoto, Shoji [Tokyo Inst. of Technology (Japan); Ishida, Akito; Takamuku, Setsue; Suenobu, Tomoyoshi; Fukuzumi, Shunichi [Osaka Univ. (Japan)

1995-11-15

167

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

168

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

169

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

170

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

NASA Astrophysics Data System (ADS)

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

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

2013-12-01

171

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

PubMed Central

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

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

2013-01-01

172

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

173

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

174

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

NASA Astrophysics Data System (ADS)

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

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

1982-01-01

175

Efficient enhancement of the visible-light absorption of cyclometalated Ir(III) complexes triplet photosensitizers with Bodipy and applications in photooxidation and triplet-triplet annihilation upconversion.  

PubMed

We report molecular designing strategies to enhance the effective visible-light absorption of cyclometalated Ir(III) complexes. Cationic cyclometalated Ir(III) complexes were prepared in which boron-dipyrromethene (Bodipy) units were attached to the 2,2'-bipyridine (bpy) ligand via -C?C- bonds at either the meso-phenyl (Ir-2) or 2 position of the ? core of Bodipy (Ir-3). For the first time the effect of ? conjugating (Ir-3) or tethering (Ir-2) of a light-harvesting chromophore to the coordination center on the photophysical properties was compared in detail. Ir(ppy)2(bpy) (Ir-1; ppy = 2-phenylpyridine) was used as model complex, which gives the typical weak absorption in visible range (? < 4790 M(-1) cm(-1) in region > 400 nm). Ir-2 and Ir-3 showed much stronger absorption in the visible range (? = 71,400 M(-1) cm(-1) at 499 nm and 83,000 M(-1) cm(-1) at 527 nm, respectively). Room-temperature phosphorescence was only observed for Ir-1 (?(em) = 590 nm) and Ir-3 (?(em) = 742 nm). Ir-3 gives RT phosphorescence of the Bodipy unit. On the basis of the 77 K emission spectra, nanosecond transient absorption spectra, and spin density analysis, we proposed that Bodipy-localized long-lived triplet excited states were populated for Ir-2 (?T = 23.7 ?s) and Ir-3 (87.2 ?s). Ir-1 gives a much shorter triplet-state lifetime (0.35 ?s). Complexes were used as singlet oxygen ((1)O2) photosensitizers in photooxidation. The (1)O2 quantum yield of Ir-3 (?? = 0.97) is ca. 2-fold of Ir-2 (?? = 0.52). Complexes were also used as triplet photosensitizer for TTA upconversion; upconversion quantum yields of 1.2% and 2.8% were observed for Ir-2 and Ir-3, respectively. Our results proved that the strong absorption of visible light of Ir-2 failed to enhance production of a triplet excited state. These results are useful for designing transition metal complexes that show effective strong visible-light absorption and long-lived triplet excited states, which can be used as ideal triplet photosensitizers in photocatalysis and TTA upconversion. PMID:23327589

Sun, Jifu; Zhong, Fangfang; Yi, Xiuyu; Zhao, Jianzhang

2013-06-01

176

Visible light-absorbing rhenium(I) tricarbonyl complexes as triplet photosensitizers in photooxidation and triplet-triplet annihilation upconversion.  

PubMed

We prepared N^N Re(I) tricarbonyl chloride complexes (Re-1 and Re-2) that give very strong absorption of visible light. To this end, it is for the first time that boron dipyrimethane (Bodipy) was used to prepare Re(I) tricarbonyl chloride complexes. The ?-conjugation linker between the ?-conjugation framework of the antenna Bodipy and the Re(I) coordination centre ensures efficient intersystem crossing (ISC). Re-0 without visible light-harvesting ligand was prepared as a model complex in the photophysical studies. Re-1 (with Bodipy) and Re-2 (with carbazole-ethynyl Bodipy) show unprecedented strong absorption of visible light at 536 nm (? = 91700 M(?1) cm(?1)) and 574 nm (? = 64,600 M(?1) cm(?1)), respectively. Interestingly, different from Re-0, Re-1 and Re-2 show fluorescence of the ligand, not the phosphorescence of the Re(I) coordination centre. However, long-lived triplet excited states were observed upon visible light excitation (?(T) = 104.0 ?s for Re-1; ?(T) = 127.2 ?s for Re-2) vs. the short lifetime of Re-0 (?(T) = 26 ns). With nanosecond time-resolved transient absorption spectroscopy and DFT calculations, we proved that the triplet excited states of Re-1 and Re-2 are localized on the Bodipy ligands. The complexes were used as triplet photosensitizers for two triplet–triplet-energy-transfer (TTET) processes, i.e.(1)O(2) mediated photooxidation and triplet–triplet annihilation (TTA) upconversion. With the strong visible light-harvesting ability, Re-1 proved to be a better (1)O(2) photosensitizer than the conventional triplet photosensitizer tetraphenylporphyrin (TPP). Significant upconversion was observed with Re-1 as the triplet photosensitizer. Our result is useful for preparation of Re(I) tricarbonyl chloride complexes that show strong absorption of visible light and long-lived triplet excited states and for the application of these complexes as triplet photosensitizers in photocatalysis, photodynamic therapy and TTA upconversion. PMID:23178459

Yi, Xiuyu; Zhao, Jianzhang; Sun, Jifu; Guo, Song; Zhang, Hongli

2013-02-14

177

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.

Angiolillo, P J; Vanderkooi, J M

1995-01-01

178

A TD-DFT study on triplet excited-state properties of curcumin and its implications in elucidating the photosensitizing mechanisms of the pigment  

NASA Astrophysics Data System (ADS)

In this Letter, we present time-dependent density functional theory (TD-DFT)-derived triplet state properties of curcumin in vacuum, benzene and DMSO. Accordingly, the photosensitizing mechanisms of curcumin are explained. It is revealed that in benzene and DMSO, excited curcumin can react with O 2 to generate 1O 2 and O2rad - through energy transfer and electron transfer, however, the O2rad --generating pathways are different in both solvents. This indicates the potential of TD-DFT in determining the excited-state properties of pigments, which is of significance in getting a deeper insight into the photodynamic mechanisms of photosensitizers.

Shen, Liang; Ji, Hong-Fang; Zhang, Hong-Yu

2005-06-01

179

Triplet-sensitized photolysis of the photoisomer of a 2,11-diaza[3,3](9,10)anthracenoparacyclophane: an adiabatic cycloreversion and a [2pia + 2pia + 2sigmas] rearrangement in a triplet state of the biplanophane system.  

PubMed

The triplet-sensitized photoreactions of the title biplanophane system 6, the photoisomer of a 2,11-diaza[3,3](9,10)anthracenoparacyclophane derivative 5, were investigated by stationary and laser-flash photolyses using xanthone (XT) and benzophenone (BP) as triplet sensitizers. When photoisomer 6 underwent XT-sensitized irradiation, a triplet cyclophane 5 and a novel polycyclic product 7 were obtained via an adiabatic cycloreversion and a formal [2pia + 2pia + 2sigmas] rearrangement, respectively. The maximum quantum yield for the formation of cyclophane 5 (0.69) and the upper-limit efficiency for the formation of polycycle 7 (0.31) were determined by laser photolysis techniques. For BP-sensitized photolysis of photoisomer 6, oxetane 8, in addition to triplet cyclophane 5 and polycycle 7, was formed by a Paterno-Buchi reaction. The quenching rate constant (k(q)) of triplet BP by photoisomer 6 (3.4 x 10(8) dm(3) mol(-)(1) s(-)(1)) was found to be 1 order of magnitude smaller than that for XT (5.0 x 10(9) dm(3) mol(-)(1) s(-)(1)). On the basis of the relationship between k(q) and the triplet donor-acceptor energy gap, the triplet energy level of photoisomer 6 was estimated to be approximately 71 kcal mol(-)(1). The photochemical and the photophysical processes involved in the sensitized photolyses are summarized in an energetic reaction diagram and discussed in detail. PMID:15527262

Okamoto, Hideki; Yamaji, Minoru; Satake, Kyosuke; Tobita, Seiji; Kimura, Masaru

2004-11-12

180

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

SciTech Connect

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

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

2008-01-01

181

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

PubMed

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

Fukuda, Ryoichi; Ehara, Masahiro

2013-10-28

182

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

183

Dynamical evolution of triplets of galaxies  

NASA Astrophysics Data System (ADS)

By means of N-body simulations we study the global dynamics of triplets of galaxies, considering initial conditions (ICs) starting from `maximum expansion' and in virial equilibrium. Unlike previous studies we treat galaxies self-consistently, but we restrict ourselves to models with spherical symmetry and do not consider the influence of a primordial common halo of dark matter. Our results indicate that a low number of triple mergers is expected at the present epoch (~10 per cent) for collapsing triplets. Initially virialized conditions yield ~5 per cent of triple mergers in ~10Gyr of evolution; hence, the three-galaxy problem has stable states. No overmerging problem for these small groups of galaxies is found. Their geometrical properties, as reflected by the Agekyan-Anosova map, do not show an excess of extreme hierarchical triplets. Unlike the three-body problem no `sling-shot' events are found during triple interactions, for both collapsing and virial ICs. The median velocity dispersion of observed compact triplets (?~100kms-1) is not well reproduced in our models at the present epoch: ?~50kms-1 for collapsing and ?~80kms-1 for virial. However, about 10 per cent of simulated triplets reaching the present epoch from maximum expansion have dynamical properties very similar to the median of Karachentev's compact triplets. Our median values agree, however, very well with the new data on triplets. We find that the median of the virial mass estimates does not overestimate, in general, the mass of triplets, but underestimates it by ~35 per cent. The median mass estimator appears as a somewhat better mass estimator. Analysis of the dynamical parameters, as well as information obtained from a pseudo-phase-plane constructed using their velocity dispersion and harmonic radius, leads us to conclude that Karachentsev's compact triplets probably represent the most advanced stage of gravitational clustering of initially diffuse triplets. To test this thesis we suggest that triplets be studied within a cosmological scenario.

Aceves, Héctor

2001-10-01

184

Quantum-chemical study of the structure of the acetyl fluoride molecule in the ground and lowest excited singlet and triplet electronic states.  

PubMed

The structure of the conformationally flexible acetyl fluoride molecule (CH3CFO and CD3CFO) in the ground (S0) and lowest excited triplet (T1) and singlet (S1) electronic states was calculated by different quantum-chemical methods (RHF, UHF, MP2, CASSCF). The equilibrium geometric parameters and harmonic vibrational frequencies of the molecules in these electronic states were estimated. The calculations demonstrated that the electronic excitation causes considerable conformational changes involving the rotation of the CH3(CD3) top and a substantial deviation of the CCFO carbonyl fragment from planarity. For large-amplitude vibrations, namely, for the torsional vibration in the S0 state and the torsional and inversion (nonplanar carbonyl fragment) vibrations in the T1 and S1 states, the quantum-mechanical problems were solved in one-dimensional (1D) and two-dimensional (2D) approximations. The results of calculations are in good agreement with experimental data. PMID:15248978

Kudich, A V; Bataev, V A; Abramenkov, A V; Godunov, I A

2004-07-01

185

Quasiclassical asymptotics and coherent states for bounded discrete spectra  

NASA Astrophysics Data System (ADS)

We consider discrete spectra of bound states for nonrelativistic motion in attractive potentials V?(x)=-|V0| |x|-?, 0 ? predicts quantized energy levels e?(n) of a bounded spectrum varying as e?(n)~-n-2?/(2-?). 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 ? in the range 0 < ? <= 2/3 we present exact implementations of such states for the parametrization ? = 2(k - l)/(3k - l) with k and l positive integers satisfying k>l.

Górska, K.; Penson, K. A.; Horzela, A.; Duchamp, G. H. E.; Blasiak, P.; Solomon, A. I.

2010-12-01

186

Excited electronic states and Raman spectra of 2-benzoylpyridine.  

PubMed

Raman excitation profiles of several normal modes of 2-benzoylpyridine were measured, and the structural changes encountered on excitations, excited state symmetries, and vibronic couplings among various excited electronic states of the molecule were investigated. Vibrational spectroscopic studies of the molecule were done in detail, and critical investigation on the electronic spectra of the molecule was also carried out. It is shown that the experimentally allowed transitions, corresponding to the band around 262 and 238 nm, occur to the excited states, where the major geometry changes involve both ring CC/CN and CO stretching vibrations. An excited state lying around 185 nm above the ground state was also found to play an important role in the scattering process. All necessary and valuable quantum chemical calculations accompany the presented spectral studies. PMID:24359660

Datta, Shirsendu; Sett, Pinaky; Chowdhury, Joydeep; Ghosh, Manash; Mallick, Prabal Kumar

2013-12-01

187

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.

Ghosh, S; Petrin, M; Maki, A

1986-01-01

188

Understanding the Photoreactivity of Dissolved Organic Carbon in Natural Waters: The Role of the Triplet Excited-State of Allochthonous and Autochthonous DOC  

NASA Astrophysics Data System (ADS)

The photochemical reactivity of DOC in sunlit waters is a major factor for the in situ processing of DOC itself and trace contaminants in streams, lakes and the ocean. There is an increasing interest in the use of wetlands to mitigate contaminant removal. Laser flash photolysis is used to determine the reaction rate constants of dissolved organic carbon (DOC) with emerging contaminants in natural waters. DOC, produced by the decomposition of plant and microbial material, is one of the most complex naturally occurring mixtures. DOC plays a major role in the global carbon cycle, the sequestration and transport of trace chemicals and contaminants, and the biogeochemistry of natural waters. Hydrolysis, direct photolysis and reactions with singlet oxygen and the hydroxyl radical account for up to 25% of the photo reactivity of natural organic matter. The remaining 75% is attributed to reactions with the triplet-excited state of DOC (3DOC*). In this study, 1H NMR is used to characterize DOC from the Black River (NC), the San Joaquin Wetlands (Irvine, CA), and coastal seawater (Crystal Cove, CA). These sites encompass both allochthonous and autochthonous organic matter from catchment, wetlands, and marine waters. We then determine the reaction rate constants of known triplet state reactants and pharmaceuticals with the 3DOC* in the natural waters and with the DOC isolated by solid phase extraction. Studies of 3DOC* could provide a measure of DOC reactivity, essential in the design of constructed wetlands for contaminant removal.

Cottrell, B. A.; Timko, S. A.; Robinson, A. K.; Weiden, L. M.; Cooper, W.

2012-12-01

189

Single-shot readout and relaxation of singlet and triplet States in exchange-coupled ^{31}p 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 ^{31}P 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

190

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

SciTech Connect

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

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

2000-01-27

191

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

192

Infrared absorption spectra of various doping states in cuprate superconductors  

SciTech Connect

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

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

1992-01-01

193

Infrared absorption spectra of various doping states in cuprate superconductors  

SciTech Connect

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

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

1992-02-01

194

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

195

Favorable performance of the DFT methods in predicting the minimum-energy structure of the lowest triplet state of WF{sub 4}  

SciTech Connect

The tetrahedral structure of the lowest triplet state of the WF{sub 4} complex was examined using different variants of the density functional theory (DFT) and conventional ab initio methods. The low-level, conventional, ab initio methods, such as SCF, MP2, MP3, and CISD, predict the tetrahedral structure to be a minimum, whereas the DFT schemes predict an imaginary frequency for the e vibrational mode. Only after recovering electron correlation effects at the MP4 and higher levels, the conventional electronic structure methods also predict the T{sub d} structure to be a second-order stationary point. This is not the correlation but the exchange part of the DFT functionals which is responsible for the discrepancy between the DFT and low-level, conventional, ab initio predictions. The lowering of symmetry to C{sub 2v} leads to a minimum on the lowest triplet potential energy surface and the electronic energy difference between the T{sub d} and C{sub 2v} stationary points amounts to 0.85 and 0.96 kcal/mol at the B3LYP and CCSD(T) levels, respectively.

Gutowski, M. [Pacific Northwest National Lab., Richland, WA (United States)] [Pacific Northwest National Lab., Richland, WA (United States); [Univ. of Utah, Salt Lake City, UT (United States). Dept. of Chemistry

1999-06-15

196

Spectra  

NSDL National Science Digital Library

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

Kaler, James

2004-07-16

197

Rotational spectra of HCCCN in some excited vibrational states  

NASA Astrophysics Data System (ADS)

The rotational spectra have been measured up to 220 GHz for HCCCN in excited vibrational states up to about 1000 cm -1; the states of ( v4, v5, v6, v7) = (0, 0, 0, 1), (0, 0, 0, 2), (0, 0, 0, 3), (0, 0, 0, 4), (0, 0, 1, 0), (0, 0, 1, 1), (0, 0, 1, 2), (0, 0, 2, 0), (0, 1, 0, 0), (0, 1, 0, 1), (1, 0, 0, 0), and (1, 0, 0, 1). Accurate molecular constants have been determined using an effective Hamiltonian newly proposed by K. M. T. Yamada, F. W. Birss, and M. R. Aliev ( J. Mol. Spectrosc.112, 347-356 (1985). By analyzing the anharmonic resonances, the unperturbed rotational constants for the v4 = 1 and for the v5 = 1 states were obtained as 4537.958(15) and 4550.6218(35) MHz, respectively.

Yamada, Koichi M. T.; Creswell, R. A.

1986-04-01

198

Tunneling Conductance and Spatial Dependences of Pair Potentials in Normal Metal-Triplet Superconductor Junctions  

NASA Astrophysics Data System (ADS)

Tunneling conductance spectra in normal metal / insulator / triplet superconductorjunctions are theoretically investigated.For the triplet paring states, we select several kinds of the symmetrieswhich are promising candidates for the superconducting statesof UPt3 and Sr2RuO4.We present a conductance formula that can treatspatially varying pair potential witharbitrary barrier height cases.In order to analyze realistic situations, thepair potentials are determined self-consistentlyusing the quasi-classical Green's function method.It is shown that the pair potentials exhibit diverse spatial dependencesnear the insulator.The conductance spectra show zero-bias conductance peaksas well as gap structures depending on the junction orientation,which qualitatively agrees withour previous calculation where the pair potentialsare assumed to be spatially constant.The agreement implies an insensitive natureof the tunneling conductance spectra onthe detailed spatial profile of the pair potential.

Yamashiro, Masashi; Tanaka, Yukio; Yoshida, Nobukatsu; Kashiwaya, Satoshi

1999-06-01

199

Stochastic Liouville equation studies of FT-EPR spectra of singlet-triplet mixing photo-chemically generated radical pair system.  

PubMed

A stochastic Liouville equation (SLE) was numerically solved to obtain pulsed Fourier-transform (FT) EPR spectra on a radical pair system created in a photo-induced chemical reaction. Numerical calculations were applied to the photo-chemical reaction of deuterated acetone and 2-propanol at low temperatures. In this reaction system, the antiphase structures of the EPR signals, so called spin-correlated radical pair (SCRP) signals of two identical isopropyl ketyl radicals and spin-polarized free isopropyl ketyl radicals were observed by FT-EPR and continuous wave time-resolved (CW TR) EPR techniques. In the present work, FT-EPR spectra of the antiphase structure signals of the radical pair themselves as well as spin-polarized free radical signals were simulated. Additionally, rising behavior of free radical signals polarized by the radical pair mechanism (RPM) was also clarified. Furthermore two-dimensional (2D) FT-EPR nutation spectra were simulated in the both cases with and without the radical pairs by the use of SLE. In these simulations, strong DC components in the nutation frequency dimension, were well reproduced as was obtained in experiments. It was shown that relaxation during the microwave pulse was essential for the appearance of the DC components. PMID:18486510

Hanaishi, Ryuji

2008-07-01

200

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

SciTech Connect

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

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

2000-04-20

201

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

NASA Astrophysics Data System (ADS)

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

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

2013-10-01

202

Low-energy chlorophyll states in the CP43 antenna protein complex: simulation of various optical spectra. II.  

PubMed

The CP43 protein complex of the core antenna of higher plant photosystem II (PSII) has two quasidegenerate "red" absorption states. It has been shown in the accompanying paper I (Dang, N. C., et al. J. Phys. Chem. B 2008, 112, 9921.) that the site distribution functions (SDFs) of red-states A and B are uncorrelated and the narrow holes are burned in subpopulations of chlorophylls (Chls) from states A and B that are the lowest-energy pigments in their particular CP43 complexes and cannot further transfer energy downhill. In this work, we present the results of a series of Monte Carlo simulations using the 3.0-A structure of the PSII core complex from cyanobacteria (Loll, B., et al. Nature 2005, 303, 1040.) to model absorption, emission, persistent, and transient hole burned (HB) spectra. At the current structural resolution, we found calculated site energies (obtained from INDO/S calculations) to be only suggestive because their values are different for the two monomers of CP43 in the PS II dimer. As a result, to probe the excitonic structure, a simple fitting procedure was employed to optimize Chl site energies from various starting values corresponding to different A/B pigment combinations to provide simultaneously good fits to several types of optical spectra. It is demonstrated that the shape of the calculated absorption, emission, and transient/persistent hole-burned spectra is consistent with experimental data and our model for excitation energy transfer between two quasi-degenerate lowest-E states (A and B) with uncorrelated SDFs discussed in paper I. Calculations revealed that absorption changes observed near 670 nm in the non-line-narrowed persistent HB spectra (assigned to photoconversion involving Chl-protein hydrogen-bonding by Hughes (Biochemistry 2006, 45, 12345.) are most likely the result of nonphotochemical hole-burning (NPHB) accompanied by the redistribution of oscillator strength due to modified excitonic interactions. We argue that a unique redistribution of oscillator strength during the NPHB process helps to assign Chls contributing to the low-energy states. It is demonstrated that the 4.2 K asymmetric triplet-bottleneck (transient) hole is mostly contributed to by both A and B states, with the hole profile described by a subensemble of pigments, which are the lowest-energy pigments (B s- and A s-type) in their complexes. The same lowest-energy Chls contribute to the observed fluorescence spectra. On the basis of our excitonic calculations, the best Chl candidates that contribute to the low-energy A and B states are Chl 44 and Chl 37, respectively. PMID:18642950

Reppert, Mike; Zazubovich, Valter; Dang, Nhan C; Seibert, Michael; Jankowiak, Ryszard

2008-08-14

203

Singlet and triplet state dynamics of charge and hydride transfer reactions of OD+ (X3[Sigma]-) with propyne  

NASA Astrophysics Data System (ADS)

We report a crossed beam study of the title reactions in the collision energy range from 0.45 to 1.23 eV (43-119 kJ/mol). Both reactions are exoergic and proceed as direct processes on a time scale much less than the rotational period of the transient association complex of approaching reactants. The charge transfer process takes place with zero momentum transfer. Density Functional Theory calculations of the structures of reactive intermediates show that a plausible pathway for hydride transfer involves initial charge transfer on a triplet surface, followed by intersystem crossing to the singlet manifold. This process is followed by rapid hydrogen atom transfer to form an intermediate that dissociates smoothly to products. The kinematics of the heavy + light-heavy mass combination result in mixed energy release at the lowest collision energy, in which both the breaking and forming bonds are extended, while at higher collision energies, the incremental translational energy in the reactants appears preferentially in product translation, consistent with induced repulsive energy release.

Liu, Li; Li, Yue; Farrar, James M.

2009-02-01

204

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

NASA Astrophysics Data System (ADS)

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

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

2011-12-01

205

Structural Diversity of Triplet Repeat RNAs*?  

PubMed Central

Tandem repeats of various trinucleotide motifs are present in the human transcriptome, but the functions of these regular sequences, which likely depend on the structures they form, are still poorly understood. To gain new insight into the structural and functional properties of triplet repeats in RNA, we have performed a biochemical structural analysis of the complete set of triplet repeat transcripts, each composed of a single sequence repeated 17 times. We show that these transcripts fall into four structural classes. The repeated CAA, UUG, AAG, CUU, CCU, CCA, and UAA motifs did not form any higher order structure under any analyzed conditions. The CAU, CUA, UUA, AUG, and UAG repeats are ordered according to their increasing tendency to form semistable hairpins. The repeated CGA, CGU, and all CNG motifs form fairly stable hairpins, whereas AGG and UGG repeats fold into stable G-quadruplexes. The triplet repeats that formed the most stable structures were characterized further by biophysical methods. UV-monitored structure melting revealed that CGG and CCG repeats form, respectively, the most and least stable hairpins of all CNG repeats. Circular dichroism spectra showed that the AGG and UGG repeat quadruplexes are formed by parallel RNA strands. Furthermore, we demonstrated that the different susceptibility of various triplet repeat transcripts to serum nucleases can be explained by the sequence and structural features of the tested RNAs. The results of this study provide a comprehensive structural foundation for the functional analysis of triplet repeats in transcripts.

Sobczak, Krzysztof; Michlewski, Gracjan; de Mezer, Mateusz; Kierzek, Elzbieta; Krol, Jacek; Olejniczak, Marta; Kierzek, Ryszard; Krzyzosiak, Wlodzimierz J.

2010-01-01

206

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

207

Triplet-triplet energy transfer between luminescent probes bound to albumins  

NASA Astrophysics Data System (ADS)

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

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

2010-08-01

208

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

NASA Astrophysics Data System (ADS)

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

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

2009-12-01

209

Were reactions of triplet silylenes observed?  

PubMed

The observation that (iPr3Si)(tBu3Si)Si: (1) yields an intramolecular C-H bond insertion product at room temperature, together with earlier computational predictions that triplet 1 is slightly more stable (or isoenergetic) than singlet 1 and additional considerations, led previous investigators to conclude that 1 is the first silylene to exhibit triplet electronic state reactivity. In this paper we test, using DFT and ab initio methods, whether the occurrence of intramolecular C-H bond insertion indeed indicates the presence of a triplet-state silylene. DFT calculations at the B3LYP/6-31+G(d,p)//B3LYP/6-31+G(d,p) level show that singlet (iPr3Si)(tBuMe2Si)Si: (9), a close model of singlet 1, inserts intramolecularly into a C-H bond of the tBu group with a barrier of 22.7 kcal/mol (22.2 kcal/mol at SCS-MP2/cc-PVTZ). However, for triplet9 the barrier of this insertion reaction is significantly higher, 34.6 kcal/mol (41.9 kcal/mol at SCS-MP2/cc-PVTZ). This implies that at room temperature the intramolecular insertion reaction of the singlet is 10(9)-10(12) faster than that of the triplet. We conclude, in contrast to previous conclusions, that the observed intramolecular C-H bond insertion reactions of 1 as well as of (tBu3Si)2Si: (2) occur from the singlet state. Furthermore, the occurrence of an intramolecular C-H bond insertion cannot serve as evidence for the presence of a triplet silylene, either in cases where the singlet and triplet states are nearly isoenergetic (e.g., 1 and 9) or even for silylenes where the triplet state is the ground state (e.g., 2), because the corresponding singlet silylenes insert intramolecularly much faster. The search for a genuine reaction of a triplet silylene has to continue. PMID:23687959

Kosa, Monica; Karni, Miriam; Apeloig, Yitzhak

2013-06-19

210

Gas phase dynamics of triplet formation in benzophenone.  

PubMed

Benzophenone is a prototype molecule for photochemistry in the triplet state through its high triplet yield and reactivity. We have investigated its dynamics of triplet formation under the isolated gas phase conditions via femtosecond and nanosecond time resolved photoelectron spectroscopy. This represents the complete evolution from the excitation in S2 to the final decay of T1 to the ground state S0. We have found that the triplet formation can be described almost as a direct process in preparing T1, the lowest reacting triplet state, from the S1 state after S2 ? S1 internal conversion. The molecule was also deposited by a pick-up technique on cold argon clusters providing a soft relaxation medium without evaporation of the molecule and the mechanism was identical. This cluster technique is a model for medium influenced electronic relaxation and provides a continuous transition from the isolated gas phase to the relaxation dynamics in solution. PMID:24728443

Spighi, Gloria; Gaveau, Marc-André; Mestdagh, Jean-Michel; Poisson, Lionel; Soep, Benoît

2014-04-23

211

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

PubMed Central

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

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

2007-01-01

212

Modulating the optoelectronic properties of large, conjugated, high-energy gap, quaternary phosphine oxide hosts: impact of the triplet-excited-state location.  

PubMed

The purposeful modulation of the optoelectronic properties was realised on the basis of a series of the large, conjugated, phosphine oxide hosts 9,9-bis-{4'-[2-(diphenylphosphinoyl)phenoxy]biphenyl-4-yl}-9H-fluorene (DDPESPOF), 9,9-bis-{3'-(diphenylphosphinoyl)-4'-[2-(diphenylphosphinoyl)phenoxy]biphenyl-4-yl}-9H-fluorene (DDPEPOF), 9-[4'-(9-{4'-[2-(diphenylphosphoryl)phenoxy]biphenyl-4-yl}-9H-fluoren-9-yl)biphenyl-4-yl]-9H-carbazole (DPESPOFPhCz) and 9-[4'-(9-{3'-(diphenylphosphoryl)-4'-[2-(diphenylphosphoryl)phenoxy]biphenyl-4-yl}-9H-fluoren-9-yl)biphenyl-4-yl]-9H-carbazole (DPEPOFPhCz). The last two are quaternary with fluorenyls as linking bridges, diphenylphosphine oxide (DPPO) moieties as electron acceptors and diphenylethers and carbazolyls as two different kinds of electron donors. Owing to the fine-organised molecular structures and the mixed indirect and multi-insulating linkages, all of these hosts achieve the same first triplet energy levels (T1) of 2.86 eV for exothermic energy transfer to phosphorescent dopants. The first singlet energy levels (S1) and the carrier injection/transportation ability of the hosts were accurately modulated, so that DPESPOFPhCz and DPEPOFPhCz revealed extremely similar optoelectronic properties. However, the T1 state of the former is localised on fluorenyl, whereas the carbazolyl mainly contributes to the T1 state of the latter. A lower driving voltages and much higher efficiencies of the devices based on DPESPOFPhCz indicated that the chromophore-localised T1 state can suppress the quenching effects through realising independent contributions from the different functional groups to the optoelectronic properties and the embedding and protecting effect on the T1 states by peripheral carrier transporting groups. PMID:23766090

Zhang, Zhen; Zhang, Zhensong; Chen, Runfeng; Jia, Jilin; Han, Chunmiao; Zheng, Chao; Xu, Hui; Yu, Donghui; Zhao, Yi; Yan, Pengfei; Liu, Shiyong; Huang, Wei

2013-07-15

213

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

NASA Astrophysics Data System (ADS)

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

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

1995-07-01

214

Oxygen uptake induced by electron transfer from donors to the triplet state of methylene blue and xanthene dyes in air-saturated aqueous solution.  

PubMed

The effects of oxygen in the photolysis of rose bengal, eosin, erythrosin and methylene blue were studied in the presence of formate and electron donors, such as ascorbic acid, aromatic amino acids or aliphatic amines, e.g. triethylamine (TEA). The overall reaction is conversion of oxygen via the hydroperoxyl/superoxide ion radical into hydrogen peroxide. The quantum yield of oxygen uptake (Phi(-O2)) increases with the donor concentration. The photoinduced formation of H2O2 is initiated by quenching of the triplet state of the dye by the donor and subsequent reactions of both the dye and donor radicals with oxygen. For methylene blue and the xanthene dyes in the presence of 10 mM ascorbic acid or 0.1 M TEA Phi(-O2)=0.07-0.25. The spectral and kinetic properties of the specific dye transients, including the radicals involved and the pH and concentration dependences, are discussed. PMID:18389155

Görner, Helmut

2008-03-01

215

Roles of singlet oxygen and triplet excited state of dissolved organic matter formed by different organic matters in bacteriophage MS2 inactivation.  

PubMed

Inactivation of bacteriophage MS2 by reactive oxygen species (ROS) and triplet excited state of dissolved organic matter ((3)DOM*) produced by irradiation of natural and synthetic sensitizers with simulated sunlight of wavelengths greater than 320 nm was investigated. Natural sensitizers included purified DOM isolates obtained from wastewater and river waters, and water samples collected from Singapore River, Stamford Canal, and Marina Bay Reservoir in Singapore. Linear correlations were found between MS2 inactivation rate constants (kobs) and the photo-induced reaction rate constants of 2,4,6-trimethylphenol (TMP), a probe compound shown to react mainly with (3)DOM*. Linear correlations between MS2 kobs and singlet oxygen ((1)O2) concentrations were also found for both purified DOM isolates and natural water samples. These correlations, along with data from quenching experiments and experiments with synthetic sensitizers, Rose Bengal (RB), 3'-methoxyacetophenone (3'-MAP), and nitrite [Formula: see text] , suggest that (1)O2, (3)DOM*, and hydroxyl radicals ((•)OH) could inactivate bacteriophage MS2. Linear correlations between MS2 kobs and Specific Ultraviolet Absorption determined at 254 nm (SUVA254) were also found for both purified DOM isolates and natural samples. These results suggest the potential use of TMP as a chemical probe and SUVA254 as an indicator for virus inactivation in natural and purified DOM water samples. PMID:23866126

Rosado-Lausell, Sahid L; Wang, Hanting; Gutiérrez, Leonardo; Romero-Maraccini, Ofelia C; Niu, Xi-Zhi; Gin, Karina Y H; Croué, Jean-Philippe; Nguyen, Thanh H

2013-09-15

216

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

PubMed

Singlet molecular oxygen ((1)O) can be a significant sink for a variety of electron-rich pollutants in surface waters and atmospheric drops. We recently found that (1)O concentrations are enhanced by up to a factor of 10(4) on illuminated ice compared to in the equivalent liquid solution, suggesting that (1)O could be an important oxidant for pollutants in snow. To examine this, here we study the degradation of three model organic pollutants: furfuryl alcohol (to represent furans), tryptophan (for aromatic amino acids), and bisphenol A (for phenols). Each compound was studied in illuminated aqueous solution and ice containing Rose Bengal (RB, a sensitizer for (1)O) and sodium chloride (to adjust the concentration of total solutes). The RB-mediated loss of each organic compound is enhanced on illuminated ice compared to in solution, by factors of 6400 for furfuryl alcohol, 8300 for tryptophan, and 50 for bisphenol A for ice containing 0.065 mM total solutes. Rates of loss of furfuryl alcohol and tryptophan decrease at a higher total solute concentration, in qualitative agreement with predictions from freezing-point depression. In contrast, the loss of bisphenol A on ice is independent of total solute concentration. Relative to liquid tests, the enhanced loss of tryptophan on ice during control experiments made with deoxygenated solutions and solutions in D2O show that the triplet excited state of Rose Bengal may also contribute to loss of pollutants on ice. PMID:24487942

Bower, Jonathan P; Anastasio, Cort

2014-03-27

217

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

PubMed

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

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

2013-12-01

218

Triplet-sensitized and thermal isomerization of all-trans, 7-cis, 9-cis, 13-cis, and 15-cis isomers of. beta. -carotene: Configurational dependence of the quantum yield of isomerization via the T sub 1 state  

SciTech Connect

The products of triplet-sensitized photoisomerization (excitation at 337 mn of the sensitizer, anthracene) and thermal isomerization of {beta}-carotene in {eta}-hexane, starting from the all-trans, 7-cis, 9-cis, 13-cis, and 15-cis isomers, were analyzed by HPLC. Direct photoisomerization (excitation at 488 and 337 mn) was also examined for comparison. Three different isomerization patterns were found in both triplet-sensitized and thermal isomerization: pattern A, cis to trans isomerization around each cis bond; pattern B, trans to cis isomerization in the central part of the conjugated chain; and pattern C, cis to another cis isomerization. In the T{sub 1} state, the pattern A isomerization was predominant even for the peripheral-cis (7-cis and 9-cis) isomers and its efficiency was extremely high for the central-cis (13-cis and 15-cis) isomers. In the S{sub 0} state, the pattern B isomerization, instead, was predominant for the peripheral-cis isomers, and the pattern A isomerization was predominant only for the central-cis isomers. The quantum yields of triplet-sensitized isomerization (decrease of the starting isomer per triplet species generated) were determined to be as follows: all-trans, 0.04; 7-cis, 0.12; 9-cis, 0.15; 13-cis, 0.87; and 15-cis, 0.98. Carbon-carbon {pi} bond orders of model polyenes in the T{sub 1} and S{sub 0} states were calculated by using the Pariser-Parr-Pople CI theory; bond lengths were optimized by using a bond order-bond length relationship. Isomerization characteristics in the T{sub 1} and S{sub 0} states observed were discussed based on the results of the calculations.

Kuki, Michitaka; Koyama, Yasushi (Kwansei Gakuin Univ., Uegahara (Japan)); Nagae, Hiroyoshi (Kobe City Univ. of Foreign Studies (Japan))

1991-09-19

219

Geometry and bonding in the ground and lowest triplet state of D6h symmetric crenellated edged C 6[3m(m-1)+1]H 6(2m-1) ( m = 2, … , 6) graphene hydrocarbon molecules  

NASA Astrophysics Data System (ADS)

Ab initio plane wave all valence electron based DFT calculations were used to explore the dichotomy of perimeter vs. interior in the electronic and geometric structure of the D6h singlet ground state and D2h lowest triplet state of planar graphene hydrocarbon molecules with crenellated (arm chair) edges and the general formula C 6[3m(m-1)+1] H 6(2m-1) where m = 2, … , 6. The largest molecule C 546H 66 was 4.78 nm across and contained 2250 valence electrons. These molecules are nominally "fully benzenoid hydrocarbons". However with increasing size, the core of central atoms abandoned any fully benzenoid geometry they had in small systems and organized into single layer graphite (graphene) structure. The perimeter atoms of the crenellation adopted a conjugated geometry with unequal bonds and between core and perimeter there were some C 6 rings retaining remnants of aromatic sextet-type properties. Compared to a zigzag edge the crenellated edge conferred stability in all the systems studied as measured by the singlet homo-lumo level gap BG 0 and the singlet-lowest triplet energy gap ? EST. For the largest crenellated system ( m = 6) BG 0 and ? EST were approximately 0.7 eV, larger in value than for similarly sized hexagonal graphenes with zigzag edges. Triplet states were identified for all the molecules in the series and in the case of the m = 2 molecule hexabenzocoronene C 42H 18, two conformations with D2h symmetry were identified and compared to features on the triplet state potential energy surface of benzene.

Philpott, Michael R.; Kawazoe, Yoshiyuki

2009-03-01

220

Triplet states in reaction center, light-harvesting complex B875 and its spectral form B840 from Rubrivivax gelatinosus investigated by absorbance-detected electron spin resonance in zero magnetic field (ADMR)  

Microsoft Academic Search

Absorbance-detected magnetic resonance (ADMR) spectroscopy was used for characterization of the triplet states in several pigment-protein complexes from Rubrivivax gelatinosus, namely the isolated reaction center, the core light-harvesting complex B875, and the B875 subunit form that absorbs in the infrared at 820 nm (B820), and, in the presence of glycerol, at about 840 nm (B840). The zero-field splitting parameters of

Vladimira Jirsakova; Françoise Reiss-Husson; Ileana Agalidis; Jacobine Vrieze; Arnold J. Hoff

1995-01-01

221

Off-centre effects in the triplet relaxed excited state of impurity ns2 ions in alkali halides  

Microsoft Academic Search

An off-centre displacement of an excited ns2 ion from a crystal lattice site is studied for Ga+, In+ and TI+ centres in alkali halides at 0.09-5 K by the time-resolved polarization spectroscopy method. A theory is developed, which considers the off-centre effects as a result of the mixing of the impurity 3nsnp and 3npnp excited states by T1u vibrations.

V. Hizhnyakov; K. Kalder; V. Korrovits; V. Nagirnyi; A. Stolovich; S. Zazubovich

1995-01-01

222

Peculiarities of the triplet relaxed excited-state structure and luminescence of a CsI:Tl crystal  

Microsoft Academic Search

Four emission bands, all belonging to the main thallium centres, have been detected in CsI:Tl, and their spectral, polarization and kinetic characteristics have been studied at 0.35-320 K. A new model is proposed for the excited states responsible for the luminescence of thallium-doped caesium iodide. In this model, the main thallium centre is considered as a cluster consisting of a

V. Nagirnyi; A. Stolovich; S. Zazubovich; V. Zepelin; E. Mihokova; E. Nikl; G. P. Pazzi; L. Salvini

1995-01-01

223

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

Microsoft Academic Search

A molecular triad consisting of a diarylporphyrin (P) covalently linked to a carotenoid polyene (C) and a fullerene (Cââ) has been prepared and studied using time-resolved spectroscopic methods. In 2-methyltetrahydrofuran solution, the triad undergoes photoinduced electron transfer to yield C-P{sup .+}-Cââ{sup .-}, which evolves into C{sup .+}-P-Cââ{sup .-} with an overall quantum yield of 0.14. This state decays by charge

Paul A. Liddell; Darius Kuciauskas; John P. Sumida; Boaz Nash; Dorothy Nguyen; Ana L. Moore; Thomas A. Moore; Devens Gust

1997-01-01

224

Triplet absorption in carbon nanotubes: a TD-DFT study  

Microsoft Academic Search

We predict properties of triplet excited states in single-walled carbon\\u000ananotubes (CNTs) using a time-dependent density-functional theory (TD-DFT). We\\u000ashow that the lowest triplet state energy in CNTs to be about 0.2-0.3 eV lower\\u000athan the lowest singlet states. Like in $\\\\pi$-conjugated polymers, the lowest\\u000aCNT triplets are spatially localized. These states show strong optical\\u000aabsorption at about 0.5-0.6 eV

Sergei Tretiak

2007-01-01

225

A new phosphine oxide host based on ortho-disubstituted dibenzofuran for efficient electrophosphorescence: towards high triplet state excited levels and excellent thermal, morphological and efficiency stability.  

PubMed

An efficient host for blue and green electrophosphorescence, 4,6-bis(diphenylphosphoryl)dibenzofuran (o-DBFDPO), with the structure of a short-axis-substituted dibenzofuran was designed and synthesised. It appears that the greater density of the diphenylphosphine oxide (DPPO) moieties in the short-axis substitution configuration effectively restrains the intermolecular interactions, because only very weak ?-? stacking interactions could be observed, with a centroid-to-centroid distance of 3.960 Å. The improved thermal stability of o-DBFDPO was corroborated by its very high glass transition temperature (T(g)) of 191 °C, which is the result of the symmetric disubstitution structure. Photophysical investigation showed o-DBFDPO to be superior to the monosubstituted derivative, with a longer lifetime (1.95 ns) and a higher photoluminescent quantum efficiency (61 %). The lower first singlet state excited level (3.63 eV) of o-DBFDPO demonstrates the stronger polarisation effect attributable to the greater number of DPPO moieties. Simultaneously, an extremely high first triplet state excited level (T(1)) of 3.16 eV is observed, demonstrating the tiny influence of short-axis substitution on T(1). The improved carrier injection ability, which contributed to low driving voltages of blue- and green-emitting phosphorescent organic light-emitting diodes (PHOLEDs), was further confirmed by Gaussian calculation. Furthermore, the better thermal and morphological properties of o-DBFDPO and the matched frontier molecular orbital (FMO) levels in the devices significantly reduced efficiency roll-offs. Efficient blue and green electrophosphorescence based on the o-DBFDPO host was demonstrated. PMID:21714018

Han, Chunmiao; Xie, Guohua; Li, Jing; Zhang, Zhensong; Xu, Hui; Deng, Zhaopeng; Zhao, Yi; Yan, Pengfei; Liu, Shiyong

2011-08-01

226

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

NASA Astrophysics Data System (ADS)

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

Jain, Sonal Kumar; Bhardwaj, Anil

2012-07-01

227

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

PubMed

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

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

2013-03-01

228

Evidence for molecular distortion involving the carbonyl group in triplet states of carbonyl derivatives of naphthalene obtained from time resolved vibrational spectroscopic studies  

Microsoft Academic Search

The C?O stretching vibration appears in the infrared spectra of 2-naphthaldehyde (1), 2-acetonaphthone (2), 2-naphthoic acid (3), methyl2-naphthaoate (4) and 1,2-dihydro-3H-benz[e]inden-3-one (5) in the state T1(???) between 1600 and 1700 cm?1. There is a strong line in the Raman spectrum of 1–5 in the state S0 arising from the C?O stretching mode, but such a line is lacking in their

M. J. van der Burgt; A. H. Huizer; C. A. G. O. Varma; B. D. Wagner; J. Lustztyk

1995-01-01

229

Triplet Sampled Radiation damage  

Microsoft Academic Search

The emission produced by mutual annihilation of a pair of triplet excitons in single crystalline anthracene was observed to be an indicator of low level gamma-ray dose. Under steady red light illumination the blue emission intensiv Fr is related to gamm-ray dose D by F = a + bD in the range 300R to 10R. Independent measurements show the effect

S. Z. Weisz; P. Richardson; A. Cobas; R. C. Jarnagin

1968-01-01

230

Triplet dark matter from leptogenesis  

NASA Astrophysics Data System (ADS)

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

Heo, Jae Ho; Kim, C. S.

2014-04-01

231

He-like triplets observed by RESIK  

NASA Astrophysics Data System (ADS)

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

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

232

Energy transfer from triplet acetophenones to 9,10-dibromoanthracene (S/sub 1/): role of its T/sub n/ state  

SciTech Connect

The efficiency of energy transfer to 9,10-dibromoanthracene (S/sub 1/) (DBA, 0.5-5 x 10/sup -4/ M) from triplet acetophenone, methyl-substituted acetophenones, and indanone (1) (0.02 M, E/sub T/ = 71.5-75.8 kcal) was measured as a function of temperature (1-57 /sup 0/C) in acetonitrile. The decay of DBA fluorescence follows double-exponential functions, with a ca. 2-ns component (direct DBA excitation) and a ca. 0.1-3-..mu..s component (sensitization by triplet ketone). The rate parameters are the same for ketones, but the amplitude of the slow component depends on the triplet energy of the ketone. With Phi/sub TS/ defined as k/sub TS//k/sub ET/, Phi/sub TS/ = 0.3 for 1 (E/sub T/ = 75.8 kcal) and 0.004 for 3,5-dimethylacetophenone (E/sub T/ = 71.5 kcal) at 20 /sup 0/C; DBA deactivates all triplet ketones with k/sub ET/ = 1.15 x 10/sup 10/ M/sup -1/ s/sup -1/. The temperature dependence of Phi/sub TS/ shows the involvement of DBA (T/sub n/), ca. 4 kcal above S/sub 1/, in a two-step exchange process: TT transfer to T/sub n/ (k/sub TTn/) and then isc T/sub n/ ..-->.. S/sub 1/. The E/sup a/ of k/sub TTn/ matches the gap between E/sub T/ and DBA (T/sub n/). Phi/sub TS/ of 1 is close to the limit set by the isc efficiency in DBA (ca. 0.3-0.4); thus, the 35-kcal exothermic triplet transfer to DBA (T/sub 1/) is unimportant compared with the near-isothermic transfer to T/sub n/.

Catalani, L.H.; Wilson, T.

1987-11-25

233

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

234

Mapping Agricultural Crops with AVIRIS Spectra in Washington State  

NASA Technical Reports Server (NTRS)

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

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

1998-01-01

235

Chemiluminescent emission spectra and possible upper-state potentials of KCl and KBr  

Microsoft Academic Search

Chemiluminescent optical spectra of potassium chloride and potassium bromide have been observed in dilute flames. In the KCl spectra 56 ``fluctuation bands'' could be resolved. A table of 66 such bands were measured for KBr, extending the observed spectral range by about 1000 Å to the red for this molecule. Possible upper-state potential curves accounting for the observations are proposed.

Kenneth J. Kaufmann; James L. Kinsey; Howard B. Palmer; Archibald Tewarson

1974-01-01

236

Electronic states and spectra of BiTe  

NASA Astrophysics Data System (ADS)

NIR/VIS emission spectra of the bismuth telluride radical, BiTe, were measured in the 3600-20 000 cm -1 region with a Fourier-transform spectrometer. BiTe was produced by reaction of bismuth and tellurium vapors and excited by energy transfer from metastable oxygen O 2( a1? g) in a fast-flow system. The spectrum of BiTe was found to be markedly different from those of the previously studied BiO, BiS and BiSe radicals. The A24? 1/2 ? X12? 1/2 transition which forms the most prominent and extended band system in these molecules was not observed for BiTe, and the X22? 3/2 ? X12? 1/2 fine structure transition shows up with a different structure and at much lower wavenumbers than in the spectra of the lighter bismuth chalcogenides. The only common feature is the C14? -1/2 ? X12? 1/2 system which is found in the range 16 500-19 000 cm -1 similar to the three other molecules. Besides the X2 ? X1 and C1 ? X1 systems, seven other transitions show up by short ? ? = 0 sequences only. With help of the data derived from the analyses of the X2 ? X1 and C1 ? X1 systems and theoretical predictions of electronic and vibrational energies and transition probabilities of the strongest transitions of BiTe by Lingott et al. [7] the spectra were assigned to the transitions C14? -1/2 ? X22? 3/2, C14? -1/2 ? A24? 1/2, A44? 1/2 ? A24? 1/2, A44? 1/2 ? X22? 3/2, B12? 1/2 ? A24? 1/2, B12? 1/2 ? A14? 3/2, and B22? 3/2 ? X22? 3/2.

Setzer, K. D.; Laufs, S.; Fink, E. H.

2010-09-01

237

Spin polarization in quantum Hall state obtained by Kerr rotation spectra  

SciTech Connect

We developed a novel system for a high sensitive measurement of Kerr rotation spectra, and Kerr rotation spectra of quantum Hall system in AlGaAs/GaAs 17 nm quantum well were measured. Spin polarization of quantum Hall states was obtained by integrating the spectra, since Kerr rotation spectra reflect spin population of electrons. The spin polarization decreased rapidly on both sides of {nu} = 1, which is ascribed to Skyrmion effect. However, the spin polarization present a flat region around {nu} = 1 which means a quantum Hall ferromagnet is not fully spin polarized.

Ito, H.; Seo, M.; Fukuoka, D.; Oto, K.; Muro, K. [Graduate School of Science, Chiba University, Chiba (Japan); Hirayama, Y. [Graduate School of Science, Tohoku University, Sendai (Japan); ERATO Nuclear Spin Electronics Project, Sendai (Japan); Kumada, N. [NTT Basic Research Laboratories, NTT Corporation, Atsugi (Japan)

2011-12-23

238

Chlorophyll triplet quenching and photoprotection in the higher plant monomeric antenna protein Lhcb5.  

PubMed

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

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

2013-09-26

239

Convergent modulation of singlet and triplet excited states of phosphine-oxide hosts through the management of molecular structure and functional-group linkages for low-voltage-driven electrophosphorescence.  

PubMed

The controllable tuning of the excited states in a series of phosphine-oxide hosts (DPExPOCzn) was realized through introducing carbazolyl and diphenylphosphine-oxide (DPPO) moieties to adjust the frontier molecular orbitals, molecular rigidity, and the location of the triplet excited states by suppressing the intramolecular interplay of the combined multi-insulating and meso?linkage. On increasing the number of substituents, simultaneous lowering of the first singlet energy levels (S(1)) and raising of the first triplet energy levels (T(1), about 3.0?eV) were achieved. The former change was mainly due to the contribution of the carbazolyl group to the HOMOs and the extended conjugation. The latter change was due to an enhanced molecular rigidity and the shift of the T(1) states from the diphenylether group to the carbazolyl moieties. This kind of convergent modulation of excited states not only facilitates the exothermic energy transfer to the dopants in phosphorescent organic light-emitting diodes (PHOLEDs), but also realizes the fine-tuning of electrical properties to achieve the balanced carrier injection and transportation in the emitting layers. As the result, the favorable performance of blue-light-emitting PHOLEDs was demonstrated, including much-lower driving voltages of 2.6?V for onset and 3.0?V at 100?cd?m(-2), as well as a remarkably improved E.Q.E. of 12.6%. PMID:23180464

Han, Chunmiao; Zhang, Zhensong; Xu, Hui; Xie, Guohua; Li, Jing; Zhao, Yi; Deng, Zhaopeng; Liu, Shiyong; Yan, Pengfei

2013-01-01

240

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

PubMed

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

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

2013-01-28

241

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

NASA Astrophysics Data System (ADS)

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

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

2013-01-01

242

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

NASA Astrophysics Data System (ADS)

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

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

2014-04-01

243

Possible Mass Enhancement by Multipole Fluctuations Excited via the Singlet--Triplet Crystal Electric Field States in PrOs4Sb12: Sb-NMR Studies Using a Single Crystal  

NASA Astrophysics Data System (ADS)

121,123Sb nuclear magnetic resonance (NMR) measurements of a high-quality single crystalline PrOs4Sb12 have been carried out in magnetic fields up to 98 kOe and in the temperature range of 0.4--30 K. From the analysis of the 121Sb Knight shift (K) and magnetic susceptibility at H? 90 kOe, the transferred hyperfine coupling constants (ATHF) are obtained. The Sb isotropic hyperfine coupling constant and anisotropic hyperfine coupling tensor are determined as ?27.6 Oe/?B and ?(149.9,42.3,-192.2) Oe/?B, respectively. The anisotropic part originates from the spin--dipolar field due to the local spin density at Sb 5p orbital transferred through the hybridization with 4f electrons. The results are consistent with the Sb12 5p molecular orbital with au symmetry predicted from the band structure calculation. ATHF for H\\parallel [001] is dependent on the magnetic field, suggesting the coupling of the Sb nuclear dipole moment with not only dipole moments but also octupole moments of the Pr 4f electrons with the same time reversal. The NMR relaxation rate depends both on magnetic field and temperature, and the temperature dependence of 1/T1 is explained by the phenomenological expression 1/(T1TATHF2)\\propto (1/T) \\exp[-?NMR(H)/T] with excitation gap ?NMR(H). Here, we found that ?NMR(H) is proportional to the largest excitation gap between ?1 and ?t- of the triplet ?4(2) state under the magnetic field. These results indicate that the crystal electric field (CEF) excitation and the degeneracy of the triplet state are important for understanding Sb-NMR results. It is strongly indicated that the mass enhancement in PrOs4Sb12 is caused by the scattering conduction electrons with multipole fluctuations via the singlet--triplet CEF excitation.

Tou, Hideki; Inaoka, Yoshihiko; Doi, Masahiro; Sera, Masafumi; Asaki, Kenji; Kotegawa, Hisashi; Sugawara, Hitoshi; Sato, Hideyuki

2011-07-01

244

Triplet exciton transport in the benzophenone-fluorene-naphthalene molecule  

NASA Astrophysics Data System (ADS)

Incoherent triplet-triplet energy transfer through the benzophenone-fluorene-naphthalene system is computationally investigated to determine triplet hopping rates. These rates have been previously measured experimentally and have also been estimated computationally. There are many complex steps associated with such a computational analysis, though, and earlier efforts resorted to a variety of semi-empirical modifications to the methods used in order to obtain results consistent with the experimental data. This has motivated an investigation in which best practice methods are applied to the system without any empirical adjustments. The calculation of triplet excitation energy and triplet-triplet electronic coupling are examined in detail using a range of computational methods from simple Density Functional Theory to the many-body Green function approach embodied in the Bethe-Salpeter Equation. This analysis includes an evaluation of the robustness of each method considered. Significantly, the investigation identifies the excited states of benzophenone as being extremely difficult to calculate using even the most advanced excitation methods, and a theory is presented as to why the molecule is both interesting and troublesome. The final rate estimates, without any empirical adjustments, are one to two orders of magnitude greater than those measured experimentally. This data, and the detailed methodological study supporting it, is expected to be helpful in future efforts to computationally scrutinize triplet exciton hopping.

McElfresh, Duncan C.

245

Charge prediction machine: tool for inferring precursor charge states of electron transfer dissociation tandem mass spectra.  

PubMed

Electron transfer dissociation (ETD) can dissociate highly charged ions. Efficient analysis of ions dissociated with ETD requires accurate determination of charge states for calculation of molecular weight. We created an algorithm to assign the charge state of ions often used for ETD. The program, Charge Prediction Machine (CPM), uses Bayesian decision theory to account for different charge reduction processes encountered in ETD and can also handle multiplex spectra. CPM correctly assigned charge states to 98% of the 13,097 MS2 spectra from a combined data set of four experiments. In a comparison between CPM and a competing program, Charger (ThermoFisher), CPM produced half the mistakes. PMID:19203245

Carvalho, Paulo C; Cociorva, Daniel; Wong, Catherine C L; Carvalho, Maria da Gloria da C; Barbosa, Valmir C; Yates, John R

2009-03-01

246

Mechanism and dynamics of intramolecular triplet state decay of 1-propyl-4-thiouracil and its ?-methyl-substituted derivatives studied in perfluoro-1,3-dimethylcyclohexane.  

PubMed

The absorption, phosphorescence and phosphorescence excitation spectra, phosphorescence quantum yields, and T(1) excited state lifetimes of four 4-thiouracil derivatives were measured for the first time in chemically inert and very weakly interacting perfluoro-1,3-dimethylcyclohexane at room temperature. The set of the 4-thiouracil derivatives comprises 1-propyl-4-thiouracil (PTU) and the related compounds having a methyl substituent at the position ? to the thiocarbonyl group, namely 1-propyl-4-thiothymine (PTT), 1,3-dimethyl-4-thiouracil (DMTU), and 1-methyl-3-trideuteriomethyl-4-thiouracil ([D(3)]DMTU). Quantitative information on the intramolecular decay of the T(1) excited state of the four 4-thiouracil derivatives is presented, and the mechanism and dynamics of this process are discussed. In the absence of self quenching and solvent induced deactivation, the T(1) decay of the four 4-thiouracil derivatives was dominated by intramolecular nonradiative processes (NR). The values of the rate constant k(NR) in DMTU and [D(3)]DMTU are about 4 times larger than that in PTT and about 3 times larger than that in PTU. The reasons for the enhanced nonradiative rate constant in DMTU are discussed. It is concluded that the faster rate of the nonradiative processes in DMTU is related to a larger contribution from mixing of the T(2) (n?*) state into the lowest energy T(1) (??*) state, as compared to the analogous coupling in PTU and PTT. This conclusion is supported by ab initio calculations performed at the EOM-CC2/aug-cc-pVDZ level of theory. The energy spacing between the T(2) (n?*) and T(1) (??*) states is estimated to be about 500, 1100, and 2000 cm(-1) for DMTU, PTU, and PTT, respectively. Among the three compounds in question, the predicted energy spacing is thus the smallest for DMTU. PMID:21594285

Wenska, Grazyna; Taras-Go?li?ska, Katarzyna; ?ukaszewicz, Adam; Burdzi?ski, Gotard; Koput, Jacek; Maciejewski, Andrzej

2011-08-01

247

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

248

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

NASA Astrophysics Data System (ADS)

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.

1993-05-01

249

Influence of an electric field on photostimulated states in NH4BPh4 films  

NASA Astrophysics Data System (ADS)

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

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

2012-10-01

250

Thomas-Fermi theory in a weak and locally uniform magnetic field and an electron-gas investigation of the electric and diamagnetic properties of the lowest triplet state of the hydrogen molecule  

SciTech Connect

This state, in which the electron spins of the constituent H atoms are parallel, is the simplest example of a nonbonding interaction between inert atoms or molecules. Of primary interest is the effect of the nonbonding interaction on the polarizability, diamagnetic susceptibility, and chemical shielding of the dimer in the range of internuclear distance where overlap effects, rather than long range forces, dominate. The approaches taken are applications and generalizations of the electron gas model of Gordon and Kim, which may be understood within the framework of density functional theory. In studying the electrical properties of the triplet, the author uses the Thomas-Fermi-Dirac approximation to Hohenberg and Kohn's universal density functional for the energy of an inhomogeneous electron gas with all parallel spins in its lowest energy state. In order to treat the magnetic properties of interacting closed shell species in the electron gas model, he derives a generalization of Thomas-Fermi applicable to a locally homogeneous electron gas in a nearly uniform magnetic field. In both cases the explicit B/sup 2/ contribution to the Dirac exchange correction is shown to diverge. With these electron gas theories, the polarizability and diamagnetic susceptibility tensors of the hydrogen triplet in the additive density approximation are calculated.

Cina, J.A.

1985-01-01

251

Crossing behavior of the singlet and triplet state of the negatively charged magnetoexciton in a GaAs/Al{sub 0.55}Ga{sub 0.45}As quantum well  

SciTech Connect

Polarized magnetophotoluminescence (MPL) measurements on a high-mobility {delta}-doped GaAs/Al{sub 0.55}Ga{sub 0.45}As single quantum well from 0 to 60 T at temperatures between 0.37 and 2.1 K are reported. In addition to the neutral heavy-hole magnetoexciton (X{sup 0}), the singlet (X{sub s}{sup -}) and triplet (X{sub t}{sup -}) states of the negatively charged magnetoexciton are observed in both polarizations. The energy-dispersive and time-resolved MPL data suggest that their development is fundamentally related to the formation of the neutral magnetoexciton. At a magnetic field of 40 T the singlet and the triplet states cross as a result of the role played by the higher Landau levels and higher-energy subbands in their energetic evolution, confirming theoretical predictions. We also observed the formation of two higher-energy peaks. One of them is completely right circularly polarized and its appearance can be considered a result of the electron-hole exchange interaction enhancement with an associated electron g factor of 3.7 times the bulk value. The other peak completely dominates the MPL spectrum at fields around 30 T. Its behavior with magnetic field and temperature indicates that it may be related to previous anomalies observed in the integer and fractional quantum Hall regimes. (c) 2000 The American Physical Society.

Munteanu, F. M. [National High Magnetic Field Laboratory-Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States) [National High Magnetic Field Laboratory-Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States); Department of Physics, Northeastern University, Boston, Massachusetts 02115 (United States); Kim, Yongmin [National High Magnetic Field Laboratory-Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States)] [National High Magnetic Field Laboratory-Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States); Perry, C. H. [National High Magnetic Field Laboratory-Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States) [National High Magnetic Field Laboratory-Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States); Rickel, D. G. [National High Magnetic Field Laboratory-Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States)] [National High Magnetic Field Laboratory-Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States); Simmons, J. A. [Sandia National Laboratory, Albuquerque, New Mexico 87185 (United States)] [Sandia National Laboratory, Albuquerque, New Mexico 87185 (United States); Reno, J. L. [Sandia National Laboratory, Albuquerque, New Mexico 87185 (United States)] [Sandia National Laboratory, Albuquerque, New Mexico 87185 (United States)

2000-02-15

252

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

253

The electronic spectrum of Si3 I: Triplet D3h system  

NASA Astrophysics Data System (ADS)

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

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

2012-05-01

254

Hydrogen triplet laser as a high average-power laser  

NASA Astrophysics Data System (ADS)

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

Barr, Thomas A.; McKnight, William B.

1993-05-01

255

Triplet extinction coefficients of some laser dyes I  

SciTech Connect

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

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

1988-07-15

256

Twins, Triplets, and Other Multiples  

MedlinePLUS

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

257

Electroweak corrections from triplet scalars  

NASA Astrophysics Data System (ADS)

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

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

2012-07-01

258

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

SciTech Connect

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

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

1989-07-27

259

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

NASA Astrophysics Data System (ADS)

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

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

2013-06-01

260

Quantitative solid-state NMR spectra of CO adsorbed from aqueous solution onto a commercial electrode  

SciTech Connect

In this communication we present quantitative, solid-state NMR spectra of CO adsorbed from solution onto a commercial Pt/C fuel cell electrode; the CO spectra are presented as a function of surface coverage, as modified by electrochemical oxidation of surface-bound CO. These data clearly portend the widespread application of quantitative solid-state NMR techniques for studies of practical electrochemical processes. In conclusion, we report quantitative {sup 13}C NMR spectra for CO adsorbed onto commercial Pt/C fuel cell electrodes. Each spectrum shown required approximately 14 h of instrument time to acquire; we are further optimizing both the NMR parameters and probe configuration for improved signal-to-noise ratios. The number and character of CO adsorption sites are clearly accessible via this approach; if used in conjunction with in situ potential control, the number of possible studies of potential-dependent processes appears to be vast. 6 refs., 2 figs.

Yahnke, M.S.; Rush, B.M.; Reimer, J.A.; Cairns, E.J. [Lawrence Berkeley National Lab., CA (United States)] [Lawrence Berkeley National Lab., CA (United States); [Univ. of California, Berkeley, CA (United States)

1996-12-04

261

Theoretical interpretation of the electroabsorption spectra of polyacene crystals. I. Role of Frenkel states  

Microsoft Academic Search

The recently proposed two-dimensional model of the coupling between the Frenkel and charge transfer (CT) excitations of a molecular crystal, successfully applied for the calculation of the electroabsorption (EA) spectra of polyacenes [Petelenz &etal;, J. Chem. Phys. 105, 4427 (1996)], is applied to probe the influence of different intramolecular excited states on the EA signal in the CT energy range.

Piotr Petelenz

1997-01-01

262

Two-magnon spectra and Ising anisotropy: The relationship between resonances and bound states  

Microsoft Academic Search

Earlier studies of two-magnon bound states are complemented by calculations of the full density of states of two-magnon excitations. An exact formulation is developed at T=0° K for the K-->=0 or Raman type of spectra corresponding to the excitation of two-spin deviations on the same or on nearest-neighbor sites for a ferromagnet with both exchange (Ising) and uniaxial (single-ion) anisotropies.

P. D. Loly; B. J. Choudhury

1976-01-01

263

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

264

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

PubMed

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

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

2013-08-19

265

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

PubMed

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

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

2013-11-28

266

New electronic spectra of the HCCl and DCCl A~-X~ vibronic bands  

NASA Astrophysics Data System (ADS)

The dispersed fluorescence spectra following the excitation of several A~<--X~ vibronic bands of HCCl and DCCl at visible wavelengths were successfully acquired in a discharge supersonic free jet expansion using an intensified charge-coupled device detector. The dispersed fluorescence spectra reveal more details of the X~1 A' state vibrational structure in these molecules than previous reports. Dispersed fluorescence spectra of all four isotopomers (HC35Cl, HC37Cl, DC35Cl, and DC37Cl) were obtained. These dispersed fluorescence spectra exhibit the vibrational structures up to ~6000 cm-1 above the zero-point level and determine the vibrational structures of HC37Cl and DC37Cl. Complete vibrational parameters including fundamental frequencies, anharmonicities, and coupling constants were determined for the HCCl/DCCl X~1 A' state. Furthermore, perturbations from the background triplet state a~3 A'' and emission to triplet state levels were observed in the spectra. The singlet-triplet energy gap from the zero-point level could be determined to be 2167 cm-1 (6.20+/-0.05 kcal/mol) in HCCl and to be 2187 cm-1 (6.25+/-0.05 kcal/mol) in DCCl. Additionally, some of the A~<--X~ excitation spectrum are reported for HCCl and DCCl.

Lin, Chia-Shih; Chen, Ying-En; Chang, Bor-Chen

2004-09-01

267

New electronic spectra of the HCCl and DCCl A-X vibronic bands.  

PubMed

The dispersed fluorescence spectra following the excitation of several A<--X vibronic bands of HCCl and DCCl at visible wavelengths were successfully acquired in a discharge supersonic free jet expansion using an intensified charge-coupled device detector. The dispersed fluorescence spectra reveal more details of the X(1) A(') state vibrational structure in these molecules than previous reports. Dispersed fluorescence spectra of all four isotopomers (HC(35)Cl, HC(37)Cl, DC(35)Cl, and DC(37)Cl) were obtained. These dispersed fluorescence spectra exhibit the vibrational structures up to approximately 6000 cm(-1) above the zero-point level and determine the vibrational structures of HC(37)Cl and DC(37)Cl. Complete vibrational parameters including fundamental frequencies, anharmonicities, and coupling constants were determined for the HCCl/DCCl X(1) A(') state. Furthermore, perturbations from the background triplet state a(3) A(") and emission to triplet state levels were observed in the spectra. The singlet-triplet energy gap from the zero-point level could be determined to be 2167 cm(-1) (6.20+/-0.05 kcal/mol) in HCCl and to be 2187 cm(-1) (6.25+/-0.05 kcal/mol) in DCCl. Additionally, some of the A<--X excitation spectrum are reported for HCCl and DCCl. PMID:15332963

Lin, Chia-Shih; Chen, Ying-En; Chang, Bor-Chen

2004-09-01

268

Linearized coherent states for Hamiltonian systems with two equidistant ladder spectra  

NASA Astrophysics Data System (ADS)

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

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

2014-05-01

269

Vibrational spectra of 1-methylthymine: matrix isolation, solid state and theoretical studies.  

PubMed

The infrared spectra of 1-methylthymine (1-MeT) in argon and nitrogen cryogenic matrices are presented, for the first time. The molecular structure, conformations, vibrational frequencies, infrared intensities and Raman scattering activities of 1-MeT have been calculated by the DFT(B3LYP), MP2 and HF methods using the D95V** basis set. The theoretically predicted intensity pattern of the IR and Raman bands has proved to be of great help in assigning the experimental spectra. Rigorous normal coordinate analysis has been performed, at each level of theory. The unequivocal and complete vibrational assignment for 1-MeT has been made on the basis of the calculated potential energy distribution (PED). Comparison of the experimental matrix isolation spectra with the theoretical results has revealed that the B3LYP method is superior to both the MP2 and HF methods in predicting the frequencies of uracil derivatives. The MP2 method consistently underestimates the frequencies of the out-of-plane gamma(C=O) and gamma(C-H) bending modes, while the HF method yields the reverse order of the frequencies of two nu(C=O) stretching vibrations. Investigation of the frequency shift of several bands, on passing from matrix isolation to solid state spectra, has provided information on the strength of intermolecular hydrogen bonding in the crystal of 1-MeT. Several ambiguities in the earlier assignments of the vibrational spectra of polycrystalline 1-MeT have been clarified. PMID:15248994

Morzyk-Ociepa, Barbara; Nowak, Maciej J; Michalska, Danuta

2004-07-01

270

Fluorescence and excitation spectra of the DO +, E1, and G1 states of the HgZn exciplex  

NASA Astrophysics Data System (ADS)

The high-lying DO +, E1, and G1 spin—orbit states of the HgZn exciplex were excited by pump and probe laser irradiation of a Hg?Zn vapor mixture in a quartz cell. The decays of these states gave rise to UV bound—free and visible bound—bound fluorescence spectra which were recorded with a monochromator, and scans of the probe dye laser produced excitation spectra in the region 4000-4600 Å. Four new spectra were recorded and analyzed, yielding molecular constants for the various states. The new data also led to improved assignments of some previously reported HgZn spectra.

Supronowicz, J.; Hegazi, E.; Atkinson, J. B.; Krause, L.

1994-05-01

271

The Pure Rotational Spectra of ZnO in the Excited a^{3}?_i State  

NASA Astrophysics Data System (ADS)

The pure rotational spectra of ZnO in the excited a^{3}?_i electronic state have been measured using direct absorption sub-millimeter techniques. This molecule was synthesized by reacting zinc vapor with N_2O in the presence of a DC discharge. Nine rotational transitions were recorded for the ^{64}ZnO, ^{66}ZnO, and ^{68}ZnO isotopomers in the v=0 state and data for the main isotopomer was measured in the v=1 state. All three spin components were observed for this state, each exhibiting lambda-doubling. The data were fit with a Hund case(a) Hamiltonian and rotational, spin-orbit, spin-spin, and lambda-doubling constants established. A bond length of 1.8436 Å was determined for this excited state, which is about 0.14 Å larger than that of the ground state.

Zack, L. N.; Pulliam, R. L.; Ziurys, L. M.

2009-06-01

272

Predicting the spin state of paramagnetic iron complexes by DFT calculation of proton NMR spectra.  

PubMed

Many transition-metal complexes easily change their spin state S in response to external perturbations (spin crossover). Determining such states and their dynamics can play a central role in the understanding of useful properties such as molecular magnetism or catalytic behavior, but is often far from straightforward. In this work we demonstrate that, at a moderate computational cost, density functional calculations can predict the correct ground spin state of Fe(ii) and Fe(iii) complexes and can then be used to determine the (1)H NMR spectra of all spin states. Since the spectral features are remarkably different according to the spin state, calculated (1)H NMR resonances can be used to infer the correct spin state, along with supporting the structure elucidation of numerous paramagnetic complexes. PMID:24823843

Borgogno, Andrea; Rastrelli, Federico; Bagno, Alessandro

2014-06-01

273

'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

274

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

PubMed

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

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

2014-06-19

275

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

PubMed Central

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

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

2013-01-01

276

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

PubMed

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

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

2009-08-01

277

Moment, energy, stress drop, and source spectra of western United States earthquakes from regional coda envelopes  

Microsoft Academic Search

We present a new method to estimate stable seismic source parameters, such as energy, moment, and Orowan stress drop, using regional coda envelopes from as few as one broadband station. We use the method to compute path- and site-corrected seismic moment-rate spectra for 117 recent western United States earthquakes. Empirical Green's function corrections were applied to our surface- and body-wave

Kevin Mayeda; William R. Walter

1996-01-01

278

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

PubMed

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

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

2012-10-26

279

Anorexia Nervosa in Identical Triplets  

Microsoft Academic Search

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

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

280

When You Are a Twin or Triplet  

MedlinePLUS

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

281

Resonance-enhanced multiphoton ionization of CH?Br?: Rydberg states, photofragmentation, and CH spectra.  

PubMed

Mass-resolved (2 + n) resonance-enhanced multiphoton ionization (REMPI) spectra of CH2Br2 in the two-photon resonance excitation region from 71?200 to 82?300 cm(-1) were recorded and analyzed. Spectral structures allowed characterization of new molecular Rydberg states. C*((1)D2) was found to be an important intermediate in the photodissociation processes. A broad spectral feature peaking at about 80?663 cm(-1) in the C(+) spectrum and frequently seen in related studies is reinterpreted and associated with switching between three- and two-photon ionization of C*((1)D2). Analysis of band structures due to transitions from the A(2)? state of CH* that were seen in the CH(+) and C(+) REMPI spectra allowed characterization of three electronic states of CH, assigned as E(2)?, D(2)?, and F(2)?(+), which clarifies a long-term puzzle concerning the energetics of the CH radical. Predissociation of the E, D, and F states to form C*((1)D2) occurs. Bromine atomic lines were observed and are believed to be associated with bromine atom formation via predissociation of CH2Br2 Rydberg states. PMID:24527983

Long, Jingming; Wang, Huasheng; Kvaran, Ágúst

2014-03-13

282

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

SciTech Connect

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

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

1980-10-01

283

Unifying darko-lepto-genesis with scalar triplet inflation  

NASA Astrophysics Data System (ADS)

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

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

2012-12-01

284

Moments of phonon density of states spectra and characteristic phonon temperatures of wide band gap materials  

NASA Astrophysics Data System (ADS)

We have re-digitized a variety of phonon density of states (PDOS) spectra, that have been published by different researchers for the wide band gap materials diamond, SiC, BN, AlN, GaN, ZnO, ZnS, and ZnSe, including calculations of the respective first- and second-order moments. 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%). Anticipated differences between phonon temperatures, eff, that are effective in controlling the observable temperature dependences of fundamental energy gaps and the respective average phonon temperatures, P, are seen to be throughout smaller than +/-10%. The estimated high-temperature limits of Debye temperatures, D(), are found to be significantly higher (by factors of order 1.4) than P. As a remarkable heuristic finding revealed by our numerical and analytical studies we can further state that, for SiC, AlN, GaN, ZnO, ZnS, and ZnSe, the individual D() values are nearly equal (within +/-5%) to the respective average optical (LO/TO) phonon temperatures pertaining to the upper sections of the corresponding PDOS spectra.

Pässler, Roland

2006-10-01

285

Tetrahydrobenzenes: Singlet-triplet separations and vibrational frequencies  

SciTech Connect

The energies and structures of the three tetradehydrobenzene (C{sub 6}H{sub 2}) isomers (ortho, meta, and para) were studied employing density functional theory (BLYP and B3LYP), complete active space SCF (CASSCF), and the coupled-cluster method with single, double (CCSD), and perturbative triple excitations [CCSD(T)] in conjunction with basis sets of up to triple-{zeta} plus double polarization quality. The meta isomer, 1,2,3,5-tetradehydrobenzene, is the most favorable cyclic isomer, but is 38 kcal mol{sup {minus}1} less stable than the hexatriyne C{sub 6}H{sub 2} global minimum. All of the cyclic isomers have singlet ground states, but these are less stable for the ortho and para isomers; hence, the singlet-triplet energy splittings for 1,2,4,5- and 1,2,3,4-tetradehydrobenzene are smaller than for ortho-benzyne. Harmonic vibrational frequency analyses [up to CCSD(T)/TZ2P] suggest that the {nu}{sub as}(C{triple{underscore}bond}C) vibration should be observable in the IR spectra of 1,2,4,5-tetradehydrobenzene at ca. 1,675 cm{sup {minus}1} but that this vibration might be too weak to be seen for 1,4-bis(trifluoromethyl)-2,3,5,6-tetradehydrobenzene.

Bettinger, H.F.; Schleyer, P.V.R.; Schaefer, H.F. III

1999-03-31

286

Coexistence of Triplet Superconductivity and Spin Density Waves  

NASA Astrophysics Data System (ADS)

We discuss the possibility of the coexistence of spin density waves (antiferromagnetism) and triplet superconductivity as a particular example of a broad class of systems where the interplay of magnetism and superconductivity is important. We focus on the case of quasi-one-dimensional metals, where it is known that antiferromagnetism is in close proximity to triplet superconductivity in the pressure versus temperature phase diagram. Over a range of pressures, we propose an intermediate nonuniform phase consisting of antiferromagnetic and triplet superconducting orders. In the coexistence region, we propose a flop transition in the spin density wave order parameter vector, which affects the nature of the superconducting state and leads to the appearance of several new phases.

Zhang, Wei; de Melo, C. A. R. Sá

2006-07-01

287

Coexistence of triplet superconductivity and spin density waves.  

PubMed

We discuss the possibility of the coexistence of spin density waves (antiferromagnetism) and triplet superconductivity as a particular example of a broad class of systems where the interplay of magnetism and superconductivity is important. We focus on the case of quasi-one-dimensional metals, where it is known that antiferromagnetism is in close proximity to triplet superconductivity in the pressure versus temperature phase diagram. Over a range of pressures, we propose an intermediate nonuniform phase consisting of antiferromagnetic and triplet superconducting orders. In the coexistence region, we propose a flop transition in the spin density wave order parameter vector, which affects the nature of the superconducting state and leads to the appearance of several new phases. PMID:16907607

Zhang, Wei; de Melo, C A R Sá

2006-07-28

288

Determination of peptide and protein ion charge states by fourier transformation of isotope-resolved mass spectra  

Microsoft Academic Search

We report an automated method for determining charge states from high-resolution mass spectra. Fourier transforms of isotope\\u000a packets from high-resolution mass spectra are compared to Fourier transforms of modeled isotopic peak packets for a range\\u000a of charge states. The charge state for the experimental ion packet is determined by the model isotope packet that yields the\\u000a best match in the

David L. Tabb; Manesh B. Shah; Michael Brad Strader; Heather M. Connelly; Robert L. Hettich; Gregory B. Hurst

2006-01-01

289

Steady-state and time-resolved fluorescence spectra for detection of colonic cancer  

NASA Astrophysics Data System (ADS)

The steady-state and time-resolved autofluorescence spectroscopic differences between normal and carcinomatous colonic tissues and the optimal excitation wavelengths were studied. The fluorescence excitation wavelengths varying form 260 to 540 nm were used to induce tissue autofluorescence, and the corresponding emission spectra were measured in the range from 280 to 800 nm. These spectra then can be assembled into an excitation -emission matrix (EEM). Significant changes in fluorescence intensity of excitation-emission matrices were observed between normal and tumor colonic tissues. Low NAD(P)H and FAD, and high protoporphyrin IX fluorescence characterize high-grade malignant tissue when compared with normal colonic tissue, and the most marked difference being at the excitation wavelengths of 340, 380, 460 and 540 nm. Furthermore, the average lifetimes for the normal and carcinomatous colonic tissues were about 4.12 and 18.8 ns, respectively. The promising applications of laser-induced autofluorescence for colonic tissue diagnosis are indicated.

Li, Buhong; Xie, Shusen; Zhang, Zhenxi

2005-07-01

290

Analysis of absorption spectra of the crystals for coherent radiation pumped solid state lasers  

NASA Astrophysics Data System (ADS)

Investigations of spectroscopic properties of yttrium-aluminium garnet Y3Al5O12 (YAG) doped with Ce, Pr, Nd, Sm, Eu, Ho, Er, Tm, Yb ions and Nd:YAG, Nd:SrLaGa3O7, Nd:SrLaAlO4, Nd:YVO4, Nd:LiYF4, Nd:PbMoO4, Nd:LGS, Nd:GGG, Nd:SVAP monocrystals have been realized. Absorption spectra of the monocrystals in the range 200 nm divided by 20 micrometers and the luminescence spectra in the range 200 divided by 800 nm were determined. Except for Pr:YAG, Sm:YAG, Eu:YAG and Pr,Yb:YAG in all other materials an appearance of strong absorption bands in the range of 780 divided by 840 nm has been stated what enabled to carry out an efficiency analysis of selective pumping with the use of GaAlAs laser diodes.

Mierczyk, Zygmunt; Kaczmarek, Slawomir; Kopczynski, Krzysztof

1996-04-01

291

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

NASA Astrophysics Data System (ADS)

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

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

2014-05-01

292

Heavy-electron superconductors, spin fluctuations, and triplet pairing  

Microsoft Academic Search

The interactions in heavy-electron fluctuating-valence metals are discussed. The conclusion is that the state is closely analogous to ''Brinkman-Rice'' Fermi liquids like ³He in which parallel-spin effective interactions are attractive and antiparallel interactions strongly repulsive; hence ''triplet'': actually odd-parity: superconductivity is the most likely possibility.

P. W. Anderson

1984-01-01

293

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

294

Vector triplets at the LHC  

NASA Astrophysics Data System (ADS)

Several popular extensions of the Standard Model predict extra vector fields that transform as triplets under the gauge group SU(2)L. These multiplets contain Z' and W' bosons, with masses and couplings related by gauge invariance. We review some model-independent results about these new vector bosons, with emphasis on di-lepton and lepton-plus-missing-energy signals at the LHC.

Lizana, Javier M.; Pérez-Victoria, Manuel

2013-11-01

295

Phase states of the gypsum thermal-annealing derivatives according to electron spin resonance spectra  

NASA Astrophysics Data System (ADS)

The electron spin resonance (ESR) spectra of SO{3/-} and SO{2/-} radical ions with a linewidth ? H ? 2.7 G and SO{3/-}( A 1) and SO{3/-}( A 2) centers with superhyperfine splitting due to the interaction with protons in platelike gypsum single crystals under X-ray irradiation have been analyzed at 25°C. Dehydrated regions with a radius >4 Å are revealed in gypsum. The ESR spectra of SO{3/-} radical ions and atomic hydrogen with ? H ? 0.3 G are found in the products of isothermal annealing of gypsum kept for 30 min after X-ray irradiation at 25°C. The dependences of the intensities of these spectra on the annealing temperature are studied in the range of 100-450°C. The temperature range of formation of ?- and ?-phase states of bassanite and ?-anhydrite are determined. The process of residual water redistribution between the channel systems of the ?- and ?-phase types of ?-CaSO4 in gypsum thermal derivatives is established.

Khasanov, R. A.; Nizamutdinov, N. M.; Khasanova, N. M.; Salimov, R. I.; Kadyrov, R. I.; Vinokurov, V. M.

2014-05-01

296

A singlet - triplet T+ based qubit  

NASA Astrophysics Data System (ADS)

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

Ribeiro, Hugo; Petta, Jason; Burkard, Guido

2010-03-01

297

Proflavin binding to poly(d(A-T)) and poly(d(A-br/sup 5/U))'' triplet state and temperature-jump kinetics  

SciTech Connect

The delayed fluorescence properties of proflavin have been exploited in studies of the excited-state binding kinetics of the dye to poly(d(A-T)) and its brominated analogue poly-d(A-br/sup 5/U)) at room temperature and pH 7. The two analyzed luminescence decay times of the DNA-dye complex are dependent on the total nucleic acid concentration. This dependence is shown to reflect a temporal coupling of the intrinsic delayed emission decay rates with the dynamic chemical kinetic binding processes in the excited state. Temperature-jump kinetic studies conducted on the brominated polymer and corresponding information on poly(d(A-T)) from a previous study provide complementary information about the ground state. The ground-state kinetic data are analyzed in terms of two alternative models incorporating series and parallel reaction schemes. A comparison of the ground- and excited-state kinetic parameters reveals that the external binding process is much stronger and the intercalation is much weaker in the excited state. That the excited-state data are only consistent with the series model suggests that delayed luminescence studies may provide a general tool for distinguishing between the two kinetic mechanisms.

Corin, A.F.; Jovin, T.M.

1986-07-01

298

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

SciTech Connect

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

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

1988-03-10

299

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

300

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

301

Environment effects on triplet-triplet energy transfer in DNA  

NASA Astrophysics Data System (ADS)

We present a quantum-chemical study of the impact of the environment on triplet exciton migration in polyA-polyT DNA sequences. Electronic couplings are estimated by combining the fragment excitation difference scheme with the polarizable continuum model. Conformational fluctuations are taken into account by considering 500 structures extracted from a classical molecular dynamics trajectory. In contrast to singlet transfer, we find that the environment effect is not strongly correlated with the coupling magnitude in vacuum, and can significantly enhance or reduce its value in individual conformations. Conformational averaging, however, leads to a net cancellation of medium effects on the overall transfer rate.

Curutchet, Carles; Voityuk, Alexander A.

2011-08-01

302

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

Microsoft Academic Search

In this dissertation, we present the study of spin-orbit perturbations between the A(2)^1 Sigma^+ and b(1)^3Pi _{o} states of the NaK molecule. A selected perturbed ro-vibrational level, A(2)^1 Sigma^+(v{s}{' },J^') - b(1)^3Pi_0(v {t}{'},J^ '), was excited from a specific level of the bound ground state, X(1)^1Sigma ^+(v^{''},J ^{''}), by a tunable, narrow-band, single-mode, cw dye-laser. Analyzing the spectrum of singlet

Hongqiao Sun

1992-01-01

303

Are Triplet Exciplexes Involved in (2 + 2) Photocycloaddition of Cyclic Enones to Alkenes,  

National Technical Information Service (NTIS)

There is no correlation between quantum yields for photocycloaddition of four representative cyclic enones to a variety of alkenes and rate constants for quenching of triplet states of these enones by the alkenes. Laser flash experiments show that electro...

D. I. Schuster G. E. Heibel P. B. Brown N. J. Turro C. V. Kumar

1988-01-01

304

Nature of the lowest energy excited state of a bis-phenanthroline [2]-catenand and its Cu(I), Ag(I) and Co(II) complexes  

NASA Astrophysics Data System (ADS)

The excited state absorption and emission spectra and lifetimes of a [2]-catenand made of two interlocked 30-membered rings (containing 2,9-dianisyl-1,10-phenanthroline-type coordinating moietes) and its Co 2+, Cu +, and Ag + complexes have been investigated in CH 2Cl 2 solution. The lowest energy excited state is established to be a triplet ligand-centered level for the Ag + complex and a triplet metal-to-ligand charge-transfer level for the Cu + complex. For the Co 2+ complex, where no emission or transient absorption can be observed, the lowest excited state is most likely to be a distorted triplet metal-centered level. No transient absorption can be observed for the lowest energy triplet excited state of the [2]-catenand in CH 2Cl 2 solution because of a fast reaction with solvent molecules.

Armaroli, Nicola; Rodgers, Michael A. J.; Ceroni, Paola; Balzani, Vincenzo; Dietrich-Buchecker, Christine O.; Kern, Jean-Marc; Bailal, Abdelhakim; Sauvage, Jean-Pierre

1995-08-01

305

Singlet-triplet superconducting quantum magnetometer  

NASA Astrophysics Data System (ADS)

Motivated by the recent experimental realization of a quantum interference transistor based on the superconducting proximity effect, we here demonstrate that the inclusion of a textured ferromagnet both strongly enhances the flux sensitivity of such a device and additionally allows for singlet-triplet switching by tuning a bias voltage. This functionality makes explicit use of the induced spin-triplet correlations due to the magnetic texture. Whereas the existence of such triplet correlations is well known, our finding demonstrates how spin-triplet superconductivity may be utilized for concrete technology, namely, to improve the functionality of ultrasensitive magnetometers.

Alidoust, Mohammad; Halterman, Klaus; Linder, Jacob

2013-08-01

306

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

307

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

NASA Astrophysics Data System (ADS)

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

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

2004-01-01

308

Triplet energy transfer in photoexcited diketones  

SciTech Connect

The rate at which excitation energy transfers between chromophores of diketones was investigated. Energy transfer (ET) was induced by irradiation of the diketones with 313nm and 366nm ultraviolet light. The most significant aspect of this work is the assignment of rates for both exothermic and endothermic ET between the chromophores of a diketone molecule. By varying the most influential factors which determine ET rates, the difference in energy between the triplet excited states of each chromophore ([Delta]E) and the length of the alkyl tether linking the chromophores, two trends emerged. First, as the [Delta]E increased between two interacting chromophores within a given bichromophoric series of compounds, exothermic ET increased and endothermic ET decreased. Second,as the alkyl tether length connecting the two chromophores increased, both the exothermic and endothermic ET rates decreased. Intramolecular ET rates were derived by fitting the experimental photokinetic data with mathematical models.

Francesco, J.V.

1992-01-01

309

Pariser-Parr-Pople model based investigation of ground and low-lying excited states of long acenes.  

PubMed

Several years ago, Angliker et al. [ Chem. Phys. Lett. 1982 , 87 , 208 ] predicted nonacene to be the first linear acene with the triplet state 1(3)B2u as the ground state, instead of the singlet 1(1)Ag state. However, contrary to that prediction, in a recent experimental work, Tönshoff and Bettinger [ Angew. Chem. Int. Ed. 2010 , 49 , 4125 ] demonstrated that nonacene has a singlet ground state. Motivated by this experimental finding, we decided to perform a systematic theoretical investigation of the nature of the ground and the low-lying excited states of long acenes, with an emphasis on the singlet-triplet gap, starting from naphthalene, all the way up to decacene. The methodology adopted in our work is based upon the Pariser-Parr-Pople model (PPP) Hamiltonian, along with the large-scale multireference singles-doubles configuration interaction (MRSDCI) approach. Our results predict that even though the singlet-triplet gap decreases with the increasing conjugation length, nevertheless, it remains finite till decacene, thus providing no evidence of the predicted singlet-triplet crossover. We also analyze the nature of many-particle wave function of the correlated singlet ground state and find that the longer acenes exhibit a tendency toward an open-shell singlet ground state. Moreover, when we compare the experimental absorption spectra of octacene and nonacene with their calculated singlet and triplet absorption spectra, we observe excellent agreement for the singlet case. Hence, the optical absorption results also confirm the singlet nature of the ground state for longer acenes. Calculated triplet absorption spectra of acenes predict two well-separated intense long-axis polarized absorptions, against one such peak observed for the singlet case. This is an important prediction regarding the triplet optics of acenes, which can be tested in future experiments on oriented samples. PMID:24308558

Chakraborty, Himanshu; Shukla, Alok

2013-12-27

310

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

311

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

Microsoft Academic Search

We demonstrate highly efficient white and nonwhite hybrid organic light-emitting diodes (OLEDs) in which singlet and triplet excited states, generated in the recombination zone, are utilized by fluorescence and phosphorescence, respectively. The excited states are formed at a blue fluorescent light-emitting layer (LEL), and the triplets diffuse through a spacer layer to one or more phosphorescent LEL(s). A key feature

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

2010-01-01

312

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

NASA Astrophysics Data System (ADS)

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

Bhardwaj, Anil; Jain, Sonal Kumar

2012-04-01

313

Multiband coupling effect on density of states and tunneling conductance spectra of ferromagnetic material  

NASA Astrophysics Data System (ADS)

The electronic density of states (DOS) of ferromagnetic materials are theoretically studied within a two-band approach in one-dimensional (1D), two-dimensional (2D), and three-dimensional (3D) systems. In the two-band approximation, s-band and d-band coupling were considered. It has been found that if the coupling vanishes, the two bands can cross at some points in the energy spectra. When the coupling between bands is present, a gap is opened up at the corresponding point, thereby avoiding crossovers. The size of the gap depends on the size of the coupling strength. For any dimensionality, the DOS with no coupling behaves like a one-band model. When presenting the coupling strength, there is a change in the slope in the DOS, corresponding to those crossing points. In particular, this change is most prominent when the coupling strength is small and it almost disappears when the coupling strength is strong. With a large coupling strength, the energy band is extended. Finally, the measurable tunneling conductance spectra of a metal/ferromagnet junction within this approximation were clearly analyzed.

Pasanai, K.

2014-05-01

314

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

NASA Astrophysics Data System (ADS)

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

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

2014-05-01

315

Charge Prediction Machine: A tool for inferring precursor charge states of Electron Transfer Dissociation tandem mass spectra  

PubMed Central

Electron Transfer Dissociation (ETD) can dissociate highly charged ions. Efficient analysis of ions dissociated with ETD requires accurate determination of charge states for calculation of molecular weight. We created an algorithm to assign the charge state of ions often used for ETD. The program, Charge Prediction Machine (CPM), uses Bayesian decision theory to account for different charge reduction processes encountered in ETD, and can also handle multiplex spectra. CPM correctly assigned charge states to 98% of the 13,097 MS2 spectra from a combined dataset of four experiments. In a comparison between CPM and a competing program, Charger (ThermoFisher), CPM produced half the mistakes.

Carvalho, Paulo C; Cociorva, Daniel; Wong, Catherine; Carvalho, Maria da Gloria da C; Barbosa, Valmir C; Yates, John R

2010-01-01

316

Perturbations in the Spectra of High Rydberg States: Channel Interactions, Stark and Zeeman Effects  

NASA Astrophysics Data System (ADS)

Rydberg states of principal quantum number n?50 have been prepared by irradiation of an atomic beam of xenon with vacuum ultraviolet (VUV) radiation. Narrowband submillimeter-wave (THz) radiation was then used to record spectra of transitions from these Rydberg states to higher or lower-lying Rydberg states. The transitions were detected by selective field ionization and recording either the electrons or the ions, the latter offering the advantage of mass selection. Rydberg states of high principal quantum number are extremely sensitive to their environment, which can be exploited to characterize the experimental conditions under which the spectroscopic measurements are carried out. The high resolution achieved in the experiments (better than 100 kHz) enabled the study of the spectral lineshapes and line positions in dependence of weak electric (down to below 100?V/cm) and magnetic fields (down to a few ?T), and of the density of Rydberg atoms and ions generated in the experimental volume. The experiments rely on the use of a pulsed, broadly tunable, laser-based source of THz radiation for survey scans, and of a phase- and frequency-stabilized submillimeter-wave backward-wave oscillator-based radiation source for precision measurements. To illustrate the use of these sources, we present the results of the spectroscopic investigations of the hyperfine structure of 129Xe Rydberg states in spectral regions where s-d interactions are expected to play a role. F. Merkt and A. Osterwalder Int. Rev. Phys. Chem. 21, 385, (2002). J. Liu and F. Merkt Appl. Phys. Lett. 93, 131105, (2008). M. Schäfer, M. Andrist, H. Schmutz, F. Lewen, G. Winnewisser and F. Merkt J. Phys. B: At. Mol. Opt. Phys. 39, 831, (2006).

Haase, Christa; Schäfer, Martin; Hogan, Stephen D.; Merkt, Frédéric

2011-06-01

317

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

NASA Astrophysics Data System (ADS)

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

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

2012-06-01

318

Dominant second harmonic in the Josephson current--phase relation: Manifestation of the long-range spin-triplet proximity effect in SFF'S junctions  

NASA Astrophysics Data System (ADS)

We present theoretical study of the Josephson effect and pairing correlations in planar SFF'S junctions that consist of conventional superconductors connected through two metallic monodomain ferromagnets. Both singlet and triplet pair amplitudes, the Josephson current-phase relations, and density of states for arbitrary orientation of magnetizations are calculated from the self-consistent solutions of Eilenberger equations in the clean limit and for moderate disorder in ferromagnets. We find that in highly asymmetric SFF'S junctions the long-range spin-triplet proximity effect manifests itself as a dominant second harmonic in the Josephson current-phase relation [1] and gives distinctive tunneling conductance spectra [2]. Unambiguous detection of the long-range spin-triplet proximity effect by tunneling spectroscopy and experimental realization of the Josephson junctions ground state degeneracy (like at 0-pi transtions) is accessible for small interface roughness and moderate disorder in ferromagnets at low temperatures. [4pt] [1] L. Trifunovic, Z. Popovic and Z. Radovic, Phys. Rev. B 84, 064511 (2011).[0pt] [2] M. Knezevic, L. Trifunovic, and Z. Radovic (to be published).

Radovic, Zoran; Trifunovic, Luka; Knezevic, Milos

2012-02-01

319

A time-resolved resonance Raman study of the T[sub 1] excited state of zinc(II) octaalkylporphyrins  

Microsoft Academic Search

The T[sub 1] excited states of zinc(II) octaethylporphyrin (ZnOEP) and zinc(II) etioporphyrin I (ZnEtio) have been studied by nanosecond time-resolved resonance Raman spectroscopy. The spectra reveal identical features for both compounds, which we attribute to the lowest-lying triplet state. Slight downshifts of C[sub [beta

R. Kumble; S. Hu; G. R. Loppnow; S. E. Vitols; T. G. Spiro

1993-01-01

320

A time-resolved resonance Raman study of the T[sub 1] excited state of zinc(II) octaalkylporphyrins  

SciTech Connect

The T[sub 1] excited states of zinc(II) octaethylporphyrin (ZnOEP) and zinc(II) etioporphyrin I (ZnEtio) have been studied by nanosecond time-resolved resonance Raman spectroscopy. The spectra reveal identical features for both compounds, which we attribute to the lowest-lying triplet state. Slight downshifts of C[sub [beta

Kumble, R.; Hu, S.; Loppnow, G.R.; Vitols, S.E.; Spiro, T.G. (Princeton Univ., NJ (United States))

1993-10-14

321

Higgs data confronts sequential fourth generation fermions in the Higgs triplet model  

NASA Astrophysics Data System (ADS)

We investigate the effect of introducing a sequential generation of chiral fermions in the Higgs triplet model with nontrivial mixing between the doublet and triplet Higgs. We use the available Large Hadron Collider data for Higgs boson production and decay rates, the constraints on the fourth generation masses, and impose electroweak precision constraints from the S, T and U parameters. Our analysis shows that a standard model (SM)-like Higgs boson state at ˜125 GeV can be accommodated in the Higgs triplet model with four generations, and thus, that four generations survive collider and electroweak precision constraints in models beyond SM.

Banerjee, Shankha; Frank, Mariana; Rai, Santosh Kumar

2014-04-01

322

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

323

Perturbations to the intersystem crossing of proflavin upon binding to DNA and poly d(A-IU) from triplet-delayed emission spectroscopy.  

PubMed Central

The steady-state prompt fluorescence, phosphorescence and delayed fluorescence spectra and triplet lifetimes of free proflavin and proflavin bound to native DNA and alternating poly d(A-IU) were obtained as a function of temperature in a buffer-glycerol solvent. The intensity of the proflavin E-type delayed fluorescence (DF) relative to both the phosphorescence (Ph) and the prompt fluorescence (F) was observed to increase with temperature, and plots of both ln (DF/Ph) and ln (DF/(F.tau T] as a function of 1/T were linear over a wide range of temperatures. Although the activation energies for the thermal repopulation of the proflavin excited singlet state from the triplet obtained from the slopes of these plots were essentially unchanged on binding, perturbations to the S1----T1 intersystem crossing rate constants extracted from the intercepts at infinite temperature were observed. The marked enhancement of the intersystem crossing that occurs with binding to the iodinated polynucleotide reflects an external heavy atom perturbation upon the intercalated dye which also induces a shortening in the triplet lifetime. With proflavin bound to DNA an enhancement to the S1----T1 intersystem crossing, though lesser in magnitude than for poly d(A-IU), is observed but with no change to the triplet lifetime. The well-studied fluorescence quenching of DNA-bound proflavin is a result of this increase in the intersystem crossing. It is proposed that these non-heavy atom enhancements in the intersystem crossing are due to distortions of the molecular plane of the bound proflavin molecule. In total these analyses provide a complete description of the excited state processes of the proflavin molecule and their variations with temperature.

Lee, W E; Galley, W C

1988-01-01

324

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

NASA Astrophysics Data System (ADS)

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

Zapata, Felipe; Marazzi, Marco; Castaño, Obis; Acuña, A. Ulises; Frutos, Luis Manuel

2014-01-01

325

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

326

Kinetics and energetics of triplet energy transfer in reaction centers from (ital Rhodobacter sphaeroides) 2.4.1.  

National Technical Information Service (NTIS)

The triplet energy transfer reaction that generates the first excited triplet state of spheroidene, (sup 3)C, in reaction centers from Rhodobacter spheroides has been examined. The formation of (sup 3)C occurs by two processes; one prompt and at a rate in...

S. V. Kolaczhowski M. K. Bowman J. R. Norris

1991-01-01

327

Singlet-triplet interaction in Group 2 M2O hypermetallic oxides  

NASA Astrophysics Data System (ADS)

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

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

2014-07-01

328

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

USGS Publications Warehouse

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

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

1980-01-01

329

Pulse radiolysis study of the triplet sensitized production of singlet oxygen: determination of energy transfer efficiences  

Microsoft Academic Search

The technique of pulse radiolysis has been used to produce aromatic and aromatic carbonyl triplet states in liquid benzene. The quenching of such triplets by Oâ(³SIGMA\\/sub g\\/⁻) leads to the production of singlet oxygen (¹..delta..\\/sub g\\/), the subsequent reactivity of which has been followed by time-resolved observation of the bleaching of diphenylisobenzofuran (DPBF). Measurement of quenching rate constants together with

A. A. Gorman; G. Lovering; M. A. J. Rodgers

1978-01-01

330

The biomolecule of 5-bromocytosine: FT-IR and FT-Raman spectra and DFT calculations. Identification of the tautomers in the isolated state and simulation the spectra in the solid state  

NASA Astrophysics Data System (ADS)

An accurate assignment of the IR spectrum in Ar matrix of 5-bromocytosine and of the IR and Raman spectra in the solid state was carried out. For this purpose Density functional calculations (DFTs) were performed to clarify wavenumber assignments of the experimental observed bands. The calculated values were scaled using scaling equations and they were compared with IR and Raman experimental data. Good reproduction of the experimental wavenumbers is obtained and the% error is very small in the majority of cases. In the isolated state all the tautomer forms of 5-bromocytosine were determined and optimized. The wavenumbers corresponding to C1 and C2b tautomers were identified and assigned in the IR experimental spectrum reported in Ar matrix. Our study confirms the existence of at least two tautomers, the amino-oxo and the amino-hydroxy in the isolated state. In the solid state the FT-IR and FT-Raman spectra of 5-bromocytosine in the powder form were recorded in the region 400-4000 cm-1 and 50-3500 cm-1, respectively. The unit cell found in the crystal was simulated as a tetramer form in three tautomers. Thus, it has been possible to assign all the 33 normal modes of vibration. The study indicates that the features, that are the characteristic of the vibrational spectra of cytosine, are retained by the spectra of 5-bromocytosine and it exists in the solid phase in the amino-oxo form.

Alcolea Palafox, M.; Rastogi, V. K.; Kumar, Satendra; Joe, Hubert

2013-07-01

331

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

332

Cooper pairs spintronics in triplet spin valves.  

PubMed

We study a spin valve with a triplet superconductor spacer intercalated between two ferromagnets with noncollinear magnetizations. We show that the magnetoresistance of the triplet spin valve depends on the relative orientations of the d vector, characterizing the superconducting order parameter, and the magnetization directions of the ferromagnetic layers. For devices characterized by a long superconductor, the effects of a polarized current sustained by Cooper pairs only are observed. In this regime, a supermagnetoresistance effect emerges, and the chiral symmetry of the order parameter of the superconducting spacer is easily recognized. Our findings open new perspectives in designing spintronics devices based on the cooperation of ferromagnetic and triplet correlations. PMID:24329463

Romeo, F; Citro, R

2013-11-27

333

Higgs triplets and limits from precision measurements  

SciTech Connect

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

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

2006-04-01

334

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

Microsoft Academic Search

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

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

2010-01-01

335

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

Microsoft Academic Search

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

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

2008-01-01

336

Peptide Charge State Determination for Low-Resolution Tandem Mass Spectra  

Microsoft Academic Search

Mass spectrometry is a particularly useful technology for the rapid and robust identification of peptides and pro- teins in complex mixtures. Peptide sequences can be iden- tified by correlating their observed tandem mass spectra (MS\\/MS) with theoretical spectra of peptides from a se- quence database. Unfortunately, to perform this search the charge of the peptide must be known, and current

Aaron A. Klammer; Christine C. Wu; Michael J. Maccoss; William Stafford Noble

2005-01-01

337

Quantum gates for the singlet-triplet T+ qubit  

NASA Astrophysics Data System (ADS)

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

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

2011-03-01

338

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

Microsoft Academic Search

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

Li Chen; Yee Leng Yap

2008-01-01

339

Repeated multiple maternities in triplet families.  

PubMed

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

Fellman, Johan; Eriksson, Aldur W

2014-06-01

340

New Results on Optimizing Rooted Triplets Consistency  

Microsoft Academic Search

A set of phylogenetic trees with overlapping leaf sets is con- sistent if it can be merged without conflicts into a supertree. In this paper, we study the polynomial-time approximability of two related op- timization problems called the maximum rooted triplets consistency prob- lem (MaxRTC) and the minimum rooted triplets inconsistency prob- lem (MinRTI) in which the input is a

Jaroslaw Byrka; Sylvain Guillemot; Jesper Jansson

2008-01-01

341

Contribution of cytosine-containing cyclobutane dimers to DNA damage produced by photosensitized triplet-triplet energy transfer.  

PubMed

Mutagenic cyclobutane pyrimidine dimers (CPDs) can be induced in DNA through either direct excitation or photosensitized triplet-triplet energy transfer (TTET). In the latter pathway, thymines are expected to receive the excitation energy from the photosensitizer and react with adjacent pyrimidines. By using state-of-the art analytical tools, we provide herein additional information on the formation of cytosine-containing CPDs. We thus determined the yield of all possible CPDs upon TTET in a series of natural DNAs with various base compositions. We show that the distribution of CPDs cannot be explained only by excitation of individual thymines. We propose that the mechanism for TTET involves at least dinucleotides as the minimal targets. The observation of the formation of cytosine-cytosine CPDs also suggests that additional pathways are involved in this photosensitized reaction. PMID:24668918

Douki, Thierry; Bérard, Izabel; Wack, Aude; Andrä, Sigrid

2014-05-01

342

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

343

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

NASA Astrophysics Data System (ADS)

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

Tai, Stephanie

344

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

NASA Astrophysics Data System (ADS)

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

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

2003-04-01

345

Threshold photoionization spectra of benzyl radical: Cation vibrational states and {ital ab} {ital initio} calculations  

SciTech Connect

We measured threshold photoionization spectra of benzyl{sup +}-{ital h}{sub 7}, benzyl{sup +}-{alpha}{ital d}{sub 2}, and benzyl{sup +}-{ital d}{sub 7} in the ground electronic state ({tilde {ital X}}{sup +1}{ital A}{sub 1}) using resonant two-photon excitation and detection of electrons by pulsed field ionization. The adiabatic ionization potentials of benzyl-{ital h}{sub 7}, benzyl-{alpha}{ital d}{sub 2}, and benzyl-{ital d}{sub 7} are 58468{+-}5 cm{sup -1}, 58418{+-}5 cm{sup -1}, and 58386{+-}5 cm{sup -1}. Excitation through a variety of vibronically mixed {tilde {ital A}}{sup 2}{ital A}{sub 2}-{tilde {ital B}}{sup 2}{ital B}{sub 2} neutral excited states allows observation of cation vibrations of both {ital a}{sub 1} and {ital b}{sub 1} symmetries. We directly measure in-plane fundamentals and infer the frequencies of certain out-of-plane fundamentals from their involvement in combinations or overtones. By comparison with harmonic frequencies from {ital ab initio} calculations, we assign 35 of 48 observed levels in the -{ital h}{sub 7} isotopomer, 15 of 22 levels in -{alpha}{ital d}{sub 2}, and 25 of 30 levels in -{ital d}{sub 7}. {ital ab initio} calculations permit a detailed comparison of the geometry, chemical bonding, and vibrational frequencies in the benzyl anion, neutral, and cation. The anion and cation, both closed-shell species, have similar geometries with relatively short exocyclic CC bond (1.371 A and 1.372 A, respectively) and with the aromatic ring compressed along the {ital C}{sub 2} symmetry axis. The neutral free radical has a longer exocyclic CC bond (1.413 A) and a more nearly sixfold symmetric ring. The natural resonance theory provides bond orders and resonance-structure weights in all three species. While no single resonance structure dominates in any of the three species, the structure with an exocyclic CC double bond is more important in the anion and cation than in the neutral. {copyright} {ital 1996 American Institute of Physics.}

Eiden, G.C.; Lu, K.; Badenhoop, J.; Weinhold, F.; Weisshaar, J.C. [Department of Chemistry, University of Wisconsin-Madison, Madison, Wisconsin 53706 (United States)] [Department of Chemistry, University of Wisconsin-Madison, Madison, Wisconsin 53706 (United States)

1996-06-01

346

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

NASA Astrophysics Data System (ADS)

We present self-consistent-field Korringa-Kohn-Rostoker coherent-potential-approximation calculations of the electronic density of states of random CucPd1-c alloys. We find strong hybridization of the palladium d bands with the copper d bands over the entire concentration range. We do not obtain a palladium virtual bound state for the copper-rich alloys and therefore contradict the interpretation generally placed on valence-band x-ray photoelectron spectroscopy (XPS) spectra for Cu-Pd. Nevertheless, our first-principles calculations of the XPS spectra are in excellent agreement with recent measurements, and we discuss why this is so. Furthermore, we compare our density of states at the Fermi energy with specific-heat measurements.

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

1986-02-01

347

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

348

Determination of Peptide and Protein Ion Charge States by Fourier Transformation of Isotope-Resolved Mass Spectra  

SciTech Connect

We report an automated method for determining charge states from high-resolution mass spectra. Fourier transforms of isotope packets from high-resolution mass spectra are compared to Fourier transforms of modeled isotopic peak packets for a range of charge states. The charge state for the experimental ion packet is determined by the model isotope packet that yields the best match in the comparison of the Fourier transforms. This strategy is demonstrated for determining peptide ion charge states from 'zoom scan' data from a linear quadrupole ion trap mass spectrometer, enabling the subsequent automated identification of singly-through quadruply-charged peptide ions, while reducing the numbers of conflicting identifications from ambiguous charge state assignments. We also apply this technique to determine the charges of intact protein ions from LC-FTICR data, demonstrating that it is more sensitive under these experimental conditions than two existing algorithms. The strategy outlined in this paper should be generally applicable to mass spectra obtained from any instrument capable of isotopic resolution.

Tabb, Dave L [ORNL; Shah, Manesh B [ORNL; Strader, Michael B [ORNL; Connelly, Heather M [ORNL; Hettich, Robert {Bob} L [ORNL; Hurst, Gregory {Greg} B [ORNL

2006-01-01

349

Spectroscopy of proton-rich 66Se up to J?=6+: Isospin-breaking effect in the A=66 isobaric triplet  

NASA Astrophysics Data System (ADS)

Candidates for three excited states in the 66Se have been identified using the recoil-? tagging method together with a veto detector for charged-particle evaporation channels. These results allow a comparison of mirror and triplet energy differences between analog states across the A=66 triplet as a function of angular momentum. The extracted triplet energy differences follow the negative trend observed in the f7/2 shell. Shell-model calculations indicate that the strength of the Coulomb isotensor part alone is not sufficient to account for this trend in the case of the A=66 triplet.

Ruotsalainen, P.; Jenkins, D. G.; Bentley, M. A.; Wadsworth, R.; Scholey, C.; Auranen, K.; Davies, P. J.; Grahn, T.; Greenlees, P. T.; Henderson, J.; Herzá?, A.; Jakobsson, U.; Joshi, P.; Julin, R.; Juutinen, S.; Konki, J.; Leino, M.; Lotay, G.; Nichols, A. J.; Obertelli, A.; Pakarinen, J.; Partanen, J.; Peura, P.; Rahkila, P.; Sandzelius, M.; Sarén, J.; Sorri, J.; Stolze, S.; Uusitalo, J.

2013-10-01

350

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

NASA Astrophysics Data System (ADS)

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

Kook, Seong-Keun; Hanson, David M.

1990-10-01

351

Triplet formation of 6-azauridine and singlet oxygen sensitization with UV light irradiation.  

PubMed

Excited state characteristics of 6-azauridine (6AUd), which is known as a medicine against psoriasis and neoplastic, were investigated with laser plash photolysis, time-resolved thermal lensing, and near IR single photon counting method. The triplet-triplet absorption spectrum of 6AUd was observed for the first time. The formation quantum yield of excited triplet 6AUd (Phi(ISC)) was estimated by acetone triplet sensitization and actinometry with benzophenone to be 1.00 +/- 0.07 (248 nm excitation) and 0.78 +/- 0.05 (308 nm excitation). This excitation wavelength effect could be explained by intersystem crossing (ISC) to the excited triplet manifolds occurring during the relaxation on the potential energy surface (PES) of the S(1)(npi*) state and be in competition with internal conversion to the S(0) state after the relaxation to the minimum of the S(1)(npi*) state. 6AUd had a lower Phi(ISC) value than 6-azauracil (6AU) with the 308 nm excitation (Phi(ISC) = 0.93 +/- 0.04 for 6AU). The nucleoside has more vibrational modes than 6AU, and therefore the ribose would accelerate intramolecular vibrational energy redistribution and the relaxation to the minimum of the PES of the S(1)(npi*) state. Sensitized singlet oxygen formation of 6AUd was also detected in the O(2)-saturated condition with quantum yields of 0.49 +/- 0.01 with the 248 nm excitation, indicating the high phototoxicity of 6AUd. PMID:20445916

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

2010-05-21

352

Identification of transitions into Rydberg states in the X-ray absorption spectra of condensed long-chain alkanes  

NASA Astrophysics Data System (ADS)

A detailed theoretical analysis of the high-resolution X-ray absorption spectra of condensed long-chain alkane molecules (hexatriacontane, C 36H 74 and heptatriacontane, C 37H 76) suggests that the resonance at 287.7 eV, which is the dominating feature in the near-edge X-ray absorption spectra of saturated long-chain hydrocarbons, is due to transitions into Rydberg states. These findings, which are at variance with the previous interpretation, are corroborated by the identification of a previously unresolved resonance at 288.2 eV in the high-resolution X-ray absorption spectra and of the observation of a strong quenching of the X-ray absorption resonances upon physisorption on a Cu(111)-metal surface.

Bagus, P. S.; Weiss, K.; Schertel, A.; Wöll, Ch.; Braun, W.; Hellwig, C.; Jung, C.

1996-01-01

353

Modelling the NeIX Triplet with Chandra Using HEG, MEG, and LETGS  

NASA Astrophysics Data System (ADS)

The grating instruments on board Chandra and XMM-Newton cover a variety of chances and limitations. While the LETGS offers the largest wavelength range with high sensitivity the MEG and the HEG have a much higher spectral resolution. A very popular method to analyze the grating spectra is the He-like triplets because they are density sensitive and a large temperature range is covered with different ions ranging from C V (~1 MK) up to Si XIII (~15 MK). However, only the LETGS wavelength range covers all these triplets simultaneously, while with the MEG the C V and the N VI triplets are not measurable and the HEG can only measure Si XIII, Mg XI, and Ne IX. The Ne IX triplet can be measured with all instrument, but with different success. The triplet line are in principle resolved by all grating, but severe blending with Fe XIX line can hamper the analysis in the hotter plasmas, e.g., active stars or flares. In those cases highest spectral resolution is highly desirable, and the LETGS is not sufficient to resolve all blending lines. The most popular X-ray calibration target is Capella and it has been observed with all gratings with significant exposure times. We gathered together all available data of the HEG and MEG (155 ksec), the LETGS (219 ksec) for comparative analysis of the Ne IX triplet. 18 emission lines can be identified in the region around 13.5 A with the HEG. Good agreement of these lines with predictions from a theoretical model constructed from the APEC line database using an emission measure distribution derived from Fe IX to Fe XXIV lines can be seen. These 18 emission lines cannot be identified in the LETGS spectrum, but we show that these spectra are consistent with the wavelengths and fluxes measured with the HEG.

Ness, J.-U.; Brickhouse, N. S.; Drake, J. J.; Huenemoerder, D. P.

2002-12-01

354

Study of the OD EPR phenomena in (COF)2 excited to single rotational levels of the 801,501,711801and501711 vibronic states: cluster formation investigated by the OD EPR  

Microsoft Academic Search

OD EPR spectra were recorded for aAu triplet levels of (COF)2, coupled by intramolecular interactions to levels of an adjacent AAu singlet state, by exciting the molecule into individual rovibronic levels of this singlet state. The spectra were recorded for J' = 0-5; Ka'=0 and J' = 1-5; Ka'=1. Spectroscopic parameters of the aAu state were estimated by fitting a

Vladimir I. Makarov; Igor V. Khmelinskii; Sergei A. Kochubei

2005-01-01

355

Fuzzy tricentric pharmacophore fingerprints. 1. Topological fuzzy pharmacophore triplets and adapted molecular similarity scoring schemes.  

PubMed

This paper introduces a novel molecular description--topological (2D) fuzzy pharmacophore triplets, 2D-FPT--using the number of interposed bonds as the measure of separation between the atoms representing pharmacophore types (hydrophobic, aromatic, hydrogen-bond donor and acceptor, cation, and anion). 2D-FPT features three key improvements with respect to the state-of-the-art pharmacophore fingerprints: (1) The first key novelty is fuzzy mapping of molecular triplets onto the basis set of pharmacophore triplets: unlike in the binary scheme where an atom triplet is set to highlight the bit of a single, best-matching basis triplet, the herein-defined fuzzy approach allows for gradual mapping of each atom triplet onto several related basis triplets, thus minimizing binary classification artifacts. (2) The second innovation is proteolytic equilibrium dependence, by explicitly considering all of the conjugated acids and bases (microspecies). 2D-FPTs are concentration-weighted (as predicted at pH=7.4) averages of microspecies fingerprints. Therefore, small structural modifications, not affecting the overall pharmacophore pattern (in the sense of classical rule-based assignment), but nevertheless triggering a pKa shift, will have a major impact on 2D-FPT. Pairs of almost identical compounds with significantly differing activities ("activity cliffs" in classical descriptor spaces) were in many cases predictable by 2D-FPT. (3) The third innovation is a new similarity scoring formula, acknowledging that the simultaneous absence of a triplet in two molecules is a less-constraining indicator of similarity than its simultaneous presence. It displays excellent neighborhood behavior, outperforming 2D or 3D two-point pharmacophore descriptors or chemical fingerprints. The 2D-FPT calculator was developed using the chemoinformatics toolkit of ChemAxon (www.chemaxon.com). PMID:17125187

Bonachéra, Fanny; Parent, Benjamin; Barbosa, Frédérique; Froloff, Nicolas; Horvath, Dragos

2006-01-01

356

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

357

Effect of protein stabilization on charge state distribution in positive- and negative-ion electrospray ionization mass spectra  

Microsoft Academic Search

Changes in protein conformation are thought to alter charge state distributions observed in electrospray ionization mass spectra\\u000a (ESI-MS) of proteins. In most cases, this has been demonstrated by unfolding proteins through acidification of the solution.\\u000a This methodology changes the properties of the solvent so that changes in the ESI-MS charge envelopes from conformational\\u000a changes are difficult to separate from the

Stephen J. Watt; Margaret M. Sheil; Jennifer L. Beck; Pavel Prosselkov; Gottfried Otting; Nicholas E. Dixon

2007-01-01

358

Triplet-sensitized cycloreversion of endoperoxides of aromatic compounds. An adiabatic reaction route  

NASA Astrophysics Data System (ADS)

Efficiencies EF Tc of triplet-sensitized cycloversion (T-cycloversion) of several aromatic endoperoxides (APOs) have been determined. From the dependence of EF Tc on the triplet state energy of the sensitizer the energies ET(??*) of reactive triplet states of APO are estimated ranging from ET(??*)? 170 kJ mol -1 for the endoperoxide of mesodiphyenylhelianthrene (MDHPO) to ET(??*)?250 kJ mol -1 for the endoperoxide of rubrene. Quantaum yields QTc of T-cycloversion could be derived from [APO]- dependent measurements of EF Tc Values of QTc=0.07±0.01 for MDHPO and QTc=0.042±0.008 for the endoperoxide of benzodixanthene resulted. T-cycloversion of the endoperoxide of homoeocoerdianthrone (HOCDPO) was found to be an adiabatic and spin-allowed reactions. S 1-excited HOCD and O 2( 3? -g are formed in equimolar amounts. Thus T-cycloversion of APOs parallels in an amazing way singlet state cycloreversion.

Katscher, U.; Schmidt, R.; Brauer, H.-D.

1993-04-01

359

Influence of matrix element effects in determining the density of states from photoemission spectra: Cu-Pd alloy  

NASA Astrophysics Data System (ADS)

It is found that a change of the photoionization matrix element with the binding energy in the valence band can cause a substantial discrepancy between the density of states and the photoemission spectrum for d-band metals and alloys even in the x-ray photoemission spectroscopy regime. This is the main cause of the controversial discrepancy between photoemission spectra and theoretical density of states predicted in the Korringa-Kohn-Rostoker coherent-potential approximation for Cu-Pd alloys, rather than the local lattice relaxation around Pd atomic sites.

Nahm, Tschang-Uh; Han, Moonsup; Oh, S.-J.; Park, J.-H.; Allen, J. W.; Chung, S.-M.

1993-06-01

360

Higgs triplets, decoupling, and precision measurements  

SciTech Connect

Electroweak precision data has been extensively used to constrain models containing physics beyond that of the standard model. When the model contains Higgs scalars in representations other than SU(2) singlets or doublets, and hence {rho}{ne}1 at tree level, a correct renormalization scheme requires more inputs than the three needed for the standard model. We discuss the connection between the renormalization of models with Higgs triplets and the decoupling properties of the models as the mass scale for the scalar triplet field becomes much larger than the electroweak scale. The requirements of perturbativity of the couplings and agreement with electroweak data place strong restrictions on models with Higgs triplets. Our results have important implications for Little Higgs type models and other models with {rho}{ne}1 at tree level.

Chen, M.-C. [Department of Physics and Astronomy, University of California, Irvine, California 92697 (United States); Dawson, Sally [Department of Physics, Brookhaven National Laboratory, Upton, New York 11973 (United States); Jackson, C. B. [HEP Division, Argonne National Laboratory, 9700 Cass Avenue Argonne, Illinois 60439 (United States)

2008-11-01

361

Renormalizing Chiral Nuclear Forces: Triplet Channels  

SciTech Connect

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

Bingwei Long, Chieh-Jen Yang

2012-03-01

362

Study of the OD EPR phenomena in (COF) 2 excited to single rotational levels of the 8 0 1 , 5 0 1 , 7 1 1 8 0 1 and 5 0 1 7 1 1 vibronic states: cluster formation investigated by the OD EPR  

Microsoft Academic Search

OD EPR spectra were recorded for a˜3Au triplet levels of (COF)2, coupled by intramolecular interactions to levels of an adjacent A˜1Au singlet state, by exciting the molecule into individual rovibronic levels of this singlet state. The spectra were recorded for J?=0?5; Ka?=0 and J?=1?5; Ka?=1. Spectroscopic parameters of the a˜3Au state were estimated by fitting a theoretical model to the

Vladimir I. Makarov; Igor V. Khmelinskii; Sergei A. Kochubei

2005-01-01

363

The steady-state and time-resolved photophysical properties of a dimeric indium phthalocyanine complex  

Microsoft Academic Search

The steady-state and time-resolved photophysical properties and some molecular orbital calculation results of a dimeric indium phthalocyanine complex with an indium–indium bond, i.e., [tBu4PcIn]2·2tmed, have been described. The results regarding triplet excited state lifetimes can be ascribed to strong intramolecular interactions existing only in the excited state of this dimer because no significant difference in the absorption spectra of the

Yu Chen; Yasuyuki Araki; Danilo Dini; Ying Liu; Osamu Ito; Mamoru Fujitsuka

2006-01-01

364

Birth weight in a large series of triplets  

PubMed Central

Background Triplets are often born premature and with a low birth weight. Because the incidence of triplet births is rare, there are relatively few studies describing triplet birth weight characteristics. Earlier studies are often characterized by small sample sizes and lack information on important background variables such as zygosity. The objective of this study is to examine factors associated with birth weight in a large, population-based sample of triplets registered with the Netherlands Twin Register (NTR). Methods In a sample of 1230 triplets from 410 families, the effects of assisted reproductive techniques, zygosity, birth order, gestational age, sex, maternal smoking and alcohol consumption during pregnancy on birth weight were assessed. The resemblance among triplets for birth weight was estimated as a function of zygosity. Birth weight discordance within families was studied by the pair-wise difference between triplets, expressed as a percentage of the birth weight of the heaviest child. We compare data from triplets registered with the NTR with data from population records, which include live births, stillbirths and children that have deceased within days after birth. Results There was no effect of assisted reproductive techniques on triplet birth weight. At gestational age 24 to 40 weeks triplets gained on average 130 grams per week; boys weighed 110 grams more than girls and triplets of smoking mothers weighted 104 grams less than children of non-smoking mothers. Monozygotic triplets had lower birth weights than di- and trizygotic triplets and birth weight discordance was smaller in monozygotic triplets than in di- and trizygotic triplets. The correlation in birth weight among monozygotic and dizygotic triplets was 0.42 and 0.32, respectively. In nearly two-thirds of the families, the heaviest and the lightest triplet had a birth weight discordance over 15%. The NTR sample is representative for the Dutch triplet population that is still alive 28 days after birth. Conclusion Birth weight is an important determinant of childhood development. Triplet status, gestational age, sex, zygosity and maternal smoking affect birth weight. The combined effects amount to a difference of 364 grams between monozygotic girl triplets of smoking mothers compared to dizygotic boy triplets of non-smoking mothers of the same gestational age. Birth weight in triplets is also influenced by genetic factors, as indicated by a larger correlation in monozygotic than in di- and trizygotic triplets.

2011-01-01

365

Ultrabright fluorescent OLEDS using triplet sinks  

SciTech Connect

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

366

Vibrational spectra of 1-methylthymine: matrix isolation, solid state and theoretical studies  

Microsoft Academic Search

The infrared spectra of 1-methylthymine (1-MeT) in argon and nitrogen cryogenic matrices are presented, for the first time. The molecular structure, conformations, vibrational frequencies, infrared intensities and Raman scattering activities of 1-MeT have been calculated by the DFT(B3LYP), MP2 and HF methods using the D95V** basis set. The theoretically predicted intensity pattern of the IR and Raman bands has proved

Barbara Morzyk-Ociepa; Maciej J. Nowak; Danuta Michalska

2004-01-01

367

Normalization of the single OPW conduction electron states in first principles pseudopotential calculations of phonon spectra  

Microsoft Academic Search

In a previous paper (Cutler et al., 1975) a more accurate expression, using explicit conduction wavefunctions, was derived for the orthogonalization hole density n0H(r) and used in nonlocal pseudopotential calculations of phonon spectra of simple and d-band metals. The results show significant differences with phonon curves obtained from the same formalism but using an approximate n0H(r). The effect of exact

R. S. Day; F. Sun; P. H. Cutler

1976-01-01

368

Manganese-induced triplet blinking and photobleaching of single molecule cyanine dyes.  

PubMed

Irradiation of solutions of the cyanine dyes Cy3, Cy3B, and Cy5 in the presence of Mn(2+) causes an increase in the yield of formation of the triplet state of the dye. This results in increased photobleaching and triplet blinking. Experiments with other divalent ions and paramagnetic molecules suggest that the enhancement in the intersystem-crossing rate is related to the paramagnetic nature of the Mn(2+) cation. The results are consistent with a model in which the formation of a weak collisional complex between the dye and the ion results in mixing of the singlet and triplet states of the dye. These findings are particularly significant in single-molecule spectroscopy and super-resolution imaging methods, in which photobleaching and blinking play an important role. PMID:24039065

Ciuba, Monika A; Levitus, Marcia

2013-10-21

369

Correct charge state assignment of native electrospray spectra of protein complexes  

Microsoft Academic Search

Correct charge state assignment is crucial to assigning an accurate mass to supramolecular complexes analyzed by electrospray\\u000a mass spectrometry. Conventional charge state assignment techniques fall short of reliably and unambiguously predicting the\\u000a correct charge state for many supramolecular complexes. We provide an explanation of the shortcomings of the conventional\\u000a techniques and have developed a robust charge state assignment method that

Lars Liepold; Luke M. Oltrogge; Peter A. Suci; Mark J. Young; Trevor Douglas

2009-01-01

370

Improved Cell Typing by Charge-State Deconvolution of matrix-assisted laser desorption/ionization Mass Spectra  

SciTech Connect

Robust, specific, and rapid identification of toxic strains of bacteria and viruses, to guide the mitigation of their adverse health effects and optimum implementation of other response actions, remains a major analytical challenge. This need has driven the development of methods for classification of microorganisms using mass spectrometry, particularly matrix-assisted laser desorption ionization MS (MALDI) that allows high throughput analyses with minimum sample preparation. We describe a novel approach to cell typing based on pattern recognition of MALDI spectra, which involves charge-state deconvolution in conjunction with a new correlation analysis procedure. The method is applicable to both prokaryotic and eukaryotic cells. Charge-state deconvolution improves the quantitative reproducibility of spectra because multiply-charged ions resulting from the same biomarker attaching a different number of protons are recognized and their abundances are combined. This allows a clearer distinction of bacterial strains or of cancerous and normal liver cells. Improved class distinction provided by charge-state deconvolution was demonstrated by cluster spacing on canonical variate score charts and by correlation analyses. Deconvolution may enhance detection of early disease state or therapy progress markers in various tissues analyzed by MALDI.

Wilkes, Jon G.; Buzantu, Dan A.; Dare, Diane J.; Dragan, Yvonne P.; Chiarelli, M. Paul; Holland, Ricky D.; Beaudoin, Michael; Heinze, Thomas M.; Nayak, Rajesh; Shvartsburg, Alexandre A.

2006-05-30

371

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

PubMed

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

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

2014-02-28

372

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

NASA Astrophysics Data System (ADS)

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

2014-02-01

373

Comparison of charge state determination methods for high resolution mass spectra  

Microsoft Academic Search

Since mass spectrometers measure mass\\/charge ratio rather than mass, determination of charge state is essential in order to determine mass. Charge state determination requires methods to accurately estimate the m\\/z difference between adjacent isotopic peaks. This is particularly difficult under conditions of low SNR and when isotopic clusters are poorly resolved. A new method for charge state determination using the

Parminder Kaur; Peter B. O'Connor

2006-01-01

374

Formation of triplet excimers and dimers in amorphous organic thin films and light emitting devices  

NASA Astrophysics Data System (ADS)

We examine triplet excimers in neat films of the phosphorescent molecule: platinum (II) (2-(4 ',6 '-difluorophenyl)pyridinato- N, C2) acetyl acetate (FPt1). This molecule was chosen because of its square planar structure, allowing it to facially pack in a crystal with an intermolecular separation of only 3.4±0.1 Å, thereby facilitating excimer formation between adjacent molecules. The transient and steady-state photoluminescent and electroluminescent properties of FPt1 are used to understand the formation of triplet excimers ( 3E0*) and dimers ( 3D*) in amorphous films grown by thermal evaporation. We find that 3E0* and 3D* have peak emission intensities at 2.07 and 1.83 eV, and have lifetimes of (1.6±0.3) ?s and (800±80) ns at room temperature, respectively. When films are optically pumped, triplet excitons form on monomers and then diffuse via thermally activated hopping to nearby excimer sites with an activation energy of (37±4) meV. We find that the energy transfer efficiency from the monomer to the excimer state approaches 100% at room temperature, and that the photoluminescence efficiency of the excimer is three times less than that of the monomer. Further, excitation of triplet aggregate states, or metal-metal dimers via the association of cations and anions of electrically pumped FPt1 is achieved in an organic light-emitting device, which achieves a maximum internal quantum efficiency of ˜14%. Electrical pumping also reveals dimer states unresolved in photoluminescent studies. The high efficiency of the triplet excimers of FPt1 is significant since dimeric species, especially triplets, are often associated with concentration quenching and low quantum yields.

D'Andrade, Brian; Forrest, Stephen R.

2003-01-01

375

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

SciTech Connect

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

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

2009-04-17

376

Novel infrared spectra for intermolecular dihydrogen bonding of the phenol-borane-trimethylamine complex in electronically excited state.  

PubMed

The intermolecular dihydrogen bonding in the electronically excited states of the dihydrogen-bonded phenol-BTMA complex in gas phase was theoretically investigated using the time-dependent density functional theory method for the first time. It was theoretically demonstrated that the S(1) state of the dihydrogen-bonded phenol-BTMA complex is a locally excited state, in which only the phenol moiety is electronically excited. The infrared spectra of the dihydrogen-bonded phenol-BTMA complex in ground state and the S(1) state were calculated at both the O-H and B-H stretching vibrational regions. A novel infrared spectrum of the dihydrogen-bonded phenol-BTMA complex in the electronically excited state was found. The stretching vibrational absorption bands of the dihydrogen-bonded O-H and B-H groups are very strong in the ground state, while they are disappeared in the S(1) state. At the same time, a new strong absorption band appears at the C[Double Bond]O stretching region. From the calculated bond lengths, it was found that both the O-H and B-H bonds in the dihydrogen bond O-H...H-B are significantly lengthened in the S(1) state of the dihydrogen-bonded phenol-BTMA complex. However, the C-O bond in the phenol moiety is markedly shortened in the excited state, and then has the characteristics of C[Double Bond]O group. Furthermore, it was demonstrated that the intermolecular dihydrogen bonds in the electronically excited state of the dihydrogen-bonded phenol-BTMA complex are strengthened, since calculated H...H distance is drastically shortened in the S(1) state. PMID:17640127

Zhao, Guang-Jiu; Han, Ke-Li

2007-07-14

377

Explicit role of dynamical and nondynamical electron correlation on singlet triplet splitting in carbenes  

NASA Astrophysics Data System (ADS)

Density functional theoretical studies have been performed on carbene systems to determine the singlet-triplet splitting and also to explore the role of electron correlation. Using an approximate method of separation of dynamical and nondynamical correlation, it is found that dynamical and nondynamical electron correlation stabilizes the singlet state relative to the triplet for halo carbenes in both BLYP and B3LYP methods. Calculations performed on higher homologues of methylene suggest that beyond CH(CH 3), both the electron correlations have leveling effect in stabilizing the singlet state relative to the triplet. It has also been observed while dynamical electron correlation fails to provide any substantial degree of stabilization to the singlet states of higher homologues of methylene in B3LYP method, an opposite trend is observed for nondynamical counterpart. Among the larger systems studied, (9-triptycyl)(?-naphthyl)-carbene has the highest stability of the triplet state whereas bis-imidazol-2-ylidenes has the most stable singlet state. Interestingly, the values of the dynamical electron correlation for each state of each system studied are different for the two methods used. The reason behind this apparent discrepancy lies in the fact that the coefficients of the LYP part in B3LYP and BLYP functionals are different.

Seal, Prasenjit; Chakrabarti, Swapan

2007-02-01

378

The excited states of Sr +CO: photofragmentation spectra and ab initio calculations  

NASA Astrophysics Data System (ADS)

The first absorption band in the photofragmentation spectroscopy of Sr +CO, is recorded in the energy region between 15 600 and 16 200 cm -1. The spectrum is characterized by a sharp peak between two zones with broad peaks. In contrast to this, the second absorption band observed in the energy interval of 19 000-23 000 cm -1 shows a regular vibrational structure accompanied by a low intensity shoulder which covers the energy up to the dissociation. Electronic multi-reference configuration interaction calculations in the 2-D nuclear configuration space with the CO bond frozen provide a qualitative explanation of the spectra.

Farantos, S. C.; Filippou, E.; Stamatiadis, S.; Froudakis, G. E.; Mühlhäuser, M.; Peric, M.; Massaouti, M.; Sfounis, A.; Velegrakis, M.

2003-09-01

379

Quenching excited triplet C{sub 60} fullerene by tetracyanoethylene in benzonitrile  

SciTech Connect

The main photophysical properties of C{sub 60} fullerene: The absorption spectra of excited singlet C{sub 60}, the inter-combinational conversion time, the quantum yield of triplet C{sub 60}, the triplet-triplet absorption spectra, and the channels and rate constants of the deactivation of triplet C{sub 60} have been established. The photochemical properties of C{sub 60} fullerene have been investigated to a lesser degree. C{sub 60} is known to be readily reduced (E{sub 1/2} = {minus}0.4 in relation to Ag/Ag{sup +}), in particular, photochemically. For example, photoexcitation of charge-transfer complexes of C{sub 60} with amines gives the radical anion C{sup {minus}}{sub 60} which is also formed in reactions of photoexcited C{sub 60} fullerene. The formation of the radical cation C{sup +}{sub 60} under the action of light has been detected in the reaction with colloidal TiO{sub 2}. The radical ion C{sup +}{sub 60} has been obtained in a homogeneous photochemical process: the reaction of unexcited C{sub 60} with excited singlet N-methylacridinium hexafluorophosphate or with the biphenyl radical cation generated in the reaction with excited singlet N-methylacridinium hexafluorophosphate. The formation of C{sup +}{sub 60} with an electron acceptor in a homogeneous process has not so far been observed. The purpose of this work has been to study the quenching of triplet {sup 3}C{sub 60} with an electron acceptor, tetracyanoethylene (TCNE), which is known to oxidize unsaturated or aromatic hydrocarbons in photochemical reactions.

Nadtochenko, V.A.; Denisov, N.N.; Rubtsov, I.V.; Lobach, A.S.; Moravsky, A.P. [Institute of Chemical Physics in Chernogolovka, Moscow (Russian Federation)

1994-01-01

380

AssignFit: A program for simultaneous assignment and structure refinement from solid-state NMR spectra  

NASA Astrophysics Data System (ADS)

AssignFit is a computer program developed within the XPLOR-NIH package for the assignment of dipolar coupling (DC) and chemical shift anisotropy (CSA) restraints derived from the solid-state NMR spectra of protein samples with uniaxial order. The method is based on minimizing the difference between experimentally observed solid-state NMR spectra and the frequencies back calculated from a structural model. Starting with a structural model and a set of DC and CSA restraints grouped only by amino acid type, as would be obtained by selective isotopic labeling, AssignFit generates all of the possible assignment permutations and calculates the corresponding atomic coordinates oriented in the alignment frame, together with the associated set of NMR frequencies, which are then compared with the experimental data for best fit. Incorporation of AssignFit in a simulated annealing refinement cycle provides an approach for simultaneous assignment and structure refinement (SASR) of proteins from solid-state NMR orientation restraints. The methods are demonstrated with data from two integral membrane proteins, one ?-helical and one ?-barrel, embedded in phospholipid bilayer membranes.

Tian, Ye; Schwieters, Charles D.; Opella, Stanley J.; Marassi, Francesca M.

2012-01-01

381

Infrared and Microwave Spectra and Force Field of DBO: The Coriolis Interaction between the ? 1and ? 2+ ? 3States  

NASA Astrophysics Data System (ADS)

The ? 1and ? 3bands of D 11BO and the ? 1band of D 10BO were observed by using an infrared diode laser spectrometer. The DBO molecule was generated by an ac discharge in a mixture of BCl 3, D 2, O 2, and He. As inferred previously, a strong Coriolis interaction was in fact found to take place between the ? 1and ? 2+ ? 3states, and an analysis of the observed ? 1spectra, which explicitly took into account this Coriolis interaction, predicted the pure rotational transition frequencies of DBO in the ? 1state. Pure rotational lines were then detected by microwave spectroscopy, confirming the validity of the infrared assignment. In the microwave experiment DBO molecules were generated by a discharge in a mixture of B 2D 6and O 2. The three fundamental bands and a hot band of D 11BO, as well as the ? 1and ? 3bands of D 10BO, were subsequently recorded in emission with a Fourier transform infrared spectrometer. DBO molecules were generated by the reaction of D 2with HBO at temperatures above 800°C in a ceramic tube furnace. All of the observed spectra were simultaneously subjected to a least-squares analysis to obtain molecular parameters in the ground, ? 1, ? 2, ? 3, and ? 2+ ? 3states. The results thus obtained improved the force field and molecular structure of the HBO/DBO molecules reported in a previous study (Y. Kawashima, Y. Endo, and E. Hirota, 1989, J. Mol. Spectrosc.133, 116-127).

Kawashima, Yoshiyuki; Colarusso, Pina; Zhang, K. Q.; Bernath, Peter; Hirota, Eizi

1998-11-01

382

A comparative study of triplet and radical-anion photoionization of propiophenone  

NASA Astrophysics Data System (ADS)

The photoionization of propiophenone via two different routes was investigated by single-pulse and two-pulse laser-flash photolysis with observation of the hydrated electron and the respective photoionizable intermediate, the triplet or the radical anion. From the dependences of the absolute concentrations on the excitation intensity, kinetic constants and quantum yields were obtained. In the presence of a large surplus of a sacrificial electron donor (triethylamine or DABCO), the reaction is cyclic, with the radical anion of the ketone first formed by photoinduced electron transfer, and then ionized by another photon to regenerate the starting material, all within the same laser flash. The quantum yield of photoionization of the radical anion is 0.25 at 308 nm. In the absence of a donor, the ketone triplet is ionized. The intensity dependences indicate a more complex mechanism than a consecutive reaction and provide evidence for an additional photoreaction of the triplet, presumably regeneration of the starting material by reverse intersystem crossing via a chemical pathway. The quantum yield of photoionization of the triplet is 0.05 at 308 nm and 0.02 at 355 nm. As the electronic configurations of the autoionizing upper excited states are very similar, it is proposed that the lower quantum yield in the case of the triplet might be due to competing deactivation channels, which are not open to the upper excited radical anion.

Goez, Martin; Zubarev, Valentin

2004-12-01

383

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

384

Charge dynamics of vortex cores in layered chiral triplet superconductors  

NASA Astrophysics Data System (ADS)

In an accompanying paper (Sauls and Eschrig 2009 New J. Phys. 11 075008) we have studied the equilibrium properties of vortices in a chiral quasi-two-dimensional triplet superfluid/superconductor. Here we extend our studies to include the dynamical response of a vortex core in a chiral triplet superconductor to an external ac electromagnetic field. We consider in particular the response of a doubly quantized vortex with a homogeneous core in the time-reversed phase. The external frequencies are assumed to be comparable in magnitude to the superconducting gap frequency, such that the vortex motion is nonstationary but can be treated by linear response theory. We include broadening of the vortex-core bound states due to impurity scattering and consider the intermediate-clean regime, with a broadening comparable to or larger than the quantized energy level spacing. The response of the order parameter, impurity self-energy, induced fields and currents are obtained by a self-consistent calculation of the distribution functions and the excitation spectrum. Using these results we obtain the self-consistent dynamically induced charge distribution in the vicinity of the core. This charge density is related to the nonequilibrium response of the bound states and order parameter collective mode, and dominates the electromagnetic response of the vortex core.

Eschrig, M.; Sauls, J. A.

2009-07-01

385

IR spectra of benzaldehyde and its derivatives in different aggregate states  

NASA Astrophysics Data System (ADS)

We have measured the IR Fourier-transform spectra of biologically active benzaldehyde and its derivatives in the gas and liquid phases. For compounds of this class, the role played by C=O, OH, and CH groups in intra- and intermolecular has been analyzed. We have revealed spectral features that characterize the participation of C=O groups of unsubstituted benzaldehyde molecules in the occurrence of intermolecular hydrogen bonds C=O...H-C with the formation of molecular dimers of different types. For 2-hydroxybenzaldehyde molecules, spectral data have been obtained that are indicative of the occurrence of intramolecular hydrogen bonds of the C=O...H-C type in solutions. In 2-methoxybenzaldehyde molecules, no intramolecular hydrogen bonds have been observed.

Tolstorozhev, G. B.; Skornyakov, I. V.; Bel'kov, M. V.; Shadyro, O. I.; Brinkevich, S. D.; Samovich, S. N.

2012-08-01

386

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

SciTech Connect

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

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

2010-06-01

387

Non-uniform Triplet Superconductivity in Low-Dimensional Conductors.  

NASA Astrophysics Data System (ADS)

The interplay between magnetic and superconducting orders is a very important problem in condensed matter physics. In the quasi-one-dimensional (quasi-1D) organic conductor (TMTSF)2PF6, an antiferromagnetic state charaterized by a spin density wave (SDW) neighbors a triplet superconducting (TSC) state in the P-T phase diagram. Experiments [1,2] suggest a coexistence region of SDW and TSC orders in the vicinity of the phase boundary. We consider a tight-binding quasi-1D electron system, and derive the Ginzburg-Landau (GL) free energy for simultaneous SDW and TSC orders. By solving the linearized GL equations in the limit where the coupling between SDW and TSC order parameters is small, a non-uniform TSC state appears with simultaneous non-uniform SDW order. References:[1] T. Vuletic et al., Eur. Phys. J. B 25, 319 (2002).[2] I. J. Lee et al., Phys. Rev. Lett. 94, 197001 (2005).

Zhang, Wei

2005-11-01

388

Study of Singlet-Triplet Gaps in ?-Conjugated Polymers versus Graphene Nanoribbons and Single-Walled Carbon Nanotubes. The Effect of Dimensionality  

NASA Astrophysics Data System (ADS)

We compute and compare the gap between the optical singlet and lowest triplet excitons in poly (para-phenylenevinylene) (PPV) with semiconducting graphene nanoribbons (GNRs) and single-walled carbon nanotubes (SWCNTs) within Coulomb correlated model Hamiltonian. The singlet-triplet gaps in semiconducting GNRs and SWCNTs are more than one order of magnitude smaller that in PPV. We ascribe this to two-dimensionality. Spatial distribution of the electron-hole separation in excitons reveals significant localization of the triplet state wave function compared to singlet state in PPV. In GNRs and SWCNTs however, singlet and triplet wave functions exhibit comparably extended spatial distributions. Singlet-triplet gap size is an indicator of the effective Coulomb interaction strength which in turn controls the exciton binding energies of these systems. Exciton binding energy plays a deciding role in light emission and device performance in photovoltaics.

Aryanpour, Karan; Mazumdar, Sumit; Zhao, Hongbo

2011-03-01

389

Spectra of electrons ejected from aligned autoionising states created by K++Ne collisions  

Microsoft Academic Search

An ejected-electron spectroscopic study has been carried out on the potassium autoionising state created by charge transfer excitation in collisions of the potassium ion with the neon atom. The ion impact energy was varied between 2.1 and 7.2 keV. A detailed analysis has been performed for the spectral profiles of autoionisation of the potassium 3p54s22P1\\/2 2 and 2P3\\/2 states. Their

A. Wada; F. Koike; K. Wakiya; T. Takayanagi; H. Suzuki

1987-01-01

390

Potential energy surface of triplet H\\/sup +\\/â : A representation in hyperspherical coordinates  

Microsoft Academic Search

A large number of full CI calculations has been performed in order to obtain an accurate representation of the potential energy surface of the molecular ion H\\/sup +\\/â in its lowest triplet state. It is found that the surface is very flat, so that the molecule is very floppy and has a great likelihood of tunneling between the three symmetry-related

P. E. S. Wormer; F. de Groot

1989-01-01

391

The potential energy surface of triplet H3(+) - A representation in hyperspherical coordinates  

Microsoft Academic Search

A large number of full CI calculations has been performed in order to obtain an accurate representation of the potential energy surface of the molecular ion H3(+) in its lowest triplet state. It is found that the surface is very flat, so that the molecule is very floppy and has a great likelihood of tunneling between the three symmetry-related minima.

P. E. S. Wormer; F. de Groot

1989-01-01

392

The potential energy surface of triplet H+3 : A representation in hyperspherical coordinates  

Microsoft Academic Search

A large number of full CI calculations has been performed in order to obtain an accurate representation of the potential energy surface of the molecular ion H+3 in its lowest triplet state. It is found that the surface is very flat, so that the molecule is very floppy and has a great likelihood of tunneling between the three symmetry-related minima.

P. E. S. Wormer; F. de Groot

1989-01-01

393

Millimeter- and submillimeter-wave spectra of platinum monosulfide (PtS) in the X3?0- state  

NASA Astrophysics Data System (ADS)

The millimeter- and submillimeter-wave spectra of PtS in the X3?0- state were observed by employing a source-modulated microwave spectrometer. The PtS radical was generated in a free space cell by using a dc glow plasma of H2S and Ar. Platinum atoms were supplied from a small piece of platinum sheet lining the inner surface of a stainless steel cathode by the sputtering reaction. Rotational transitions were recorded for four dominant isotopomers, 194PtS, 195PtS, 196PtS, and 198PtS in the X3?0- ground state, and the spectroscopic constants for each isotopomer were determined using a Hund's case (c) Hamiltonian. The lower limit of the 3?0--3?1- energy separation is estimated from a Hund's case (a) analysis.

Okabayashi, Toshiaki; Yamamoto, Takuya; Kurahara, Taku; Mizuguchi, Den-ichiro; Mizuno, Shohei; Tanimoto, Mitsutoshi

2012-08-01

394

Vibrational spectra of isomeric pyridinic carboxylic acids in solid state and in solution and their SERS studies in silver sol  

NASA Astrophysics Data System (ADS)

Raman spectroscopic studies of three isomeric pyridinic carboxylic acids, viz. picolinic, nicotinic and iso-nicotinic acid in solid state, in aqueous solution and in silver hydrosol, in the frequency range 900-1750 cm -1, have been made. Assignments of the observed bands have been proposed in relation to the molecular forms present in solid state and in solution. Different degrees of intensity enhancements of the Raman bands in surface-enhanced Raman scattering (SERS) have been observed in all the three isomeric molecules. In iso-nicotinic acid, the intensity enhancement has been found to be minimum. Comparisons of Raman spectra in aqueous solution with those due to SERS in silver sol indicate that picolinic and nicotinic acid adsorb perpendicularly to the sol surface whereas in iso-nicotinic acid it occurs via donation of a ?-electron of the aromatic ring, i.e. the plane of the ring lies parallel to the surface of the sol.

Chattopadhyay, S.; Brahma, S. K.

1993-04-01

395

Hydrophobic-Radical Influence on the Structure and Vibrational Spectra of Zwitterionic Glycine and Alanine in the Condensed State  

NASA Astrophysics Data System (ADS)

The structure and vibrational spectra of zwitterionic glycine and alanine in aqueous solution and the solid state were calculated in the B3LYP/6-311++G(d,p) approximation. The environment infl uence was taken into account by two methods, i.e., the self-consistent reaction fi eld (SCRF) model and a clear accounting for the effects of hydrogenbonds (complexes with water molecules). The geometric, energetic, and spectral characteristics required to establish that a hydrophobic radical affected the ability of glycine and alanine to form H-bonds were determined. It was found by comparison with experiment that zwitterionic glycine and alanine in the condensed states had to be surrounded with three water molecules, one of which was situated between the N+H3 and COO- ions, in order to calculate their vibrational (IR and Raman) spectra. The formation energies of the alanine complexes with water were 56.47 kcal/ mol and 12.55 kcal/mol greater than those of glycine for formation of a complex with one water molecule situated between the ionized groups and with three water molecules, respectively.

Ten, G. N.; Kadrov, D. M.; Baranov, V. I.

2014-05-01

396

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

NASA Astrophysics Data System (ADS)

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 of the optical spectra is developed for these materials. The optical spectra in the incommensurate state, especially of improper ferroelectric K2SeO4, are discussed with emphasis on the commensurate-incommensurate transition, in comparison with 2H-TaSe2 with discommensuration effect. We study the effects of the residual Fermi surface on the Raman linewidth, the interference between the diamagnetic and paramagnetic contribution to the Raman tensor.

Nagaoso, Naoto; Hanamura, Eiichi

1984-02-01

397

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

398

Light-induced states in attosecond transient absorption spectra of laser-dressed helium  

NASA Astrophysics Data System (ADS)

Laser-dressed absorption in atomic helium is studied, both theoretically and experimentally, by transient absorption spectroscopy using isolated 400-as pulses centered at 22 eV and 12-fs near-infrared (NIR) pulses with 780-nm central wavelength. Multiple features in the helium singly excited bound-state spectrum are observed only when the NIR and attosecond pulses are overlapped in time. Theoretical analysis indicates that these light-induced structures (LISs) are the intermediate states in resonant, second-order processes that transfer population to multiple dipole forbidden states. The use of broadband, coherent extreme ultraviolet (XUV) radiation allows observation of these LISs without specifically tuning to a two-photon resonance, as would be required with narrowband XUV light. The strength and position of the LISs depend strongly on the NIR intensity and the pump-probe delay.

Chen, Shaohao; Bell, M. Justine; Beck, Annelise R.; Mashiko, Hiroki; Wu, Mengxi; Pfeiffer, Adrian N.; Gaarde, Mette B.; Neumark, Daniel M.; Leone, Stephen R.; Schafer, Kenneth J.

2012-12-01

399

Studies on bound-state spectra of Manning-Rosen potential  

NASA Astrophysics Data System (ADS)

Accurate ro-vibrational energies, eigenfunctions, radial densities, expectation values are presented for the exponential-type Manning-Rosen (MR) potential. Bound states, accurate up to ten significant figure are obtained by employing a simple, reliable generalized pseudospectral (GPS) method. All 55 eigenstates with n ?10 are treated for arbitrary values of potential parameters, covering a wide range of interaction, through a non-uniform, optimal spatial radial discretization. A detailed investigation has been made on energy changes with respect to screening and other potential parameters. A systematic estimation of critical screening parameters is given for these eigenstates. Special emphasis has been given to higher states and in the vicinity of critical screening region. A thorough comparison with literature results is made wherever possible. This surpasses the accuracy of all other existing methods currently available. Several new states are reported for the first time. In short, a simple, efficient scheme for accurate calculation of this and other molecular potentials is offered.

Roy, Amlan K.

2014-03-01

400

Superscars in Billiards: A Model for Doorway States in Quantum Spectra  

SciTech Connect

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